Also known as flash overflow, overflow edge, and so on, mostly in the mold closing position to score, such as: the parting surface, slide the slip position, insert the gap, porosity, etc. rams. Bur not resolved will be further expansion, thereby forming a partial imprint mold trap collapsed, causing permanent damage. Cracks and pores inserts ejector burrs also stuck in the mold of the article, the impact of the release.

Equipment:
(1) Machine genuine insufficient clamping force. When selecting the injection molding machine, clamping force rated machine to be higher than projected longitudinal tension injection molded article formed in the injection area, or will result in expansion mode, the occurrence of burrs.
Poor (2) adjust the clamping device, the toggle mechanism does not straighten, or left and right or up and down to produce uneven mold, mold parallel phenomena can not be achieved while the mold is closed and tight one side and the other side not of tight situations the occurrence of burrs during injection.
(3) The mold itself parallel poor, or not inserted parallel or not parallel template, or rod uneven force distribution, deformation unevenness, which will cause mold does not close and produce flash.
(4) loopback badly worn only; spring nozzle spring failure; cylinder or screw wear too much; the feed inlet cooling system failure caused by a "bridge" phenomenon; inadequate set-cylinder injection quantity, the cushion is too small, etc. may cause flash repeatedly, the importance of timely repair or replacement of parts.

Molds:
(1) mold parting surface accuracy is poor. Activity templates (such as plate) deformation warping; parting surface stained with foreign matter or mold frame surrounding protruding skid printing glitch; old die earlier flight because of fatigue side extrusion leaving the cavity surrounding the collapse.
(2) mold design unreasonable. The creation of the position of the mold cavity through partial, unilateral mold tension will make the injection occurs, causing flash; plastic good liquidity, such as polyethylene, polypropylene, nylon, etc., in a molten state low viscosity, easy access to activities or fixed slit, the higher requirements of the mold manufacturing precision; in without compromising the integrity of the product should be placed on the quality of the center of symmetry, the product thick part of the material, while the lack of material can be prevented with the burr side situation; when the product or near the center of the shaped hole, open side gate is customary in the hole, in the larger injection pressure, resulting in insufficient mold clamping force if the force is not enough to support this part of slight warping flash, such as when the mold side with active members on its side of the projected area is also affected by the molding pressure, if the support is not enough can also cause flash; sliding core with bad accuracy or fixed core and cavity installation position shift The formation of burrs; poor exhaust cavity in the mold parting line grooves or exhaust vent is not open ditch is too light or too dark or too large will cause foreign body obstruction by flash; for multi-cavity mold should be attention to the shunt closing gate design is reasonable, otherwise it will cause uneven force filling produce flash.

Technological aspects:
(1) injection or the injection pressure is too high too fast. Because of the high speed, the mold opening force increases lead to flash. To be adjusted according to product thickness injection speed and injection time, thin products use high-speed rapid filling, after filling into the note no longer; thick products use low-speed filling and let the skin before reaching the final pressure is generally fixed.
(2) caused by excessive charging flash. It is noteworthy that not to prevent excessive sag injected melt, so depressed may not be "filled", and flash it will appear. Application of this case to extend the injection time or dwell time to resolve.
(3) barrel, nozzle temperature is too high or the die temperature is too high will cause the plastic viscosity decreased, increased mobility, resulting in flash in the case of fluid into the mold.

Raw materials:
(1) plastic viscosity is too high or too low may occur burrs. Low viscosity plastics such as nylon, polyethylene, polypropylene, etc., should increase the clamping force; absorbent plastic or water-sensitive plastic at high temperatures will significantly reduce flow viscosity, increase the likelihood of burrs, These plastics must be completely dry; incorporation of recycled materials too many plastic viscosity will decline, if necessary, to supplement the residence ingredients. Plastic viscosity is too high, the flow resistance increases, resulting in back pressure so that the cavity pressure increase, resulting in insufficient clamping force and produce flash.
(2) particle size uneven plastic materials will increase quantity of flux, parts or complaints, or flash.