220 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



This is merely an instance of how many efforts have been made and 

 what types of processes have fallen by the wayside. This does not 

 mean that they are impractical or that under favorable conditions 

 they would not be revived. 



GLASS FIBERS AND FILAMENTS 



Fiberglas (or glass fibers) has been lifted out of the category of 

 curiosities, and is now a textile raw material, with many potential 

 applications. It is being produced by two processes — the continuous- 

 filament process and the staple-fiber method — by Owens-Corning Fiber 

 Glas Corporation. In its manufacture glass marbles are fed into an 

 electrically heated furnace, which has a trough or V-shaped bushing 

 made of metals of a higher melting point than glass. In the continuous 

 process, molten glass, entering the wide top end of the bushing, is 

 "drawn" downward by gravity, the glass emerging from 102 tiny holes 

 in the bottom of the bushing. The filaments, averaging 0.00017 to 

 0.00020 inch in diameter, are combined to make one strand measuring 

 0.024 inch in diameter for winding on bobbins. A number of strands 

 can be plied together to produce a yarn of any size. 



In the staple process, the molten marbles are forced downward 

 through holes of the same type as in the continuous process, but, in- 

 stead of being "drawn," they are blown downward by steam under high 

 pressure. Passing through a burst of flame to eliminate moisture, the 

 fibers, averaging 8 to 15 inches in length, gather upon, and are drawn 

 from, a revolving drum. The accumulation of "sliver" follows 

 grooved wheels to be wound on revolving spools. The subsequent 

 spinning operation is carried out on regular textile machinery. 



Spun yarns have been made as fine as 100s cotton count. The yarn 

 is put up on beams, cones, tubes, bobbins, and spools, as desired. The 

 physical and chemical properties of glass filaments and fibers are very 

 interesting. The fibers are produced in various colors which are not 

 affected by heat, light, or weather. The fibers are solid, circular in 

 cross sections, and smooth. Fiberglas is fireproof, resistant to acids 

 (except hydrofluoric and phosphoric) , weatherproof, and mildewproof . 

 Good dialectric properties and good thermal-insulating characteristics 

 are very pronounced. Glass fiber is attacked by strong or hot solu- 

 tions of caustic soda. 



Fiberglas has a high tensile strength which can be varied by chang 

 ing the glass formula. In general, finer yarns have a greater tensile 

 strength than coarser yarns of the same size. The tensile strength and 

 elongation of the basic 102-filament fiberglas yarn are as follows: 

 Tensile strength, 6.3 grams per denier ; elongation, 1 to 2 percent. 



The strength expressed in grams per denier of yarns spun from the 

 staple fiber type is somewhat lower and elongation is higher, 2i/^ to 4 



