Friction coeff. between Al 6061 and 440C Steel 1

[Transient1]

Hi,

I have no. 2 440 C steel fasteners being used to fasten a aluminum flange. I've found one value for aluminum on soft steel (dry) equal to about .61.However, 440C i would not consider a soft steel. Also, Does it matter which one is the fastener? Thanks for your help.

 

[CoryPad]

No lubricant/coatings involved? If not, then I would assume something around 0.4 to 0.5.

Regards,

Cory

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

 

[gfbotha]

From my tables the value of .61 seems to be for dry and static. During the torque event, the conditions might typically vary between static and kinetic... More often than not, there might also be traces of residual lubricant on your fasteners. Therefore I agree with a lower value of say 0.45 as recommended by Cory.

If the aluminium is anodized, I would guess the value could even drop as low as say 0.2

Regards
G

 

[gfbotha]

Just thought - are you not using (large) s/steel washers anyway?

 

[Transient1]

We are using steel washers but they fit just under the bolt head (so I wouldn't call them large). Thank you all for your input. What reference would have the most friction coefficient combinations?
In general, is it an okay assumption that the fastener/washer/surface interface is equal to the steel fastener/aluminum interface?

 

[CoryPad]

Handbook of Bolts and Bolted Joints available here:

http://www.crcpress.com/shopping_ca...?sku=DK5574&isbn=9780824799779&parent_id=&pc=

It is not a valid assumption that a stainless steel fastener head rotating against a steel washer surface will have the same friction coefficient as the stainless steel threads rotating against aluminium threads. If there were a lubricant, then it would more valid.

Regards,

Cory

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

 

[gfbotha]

The size and strength of washers has to do with load distribution in order to limit the maximum contact pressure on the soft metal surface. The frictional torque behaviour will be different for different metal pairs, i.e. you cannot assume it to be the same. In this case it is likely that the lowest friction will occur between the fastener and the washer.

Applicable data about friction coefficients are not always easy to find; of course some are published in good mechanical design handbooks.

 

[dimjim]

Aren't you going to need the screw surfaces wet painted at
assembly to prevent corrosion of the different material
interfaces? Paint will act as a lubricant.

 

[Transient1]

Yes, the surface is either painted or plated. I don't have the spec in front of me.

 

[kenvlach]

Transient1 ,
Please don't post questions while either not knowing or withholding crucial facts.

 

[drawoh]

Transient1,

Do you have any control over the finish of the aluminium? An anodize surface drastically reduces the friction coefficient.

Tightening screws on a painted finish make a mess of the paint. I have no experience with plating.

JHG

 

[Transient1]

The finish was Ag plated. Thanks to everyone.