GB791568A - Improvements in axial flow compressors - Google Patents

Abstract

In an axial-flow compressor, the portions of the housing adjacent the paths of the rotor blade tips are coated with an abradable skin that can be machined by the blade tips in motion. The coating may be applied to the housing by brushing, spraying, or by the use of a roller or spreader. Alternatively, it may be in sheet or tape form bonded to the housing. The coating is heated at a temperature rising from 100 DEG F. to 500 DEG F. in hourly steps of 100 degrees to harden it, and is then machined to a thickness of, say, 0.01 to 0.03 inches. The tips of the rotor blades can, if necessary, machine the coating to establish a minimum working clearance. The coating may comprise a mixture of a filler such as powdered graphite or finely-divided asbestos, or both, with a heat hardenable silicone resin, a thermosetting resin, e.g. phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde and certain fluoro-carbon resins, or a heat hardenable material such as sodium silicate, with the addition of a volatile solvent or diluent. Other fillers which may be used are glass fibre, silica flour or other ceramic material, powdered spent catalyst or powdered metals such as aluminium, antimony, tin and lead. The solvent or diluent may include secondary butyl acetate, mineral spirits, xylene, toluene or other liquid hydrocarbons. Plasticizers, such as various phthalates and glycol esters, may be included to improve the flexibility of the coating at low temperatures.ALSO:A coating composition comprises a heathardenable silicone resin or a thermosetting resin such as phenol formaldehyde, urea formaldehyde, melamine formaldehyde, or a fluorocarbon resin, with a filler such as powdered graphite, finely-divided asbestos, glass fibre, silica flour or other ceramic material, powdered spent catalyst, tin and lead, and a solvent or diluent such as secondary butyl acetate, mineral spirits, xylene, toluene or other liquid hydrocarbons. Plasticizers, such as various phthalates and glycol esters, may be included to improve the flexibility of the coating at low temperatures. After application, the coating is cured by heating it at a temperature rising from 100 to 500 DEG F. in hourly steps of 100 degrees. In general, the composition can be made by adding up to 2 gm. of powdered graphite or asbestos or both per c.c. of a mixture comprising 15-45 per cent of one or more silicone resins, up to 75 per cent of volatile solvent or diluent or both, and, optionally, 7-12 per cent of finely-divided metallic powder. A preferred composition comprises 7-45 per cent of heat-hardenable silicone resin, 15-55 per cent of powdered graphite or finely-divided asbestos or both, up to 10 per cent of finely-divided aluminium or other metal, and up to 65 per cent of volatile matter. The composition can be made by adding about 1 gm. of powdered graphite or finely-divided asbestos per c.c. of a silicone resin paint. Alternatively, 0.25 gm. of powdered graphite is added per c.c. of a liquid mixture comprising 7 per cent of powdered aluminium, 40 per cent of a heat-hardenable silicone resin, and 53 per cent of toluene.