Helical spring washers 5

[sdz]

I know this has been asked before (

http://www.eng-tips.com/viewthread.cfm?qid=103389)

but hopefully this time...

What bolt load is required to flatten a Metric helical spring washer? Is it specified in some standard?

Now I know they are considered pretty useless as a lock washer. What I'm trying to find is the load required to flatten them, and consequently if the washer is flattened can we take that to indicate a bolt tension, and how reliable is it?

 

[MotorCity]

I cannot offer any response to your question, but may I ask if these are being used in a structural application and if so, how are they being used? I have never used or specified them before and just curious.

 

[Tmoose]

Hi SDZ,

"What I'm trying to find is the load required to flatten them..."
My impression from finding them in a variety of devices is they flatten pretty easily, and the tendency for some to tear up the surfaces they touch likely makes future embedment of the joint surfaces pretty likely, to the detriment of the bolt clamping force.

As I recall the inch and metric specs I've seen are purely dimensional.
Like this -

https://mdmetric.com/fastindx/uf32_39.pdf

 

[Screwman1]

Yup, Moose is right, the loads are all over the place and they tend to be very low in relationship to the yield strength of the accompanying fastener. We looked at this many years ago and it wasn't a viable concept.

Dick

 

[EdStainless]

If joint tension is what you need look at using bellville washers. At least they have a predictable falttenign force.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[sdz]

Thanks all. Pretty much what I thought.

MotorCity, they are being used on U bolts to secure antenna poles to mounting brackets. A very common application but I have never found any data on what the connection can carry.

 

[SwinnyGG]

You would be well served to eliminate helical spring washers from your arsenal of tools to prevent vibration loosening.

Ed's tip about using bellville washers as a tension indicator is a useful one, however.

 

[Guest102023]

I'll pile on and add that helical so-called lock washers have been thoroughly discredited as part of an engineering approach to fastening.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[Tunalover]

brimstoner is right. Helical split lock washers don't work. In fact they tend to lower the joint's natural frequency while they drive up the part count and associated costs.

Tunalover

 

[Tunalover]

Just to get in the last word and add weight to the assertion that helical split lock washers don't work, search for and download:
NASA FASTENER DESIGN MANUAL RP-1228. The manual devotes only a sentence or two to this topic but it's enough to make you question your belief system before using these washers.


Tunalover