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CHAPTER6

EXPERIMENTAL DETAILS

This chapter presents the details of the main work of this project

which includes the design and experimentation to produce and

inspect the alloy steel castings. Further, an attempt is made to give

the complete details regarding the manufacturing process of Straight

and flanged bar casting from pattern making to the inspection. It

includes the properties of the material, composition, pouring

conditions, allowable process parameters, and finally the results and

their analysis.

6.1 STRAIGHT AND FLANGE BAR CASTINGS

In this present work, straight and flanged bar castings are

produced with different weights. These castings are in small weight

category, as can be seen from Fig:6.1. For analyzing the defects

occurring in this casting, it is necessary to know the actual processing

conditions; gating design (which can be seen in Fig:6.2), etc.. The

manufacturing details of this casting are given below in detail.

1. Material: Alloy steels 2. Grade: 25

3. Casting weight: 50 Kg 4. Bunch weight: 80 Kg

5. Pattern material: Teak wood 6.Moisture Content: 3.6 – 4.0%

7. Permeability: 120 – 160, 8.Compactability: 42 -50

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9. Mould Hardness: center / edge-: 80 / 85 -90 /80.

10.Silica sand: 45 -50 %

11. Silica sand: 50 – 60 % 12.Active clay: 8 – 9 %

13. Versatile matter: 3.5 – 4.5 %

Fig:6.1Straight bar casting. Fig:6.2 Flanged bar casting.

6.1.1 Production of Castings

Experiments were conducted to verify the use of simulation in

an industry casting environment. The selected Castings were straight

and flanged bar made from Alloy steels (IS1030 and IS2644 their

chemical composition and Mechanical properties are shown in the

tables 6.1, 6.2 and table 6.3, and 6.4 respectively). The tests

conducted in this experiments used to find potential defects in the

casting models with different criterions and compare them with the

real casting design and to find possible outcomes to modifications

attempted to improve the existing casting design. The Riser Design

and Gating Design were also used to try to improve the existing

casting design and develop riser and gating systems for the casting.

Details of the riser and gating system design are furnished in

Appendix B. from scratch and compare the calculated dimensions and

resulting simulations with the existing casting design.

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Table: 6.1Cast Steel IS 1030

Grade C Si Mn P S Cr Ni Mo Cu V

200-

400W

0.25 0.60 1.00 0.040 0.035 0.35 0.40 0.15 0.40 0.05

Table: 6.2 Mechanical Properties

Grade Tensile Strength MPa min.

Yield Stress MPs Min.

Elongation Percent

Min.

Reduction of Area Percent

Min.

Impact Strength J Min.

Angle of Bend

Degrees Min.

200-400W

400 200 25 40 45 90

Table: 6.3 Cast Steel IS 2644

Grade C Si Mn P S Cr Ni Mo Cu V

200-

400W

0.25 0.3-

0.5

1.1-

1.4

0.035 0.035 0.5 0.40 0.15 0.40 0.05

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Table: 6.4 Mechanical Properties

Grade Tensile Strength MPa min.

Yield Stress MPs Min.

Elongation

Percent Min.

Reduction of Area Percent

Min.

Hardness BHN Min

II 640 415 20 40 200

6.1.2 Casting Design

The casting chosen in this work is a straight bar and flanged

bar made from IS1030 and IS2644. Fig: 6.3 shows a figure of the

actual finished castings with machining.

Fig: 6.3 Actual Finished Castings

6.1.3 Pattern and Mould

As a part of the preparation of the pattern for the straight and

flanged bar as considered, a log of teak wood of appropriate

dimensions is taken and the patterns are prepared in pattern shop to

required dimensions by adopting allowances. The pattern prepared is

a split type of pattern. Yellow colour on surface of pattern represents

the surface to be machined. The prepared patterns are now carried to

the moulding section. The patterns for the cope and drag are shown in

Fig:6.4 and the finished cope and drag moulds are shown in Fig:6.5

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Fig:6.4split piece pattern left and Full pattern Right side

Fig: 6.5 The Cope Mould Right and Drag Mould Left side

6.1.4 Mould preparation

The sand of prescribed grain size of 60 GFN (250microns) is

taken and is added with silicate oil of standard proportion and is

placed in Muller machine for the perfect mixing. This is essential to

ensure uniform distribution of various components in enter bulk of

the sand. The mostly commonly used Muller machine consists of two

Muller wheels in equal number of plough blades all of them connect to

a single drive source. The Muller wheels are large and heavy and they

continuously roll inside the Muller bowl. The plough blades ensure the

sand is continuously agitated. The combined action makes the silicate

oil is distributed uniformly throughout the sand. The composition of

the sand and the oil is given in the Table: 6.5

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TABLE: 6.5 Moulding Sand Composition

SILICA SAND(in kgs) SILICATE OIL(in kgs)

250 1

The quartz sand is also mixed with silicate oil with

certain compositions and is placed in the Muller machine. To increase

the collapsibility of the sand. Iron oxide powder, Silicon oxide powder

& O3 powder are also added to sand. Iron Oxide powder is added to

increase hot strength. The perfectly mixed Quartz sand which is in

pink colour is obtained due to the adding of certain composition of

Red oxide to it for easy identification. The Quartz sand as high

refractiveness & bonding. Hence it is used as facing sand especially in

pattern contact area. For roughly 3 to 4 inches & then the silica sand

is used besides the Quartz sand to make cost reduction, hence it

known as back up sand. The uniformly mixed sand is placed in mould

box around the patterns of straight and Flanged bar which consists

of the replica of the accurate dimensions of the sprue and gate, as

shown in Fig:6.6 For the present work, CO2 sand moulding technique

is chosen.

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Fig:6.6 shows the dimensions of the gating system.

6.1.5 CO2 Moulding Process

The principle of working of the CO2 process is based

on the fact that if co2 gas is passed through a sand mix containing

sodium silicate as the binder, immediate hardening of sand takes

place as a result of the chemical action between sodium silicate and

CO2.The bonding strength obtained by the hardening action is

sufficient to eliminate baking or drying of the mould and the metal

can be immediately poured. The chemical reactions taking place are of

complex nature, though the main reaction can be represented in

simplified form as:

Na2O. mSiO2. xH2O + CO2 Na2CO3 + mSiO2 .xH2O

The SiO2 obtained from the reaction contains a certain number

of water molecules and is represented as SiO2.xH2O, which is called

silica gel. This silica gel is responsible for giving the necessary

strength to the mould. The CO2 gas is passed through the mould for

5minutes to obtain required hardness. Now the patterns from the

mould are removed.

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6.1.6 Assembled Mould

After preparation of cope and drag boxes, the cope is placed on

top of the drag and then the molten metal is poured into the mould

through the sprue at 15500C with a super heat of 250C. The top open

riser is covered with magnesium based exothermic top to keep the

riser hot and feed the casting for an extended period of time. Fig:6.7

shows an assembled mould filled with liquid metal and top risers

covered with the exothermic insulation. The exothermic insulation

would be approximately 1.25 inches thick. The castings were then

stripped out of mould after 24 hours of pouring.

Fig:6.7 Pouring of liquid metal in to the Mould.

Entire work was carried in seven trials, the typical Auto Cad models

for Trial 1 is as shown in Fig 6.8 and that for Trial 2 which consists

of a modified gating system as per calculations is as shown in Fig:6.9.

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Fig:6.8 Casting with initial gating Fig:6.9 casting with modified-

-gating system

6.2 CASTINGS PREPARATION FOR NDT EXAMINATION:

The castings after allowing cooling for 24 hours are then taken

to fettling section where they are stripped off from the moulds by

destroying the moulds. The straight bar casting after removing from

the mould is as shown in Fig:6.10. The casting now is knocked and

fettled as shown in Fig:6.11. The castings are now carried to grinding

section located just besides the fettling section. In grinding process

any unwanted extra metal is removed from the casting as shown in

Fig:6.12. Once the casting is ground it is carried to machine shop

where it is machined to required dimensions. The machining process

is carried out on a lathe machine as shown in Fig:6.13. The machined

casting is now ready for testing as shown in Fig:6.14.

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Fig:6.10 Casting with runner and feeders Fig:6.11Straight bar after

fettling

Fig: 6.12 Grinding of the casting Fig:6.13 Machining of the casting

Fig: 6.14 Machined casting ready for testing

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6.3 INSPECTION AND TESTING OF CASTINGS

After simulation trials, alloy steel castings are produced with same

composition, and geometry, as per the conditions taken up in

simulation. This testing is used to validate the results of simulation

process.

The following widely used non-destructive tests are conducted

as per requirements of the case study unit.

(1) Visual inspection; (2) Fluorescent dye penetrant inspection;

(3) Magnetic particle inspection; (4) Ultrasonic test.

6.3.1 Visual Inspection :

Castings are subjected to a visual inspection to ensure that the

external surface that fail to meet the customer and manufacturer

requirements. Visible defects that can be detected provide a means for

discovering errors in the pattern or in the moulding, and casting

process. In the present study large blow holes formed in the castings

prepared for trail 1 is as shown in Fig:6.15

Fig: 6.15 defects that can be identified by Visual Inspection

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6.3.2 Liquid dye penetrant test:

Penetrant testing helps to detect small discontinuities such as

shrinkage, porosity and cracks open to the surface which tend to

retain penetrant. Smooth or machined casting surface provide more

satisfactory conditions for the test.

universal testing procedure:

1.Clean the surface of the tested casting free of dust and dirt with the

help of piece of cloth

2. Brush the surface of the casting to remove scale, paint, rust etc., by

a soft brush

3. Spray the cleaner to remove oil, grease, etc.,

4. Apply the dye penetrant by spraying allow 3 to 5 minutes for dye to

penetrant into the cracks.

5. Again spray the surface with the cleaner to remove the excess dye.

6. Spray the developer on the surface to give a thin layer. This layer

absorbs the penetrant from the cracks and red spots appear on the

surface to give a visible indication of the defects.

The liquid pentrant process as mentioned above is carried out as

shown in Fig:6.16(a) & Fig:6.16(b)

Fig: 6.16(a) Liquid Pentrant testing process

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Fig: 6.16(b) Liquid Pentrant testing process

6.3.3 Magnetic Particle Inspection:

This method of inspection is used on magnetic ferrous castings for

detecting invisible surface or slightly subsurface defects. Deeper

subsurface defects are not satisfactorily detected because the

influence of the distorted lines of magnetic flux on the magnetic

particles spread over the casting surface becomes weaker with the

distance, so that sensitivity falls away rapidly with the depth.

Procedure: The steps involved in testing are as follows.

1. Magnetising the component

2. Applying magnetic particles on the component

3. Locating the defects.

The magnetic particle testing process is carried out and it was shown

in the Fig:6.17

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Fig:6.17 Magnetic Particle testing process

6.3.4 Ultrasonic Testing:

Ultrasonic Testing used to detect internal defects in castings, based

on principle of reflection of high frequency sound waves. If surface

under testing contains some defect, the high frequency sound wave,

when emitted through the casting, will be reflected from the surface of

the defect and return in a shorter period of time. For detecting the

length of time, an oscillograph is used. The path of travel of sound

wave is plotted on the C.R.T. Screen of the oscillograph where it can

also be measured.The ultrasonic testing process is carried out as

shown in Fig.6.18 to Fig.6.21.

Fig:6.18 ultrasonic Inspection Fig:6.19 ultrasonic Inspection.

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Fig:6.20 Inspection of the straight bar Fig:6.21 Inspection of flange.

Fig:6.18 to 6.21 shows the ultrasonic Inspection of the straight bar

and flanged bar produced an indication which confirmed the

shrinkage defect at flanged bar end.

6.4 EXPERIMENTAL OBSERVATIONS:

Straight and Flanged bar castings have been produced in

foundry with cast metals as IS1030,IS2644and CO2 sand as mould

material. The experimental observations made on straight and the

flanged bar castings were found to be in correlation with that

predicted by using ProCAST simulation. Blow holes were observed on

the straight bar near the flanges on both sides as predicted by

simulation, porosity was also observed as predicted from the

simulation results.

Using the results of computer simulation, foundry tooling and

prototype castings were made, NDT,and mechanical tests as well as

metallographic examinations of the heat treated IS 1030 and IS2644

alloy steel castings were carried out. results of investigations, a

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satisfactory quality of the new range of castings has been stated, and

obtaining of the required mechanical parameters was confirmed.

Fig: 6.22 Blow holes on straight bar Fig: 6.23 Blow holes near

flanges

Fig: 6.24 Surface defect on flanges

With the help of die penetrant test surface pin holes and surface

cracks were observed in the flanged bar when riser is not present were

shown in Fig.6.22-6.24. Sand inclusion was observed on one of the

flanges which were not present in the results of simulation; this may

be because of the variation in case of experimental conditions when

compared to conditions under which simulation is carried out.

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6.5. RESULTS

In visual inspection method we can find the macro defects

like large blow holes obtained in the flanged bar prepared from thumb

rules as shown in above figure. The casting thus obtained is directly

rejected because of such large blow holes. The dimensions of the

casting are also measured in the visual inspection testing. The next

NDT method is liquid pentrant testing method; in this method of

testing, the castings prepared were observed for any surface pinholes

and surface cracks. However the casting with very few pinholes is not

rejected and it is repaired through welding techniques, and the

casting is accepted. With the help of liquid pentrant test, we can only

find the surface defects. Magnetic particle testing is one of the

economic non destructive tests; in this method we are able to find the

cracks on the surface which are very thin and almost of negligible

thickness. It is also used to find surface defects and it is more

accurate and economical compared to liquid pentrant test. Similarly,

liquid pentrant test was carriedout and it is observed that the straight

and flanged bar castings found some pinhole defects as shown in

Figures 6.25 and 6.26.

Fig:6.25: pin holes straight bar Fig:6.26: pin holes on flange end

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Fig:6.25 & Fig:6.26 shows the Liquid Penetrant Inspection of the

straight bar and flanged bar produced an indication which

confirmed the suspected pin holes.

6.6 METALLOGRAPHIC EXAMINATION:

Samples cut from the sectioned castings were then investigated for

micro structural analyses to study effect of solidification

Microstructural examination was conducted on the alloy steel casting

samples AISI 1030 & 2644 using Metallurgical microscope at BHEL

Hyderabad, Microstructure of the each sample is given below:

Microstructure of AISI 1030 is shown in Fig:6.27 it consist of Pearlite

(approximately 40%) in a matrix of Ferrite (approx. 60%) and ASTM

grain size no: 7. Also round shaped MnS inclusions of thin series

rating: 2 as per ASTM E45.

Fig. 6.27 Microstructure of cast specimen IS1030, grain size : ASTM

NO: 7,

Microstructure of AISI 2644 was shown in Fig:6.28 consist of Pearlite

(approximately 45%) in a matrix of Ferrite (approx. 55%) and ASTM

grain size no: 5. Also round shaped MnS inclusions of thick series

rating: 3 shown in Fig:6.29 as per ASTM E45.

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Fig:6.28 Microstructure of cast specimen IS2644 Pearlite (grey color)

in matrix of Ferrite (white background).

Fig:6.29 MnS inclusions thin series : 3

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6.7 CONCLUSIONS AND REMARKS:

From the previous sections it is quite obvious that the main purpose

of nondestructive testing is to determine the correctness of a

particular part or a system to agreeably perform its intended function.

With this purpose, the field of nondestructive testing can be a

significant contributor to increased efficiency and utilization of

machines and materials as well as a key item in assure safe routine.

Limits of defect detect ability are of serious concern to both

manufacturers and users of castings. Due to the complex nature of

castings and the casting process, it is difficult to set definite rules for

inspection systems to detect sub-surface defects. Hence, the thrust of

this present work was to investigate, within the specified domain, the

possibility of detecting sub-surface gas porosity defects in alloy steel

sand castings with rough surfaces. The experimental results were

used as a framework in building an inspection procedure for alloy

steel sand castings.