In this guide 6 sections
Watch for flash along the parting line, vents that clog sooner between cleans, nicks on cavity edges and parts that stick or tear on demoulding. Each one shows in the shot count and cleaning log before scrap climbs. Pull the mould when the trend crosses a limit you set, not after a customer complaint.
Flash at the parting line comes first
Thin flash is usually the earliest sign. The steel lands that seal the cavity wear down, and compound squeezes through the gap. Run a thumbnail along the cut edge of a part. Burrs that were absent last month mean the land is breaking down.
Do not trim it and move on. Write the flash against the mould number and the shot count on the shift sheet. A press that needs more clamp tonnage to hold the same flash is warning you, because pressing harder only batters the edges further.
- Flash width at a fixed point on the part
- Clamp pressure used on the last three runs
- Shot count since the last land inspection
- Operator note on whether trimming time rose
Vents block faster as the mould ages
Vents are shallow slots that let trapped air escape. Release agent and burnt compound residue fill them. Blocked vents leave short fills, blisters and flow marks near the last point to fill.
The useful number is shots between cleans. If a mould once ran two thousand shots before the vents choked and now chokes at a few hundred, the vent depth or the surface finish has changed. A cleaning log with dates and shot counts shows that drift plainly. Without it, everyone argues from memory.
Check the vent slots with a feeler gauge when you strip the tool. A vent worn too deep lets rubber flow into it and leaves a thin fin on every part. That is a repair, not a clean.
Cavity damage and sticking show up in the parts
Pitting, rust spots and scratches on the cavity surface copy straight onto every part. Dents from a careless pry bar do the same. Check the cavity under a lamp at each clean, and note the cavity number, because a multi-cavity mould wears unevenly.
Sticking is the other warning. Parts that tear at the thin lip, or need a scraper to come out, point to a worn finish or a depleted plating. Torn parts are not just scrap. Rubber left behind then bakes into the next cycle and spoils the cavity further.
- Cavity number for every rejected part
- Date and cause of any pry bar contact
- Plating or coating type and last refresh
- Count of torn parts per shift
What the shot count and cleaning history would have shown
Most shops find out about wear from the rejects. The history was available much earlier. A rising count of flash complaints, shorter gaps between cleans and more torn parts per hundred shots all trend upward weeks before a lot is held.
Set a repair trigger for each mould. It might be total shots since overhaul, or a limit on shots between cleans, or a flash width. When any one is crossed, the mould is flagged for the toolroom and the planner sees it before booking the next order.
Keep it simple. Nobody wants forty fields on the shop floor. A mould card with six lines is enough if operators fill it in at every changeover. Short, regular entries beat long, occasional ones.
Build the repair trigger into the schedule
A repair takes the mould off the press for days, so planners need warning. Give every mould a card or record with its overhaul date, running shot count, cleaning dates and open defects. Update it at each changeover.
Start small. Choose your five busiest moulds and record shots and cleans for one month. Then compare the trend with your reject sheet and set the first trigger from what you see.
Mould health card
Kept on one card for each mould. The top block holds mould number, cavity count, compound used and last overhaul date. A table below has columns for date, shots run, cleaned yes or no, flash width, vent condition, torn parts and initials. The footer holds the repair trigger and a box for the toolroom to sign off.
Open a blank worksheet to printQuestions owners ask
How often should a rubber mould be inspected?
Tie it to shots, not the calendar. Look at the lands, vents and cavity at every clean, and do a fuller strip and check at a shot count you set from past repairs.
Is flash always a sign of mould wear?
No. Overfilled preforms, low clamp force or a dirty parting line also cause it. If flash grows on one mould and not on others using the same press, suspect the mould.
Why record the cavity number on rejects?
Cavities wear unevenly. Knowing that cavity six produces most torn parts lets the toolroom repair one insert instead of reworking the whole tool.
Can a spreadsheet hold this history?
Yes, for a handful of moulds. It gets hard when several shifts update it and planners need the flag at booking time, which is where a shared system helps.