Rotary unions help deliver coolant to the cutting zone

Machine tool users wouldn’t benefit from through-spindle coolant (TSC) without rotary unions, which bring together spinning and stationary components to improve coolant delivery.

While flood-coolant systems spray coolant onto the workpiece near the cutting tool, TSC systems move coolant through the machine tool to the cutting edge. “If you have coolant coming through the center of the spindle, it’s going to get right where it needs to go”—the bottom of a hole, for example, said Kevin Holdmann, owner of TAC Rockford (Ill.), a maker of rotary unions and other machine components. “But if you’re spraying coolant from the outside, you’re just hoping.”

TSC proponents claim it offers a number of advantages compared to flood coolant. These include improved cooling and lubrication of cutting tools and machined parts, increased cutting speeds and tool life, reduced coolant consumption and more-effective chip evacuation.

In TSC systems, coolant flows through a rotary union into the machine spindle. Rotary unions are mechanical devices that move fluids from a stationary source, such as a pipe, to a rotating machine part.

The key components of typical rotary unions used in machine tools are:

■ A rotor that spins with the spindle;

■ a stationary element that closes against the rotor;

■ a housing that connects the stationary element to the hose supplying the fluid; and

■ seals that contain the fluid in the union.

Deublin Co., Waukegan, Ill., sells its rotary unions mainly to machine tool OEMs, according to Matt Bell, the company’s global machine tool market manager. “There are cases where we supply unions to customers looking to retrofit machines to add TSC,” Bell added, “but the machines must have the framework to handle it.” This includes a hollow spindle or at least a passage through it.

When choosing a rotary union for a particular machine tool, important considerations include the application’s operating parameters (fluid type, pressure, temperature, and rotational speed and direction) and the type of connection to the machine.