SpecialFocus

f the variety of performance plastics available for use in the heavy equipment industry, monomer cast nylon type 6 and type 6/12 materials are a tried-and-true staple. For anything from a pivot bushing in an engine cowling to a cushion pad at the top of a piling, cast nylon 6 and 6/12 has been trusted to perform in a wide variety of applications and environments for more than 60 years. You may ask, what is it about this material that makes it a good fit for heavy equipment and how has it been able to be depended on for so long?

Cast nylon type 6 and 6/12 share some common benefits among many performance plastics materials that are used in heavy equipment. These unique benefits address problems in applications that can arise when using metal materials such as brass, bronze steel and other metals. The obvious ones include their perseverance in the elements. Performance plastics do not rust or corrode. They hold up well to the heat and cold. Also, they are much lighter than steel, metal and alloy materials making equipment more efficient, capable of increased payloads and reducing fuel consumption. Many performance plastics are useful for preventing wear between moving steel components. They also assist in dampening vibration and reducing noise which also improves equipment operation and operator safety. Cast nylon 6 and 6/12 possess these advantages for heavy equipment and many more.

Monomer cast nylon 6 is often unnecessarily discounted from consideration because of moisture absorption. Since exposure to damp and wet environments are typical for heavy equipment, it is prudent to consider this aspect when selecting the best material for a given component. In most side-by-side comparisons, nylon is shown to have many times more moisture absorption than other performance plastics materials. It is important to note, however, that moisture absorption is calculated by the percentage increase in weight when submerged compared to original, dry weight. Often, this percentage is misinterpreted as the change in physical size of a cast nylon shape. Since nylon can absorb upwards of 6 percent by weight, this can lead to a significant misunderstanding. Most manufacturers offer guidance on how to design a component factoring in slight dimensional changes due to moisture absorption. An unexpected benefit of moisture absorption is that once a monomer cast nylon component has reached equilibrium with its environment, it has improved impact resistance.

Cast nylon 6 can withstand a compressive load of approximately 4,000 psi for an extended period. To give that some perspective, consider a 5″ x 5″ block. At 4,000 psi this block can hold a uniformly applied compressive load of 50 tons without any subsequent deformity. That is more than the gross vehicle weight (GVW) of most 18-wheelers seen on the highways. The applications of such compressive strength allow for cast nylon’s long-term success for use as outrigger pads and cribbing blocks. Cast nylon’s flexibility and ability to form under a load allows for increased contact area under a compressive load which, in turn, provides for a larger contact area for the load to be dispersed. This means it could carry even higher loads compared to other materials that do not flex or give. The combination of compressive strength and shear strength allows for monomer cast nylon to be used as a gear, gear rack, low torque pinion, drive gear or chain sprocket.

The production methods of monomer cast nylon 6 and 6/12 allow for its adaptability to the enormous variety of components found in the heavy equipment industry. The base monomer used to create monomer cast nylon 6 and 6/12 is a liquid of very low viscosity when at the appropriate processing temperature. Because of that, if the forms used to produce a cast nylon shape (also known as molds or tooling) are essentially watertight (and meet a few other criteria), they are suitable for making a monomer cast nylon shape. Processing pressures are negligible and processing temperatures are not significantly hot. This translates to much lower set-up costs than extruded, compression molded or injection molded shapes and these molds can be produced very quickly. As heavy equipment rapidly changes and evolves to meet today’s demand, monomer cast nylon manufacturers are easily able to keep up by adapting their product offerings.

Another unique characteristic of the production of monomer cast nylon is the ability to produce numerous different grades. These grades can be paired to the demands of each specific application. Where there is a need for lower coefficient of friction between mating parts, a lubricant filled monomer cast nylon is available. This is ideal for telescoping boom pads, knuckle bushings, slide blocks and chain guides. If a component is exposed to heat, a heat stabilized cast nylon 6 is readily available. This is useful under the hood for hanger bearings, bushings, pillow blocks or support blocks. For areas of high compressive loads coupled with sliding movement, there are wear resistant grades of monomer cast nylon available, these are ideal for track slides, ram sleeves and scrapers.

From a cost standpoint, monomer cast nylon raw materials are relatively inexpensive compared to materials of similar compressive, tensile and flexural properties. Also, nylon 6 and 6/12 are easily and efficiently machined on typical CNC and manual machines. Factoring in the ability to produce parts close to the size of the desired component, the heavy equipment industry benefits from a reasonably priced, durable cast nylon 6 and 6/12 parts. Furthermore, this material is readily recyclable, ensuring monomer cast nylon’s continued use for many more decades.

Calvin Petersen is the general manager of Nylatech, Inc. For more information, contact Nylatech, Inc. at P.O. Box 455, Everson, WA 98247-0455 USA, (800) 506-9566 or (360) 966-2838, fax (360) 966-5319, info@nylatech.com or www.nylatech.com.