GUIDE TO SELECTING NYLON STOCK SHAPES FOR WEAR-RESISTANT APPLICATIONS

For wear-resistant applications, nylon's toughness, low coefficient of friction and good abrasion resistance make it an ideal replacement for a wide variety of materials from metal to rubber (see applications table).

• Nylon weighs about 85% less than bronze.
• Nylon reduces lubrication requirements, and eliminates galling and corrosion problems.
• Nylon provides good sound dampening characteristics.
• Nylon is available in a broad range of grades and stock shape sizes, including both extruded shapes and near-net shapes.

While there are many basic types of nylons, the two most widely used grades are type 6/6 and 6. Various grades of each are available to meet specific end-use requirements.

Nylon 6/6 stock shapes are extruded and available in a variety of cross sections including rod, strip, tubing, custom profiles and plate.

Nylon 6 products are cast from caprolactam. It is typically supplied in rod, plate, tubular bar or custom shapes including near net castings and finished parts.

Nylon is easily fabricated into precision parts using standard metalworking equipment. Standard tooling is acceptable for cast nylon, extruded 6 and 6/6, including molybendenum disulfide-filled, talc-filled and calcium carbonate-filled grades. Carbide, carbide-tipped or polycrystalline diamond tooling is suggested for glass fiber reinforced, carbon fiber reinforced and graphite filled nylon.

Nylon has a proven record of outstanding service in a multitude of parts for such diverse fields as paper, textiles, electronics, construction, mining, metalworking, aircraft, food and material handling.

Of the two major types of nylons, 6/6 is slightly more heat resistant than 6. The short-term heat resistance of 6/6 is about 250°F, under no load (230°F for 6). The long-term temperature limit (continuous service temperature, CST) for 6/6 is 210°F (200°F for 6).

Slightly higher CST is possible with heat stabilized and filled grades. For example, molybendenum disulphide (MoS2)-filled nylon 6/6 has a CST of 220°F; and, heat-stabilized nylon 6 has a CST of 260°F.

Nylons have excellent resistance to hydrocarbon fuels, lubricants, and many organic solvents. They are, however, attacked by strong acids, oxidizing agents and concentrated solutions of certain salts.

Nylon 6/6 and 6 absorb moisture in high humidity or when submerged. Strength and wear resistance also decrease with increased water content. Equilibrium moisture content of nylon 6/6 and 6 at 50% relative humidity is approximately 2.5% and can be as high as 8% at saturation.

In general, small parts are most economical to machine from extruded nylon stock shapes. Large parts are more economical to machine from near-net cast nylon shapes. Near-net shapes, which require minimal finish machining, increase savings by reducing material cost and machining time. Like injection molding, casting allows the one-piece part combines several parts into one, thus reducing manufacturing, assembly and maintenance costs.

Small general purpose wear and structural parts -- Of all the unmodified nylons, extruded nylon 6/6 is the strongest, most rigid and has one of the highest melting points. Unmodified nylon 6/6 is stocked in both natural and black. Other colors are available on a custom basis. Unmodified nylon 6/6 stock shapes are FDA, USDA, NSF and 3-A Dairy compliant.

Small parts with improved load-bearing capability -- MoS2-filled nylon offers improved strength and rigidity. With a lower coefficient of linear thermal expansion than nylon 6/6, MoS2-filled nylon parts maintain better fit and clearances, and have less tendency to seize as bearings.

Small parts with improved load capacity or for improved frictional characteristics -- For applications requiring higher compressive strength and rigidity, 30% glass reinforced nylon 6/6 is available. It is stocked in diameters ranging from 10-mm to 150-mm (or .394 in. to 5.910 in.) lengths.

Large general purpose wear and structural parts -- Heat stabilized nylon 6 offers long-term thermal stability to 260°F. It is blue in color.

Unmodified type 6 nylon offers the highest strength and hardness of the nylon 6 grades. Natural (off-white), it is FDA, USDA and 3A-Dairy compliant.

Large parts with improved load bearing capability - Nylon 6/6 that contains finely divided particles of MoS2 offers enhanced load bearing capabilities, while maintaining the impact resistance inherent to nylon. It is the most commonly used grade for gears, sheaves, sprockets and custom parts. It is gray-black in color.

Large parts having the best wear resistance and lowest coefficient of friction -- Nylatron® NSM Nylon -- Proprietary type 6 nylon formulation produced using DSM's Monocast® process. Solid lubricant additives impart self-lubricating, high pressure/velocity and superior wear resistance characteristics. Nylatron NSM was developed specifically for demanding applications where larger size parts are required. It is ideal for bearings, gears and wear pads. In wear applications, Nylatron NSM lasts up to 10 times longer than standard type 6 nylon.

Large parts with improved load capacity or for improved frictional characteristics - Oil/MoS2-filled nylon 6/6 combines load capacity and improved frictional characteristics. It excels in higher pressures, and at low speeds-up to 40 fpm. It offers 20% lower coefficient of friction, 50% greater limiting PV, and a lower "k" factor than MoS2-filled nylon, and the lowest "slip-stick" of any nylon product making it ideal for slide pads, thrust washers and trunion bearings. It is dark blue in color.

For more information, contact Michael Oliveto, DSM Engineering Plastic Products, 2120 Fairmont Ave., Reading, PA 19612-4235, 800-366-0300, Fax: 800-366-0301, e-mail: communications@dsmepp.com, Web: www.dsmepp.com.