Compression Moulding Press Troubleshooting: Causes & Fixes

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Problems on this page:

Parts under-cured or over-cured Flash too thick Short fills or voids Parts sticking in the mould Hydraulic press slow or losing pressure Mould fouling building up Operator safety and two-hand control faults Long mould changes

Parts under-cured or over-cured

Hits OEE: Quality

Symptoms: Parts come out soft and tacky, or brittle and discoloured.

Platen or mould temperature off the setting

Check the platen temperatures with a surface probe at several points.

Cure time changed

Compare the cure time with the approved recipe for the compound.

Compound older than its shelf life or stored warm

Check the compound batch date and storage conditions.

Heating uneven across the platen

Check the heater elements or the thermal oil flow in each platen zone.

Prevention: Hardness or cure tests on parts from each batch.

Flash too thick

Hits OEE: Quality

Symptoms: Parts carry thick flash that needs extra trimming.

Preform weight too high

Check the preform or charge weight against the recipe.

Clamp pressure too low

Check the hydraulic pressure at the press.

Mould parting faces worn or dirty

Clean the parting faces and check them for wear.

Platens not parallel

Check platen parallelism.

Prevention: Flash thickness checked on samples.

Short fills or voids

Hits OEE: Quality

Symptoms: Parts are incomplete or have voids and air traps.

Preform weight too low or placed wrongly

Check the preform weight and its position in the cavity.

Air not escaping

Check the bump or degassing cycle and the mould vents.

Compound scorching before the mould closes

Shorten the loading time or check the mould temperature.

Press closing too slowly

Check the closing speed.

Prevention: Short fills recorded per cavity.

Parts sticking in the mould

Hits OEE: Availability

Symptoms: Parts tear or stay in the cavity at demoulding.

Mould release agent missing or uneven

Check how and how often release agent is applied.

Mould surface fouled

Clean the mould with the method approved for it.

Part over-cured and brittle

Check the cure time and temperature against the recipe.

Ejectors not working

Check the ejector pins and their drive.

Prevention: Sticking and torn parts recorded per mould.

Hydraulic press slow or losing pressure

Hits OEE: Availability

Symptoms: The press closes slowly or loses clamp pressure during the cure.

Hydraulic oil hot or low

Check the oil level, the cooler and the oil temperature during long cures.

Pump worn

Measure the pump output and pressure under load.

Valve leaking internally

Check the holding valves for internal leakage.

Ram seals leaking

Check the ram for leakage past its seals at the next planned stop.

Prevention: Clamp pressure during the cure logged per cycle.

Mould fouling building up

Hits OEE: Quality

Symptoms: Deposits build up on the mould surface and mark the parts.

Compound ingredients depositing on the mould

Discuss the compound with the compounder if fouling is fast on one recipe.

Mould cleaning interval too long

Clean the mould at an interval based on cycles, not on visible fouling.

Release agent building up

Apply less release agent and check the spray pattern.

Mould temperature too high

Check the mould temperature against the recipe.

Prevention: Mould condition checked each shift.

Operator safety and two-hand control faults

Hits OEE: Availability

Symptoms: The press will not close, or stops on a safety fault.

Two-hand control buttons worn or not pressed together

Check the two-hand buttons and their timing; never bridge them.

Light curtain misaligned or dirty

Clean and align the light curtain.

Guard switch out of adjustment

Adjust the guard switch so it proves the guard is closed.

Safety relay fault

Have the safety circuit tested by qualified staff.

Prevention: Safety functions tested at each shift start.

Long mould changes

Hits OEE: Performance

Symptoms: Mould changes take long, and the first parts after the change are scrap.

Mould not preheated before mounting

Preheat the next mould in a separate oven or on a spare platen.

No lifting aid for heavy moulds

Use a mould cart or crane; moulds are heavy and hot.

Settings not stored per mould

Store temperatures, pressures and cure times as a recipe per mould.

Clamping with many loose bolts

Use quick clamps where the press allows.

Prevention: Mould change time recorded.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: hydraulic press · thermal oil heater · injection moulding · tyre curing press · two roll mill

Stop the same fault coming back

Recurring compression moulding press stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover