Plastic mold injection molding how to prevent plastic melt rupture

　　When the melt is injected into the cavity with large volume at high speed and high pressure, the melt rupture phenomenon is extremely easy to occur. At this time, transverse fracture occurs on the melt surface, and the fracture area is rough enough to form paste spots on the surface of the plastic parts. Especially when a small amount of molten material is directly injected into the cavity which is easy to be too large, the melt rupture is more serious and the paste spot is larger.
　　The essence of the melt fracture is due to the elastic behavior of polymer melt material, when the liquid flow in the cylinder, close to the cylinder near the wall friction, melting Yin force is bigger, the speed of the flow of the molten material smaller, once the molten material from the nozzle outlet, Yin forces on pipe wall disappeared, and the central cylinder of liquid flow rate is extremely high, are compared.in the molten material is the center of molten material carrying and accelerate, due to the flow of the molten material is relatively continuous, inside and outside the flow of the molten material will rearrange the speed, average speed.
　　In this process, the melt will undergo a sharp change in stress and strain. Due to the extremely fast injection speed, the stress received is particularly large, far greater than the strain capacity of the melt, resulting in melt fracture.
　　If molten material in the flow channel in case of sudden change of shape, such as diameter shrinkage, expand and dead Angle, etc., molten material stay in the corner and circulation, it is different from the normal force of melting, shear deformation is bigger, when its mixed in the normal flow of material out, because of the inconsistent deformation recovery, can not close, if the disparity is very big, the fracture rupture occurred, the form is also melt fracture.
It can be seen from the above that it is necessary to overcome the breakdown of trapped melt and avoid the occurrence of paste spots:
　　The first is to pay attention to eliminate the blind Angle in the flow channel, make the flow channel as streamline as possible;
　　The second is to increase the material temperature, reduce the melting material relaxation time, so that the deformation easy to restore and bridge;
　　The third is to add low molecular weight in the raw material, because the lower the molecular weight of the melt, the wider the distribution, the more conducive to reduce the elastic effect;
　　The fourth is the appropriate control of injection speed and screw speed;
　　Fifth, it is very important to set the gate position reasonably and choose the right gate form. Practice shows that it is ideal to use the enlarged point gate and the latent gate (tunnel gate). The best choice for the location of the gate is to inject the molten material into the transition cavity before entering the larger cavity, so that the flow material does not directly enter the larger cavity.