Glass fiber reinforcements are available in many product forms developed to perform best in a variety of composite molding processes. Most people are only familiar with the processes they use or read about, but Table 2 contains a list of several product forms and processes where they are typically used.
Sizing, tex/yield/denier and filament diameter are differentiators that affect the performance of these products. Many of the product forms listed are offered in a fairly narrow range of these differentiators. For instance, yarns usually have very fine filament diameters, and very low tex (small) strands are used as inputs for yarn-based fabric tapes. Single-end and multi-end rovings – the highest volume products in the composites industry – have the widest selection of differentiators. I will cover these in more detail to illustrate the effects of sizing, tex/yield/denier and filament diameter.
It takes multiple filaments to make up a roving (strand) of glass reinforcement. Smaller filaments are harder to make, more costly and more difficult to wet out. However, in many processes and applications, smaller filaments result in higher strength products. The converse is true for larger filaments. Normally, 2,000 to 4,000 filaments make up a single roving. Far fewer filaments are used in yarns. Rovings, like yarns or strings, are offered in various tex/yield/denier. Units of tex are measured in grams per kilometers, while units of yield are measured in yards per pound. Units for yarns are measured in denier (grams per 9,000 meters). All of these measurements indicate the size of the strand of glass. Generally speaking, most reinforcement rovings are greater than 300 tex, while yarns are usually less than 300 tex.