plastic raw materials forming process mainly involves plasticization, mold filling, and after cooling and forming, it becomes the finished product . It is a process of heating and cooling, and it is also a process of changing plastic from particles to different shapes. The following will explain the processing process from the perspectives of different stages:
1
Screw
PP processing is mostly based on the screw to drive fluidity, so the design of the screw has a great impact on . The diameter size affects the output, the compression ratio affects the pressure value and the output and the effect of the finished product. This also includes the mixing effect of a variety of materials (color masterbing, additives and modified agents). The flow of raw materials mainly depends on the heater, but the turning of raw materials will also produce friction and heat energy to accelerate the flow. Therefore, the compression ratio of the screw is small and the flow is small, and the rotation speed must be increased. The friction and heat energy must be more than that of the screw with a larger compression ratio.
So it is often said that there is no master in plastic processing, and the person who carefully understands the performance of the machine is the master. The raw material is heated not just a heater, but must be included in the friction heat and suffocation time. So this is a practical problem, and experience helps solve production problems and efficiency. If the screw needs to be kneaded, the kneaded effect is particularly good. Sometimes two-stage different screws or double-axis screws are designed and screws of different sections are divided into different forms to achieve various kneading effects.
2
melting
device heater allows raw material particles to gradually melt into a fluid flow, mainly suitable for temperature adjustment with different raw materials. Raising the temperature will accelerate the flow of raw materials, which can increase efficiency but may not necessarily ensure yield, and a suitable balance must be achieved.
Another good effect and the characteristics of PP in high thermal cracking are best for the raw materials to smoothly flow to the die head during production to avoid insufficient filling or reflux. Reflux means that the raw materials flow faster than the output rate, which will eventually lead to an increase in the average flow efficiency equals an increase in MFR. It is one of the methods available for processing, but it also causes an abnormal state of MFR distribution that may increase in instability and may increase in the defect rate.
However, because the application is not a product with high size and precision, the impact is not much.
3
mold or die
plastic re-shaping relies on molds or die heads. The injection molding product is three-dimensional, and the mold is relatively complex and needs to consider the shrinkage problem. Others are flat, strip-shaped, and needle-shaped continuous product dies. If it is a special shape, it is classified as special shape. Pay attention to the problem of immediate cooling and setting.
Most of the design of plastic machines is like injection syringe . The amount of squeezing pressure driven by the screw will cause huge pressure at the small outlet, improving production efficiency. When the die head is designed as a plane, how to evenly distribute the raw materials on the entire surface, the design of the hanger die head is very important, and the precise pressing opportunity increases the fish gill type pump to stabilize the supply of raw materials.
4
Cooling
In addition to the runner gate filling raw materials, the injection mold also has cooling waterway cooling raw materials design. The compression molding relies on the cooling water channel inside the roller to achieve cooling effect. In addition, there are also wind knives, cooling water is directly poured on the blow bag, and hollow air is used to achieve cooling methods.
5
extension
finished product reprocessing and extension will enhance the effect. For example, the packaging belt drives differently with the front and rear rollers, which will cause the extension effect. The tension resistance of the oriented extension part of the finished product is strengthened and it is not easy to tear off , but it is very easy to tear it open in the horizontal direction.
molecular weight distribution will also affect the extension effect during high-speed production. All finished products, including fibers, have varying extensions. Vacuum and air compression molding can also be regarded as another form of extension.
6
shrinkage
Any raw material has a shrinkage problem. The reason for shrinkage comes from internal stress during thermal expansion, shrinkage and crystallization.Generally speaking, thermal expansion and contraction are easier to overcome. It can be done by processing to extend the cooling time and maintaining pressure. The crystallization raw materials often have greater shrinkage differences than non-crystalline. is about 16/1000 in terms of PP, but ABS is only about 4/1000 in terms of . The difference is very large. This part needs to be overcome on the mold, or additives that reduce the shrinkage rate are often added. LDPE is often added to press the plate to improve the necking problem.
7
Typical application scope
Automotive industry (mainly using PPs containing metal additives: fenders, ventilation ducts, fans, etc.), Instrument (dishwasher door pads, dryer ventilation ducts, washing machine frames and covers, refrigerator door pads, etc.), Daily consumer goods (lawn and gardening equipment such as lawnmowers and water sprayers, etc.).
