Brass threaded stud failure
Brass threaded stud failure
(OP)
Can anyone shed any light on why this threaded stud is failing?
The manufacturer of this stud is looking into it but I'm looking for some additional insight.
The part is brand new and installed in an indoor office type environment. This is happening during installation at the end users sites. They "claim" they are NOT over torquing these connections. Its a straight cut not the typical 45 deg angle I always see with a typical over torque situation.
The material is 360 brass (nickel plated). It is a 1/4"-20 threaded stud that is used with an electrical connection. (larger terminal block). There is a compression lug that is slipped over the stud (approximately the thickness of where the break happened to where the mating/landing surface it) and then a zinc plated steel flat washer/keps nut is torqued down (40 in-lbs. max)
This terminal block is used in one of our products and are customers are having failures like this and they claim its happening way before the stated max torque is being applied.
I can get more pictures if necessary.
I do not have any method of testing hardness or anything other than visual examination.
The manufacturer of this stud is looking into it but I'm looking for some additional insight.
The part is brand new and installed in an indoor office type environment. This is happening during installation at the end users sites. They "claim" they are NOT over torquing these connections. Its a straight cut not the typical 45 deg angle I always see with a typical over torque situation.
The material is 360 brass (nickel plated). It is a 1/4"-20 threaded stud that is used with an electrical connection. (larger terminal block). There is a compression lug that is slipped over the stud (approximately the thickness of where the break happened to where the mating/landing surface it) and then a zinc plated steel flat washer/keps nut is torqued down (40 in-lbs. max)
This terminal block is used in one of our products and are customers are having failures like this and they claim its happening way before the stated max torque is being applied.
I can get more pictures if necessary.
I do not have any method of testing hardness or anything other than visual examination.





RE: Brass threaded stud failure
RE: Brass threaded stud failure
On that design, shouldn't the compression (bearing stress) on the connector which is directly proportional to the tension in the stud be the design control? Can you get the desired bearing stress on the connector at a lower torque? The compression lug area, (Pi/4)(d^2 - di^2) or the washer may have too much bearing area to get the compression stress (bearing stress) you want on the connector; or the stud should be larger to provide that compression at a lower tensile stress in the stud. Then you add the torsional stress in the stud, again a max. at that location, and you see what you get, some percentage of the time. This is probably happening where the thread die is leaving a ding of some sort in the cut thread. Would a rolled thread be better, for its shape and cold working of the thread shape?
RE: Brass threaded stud failure
Questions:
Correct material?
Correct torque control/calibration?
Kep washer/nut behaving correctly as it is tightened?
Have you run any testing independantly of the customer/end user?
Ted
RE: Brass threaded stud failure
RE: Brass threaded stud failure
Was someone being 'helpful' by adding a lubricant to the assembly process?
Ted
RE: Brass threaded stud failure
The stud continues into the inside of our product and we have torqued thousands in our assembly environment without a single breakage..
We did find out what seems to be the issue though...
The installers were using a nut driver to start the nut before using a torque wrench and if the handle of the nut driver is pulled off axis (@ about 30 degrees off the stud axis) the studs were simply snapping off. It took very little shearing force to snap them off.
I guess we need to include a warning.. "Nut drivers are not handles or pull up bars" :)
We are having the manufacturer of the block investigate different alloys or heat treating to prevent this in the future..
RE: Brass threaded stud failure
A similar problem happened awhile back, and we finally realized that a batch of cheap flanged nuts had thread axis mis-aligned to the flange/washer, resulting in point contact and bending of the stud when the nut bottomed.
RE: Brass threaded stud failure
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Ted
RE: Brass threaded stud failure
We had the sales rep from the company come in today and torque down a lug and remove it from EVERY stud on the customers side for all the blocks we had in house.. :) Not a single failure.
Hi Michael if you come across this post. Good job buddy
RE: Brass threaded stud failure
Ted
RE: Brass threaded stud failure
RE: Brass threaded stud failure
It is good when you can solve it for them. Old fashioned customer service.
Ted
RE: Brass threaded stud failure
RE: Brass threaded stud failure
You also may need to look at the combined load of bending and axial stresses in the bolt. Looking at your attachement, brittle failure with raised elements is indicative of excessive tensile loading.
Has to be coming from somewhere. Look at the nature of the application.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada