The injection molding machine oil cooler is a water-cooled heat exchanger on the hydraulic return line. Hot oil coming back from the valves and cylinders flows around a bundle of tubes (shell-and-tube type) or between thin plates (plate type), while cooling water flows on the other side and carries the heat away, so the oil reaches the tank at a steady working temperature. A cooler that is scaled up, short of water or leaking is a common cause of hydraulic oil running hot or turning milky.
How the oil cooler works
The cooler sits on the return line, as shown in the drawing, where the oil pressure is low. It is therefore built for return-line pressure, not for the full system pressure.
- Shell-and-tube cooler: cooling water flows through the tubes and the oil flows around them inside the shell. Baffles in the shell make the oil cross the tubes several times. The end covers at each end can usually be removed to reach the tubes.
- Plate cooler: a stack of thin, pressed plates with oil and water flowing in alternate channels. It is compact, but the narrow channels block more easily with dirty water. Brazed plate coolers cannot be opened.
- Flow direction: oil and water normally flow in opposite directions (counterflow), which transfers the most heat. Connect the water to the ports marked on the cooler.
The water comes from the machine's cooling water manifold, supplied by a cooling tower or a chiller. A hand valve, thermostatic valve or solenoid valve on the water line controls how much cooling the oil gets. For the temperature the oil should run at, see oil temperature.
Shell-and-tube or plate cooler
| Shell-and-tube | Plate | |
|---|---|---|
| Size for the same cooling | Larger | Compact |
| Tolerance of dirty water | Better | Channels block more easily |
| Cleaning the water side | Tubes can usually be brushed after removing the end covers | Gasketed types can be opened; brazed types only flushed with cleaning solution |
The oil cooler / heat exchanger we supply is available as a shell-and-tube or plate type, water-cooled, rated up to 2 MPa on the oil side and 0.6 MPa on the water side.
Signs of a cooler problem
- The oil temperature creeps up over weeks while production stays the same: the water side is fouling.
- The oil is hot but the water leaves the cooler barely warmer than it entered: heat is not getting through, because of scale or because the water bypasses the tubes.
- The water leaves the cooler very warm and the flow is weak: a blocked strainer, a closed or stuck valve or a low supply.
- The oil turns milky, or the tank level rises: water is leaking into the oil.
- An oily film in the cooling water, or a tank level that falls with no visible leak: oil is leaking into the water.
- Drips at the end covers, gaskets or connections.
Why oil coolers fail
- Scale from hard water, and mud and algae from open cooling towers, which coat the tubes or plates.
- Corrosion, including pitting in poorly treated water and corrosion where different metals meet.
- Erosion from sand or from water flowing too fast through the tubes.
- Freezing when a machine stands in a cold building with water in the cooler.
- Pressure peaks in the return line or water hammer in the water line.
Cleaning and testing the cooler
- Stop the machine, lock out the power, close the water valves and drain both the water and the oil side.
- On a shell-and-tube cooler, remove the end covers and clean the straight tubes with a brush or rod of a suitable size, then flush them.
- Remove scale by circulating a descaling product that is suitable for the cooler's metals, following its supplier's instructions, then flush thoroughly.
- To check for internal leaks, pressurize one side, within the cooler's rating, and watch the other side for water or bubbles.
- Refit the end covers with new gaskets, reconnect the water in the right direction and bleed the air from the water side.
If water has got into the oil, repair the cooler first and then change the oil: see hydraulic oil and the article on hydraulic oil problems.
Keeping the cooler working
- Use treated, filtered cooling water and clean the strainer on the water supply regularly.
- Record the water temperatures in and out and the oil temperature when the cooler is clean. Later readings show when it starts to foul.
- Drain the cooler if the machine will stand in a building that may freeze.
- Check that the water control valve opens and closes as it should.
What to send for a replacement quote
- The nameplate or model code on the cooler, and photos.
- The type: shell-and-tube or plate.
- The overall length, the shell diameter or plate pack size, and the mounting dimensions.
- The size and position of the oil and water connections.
- The machine brand and model, and its pump size or motor power, because they set how much heat the cooler must remove.
Request a quote. For the rest of the oil circuit, see the oil tank and the hydraulic system guide.
Updated by the IMSPARES technical team.