Busbar preparation

[garycvv]

Hello,
I'm working on a project that involves bolting two aluminium bus bars together. I'm after some information about how to created the bolted joint.
Is there a recommeded surface roughness and flatness for the two mating parts? I've found a reference from Bruker that mentions a German standard (DIN 43 673) that recommends a contact pressure between 7 and 20N/mm^2, with 20N/mm^2 being the maximum. The bruker data sheet also mentions that the surface should be 'flat, clean and uniformly roughened'. Does anyone have a figure for what these should be? I need specify it on a manufacturing drawing.
I've been unable to get hold of DIN 43 673, is there an equivalent british or ISO standard?
Many thanks

 

[waross]

A more important issue with aluminum bus bars may be when to roughen the surface.
Aluminum rapidly forms a surface layer of oxide which is a poor conductor.
One method of preparation is to lightly brush the contact surface with a wire brush in an angle grinder. Then immediately treat the surface with an anti-oxidant such as Penetrox.
How soon is immediate? Brushing and then taking a 10 minute coffee break before applying the Penetrox may be too long.
How much to brush? Lightly, just enough to see a difference in the look of the surface.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[unclebob]

I have no reference to this but, most of the time, we use 3/8th and 1/2 diameter grade 5 bolts. For 3/8th, a torque of 25-30 lbf*ft is used
and 50-55 lbf*ft for 1/2, when using standard flat and lock washers. Torque is higher when using Belleville type washers.

 

[prc]

The IEC standard that deals with electrical contacts is IEC/TR60943 ed2.1-2009 Guidance for permissible temperature rises for terminals of electrical equipment. This technical report from IEC is the best tutorial on electrical contacts -theory and application -eventhough the title is slightly misleading.
Since aluminum being a softer material,large diameter plain washers are used to limit the specific loading.( ~3D where d= dia of bolt) If bare aluminum is used, the surface shall be brushed with abrasive cloth or brush and immediately applied with contact grease like penetrox A(Burndy) or Nikkei S-200 or equivalent. Relatively high surface roughness is used (Ra6.3) with a contact pressure of approx 10 Newton/A.

 

[garycvv]

Hello,
Thank you for the replies. Similar to your suggestions I've come across a paper that recommends that the surface should be rough in order for the two mating faces to punch through the oxide layer to make a better contact.
One of the questions I'm coming across is thermal cycling of the joint, and the use of Belleville springs to retain preload. I've come across a few worked examples but they all seem to be for the same basic set up. I think this might have originated in the 'Handbook of Bolts and Bolted Joints' but the same example appears in many places including here:

http://www.solonmfg.com/springs/pdfs/elecconnwhitepaper.pdf

I've tried to follow the worked example but I believe it has several errors. Has anyone else spotted these errors? Or am I missing something really obvious.
Thanks