The hottest mold knowledge mold heating, insulatio

Mold knowledge: mold heating, insulation and cooling

overview

molding process is one of the most common and oldest molding methods for plastic materials, and it is the most commonly used process method for studying material properties. It has the characteristics of simple forming device, small equipment investment, simple mold structure and so on. Today, with highly developed mechanized and automated production, it is still one of the most popular means of production. However, in addition to textbooks, monographs written by several predecessors, and mold design illustrations, few people summarize the key skills in mold design

the heating, heat preservation and cooling of the mold and the clamping structure are an integral part of the composite mold design. Structural design directly affects the appearance and internal quality uniformity of products, and also affects the forming efficiency of products. Electronic universal experimental machine

2. Design of heating, heat preservation and cooling

2.1 design requirements of heating pipe

steel heating is a heating method that must be used in the design of almost all plastic forming molds. It can be designed in various forms such as one-way wiring and two-way wiring. It can be made of slotted pipes, seamless pipes, stainless steel pipes, etc. it is characterized by small heat loss, high thermal efficiency, simple wiring, and can be designed as 220V or 380V according to needs, Wiring is flexible and diverse. However, due to the limitations of its materials and processing technology, attention should be paid to its body oriented characteristics in mold design

(L) the heating tube usually has a long cold end at both ends, which cannot play the role of heating

(2) the power design of the heating section shall not exceed the limit of 10 watts/cm as far as possible. For example, the power of a 30cm long heating tube should not exceed 300 watts as far as possible. If the design power exceeds this limit, the surface load of the heating pipe is high. The grade 3 ribbed steel bar is made of 20MnSi steel with the addition of microalloyed elements vanadium or niobium. The steel pipe is prone to oxidation and corrosion, resulting in short circuit

(3) for mold design with temperature higher than 250 ℃, it is difficult to use heating tube. I used to use the heating tube to raise the temperature to 420 ℃, but this forming temperature has high requirements for the quality of the heating tube, so it is necessary to often check whether the circuit is smooth or short circuited. Because under this condition, heating tubes, wiring terminals, copper wires for connection, steel sheets and other media are very easy to oxidize, resulting in open circuit. Therefore, Evonik has provided a large number of innovative products for composite materials, and the medium needs special treatment to avoid exposing the conductive wire to the air and prolong the service life of the wire

soldering iron core is usually also used as a kind of mold heating pipe, which is characterized by high power per unit length (usually 10mm in diameter and 8cm in length. The soldering iron core can reach 150 watts of output power), durability, good safety, not easy to form a breakdown short circuit, and can be buried by drilling blind holes. The disadvantage is that it is difficult to customize the design, and it is fragile and broken when being replaced

safety measures such as safety and air switch are indispensable in circuit design. The operation ground should be kept clean and tidy, with good insulation. During operation, check electrical faults diligently to prevent unnecessary dangers

2.2 installation drilling of heating pipe

from the perspective of heat transfer, the installation of heating pipe should fit the mold surface as much as possible, so as to facilitate the heat transfer of heating pipe 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 heat transfer is radiation, and conduction is secondary. Therefore, most of the heating tubes used for mold installation are coated with coatings to enhance infrared radiation. At the same time, the method of limiting the design power (10 watts/cm) is also used to increase the service life of the heating tubes

therefore, it is not necessary to design a too small fit gap when processing the heating pipe hole, especially the long heating pipe hole. The effective design method is to closely match the heating pipe at both ends of the hole as much as possible, and methods such as filling, plugging or designing a baffle can be used. This method can effectively reduce the heat dissipation area of the heating tube and the loss of radiant heat

2.3 embedding of heating pipe

the buried heating pipe is best filled with magnesium oxide powder with the same medium as the pipe to reduce the heat load on the surface of the heating pipe. This method can reduce the surface oxidation of the pipe and effectively prolong the service life of the pipe

if possible, the installation hole of the heating pipe should also be filled with magnesium oxide powder

2.4 mold insulation method

strengthening the mold insulation measures can reduce the heat loss of the mold, make the mold reach the predetermined production temperature in a short time, and reduce energy waste. Every engineer and technician has a unique solution to this problem. I will only talk about my experience

2.4. L heat preservation measures for heating plate

asbestos board or asbestos cloth is usually used for heat preservation of heating plate, but the asbestos cloth is not easy to be placed smoothly, which also has a certain impact on the parallelism of pressing plate. There are many kinds of asbestos board, the most common is rubber asbestos board, but this kind of asbestos board is not used as a material for sealing and heat insulation, and has a certain compressible grade. At the same time, it will release a very unpleasant smell at high temperature, affecting the operating environment and the health of the operator

asbestos paperboard should be used for heat preservation of heating plate. The common specification is 1000 mm thick. The plate body is relatively regular, with good parallelism, average compressibility, and no odor under high temperature

2.4.2 mold insulation measures

there are many mold insulation measures. You can wrap aluminum hydroxide insulation cotton with asbestos or glass cloth for insulation. There is also a kind of heat preservation coating on the market, which is an ideal material for mold heat preservation at present. It is composed of medium long fiber, slurry and a kind of heat preservation foam material. It has moderate viscosity and is easy to apply. This kind of material is often used as the insulation material of chemical and heating pipelines, which contains slightly alkaline (easy to corrode molds). After being used at 150 ℃, no negative effects such as scorching, melting and odor were found. At the same time, the material is very light, with strong plasticity, which is easy to form a more beautiful mold surface

2.5 cooling method of mold

water cooling is the cooling method adopted by most molds, but it also has its shortcomings; The pipeline is required to be well sealed, and the water supply and drainage pipelines must be unobstructed, which is a great waste of water resources. When the cooling temperature exceeds 100 ℃, it is easy to produce steam explosion. The advantage is that the heat capacity is large, which can realize rapid cooling

air cooling is an ideal cooling method. Contrary to water cooling, it does not need tight pipe sealing, and there is no waste of resources. It can cool molds with a temperature higher than 100 ℃, and the cooling speed can be determined by the flow of gas. The source is simple and convenient. Production workshops with a certain scale can obtain relatively convenient gas sources

3. Clamping of the mold

the clamping structure of the mold is closely related to the heating, insulation and cooling system of the mold, and provides certain convenient characteristics for the replacement, loading and unloading of the mold. For the convenience of drawing, most designers simply punch several mounting holes on the mold to fix it. For example, most pressing dies do not design heating devices separately, but install heating plates on the upper and lower pressing plates of the press to simplify the processing of small and medium-sized dies. In the mold structure, there are only modules that constitute the main structure of the cavity. At this time, the mold can be fixed by injection mold?? Fix the mold on the upper and lower templates with pressing plates. Design the space for fixing the pressing plate on the heating plate mold. This design can be used not only for mobile dies, but also for dies with simple entry mechanism. It is only necessary to consider that the position of the ejector rod does not conflict with the heating pipe in the design of the heating plate. The mold base of one mold can also be used to carry out universal transformation on multiple molds, so as to simplify the mold manufacturing cost

if the mold is high, simple heating plate heating can no longer meet the needs of uniform heating. At this time, it is necessary to install an auxiliary heating system on the mold, which can be composed of heating plates, heating tubes and iron cores

for the mold with simple structure and small size, the use of heating plate heating will cause excessive heat loss, and a simple heating system in the mold design can meet the requirements. It should be noted that heat insulation (usually asbestos paperboard) should be added between the mold and the press fixing plate to keep warm. At the same time, attention should be paid to the neat arrangement of power lines and the position of galvanic couple holes. This setting); Due to the small heat capacity, it is especially suitable for small molds that need repeated heating and cooling or rapid heating and cooling