CORPORATE TRAINING AND PLANNING 1. 2 INTRODUCTION Blow Moulding process is widely used for producing bottles or other hollow objects, due to its least

CORPORATE TRAINING AND PLANNING

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INTRODUCTION

• Blow Moulding process is widely used for producing bottles or other hollow objects, due to its least expensive & simplest process to manufacture.

• It offers a number of processing advantages,such as moulding of irregular curves,low stresses,variable wall thickness,the use of polymers with high molecular weight & favourable moulding cost.

• Blow moulding is operated using low moulding pressure & hence result in Low Internal Stresses.

• Commonly used materials are:PE,PVC,PET,PC, PA, POM.


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• It is principally a mass production method.

• Blow Moulding is an alternatives process to other process like

Injection Moulding. Rotational moulding

Thermoforming

• Since the mould used for the process consists of female cavity, it is easy to vary wall thickness & weight of the part.

• This is done either by changing machine parts or melt conditions.


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Fig 4.1


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PRINCIPLE

• Material is fed into a heated barrel of Extruder.

• With the help of screw rotation & heaters the plastic is melted and homogenised.

• Melted material is forced through a set of die to form a tube or parison (Hot Plastic tube)

• parison is introduced into a mould,The mould closes & pinches off.


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• Blow pin is inserted through the open end of the parison to form a neck.

• Finally air is introduced through the blow pin to inflate the parison inside the mould.

• By this, the molten Polymer copies the details of the Mould.

• Lastly the moulded product is cooled & ejected.

• In the finishing stage, the part undergoes, trimming, finishing, Printing-Labeling & decorating.


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BASIC REQUIREMENTS

• Homogeneous melt of plastic material.

• Formation of the molten resin into a hollow tube or parison.

• Sealing the ends of the parison in the closing mould,except the area through which blowing air can be supplied.


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• Inserting the blow pin or mandrel through the open end of the parison.

• Blowing or inflating the parison inside the mould.

• Cooling the blow moulded part.

• Ejecting the part & trimming flash if needed.

• Finishing & decorations on the product.


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BLOW MOULDING METHODS

• Based on the method used to create the parison or preform, two types of blow moulding are recognised.

1. Extrusion Blow Moulding that uses an extruded tube.

2. Injection Blow Moulding that uses an Injection Moulded preform.


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• Extrusion Blow moulding

• Injection Blow moulding

• Stretch Blow moulding.

• Press Blow moulding & Dip Blow moulding for squeeze.

• Multilayer Co extrusion Blow moulding.

Blow moulding methods commonly used in Industries are :-


12Table 4.1


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BLOW MOULDING MACHINES & THEIR CONSTRUCTION.

Blow moulding machine consists of two parts:

1. The parison Forming Unit(Extruder).

2. The Blow moulding unit.


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BLOW MOULDING UNIT

• Made off two female cavities that close around a parison.

• Pinch-off at one or both ends.

• One entrance for the blowing air.

• A cutout section.


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MOULD MATERIALS USED

• For Mould Parts:aluminum,aluminum alloys,Steel, Beryllium-Copper(Be/Cu) & Cast Zinc alloys.

• For Pinch off section:Beryllium-Copper or Steel inserts.Be/Cu Provides high thermal conductivity.

Steel Insert provides wear resistance & toughness.


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Blow Moulds can be made by :

1. Casting2. Machining 3. Electroforming

• Casting is more popular techniques for aluminum moulds.


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OPERATIONS & FUNCTIONS

Blow Mould Closing operations by:

• Pneumatic System

• Mechanical System &

• Hydraulic System.

Clamp Platen mechanism serves following Functions :

• Hold & align the mould halves.

• Hold the mould closed against the pressure of blowing air.


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CLAMPING FORCE

Clamping Force required:

FC=APf

FC-Clamping Force.

A-Projected Area.

P-Blow Pressure(Usually in the range of 0.5to1.5MPa).

f-Safety factor(25% extra)


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PLASTIC MATERIALS

• Those Materials which show high melt strength & good stretch properties at the extrusion temperature are suitable for formation of parison & blowing.

Following Polymers are more often blow moulded:

• PE(LDPE,HDPE,HMHDPE)

• PP,PVC,PA,PS,PC,PET,EVA,SAN,TPE


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• LDPE us used for more flexible items.

• HDPE is used for Rigid Bottles, Chemical Drums, gasoline tanks.

• PP is used because of high stiffness, good chemical resistance, clarity and good glass and good resistance to high temperature.

• PVC & PS for general purpose articles requiring transparency at modest cost.


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• RPVC – Can be bi axially oriented in extrusion stretch blow moulding.

• PC is used for containers which show good transparency, excellent impact strength, good heat resistance, good printability.

• PET is used in basically oriented stretch blow moulding & commonly used for carbonated beverages, packaging of drinks pharmacy products & water bottles.

• EVAL (Ethylene Vinyl Alcohol) is used as barrier layer in Multilayer containers.


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PROCESSING TEMP.OF PLASTICS

Polymer Proc. Temp. Drying Temp. Cavity Temp.

LDPE 160-170 50-70 5-30LLDPE 160-180 50-70 5-30HMHDPE 160-210 50-75 10-30PP 170-220 50-80 20-50PVC 170-200 50-70 15-35PS 250-280 50-70 20-40PC 280-300 70-100 50-70PA 190-240 70-100 20-40PET 240-255 120-140 10-20


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EFFECT OF PROPERTIES OF PLASTICS ON QUALITY

Following plastic material Parameters effects the quality of blow moulded products:

•Melt Flow Index(MFI).

•Melt Strength.

•Density.

•Molecular Weight Distribution.

•Extrudate Swell &

•Finish


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EXTRUSION BLOW MOULDING

Different types of Extrusion Blow moulding:

1.Continuous a.Single station Method

b.Twin Station Method.c.Rotary Table Method.

2.Intermittenta.Reciprocating Screw.b.Ram &c.Accumulator Head


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RECIPROCATING SCREW EXTRUDER

• When making large parts, the parison becomes so large and heavy that it sags under its own weight and it becomes thinner and thinner as it is extruded.

• Here, the resin is plasticated by the rotating screw and the melt accumulates in front of the screw.

• The screw retracts to accommodate the melt, then it is pushed forward by hydraulic means, forcing the melt through the die head to form a parison (see Fig. ).


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• At that point, the mould closes, the blow air inflates the parison, forcing the hot plastic towards the mould cavity walls. After sufficient cooling the blow moulded part is ejected.

• During the blowing and cooling stages, the screw retracts and accumulates another charge.

• Even if the blowing and cooling times remain the same as in any other process, the overall reduction in cycle time can be significant, making it possible to produce larger objects that could be made with normal extruder of the same size.


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RAM ACCUMULATOR EXTRUSION

• The ram accumulator type blow moulding is recommended for larger parts.

• This type of machine (see Fig ) is used to make parts, weighing up to 50 pounds.

• The main applications are industrial parts, shipping containers, and toys.

• The size of the extruder is independent of accumulator size, and in some cases more than one extruder is used.


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The main disadvantage of the system is that the first material to enter the accumulator is the last to leave, (FILO).

This makes the process unsuitable for heat-sensitive materials.

A variation on ram accumulators that provides first-in, first-out material flow is the accumulator head machine.


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• In this case, melt from the extruder enters the accumulator head from the side and flows around a mandrel; a tubular plunger pushes the entire shot through the die.

• Parts as large as 300 pounds can been produced by this method.


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ACCUMULATOR HEAD METHOD

• This method also utilises the external accumulator that can be many times larger than the volume of a reciprocating screw cylinder.

• It is designed to produce containers with capacity of 100 to 400 L. Here, one to four extruders continuously fill the accumulator head with enough plastic for a complete parison shot.

• The container is annular, that makes it possible to produce parisons with more uniform circumferential wall thickness.


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• After the correct charge has been accumulated, a hydraulic ring piston drives out the melt to form a parison, which is then placed in the mould and blown.

• The parison is extruded by moving an annular ring plunger downward to displace the material through a die bushing and mandrel.

• Fig. 4.5 shows the die head accumulator, which can produce large HMW-HDPE containers.


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EXTRUDER & ITS FUNCTION

• Extrusion plant for blow moulding consists of :

The Extruder.parison Die Head & Mould.

• Function of the extruder :To produce homogeneous melt.

• Screw L/D ratio of 20 to 24 is preferable.


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i. Different types of polyethylene with widely differing melt viscosities must be processed.

ii. Single‑screw extruders for PVC must plasticate powder blends for crystal clear, impact resistant and glossy bottles with melt temperatures close to the decomposition limit, whereby the addition of processing aids is severely limited.

Special requirements for the blow moulding extruder are:


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iii. The melt must be conveyed against high die resistance, that is, with a high melt pressure at the screw tip.

iv. The melt temperature must be kept as low as low as possible to avoid parison elongation.

v. The addition of dyes, stabilisers and varying quantities of reground material must be possible without difficulty.


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• The parison die connected to the extruder into which the melt is fed from the side has the function of deflecting the melt through 900 and forming a parison through annual cross section and a defined wall thickness.

• Upto a container size of 25-30lit, the continuous parison extrusion can be used.

• For larger container sizes, the discontinuous extrusion process must be used.


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• The extruded parison is picked up by the closing mould and transported under the blowing station where the moulding is inflated, generally with a pressure of 0.8 to 1 MPa, and thus simultaneously cooled.

• To reduce the blowing and cooling time (60‑80 percent of the total cycle time), intermittent blowing is frequently used. This results in an additional cooling effect, which is amplified by blowing on to critical zones, particularly in the base and neck areas.


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• In all blow mould parting line flash is pinched off outwardly.

• Flash in the case of bottles with symmetric design, can account for 20‑25% of the material used and for over 50% in case of a symmetric mouldings.

• The proportion of flash or its reworkability for production can be decisive for the economics of the process.


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• Extrusion blow machines have a variety of ancillary equipment, viz. blowing and ejection stations, flash removal, weighing and density determination, discharge stations, filling, locking, printing and labelling of containers, etc.

• In mass‑production line extrusion blow machines are automated, electronically controlled and hydraulically or pneumatically actuated.

• Extrusion blow moulding is the preferred process for forming containers and other hollow products of all sizes and shapes.


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• The die set is attached to a plasticating extruder through a cross assembly from which the parison is extruded.

• The design of die assembly is most important in determining the quality of the parison and hence the blow moulded product.

EXTRUDER DIE HEAD AND DIE ASSEMBLY


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• To facilitate the melt flow and to prevent accumulation of plastic, the surfaces of the die and the core should be well polished.

• If the surface of the channel is rough, stagnant flow layers of the polymer may form, the material will eventually degrade, causing dark streaks to appear in the parison.

• Roughness in flow channels may also cause the parison rupture. Streamlining the shape of flow channels also helps to prevent areas of stagnation and welding of the plastic streams after it has flown around the head mandrel.

DIE HEAD ASSEMBLY


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• An annular restriction called a "choke" is often placed on the mandrel to increase the head pressure.

• This choke decreases the cross‑sectional area of the annular flow channel and builds up melt back pressure in the weld area just past the flow deflector, upstream from the choke.

• If a choke is used and flow is not streamlined polymer or hard gels may get trapped in the channel.


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• In addition to ensuring uniform flow conditions in the extrusion head, it is necessary to control the flow leading to the die orifice.

• A tapered approach angle to the die orifice is recommended for most applications. Each type of material will require a different approach angle.

• The ratio of wall thickness at the die orifice to the length of die land is a controversial subject, for linear polyethylene, for example, the die length as high as twelve to twenty times the wall thickness is recommended by material suppliers.


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DIE ASSEMBLY

• Die Assembly.(To convert a Plastic melt into a tubular shape).

1. Torpedo-head or spider type dies(center fed dies). [used for heat sensitive materials like PVC].

2. Pinhead dies(side fed dies).[used for heat stable materials like poly olefins].


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• The torpedo head dies are generally recommended for the use of heat sensitive material like PVC.

• The pinhead dies or side fed dies are commonly used for heat stable material such as poly olefins.

• The side feed dies are generally difficult to centre and they may cause serious problems with the weld line, the spider-type torpedo dies eliminate most of these problems but they are more complicated.


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• Furthermore, the possibility of stationary flow with resultant decomposition is considerably less with a centrally fed than with a right-angle fed extrusion head.

• For example, side fed extrusion heads with core pins that work satisfactorily with PE usually produce weld lines with PVC.

• Thus, for the latter plastic, a centrally fed torpedo head is used - it minimises the interruption of material flow and prevents movement of the mandrel under generated high pressure.


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PARTS

• Die & core pin design :

The die & core pin is used to determine the inside & outside diameter of the parison tube.

• Blow pin or mandrel :

The blow pin is designed to form the neck & it has a provision to supply compressed air or blow to inflate the parison.


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PARISON

• An uniform parison is of paramount importance.

• Extruder must deliver an extrudate with in close dimensional tolerance.

• Irregular extruder output causes weight variations from one blow part to the next.

• Temperature of the parison should be controlled.

• parison “draw down” results from gravitational pull on the plastic during extrusion.


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• The bottom becomes heavier while the top thins down. The lower the melt viscosity the greater the drawdown.

• Drawdown can be reduced by: using polymer grades with long-chain branching, lowering the melt temperature, increasing the extrusion rate.

• Also, the parison programming can be used to compensate for drawdown.

• parison extrudate swell occurs when the melt exits from the parison die.


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PARISON SWELL FOR VARIOUS POLYMERS

Polymer Extrudate Swell(%)

LDPE 30-65

HDPE 20-60

RPVC 30-35

GPPS 10-20

PC 5-10


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PARISON WALL THICKNESS CONTROL

Objectives:

• A method of minimization of the weight at its maximum mechanical performance.

• Cost Saving.

Techniques:

• parison Programming &

• Die Shaping.


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PARISON PROGRAMMING

• Programming controls the wall thickness as the parison emerges from the die.

• The draw bar is attached to a mandrel that forms the inside of the parison.

• A bushing shapes the outside of the parison.


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• The parison thickness changes with vertical movement of the mandrel.

• The sequence of mandrel & bushing movements constitute the parison programming.

• The programming is accomplished electronically, either by mechanical means, with a patch panel, or by a microprocessor.


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DIE SHAPING

• Used to improve wall distribution of a blow moulding part.

• Irregularly shaped parts such as gas/fuel tank usually need die shaping.

• The shaping can be done either on a bushing or on a mandrel depending upon the easy machining.

[Usually bushing for diverging die & mandrel for converging die].


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• Frequently, a combination of programming and die shaping gives the best results.

• For example, this is the case for a conical – shaped part where shaping is cut on a converging mandrel.

• The die mandrel moves up to the maximum die gap to extrude thick parison for the corner.


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MELT TEMPERATURE

High Melt Temperature :

1.Leads to better finish as well as better physical & mechanical properties.

2.May cause parison sag.

3.Requires longer cooling cycle & cause more shrinkage.


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Low Melt Temperature :

• Results in better shaped parison, shorter cooling cycle & less shrinkage.

• Too low melt temp leads to non-homogenous melt as well as inferior mechanical & physical properties.

• It is desirable that the parison have the lowest practical melt temp.


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BLOWING AIR

• Expands the parison tube against the mould walls.

• Forcing the material to assume the shape of the mould & duplicate surface details.

• During the expansion phase high volume of air is desirable for the rapid accomplishment of the expanded parison against the mould walls.


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• The maximum volumetric flow rate into the cavity at a low linear velocity can be achieved by making the air inlet orifice as large as possible.

• The pressure of the blowing air influences the surface details in the moulded item.

• Some PE containers with heavy walls can be blown and pressed against the mould walls by air pressure as low as 200 to 300 kPa.


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• Large items such as 5 L bottles require still higher air pressure (600 to 800 kPa).

• The clamping force of the mould platens must be sufficient to withstand the blowing pressure inside the blow moulds.

• An excess of 25‑50% of pressure over the calculated value of projected area of the product items blowing pressure is advisable.


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SURFACE IMPERFECTION

• Die lines & scratches are surface imperfections formed on parison.

• Cleanliness of the parison die is important in reducing these lines.

• Chrome plating of the die & Teflon coating may be helpful.

• Die lines can be minimized by by the actions (Increasing blowing speed,Increasing air pressure,increasing mould temp.)that minimize cooling of the melt until it is pressed against the mould surface.


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SHRINKAGE

• Length wise shrinkage.

• Horizontal shrinkage occur in wall thickness.

• May be reduced by raising the blowing pressure & lowering the temp.of the mould.

• High shrinkage is observed in HDPE(Due to crystallinity) & thicker-walled products(due to slower cooling rate).


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PRINCIPLES OF PRODUCT DESIGN

• Following factors are considered to design the blow moulded containers & other complex shapes:

1. Resin,Size & weight of the product.2. mould,contour,inserts,surface texture.3. Engravings,sharp corners & straight

angles.4. Parting lines.


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PINCH-OFF FLASH

• The pinch-off is the section of the mould where the parison is squeezed & welded together.Its design:

• Should be structurally sound to with stand pressure.

• Should push a small amount of plastic material into the interior of the part.

• Should leave a thin pinch line to provide a clean break point for flash removal.


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• To perform this, most moulds use rugged, double angle pinch‑off (see Fig. 4.10).

• Its land will stand up to the pressure and will provide a clean break point.

• The 30° provides a slight back pressure and causes the melt to thicken in the weld area.

• The flash pocket depth is related to the pinch‑off area and is very important for proper moulding and automatic trimming of the part.

PINCH OF DESIGN


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• The width of the pinch‑off edge depends on the material to be processed, the wall thickness, the closing speed and the blowing time.

• For short runs, the pinch‑off can be made of aluminum, but for long production runs the moulds have inserted pinch off areas made of steel or beryllium‑copper.

• Too big a relief angle can hinder the adequate cooling of the edge zones, which in turn could result in dull spots next to the weld line.


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• With too small a relief angle a cooled‑off seam might be pushed into the mould cavity forming a deep groove along the weld line.


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• As shown in Fig. 4.11, the cycle time is made off :- Blowing time + mould closing time + blow pin insert time + cooling time + ejection or removal time .

BLOW MOULDING CYCLE


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Blow Ratio :

• The blow ratio is the ratio of the outer diameter of the blown container divided by the outer diameter of the parison.

• The required die gap can be approximately calculated multiplying the desired wall thickness of a blown bottle by the blow ratio.


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DRUMS OR BARRELS

• With this Moulding technique,a hollow,semi-hollow or completely solid ring can be moulded .

• Solid ring can be produced with good consistency,but hollow & semi-hollow ones are difficult.

• Preferred material is HMWHDPE.


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FLUORINATION FOR BARRIER PROPERTIES

• HDPE containers(used in fuel tanks) may be fluorinated i.e treated with fluorine gas.

• It improves the barrier properties.

• Two fluorination processes are used:

• Injection of fluorine gas during the blowing cycle.

• moulded container may be exposed to fluorine gas at elevated temp.


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INJECTION BLOW MOULDING

• An ideal combination of Injection & blow moulding.

• It includes three stages:

1. Formation of preform by using injection moulding.

2. Transferring the preform into the blow moulding.

3. Passage of air or gas pressure through the core rod to blow the thermoplastic resin into the cavity walls of the blow mould.


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MOULDING PROCESS • There are three station & four station

Injection blow moulding system.

• The difference between the three & four station indexing heads is the dry cycle time.

• Injection unit,a blow station,& a ejector or stripping station are the three station in Injection blow moulding machine using three station.

• The four station machine has a safety or core rod conditioning station.


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FIG 4.13


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FIG 4.14


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• The injection blow moulding becomes economic at the level of one million to seven million units of small containers (300 mL or smaller capacity).

• The investment cost is greater for the injection blow moulding than for the extrusion blow moulding. However, the quality of containers moulded using the former method will be superior.

• The injection blow moulding is used primarily for the production of cosmetic and pharmaceutical containers.


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ADVANTAGES OF INJECTION BLOW MOULDING

• Accurate shaping of the neck.

• A high level of dimensional accuracy.

• Minimal weight tolerances.

• The highest quality surface finish.

• Production absolutely free from waste.


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• Crystal-clear containers for pharmaceutical application.

• Finished bottle without weld line & scrap.

• Secondary/finishing operations can be avoided.

• Multi-cavities can be operated.


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DISADVANTAGES OF INJECTION BLOW MOULDING

• The preform design generally establish the core rod length & diameter.

• The process is more expensive than extrusion blow moulding.

• Compromise between preform wall thickness and blow up ratio.

• The ratio of the maximum wall thickness to minimum wall thickness across a preform cross-section should be less than 1.5 to prevent weld lines.

• Preform thickness greater than 6 mm is unstable during blowing since the thick section cannot be properly conditioned.


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• Injection blow moulds should be machined to precise tolerances for their critical function in the moulding cycle.

• The preform moulds are more important since they are subjected to direct injection pressure. Care should be taken to see that the core rod is concentric.

• The parison (preform) neck ring forms the finished shape of the threaded neck section of the container.

• It also centres and securely retains the core rod inside the preform cavity to prevent core rod deflection during the injection (see fig.4.15).

MOULDS FOR INJECTION BLOW MOULDING


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• The preform mould consists of stationary & movable halves.

• The cavity dimensions are determined by the core rod layout.

• Temp. control is an important part of the cavity design.

• The neck finish is formed in the preform neck ring the blow mould nock ring secures the already formed neck finish.


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• The blow mould cavity also consists of stationary & movable halves & are used to shape the final form of containers.

• Cavities are made from tool steel,pre hardened steel,aluminum or beryllium copper depending upon the type of plastic material.

• They are subjected to the minimal clamp pressure needed to withstand preform blowing air pressure of 700 to 1200 kPa. The most important in the mould cavity design is the provision of maximum cooling.


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STRETCH BLOW MOULDING

Principles

• It is mass production process

• Stretch blow moulding is a process on which stretching is done before blowing.

• The stretch blow moulding method can be applied to both injection and extrusion blow moulding process.

• Each plastic material has a temperature limit at which it can be stretched to get optimum orientation and properties.


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• Biaxial stretch blow moulding is the method in which the stretching is done in both longitudinal and transverse direction.

• Biaxial orientation increases the tensile strength,gas barrier properties,drop impact strength and clarity of plastics.

• The various materials suitable for stretch blow moulding are PET,PVC,PS,SAN,POM,PP.


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• Containers made by Stretch Blow Moulding are used for –

• Packing of Oil.• Wine, Sprits.• Milk. • Mineral Water. • Carbonated Drinks. • Soft Drinks & Medicine.

APPLICATION


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Plastic

Material

Orientation

Temperature (0c)

Stretch

Ratio

PET 105-120 16/1

PP 128-140 6/1

PVC 100-115 7/1

PS 140-160 12/1

SAN 120-128 12/1

• The Orientation temperature & Stretch ratios of same materials are given in the table.


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INJECTION STRETCH BLOW MOULDING

Single Stage Process

• The Preform produced by Injection moulding.

• Thermal conditioning & Stretching of the preform can be performed by

1. Single Stage Process2. Two Stage process

• The preform is then sufficiently cooled in the mould.


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• In one or more tampering stations the injection moulded preform is heated upto the stretchable temperature.

• The blowing and stretching are performed with the help of a telescopic stretch rod.


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PET STRETCH BLOW MOULDING PROCESS

• The PET preform is injection moulded in the first station and upon proper cooling, the cavity mould half drops down and the core rod mould half rises.

• The table indexes 90° to the conditioning station, where the preform is conditioned by internal and external core‑rod heaters to the proper temperature for stretch blow moulding.

• The table again indexes 90° to the third station, where the preform is stretch blow moulded.


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TWO STAGE PROCESS

• In this process the injection moulded preform can be produced any time at any place.

• The preform is to be re-heated before stretching and blowing.

• In the process the preforms are transported through an oven where they rotate continuously to attain even temperature through out the surface.

• Usually the threaded area is protected form heating by heat shield.


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• After heating the preforms exit from the oven and are allowed to equilibrate.

• Since the preforms are usually heated by IR heaters the temp on the outside skin is higher then the inside skin.

• During equilibration, the outside skin temperature drops while inside skin temperature rises.

• Then it is transferred to blowing section

• The blow moulds closes at the threaded area of the preform and clamped to required tonnage.


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• The stretch rod enters the preform through the preform towards the bottom of the mould.

• The air is then blown in to the mould up to the required pressure

• The bottle cools due to contact with the cold mould.

• The blown air is exhausted,the rod retracts and the mould open to eject the bottle.


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ADVANTAGES AND DISADVANTAGE

Single stage process :

Advantages

• Low investment

• Requires no capping ring

• All process are done at one place.

Disadvantages

• Low barrier properties

• The products are heavier

• Requires more skilled operation.


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TWO STAGE PROCESS

Advantage• Low cost per bottle

• The products have low weight

• High barrier properties

• High productivity

• Preform making and bottle making can be done at different places.


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Disadvantages

• High capital investment

• More blemishes than single stage

• Requires capping ring on the preforms.


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Comparison Between Single & Two-stage Process

Single Stage Process Two Stage Process

• Low investment.

• Requires no capping ring.

• Low volume production.

• Higher weight bottle.

• Low efficiency.

• Require more skilled operator.

• High investment.

• Requires capping ring & bumper role.

• High barrier properties.

• Lower weigh bottle.

• High efficiency.

• Required operator.


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• Stretching leads to biaxial orientation of the molecular structure.

• Hoop ratio is defined as the ratio of the largest inside diameter of the blown bottle (D1)to that of preform before blowing.(D2)

RH = D1/D2 , If range from 4 to 7

• Axial ratio is defined as the ratio of length measured after axial stretching of the container(L1) to the original length of the preform.(L2)

RA = L1/L2, If ranges from 14 to 26

ORIENTATION AND ITS EFFECTS


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• Total blowup ratio is equal to the hoop ratio multiplied by the axial ratio.

Rtotal = D1 X L1

D2 X L2

• Each plastic has its own natural maximum stretching limit.

• In case of PET bottle to held the pressure of soft drink,the blow up ratio should be 10


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EXTRUSION STRETCH BLOW MOULDING

Process

• The preform mould closes around the parison.

• The pre blow mandrel is lowered in the parison to calibrate the bottle neck.

• The blowing air blows the preform at the same time. The bottom scrap is then removed.


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• The mould opens, the preform retained by the pre blow mandrel is transferred to stretch blow mould.

• The blowing is carried out with the assistance of mechanical for longitudinal and pneumatic for latitude stretching.

• After cooling takes place, the mould opens to takeout the product for post moulding operation.


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MULTILAYER BLOW MOULDING PROCESS

• Co-extrusion blow moulding offers to produce containers having several layer of plastic.

• The process makes it possible to combine various materials which attributes to create a product for a particular application.

• The co-extruded blow mould containers gaining importance for packaging of various sensitive food,with high barrier properties.


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• The process require a parison die designed to over lap several parisons to produce a single parison consisting multiple of layers.

• The co-extruded parisons are generally processed by extrusion blow moulding.

• The principle purpose of this method is to improve the barrier properties.


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• To improve adhesion between the two layers,tie layers have to be used.

• A five layers structure consists of one inside and one outside structural layer, a central functional layer and two adhesive layers one on each side of the functional layer.


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PLASTIC MATERIALS FOR MULTILAYER BLOW MOULDING

Structural Materials :

• The plastic material suitable for extrusion blow moulding are considered as structural materials.

• These materials posses good melt strength good strain hardening characteristics and can be deformed when blown.

• Some structural materials are LDPE,LLDPE,HDPE,PP,PET and PVC

• Some engineering plastic such as PC,Polysulfone are used for special application.


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BARRIER MATERIALS

• These plastic materials shows good resistance over gas and water vapour permeability.

• Some best barrier materials are Ethylene Vinyl Alcohol , Polyamide, Polyvinyledene Chloride .

• EVA and PVDC are best known barrier materials to Oxygen,Co2, Moisture


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• Aromatic Polyamides combine high barrier properties with high distortion temperature.

Two types of adhesives resins used are :

1. Directly synthesized co-polymer or terpolymer

2. Polyolefin grafted with anhydride or epoxy compound


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CO-EXTRUSION EQUIPMENT

• The extruders must supply several streams of melted material to the die.

• The melt stream stability and the uniformity is most important.

• Usually single screw extruders are used


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• The screw design must take into account the melt characteristics like flow rate, head pressure and melt temperature.

• The L/D ratio preferably should be more than 20:1

• The size and number of extruders make their arrangement around the die to be done carefully for maintaining proper flow


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DIES

• Co-extrusion dies have the main function to maintain the proper order and the desired thickness to form a parison.

• In co-extrusion die the design parameters for all materials in the system must be meet simultaneously.

• Co-extrusion dies are of a center fed rather than a spider head type.

• Important types of extrusion dies are –

– Die body construction / layers combinations.– Manifold Design


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• The major requirement for the die design are-

1. Proper arrangement to accommodate multiple melt feeds.

2. Formation and location of weld lines where the melts combine to form the annular shape of each lays.

3. How best to combine the layer into the parison inside the die.


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Press Blow Moulding

• Press Blow moulding is used to produce smaller parts ranging from 1 to 200ml.

• Most wall sections are less than 0.6mm

PRESS & DIP BLOW MOULDING PROCESS


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Press blow moulding consists of :-

• The injection moulding assembly, include the cavity section, and the extrusion blow mould.

• A full cycle consists of four operation phase


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• In the first, an injection mould cavity for forming the parts head or neck moves down between the two half of the blow mould and is placed tightly on top of the melt nozzle.

• The newly formed head or neck section is cooled in the injection cavity.

• The melt is still attached to the solidified moulding that serves as a drawing collar for the parison.


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• The Injection mould rises from the nozzle lifting a parison like preform with it.

• The nozzle serves as an extrusion die.

• As soon as the injection mould reaches its starting position the extrusion stops.


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• The blow mould is clamped in position around the parison and air entering at the neck forces the soft,hot parison against the cooled wall of the mould cavity.

• When the part is cool enough, the blow mould opens up and the product is removed.

• Post treatment operations such as trimming to final length, deflashing and flaming, etc.is done.


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ADVANTAGE

• It does not produce scrap during the injection moulding part of the cycle.

• In press blowing equipment a small amount of scrap is trimmed and separated inside the machine.

• Less wall thickness products can be manufactured.


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APPLICATION

• Squeeze tubes, bellows,pharmaceutical, medical,cosmetic and industrial applications that require not-standard closures for thin walled pliable containers and tubes.

Plastics which are successfully press blow are :

PEPPPSABSPAPolyurethanePVCEVAc etc.


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DIP BLOW MOULDING

Dip blow moulding is a low pressure injection blow moulding.

The process was 5 steps.

• First,melt is extruded into a storage pot.

• The pot is made of two parts.dipping barrel and recuperator piston.

• The recuperator piston moves towards the neck cavity, acting as a piston and filling the cavity with melt.


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• The dipping mandrel is fully inserted into the pot and the bottle neck is formed.

• The mandrel is progressively withdrawn form the pot, followed by the recuperator piston.

• Their relative speed controls the volume of melt that is extruded coating the mandrel.

• This enables a parison thickness profile to be implemented.


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• When the melt pot is completely withdrawn, a knife cuts off the parison.

• The mandrel rotates vertically to the blowing station.

• The opposite mandrel moves towards the coating station.


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• The longitudinal coating process with transverse stretching during blowing imparts biaxial orientation.

• This results in increased drop strength of the bottle.

• The preform is blow into shape.


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ADVANTAGES

Compared with injection blow moulding, it has

• Lower tooling cost

• Capacity to form single bottles with upto 700ml vol.capacity.

Applications

Clean, accurately moulded, scrapless small bottles


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Blow moulding of Engineering thermoplastics Machines and process methods

• Extrusion blow moulding is the main processing method used for engineering thermoplastics.

• Continuous parison formation processing equipment is used to produce containers or small industrial parts.


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• The accumulator head blow moulding process is used with engineering thermoplastics to form intermediate or larger parts.

• parison programming or changing of the parison annular thickness during its formation is used to provide more uniform distribution of the material in the part.


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Blow moulding machines are classified by :

1. Extruder size2. Extruder output3. Accumulator capacity4. Platen size 5. Clamp pressure capacity.• Screw diameter typically range from 50 to

150mmwith a length / diameter ratio from 18/1 to 30/1.

• 24/1 is the most common.


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• Screw configuration range from single stage, single flight to more complex barrier and mixing screws.

• High shear section, that is needed for polyolefins may overheat sensitive engineering plastics.

• This results in polymer degradation and low melt strength.


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PARISON PROGRAMMING

• The up and down movement of the mandrel during forming cycle changes the parison thickness.

• The die line created by deposition of foreign material or the accumulation and scratches.

• Scratches & Imperfections on the mandrel or die ring cause die lines.

• The die line results in a poor part finish.

• The design and surface finish of the dies are critical factors in providing a parison free from defects.


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MOULDS FOR ENGINEERING THERMOPLASTICS

• aluminum and steel mould are used. It is due to the fact that

• They are smoother (low porosity)

• They provide more uniform surface finish than cast aluminum.

• aluminum moulds require steel or hardened pinch off inserts to prevent coining of parting line.


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MOULD TEMPERATURE CONTROL

• Polyolefins are processed in chilled moulds.

• Engineering thermoplastics are moulded in heated moulds.

• Mould temperature of 70-80º C is common when good mould surface reproduction is required.


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ADVANTAGES OF ENGINEERING THERMOPLASTICS

• The engineering thermoplastics offer a number of performance advantages compared with polyolefinic materials.

• Greater stiffness or the ability of a material to resist deflection under load.

• Higher resistance to stretching.


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• Impact strength dependent on the material and environmental factors.

• Greater hardness, i.e,resistance to surface penetration from a concentrated load.

• Greater resistance to deflection of the part under load at an elevated temperature.


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• Crystalline engineering plastic, like polyamides and polyesters offer excellent resistance to a wide range of chemicals and solvents.

• Improved capability of the material to reproduce the mould surface and details.

• Engineering thermoplastics generally shrink less than that of polyolefins.


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APPLICATION

• The engineering plastic is a processable polymeric material , capable of being formed to precise and stable dimensions, exhibiting high performance at the continuous use temperature above 100ºc, and having tensile strength in excess of 40MPa.

• Business machine housings,covers and ducts.

• Medical equipment housing, ducts, furniture components and stretchers.


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• Automotive instrument panel, seat components,bumpers, spoilers and under-hood ducts and fluid reservoirs.

• Furniture door, drawer fronts, seating and cabinets.

• Appliance doors, ducts, housings and covers.


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MATERIALS

• Polycarbonate

• Polyamide

• Polyesters

• Polyphenylether and alloys of these polymers are commonly blow moulded.


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PET BLOW MOULDING PROCESS AND APPLICATION

• The PET bottle manufacturing process consists of injection moulding of a closed bottom preform.

• The preform is reheated to the blow moulding temperature, which is about 10 to 20º c.(18 to 36ºF) above the glass transition temperature.

• Stretching of the preform is done axially in the blow mould by a stretch rod.


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• Simultaneously compressed air is introduced into the preform to biaxially expand the preform.

• The melt processing of PET requires that it must be very dry before it is moulded.

• Any water that may be present in molten PET will be rapidly consumed by chemically reacting with the polymer in a process called “hydrolysis”.


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• The temperature of the melt is one of the most important parameters to be considered when injection moulding of bottle performs.

• The temperature affects the crystalline behaviour of PET.


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• The reheat blow (RHB) process is widely used to produce oriented containers (bottles) for carbonated beverages.

• There are two steps to the process.

• In the first step, the resin,PET, is injection moulded into an amorphous preform.

• It is then heated to exceed the resin’s glass transition temperature for proper orientation.

• It is then blow in a mould with high pressure air to obtain the desired bottle shape.


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APPLICATION

• Bottles for carbonated beverages.

• Containers for fruit, juice, drinks.

• Containers for Oils, Pickles, Vinegars, Liquors.

• Container for canned milk,water bottle.


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CONTROLS IN BLOW MOULDING OPERATION

• In blow moulding operation there are different categories of controls which play the most important role for performance and quality of the products.

• The machine control affects some characteristics of the machine itself such as temperature, screw speed etc.

• For blow moulding process, accurate control of time, temperature and position is a vital requirement.


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• Temperature control is required for the extruder barrel, the mould, the die head, hydraulic oil and polymer melt.

• The filling of the head, the ramming of the parison, the wall thickness of the parison and the press clamp are all position-controlled.

• The blowing /cooling cycle is controlled through microprocessor.

• Product controls measure are those which and control some characteristic of the final product like weight and wall thickness of the component.


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MATERIAL AND PARTS HANDLING AND FINISHING

Auxiliary equipments

• Air compressor, hopper loader, mould temperature controllers,oven drier, scrap grinder and dry blender are required as auxiliary equipments.

• The surface treating equipment, trimmer,reamer and conveyor system as well as finishing and decorating equipment,printing and labelling equipments are also needed.


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STRIPPER

• A stripper is a simple device for parts handling at the blow moulder.

• It is activated either by a mechanical linkage or an air cylinder interconnected with the moulding machine.

• The operations includes a vertical down stroke that pushes the moulded part from the die.

• This strip it from the blow pin and separate the part with its flash from the parison at the extrusion die face.

• The stripper runs automatically, discharging the parts onto a conveyor or into a chute for further handling.


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NECK FINISHING

• Neck finishing is typically the facing or machining of the sealing surface at the top of the thread opening.

• The surface must be correct in dimension and squarely cut so as not to have a top edge.

• Many industrial parts are fly cut when round openings or holes are required to complete the product.


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• Cutter design range from a single flute with no spiral to multiple spiral flutes, made of hardened tool or carbide compounds.

• Container neck inside diameter sizing and top spot facing is done in one step with a dual-purpose cutter.


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POST MOULDING & FINISHING OPERATION

1. Drilling

2. Reaming

3. Cutting

4. Trimming

5. Deflashing


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DRILLING

• Making holes of 25mm or of less in diameter.

• Common on many industrial parts and containers.

• For larger holes fly cutting is used.

• For smaller holes standard drill bit is used.

• For plastics drill bits designed with minimal spiral.


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REAMING

• Work piece should be held firmly.

• Provides high quality finish with excellent accuracy.

• The spindle speed is 200-400 rpm.

• This operation is performed in a milling machine with a clamping force.


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CUTTING

• Performed by hard using standard knifes or specially contoured or ground knives.

TYPES

1. Spin Trimming2. Routing

SPIN TRIMMING

• Knife blades are mounted in jugs or fixtures

• They advanced into rotating parts or parts are rotated into blades.


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ROUTING

• It is another method of culture.• Produces a cut of good quality.

• It is adaptable to irregular stapes and large parts.

• Router may be free end or to follow a template or may be fully automated.


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TRIMMING

• Trimming equipment is located adjacent to blow moulding machine.

• Some machinery trims the product in the mould or in a post moulding station.

• After trimming product is collected in containers via conveyor belt.


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Advanced Trimming Technique

1. Laser cutting Trimming

2. Water Jet Trimming


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DECORATION METHODS

• Blow moulded products mostly finished by coating or printing over the surface.

• Decoration carried out by Coating, Printing or Labeling.


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SURFACE PREPARATION AND TREATMENT

To apply coating or print ink over plastic surface some treatment is needed.

Surface clearing treatment of plastic products:-• Solvent Clearing & Etching

• Chemical etching treatment

• Flame treatment

• Corona discharge

• Plasma treatment


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FLAME TREATMENT

• Used for sheets and irregular moulded items.

• Used to improve ink adhesion to polyolefins and other plastic containers.

• It oxidises the surface and makes it easily wettable

CORONA DISCHARGE

• Used for films & sheets.

Plasma treatment (cold gas)• Effective box expensive.• Rarely used for packaging containers.


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SCREEN PRINTING

• It is a stencil process

• Ink is forced through the open areas of screen by squeegee.

• Ink spreads out and gives continuous ink coating

• Process is inexpensive and versatile


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PAD PRINTING

• An offset gravure process.

• The ink is applied in cliché.

• Excess ink is removed by a doctor blade.

• A silicone rubber pad picks up the ink and transfer it to the part to be printed.

• Process is suitable for irregularly shaped and rough surfaces.


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HOT STAMPING

• By Applying heat and pressure, the pigmented coating form a carrier films is transferred to the part to be printed.

• A flat die is used to transfer the foil only.


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IN MOULD LABELLING

• Inserts are used

• Inserts consists plastic film pre-printed with required decoration.

• Insert is placed inside the mould.

• It becomes an integral part of the moulded article.


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QUALITY CONTROL OF BLOW MOULDING PROCESS

• In line quality control and testing facilities is needed at the manufacturing place.

• Inspections and quality assurance testes should follow specifications as per standard.


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TESTS

• Container weight

• Wall thickness

• Overflow capacity

• Neck & Thread dimensions

• Drop impact resistance

• Visual inspections for contamination

• Additive and colour homogeneity

• Other required tests as required to meet the specifications.


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FAULTS,CAUSES AND REMEDIES IN BLOW MOULDING PROCESS

FAULTS CAUSES ACTIONS

parison too long

Excess extrusion output

Melt too fluid leading to parison sag.

Reduce screw speed.

Reduce barrel temperature

Reduce die head temperature.

parison too short

Insufficient extruder output.

Too low a melt temperature

Increase screw speed.

Check heaters are functioning.


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parison diameter too large

Incorrect die selections

Excess die swell

Check

Raise melt temperature.

parison diameter too small

Incorrect die selection.

Excess parison sag

Check

Lower melt temperature.

Excess parison wall thickness

Incorrect setting of parison thickness controller.

Excess die swell

Check



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parison wall too thin

Incorrect setting of parison thickness controller.

Excess parison sag.

Check

Lower melt temperature.

parison curls outward as it leaves the die.

Die temperature too low.

Raise die temperature

parison curls inwards as it leaves the die.

Die temperature too high.

Lower die temperature.


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parison veers to one side.

Die and mandrel not concentric.

Incorrect setting of parison wall thickness control.

Adjust.

Sharkskin (rough on inside).

Die head temperature too low.

Melt temperature too low.

Raise die head temperature.


Longitudinal marks on parison surface

Dirty die.

Damage die.

Clean.

Repair


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Weld lines on parison

Melt not re-welding after passing through spider.

Build up back pressure between spider and die lips by lowering die/die head temperatures.

Increase land length of die.

Increase melt temperature.

Burn marks (PVC).

Decomposition. Check melt temperature.

Check no dead spots.

Check tip of screw not too hot.

Dark particles.

Contamination

Decomposition

Check

Check dead spots.


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Poor neck/flash separation.

Blow pin badly set.

Damages cutting sleeve.

Check and adjust.

Replace.

Displaced punt weld.

Bent parison.

Blunt parison knife.

Check parison faults.

Replace.

Deformed moulding.

Moulding ejected too hot.

Increase cooling time.

Check cooling water supply to mould.


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Tail flash on bottle.

Short parison. See parison faults.

Moulding does not fully inflate.

Insufficient air.

Raise air pressure.

Increase blowing time.

Moulding sticks to mould.

Mould too hot.

Moulding too hot.

Check mould temperatures.

Increase cooling time.

Reduce melt temperatures.

Documents

CORPORATE TRAINING AND PLANNING 1. 2 INTRODUCTION Blow Moulding process is widely used for producing bottles or other hollow objects, due to its least