ROI: Scale RTV Jackets vs Jump to LSR Steel

Single-cavity RTV vacuum casting and multi-cavity LSR injection are not two sizes of the same mold. One is a technician with a platinum or tin jacket. The other is a hot-cavity, cold-runner press with cavitation. ROI is whether the second *factory* pays for itself *before the product dies*, on drivers you can name.

On this site you usually scale RTV: more cavities in the tray, a mother mold, spare skins, recast terms. You do not “upgrade” a chocolate cavity into a LIM shoe. Do not compare “mold price” to “piece price.” Compare a horizon (12 or 24 months is enough for most custom programs) of labor, scrap, material form, setup, and the recut you will do if CAD is not frozen. Invented dollar paybacks are how teams buy eight LSR cavities for a geometry that will change in March — and abandon a jacket that was still the right object.

Name the two factories

Staying (this site): an RTV tool (usually platinum-cure jacket around a master; tin-cure is cheaper and less stable). Cycle is mix, degas, pour or dump, cure, demold, trim. Shrink and flash behave like casting. Chemistry is the mold rubber, plus whatever you dump. Jacket life is counted in dumps, not in SPI class.

Leaving to a parts OEM: LSR on metal, typically an aluminum 1-cavity bridge or a steel 2-/4-/8-cavity production tool with cavity heat and a cold-runner. Cycle is clamp, inject, cure, eject. Flash is a shutoff. Shrink is production shrink. Grade should be the production platinum LSR. The *article* is now a molded silicone part, not a dump from a cavity.

There is a missing middle on the parts path: aluminum 1-cavity LSR. Many “RTV to 8-cavity steel” ROI models skip it and then discover LSR fill, vestige, and shrink on the most expensive tool. Put the middle in the model even if you skip it in the buy.

There is also a missing middle on this site: multi-cavity RTV with a rigid jacket. A lot of “we must go LSR” slides skip a 8–12 cavity tray that still dumps pectin.

Drivers, not stickers

Write one line each. Ranges of *structure* are allowed. Fake unit prices are not.

T_tool. RTV: master + jackets, recurring as jackets die. LSR: class intent (105/104/103…), cavity count, cold deck vs open sprue, vacuum, slides, tryout, FAI. Multi-cavity is a step-change in plates, balancing, and tryout, not “N times a single cavity.” Multi-cavity RTV is a step-change in box, keys, and mother, not N times a glove.

T_mod. First geometry change. RTV makes this small (recast or master patch). Hardened multi-cavity steel makes this large. If CAD is live, T_mod is not zero.

C_labor. RTV cell time per good dump (mix through pack). LSR: tend, destage, inspect. Cavitation cuts press occupancy; it does not automatically cut destage if every cavity flashes. A 12-cavity RTV tray cuts pour labor per dump; it does not remove mix and degas.

C_mat. Mass × grade × (1 + runner/jacket waste). RTV waste is cups, sprues, and failed pours. LSR waste is start-up, cured sprue if you refused a cold-runner, and purge at color change. Production LSR gum is often a different cost structure than the RTV casting compound. Put both grades on the sheet.

C_scrap. RTV scatter, bubbles, jacket wear. LSR start-up shots, imbalance on new multi-cavity tools, post-cure mishaps.

C_setup. Per batch. Multi-cavity LSR raises MOQ thinking. A beautiful annual volume that arrives as 200-piece releases puts setup back on RTV’s side.

C_quality. The cost of a part that *looks* like production but is not: wrong shrink, wrong compression set, wrong extractables. This is the driver that kills “RTV is cheaper” when the product needs LSR chemistry now — a *part*, not a cavity.

Horizon H: T_tool + T_mod + Σ(C_labor + C_mat + C_scrap + C_setup + C_quality events).

ROI is the *delta* on those C terms versus the *delta* on T_tool and T_mod. If you cannot fill C_labor from a timed RTV cell, you do not have ROI. You have a slide.

A crossover you can run without fake prices

1. Time the current RTV cell on a normal lot. Convert to hours per 1,000 good dumps or parts.
2. Get constructions quoted as *stacks*, not as piece prices: (A) stay RTV, more cavities + spare skin, (B) 1-cavity aluminum LSR, (C) steel at the cavity count you think you want. Same flash spec, stated cycle or dump rate, stated waste, stated scrap assumption, stated batch size.
3. Freeze H and freeze batch size. Annual quantity without batch size is a lie.
4. Ask whether the *object* is already a molded LSR part. If the product requires a healthcare, self-lubricating, or specified platinum LSR *article*, RTV stand-in parts do not belong in the “savings” column. Switch factory first, cavity count second. If the object is still a dump cavity, stay here and add cavities.
5. Apply T_mod: number of drawing changes expected in H. Each change on steel is a recut class. Each change on RTV is a new jacket or a patched master.

The LSR upgrade wins when labor hours plus scrap plus chemistry-mismatch risk in H exceed the LSR tool stack, *and* the CAD is frozen enough that you will not pay for the steel twice, *and* you actually need a molded part.

The upgrade loses when volume is real on a spreadsheet, geometry is still competing, you skipped aluminum, and the object was still a gummy tray.

When multi-cavity is the expensive part of the sentence

Cavitation pays when cure time dominates and the press is the constraint: more cavities, same heat, more parts per hour, *if* yield holds. It does not pay when:

• Annual volume will not keep that press fed.
• Releases are small; you will still pay setup and start-up scrap on a large tool.
• The part is unbalanced (thick/thin) and 8 cavities will teach you 8 ways to flash.
• You have not run even 1-cavity LSR, so shrink and gate vestige are unknown.

A common failure is treating “single-cavity RTV → multi-cavity LSR” as one decision. It is two: process change (cavity you dump into → LSR on metal) and capacity change (1 cavity → N). Process change can have positive ROI at hundreds of parts if labor or chemistry demands a *part*. Capacity change needs a frozen drawing and a real annual quantity. Capacity on a *cavity* is more RTV cavities, not steel.

RUUIPON Mold Structure Decision: Scale RTV first: open-back vs two-part vs core, then cavity count in the tray, then mother. Jump to LSR only when the object is a molded part. Geometry can override quantity.

Common mix-up: piece price at 10,000 as ROI

A lot of RFQs pick the smaller unit cell and call it payback. In the shop that usually means no batch size, no T_mod, and a jacket you still needed.

What to ask when you're buying

• Is the object a dump cavity or a molded LSR/HCR part?
• Timed RTV cell hours per 1,000 good dumps?
• Stack quotes: stay-RTV multi-cavity vs Al 1-cavity LSR vs steel N-cavity?
• Batch size you will actually pull, not the annual forecast?
• How many drawing changes in horizon H?

Worked example

You're dumping a 45 × 28 mm gummy, 1-cavity platinum glove today, ~6,000 / season, CAD still moving logos. Stay: 8–12 cavity RTV tray, resin jacket, spare skin, recast clause. Do not jump to 8-cavity LSR steel — wrong object. If a sister SKU is a 50A LSR button, frozen, 80,000 / yr, run the driver sheet on a parts OEM and put aluminum 1-cavity on the same sheet before eight cavities.

We would not recommend eight LSR cavities for a geometry that will change in March

We would not recommend skipping multi-cavity RTV when the object is still a dump, skipping aluminum on a true LSR part, or treating jacket replacement as zero in the RTV column. We would not freeze ROI on annual quantity without batch size.

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 | | --- | --- | | First food / gummy RTV layout | 8–12 cavities is a common kickoff band | | RTV skin wall | Often 8–15 mm, Shore 10A–20A with jacket | | Platinum shrink | About 0.1–0.3% | | LSR / HCR shrink (contrast) | About 2–3% / 1.5–2.5% | | Horizon | 12 or 24 months is enough for most custom programs | | ISO 3302-1 | M2 common; ROI is not a class |

Copy this into an ROI / scale RFQ

• Construction: RTV jacket count vs LSR class, cavities, runner type
• Cycle or cell time, and whether cure dominates (LSR) or mix/dump dominates (RTV)
• Runner or pour waste as a fraction; trim method; scrap assumption
• Setup per batch; quoted MOQ; stated PM / jacket replacement interval
• Grade: name the LSR and the RTV compound separately

Send timed cell hours, batch size, and whether this is still a cavity. We'll quote more jackets — or send you to a parts stack. Custom RTV molds.

Related: 1 vs 8 cavity, when to switch RTV to steel, prototype-to-production.

FAQ

At what annual volume should I leave RTV for LSR steel? There is no universal quantity. Leave when the *object* is a molded part and timed labor, scatter, or production chemistry already beat a 1-cavity LSR stack on your horizon. Tens of thousands of a frozen *part* is usually steel; hundreds of a *dump* may still be RTV if the cavity is the product.

Is aluminum 1-cavity LSR a better ROI step than jumping to 8-cavity steel? Often, *if* you need LSR at all: aluminum teaches fill, vestige, shrink, and flash on a tool you can recut. Eight-cavity steel teaches those on the tool you cannot afford to recut twice. If you still need a dump cavity, aluminum LSR is the wrong factory.

Does a cold-runner multi-cavity always win on material? No. A valve-gated cold deck cuts cured sprue waste; it also raises T_tool. On a large industrial part with a hidden gate and modest volume, an open cold sprue can win. Tiny parts where the tree outweighs the rings are the classic deck win. RTV has no deck; waste is cups and failed pours.

How do I treat jacket replacement in the RTV column? As recurring T_tool, not as zero. Platinum jackets die from tear, stretch, and inhibition; tin jackets die faster and with more dimensional drift. Count jackets per horizon. Ignoring them makes RTV look cheaper than the cell you actually run.

What batch size should I freeze in the model? The release quantity you will actually pull, not the annual forecast. Multi-cavity LSR economics assume the tool stays in the press, so 200-piece drops can erase cavitation with start-up scrap. Seasonal gummy dumps are a campaign, not a 10,000-break.