An injection mould that has stood idle for a long time is often covered in oxide film and rust, with dust stuck to old grease on its surfaces. This is especially true in unheated stores and workshops, where winter humidity and condensation take their toll.
Because the tolerances are so tight, such a mould cannot be restored on a machine tool: all the work is done by hand with fine abrasive cloth and dedicated products. Below is a procedure tried and tested in a training workshop.
What you will need
Important: Isolate the heaters and let the mould cool before you start. Do not abrade moulding surfaces or precision fits, as you may change the dimensions of the parts.
Step 1
Dismantle the mould
Split the mould and start with the injection half, where the melt enters the cavity. Lay the parts out on the bench in order, like an exploded drawing: reassembly is much easier that way.
Treat seized fixing screws with WD-40 Specialist Penetrant, wait a few minutes and only then undo them with a hex key. Next dismantle the ejector half: slides, ejector pins, sprue puller and cores.
Step 2
Clean the surfaces
Spray the parts generously with WD-40 Multi-Use. The thin straw reaches hidden channels and holes. Give it a few minutes to dissolve the greasy film, then wipe with a cloth. Where dirt has dried on, use a stiff nylon brush.
Clean heater and thermocouple connectors with WD-40 Specialist Contact Cleaner: it removes dirt and moisture and evaporates without residue.
Step 3
Polish the parts
Remove the oxide film with abrasive cloth, working gradually from 150 to 400 grit. Back the cloth with a flat block so you do not create hollows. Use WD-40 Multi-Use as the lubricant for the cloth: it glides more evenly and the surface is cleaned at the same time.
Do not polish precision fits or moulding surfaces: cleaning is enough there.
Step 4
Reassemble the mould
Assemble the simpler injection half first, then the ejector half with the slides for undercuts and the ejector plate. Follow the correct sequence to avoid damaging ejector pins, sprue puller, slides and cores. Protect every part against corrosion with WD-40 Multi-Use as you go.
Step 5
Lubricate the moving parts
Grease guide pillars and bushes with WD-40 Specialist White Lithium Grease: it forms a substantial layer that lasts. Apply only a very thin film to ejector pins and the ejector plate and wipe off the excess carefully so no grease reaches the cavity.
To help parts release, you can apply a thin coat of WD-40 Specialist Silicone to the moulding surfaces. Bear in mind that silicone on the part can affect later painting, printing or bonding, so reject the first shots after treatment.
Step 6
Test and preserve
Cycle the closing and ejection by hand a few times to make sure everything moves smoothly. If the mould is going back into storage, treat all exposed steel surfaces with WD-40 Multi-Use and keep it closed in a dry place.
Tip: Photograph every stage of dismantling on your phone. With moulds that have many slides and ejectors, this saves hours on reassembly and prevents mixed-up parts.
What next
Clean the parting line and cavity after each production run, and preserve the mould with WD-40 Multi-Use before any downtime. Check pillars and bushes regularly and renew the White Lithium Grease according to your maintenance schedule.
These uses come from the experience of WD-40 users in many countries. Always follow the instructions and warnings on the product label.
More guides in «How to use».