Aluminum Brazing

[Anonymous]

Here is a product that will weld - braze aluminum. Dura-Fix 3 in 1 Rod comes as metallic rods which do a great job.
You can use a standard gas torch to braze - weld all sorts of aluminium jobs. The melting point of this stuff is 732F.
The only problem is that the material itself has only 24.9% of the conductivity of copper. This might not be too bad if you are joining aluminum to aluminum with both pieces touching each other.
Last time I bought some, the distributors were:
Weeks distributors,
36 Carolina St,
Taylors, SC 29687
24 Hour order number (803-282-0880) The stuff used to sell for $29.00 a pound.
You might do a search on a search engine for the stuff. All the best, Dave. * * *

 

[Anonymous]

HI Dave and all
I am under the impression that some of the old Garrett ADS Deepseaker coils had an aluminum winding and many of these coils have now failed because of electrolosis problems created by dissimilar meals. Probably a bit of moisture would speed up the process of electrolosis and render the coil inoperative. I sold a coil a surplus 8in coil a while back because both the coils on a ADS that was in for repair were faulty. I only wish I had got hold of the dead coils for a post mortem.
I think there are enough problems with detectors without introducing further problems by using dissimillar metals in the coils.
Cheers
Steve D

 

[Anonymous]

MORE HISTORY ON ALUMINUM WIRE IN LOOPS
For a long time the White's 950 loop used aluminum wire, and it was widely believed to be a serious source of headaches. They were using crimp connections. I think they finally switched back to copper but not sure.
COPPER-PLATED ALUMINUM WIRE
A long time ago I was looking into aluminum wire for loops and found a company (sorry, don't remember who, but I could probably track it down if somebody was seriously interested) which sells copper-plated aluminum wire. Such an oddball item is too expensive for volume production of regular searchcoils, but might affordable for a specialty product or for prototyping.
"POOR MAN'S LITZ"
For straight-line wiring, ordinary stranded wire is a little better than solid wire. Braided wire is quite a bit better, but pretty much unavailable except in very heavy gages.
However, in constructing coils, proximity effect (one turn of wire being a "target" for the adjacent turn) is far more important than skin effect. For this reason, in the frequency ranges we're talking about, insulated stranded wire can be a big improvement over solid wire.
DON'T OVERKILL ON THE LITZ
Litz is made of tiny wires. Tiny wires have a tendency to dissolve in solder or to become brittle at the solder joint and break.
Therefore it is prudent practice when buying Litz, don't get stranding any finer than you really need.
It is possible to buy trifilar twisted wire (vendor: MWS) which would be a big improvement over solid in a situation where solid was almost, but not quite adequate. The stuff is probably expensive, though.
For prototyping purposes you can twist or braid wire yourself-- a bit awkward and possibly time-consuming, but doable.
--Dave J.

 

[Anonymous]

Hi Steve,Dave
In regards to connecting aluminium to copper if you use the right connection to copper.Many years ago when I was making my living as electrian I installed many large cables as mains to houses,using aluminium,and fitting off with special terminals,this included to my own house it has been there for 25 yearsand that with no problems.I am sure with the right terminals you would have no problems.
But why would Whites use aluminium wire in coils.
Regards Frank Wallis

 

[Anonymous]

Ok I am not a technican or more but, I remember in my old school days that copper was more conductive than aluminum and silver was more than both of them with gold being the best. I am wondering why aluminum would be used for coils unless it`s for the weight. Isn`t the conductivity of the wire important to a coil? And with the price of silver being so low now, wouldn`t a silver wire coil be exceptionally better? Thanks, John

 

[Anonymous]

Per unit volume, aluminum has good but not exceptional conductivity. However, aluminum is so much lighter than the high-conductivity metals, that pound for pound (or kilo per kilo of you prefer) aluminum provides more conductance than the other metals you mentioned.
Power companies customarily use aluminum cable in their high-power lines, because it not only offers more conductivity per pound than copper, but offers more strength as well so they can string up fatter cables.
Metal detector manufacturers are interested in aluminum wire because it offers a potential weight reduction of an ounce (28 grams) or more. That might not seem like much until you've swung a searchcoil for a couple hours straight.
Also in the quest for weight reduction, the White's 950 coil is embedded in urethane foam, not the more customary epoxy.
--Dave J.

 

[Anonymous]

In the U.S.A. aluminum house wiring is forbidden by law, because it caused so many fires when it was first introduced back in the 50's. Of course power companies use aluminum for distribution.
Power companies have great economic incentive to use aluminum in preference to copper, and to have the connections be reliable. Therefore they have mastered the the technology of making reliable connections, and invest in proper training of personnel so that the installations will be done correctly.
--Dave J.

 

[Anonymous]

Hi Dave
We only use it for power supply to installations,and not the internal connections.When I used it,I layed them underground.Why would Whites use it in coils.
Regards Frank Wallis

 

[Anonymous]

Hi JCP/CT
Gold has only got the conductivity of about aluminium.
Regards Frank Wallis

 

[Anonymous]

White's used to use (and perhaps still does use?) aluminum wire to reduce weight in their 950 size searchcoil.

 

[Anonymous]

Hi Dave,
I use aluminium wire on my low freq tuned 60cm (24") Mono SD type coils for weight reasons.
The whole coil (without skidplate) weighs in at 1.4kg. (the old 18inch mono fibreglass is 1.2kg.)
so it's still a practical alternative if you are going to swing it by hand, given that using copper to do the same job with the same inductive properties I need weighs in at 2.5kg all up.
I found the best answer to corrosion/metal dissimilarities, is to use legnths of 0.6mm annealed Aluminium welding wire which you will find doesn't corrode and use a small bit of copper tube crimped at each end.
I'm not sure of the properties of that Aluminium welding wire, but it's an arm saver and an easy resource to get hold of! <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT="">
Insulating it is "fun" though... but that's another story. <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">
-gaz