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(Mechanical)
(OP)
9 Sep 11 15:38Hi guys,
I need an info on Belleville washers. I want to know what is the max number of times a single belleville washer can be used/reused. I want to know this because the mechanics where I work were once told to only use the same washer twice. We have a LOT of washers here and I wonder if they could use them more than 2 times.
Thanks a lot for your time,
Simon
(Mechanical)
9 Sep 11 15:52sounds like a question for the manufacturer about specific part numbers.
then there may be a problem of keeping track of how many time they have been re-used
(Mechanical)
9 Sep 11 16:05Tmoose
might have the right idea, check with the manufacture of the washers that you're using and see what they have to say about the fatigue life of their particular products.I just did a simple Google search and turned up many instances where the manufactures of Belleville Washers go out of their way to promote the idea that they have done extensive fatigue testing and they assure the buyer that their products are resistant to fatigue failure.Based on this impression, it would appear that this is an issue which the manufactures are talking about without really being prompted to do and as such it suggests a couple of things. 1) it feels as if there has been problems in the past, which could very well explain why your mechanics warned you about this, but 2) it would also appear that the manufactures may have responded to this by producing better products and backing them up with test data. I would say thatmight have the right idea, check with the manufacture of the washers that you're using and see what they have to say about the fatigue life of their particular products.
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(Aerospace)
9 Sep 11 16:07it'd depend on whether the washer has been deformed ... no?
(Mechanical)
9 Sep 11 16:12Hi trudelsThis site has an FAQ asking you're question.Regardsdesertfox
(Mechanical)
(OP)
9 Sep 11 16:17Thanks a lot guys for your answers, I will contact my supplier to have more info!
Thank again
(Mechanical)
10 Sep 11 12:42There are a tremendous amount of computational engines for stress analysis on the web. Your issue is one of cyclic loading and lifetime. You can definitely re-use a Belleville Washer stack more than twice, depending on your application. In my experience, rare to use them only twice, probably a mis-spec of the application. They are way more reliable than that!Do the research and ensure the Belleville Washer application suits the components needed.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
(Materials)
10 Sep 11 13:29I would definately follow the advice posted above about contacting you spring manufacturer for information on the specific characteristics of your spring as there are numerous designs for different applications.If you want to educate yourself on the application and design of disk spring components here is a link to the Schnoor handbook.Key Bellevilles has a CD for the design and application of disk springs
(Mechanical)
10 Sep 11 16:38trudels,Roark's Equations has a section explaining Belleville washers. You can work out the stress for yourself, and analyse for fatigue. They are springs. They are under a lot of stress.
JHG
(Industrial)
10 Sep 11 17:54I used to work with machine tools and they are often used to securely hold tools in place. These tools could be subjected to 'tool changes' many hundreds of times per shift. This would constantly be putting the washers under stress/fatigue. In seven years I didn't have to replace a single one.
That said I have seen failures with them in my current job, but they are subjected to far greater forces (400 Tonne presses) and in a harsh environment (concrete products).
(Aerospace)
11 Sep 11 14:10Agree with Grindy. We own many CNC machines and have rebuilt many draw bar systems that retain a machine tool holder in the spindle. It is very common to get approx 100,000 tool changes without issue. They are usually compounded in series and parallel to achieve a target amount of travel and force. They are usually compressed to max every time, then released BUT they are usually at about 20-40% of compression when released so they retain a draw force on the tool when running in the spindle.
IMO, you can get a lot of cycles from them. IMO, the nasty vibrations and harmonics from machining largely contributes to the failure of the washers, not just the fatigue limits.
Want more information on volute springs inconell718? Feel free to contact us.
(Mechanical)
11 Sep 11 18:40I know of a product where belleville washers are used as spring packs for actuators where the actuator can and often does drive into the spring pack when subjected to high operating torque. The flexure of the spring pack allows the mechanism to flex so that a torque switch can be made (or broken) when the flexure exceeds a preset value.
These washers flex to some extent every time the actuator operates if it is operating at or near its rated torque and only flex to the maximum extent so as to trip the torque switch if the design torque value is exceeded.
These belleville washers certainly are "reused" time and time again without ever being disassembled.
rmw
(Automotive)
12 Sep 11 18:10My Honda VF750F uses a belleville washer to clamp the clutch pack. Still working fine after 28 years.
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(Mechanical)
13 Sep 11 10:28A lot depends on your type of application and requirement for reliability. In race cars, teams typically use new parts everytime they rebuild the car between races. Might be excesssive and waste some good parts, but they can't afford any chances. Nuts, bolts and washers are the most common parts that are not reused.
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Ben Loosli
(Structural)
13 Sep 11 12:10Tend to agree with looslib...
The mfg will probably say change them every time - since they are in the business of "selling" them.
For non-critical apps - I am sure they can be re-used. But if you are building space shuttles or holding jet engines on airplanes or building race cars - I think I would use new ones every time.
(Mechanical)
13 Sep 11 17:04Sometimes NEW = Never Ever Worked (before), especially in this age of components from suppliers from far away. Not that it was all good in the good old days, or sometimes they make 'em much better than they used to, but..............
Some moderately strict MIL spex allow reusing nylon locking nuts multiple times, or until the prevailing torque drops below some nominal value.
Some Bellevilles are designed so as to not exceed their yield strength when squashed completely flat, so would be hard to damage in that regard by tightening very hard.
(Aerospace)
14 Sep 11 04:26I am watching this post for sometime and without dis-respect I am disappointed with the shallow discussion regarding Belleville spring selection and design. No one even mentioned that the theory and closed form design and analysis formulations or Belleville springs (cone disc springs) are well known for decades. Every engineering graduate student should be able to use those formulas to design a new spring and to check how an existing of off the shelf spring will fit the design goals.
When a Belleville spring is compressed to flat or even beyond flat, three types of stresses are usually needed to be taken into account. One is a compressive strength at the top inside diameter of the spring and the other two are tensile strength (one at the bottom large outside diameter and one at the top inside diameter of the disc). Therefore, for cyclic operation only the tensile stresses should be taken into account. However, most if not all Belleville spring manufacturing processes include a preset (scraging or set remove as it is sometimes called) process as that last process that induces favorable residual compressive stresses at the points where tensile stress governs the design. Therefore, much higher loads are able from such a spring compared to a spring that didn't include a preset process in it's manufacturing process.
(Mechanical)
14 Sep 11 11:48israelkk,I set up a spreadsheet using the Belleville spring equations from Roark's, and some similar equations from the SAE spring handbook. I wanted to design my own Belleville springs. As a sanity check, I pulled out my Schnorr catalogue, and I punched in their values. My spreadsheet and Schnorr were in fairly close agreement. I was happy.Your preset would increase the maximum stress a bit, but the Schnorr washers can be compressed flat, according to my calculations. Couldn't you just punch them out of (fairly) soft metal and then heat treat them?I wound up designing some delrin lens preloaders, and I left strict instructions tocompress them flat.
JHG
(Mechanical)
14 Sep 11 21:33Nice tutorial for our shallow minds israelKK, He now knows the theory behind how they are made, but you didn't answer the OP's question - how many times can he reuse his belleville washer?
rmw
(Aerospace)
15 Sep 11 01:08rmw
Knowing the formulations, the loads and deflections on a spring, a competent designer can easily calculate/estimate the stresses and the fatigue life. To answer a question, preliminary specific data is needed including the spring dimensions, loads and deflections. The fact that none of this is given by trudels and your post proves my point.
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There are some cases where flange springs must be stacked on one side of the flange. This might be because a tensioner is being used to load the studs. It also may be difficult to access one side of the flange. In addition, there are some applications where the flange is not bolted through, such as a valve bonnet or if one of the flanges is tapped. In these cases, if the recommendation is to use two springs (or parallel spring sets) in series, we recommend that it is verified that the clearance hole in the flange is less than or equal to the clearance hole of the flange washer. If the clearance hole is larger, then the convex side of the washer nearest the flange could "extend" into the hold of the flange and alter the loading charactertistics. Since the clearance holes in standard flanges is almost always larger than the clearance ID of the Solon Flange Washers, we would minimally recommend that a flat washer with an ID equal to the ID of the Solon spring be used. The flat washer should be a hardened washer to prevent embedment. Another option would be to use a thrid flange washer (or parallel washer set) on this side of the flange. Using an odd number of springs in series will ensure that the convex side of the first spring can contact the flange. The added spring will always provide additional elasticity so joint performance will be improved over two springs.
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