Transfer moulding design

Source Reprinted with permission from Abraham D, McCarthy R, Design of polymer composite stmclural components for manufacture by resin transfer moulding (RTM), SAMPE Europe Conference and Exhibition. Proc of 2Cf International SAMPE Europe Conference of the Society for the Advancement of Materials, Paris, France, 407-415, 1999. Copyright 1999, The Society for the Advancement of Material and Process Engineering (SAMPE). 

New glass fibre-reinforcement products for u.se in fibre-directed preform processes are another focus of development, designed specifically for liquid composite moulding applications such as resin transfer moulding with thermoset polyesters. 

In resin transfer moulding, the resin is injected into a mould containing layers of fibres or a preform at low pressure. The process cycle time is less than 3 minutes, and the fibre content of the composite product is up to 50%. The advantages of the process are design flexibility, ability to manufacture larger structures, low cost (thanks to the low pressures involved) and rapid manufacture. As with sheet moulding, resin transfer moulding is widely used in the automotive industry to manufacture a variety of parts for cars and other vehicles. 

Bechly ME, Clausen PD, Snaith H. Structural Design, Manufacture, and Testing of Resin Transfer Moulded Blades for Small Wind Turbines. Bury St Edmunds, UK Mechanical Engineering Publications, 1997. ISBN 1-86058-034-3. 

A low viscosity epoxy designed for vacuum bag and resin transfer moulding. 

We can focus on a few of the most innovative end uses. Some of the most exciting and high profile applications are in the BMW i3, which is one of the world s first purpose-designed electric vehicles. The BMW i3 makes extensive use of composite materials in its body structure. In addition, SGL Automotive Carbon Fibres, a joint venture between SGL Group and the BMW Group, converts recycled carbon fibres into non woven fabrics. These are converted into components, such as the roof of the BMW i3, using the resin transfer moulding process [10]. 

Bulk applications of PF resins utilize novolaks in formulations designed for rapid cure. Traditionally, components were manufactured by compression or transfer moulding, the latter being preferred for products with moulded-in inserts. Injection moulding is gaining in use, for example for electrical components, electric iron handles (see Chapter 9), or saucepan handles (see below). 

One factor which affects the cost of both compression and transfer moulded parts is the fact that a certain amount of material may flash between the two parts of the mould while the molten material is under pressure. The amount of flash depends on the mould design but if it is appreciable it must be removed. In the case of small objects a simple tumbling process is usually sufficient but larger parts may have to be treated on a linisher or similar device. 

The final clamping action forces rubber through the sprue holes leaving a thin (0.13-0.25 mm) transfer pad. The mould is designed with load springs to break open the plates and to help support the top plate and plunger when bottom injection is used. 

In an extension of moulding-in printed decorations, using polyester resins and lay-up by hand, designs can be transferred from the printed substrate and sealed into the surfaces of articles—the feedstock originally carrying the effect being removed afterwards. 

In 1983, electrolytic dissolution was exploited in the metallurgical industry for the batchwise determination of soluble aluminium in steels by flame atomic absorption spectrometry [27]. A specially designed spoon transferred a few millilitres of the red-hot molten material to a diskshaped mould where the material solidified when cooled. The resulting pellet was placed on the electrolytic chamber and, after the dissolution step, an aliquot of the electrolytic solution was taken and analysed for aluminium. With an advanced electrolytic chamber design, electrolysis time was reduced to about 40 s. The feasibility of batchwise electrolytic... 

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