Piston Rings, Rotary Joint Seals & Fiberglass Gathering Shoes

Rotary joints, also known as rotary unions, rotary swivels, or rotary couplings, are mechanical devices used to transfer fluid from a stationary pipe to a piece of rotating equipment. They are used in rotary equipment to cool, heat or transfer fluid power in the form of steam, heat transfer oil, coolants, hot water, hydraulic fluids, lubricating oils, or air. The rotating equipment can be heat exchanger rolls, machine tool spindles, gear boxes, and air clutches.

Rotary joint assemblies contain stationary housing which support a shaft made up of bearings, allowing the shaft to rotate freely within the housing. Spring-loaded mechanical seals are used to seal the fluid within the housing. The mechanical seal faces are selected based on the fluid being transferred, and often the seal faces are made of carbon/graphite material. The self-lubricating carbon/graphite seal rings for rotary joints often have concave or convex sealing faces to accommodate misalignment resulting angular oscillation, or vibration. Excellent mechanical strength and wear resistance make Metcar material ideally suited for these applications.

Our self-lubricating, carbon/graphite piston rings and guide rings are used when there is a need for compressed gases that do not contain oil or grease. In a reciprocating compressor, oil-free gases such as air, steam, refrigerants, hydrogen, hydrocarbons, chlorine, nitrogen and oxygen can be compressed to pressures of over 800 psi.

Segmented Metcar carbon/graphite rings with overlapped joints are placed in a radial groove in the reciprocating piston with little clearance between the width of the groove and the width of the piston ring. A metal leaf spring expander ring in the ID of the segmented piston ring is used to exert outward force to hold the piston ring OD against the cylinder bore. Wear life up to 10,000 hours is possible when the compressor and piston rings are correctly designed.

Carbon/graphite piston rings are usually used in conjunction with carbon/graphite guide rings or carrier rings. The function of the piston rings is to seal the high-pressure gas, and the function of the guide rings is to hold the piston centered with respect of the cylinder bore. Therefore, the guide ring must be in close contact with the piston and the housing bore. Guide rings can be either solid rings or segmented rings with butt joints.

Carbon/graphite gathering shoes are used to guide and gather together individual glass filaments to form bundles of filaments called fiberglass strands. Glass filaments are formed by pulling molten glass through small holes in a metal plate. The molten glass filament is about 0.0002 to 0.0014 inches in diameter. About 100 to 1500 filaments traveling at about 25 to 200 miles/hr are gathered together to form one strand. The strand is then wound onto large spools or it is pulled into a chopper that produces short lengths of strand called “chopped fiberglass.”

Several Metcar grades are used for the manufacturer of fiberglass gathering shoes, pad wheels and wobble wheels. To be suitable for these applications, materials must be low in friction to prevent breakage of the filament when pulling or guiding it through the process. Materials that do not provide sufficient lubrication degrade, fray, and even break the filament. Metcar self-lubricating carbon/graphite materials are particularly suited for this application because of their excellent lubricating qualities and good resistance to wear.

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