GTBL042-13 GTBL042-Callister-v2 August 29, 2007 8:52
Summary • 563In addition to the styrenic block copolymers, there are other types of TPEs,
including thermoplastic olefins, copolyesters, thermoplastic polyurethanes, and elas-
tomeric polyamides.
The chief advantage of the TPEs over the thermoset elastomers is that upon
heating aboveTmof the hard phase, they melt (i.e., the physical crosslinks disap-
pear), and, therefore, they may be processed by conventional thermoplastic forming
techniques [e.g., blow molding, injection molding, etc. (Section 14.13)]; thermoset
polymers do not experience melting, and, consequently, forming is normally more
difficult. Furthermore, since the melting-solidification process is reversible and re-
peatable for thermoplastic elastomers, TPE parts may be reformed into other shapes.
In other words, they are recyclable; thermoset elastomers are, to a large degree, non-
recyclable. Scrap that is generated during forming procedures may also be recycled,
which results in lower production costs than with thermosets. In addition, tighter con-
trols may be maintained on part dimensions for TPEs, and TPEs have lower densities.
In quite a variety of applications, the thermoplastic elastomers have replaced the
conventional thermoset elastomers. Typical uses for the TPEs include automotive
exterior trim (bumpers, fascia, etc.), automotive underhood components (electrical
insulation and connectors, and gaskets), shoe soles and heels, sporting goods (e.g.,
bladders for footballs and soccer balls), medical barrier films and protective coatings,
and as components in sealants, caulking, and adhesives.SUMMARY
Ferrous Alloys
With regard to composition, metals and alloys are classified as either ferrous or non-
ferrous. Ferrous alloys (steels and cast irons) are those in which iron is the prime
constituent. Most steels contain less than 1.0 wt% C, and, in addition, other alloy-
ing elements that render them susceptible to heat treatment (and an enhancement
of mechanical properties) and/or more corrosion resistant. Plain low-carbon steels
and high-strength low-alloy, medium-carbon, tool, and stainless steels are the most
common types.
Cast irons contain a higher carbon content, normally between 3.0 and 4.5 wt% C,
and other alloying elements, notably silicon. For these materials, most of the carbon
exists in graphite form rather than combined with iron as cementite. Gray, ductile
(or nodular), malleable, and compacted graphite irons are the four most widely used
cast irons; the latter three are reasonably ductile.Nonferrous Alloys
All other alloys fall within the nonferrous category, which is further subdivided ac-
cording to base metal or some distinctive characteristic that is shared by a group of
alloys. The compositions, typical properties, and applications of copper, aluminum,
magnesium, titanium, nickel, lead, tin, zirconium, and zinc alloys, as well as the re-
fractory metals, the superalloys, and the noble metals were discussed.Glasses
Glass–Ceramics
Also discussed in this chapter were various types of ceramic materials. The famil-
iar glass materials are noncrystalline silicates that contain other oxides; the most