Split mould

In injection moulding, polymer granules are compressed by a ram or screw, heated until molten and squirted into a cold, split-mould under pressure (Fig. 24.3b). The moulded polymer is cooled below T, the mould opens and the product pops out. Excess polymer is injected to compensate for contraction in the mould. The molecules are oriented... 

In vacuum and blow forming, sheets produced by extrusion are shaped by vacuum or pressure forming. Heat-softened sheet is pressed into a mould by atmospheric pressure when a vacuum is created between the mould and the sheet. Fig. 24.4(a). Plastic bottles are made by blowing instead heated tube is clamped in a split mould and expanded with compressed air to take up its shape (Fig. 24.4b). Both methods are cheap and quick, and can be fairly accurate. 

As a mould for high pressure we generally use a cylinder and plunger for rather short stars, but for longer stars a split mould, which is described in 1. 3. 

Uniaxial Compression - Williams Method This method was developed by Williams, Birks and Bhatta-charya24. A compact is first formed in a split mould by applying an axial compressive force, the mould is then removed to leave a cylindrical specimen with its axis vertical. The compressive vertical stress needed to cause failure of the specimen is then found and this is the unconfined yield stress for the consolidating stress used in the compaction of the specimen. The failure function is found by forming a number of compacts under different consolidating stresses and finding the unconfined yield stress for each specimen. 

Note that a portable tester based on the same principle as the compression tackiness tester is defined by a British Standard for testing of soils16. It uses a split mould 38 mm in diameter and 76 mm long (note the 2 1 ratio), with the sample of soil extruded into it from a sampling tube. The load is applied manually by a rotary handle and a lead screw, through a calibrated spring. 

In injection moulding, plastic granules are heated until they have a sufficiently low viscosity to be injected under pressure into a cold, split mould. The shaped plastic is cooled and released. 

Blow moulding describes any shaping process in which air is used to stretch and form plastic materials and can be compared to inflating a balloon. A hot thermoplastic tube, usually made by extrusion, can be inflated with compressed gas while inside a cooled split mould. Hot thermoplastic tubes or parisons can also be blown into free shapes without the aid of a mould (Figure 3.33). Plastic bottles, drums, car fuel tanks and other containers are often made using blow moulding (Figure 3.34). 

Injection moulding Premixed resin and short fibres are heated and forced into a split mould cavity Medium size, intricate shapes, high throughput, mainly thermoplastics, low fibre content... 

POP mixed with 10% Portland cement by weight was also used to prepare cylindrical specimens to have relatively higher uniaxial compressive strength and to represent higher wall strength, in case of jointed specimens. A total of 110 gm mixture was taken containing 11 gm Portland cement and was thoroughly dry mixed with a stirrer. This POP with cement mix was then mixed with specific quantity of water (always kept constant for every sample) to cast cylindrical specimens with split moulds similar to POP without cement mix specimens. These specimens of POP with ce-... 

Matched metal moulding techniques have limitations when used to process composite materials of this form. In addition, a complicated and costly split mould would be required to remove the male section from the Inside diameter of the bellows after moulding and curing the epoxy resin. A flexible, self-releasing silicone rubber mould core offers a simple solution. 

The basic requirements of the extrusion blow-moulding process are to extrude a molten plastic tube (the parison), clamp it in a cold split mould, expand the parison by means of compressed air, cool the shaped moulding, remove from the mould and trim as necessary. Interest in the present work centres on the example of the Acitainer, which is produced by this process. 

The moulding material is heated until plastic in a transfer pot from which it is pushed by a plunger through a series of runners into the heated split mould where it cures. Fig. 15.9. The two halves of the split mould are attached to the heated platens of a hydraulic press in the same way as for compression moulding. 

The mould is split into two halves and is made up of 13 sections. The powdered sample is poured loosely into the segmented split mould and consolidated by application of weights to stresses generally above 100 kPa for a period of time (Figure 1.22). 

Compression moulding process mainly used to manufacture thermosetting plastics products. It employs a split mould which is heated, opened to receive the moulding material and then closed under pressure. 

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