Achieving Optimal Rotary Joint and Rotary Union Performance

3500 SXB Rotary JointsAchieving optimal equipment performance is a goal of importance to management and operations. As manufacturers design new machines to operate at higher speeds, higher temperatures, and increased efficiency, consideration must be given to the rotary joint or rotary union to ensure that it is capable of performing at these operating conditions. The proper equipment and maintenance of equipment are important in realizing optimal performance of the entire operation.

Once the rotary joint has been properly installed, the primary wearing component is the seal ring. The seal ring should be replaced after the maximum seal ring wear has been reached. If not replaced, metal surfaces could rub together and cause irreparable damage to the rotary joint.

In most designs today, manufacturers use a carbon graphite seal ring with a spherical surface on one side, and a flat surface on the opposite side to mate with the flanged enclosures of the rotary joint. Seal rings are made up of carbon-based flour, fillers such as petroleum coke, natural or synthetic graphite, or a lamp black, binders consisting of metal, resins, or pitch; and additives such as silica, silicon carbide, or film formers.

A batch is produced and mixed together at around 600° F and then sized for molding. The batch is pressed into a die and baked at around 2,000° F. The binders melt and cement the parts together. Some of the binders vaporize, producing pores. After baking, the rings are rough machined to shape, and the pores are filled with an impregnate prior to final machining.

Machine speed, pressure, and temperature are critical to wear characteristics of mechanical seals. The actual compressive load applied to the seal ring, which makes it a positive seal, is directly related to the operating pressure. As the pressure increases, so does the load on the seal. Increasing this load, along with machine speed, increases the frictional power consumption of the rubbing surfaces and generates higher temperatures. In general, the wear rate of a seal will increase with both operating speed and pressure.

When all the costs of seal failure are considered, selecting the right seal material is an important factor. Kadant Johnson is continuously researching and testing new seal materials to deliver even greater longevity and reliability for its rotary joints and unions.