Six key points of PP plastic bottle injection molding

Update:25-05-2019
Summary:

The processing of plastic raw materials is mainly the m […]

The processing of plastic raw materials is mainly the melting, flowing, and cooling of the rubber pellets into finished products. It is a process of heating and then cooling, and also the process of changing plastics from particles to different shapes. The following will explain the processing at different stages. process.
1. Melting
The device heater (Heater) allows the raw material particles to gradually melt into a fluid flow, which is mainly suitable for temperature adjustment of different raw materials. Increasing the temperature will tend to accelerate the flow of the raw materials, which may increase the efficiency but may not ensure the yield, and must be suitable. Balance.
Another good effect and PP high thermal cracking characteristics, it is best to make the raw material smooth and smooth to the die during production to avoid the lack of filling or reflow phenomenon, the reflow represents the flow of raw materials faster than the output rate, and finally The increase in the average flow efficiency is equal to the increase in MFR, which is one of the methods available for processing, but it also causes the abnormality of the MFR distribution to cause an increase in instability, which may lead to an increase in the defect rate.
However, the PP finished product is not a product with high dimensional precision because of the application relationship, so the impact is not great.
2, screw
Most of the PP processing relies on the screw to drive the fluidity, so the screw design has a great influence. The diameter of the screw affects the output. The compression ratio affects the pressure value and also affects the output and finished product. This also includes a variety of materials. The mixing effect of (color masterbatch, additive and modifier).
The flow of raw materials mainly depends on the warmer, but the friction of the raw materials will also generate frictional heat to promote the fluidity. Therefore, the screw compression is smaller than the small-driven flow, and the rotational speed must be increased, so that the frictional heat energy is more than the screw with a large compression ratio.
Therefore, it is often said that there is no master in plastic processing, and the person who knows the performance of the machine carefully is the master. The heating of raw materials is not just a warmer. It must be included in the friction heat and retention time.
So this is a practical issue, and experience helps production problem solving and efficiency. If the screw needs to be particularly good in mixing, sometimes a two-stage different screw or twin-shaft screw will be designed and different types of screws will be set up to achieve various mixing effects.
3, mold or die
The plastic re-setting relies on the mold or the die. The injection molded product is three-dimensional. The mold is also complicated and the shrinkage rate is considered. Others are flat, strip and needle continuous product die. If it is a special shape. To be classified, you need to pay attention to the immediate cooling problem.
Most of the design of plastic machines is like an injection syringe. The extrusion force driven by the screw will cause great pressure on the small outlet and improve production efficiency. When the die is designed to be flat, how to distribute the raw materials evenly over the entire surface, the design of the hanger die is very important, and the excavation opportunity increases the supply of stable raw materials for the surimi pump.
4, cooling
In addition to the sprue gate pouring material, the injection mold also has a cooling water channel cooling material design. The extrusion molding relies on the cooling water channel in the roller to achieve the cooling effect, except for the air knife, the cooling water is directly sprayed on the blowing bag, and the cooling method such as hollow blowing.
5, extended
The rework extension of the finished product will enhance the effect. For example, the belt belt is driven by the front and rear rollers to cause the extension effect, and the tensile extension of the finished product is not easy to tear, but the transverse direction is easy to tear. The molecular weight distribution also affects the elongation during high-speed production. All extruded products, including fibers, have unequal extensions. Vacuum and pressure forming can also be considered as another form of extension.
6, shrinkage
Any raw material has a problem of shrinkage, which is caused by thermal expansion and contraction and internal stress generated by crystal formation.
Generally speaking, thermal expansion and contraction are easier to overcome, and it can be extended in processing to prolong the cooling time, and the pressure can be maintained continuously. The crystallization raw material tends to have a larger shrinkage difference than non-crystallization, and is about a thousandth in terms of PP. Sixteen, but ABS is only about four thousandths, the difference is very large. This part should be overcome on the mold, or often added with additives to reduce shrinkage. The extrusion plate also often adds LDPE to improve the necking problem.