6 Reasons To Consider Rolled Threads

Because the steel grain structure is cold forged, rather than cut, rolled threads are up to 30% stronger…

Sketch iluustrating grain flow lines due to cold work of rolling.

While the strength of a thread is a function of section thickness, a thread rolled rather than cut thread is usually superior in mechanical properties, all other things being equal- here are 6 reasons why:

  1. The flow of the material by cold work during rolling reinforces the shape.
  2. The cold working strain increases mechanical properties, Surface Hardness,Tensile Strength, Yield Strength, and the Yield Strength / Tensile Strength ratio.
  3. The surface finish of the thread flanks is usually smoother due to the burnishing action of the rolls.Smoother finish means better fatigue life and fewer opportunities for stress risers.
  4. There is more material (section thickness). This results in material savings*, since the diameter of the blank will be between the major and minor diameter of the thread, rather than greater than the major diameter for a cut thread.
  5. The compressive stresses on the threads resulting from rolling improves the fatigue life.
  6. The root of the thread has a smoother radius, improving fatigue life.

Schematic view of the thread rolling process.

Pictures courtesy PMPA member Ray Industries

Click here for a video of the thread rolling process in action from PMPA member Rolled Threads Unlimited LLC.

*I got my first “learnin” on rolled threads at my customer Keystone Threaded Products back when my hair was not silver and B.K. (Before Kids): “Why do you always buy funny sizes Jim?” I asked. That was a great first lesson on how engineering can add savings:

Blank diameter will be between major and minor diameter = $ Saved.

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