Guest post by Lib Pietrantoni, CJWinter
Flaking threads and thread damage can be avoided when thread rolling thin walled parts.
Distortion during the thread rolling process can cause
- Non-uniform thread geometry
- Collapse of threaded portion of part
These are particularly troublesome issues on thin walled parts.
These can be avoided if you assure that a minimum wall thickness is maintained for the process.
Larger nominal thread diameters require thicker minimum wall thickness; so do coarser thread pitches.
The way that you roll the thread can also be a factor.
According to Lib Pietrantoni at CJWinter, specialized pneumatic radial-pinch-type thread rolling machine attachments can apply equalized rolling pressure across the workpiece, ensuring thread concentricity, eliminating side pressure on both the parts and the machine, and allowing precise control of the penetration rate — especially important for thin-walled parts.
You can download the Thread Rolling Reference Chart at CJWinter’s website: reference chart
As a steel mill Quality Metallurgist, I saw my share of complaints that “the steel was flaking- it must be the steel.”
But the lab results never found the flaking anywhere except where the thread had been rolled – it was never on the bars as shipped.
Pay attention to minimum wall thickness when thread rolling!
And don’t forget to pass this handy chart along to the engineer at your customer that is designing the parts that you make.
Thanks to Lib Pietrantoni at PMPA member CJWinter for providing this reference information.