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PA6

Poliamida 6 (Nylon)

PA6·Polyamides·Semi-crystalline

Nylon 6 (PA6) is the most versatile engineering plastic for mechanical parts: gears, bearings, bushings, fasteners and anything that moves, rubs or carries load. Excellent wear resistance, natural self-lubrication, superior toughness and reasonable cost make it the default material when a part has to survive millions of cycles without breaking — from automotive to appliances, technical textiles and industrial hardware.

But it has an Achilles heel: it absorbs water from the air (up to 2–3% at saturation), and that changes its properties and dimensions. Moisture makes it tougher but less rigid; poor drying degrades it catastrophically via hydrolysis during injection. Here we have compiled the reference ranges from the PDS, plus the questions that come up over and over on the shop floor: how to dry it, when PA6 vs PA66 makes sense, when to switch to POM, what glass fiber (PA6-GF) does, and why new gears creak for 24 h until they acclimate.

Share your experience in the comments — ranges vary by manufacturer, grade (neat, GF, lubricated, FR) and ambient humidity, and collective discussion is what gets us out of trouble on the floor.

The ranges shown in these data tables were compiled by the MVPS team from various parameter sheets and literature, integrating the lower and upper limits for each material type.

This information must be carefully reviewed when developing injection molding processes. Final ranges and processing tolerances are the responsibility of the engineer in charge.

These ranges are not recommended for developing specific process tolerances. MVPS always recommends requesting and consulting the supplier's data sheet.

General Properties

Chemical StructureSemi-crystalline
Specific Gravity (Density)1.13:1
L/D Ratio18 – 22:1
Compression Ratio2 – 2.5:1
Tonnage Factor6.18 – 7.72kN/cm²
Thermal Diffusivity0.151mm²/s
Max Shear Rate60,0001/s
Shrinkage0.5 – 1.5%
Regrind30%
Heat Deflection (HDT) @ 1.82 MPa140°C
Glass Transition (Tg) @ 10°C/min60°C
Vicat Softening @ 50N180°C

Drying

Drying Temperature74 – 99°C
Drying Time6 – 16h
Recommended Moisture0.2%
Recommended Dryer TypeDesiccant
Dew Point-40°C

Temperatures

Melt232 – 288°C
Nozzle232 – 288°C
Front227 – 282°C
Middle216 – 277°C
Rear204 – 260°C
Demolding96 – 102°C
Mold (Cooling)79 – 91°C
Feed Throat10 – 49°C

Processing

Back Pressure3.4 – 6.9bar
Screw Speed50 – 80RPM
Injection SpeedLow – Medium
Barrel Occupancy20 – 70%
Injection Pressure750 – 1,250Pbar
Holding Pressure188 – 1,000Pbar
Cushion3.2 – 6.4mm

Mold

Runner Diameter3.05 – 6.1mm
Gate Diameter0.76 – 1.52mm
Gate Area0.46 – 1.82mm²
Wall Thickness0.76 – 4.57mm

Venting

Depth (Vent Depth)0.0203 – 0.0406mm
Land (Vent Land)0.508 – 1.02mm
Width (Vent / Clearance)3.05 – 10.2mm
Relief (Relief Channel)0.127 – 0.254mm

Frequently asked questions

PA6 is a semi-crystalline engineering thermoplastic obtained by ring-opening polymerization of caprolactam (a cyclic 6-carbon monomer). Result: linear chain with amide groups (–CO–NH–) that form inter-chain hydrogen bonds — those bonds are the source of its toughness, wear resistance and… its affinity for water. Density ~1.13 g/cm³ (1.35 with 30% glass fiber).
Amide groups attract and bond to water molecules. At equilibrium at 50% RH it absorbs ~3%; at 100% RH, up to 9–10% of its weight. Moisture plasticizes the material: a dry part is rigid and brittle, a conditioned part is tough and ductile. Implications: (1) the part grows dimensionally ~0.6% per 1% moisture absorbed, (2) stiffness drops 30–50% going from dry to conditioned, (3) impact rises significantly. Design considering the conditioned state (equilibrium with the use environment), not the dry as-molded state.
At injection temperatures of 230–260°C, absorbed moisture (>0.2%) reacts with the polymer chain via hydrolysis, breaking it and dropping molecular weight. Result: 30% loss in tensile strength, 15–20% in impact, silver streaks, bubbles and brittle parts. Always desiccant: 80°C for 4–6 h, dew point ≤ –30°C, target moisture ≤ 0.2%. If material came ready-to-mold in sealed bags with desiccant and you opened just for use, you can skip drying for a short shift; if open >2 h on the floor, drying is mandatory.
PA66 wins on: service temperature (HDT ~255°C vs 220°C for PA6), stiffness, creep resistance under sustained load, better dimensional stability (absorbs less moisture), under-hood automotive. PA6 wins on: impact and toughness (especially at low temperature), easier processing (melts at 220°C vs 260°C), better surface finish, cost (~15–20% cheaper). Rule of thumb: gears and bearings at high temperature → PA66. Mechanical parts at room temperature with impacts → PA6. Technical textiles (rope, fabric) → PA6 almost always.
Depends on environment: POM wins on dimensional stability (absorbs <0.2% vs 3% for PA6), precision, dry-running (self-lubrication at low speed), broader chemical resistance. PA6 wins on impact, wear resistance under high load, higher continuous-use temperature tolerance (90 vs 80°C), cost. Rule of thumb: if the gear lives in a dry environment at low speed → POM. If it sees high loads, impacts or variable humidity → PA6 (especially PA6-GF). For submillimeter precision → POM. For large industrial gears → PA6.
Typical loading: 15%, 25%, 30%, 50% by weight. Each 10% of GF: ~30% more stiffness, ~40% more tensile strength, ~25% less shrinkage (from 1.5–2% down to 0.3–0.8%), better dimensional stability under humidity. Downsides: loses toughness, attacks screw flights (raise L/D and consider bimetallic screw), surface with visible fibers if mold isn't hot enough (>80°C). For structural parts (housings, supports, brackets) → 30% GF is the sweet spot. For precision gears → consider GF + internal lubricant (PTFE, MoS₂).
Typical shrinkage 1.5–2% unfilled, 0.3–0.8% with 30% GF. But there's an additional process: post-molding, the part absorbs ambient moisture and grows dimensionally 0.5–1% in the first 48–72 h until reaching equilibrium. Gears creak because they came out of the mold undersized (when dry) and haven't yet acclimated to the final environment. That's why many OEMs specify pre-conditioning: immerse the part in 80°C water for 2–4 h, or leave it 48 h at 50% RH before measuring/using.
The PDS marks 41–79°C unfilled, 80–100°C for PA6-GF. Hotter (70–80°C unfilled, 90–100°C with GF) = higher crystallinity (more rigidity and final dimensional stability), better surface, better detail reproduction. Cooler = shorter cycle but part with incomplete crystallinity that will slowly crystallize in service (= dimensions that change over time). For gears and precision parts: always ≥80°C.
The PDS marks 25% as the maximum. Each reprocess slightly degrades molecular weight and increases moisture sensitivity. For load-bearing structural parts (gears, brackets) many OEMs limit to 10% or forbid regrind. The trick with recycled PA6: always re-dry it before each cycle — regrind absorbs moisture from ambient air faster between operations than virgin material.
Not by default — pure PA6 yellows and loses toughness under UV in just a few months. For outdoor use you need grades with UV stabilizers (HALS + UV antioxidants) or the classic PA6 with carbon black, which is the most UV-resistant but loses the color option. For under-hood applications (high temp + possible indirect UV) → PA66-GF with thermal stabilization. For garden tools or outdoor electrical connectors → black PA6 always.

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