PA (Nylon) Injection Molding Technique

1. Preparation of Raw Materials

PA (polyamide) readily absorbs moisture from the air, which can negatively affect molding by reducing melt viscosity and causing surface defects such as bubbles and crazing. Mechanical properties can also degrade significantly.

• Drying is essential before molding.

• Vacuum drying is preferred:

• Temperature: 85–95°C

• Time: 4–6 hours

• Hot air drying can also be used:

• Temperature: 90–100°C

• Time: 8–10 hours

• After drying, PA materials should not be left exposed to air for more than 1–3 hours.

2. Melting Temperature

The barrel temperature should be selected based on the melting point of the specific PA grade, as well as part geometry and machine type.

• PA6: 220–300°C

• PA66: 260–320°C

• Processing window is narrow—strict control is necessary to avoid degradation.

Barrel Temperature Zones:

• Middle section: 20–40°C above melting point, 20–30°C below decomposition point

• Front section: 5–10°C lower than middle section

• Rear section (feed zone): 20–50°C lower than middle section

• Ensure effective cooling of the feed throat to prevent premature softening.

3. Injection Pressure

Injection pressure has a minor influence on final part strength but is critical for proper fill and surface quality. It depends on:

• Machine type

• Melt temperature

• Part geometry

• Mold design

4. Injection Speed

Injection speed should be optimized based on:

• Wall thickness

• Melt temperature

• Gate size

Avoid overly fast injection, which may cause:

• Material degradation due to excessive shear

• Discoloration

• Bubbles and burn marks

5. Screw Speed

Use moderate screw speed:

• Too fast → risk of overheating and material degradation

• Too slow → reduced plasticizing quality and lower productivity

6. Back Pressure

Use minimal back pressure necessary to ensure consistent melt quality:

• High back pressure can cause shear degradation and discoloration

7. Mold Temperature

Mold temperature significantly affects part properties:

• Higher mold temp → improves tensile strength, hardness, and dimensional stability

• Lower mold temp → better for thinner parts requiring elongation and clarity

• Higher mold temp increases shrinkage rate

8. Molding Cycle

Cycle time depends on part thickness:

• Thin-wall parts: Shorter injection, holding, and cooling times

• Thick-wall parts: Longer times are needed to prevent:

• Shrinkage

• Sink marks

• Voids and bubbles

9. Post-Processing

Post-molding treatments are necessary to relieve internal stresses and prevent shape distortion during storage and use.

10. Annealing

Used for high-precision parts:

• Annealing Medium: Oil or paraffin

• Temperature: 10–20°C above usage temperature

• Time: 10–60 minutes (based on part thickness)

11. Humidifying

For parts intended for use in humid or aqueous environments:

• Place in boiling water or potassium acetate solution

• Duration: 1–2 days

12. Residence Time

Avoid extended melt residence time in the barrel if temperature exceeds 300°C:

• Max recommended hold time: 20 minutes

• For long pauses, reduce barrel temperature to ~200°C

• Use HDPE or PP to purge and clean the barrel if necessary

If you need any PA (nylon) injection mould, welcome to contact Shine (email: shine@swymould.com or Phone: +86 15757668880), thanks!