8 precautions for mold design: temperature control system design

Time:2021-06-06 11:47:21 / Popularity: / Source:

Temperature control system design:
1. In design of automotive injection molds, each mold needs to use Moldflow software for cooling deformation analysis during design process, then adjust temperature control design system for areas with large product deformations or areas with high molding temperatures.
2. Design cooling water circuit for fixed mold as far as possible in accordance with shape of product.
3. Three-meter principle: Total length of cooling water path (length in series) should not be too long in design, preferably within 1.5~2M.
4. Center distance between cooling water channels is generally 5 to 7 times diameter of water hole.
5. Crossing angle of inclination waterway is less than or equal to 35°.
6. Length of dead water produced by intersection of two waterways is not easily greater than 100MM.
7. Hot runner nozzle must be equipped with a cooling water circuit, cooling system should be designed separately as much as possible.
8. Inlet and outlet of cooling water circuit should be designed as far as possible on non-operating side of molding machine personnel.
9. Try to avoid sloping waterways connecting to core waterways, and do not design double-angle waterways.
10. Generally, medium and large molds must be equipped with ground water collection blocks to achieve the best cooling water circuit.
Mold temperature has a great influence on molding quality and molding efficiency of rubber parts. In a mold with a higher temperature, molten rubber has better fluidity, which is conducive to filling cavity with rubber and obtaining a high-quality surface of rubber part, but it will make rubber curing time longer and easy to deform when ejected. For crystalline rubber, it is more conducive to crystallization process, avoiding changes in the size of rubber parts during storage and use; in a mold with a lower temperature, it is difficult for molten rubber to fill cavity, resulting in an increase in internal stress, a dull surface, defects such as silver streaks and weld marks.
Different rubber materials have different processing technology, surface requirements and structures of various rubber parts are different. In order to produce rubber parts that meet quality requirements in the most effective time, mold is required to maintain a certain temperature. The more stable, the more consistent requirements on size, shape, appearance and quality of produced rubber parts will be. Therefore, in addition to mold manufacturing factors, mold temperature is an important factor in controlling quality of rubber parts, mold temperature control methods should be fully considered during mold design.

10.1 Principles and methods of mold temperature control

10.1.1 Principles of mold temperature control

In order to ensure that plastic parts with high appearance quality requirements, stable dimensions and small deformation are produced in the most effective time, basic principles of mold temperature control should be clearly understood when designing.
(1) Different rubber materials require different mold temperatures. See section 10.1.3
(2) Molds with different surface qualities and different structures require different mold temperatures, which requires pertinence in the design of temperature control system.
(3) Temperature of front mold is higher than temperature of rear mold, and temperature difference is generally about 20~30o.
(4) Temperature of front mold required by fire pattern is higher than temperature of front mold required by general smooth surface. When front mold requires hot water or hot oil, temperature difference is generally about 40o.
(5) When actual mold temperature cannot reach required mold temperature, mold should be heated. Therefore, when designing mold, full consideration should be given to whether heat brought by rubber material into mold can meet mold temperature requirements.
(6) Except for heat radiation and heat conduction, heat brought into mold from rubber material is consumed, most of heat needs to be taken out of mold by circulating heat transfer medium. Heat in easy heat transfer parts such as beryllium copper is no exception.
(7) Mold temperature should be balanced, there should be no local overheating or overcooling.

10.1.2 Control method of mold temperature

Mold temperature is generally controlled by adjusting temperature of heat transfer medium, adding heat insulation boards and heating rods. Heat transfer medium generally uses water, oil, etc., its channel is often called a cooling water channel.
To reduce mold temperature, it is generally achieved by passing "mechanical water" (about 20oC) through front mold and "frozen water" (about 4oC) through rear mold. When passage of heat transfer medium, that is, cooling water passage, cannot pass through certain parts, materials with higher heat transfer efficiency should be used to transfer heat to heat transfer medium, as shown in Figure 10.1.1, or a "heat pipe" for local cooling .
Raising mold temperature is generally achieved by passing hot water and hot oil into cooling water channel (heated by a hot water machine). When mold temperature is high, in order to prevent heat loss due to heat conduction, a heat insulation board should be added to mold panel.
In hot runner mold, runner plate has a high temperature requirement and must be heated by a heating rod. In order to avoid heat of runner plate from being transferred to front mold, which makes front mold difficult to cool, design should minimize its contact surface with front mold.

10.1.3 Injection temperature and mold temperature of commonly used rubber materials

Following table shows commonly used rubber injection temperature and mold temperature when surface quality of rubber part has no special requirements (that is, general smooth surface). Mold temperature refers to temperature of front mold cavity.
Compound name ABS AS HIPS PC PE PP
Injection temperature (℃) 210~230 210~230 200~210 280~310 200~210 200~210
Mold temperature (℃) 60~80 50~70 40~70 90~110 35~65 40~80
Compound name PVC POM PMMA PA6 PS TPU
Injection temperature (oC) 160~180 180~200 190~230 200~210 200~210 210~220
Mold temperature (oC) 30~40 80~100 40~60 40~80 40~70 50~70

10.2 Cooling system design

10.2.1 Principles of Cooling System Design

(1) Distance between hole wall of cooling water channel and surface of cavity should be as equal as possible, generally 15~25mm, as shown in Figure 10.2.1.
(2) Number of cooling water channels should be as large as possible, they should be easy to process. Generally, diameter of water channel is Æ6.0, Æ8.0, and Æ10.0, distance between two parallel water channels is 40~60mm, as shown in Figure 10.2.1.
(3) All molded parts are required to pass through cooling water channels, unless there is no position. Strengthen cooling of parts where heat accumulates, such as battery pocket, speaker position, thick glue position, and gate. A board, B board, nozzle board, gate part are determined according to situation.
temperature control system design 
(4) Reduce temperature difference between water inlet and water outlet. Temperature difference between inlet and outlet water will affect uniformity of mold cooling, so direction of inlet and outlet should be marked during design. Mold must be marked on mold base when mold is made. Water transportation process should not be too long to prevent excessive temperature difference between inlet and outlet water.
(5) Minimize existence of "dead water" (medium that does not participate in flow) in cooling water channel.
(6) Cooling water channel should be avoided at foreseeable welding marks of plastic parts.
(7) To ensure minimum side distance of cooling water channel (ie minimum steel thickness around water hole), when length of water channel is less than 150mm, side distance is greater than 3mm; when water channel length is greater than 150mm, side spacing is greater than 5mm.
(8) When cooling water channel is connected, it should be sealed with "O" type glue, sealing should be reliable and without water leakage. See 10.2.2 for sealing structure.
(9) Other cooling methods, such as beryllium copper, heat pipes, etc., should be adopted for parts with difficulties in arrangement of cooling water channels.
(10) Reasonably determine location of cooling water joint to avoid affecting installation and fixation of mold.

10.2.2 Sealing structure of "O" type sealing ring

Structure of commonly used "O" seal ring is shown in Figure 10.2.3.
temperature control system design 
Commonly used sealing structure is shown in Figure 10.2.4. Refer to list for common assembly technical requirements:
temperature control system design 
Unit: mm
Sealing ring specifications Assembly technical requirements
13.0 2.5 8.0 1.8 3.2
16.0 11.0
19.0 14.0
16.0 3.5 9.0 2.7 4.7
19.0 12.0
25.0 18.0

10.2.3 Cooling example

(1) Shallow cavity cooling. Front mold is shown in Figure 10.2.5, and back mold is shown in Figure 10.2.6.
temperature control system design 
(2) Deep mold cavity cooling. As shown in Figure 10.2.7.
Principles of mold temperature control 
(3) Small high and long core cooling. Figure 10.2.8 adopts diagonally crossing cooling water channels; 10.2.9 adopts cooling water channels in the form of sleeves.
Principles of mold temperature control 
(4) Parts where cooling channel cannot be processed are made of heat-conductive materials to transfer heat. As shown in Figure 10.2.10.
Principles of mold temperature control 
(5) Huff mode is cooled. As shown in Figure 10.2.11. A cooling water channel is set on Huff block, an escape groove for water outlet and water inlet pipes is set on mold blank.
Principles of mold temperature control 
(6) Forming top block is cooled. As shown in Figure 10.2.12. An avoidance slot is provided at the joint of water outlet and inlet pipes of top block, size of avoidance slot should meet movement space of water diversion pipe when top block is ejected.
Principles of mold temperature control 

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