RTV Removable Core or Plug: Structure Call | RUUIPON

A removable core or plug is how you mold a through-hole, a bottle neck, a planter drain, or a jewelry bail that would tear a one-piece glove. You are not asking for "stronger silicone." You are asking for a piece of the tool that comes out along its own axis so the RTV skin never has to stretch around a hook. Run the RUUIPON Mold Structure Decision before you type a new Shore A into the chat: flat back → open-back tray. Deep undercuts that will not peel → two-part, or a plug/core. Large wet casting → mother mold on top of that. A plug is a structure line on the RFQ, with its own draft, keys, and a note that it is not the jacket.

RUUIPON builds plug and inner-core platinum tools 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. Steel cores in an LSR tool are wydsilicone.com. Inner-core design: inner core. One-piece vs split service: one-piece vs split.

Does not apply when the hole can be drilled after the cast (often cheaper on jewelry), when you meant a mother-mold jacket (the jacket is outside; the plug is inside the cavity), or when the "core" is an LSR cold-runner insert. Food through-holes still need a food-path platinum skin — a craft plug in a chocolate well is not a 177.2600 argument. Concrete planters and lost-wax jewelry cores are not food.

Structure Decision: when the plug is the answer

Walk the part the way the operator will demold.

1. Flat back, open cavity, no hook. Open-back skin. No plug.
2. Two-sided part, peel possible along one equator. Keyed two-part. Still no plug if arms and holes release.
3. A feature that is a tunnel, a neck, or a bail the rubber would have to invert through. Removable plug or core, drafted along the extract axis, keyed so it returns to the same shut.
4. Wet, tall, or 10A–20A with hydrostatic load. Mother mold / jacket *in addition* to the plug. Extra rubber wall is usually the wrong substitute.

A plug can be rigid (printed and sealed, CNC plastic, aluminum) or a second RTV hardness. Rigid plugs hold a round hole. Soft plugs can flex out of a mild undercut and then you argue about ovality. We would not spec a floppy 10A plug as the diameter of a bottle neck you will sell as round.

Draft on the plug is real draft, often more than people put on the outer split, because the operator is pulling a stick out of rubber. Polish the plug if the hole is a show surface. Seal an SLA plug or platinum will inhibit at the bore.

The photo that would prove a plug tool is the core on its axis next to the open skin, a witness cast with a clean bore, and paint marks that match keys. A screwdriver in a torn glove hole is the failure photo.

Plug versus split versus glove — do not stack all three by accident

Glove (open-back wrap) is cheapest in rubber grams and fails on two-sided undercuts. Split locates a parting on the equator. Plug exists for the feature that is *inside* after the split is open. Buyers ask for a two-part *and* a glove *and* three plugs because a render looked complex. Walk one demold path. Extra plugs are extra flash rings and extra tear sites.

Keys on a plug are not mushroom pips in a 10A film. Drafted bosses, enough wall, same open-vector rules as a two-part flange.

Food cavities with a plug (a filled chocolate sphere that needs a fill hole) still follow platinum + extraction docs. We would not patch a torn plug well with Sil-Poxy and keep that food path.

Typical shop values

Caption: Typical shop values.

Common mix-up: core equals jacket equals "just raise Shore"

A jacket is the mother mold outside the skin. A core/plug is the piece that makes the hole. Raising Shore so a glove can invert through a neck usually locks the pour in the well or tears the lip. The cousin mix-up is printing a plug in raw SLA and pouring platinum against it. Inhibition at the bore looks like a sticky tunnel you cannot wash into a food pack.

Worked example (anonymized)

A resin planter, drain hole through the floor, mild undercut rim. First RFQ asked for a one-piece glove in 30A "so the hole pops." We ran Structure Decision: rim wanted a split or a stretch that would oval the drain; drain wanted a drafted rigid plug from the floor; wet dump wanted a jacket. Quoted platinum ~15A skin, CNC plastic plug with draft, resin jacket, USD $50 CAD because the STL was hollow and the hole was a surface, not a solid. Proto 3–7 business days after lock. Production MOQ 20 of that stack. Planter is not a food cavity.

We would not recommend

We would not recommend inverting a one-piece glove through a neck to avoid a plug.

We would not recommend a 10A rubber plug as a diameter spec.

We would not recommend an unsealed SLA plug on a platinum food bore.

We would not recommend treating the jacket quote as if it included cores.

flowchart TD
  A[RUUIPON Mold Structure Decision] --> B{Flat back, no hook?}
  B -->|yes| C[Open-back]
  B -->|no| D{Will silicone peel the undercut safely?}
  D -->|yes| E[Two-part keyed split]
  D -->|no — tunnel/neck/bail| F[Removable plug or inner core]
  F --> G{Large wet dump?}
  E --> G
  C --> G
  G -->|yes| H[Add mother-mold jacket]
  G -->|no| I[CAD lock → 3–7 days → MOQ 20]
  H --> I

What to ask when you're buying a plug tool

• Is the hole as-molded, or cheaper to drill after the cast?
• Plug axis and draft — in the CAD, not "shop will figure it out"?
• Rigid plug or a second rubber, and who owns ovality?
• Jacket in addition to the plug?
• Food vs craft (jewelry/concrete are not food)?

Related: split mold, planters, contact.

RFQ copy-pack — plug as a structure line

Email [email protected]:

Structure Decision outcome: open-back / two-part / plug / jacket Hole or neck: as-molded vs drill after Plug: rigid CNC or sealed print — drafted in CAD Skin: platinum 1:1 or 10:1, Shore band Duty: food / resin planter / jewelry bail (jewelry is not food) CAD: locked / USD $50 if you model the plug Prototype 3–7 business days after CAD lock, then MOQ 20 / design

Send the hole axis and whether it must be as-molded. We will quote a plug, not a harder glove. Phone +86 135 3006 2969. Xinhe Blvd, Shajing, Bao'an, since 2018.

FAQ

Do I always need a removable core if there is a hole? No. Many jewelry holes are drilled after. Mold the plug when the bore is a show surface or a neck you cannot drill straight.

Is a plug the same as a mother mold? No. Jacket is outside. Plug is inside. Tall wet parts often need both.

Can the plug be 3D printed? Yes after wash, UV, and a seal if it sees platinum. Raw SLA is an inhibition risk, especially on a food bore.

Will a plug stop flash on the split? Only at the bore. Split flash is keys and shut. Do not expect one plug to replace a two-part when the equator still needs a seam.

If the plug sticks, should I raise Shore on the skin? Usually no. Add draft, a polish, or a *craft* release on the plug. Food bores: do not oil a chocolate well to hide missing draft. Recast the plug CAD.