Lockwashers - To Use or Not to Use 9

[kthree]

About the same time Ed introduced us to the Beetles I was working as assembly labor in a shop whose propriatary line was mfgd mostly from cast iron and structural steel. At that time it was explained to me that lockwasers were used under a (NC) nut or a screw head when they pulled up against steel but a lockwasher wasn't necessary when the mating surface was cast iron. And it seemed they had many years of success in this procedure to support their claim. Now my circle has brought me back to a very similar cast iron and steel situation. Now that I am more aware of time involvement in the production process, I am amazed at the substantial amount of time our assemblers spend fumbling with the thousands of lockwashers we go through every month. Captive lockwashers and serrated flanges have been looked at so far. Neither has offered a set of pros and cons we are anxious to accept. Any ideas, comments, or suggestions anyone would wish to share in this matter would be greatly appreciated. Thanks, K.

 

[IRstuff]

Why not? Millions of people have less than $10,000 of retirement savings, and they ARE all wrong.

TTFN

 

[Fabrico]

The US government, US military, and US Navy all have specifications for split lock washers. Does anyone really think NASA is void of lock washers on every piece of ground equipment, test equipment, and all their structures?

How or why this led from cast iron and structural steel, as the O/P mentioned, straight into aerospace and retirement savings, is entirely up to persons here other than myself.

What's at issue here is not application, popularity, or personal preference, but the making of completely false and misleading statements. Doing so helps no one, especially ENG-TIPS FORUMS.

 

[arto]

The only place lockwashers are regularly seen is in Electrical Connections as GregLocock sez.

{always thought that was because the EE's didn't know better ;-) - makes 'em feel like they're doing something.}

Loctite would tend to insulate the joint & there's not much room for a torque wrench in an electric box anyhow. They'd probably strip/stretch a lot of threads if they went tight enough - you'd have to use strain-hardened stainless or silicon-bronze bolts to get a high enough preload to hold tight - plus the terminals are often soft metal.

 

[MintJulep]

The ASME also has a standard for lock washers. In that standard it states:

The word lock appearing in the names of products in this standard is a generic term historically assoicated with their identification and is not intended to imply an indefinite permanency of fixity in attachments where the fastners are used.

 

[CSLufkin]

For what it is worth, I have a friend who is a Caterpillar mechanic and he says Cat uses very few lock washers. Instead they use a hardened flat washer and stress the proper torque/fastener stretch. This holds true for cast iron, steel and aluminum parts.

 

[btrueblood]

Yup. I've never seen a lockwasher on a track bolt. Nor on cylinder heads.

 

[mhorn]

Fastener manufacturers can, and do, supply fasteners with the adhesive locking compound "pre-applied." These parts are processed to include a dry band of adhesive on them (Dri-Loc, Scotchgrip, etc.). This eliminates the need for installers to apply a liquid adhesive, it's already done.

There are a number of other "locking elements" available that can be pre-applied, including a nylon patch which can be applied with 180^ or 360^ coverage.

 

[Screwman]

Agreed on the uselessness of lock washers compared to proper joint design and tightening strategy.

Notice that NO automotive companies have specs for lock washers active for new design.
The heavy truck industry doesn't either.
Nor do the diesel engine companies.

The only place that I still see some lock washer use is on farm equipment...primarily in those places where there is likely going to be field adjustment. In those cases I have been told that they are used because the end user farmers often don't retighten the fasteners up to their full target preload. The lock washers tend to hold things together somewhat under the low load conditions. I was also told that the farmers complained when the washers were taken off, even though testing showed that they provided no benefit, so they were put back on some pieces of equipment.

If you are concerned about viration loosening and have a joint design that doesn't allow propoer clamping, then you should look into some type of a prevailing torque thread design on the fastener or nut or the use of a preapplied thread locking adhesive. Both of those work well and are the most commmon solution used by industry today.

 

[maur]

HD flat washers along with 'nylok' style nuts anyone?

 

[Screwman]

Not bad Maur; but I would just use a Nylock flange nut and eliminate the separate flat washer. One less item to make sure is properly assembled. Flange nuts will give adequate bearing surface for all but the highest clamp loads or softest materials. Nylock nuts are good on prevailing torque and they tend to have less friction variation than deflected metal locknuts.

 

[blfarrar]

If you want lock washers that do work try Schnorr Washers - these do the business & are fitted to tiens that are critical - such as parts in printing machines & aerospace where detachment of even the screw or nut into the mechanism is not an option.
Search the webfor a local supplier

Bruce L Farrar.
Works Engineering Manager
Marshalls Mono PLC.Brookfoot Works.
Halifax W.Yorks UK

 

[spectreeng]

Even though this is coming from Nord-Lock's website, I found their video to be pretty informative - it shows bolt tension drop off with vibrated joints. They test their system against spring washer, nyloc, deformed thread, and even double nut. All of which lost tension with vibration. I guess Nord's theory is that an initial rise in bolt tension is needed in the loosening direction in order to prevent loosening. The drawback with their system is that the cam surface between the two washers has to be the lowest friction surface.

http://www.nord-lock.com/video/nl_uk.wmv

 

[SomeYahoo]

Star to spectreeng for the video. Now I may be able to convince co-workers that spring washers are the work of the devil!