What is a PVC Injection Molding Machine?-Ningbo Beilun Highsun Machinery Co., Ltd.

What is a PVC Injection Molding Machine?

PVC injection molding machines are specialized injection molding equipment for polyvinyl chloride (PVC). Due to the unique characteristics of PVC (such as heat sensitivity and corrosive decomposition gases), the design and functionality of these machines must be optimized to suit these characteristics.

Content

1 1. PVC Material Characteristics
2 2. PVC Injection Molding Machine Characteristics
3 3. Typical Applications
4 4. Operating Precautions

1. PVC Material Characteristics

Poor thermal stability: PVC easily decomposes at high temperatures, releasing corrosive hydrogen chloride (HCl) gas.
High melt viscosity: High injection pressure and screw design are required to ensure fluidity.
Additive dependency: Stabilizers and plasticizers are often required, impacting processing.

2. PVC Injection Molding Machine Characteristics

Screw: Small aspect ratio (L/D) (typically 18:1-20:1) and low compression ratio (1.4-1.8) to avoid excessive shear heating.
Barrel: Chrome-plated or nickel alloy for corrosion resistance; high temperature control accuracy (±1°C) to prevent local overheating. Temperature Control System: Multi-stage precision temperature control (4-6 zones) ensures slow and uniform plasticization of the PVC. The barrel nozzle may adopt an open design to reduce melt retention.
Corrosion Prevention: The exhaust system is equipped with corrosion-resistant devices (such as stainless steel exhaust valves). Some models are equipped with a gas neutralization device to handle HCl.
Mold Design: Runners and gates must avoid dead corners to prevent PVC retention and decomposition. Copper alloy molds may be used to improve thermal conductivity.

3. Typical Applications

Rigid PVC: Pipe fittings, door and window profiles, electronic housings.
Soft PVC: Seals, toys, medical tubing (medical-grade PVC required).
Others: Cable sheathing, wood-like decorative materials.

4. Operating Precautions

Temperature Monitoring: Overheating is strictly prohibited (typically, the barrel temperature should be ≤200°C).
Cleaning and Maintenance: Regularly clean the screw and barrel to prevent carbonized material accumulation.
Raw Material Pretreatment: The PVC may require drying (humidity ≤0.1%), but some formulations do not require drying.

PVC Injection Molding Machine FAQ Quick Reference

Problem Type	Specific Symptoms	Possible Causes	Solutions
Poor plasticization	Uneven melt, unmelted particles	1. Screw compression ratio too low 2. Improper barrel temperature setting 3. Excessive screw speed	1. Replace a screw with a higher compression ratio 2. Adjust the temperature control stages (increase the rear section temperature) 3. Reduce screw speed
Material decomposition	Yellowing, black spots, or bubbles in the product	1. Barrel/nozzle temperature too high 2. Excessive melt retention time 3. Poor raw material thermal stability	1. Reduce temperature (especially the nozzle area) 2. Shorten the cycle time or clean the barrel 3. Add heat stabilizer or replace the raw material
Corrosion Damage	Rust or wear on the screw/barrel surface	1. HCl corrosion caused by PVC decomposition 2. Raw material contains impurities (such as metal particles)	1. Use a chrome/nickel alloy screw and barrel 2. Install a raw material filter
Insufficient injection	Parts with missing material or incomplete filling	1. Insufficient injection pressure 2. Melt temperature too low 3. Poor mold venting	1. Increase injection pressure or speed 2. Increase material temperature appropriately 3. Add venting slots or reduce mold clamping force
Flow marks/silver streaks	Surface markings or silver streaks on the part	1. High raw material moisture content 2. Large melt temperature fluctuations 3. Mold temperature too low	1. Pre-dry raw materials (80°C x 2 hours) 2. Check temperature control system stability 3. Increase mold temperature (40-60°C)