Page 259 - Mechanical Engineer's Data Handbook

ENGINEERING MATERIALS 247
costly but will operate up to 200°C and is used for ‘foam’, a liquid rubber expanded to form open or
high-temperature seals and gaskets. closed cells and stiffer than sponge; and ‘expanded’, a
solid rubber blown with mainly closed cells - it is stiffer
Elastomers than sponge. Uses include gaskets, seals, thermal
insulation, cushioning, shock absorption, sound and
Cellular rubbers There are three types: ‘sponge‘, vibration damping, buoyancy and sandwich construc-
solid rubber blown to give an open-cell structure; tions.

6.13.5 Properties of plastics
Typical physical properties of plastics

Tensile
P strength Elongation E
Properties of plastics (kg m- 3, (Nmm-’) (%) (GNm-2) BHN Machinability
Thermoplastics
PVC rigid 1330 48 200 3.4 20 Excellent
Polystyrene 1300 48 3 3.4 25 Fair
PTFE 2100 13 100 0.3 - Excellent
Polypropylene 1200 27 200-700 1.3 10 Excellent
Nylon 1160 60 90 2.4 10 Excellent
Cellulose nitrate 1350 48 40 1.4 10 Excellent
Cellulose acetate 1300 40 10-60 1.4 12 Excellent
Acrylic (Perspex) 1190 74 6 3 .O 34 Excellent
Polythene (high density) 1450 2&30 20-100 0.7 2 Excellent
Thermosetting plastics
Epoxy resin 1600-2000 68-200 4 20 38 Good
(glass filled)
Melamine formaldehyde 1800-2000 6&90 - 7 38 Fair
(fabric filled)
Urea formaldehyde 1500 38-90 1 7-10 51 Fair
(cellulose filled)
Phenol formaldehyde 160&1900 38-50 0.5 17-35 36 Good
(mica filled)
Acetals (glass filled) 1600 58-75 2-7 7 27 Good

BHN = Brinell hardness number, p =density, E = Young’s modulus.
Relative properties of plastics

Tensile Compressive Machining Chemical
Material strength strength properties resistance

Thermoplastics
Nylon G E
PTFE G E
Polypropylene F E
Polystyrene G F
Rigid PVC G E
Flexible PVC P P