Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old May 14th 05, 01:23 AM
rich brenz
 
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Default Aluminum soldering

I have some small pieces of aluminum I wish to join, and have Al solder
and flux. The flux has no directions but does say to apply to parts and
do not overheat. Should the flux be wiped off before attempting to
solder? When I try to leave the flux in place, it turns dark brown,
smokes a lot, and seems to prevent the solder from adhering? Any useful
suggestions?(Other than "try brazing" or "get a welder"...)

Rich

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Old May 14th 05, 03:06 AM
Mark J
 
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I'm not all that familiar with the term aluminum solder. I do have
some of the low temp (750F?) aluminum rods that you occasioanlly see on
late night infomercials and are sold at auto swap meets and flea
markets. They work well on aluminum and pot metal and pretty much form
a soldered joint.

I've fabricated some objects out of discarded aluminum sign stock with
a combo of folded edges and seams filled with these low temp rods and
ground/sanded smooth. The work has held up well in a vibration prone
section of a motorcycle.

The rods I have don't need flux, but they do specify to not overheat.
OA is too hot. Simple propane torch is recommended.

Try your solder without the flux and use low heat like a propane torch
and see what happens. Make sure the joining surfaces are clean right
before starting. Clean aluminum usually means degreased with acetone
and wire brushed with a stainless brush never used for anything else.

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Old May 14th 05, 09:10 AM
Gary Wooding
 
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rich brenz wrote:
I have some small pieces of aluminum I wish to join, and have Al solder
and flux. The flux has no directions but does say to apply to parts and
do not overheat. Should the flux be wiped off before attempting to
solder? When I try to leave the flux in place, it turns dark brown,
smokes a lot, and seems to prevent the solder from adhering? Any useful
suggestions?(Other than "try brazing" or "get a welder"...)

Rich


It sounds as if you are heating the flux too much.

The process of soldering is essentially the same for all metals. The
solder is a metal (usually an alloy) that has a lower melting point than
the stuff to be joined. Basically, you just heat the work (the bits you
want to join) until its hot enough to melt the solder which turns to
liquid and wets the work. When you remove the heat, the solder freezes
and the joint is made. The important part is that the liquid solder
_wets_ the work. Just like water won't wet a greasy or dirty surface,
the solder won't wet a dirty surface, that's why you must ensure that
both the joint and the solder are clean. That's the theory bit.

In practise its a bit more complicated, 'cos what happens is that the
heat causes both the work and the solder to combine with the oxygen in
the air to create oxides. The oxides act as a barrier, rather like dirt,
that prevents the solder from wetting the joint. The trick is to stop
the oxygen from getting to the joint. That is the job of the flux. As
you heat the joint the flux flows over it to shield it from the oxygen.
When the joint reaches the proper temperature the solder melts and the
joint is made.

Some metals, aluminium and stainless steel for example, oxidise very
rapidly (in seconds) at normal room temperature, so flux for these
metals has the extra job of getting rid of existing oxide as well as
preventing new stuff from forming. This is the reason that these metals
are, traditionally, difficult to solder.

The final problem is that no flux is perfect. If you heat them too much
they lose their properties and the solder refuses to stick. If you heat
the solder and flux directly you will almost certainly destroy the flux.
The secret is to clean the joint and flux it, then heat the _joint_
until its hot enough to melt the solder. If you just heat the solder it
will melt and turn into a ball, the tendency is then to apply more heat
which tends to burn the flux. If the _joint_ is hot enough to melt the
solder it will flow into the joint all by itself.

In summary then. Use the correct flux for the solder and metal you are
using. Clean the joint properly, apply the flux and heat the joint until
the solder flows. A good trick is to place a little bit of solder on the
joint before applying the heat, then, when you heat the joint enough to
melt the solder you can apply more solder if required.

I hope this helps.

--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)
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Old May 14th 05, 02:25 PM
rich brenz
 
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Thanks Gary,
Here's the real life problem...
After cleaning the Al with a clean wire brush, I apply the flux. I heat
the joint and LONG before the joint has reached the melting temp. of the
solid solder, the flux begins to smoke and turn black forming a nice
hard barrier between the workpiece and the applied solder. As things
currently stand, it seems that I can't help but scorch the flux, to my
chagrin. When all is said and done, I'm left with 2 separate pieces of
nicely scorched Al. BTW, the solder and flux were purchased as a kit.

Rich
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Old May 14th 05, 08:52 PM
Jeff Wisnia
 
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rich brenz wrote:
I have some small pieces of aluminum I wish to join, and have Al solder
and flux. The flux has no directions but does say to apply to parts and
do not overheat. Should the flux be wiped off before attempting to
solder? When I try to leave the flux in place, it turns dark brown,
smokes a lot, and seems to prevent the solder from adhering? Any useful
suggestions?(Other than "try brazing" or "get a welder"...)

Rich



It also helps to use a stainless steel wire brush and scrub the aluminum
surface you are attempting to wet THROUGH a puddle of molten solder. The
solder shields the freshly brushed surfaces from air and prevents new
oxides from forming.

Years ago I used to astound doubting Thomases by getting regular 60-40
electrical solder to wet and bond to aluminum using that trick.

I was tought by a very smart guy who occassionally shares his wisdom on
this newsgroup that the same trick helps to get "maximum bonding" of
epoxy to metal. Smear the epoxy on the degreased metal and then wire
brush right through it.

Makes sense to me...

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"


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Old May 15th 05, 12:36 AM
Tim Williams
 
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"Jeff Wisnia" wrote in message
...
I was tought by a very smart guy who occassionally shares his wisdom on
this newsgroup that the same trick helps to get "maximum bonding" of
epoxy to metal. Smear the epoxy on the degreased metal and then wire
brush right through it.

Makes sense to me...


Use sandpaper if you want to use that wire brush again. G

(Not DAMHIKT, but it seems to me...)

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms


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Old May 15th 05, 07:00 AM
Don Foreman
 
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On Fri, 13 May 2005 19:23:54 -0400, rich brenz
wrote:

I have some small pieces of aluminum I wish to join, and have Al solder
and flux. The flux has no directions but does say to apply to parts and
do not overheat. Should the flux be wiped off before attempting to
solder? When I try to leave the flux in place, it turns dark brown,
smokes a lot, and seems to prevent the solder from adhering? Any useful
suggestions?(Other than "try brazing" or "get a welder"...)

Rich


That sounds like the organic flux used with Harris Alsolder500 and
Allstate Strongset 509. The flux must be present when soldering for
the solder to wet the aluminum These materials work well if you can
avoid burning the flux, but that's not easy to do. The trick is to
keep flame away from the flux. If the flame ever touches the flux,
yer screwed. Either heat by conduction from an unfluxed area, or use
a hot air gun.

Some easier-to-use aluminum solders a
aerosolder , see
http://www.tinmantech.com/html/alumi..._brazing_.html

#33 from http://www.aladdin3in1.com/catalog2.htm use #585 flux

The fluxes used with these materials work OK with a torch. I like
the aerosolder best. That flux turns water clear at about the right
heat for soldering, which is about 780F. It's a lot easier to use
than the organic stuff. There is no sodium flare with these
fluxes, so you don't need special goggles as in aluminum brazing.

I don't like the "miracle rod" or "rub on rod" , as Aladdin #31
"three-in-one" and others for aluminum, though they do work well on
whitemetal. They basically are whitemetal! I think the other
materials mentioned here make much better and stronger joints.

As others have mentioned, buy a stainless "toothbrush" from a welding
store for cleaning the metal. They're under 2 bux. Anchor is one
good brand. The Chinese ones are so soft they're about useless.


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Old May 15th 05, 07:37 AM
Don Foreman
 
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On Sat, 14 May 2005 17:36:44 -0500, "Tim Williams"
wrote:

"Jeff Wisnia" wrote in message
...
I was tought by a very smart guy who occassionally shares his wisdom on
this newsgroup that the same trick helps to get "maximum bonding" of
epoxy to metal. Smear the epoxy on the degreased metal and then wire
brush right through it.

Makes sense to me...


Use sandpaper if you want to use that wire brush again. G

Stainless toothbrushes cost less than $2 at a welding store.
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Old May 15th 05, 09:32 AM
Gary Wooding
 
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Default

rich brenz wrote:
Thanks Gary,
Here's the real life problem...
After cleaning the Al with a clean wire brush, I apply the flux. I heat
the joint and LONG before the joint has reached the melting temp. of the
solid solder, the flux begins to smoke and turn black forming a nice
hard barrier between the workpiece and the applied solder. As things
currently stand, it seems that I can't help but scorch the flux, to my
chagrin. When all is said and done, I'm left with 2 separate pieces of
nicely scorched Al. BTW, the solder and flux were purchased as a kit.

Rich

You don't say what solder, flux, or type of heat you are using. Some
aluminium solder I've used requires no flux at all. Here in UK its
called Technoweld, but its not really welding. In USA its probable got
another name.
The technique, as others have mentioned, is to first 'tin' the joint by
first scrubbing it with a stainless toothbrush and then scratching it
with a stainless toothpick while applying heat until the solder melts.
It works by mechanically removing the oxide from the material while it
is shielded by the solder. When both parts of the joint have been
tinned, you hold them together and apply heat to melt the solder to make
the joint. You can add more solder as required - once the joint is
tinned it won't oxidise. It works very well, but is no good at all for
'capillary' soldering where the solder runs into small fluxed spaces by
capillary attraction. I suspect this where the name Technoweld comes
from 'cos welding is similar in this respect.

--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)
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Old May 16th 05, 06:16 PM
Jeff Wisnia
 
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Default

Don Foreman wrote:
On Sat, 14 May 2005 17:36:44 -0500, "Tim Williams"
wrote:


"Jeff Wisnia" wrote in message
...

I was tought by a very smart guy who occassionally shares his wisdom on
this newsgroup that the same trick helps to get "maximum bonding" of
epoxy to metal. Smear the epoxy on the degreased metal and then wire
brush right through it.

Makes sense to me...


Use sandpaper if you want to use that wire brush again. G

Stainless toothbrushes cost less than $2 at a welding store.


Which is less than what a cup of coffee costs these days at most "sit
down" restaurants here in Red Sox country these days.

I finally admitted to myself that I was getting old when I realized that
just the sales tax on a cup of coffee here in Taxachusetts now costs
about twice as much as a cup of coffee cost me when I first began
drinking it. (5) G

BTW, a couple of ounces of acetone still costs far less that $2 and will
clean uncured epoxy off a small wire brush well enough for reuse...

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."


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