Competitive coating

Through work to develop a long-life die coat for the low-pressure and gravity die casting industry, a new insulating coating has been developed that can last up to 10 times longer than traditional coatings.

CASTcoat, as it is called, is a low maintenance coating with adaptable insulating properties. The coating – essentially a strong, porous ceramic layer that is resistant to wear and tear – is applied to a die using a thermal spraying technique.

CSIRO scientists Dr. Mahnaz Jahedi and Stefan Gulizia, and a University of Queensland PhD student, Mary Giannos, initially developed CASTcoat. The CSIRO scientists then developed the technology for an industrial environment as part of the Cooperative Research Centres for Cast Metals Manufacturing (CAST) program, from where the product derived its name.

In conventional low pressure and gravity die casting processes, filling the die cavity is slow and the metal die has the capacity to rapidly extract heat from the molten alloy. Traditionally, die coats act as insulators to prevent premature solidification of the casting, but they also control the quality of the end product.

While these coatings provide adequate insulation and prevent premature solidification of the alloy, they offer poor resistance to wear, because of weak bonding. Their application is also highly operator-dependent. It is not uncommon for coatings to be completely replaced after a few shifts. Even after only a few uses or 'shots', localised damage on the coating surface in the die cavity often needs to be repaired, a process called 'touch ups'.

CASTcoat overcomes traditional problems because of its use of thermal spray technology. Instead of using a silicate-based binder, bonding is created by partial melting of the actual ceramic particles, fusing them together.

The resulting bond is far stronger than traditional binders. This means high wear-resistance and durability, ensuring the die is better protected, with none of the constant touch-ups required by conventional die coats.

In a current European trial, a car parts producer that supplies well-known automotive manufacturers has been trying out the process.

Dr. Jahedi says the company applied CASTcoat before Christmas and by the second week of January it still had not needed replacing: ' Using conventional methods, the insulating coat would have been replaced many times by then.'

Successful industry trials have now led to the commercialisation of CASTcoat by Acheson Industries (part of the ICI group), which has taken up an exclusive licence for the technology.

While the main users will be companies that manufacture lightweight allow parts for the automotive industry, the durable insulating coat can be used across a variety of applications, such as molten metal handling or wherever any insulating and wear-resistant coatings are needed, says Dr. Jahedi.