SMC LD
Grade
GB GB/T 25054
LD = low-density SMC with hollow glass microspheres
Use where mass reduction of 25–35 % versus standard SMC matters more than peak stiffness (vehicle closures, truck panels).
Values for the LD condition
Other SMC grades and fills
SMC is listed in 6 conditions; see the grade overview at SMC.
Compare all 6 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
LDThis page Low-density SMC with hollow glass microspheres | Use where mass reduction of 25–35 % versus standard SMC matters more than peak stiffness (vehicle closures, truck panels). | — | 55 | 1.3 | 87 Shore D |
Low-profile Class A surface SMC | Choose when the molded part must be primed and painted to a Class A automotive finish with near-zero shrinkage. | — | 65 | 1.2 | 90 Shore D |
Flame-retardant / electrical grade SMC | Pick for switchgear, busbar supports, meter boxes and insulating parts needing V-0, high CTI and glow-wire performance. | — | 65 | 1.2 | 90 Shore D |
Vinyl-ester matrix SMC | Choose for chemical plant covers, flue components and hot-water contact where standard polyester SMC hydrolyzes. | — | 85 | 1.7 | 90 Shore D |
HS/HMC | Select for load-bearing brackets, bumper beams and structural reinforcements where SMC must approach laminate stiffness. | — | 180 | 1.8 | 92 Shore D |
CF-SMC | Use where the highest specific stiffness in a compression-moldable thermoset is required (motorsport, aerospace brackets). | — | 250 | 1 | 92 Shore D |
What is SMC LD?
SMC LD is SMC in the LD grade — use where mass reduction of 25–35 % versus standard SMC matters more than peak stiffness (vehicle closures, truck panels). SMC LD has a tensile strength of 55 MPa (7.98 ksi), stronger than 61% of polymer grades. Elongation at break is 1.3% and the elastic modulus is 8 GPa (1.16 Msi). SMC LD has a density of 1.3 g/cm³ (0.047 lb/in³), heavier than 69% of polymer grades. Its glass-transition temperature is 115°C (239 °F).
Advantages
- Low, predictable mold shrinkage — 0.05%, better than 100% of polymer grades
- Stiff — 8 GPa (1.16 Msi), better than 91% of polymer grades
- Low embodied carbon — 3.2 kg CO₂/kg, better than 81% of polymer grades
- Good UV / weathering resistance — 55/100, better than 77% of polymer grades
Limitations
- Limited ductility — 1.3%, worse than 98% of polymer grades
- Limited formability — 5/100, worse than 95% of polymer grades
- Difficult to weld — 5/100, worse than 89% of polymer grades
- Difficult to machine — 38/100, worse than 83% of polymer grades
- Needs corrosion protection — 70/100, worse than 78% of polymer grades
SMC LD properties
Typical room-temperature values for SMC LD; 23 are specific to this condition. Other listed values are SMC reference data and may not represent this condition. Bars are the position among polymer grades.
Physical4
SMC LD has a density of 1.3 g/cm³ (0.047 lb/in³), heavier than 69% of polymer grades. Its glass-transition temperature is 115°C (239 °F).
Mechanical12
SMC LD has a tensile strength of 55 MPa (7.98 ksi), stronger than 61% of polymer grades. Elongation at break is 1.3% and the elastic modulus is 8 GPa (1.16 Msi).
Thermal10
SMC LD is rated for continuous service to 130°C (266 °F). It conducts heat at 0.18 W/m·K (0.104 BTU/hr·ft·°F), worse than 73% of polymer grades. Thermal expansion is 25 µm/m·K (13.9 µin/in·°F).
Electrical7
SMC LD is an electrical insulator with a dielectric strength of 15 kV/mm (381 V/mil) and a resistivity of 1×10¹¹ 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 SMC LD takes about 60 MJ of energy and emits 3.2 kg of CO₂ — less than 96% of polymer grades. Typical recycled content is 0%.
Manufacturability6
SMC LD's machinability is fair (38/100, worse than 83% of polymer grades); weldability not recommended (5/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SMC LD
Is SMC easy to machine?
Highly abrasive — drill and trim with PCD or diamond-coated tooling at high speed/low feed, back the part to avoid edge chipping, and extract glass dust.
Can SMC be welded?
Thermoset — cannot be welded; join by structural adhesive (urethane/epoxy), molded-in inserts, bolts or rivets.
Can SMC be formed, bent or molded?
Compression mold matched-metal at 140–160 °C, 5–15 MPa, ~30–45 s/mm wall; charge 40–70 % of cavity area and keep flow paths short to control fiber orientation and knit lines.
What surface finishes work on SMC?
In-mold coating or primer-surfacer plus 2K polyurethane paint for Class A; deflash edges, degrease and lightly abrade before bonding or painting; no plating without special conductive pretreatment.
SMC 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 (styrene-croorthophthalic/isophthalic UP; vinyl ester in VE grade | 20 – 32 | 26 |
| glass fiber (chopped, 12–50 mm)45–65 % in HS/HMC grades | 20 – 35 | 28 |
| low-profile additive (thermoplastic, PS/controls cure shrinkage / Class A surface | 2 – 6 | 4 |
| zinc stearate / internal mold release | 2 – 5 | 3.5 |
| MgO or Mg(OH)2 thickenerB-stage maturation | 0.5 – 1.5 | 1 |
| peroxide initiator (TBPB/TBPO) | 0.5 – 1.5 | 1 |
| pigment / additives | 0.5 – 3 | 1.5 |
| calcium carbonate fillerreplaced wholly/partly by ATH in FR grades | ≥ 30 (balance) | — |
SMC LD — frequently asked
What is SMC LD used for?
SMC LD is typically used for electrical switchgear housings, automotive body panels, bathroom fixtures and junction boxes. In short: low-cost structural thermoset; good high-voltage insulation; not weldable or recyclable.
What is the tensile strength of SMC LD?
SMC LD has a typical tensile strength of 55 MPa (7.98 ksi) — stronger than 61% of polymer grades. Strength varies by condition: see the 6 listed tempers.
Is SMC LD easy to machine?
Not especially — machinability is rated fair (38/100, worse than 83% of polymer grades). Highly abrasive — drill and trim with PCD or diamond-coated tooling at high speed/low feed, back the part to avoid edge chipping, and extract glass dust.
Can SMC LD be welded?
Not readily — weldability is rated not recommended (5/100). Thermoset — cannot be welded; join by structural adhesive (urethane/epoxy), molded-in inserts, bolts or rivets.
What surface finishes work on SMC LD?
In-mold coating or primer-surfacer plus 2K polyurethane paint for Class A; deflash edges, degrease and lightly abrade before bonding or painting; no plating without special conductive pretreatment.
Can SMC LD be formed, bent or molded?
Compression mold matched-metal at 140–160 °C, 5–15 MPa, ~30–45 s/mm wall; charge 40–70 % of cavity area and keep flow paths short to control fiber orientation and knit lines.
What is the maximum service temperature of SMC LD?
SMC LD is rated for continuous use to about 130°C (266 °F), and briefly to 180°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- GB/T 15568 (SMC) — SAC (2008)
- ISO 527-4 / ISO 14125 — tensile and flexural properties of fiber-reinforced plastic composites — ISO (1998)
- Engineered Materials Handbook Vol. 2: Composites — ASM International (1987)
- SMC compound technical datasheets (Menzolit, Polynt Composites, IDI Composites, Continental Structural Plastics) — various (2023)
- UL Yellow Card / IEC 60112 CTI and UL 94 listings for polyester molding compounds — UL Solutions (2023)
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.