The moulding machine

A Battenfeld (Siemag) Structomat ST 2500/400 S-C-150 machine was used to mould the tank. This has a 150 ton clamping force with a separate screw preplasticizer barrel feeding an accumulator. 

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Finishing and polishing the mould surfaces is also extremely important because the melt will tend to reproduce every detail on the surface of the mould. Finally the mould will have to be hardened to make it stand up to the treatment it receives in service. As a result of all the time and effort which goes into mould manufacture, it is sometimes found that a very complex mould costs more than the moulding machine on which it is used. Several features of the mould are worthy of special mention. 

Example 4.6 The mould shown in Fig. 4.35 produces four cup shaped ABS mouldings. The depth of the cups is 60 mm, the diameter at the is 90 mm and the wall thickness is 1.0 mm. The distance from the sprue to the cavity is 40 mm and the runner diameter is 6 mm. Calculate the clamp force necessary on the moulding machine and estimate how the clamp force would change if the mould was designed so as to feed the cups through a pin gate in the centre of the base (as illustrated in Fig. 4.38). The clamp pressure data in Fig. 4.42 should be used and the taper on the side of the cups may be ignored. 

A practical difficulty which arises during injection moulding of reinforced plastics is the increased wear of the moulding machine and mould due to the abrasive nature of the fibres. However, if hardened tool steels are used in the manufacture of screws, barrels and mould cavities then the problem may be negligible. 

Harmful gases and vapours are given off by some plastics materials, so the moulding machine must be fitted with adequate extraction equipment. 

The pressure exerted on the rubber in the cavity is related to the available pressure from the moulding machine, the speed of injection and the size of the runner through which it must flow to reach the mould cavity. The smaller the cross-sectional area of the runner, the higher is the pressure gradient between the point of injection and the cavity. If the length of the runners is the same to each cavity, there will be an equal rate of fill to all the cavities. If the path lengths are unequal, some cavities will fill before the others. Once a cavity has filled, it, and the related runner system, will rapidly achieve the full available... 

The equation above shows that the birefringence is a function of both the material and the process. The stress optical coefficients are material constants, whereas the induced stresses are influenced by both the material and the process. Which of both contributions, that by orientation and that by thermal stresses, has the largest influence in the case of injection moulded CD substrates made of PC Wimberger-FriedI et al. (8) have made a careful analysis of the distributions of An in such substrates. The material used was Makrolon CD-2000 from Bayer, and the moulding machine used was of the Meiki Dynamelter type. 

Another solution is a mould design that enables the insulating chamber to be opened on the moulding machine and cleaned out (Figure 10.1). 

Under this heading of manipulation is included any process whereby the solid plastics material, usually in powder or nib form, is converted to the finished end product. It embraces moulding by compression, transfer, injection or extrusion, blow moulding, rotational moulding, and any process whereby a layer of comminuted plastics material is heat-sintered into a finished unit. In all of them the product designer has to work very closely with the manufacturer not only of the plastics material, but also with the mould maker and to an ever-increasing extent with the maker of the moulding machine. 

Ejection equipment is usually actuated mechanically by the opening stroke of the moulding machine. If this simple arrangement is insufficient, ejection can be performed pneumatically or hydraulically. 

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