Moulding processes injection

Note The injection/compression moulding process capability maps 1, 2 and 3 are used for large parts with a major dimension greater than 50 mm typically and/or for large production volumes. Map 4 is for injection moulded parts that have a major dimension less than 150 mm and which are produced in small volumes. 

Polynorbomene is also of interest to the plastics processor since by using a dry blending process for mixing and a modified injection moulding process for fabricating, the use of conventional rubber-processing equipment may be avoided. 

Paste injection moulding processes have also been developed. In one technique used for applying PVC soles to shoe uppers the paste is injected by gas under pressure into a hot mould, the last and shoe upper forming the top half of the mould. The paste gels in the mould, adheres to the upper in the presence of a suitable adhesive and is stripped hot from the mould. 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Whilst the injection moulding process has now been widely accepted for phenolics the transition from compression moulding has been less extensive with U-F materials. The basic reason for this is that the U-F materials are more difficult to mould. This has been associated with filler orientation during moulding, which can lead to stress peaks in the finished product which the somewhat brittle resin in less able to withstand than can a phenolic resin. 

The success of transfer moulding prompted further developments in this area and clearly it was only a relatively small step to an injection moulding process for thermosets as described in Section 4.3.10. 

In some compositions the PIB is plasticized with ethyl oleate to improve low temp properties. .. Since the propint is a stiff paste it can be inserted into a rocket motor by a type of injection moulding process (Refs 3 5)... 

The hydrophilic/hydrophobic SIN composition of PDMS with poly(HEMA) and poly(AAC) were proposed as a potential apphcation for high-permeability soft contact lenses. Other sUicone-containing IPNs for contact lenses include polymerization of MMA in the presence of polymerized methacryloxypropyl trimethoxysilane, the cross-linking of a polymeric hydrogel of a copolymer of NVP during the final compression or injection-moulding process. 

The application of instrumentation to the automatic control of a sequence of operations, e.g., injection moulding processes. Once the mould has been loaded with inserts (assuming a rubber to metal bonded part) into the press, the operation of a push-button starts the controller which closes the press, injects the rubber, controls the cure cycle, recharges the injection unit, opens the press, operates the ejectors and presents the mould for cleaning and loading of inserts. 

Poly(butylene terephthalate) (PBT) is a semicrystalline, thermoplastic polyester which is completely analogous to PET except that it has a longer, more flexible butylene chain linkage which imparts a rapid crystallization rate, thus making PBT well suited to injection moulding processes. This polyester is used widely for electrical and electronic components due to its high temperature resistance and good electrical properties (Chapter 8). 

Injection is by far the most used moulding process but compression and compression-transfer are used for specific cases. Rotomoulding is specifically used for polyethylene and a few other powdered resins. Slush moulding is broadly used for automotive dashboards. Generally ... 

ECTFE can be processed by conventional molten-state methods such as extrusion, injection, compression, transfer, rotational and blow-moulding processes. 

Injection and blow moulding are by far the most used of the moulding processes but compression is sometimes used for specific cases. 

Toronto, 27th April-2nd May 1997, p.2060-4. 012 MICROCELLULAR CROSSLINKED EVA FOAM BY INJECTION MOULDING PROCESS LeeJJ... 

The injection moulding process for producing a microcellular crosslinked EVA has several advantages over the conventional compression moulding process reduced cycle time, labour and scrap. The presence of skin adds aesthetic value and ability to engrave logos in one step. However, the injection moulding process has... 

Journal of Vinyl and Additive Technology 2, No.2, June 1996, p.167-9 MICROCELLULAR FOAMING OF POLYPROPYLENE CONTAINING LOW GLASS TRANSITION RUBBER PARTICLES IN AN INJECTION MOULDING PROCESS Chicheng Wang Cox K Campbell G A Clarkson University... 

PBTP crystallises considerably more rapidly than PETP. In an injection moulding process, where short cycle times are required, and thus rapid crystallisation during the rapid cooling in the mould, PBTP may, therefore, be preferred. PETP would stay amorphous, and, therefore, not usable above its Tg (69 °C). 

Three types of moulding processes are available - compression, transfer and injection moulding. In compression moulding the rubber blank is placed directly into the cavity of the mould where it is heated by conduction which causes rubber flow by application of pressure. Transfer moulding uses prewarmed rubber which is heated during transfer and forced through small orifices into the mould cavities in a three-part mould. In the injection moulding process, the rubber compound is pushed under pressure from an injection head where it has been heated and plasticized into a closed heated mould where cure is completed. 

Table 14.1 Comparison of compression, transfer and injection moulding processes...

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