With the rapid development of my country's plastics industry, the uses of plastics are becoming more and more widespread, and the requirements for plastic products are becoming higher and higher. For the injection molding machine industry, there are more and more studies on screws used to mold various products. In fact, it is difficult to meet the molding requirements of blending, coloring, and homogenization of different raw materials using the traditional three-stage universal screw. In order to comply with market requirements and based on the process characteristics and formula requirements of some raw materials during processing, our company has designed several new screws, which have better solved the shortcomings of the screw barrel in the injection process and achieved good results. . This article will give a brief introduction to several of the screw structures and applications.

1. The structure and application of the mixing ring screw.
       The characteristic of the machine mixing ring screw is that the mixing element is installed at the metering section, which mainly plays the role of mixing and homogenization. Based on mechanical manufacturing process considerations, there are generally two types of structures, namely pin type and barrier type.

The pin-type mixing element makes full use of the diversion effect of the pin during the plasticization process. During the diversion process, the tiny pieces that have not been plasticized in the previous section will absorb heat from the molten material from time to time, thereby making the entire molten material The temperature decreases. When the plastic passes through the pins, the solid phase in the material is crushed and refined, and the melting time is shortened. And due to repeated mixing, plasticized melt can be obtained. This structure is more suitable for raw materials that require higher temperature control and require less temperature rise during processing. Such as HPVC, PET transparent materials, etc. In the design, attention should be paid to the selection of parameters such as the location, number and circulation area of ​​the pins.

During the plasticizing process, the barrier-type mixing element uses the shearing effect of the barrier ribs between the feed chute and the discharging chute to further homogenize the remaining unplasticized tiny pieces. can also be mixed. With this structure, the material should contain a certain amount of solid phase material before entering the mixing section to maximize the efficiency of this element. Its color mixing and plasticizing effects are relatively good, but for some products with high transparency or raw materials with poor thermal stability, attention should be paid to the parameter selection of the mixing components.

2. The structure and application of the separation screw.
       The structural characteristic of the separation screw is to add a secondary spiral edge in the melting section to divide the main thread groove into two parts. During the plasticizing process of the screw, solid-liquid phase separation is formed, and the solid phase material is completely separated. It remains in the solid phase tank, and the gas in the solid phase tank is discharged from the material under the action of pressure, reducing bubbles in the product. At the same time, the heat exchange area between the solid phase material and the inner wall of the barrel is increased.

There are many structures of separate screws. In actual design and experiments, it is believed that in terms of the convenience of machining and the use effect, the main and auxiliary threads have the same lift, and the liquid phase groove and solid phase groove width of the screw groove should be kept equal. Starting from the compression section, the depth of the solid phase tank suddenly becomes shallower, while the depth of the liquid phase tank gradually becomes deeper until the end of the homogenization section. This structure is beneficial to products with high transparency and raw materials with poor thermal stability. And it has strong adaptability to raw materials.

The design of the separated screw must reasonably select the screw parameters based on the actual situation, including the compression ratio, the distribution of the three sections, and the position of the auxiliary thread.

3. The structure and application of double-wave screw.
       The structural characteristic of double-wave screw is to add a parallel secondary helix to the groove of single-wave screw, and the pitch is equal. The secondary helix is ​​lower than the main helix, and the wave crest of one groove is Corresponds to the trough of another spiral channel. During the plasticizing process, not only the materials on the main and auxiliary screws are sheared periodically, but also the materials on the main and auxiliary screws can be continuously concentrated, which is conducive to homogenization. Therefore, compared with other screws, it can not only improve the plasticizing ability , and can increase the mixing effect. It is suitable for injection molding of fillers, pigments, and foamed materials to obtain uniform components. It is also suitable for heat-sensitive raw materials such as HPVC to reduce degradation.

This type of screw requires relatively high processing accuracy and is difficult to process, so it is used less often.