Resin casts plastic in new mould

An inventive Yorkshire pattern maker has developed a way to produce plastic components using conventional metal foundry sand moulding techniques.

The Dartek process developed by 59-year-old self-employed pattern and mould maker, Dave Darby of Guisborough, promises to cut the cost of making moulds and dies for plastics injection moulding and for the vacuum forming of plastics.

Most metal castings are produced in a foundry, using moulds made from sand compacted around a pattern or core.

The pattern is placed in a metal box and fine sand mixed with a resin binder is poured in and rammed around it. Excess sand is removed and the box and its contents heated to bind the mould. The pattern or core is then removed.

But the resulting sand mould is no good for plastics moulding – it is too weak to be reused and it is also porous. With metal casting this is a useful characteristic as metal gases are allowed to escape rather than form bubbles in the casting. Molten plastics, however would seep into the sand moulds.

With the Dartek system the sand mould is hardened by dipping it into a liquid resin hardener which ‘soaks’ into the sand and cures. This produces a tough, glass-like mould, which can be used repeatedly to produce batches of plastics mouldings.

Strength increase

In metal casting, a new sand mould has to be made for each casting since the heat from the molten metal destroys the binder holding the sand together. But in the Dartek process the strength of the sand mould is increased by more than 20 times, while porosity is reduced.

Darby said that with the right sand a good surface quality can be achieved. The technique can also be used to produce one-off prototypes and jigs and fixtures in hardened sand.

Darby said the process requires traditional pattern making and foundry skills. It does away with the need for expensive tool-making equipment and skilled machine tool operators to produce the metal moulds normally used for plastics moulding.

Dartek moulds can also incorporate cooling channels to help cool the molten plastic after moulding.

This week Darby received a £50,000 award from NESTA, the National Endowment for Science, Technology and the Arts, to help him commercialise his process which he has been developing for five years. NESTA has also appointed a ‘project champion’ to look at the market for Dartek.

Marketing hopes

‘Give me a drawing and I’ll make it – that’s my expertise,’ Darby said. ‘What I need now is marketing advice. I really need this project champion to point me in the right direction, where to look. When you work on your own, you don’t get out much.’A spokeswoman for NESTA said the project was chosen because it combines old methods of production with new areas of technology and solves the contemporary issue of time compression facing most manufacturing companies.

‘The product should also provide developing countries, which lack the capital to invest in modern production methods, with an opportunity to produce simple products at low costs,’ she said.