When the melt is injected into a cavity with a large volume under high-speed and high-pressure conditions, melt fracture is very easy to occur. At this time, the surface of the melt appears transverse fracture, and the fracture area is roughly mixed on the surface of the plastic part to form a paste spot. Especially when a small amount of melt is directly injected into the cavity that is prone to be too large, the melt fracture will be more serious, and the paste spot will be larger. The nature of melt fracture is caused by the elastic behavior of the polymer melt. When the melt flows in the barrel, the melt near the barrel is rubbed by the barrel wall, and the negative force is large, and the flow speed of the melt Smaller, once the melt is injected from the nozzle, the negative force acting on the tube wall disappears, and the flow rate of the melt in the middle of the barrel is extremely high. The melt at the barrel wall is carried by the melt at the center and accelerated. Th...