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Plastics lose weight with glass bubbles

2020-07-20 13:48:20 138

The next time you watch your bowling ball roll down the gutter, think about how impressed your teammates will be when you turn around to tell them Brunswick Bowling & Billiards, a div. of Brunswick Corp., has been using glass bubbles to control the weight of its 9 to 16-lb balls as early as the 1980s.

Glass bubbles, otherwise known as glass microspheres, have been used as a weight-reducing additive in plastics for years. They come as a dry, white-looking powder and are made from a water resistant and chemically stable soda-lime-borosilicate glass. These glass bubbles (GBs) are water resistant, noncombustible and nonporous so they do not absorb the resin they are mixed with. Older grades range in sizes from 70 to 35 microns with densities from 0.1 to 0.3 gm/cc and strengths of 250 to 2,000 psi. These collapsible strengths are suitable for zero to low-pressure processes. In the case of bowling balls, Brunswick adds glass bubbles to liquid polyester during an open-pour casting operation to make the ball’s inner core.

Ray Edwards, director of Consumer Products R&D for Brunswick Bowling explains, “Other methods to reduce weight for bowling balls such as foaming or injecting air into the matrix don’t give the kind of precise measuring needed to reach the target density. The use of GBs in bowling balls takes what would be an impossible density control issue and makes it manageable.”

Edwards offers an example of how GBs control density: “By regulation, all bowling balls must be between 8.500 and 8.595-in. diameter to be legal for use in competition. The weight of the balls vary from 8 to 16 lb. To make a 10-lb ball that has a 3.67-lb urethane coverstock (the outermost surface of the ball), the 7.7-in. spherical core has to weigh 6.33 lb. The polyester resin used in the core has a specific gravity of 1.23. When the polyester is mixed with the appropriate volume of glass microspheres, the casting mixture can be formulated to have the desired specific gravity of 0.734,” he says.

Glass bubble has a collapsible strength around 30,000 psi making it suitable for processes like sheet-molding compound (SMC), bulk-molding compound (BMC), resin-transfer molding (RTM), reaction-injection molding (RIM), and pultrusion. It can replace fillers such as clay, acrylics, hydrocarbon-based resin, carbon fiber, organic fillers, and nanoparticles. The GBs are 16 microns in diameter with a density of 0.6 gm/cc, which is one-fifth the density of the most widely used reinforcing fillers such as talc, glass fibers, and calcium carbonate. With this density and strength, the GBs score high for reduced weight, reduced cycle times, less warpage, and acceptable surface finish with improved strength. The automobile industry quickly adopted this new technology.

This article comes from machinedesign edit released