In this guide 6 sections
Record five things in order: recipe version, mixer batch, rheometer cure result, mould cure time and temperature, then trimming or rework. Tie each cured lot to its compound batch. A seal complaint can then be traced back to the exact mix in minutes.
Fix the recipe version first
Every compound has a formula: polymer, carbon black or silica, plasticiser, curatives and accelerators. The formula changes over time as a supplier switches or a customer asks for a harder shore.
Give each recipe a code and a version. Record the version on the mixing sheet every time. A complaint about a seal made last spring is useless if you cannot say which recipe went into it.
Keep old versions readable. Never overwrite them.
- Compound code and version number
- Date the version took effect
- Approved by, with the reason for change
- Customer approval reference where required
Capture the mixer batch
The mixer, whether an internal mixer or a two-roll mill, produces a batch. Give it a number and write down the weights of each ingredient actually added, not the weights on the recipe card.
Note the raw material lots for polymer and curatives. When a supplier recalls a lot of accelerator, you need to name every batch that used it.
Add the operator, the mixing time and the drop temperature. A short dump cycle often explains a scorchy batch. Write it down.
Record the rheometer result before release
Test a sample from each batch on the rheometer and store the curve values: minimum torque, scorch time and the time to reach the target cure. These tell you if the compound will behave in the mould.
Set a pass band for each compound. A batch outside the band is held, reworked on the mill or scrapped. It does not reach the press by accident.
Attach the result to the batch number. That single link is the most valuable record in the chain. Guard it.
- Minimum and maximum torque
- Scorch time
- Time to full cure (T90)
- Hardness and specific gravity checks
Link the batch to the mould and the cure
At the press, record which batch fed which mould, the cure time, the platen temperature and the date. A cured lot number then points back at one mixer batch or several.
Add trimming and rework. Flash trimming, post-cure in the oven and re-inspection all affect the final part. Log them with quantities and rejects.
A worn cavity raises rejects in that cavity only. Record the cavity number where the mould allows it.
- Mould number and cavity
- Cure time and platen temperature
- Post-cure oven time
- Rejects by reason, such as short shot, flash or blister
Trace a complaint backwards
Test the trace with a real complaint from the last quarter. Start from the customer’s lot number on a gasket, find the press record, then the mixer batch, then the recipe version and raw material lots.
If any link breaks, close that gap first. A paper traveller attached to each tub of compound often fixes it before any software is built.
Compound batch traveller
A form for one page that travels with each mixer batch. Blocks cover the recipe code and version, the weights added with raw material lots, and the rheometer values with a pass or hold mark. Further blocks record presses and moulds fed, cure time, post-cure, trimming and rejects. The last box lists customer lot numbers shipped.
Open a blank worksheet to printQuestions owners ask
How long should batch records be kept?
Keep them at least as long as the customer’s warranty or the part’s service life, whichever is longer. Check any contract or standard that applies to your product.
Do small moulding units need this?
A simple version helps any unit supplying seals or gaskets to a manufacturer, because one complaint can touch many parts made from the same batch.
Can paper tickets do the job?
Yes, if every tub and every tray of parts carries a batch number. Software helps when you need to search by customer lot or raw material lot.
What if one batch feeds several moulds?
Record each mould against the batch. The trace then forks, and you can list every lot that could be affected.