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What should we pay attention to when PET bottle preform injection molding?

What should we pay attention to when PET bottle preform injection molding?

  • Categories:Industry News
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  • Time of issue:2019-07-22

(Summary description)1. Treatment of plastics Because the PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, the pellets are more sensitive to water at high temperatures. When the water content exceeds the limit, the molecular weight of PET decreases during processing, and the products become colored and brittle. Due to this, the material must be dried before processing. The drying temperature is 150°C for more than 4 hours, generally 170°C for 3-4 hours. The dryness of the material can be checked by the air shot method.​​ Generally, the proportion of recycled materials should not exceed 25%, and the recycled materials should be dried.​​ 2. Selection of injection molding machine Because PET has a short stable time after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (water-containing material) should not be less than machine injection. 2/3 of the amount. Based on these requirements, Ramada has developed a series of small and medium-sized PET plasticizing systems in recent years. Clamping force is selected according to greater than 6300t/m2.​​ 3. Mold and gate design PET preforms are generally formed by hot runner molds. There should be a heat shield between the mold and the template of the injection molding machine. The thickness of the heat shield is about 12mm, and the heat shield must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.​​ 4. Melt temperature Can be measured by air-shot method. 270-295℃, the enhanced GF-PET can be set to 290-315℃, etc.​​ 5. Injection speed Generally, the injection speed should be fast, which can prevent premature solidification during injection. But too fast, the high shear rate makes the material brittle. Shots are usually completed within 4 seconds.​​ 6. Back pressure The lower the better, so as not to wear out. Generally not more than 100bar. Usually not needed. 7. Residence time Do not use excessive residence times to prevent molecular weight loss. Try to avoid temperatures above 300°C. If the downtime is less than 15 minutes. It only needs to be air-shot; if it takes more than 15 minutes, it should be cleaned with viscosity PE, and the temperature of the barrel should be lowered to the PE temperature until it is turned on again.​​ 8. Precautions (1) The recycled material should not be too large, otherwise it is easy to "bridge" at the blanking place and affect the plasticization.​​ (2) If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and opacity. The mold temperature is low and uniform, the cooling speed is fast, and the product is transparent with less crystallization.

What should we pay attention to when PET bottle preform injection molding?

(Summary description)1. Treatment of plastics

Because the PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, the pellets are more sensitive to water at high temperatures. When the water content exceeds the limit, the molecular weight of PET decreases during processing, and the products become colored and brittle. Due to this, the material must be dried before processing. The drying temperature is 150°C for more than 4 hours, generally 170°C for 3-4 hours. The dryness of the material can be checked by the air shot method.​​

Generally, the proportion of recycled materials should not exceed 25%, and the recycled materials should be dried.​​

2. Selection of injection molding machine

Because PET has a short stable time after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (water-containing material) should not be less than machine injection. 2/3 of the amount. Based on these requirements, Ramada has developed a series of small and medium-sized PET plasticizing systems in recent years. Clamping force is selected according to greater than 6300t/m2.​​

3. Mold and gate design

PET preforms are generally formed by hot runner molds. There should be a heat shield between the mold and the template of the injection molding machine. The thickness of the heat shield is about 12mm, and the heat shield must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.​​

4. Melt temperature

Can be measured by air-shot method. 270-295℃, the enhanced GF-PET can be set to 290-315℃, etc.​​

5. Injection speed

Generally, the injection speed should be fast, which can prevent premature solidification during injection. But too fast, the high shear rate makes the material brittle. Shots are usually completed within 4 seconds.​​

6. Back pressure

The lower the better, so as not to wear out. Generally not more than 100bar. Usually not needed.

7. Residence time

Do not use excessive residence times to prevent molecular weight loss. Try to avoid temperatures above 300°C. If the downtime is less than 15 minutes. It only needs to be air-shot; if it takes more than 15 minutes, it should be cleaned with viscosity PE, and the temperature of the barrel should be lowered to the PE temperature until it is turned on again.​​

8. Precautions

(1) The recycled material should not be too large, otherwise it is easy to "bridge" at the blanking place and affect the plasticization.​​

(2) If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and opacity. The mold temperature is low and uniform, the cooling speed is fast, and the product is transparent with less crystallization.

Information

1. Treatment of plastics

Because the PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, the pellets are more sensitive to water at high temperatures. When the water content exceeds the limit, the molecular weight of PET decreases during processing, and the products become colored and brittle. Due to this, the material must be dried before processing. The drying temperature is 150°C for more than 4 hours, generally 170°C for 3-4 hours. The dryness of the material can be checked by the air shot method.​​

Generally, the proportion of recycled materials should not exceed 25%, and the recycled materials should be dried.​​

2. Selection of injection molding machine

Because PET has a short stable time after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (water-containing material) should not be less than machine injection. 2/3 of the amount. Based on these requirements, Ramada has developed a series of small and medium-sized PET plasticizing systems in recent years. Clamping force is selected according to greater than 6300t/m2.​​

3. Mold and gate design

PET preforms are generally formed by hot runner molds. There should be a heat shield between the mold and the template of the injection molding machine. The thickness of the heat shield is about 12mm, and the heat shield must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.​​

4. Melt temperature

Can be measured by air-shot method. 270-295℃, the enhanced GF-PET can be set to 290-315℃, etc.​​

5. Injection speed

Generally, the injection speed should be fast, which can prevent premature solidification during injection. But too fast, the high shear rate makes the material brittle. Shots are usually completed within 4 seconds.​​

6. Back pressure

The lower the better, so as not to wear out. Generally not more than 100bar. Usually not needed.

7. Residence time

Do not use excessive residence times to prevent molecular weight loss. Try to avoid temperatures above 300°C. If the downtime is less than 15 minutes. It only needs to be air-shot; if it takes more than 15 minutes, it should be cleaned with viscosity PE, and the temperature of the barrel should be lowered to the PE temperature until it is turned on again.​​

8. Precautions

(1) The recycled material should not be too large, otherwise it is easy to "bridge" at the blanking place and affect the plasticization.​​

(2) If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and opacity. The mold temperature is low and uniform, the cooling speed is fast, and the product is transparent with less crystallization.

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