Quality Control for Custom RTV Silicone Molds
A quality page should show how we tell a CTQ from a cosmetic dimension. If you're buying a custom RTV mold, inspection is master-to-CAD, compound identity, Shore A when specified, cavity dimensions with a measurement condition, surface/tear checks, registration, a functional dump, and a golden-sample record for the reorder. "QC passed" with no CTQs and no method is a sticker, not a plan. Soft silicone changes shape under a caliper; a tolerance without relaxed / on a plate / in the jacket / loaded is incomplete.
RUUIPON inspects RTV tools in Bao'an before pack. We do not inspect LSR cold-runner parts on this line. Food-contact is a compound document path: 21 CFR 177.2600 is extraction testing, not an FDA-approved factory stamp. See materials and compliance.
What we inspect (and what we sample)
| Check | Typical when | Notes |
|---|---|---|
| Master / CAD revision | Every new job | Wrong revision is the most expensive miss |
| Compound / lot identity | Every lot | Match the quote; no silent substitute |
| Shore A | When specified | Skin vs jacket are different numbers |
| Critical cavity dims / volume | Every mold or first-article plus sample | Method named |
| Multi-cavity map | Production trays | Don't inspect cavity 1 and ship 48 |
| Surface, bubbles, tears, logo | Every mold | Raking light on the pocket |
| Keys / core / jacket assembly | Split and hollow tools | Cannot assemble backwards |
| Functional dump | Prototype plus when CTQ is grams or peel | Real material, not water only |
| Pack | Every shipment | See packaging and shipping |
| Golden sample / change control | After approval | Reorder must cite it |
Ask which of those are 100 percent and which are sampled. A production-critical depositor tray and a craft sculpture should not share the same sampling story.
Common mix-up: measuring soft rubber like a steel insert
Two inspectors can fail the same 10A tray because one squeezed the caliper. Write the condition: relaxed on a surface plate, seated in the mother mold, assembled on the master, or under a defined load. ISO 3302-1 M2 is a common default class on rubber drawings. It is a class, not a synonym for precision.
Measurement condition is part of the CTQ
Pick CTQs that actually reject product: cavity volume/grams, sealing diameter, wall, core location, tray flatness, registration, logo depth, the interface that mates a lid or a depositor nest. Don't put 40 dimensions on the report and miss the one that makes outer-row gummies heavy.
Typical shop values
| Item | Typical shop value |
|---|---|
| Cavity Shore | 10A–20A platinum RTV (jacket behind loaded trays) |
| Platinum shrink | ~0.1–0.3% linear |
| Drawing class (if you need a rubber default) | ISO 3302-1 M2 unless you name tighter and a method |
| Loaded-tray edge sag, unsupported | About 0.5–1.5 mm |
| Outer-row vs center on a sagging gummy tray | Often 3–6% heavy |
| Prototype window / MOQ | 3–7 days after CAD lock; MOQ 20 after approval |
Reference values only. Confirm material-specific limits against the supplier’s technical data and agree project acceptance criteria before production.
Failure: passed molds that don't dump on weight
Symptom: Incoming inspection green, production grams off; one cavity pretty, edge cavities fat; Shore about 20A by thumbnail; reorder feels different.
Confirm: Re-measure the same CTQs with the written method. Weigh a full dump map. Check lot vs the golden-sample compound. Check whether production omitted the jacket.
Fix: Quarantine the lot. Recast against the locked master if the skin is wrong; rebuild the jacket if the support is wrong. Don't add a visual inspector as the corrective action.
Worked example: 24-up chocolate bar, logo depth CTQ
A chocolatier named logo depth and bar weight as CTQs, measured with the tray seated in its jacket on a plate. We checked master depth before pour, Shore on the skin, then a cocoa-butter dump on cavities at center and both outer rows. Visual-only QC would have shipped a tray that looked sharp and dumped heavy at the edge. We would not have signed QC passed on cavity 1 alone.
What to ask when you're buying
- Which dimensions are CTQ, and in what measurement condition?
- What is 100% vs sampled on a 20-piece MOQ vs a 200-piece repeat?
- Is a functional dump in the quote, and in which material?
- How is Shore taken, and on the skin or the flange?
- What document follows the compound lot, and what happens if the grade changes?
When this page is the wrong route
A one-off art mold with no dimensional CTQ still needs a visual and a peel check, not a 12-page FAI. If you need PPAP-style steel-tool reports for molded silicone parts, that's a finished parts program. Don't paste an LSR IQC form onto an RTV jacket. Geometry can override quantity: two molds of a medical-adjacent skin-contact tool may need more documentation than 50 craft trays.
Related: prototype validation, materials and compliance, factory audit, contact.
RFQ: QC plan the inspector can run
Copy this.
- CAD/master revision to inspect against
- CTQ list + tolerance + measurement condition
- Shore A if controlled, and where on the mold
- Functional test: weight, fit, flatness, registration, demold
- Visual limits: flash, bubbles, tears, logo fill
- Sampling: every mold vs first-article + n per lot
- Golden sample ID for reorders
- Food-contact docs if required (compound-matched)
Send the CTQ list and how you will measure a soft mold on your incoming bench. We will mirror that method in Bao'an so the two reports can be compared. [email protected] · +86 135 3006 2969.
We would not recommend calling a mold QC passed with no CTQs
We would not recommend inspecting one cavity of a 48-up and shipping the rest. We would not recommend thumbnail Shore as the hardness record. We would not substitute compound on a reorder without a written change.
RUUIPON Mold Structure Decision:
- CTQs and measurement condition named? - yes -> Flat back?
- Flat back? - yes -> Open-back RTV + tray flatness if loaded
- Flat back? - no -> Deep undercuts?
- Deep undercuts? - cannot peel -> Inspect keys, plugs, cores as CTQs
FAQ
What's the difference between prototype sign-off and production QC? Prototype proves the design. Production QC proves each mold (or a sample of the lot) still matches that design. Don't skip either and call the other the inspection.
Can you inspect Shore A on every mold? Yes if you name it as a CTQ. On a 10A-20A skin, take it on a thick enough pad, not on a knife-edge flange, and write the method.
Do you issue an FDA certificate with QC? No factory stamp. Food jobs get the compound/lot pack you named: 21 CFR 177.2600 extraction and/or LFGB on the grade used. QC photos are not that pack.
How do you handle multi-cavity variation? Map, don't spot-check the prettiest pocket. Outer rows are where sag shows up.
What should be measured on a reorder? The same CTQs, same method, same golden sample. If master, Shore, or structure changed, it's not a reorder. It's a new first article.