Bolt tightening torque for Non steel material 3

[engmechs]

Hi all,

I worked in an electro-mechanical dept, & my coworker asked me about bolt torque rating for various sized bolts. I then showed him what my normal reference chart to him, but he showed me the electrical contactor & fuse flanges are made of Copper/ Nickel type material, which is softer material than steel. I don't think the standard torque rating would apply to this material.

Will it take proportional approach in this case, ie. multiple the tensile strength ratio (of 2 materials) to the standard torque rating? What is the torque rating on bolts for non-steel mounting flange application?

Please advise.

engmechs

 

[desertfox]

Hi engmechs

The torque on joints whether it be steel or some other material must be based on the external load and conditions
the joint actually see's.
If you have that information then we may be able to help you further.

regards

desertfox

 

[engmechs]

Hi desertfox,

There is no external loading on these parts (ie. stationary state all the time), and they are located inside a big electro-mechanical enclosure. (indoor environment)

Regards,

engmechs

 

[MintJulep]

If there is no load, then you don't need a bolt.

 

[Philrock]

Steel bolts with non-ferrous mating hardware is very common, especially steel bolts in holes tapped in aluminum.

It's always a good idea to calculate stresses: tensile, bearing, and shear.

Tensile stresses in the bolt threads. Shear stresses in the bolt threads due to tightening torque. In your case there is no external shear load, so you don't have to worry about that type of load in the threads. Shear stripping stresses in the threads - in your case, it's almost a sure thing the threads in the hole will be the limiting factor for this type of stress. Bearing compressive stresses - under the bolt head, for example.

You'll need to know the length of engagement, considering only full threads, the limiting strengths of all components, and have an estimate of the coefficient of friction in the threads and in the bearing surfaces.

Remember that the transfer function between tightening torque and stresses is not very reliable without extensive testing under your exact conditions. Without testing, it is common to allow for +/-30% error in the transfer function.

There is software for doing all this, or it can be done in a spreadsheet.

 

[Gymmeh]

Can you or a machinist drill and tap 5 holes in the same material and set up a torque test. Bolts are relitivly cheap and the will confirm any calcs, pritty quickly. You can probably manage this before lunch time friday.

 

[desertfox]

Hi engmechs

If there is any temperature involved because its an electrical joint then that can have a bearing on the
stresses in the bolt and joint materials.

regards

dsertfox

 

[engmechs]

Hi desertfox,

The enclosure is installed inhouse, & anticipated temp. is around 40 to 50 deg.C.

Regards,

engmechs

 

[Gymmeh]

Your problem doesn’t sound like one which requires intense calculations to get it correct, IE limited vibration, limited applied load, relatively low temp.

I would just specify Turn-of-the-Nut so for a fast accurate preload. For example: quarter to half past the lock washer engaging.

 

[desertfox]

Hi engmechs

When I said about temperature what I should said was temperature rise, ie if there is a lot of current through the joint during normal operation or worse still say abnormal current (short circuit current)then the resulting temperature rise can have a dramatic effect on the mechanical stresses of the bolt material and joint materials.
Now this may not be ultimate reference for your application
but "Copper for busbars" by the Copper development Corporation as a table of joint area, bolt size and torque settings which can be viewed on line and here is the link:-

http://www.cda.org.uk/Megab2/elecapps/pub22/sec7.htm#Bolting Arrangements

regards

desertfox

 

[engmechs]

Hi Desertfox,

It is a great reference chart. It is very informative, & could serve for my needs. This is pretty close for what I need to show to my co worker.

Thanks again,

engmechs

 

[desertfox]

Hi engmechs

Your welcome

desertfox