The control of the mold temperature is an important consideration in the injection molding process. Not only will it be reflected in the performance and appearance of the product, but the production efficiency of the product will also have a great relationship with the control of the mold temperature.
In injection molding, about 80% of a product’s time is used to reduce heat in the mold and cool the product. If the mold temperature is too low, it will cause defects such as scratches, cracks, and cold lines. At this time, a heating system is required to control the mold to reach a certain temperature, thereby improving the fluidity of the material and the cooling rate of the mold.
The control of the mold temperature should be adjusted according to the material performance, working environment, mold structure, quality requirements, etc. When the mold is keep the stable temperature, the stability and consistency of the product must be guaranteed during mass production. The following factors that affect the mold temperature:
1.Design of water channels in the plastic injection mold
1) The cooling pipe should be close to the shape of the glue level surface. The optimal distance between the cooling pipe and the glue level surface of the product should be 10-15mm to ensure that the mold can quickly transfer the temperature.
2) When the height difference of the glue level surface is large or the glue level is thick, it is necessary to “drain well” to ensure the temperature of each area of the mold is consistent.
In the plastic mold design, the diameter of the head of the water connector is larger than the diameter of the water channel to ensure that the excess water circulation inside and outside the mold is the same.
For waterways with a diameter of 6 it is best to use 1/8 nozzles, for a waterway with a diameter of 8 it is better to use 1/4 water nozzles, for a water channel with a diameter of 10 it is better to use 3/8 water nozzles and a water channel with a diameter of 12 It is best to use a 1/2 tap.
4) The pipes are evenly arranged, the distance between the pipes cannot be too far or too close, and the distance between the pipes and the pipes is 3 to 4 times the diameter of the waterway. The cooling effect is the best.
5) When processing the water channel, it is usually processed by a rocker drill. The processing error is relatively large. It should be noted that the distance of the water channel from the insert, thimble, and screw must be at least 4mm to prevent the water channel from breaking the hole.
6) When using water as a medium to control the temperature of the mold, after the production is completed, the residual water in the mold water channel should be cleaned up in time to prevent the pipeline from rusting and corroding and blocking the pipeline with scale, reducing the mold transfer effect and cooling rate.
The number of serial channels of the surrounding water channel should not be too much. Under the premise of the structure, the diameter of the water hole should be the maximum amount. The temperature of the inlet and outlet water is optimally controlled at 3℃-5℃ during the circulation of the mold water channel.
Nowadays, there are more and more types of plastics. Different manufacturers have different raw material fillers and ratios. The materials have different thermal conductivity, thermal deformation temperature, and specific heat capacity. In the production, manufacturers need to provide data. There are many injection mold temperature ranges of materials on the network. In actual production, the choice of injection mold temperature should be based on the process card and work experience as a reference, maintaining a constant production cycle and cooling time, and applying the mold temperature according to actual production conditions and quality requirements. There is no uniformity and planning.
For injection mold，
Water chiller: During mass production, the temperature of the mould will increase with the opening and closing of the mould. If only the circulating water is used, it can only play the role of cooling, and the water temperature cannot be accurately controlled. Therefore, cold water is added at this time. The machine lowers the mold temperature to shorten the cycle and increase productivity. The control accuracy is about 5 degrees.
Thermostat: The thermostat uses oil or water as the medium, which has the effect of increasing and stabilizing the mold temperature. During mass production, the injection mold temperature exceeds the set temperature of the controller. The controller of the thermostat opens the water inlet pipe and cools the injection mold until the set value. When the mold temperature is lower than the set value of the thermostat, the controller will Turn on the heating system and raise the injection mold temperature. The control accuracy of the thermostat is 0.1℃, which can effectively improve the fluidity of the material, and the size and surface finish of the product.
3.The connection method of the external pipe of the mold
1) Due to the material properties and injection mold structure, after the
product is molded, mold defects such as cracks, mold release scratches, and poor finish will occur due to the injection mold temperature being too low. For example: the transparent product produced by using the ps material, stress cracking occurs after the product is taken out, the local temperature of the injection mold temperature is raised, (the slider is connected with hot water), which can solve this defect well for injection mold.
2) As mentioned in 1-7, the temperature difference between the inlet and outlet water is controlled at 3℃-5℃, but due to the long-term use of the injection mold, it will inevitably cause water blockage, as shown in the figure, when the water flow direction, the inlet water walks from above, When it comes out below, the product tends to deform after being pushed out. However, when the direction of the water flow is changed, the product enters from below and exits from above, the product does not appear to be deformed by ejection.
3) When there are many water channels in the injection mold, when the mold is reinstalled, the straight-through water transport is usually changed to the wrap-around (series) water transport, but in production, the current carrying capacity becomes smaller, (as shown in the figure (Long products shown) The temperature of the lower end of the injection mold core will be lower than the upper end, and the temperature of the upper and lower injection molds will be inconsistent, resulting in warpage and deformation after the product is taken out.