Injection molding process of 5 common plastics

Today, Hejia Tech will take you to learn in detail about the injection molding process of 5 common plastics. The reason why they are "universal" is because of their large production volume, wide application, and relatively low price. Although both are called injection molding, there are significant differences in process parameters due to their different material properties.

The following are the key points of injection molding process for each type of plastic:

1. PP

- Injection speed

To reduce internal stress and deformation, high-speed injection should be chosen, but some grades of PP and molds are not suitable

- Melt Temperature

The temperature setting during injection processing should not exceed 275 ℃, and the melting section temperature is best at 240 ℃.

- Adhesive back pressure

The back pressure of the melt adhesive can be adjusted to 5 bar, and the back pressure of the color powder can be appropriately increased.

2. PE

- Barrel temperature: As PE is a crystalline polymer, the grains absorb a certain amount of heat during melting, so the barrel temperature should be 10 degrees higher than its melting point. For LDPE, the barrel temperature is controlled at 140-200 ℃, while for HDPE, the barrel temperature is controlled at 220 ℃. The minimum value is taken at the rear of the barrel, and the maximum value is taken at the front.

- Mold temperature: The mold temperature for LDPE is usually controlled at 30 ℃ -45 ℃, while the temperature for HDPE is correspondingly increased by 10-20 ℃.

- Injection pressure: Due to the good fluidity of PE, except for thin-walled and slender products, a lower injection pressure should be carefully selected, generally 50-100MPa. The shape is simple. Plastic parts with larger walls can have lower injection pressure, while those with larger walls can have higher injection pressure.

3. PVC

Typical application scope: water supply pipelines, household pipelines, house wall panels, commercial machine shells, electronic product packaging, medical equipment, food packaging, etc.

Injection mold process conditions:

1. Drying treatment: Drying treatment is usually not required.

2. Melting temperature: 185~205 ℃ Mold temperature: 20~50 ℃.

3. Injection pressure: can reach up to 1500 bar.

4. Holding pressure: can reach up to 1000 bar.

5. Injection speed: To avoid material degradation, a considerable injection speed is generally required.

6. Runner and sprue: All conventional sprues can be used.

7. Chemical and physical properties: Rigid PVC is one of the most widely used plastic materials.

4. PS

Typical application scope: product packaging, household items (tableware, trays, etc.), electrical (transparent containers, light source diffusers, insulation films, etc.).

Injection molding process conditions:

1. Drying treatment: Unless stored improperly, drying treatment is usually not required. If drying is required, it is recommended to dry at 80 ℃ for 2-3 hours.

2. Melting temperature: 180-280 ℃. The upper limit for flame-retardant materials is 250 ℃.

3. Mold temperature: 40-50 ℃. 4. Injection pressure: 200~600 bar.

4. Injection speed: It is recommended to use a fast injection speed.

5. Runner and sprue: All conventional types of sprues can be used.

5. ABS

Typical application scope: automobiles (instrument panels, tool doors, wheel covers, mirror boxes, etc.), refrigerators, high-strength tools (hair dryers, mixers, food processors, lawn mowers, etc.), telephone housings, typewriter keyboards, entertainment vehicles such as golf carts and jet sleds.

Injection molding process conditions:

1. Drying treatment: ABS material has hygroscopicity and requires drying treatment before processing. It is recommended to dry for at least 2 hours at 80-90 ℃. The material temperature should be ensured to be less than 0.1%.  

2. Melting temperature: 210~280 ℃; Suggested temperature: 245 ℃. Mold temperature: 25~70 ℃. The temperature of the mold will affect the smoothness of the plastic parts, and lower temperatures will result in lower smoothness.

3. Injection pressure: 500~1000 bar.

4. Injection speed: medium high speed

The above are the 5 general plastic molding processes explained to you by Hejia Tech. Hejia Tech is a company specializing in injection molding,and we have more than 20 years of experience in injection mold and product R&D,providing one-stop professional service.