Rolled threads result in better rods with improved tensile strength, shear & fatigue resistance.
- Static tensile tests on parts formed through thread rolling show overall increases in strength of about 30%
- Fatigue strength is improved by up to 75%.
- Rolled threads have increased resistance to stripping because such failures are compelled to take place across, rather than with, the grain flow.
Thread rolling produces strong, smooth, precise, and uniform external thread forms with results that are much different and better than other types of threading processes. Often, rolled threads are not only preferred but also required by design because of their superior tensile, shear, and fatigue strength.
Other processes like cutting, grinding, and chasing remove material to produce the thread form, but thread rolling displaces the material with hardened steel dies. These dies typically have hardness between Rc58-Rc63 and there is a specific set of dies for each thread size and each thread form.
The result of moving the material grains (molecules) into the shape of the thread rather than weakening it by removing material, is that the grains become denser at the critical parts of the thread, especially in the root and on the flank below the pitch diameter. This effect improves the quality of the thread form. Additionally, the burnishing action of the steel dies produces an excellent (better than Ra32) micro-finish. The superior finish improves assembly between external and internal threads and reduces wear between mating components, thereby extending their life.
For over 25 years Heartland has been machining rods with rolled threads for oil and gas applications including; Natural gas compressor piston rods and Frac pump stay rods.
Specifically Heartland offers cost competitive turnkey rods that requiring tight tolerances and rolled threads. We can accommodate rods up to 60” long with milled components and threads as large as 2 ½ – 8 UN or 2 ¾ – 12 UN.