Because an open hot runner can only be injected into the mold by breaking through the condensation gate when the injection machine screw advances, and conversely, it can only be closed by condensing with the gate when the screw retreats inside the injection machine. So the selection of gate size is usually quite important, otherwise due to the temperature in the gate area, either condensation will block the hot nozzle and prevent the injection of glue, or there will be wire drawing and drooling at the hot nozzle gate. When the screw retreats, if the sprue cannot condense at the same time, it will create a reverse suction force on the mold cavity, which is not conducive to maintaining pressure in the cavity. Commonly used hot runners include sprue hot runners, straight sprue hot runners, and submerged sprue hot runners with branch runners. Due to its simple structure, easy mold processing, and low maintenance costs, as well as the fact that the appearance requirements for injection products are not too high or procurement costs are taken into account, there are still many users who use this type of hot runner without water or very few water nozzles after use. Commonly used hot runners include sprue hot runners, straight sprue hot runners, and submerged sprue hot runners with branch runners.

The needle valve type hot runner, when the gate of the hot nozzle moves forward with the screw of the injection machine during the injection of the first mock examination with multiple hot nozzles, can adjust the valve needle to open the gate and inject glue in order through the gas (liquid) pressure, which can adjust the water inclusion line, shrinkage, warpage and other problems of the product appearance. On the contrary, when the screw in the injection machine retracts, the valve needle can be adjusted in order by gas (liquid) pressure to close the gate without injecting glue. This sequential control can also compensate for the uneven filling of the mold cavity when multiple nozzles are simultaneously spraying glue. In addition, the needle valve type hot runner gate is made slightly larger to reduce the shear heat at the glue outlet. By instantly opening and closing the glue outlet, the mold cavity is filled quickly, the pressure is maintained well, and there is no drawing or drooling. The needle valve type hot runner can be used for injection molding of laminated cavity molds and multi cavity family products. The needle valve type hot runner structure is relatively complex and requires high precision and maintenance for mold processing. Although users consider purchasing costs, it has many advantages and is also adopted by most users.

Needle valve hot runner is divided into three types: cylinder type needle valve hot runner, 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 readily available compressed air in the injection workshop, and the connecting pipe is directly input into the hot runner cylinder. However, due to limited air pressure, it is also widely used by users. The oil cylinder 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 an oil pressure pipe and input into the hot runner oil cylinder. This method is commonly used for injection molding of plastic parts with large surface area and wall thickness due to the high hydraulic pressure. The spring type needle valve hot runner adopts a 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.