2008:221 CIV

M A S T E R ' S T H E S I S

New type of slewing bearingfor ship crane

John Lovén Tommy Nordin

Luleå University of Technology

MSc Programmes in Engineering Mechanical Engineering

Department of Applied Physics and Mechanical EngineeringDivision of Machine Elements

2008:221 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--08/221--SE

Abstract MacGREGOR (SWE) AB Crane division, located in Örnsköldsvik, Sweden, is part of the

Cargotec Corporation. MacGREGOR develops and manufactures cranes for shipboard

cargo handling. A typical MacGREGOR ship crane consists of four main modules, the

pedestal, the foundation, the crane house and the jib. The slewing bearing connects the

crane house to the foundation, allowing the crane to rotate around its vertical axis. If the

bearing should fail and split, the crane house will fall down which is a safety issue. The

current slewing bearing design requires a narrow flatness tolerance of the foundations top

surface which complicates the assembly process.

The purpose of this project was to investigate the possibility to use a double slewing

bearing design in order to create a safer and more easily assembled crane. Initially, a

problem analysis was performed in order to understand the scope of the project. A series

of ideas were developed through brainstorming sessions and discussions with handpicked

personnel at MacGREGOR. The ideas were narrowed down and refined into concepts.

The concepts were evaluated and ranked by predetermined criteria derived from the

needfinding process. Two of the concepts were chosen to be further investigated in the

detail design phase, where it was found through numerical calculations that due to the

stiffness of the top bearing, not enough moment could be distributed to the lower bearing

for the design to be feasible. Therefore, finite element analyses were made of the stay

connecting the bearings in order to find a stiffer design, however the results only

confirmed the numerical calculations.

When it became clear that the moment distribution to the lower bearing was insufficient

an alternative design was examined in order to solve the safety issue with a more

effective approach. A safety hook concept was discarded earlier in the project since it fell

outside the delimitations. However, since it now seemed as a realistic alternative it was

investigated in order to remedy the safety issue.

An internal safety hook design was produced. Finite element analysis and numerical

calculations suggested that the design would have to be rather robust. The weight of the

hooks implied that the assembly could be difficult. It is therefore recommended to design

an external safety hook solution.

Glossary

Pedestal

Foundation

Slewing-

bearing

Crane house

Jib

Outreach

Crane house bottom plate

Slewing-

bearing

Blank

Sheet casing

Ring

Cone

Foundation

bottom plate

Table of Contents 1 Introduction ................................................................................................................. 5

1.1 Background ......................................................................................................... 5

1.2 Company description .......................................................................................... 5 1.3 Purpose ................................................................................................................ 6 1.4 Goal ..................................................................................................................... 6 1.5 Delimitations ....................................................................................................... 6

2 Methods used .............................................................................................................. 7

2.1 SIRIUS Masterplan ............................................................................................. 7 2.2 Planning .............................................................................................................. 7 2.3 Problem analysis ................................................................................................. 7

2.3.1 Needfinding..................................................................................................... 7 2.3.2 Benchmarking ................................................................................................. 9 2.3.3 Related technology.......................................................................................... 9 2.3.4 Scope ............................................................................................................... 9

2.4 Product characteristics ........................................................................................ 9 2.5 Concept generation ........................................................................................... 10

2.6 Concept evaluation and selection...................................................................... 10 2.7 Detail design ..................................................................................................... 13

2.7.1 Software ........................................................................................................ 13

2.7.2 Stress analysis ............................................................................................... 14 2.7.3 Bearing design .............................................................................................. 14

3 Current solution ........................................................................................................ 17

3.1 The existing design ........................................................................................... 17

3.1.1 MacGREGOR Crane GL4528 ...................................................................... 17 3.1.2 Slewing bearing ............................................................................................ 18

3.2 Manufacturing and assembly ............................................................................ 18 4 Implementation and results ....................................................................................... 21

4.1 Product development ........................................................................................ 21

4.2 Planning ............................................................................................................ 21 4.3 Problem analysis ............................................................................................... 22

4.3.1 Needfinding................................................................................................... 22

4.3.2 Benchmarking ............................................................................................... 26 4.3.3 Related technology........................................................................................ 28

4.4 Product characteristics ...................................................................................... 30

4.5 Concept generation ........................................................................................... 30 4.6 Concept evaluation and selection...................................................................... 32 4.7 Detail design ..................................................................................................... 35

4.7.1 Numerical analysis ........................................................................................ 35

4.7.2 Finite element analysis .................................................................................. 39 5 Final results ............................................................................................................... 44 6 Discussion ................................................................................................................. 45 7 Recommendations ..................................................................................................... 47 8 References ................................................................................................................. 52 Appendix ........................................................................................................................... 54

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1 Introduction This project was performed as a master thesis work in the Master of Science program in

mechanical engineering, mechanical design at Luleå University of Technology. The

project was assigned by MacGREGOR (SWE) AB Crane Division, located in

Örnsköldsvik, Sweden, where the project also was performed during the period of mid

August to December 2008.

1.1 Background

The typical MacGREGOR ship crane consists of four main parts; the pedestal, the

foundation, the crane house and the jib. Between the crane house and the foundation the

slewing bearing is mounted, allowing the crane to turn around its vertical axis by a

hydraulically powered slewing gear unit. The bearing is designed to withstand the axial

and radial loads as well as the tilting moment generated by the maximum load at

maximum outreach. It is crucial for the slewing bearing to have a long service life. If the

bearing should fail and split, the crane house will fall down.

The current solution craves a narrow tolerance regarding the flatness of the blank’s top

surface which the bearing is bolted onto; otherwise the bearing will become distorted

when mounted. Before shipyard assembly, the blank is welded onto the top of the

foundation and machined to its final shape. The heat generated in the welding process,

when the foundation and pedestal are assembled at the shipyard, causes the blank to

deform leading to difficulties staying within the range of tolerable flatness thus

complicating the assembly process. If the welding instructions provided by

MacGREGOR are followed, the risk of blank deformation is minimized. (1)

1.2 Company description

MacGREGOR Group is part of the Cargotec Corporation and is the global market leader

in providing marine cargo handling solutions. Cargotec Corporation offers handling

systems and related services for the loading and unloading of goods on land and sea.

Cargotec Corporation includes MacGREGOR Group, Kalmar and HIAB, operates in

close to 160 countries and has 11,000 employees. (2) MacGREGOR Group offers cargo

flow solutions including hatch covers, lashing systems, solutions for passenger and

rolling cargo, dry bulk handling, offshore handling solutions, port and terminal solutions

and cranes. MacGREGOR Group operates in 50 countries and has just over 2200

employees in 2007. (3)

MacGREGOR (SWE) AB Crane Division, from here on referred to as MacGREGOR,

develops and manufactures a wide range of cranes for shipboard cargo handling. The

development and design office is located in Örnsköldsvik, Sweden. Production takes

place near major shipyards by long-term partners in Poland, Croatia, China and Korea.

MacGREGOR supplies basis and components from all over the world to the production

partners through the logistic-centers in Nantong, China and Hamburg, Germany. The

production partners manufacture the steel design, assemblies the components, finishes

and tests the product according to instructions given by MacGREGOR (1)

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Established 1937 in Whitley Bay, England, MacGREGOR & Company offered a

revolutionary steel hatch cover for cargo transportation at sea. In 1983, after a merger

with Navire, MacGREGOR-Navire was formed. (2) (3)

Hägglund & Söner started out in 1899 as a carpentry shop and grew to be one of the

biggest machine shops in the north of Sweden, manufacturing, amongst other things,

buses, mechanical loaders and airplanes. The company was bought by ASEA in 1972 and

in 1991 by Incentive AB. (4) Hägglunds & Söner was divided into divisions and in 1993

the Marine division was merged with acquired MacGREGOR-Navire and today’s

MacGREGOR Group was formed. (2) Cargotec Corporation, which acquired

MacGREGOR Group in 2005, was formed after a demerger from KONE Corporation the

same year (2).

1.3 Purpose

The purpose with the project is to design a safer slewing bearing solution preventing the

crane house to fall down if the bearing should fail. Also a more admissible flatness

deviation is desired to simplify the assembly process. (1)

1.4 Goal

To design a cost efficient slewing bearing solution which allows more flatness deviation

and prevents the crane house to fall down if the bearing should fail. (1)

1.5 Delimitations

This project does not consider a general MacGREGOR crane but a specific model with

predetermined load cases applied on a particular slewing bearing designed by Rothe Erde.

Because of the limited time schedule no extensive benchmarking is made regarding

competitor products, only a brief literature study is performed. No prototype will be

manufactured thereby all testing of the design will be restricted to computer simulation.

The cost of the design is estimated by the physical weight of the structure using data

supplied by the manufacturing partners.

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2 Methods used Methods used incorporate the theory involved in methods described in literature and

procedures used by MacGREGOR.

2.1 SIRIUS Masterplan

SIRIUS Masterplan, appendix 1, is a guide to be used during creative product

development. It is developed by Luleå University of Technology and is used in the final

year course named SIRIUS for students graduating with a Master of Science degree in

Mechanical Engineering, Mechanical Design. In this course, the students practice

creative product development in projects running over the whole academic year with real

companies as sponsors.

2.2 Planning

Planning is crucial in order to cover all aspects of the project and finish on time. SIRIUS

Masterplan suggests what needs to be done in the planning phase. Team roles need to be

defined so that responsibilities can be delegated and clarified within the group. Individual

and group goals need to be discussed to clarify expectations and goals and thereby

avoiding misunderstandings. The coaching role needs to be understood by the members

of the group and the coaches themselves. Therefore, the group members and coaches

need to discuss the preferred coaching strategy. To estimate costs, a budget should be

created and continuously updated. A Gantt chart should be produced and continuously

updated throughout the project showing phases and milestones in relation to the overall

plan. SIRIUS Masterplan also points out that planning is a continuous activity which

needs to be revised and updated along the way.

The Gantt chart, according to Johannesson et al. (5), is used to visualize the time

consumption and start/finish points for the main activities in a project. The method is

usually used in an early stage of a project; it is a purely informative method and is

therefore not suited for follow-up or process control. The Gantt chart can be visualized in

a coordinate system where the activities are denoted on the y-axis and the x-axis

represents time. Each activity is constituted by a horizontal line where the length

corresponds to the estimated time consumption of the activity.

2.3 Problem analysis

Problem analysis is necessary in order to solve the correct problem and satisfy the needs

at hand and thereby achieving the best possible results and outcome. In SIRIUS

Masterplan this phase is called Design Space Exploration. It consists of four phases;

Needfinding, Benchmarking, Related Technology and Scoping.

2.3.1 Needfinding

Needfinding is about finding the actual needs that the project has to satisfy in order to be

successful. When a product satisfies needs, it offers perceived benefits to the customer

which is a condition for making it a successful product (6). Ulrich and Eppinger have

developed a method where needfinding is a part of the product development process. This

method is based on close interaction between those who have detail control of the product

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and the customers. This method is suitable for development of new as well as refinement

of old products. Some of the goals of this method are to (6):

- Focusing the product on customer needs. - Identify needs; hidden, latent or explicit. - Act as fact basis for the product characteristics. - Making sure that no critical needs are missed.

(After Ulrich and Eppinger (6))

Ulrich and Eppinger’s method consists of five steps (6):

1. Gather raw data from customers. 2. Interpret the raw data in terms of customer needs. 3. Organize the needs into a hierarchy of primary, secondary, and (if necessary)

tertiary needs.

4. Establish the relative importance of the needs. 5. Reflect on the results and the process.

(Ulrich and Eppinger (6))

Step one, gathering raw data from customers, can be performed by conducting interviews,

using focus groups and observing the product in use. Written surveys are not

recommended at this early stage in the needfinding process. By interpreting the raw data,

need statements can be written. From the same raw material, e.g. interview notes,

different interpretations can lead to different need statements. Therefore, it is useful to

have more than one team member writing statements. There are a few guidelines to keep

in mind when writing need statements. It is important how the need is expressed; the

language should not imply how the product might achieve something, only what it must

achieve. It is important to express the needs at the same level as the raw data and to avoid

leaving out information. Also, the needs should be expressed as an attribute of the

product in order to ensure consistency and simplify translation into product

characteristics. Furthermore, positive phrasing is preferred over negative and wording

that applies a level of importance should be avoided. (6)

Step three in the needfinding process is organizing the needs into a hierarchy. In most

cases the hierarchy has two levels; primary and secondary needs. However, if needed a

third level, tertiary needs, can be added. The needs should be grouped in a way that is

consistent with the customer’s way of thinking. (6)

In step four, the relative importance of the needs is established. This can be achieved

either by performing customer surveys which is more accurate, or by the development

team which is faster and less costly. The customer surveys can be limited to needs that

give rise to major difficulties or costs. (6)

The final step in the process is reflecting on the results and the process. The results need

to be challenged and the group should reflect whether or not some areas need further

investigation or not. (6)

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2.3.2 Benchmarking

Benchmarking is finding out more about your competition. Knowing what you have to

compete against is of great importance in order to gain commercial success (6). This

knowledge is also critical when determining details of the product specification which in

turn determines the product’s market position (6). Stuart Pugh (7) suggests various

formats such as catalogues and trade information journals where such information can be

found. This can also be achieved by purchasing, testing and examining competitor

products (6).

2.3.3 Related technology

In the phase related technology, inspiration and lessons are gathered from other market

areas and other types of products. This is important in the early stages of concept

generation since new ideas might aspire from unexpected sources. Ulrich and Eppinger

suggest finding information through online directories and also points out that this is a

task requiring persistent and resourceful work (6).

2.3.4 Scope

Needfinding, Benchmarking and Related Technology works as basis when determining

the scope of the project. The scope limits the design space which defines which problem

or problems that are to be solved. Defining a suitable scope helps prepare for the next

step in the process where a mission statement and product characteristics are defined.

2.4 Product characteristics

The product characteristics document is defined using the knowledge gained in the

problem analysis phase. Here the criteria that the product will have to fulfill are stated.

The specification is enhanced during the course of the project, while a technical solution

and a product concept are developed. As Ulrich and Eppinger (6) points out, product

characteristics can be established several times throughout a project. There are a few

fundamental guidelines to keep in mind when forming a product characteristics document

according to Johannesson et al. (5).

Selection If the specification is too extensive the most important criteria and

functions should be selected.

Grouping If a smaller amount of criteria or functions cannot be selected they can be

grouped to be more manageable; for example they can be grouped in

levels or subject areas.

Formulation The criteria and functions should be carefully formulated in order not to be

misinterpreted. The formulation should not state technical solutions such

as “drill holes” in comparison to “make holes”.

Verification It is important to describe the limits and boundaries of the criteria and

functions. Make the criteria measurable and verifiable.

Importance The selected criteria’s importance should be stated for respective function.

This can also be implemented on groups of criteria.

(After Johannessson et al. (5))

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2.5 Concept generation

Brainstorming is a commonly used method for concept generation. The method is best

suited for a group of 5-15 individuals supervised by a leader. The purpose with the

brainstorming session is for the group to generate as many ideas as possible without

analyzing generated results. There are four fundamental rules according to Johannesson

et al. (5) in brainstorming;

Criticism is not allowed Give no comments what so ever concerning others ideas, not

positive nor negative. The same thing goes for your own

ideas; try to think spontaneous without judging the value of

the idea. Your idea could trigger another participant to a better

idea.

Strive for quantity It is important to generate many ideas since this increases the

chance that one of them might be really good. One

fundamental thought of the method is that a less successful

idea could lead to a more successful one.

Think outside the box Unconventional ideas are welcome. It has proven itself that an

odd and unusual idea can be modified into a perfect solution

to the problem. Just because a solution is unconventional does

not necessarily mean it is not right.

Combine ideas Combine and complement thought up ideas. Listen to other

participants ideas and associate your own from them. New

solutions can be found by merging two different ideas.

(After Johannesson et al. (5))

2.6 Concept evaluation and selection

Selecting one or more concepts for development is a process achieved through evaluation

against customer needs and relative comparison. This is an iterative process where the

number of concept alternatives may increase temporarily through combination and

improvement of various concepts. (6)

There are several methods for selecting concepts. Use of decision matrices provides a

structured and objective method for concept selection. Objectivity is important since

concept selection should be based on rational decisions, influence of organizational,

personal and arbitrary factors are unwanted. Ulrich and Eppinger also points out other

benefits when using a structured method: The result is likely to become more competitive

and customer focused, to have improved manufacturability, help the organization in

improving product development in general and also to be documented for future use. (6)

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Ulrich and Eppinger (6) describe a two stage process for concept selection based on

decision matrices, the stages have different purposes and each stage consists of six steps:

1. Prepare the selection matrix. 2. Rate the concepts. 3. Rank the concepts. 4. Combine and improve the concepts. 5. Select one or more concepts. 6. Reflect on the results and the process.

(Ulrich and Eppinger (6))

The first stage, concept screening, narrows the number of alternatives quickly and uses a

Pugh matrix developed by Stuart Pugh (7). The decision matrix is prepared by stating

selection criteria in the first column and the different concepts along the first row, an

example is shown in Table 2.1. The selection criteria are chosen from the identified

customer needs. There should be about 5 to 10 different criteria covering both customer

and organizational needs without being too detailed. A reference concept is chosen to

which all of the other concepts are compared against. This can be an existing or

competitor product as well as one of the available concepts.

Next step is to rate the concepts. The reference concept is given the value zero for all

criteria. The other concepts are now compared against this reference by giving a relative

score for each criterion; “better than”, “same as” or “worse than”, expressed as +, 0 or -.

Scoring should be performed by working through one criterion at a time. However, when

having a large number of concepts it can be easier to rate one concept at a time.

When having rated the concepts, ranking is performed by summing up the number of

“better than”, “same as” and “worse than”. After making sure that the results are valid

possible improvement or combination of concepts should be investigated. Ulrich and

Eppinger points out two issues to consider:

- Is there a generally good concept which is degraded by one bad feature? - Are there two concepts which can be combined to preserve the “better than”

qualities while annulling the “worse than” qualities?

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Table 2.1 Example of a Pugh matrix

Concepts

Selection criteria Concept A Concept B Concept C Concept D

Criterion A - 0 + +

Criterion B + 0 - +

Criterion C 0 0 - 0

Criterion D + 0 - +

Sum +'s 2 0 2 3

Sum 0's 1 4 0 1

Sum -'s 1 0 3 0

Net score 1 0 -1 3

Rank 2 3 4 1

Continue? Yes No No Yes

If new concepts arise, these are added to the matrix and rated the same way as before.

The new concepts can be named so their origin can be traced, for example a combination

of concept A and concept B can be called AB. If a concept is refined a + sign is added as

a suffix. For instance, concept A becomes A+ when refined. Based on previous steps, the

appropriate concepts are selected for further development. Also, decisions should be

made determining whether another round of concept screening or the more detailed

process of concept scoring should be applied. The final step is reflecting on the results

and the process. If not all team members agree on the outcome this can be a sign of

forgotten or unclear criteria. Group consensus also increases commitment of individual

group members and reduces the likelihood of making mistakes. (6)

The second stage, concept scoring, provides a higher resolution of the results due to the

more complicated matrix used. Here the concept selection process is based on the same

six steps as concept screening with some modification. Similar to previously described

matrix preparation, a reference concept is chosen. The criteria, or needs, can be expressed

in more detail than in concept screening through the use of secondary or tertiary needs,

described in section 2.3.1. The criteria are also weighted, which can be achieved through

various methods. In order for the results to be reliable, it is important to weight the

criteria as objectively as possible. In order to avoid subjective influence, Johannesson

et.al suggests a method with pair wise comparison (5). The criteria are put in the top

column and the first row of a matrix, see Table 2.2 Pair wise comparison of criteria When

comparing, the criteria get to share a value of 1. If one criterion is more important than

the other, it is given the entire value of 1 and the less important gets the value 0. If two

criteria are considered to be equally important, a value of 0,5 is given to each. The

diagonal squares are left empty since criteria are not compared against themselves. The

values are then added for each row resulting in a criteria sum. The criteria sum is divided

with a total sum which results in criteria weights.

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Table 2.2 Pair wise comparison of criteria

Criteria weighting by pairwise comparison

A B C D E F G Sum Weight

A -

B -

C -

D -

E -

F -

G -

Total sum

A different scale for scoring, ranging from 1 to 5 is recommended to give higher

resolution. Also, it may be appropriate not to have one concept as reference for all criteria.

Having a concept as reference which is the best in one area may lead to what Ulrich and

Eppinger call “scale compression”. Ranking of the concepts is achieved by multiplying

the rating with the weight and then sum all weighted ratings resulting in a total score. As

in the concept screening, the team members should still try to find possible ways to

combine and improve the concepts. The final selection of concept or concepts for further

development should be performed carefully. A sensitivity analysis can be performed

where ratings and weights are varied to determine the impact on the final score. The

uncertainty surrounding a concept can also play a role in its perceived feasibility and

likelihood to be selected. When reflecting on the results and outcome, the team should

feel that the concept with most potential was chosen and that no important issue has been

left uninvestigated. (6)

2.7 Detail design

During detail design, both tools and methods are used. The softwares provided by

MacGREGOR are the main tools used and the methods are stress analysis and bearing

design.

2.7.1 Software

I-deas 12 is a computer aided design, manufacturing and engineering analysis software

released by UGS in 2006 (8). This is the software currently used by MacGREGOR for

part modeling, assembly and drafting. In this project, I-deas is used mainly in the detail

design process where the chosen concept is modeled and refined. Simulation and strength

analysis is also performed with the use of I-deas.

Matrix Navigator, provided by MatrixOne Inc., is a PLM (Product Lifecycle

Management) software used by MacGREGOR mainly for handling order specifications

and drawings. Internally it is called MacARK and is integrated with I-deas for creating

drawings.

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2.7.2 Stress analysis

To analyze the structures involved in this project in terms of stress and deformation, the

finite element method (FEM) has been used. This is a well known tool which is often

used and is incorporated into I-deas. In this project it is used in the detail design phase to

confirm numerical analysis and also to get an idea on how structures behave when

exposed to stress.

2.7.3 Bearing design

The process of bearing selection requires collaboration between the customer and the

manufacturer. The customer in this case is MacGREGOR and the manufacturer Rothe

Erde. Rothe Erde has been a long time supplier of slewing bearings for MacGREGOR

which have resulted in a close relationship between the two.

As on other parts of the crane, MacGREGOR’s module design philosophy is applied on

the slewing bearing as well. A limited amount of bearings are available, each covering a

range of crane types and capacities. The module philosophy renders it possible for

MacGREGOR to have limited amount bearings available which reduces costs and

simplifies the process of bearing selection for a particular order.

The slewing bearings that MacGREGOR use are developed together with Rothe Erde to

fit the needs at hand. The development of a bearing is an iterative process which includes

communication of various formats between MacGREGOR and Rothe Erde. The slewing

bearings used by MacGREGOR are attached to the companion structures with the use of

high-strength prestressed bolts. The focus for MacGREGOR during the development

process is on the bolts sizes and the bearing diameter. The raceway and sealing design is

entirely up to Rothe Erde.

Rothe Erde has developed a method were the bearing selection and development of

surrounding structures is a joint task with the responsibility spread between themselves

and the customer. Previously, analysis has only been made by the manufacturer or the

customer. Experience has shown that such methods where the manufacturer has to gain

knowledge about the customers’ companion structures or the customers has to get

information to be able to correctly model the bearing, are time consuming. With this in

mind, as well as other criteria, the current method based on finite element analysis (FEA)

was developed.

When using this method, the model is divided into three separate part models; the upper

and lower companion structure and the bearing. The customer creates separate finite

element models for the upper and lower companion structure. Instructions from Rothe

Erde are then given on how to adjust the models so that a problem-free combination with

the finite element model of the bearing is possible. (9)

The process starts with MacGREGOR performing a slewing ring calculation based on

loadcases which form the basis for the bearing design. The loadcases are determined by

classification societies and Rothe Erde. The loadcases defined by classification societies

focuses on the design of the bolt joints meanwhile Rothe Erde needs loadcases for the

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design of the rolling elements and raceways. The input values in these calculations

depend on the crane type and the situation the crane is to be used in, e.g. SWL, outreach,

type of cargo etc.

A drawing is also created which describes proposed bolt sizes and general dimensions of

the bearing. Here, assembly, maintenance, available space and other criteria play a crucial

role in determining the design space available for Rothe Erde.

When MacGREGOR and Rothe Erde has come to agree on a general design, the process

continues with MacGREGOR developing models that Rothe Erde can use when

developing the bearing itself. These models of the companion structures, i.e. the crane

house and foundation, are created according to instructions given by Rothe Erde.

According to the strength analyst (10) at MacGREGOR, the models of the crane house

and foundation are created as follows:

- A Cartesian coordinate system is used where the Z-axis of the model is coincident with the Z-axis of the bearing and is directed vertically upwards.

- On the flange surfaces of the crane house and foundation, as many nodes as there are bolts are created. The nodes are evenly placed around the bolt circle

each having six degrees of freedom. These nodes are referred to as interface

nodes.

- The first interface node is placed in the XZ-plane, see Figure 2.1. - A node in the centre of the node-circle, with X=0 and Y=0 and the same

global Z-coordinate as the other nodes, is also created.

- The nodes are numbered, increasing around the Z-axis in a positive direction, beginning at the position where X=0 and finishing in the centre node. The

final model does not include nodes with a higher number than the centre node.

Figure 2.1 Nodes created on the flange surface of the bearing

- The interface nodes that act as bolts have to be joined to the surrounding elements in a way that allows them to transfer translations and rotations in all

directions. When using a structure made of shell elements, the nodes can be

directly joined to that structure with the required six degrees of freedom. If a

solid element structure is used, the nodes have to be joined using rigid

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elements. Otherwise, the nodes will only be able to translate translational

movements.

- The nodes on the lower edge of the pedestal are attached to the centre node with rigid elements. Normally, these nodes are constrained globally to the

coordinate system.

- The interface nodes on the crane house are locked, constraining all translations and rotations.

- The calculated loads are applied on the model and the results are evaluated. If unexpected deformations occur near the interface nodes on the flanges, the

structure can be stiffened with the help of rigid elements.

- When the results are satisfying, i.e. the model has correct tension concentrations and levels, they are written to a universal file (.unv). This file

is later used by Rothe Erde as basis for the load vector in the bearing

calculation.

- In order for the stiffness matrices to be written in required format, data set 612, and also for the mass and stiffness matrices to be written in separate files,

denoted M.unv and S.unv, a file substruc.prg in I-DEAS has to be replaced.

The replacement file is provided by Rothe Erde.

- A Master Dof Set in I-DEAS is created restricting degrees of freedom for the interface nodes.

- The stiffness matrices are reduced by using Guyan’s method so that a small file is created which can be sent to Rothe Erde. This is a process of static

condensation which reduces the stiffness matrices created to the degrees of

freedom of the connecting nodes.

- An email is sent to Rothe Erde with files containing loads and stiffness matrices for the upper and lower companion structures.

With the three files, Rothe Erde performs calculations and determines whether the by

MacGREGOR proposed design works or not. Rothe Erde sends the results through email

in the form of universal files containing Restraint Sets which describes deformations in

the nodes. The model of the crane house and foundation is written into a universal file

into which the Restraint Set from Rothe Erde is incorporated. This file is saved and

imported into I-deas. After checking that the Restraint Set from Rothe Erde is

incorporated, i.e. nodes have constraints, the model can be solved regarding stress and

deformation. (10)

When MacGREGOR and Rothe Erde have come to agree on a final design, the bearing is

included in the list of available bearings, meaning it can be used for a range of crane

types. During 2008, MacGREGOR is in the process of replacing their available slewing

bearings with newly developed ones. These new slewing bearings have a different design

and form a whole new set of modules.

17

3 Current solution The current solution is the design of the components as well as the manufacturing and

assembly involved.

3.1 The existing design

The existing design consists of the GL4528 crane in general and more specific, the

currently used slewing bearing.

3.1.1 MacGREGOR Crane GL4528

This project is based on the MacGREGOR electro-hydraulic deck crane type GL with a

hoisting capacity of 25-100 tons at a jib radius of 20-42 meters with a hoisting speed of

24-44 m/min. The GL crane is designed as a cargo handling crane for container ships,

bulk carriers and cargo ships. The particular order of which the project refers to is

designed to handle a SWL of 45 ton at 28 meters outreach and a 40 ton SWL at 30 meters

outreach. By designing the crane for a specific SWL at a specific outreach instead of the

overall maximum SWL at the maximum outreach the crane can have a slimmer design

and is thereby more cost efficient.

The GL crane is modularly based in order to achieve a stable design with high quality and

a stable production by having common components for many different crane types. This

also leads to shorter lead times for the design and production as well as a reduction of the

number of spare parts. Some of the modules can be seen in Figure 3.1 below.

Figure 3.1 Some modules included in the GL crane assembly

18

Most of the equipment and components are assembled inside the crane house making

inspections and maintenance of the machinery easier and weather independent. An

exception is made for the oil cooler which is located on the top of the crane house in

order to be kept away from dusty environments and to provide a more efficient cooling.

3.1.2 Slewing bearing

For a crane of type GL4528, a three-row roller bearing from Rothe Erde is used, which

internally is called RE16, see Figure 3.2. RE16 replaces a similar bearing called RE6. On

crane types with smaller capacities single-row ball bearings are used.

The bearing consists of an outer [1] and inner [2] ring, the outer attached to the crane

house [3] and the inner to the blank [4] in the foundation [5]. The rings are attached with

the use of high-strength prestressed bolts [6] in bolt circles evenly spread around the

flanges of the bearing. The outer ring is larger in diameter and sits outside the inner ring.

The outer ring is divided horizontally in order for assembly of the slewing bearing to be

possible [7]. The bearing has internal gears [8] placed on the inner ring. In the interface

between the outer and inner ring there are three rolling elements [9], transmitting axial

and radial forces, making it possible for the crane to slew around its own axis. Two seals

[10] keep unwanted material from entering the raceways. Grease nipples [11] are placed

around the inner ring, for lubrication of the raceways.

Figure 3.2 Slewing bearing RE16

3.2 Manufacturing and assembly

MacGREGOR cranes are manufactured by production partners in China, Korea, Poland

and Croatia thus offering logistical benefits for ship owners and shipyards. MacGREGOR

provides the design, key components, continuous production supervision, quality control

and testing. At the partner’s manufacturing plants the crane modules such as the crane

19

house, jib and foundation are welded. The bottom plate of the crane house is machined

with a horizontal boring mill in order to achieve the tolerance required by the slewing

bearing considering planarity. The result of the machining can be seen in Figure 3.3

below, where the crane house is lying on the side with the bottom plate facing the camera

showing the machined outer ring surface prepared for the slewing bearing and four

circular holes prepared for the slewing gears.

Figure 3.3 Machined crane house

The slewing bearing is one of the many modules included in the crane’s design. It is

bolted to the crane house bottom plate through the outer ring of the bearing and to the

flange on top of the foundation through the bearing’s inner ring. In Figure 3.4 below the

bottom plate of the crane can be seen with the slewing bearing bolted onto it.

Figure 3.4 Slewing bearing mounted on crane house

20

The forged top flange i.e. the blank is preheated to 150° C to avoid faulty eccentric

running when welded onto the foundation where it is machined to fulfill the required

flatness tolerance. The crane house is completely assembled with all components and

equipment mounted inside at the manufacturing plant. The crane house, jib and

foundation are then transported to the shipyard where the pedestal has been

manufactured.

The narrow flatness tolerance required by the slewing bearing demands a careful welding

procedure when the foundation is welded to the pedestal. There is no gap allowed

between the foundation and the column before welding, nor is it allowed to push or pull

the foundation to make it fit. The welding procedure is then carried out by two welders

working simultaneously on opposite sides of the welding zone. The flatness of the top

flange of the foundation is then checked and must be within tolerance otherwise it is

necessary to machine the surface in place or cut down the foundation and reweld it. The

permissible gap is only 0,20 mm for a Ø2500-4000 mm top flange.

21

4 Implementation and results Implementation and results documents how the methods described in section 2 were used

and what results were gained. The final conclusions will be described in section 5.

4.1 Product development

The methodology used in this project is developed to fit the problem at hand where

SIRIUS Masterplan functions as a guide, inspiration and reference. See appendix 1.

Stage one in SIRIUS Masterplan, describing the planning phase is used with the

exception of creation of a budget. Team roles, group and individual goals, coaching

strategy and a Gantt chart are discussed and defined. Here, discussions also lead to the

chosen methodology and SIRIUS Masterplan is modified to fit the situation.

In this project, phase two called design space exploration is redefined and renamed and is

called problem analysis. This is done since an extensive benchmarking process is not

possible to carry out. For instance, no competitor cranes can be tested or evaluated. Also,

since the problem is already known and this project is about evaluating a double bearing

solution, part of the scope is already defined. As a whole, the design space is well known

and the work in the problem analysis phase focuses on gaining knowledge surrounding

the current solution.

The roadmap phase is used to some extent; a mission statement is not produced since a

similar one already is defined in the project description. The results from the problem

analysis phase form the product characteristics, which are defined with measurable

criteria. The product characteristics are updated throughout the project.

Concept generation, evaluation and selection, which constitute the concept design and

prototyping phase, is work based on various methods and extensive discussion using

experience both from students and MacGREGOR. Here, some of the methods used

originate from the suggestions given in SIRIUS Masterplan. Also, suitable literature

provides detailed information about various methods for generating, evaluating and

selecting concepts.

Detail design and manufacturing constitutes the final phase for this project. No

prototyping or manufacturing of concepts is made. Instead the final design is delivered as

3D models and drawings.

4.2 Planning

First, a general project plan, appendix 2, is developed describing team roles, goals,

coaching strategy and what work that needs to be done in the major phases of the project.

The phases are specified with SIRIUS Masterplan functioning as basis and the content of

each phase defined by the group members. Responsibility over different aspects of the

project is divided between the group members which clarifies the team roles. The

individual and group goals are also defined and a coaching strategy is developed. With

the support of the general plan, a Gantt chart is created showing a timeline from the

22

project’s start to finish, appendix 3. The project plan is approved by coaches before work

proceed.

4.3 Problem analysis

In order to analyze the current situation correctly and thereby understanding the problems

at hand, and doing this without leaving out any crucial information, the work is divided

into three different areas; needfinding, benchmarking and related technology.

The needfinding is carried out as a combination of individual research and interviews

with various resources within MacGREGOR. The individual research is focused on

online resources and suitable literature. Interviews are in the form of casual meetings

with experts in different fields as welding, manufacturing, service, design, strength

analysis, slewing bearing selection etc. Due to difficulties with closely inspecting and

evaluating competitor products, only information provided by the manufacturers

themselves is used for benchmarking. This gives an overview of what manufacturers that

exist on the market today and it also gives a general idea of their design. Work in related

technology is focused on online resources. The idea here is not to closely investigate

other types of technology but to get inspiration and ideas for concept generation.

4.3.1 Needfinding

The new solution has to match or exceed the current solution’s performance and at the

same time motivate any increase in costs. The current solution’s level of performance in

some areas is also the reason why this project came to be. In order to know how and in

what areas the new solution has to perform, the needs involved in this project are

investigated. The needfinding process described by Ulrich and Eppinger (6) provides

support and is used throughout this phase of the project.

The first step in the method described in section 2.3.1 about needfinding, is gathering raw

data. Since interviewing customers and end users of ship cranes is not feasible for this

project, resources at MacGREGOR are used instead. Here, service engineers and experts

with close relationships with customers and end users are informally interviewed on

various occasions. Also, besides doing interviews, individual research focusing on

examining the current solution is performed.

By learning about the current solution’s advantages and drawbacks, needs that are to be

met within the scope of this project can be determined. Therefore, the analysis of the

current solution, presented in section 3, and the needfinding process are combined and

carried out simultaneously.

The raw material is documented as notes from interviews and knowledge gathered

throughout the process. A document describing the needs is created which is

continuously updated as needs are added, refined or revised. The gathered knowledge and

raw data are translated into customer needs, which is step two in the needfinding process

described by Ulrich and Eppinger (6). For example, it is realized that the ship crew needs

to be able to enter and exit the cabin from the ship deck without having to climb on the

outside of the crane itself. This is then translated into a need statement saying that the

23

new solution needs to allow entry and exit through the crane house floor. Step three in the

process is organizing the needs. Similar needs are gathered under one primary need

creating a hierarchy of two levels. This simplifies further use of the needs when creating

criteria for the concept evaluation phase. The relative importance of the needs, step four

in the process, are not determined at this stage in the project. This will be done when

weighting criteria for the concept evaluation process. This process is iterative, and every

loop improves the needfinding’s accuracy. It is also realized that not all needs can be

determined at once at an early stage in the project. Therefore, the needs are continuously

updated as knowledge increase throughout the project.

The needs this project has to fulfill are presented, explained and analyzed below. The

needs are arranged, beginning with safety, manufacturing, assembly and costs which are

central to this project. These are followed by crane house design, pedestal design, jib

parking and space requirements which are more connected to design issues. Entry and

exit, inspection and maintenance are more towards end user needs. Mechanical needs are

separate and constitute a category of its own. These needs are summarized in a document

called “Needfinding Criteria” for easier use later in the project, see appendix 4.

Safety

One of the major reasons why this project was initiated was the wish for increased safety.

In the past, due to poor maintenance, slewing bearings have broken down causing the

crane to fall down from the foundation. This have so far only happened on single row ball

bearings. Also, cracks beneath the blank on the foundation have led to similar

consequences in cases where the crane has been exposed to considerable overload. By

having a design with two bearing positions, failure of one bearing or crack development

would not have such disastrous consequences. Therefore, the solution should not allow

the crane house to fall down if one of the bearings should fail or a crack near the flange

develops.

Manufacturing

The slewing bearing that is to be replaced is manufactured by Rothe Erde and delivered

to a MacGREGOR production partner for assembly on the crane house. The companion

structures are manufactured by the production partner, which will also have to be the case

for the new solution.

Assembly

Due to a combination of low tolerable flatness deviation of the companion structures and

complicated weld joints, the yard mounting of the crane house is an expensive and

demanding procedure. The tolerated out of flatness, given by Rothe Erde, for each of the

machined contact surfaces is 0.2 millimeters. For MacGREGOR, these surfaces are the

bottom of the crane house and the blank on the foundation. The bottom of the crane

house is machined after all welding is done and it is therefore not an issue to clear the

maximum tolerated out of flatness. The foundation however, is machined and then

welded in the yard onto the pedestal which is usually constructed by the yard themselves.

This means that the tolerated out of flatness on the blank when welding the foundation

onto the pedestal, is often less than 0.2 millimeters.

24

The new solution should simplify assembly either by decreasing the effect allowable

flatness deviation has on the assembly or by increasing the tolerable out of flatness itself

given by the bearing manufacturer.

Bolt tightening is performed with a hydraulic tension cylinder. This tool requires space

depending on the bolt size chosen. This has to be taken into account when determining

the size of the surfaces on which the bolts are to be placed. Experience has also shown

that due to inaccuracy when rolling the circular walls and needed accessibility for bolt

tightening the bolt circle diameter has to be placed an extra eight millimeters from the

nearest wall.

Costs

Any increase in cost the new solution will result in has to be motivated by increased

advantages in other areas, e.g. manufacturing or assembly. A more thorough evaluation

of this issue can be seen in appendix 5.

Crane house design

The current slewing bearing solution is compact, which is an advantage when all

components need to fit inside the crane house. No components are placed below the

slewing joint, i.e. the slewing bearing, meaning that no complicated rotatable joints need

to be involved. Also, it means that a complete crane with foundation can be delivered to

the shipyard and be ready for assembly. The new solution should strive to keep current

placement of components. However, if considered necessary because of other advantages,

modification of the crane house can be motivated.

Pedestal design

There are mainly three types of foundations used depending on the design of the pedestal.

Type A foundation has a circular bottom end with a smaller diameter than the upper

flange. This gives it a conical design. A foundation of type B is circular with the same

diameter through the whole length. A foundation of type C is circular near the top flange

and quadratic at the bottom end. Each of these three fits onto different types of pedestals

and for a GL crane, type C is most common. The solution should be valid for all types of

pedestals

Jib parking

Jib parking arrangements vary and are individually designed for each specific crane

delivered. If the crane jib is sea stowed using a cable parking arrangement, the jib’s

slewing movement is locked by features attached to the foundation. If the crane jib is

locked using jib support features, these can be placed on another crane’s foundation. The

conclusion is that the design has to allow for attachment of jib support or slewing lock

features.

Space requirements

The crane’s space requirement on the ship should not increase since this would affect the

ship’s loading capacity.

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Entry and exit

The new solution has to allow the crew to enter and exit through the floor of the crane

house from inside the pedestal.

Inspection

At the factory, after mounting the slewing bearing on the crane house and before shipping

it to the yard, the gear backlash is measured. This procedure requires access to the gear

teeth with a thickness gauge.

After the crane is mounted, and final inspections are made, the slewing bearing play is

measured. This is done in order for the ship crew to keep a record over the slewing

bearing wear. Measurements should be taken every six months and if the play exceeds a

certain value, the slewing bearing should be replaced. The solution should allow for

bearing wear to be measured.

It should also be possible to discover cracks or any other damage on the crane

components. Therefore, the design should not hide or cover critical areas where such

cracks or damage can arise.

Maintenance

Maintenance has to be easy to perform. Therefore, items such as lubrication nipples have

to be easily accessed. Grease sampling, which is performed every twelve months in order

to check the bearing’s condition, demands access to the slewing bearing seal on the inside

of the crane.

Mechanical

According to the scope of this project, the new solution is meant to replace the current

design involving a specific crane type and slewing bearing. Therefore it is assumed that

the mechanical specifications will be the same as today. These specifications form a basis

which determines what components that needs to be used and how they have to perform.

The specifications that affect the slewing bearing design are in the form of loadcases. The

loadcases used in this project are the same as used for development of slewing bearing

RE16.

Beside the loadcases, the crane must have an unlimited slewing range. This means that no

features or components can restrict its movement. The solution will be designed to fit

current conditions when pedestals of type A, B and C are used. If needed, this issue can

be discussed and the decision revised.

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4.3.2 Benchmarking

Benchmarking is work consisting of finding competitor products and more specifically,

investigate the slewing bearing solution.

Neuenfelder Maschinenfabrik

NMF, short for Neuenfelder Maschinenfabrik, founded in 1970 and located in Hamburg,

Germany, produces cranes and hydraulic equipment. NMF currently offers heavy-lift

cranes with maximum rated loads of up to 1000 tons. The DK II, seen in Figure 4.1,

which has the highest production volume, is a general purpose cargo crane that is offered

for loads from 20 up to 80 tons with a jib radius of 16 to 35 meters. The DK II Heavy

model has capacities from 100 to 600 tons with a jib radius from 14 to 35 meters. (11)

Figure 4.1 NMF DKII crane

Liebherr

In 1949 the Liebherr family business was founded by Hans Liebherr. The Liebherr Group

is still owned by the family and is divided into independent company units. Liebherr offer

ship cranes of various types where the CBB wire-luffing crane, seen in Figure 4.2, is a

container and multi-purpose handling deck crane. It is offered for loads between 25-45

tons with a jib radius of 24 to 32 meters. (12)

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Figure 4.2 CBB 45(40)36/25(28)31crane

IHI – Japan

Ishikawajima-Harima Heavy Industries Co., Ltd, founded in 1853, manufactures IHI

deck cranes. (13) Products include single and double deck cranes, four-rope grab cranes,

hose handling and gantry cranes. (14)

TTS/LMG

TTS-LMG is part of the TTS Marine Cranes Division after LMG being taken over by

TTS Marine ASA in 2004 (15). Three different types of wire luffing cargo cranes are

offered; KL, KS and K which offer SWL’s from 30 to 45 tons and maximum outreaches

up to 32 meters. (16)

Tsuji Heavy Industries Co., Ltd

Tsuji Heavy Industries Co., Ltd is based in Japan and offers through their marine

equipment division offer deck cranes of various types with lifting capacities up to 400

tons. The HD series has capacities from 30 to 40 tons with maximum jib radiuses from 20

to 30 meters. (17)

Kawasaki Precision Machinery, Ltd

Kawasaki Precision Machinery Ltd (KMP), based in Japan, was established in 2002 when

separating from Kawasaki Heavy Industries Group. KPM offers single, twin, semi-slim

and hose handling cranes where the single type cranes have capacities from 150 to 500

tons. (18)

Mitsubishi Heavy Industries, Ltd

Mitsubishi Heavy Industries, Ltd (MHI), established in 1950, developed their first

electro-hydraulic deck crane in 1972 and has since then delivered approximately 4000

units worldwide. (19)

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Huisman-Itrec

The heavy lift mast cranes, see Figure 4.3, offered by Huisman-Itrec have capacities from

200 to 7500 tons. These cranes have a fixed welded steel mast attached to the vessel. The

slewing platform, which the jib is attached to, pivots together with the masthead. The

winches are fixed below the mast foot in the ship’s hull which limits the slewing range to

450 degrees. The lower bearing is because of the welded mast structure not a limiting

design item. (20)

Figure 4.3 Huisman-Itrec heavy lift mast crane

Summary MacGREGOR’s major competitors have cranes with a single slewing bearing solution.

An exception is Huisman-Itrec which has a completely different design. These cranes

however, are mainly used for heavy lift situations and cannot be seen as competitors to

MacGREGOR cranes. However, as inspiration for a double bearing solution they are

interesting.

4.3.3 Related technology

Interesting products in other markets have been investigated where efforts have been

focused on how slewing bearings are used.

Excavator

The excavator generally consists of an articulated arm with a bucket and an operator’s

cabin mounted on a pivot on top of the tracks or wheels of the machine as shown in

Figure 4.4. The pivot consists of a slewing bearing with an internal gear allowing the

excavator to rotate. The slewing bearing experiences both axial and radial loads as well

as a tilting moment as the arm of the excavator operates. (21)

29

Figure 4.4 Excavator with red marker indicating location of slewing bearing, cross section of slewing

bearing is shown in lower left corner

Rudder propellers

The rudder propeller, seen in Figure 4.5, is mounted on a vertical shaft allowing the

propeller unit to rotate perpendicular to the propeller’s propulsion direction thus

eliminating the need of an actual rudder. The load created by the propeller’s thrust results

in radial and axial loads as well as a tilting moment on the slewing bearing supporting the

rudder shaft. The weight of the propeller unit also generates an axial load in the pivotally

suspended slewing bearing. (21)

Figure 4.5 Stern rudder propeller with red marker indicating location of slewing bearing, cross

section of slewing bearing is shown in lower left corner

Wind energy turbines

The turbine housing, seen in Figure 4.6, is pivotally mounted to a slewing bearing on top

of the column allowing the housing to rotate into a favorable angle relative the direction

of the wind. The slewing bearing is designed to withstand the axial and radial loads in

addition to the tilting moment generated by the rotor. (21)

30

Figure 4.6 In the mid lower part of the figure the mentioned slewing bearing can be seen along with

two cross section images of a single row respectively a double row ball bearing configuration

4.4 Product characteristics

The product characteristics are developed from the needfinding criteria described in

section 4.3.1. The criteria are modified into measurable demands which the product has

to meet in order to be successful. Final decision regarding each of the product

characteristics are discussed with resources from MacGREGOR and the bearing

manufacturer.

Directly after finishing the needfinding phase, a first version of the product

characteristics was developed and discussed with the project supervisor. Some issues

could not be decided upon, such as costs and possible modifications. These were later

revised as the project proceeded. The final version of the product characteristics can be

seen in appendix 6.

4.5 Concept generation

The concept generation process of this project was conducted at MacGREGOR during

two brainstorming sessions and complementary work throughout the period of week 38.

With the support of various colleagues at the company a series of sketches were created

according to the description below.

First session

The first brainstorming session was performed on Monday the 15th of September, in

cooperation with handpicked recourses from various departments at MacGREGOR.

Initially the participants were briefly informed of the conditions of the project, regarding

the double slewing bearing application. All participants had prior to the meeting received

a document, enclosed in appendix 7, containing information about the first session. The

given information was deliberately restricted with the intention to obtain fresh ideas, not

influenced by prior knowledge of the project. The participants were then given sketching

materials and asked to denote as many concept drawings of a double slewing bearing

31

solution as they could, without communicating with each other. These sketches were then

collected and shown to the group, one at a time, for the participants to explain them to

each other, aiming to associate to new ideas.

After the meeting, the sketches were compiled in to the following three categories,

enclosed in appendix 8; Dual bearing similar size, Dual bearing variable size and Outside

the box. A fourth category with Safety Hook solutions was compiled and laid aside.

These compilations along with a document of information, enclosed in appendix 7, were

sent to the participants prior to the second meeting.

Second session

The second brainstorming session held on Thursday the 18th of September, aimed to

further develop the previously generated ideas and narrow them down to more thought

trough concepts. The meeting also aimed to discuss the assembly problem regarding the

narrow tolerance of flatness of the foundation’s top surface. However the meeting came

to be more about discussing current problems rather than discussing innovative designs

meant to solve them. Nevertheless this resulted in further information regarding the

problems of the current design solution of the slewing bearing’s ambient structures. It

was therefore decided to enhance the previously produced concept sketches through

discussions within the project group.

Summary

The discussions lead to five refined concepts, shown below in Figure 4.7 and enclosed in

appendix 9, that emerged from the sketches created in the first brainstorming session.

These concepts were then brought to the next phase, the concept evaluation.

Figure 4.7 Refined concepts

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4.6 Concept evaluation and selection

The concept evaluation process was performed in cooperation with handpicked personnel

at MacGREGOR. The group involved in the concept generation phase were invited to

participate since they were already aware of the background of the project and the

previously generated concepts.

Prior to the meeting an evaluation matrix was created in order to compare the concepts

relative to each other regarding a set of predetermined criteria. The criteria originated

from the needfinding results and the product characteristics document. The criteria were

weighted by pair wise comparison, seen in Table 4.1, in order to find the decisive design

factors. Scores were set, comparing the importance of a row relative a column in the

matrix, according to; much more important=1, equally important=0,5 and much less

important =0. The criteria implemented in the matrix were as follows:

Manufacturing Machining complexity affecting time required for the

manufacturing process.

Assembly Time needed (both at partner manufacturing plant and shipyard)

for bolt tightening, welding etc.

Safety Effects of bearing failure.

Maintenance Accessibility for performing bearing lubrication and grease

sampling.

Inspection Accessibility for measuring gear backlash and bearing wear.

Entry & Exit Ease of entering and exiting the crane through the pedestal and

foundation assuming that existing regulations are fulfilled.

Modifications needed Modifications needed in order to incorporate solution into existing

design and component placement regarding pedestal and

foundation.

Table 4.1 Criteria weighting by pair wise comparison

Manufacturing Assembly Safety Maintenance Inspection Entry&Exit Mod. Needed Sum Weight

Manufacturing - 0,5 0 0,5 1 1 1 4 0,19

Assembly 0,5 - 0 0,5 1 1 1 4 0,19

Safety 1 1 - 1 1 1 1 6 0,29

Maintenance 0,5 0,5 0 - 0,5 1 1 3,5 0,17

Inspection 0 0 0 0,5 - 1 1 2,5 0,12

Entry & Exit 0 0 0 0 0 - 1 1 0,05

Mod. needed 0 0 0 0 0 0 - 0 0,00

Total sum 21 1,00

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The results of the criteria weighting demonstrated in Table 4.1, shows that safety is the

single most important design criteria, which reflects the purpose of the project; to prevent

the crane house from falling down in case of a bearing failure. Ranking at number two,

manufacturing and assembly are judged to be equally important, derived from the fact

that the two are closely dependent of each other. A thorough manufacturing process is

required in order to attain accurate components, which simplifies the assembly process.

Furthermore, it is of equal importance to perform the assembly in a scrupulous manner,

otherwise the thorough manufacturing is pointless. Maintenance, ranking at number three,

has as well as inspection, ranking fourth, an impact on the safety of the construction. In

order to attain a long service life the structure must be regularly maintained and inspected

to prevent premature failure. The entry & exit criteria proved to have little importance

compared to the other criteria as long as all the existing regulations were followed.

Ranking a total weight of zero, thus ending up last, the criteria modifications needed will

have no impact in the concept evaluation. This since MacGREGOR saw no problems in

redesigning their product in order to fulfill the other criteria.

For each criterion in the concept evaluation matrix in Table 4.2, a concept was chosen to

serve as a reference to which the other concepts would be compared. The chosen

reference concept was assumed to have an average score regarding that specific criterion

therefore it was given the average score of three. The scoring was done according to;

much worse than =1, worse than =2, same as =3, better than =4, much better than =5. The

reference concept for each criterion is marked by a filled box in the concept evaluation

matrix below. The current solution is represented in the RE16 column. The concept C+++,

seen in appendix 9, F1 and F2 was developed during the sessions and added to the matrix.

Table 4.2 Concept evaluation matrix

RE16 A++ B++ C++ H+ C+D+ C+++ F1 F2

Manufacturing 4 3 3 1 2 1 2 4 4

Assembly 4 3 3 2 3 1 4 4 4

Safety 1 3 3 2 3 2 5 3 3

Maintenance 4 4 4 4 3 3 2 4 4

Inspection 5 4 4 2 3 2 2 5 4

Entry & Exit 5 4 4 5 3 4 5 5 4

Mod. needed 5 4 4 3 3 2 3 5 4

The weight calculated in Error! Reference source not found. was then multiplied by the

scores presented in Table 4.2 resulting in the final scoring matrix shown in Table 4.3.

34

Table 4.3 Weighted concept evaluation matrix

Weight RE16 A++ B++ C++ H+ C+D+ C+++ F1 F2

Manufacturing 0,19 0,76 0,57 0,57 0,19 0,38 0,19 0,38 0,76 0,76

Assembly 0,19 0,76 0,57 0,57 0,38 0,57 0,19 0,76 0,76 0,76

Safety 0,29 0,29 0,86 0,86 0,57 0,86 0,57 1,43 0,86 0,86

Maintenance 0,17 0,67 0,67 0,67 0,67 0,50 0,50 0,33 0,67 0,67

Inspection 0,12 0,60 0,48 0,48 0,24 0,36 0,24 0,24 0,60 0,48

Entry & Exit 0,05 0,24 0,19 0,19 0,24 0,14 0,19 0,24 0,24 0,19

Mod. needed 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00

Total score

3,31 3,33 3,33 2,29 2,81 1,88 3,38 3,88 3,71

The results from the weighted concept evaluation matrix were then compiled in

descending order from the highest total score in Table 4.4 below.

Table 4.4 Concepts ranked concerning score received in the weighted concept evaluation

Rank Concept Total score

1 F1 3,88

2 F2 3,71

3 C+++ 3,38

4 A++ 3,33

5 B++ 3,33

6 RE16 3,31

7 H+ 2,81

8 C++ 2,29

9 C+D+ 1,88

The two highest ranking concepts were conceived during a concept evaluation meeting,

and fell under the category Safety Hook. They were still evaluated as a reference to the

other concepts but not further developed since they fell outside the delimitations of the

project. The two lowest ranking concepts were left out from further analysis due to their

low scores in the ranking and for individual scarcity. In the case of C++ there was an

improved version C+++, which was developed in an evaluation meeting, see appendix 9.

The C+D+ concept was predicted to be too complex to manufacture and assemble from

an economical point of view. Furthermore, both required an additional foundation

mounted below to make the transition from the circular cross section of the slewing

bearing to the square cross section of the pedestal.

The remaining four concepts were divided into two categories, depending on the size and

location of the slewing bearings; category one, containing concepts A++ and B++;

category two, containing concepts C+++ and H+. This was done in order to simplify the

concept selection by pairing up the concepts in consideration of their properties. The pros

and cons of the categories were then taken in consideration to determine which category

would be best suited for further development in the detail design phase. It was estimated

that category two would bring difficulties concerning the circular tolerance needed at the

flanges when mounting the bearings. The tolerance would be hard to keep when welding

35

the sheet casings to the flanges, since the heat generated in the welding process would

cause the flanges to distort. Also the pair wise assembly of the bearings linked by the

sheet plate cylinders would result in tolerances in the vertical plane. These tolerances

would complicate the assembly. Furthermore the rotating outer casing of the foundation

of C+++ would complicate the placing of jib parking structures.

Category one on the other hand presented some important advantages, such as being

applicable on all three MacGREGOR foundation types, as well as inclined pedestals

without adding unnecessary height as would be the case of category two foundations. In

addition the component costs would be held down due to the smaller lower bearing and

the fact that less steel is required. Additionally the lower slewing bearing becomes

weather independent since it is mounted inside the foundation, making inspections and

maintenance easier. Category one presents yet another important advantage being safe

even if fissuring in the weld between the foundation and the blank causes fractures,

leading to separation between the two. The structure is in such cases supported by the

stay anchored in the lower bearing position. Supported by the previous mentioned facts,

category one was chosen to be brought into detail design.

4.7 Detail design

Category one including conceps A++ and B++ were, as previously described in the

concept evaluation and selection section of this report, chosen to be further developed

and investigated in the detail design phase of this project. Initially in the detail design

phase a numerical analysis was performed in order to learn the moment distribution

between the two bearings, it was also to be used to confirm the results of the finite

element analysis. Here follows a description of the work perfomed during the detail

design phase.

4.7.1 Numerical analysis

In order to understand the interaction between the two bearings, regarding the moment

distribution, a numerical analysis was performed. The moment distributed to the lower

bearing is directly dependent of the deformation of the top bearing and the stay

connecting the bearings.

The bearing play increases with time due to wear. This causes the bottom plate of the

crane house to tilt relatively the bottom plate of the foundation, thus deforming the stay

connecting the two surfaces. According to Rothe Erde the maximum permissible increase

of bearing clerance in a single row ball bearing is 3 millimeters, as shown in Figure 4.8.

The initial play is approximetly 0,7 millimeters. (22)

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Figure 4.8 Measurement of bearing play (The stay is excluded in this figure)

The force distributed to the lower bearing by the stay due to the relative incline of the two

bottom plates can be calculated from the inclination angle δ, where

(4.1)

. (4.2)

The force needed to deform the stay the given angle δ, shown in Figure 4.9, can be

derived from the elementary cantilever beam equation

, (4.3)

thus assuming that the stay is rigidly clamped to the bottom plate of the crane house and

that the applied load causes the stay to deform as much as the relative incline suggests.

The stay is defined as a massive cylindrical steel beam with moment of inertia according

to:

(4.4)

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Figure 4.9 Reaction force acting on the deformed stay

By combining the elementary case equation (4.3) with the moment of inertia equation

(4.4), the reaction force acting on the stay can be expressed according to;

(4.5)

Numerically, the reaction force F in the initial unworn condition is given by

, (4.6)

and with the maximum permissible bearing play,

. (4.7)

In addition to the bearing play, the deformation of the pedestal and foundation contributes

to the deformation of the stay as well, as seen in Figure 4.10. The relative incline between

the bottom plates increases with increased load. The relative incline can be derived from

the elementary cantilever beam equation:

. (4.8)

The pedestal and foundation is approximated by a cylindrical shell of uniform diameter

equivalent to the flange of the foundation, with moment of inertia according to

, (4.9)

where r2, is the radius of the pedestal and T, is the plate thickness.

38

Figure 4.10 Deformation of pedestal and foundation causing relative incline of bottom plates

By combining the elementary case equation (4.8) with the moment of inertia equation

(6.9), the relative incline can be expressed according to

. (4.10)

Numerically the relative incline of the two plates is given by

. (4.11)

The reaction force acting on the stay due to this inclination is given by equation (4.5),

numerically this gives,

(4.12)

39

The total reaction force acting on the stay in the case of a new bearing is given by adding

the results of equations (4.6) and (4.12),

. (4.13)

For the worn bearing the corresponding results are given by equations (4.7) and (4.12),

. (4.14)

The reaction force F acting on the stay, shown in Figure 4.11, is known, hence the

moment about the stay can be calculated in order to learn the distribution between the

two bearings. Using the numerical results from equation (4.13) respectivelly (4.14) the

corresponding moment distributed to the lower bearing in the initial respectivelly the

worn scenario can be calculated according to,

(4.15)

. (4.16)

Figure 4.11 Moment equilibrium about the stay, forces acting on lower bearing

4.7.2 Finite element analysis

To get an idea of how a concept from category one would work in practice, simulations

were made using an existing 3D model of a type GL crane. The model did not represent

the crane involved in our project, it was of the same type but had a lifting capacity of 32

tons at an outreach of 37,2 meters.

The 3D model was developed by Johan Lif, a student performing his thesis work at

MacGREGOR in the fall of 2008 (23). The model was created in I-deas as a surface

model with simplified geometry used to investigate stress propagation in the foundation.

The applied load was equivalent to lifting 32 tons in addition to the weight of the crane

arm. The whole model was meshed using surface elements with corresponding thickness

to each individual plate. The bearing was represented by 100 solid beam elements with a

diameter of 36 mm connecting the bottom plate of the crane house with the flange of the

40

foundation. This can be seen in Figure 4.12 below. These beam elements act as the 100

bolts connected to each of the two rings of the real bearing. The beam elements are

placed at the actual bolt locations thereby translating the stresses into the foundation in a

realistic way. Concept B++ was incorporated into the model by simply connecting the

bottom plate of the crane house with the bottom plate of the foundation with four beams

as seen in Figure 4.12.

Figure 4.12 Four beams acting as a stay between the two bearing positions. Foundation removed in

this view

On the bottom plate of the crane house, the beam elements were each connected to a

centre node of a circular rigid element positioned near the bolt circle. In the bottom plate

of the foundation, all four beams were connected to the same node. This node was in turn

coincident with and connected to a centre node of a circular rigid element. The

connection between these two nodes was of type coupled DOF. By using a coupled DOF

connection the degrees of freedom between these two nodes could easily be controlled.

The main reason to use a coupled DOF was however to be able to determine the forces

acting on the lower bearing, by simply requesting to list constraint forces as one of the

results.

The simulation was set up as linear static. Boundary conditions consisted of a restraint set

and a constraint set. The restraint set locked all movements of the bottom edge of the

pedestal. The constraint set was the coupled DOF acting as the lower bearing. The

coupled DOF was set to allow translation along and rotation around the Z axis due to the

natural behavior of a bearing only translating radial forces. Simulations were also made

41

with all degrees of freedom locked, these showed however that forces along the Z axis

were small and had no impact on the resulting force.

Simulations with beams of five different cross sectional areas were performed. The

results are displayed in Figure 4.13 below. This figure shows the resulting force on the

node as a function of beam type. The re