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Other Benefits of Glass Bubble

2018-07-30 15:12:23 49

There are several other benefits of adding glass bubbles into polymers in addition to weight reduction. These can be outlined as improved warpage and dimensional stability, increased productivity due to faster cooling cycles, decreased coefficient of linear thermal expansion (CLTE), decreased acoustical transmission, increased bulk modulus, hardness, scratch resistance, and heat distortion temperature.

In injection molding, shrinkage and warpage constitutes a major problem resulting in decreased productivity. Comparing the geometry of glass bubbles to other fillers, the spheres stand out as being isotropic and create isotropic physical properties in composites. Since they are spherical they do not align in the polymer flow direction like high aspect ratio fillers such as fibers or talc and therefore have a better balance with respect to CLTE, impact, strength and other physical properties.

Glass bubbles decrease the amount of differential shrinkage which results in reduced warpage compared to high aspect ratio fillers are used. An example is shown in Figure 4 for glass fiber filled nylon 6 and talc filled PP. Differential shrinkage is shown as a result of different amounts and types of fillers as well as different post injection hold pressures (pack pressure). Differential shrinkage is higher in the cases where there is high aspect ratio filler present (fiber or talc) without glass bubbles.

Productivity improvements can occur with the addition of glass bubbles. This is due to faster cooling cycles such as in injection molding or thick extrusion profiles. The overall volumetric heat capacity of glass bubble filled polymers is lower than that of their unfilled counterparts resulting in faster cooling from the melt. A study was made at 3M on an injection molded cabin air filter frame where PP containing 20wt.% talc was reformulated by removing the talc and adding the same amount of glass bubble on a volume basis. Figure 5 shows the cycle as a function of time (seconds) for the talc system (PPTV20) vs. the glass bubble containing material (PPGB20). The optimized cycle was reduced 3.4 seconds with PPGB20 compared to a total cycle time of 16.6 seconds with PPTV20. This is a 20% reduction in cycle time or, stated in terms of productivity, a machine that is capacity constrained can make 20% more parts in a given period of time.

This article comes from appliancedesign edit released