Conformal Cooling vs RTV Pour Exotherm Control

“Conformal cooling” is a thermoplastic phrase. LSR tools are hot. If you copy a 30% cooling-time claim from a PP insert onto a LIM cell, you are optimizing the wrong half of the cycle.

Liquid silicone rubber is injected cool through a cold-runner / cold deck into a heated cavity (typically about 160–200 °C) and vulcanizes. The bottleneck is getting heat into the thickest rubber while keeping the deck cold enough that the next shot does not scorch in the drop. Conformal channels earned their keep in high-volume LSR when they do those two thermal jobs, not when they “cool the part like ABS.”

On this site there is no cold deck and no 180 °C cavity. The analog is thermal control of a pour: platinum addition is exothermic; a 15 kg texture block stores heat; a chocolate or gummy jacket may need a mother mold that stays dimensionally quiet while you dump. Water channels in a resin jacket, if they exist, temper the *dump* or pull exotherm from a thick pour. They do not cut an LSR cure from 40 s to 12 s. Do not RFQ DMLS conformal inserts for a 12A skin.

Where the seconds actually are

A high-volume LSR cycle is roughly: close, (vacuum), inject, cure, open, pick. Cure dominates once the deck and robot are competent. Cure time scales with thickness and with how evenly the steel sits at setpoint.

Straight cartridge heaters in a block leave cold cores and hot corners. A 6 mm boss next to a 0.6 mm membrane will wait on the boss. Operators then raise the whole tool temperature, the membrane over-cures or sticks, and the boss is still green in the middle. That is the cycle you are trying to buy back.

Conformal *heating* (hot oil, pressurized hot water, or circuits that let you place energy next to the thick steel) shortens the wait on the slow feature without cooking the fast one. Published academic work on conformal heating channels in LSR inserts is about uniform vulcanization, not about freezing a part. Believe that framing.

After eject, the part cools in a nest or in a bin. That is rarely the press bottleneck. Most LIM tools should stay hot.

RTV clock: work time to degas and pour; demold when a witness coupon of the same thickness tears clean. A 200 g jewelry mold dumps reaction heat into the room. A 15 kg block stores it. The core can run hotter than the TDS “room temperature” cure while the face against a cold master lags. Layered pours beat a single under-catalyzed brick. Heat *after gel* if the grade allows — not a blast on mixed liquid in a bucket.

If you ignore the thick section, the defect is a 12-second LSR fill and a 40-second cure you blamed on the robot — or a sticky RTV master face you blamed on “not enough catalyst.”

Two circuits, two setpoints — and a pour box

High-volume LSR shoes often need:

1. Cavity / core thermal circuit (hot). Follow the contour of deep cores, bellows, and thick pads. Additive inserts shine on a long, slender core that a cartridge cannot enter. Gun-drill plus baffles still win on simple plates.

2. Cold-deck circuit (cold). Water in the 20–50 °C class on the manifold and drops. This *is* cooling, and it is mandatory. A beautifully conformal hot core next to a starved nozzle jacket is a plugged gate.

Do not cross-connect the two. A single “conformal cooling” manifold that is trying to be 180 °C and 30 °C is a misunderstanding.

2-shot PC/ABS + LSR cells add a third map: the plastic half is cooled like a thermoplastic tool. Insulation between halves is the cycle-time feature people forget.

RTV box:

• Thermal mass of the master and mother (plaster vs resin vs aluminum shell).
• Shop temperature recorded with the batch (16 °C winter vs 30 °C summer moves a large mold more than a 2% ratio tweak).
• Optional water in a *rigid jacket* for dump temperature (chocolate temper) — a process aid for the *cast*, not an LSR cycle lever.
• Never run cold water through an LSR *cavity* plate you still need at 160–200 °C.

What actually reduces cycle (and what does not)

Helps LIM: uniform cavity temperature; heated cores on thick hollows; a cold tip so you can run a fast inject without a scorch plug; vacuum and a valve gate so you are not adding pack-and-flash delays.

Helps RTV: slow or long-pot grade for a large pour; degas; layered lifts; after-gel warm cure per grade; a glove plus mother instead of a solid cube; a jacket that does not sag.

Does not magically help:

• Copying a 20–40% “conformal cooling” case study from a plastic bumper onto LSR *or* onto a jacket.
• Lowering LSR cavity temperature to “cool faster.” You extended vulcanization.
• Additive channels in an aluminum tryout you will throw away — or in a 15A RTV skin.
• Channels so close to a medical land that they dish the shut-off under pressure.

HCR compression plates are heated differently (often platens). Conformal inserts can still even a deep compression core. They will not turn a 4-minute HCR cure into a 20-second LIM cure, and they will not turn a 16-hour platinum block into a same-shift demold by themselves.

Reliability is part of cycle time

A clogged conformal channel in a 16-cavity medical tool is a week of downtime. Specify fluid, filtration, pressure test, spare inserts, thermocouples in the *insert*. ISO 13485 teams should treat temperature maps as process parameters.

An RTV analog of that downtime is a thick pour that exotherms, tears, and forces a recast. Specify mix, degas, lift thickness, and a witness coupon. Cheaper than DMLS.

RUUIPON Mold Structure Decision: Large wet casting or thick dump? → mother mold (thermal mass + stiffness). Deep hollow? → core, not a solid cube that stores heat. Soft Shore? → jacket; do not add metal channels to the rubber.

Common mix-up: conformal cooling on an RTV RFQ

A lot of RFQs paste a plastic AM-insert slide onto a gummy tray. In the shop that usually means a confused quote and a still-floppy 12A skin.

What to ask when you're buying

• Object: high-volume LSR (heat in / deck cold) or RTV pour/dump thermal control?
• Thickness map: thickest and thinnest?
• Cold-deck yes/no (LIM); after-gel warm cure yes/no (RTV)?
• Are you buying conformal *heating* of the cavity, cooling of the deck, or neither?
• Target cycle as a goal, not a dare — and jacket replacement interval on RTV?

Worked example

You're running a 16-cavity LSR gasket, 2.5 mm thick, 200,000 / yr — parts OEM: even the cavity heat, keep the deck at 20–50 °C, maybe a conformal core if a boss is the last-to-cure. You're also pouring a 12 kg platinum texture block for architectural panels: long-pot grade, degas, two lifts, mild after-gel warm, resin mother. Do not DMLS the block.

We would not recommend cold water in an LSR cavity plate you still need at 180 °C

We would not recommend a PP-style cooling-time percentage, additive channels in a throwaway aluminum tryout, or conformal inserts as a substitute for a valve-gated cold-runner. We would not heat mixed RTV in a sealed bucket to “shorten cycle.”

Typical shop values

Reference values only. Confirm material-specific limits against the supplier’s technical data and agree project acceptance criteria before production.

| Item | Typical shop value | | --- | --- | | LSR cavity | About 160–200 °C | | Cold deck / drops | Water about 20–50 °C | | Platinum RTV mix | 1:1 or 10:1; degas until the foam collapses | | Platinum shrink | About 0.1–0.3% | | RTV skin wall | Often 8–15 mm; thick dumps are lifts, not AM channels | | ISO 3302-1 | M2 common; cycle time is not a class |

Copy this into a thermal-circuit RFQ

• Process: high-volume LSR or RTV pour / dump jacket
• Thickness map; target cycle as a goal
• Cold-deck yes/no; conformal heating of cavity vs cooling of deck vs neither
• For RTV: grade (slow/regular), lift plan, after-gel warm cure, mother type
• Thickest section and thinnest

Send the thickness map. We'll even a pour or tell you the conformal insert belongs on a steel core. Custom RTV molds.

Related: platinum catalyst ratios, ROI RTV to LSR, what tooling means.

FAQ

Does conformal cooling cut LSR cycle time the same way it does for thermoplastics? No. Plastic cycles wait on freezing; LSR cycles wait on vulcanization in a hot tool. Conformal channels help LSR when they even out *heat* in the cavity and keep the *cold deck* cold. A PP-style cooling-time percentage does not transfer. It does not transfer to RTV either.

Should I run cold water through conformal channels in the LSR cavity plate? Not if you still need that plate at 160–200 °C to cure. Cold water in the cavity extends cure or under-cures thick sections. Put cold water in the deck and tips. Put hot fluid or heaters in the cavity, conformal if the geometry needs it.

When is a 3D-printed steel insert worth it on an LSR tool? When a deep core or thick pad cannot be heated evenly with cartridges or drills, and the cavity count and life will pay for the insert. It is not a default on a flat gasket plate, and it is not an RTV jacket.

Can conformal channels replace a valve-gated cold-runner for speed? No. The runner type decides waste, vestige, and whether the drop scorches; thermal channels decide temperature uniformity. High-volume cells usually need the deck *and* the heat map. RTV has neither; it has pot life and lifts.

Will lowering cavity temperature let me eject sooner? You will eject a greener LSR part. Thin lips tear, dimensions drift after post-cure, and thick bosses may still be raw. Raise uniformity, then trim seconds from a fully cured window. On RTV, demold on a witness coupon, not on a colder room.