BMC HT
Heat-treated state
HT = heat-resistant / high-CTI arc-resistant BMC
Specify for motor commutators, arc chambers and lamp bases running above 160 °C with arc/track exposure.
Values for the HT condition
Other BMC grades and fills
BMC is listed in 8 conditions; see the grade overview at BMC.
Compare all 8 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Thermally conductive mineral/ceramic-filled BMC | Use for LED heat-sink housings and encapsulations that need 1–3 W/m·K while staying electrically insulating. | — | 30 | — | — |
Low-profile / Class-A surface BMC | Choose for visible pigmented or painted parts (automotive lamp bezels, appliance fronts) needing near-zero shrink and smooth surface. | — | 35 | 0.5 | 98 HRM |
Carbon/graphite-filled conductive BMC | Use where ESD dissipation or bulk electrical conduction is required (fuel-cell bipolar plates, static-safe housings) rather than insulation. | — | 35 | — | — |
Flame-retardant BMC, UL 94 V-0 / 5VA | Pick when a UL 94 V-0 or 5VA rating and glow-wire performance are mandatory (breakers, contactors, EV connectors). | — | 38 | 0.4 | 105 HRM |
High-whiteness reflector BMC | Choose for LED reflectors and lamp cups needing high initial reflectance with minimal yellowing after thermal/UV ageing. | — | 38 | 0.4 | 105 HRM |
HTThis page Heat-resistant / high-CTI arc-resistant BMC | Specify for motor commutators, arc chambers and lamp bases running above 160 °C with arc/track exposure. | — | 40 | — | — |
Vinyl ester matrix BMC | Pick when the part sees acids, chlorides, hot water or steam that would hydrolyse standard orthophthalic polyester BMC. | — | 50 | 0.7 | 105 HRM |
High-strength BMC, 22–30% longer glass fiber | Use for load-bearing or pressure-containing mouldings (pump housings, structural brackets) where impact and flexural strength dominate. | — | 60 | 0.8 | — |
What is BMC HT?
BMC HT is BMC heat treated to HT — specify for motor commutators, arc chambers and lamp bases running above 160 °C with arc/track exposure. BMC HT has a tensile strength of 40 MPa (5.8 ksi), weaker than 56% of polymer grades. Elongation at break is 0.5% and the elastic modulus is 11 GPa (1.6 Msi). BMC HT has a density of 1.95 g/cm³ (0.0704 lb/in³), heavier than 97% of polymer grades. Its glass-transition temperature is 120°C (248 °F).
Advantages
- Conducts heat well — 0.6 W/m·K (0.347 BTU/hr·ft·°F), better than 99% of polymer grades
- Stiff — 11 GPa (1.6 Msi), better than 97% of polymer grades
- Low, predictable mold shrinkage — 0.15%, better than 97% of polymer grades
- High service temperature — 180°C (356 °F), better than 85% of polymer grades
- Low embodied carbon — 3 kg CO₂/kg, better than 83% of polymer grades
Limitations
- Limited ductility — 0.5%, worse than 100% of polymer grades
- Limited formability — 3/100, worse than 99% of polymer grades
- Heavy — 1.95 g/cm³ (0.0704 lb/in³), worse than 97% of polymer grades
- Difficult to weld — 3/100, worse than 95% of polymer grades
- Difficult to machine — 35/100, worse than 84% of polymer grades
BMC HT properties
Typical room-temperature values for BMC HT; 10 are specific to this condition. Other listed values are BMC reference data and may not represent this condition. Bars are the position among polymer grades.
Physical4
BMC HT has a density of 1.95 g/cm³ (0.0704 lb/in³), heavier than 97% of polymer grades. Its glass-transition temperature is 120°C (248 °F).
Mechanical12
BMC HT has a tensile strength of 40 MPa (5.8 ksi), weaker than 56% of polymer grades. Elongation at break is 0.5% and the elastic modulus is 11 GPa (1.6 Msi).
Thermal10
BMC HT is rated for continuous service to 180°C (356 °F). It conducts heat at 0.6 W/m·K (0.347 BTU/hr·ft·°F), better than 99% of polymer grades. Thermal expansion is 25 µm/m·K (13.9 µin/in·°F).
Electrical7
BMC HT is an electrical insulator with a dielectric strength of 15 kV/mm (381 V/mil) and a resistivity of 1×10¹² Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 78% of polymer grades. UV resistance is good.
Sustainability4
Producing a kilogram of BMC HT takes about 55 MJ of energy and emits 3 kg of CO₂ — less than 98% of polymer grades. Typical recycled content is 0%.
Manufacturability7
BMC HT's machinability is fair (35/100, worse than 84% of polymer grades); weldability not recommended (3/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with BMC HT
Is BMC easy to machine?
Cured BMC is abrasive and brittle — use PCD or diamond-coated tooling, high speed / low feed, support the part and vacuum the dust; drill from the moulded side to avoid chip-out.
Can BMC be welded?
Thermoset: cannot be welded; join by mechanical fasteners, moulded-in inserts, or epoxy/MMA adhesives after light abrasion and solvent wipe.
Can BMC be formed, bent or molded?
Injection, injection-compression or compression mould with stuffer-feed screws at 20–45 °C barrel and 140–180 °C tool, ~30–60 s/mm cure; vent well for styrene and avoid fibre-degrading high shear gates.
What surface finishes work on BMC?
As-moulded surfaces take flash removal by tumbling or media blast; low-profile grades accept primer and 2K polyurethane paint, and vacuum-metallizing after a UV base coat for reflectors.
BMC chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| unsaturated polyester resin (in styrene)ortho/iso-phthalic UP; vinyl ester in VE grades | 18 – 32 | 25 |
| glass fiber (chopped, 3–12 mm)higher in HS-GF25 structural grades | 10 – 30 | 18 |
| low-profile thermoplastic additivePS/PVAc shrink-control additive | 0 – 6 | 3 |
| internal mould release (zinc stearate) | 1 – 3 | 2 |
| peroxide initiator (TBPB/BPO) | 0.5 – 1.5 | 1 |
| thickener (MgO/Ca(OH)2), pigment, additi | 0.5 – 3 | 1 |
| calcium carbonate / mineral fillerreplaced partly by ATH in FR grades, by Al2O3/BN in TC grades | ≥ 35 (balance) | — |
BMC HT — frequently asked
What is BMC HT used for?
BMC HT is typically used for circuit breaker housings, appliance components, automotive under-hood parts and electrical insulators. In short: net-shape thermoset insulator; stable to 150 °C; V-0 flame-retardant grades.
What is the tensile strength of BMC HT?
BMC HT has a typical tensile strength of 40 MPa (5.8 ksi) — weaker than 56% of polymer grades. Strength varies by condition: see the 8 listed tempers.
Is BMC HT easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of polymer grades). Cured BMC is abrasive and brittle — use PCD or diamond-coated tooling, high speed / low feed, support the part and vacuum the dust; drill from the moulded side to avoid chip-out.
Can BMC HT be welded?
Not readily — weldability is rated not recommended (3/100). Thermoset: cannot be welded; join by mechanical fasteners, moulded-in inserts, or epoxy/MMA adhesives after light abrasion and solvent wipe.
What surface finishes work on BMC HT?
As-moulded surfaces take flash removal by tumbling or media blast; low-profile grades accept primer and 2K polyurethane paint, and vacuum-metallizing after a UV base coat for reflectors.
Can BMC HT be formed, bent or molded?
Injection, injection-compression or compression mould with stuffer-feed screws at 20–45 °C barrel and 140–180 °C tool, ~30–60 s/mm cure; vent well for styrene and avoid fibre-degrading high shear gates.
What is the maximum service temperature of BMC HT?
BMC HT is rated for continuous use to about 180°C (356 °F), and briefly to 230°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM D1201 — Thermosetting Polyester Molding Compounds — ASTM International (2019)
- ISO 14526 / ISO 12114 — SMC and BMC compounds, cure and test methods — ISO (2018)
- Engineered Materials Handbook Vol.2: Engineering Plastics (thermoset molding compounds) — ASM International (1988)
- BMC / TMC compound datasheets (IDI Composites, Menzolit, Polynt-Reichhold, Bulk Molding Compounds Inc.) — various (2023)
- UL Yellow Card / Prospector data for thermoset polyester molding compounds — UL Solutions (2024)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.