Co-efficient of Friction related to Fasteners

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BUVANESWARI

#1
Hello Friends!!

1)Define Co-efficient of Friction in related to fasteners.
2)Factors affecting Coefficient of Friction
3)How is it determined?
4)How co-efficient of Friction affects parts failure in regards to ELV compliance?
 

Miner

Forum Moderator
Staff member
Super Moderator
#2
Re: Co-efficient of friction problem

Hello Friends!!

1)Define Co-efficient of Friction in related to fasteners.
2)Factors affecting Coefficient of Friction
3)How is it determined?
4)How co-efficient of Friction affects parts failure in regards to ELV compliance?
1) The definition of coefficient of friction does not change for a fastener. Picture a threaded fastener as an inclined plane that has been wrapped around a cylinder. The flanks of the thread form the surface of this inclined plane. While the geometry is a little more complex than this (e.g., the surface is tilted), it essentially holds true.

2) lubrication, plating, type of plating, contamination, etc.

4) In threaded fasteners, there are two basic issues that could occur. If a threaded fastener is contaminated with oil the friction is reduced. This means that at a given torque, the fastener will turn more times than it would have under typical friction. This places a higher tensile load on the fastener that could lead to immediate tensile failure, or a longer term failure. Another situation is a threaded fastener with a heavy plated coating. This could increase the friction leading to fewer turns under the same torque, which in turn places a lower tensile force on the fastener. This may lead to failures from inadequate clamp forces or long term loosening of the fastener.
 
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Umang Vidyarthi

#3
Hello Friends!!

1)Define Co-efficient of Friction in related to fasteners.
2)Factors affecting Coefficient of Friction
3)How is it determined?
4)How co-efficient of Friction affects parts failure in regards to ELV compliance?
Miner has guided you well on your querry. Have a look here for 'factors affecting friction and coefficient of friction for nut & bolts.

Here are some good vidieos on Friction.

Attached is a study on 'Friction coefficient of fastners' , conducted by SAKAI Tomotsugu of Toyota motor co. This will put you into the picture.

To the best of my knowledge, ELV compliance for fasteners is a change of passivation in zinc plating. How much coeff. of friction affects is beyond me.

Hope this helps

Umang :D
 

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harry

Super Moderator
#5
In the context of RoHS, ELV, fasteners and coefficient of friction, it is worth noting the following:

Cr6+ (Hexavalent chrome) is banned. Hexavalent chrome has good properties such as low coefficient of friction, anti galling and high hardness not found in the many other substitutes such as Cr3+ (Trivalent chrome).

To overcome this, the use of an ‘organo-mineral type of lubricant topcoat’ is often employed as a friction modifier to help improve the coefficient of friction (most automotive specification called for coefficient of friction for fasteners of between 0.10-0.15).
 

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