Factories often utilize equipment known as rotary tables-large, rotating platforms where workpieces are placed and indexed to various stations for processing. These are commonly found alongside machinery such as lathes, milling machines, and welding robots.
Once a workpiece is placed on the table, it must be securely clamped; otherwise, the centrifugal force generated during rotation could cause it to fly off. Clamping is typically achieved using hydraulic fluid or compressed air. A hydraulic or pneumatic cylinder exerts force to hold the workpiece firmly in place.
This presents a challenge: the workpiece rotates, yet the hydraulic fluid and air are supplied via stationary piping. As the table turns, the hoses twist along with it. While they might withstand a few rotations, excessive twisting can snap the hoses or cause fittings to loosen, leading to fluid or air leaks. This results in a loss of clamping force, potentially causing scrapped parts or-in the worst-case scenario-workpieces flying off and injuring personnel.
This is where the rotary union comes into play. Mounted on the rotary table's central axis, it connects the stationary hydraulic power unit or air supply to the clamping fixture on the rotating platform. Regardless of the table's rotation speed or the number of turns, the flow of fluid or air remains uninterrupted, and the seal remains intact without suffering wear from the rotation.
However, simply maintaining flow is insufficient; precise control is also required.
Different workpieces have varying clamping force requirements. Thin sheet metal parts may deform if clamped too tightly, while thick components may shift if clamped too loosely. Consequently, parameters such as pressure, flow rate, and actuation speed must be adjusted according to the specific workpiece. This is where a rotary timing valve is utilized. Installed downstream of the rotary union and rotating in sync with the table, it precisely regulates the flow and pressure of the hydraulic fluid or compressed air. It dictates exactly when to apply pressure, when to release it, and the magnitude of the force applied.
Consider this scenario: a workpiece requires rapid initial clamping, followed by a slow pressure increase and hold phase, and finally, rapid release. Since the pressure and flow requirements differ across these three stages, the rotary timing valve automatically switches settings at pre-programmed intervals, eliminating the need for manual adjustment. Furthermore, because it rotates with the table, the control logic remains consistent regardless of the workpiece's angular position, ensuring reliable operation throughout the rotation.
There is also a practical constraint to consider: limited space. Space at the central axis of a rotary table is extremely limited, yet it must accommodate hydraulic lines, pneumatic channels, and control valves without any mutual interference. Consequently, the rotary unions and valves currently in use are trending toward miniaturization-packing multiple channels into a compact footprint; some single units can simultaneously handle hydraulic fluid, compressed air, and coolant, and even transmit electrical signals.
Ultimately, the stable operation of a rotary table hinges on two critical components: the rotary union, which ensures an uninterrupted supply of fluid and air, and the rotary timing valve, which guarantees precise force and speed. A failure in either area-whether the workpiece fails to clamp securely or becomes deformed-will bring the entire production line to a halt.
While the concept is straightforward, clamping requirements vary by workpiece; selecting the right component demands a precise match of fluid type, operating pressure, rotational speed, and spatial dimensions-there is no room for error.