Rolling process is an important branch of plastic molding processing. Since the advent of the last century in 40s, after more than half a century of development, its equipment and technology are becoming more and more perfect. It has been widely used in the developed countries of Europe, from small children's toys to automobile plastic parts and until huge engineering plastic products. Especially large and special hollow products, due to the limitations of traditional technology, they can only be completed by rotational molding process.
. Rolling molding process
The principle of process
The plastic is added to the mold first, then the mold is rotated along the two vertical axis and heated, and the plastic in the mold is gradually coated and fused to the whole surface of the cavity under the action of gravity and heat.
Forming process
Detailed description of rolling molding process
Two. Control points of rolling molding (influencing factors)
. Influence of properties of raw material resin
The fluidity, particle size distribution, apparent density and particle size of resin powder affect the molding products. According to the experimental analysis, the higher the peak position of particle size distribution and the finer the particle, the better the comprehensive performance of the product. However, considering the overall production cost and efficiency, it is best to set the peak value of particle size between 60 and 80 in production practice.
2. Effect of heating temperature and time on rotational molding
The selection of heating temperature and heating time is influenced by many factors. The most important factors are resin, mould and product.
For example, the temperature of the polythene rolling molding heating furnace is usually 250 to 400 degrees C. The heating conditions of the specific product rolling can be determined by the experiment, and the initial test conditions can be obtained at 220 degrees C, 0min.
If a product is not plasticized or there is a small bubble in the wall of the product (the gas in which the melt is not fully discharged), the heating time should be extended or the heating temperature should be properly raised. If the product is yellow, it is indicated that the material is overheated and the thermal oxidation aging phenomenon is produced. It is necessary to shorten the heating time or appropriate appropriate time. Reduce the heating temperature.
3. Effect of rotating speed and heating speed on rotational molding
Under normal circumstances, the mold speed control is 6 to 35rpm.
This depends on the shape and structure of the product. If it is a cylindrical product, the line speed can be high; if it is a non regular product with angular, corner, and free, the line speed will be lowered accordingly. If the rotational speed can not be correctly estimated, the speed can be adjusted through the state of the powder mold.
4. Influence of cooling on rolling molding
Cooling is a very important part of the whole rotational molding process. When all the material is melted in the mold cavity, it can start to heat insulation.
At present, the cooling methods of rotational molding industry are generally two types: water mist and air cooling. Water fog has high cooling efficiency, but the product is prone to shrinkage deformation. The air cooling efficiency is low, but the quality stability is good.
5. Influence of demoulding agent
Organosilicon resin demoulding agent, if applied properly, can make the product easy to remove from the mold, thus improving production efficiency, reducing the damage that may be caused by the mold release and repeated use of a mold release agent once and again.
Practice shows that before the silicone resin is coated, the surface of the mold cavity must be cleaned up. The silicone resin should be coated evenly, and the coating should not be too thick. After coating the solvent, the organic silicon resin should be heated to make the solvent volatilized, and then heated for more than 2 hours at high temperature (250 C) at high temperature (220 degrees centigrade), so as to get the good mechanical strength of the demoulding agent layer.
Three. The main features of rolling
Advantages
, rolling mold cost low - the same size of the product, the cost of rolling mold is about blow molding, injection mold cost of /3 to /4, suitable for large plastic products;
2, rotational molding products edge strength is good - rotational molding can achieve the thickness of the product edge more than 5mm, completely solve the problem of thin edge of hollow products.
3. All kinds of inlay can be settled by rolling plastic.
4, the shape of rotational molding products can be very complex, and the thickness can exceed 5mm.
5. All closed products can be produced by rolling plastic.
6. Rotational molding products can be filled with foam materials to achieve insulation.
7, no need to adjust the mould, the wall thickness of rotational molding products can be adjusted freely (above 2mm).
8. It is suitable for molding large and extra large parts.
9, rolling molding is very easy to change the color of the products - rolling molding each time the material is directly added to the mold, so that all the materials are entered, and after the product is removed from the mold, the material needed for the next molding is added. When we use more and more moulds to shape the same plastic products, we can also add different colors of material to different moulds and roll out plastic products of different colors.
0, save the raw material - the wall thickness of the rolling product is more uniform and the chamfering is slightly thicker, so it can give full play to the material efficiency and save the raw material. In addition, in the process of rolling molding, there is no waste material such as runner, gate and so on. Once the debugging is good, there is no return material in the production process, so the process is for material. The utilization rate is very high.
Four. The application range of rolling products
, container type rolling parts
It is widely used in storage tanks and various liquid chemicals, such as acid, alkali, salt, chemical fertilizer, pesticide, etc., gasoline containers (gasoline tanks and cars, aircraft tanks), battery shells and so on.