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Proper use of Flat Washers, Lock Washers Et. Al.Helpful Member!(3) 

wd4dui (Electrical) (OP)
30 Mar 05 15:03
I am working for a company that produces military hardware and I am having a hard time convincing anyone here that the use of a flat washer is necessary when fastening irridited aluminum parts. They insist that only a lock washer is required. I have shown them the result of using no flat.....pitted and chewed parts from the locks. I have searched everywhere to find a document to show them something that supports my position. Also, we stainless hardware from #2 to 1/4' machine screws. Would it not be better to not chew up the irriditing and allow electrolisis to start? If the irridite is not comprimised a better resistance to dissimalr metal corrosion? Most of our stuff is used in salt air and other harsh environments. Any info would be appreciated greatly. Thanks
Rob
WD4DUI@bellsouth.net
Helpful Member!(2)  CoryPad (Materials)
30 Mar 05 17:10
You are correct regarding the proper joint design, but I can't think of a reference that answers your question directly.  Perhaps Handbook of Bolts and Bolted Joints or NASA RP1228 Fastener Design Manual would be suitable.

The Handbook is available at:

http://www.dekker.com

The Manual is available at:

http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1990/RP-1228.html

Regards,

Cory

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

CMfgE1 (Mechanical)
31 Mar 05 3:25
If your making military hardware I would think that you are being held to a specific quality standard. If your company is not ISO certified than you will be held to the MIL standard. In those standards it will specify what is required for all aspects of manufacturing for the military.

Try this site   http://assist.daps.dla.mil/quicksearch/

It will help you search for the right standard. You might have to purchase the standard but I know for some you dont.



Good Luck
tlee123 (Mechanical)
31 Mar 05 10:34
Rob,

You may be right in terms of corrosion, but adding a flat washer is wrong and will defeat the action of the lock washer.

Without the flat washer, the lock washer digs into the fastener and the part being fastened. This is how the lock washer "locks".

Now if you add a flat washer to protect the part from damage from the lock washer, the flat washer will be locked to the lock washer but the flat washer won't be locked to the part being fastened.  This is bad.

Tom

Helpful Member!  NickE (Materials)
31 Mar 05 10:51
except that split washers dont work and here's why:

Thread108-114051

wd4dui (Electrical) (OP)
31 Mar 05 11:57
Thank you all for the great info on the "Evil" lock washer. Think I will suggest Lock-tite, super glue, elmer's glue, duct tape or chewed bubble gum (Bazooka of course) and flat washers. The lock-tite will probably suffice.

Thanks again!

Rob

WD4DUI@Bellsouth.net
rorschach (Petroleum)
19 Apr 05 10:41
tlee123 is correct, there is another issue as well, toothed lock washers that dig into the surface improve conductivity/bonding for enclosure parts that need grounding for EMI purposes.
aviat (Aerospace)
20 Apr 05 0:36
There are a lot of better ways to get a good bond than mutilating the component with a toothed lock washer. Installing lock washers without plain washers will result in scratches, which can cause cracks in highly stressed structure, as well as increased corrosion susceptibility. One of many references for this is found under lockwashers at the following site.

http://www.faa.gov/certification/aircraft/av-info/dst/43-13/Ch_07-05.doc
Tmoose (Mechanical)
20 Jun 05 17:47
http://www.dotars.gov.au/transreg/vsb/PDF/vsb_06_h.pdf

page 4.  "Spring type washers are not allowed on structural members"
tunalover (Mechanical)
20 Jun 05 20:12
Guys-
Toss the helical-split, internal-toothed, and external-toothed lock washers.  I've tested these on railroad equipment.  Bolted joints without are better than with!  The lockwashers make the joints softer and drive the natural frequencies down.  Instead use Bellville, wavy-spring, or cupped spring washers!

Best of all, use prevailing-torque locking methods ala nylon patched screws or self-locking nuts with nylon locking element.

If you find a credible reference that did a formal study on lock washers, I WOULD LOVE TO HAVE IT!

Tunalover

CoryPad (Materials)
21 Jun 05 13:35
Tunalover,

I think you could get some data from the original work done by Junker.  Here is a link to an SAE paper that you could have faxed or mailed to you for ~ $10:

http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=690055

Regards,

Cory

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

tunalover (Mechanical)
21 Jun 05 18:49
Thanks Corypad!

Tunalover

ctopher (Mechanical)
21 Jun 05 23:03
In addition to the washers, for military hardware there is usually lockwire also.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site

FAQ559-1100
FAQ559-716

TonyCro (Mechanical)
22 Jun 05 5:16
For rotating applications We're moving away from spring washers (trying to but diffcult to convine some of the merits) to Nord lock washers, see http://www.nord-lock.com/
 
Tony.
sprintcar (Mechanical)
22 Jun 05 10:19
In racing applications where grade 8 bolts are used to attach the exhaust header to the aluminum head, I've been using hi-temp RTV silicone sealant on the bolt threads (sae 3/8-16). This seems to hold everything regardless of the vibration, steel header flange and the gasket.  Plus, it comes off easily and doesn't ruin the threaded inserts in the head. I've used all the LocTite products (good stuff) but this seems to work better with the temperature variations.

Just good old race track engineering......

"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut."
-- by Albert Einstein

NickE (Materials)
22 Jun 05 11:03
sprintcar- that sounds pretty good. Like the RTV is filling the gap btw the root and crest of the thread fit and acting like a nylock. Without the extreme adhesion of Loktite.
arto (Mechanical)
22 Jun 05 13:16
speaking of racing.... http://www.stage8.com/AutomotiveStart.htm
They use these on railroads, heavy equipment, machinery too.

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