Pressure Pot vs Vacuum Chamber for RTV Molds | RUUIPON

A vacuum chamber and a pressure pot do opposite things. Vacuum on mixed platinum RTV *pulls air out of the rubber* before it sees the master — that is our default on food logos, thick gloves, and transparent resin tools. A pressure pot *compresses remaining bubbles* in a closed volume, usually *your* resin, wax, or PU sitting in a finished cavity. Using a pressure pot "instead of vacuum" on the RTV mix does not remove air; it hides bubbles until a hot dump or a post-cure grows them back. Using vacuum on an unsealed mold box while you pour can suck air *in* through leaks. Pick the machine for the step.

RUUIPON vacuum-degases platinum A/B in Bao'an since 2018. Prototype is 3–7 business days after CAD lock. Production is MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. Jewelry resin pressure-casting is a craft dump — jewelry is not food. LSR *parts*: wydsilicone.com. Vacuum service: vacuum-degassed platinum.

Does not apply when you are injection-molding LSR in a heated cavity with a cold-runner (no RTV cup, no garage pot), when the "bubbles" are inhibition craters, or when the box cannot be sealed for pressure and you want us to pretend it can. Autoclaves and industrial pressure vessels for composites are a different RFQ.

Which machine sits on which step

Vacuum, mixed RTV, in a cup with headspace. Pull until foam rises and collapses. This is how we keep pinholes off a chocolate serif and a clear resin face. A brush / detail coat still wets verticals; vacuum does not replace it.

Pressure, RTV curing in a *closed, rated* box. Some craft shops do this to shrink leftover bubbles in the *rubber*. We would not treat it as the food-cavity degas method. Compressed air is still in the mass. Heat later can pop it. Documented food trays get cup vacuum.

Pressure, *your* dump in the finished mold. This is the usual good use of a pot: epoxy jewelry, PU figurines, a resin plaque. The cavity face must already be smooth. A pot will not erase a crater cured in the RTV. If the empty well is glossy and the part is pocked, change the *cast* process.

Vacuum, your dump. Useful for some resins in a dedicated casting chamber. Different viscosity, different cycle. Do not copy the RTV collapse SOP onto a thin UV jewelry resin and cook the pot life.

Typical shop pressure bands for resin casts are often in a 40–60 psi conversation on equipment rated for it. We do not invent a psi spec for your unrated bucket. If the box is plywood and hot glue, it is not a pressure vessel.

The photo that would prove the split is: (1) a cup at foam collapse, (2) a raking-light empty cavity, (3) a pressure-pot gauge on a *casting* with a rated lid. One selfie with a compressor is not three proofs.

Typical shop values

Caption: Typical shop values.

Common mix-up: "I have a pot so I don't need vacuum"

A resin artist buys a pressure pot, skips cup vacuum on the *mold* rubber, and sends us photos of a pitted cavity asking for a recast in "stronger Shore." Shore A does not remove trapped air. The cousin mix-up is vacuuming a leaky mold box during the RTV pour and blaming the grade when the face is foamy at every clay dam. Dam the box, vacuum the cup, pour. A third: putting a food tray in a shop pot to "make it safer." Pressure is not 21 CFR 177.2600.

Worked example (anonymized)

A 24-up UV jewelry plaque. The buyer had a 60 psi pot and no vacuum chamber. First RTV skin, pressure-cured in a taped box, looked acceptable until a warm UV cycle raised pinholes in the logo wells. We remade with cup vacuum to collapse, brush coat, open-back plaque on a board (sag 0.5–1.5 mm without it), platinum 1:1. They kept the pot for the *resin* dump, which is the right job. CAD USD $50 because we only had photos of a pendant. Proto 3–7 business days after lock, then MOQ 20. Jewelry remaining not food — no 177.2600 pack on this PI.

We would not recommend

We would not recommend a pressure pot as the degas method on a food-contact RTV cavity.

We would not recommend pressurizing a hot-glue plywood box as if it were a rated vessel.

We would not recommend recasting the RTV to hide bubbles that only appear in the resin.

We would not recommend raising Shore A because a pot "didn't work."

flowchart TD
  A[See bubbles] --> B{Where?}
  B -->|In the mixed RTV cup or cavity face| C[Vacuum the rubber until collapse]
  B -->|Only in the resin/PU part, empty well smooth| D[Pressure-pot the dump if equipment is rated]
  B -->|Sticky face, cured back| E[Inhibition — not a pot or vacuum miss]
  C --> F[Brush coat still required]
  D --> F

What to ask when you're buying

• Will the RTV skins be cup-vacuumed, box-pressured, or both — in writing?
• Is my pot for the *cast* or did someone plan to skip vacuum on the mold?
• Food cavity or craft (jewelry/concrete are not food)?
• Is the mold box even sealable, and is the pot rated?
• CAD lock, then 3–7 business days, then MOQ 20?

Related: resin molds, jewelry resin, contact.

RFQ copy-pack — name both machines

Email [email protected]:

RTV: platinum 1:1 or 10:1, cup vacuum until collapse — required Cast: resin / PU / wax / food dump (food is not a pot substitute for docs) Buyer has a pressure pot for the dump: yes/no, rated psi Do not skip RTV vacuum because a pot exists CAD: locked / USD $50 if you model Prototype 3–7 business days after CAD lock, then MOQ 20 / design

Send which machine you own and which step it is for. We vacuum the rubber. You pressure the dump if that is your process. Phone +86 135 3006 2969.

FAQ

Can a pressure pot replace vacuum degassing of RTV? Not on the food and clear faces we will document. A pot shrinks bubbles; it does not remove them. Heat can grow them back.

Should I put the whole mold box in the vacuum chamber? Only with a setup designed for it. A leaking dam will pull air into the face. Our default is cup vacuum, then pour.

What psi should I run on jewelry resin? Follow your resin TDS and a *rated* pot. Typical craft talk is often a 40–60 psi band. We will not invent a psi for an unrated bucket, and jewelry is not food.

If I vacuum the RTV and pressure the resin, do I still need a brush coat? Yes. Vacuum and pressure do not wet a serif. The detail coat does.

Does ISO 3302-1 M2 mean I can skip vacuum? No. M2 is a rubber drawing class. It is not a degas method.

Shop sequence we would actually run

1. Weigh platinum 1:1 or 10:1. Fold, scrape, second cup.
2. Vacuum the cup until foam collapses; slow break.
3. Brush a detail coat on the master; let it skin if the grade wants it.
4. Pour the bulk in a thin stream. Dam is already leak-checked with water or a dry fit — not during the live pour.
5. Cure the RTV at the grade's shop temperature. Do not rush it into a pot to "help vacuum."
6. Demold, trim, jacket if the dump is wet or tall.
7. *Your* resin or PU goes in the cavity. If you own a rated pot, that is this step.

Concrete countertop and lost-wax jewelry dumps still follow this split. They do not pick up a 177.2600 pack because a chamber or a pot was in the room. Tooling charge ≠ a free second machine cycle when you change the CAD. Licheng Technology Industry Park, Xinhe Blvd, Shajing, Bao'an.