The fiberglass reinforcing mats covered by this specification are
intended for use for making glass reinforced plastic items,
particularly those of larger size, having irregular thickness, compound
curvature or requiring deep draws. Reinforced plastic items made from
mat are usually intermediate in cost between those made from glass
cloth and those made by spraying a mixture of chopped glass fibers and
resin (see 6.3).
Type I mat is used primarily for band layup work, as for building
boats. The high solubility binder gives that mat sufficient strength
for carrying it into place when dry. However, when wet with resin, the
binder softens permitting the mat to be fitted over irregular contours.
Class 2 mats produce laminates having smoother surfaces than are
obtained with class 1.
Type II mat is used primarily for matched die molding. Its low
solubility binder holds the mat together when resin is introduced into
the mold as high temperature and pressure, thereby preventing the glass
fibers from being washed out of place by the rapidly moving resin. This
type has been used for molding gunstocks.
Type III is used primarily in matched die molding of heavy sections of
compound curvature. Since its glass filaments are not coated with
binder, it tends to wet out faster when immersed in resin than do the
resin-bonded mats.
Type IV mat is used both for matched die molding, particularly in heavy
sections requiring deep draws. Laminates made from it may not be quite
as rigid as those made from chopped strand mat because its glass
filaments are initially curved.
Type V mats are used primarily for hand layup operations where great
dry or wet strength is needed so that large pieces can be carried into
place without distortion and breakage, when thick layers are desired,
and when the finished item requires high strength. When the backing is
unidirectional glass roving, the resulting laminate can have very high
strength in one direction. The labor cost of applying type V mat
usually is lower than that of applying the backing material and chopped
strand mat as separate operations.
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