Source of Belleville washers for 300kgf fixture?

HaldorEE

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I was hoping to follow your lead ;).
I just bought 5 different packs of springs (all in 5/16" bolt size) from McMaster Carr. I will let you know what I discover.

I am interested in each versions spring constant. Also how consistent that spring constant is for several examples (I will test 4 of each). And also how linear the spring constant is. I will measure force at 50% and 100% compressed.
 

fafrd

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I just bought 5 different packs of springs (all in 5/16" bolt size) from McMaster Carr. I will let you know what I discover.

I am interested in each versions spring constant. Also how consistent that spring constant is for several examples (I will test 4 of each). And also how linear the spring constant is. I will measure force at 50% and 100% compressed.
Looking forward to what you learn...
 

cinergi

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I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70.
 

cinergi

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I thought I’d checked them, but apparently not...

That’s probably the best deal yet I’ve seen on calibrated washers, but still significantly more than the ‘unrated’ washers.

For example, the 5/16” 110-159 lbs washer is close to perfect, but at $3.36 for 3, that’s $1.12 each.

But with 0.762mm (0.03”) deflection, you’ll need 8 per rod or a minimum of 32.

But $36 per 8S 280Ah battery is a good starting point...

FWIW the springs I just purchased can handle 8s and cost about $16.
 

fafrd

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I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70.
Two in parallel (back to back) equals 70 with twice the displacement.

Two in series (nestled) equals 140 with the same displacement as a single washer.
 

fafrd

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Two in parallel (back to back) equals 70 with twice the displacement.

Two in series (nestled) equals 140 with the same displacement as a single washer.
Thinking about it, I may have the terminology backwards.

Opposite orientation doubles displacement with the same force.

Similar orientation (nestled) doubles force with the same displacement.

If your washers have only 70lbs of force, you need to nestle two of them to get to 140. Then, assuming you need displacement that is 8-10 times the displacement of a single washer, you’ll need 8-10 nestled pairs positioned back to back.

So 32-40 washers for each of 4 threaded rods or 128-160 washers total,
 

HaldorEE

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I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70.
Two in parallel << double force when flat.
Two in series <> = same force when flat, but double the travel to get there (half the spring rate).
 

fafrd

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Two in parallel << double force when flat.
Two in series <> = same force when flat, but double the travel to get there (half the spring rate).
Now why didn’t I think of using < and > to make a diagram - brilliant!

So if using 70lb washers with 0.75mm deflection to manage an 8S battery with 0.75mm expansion per cell, you would need to use 16 washers on each threaded rod oriented like this:

<<>><<>><<>><<>>

Compared to what you could do with 8 150lb 0.75mm washers which would look like this:

<><><><>
 

HaldorEE

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I am thinking about making a progressive spring. With a single 140 lb washer in series with three 190lb washers also in series.

To set the preload, start with discharged cells and tighten the nuts until the 140 lb washers are flat. The three 190lb washers will allow for 3mm of travel before the pressure reaches 190 lb.
 

Bob B

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Two in parallel << double force when flat.
Two in series <> = same force when flat, but double the travel to get there (half the spring rate).
Yes .... below from the manual.

Belleville washer stacking.png
 

HaldorEE

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I also think you are not supposed to stack more than 4 washers together. I think that means in parallel so <<<<>>>> is OK. But <<<<<>>>>> is not.

I believe that this <><><>is ok, however.

Here is an idea of what I mean about by a progressive spring:

><><

I am doing an 8S battery with two sets of 4 cells being compressed in the same fixture. Each of four outer threaded rods will have from 140 - 195 lb (exerting from 10 to 14 PSI on the cells). The middle pair of threaded rods will have from 280 - 390 lb which shared by two sets of cells splits evenly into the same 140 - 195 lb.

Looking down on the compression fixture from above.

><>< 140 to 195 lb

4 Cells

><>< 280 to 390 lb

4 Cells

><>< 140 to 195 lb

Key to washer rating (if you are color blind this is not going to make much sense):

< = 140 lb washer
< = 195 lb washer
< = 280 lb (or two 140 lb in parallel) washer
< = 390 lb (or two 195 lb in parallel) washer

This same thing could be done using a wound spring, but it would definitely have to be a custom spring.
 

Bob B

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I also think you are not supposed to stack more than 4 washers together. I think that means in parallel so <<<<>>>> is OK. But <<<<<>>>>> is not.

I believe that this <><><>is ok, however.

Here is an idea of what I mean about by a progressive spring:

><><

I am doing an 8S battery with two sets of 4 cells being compressed in the same fixture. Each of four outer threaded rods will have from 140 - 195 lb (exerting from 10 to 14 PSI on the cells). The middle pair of threaded rods will have from 280 - 390 lb which shared by two sets of cells splits evenly into the same 140 - 195 lb.

Looking down on the compression fixture from above.

><>< 140 to 195 lb

4 Cells

><>< 280 to 390 lb

4 Cells

><>< 140 to 195 lb

Key to washer rating (if you are color blind this is not going to make much sense):

< = 140 lb washer
< = 195 lb washer
< = 280 lb (or two 140 lb in parallel) washer
< = 390 lb (or two 195 lb in parallel) washer

This same thing could be done using a wound spring, but it would definitely have to be a custom spring.
I'm not color blind ... but that is hard to see .... maybe bold larger font ...LOL
 

fafrd

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I am thinking about making a progressive spring. With a single 140 lb washer in series with three 190lb washers also in series.

To set the preload, start with discharged cells and tighten the nuts until the 140 lb washers are flat. The three 190lb washers will allow for 3mm of travel before the pressure reaches 190 lb.
I thought of doing something similar and if you are paying full price for fully-rated Belleville washers, that’s probably the best way to go (assuming it works as expected).

Alternatively, the same thing can be achieved using multiple weaker washers in series (>>).

if you have a bag full of 75lb Belleville washers and you need a total of 8 washers in parallel (<>) to deliver 6mm of deflection.

<><><><> will deliver ~6psi across the entire 6mm of deflection while

<><><<>><<>> (12 washers total( will deliver ~6psi for the first 3mm of deflection and ~12psi for the second 3mm of deflection.

Or you could go with
<>><<>><<>><<>><<>>> (1+16+3 = 20 washers total) which would maintain pressure of 6psi without any deflection, then maintain 12psi for a full deflection range of 6mm bd then allow a further deflection of up to another 0.75mm at 18psi should that ever be needed.

Knowing ‘expected’ and ‘maximum’ deflection extents would be very helpful.

But yeah, using different size belleville washers along the spring to increase pressure when you want to reduce further expansion is a good idea.
 

Bob B

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@HaldorEE .....That's better ... but still gonna be hard to distinguish color differences

>>> <<< >>> <<<

Those are 22 font size ... bold. Could even go larger.
 

HaldorEE

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While I am waiting for my new source of Belleville Washers to get here (McMaster Carr). I decided to do a trial run of my test setup.

I am using a 2000 newton (449 lb) capacity load cell with a 5/16" stainless steel bolt and nut plus a 1/4" thick mild steel base plate and a thick fender washer on top of the load cell. I set my torque wrench for the lowest setting on it (20 in.lb) to see what kind of clamping pressure that puts on the load cell.

20 in.lb of torque is putting an average 425 lb of tension force on the 5/16 bolt.

Be very careful when tightening down the bolts on your compression rig. It is really easy to put a lot more clamping force on them than you think you are. 660 lb (12 PSI) total, is only 165 lb each on four threaded rods. I am going to use a progressive spring arraignment with a 140 lb Belleville disc spring combined with four 190 lb Belleville disc springs in series. To set the spring preload I am going to tighten the nut until the 140 lb washer is flat. This should limit the compressive forces on the cells to a range of 10 PSI to 14 PSI.

Pic of my test rig.

PXL_20210110_221745078.jpg

Here is what I recorded for 3 tightening/loosening cycles.

20_IN_LB.jpg

I got 62 lb compressive force just finger tightening the nut (socket only, no ratchet).

FingerTight.jpg
 
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HaldorEE

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20 in.lb torque is only 2.6 N.m, no wonder people are having problems stripping threads when tightening the screws on their EVE load cells.

I am definitely going to use a torque wrench when installing the nuts on my bus bars. I think I saw a figure of 4 N.m recommended in another thread? That would be 35 in.lb
 

fafrd

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20 in.lb torque is only 2.6 N.m, no wonder people are having problems stripping threads when tightening the screws on their EVE load cells.

I am definitely going to use a torque wrench when installing the nuts on my bus bars. I think I saw a figure of 4 N.m recommended in another thread? That would be 35 in.lb
So if I understand correctly, your saying that finger-tightening a socket is applying twice the recommended torque to busbars/terminals, correct?

I just finger-tightened (through a socket( the 1/4” nuts on single-cell jig I made and when I then used the torque-wrench to apply what I’ve estimated to be 12psi / 165lbs I added anew turn or so to the nut (confirming that a socket finger-tightened applied well under 165 lbs, but your 62 lbs sounds very credible).

Was that as tight as you could go by hand or just snug?

p.s. you could probably start a side business hand-tightening various battery-related things and letting us know the approximate range. I’ve been hand-tightening my bus-bars with a Philips-head screwdriver, for example, and would love to know what force is possible to apply by hand using a Philips head bit between finger-tips.
 
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