Casting moulding machines

Another comparatively recent development is poly(butylene terephthalate) heavily filled for electroplating applications. For a plastic it has unusually high density and so gives components much heavier than would be made with conventional unfilled polymers. In some instances this is regarded as desirable—the heavier mouldings are closer in weight and in feel to components cast or machined from metal. Since they are more familiar they are perceived to be of better quality—a concept apparently quite important for uses such as bathroom fittings and plumbers requisites. 

Flow in the nozzle of a moulding machine [102] and its pipeline [101], filling and curing in a casting mould [103], in a semi-circular tank [104], rotating mould [105], etc., was considered. 

A number of procedures exist for the production of moulds, and selection of the most appropriate will depend on cost and the number of mouldings that will be required. Polyurethane forms foams at low pressures, so that it is often practicable to use cheap cast moulds rather than expensive machined ones. 

Up to now, adaptronics has mainly been an object of research at universities, and the industry has only just started to apply adaptronic systems a most recent example is an intelligent mineral casting mould [182]. This machine bed for machine tools is to adapt itself to changing thermal conditions, thereby preventing the structure from any deformations. To accomplish this, temperature sensors are embedded into the mineral casting material (polymer concrete) cooling elements, which are integrated into the bed, serve as actuators. 

Two general types of machine are used for ingot casting - the rotary wheel caster and the straight line chain mould machine. The casting wheel uses a rotary table with water-cooled moulds arranged around the outer periphery of the wheel. Molten metal is poured into the moulds at a fixed station. The mould... 

This category can be said to inclnde qnantum tunnelling composites which are cnrrently nnder development. These unusual materials are insulators under normal operating conditions but become metal-like conductors when pressure is applied. Such materials can be used for sensors and switch substrates for example. They can be cast, extruded, moulded, machined or screen printed by standard processes. 

The foundation for this technology is that products are built up layer by layer using laser-fused metal powders of polymers. Thus, rather than casting or machining a metal item or injection moulding a plastic product, this item is created from a series of very thin layers of material. 

Use generous radii/fillets on castings, mouldings and machined parts... 

These super-alloys are remarkable materials. They resist creep so well that they can be used at 850°C - and since they melt at 1280°C, this is 0.72 of their (absolute) melting point. They are so hard that they cannot be machined easily by normal methods, and must be precision-cast to their final shape. This is done by investment casting a precise wax model of the blade is embedded in an alumina paste which is then fired the wax bums out leaving an accurate mould from which one blade can be made by pouring liquid super-alloy into it (Fig. 20.4). Because the blades have to be made by this one-off method, they are expensive. One blade costs about UK 250 or US 375, of which only UK 20 (US 30) is materials the total cost of a rotor of 102 blades is UK 25,000 or US 38,000. 

Such lenses may be made by machining from rod. More recently processes have been developed where the monomers are cast polymerised in tiny plastics moulds whose cavity corresponds to the dimensions of the lens and using procedures very reminiscent of those described for the manufacture of acrylic sheet (see Section 15.2.2). 

Other, more recently developed, uses include microwave oven parts, transparent pipelines, chemical plant pumps and coffee machine hot water dispensers. One exceptional use has been to produce, by an extrusion moulding process, very large rollers for textile finishing for use where cast nylons cannot meet the specification. Also of growing interest are medical equipment applications that may be repeatedly steam-sterilised at 134°C, filtration membranes and cartridges for ink-jet printers. 

Materials used for insulating sheaths should be inert and easy to machine they are generally plastics or casting epoxy resins. Epoxy resins are easier to handle because of their moulding ability but they are not chemically inert to certain species, including many non-aqueous solvents. Additionally, care must be taken when preparing the epoxy resins that air bubbles do not appear in the mixture prior treatment of the adhesive and hardener mixture under vacuum for a short while reduces the problem. 

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