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l Overview
The molding process is the most common plastic material, the oldest one of the molding method, and is a technological method most commonly used study material properties. Forming device is simple, small investment, simple mold structure, mechanization and automation of production is highly developed, is one of the most popular means of production. However, compression molding mold design can refer to the literature of key skills in addition to textbooks, several predecessors, written by professionals, other than the legend of mold design, few people sum up the mold design.
Heating, insulation and cooling of the mold and clamping structure is an integral part of the composite mold design. The structural design of a direct impact on product appearance and internal quality and uniformity, but also affect the forming efficiency of the product.
2, heating, insulation and cooling design
2.1 heat pipe design requirements
Steel heating is almost all plastic mold design heating means can be designed for one-way wiring, bi-wiring and other forms, material can be slit pipe, seamless pipe, stainless steel pipe, characterized by the heat loss small, high thermal efficiency, a simple cable, according to the needs designed for 220V or 380V, and wiring is flexible. However, due to the limitations of the materials and processing technology, mold design should pay attention to the body characteristics.
(L) heating pipe at both ends usually have a longer cold side, and can not play the role of heating.
(2) heating section of the power of design as far as possible not more than 10 watts / cm limit. Such as 30 cm long heating power as possible should not exceed 300 watts. Design power exceeds this limit, the heating tube in a higher surface loading, the pipe easily oxidized corrosion, causing a short circuit.
(3) For temperatures above 250 ° C mold design, the use of the heating pipe has some difficulties. I used to use the heating pipe temperature reached 420 ° C, but this molding temperature require a higher quality of the heating pipe, you need to frequently check the circuit patency and short-circuit or not. Under these conditions, heating pipes, terminals, the connection of copper wire, steel and other media are very susceptible to oxidation, resulting in open circuit. Therefore, the power transmission medium require special handling to avoid conductive wires exposed to the air, to extend the life of the wire.
Iron core is usually used as a mold heating pipe is characterized by high power per unit length (usually 10mm diameter, 8cm long the specifications of the iron core can achieve 150 watts of output power), durability, safety, good, easy to form a short-circuit breakdown by drilling blind holes laid, the drawback is that hard to custom design, brittle, replace them when off.
Indispensable to the insurance policy of insurance, air switch, circuit design and operation to maintain a clean, well-insulated, diligent operations to inspect an electrical failure, to prevent unnecessary risk.
2.2 heating pipe installation drilling
Understand the heat transfer point of view, the heating pipe installation to fit the mold surface as possible, to facilitate the heating tube heat as soon as possible to pass to the mold. In fact heating tube and the mold is not much contact area, the nature of heat transfer by radiation, conduction is minor. Mostly for die mounting surface of heating tube are coated with a coating to enhance the infrared radiation, but also ways to limit the design power (10 watts / cm) growth in the service life of the heating tube.
Therefore, in the processing of heated pore, especially the processing of the long heating pore is no need to design is too small with the gap, effective design in both ends of the hole as far as possible with the heating pipe tight tie, can be used to filling and sealing off or design of blanks and other methods. This approach can effectively reduce the area of heat pipe cooling and radiation heat loss.
2.3 heating pipe laying
The laying of heating pipes, preferably with the same medium of magnesium oxide powder in tube filling, in order to reduce the heat load of the heating tube surface, this method can reduce the tube surface oxidation, effectively extending the life of the tube.
Able to do so, the heating pipe mounting holes is best poured into the magnesium oxide powder.
2.4 mold heating methods
Insulation measures to strengthen the mold can reduce the heat loss of the mold, and allows mold to achieve the desired production of temperature, within a short period of time to reduce energy waste. Each engineering and technical personnel have a unique solution on this issue, I can only talk about my experience.
2.4 l heating plate of insulation measures
Heating insulation board is usually asbestos board or stone, cotton insulation, asbestos cloth is not easy to be placed flat on the plate parallel degree of assurance given. Many different types of asbestos sheet of the most common rubber asbestos, asbestos board not sealed thermal insulation materials for use with a certain pressure level wins, while at high temperatures will release a very difficult smell, affect the operating environment and the health of the operator.
Insulation of the heating plate should be used asbestos cardboard, common specifications are 1000 × 1000,3-5mm thick, the plate body is more regular, better parallelism, compressibility average high temperature odor generation.
2.4.2 mold insulation measures
Mold insulation measures can be used asbestos cloth or glass cloth wrapped in aluminum hydroxide cotton insulation for insulation. Now on the market an insulation coating is currently used as a mold insulation material, which the Chinese and the long-fiber pulp and a thermal insulation foam mixture viscosity moderate, easy to apply. This material is used as chemical, heating pipes, insulation material, a little-containing alkaline (corrosive mold). 150 ℃ under the conditions of use not found the charred, melted, odors and other negative impact. At the same time the material is very light, strong plasticity, easy to form the mold surface of the more beautiful.
2.5 mold cooling methods
Most of the mold cooling water cooling, but also has its drawbacks; requirements of the pipe seal better, the road must be smooth up and down pipes, waste of water resources. When the cooling temperature exceeds 100 ℃, easy to produce a steam explosion. The advantage is that the heat capacity, can achieve rapid cooling.
Air cooling is a cooling and water cooling to the contrary, it does not require tight pipe seal, there is no waste of resources, can be cooled to a temperature higher than 100 ° C mold, can determine the speed of the cooling gas flow to and sources of simple and convenient, there is a certain scale of production workshop can be made more convenient source of gas.
3, the mold clamping
Mold clamping structure is closely related to the mold heating, insulation and cooling systems, as well as the replacement of the mold, loading and unloading convenience features. Most designers of convenience, simply make some mold to fix the mounting holes. Cases is that most of the die are not individually designed heating device, but in the press on the upper and lower plate to install the heating plate in order to simplify the processing of small and medium-sized mold. The mold structure constitutes the cavity of the main structure of the module only. The mold can be a fixed approach to injection mold?? Platen mold fixed in the upper and lower template. Space can be designed fixed plate in the mold of the heating plate. This design not only for the movable die, die can also be used with simple items out of institutions. Only need to take into account in the design of the heating plate mandrel position and heating controls are not in conflict can. A mold of the mold can also use multiple mold versatility transformation to simplify the mold manufacturing costs.
If the mold is higher, a simple hot plate and heat can not meet the uniform heating needs, then install the auxiliary heating system in the mold, can Mountain heating plate, heating pipes and iron core constitutes
Simple structure, small size of the mold, the hot plate and heat will cause greater than heat loss, mold dead simple design of the heating system can meet the requirements. Important to note that you want to add thermal insulation between the fixed plate of the mold and press (usually to the use of asbestos cardboard) insulation, need to pay attention to the arrangement of the power cord neat and galvanic hole location. This set); smaller heat capacity, especially suitable for repeated heating and cooling or rapid heating and cooling of small mold.
