Advice on soldering/brazing thin heat fins to copper tube?

Firstly, hello all. :)

Not sure which sub-forum I should have posted this in, so if it's in the wrong one could a kind passing mod please move it?

My query isn't strictly refridgerationy, but I fgured you guys would have a lot of experience of soldering/brazing copper...

I'm building from scratch a large passive heat exchanger/radiator - the problem I have is in trying to solder thin heat fins (0.005"/0.125mm) to round copper pipe (0.4mm or 0.6mm thick walled). If possible I'd prefer to use high silver content solder (better heat transfer than tin and all).

This is my first time soldering metalwork and not sure what I'll need to solder the fins to the pipes.

Trying to keep things as cheap as possible, so don't want to have to buy an expensive blow torch if I can help it.

Things are also tricky as the fins are going to be 1cm apart so soldering is going t be a bit hampered. I picked up a small butane pencil blow torch from ebay for a few quid - is this going to be of any use?

I understand the large surface area to volume of the heat fins is likely to make soldering tricky as the heat will be dissipated very quickly... Would using high silver solder be out of the question, and does a small butane blow torch have any hope of soldering high Ag solder?

Any help massively appreciated. :)

Cheers,

Tom

Why would you solder fins. They are usually just pressed to pipes or pipes expanded after mounting of fins. You cant evenly heat thick pipe and thin fin to braze them and probably could solder them. But good enough contact is even when they are only pressed at pipes.

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Originally Posted by Tom G

Firstly, hello all. :)

Not sure which sub-forum I should have posted this in, so if it's in the wrong one could a kind passing mod please move it?

My query isn't strictly refridgerationy, but I fgured you guys would have a lot of experience of soldering/brazing copper...

I'm building from scratch a large passive heat exchanger/radiator - the problem I have is in trying to solder thin heat fins (0.005"/0.125mm) to round copper pipe (0.4mm or 0.6mm thick walled). If possible I'd prefer to use high silver content solder (better heat transfer than tin and all).

This is my first time soldering metalwork and not sure what I'll need to solder the fins to the pipes.

Trying to keep things as cheap as possible, so don't want to have to buy an expensive blow torch if I can help it.

Things are also tricky as the fins are going to be 1cm apart so soldering is going t be a bit hampered. I picked up a small butane pencil blow torch from ebay for a few quid - is this going to be of any use?

I understand the large surface area to volume of the heat fins is likely to make soldering tricky as the heat will be dissipated very quickly... Would using high silver solder be out of the question, and does a small butane blow torch have any hope of soldering high Ag solder?

Any help massively appreciated. :)

Cheers,

Tom

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Hi Tom, As Nike says why would you braze fins onto pipe its a great way to melt the fins

Norm :eek:

Well I'd like to solder them to get better thermal contact, and commercially made radiators often have soldered fins to get better thermal transfer from pipe to fin.

I suppose I could try freezing the pipe and threading it through the holes when cold in the fins in the hope the pipe would then expand after to get a slightly tighter contact, but I'm not sure how much difference this is likely to make or how it would compar to solder in terms of contact...

So you think the fins are likely to melt if I try soldering? :(

Hi Tom,
High Ag solder is HMP (high melting point).

Presume your attempting to solder Cu fins to Cu pipe? As mentioned before, the majority of refrigeration heat exchangers are Cu pipe expanded into Aluminium fins, relying on mechanical contact to achieve the thermal transfer.

Can we know what the intended use is for? Perhaps we can then offer suggestions.

My main question is "What size pipe"?, as the larger it is the greater thermal sink it will be, and hence the more heat required, which your little pencil torch will have no hope of delivering.
Soldering copper will require meticulous cleanliness, the correct flux and will probably need to be done in an inert atmosphere to avoid oxidation of adjacent fins etc.
I think that you might want to ask advice of car radiator repair shop. They might use a solder bath and be able to offer guidance.

In our industry, we are used to 'hard soldering' as opposed to soft soldering. This is done with 'silver solder' and is like brazing (ie using fuel / oxygen) at much higher temperatures than soft soldering.

Soldering alu on Copper? If you ask me, impossible. Ans especially impossible due to the small thickness of the fins.
drill the aluminum fins all in one package pressed together, same size of soft copper pipes.
Insert your tubes and adjust proper fin spacing.
Solder bends and expand it with water till 50 to 80 bar (hand pump like the plumbers use)
Why not use an old counter evaporator which you can find everywhere almost for free?

Thanks for your replies guys -

I'm trying to solder 0.125mm(0.005") thick copper fins to either 0.4mm thick flattened 15mm diameter copper pipe or to 0.6mm thick walled 6mm outer diameter round copper pipe. So it's copper to copper soldering.

Oh, forgot to mention, the heatsink is to be used as a large passive/low-speed-fan heat exchanger/radiator for pc watercooling. The max pump pressure is about 3.1m of head - not sure what that equates to in PSI...

The amount of silver solder used will probably be more than the price of a used heat exchanger, plus all the time taken.
It`s hard enough to solder a capillary tube into a large pipe, .005" copper will dissolve as soon as you show the torch to it.

Here`s an example:

http://cgi.ebay.co.uk/Ariston-Microg...1%7C240%3A1318

Something like this then

Cheers glenn, but the reason I'm making it is partly for the fun of it, and also to run largely passive - so wider fin spacing. Plus I'd rather have copper tubes (other copper parts in water loop so no galvanic corrosion that way) and copper fins - better thermal conductor.

Guess I'll just have to do a little feasability test with low temperature solder - 95%tin/3%Ag/Cu or similar and give up on the idea of high temp stuff.

May well give a radiator repair shop a call and see whether they have a brazing kiln to do low temp brazing of the thing and how much they'd charge. :)

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Originally Posted by Peter_1

Something like this then

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Haha, yeah pretty much. :) but with lots of parallel microbore/flattened tubing (to match flow resistance to 1/2" diameter inlet and outlet and reduce pressure loss) rather than industrial sized stuff.

Perhaps following method can work (worth a try) presolder/cover completely the copper tubes with tin solder (like used by plumbers)
heat the tube with a small flame burner and apply liquid flux and tin-solder.
Then slide the fins over it and apply liquid flux on the copper.
There is also tin-solder paste available (some sort of flux mixed with tin-solder powder) which you rub on the fins.
Apply heat with a heatgun (like used to scrape of paint)

Sorry, I first thought you would like to solder alu fins.

The solder paste was used in the past and perhaps still now by coach workers when they soldered a new plate over a rusted one (I've done this 25 years ago) So perhaps you can find it there.http://img.hisupplier.com/var/userIm...1111162443.jpg

Or, if copper on copper how about a large electric soldering iron and soft solder.

In the automotive industry, copper fins are assembled in a matrix - the tubes are then pushed through - a mandrel is inserted into the tube - the tube is then expanded onto the fin matrix.

It is possible to soft-solder a low-melting point solder onto the tube outer surface, before insertion into the fin matrix.

The industry then places the fin/tube assembly into an oven, where the low melting point solder melts & provides the necessary fin-tube junction. The melting point is actually quite low & could be performed in a home-made, externally-insulated 'hot-box'. The alternative is to visit your friendly radiator manufacturer & ask him to let you put your project into his oven.

You can still buy solder paste (flux and solder)....its used for surface mounted pcb components.
Normally in syringe packaging for ease of application. Cost might be factor. Look at RS components, or CPC.
Try pre-tinning your pipes and wiping so that thin layer of solder remains. You could possibly use a hot air gun.

Quote:

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Originally Posted by desA

In the automotive industry, copper fins are assembled in a matrix - the tubes are then pushed through - a mandrel is inserted into the tube - the tube is then expanded onto the fin matrix.

It is possible to soft-solder a low-melting point solder onto the tube outer surface, before insertion into the fin matrix.

The industry then places the fin/tube assembly into an oven, where the low melting point solder melts & provides the necessary fin-tube junction. The melting point is actually quite low & could be performed in a home-made, externally-insulated 'hot-box'. The alternative is to visit your friendly radiator manufacturer & ask him to let you put your project into his oven.

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Thanks for the information - very usefuul :). I think I'm going to try piercing the holes slightly smaller than the pipes to get a tight fit/sleeve aroun the pipes, thread through the pipes almost all the way through, brush on some solder paste around each fin bit and then push through the last .5cm/0.2" ish, and then bake (though need to check I can get a local auto radiator repair place to do this).

What do you mean by an externally insulated hotbox? I imagine I can't just bake it in the oven? (!)

Quote:

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Originally Posted by Electrocoolman

You can still buy solder paste (flux and solder)....its used for surface mounted pcb components.
Normally in syringe packaging for ease of application. Cost might be factor. Look at RS components, or CPC.
Try pre-tinning your pipes and wiping so that thin layer of solder remains. You could possibly use a hot air gun.

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I've been looking at either Solderplus 96.3%tin/3.7%silver (£2.50/100g + a few quid p&p) or Easyflow solder paste - anyone have any experience of using either?

Dear Tom,

Are you trying to braze / solder aluminium fins or copper fins to Copepr tubes. If the soldering is for copper fins then I advice you to use a liquid flux in between the fins & tubes. Use flame as low as you can . The melting temperature of tin is around 200 deg.C.

If you want to solder aluminium fins to copper tube then best is to to give first a coat of tin on aluminium fins & copper tube seprately. Then insert the fins over the copper tubes. Once the these are inserted then gently put a flame on the assembly & it will join. You have to be very careful as the aluminium should not get overheated. This is the cheapest way to do.

For flux you can get from electronic spare parts shop. The flux in two types. One is polish & other is liquid. Should try with liquid flux first. If the problem of evopration occures then mix both liquid & wax polish.

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Originally Posted by Jagjit

Dear Tom,

Are you trying to braze / solder aluminium fins or copper fins to Copepr tubes. If the soldering is for copper fins then I advice you to use a liquid flux in between the fins & tubes. Use flame as low as you can . The melting temperature of tin is around 200 deg.C.

If you want to solder aluminium fins to copper tube then best is to to give first a coat of tin on aluminium fins & copper tube seprately. Then insert the fins over the copper tubes. Once the these are inserted then gently put a flame on the assembly & it will join. You have to be very careful as the aluminium should not get overheated. This is the cheapest way to do.

For flux you can get from electronic spare parts shop. The flux in two types. One is polish & other is liquid. Should try with liquid flux first. If the problem of evopration occures then mix both liquid & wax polish.

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Hi Jagjit - it's 0.127mm thick copper fins 370mm x 50mm in size each, with 48 punched 6mm diameter holes for the 6mm tube to run through. They're going to be soldered to 6mm outer diameter soft microbore copper.

I've made a home made clamp/press to mass-produce the fins and ensure the holes are in exactly the same place for each fin, and speed up producing ~120 fins. It's akin to some sort of 18th century press! It'll clamp each fin down and a nail filed to a spike (by using it as a drill bit and filing against a flat metal file) will be punched down into each of 48 6mm holes, to provide a sleeve for the fins to go through and provide a tight fit for capillary action when soldering.

I think liquid solder paste in definitely the way to go - individually soldering 4800+ individual joints would take a while I think! The issue I have at the moment is how much preparation of the copper I need - the 6mm microbore tubing has been straighteded and cut a few weeks ago, and has now no doubt oxidised. So I'll need to either sand it, or if it's possible treat it with acid to deoxidise it- I wonder if I could just use vinegar(acetic acid) and then wipe off just prior to applying the paste and sliding the fins on?

Any idea how long I could leave solder paste on before heating (putting in oven, hopefully at a radiator repair shop)?

Gah, I want to post links to some photobucket pictures of what's been done before, but I need 15 posts before I can do that, so please excuse the following 5 spam posts!

Filler post

Another filler post.

Yet another filler post.

And another..

Final one....

Okay, Here's some pictures of what's been assembled so far and roughly what the assembled radiator should look like:

http://i220.photobucket.com/albums/d...1/dccab405.png

http://i220.photobucket.com/albums/d...1/28a57358.jpg

http://i220.photobucket.com/albums/d...1/53df50fc.jpg

http://i220.photobucket.com/albums/d...1/69e6480f.jpg

http://i220.photobucket.com/albums/d...1/2b0f88c3.jpg

http://i220.photobucket.com/albums/d...1/40bd5666.jpg

http://i220.photobucket.com/albums/d...1/b77d1b52.jpg

http://i220.photobucket.com/albums/d...1/92d0f497.jpg

Press/clamping for punching hole - will have a grid of 48 holes drilled through the top:

http://i220.photobucket.com/albums/d...1/dd514da9.jpg

http://i220.photobucket.com/albums/d...1/02568d95.jpg

http://i220.photobucket.com/albums/d...1/02568d95.jpg

http://i220.photobucket.com/albums/d...1/2f8a0392.jpg

http://i220.photobucket.com/albums/d...1/ef2efa87.jpg

http://i220.photobucket.com/albums/d...1/6509eac0.jpg

http://i220.photobucket.com/albums/d...1/1e79ea2a.jpg

Are you still making this - or is it done ?

miles.brennan@blueyonder.co.uk

i have somewhere in mi workshop an electric solder tool for CU. it works like this; you put some pre-mixt lubricant of flux and solder on the pipe and the welding piece,than you put the clamp on ,and push the button.when the welding starts the lubricant melts.when the welding looks like a fresh solder point,let the start button go,and your weldin gets hard. and is done. its a good system,but i dont do waterworks anymore,so its retired.

ice

Quote:

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Originally Posted by icecube51

i have somewhere in mi workshop an electric solder tool for CU. it works like this; you put some pre-mixt lubricant of flux and solder on the pipe and the welding piece,than you put the clamp on ,and push the button.when the welding starts the lubricant melts.when the welding looks like a fresh solder point,let the start button go,and your weldin gets hard. and is done. its a good system,but i dont do waterworks anymore,so its retired.

ice

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As you pointed, that is soldering tool, and i would not use it in refrigeration circuit, only on water part of refrigeration/heating equipment and installations.
I use this one for that purpose: great tool for copper pipes up to 28mm diameter. Good for tight spots.

http://www.rems.de/maint_img/16-REMS...c877d9252f.jpg

yep Nike123, that what i was talking about.and...i won't use it for refrig applications.

ice

Still in the process of making this, though plans have changed a bit - found a lot of copper sheet going cheap so I'm using 0.9mm thick copper fins now - currently about halfway through drilling 6mm holes (48 holes in each 39.5cm x 5cm fin).

I have a butane propane mix brazing torch - one of the ones that uses the 600ml cans, so will see how that goes for soldering sometime later in the week I expect once the holes are drilled. As I say, the holes aren't fully done, and the fins will be straightened before assembly of the final piece, but here's a mock-up of 20 of the copper fins/strips with some nails/drill bits where the 6mm copper pipe will go:

http://i220.photobucket.com/albums/d...1/df811ccf.jpg

http://i220.photobucket.com/albums/d...1/a6633fd9.jpg

http://i220.photobucket.com/albums/d...1/8e2d84d0.jpg

http://i220.photobucket.com/albums/d...1/be5bc9d5.jpg

http://i220.photobucket.com/albums/d...1/ae863cd6.jpg

For those who has problems with showing these images, go to your User CP page=>Control panel=>Setings&options=>Edit options=>Thread display options=> and set
Image with at 700 or lower.
Image Height leave at 0.
Save and come back.

back in apprentiship days,hermetic tails where welded to the can by slipping a ring of solder over the tube,whack in the oven with nitro etc,crank up the temperature and presto 100% every time.

Suggest you get it subcontract furnace brazed, I know that some of the heat exchanger guys just used to drill a hole in each of the fins above the joint and push a Copper Phosphorus braze rod through the hole for the length of the tube and also pre-ring the return bends (if these were to be brazed). Others used brazing paste once the unit was assembled, it can be a bit hit and miss with paste though, as it tends to run to just where you don't want it.
The whole assembly was then passed through a reducing atmosphere furnace - all done in one go and the job stayed bright and clean. Otherwise you are going to have all the joint areas covered in scale and oxides...

Where abouts are you and I can see if I can pass you to a possible subcontractor ?

I agree with Pete;

To try and solder ( braze ) dissimilar
metals is an art in itself and brazing is too. You stated you never brazed? For a person to braze 2 copper tubes of 3/8 or even 1/4 is hard if the person has never brazed, but to try and do alluminum fins to copper ( again dissimilar metals ) even with flux is near impossible and certainly for a beginner IS impossible.

When we hire HVAC guys, we have em braze; that's the first thing we do. IF THEY CAN BRAZE THEY HAVE EXPERIENCE, if they can't then they may have SOME, but not a lot.

Remember these things shake and rattle and "soft solder" with a small torch OR a soldering gun will break.

There are lots of thermally conducting epoxies and resins for sale might make your life more easy than solder and brazing. See here