Hydraulic Pump of Injection Molding Machines
– By Zafar Kamal
The pump pushes the fluid through the lines. The pumps most commonly used on injection-molding machines are the balanced-vane type. The pumping unit of cartridge includes a cam ring, a slotted rotor, and vanes held between, with a wear plate and pressure plate at the sides. Pockets are formed by each two adjacent vanes, the ring rotor, and the side plates. As the pump rotates, the volume of each pocket become larger or smaller as the contour of the cam ring pushes the vanes in and out of the rotor slots. Ports in the side plates, connected to the pump inlet port, admit oil into the rotating cartridge to fill the pockets as they increase in size.
Other ports in the sideplates are connected to the pump discharge port and accept oil discharge from the rotating cartridge when the pocket decrease in volume. Two inlet ports are diametrically opposite each other, as are the two pressure (outlet) ports, to provide the hydraulic balance which eliminates all pressure-induced loads, resulting in longer pump life and less maintenance. The pump can also be called rotary fluid motors since they impart rotary motion to a load. In general, they permit an extreme range of speed adjustments and have a good ratio of size and weight to horsepower. Fluid motors can be stalled out under load without damage.
Vane type pumps can operate at pressure in excess of 2000psi. Their maximum speed is generally about 2200 rpm, with the maximum output rating of 125 hp. External-spur-gear type pumps are available in a range of sizes, with peak operating pressure of 1500 psi, top speed of 2400 rpm, and maximum output of 50 hp.
Internal gear models are available with speed capabilities up to 3600 rpm. They generally develop up to 3 hp at 1200 psi. Piston-type hydraulic motors can generally develop up to 300 hp at oil pressure of 3000 psi, with some models to operate at pressure up to 5000 psi. Continuous operating speeds range up to a maximum of 5000 rpm.
