Lock washer witth teeth useful? 1

[mechengdude]

I know the question has been asked regarding helical lock washers, "Is a lock washer beneficial?" and I have seen the NASA reports and threads on this website with the consensus that NO helical lock washers are in essence useless.

Now, I didn't see anything regarding what I call a star washer.

http://www.mcmaster.com/#lock-washers/=bo70yv

Anyone have any data on the ability of a star or toothed lock washer to provide any locking ability above and beyond the applied torque.

thanks,

 

[TVP]

Here are some links to vibration loosening test data that include toothed lock washers:

http://www.hardlock.co.jp/pdf/asme2006pvp_jp.pdf

http://www.sae.org/events/bce/presentations/2008jungmann.pdf

http://www.henkelna.com/us/content_data/166733_LT4985_Threadlocking_Guide_032010_Web.pdf

 

[HDS]

TVP

Good references.
Do you have a copy of asme2006pvp_jp.pdf with the figures?

 

[TheTick]

Check out the Nord-Locks. Ran across them the other day while doing patent search. Looks interesting.

http://www.duncanbolt.com/suppliers/pdf/nordlockcatalog.pdf

 

[CoryPad]

"Star" washers really are no better than split helical washers. They use the same mechanism (slight embedment into the mating parts), which is not reliable. Considering the time, money and expertise spent on these parts, you would be served better by generating more preload (better tightening tool/procedure, larger screw diameter, higher strength screw, lower friction coating, etc.) or by using thread adhesive.

 

[IRstuff]

Star and other similar washers have already been discussed and the conclusion remain unchanged; they don't do much.

thread404-230741
faq404-1257


TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[JohnRBaker]

Also depending on what it is that you're manufacturing, so-called 'shake-proof' or 'star' washers may not even be allowed.

I worked 14 years as a Design Engineer for a large multinational capital goods manufacturer of food and chemical processing equipment and at least in the food machinery division (where I worked) we were not allowed to use 'star' washers as they were considered unsanitary because they provided a habitate for 'vermin' to grow. We used to us split washers, but eventually went to either upset-nuts (self-locking nuts) and/or Locktite. And on large fasteners, after fully torquing it down, we would simply cross drill and drive a solid pin through the nut/bolt assembly.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[KENAT]

In fairness though, regulatory compliance folks seem to like them for ground points and the like.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[TVP]

HDS,

The figures were at the end of the .PDF file. Figures 10 and 11 just were not labeled properly.

 

[metman]

In TVP's first posting, second link there are opposing cam surface lock washers. The tick provides a link for these also at

http://www.duncanbolt.com/suppliers/pdf/nordlockcatalog.pdf

I have used these in the design of a $40,000 gear case for clamping bearing housings with good results on an underground coal mining machine. One the the selling points was that they are used on army tanks.

Of course correct preload is required. I like 60% of yield.

 

[ScottyUK]

Are the NordLock type suitable for joints which may need to be split again in future, or are they a one-shot device? How badly does the component surface get chewed up by the washer during loosening? I'm currently arguing the toss with a switchgear manufacturer about use of helical spring washers which appear to be of little or no use as a locking device.


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If we learn from our mistakes I'm getting a great education!

 

[metman]

ScottyUK

You might try contacting Nordlock online and ask them.

It should be an easy test to perform.

If galling is a problem at disassembly, yuo could use anti-sieze compound on the affected surfaces during initial assembly.

 

[Tmoose]

Sorry to hijack the thread - Scotty UK, are the fasteners "secured" by the helical Lock washers loosening in sservice?

 

[ScottyUK]

metman,

Yeah, will do. Just curious to hear any unbiased opinions.

tmoose,

Not noticeably. There's nothing especially highly loaded in this equipment: the most critcal joints are busbar connections, and copper is obviously fairly ductile so it would deform under very high loadings, but I've followed the threads on locking fasteners with interest. From my perspective if there is no benefit to having a helical lock washer and we can eliminate something which has the potential to be dropped into the gear then I am 100% in favour of it. If we need a locking washer then we should at least have one which works. The number of dropped washers which seem to accumulate in the bottom of a switchboard during its life is quite surprising, and it wouldn't be too difficult for one lodged in the wrong place to initiate a major arcing fault within the board.


Apologies for dragging the thread all over the place. If this discussion is going to develop then maybe we should start a new thread and ask admin to tidy up a bit.


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If we learn from our mistakes I'm getting a great education!

 

[WoodrowJWeen]

Busbar to busbar connections in switchgear are usually secured by belleville washers (conical spring washers).

 

[dinjin]

I think any thick washer would be beneficial in increasing the effective clamped length but not
for locking purposes.