MIL-M-43248C

Abstract

This specification covers a group of mats made of randomly oriented strands of glass filaments, with or without surfacing mats and backings. These mats are produced by continuous processes and are used primarily for making glass reinforced plastic items by either the wet layup or matched die molding process (see <a>6.1</a>). This specification does not cover surfacing mats per se, mats for use in the paneling market, or those made by batch processes or with very short strands. <b><u>Intended Use:</u></b> 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 <a>6.3</a>). 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. <br>