How DMC is made and moulded
Dough moulding compound is made in batches. Resin, mineral filler, initiator, release agent and pigment are mixed to a paste in a heavy-duty mixer; short chopped glass is then added and folded in until the mass becomes a stiff dough. The dough is stored, weighed into charges and moulded — usually by compression moulding in a heated tool, and in some plants by transfer or injection moulding.
DMC fills intricate shapes well, which is why it is used for electrical housings and switchgear parts, meter boxes, fittings and compact components with ribs, bosses and moulded-in inserts.
Questions that decide the family
Part and compound questions
- What is the part, and does it carry electrical, flammability or dimensional requirements?
- Will it see heat, moisture or chemicals in service?
- What filler and glass content is the compound designed for?
- Compression, transfer or injection moulding?
- How long must the dough be stored before moulding?
The three DMC resin families
The orthophthalic resin is the DMC/SMC Resin (SPR 201 SMC · DMC), with a published TDS. SPR 301 DMC is the isophthalic option; it shares the catalogue’s combined SMC / DMC specification with SPR 301 SMC. SPR 401 DMC is the terephthalic option, with its own, more viscous specification.
The catalogue chooses between them by what the compound and part require rather than by a ranking.
Published typical values
| Property | DMC/SMC Resin (SPR 201 SMC · DMC) | Isophthalic DMC Resin (SPR 301 DMC) | Terephthalic DMC Resin (SPR 401 DMC) |
|---|---|---|---|
| Chemistry | Orthophthalic unsaturated polyester resin | Isophthalic unsaturated polyester | Terephthalic unsaturated polyester |
| Viscosity (typical) | 600 cPs (at 25°C) | 800–1,400 cPs at 25 °C | 1,200–2,200 cPs at 25 °C |
| Gel time / pot life (typical) | 12–18 minutes (at 25°C; review current TDS for test context) | 12–18 minutes at 25 °C | 14–22 minutes at 25 °C (ambient QC) |
| Styrene content (typical) | 35% | 31–36% by weight | 31–36% by weight |
| Reference cure | Not published | MEKP 1.5% + Cobalt Octoate 0.4% — added separately during use | MEKP 1.5% + Cobalt Octoate 0.5% — added separately during use |
| Source of values | DMC/SMC Resin TDS | 2026 catalogue; grade TDS | 2026 catalogue; grade TDS |
Typical values from each product’s own published data. Gel times are ambient 25 °C quality-control figures; DMC cures in a heated tool with the compound’s own initiator.
What the compounder controls
The dough’s formulation — filler grading and loading, fibre length and content, initiator and inhibitor balance, release — decides its flow, shelf life and moulded properties. Electrical and flammability performance in particular are properties of the formulated, moulded compound, proven by testing moulded specimens. No such values are published for the resins.
Trials
Mix a production-scale batch with the candidate resin at the intended filler loading, then check dough consistency, storage behaviour, flow into the production tool, knit lines, cure cycle and the moulded surface. For a change of resin family on an existing part, compare moulded specimens against the part’s current requirement.