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BLOW MOULDING PROCESS

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

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BLOW MOULDING PROCESS

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  1. BLOW MOULDING PROCESS CORPORATE TRAINING AND PLANNING

  2. 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. CORPORATE TRAINING AND PLANNING

  3. 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. CORPORATE TRAINING AND PLANNING

  4. Fig 4.1 CORPORATE TRAINING AND PLANNING

  5. 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. PRINCIPLE CORPORATE TRAINING AND PLANNING

  6. 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. CORPORATE TRAINING AND PLANNING

  7. CORPORATE TRAINING AND PLANNING

  8. 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. BASIC REQUIREMENTS CORPORATE TRAINING AND PLANNING

  9. 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. CORPORATE TRAINING AND PLANNING

  10. BLOW MOULDING METHODS • Based on the method used to create the parison or preform, two types of blow moulding are recognised. • Extrusion Blow Moulding that uses an extruded tube. • Injection Blow Moulding that uses an Injection Moulded preform. CORPORATE TRAINING AND PLANNING

  11. Blow moulding methods commonly used in Industries are :- • Extrusion Blow moulding • Injection Blow moulding • Stretch Blow moulding. • Press Blow moulding & Dip Blow moulding for squeeze. • Multilayer Co extrusion Blow moulding. CORPORATE TRAINING AND PLANNING

  12. CORPORATE TRAINING AND PLANNING Table 4.1

  13. Blow moulding machine consists of two parts: The parison Forming Unit(Extruder). The Blow moulding unit. BLOW MOULDING MACHINES & THEIR CONSTRUCTION. CORPORATE TRAINING AND PLANNING

  14. CORPORATE TRAINING AND PLANNING

  15. 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. BLOW MOULDING UNIT CORPORATE TRAINING AND PLANNING

  16. 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. MOULD MATERIALS USED CORPORATE TRAINING AND PLANNING

  17. Blow Moulds can be made by : • Casting • Machining • Electroforming • Casting is more popular techniques for aluminum moulds. CORPORATE TRAINING AND PLANNING

  18. 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. OPERATIONS & FUNCTIONS CORPORATE TRAINING AND PLANNING

  19. 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) CLAMPING FORCE CORPORATE TRAINING AND PLANNING

  20. 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 PLASTIC MATERIALS CORPORATE TRAINING AND PLANNING

  21. 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. CORPORATE TRAINING AND PLANNING

  22. 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. CORPORATE TRAINING AND PLANNING

  23. PolymerProc. Temp.Drying Temp. Cavity Temp. LDPE 160-170 50-70 5-30 LLDPE160-180 50-70 5-30 HMHDPE160-210 50-75 10-30 PP170-220 50-80 20-50 PVC170-200 50-70 15-35 PS 250-280 50-70 20-40 PC280-300 70-100 50-70 PA190-24070-100 20-40 PET240-255 120-140 10-20 PROCESSING TEMP.OF PLASTICS CORPORATE TRAINING AND PLANNING

  24. Following plastic material Parameters effects the quality of blow moulded products: Melt Flow Index(MFI). Melt Strength. Density. Molecular Weight Distribution. Extrudate Swell & Finish EFFECT OF PROPERTIES OF PLASTICS ON QUALITY CORPORATE TRAINING AND PLANNING

  25. Different types of Extrusion Blow moulding: 1.Continuous a.Single station Method b.Twin Station Method. c.Rotary Table Method. 2.Intermittent a.Reciprocating Screw. b.Ram & c.Accumulator Head EXTRUSION BLOW MOULDING CORPORATE TRAINING AND PLANNING

  26. 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. ). CORPORATE TRAINING AND PLANNING

  27. 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. CORPORATE TRAINING AND PLANNING

  28. CORPORATE TRAINING AND PLANNING

  29. 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. CORPORATE TRAINING AND PLANNING

  30. CORPORATE TRAINING AND PLANNING

  31. 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. CORPORATE TRAINING AND PLANNING

  32. 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. CORPORATE TRAINING AND PLANNING

  33. 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. CORPORATE TRAINING AND PLANNING

  34. 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. CORPORATE TRAINING AND PLANNING

  35. CORPORATE TRAINING AND PLANNING

  36. 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. EXTRUDER & ITS FUNCTION CORPORATE TRAINING AND PLANNING

  37. CORPORATE TRAINING AND PLANNING

  38. Special requirements for the blow moulding extruder are: • Different types of polyethylene with widely differing melt viscosities must be processed. • 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. CORPORATE TRAINING AND PLANNING

  39. The melt must be conveyed against high die resistance, that is, with a high melt pressure at the screw tip. • The melt temperature must be kept as low as low as possible to avoid parison elongation. • The addition of dyes, stabilisers and varying quantities of reground material must be possible without difficulty. CORPORATE TRAINING AND PLANNING

  40. 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. CORPORATE TRAINING AND PLANNING

  41. 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. CORPORATE TRAINING AND PLANNING

  42. 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. CORPORATE TRAINING AND PLANNING

  43. 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. CORPORATE TRAINING AND PLANNING

  44. EXTRUDER DIE HEAD AND DIE ASSEMBLY • 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. CORPORATE TRAINING AND PLANNING

  45. DIE HEAD ASSEMBLY • 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. CORPORATE TRAINING AND PLANNING

  46. 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. CORPORATE TRAINING AND PLANNING

  47. 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. CORPORATE TRAINING AND PLANNING

  48. Die Assembly.(To convert a Plastic melt into a tubular shape). Torpedo-head or spider type dies(center fed dies). [used for heat sensitive materials like PVC]. Pinhead dies(side fed dies).[used for heat stable materials like poly olefins]. DIE ASSEMBLY CORPORATE TRAINING AND PLANNING

  49. 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. CORPORATE TRAINING AND PLANNING

  50. 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. CORPORATE TRAINING AND PLANNING

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