Key Design Techniques for injection mold cooling system

Time:2019-08-19 09:09:24 / Popularity: / Source:

Injection mold cooling system is a core part of mold and is very important for entire injection molding. Injection mold cooling system removes heat transferred from high-temperature plastic to mold as quickly as possible, thereby keeping temperature of mold within a certain range, and allowing product to cool quickly and obtain the best product quality.
In order to improve production efficiency and ensure product quality, design of injection mold cooling system should follow following principles:

Reasonably determine size and spacing of cooling water holes

Distribution of mold temperature is closely related to size and density of water holes. The larger pore size of cooling water hole, the denser arrangement between water holes, and the more uniform mold temperature distribution. In general, it is more common to have a center-to-center distance between pipes of 3 to 5 times diameter. Cooling ducts shown in Figures 2-3a) and b) ensure that temperature distribution on the surface of cavity is uniform, and structure shown in Figure 2-3 c), d) is too large due to distance between cooling pipes. Temperature distribution on the surface of cavity is very large, ranging from 45℃ to 61.66℃, resulting in uneven shrinkage of all parts of product.

Distance between cooling pipe and surface of cavity should be reasonable.

Distance and thermal resistance are too large, which will reduce cooling efficiency; and if distance is too small, which causes surface temperature of cavity to be uneven. According to experience, it is suitable that distance from cooling channel to surface of cavity is between 1 and 2 times diameter of pipe. For parts with constant thickness, distance from water hole to surface of cavity is preferably equal for uniform cooling. As shown in Figure 2-4, a) is better than b). For parts with varying thickness, cooling should be enhanced at wall thickness. Figure c) is better than b).
Injection mold cooling system 

Water is paralleled to enhance cooling at the gate

Since melt is injected into cavity from gate, temperature near gate is the highest, it is necessary to strengthen cooling near gate, use this as population of coolant, and make overall flow direction of cooling water tends to be same as direction in which plastic melt flows (water is parallel). Figure 2-5a) shows cooling water path at the center of gate; Figure 2-5b) shows cooling water path for film gate.
Injection mold cooling system 

Minimize temperature difference between water and inlet water of mold cooling pipe

Coolant has an endothermic process in mold, and outlet water temperature is higher than inlet water temperature. However, if temperature difference between these two is too large, surface temperature of cavity is uneven, which may cause uneven cooling of plastic parts, especially for relatively large plastic parts, this effect is more obvious. Therefore, in order to make cooling rate of whole product substantially same, in addition to shortening cooling circuit, arrangement of cooling water channels can be reasonably arranged to effectively reduce temperature difference between water and inlet of cooling pipe. Design of cooling duct in the form of Figure 2-6a) is not very reasonable.
Injection mold cooling system 

Layout of waterway should take into account structure of plastic parts and nature of plastic

For different plastic parts, layout of cooling circuit should take into account particularity of its size and shape. As shown in Figure 2-7a), cooling circuit arrangement of thin-plate plastic parts is arranged. Moving and fixed-mode cooling water holes are equally spaced from cavity; Figure 2-7b) shows cooling water path arrangement of a medium-thickness curved plastic parts, distance between cooling water hole of die and cavity, and punch drill oblique hole obtains a loop similar to shape of cavity. Different plastics will have different shrinkage rates, and there will be differences in the arrangement of cooling waterways.
Injection mold cooling system 
Injection mold cooling system 

Joints of cooling water pipes should be designed on the same side of mold

Cooling channels are connected by hoses. For convenience of connection and space reduction, it is best to design on the same side of mold. Water pipe joint should be lower than outer surface of mold to prevent damage to mold handling joint and affect sealing of cooling water channel. At the same time, in order not to affect operation of workers, joints are generally placed on the back of injection molding machine. Structural design of cooling water channel must pay attention to its processing technology, and it is easy to process and manufacture, and simple processing such as drilling is used as much as possible. For panel-mounted cooling water channel, pay attention to waterway seal to prevent cooling water from leaking into cavity and causing cavity to rust.

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