Flux query

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Andy W
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Flux query

Postby Andy W » Fri May 21, 2010 1:33 pm

I'm just about to sandwich together the inside and outside layer of a coach side using my RSU. It crossed my mind that when this is done with two relatively large pieces of brass (as opposed to detail items) there will be some residue of flux trapped between the layers. I use Powerflow flux. Will this eat away the metal from inside, so that in a few years I'll have a holed coach?

Thanks

Andy
Make Worcestershire great again.
Build a wall along the Herefordshire border and make them pay for it.

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Jol Wilkinson
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Re: Flux query

Postby Jol Wilkinson » Sat May 22, 2010 9:26 am

Andy,

I don't like PowerFlow for this type of job, it's too aggressive (I think it is intended as a plumbers flux, and is designed to work in those environments).

I've used 12% phosphoric acid flux on a number of loco smokebox wrappers - a similar layered approach - going back twenty or so years, without any problems yet. As it is water based it boils off below the melting point of the solder. I shall be using it on an old Modellers World LNWR 12 wheel diner that I'll be starting soon (!), which has layered sides and I don't anticipate any problems.

Jol

nberrington
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Re: Flux query

Postby nberrington » Sat May 22, 2010 1:32 pm

I would hope that oxidation is not possible as the two layers should be sealed from the atmosphere once the solder melts. So far I haven't seen any problems in kits from 20 years back.
Can't say the same for exposed joints (eg corners.) Take great care to wash away all residue and neutralize it. Otherwise bubbling paint and wicked deposits are the order of the day.

Neil

allanferguson
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Re: Flux query

Postby allanferguson » Sat May 22, 2010 8:40 pm

When applying layers of panelling it has been my practice to drill a hole (or holes) in the inner (hidden) layer, and solder through those from the back. Hold the front layer in place with transparent tape -- it should survive just long enough..... I should say that I have never used an RSU so can't comment on that. For flux I use phosphoric acid (Jenolite) and have never had problems with residues provided it's well rinsed afterwards.

martin goodall
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Re: Flux query

Postby martin goodall » Sun May 23, 2010 9:48 pm

allanferguson wrote:........... Hold the front layer in place with transparent tape -- it should survive just long enough..... .


If you want an adhesive tape that will withstad the heat of soldering, you could try "Hot Tape" from Carr's (C&L) - it is red in colour and (as its name implies) it is designed to withstand heat.

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Stephen F
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Re: Flux query

Postby Stephen F » Mon May 24, 2010 9:00 am

Ealing
I mainly use a flux called LR9, which I got from Milton Keynes metals (http://www.mkmetals.co.uk/product/2566/0), which is good as gold on brass. I don't know what it's composed of. It's not so good with steel though, and needs careful cleaning to avoid corroding. I discovered that making my first turnout :shock:

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Stephen F
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Re: Flux query

Postby Stephen F » Mon May 24, 2010 9:08 am

Though maybe your best bet would be to tin both pieces, wash them thoroughly (maybe use vinegar and water?), and then sweat them together. As long as you're quick about it, you should get a good bond I think.

Steve

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Will L
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Re: Flux query

Postby Will L » Mon May 24, 2010 3:43 pm

Stephen F wrote:Though maybe your best bet would be to tin both pieces, wash them thoroughly (maybe use vinegar and water?), and then sweat them together. As long as you're quick about it, you should get a good bond I think.


While tinning will work if you can get both halves up to temprature e.g. small things. Doing anything of any size, like a coach side for instance, you will find it impossible to get good results, at least with a soldering iron, as you will find it impossible to get the whole thing over the melting point of the solder. The result is the overlay will not sit flat. Might get there with blow torch or by putting the whole thing on an cooker hotplate, but I'm not sure you really want to get the coach side that hot in the first place, and you can only do it once.

I've done a number Etched coaches over the last 15/20 yaers, mostly LNER prototypes from D&S with lots of overlays. I've allays settled on soldering round the edges, I've used all sort of fluxes and I've never had any trouble with overlays corroding through.

The tough one is getting the sole bar overlays down nicely (start from the middle and work outwards, Kirby grips are very handy for holding things in the right place while you work).

Will

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Andy W
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Re: Flux query

Postby Andy W » Wed May 26, 2010 11:49 am

Thanks for all the responses - interesting. I'm confident the surfaces are clean - I've used Shiny Sinks to clean up and the coach sides look good. It's the hidden stuff inside the sandwich that worries me. I think I'll take Jol's advice and switch to a less corrosive flux. Meanwhile this particular coach will have to serve as a test. I'll post back in a few years to let you know if it has melted away.
Make Worcestershire great again.
Build a wall along the Herefordshire border and make them pay for it.


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