Combined injection device for pushing molten HDPE (high-density polyethylene)

The combined injection device for pushing the molten HDPE comprises a charging barrel and a gun head, a pressure relief head is additionally arranged between the charging barrel and the gun head, a plurality of pressure relief holes are formed in the contact position of the charging barrel and the inner end of the pressure relief head, and the inner end of the pressure relief head blocks the pressure relief holes; and the charging barrel, the pressure relief head and the gun head are communicated. The outer end of the pressure relief head is a flange plate, the outer diameter of the flange plate is matched with that of the charging barrel, and the flange plate is connected with the end face of the charging barrel through a plurality of bolts; the outer diameter of the inner end of the pressure relief head is in interference fit with the inner diameter of the charging barrel, a groove is formed between a flange plate of the pressure relief head and the inner end, and a pin penetrates through a pin hole in the