Sheet molding compound (SMC)

The material. Layup and filament winding methods of shaping composites are far too slow and labor intensive to compete with steel pressings for car body panels and other enclosures. Sheet molding compounds (SMCs) over­come this by allowing molding in a single operation between heated dies. To make SMC, polyester resin containing thickening agents and cheap par­ticulates such as calcium carbonate or silica dust is mixed with chopped fibers—usually glass—to form a sheet. The fibers lie more or less parallel to the plane of the sheet but are randomly oriented in-plane, with a volume fraction between 15% and 40%. This makes a "pre-preg" with leather – or doughlike consistency. When an SMC sheet is pressed between hot dies, it polymerizes, giving a strong, stiff sheet molding.

Composition

(OOC—C6H4—COO—C6Hi0)n + CaCO3 or SiO2 filler + 15 to 40% chopped-glass strand.

General properties Density 1800 – 2000 kg/m3 Price *5.81 – 6.39 USD/kg Mechanical properties Young’s modulus 9 – 14 GPa Yield strength (elastic limit) 50 – 90 MPa Tensile strength 60 – 100 MPa Compressive strength 240 – 310 MPa Elongation 2.5 – 3.2 % Hardness—Vickers *15 – 25 HV Fatigue strength at 107 cycles *20 – 36 MPa Fracture toughness *5 – 13 MPa. m1/ Thermal properties Glass temperature 147 – 197 °C Maximum service temperature 180 – 220 °C Thermal conductor or insulator? Good insulator Thermal conductivity 0.27 – 0.5 W/m. K Specific heat capacity 1050 – 1090 J/kg. K Thermal expansion coefficient 18 – 33 p, strain/°’

SMC cycle shed. (Image courtesy of the ACT Program, McMaster University.)

Electrical properties

Electrical conductor or insulator? Electrical resistivity Dielectric constant Dissipation factor Dielectric strength

Ecoproperties: material

Embodied energy, primary production CO2 footprint, primary production Water usage

Eco properties: processing

Simple composite molding energy Simple composite molding CO2 Advanced composite molding energy Advanced composite molding CO2

Recycling

Recycle fraction in current supply

Typical uses. Sheet pressings of all types, competing with steel and alumi­num sheet. Car body panels; enclosures; luggage and packing cases.

Bulk molding compound (BMC)

The material. Layup and filament winding methods of shaping composites are far too slow and labor-intensive to compete with steel pressings for car body panels and other enclosures. Sheet molding compounds (SMCs) and bulk (or dough) molding compounds (BMCs or DMCs) overcome this by allowing molding in a single operation between heated dies. To make BMC, polyester resin containing thickening agents and cheap particulates such as calcium carbonate or silica dust is mixed with chopped fibers—usually glass—to form a sheet. The fibers lie more or less parallel to the plane of the sheet but are randomly oriented in three dimensions, with a volume fraction between 10% and 25%. This makes a "pre-preg" with leather – or doughlike consistency. BMC is molded in closed, heated dies to make more complex shapes: door handles, shaped levers, parts for washing machines, and the like.

Composition

(OOC—C6H4—COO—C6Hio)n + CaCO3 or SiO2 filler + 15 to 40% chopped-glass strand.

General properties Density 1800 – 2100 kg/m3 Price *4.75 – 5.22 USD/kg

Mechanical properties Young’s modulus	12	– 14	GPa
Yield strength (elastic limit)	25	– 55	MPa
Tensile strength	34	– 70	MPa
Compressive strength	140	– 180	MPa
Elongation	1.4	– 1.9	%
Hardness—Vickers	*7	– 16	HV
Fatigue strength at 107 cycles	*12	– 27	MPa
Fracture toughness	*3	– 6	MPa. m1/2

Thermal properties Glass temperature	147 –	197	°C
Maximum service temperature	140 –	210	°C
Thermal conductor or insulator?	Good insulator
Thermal conductivity	0.27 –	0.5	W/m. K
Specific heat capacity	*1110 –	1160	J/kg. K
Thermal expansion coefficient	24 –	34	p, strain/°C

A BMC (or DMC) molding. BMC is used for door handles, casings for electrical and gas, and most small moldings in cars.

Electrical properties

Electrical conductor or insulator?	Good insulator
Electrical resistivity	1 X 1018	– 1 X 1019 p, ohm
Dielectric constant	4.2	– 5
Dissipation factor	0.002	– 0.008
Dielectric strength	10	– 18 106 V/m

Ecoproperties: material
Embodied energy, primary production	109	– 121	MJ/kg
CO2 footprint, primary production	7.5	– 8.5	kg/kg
Water usage	*89	– 280	l/kg

Ecoproperties: processing Simple composite molding energy	*11.3	– 12.4	MJ/kg
Simple composite molding CO2	*0.90	– 0.99	kg/kg
Advanced composite molding energy	*18.4	– 20.3	MJ/kg
Advanced composite molding CO2	*1.48	– 1 .63	kg/kg

Recycling
Recycle fraction in current supply	0.5	– 1	О/ %

Typical uses. Car battery cases; door handles and window winders; wash­ing machine parts such as lids; automotive vents, distributor caps and other small moldings; casings for telephones, gas, and electricity meters.