Shore A for Gummy, Resin, Concrete Molds | RUUIPON

Shore A is a durometer on the cavity rubber, not a quality grade and not a dump recipe. A gummy tray, a PU resin figurine mold, and a concrete paver glove can all sit in overlapping Shore bands and still need different skins, different jackets, and different tear stories. If you send "make it 30A" without naming the pour, you are asking us to guess which of those three tools you bought.

RUUIPON builds the RTV tool — master, box, A/B, vacuum, keys, jacket — in Bao'an since 2018. Prototype 3–7 business days after CAD lock. Production MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. This page is the Shore chart across three pours. The 10A-vs-30A call for a hooked resin part is a different article.

Does not apply when you are specifying Shore on a molded silicone *part* (HCR compression or LSR injection). That durometer is the article, not the cavity. Route those drawings to wydsilicone.com. It also does not apply when the dump is chocolate or ice and you already have a food-tray spec — those Shore bands live on the food-mold pages.

Read the pour first, then the number

Gummy (pectin or gelatin dump). You need a soft peel so the gel leaves the cavity without tearing a thin ear or a score line. Typical cavity skin: Shore 10A–20A. A loaded sheet wants a rigid jacket; unsupported outer rows sag about 0.5–1.5 mm and read 3–6% heavy vs center. Harder Shore on the skin does not fix sag. Jacket does.

Resin (PU, epoxy, UV). You need the skin to stretch around undercuts and then recover, plus enough tear strength at logos and thin walls. Start 10A–20A on a glove that peels; 20A–30A when the wall is thin and the jacket is doing the stiffness. If the part will not peel, Shore is the wrong first lever — split, plug, or core. That sequence is on Shore 10A vs 30A for complex resin.

Concrete / cement / plaster. The dump is abrasive and heavy. The skin still wants to flex off texture, but the mother mold (jacket) takes the weight. A 10A–20A skin in a stiff jacket is common. A 40A block with no jacket feels "strong" in the hand and still slumps on a wet paver pour. Abrasion life is a recast plan, not a harder durometer guessed in email.

Typical shop values — one Shore chart, three pours

Caption these as typical shop values, not a measured lot.

Platinum mix is 1:1 or 10:1 by grade. Platinum linear shrink after a full cure is typically about 0.1–0.3%. ISO 3302-1 M2 is a common drawing-class default for a rubber *article*; it does not pick Shore A for a cavity.

We would not recommend

We would not recommend one Shore for "all custom molds" on a PO that mixes gummy trays and concrete gloves. You will get the wrong skin on one of them.

We would not recommend raising cavity Shore to stop tray sag. Sag is a missing jacket. The edge of a loaded sheet moving 0.5–1.5 mm is a structure miss.

We would not recommend 40A+ on a deep-undercut resin figurine "so it lasts." You will tear the mold at the hairline instead of peeling it. Raise tear grade, add a jacket, or split — in that order.

We would not recommend quoting an LSR 50A *part* compound as the cavity rubber because the TDS said 50A. Different object.

Worked example (anonymized)

Three RFQs arrived the same week with "Shore 20A" in the subject line.

1. A 24-cavity pectin gummy, 4.0 g target, half-sheet. We poured a platinum 15A skin on a rigid jacket. Outer-row weight is a jacket and fill problem, not a 30A request. Prototype after CAD lock in the 3–7 day window. MOQ 20 followed a dump test, not the Shore guess.

1. A 70 mm PU bust with undercut ears. Same 20A ask. Structure call first: not a flat back, peel was unsafe on the ears → keyed two-part, 15A skin, jacket. 20A as a one-piece glove would have torn at the ear root.

1. A 300 mm textured concrete tile. Same 20A ask. 15A skin, thick mother mold, platinum. The buyer had wanted 40A "for concrete." We kept the soft skin and put stiffness in the jacket. First pour released the texture; abrasion is a recast conversation after the run, not a durometer bump.

Three pours, overlapping Shore, three tools. The chart is the decision, not a single number.

The photo that would prove the jacket point: a loaded gummy sheet on a bench, straightedge across the outer row, 0.5–1.5 mm gap at the edge — cavity Shore unchanged.

Common mix-up: harder Shore means a longer-life mold

Buyers treat Shore A like rock well hardness. In the shop, a hard cavity on a hooked part fails by tearing at the first aggressive demold. A soft high-tear skin in a jacket fails later, by abrasion or by a nicked logo, and recasts from the unsanded master. Life is tear grade + jacket + how you demold + whether you kept the pattern. See tear strength vs hardness.

A tooling charge is not unrestricted ownership of that master. If you need custody for the recast, write it on the PO.

What to ask when you're buying

• What is the dump, peak °C, and is it sticky, fatty, or abrasive?
• Cavity Shore vs jacket Shore — are they specified separately?
• Loaded tray or heavy pour: jacket / mother mold yes/no?
• Target piece weight or cavity volume (gummy grams are not millilitres)?
• Recast plan after abrasion or nicked logos — is the unsanded master staying?

How we put a number on the RFQ without guessing

Name the dump. Name whether the part peels as an open-back or needs a split. Then pick a cavity band from the chart. Then decide jacket. Only then is "20A" a spec. If you only have photos, we still need one millimetre datum and the $50 simple 3D line when that CAD scope applies — files for a quote.

Related: pectin gummy molds, PU resin molds, concrete / cement molds, contact.

RFQ copy-pack — Shore across three pours

Copy to [email protected]:

• Dump: gummy (pectin/gelatin) / resin (name the system) / concrete-plaster
• Peak °C, sticky/fatty/abrasive notes
• Cavity Shore if you have a target; jacket Shore separately if you care
• Geometry: open-back vs split vs core (or "shop to propose")
• Grams or cavity volume; tray size and cavity count if it is a sheet
• Files in mm, or a sample, or scaled photos
• Quantity: prototype, then MOQ 20 per design
• Simple 3D: USD $50 only when that CAD scope applies

Matched next step: send the dump name with the file, not a Shore number alone. Phone +86 135 3006 2969. Licheng Technology Industry Park, Xinhe Blvd, Shajing, Baoan.

FAQ

Is Shore 20A the universal custom-mold default? It is a common *start* for several pours, not a universal spec. Gummy sheets, peelable resin, and concrete skins often live in 10A–20A. Thin jacketed walls may go 20A–30A. The dump and the structure move the number.

Can one Shore cover gummy and concrete if I only want one rubber on the shelf? You can overlap the cavity band (10A–20A). You cannot overlap the jacket, the abrasion plan, or the food-doc path. Two POs, two tools, even if both say 15A.

Does a harder cavity stop outer-row gummies from running heavy? No. Outer rows run 3–6% heavy when the sheet sags 0.5–1.5 mm. That is a jacket and fill issue. Raising Shore on the skin is the wrong lever.

Should concrete molds be 40A because concrete is heavy? Put the stiffness in the mother mold. Keep a softer skin so texture releases. 40A without a jacket still slumps, and it peels worse.

If I do not know Shore, can you pick it after CAD lock? Yes — after you name the dump and we mark structure. Prototype is 3–7 business days after that CAD lock, not after the first Shore guess in chat. Production MOQ stays 20 per design. The $50 CAD line applies only when we still need to model.