# Reusing Bellville Washers



## Lone Crapshooter

I have a 27 year old and a 10 year old line up of 15KV switchgear that the cables are attached with lugs and 1/2" bolts BELLEVILLE washers and nuts.
The contractor doing the job ask me about reusing the Bellville washers. 
I told him that I did not know if the bellville washers could be reused. 
Any thoughts on this mater?
Thanks LC


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## brian john

I took an online class on torquing and I BELIEVE the answer was no.

But I could be wrong

http://www.ecmweb.com/content/belleville-blues


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## TGGT

I've done it. Haven't lost sleep over it.

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## joebanana

We used to reuse them all the time on the SCR heatsinks on a GE co-gen HRSG generator at UNOCAL.


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## brian john

joebanana said:


> We used to reuse them all the time on the SCR heatsinks on a GE co-gen HRSG generator at UNOCAL.


I have too but always questioned the practice, they seemed to have the proper spring.

With torquing a connection utilizing Belleville washers do you torque for the bolt which depending on the hardware could flatten the washer or is there a specific torque for the washer?


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## joebanana

brian john said:


> I have too but always questioned the practice, they seemed to have the proper spring.
> 
> With torquing a connection utilizing Belleville washers do you torque for the bolt which depending on the hardware could flatten the washer or is there a specific torque for the washer?


We'd stack a few alternating cup-up, cup-down, and tightened until the gap closed all the way. It's not an exact science, one of those "close enough for the application". The basic idea was as an "indicator" of when to stop torquing, before the stud pops out. We were under the supervision of the factory engineer, for what it's worth.


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## joebanana

brian john said:


> I have too but always questioned the practice, they seemed to have the proper spring.
> 
> With torquing a connection utilizing Belleville washers do you torque for the bolt which depending on the hardware could flatten the washer or is there a specific torque for the washer?


...........


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## paulengr

Any spring is reusable as long as you don't exceed the limit where it permanently reforms. Over time it loses some spring tension somewhat whether it is under tension/compression or not. The spring constant stays constant but the length changes. So no problem reusing Belleville washers. Their purpose is closing the gap to keep the joint force consistent during expansion and contraction. There is an order to them and you need to follow it such as 3 cups up, 3 cups down, not alternating. Stacking in the same direction increases tension. In the opposite direction increases the amount of expansion they take up. Almost all specs have them all the same way or maybe two sets but never every other one alternating that I've seen.

Torquing is really a terrible way to set a bolted joint because what you really want to control is clamping force. About 80% of the torque goes into overcoming friction in the threads and other places so very little "torque" actually develops clamping force. Ideally use a clamp force indicator. There is an ultrasonic tool that measures bolt stretch which knowing the material and geometry is extremely accurate (A few percent). There are direct torque indicating washers for structural bolts that have a collapsing section that is good to about 5% error but I've looked into them and none are made to common electrical sizes. Stepping up from there a torque wrench along has about a 25% error and so does using a thread lubricant such as molykote or Loctite (as a lubricant, ignoring the adhesive). Combined has around 10% error, which is your best cheap and simple bet. There are also torque sticks which are basically extensions you use with a socket on an impact wrench which is much simpler than messing with torque wrench settings and calibration issues since you can't calibrate a solid piece of aluminum.

The jury is out on reusing bolts but nuts shouldn't be reused. The nut threads are softer than the bolts and purposely deform during tightening. Also there is no such thing as a lock washer. None of the so called locking designs have proven to give any resistance to loosening in a Junkers (simulated Jost effect which is what causes loosening) except the ones that dig in and those cause stress risers at the joint which accelerates corrosion, fretting, and stress risers leading to cracks. Lock nuts all of which rely on a deformed thread or deforming nylon (nylocks) definitely work as does safety wiring if done right (drill a hole through the nut and bolt and wire it so it can't loosen).

A few things really help prevent loosening more than any other. First make sure everything is clean. It should be no surprise that grains of sand act like little bearings and float everything. Second use a thread lubricant like Molykote. It has been tested and doesn't affect electrical joints. You can use Loctite or Nylocks but don't forget electrical joints expand a lot from heating so this stuff can burn/melt and differential expansion fails Loctite. I've tested Loctite in a dryer where it shouldn't be and it goes to about 200-300 C for a few weeks, so my suggestion is avoid. Use a torque wrench or an impact and torque sticks. The torque sticks are set up for a specific range so watch out using the high torque Milwaukee's or the wimpy brands that are 100 ft lbs. Make sure the bolt fits well in the joint. Loosening happens because of the Jost effect which us where vibration gets it loose then shear gets it to spin. If the bolt fits the hole the nut can't tilt "sideways" so the Jost effect becomes impossible. A 1/4-20 in a hole meant for half inch stacked with flat washers is a bad idea. Finally throw away split washers which are technically called helical spring washers. They are meant to work like Bellevilles but they don't work and testing shows they enhance loosening. Double hitting does work too but it is very tricky to make it work and the standard practice doesn't do anything.


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## Wiresmith

you can reuse it if it has not been stressed to it's yield point (when it permanently deforms to any degree)


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## Wiresmith

paulengr said:


> You can use Loctite or Nylocks but don't forget electrical joints expand a lot from heating so this stuff can burn/melt and differential expansion fails Loctite. I've tested Loctite in a dryer where it shouldn't be and it goes to about 200-300 C for a few weeks, so my suggestion is avoid.


which loctite did you use? 2620 goes to 345C easily

LOCTITE® 2620 Ultra High Temperature, High Strength Red Threadlocker locks and seals threaded fasteners in applications that require continuous temperature resistance up to *650F*.This high strength threadlocker comes in a convenient syringe for easy dispensing.


300c is only 572f


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## frenchelectrican

Yes and No depenending on what it set up for.

Most case I can able reused as long it the Belleville washer is not perament deformed.

But there is some highlighted note if the manufacter or equiment mention to replace it., then you have to replace it. 

Bolt and nuts genrally if low toqure it can used it again but with higher toqure useage always end up put a new bolt and nuts. ( they can strech when you toqure it down good )


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## paulengr

“Controlled” to 250-300 C but it was a fluidized bed dryer so on startup or if it got empty excursions up to 600 C would occasionally happen. Temperature doesn’t matter anyway in the face of expansion if the parts don’t move together...all adhesives fail in the face of most thermal expansion conditions of any appreciable magnitude. That’s why for instance 2-3% phis bonding in low cement alumina works so well...but that’s getting way away from this.


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## MechanicalDVR

Reuse them as long as they still have some body in them.


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## GeorgeEngr

I know this thread is a bit older but I stumbled upon it thru another search. As a manufacturer of Belleville springs, I thought I would contribute a post from our knowledgebase with reference to the question of reusing Belleville springs:

A Belleville spring can be used indefinitely as long as it is not damaged in some way. It is perfectly acceptable to reuse the springs many times in bolted applications. However, it is important to note that as highly stressed parts, Belleville springs can be prone to failure if they have been compromised in some way. Parts can be damaged by excessive cycling, corrosion, exposure to temperatures beyond the material ratings, and mechanical damage such as galling. Some recommended practices to determine if springs are acceptable reuse include:

1. Inspect the springs for mechanical damage. If the spring surfaces are galled or damaged excessively, we recommend that they be replaced.
2. Inspect the springs for signs of corrosive damage. This includes any cracking or severe pitting on the surface.
3. Measure the deflection remaining in the springs. This can be done by measuring the overall height and subtracting the thickness of the spring. Compare this value to the minimum deflection listed on the product spec. Some amount of lost deflection may be acceptable. However, if the remaining deflection is less than 75% of the minimum listed deflection, this is a sign that the spring may have been overstressed or exposed to excessive temperatures and has yielded somewhat. Spring deflection lower than 75% of the minimum should be replaced.


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## joe-nwt

Good info. Thanks!


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