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Heating, heat preservation and cooling of mold Nov 30, 2017

The heating, heat preservation, cooling and clamping structure of the die are an indispensable part of the design of the composite die. And the design of the structure will directly affect the appearance of the product and the uniformity of the internal quality and the efficiency of the product. How is the heating, heat preservation and cooling of the mold done?

1. Design requirements of heating pipe

Steel heating is almost all plastic mold design must be used in heating means can be designed for one-way connection, two-way connection and other forms of material can be used on a tube, seamless tube, stainless steel tube, is characterized by low heat loss, high thermal efficiency, simple wiring, can be designed according to the requirements of 220V or 380V. Flexible cable for the type. However, due to the limitation of its material and processing technology, it is necessary to pay attention to the characteristics of the mold in the mold design.

(1) the heating pipe usually has a long cold end at both ends, and it can not play the role of heating.

(2) the power design of the heating section is not more than 10 watts / centimeter. Like 30 centimeters long heating pipe, the power is not more than 300 watts as far as possible. If the design power exceeds this limit, the surface load of the heating tube is high and the steel pipe is easily oxidized and corroded, which causes short circuit.

(3) it is difficult to adopt a heating tube for the design of a mold with a temperature above 250 degrees C.

Special treatment is needed for electric transmission medium, so as to avoid exposing the conductive wire to the air and prolong the service life of the wire.

The iron core is usually used as a mold heating tube, is characterized by high power per unit length (usually diameter 10mm, length 8cm specifications of the iron core can reach 150 watts of output power), durable, good safety, easy to form short circuit breakdown, can drill through the blind hole to bury, are difficult to design custom. Dismantle the fragile, broken.

In the circuit design, there are indispensable insurance measures, such as insurance and air switch. The operation must be kept clean and tidy and well insulated. In operation, we must be diligent in checking electrical faults and preventing unnecessary dangers.

2. The installation of the heating pipe

It is understood from the heat transfer point of view that the installation of the heating pipe should be fitted to the surface of the die as much as possible to facilitate the heat transfer to the mold as soon as possible. In fact, there is not much contact area between the heating tube and the mold. The essence of the heat transfer is radiation, and the conduction is secondary. Therefore, most of the surface of the heating pipe used for mould installation is coated with infrared radiation enhancing coating, and the design power (10 watts / cm) is applied to increase the service life of the heating tube.

Therefore, when processing heating tube holes, especially for long heating pipe holes, there is no need to design too small fit gaps. Effective design method is to closely cooperate with heating pipes at both ends of the holes, and we can use tamping, blocking or designing baffle. This method can effectively reduce the heat dissipation area of the heating tube and the loss of radiation heat.

3. Buried heating pipe

The laying of heating pipe and tube, the best use of magnesium oxide medium at the same filling, in order to reduce the heat load of the heating pipe surface, this method can reduce the surface oxidation tube, prolong the service life of the tube. If possible, magnesia installation of heating pipe holes are filled with the best.

4. Heat preservation method of die

The heat preservation measures of the mould can reduce the heat loss of the mould, which can make the mold reach the predetermined production temperature in a short time and reduce the waste of energy.

1) the heat preservation measures of the heating plate

The heat insulation of the heating plate is usually insulated with asbestos board or stone cotton cloth, but the stone cotton cloth is not easy to be put and smooth, and it also has definite influence on the guarantee of the parallelism of the press plate. Many kinds of asbestos board, asbestos rubber plate is the most common, but this is not right for asbestos sealing for the insulation material, has a certain level can win, in the high temperature and will release a very unpleasant smell, affecting the operation environment and the operation of the health of people.

The insulation of heating plate should be made of asbestos board. The common specifications are 1000X1000, 3-5mm thick, the plate is regular, the parallelism is better, the compressibility is relatively average, and no odor is produced at high temperature.

2) the insulation measures of the mould

There are a lot of heat preservation measures for the mould, which can be insulated by the cotton or glass cloth wrapped with aluminum hydroxide. Now, there is another thermal insulation coating on the market, which is an ideal material used for mould insulation at present. It is made of medium long fiber, slurry and a kind of thermal insulation foam material, which is moderately sticky and easy to smear. This material is often used as a thermal insulation material for chemical and heating pipes, which is slightly alkaline (easy to corrode mould). The effects of burning, melting, odor and other negative effects were not found at 150 C. At the same time, the material is very light, the plasticity is strong, easy to form a more beautiful mold surface.

5. Cooling method of die

Water cooling is the cooling way adopted by most molds, but there are also some disadvantages. It requires better sealing performance of pipeline, and the pipeline must be smooth and water resource is wasted. When the cooling temperature is over 100 centigrade, it is easy to produce steam explosion.  The advantage is that the heat capacity is large, and the rapid cooling can be realized.

Air cooling is an ideal method of cooling water, and on the contrary, it does not require strict pipeline sealing, there is no waste of resources, mould cooling temperature higher than 100 DEG C, the gas flow rate to determine the rate of cooling, and simple and convenient, has a certain scale of production workshop can make comparison convenient source.