Disc spring (steel) calculation help

[dejan95]

I have a problem I would need help with, if someone would be nice enough.

I will be using disc springs. I need for springs to deflect for 1 mm between 6000N and 9000N.

My question is, does the number of the pieces in all series needs to be the same or can it be different (as shown in the picture)? For example, if I need a specific force to multiply by 3 I will use three pieces, and then if i need a deflection to multiply ba 5 i can add on top of that 4 sets of one piece of disc springs?

Or can someone help me with choosing the correct number of series and sets od disc springs to reach 1mm deflection between 6k abn 9KN. The springs can be prestressed on 6kN.

Thank you guys in advance!!

 

[MintJulep]

does the number of the pieces in all series needs to be the same or can it be different

If you want the force v. deflection to be linear as shown in your graph then they need to be the same.

 

[dejan95]

Thank you, I understand.

So for example, could I use this spring. And if I want linear i would add 4 pieces in parralell (4x2521N=10kN - a bit more than desired but still ok), and i would have 13 in series to get deflection from >1mm (if i prestressed it to s2 to get 6780N). Would this work?

 

[EdStainless]

It should. We always ordered extras in case we needed a little more travel, a spring got damaged, or someone messed up on installation.
The bearing washers on the ends need to be extra heavy and hardened.
And in tall stacks we would install intermediate flat washers sometimes.
We lubed them with a MoS2 grease (Lubriplate usually).

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P.E. Metallurgy, consulting work welcomed

 

[drawoh]

dejan95,

Disc springs are explained in detail in Roark's Equations for Stress and Strain.

I suggest you draw a section view of your mechanism. I don't know about you, but I need pictures.

If disc springs are stacked face to face, you multiply the spring rate. If you stack them edge to edge, you multiply the deflection.

Mixing disc spring sizes probably can be made to work, but it will be a pain in the ass for everyone involved. Carefully examine the figure I have already recommended that you draw.

If you need a certain deflection at a minimum stack height, look into medium force die springs. These are coil springs made by several manufactures to a standard of some sort. The springs you want will be painted blue. If this works for you, it will be way cheaper, simpler and more reliable.

--
JHG

 

[desertfox]

Hi dejan95

Sorry I cannot read the disc spring references you have quoted can you either write the references in a post or repost a clearer picture of the references.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dejan95]

Thank you guys, i solved it as shown in the picture bellow. Can someone advise me how to avoid the bottom part loosening (its a M30 thread). With the bottom part I will prestress the springs, but once they are set the bottom part shouldn't unscrew (get loose).

 

[desertfox]

Hi dejan95

I think the screwed ring will come undo over time, I have seen a similar thing happen on a pneumatic valve that was operating, we set the spring preload and over a short period of time the screw came undo.
You need to dowel the screwed ring in place after assembly.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[EdStainless]

Make sure that there is enough clearance for the washer, you don't want to risk them rubbing on the walls.
Some positive lock is needed, a pin is likely the best.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dejan95]

Thank you all again.

How could i dowel the screwed ring in place? Can i use DIN 553 - Slotted set screws with cone point or will it damage the thread?

 

[desertfox]

Hi dejan95

Drill through the outer wall of the cylinder and into the M30 thread, so basically drill at ninety degrees to the axis of the piston and put a blind dowel in.
You can make the dowels removable if you need to take the thing apart.


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[EdStainless]

Drill the hole in the outer collar.
Load the washers and pre-set the washers.
Cycle the load a few times and check the per-set.
When you are happy drill into the body and set the pin.
A rolled pin would work for this. It will stay in place well and still be removeable.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[3DDave]

In the past with disk springs - they are extremely sensitive to the thickness and initial coning operation - we saw variations of -50% to +100% of supplier quoted forces at given deflections and that the springs would change set height over the first several operations. what we ended up doing was to pre-flatten every spring 5 times so they would stop drifting in load. The application was to produce a given force so we ended up with sets going onto a spring tester and recording the height at the required load. It reduced the variation to a few percent.

You could use a bit of locking compound, but you didn't detail the criteria for setting the spring load, such as if there is a large amount of time between putting the parts together and then adjusting the threaded part.

 

[BrianE22]

Probably not enough thread on the blue male part but maybe a double nut (actually just single since the blue part is acting as one nut).