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PVC is a versatile thermoplastic available in two main forms:
Rigid PVC (uPVC): Hard, durable, and used in construction.
Flexible PVC: Plasticized for flexibility, used in cables, hoses, etc.
PVC is widely used because it’s:
Flame-retardant (self-extinguishing)
Resistant to water, chemicals, and corrosion
Cost-effective and durable
PVC injection molding involves melting PVC pellets and injecting them into a steel mold to form parts. However, PVC requires extra care due to its thermal sensitivity — it can decompose and release toxic gases (like HCl) if overheated.
Feeding & Melting: PVC pellets are slowly heated (usually ~160–200°C). Precise temperature control is crucial.
Injection: Molten PVC is injected into a closed mold at moderate pressure.
Cooling: The part cools and solidifies in the mold.
Ejection: The finished part is removed from the mold.
Post-processing: Trimming, printing, or assembly if needed.
| Industry | Applications |
|---|---|
| Construction | Pipe fittings, window profiles, wall panels |
| Electrical | Cable connectors, insulators, switch housings |
| Medical | IV components, tubing (usually from flexible PVC) |
| Consumer Goods | Credit cards, cases, furniture parts |
| Property | Rigid PVC | Flexible PVC |
|---|---|---|
| Density | ~1.4 g/cm³ | ~1.1–1.3 g/cm³ |
| Tensile Strength | High | Medium |
| Impact Resistance | Moderate | High |
| Flexibility | Low | High |
| UV Resistance | Good (with additives) | Moderate |
| Chemical Resistance | Excellent | Excellent |
| Flame Resistance | Self-extinguishing | Self-extinguishing |
Melt Temperature: 160–200°C (must not exceed 210°C)
Mold Temperature: 40–60°C
Injection Pressure: 700–1,200 bar
Screw Speed: Low to avoid shear and overheating
Drying: Usually not required, but may be dried at 60°C for a few hours if needed
Corrosion-resistant steel (like stainless) is required due to HCl gas.
Venting is critical to release gases and avoid burn marks.
Smooth flow paths reduce shear and risk of degradation.
Moderate gate size and well-balanced runners help prevent pressure imbalances.
Excellent chemical and weather resistance
Good dimensional stability
Self-extinguishing (fire retardant)
Durable and impact-resistant (especially with modifiers)
Wide range of applications (rigid and flexible grades)
| Issue | Description |
|---|---|
| Thermal Degradation | Overheating releases toxic HCl gas; needs precise temperature control |
| Tooling Corrosion | Requires rust- and acid-resistant mold materials |
| Flow Properties | Higher viscosity makes it harder to fill thin walls |
| Odor & Gas Venting | Proper exhaust systems needed for operator safety |
| Additive Sensitivity | Requires stabilizers and plasticizers to modify performance |
| Property | PVC | ABS | PP |
|---|---|---|---|
| Chemical Resistance | Excellent | Moderate | Excellent |
| Heat Resistance | Moderate | Moderate | Moderate |
| UV Resistance | Good (with additives) | Fair | Poor |
| Flame Retardance | Very good | Poor | Poor |
| Flexibility | Variable (rigid or soft) | Moderate | High |
| Cost | Low | Moderate | Low |
| Defect | Cause | Solution |
|---|---|---|
| Burn Marks | Overheating or poor venting | Lower melt temp, improve venting |
| Short Shots | High viscosity or poor flow | Increase temp (within safe range), adjust pressure |
| Discoloration | Degradation | Lower screw speed, reduce residence time |
| Flash | Excessive injection pressure | Tighten clamp, balance mold |
Use PVC if you need:
High durability and weather resistance
Fire resistance
Strong, chemically resistant parts at low cost
Avoid PVC if:
The part requires exposure to high temperatures
You lack ventilation or corrosion-proof equipment
Precision or high gloss finishes are a priority
Due to the toxic fumes and potential for tool corrosion, PVC injection molding should always be performed using specialized equipment and under proper ventilation. Choosing the right heat stabilizers and mold materials is essential for long-term mold health and part quality.
