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| Electrical contacting on aluminium busbar |
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| TERRA Operative:
When I used to service welders, they often used aluminium busbars and windings in the transformers. These busbars would pass up to 2000A at 50-80v or so at full output on the larger machines. To make terminations, standard practice was to sand the aluminium with fine grit emery paper, then immediately smear it with a good amount of jointing compound then attach the lug with a bolt as usual and torque to spec. I never had a burnt termination doing that. Before I started working there and made the other techs do the joints the same way, there were a number of joint failures after extended use due to the oxide layer and dissimilar metals etc. |
| damien22:
--- Quote --- then immediately smear it with a good amount of jointing compound --- End quote --- What can of join compound were you using ? Had the idea of similar process, by threading the holes a bit smaller, adding grease and then when putting the screw it would break the oxide layer and the grease would avoid oxidation but I don't know how well that would go over time... |
| MagicSmoker:
--- Quote from: damien22 on February 27, 2019, 11:42:30 am --- --- Quote ---Plate the aluminum bus bars with nickel; problem solved. --- End quote --- As discussed, we couldn't find any supplier that can do this sort of plating beyond 1m length --- End quote --- I was able to get large aluminum bus plates for a locomotive drive system (>1m x 1m) nickel plated at a local shop for a very reasonable price and this isn't even a particularly big city; surely there is someone not too far away who can handle something larger than 1.3m... Electroless nickel is one of the most common surface treatments for a wide variety of materials, after all. Despite wraper's opinion - which does not seem to be informed by actual experience - no alternative comes anywhere close to cost vs. ampacity of aluminum, even factoring in the nickel plating of the latter. Copper is anywhere from 4-8x more expensive than aluminum on an ampacity basis and this comparison only gets worse if you need the bus bar to be thicker/bigger than is strictly necessary for mechanical reasons, rather than ampacity. No brass or bronze should even be considered unless this is a marine application and you have, shall we say, an unrestricted budget. Pre-posting edit - saw TERRA Operative's comment and while threading aluminum and making connections to it directly is possible if the surface is prepped well, that last bit - relying on the competence of assembly technicians now and service techs later - is often the main argument against using bare aluminum. The type of anti-oxidation grease most commonly used in the US is "NoAlOx" which is basically a suspension of zinc particles in silicone dielectric grease. Probably something similar is available over there. |
| TERRA Operative:
I can't remember the brand of grease we used beyond it being a slightly green/brownish grey and being in a tall squeeze bottle with a red lid..... (10 years ago is too long for my brain to remember those details.... :D ) Also, for a bit of clarification, we didn't thread into the aluminium busbar, we used nuts and bolts (and washers and spring washers) with through-holes to enable us to really torque down the lug without tearing out weaker aluminium threads. |
| damien22:
--- Quote ---Electroless nickel is one of the most common surface treatments for a wide variety of materials --- End quote --- As I understand its more special for aluminium as you need to have some special treatment before hand to remove the oxide layer otherwise the plating will not hold over time. --- Quote ---However, to electroless nickel plate (or any other plate) onto aluminum alloys successfully with good adhesion, the oxide film must be removed and remain so during plating deposition. --- End quote --- https://www.pfonline.com/articles/adhesion-of-electroless-nickel-deposits-to-aluminum-alloys and only very specialized companies does it as far as I understand. |
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