GB707556A - Improvements in and relating to filters - Google Patents

Abstract

In a process for making a filter for use in melt spinning or extrusion a compact mass of substantially uniform spherical particles, preferably of glass, is caused to stick together at the points of contact of the particles while they are held in a restraining ring, preferably of metal, placed on a flat surface. The ring preferably decreases in internal diameter from top to bottom. In an example spheres of diameter 0.035 cms. of lead glass are placed in a former, comprising a steel alloy ring decreasing slightly in diameter in a series of steps from top to bottom, on a plane stainless steel block, and are packed tightly by the surface tension effect of water with which they are wetted. A straight edge is dragged across the ring to level off the contents and the whole is dried before placing in an oven at a temperature of 700 DEG C. where it remains for 15 minutes. After cooling, the ring together with the disc of glass spheres set within it is removed from the stainles steel block by slight tapping. The choice of steel alloy for the ring depends upon the relative expansion coefficients of the glass and the steel. To facilitate salvaging of the ring on disposal of the glass disc a close-fitting thin metal liner may be incorporated between the glass and the ring and it may be so shaped that a flange lies in contact with the ring or the glass or with both. This flange may act as a gasket in, e.g., melt spinning apparatus. The filter may be used while still in the restraining ring and may be strengthened by supports, extending across its face, such as struts or metal gauze attached to the restraining ring. The stainless steel block on which the filter is placed during making may be oxidized. The spherical particles may be coated with a very thin layer of adhesive (which according to the Provisional Specification may be resin) to stick them together.