• Composites Research
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• v.23 no.5
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• pp.30-38
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• 2010

Observing of GMT-Sheet in molding conditions, we have investigated unexpected phenomenons of moldings surface. In microscope investigation, we observe that there exist deficiencies on the surface of GMT-Sheet moldings, such as the spherulite, fiber projection, crack, fiber exposure, micro-weldline, pinhole and winding. They are caused to arise unevenness and phenomenons influence polish on surface. Especially, the major cause of the unevenness, effected to surface roughness, is a shrinking of matrix in the process of holding pressure and cooling temperature. The higher holding pressure load in a molding process and the lower demolding temperature in an annealing experiment, the better GMT-Sheet moldings improved its appearance.

• Composites Research
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• v.24 no.6
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• pp.31-36
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• 2011

According to the evaluation on GMT-sheet by molding conditions, fiber projection on the moldings surface was investigated. Fiber projection is one of the major defects on moldings surface due to matrix shrinkage. That is, fiber projection happens from different shrinkage of matrix and glass fiber. Height of fiber projection from moldings surface becomes smaller when molding pressure is higher during holding pressure and cooling process. Height of fiber projection is dominantly affected by molding pressure. With consideration of molding pressure, the formation of surface unevenness and change in fiber projection height was elucidated. In addition, coating layer is effective to suppress surface defects, and there is no fiber projection or crack in case that coating is applied. Coating layer improves surface roughness up to the level of the polypropylene which is a single material.