Nord Lock in combination with Belleville washer to maintain preload? 3

[potrero]

Background:
Nord Lock wedge locking washers have a great reputation for resisting vibrational loosening of bolted joints. In some applications the preload on the joint may be at risk of diminishing due to creep, relaxation, thermal expansion or etc, and in these kinds of applications the basic Nord Lock isn't recommended. Nord Lock has released a new product, Nord Lock "X-series" washers which appear to be a hybrid Belleville washer + Nord Lock wedge locking washer which can solve this problem. However, the X series is currently only available in a zinc plated steel, not in stainless steel, so applications exposed to corrosive environments aren't covered by this solution. Also the X-series are only available starting at M6 to M20, a limited range compared to the baseline Nord Lock product.

Question:
Could anyone comment on or provide references to any studies or applications in which Nord Lock washer has been installed in combination with Belleville washers (to maintain preload in a live-loaded configuration?
The idea would be to use the Belleville washer or stack to provide both:
- an easy, reliable, and time-saving way to ensure proper torque without requiring the use of a torque wrench (ie: the "torque-till-it's-flat" method),
- ability to maintain proper preload on the Nord Lock washer despite changes in the joint that would have otherwise diminished the preload (such as creep, relaxation, thermal expansion, or etc)

A good example of the use of Bellevilles to maintain preload is here:
"Using Belleville Springs To Maintain Bolt Preload" by George P. Davet, B.S.M.E.

http://www.sealing.com/fileadmin/docs/Using_Bellville_springs_to_maintain_bolt_preload.pdf

 

[hydtools]

I would think the spring steel of the washer would be too hard for the Nordlock to bed into to work.

Ted

 

[potrero]

@hydtools - the Belleville and Nord Lock washers may be of various materials. In this particular application we need something more corrosion resistant than zinc plated steel, so both the Bellevilles and the Nord Locks would likely by made of stainless steel. Belleville washers are commonly made from 301/302 stainless steel, and Nord Lock washers are available in EN 1.4404 (ie 316).

Nord Lock says their stainless steel washers have hardness ≥ 520HV0.05 (

http://www.nord-lock.com/wp-content/uploads/2012/06/NL-washers_brochure_US_04-2014.pdf)

302 stainless steel hardness ranges from 37-41 RC at 3/4 hard, to 41-47 RC at full hard. (

http://www.nks.com/302_stainless_steel.html)

40 Rockwell C is roughly 400 Vickers. (

http://www.seeger-orbis.com/technology/hardness-conversion/)

So, the stainless Nord Locks should be able to engage in 302 stainless steel according to these numbers.

 

[SwinnyGG]

If you put a washer of any kind under or on top of the nord-lock, you are making the nord-lock useless.

 

[MintJulep]

jgKRI's insight is excellent.

 

[potrero]

Right, that makes sense. Hence the X-series' reason for existence. Is there any other way around its limitations?

 

[MintJulep]

You might want to look into Schnorr "Safety Washers"

http://schnorr.com/product-details/safety-washers/

Basically they are serrated Bellville washers.

 

[Screwman1]

Use a fastener with an adequate L/D ratio (5:1 or so), get good smooth bearing surfaces and joint interfaces, tighten it properly to the correct clamp load and then leave it alone. Stacking Nord-Loks and bellevilles is just going to be a ton of variability that you don't need to add to the joint. If you need to retain clamp load reduce the diameter of the fastener and add a hardened spacer to increase the effective length.

 

[3DDave]

I remain skeptical of washer solutions in general as most of the joint problems I've come across are loss of compression, not unexpected rotation. A fastener that turns after it's loose is a symptom of something having gone wrong which lockwire and other systems just cover up. I'm not keen on the addition of nut lubricant in a failed-shear Junker test that promotes Nord-lock.

 

[Tmoose]

"creep, relaxation, thermal expansion or etc, and in these kinds of applications the basic Nord Lock isn't recommended."

Hi potrero,
Does Nordlock discuss that on their website somewhere ?

thanks

Dan T

 

[Tmoose]

http://cdn.nord-lock.com/wp-content/uploads/2015/10/NLX_product_leaflet_70203EN.pdf

The X series brochure on page 2 seems to indicate, by using the international circle/diagonal slash symbol, they are NOT suitable when " Mating surfaces must be locked in place ."

I have not studied the tech data available from Nordlock, but my hunch is that statement/symbol means the integral belleville is a relatively thin standard belleville, or otherwise incapable of exerting the preload that a REAL bolted joint needs.

As I recall My previous investigation into Bellevilles to create preload equivalent to a well done bolted joint ( per Screwman1's post) resulted in a stack of heavy duty standard bellevilles even taller than IHOP's full stack, arranged in parallel for maximum force.

https://olo-images-live.imgix.net/e...ll&bg=#fff&s=85a0991a9be9ee0c49174e135413f500

 

[Strong]

I found this interesting product:

http://www.katofastening.com/lockone.html

I have not used it, nor do I sell it.

You will probably have to test one or more locking devices and configurations and not rely on sales claims or other limited information.

Walt