Boron Nitride Release Coatings

Abstract

Boron nitride is an advanced ceramic material with outstanding chemical and thermal properties. It is often called white because it has a graphite-like structure, but in contrast to graphite, it is white. It is an excellent high-temperature solid lubricant, is stable at high temperature and most important for casting and foundry applications is not wetted by many metallic melts like aluminium, magnesium and zinc. In order to be able to use the advantages of boron nitride in casthouse and foundry applications, we developed coatings on the basis of boron nitride particularly for the application within casting shops. These coatings are applied like ordinary house paints by brushing or using a spray gun. They are perfect release agents used in aluminium foundries for the protection of ladles, dies ingot mould, permanent moulds thermocouples and ceramic structures. These coatings provide an excellent nonsticking and lubricating surface to which neither aluminium nor magnesium will adhere. Boron nitride coatings are also proven release agents for coating thimbles, transition plates and refractory linings of distribution troughs of DC casting machines. During casting breaks, these coatings ensure the perfect and easy release of remaining aluminium without damaging the refractory substrate. Boron nitride release coatings are available as water-based paints as concentrates as well as ready-to-use formulations. For an easier application in suitable environments, these coatings are available in aerosol cans too. In contrast to graphite coatings and other (red mud) readily-used coatings boron nitride release coatings are stable in air (up to 1000°C), show excellent non-wetting behaviour (the best in the field of ceramics) and very good lubrication properties even at high temperatures. These very advanced characteristics make boron nitride release coatings a product of the first choice to foundrymen. 7 Australian Asian Pacific Conference Aluminium Cast House Technology Edited by P.R. Whiteley IMS (The Minerals, Metals & Materials Society), 2001