Blow moulding injection

Injection and extrusion blow moulding take their names from the methods used to produce the tube for blowing. In extrusion blow moulding the tube is called the parison, in the case of injection blow moulding it is termed a preform. Thus in injection blow moulding, injection moulding is used to produce the preform. 

The process sequence for injection blow moulding is as follows  

Like extrusion blow moulding, injection blow moulding places very specific demands on the raw material it uses and is intolerant to contaminants. Regrind from inhouse waste may be utilised providing attention is paid to cleanliness. 

Although we do not have a case study to feature the injection blow-moulding process it is described briefly below, for interest and completeness. 

The process uses crystallizable polymers, of which the most important in PET. The first step is to injection mould (hence the name) a parison, or preform as it is more usually termed here. The preform is closed at the bottom and is considerably shorter and thicker than the final bottle. It is rapidly cooled (quenched) by using chilled water to cool the injection mould and this ensures that it is in its amorphous condition, i.e. no crystalline structure. Next it is reheated with infra-red elements to above its Tg, about 90-100 C for PET and enters the bottle mould and the mould is closed. The blow pin enters and pushes the soft preform downwards almost simultaneously the blow occurs, compressed air blowing the material outwards. The result is biaxial orientation - downwards from the movement of the blow pin, outwards from the action of the expanding air. The orientation induces crystallization, but in the form of lamellar crystals rather than spherulitic ones. This type of crystallization is strain-induced, and is characteristic of synthetic fibres and film, e.g. Melinex. It gives a transparent product with enhanced physical properties, both important for bottling carbonated drinks. The alternative name for the process is the stretch-blow process. Its main feature as a process is the control of the crystallinity of the polymer at its different stages. 

In Section 4.2.7 we considered the process of extrusion blow moulding which is used to produce hollow articles such as bottles. At that time it was mentioned that if molecular orientation can be introduced to the moulding then the properties are significantly improved. In recent years the process of injection blow moulding has been developed to achieve this objective. It is now very widely used for the manufacture of bottles for soft drinks. 

The steps in the process are illustrated in Fig. 4.48. Initially a preform is injection moulded. This is subsequently inflated in a blow mould in order to produce the bottle shape. In most cases the second stage inflation step occurs immediately after the injection moulding step but in some cases the preforms are removed from the injection moulding machine and subsequently re-heated for inflation. 

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Uses reported include motor housings for portable fans, food blender bases, tape storage housings, tough, clear toys, injection blow moulded products and thermoformed packages. 

All the molten-state processing methods are usable, mainly extrusion, injection, blow moulding, co-extrusion, welding. 

All molten-state methods are usable extrusion, injection, compression, thermoforming, co-injection, blow moulding, machining, welding. 

Injection blow moulding, in which the parison is injected into a first mould and then blown in a second mould having the shape of the final recipient. This process is more expensive and the cycle time is a longer. The aspect and dimensional quality are better compared to extrusion blow moulding. 

Blow moulding is the most common process for making hollow articles such as bottles. There are two main types of blow moulding, injection blow moulding and extrusion blow moulding. 

Injection blow moulding is used for the production of hollow objects in large quantities. The main applications are botdes, jars and other containers. The Injection blow moulding process produces bottles of superior visual and dimensional quality compared to extrusion blow moulding. The process is ideal for both narrow and wide-mouthed containers and produces them fully finished with no flash. 

Injection The injection blow moulding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mould. The preform mould forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. 

Ejection After a cooling period the blow mould opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and leak-tested prior to packing. The preform and blow mould can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow moulding and ejection. 

Alpha Packaging manufactures botdes and jars made from polyethylene terephthalate (PET) and high-density polyethylene (HDPE) for the pharmaceutical, nutritional and personal care markets. Technologies used include injection blow moulding, injection stretch blow moulding, and extrusion blow moulding. Alpha manufactures stock and custom containers in a variety of styles and colours. 

Alpha was founded in 1969 and is based in a 210,000 square-foot headquarters in St. Louis, Missouri, which houses injection blow moulding equipment for both PET and HDPE bottles and jars. Alpha also has plants in Brooklyn and Salt Lake City. 

Injection blow moulding A blow moulding process in which the parison to be blown is formed by injection molding. 

Although both processes can produce reasonably good quality large containers, injection stretch blow moulding is more widely used for pharmaceutical containers. The first stage of moulding is basically as injection blow moulding. In the second... 

Details of the neck region of an injection-blow moulded PET botde. The bottle on the left has been heat treated at 120 °C, while the neck of a preform is shown on the right... 

Modern blow moulding is separated into two major sub-divisions -extrusion blow moulding and injection blow moulding. Extrusion blow moulding was formerly by far the most dominant technique. Injection blow moulding has in recent years emerged as a major section for the production of bottles for carbonated drinks, using especially poly(ethylene terephthalate), PET, polymer. 

In injection-blow moulding the parison is injection moulded on to a steel rod (see Fig. 7.41, Station 1). The rod and parison are then rotated to the 2nd Station (the blow mould) where air is blown into the parison to cause it to take up the shape of the mould. The rod and bottle are next rotated to the 3rd Station at which (he mould opens and the bottle is ejected. 

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