Paper Dewatering Foils

Advanced silicon nitride and sialon ceramic paper dewatering foils are used in paper manufacture during the water removal stage. This is a very demanding wear application requiring an engineering ceramic possessing a unique set of properties including wear resistance and thermal shock resistance. Sialons are alloys of silicon nitride, and they possess the demanding properties required for this application.

During the manufacture of paper a section of the process involves removing water from the fibre⁄water pulp. To do this, the pulp is spread over a fabric mat which travels over a series of suction boxes. These boxes apply a vacuum which draws the water out of the pulp as the fabric travels over them.

The suction boxes consist of a series of rows of foils, which can be many metres long. The foil can be made of high density polyethylene (HPDE) or ceramic material. Advanced ceramics are used in high speed applications. The foils are ground to give a mirror finish, which is important for the quality of finish of the paper.

Initially, alumina was the ceramic of choice. However as machine speeds have increased up to 100km⁄min, so the requirement for greater wear resistance has emerged. This is where Syalon 101 comes in. It is a strong, tough fine ceramic offering excellent wear resistance and thermal stability, making it the ideal choice for modern high speed applications.

Traditionally, the foils were made up of ceramic segments 20-40mm wide. Thus a 10m long foil would consist of typically 500 pieces butted together. This can lead to a problem known as 'piano keying', in which segments move to ruin the perfectly flat foil surface. To reduce this problem International Syalons developed a patented method of producing segments up to 750mm long. This therefore greatly reduces the number of segments and minimises the chance of 'piano keying'.