Nylon 6/6
Also: PA66, PA 6.6, nylon 66, polyamide 66, Zytel, Nylon 101, Tecamid 66, Ertalon 66 SA, Nylatron GS (MoS2-filled), Nylatron, glass-filled nylon, PA6 / nylon 6 (the sibling)
Nylon 6/6 is the tough, wear-resistant workhorse plastic for gears, bushings and molded housings. Strong and cheap, but it absorbs water and grows. Values dry as molded.
Sourcing Nylon 6/6 parts or stock?
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At a glance
| Density | 1.14 g/cm³ (0.041 lb/in³) |
|---|---|
| Tensile strength | 83 MPa (12 ksi) at yield, dry as molded; about 62 MPa (9 ksi) at 50% RH |
| Yield strength | 83 MPa (12 ksi) tensile yield, dry as molded |
| Hardness | Rockwell R 120 (M 85), dry; about R 108 conditioned |
| Elongation | 20-50% dry; up to 150% or more conditioned |
| Modulus of elasticity | 3.0 GPa (0.43 Msi) tensile, dry; about 1.5 GPa (0.22 Msi) at 50% RH |
| Thermal | Melts at 255-265 °C (491-509 °F); Tg about 50-70 °C (120-160 °F) dry, lower wet; continuous service 93-105 °C (200-220 °F), heat-stabilized grades to 120 °C (250 °F); HDT 75-90 °C (165-195 °F) at 1.82 MPa unfilled |
| Composition | Polyhexamethylene adipamide, from hexamethylenediamine and adipic acid; unfilled, with heat stabilizer in most grades |
Typical values, Natural extruded rod and plate (Nylon 101 type), unfilled, dry as molded, 23 °C (73 °F). Confirm against the mill certificate and the purchase spec.
- MachinabilityGood
- Machines easily but chips are stringy and the part deflects under clamping; use sharp positive-rake tools and light cuts. Tolerances of ±0.1 mm (±0.004") are practical; tighter must state the humidity the part will live at.
- WeldabilityFair
- Molded parts weld by ultrasonic, vibration and hot-plate methods; the joint must be dry. Solvent bonding needs aggressive solvents (formic acid, phenol) that shops avoid; epoxy and cyanoacrylate bond after surface prep.
- FormabilityPoor
- Crystalline with a sharp melt; thin film thermoforms, but sheet and plate are not bent or formed in practice. Machine from stock or mold.
- Corrosion resistanceGood
- Resists oils, greases, fuels, alcohols, ketones, aliphatic and aromatic hydrocarbons, weak alkalis. Attacked by strong acids, phenols, formic acid, zinc chloride and oxidizers; hydrolyzes slowly in hot water above about 60 °C (140 °F). UV degrades natural stock; buy black outdoors.
Nylon 6/6 (PA66) is a semi-crystalline polyamide with a good balance of strength, stiffness, toughness, fatigue life and wear resistance at a low price. It is the most-molded engineering plastic after ABS and polycarbonate, and extruded natural rod and plate (often sold as Nylon 101) are stocked by every plastics distributor for machined gears, wear strips, rollers, sheaves, bushings and insulators.
Its defining quirk is moisture. Dry as molded it is stiff (about 3 GPa) and strong (about 83 MPa yield); at equilibrium with 50% relative humidity it holds about 2.5% water, its modulus drops by half, its impact strength roughly doubles, and it grows about 0.2-0.3% in every direction. Saturated in water it holds 8-9% and grows up to 1%. Producers publish two columns, DAM (dry as molded) and conditioned, and a part machined dry to a tight fit will bind after a humid summer.
Nylon 6 (PA6, cast nylon) is the sibling: slightly softer, tougher, a little more absorbent, and available cast in large slabs, tubes and rings that extruded 6/6 cannot reach. For large sheaves, wear plates and thick bushings, cast nylon 6 is usually what the shop quotes; for small precision parts and molded parts, 6/6.
Heat treatment
Not heat treated for strength. Stress relieve machined parts that must stay flat at about 150-165 °C (300-330 °F) in oil, roughly 30 minutes per 6 mm (1/4") of thickness, slow cool. Parts that will live in a humid environment are often "conditioned" (soaked in water or steam to equilibrium) before final machining so the size they are measured at is the size they will stay.
Tempers and conditions
- Natural (extruded, Nylon 101 type)
- Black (UV-stabilized)
- MoS2-filled (Nylatron GS)
- Glass-filled 30% (molded)
- Heat-stabilized
- Oil-filled / lubricated bearing grades
- Cast nylon 6 (the large-shape alternative)
- FDA grades
Stock forms
- Round rod
- Plate and sheet
- Tube
- Hex and square bar
- Cast slabs, rings and tubes (nylon 6)
- Molding pellets
Relative cost
Tier 2 of 5. About 1.5-2x HDPE per pound, a little below acetal; cast nylon 6 is cheaper still in large shapes. Glass-filled and lubricated grades cost more.
Typical applications
- Gears, sprockets, sheaves and cam followers
- Bushings, wear strips, guide rails and slide pads
- Rollers, casters and pulleys
- Molded housings, connectors, cable ties and fasteners
- Automotive under-hood parts (glass-filled, heat-stabilized)
- Electrical insulators and standoffs
- Hammer heads, impact pads and chain guides
Process compatibility
How Nylon 6/6 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | GoodGood | Easy to cut; stringy chips and moisture growth are the issues. Machine, then let the part condition before final inspection of tight fits. |
| CNC Milling | GoodGood | Sharp carbide, high speeds, climb milling for finish; clamp lightly because plate deflects and springs back. |
| CNC Turning | GoodGood | Bushings, rollers and sheaves from rod; polished inserts and a chip breaker keep the string under control. |
| Gear Cutting | GoodGood | Hobbed and shaped nylon gears are common for quiet, unlubricated drives; allow backlash for moisture growth. |
| Injection Molding | ExcellentExcellent | A leading molding resin; the pellets must be dried, and glass-filled grades warp less and hold more heat. |
| SLS 3D Printing | FairFair | SLS prints nylon, but PA12 or PA11, not PA66: lower strength and stiffness, useful as a prototype stand-in. |
| FDM 3D Printing | FairFair | Nylon filament prints on a heated, enclosed machine if kept bone dry; expect warp and lower strength than molded PA66. |
| Waterjet Cutting | GoodGood | Clean way to profile plate and sheet; the part absorbs some water at the cut edge and dries out again. |
| Laser Cutting | FairFair | Thin sheet and gaskets cut on CO2 lasers with a slightly browned edge; thick plate melts and re-fuses. Prefer routing or waterjet above about 3 mm (1/8"). |
| Vibratory Finishing | GoodGood | Deburrs molded and machined parts well; dry media leaves the surface matte. |
| Bead Blasting | FairFair | Uniform matte finish; keep pressure low so the media does not embed in a soft, conditioned surface. |
| Anodizing | Not recommendedNot recommended | Aluminum-only process; nylon cannot be anodized. Buy pigmented stock or dye the part (nylon dyes well with acid dyes). |
| Plating | Not recommendedNot recommended | Nylon can be electroless plated after an etch, but it is a specialty; plating-grade ABS is the usual route to a plated plastic part. |
Compare Nylon 6/6
Design and sourcing tips
- State the moisture condition with the tolerance: "dimensions apply at 50% RH equilibrium" or "machined dry, allow +0.3% growth". A tight fit machined dry will seize wet.
- Design bearings and gears with extra clearance and backlash: nylon grows with moisture and has a CTE of about 80-100 um/m·K.
- For thick bushings, big sheaves and wear plates, allow cast nylon 6 as an alternative; extruded 6/6 is not stocked in large sections.
- Use glass-filled 30% nylon in molded parts that must hold shape under load and heat; unfilled nylon creeps under sustained stress, especially wet.
- Choose acetal instead where size stability matters more than toughness, and UHMW where abrasion matters more than stiffness.
- Keep natural nylon out of direct sun or specify black, UV-stabilized stock: natural grades chalk and embrittle outdoors.
Frequently asked questions
- What is the difference between nylon 6 and nylon 6/6?
- Both are polyamides. Nylon 6/6 melts about 40 °C higher, is a little stiffer and harder, and absorbs slightly less water. Nylon 6 is tougher, machines a little more easily, and is available as cast slabs, rings and tubes in sizes extruded 6/6 cannot reach. For most machined parts either works; specify 6/6 for higher heat and stiffness, cast 6 for large shapes.
- Does nylon absorb water?
- Yes, more than any other common engineering plastic: about 2.5% at 50% relative humidity and 8-9% saturated for nylon 6/6. Absorbed water lowers stiffness and strength, raises toughness, and grows the part about 0.2-0.3% at room humidity and up to 1% saturated. Design fits and tolerances for the humidity the part will live at.
- Is nylon stronger than Delrin?
- Dry, nylon 6/6 is stronger and stiffer at about 83 MPa (12 ksi) yield versus about 69 MPa (10 ksi) for acetal homopolymer. At normal humidity nylon falls to about 62 MPa (9 ksi) and roughly half its dry stiffness, while acetal barely changes. Nylon wins on toughness and wear; acetal wins on stability and machinability.
- Can nylon be machined to tight tolerances?
- To about ±0.1 mm (±0.004") routinely, and ±0.05 mm (±0.002") on small features in a stable shop, but only for the moisture condition the part was machined in. Stress relieving before finishing and conditioning the part (soaking to equilibrium) before final inspection are what make tight nylon parts repeatable.
Processes that commonly use it
Related materials
Where to verify these values
- DuPont Zytel and Celanese / BASF Ultramid PA66 resin data sheets
- Ensinger TECAMID 66 and Mitsubishi Chemical Advanced Materials Nylatron / Ertalon stock-shape data
- ASTM D6779 and D5989
- ASTM D638, D790 and D570 (water absorption) test methods
