Downdraw process

For structural applications, pure silica fibers are pulled from high purity silica rods as shown in Figure 3, top right. Gas flame or electrical furnaces are used to soften and melt the ends of the preform rods sufficiently for drawing. Each individual silica filament obtained in this downdrawing process has a diameter of 9 pirn, and yarns and/or rovings with up to 4800 filaments are then made available to the trade, where they are used either as woven reinforcement fabrics, or as yams, rovings, and threads for various specialty uses. 

Quaternary calcium aluminate glass fibers were also downdrawn from preforms on a laboratory [9] and a development unit [41], Downdrawing is a valid, but costly, method for fiberizing fragile melts. In addition, only one of >500 compositions could be fiberized on a conventional melt fiberizing unit [17], This process is not suitable for fragile melts. 

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