Cold Forming Rotary Shoulder Connections

Welcome to CR4.

Answer regarding Thread rolling in general:

Preparing the thread by rolling as opposed to cutting has two Major advantages.

1) Because the material is rolled rather than cut, the cold work and redistribution of the flow lines make the material stronger. I will send you data on this in the morning, my computers microscan is refusing to let me access the data I need...

2) Because the material is rolled (burnished) rather than cut, the threads will have a smoother surface, thus operating more easily in assembly.

Minor advantages include threads are less susceptible to damage and a higher strength to weight ratio, and takes less machine time to produce.

You did not specify the API thread form specifically, so I cannot comment on the API application.

As to improve life of a connection, Again more specifics are needed. Couplings? Drilling? Many assemblies/disassembly cycles?

I would argue the lack of stress risers from cut threads and the smoother burnished finish and surface in compression all argue against fatigue type failures compared to machined threads. But you have not described what is the cause of loss of life that you are concerned about.

I don't think I have any have data regarding burnishing only the root of a cut thread.

I'll send you some data in the AM.

milo

Thank you for your response.

I am interested in any Facts that burnished thread forms - API root of the threads - extended life of the connection in Deep Hole on or off shore drilling. I was hoping to find an organization like API that may have documented stress tests findings that could be reviewed.

Holy grail:

http://www.onepetro.org/mslib/app/Preview.do?paperNumber=00003429&societyCode=SPE

Good support:

First link is best

http://www.springerlink.com/content/kg6l302m1645124v/

http://www.springerlink.com/content/m1218q8325055103/

Rolled thread 70% improved fatigue life reference:

A rolled thread also has up to 70% increased fatigue resistance over a cut thread.

link: http://www.threading101.com/files/article_threadrolling-on-a-cnc.html

Gereneral confirmation of role of burnishing on fatigue life:

See 30.3.1 here:

http://www.scribd.com/doc/11621736/30-Super-Finishing-Processes

I'd do it in a heartbeat, The cost of not doing it is HUGE.

milo