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Foam injection eliminates need for defect-hiding textured surfaces

A new process for molding airbag covers promises a 30% reduction in the amount of material used, less distortion in finished parts, and easier designing for engineers. At K 2013, Research institute Fraunhofer Institute for Chemical Technology ICT (Pfinztal, Germany; Stand 7/B05) will showcase thermoplastic foam injection (FIM) as a means to produce structural parts like airbag covers without the striations that can form during standard foam injection.

September 30, 2013

2 Min Read
Foam injection eliminates need for defect-hiding textured surfaces

A new process for molding airbag covers promises a 30% reduction in the amount of material used, less distortion in finished parts, and easier designing for engineers. At K 2013, Research institute Fraunhofer Institute for Chemical Technology ICT (Pfinztal, Germany; Stand 7/B05) will showcase thermoplastic foam injection (FIM) as a means to produce structural parts like airbag covers without the striations that can form during standard foam injection. Typically those surface marks are hidden thanks to the textured appearance. Fraunhofer Institute for Chemical Technology ICT (Pfinztal, Germany), now believe they can eliminate these striations, making the FIM the process suitable for highly visible components without the need for a textured surface.

A FIM machine operates as a standard injection press would, with one key difference: it introduces a propellant into the melt, and when this mixture is sprayed into the mold, the air pressure drops dramatically. Fraunhofer compares it to carbonated liquid in a bottle which is shaken, then opened. The reaction converts the polymer into a foam. The finished part is therefore not isopycnic, meaning equally dense inside and out, but instead has a structure more like a sandwich, with the softer foam on the interior, while the outer surface is solid and hard.

Fraunhofer notes that in a standard process, striations appear because the hot polymer melt forms foam bubbles as it flows through the cooled tooling. These bubbles are compressed by pressure of the melted polymer against the tooling, so that the irregularities become rigid along with the melt and remain visible at the surface of the finished piece. ICT researcher Andreas Menrath said FIM avoids the formation of striations by differentially heating the tooling. The polymer remains malleable longer due to the higher tooling temperatures it comes into contact with during injection. In this way, the bubbles do not become rigid immediately, but instead the surface is pressed smooth.

The researchers are also working on an additional means to prevent striations, including insulating the tooling so that it retains the heat within the polymer longer. The engineers are presently testing various materials and coating thicknesses. The scientists will be displaying an FIM machine at K producing foam-injected frisbees right on site.
 

Glass-based coating lends scratch resistance
Researchers of the Institute of Interfacial Process Engineering and Plasma Technology (IGVP) have also developed a new glass-based coating in conjunction with Fraunhofer, which will be featured at K. The scientists have combined light weight and hardness, utilizing the high-rate deposition of a glass layer by plasma technology and eliminating the need to apply paint or varnish. The researchers will be displaying this new coating on a sample frisbee at K.
 

Recycled Styropor
An additional frisbee consisting of recycled Styropor will be shown, reclaiming a materials—expanded polystyrene—that has always been considered unrecyclable. The CreaSolv process produces recycled plastics whose quality is just as high as virgin plastic.

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