Glass fiberizing process
Philippe Derain of EFD Induction France gives a brief introduction to one of the lesser-known uses of induction heating: glass fiberizing.
Glass fiberizing—the science of turning molten glass into fine fibres—requires a steady source of heat, sand, recycled glass…and an understanding of how candyfloss is made.
Next time you visit a funfair or circus, take a few minutes to see how candyfloss—known as cotton candy in the US—is made. You’ll see how melted sugar is spun at high speeds to form fine, long filaments. These then cool rapidly in the air to form a mass of low-density ‘floss’—the sweet bundle we remember from our childhoods.
An almost identical method is used to produce glass fiber. Heated glass is fed into a spinner that rotates at high speeds. The lower edge of the spinner features numerous tiny holes. As the spinner rotates, the molten glass is forced through the mesh of holes, exiting as filaments that cool upon contact with the air. The cooled filaments are then collected as mats of entangled fibers which are subsequently formed into continuous rolls called ‘blankets’, or into pre-cut shapes, usually squareshaped slabs called ‘batts’. Two of the best-known applications for glass fiber are thermal and sound insulation, made possible by glass fiber’s extremely high ratio of surface area to weight.
Two factors are especially critical for successful glass fiberizing. First, the molten glass must be fed at the correct rate into the rotary spinner. Second, the molten glass must be consistently maintained at the correct temperature. Unwanted temperature fluctuations, for example, can result in inconsistent fiber characteristics, which in turn compromise the insulation capabilities of the final product. However, maintaining a stable temperature is extremely challenging—especially at the approximately 1,400°C typical of glass fiberizing. Fortunately, maintaining a stable temperature is one of the main features of induction heating, which is why induction is widely used in the glass fiberizing industry.
EFD Induction glass fiberizing systems typically include: a Sinac converter, a matching station specially tuned for glass fiber spinners, concrete-insulated induction coils and a cooling unit. The EFD Induction Sinacs used for glass fiberizing are usually in the 50-100 kW power range, but much higher ratings are of course available. Medium frequencies are common for this application, typically up to 10 kHz. But as the Sinac features IGBT transistors and EFD Induction’s patented switching technology, the Sinac can operate at frequencies up to 200 kHz. The power supply chosen for glass fiberizing is usually determined by the diameter of the spinner plate.
Growing concerns about global climate change— plus spiraling energy costs for consumers—have helped generate strong demand for thermal insulation materials, particularly for the proven method of glass fiber. Many governments even offer subsidies or other incentives for house owners to retrofit their properties with glass fiber insulation. Demand for glass fiber has also been driven by a growing awareness of the importance of quiet indoor climates. Another driving force has been the regeneration of city centers, and the vogue for dense city living, with urban dwellers opting to live in apartment buildings. EFD Induction has developed specialist expertise to meet this growing demand for glass fiberizing. In fact, our glass fiberizing solutions can be found in Finland, France, Germany, India, Italy, Kuwait, Norway, Poland, Russia, Spain, Sweden, Switzerland and Turkey.
Philippe Derain, Export Sales Manager at EFD Induction in France, explains the art and science of glass fiberizing.