Nylon (PA) Injection Molding: A Buyer's Guide, Including Glass-Filled Grades

Nylon (polyamide, PA) is a primary engineering resin when you need strength, wear resistance, and survival under heat and chemicals: gears, bearings, brackets, under-hood parts. It is often glass-filled to raise strength and stiffness further. Place the grade decision inside the material selection guide, with moisture and warpage planned upfront.

Nylon Characteristics

Nylon is a family of engineering thermoplastics; PA6 and PA66 are the most common. Strength, toughness, wear resistance, and chemical and heat resistance are the usual reasons to specify it. Trade names include Ultramid and Zytel.

Buyers pick nylon for functional capability: structural loads, wear and abrasion on moving parts (gears, bushings), and heat/chemical resistance for under-hood environments, fuels, oils, and solvents. Glass-filled grades (for example 30% glass) raise stiffness and strength sharply.

Essential Planning Constraints

Moisture absorption: Nylon is highly hygroscopic. It absorbs water from air during processing and in service. Undried nylon causes splay and degradation in molding. In service, absorbed moisture can slightly change dimensions and properties.

Warpage in glass-filled grades: Glass boosts strength but shrinks differently along fiber flow versus across it. That anisotropic shrink makes glass-filled nylon prone to warpage. Flat or precise parts need careful design and tooling.

Processing Realities

The process window hinges on moisture. SABIC’s LNP processing guide categorizes all nylon grades (6, 6/6, 6/10, 6/12, 11, 12) as requiring drying before molding. Baseline is typically 3–4 hours at a dew point of 0 °F (−18 °C) or lower.

Unlike commodity resins where drying may only protect cosmetics, molding wet nylon at melt temperature attacks the polymer chain. The part may look fine and still be measurably weaker. When you qualify a molder for nylon, ask what dew point their dryer holds and whether they measure residual moisture, not only whether they “dry the material.”

Illustrative ranges (unfilled PA):

• Drying: ~80 °C for 4 h or more (critical).
• Melt temperature: ~230–290 °C.
• Mold temperature: ~40–90 °C.
• Mold shrinkage: ~0.8–1.5%+ (glass fill lowers this but adds directionality). (Confirm actual settings with the specific resin datasheet.)

The Impact of Glass Fill

Glass fiber changes dimensional behavior. Glass-fiber-reinforced compounds typically shrink one-third to one-half as much as unreinforced resin, and they shrink anisotropically.

Switching from unfilled nylon to 30% glass on an existing tool usually yields a larger part than intended, distorted differently. For complex parts, prove shrink on a prototype tool before committing to production steel.

Comparing Nylon

Against acetal/POM, nylon is generally tougher, more heat-resistant, and takes glass reinforcement better. Acetal absorbs less moisture and is more dimensionally stable and lower-friction. Match the choice to load, wear, heat, and dimensional needs in the material selection guide.

Buyer FAQs

What is nylon used for in injection molding?

Strong, wear-resistant functional parts: gears, bearings, bushings, automotive under-hood components, power-tool parts, structural brackets. Glass-filled nylon for high-load structural roles, sometimes replacing metal. If moisture-stable precision matters more than toughness, compare acetal before you lock nylon.

Why does nylon absorb moisture, and does it matter?

Nylon is hygroscopic. Undried nylon degrades in molding (weak parts, splay). In service, moisture can shift dimensions and properties, so tolerances may need adjustment. Require dew-point capability and residual moisture measurement in qualification for any drying-required nylon grade.

Why is glass-filled nylon so common?

Glass (often 30%) raises strength, stiffness, and heat resistance. Trade-offs: anisotropic shrink (warpage risk) and abrasiveness to tooling. Put warpage management and tool-steel wear expectations in the RFQ when you specify glass fill.

Nylon vs acetal (POM), which is better for gears?

Nylon for higher load or heat. Acetal for precision, low friction, and less moisture sensitivity. Decide from the duty cycle, not a generic preference, and name the grade in the RFQ.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, sell materials, or certify suppliers. Material behavior is grade-specific. Confirm properties and suitability against the manufacturer’s datasheet and your supplier’s engineering review.