Split lock washers - Any uses??? 2

[Binary]

I've read through all the threads on this site and some of the reference links as well.

The general opinion is that split lock washers are of no value to prevent loosening.

My question is:

Do they have any use at all or are they just remnants from an earlier time?

I've recently joined a company where they are mandated everywhere. Before this site, I would not have questioned that practice. Now, I do. I'm just seeking all the information I can before I challenge the practice.

Again, do they have any use or any value that you know of or are they a pure waste of time, money, and inventory space?

 

[dik]

I wasn't aware that they are of little use except for high strength bolt connections. I can see for high strength bolts that the preload is likely greater than the force created by the lockwasher. If I require a loose or snug fit, I usually peen the threads.

For lesser connections, the 'split' keeps a bit of tension on the nut to resist turning off as well as the bevel of the split is acting opposite the the nut removal.

 

[boo1]

The split lock washer provides very little vibrational resistance. Proper preload and/or thread lockers should be specified.

Mechanical Engineering mag. had a very good article ~1988 or check with manufactures like Locktite.

 

[CoryPad]

Binary,

I agree with dik (except for peening the threads, which I don't understand). For joints that require preload (tension loaded joints, joints with vibration, etc.), then split washers are useless. For joints that just need "to be there", then they may provide a little preload. I see no justification for a split washer since the cost to design, purchase, store, and assemble them cannot compete with the cost of using an appropriate preload with a standard screw.





Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[strokersix]

I do not use split helical lock washers in my design work, nor do I use them in my personal hobby work as I agree with the above responses. However, the following dissenting opinion is written in J H Bickford's 3rd edition "An Introduction to the Design and Behavior of Bolted Joints" on page 561:

"Recent research....suggests that this device is more effective than it appears to be. .....while this washer is flattened by bolt tension equal to only 5% of its proof load, increasing bolt preload to 70% of proof will cause the trapezoidal cross section of the washer to roll and twist down on the outside diameter, which also grows. This complex action results in a washer spring rate which can approach 65% of the spring rate of the fastener. That spring rate will dominate the behavior of the fastener under load, and will reduce the amount of preload lost under a given applied load."

 

[boo1]

The reference strokesix lists, is for Helical Spring Washer not split washers. Table 16.3 if the same refence lists spring washer second to last in number of cycles to loosen a nut.

 

[dik]

CoryPad:
Only if the bolts are finger tight or snug, then I peen the threads to keep the nuts from working loose.

 

[Binary]

boo1 - just out of curiosity, what's the last one on that list?

All - I've seen Bickford's book referenced several times. Do you think it's worth the $150? (Dekker's got some great titles but man are they expensive).

 

[kenvlach]

I have a legitimate use for split ring lock washers – bolting together aluminum busbar. As aluminum very slowly creeps, the contact pressure would drop below the desired 1000 psi without some spring loading. Note: SS bolts, nuts, split washers and thick flat washers are coated with EJC (electrical joint compound) to prevent galvanic corrosion.

So, the principle is that the split ring washers can be used to maintain pressure despite some minor creep of the bolted material. This condition might also apply when bolted connections are heated.

Any comments?
Ken

 

[CoryPad]

Ken,

Why do you use a split ring washer rather than a conical spring washer? The conical washers (aka Belleville) are very common, and can be designed with just about any force-displacement relationship you could want. Plus, they have uniform circumferential pressure instead of the non-uniform pressure of the split ring washer. This would be a better engineering solution, in my opinion.

Binary,

I don't recommend Bickford's book - he is the editor of a better one that includes most of the info from his book. Read faq725-600 for more information.





Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[boo1]

Binary, the worst preformance nut is:
"Plain nut, with or without tooth-type lock washer" - Relative number of cycles required to shake nut from bolt was one.

Ken, CoryPad has a good point the Belleville would be more effective retaining the preload.

The book, I would not reommend buying.

 

[kenvlach]

CoryPad & boo1,
Agree, and ALCOA does recommend Belleville washers. But my application isn't so demanding, so we went with split ring+flat washer because the cost is only 1/10 that of Belleville washers.

I would like comments on use of any spring-type washers in creep-type applications (where the bolted material is intrinsically soft or may undergo heating). Seems justifiable to me.

Ken

 

[BHH]

Helical split ring lock washers were invented backin the days when carriages were held togeter with bolts. Their purpose was to act as a spring to retain tension on a bolt as the wood compressed under the additional loads encountered in use. If you have an application where you expect imbedding or cold flow then the split ring lock washer is useful. The lock washer does very little to prevent loosening from vibration.

Studies have show that the primary cause of loosening comes from sliding of the male thread inside the female threads where there is a side load. With each "slip" the thread unwinds a minute amount until it has lost preload. A split ring lock washer does nothing to prevent this movement and so does not help retain the preload. Other products such as thread locking adhesives and plastic patches that prevent the movement are far more effective.

A very good reference on this subject is NASA Publication 1228 by Richard T. Barrett published in 1990. It can be ordered by calling (703) 605-6000 and asking for NTIS Order #N90-18740/2 or by going online

BHH