Spring lock washer vs. internal tooth lock washer.

[bsmet95]

My company manufactures bridge crane and monorail systems. We have a current field issue in which the screw holding a trolley wheel keeps loosening. The screw is locked in place with an internal tooth lock washer, as shown in the illustration. The end user has asked for a torque value for this bolt. We normally use lock washers. Would a spring lock washer be a better option for this application?

 

[MintJulep]

No.

Lock washers don't lock anything.

As a start, see faq404-1257

There are many discussions on this site about preventing threaded fasteners from loosening.

 

[dik]

There's a lot of information about spring lock washers not working well... see the attached:

http://www.boltscience.com/pages/helicalspringwashers.htm

I've used Belleville washers on a lot of electrical equipment that thermally cycles with good success in not having them loosen. You might want to look into that type of fastener.

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[3DDave]

Do a calculation about how much stretch there is in the bolt and compression in the plate. Then ask if there was local yielding how much of that preload would be eliminated. The best bet is to use a very hard washer and a grade 8 bolt and a high torque; about 80% of yield strength. Since the end of the bolt can be accessible (leave the cap off) you may be able to put a micrometer over the length of the bolt to measure its elongation directly.

 

[EdStainless]

No lock nut on the back?
Do you use thread lock adhesives?

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

 

[bsmet95]

We don't usually use thread lock.

 

[BrianE22]

I'd think an external toothed washer might hold better since it is digging in at a larger radius.

 

[Tmoose]

Thanks (and a star) for the drawing with detailed construction information. Some dimensions and load would make it even better.

How many users have a loosening problem?
Is this size trolley a new product, or a "mature" product with dozens of successful installations elsewhere?
Any chance your trolley is being grossly overloaded?
Is the trolley wheel bearing a ball or roller bearing?
Or a plain bearing /bushing of some sort?

If the wheel has loosened a few times, component mating surfaces may now be so torn up that "embedding" is now unavoidable and all bolt preload will be lost after brief service.

By inspection the head/shoulder on the threaded insert looks pretty thin to resist the clamping force I expect I would want to exert with the bolt. As others said, the first line of defense against fastener loosening is correct tightening, which will induce preload/clamping force greater than all loads experienced in service.

Here is a line out of some Military document about fasteners.

075-5.6.1 GENERAL. Many installations aboard ships, especially older ships, still use lockwashers in diesel engines and similar equipment to prevent threaded fasteners from loosening. These may be replaced with the same type of fastener if loosening has not been a problem. If loosening has been a problem, however, replace the lockwashers with self-locking fasteners. S9086-CJ-STM-010/CH-075R2
​

 

[desertfox]

Hi

Try using nordlock washers

http://www.nord-lock.com/nord-lock/wedge-locking/washers/introduction/

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[BrianE22]

If you can use spacers, try a longer bolt. It will be axially and torsionally softer.

 

[bsmet95]

Thanks for all the responses. Tmoose, I will get that info.

 

[XL83NL]

This vid is also interesting to see

http://www.boltscience.com/pages/vibloose.htm

 

[bsmet95]

I have additional info.
The trolley is a mature product. This particular issue came up only recently, and affects only a few units. I haven't gotten any word yet on if it's being overloaded or if there is any damage.
Additional info is on the updated attachment.