Flash, also known as overflow, overflow, and blade, mostly occurs in the mold separation position, such as: the parting surface of the mold, the sliding mechanism, the exhaust hole, the exhaust pin, the gap of the insert, the pore of the ejector rod, etc.

(1) Materials

The viscosity of the material is too low. Highly absorbent or water-sensitive plastics will greatly reduce the flow viscosity and increase the possibility of flashing;
The viscosity of the material is too high, resulting in an increase in flow resistance, a large back pressure is generated, and the cavity pressure is increased, resulting in insufficient clamping force and flash.

(2) Mold

There are foreign bodies on the parting surface or protruding burrs around the template;
The accuracy of the mold parting surface is poor, and the movable template is warped and deformed;
insufficient mold stiffness;
The mold design is unreasonable, and the opening position of the mold cavity is too biased, which will cause tension on one side of the mold during injection, causing flash.

(3) Molding process.

Excessive injection volume;
Injection pressure is too high or injection speed is too fast;
The clamping force is set too low;
The holding pressure is too high, and the speed and pressure are switched too late;
The melt or mold temperature is too high.

(4) Injection machine

Insufficient clamping force of the injection machine;
The clamping device is poorly adjusted, and the clamping force is applied unevenly
The check ring is seriously worn, or the barrel and screw are too worn
The parallelism of the mold is not good, the installation is not parallel, or the force and deformation of the tie rod are unevenly distributed.

(1) If the flash phenomenon occurs in the filling stage, the possible solutions are as follows:

• If the mold is damaged or there is an error in the parting surface fit, the mold needs to be modified;
• Appropriately reduce the injection speed or the temperature of the plastic;
• Reduce the thermal deformation of the mold by adding a gasket in the center of the template.

(2) If the flash phenomenon occurs in the shrinkage stage, the possible solutions are as follows:

• Reduce the feeding pressure or reduce the feeding rate, and check whether the clamping force is appropriate;
• The injection speed is too slow, and the material has a large effective viscosity, resulting in an increase in pressure loss in the mold cavity, check and analyze the reasons for the change of the effective viscosity of the material, and adjust the injection process according to the specific causes;
• Detect the deformation of the mold and solve the deformation of the mold.