The most complete hot runner mold related knowledge in history

One of the main functions of the hot runner is to keep the plastic melt in the hot runner at the correct processing temperature throughout the injection cycle, holding and cooling of the molding cycle. Thereby achieving no cold water outlet, reducing secondary processing, shortening the injection cycle, improving product consistency, achieving mass production and reducing production costs. This is followed by a relatively gentle transport of the plastic melt to minimize the pressure and shear stress applied to it. Thereby, the stress in the production, the injection pressure and the deformation of the product can be reduced, and the machining ability can be improved. The above advantages can be fully automated, improve user productivity, production profit and competitiveness.

Second, hot sputum, hot runner mold precautions

Shot amount

Appropriate hot nozzles should be selected according to the size of the rubber parts and different rubber compounds. Suppliers generally give the maximum amount of shots for each hot nozzle relative to a different flow compound. Because of the different materials, their fluidity is different. In addition, attention should be paid to the size of the nozzle opening of the hot nozzle, which not only affects the amount of shot, but also has other effects. If the nozzle opening is too small, the molding cycle will be extended; if the nozzle opening is too large, the nozzle opening is not easy to be closed, and it is easy to flow or draw.

2. Temperature control

The temperature of the hot nozzle and the hot runner plate is directly related to whether the mold can operate normally, and the temperature is generally controlled separately. Regardless of the internal heating or external heating method, the temperature in the hot nozzle and the hot runner plate should be kept uniform to prevent local overcooling and overheating. In addition, the power of the heater should be such that the hot nozzle and the hot runner plate can be raised from the normal temperature to the required working temperature within 0.5 to 1 h, and the heating time of the hot nozzle can be shorter.

3. Thermal insulation

The hot runner and the hot runner plate should have better insulation with other parts such as the mold panel and the A plate. The heat insulating medium can be used as a asbestos board or air. Except for the parts that need to be contacted, such as positioning, support, and sealing, the thickness of the insulating air gap of the hot nozzle is usually about 3 mm; the thickness of the insulating air gap of the hot runner board is not less than 8 mm.

The support between the hot runner plate and the mold panel and the A plate is a heat insulating block having a heat insulating property, and the heat insulating block is made of a material having a low heat transfer rate. The panels of the hot runners and hot runner molds should generally be covered with 6~10mm asbestos sheets or bakelite as insulation. The thickness of the insulation mat is generally 10 mm. In the above figure, in order to ensure good thermal insulation effect, the following requirements should be met: D1 ≥ 3mm; D2 is determined by the size of the hot sluice step; D3 ≥ 8mm, depending on the thickness of the central insulation block; D4 ≥ 8mm .

4. Insulation pad

The thermal insulation block between the hot runner plate and other parts of the mold not only acts as a heat insulator, but also supports the hot runner plate, the support point should be as small as possible, and the force is balanced to prevent deformation of the hot runner plate. For this reason, the insulation block should minimize the contact area with other parts of the mold.

5. Positioning

In order to prevent the rotation and overall offset of the hot runner plate and satisfy the thermal expansion of the hot runner plate, the hot runner plate is usually positioned by a combination of center positioning and groove positioning.

6. Thermal expansion

Since the hot runner and the hot runner plate are thermally expanded, the mold should be designed with a budget expansion amount, and the design size should be corrected so that the expanded hot nozzle and hot runner meet the design requirements. In addition, a certain gap should be reserved in the mold, and there should be no structure that restricts expansion. The hot boring nozzle mainly considers the axial thermal expansion amount, and the radial thermal expansion amount is corrected by the gap of the fitting portion; the hot runner plate mainly considers the length and width directions, and the thickness direction is adjusted by the gap between the heat insulating block and the stencil.