PVC

PVC is the third most widely used plastic, offering a well-balanced combination of mechanical strength, chemical resistance, and weatherability. It performs reliably in both indoor and outdoor applications, maintains good toughness across a wide temperature range, and adapts well to various formulations such as rigid, flexible, and reinforced grades.

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Contents

1.Advantages of PVC Injection Molding

2.Applications of PVC Molded Parts

3.Tips for Better Surface Finish

4.Optimal Molding Parameters

1. Advantages of PVC Injection Molding

Excellent chemical resistance and strong weatherability

Good toughness with stable mechanical performance

Flame-retardant properties and reliable dimensional stability

PVC injection molding is widely used in construction, electrical components, piping systems, medical products, and industrial equipment.

We have produced PVC molded components for:

Mechanical equipment: customized PVC components and functional parts tailored for diverse industrial applications.

2. Application Fields of PVC Injection Molding

Automotive: cable insulation, sealing components, interior trims, protective sleeves

Electrical Appliances: connector housings, insulation parts, switch components

Consumer Products: water pipe joints, garden fittings, protective covers

3. How to Achieve a Good Surface Finish for PVC Injection Molded Parts

The appearance of PVC parts depends heavily on mold condition, temperature control, and processing stability. Since PVC has narrow processing temperature windows and is prone to thermal decomposition, precise control and proper formulation are essential.

3.1 Mold Quality

Cavity finish: Scratches, pits, or rough surfaces easily appear on glossy PVC parts. Cavities are polished or chrome-plated to prevent defects.

Cleanliness: PVC decomposition residues may cause burn spots. Regular and thorough cleaning is necessary.

Draft angle: Adequate draft prevents drag marks, which are more noticeable on PVC parts due to their relatively soft surface.

Venting system: Poor venting leads to burn marks or black spots because PVC decomposes quickly at high temperature. Venting grooves and pins are optimized.

Gate and runner design: Smooth transitions and appropriate gate size reduce shear heat, lowering the risk of PVC degradation.

3.2 Molding Parameters

Injection speed: Too fast increases shear heat and may cause yellowing; too slow may result in flow lines. Balanced speed is crucial.

Cooling system: Uniform cooling minimizes deformation, especially for rigid PVC components.

Holding pressure & time: Proper settings help avoid sink marks and maintain dimensional stability.

Melt temperature: PVC has a strict temperature limit; excessive heat can cause black spots, yellowing, or fumes. We maintain a narrow and safe temperature range.

3.3 Raw Materials

Granule uniformity: Consistent particle size ensures stable melting and reduces surface defects.

Moisture content: PVC absorbs little moisture, but pre-drying may be required for certain formulations to avoid bubbles.

Additive and colorant dispersion: Poor dispersion can cause streaks, uneven gloss, or color inconsistency. We ensure uniform mixing.

Impurities: Even minor contaminants can cause black dots due to PVC's thermal sensitivity. Materials are kept clean and screened.

Recycled content: Excess recycled PVC may increase brittleness or reduce surface quality. Ratio is strictly controlled.

4.Best Parameters for PVC Injection Molding

4.1 Key Properties

Moisture Sensitivity: PVC is not highly hygroscopic, but slight drying (60–70 °C, 1 hour) helps avoid bubbles for certain grades.

Flow Behavior: PVC has a narrow processing window and is shear-sensitive; low shear and moderate pressure ensure stable filling without degradation.

Shrinkage Rate: 0.2–0.6% (much lower than PP/PE), allowing high dimensional accuracy.

Machine Type: Screw-type machines with temperature-controlled feeding zones are recommended to avoid overheating.

Injection Volume: Ideal usage is 50–70% of machine capacity to prevent excessive residence time, which may cause material degradation.

Runner Design:

- Main runner: ≤100 mm

- Sub-runner: 4–8 mm

- Designed to reduce shear heat and maintain smooth flow.

Ejection Force: Should be moderate; PVC parts may deform if ejected too forcefully, especially soft PVC.

Post-Treatment: For rigid PVC parts, post-annealing at 60–80 °C for 1 hour improves dimensional stability and reduces internal stress.

4.2 Typical Molding Parameters

The molding parameters for PVC parts vary depending on the grade (rigid or flexible), stabilizer system, part thickness, and required surface finish. Since PVC has a narrow processing window and is sensitive to overheating, precise temperature and shear control are essential to prevent yellowing, burn marks, or degradation.

These parameters serve as general guidelines. Fine-tuning is required based on part thickness, stabilizer formulation, screw design, and runner layout to achieve optimal surface finish, mechanical strength, and color stability without risking PVC decomposition.