Inspecting Torsion Spring Torque 1

[swertel]

Some days I want to place a bullseye on my desk so I have a target to bang my head against.

We have configurations of custom designed torsion springs. Part of the inspection is to verify torque at certain angles - the initial position and final position per the as-assembled interface.

For some reason, although we've been using these parts for years, our receiving inspection department doesn't know how to check for these torques. I'm guessing there has to be an off-the-shelf tool to check torsion springs (similar to spring rate gages for compression/extension springs). I haven't come across anything yet so I thought I'd ping the experts while I expand my internet search.


--Scott

http://wertel.eng.pro

 

[israelkk]

The most important thing to understand is that the spring body coils should touch (supported by) the inner shaft. Otherwise bending of the spring body will introduce phantom undesired rotation angle.

Therefore, the torsion spring inner diameter has to be larger than the inner rod but eccentric to it such that the inner diameter of the spring always touches the inner rod.

When the spring ends are loaded the spring "roles" over the inner rod. The rod prevents the bending of the spring body due to the load at the spring arm.

A testing machine of torsion spring is constructed from two round plates rotating around a common shaft. The plates have holes on them where the spring ends are inserted or pins are inserted and support the spring ends. Then one plate is rotates over the common shaft while the torque and the angle rotation "of the plate" is measured. As I mentioned earlier, the inner diameter of the spring must be supported all the time over the common shaft. So the spring is actually eccentric to the axis of the plates and the common shaft.

 

[swertel]

Thanks for the advice. Things I probably wouldn't have thought of until after a fixture was designed.

I found a few torsion spring testers on the open market. The good ones, from what I can tell from reading about them, cost about US$5000-$7000 and function exactly like you state (based on pictures and user manuals). There are some cheaper hand-held torque meters that I could utilize in a custom fixture. If management goes that route, I'll be sure to make sure the ID of the spring is always in contact with the inner rod in the fixture design.

Thanks,

--Scott

http://wertel.eng.pro

 

[israelkk]

The ID of the spring should always be in contact with the inner rod not only on the testing fixture but in the working system too. Otherwise the actual torques and deflection will be different than the tested and calculated. If you have an in house machining facilities and a load tester such as Chatillon you can produce a simple tester for the spring. Any respectable spring manufacturer should have one and using his testing facilities will be much cheaper compared to purchasing one that will sit on the shelf.

http://www.chatillon.com/Our Products/Chatillon Force Gauge/LG_forcegauge.html