Hollow ceramic components produced by rotary moulding cuts costs
Rotary moulding, widely used to manufacture hollow polymer objects, can be adapted to reduce production costs in the ceramic industry, according to research conducted at CERAM, Loughborough University and Queens University Belfast, all in the UK.
Project Manager Dr Ihsan Al-Dawery of CERAM explains that one of the main limitations of the slip casting method currently used is that it requires the porous plaster-of-paris moulds to absorb excess water from the clay suspensions before producing the final hollow form. This causes rapid degradation of the mould and restricts its use to as little as 40 casts. An estimated 3,000t of plaster waste is generated from the ceramic industry in the UK per annum.
Furthermore, once the required wall thickness of the cast item (about 3-5mm) is attained, excess slurry or slip is removed from the mould. The tipped slip represents potential waste, and, in any case, additional effort is required (such as rheological adjustment) to recycle it internally. Manufacturers therefore have to bear the cost of storage, shipping and disposal.
Working with the support of the Sustainable Technologies Initiative, which is funded by the DTI, DEFRA and research councils, including EPSRC, Al-Dawery and his colleagues investigated rotary moulding as a possible solution. He says, ‘No research has ever been conducted for [such] processing of ceramic materials'.
The technology involves replacing powdered polymer with ceramic slip in a closed mould that is rotated around two axes while being heated in an oven. As the temperature rises, the slip becomes more viscous and solidifies. Patented chemical additives were employed to enable ‘direct consolidation' of material. Al-Dawery says, ‘the process is much more environmentally friendly as whatever goes inside the mould as suspension becomes the final product. There is no excess.'
Moreover, there is also a shift in the mould's purpose. No longer required to absorb water from the slurry, it is now made from aluminium, stainless steel or plastic resin, with the ability to produce at least 10,000 casts in each mould. This opens up opportunities for CAD-CAM and so faster introduction of new product shapes.
Researchers at Loughborough University and Imerys, based in Paris, France, also worked to minimise the slurry's water content, aiming for an 80:20 solid:liquid composition.
From waste to weight reduction - unlike in pressure casting, there is no longer the need for backing plates to support the mould material from the application of force. ‘A washer basin mould weighs about 300 kilos for pressure casting - in rotary moulding, the weight reduces to about 50 kilos,' adds Al-Dawery.
With such advantages, the new method for processing hollow ceramic items speeds up production, and, in turn, researchers say, reduces costs by 30-40%. Trials with a range of cast shapes were conducted, and results showed that for a cream jug with a handle, manufacturing was about four times faster than conventional practices. This is because there is no need to apply pressure, remove excess slurry, or rinse and dispose of old moulds and produce new ones, enabling more efficient use of resources.
Having secured funding from the EPSRC for another year, Al-Dawery is confident of the commercial opportunities for applying rotary moulding in this way. Further investigation, however, is required to eliminate pinholing on ceramic glazes and to extend the process from sanitary and tableware to advanced ceramic materials. He says, ‘It's a development that will help the UK industry to survive.
Ihsan Al-Dawery, email: firstname.lastname@example.org.