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Custom 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. Rotary joints are used in rotary equipment to cool, heat or transfer fluid power. The fluid being transferred can be steam, heat transfer oil, coolants, hot water, hydraulic fluids, lubricating oils, or air, and the rotating equipment can be heat exchanger rolls, machine tool spindles, gear boxes, and air clutches.

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 and nitrogen can be compressed to pressures over 800 psi.

Carbon-graphite gathering shoes are used to guide and gather together individual glass filaments to form bundles of filaments call “fiberglass strands”

Metallized Carbon Corp. supplies carbon-graphite rotary joint seal rings, guide bushings, piston rings, guide rings, carbon graphite gathering shoes, pad wheels and wobbles wheels to customer specifications. Our technical department is available for design assistance and to recommend the best Metcar grade for specific applications.

Seal Rings  · Piston Rings  · Fiberglass Gathering Shoes

Seal Rings
Rotary joint assemblies consist of a housing which supports a shaft with bearings that allow the shaft to rotate freely within the stationary 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. This is because many rotary joints are designed to accommodate angular oscillation, or vibration that occurs because the rotating roll or drum is not perfectly aligned with the stationary fluid supply pipe. Some rotary joint designs also utilize cylindrical, carbon-graphite guide bearings. Excellent mechanical strength and wear resistance make Metcar material ideally suited for these applications.

A good example application for rotary joints with carbon-graphite seal rings is in the paper industry. After forming, the wet paper, or “paper web” is continuously dried by rolling over a series of heated cylinders called “paper drying cans”. These continuously rotating “paper cans” are about three or four feet in diameter and they are heated with steam. The steam is transferred into and out of the continuously rotating “paper drying cans” through rotary joints with carbon-graphite seal rings.

Piston Rings
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. To achieve long wear, it is important that the spring exerts only about two psi of contact pressure between the piston ring segments and the cylinder bore. It is also important that the housing bore be polished to a 16 micro-inch surface finish or better. At least two rings with off-set segment joints are need to seal 100 psi. Extra sets of rings are needed to seal higher pressures. 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.

Fiberglass Gathering Shoes
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”. The glass filaments and strands are guided into rollers or into choppers by rotating carbon-graphite wheels known as fiberglass guide shoes.

Several Metcar grades are used for the manufacturer of fiber glass 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 there excellent lubricating qualities and good resistance to wear.


·  Glass Handling

·  Piston Ring


Metcar Physical Properties
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