When to Use Cast Nylon Stock for Machining

Nylon stock shapes - rod, bar and plate - are available as both extruded and cast stock for machining. The question is when should you use cast and when to use extruded?

Naturally, the first step is to be sure that nylon is the material of choice for the application. Then, you can begin to choose between the cast and extruded forms.

Step 1: Determine what's available. Most standard cast nylon stock shapes are made from type 6 nylon, whereas standard extruded stock generally is made of type 6/6 nylon. Extruded type 6/6 nylon was the first nylon made available in stock shapes. This occurred in 1946 when extruded nylon stock shapes were introduced by The Polymer Corporation, which today is Quadrant Engineering Plastic Products.

Step 2: Check the physical properties. Table I contains typical physical properties for cast and extruded nylon stock shapes. Although there are physical property differences between cast and extruded nylon, they are generally insignificant for most applications.

Step 3: Identify the size of stock shape needed. Table II is a guide to cast and extruded nylon stock shapes. Larger sizes and custom lengths/widths are possible in cast nylon.

In the past, some fabricators have chosen cast nylon shapes over extruded shapes because of high internal stresses and inconsistent density in the extruded products. With modern extrusion technology fabricators can use extruded nylon stock shapes for machining challenging parts. Large extruded nylon stock shapes are available virtually stress-free and with a consistent density across the shape.

Step 4: Choose the grade of nylon for the application. Just as there have been processing advances, there also have been formulation advances. For example, QUADRANT's proprietary, self-lubricating Nylatron® NSM offers a limiting PV of 15,000, compared to a PV of 3,000 for standard nylon. Today, both cast and extruded nylon are available in heat-stabilized, load-bearing and lubricated grades. Fiber reinforced grades are available only in extruded shapes.

Fabrication: Both cast and extruded nylon stock shapes are easy to machine on standard metalworking and woodworking equipment. Positive tool geometry with ground peripheries are recommended. Carbide-grade tooling with polished top surfaces should be used. Coolants (water mist with soluble oil) are not required, but may be used for optimum finishes or close tolerances.

Cost analysis: Typically, the cost of a large cast stock shape is less than an extruded stock shape of similar size. For example, a 5-in. diameter cast rod can be about 10% less than its extruded counterpart. A 3-in. thick cast plate can cost about 15% less than extruded plate. Smaller shapes typically cost about the same.

For more information, contact Quadrant Engineering Plastic Products, Inc., P.O. Box 14235, Reading, PA 19612-4235, 800-366-0300, Fax: 610-320-6868.