Two color mold pressure holding four major considerations

Two color mold pressure holding four major considerations:

    The function of the pressure-holding phase of the two-color mold is to continuously apply pressure, compact the melt, and increase the density of the plastic to compensate for the shrinkage behavior of the plastic. This article Dongguan Rongsheng Industrial will briefly explain the precautions for the pressure holding of the two-color injection mold.

First, in the pressure holding stage, due to the relatively high pressure, the plastic exhibits partial compressibility. In the higher pressure areas, the plastic is denser and has a higher density; in the lower pressure areas, the plastic is looser and the density is lower, thus causing the density distribution to change with position and time.

Second, in the two-color mold holding process, because the cavity is filled with plastic, the back pressure is higher. During the pressure-preserving compaction process, the screw of the injection molding machine can only slowly move forward slightly, and the flow speed of the plastic is also slow. The flow at this time is called pressure-holding flow. Since the plastic is accelerated and solidified by the mold wall during the pressure holding stage, the melt viscosity is also increased rapidly, so the resistance in the mold cavity is large.

Third, the plastic flow rate during the pressure holding process is extremely low, and the flow no longer plays a leading role; the pressure is the main factor affecting the pressure holding process. During the packing process, the plastic has filled the cavity, and the gradually solidified melt acts as a medium for transmitting pressure. The pressure in the cavity is transferred to the surface of the mold wall by means of plastic, which has a tendency to open the mold, so that a suitable clamping force is required for the mold clamping. The mold-up force will slightly open the injection mold under normal conditions, which is helpful for the exhaust of the two-color injection mold; however, if the mold-up force is too large, the molded product may be burred, overflowed, or even opened.

4. In the later stage of the two-color mold holding pressure, the material density continues to increase, the plastic parts are gradually formed, and the pressure holding stage is continued until the gate is solidified and sealed. At this time, the cavity pressure in the pressure holding stage reaches a high value.