The possibility of black spots in injection molds
Injection molds are also one of the common types of molds. In the manufacturing process, we often find black spots or cause discoloration and coking during injection molding. This is a common problem in the manufacture of injection molds. The main cause of this problem is plastic or The added ultraviolet absorber, antistatic agent and the like are decomposed by overheating in the cylinder, or the residence time in the cylinder is too long, so that decomposition and coking are formed, and the melt is injected into the cavity. In order to avoid these problems, we can analyze from the following four aspects:
1. Machine side:
(1) Due to the loss of control of the heating control system, the barrel is overheated and the decomposition is blackened.
(2) Due to the defects of the screw or the barrel, the melt is caught and accumulated, and it is subjected to long-time fixed heating to cause decomposition. The plastic head kit should be inspected for wear or metal foreign objects.
(3) Some plastics, such as ABS, are subjected to high heat in the cylinder and cross-linked and coked. Under the condition of almost maintaining the original particle shape, it is difficult to melt, and is crushed by the screw to be entrained into the workpiece.
2, the mold side:
(1) The mold is not exhausted, it is easy to burn, or the size of the pouring system is too small, and the shearing is too strong to cause coking.
(2) There are improper oil lubricants and mold release agents in the mold.
The plastic has too much volatile matter, too much humidity, too much impurities, too much recycled material, and is contaminated.
(1) The pressure is too large, the speed is too high, the back pressure is too large, and the speed is too fast, the material temperature is decomposed.
(2) The barrel should be cleaned regularly to remove additives that are less resistant than plastic.