Flexible sliding surface seal for double band presses, includes rigid wire- and fibrous polymer reinforcement in polyimide matrix deposited by evaporation in layers and subsequently cured

摘要

The metallic holding strip (3) bonded to the sliding material (1, 1') is hermetically sealed. To resist friction and shear stresses an undercut surface profile is formed on a wire fabric (2, 2') in e.g. linen binding. The wire fabric is made rigid to resist movement, by thermal sintering. The sliding material is preferably polyimide, made by sinter-pressing of powdered, dried, non-imidized polyimide, into the holding strip and wire fabric, using totally enclosing molds under high pressure. The temperature rises in a suitable and known manner from 120[deg]C to 380[deg]C during pressing. The polyimide is compressed to full homogeneity into the fabric, at the same time becoming fully- or partially imidized. The sliding material is preferably polyimide. Its solution contains typically 15%-55% solids, in e.g. N-methyl ketone. It is coated layer-by-layer at intervals as a liquid film, each coat being 0.05-0.3 mm thick. The coats are applied to the sides of the wire fabric on the holding strip. Commencing below 120[deg]C, the temperature is raised, drying cautiously such that the polymers do not gel within the solution. Drying is effected as rapidly as possible following the first coating, building up successive films up to the required thickness. Typically each is reduced to less than 5% solvent before re-coating. Reinforcement is laid into the wet polyimide films applied, immediately, before or during temperature increase to 120[deg]C. Whilst the viscosity is falling with rising temperature, a tangled fleece, flocks or yarns in fabric or braided arrangement, e.g. of carbon, aramid or similar chain polymers, in woven or flocked form is inlaid, floating in the film, wetted completely and encapsulated cavity-free during drying. Many such successive layers are applied, and the temperature is raised from 120[deg]C to 380[deg]C causing full imidization. This is so complete that laboratory determined-weight loss for the polyimide formulation, even after years of operation e.g. in a double band press, does not exceed 0.5%. Further preferred details of construction are provided, based on the foregoing principles.