Universal mechanical seal

Abstract

Seals of a new type [1-3] developed by the limited partnership TOO I~KOGERMET can be classed as combination contact mechanical seals. The structural elements of these seals incorporate features of labyrinth, face, and radial seals. The simplest version of these seals includes two seal rings with the faces ground against each other; these are positioned in the packing gland of the machine, in a rubber sleeve. The openings of the rings are shifted relative to the axis of the shaft or rod so that their centers are on a single line with the center of the shaft, i.e., are turned by an angle of 180". The seal rings are pressed against each other with their side surfaces by means of a flange and collar in the rubber sleeve. Thus, the two seal rings make an elastic contact on both sides with the shaft and with each other, closing off the leakage of liquid along the shaft axis and also through the annular slot in the plane of the ring. In the interest of higher efficiency of sealing in the actual equipment, several pairs of seal rings are used, installed in series and oriented so that lines connecting their centers will be turned by an angle ct = r/n, where n is the number of pairs. In this arrangement, the inner surfaces of the rings and the surface of the shaft form a contact-labyrinth slot, in which a high hydraulic pressure is generated by flow of the liquid. At the start of operation, the rings and the shaft touch along a line or along a very narrow band. As the seal is worn in, the contact spot becomes larger. In a completely broken-in pair, two rings pressed toward the shaft from opposite sides completely cover the slot. Depending on the end-use, the seal rings and shaft may be made of antifriction, anticorrosion, or antiwear material (steel or copper alloys, cast iron, hard alloys, composites, graphite, materials based on glass, ceramics, plastics, or various coated materials). The sleeve may be made of various types of oil-resistant rubber, including silicone and fluorinated rubbers. In extreme service-for example, in media that will dissolve rubber, or at very low or very high temperatures-the elastic sleeve is made of pressed wire. In aircraft and ship construction, "metallic rubber" is widely used to fabricate vibration dampers, springs for fluoroplastic cup seals, and many other items. The mechanical seal developed by TOO I~KOGERMET can be called "universal" not only in that, owing to the extremely simple shapes of its parts, practically all of the rigid materials known in seal technology can be used. This seal is universal in that it can be used as a component of moving pairs with rotating, reciprocating, or screw motion-and with considerable radial and axial play, angular misalignment, and relative displacements of the axes of the shafts or rods of the machine. The seal can operate in pumps and compressors, mixers, engines, hydraulic and pneumatic equipment, shutoff valves, and other machines and units; it can operate in neutral or aggressive media and in media with high contents of particulate matter, at low or high temperatures and under low or high loads. In comparison with the closest analogs, for example ring seals (piston, floating, or sectional seals with spring-loaded rings), this type of mechanical seal has three major advantages: considerably less leakage; longer service life; high technological efficiency and low cost of manufacture and service. It should be noted that the installation of the seal rings in a resilient sleeve in an eccentric position relative to the axis ensures constant contact of the rings with the shaft or rod during the entire life of the seal. In the course of operation, wear of the friction pair is automatically compensated, and the rubbing surfaces are lapped; therefore, the seal operates for an extended period with minimum leakage, while the resilient element does not wear but only plays the role of a spring.