Open-Back RTV Trays for Flat-Back Magnets | RUUIPON
Flat-back magnets follow the Structure Decision: open-back, not a two-part block. Fill line, magnet well, platinum if food. Typical shop. MOQ 20, $50 CAD.
Kyler Yang · Founder7 min read
If the back of the part is flat — a fridge magnet, a badge, a logo tile — the RUUIPON Mold Structure Decision says open-back. You pour resin (or plaster, or chocolate if it is actually food) into an open cavity and scrape or fill to a line. You do not box a two-part block around a flat-back object unless you have a real undercut that will not peel. Extra split, extra keys, extra flash, extra cost. The magnet well, if you need one, is a pocket in that open cavity with a depth you lock in millimetres, not a surprise after first dump.
RUUIPON pours those open-backs in Bao'an, Xinhe Blvd, Shajing, since 2018. Mix is 1:1 or 10:1 by weight. Prototype is 3–7 business days after CAD lock of fill line and well depth. Production is MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. Platinum shrink after a full cure is typically about 0.1–0.3%. LSR/HCR *parts* that *are* magnets or overmolds: wydsilicone.com.
Does not apply when the "magnet" is a fully round figurine with a magnet glued in a recess on a curved back — that may still be a split. It also does not apply to magnetic polycarbonate chocolate molds. Food chocolate magnets still want platinum, not tin, and a food pack.
Fill line, magnet well, and why a block fights you
Open-back means the pour face *is* the back. Scrape to a land we cut, or fill to a scribe. If the magnet must sit flush, the well depth is magnet thickness plus adhesive film minus any dome you want. If you skip that number, first dumps leave the magnet proud or buried.
Undercuts on the *show* face can still peel in 10A–20A if they are honest. Deep hooks that will not peel push you to a plug, not to a full two-part box around a flat back. Jacket the tray if it is large and loaded — unsupported edge sag is typically about 0.5–1.5 mm, enough to make a row of magnets uneven.
flowchart TD
A[Magnet / badge RFQ] --> B{Flat back?}
B -->|yes| C[Open-back tray]
B -->|no| D[Split / glove / core as usual]
C --> E[Lock fill line mm]
E --> F[Magnet well depth mm if needed]
F --> G{Loaded multi-up?}
G -->|yes| H[Jacket]
G -->|no| I[Pour, scrape, demold]The photo that would prove an open-back call: cavity with a millimetre stick on fill line and well, first dump scraped, magnet seated. A boxed two-part flask around a coin magnet is the anti-photo.
ISO 3302-1 M2 is a common dump class. It does not invent a well depth. $50 CAD applies when the buyer sent a PNG of a logo and a 25 mm magnet with no well.
Failure: proud magnet, starved logo, split flash you did not need
Symptom: magnet sits proud; logo serifs starve at the scrape; or a two-part tool flashes a seam across a badge that should have been open.
Cause: well too shallow; scrape land too aggressive on a thin logo; Structure Decision skipped.
Confirm: measure well with a depth mic or a marked pin. Compare to the magnet + adhesive stack.
Fix: recast the well. Do not glue magnets on a proud back and call it CAD. Do not raise Shore to "hold a scrape" if the land is wrong.
Resin magnets pick up inhibition from a dirty cup the same as any platinum job. Food-adjacent fridge magnets that will touch snacks still want the food path or a written craft-only.
Typical shop values
Caption: typical shop values, not a named PO.
| Item | Typical shop value |
|---|---|
| Mix / shrink | 1:1 or 10:1 by weight; platinum about 0.1–0.3% |
| Cavity Shore | 10A–20A for detail; 20A–40A if the scrape is aggressive |
| Loaded sag without jacket | about 0.5–1.5 mm |
| Prototype | 3–7 business days after CAD lock |
| Production MOQ | 20 pieces per design |
| Simple 3D | USD $50 when that CAD scope applies |
| Drawing class | ISO 3302-1 M2 as a common default |
Structures we would not quote first
We would not recommend a two-part block on a flat-back magnet "for quality."
We would not recommend skipping the well depth because "we will glue it later." Later is a proud stack.
We would not recommend tin for a chocolate logo magnet.
We would not recommend treating a PNG without millimetres as CAD lock.
A tooling charge is not unrestricted ownership of the well CAD. Recasts follow the locked depth unless you pay to change it.
Worked example: 40 mm logo magnet, boxed as two-part
Craft resin logo, 40 mm, buyer asked for a keyed two-part "like our figurine." First dumps flashed a film across the face and the magnet sat proud on a flat back with no well. Recast as open-back, 20A, well depth locked to the 2 mm magnet + film, scrape land around the logo. $50 CAD applied (PNG only). Prototype 3–7 business days after that CAD lock. Production MOQ 20 of that design. Related: resin molds.
Multi-up sheets look cheap until sag dishes the outer wells. A 12-up magnet tray without a jacket can leave the outer row thick and the center thin when you scrape to a land that is no longer planar. That is not a mix-ratio problem. Jacket first, then argue Shore. If the dump is food chocolate logo magnets, add the wash and 177.2600 line on the same PO as the well depth. Craft resin magnets can skip the food pack and still need the well.
Glue-on magnets after a flat scrape are a valid SOP when the well would steal logo depth. Write "no well, glue-on" so we do not cut a pocket that thins a 1 mm logo. The Structure Decision does not force a well. It forces open-back when the back is flat.
Mix-up: fridge magnet means magnetic silicone
The dump is resin or chocolate with a magnet glued or seated. Conductive or magnetic silicone *parts* are a WYD conversation. The other mix-up is a dome-back "magnet" that is actually a cabochon — still open-back, still a fill line, no well.
What to ask when you're buying the open-back
- Flat back confirmed, or is there a curve/undercut?
- Magnet OD × thickness, and flush vs recessed?
- Dump chemistry — resin vs food?
- Jacket for a multi-up sheet?
- After CAD lock, 3–7 business days, then MOQ 20 / design?
Related: custom logo molds, contact.
RFQ copy-pack — flat-back open-back
Paste into [email protected]:
Object: open-back RTV tray for flat-back magnets/badges (not an LSR part) Dump: resin / plaster / chocolate (platinum if food) Magnet OD x thickness mm, flush or proud Fill line and well: lock or USD $50 CAD if that scope applies File: STEP / STL / photos with a millimetre scale Prototype 3–7 business days after CAD lock, then MOQ 20 per design
Send well depth and a flat-back confirmation, not "two-part like last time." We run the Structure Decision — not a blank free quote. Phone +86 135 3006 2969. Licheng Technology Industry Park, Xinhe Blvd, Shajing, Bao'an. Shop since 2018.
FAQ
Do flat magnets need a two-part mold? Usually no. Open-back plus a fill line. Split only if the back is not actually flat.
How deep should the magnet well be? Magnet thickness plus adhesive film, minus any dome you want. Put millimetres on the RFQ.
Can I pour chocolate into a resin magnet tray? Not as a food path unless it was platinum, washed, documented. Do not borrow a craft TDS.
Will a jacket change the magnet seat? A jacket fights sag so a row of wells stays even. It should not steal well depth if CAD locked it.
Is a PNG enough for CAD lock? Not without millimetres. $50 CAD when that scope applies, then 3–7 business days. MOQ 20 per design.
Ready to order custom silicone molds?
Free quote for OEM/ODM projects. MOQ 20 · Prototype 3-7 days · FDA/LFGB available.