PVC injection molding products

Because of its low price, PVC materials are inherently anti-inflammatory, strong and strong, have good chemical resistance, and have a shrinkage rate of 0.2-0.6%. The products are increasingly used in electrical appliances, machinery, construction, daily necessities, toys, and packaging. Based on the characteristics of PVC materials, the analysis of the product injection molding process is as follows:

1. Characteristics of PVC materials

PVC has poor thermal stability, the molding temperature is close to the decomposition temperature, the fluidity is poor, and it is easy to form bad defects in appearance. PVC material has poor heat resistance and is most likely to be scorched, generate acidic gas and corrode the mold. Plasticization can be added during processing Generally, additives must be added to increase its fluidity. It has good strength, electrical insulation, and chemical resistance.

2. Mold and gate design

In order to shorten the injection molding cycle, the shorter the injection nozzle, the better. The cross section should be circular. The diameter of the injection nozzle should be at least 6 mm, tapered, and the inner angle should be 5 degrees. It is best to add a cold slug well and a cold slug. The well prevents poorly melted semi-solid materials from entering the mold cavity, which would affect the surface finish and product strength.

The draft angle should be between 0.50 and 10 to ensure that there is sufficient exhaust equipment in the mold cavity. The commonly used exhaust hole size is 0.03-0.05mm deep and 6mm wide, or the clearance around each ejector pin is 0.03-0.05 mm. The mold should be made of stainless steel or hard chrome plated.

3. PVC molding process

PVC is a heat-sensitive plastic. Overheating or excessive shearing will cause decomposition and spread rapidly, because one of the decomposition products (such as acid or HCI) will produce a catalytic effect, causing further decomposition in the process. The acidic substance will corrode the metal and change it. If it becomes dented, the protective layer of the metal will peel off, causing rust, which is even more harmful to the human body.

1. Screw padding: The screw padding is between 2 and 3mm, and the chance is greater for large-scale applications.

2. Injection volume: The actual barrel residence time cannot exceed 3 minutes.

3. Barrel temperature setting:

The temperature provided can only be used as a reference. Appropriate adjustments should be made according to the actual conditions of the machine and raw materials. It may also exceed the recommended range.

4. Barrel residence time: Under temperature control of 2000C (rubber material), the barrel residence time can exceed 5 minutes at most.

5. Injection speed: The injection speed should be slow, otherwise excessive shearing will degrade the material. When using UPVC to produce extremely smooth thick-walled products, multi-level injection speeds should be used. If there are light brown stripes radiating from the gate, that is Indicates that the injection speed is too fast.

6. Back pressure: The commonly used surface value is 5bar. Increasing the back pressure is beneficial to color mixing and exhaust, but the back pressure should be as low as possible.

7. Shutdown: Due to the low overheating stability of PVC, the shutdown step is very important. The barrel must be clean without leaving any PVC. Other thermoplastics with high overheating stability that are not resistant to PVC can be used (such as PMMA, PP, LDPE, or GPPS), do not mix POMT UPVC in the same barrel, otherwise it will cause excessive chemical reaction and cause serious damage to the machine.

8. Mixing ratio: The maximum mixing ratio of the nozzle material is 20%, otherwise it will affect the quality of the product.

9. Typical products: The main uses of UPVC are to manufacture drainage pipes, or casings of computers and televisions, water filter tanks, photocopier casings, electric meters and gas casings, transparent covers of printing machines, ventilation styles and various electronic parts wait.