With rapid development of social economy, our lives are almost inseparable from convenience brought to us by plastics, quality standards for plastic products are becoming more and more stringent and refined. Control of mold temperature is an important consideration in injection molding process. It will not only be reflected in performance and appearance of product, but also production efficiency of product is also closely related to control of mold temperature.
In injection molding, about 80% of time of a product is spent on reducing heat of mold and cooling product to shape. When mold temperature is too low, it will cause scratches, cracks, cold material lines and other defects. At this time, heating system is needed to control mold to reach a certain temperature, thereby improving fluidity of material and cooling rate of mold.
Control of mold temperature should be adjusted according to performance of material, working environment, mold structure, quality requirements, etc. After mold is kept at a constant temperature, stability and consistency of product should be guaranteed during mass production. Following factors mainly affect mold temperature:

1) Cooling channel should be close to shape of glue surface. The most suitable distance between cooling channel and product glue surface should be 10-15mm to ensure that mold can quickly transfer temperature.
2) When height difference of glue surface is large or glue is thick, it is necessary to "dig a water well" to ensure that temperature of each area of mold is consistent.
3) When designing water channel, head diameter of nozzle should be larger than diameter of water channel to ensure that water flow inside and outside mold is same. It is best to use a 1/8 nozzle for a water channel with a diameter of 6, a 1/4 nozzle for a water channel with a diameter of 8, a 3/8 nozzle for a water channel with a diameter of 10, and a 1/2 nozzle for a water channel with a diameter of 12.
4) Pipes are evenly arranged, and distance between pipes should not be too far or too close. Interval between pipes is 3 to 4 times diameter of water channel for the best cooling effect.
5) When processing water channels, it is usually processed by a radial drill, and processing error is relatively large. It should be noted that distance between water channel and insert, ejector pin, and screw should not be less than 4mm to prevent water channel from breaking hole position.
6) When using water as a medium to control mold temperature, after production is completed, clean residual water in mold water channel in time when machine is removed to prevent pipeline from rusting and corrosion and scale from clogging pipeline, reducing mold transfer effect and cooling rate.
7) Number of series water channels of surrounding water channel should not be too many. Under premise of structural permission, water hole diameter should be the maximum. When mold water channel circulates, inlet and outlet water are best controlled at 3℃-5℃ mold temperature.

 

Nowadays, there are more and more types of plastics. Different manufacturers produce raw material fillers and proportions with different materials. Thermal conductivity, thermal deformation temperature, and specific heat capacity of materials are different. Manufacturers need to provide data in production. There are many mold temperature ranges for materials on Internet. In actual production, selection of mold temperature should be based on process cards and work experience as a reference, maintaining a constant production rhythm and cooling time, applying mold temperature according to actual production conditions and quality requirements. There is no uniformity and planning.
There are two main types of mold temperature control:
Chiller: During mass production, as mold opens and closes, mold temperature will increase. If only circulating water is used, it can only play a cooling role, and water temperature cannot be accurately controlled. Therefore, adding a chiller to reduce mold temperature can shorten cycle and improve productivity. Control accuracy is about 5 degrees.
Temperature controller: Temperature controller uses oil or water as a medium and has function of increasing and stabilizing mold temperature. During mass production, mold temperature exceeds set temperature value of controller. Controller of temperature controller opens water inlet pipe to cool mold to set value. When mold temperature is lower than set value of temperature controller, controller will turn on heating system to increase mold temperature. Control accuracy of temperature controller is 0.1℃, which can effectively improve fluidity of material and size and surface finish of product.
Following material mold temperature range table is for reference only.

1) Due to material properties and mold structure, mold temperature is too low after product is molded, and there will be molding defects such as cracking, demolding scratches, and poor finish. For example: transparent products made of PS materials will produce stress cracking after product is taken out. Increasing local temperature of mold temperature (connecting slider with hot water) can solve this defect well.
2) As mentioned in 1-7, temperature difference between inlet and outlet water is controlled at 3℃-5℃, but long-term use of mold will inevitably cause water blockage. As shown in figure, when water flow direction is from top and out from bottom, product ribs are deformed after ejection. When water flow direction is changed to enter from bottom and exit from top, product does not deform after ejection.

 

3) When there are many water channels in mold, straight-through water transportation is usually changed to a surrounding (series) water transportation when mold is installed. However, in production, because current carrying capacity of water flow becomes smaller, (as shown in figure for long strip products) temperature at the bottom of mold core will be lower than top, upper and lower mold temperatures are inconsistent, resulting in warping and deformation of product after removal.