drying out of flux / prefluxing of silver solder. - Model Engineer

Hi all some help please.

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In preparing for silver soldering has anyone fluxed joints before riveting and allowed the flux to dry out in the right place between the joint, say overnight; before silver soldering. My boiler sections are currently fixed together with screws and I would like to be sure the flux has fully coated the surfaces before actually removing these and finally replacing them with Rivets. I presume the water in the flux mix is only there to allow the flux to flow or seep into the joints which it would not do if dry, or does it serve some deeper chemical purpose? my concern would be that the air pressure of the flame might blow the dry flux out from the joints if applied directly Hope this makes sense.

Kind regards all

BK.

hi brian,

i partly do what you propose in that for miniature loco boiler work i apply the flux then let it dry out a bit for an hour or so.

as for flux between joints riveted together, there are perhaps 2 points worth considering. the joints should be cleaned beforehand and roughed up, then riveted. if you have less than 2 thou gap between the riveted joints you wont get silver solder penetration. there are tricks to overcome this – centre popping the joint all along leaving the raised bit created by the centre punch, or coarsely filing criss cross lines (something i do for foundation ring sections).

if the joint is clean before riveting and the riveting is done shortly before silver soldering ie not left on the bench for a few months, then it is only necessary to apply the flux either side of the joint and not between.

remember that all rivet heats must have silver solder applied, and ideally the rivets should not be tight.

just my own personal approach of course.

cheers,

julian

The job of the flux is to prevent oxidation of the joint when heat is applied. Oxidation will prevent the solder from flowing. Many propriety fluxes can do a limited amount of cleaning, but you shouldn't rely on that – its best to get the joint as clean as you can before applying the flux.. The water is simply to make it easy to apply the flux to the joint – it has no magic properties. When the joint gets close to the solder melting temperature, the flux will fuse into a clear liquid; as long as as it coats the joint then no oxygen can can intrude. There's a "gotcher" though, if you heat flux for to long, or at too higher temperature, you burn it and it loses its ability to exclude oxygen.

Hi BK,

It depends on the flux: Easyflow is quite sensitive – if it goes brown then its burnt. This can occur as quickly as a minute or two. High temperature fluxes, such as Tenacity, can withstand higher temperature for longer, but there's a catch: when the joint has cooled down, the flux forms a hard, glass-like, covering. Very hot water removes the Easyflow, but has no effect on Tenacity which often has to be chipped off.

Never heat the solder directly, it will ball up and refuse to flow; the normal reaction is then to keep blasting the area which simply ends up burning the flux. Heat the joint; sneak up on it from various directions, but avoid directly heating the solder. When the joint is hot enough it will melt the solder which will then run into the joint.

hi brian,

re gary's 'gotcha' i use Thessco F or J&M Tenacity 4A for copper silver soldered loco boiler work where prolonged heating is involved. under no circumstances use ordinary easyflo flux. if the job doesnt get up to heat within say 10 minutes with propane and the joints being silver soldered not done within a few minutes then you will have flux exhaustion problems. (i have never found adding extra flux part way though satisfactory).

this is an idea of the quantity of flux i use – quite a lot. mixed to a stiff paste with as bob says a drop of washing up liquid, and then left to dry a bit before lighting up.

your 2 thou shim is a very good idea when riveting. i try and use as few rivets as possible.

good luck!

cheers,

julian

Edited By julian atkins on 13/01/ 08:13:37

Gary and Julian thank you. What a great example of " a picture speaks a thousand words" I would never have considered the block in the firebox to conserve heat and protect other areas, and the view of the flux gives me a really good idea of the amount and consistency.

Kwil – I usually partly thread but being daft I often forget when making the bushes and go all the way through. Not had any failures with the fully threaded bushes yet.

Anyhow I can forget about boilers now for a fortnight – snow has fallen and the slopes are beckoning — off skiing hooray !!

Kind regards all

BK.

Hi all,

There's a distinct difference how the flux will perform when sliver brazing steel than when dealing with copper or brass; copper / brass / unleaded gunmetal/ drawn bronze etc, the flux will all work and react in much a similar manner and the Easyflo type flux is most suitable for the much smaller assemblies, but as Julian has said a more a suitable flux where prolonged heating is required such as boiler construction, mechanical cleaning is the norm, but not emery cloth etc, before the application of any flux. Also it is essential to reflect as much heat back onto the job whilst its being heated, the Themalite or similar block being very suitable. Steel should be treated in a very similar manner, mechanically cleaned but using a flux capable of more prolonged heating is required and plenty of it, remember flux is relatively cheap so don't skimp on it. and when silver brazing steel try to bring the job to the correct temperature as quick as possible, support the job off of the hearth on some odd pieces of fire brick rubble to allow the heat to circulate all around the job. Following any silver brazing job let it cool to black even down to a point where you can comfortably pick it up and let the job soak for a couple of hours in clean cold water, you will find the majority of the flux residue will then just rub off. One thing, avoid Borax etc like the plague, the flux when heated goes like glass and is nearly as hard, you'll spend hours trying to clean the job, use a flux compounded and matched to the sliver brazing process.

Regards,

Bob Youldon

The basic principle of silver soldering is capillary flow.

Everything that you do for strong sound joints and be successful is to promote that capillary flow.

For capillary flow to occur there must be a gap.

For more information, please visit Flux Drying Machine.

No gap = no flow = no joint

As described earlier, centre punching or roughing up the surface with a coarse file will help produce a 0.1mm gap. Placing foil in the joint will also work but consider using silver solder foil that you do not have to remove.

Pre-cleaning copper, chemically or otherwise, prior to silver soldering is often unnecessary

At the first instance that you apply heat, you create more oxide on the surface that you hve so painstakingly removed. Joint cleanliness, removing oxides and keeping the surface free of oxide, is the job of the flux. Simply make sure the joint is free of oil and grease which the flux cannot tackle. The temperatures involved will drive off any grease from the hands. Note. This comment does not apply when soft soldering

Use a flux that will operate for the heating period.

If necessary use a long life flux eg HT5. Its residues are more difficult to remove but clean the joint afterwards in 10% caustic soda. Flux which becomes exhausted will not keep the joint free of oxides.

The alloy will always flow to where it is hottest.

Heat the joint in the area to where you want the alloy to flow in relation to where you are applying the alloy. This ensures there are no cold spots in the joint that will cause the alloy to freeze, stop flowing and lead to a lack of penetration. As per Gary

HEAT THE JOINT NOT THE ALLOY

For more detailed information go to **LINK**

Stick to the principles af capillary flow and you will be successful!

Keith

Edited By CuP Alloys 1 on 13/01/ 13:30:39

A further idea which may help is to use charcoal as a packing around the part to be soldered. Heat from the torch will light the charcoal so it becomes as it were a negative insulator – adding its own heat, not taking it away. A further advantage is that the extra CO from the hot charcoal provides a reducing atmosphere, easing the job of the flux.

Ordinary barbeque charcoal is good, or collect the black lumps of residue from a wood stove. The only extra to remember is to quench the charcoal thoroughly with water or it will continue to glow quietly and might set the shed on fire.

Regards, Tim

Interested to see Julian's comment on his use of a nozzle for boiler work, I have struggled with a (10.3kw) on my Emma Victoria boiler (not that I have got very far with that in , will the year of great progress!!) As they say I am 3 years into a 3 year project, well that was my original expectation.

So now have a , not yet put it to the test but Julians comment gives me new heart, accepting Julian's greater expertise is also a big factor.

Got as far as cutting the boiler for the firebox and one failed attempt at the silver soldering on the extension piece (with the nozzle) a quick light up of the shows a fieresome flame.

I have high expectations of this new nozzle as I have always thought I took all the right care in preparation but most time ended in frustration( apart from small components) the problem I seem to struggle with is complying with the 'rule' of keeping the flame away from the flux/solder,

Bill D.

This is a question our experts keep getting from time to time. Now, we have got the complete detailed explanation and answer for everyone, who is interested!

There are two types of flux-cored wires — gas shielded and self-shielded. Gas-shielded flux-cored wires require external shielding gas, and the slag is easy to remove. Consider using gas-shielded flux-cored wires when welding on thicker metals or in out-of-position applications.

1. What does the 6 stand for in ER70S-6?

As an example, for a commonly used solid wire — AWS ER70S-6 — the “ER” indicates that the filler metal is an electrode or rod; the “70” signifies that it has a tensile strength of 70,000 pounds per square inch (psi), and the “S” means that it is a solid wire.

2. What is the difference between ER70S2 and ER70S-6?

Both the wires can be used for similar jobs due to their identical capabilities. The major difference between the two products is prominent when the user is operating on contaminated or rusted surfaces, in which case the ER70S6 provides better penetration and higher quality of welds.

3. Is flux core wire good?

The LINCOLN ELECTRIC NR-211 flux-core wire is a good quality reel that, when welding, cools quickly to keep heat out of your project. It also produces very minimally spatter. The slag has good coverage but is easily removed, making cleanup a breeze. Unfortunately, the range is very small.

4. Does flux core wire go bad?

Flux core wire is not solid, so contaminants such as moisture can enter the wire. So, if flux core wires are exposed to moisture for a long time, they will go bad. ... While flux core wire can go bad, it does not merely go bad for no reason or without any signs.

5. Can you use flux-cored wire with gas?

You can use gas with a regular flux core, but it is a total waste of gas. The flux in dual shield wire doesn't shield the weld, it causes better deposition rates and weld characteristics in the weld. Gas is needed with a dual shield to shield the weld, but not with flux cored.

6. What's the difference between .30 and .35 flux wire?

A flux core wire that features a 035 electrode implies that it is thicker than one, which measures 035 by. 005 inches. ... The thicker the diameter of a wire, the deeper the penetration. While 035 flux core wires work well with 250 V machines, 030 flux-cored wires deliver great performance when used with 210 V machines.

  Flux Cored Wire Gas-shielded 

7. How do I choose flux core wire?

030-inch diameter is a good all-around choice for welding a wide range of metal thicknesses. For welding thicker material at higher total heat levels, use. 035-inch wire (or . 045-inch wire if it's within your welder's output range).

8. What is the most preferred MIG wire solid or flux core?

The first reason why you may prefer gas-shielded solid core wire for MIG welding is the most obvious: You don't have to clean up the flux when you're done welding. The shielding gas saves you a clean-up step and helps you immediately create a clean weld.

9. How can you tell the difference between flux core and solid wire?

Solid wire provides deep penetration in the root and usually has little spatter. Flux-cored wire has a larger ball-type transfer and produces low spatter levels. In addition, flux-cored wire produces a rounder penetration profile with excellent sidewall fusion.

10. Can I use solid wire without gas?

While solid MIG wire requires a shielding gas to protect the weld, typically a mix of Argon and CO2, there's also flux-cored MIG wire that shields the weld on its own without the help of gas.

11. How long can you store flux core wire?

Flux cored wire should not be stored for more than 5 years. The older wire should be redried before use. Storeroom temperature should be kept as even as possible, temperature variations should not exceed ± 5°C.

For more Flux Cored Wire Self-shieldedinformation, please contact us. We will provide professional answers.