Heat Exchange System for Injection Molds

The heat exchange system of the injection mold and the temperature adjustment ability of the injection mold not only affect the quality of the plastic parts, but also determine the production efficiency.


1. Ways to improve mold temperature regulation ability


(1) Cooling channels with the largest possible size and as many quantities as possible are set up on the injection mold to increase the heat transfer area, shorten the cooling time, and achieve the purpose of improving production efficiency.


(2) Select injection mold materials with high thermal conductivity. The injection mold material is usually steel, but in some places where heat dissipation is difficult, copper and aluminum alloy can be used as inserts, the premise is to ensure the rigidity and strength of the injection mold.





(3) Normal temperature water is generally used as the cooling medium. It is better if the temperature difference between the outlet and inlet of the cooling water is less than 5°C. The flow rate of the cooling water should be as high as possible, and the flow state should be turbulent flow.


(4) The thinner the wall thickness of the plastic part, the less cooling time is required. Conversely, the thicker the wall thickness, the longer the required cooling time.


(5) The distribution of the cold circuit, that is, the distance between the cooling circuit and the cavity and the interval between the channels, should be able to ensure uniform temperature on the surface of the cavity.


(6) Strengthen the cooling of the gate. When the plastic mold is filled, the temperature near the gate is high, so the cooling near the gate can be enhanced.


2. Regulations and Legends of Water Transportation Design


1. Design of water transport channel


Commonly used specifications for water transport channels are Φ6mm, Φ8mm, Φ10mm, and Φ12mm. Shanghai Mulan Injection Mold Factory uses large-diameter channels to increase heat exchange capacity when designing. Cylindrical pipe thread or tapered pipe thread used for thread sealing, tap the corresponding cylindrical internal thread with BSPT type tap for the threaded hole. 1/4in specification is preferred if there are no special regulations above. Pay attention to the following points when designing the water delivery channel. The water transport channel must be drilled more than 4mm in order to have cooling effect; the same loop and the cross section of the waterway must be equal; the water pipe must be a loop to avoid stagnant water.





2. The external water delivery system of the mold


The threaded connection of the inlet and outlet of the mold water channel is 1/4in pipe thread, and the water pipe joint is 'nylon quick connector'. When there are more than three sets of water transport circuits, the water transport in and out should be concentrated on the splitter plate, the splitter plate should be set on the non-operating side of the injection mold, and the water transport in and out should be marked on the mold.


3. Water delivery system for special parts of the mold


If the structure of the injection mold is limited, when using a specially designed faucet and water pipe joint, in addition to the needs of the injection mold, a set of spare parts for the special faucet and joint must be provided at the same time.


4. Water hole layout


The cooling range is 25~30mm from the water hole to the surface of the finished product, and the small mold can be appropriately reduced to save the mold core material. Generally, the distance between the two water holes of the mold is 50~70mm, and the distance between the two water holes of the large mold can reach 70~90mm.


5. Cooling system design principles


(1) The layout of the cooling water channel should be reasonable


When the wall thickness is uniform, the distance between the cooling channel and the cavity surface is equal, and when the wall thickness is uneven, the cooling is strengthened at the wall thickness. During the process of filling the cavity of the plastic part, the temperature is generally high near the gate, and cooling should be strengthened. For this reason, the cooling water should flow from the vicinity of the gate to other places. The cooling water of the mold cavity, core, slider, top block, etc. should be evenly distributed to ensure balanced cooling of each part, to achieve continuous and stable mold temperature. At the same time, the cooling of the gate material should be taken into account to achieve a short production cycle.





(2) The cooling water channel should avoid being close to the parts that may produce weld marks.


(3) The cooling circuit structure should be easy to process and clean, and its aperture is generally 8~12mm.


(4) The straight-through water hole is simple and convenient, and the two ends are made to steal holes, but the length of the hole should not exceed 70mm.


(5) There should be as many cooling channels as possible, and the cross-sectional size should be as large as possible.


(6) Cooling should be strengthened at the gate.


(7) The temperature difference of the cooling water channel should be as small as possible.


(8) The cooling water channel should be set along the shrinkage direction of the plastic.


(9) The distance from the cooling channel to the surface of the cavity should be as large as possible.


(10) Ensure that the strength of the injection mold is not affected when setting the water delivery path of the injection mold and its processing.


(11) The layout of the water holes is prone to interference, and the water holes are required to be well sealed and the injection mold does not leak.


(12) The water hole can be set on the mold core or on the body plate. Be careful not to interfere with the return pin when it is set on the body plate, and reduce dead water ditch.


(13) The forming part generally requires cooling, so it is sometimes considered to drill water holes diagonally.





3. Local mold temperature control


For the heat exchange system of the injection mold, drill holes in the appropriate part of the injection mold, insert the electric heating rod, and connect to the automatic temperature control regulator. Shanghai Mulan Injection Mold Factory can control the local temperature of the injection mold. This heating form is simple in structure, easy to use, clean and hygienic, and the heat loss is smaller than that of the electric heating coil, but attention must be paid to local overheating conditions when using it. Note that some electrical components should be designed above the water transport interface as much as possible to prevent water leakage from dripping on the electrical components.