Hot runner molds can be divided into open hot runner molds and needle valve hot runner molds.
Because the open hot runner is injected into the mold by breaking through the condensation gate when the injection machine screw advances, on the contrary, when the screw retreats in the injection machine, the glue outlet can be closed with the gate condensing. Therefore, it is usually very important to choose the size of the gate. Otherwise, due to the temperature in the gate area, either condensation will block the hot nozzle and no glue will be injected, or there will be wire drawing at the gate of the hot nozzle and drooling. In addition, if the gate cannot be condensed at the same time when the screw retreats, a reverse suction force will be formed on the mold cavity, which is not conducive to maintaining the cavity pressure. Commonly used gate hot runners, straight gate hot runners, and submerged gate hot runners with split runners. Due to the simple structure of the open hot runner, the mold processing is simple and the maintenance cost is low, and the requirements for the appearance of the injection product are not too high or the purchase cost is considered, there is no nozzle or few nozzles after use, so use this kind of There are still many users of hot runners. Commonly used gate hot runners, straight gate hot runners, and submerged gate hot runners with split runners.

For the needle valve type hot runner, when the gate of the hot nozzle is injected with the screw of the injection machine during injection of multiple hot nozzles in one mold, the valve needle can be adjusted to open the gate in sequence through the gas (liquid) pressure to inject the glue. Adjust the water line, shrinkage and warpage of the product appearance. On the contrary, when the screw in the injection machine moves backward, the valve needle can be adjusted in sequence to close the gate without injecting glue through the gas (hydraulic) pressure. This sequential control can also compensate for the defect of uneven filling of the cavity when multiple hot nozzles are shot at the same time. In addition, the needle valve type hot runner gate is made slightly larger to reduce the shear heat of the glue outlet. By instantaneously opening and closing the glue outlet, the cavity is filled quickly, the pressure is kept well, and there is no wire drawing and drooling. The needle valve type hot runner is only possible for the injection molding of laminated cavity molds and multi-cavity family products. The needle valve type hot runner structure is relatively complex, and the machining accuracy and maintenance of the mold are relatively high. Although the user considers the purchase cost, it has many advantages and is also adopted by most users.
The needle valve type hot runner is divided into three types: cylinder type needle valve hot runner, oil cylinder type needle valve hot runner and spring type needle valve hot runner. The cylinder type needle valve hot runner uses air pressure to push the valve needle to open or close the gate to complete the injection mode. This method is convenient to use because there is ready-made compressed air in the injection workshop, and the air connection pipe is directly input into the hot runner cylinder. However, the air pressure is limited and is also used by a large number of users. The cylinder type needle valve hot runner uses hydraulic pressure to push the valve needle to open or close the gate to complete the injection mode. It needs to be connected to the oil pressure pipe and input into the hot runner cylinder. This method is often used for large surface area and large wall thickness due to large hydraulic pressure. injection molding of plastic parts. The spring-type needle valve hot runner adopts the locking spring compression method to push the valve needle to open or close the gate to complete the injection mode. The pressure adjustment is relatively small, but it is easy to use and has fewer users.