Complex cast parts such as turbocharger housings play a central role in the design of modern high-performance engines. Due to its particular characteristics silica sand has its limits as a moulding material when it comes to casting finely structured components, reduced wall thicknesses and perfect surfaces. Thanks to its high temperature load strength and a strong resistance to metal penetration, Kerphalite™ KF, a special sand, has proven itself suitable for these types of applications in many foundries.
In central Europe, silica sand is available in large quantities and in good qualities, and is widely used in foundries as an economical basic moulding material. But it also has negative properties, which may lead to problems when producing sophisticated castings. These particularly include the so-called quartz inversion, i.e. the abrupt expansion of the specific volume at 573°C. It occurs during virtually every casting process and may lead to sand expansion defects, mainly in the form of finning (also called veining). The moulding material can crack under high temperature load, allowing liquid metal to seep into the resulting cracks and cavities.
Suitable alternative for silica sand
Foundries aim to avoid these casting defects and reduce the costly effort needed to rework the casting. This is all the more important when considering that casting geometries are becoming ever more complex and the demands for their dimensional accuracy and surface quality are becoming ever more exacting. If foundries want to avoid using more binding agents or adding gas-forming additives, they need a suitable alternative to silica sand as a moulding material. Kerphalite KF is a special sand with low thermal expansion, high refractoriness and a special grain geometry that enables very high core surface densities.
From stalky crystals to a special sand
Kerphalite KF is a natural material based on andalusite and processable with all binder systems and moulding processes. Kerphalite KF has a low density (similar to silica sand) and can be used in pure form or as a blend with silica sand, as required. When blended, the share of Kerphalite KF should be between 30 and 100 percent. In this way, the user is able to adjust the sand blend to be both cost-effective and process efficient. The special moulding material is easily processable with all common binder systems. It is suitable for the Cold-Box as well as for the shell moulding process or the furan resin processes in iron as well as in steel castings. Kerphalite KF has also been used for 3D printing cores for over ten years.