Hot Press, Lab Press, Compression Moulding

Hot press, or some people called it lab press, compression moulding, is use to prepare test specimen of rubber, plastic or composite material. It differs in capacity (tonnage), single or double daylight.

There are some common problems/issues associate with hot press, whether problem is from the machine or from other factors, we will share some of the problems and how we solve it.

1. Platen unable to heat up

The most common root cause for this problem is the heater. There is high chance the heater was burnt. We can check by measure its resistance. If the circuit is open, the heater is burnt. If the resistance is fine, we might need to check the relay, contactor and the temperature controller.

We should also check if any emergency switch is activated and if there are any manual switch to turn on the heater. We should verify the functionality of the switches.

2. Platen unable to move up/ Unable to build up pressure

If the platen unable to move up, we need to check several items.

The most common root cause is malfunction safety or emergency switches.

Check functionality of all the switches and ensure any guard/safety door or mesh is closed properly.

Next, we can check if the power supply is normal. 415V must present for all three phases. Some machine might have PLC memory and performing certain steps such as cooling process. Try turn the control to manual operation.

Check if the motor pump is running, if the motor pump is running but the platen still doesn’t move, check the limit switches if activated.

Next, we check the dump/return valve. A stuck/open valve means the valve continue to allow fluid to return to the tank and unable to build up pressure.

We should also check the inlet valve if it can operate, if the valve is not working (stuck or burnt coil), the oil unable to go into cylinder and build pressure.

3. Temperature no display or display error

If the machine unable to display temperature, we can inspect several parts.

First, we check if there is power supply to the temperature controller. Check if any fuse is burnt.

Next, check the condition of the thermocouple/sensor. Check if the wiring is damaged or disconnected.

If this condition happens after a new controller replacement, check if correct input thermocouple type is selected. A wrong input type will cause readout error/not accurate or does not display at all.

4. Machine does not follow the sequence / program

This condition can happen due to several reasons.

First, we need to check the limit switch and all the proximity sensor. Some machine can adjust the mould thickness, the machine will slow down when reaching the set height. If the machine will not slow down and run at full speed and compress, the sensor/proximity switch may not in good condition. Usually there is a led light to indicate the working condition, we can try trigger it manually with a metal part and check if the light blinks/change colour.

Check if the setting temperature is achieved, some machine may programme to execute only when the target temperature is met.

Try restart the machine, some machine has memory function and it might still perform some undone sequences. Restart the machine will clear the pending sequence and start afresh.

The PLC controller might have some problem, the memory/program might have lost or the unit is malfunction. Replace a new controller and re-program it usually solves this issue.

5. Loud motor noise

If a we hear loud noise when we turn on the motor pump, the most common cause is the motor fan blade. There might be some debris or foreign object in the fan. It can also happen when the blade is broken or melted due to heat. We can remove the fan cover and inspect the condition, clean or replace a new fan if required.

If the noise is some sharp whistling noise, it is likely the motor bearing is bad/worn. We can get a professional to replace just the bearing or replace the whole motor if the cost is comparable.