Hot runner mold can be divided into open hot runner mold and needle valve hot runner mold.
Because the open hot runner can be injected into the mold by breaking through the condensing gate when the injection machine screw is advancing, the glue outlet can be closed by condensing with the gate when the screw is retreating in the injection machine. Therefore, the size of the gate is usually very important, otherwise due to the temperature of the gate area, either condensation blocks the hot nozzle can not shoot glue, or there is wire drawing and salivation at the hot nozzle. There is also a screw backward if the gate can not be condensed at the same time, the mold cavity will form a reverse suction, is not conducive to the cavity pressure. Commonly used little gate hot runner, straight gate hot runner, submerged gate hot runner with diverter. Because the open hot runner structure is simple, the mold processing is simple and the maintenance cost is low, and the appearance requirements of the injection product are not too high or the procurement cost is considered, there is no water nozzle or very little water nozzle after use, so there are still more users using this hot runner. Commonly used little gate hot runner, straight gate hot runner, submerged gate hot runner with diverter.
In the needle valve hot runner, when the hot nozzle gate is injected with the injection machine screw, the valve needle can be adjusted in order to open the gate and shoot glue through the gas (liquid) pressure, which can adjust the water line, shrinkage and warping of the product appearance. On the contrary, when the screw in the injection machine recedes, the valve pin can be adjusted in sequence by gas (liquid) pressure without spraying glue. This kind of sequential control can also compensate the defect of uneven filling of cavity when multiple hot nozzle shoot glue at the same time. In addition, the needle valve hot runner gate is made slightly larger, reducing the shear heat of the glue mouth, by instantly opening and instantly closing the glue mouth, the cavity is filled quickly, the pressure is good, there is no wire drawing and salivating, and the needle valve hot runner can be used for the laminated cavity mold and multi-cavity family product injection molding. Needle valve hot runner structure is relatively complex, the mold processing accuracy and maintenance is relatively high, although the user due to the consideration of procurement costs, but it has many advantages, it is also used by most users.
Needle valve hot runner is divided into cylinder type hot runner, cylinder type hot runner and spring type hot runner. The hot runner of cylinder type needle valve uses air pressure to push the valve needle to open or close the gate to complete the injection mode. This mode 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, the air pressure is limited, and it is also used by a large number of users. Because the hot runner of the cylinder needle valve adopts 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 tube into the hot runner cylinder. This method is often used for the injection molding of plastic parts with large surface area and large wall thickness because of the large hydraulic pressure. The spring-type needle valve hot runner uses the locking spring compression mode 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 convenient to use and fewer users.