Plastic products for home appliances are mainly moulded by injection moulding, extrusion, thermoforming, hollow moulding, lamination moulding, compression moulding, transfer moulding, foam moulding, pouring moulding, insert casting, block casting, etc., of which injection moulding is the main one.
In recent years, some new plastic processing technology and new equipment have been applied in the molding of home appliance plastic products, such as precision injection molding, rapid molding technology, core injection technology, gas-assisted/water-assisted injection molding technology, electromagnetic dynamic injection molding technology and laminated injection molding technology, etc.
- Precision injection moulding
High precision and repeatability in terms of size and weight of the product can be guaranteed. Injection moulding machines using this technology can achieve high injection pressures and speeds. High precision control of the injection process parameters is possible because the control is usually open-loop or closed-loop.
Usually, precision injection moulding requires a high degree of precision. At present, small and medium-sized precision injection moulding machines can be produced in China.
- Rapid prototyping technology
It has been developed rapidly along with the diversification of home appliances and their constant renewal, and is mainly used to prepare plastic shells for home appliances. The advantage of this technology is that small batches of plastic parts can be produced without the need for moulds.
At present, the more mature rapid prototyping methods are laser scanning and liquid light curing, of which laser scanning is more commonly used. Laser scanning equipment is composed of a laser light source, scanning device, powder spreading device and computer. The process is that the laser head controlled by the computer is scanned according to a certain trajectory, and at the location where the laser passes, the plastic micro-powder is heated and bonded together, and after each scan, the micro-powder device spreads a thin layer of powder, so that after repeated scans, products with a certain shape and size are formed.
Now, some domestic enterprises have been able to produce laser scanning molding machines and plastic micronized powder, but the performance of the equipment is not stable, and the variety of micronized powder grades are also small.
- Core injection technology
It is usually used for shaped cavity products that require high cavity roughness and precision and cannot be processed by hollow molding or rotational molding methods.
At present, this technology has been applied in foreign countries, but it is still being applied in China on an individual basis. The processing principle of this technology is that the cavity is first formed into a core, and then the core is used as an insert for injection moulding.
The heating of the injection moulded part causes the core to melt and flow out, thus forming the cavity. The most important aspect of using this technique is the need to know the core material and the melting point of the moulded part. Usually, the core material can be a general purpose plastic, a thermoplastic elastomer or a low melting point metal such as lead or tin, depending on the situation.
- Gas-assisted/water-assisted injection moulding
A wide range of injection moulded parts can be moulded, a typical product being the housing of a television set. During injection moulding, gas or superheated water is injected into the cavity almost simultaneously with the plastic melt.
At this point, the plastic melt covers the gas or superheated water, and the moulded plastic product is a sandwich structure, which can be demoulded by discharging the gas or water after the mould is set. These products have the advantages of material saving, small shrinkage, good appearance and good rigidity. The key part of the moulding equipment is the gas or water auxiliary device and its control software.
In recent years, although the domestic research on this more, the application rate is also faster, but the domestic equipment is not yet stable.
- Electromagnetic dynamic injection moulding technology
This technology makes the screw vibrate reciprocally in the axial direction through the action of electromagnetic force. As the plastic is microplasticised during the preplasticisation stage, it results in a denser structure in the holding phase and reduces the internal stress of the product.
This technique can be used to mould demanding products such as discs. When used in the moulding of common products, the quality of the product can be improved.
- Lamination injection moulding technology
In this technique, a special printed decorative plastic film is clamped into the mould before injection moulding. The printed film can be heat deformed and then laminated to the surface of the plastic part, which is not only beautiful and firm, but also eliminates the need for post-decoration.
For example, a refrigerator or an automatic washing machine usually requires more than 100 pairs of plastic moulds, an air conditioner requires more than 20 pairs, and a colour television requires 50-70 pairs of plastic moulds.
At the same time, the technical requirements for plastic moulds are relatively high, and often require the processing cycle of the mould to be as short as possible, thus greatly promoting the development of mould design and modern mould manufacturing technology. In addition, some of the more difficult moulds such as hot runner injection moulds, laminated injection moulds, etc. in the domestic application is gradually increasing.