Briefly analyze mold heating, holding and cooling

   Steel heating is almost all plastic molding mold design must use heating means, can be designed for one-way wiring, two-way wiring and other forms, the material can be used with seam pipe, seamless pipe, stainless steel pipe, etc., is characterized by small heat loss, high thermal efficiency, simple wiring, can be designed according to needs for 220V or 380V, wiring is flexible and diverse. However, due to the limitations of its materials and processing technology, it is necessary to pay attention to its body-oriented characteristics in mold design.

(1) The heating tube is usually a cold end of ≥5mm at both ends, which cannot play a heating role.
(2) The power design of the heating section should not exceed the limit of 15 watts/cm as far as possible. Such as 10*90mm specification heating tube, power should not exceed 400 watts as far as possible. If the design power exceeds this limit, the surface load of the heating pipe is high, and the steel pipe is easy to oxidize and corroded, resulting in short circuit.
(3) For mold design with a temperature higher than 300 ° C, it is difficult to use heating pipes.
Linzhi has used the heating tube to temperature up to 620℃, but this molding temperature has extremely high requirements for the quality of the heating tube, and it is necessary to check the patency and short circuit of the circuit frequently. Because under this condition, the heating tube, terminal, connecting copper wire, steel sheet and other media are very easy to oxidize, resulting in a break. Therefore, the electric transmission medium needs special treatment, try to avoid exposing the conduction wire to the air, and extend the service life of the wire. The iron core is usually used as a kind of mold heating tube, characterized by high power per unit length (usually 10mm diameter, 8cm long specification of the iron core can reach 150 watts of output power), durable, good safety, not easy to form a breakdown short circuit, can be buried by drilling blind holes, the disadvantage is difficult to custom design, fragile, broken when disassembly. Insurance, air switch and other insurance measures are indispensable in the circuit design, and the operation should be kept clean and tidy, well insulated, and diligent in checking electrical faults during operation to prevent unnecessary dangers.

2. Drill a hole to install the heating pipe

      From the point of view of heat transfer, the installation of the heating tube should be as close as possible to the surface of the mold, so as to facilitate the heat of the heating tube to be transferred to the mold as soon as possible. In fact, the heating tube and the mold do not have much contact area, the essence of heat transfer is radiation, and the conduction is secondary. Therefore, most heating tubes used for mold installation are coated with a coating that enhances infrared radiation, while limiting the design power (15 watts/cm) to increase the service life of the heating tubes. Therefore, when processing heating pipe holes, especially the processing of long heating pipe holes, it is not necessary to design too small coordination gap, and the effective design method is to closely cooperate with the heating pipe as far as possible at both ends of the hole, which can be filled, blocked or designed to stop the plate. This approach can effectively reduce the heat dissipation area of the heating tube and the loss of radiation heat.

      The heating tube buried by forest is filled with the same magnesium oxide powder as the medium in the tube to reduce the heat load on the surface of the heating tube. This method can reduce the surface oxidation of the tube and effectively extend the service life of the tube.

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

Mold insulation measures are many, can be wrapped in asbestos cloth or glass cloth aluminum hydroxide insulation cotton for insulation. There is also a thermal insulation coating on the market is currently used as an ideal material for mold thermal insulation, it is composed of long fiber, slurry and a thermal insulation foam material mixed, moderate viscosity, easy to apply. This material is commonly used as a thermal insulation material for chemical and heating pipelines, which is slightly alkaline (easy to corrod molds). No negative effects such as burning, melting and odor were found after use at 150℃. At the same time, the material is very light, strong plasticity, easy to form a more beautiful mold surface.

      Water cooling is the cooling method used by most molds, but it also has its disadvantages; It is required that the sealing of the pipeline is better, and the upper and lower water pipelines must be unobstructed, and the waste of water resources is larger. When the cooling temperature exceeds 100℃, it is easy to produce steam explosion. The advantage is that the heat capacity is large and rapid cooling can be achieved. Air cooling is a more ideal cooling method, and water cooling is the opposite, it does not need a tight pipe seal, there is no waste of resources, can cool the temperature of the mold above 100 ° C, can determine the cooling speed through the flow of gas, and the source is simple and convenient, there is a certain scale of the production workshop can obtain a more convenient air source.