Torque Joint Rate

Started by Hippie, 05-08-2009 -- 06:53:30

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Hippie

05-08-2009 -- 06:53:30
Is anyone doing torque joint rate calibration? I'm looking for as much information as I can find.  I appreciate any help.
Peace Ya'll

Hippie

#1
05-08-2009 -- 10:10:06
It's calibration of powered torque tools used in an assembly process.  You determine what type of joint you have. (hard,medium,or soft) You are measuring both dynamic applied torque and the angle of rotation of threaded fasteners.
Peace Ya'll

scottbp

#2
05-08-2009 -- 12:51:45
I know you can get joint rate simulators to attach to torque transducers on torque cal benches, they are basically a stack of curved washers on a threaded rod with a nut on top. By varying the thickness of the stack you can vary the "hardness" of the joint.
Kirk: "Scotty you're confined to quarters." Scotty: "Thank you, Captain! Now I have a chance to catch up on my technical journals!"

Hippie

#3
05-11-2009 -- 06:24:24
Yes, I am aware of the joint simulators. I have several.  I just ain't buying this labs procedure. Too many variables and inconsistances.
Peace Ya'll

Hawaii596

#4
05-11-2009 -- 13:12:02
In my previous life, they used run-down adapters. 

A little editorialization:  There is no traceability in dynamic torque.  I studied this at some length in the last couple of years.  Basically, static torque (I'm not a torque geek) is length times force.  When calibrating electric torque (such as Mountz/Hios/Jergens/etc.) CL-6000, etc. there is also the dynamic component that is not spec'd in any torque calibrator.  Our lab calibrated a bunch of electric torques and when we switched brands, we had to do a lengthy study and document all the data as to why virtually every electric torque screwdriver went out of tolerance, but that they weren't actually out of tolerance.  You can do your own study on this by taking two different brand name torque calibrators, running a repeatability in static torque at a given setting and comparing the two calibrators results, and even adjusting them and the torque driver for statistically equal results.  Then, at the same setting, set up an electric torque driver and repeat at the same setpoint.  What you'll see is if static readings are about equal, there will be a definable shift in dynamic, because no two brand names (even no two transducers of the same brand name and model) will match dynamic to static.  That is because the response time is not spec'd.  It's like having an AC voltmeter that is spec'd at 60 Hz (so to speak) and using it at 10 KHz (so to speak).  If you compare two AC voltmeters only spec'd at 60 Hz, you won't get definable accuracy if you use it at 10 KHz.

I have tucked away a number of articles about dynamic torque; and probably can dig up some of the emails I exchanged with a guy at the national standards labs in Germany, NIST, and Japan.

If you're calibrating Hios CL-6000, CL-7000 or similar, you need to learn about the right spring for the right part of range where they are to be set.  I highly recommend if you must "calibrate" (not truly traceable), they be sealed and set for a given setting.  Then re-calibrate for new settings as needed.

There are a few decent procedures around which I can dig out.  You need to identify the correct run-down adapters for the ranges you want to calibrate, excercise CW and exercise CCW at least 5 times for the setting.  Then take five CW and five CCW readings.  As for tolerances, they need to be based on pre-setting the unit with a given torque calibrator.  I'll save tolerance comments for a future posting.

If you contact CDI, or other torque calibrator manufacturers, they should have run-down adapters available.  We set some exercise screws in a machine shop fabricated metal block to use to exercise the torques.  Then we had the run down adapters attached to between the torque driver and the transducer.  The run down adapter had a spring and a stack of warped washers to provide the proper "soft landing" for the driver during cal.  If you get on the phone with CDI and discuss, they can help you select the correct adapter for your application.  There are different run down adapters depending on the given in-lb setting you need.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

Hippie

#5
05-11-2009 -- 13:46:41
Thank you for your input.  I am currently using a Crane Torquestar analyzer and Crane/CDI simulators.  I haven't been able to find much published data concerning a procedure.  However, I would certainly appreciate any data that you could share.
Peace Ya'll

Hawaii596

#6
05-11-2009 -- 13:48:56
I'll have to dig through my archives and arrange to send you something.  The reason there is so little on this is because of the lack of traceability on these "calibrations."  Its essentially a repeatability/correlation.  Let me do some digging.  I'll send you a PM to see if you want them emailed, or you can PM me with your email address if you want.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

Hippie

#7
05-11-2009 -- 13:55:21
Sure,Thats great.  my home E-mail is listed on my profile. Kind of leery getting stuff at work.  I'm the new guy here.  So I don't know all the secret rules regarding that sort of thing. Thanks alot.
Peace Ya'll

Hawaii596

#8
05-11-2009 -- 13:59:18
I just sent you a procedure to your home email address.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

Hippie

#9
05-11-2009 -- 14:06:02
Thanks.  I really appreciate your help.  This new to me so I will be digging deep to learn all that I can. 
Peace Ya'll
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