What Is a Rotary Joint?
A rotary joint is a joint that can form a flow path for water, air, oil, etc., between a fixed pipe and a rotating shaft. It is sometimes called a rotary joint or swivel joint.
Rotary joints make it possible to supply fluid continuously to a rotating body and circulate the fluid inside. This function can be used to add functions such as cooling and lubrication to the rotating rolls or to supply power source fluid to equipment on the rotating body.
Uses of Rotary Joints
Rotary joints can supply fluids such as water, air, and oil to rotating bodies. They are used to provide cooling and lubrication functions and power sources to rotating bodies.
A typical example of a cooling application is a cooling roll (chill roll). Cooling rolls are used to cool products on the surface of rolls by circulating a refrigerant such as water or oil inside the rolls that convey sheet products, and rotary joints are used to supply the fluid.
In the steel industry and other industries, a rotary joint may be used to supply oil as a hydraulic power source to a cylinder connected to a rotating winding shaft.
Principle of Rotary Joints
Rotary joints consist of a stationary channel, a rotating channel, and a seal to seal these channels. The stationary channel is located on the axis of rotation or the circumference and is always connected to the rotating channel, thus enabling a continuous fluid supply to the rotating body.
Rotary joints are available from those with one port to those with 20 or more ports. The number of ports is set according to the number of fluids to be used. In cooling rolls, which are often used in factories that handle sheet products, water is the only refrigerant used in most cases. In this case, a rotary joint with two ports is used, one for the outward flow and the other for the return flow. Shield machines used for tunneling require the supply of many fluids, such as mud removal fluid, hydraulic oil, and grease. Rotary joints with many ports are specially designed for this purpose.
The material of the rotary joint must be changed according to the temperature and corrosiveness of the fluid being used. When supplying high-temperature fluids, a product with a high heat-resistant seal should be selected, and when supplying highly corrosive fluids, a stainless steel or copper alloy rotary joint should be selected.