Crazing is silvery white filamentous speckle occurring on the surface or near-surface of injection products along the direction of melt flow. It is resulted from the moving of gas in the resin which is then stored in between the melt and surface wall of cavity and subsequently crushed. Crazing sometimes is also called mica mark, silver line or silver speckle.

The most essential reason for the occurrence of crazing is that volatile gas is contained in the melt, withal the following measures can be taken:

1) As for raw materials. In allusion to degradation gas crazing, resins with uniform granularity are

required to be used, dosage of recycled materials should be reduced, promptly clear the remnant foreign materials in the barrel, and when necessary replace the additives such as lubricating agent which can decompose easily; in allusion to aqueous vapor crazing, the plastic raw materials should be strictly dried and the plastication back pressure of screw should be improved.

2)  As for molding technics. In allusion to degradation crazing, the temperature of barrel and nozzle should be reduced, the retention time of melt in the barrel should be shortened to avoid partial temperature rising, properly reduce plastication and injection pressure to avoid high temperature of materials under high pressure; in allusion to aqueous vapor crazing, properly raise plastication pressure, increase compression ratio of screw, reduce rotation speed of screw and use barrel and screw with exhausting function.

3)  As for mold design and injection operation. In allusion to degradation crazing, properly increase section dimension of sprue, runner as well as gate, reduce shearing rate of melt, expand space of cold-slug well and improve exhausting condition of molds; in allusion to aqueous vapor crazing, add mold exhausting channel, check whether the cooling water channel is leaking and whether the surface wall of cavity is affixed with moisture.