Brief description of injection molding processing technology 1

Plastics is a new type of material that is artificially synthesized by people using chemical methods. The use of various plastics processed products has become an indispensable production and living material for various sectors of the national economy and people's lives. Injection molding is the most commonly used method in plastic molding processing. Injection molding can realize production automation, high-speed, and has extremely high economic benefits.

In the face of huge market demand, various businesses have invested large amounts of money in the injection molding industry, purchased injection molding machines and raw materials, then, how can we turn raw materials into products? This involves the injection molding processing technology. Only by mastering this technology can we process high-quality products and create higher production efficiency.

Injection molding is a cyclic process, and each cycle includes the following: raw material pretreatment quantitative feeding - melt plasticization pressure injection injection mold cooling cooling mold removal and product handling. The injection molding processing technology is also the parameter required for control and the problem to be noticed in each process of the entire cycle. The following is a brief description of the process technology in each process.

The first is the pretreatment of raw materials, including the drying and color mixing of raw materials. Some plastics, such as polycarbonate (PC), polyamide (PA), and polyethylene terephthalate (PET), because they contain hydrophilic substances on their macromolecules, are easily hygroscopic, causing them to have different levels of moisture. When the moisture content is higher than the specified level, the surface of the product is accompanied with defects such as silver thread, markings, and air bubbles. When the moisture content is high, the polymer material is degraded. In general mass production of plastics should be used boiling or air drying, each plastic has the best drying temperature and drying time, too much time, the effect is not good, some plastic drying temperature and time in Table 1 (to letter Easy SDL straight knot hopper as an example):

Table I

No. Drying humidity of raw materials (degrees) Time (hours)
1 PE, PS, PP 80 2-3
2 NYLON SERIV 75 4-8
3 ABS, AS 80-85 2-4
4 PC 120 4-7
5 PVC 70 1-5

However, if a hydrophilic plastic such as PET is dried, it is impossible to use only an ordinary drying hopper. A vacuum oven or a dehumidifier is also required, and a dehumidifier can be used for continuous production. When the company processed PET preforms, it used a Sidson SD-90 dehumidifier to continuously dry at 140 degrees for 5 hours, removing 98% of the moisture content. The effect was very significant. As for the color mixing, generally used mixer, if you need to accurately control the masterbatch content, you can use masterbatch mixer, such as Sweden's CF series can be controlled according to the operation of the machine to control the masterbatch measurement.

The second is the quantitative addition, which is related to the accuracy of the machine.

The third is melt plastication. The main points to be mentioned in this process are the following three aspects:

1. Correctly select the barrel and screw; according to the processing performance of the plastic, select the correct barrel and screw. Our company has developed a number of special screws and barrels for customers to choose from for the characteristics of some plastics, such as: exhaust screw, separate screw, special screw and barrel for thermosetting plastic, PVC screw, PC screw and double metal material Tubes, screws and so on.

2. The setting of heating temperature; The choice of barrel temperature is related to the characteristics of various plastics. Each plastic has its own viscous flow temperature (T1) and melting point (T2), in addition to a decomposition temperature (T3).

The optimum temperature of the barrel should be between T1-T3 or T2-T3. If the range is smaller, the barrel temperature should be lower, otherwise it can be increased. The temperature of several commonly used plastics is shown in Table II. (to be continued)