Silver solder problems

I wonder if anyone can help me understand why, that sometimes when I silver solder together two components made from phosphor bronze and using solder paint, I find that the solder forms itself into tiny balls which absolutely refuse to melt even though the components were heated to red. Apart from understanding why it has happened, I would be very interested in discovering how it can be corrected. One other difficulty I have encountered with the solder paint is that sometimes when the components are heated, the flux doesn't melt and forms a black crust over the site, completely obscuring the joint from view. Bernard

Are you shure it phos bronze you will get that effect if its ally bronze:- try a strong magnet on it if its ally bronze the magnet will stick.

The black crust is supose to happen, uts just the flux doing its job.

Stew

Sounds like you are not heating the objects quickly enough, and the flux is then getting exhausted and going black. Further heating has nil effect. Lots of little molten bits, no adhesion and solder that won't flow..

If you can't turn the wick up any more, try more effective shielding/heat retention, and reflect heat back into the work.

What should happen is the flux will melt, keep the heat on, the flux goes runny, move hte torch a bit sideways but keep the job hot, touch the rod dipped in flux to the job, and the rod melts and flashes round the whole joint in one. Job done - so long as you heat the work and get it hot enough quick enough. If you cannot do that try Tenacity flux or get a torch with enough thermal capacity. .

Bernard can you confirm the type of solder youi are using as the term "paint" is usually applied to soft solder (silver to Americans) and what we in the UK call silversolder when sold in liquid form is usually refered to as "paste"

The soft solder paint can leave a black film over the flux.

J

Jason

The silver solder I used is Johnson Mathey's Silverflo 55 and they call it 'paint'. I'm surprised its behaving so erratically, because I seem to get a different reaction every time I use it, although that's probably because I'm using different metals. I'm really intrigued by the little balls that have formed and won't melt no matter how hot I get them.

Stewart

I've checked the phosphor bronze and it is definitely not magnetic.

Could be that the silver solder paste is melting before the parent metal is hot enough, this can cause the silver solder alloy to separate into it's constituents and cause the effect you describe.

There is a huge amount of information in the technical section of JM's website which may well be worth a visit. **LINK**

Ian.

Have you had any soft solder near the parts previously as this can affect the silver solder. I have also hear that the silver solder paste has a limited shelf life so it could be getting past its best.

Also if its a large part that is taking a long while to get upto heat you may be exhausting the flux in which case use separate Tenacity No5 and stick solder.

J

Hi

Try the Cup Alloys web site that is full of information. Is it a Seviert torch you are useing.

Bob

Hi Springbok

The torch I am using is Cup Alloys Turbo Torch and the componets I'm joining are very small (about 700mm x 15mm dia). I have e-mailed Cup Alloys explaining the problem but not sure if I will receive a response from them.

Hi JasonB

There hasn't been any soft solder near the parts and I will follow up your tip about shelf life with Johnson Matthey and report back.

Bernard

I would not call 700x15mm small particularly if its solid bar rather than tube. It will have a heat sink effect so what I said about exhausting the flux is quite likely.

J

Hi Bernard

I had the same problem when silver soldering the top bush in the barrel on my tich

afer throwing 3 rods at it. I managed to get it soldered in place, but when cold pushed out very nicely!!

it turned out to be leaded bronze found in a scrap bin (my hobby!), i guess the moral of the story is only use it if you know where it came from, an exactly what the material is. as is cost me 3 rods of silver solder

I hope this helps

Nigel

Jason B

Ouch!!

My 700mm dimension should have been 70! The perils of the metric system. I imagine this makes quite a difference - apologies.

Bernard

Had the same prob on my boiler and mucked about with flux and pickling and 3 different melting points for the solder.

In the end it was all about heat.

I created a small hearth with three heat bricks from the BBQ shop; one flat and the others closing the back left corner. this reflects a lot of the heat back onto the job. I made sure that the heat sink was warmed up befor bringing the solder site to temp by moving the torch around on the large bit of metal first. I dipped the rod in flux before applying, brought the solder point to final heat quickly and then ''moved the heat" (rather than spot heating) to points where the solder did not flash.

This works most of the time and then I smile

david

Hi Bernard

Ref Cup Alloys, Would be very surprised if they do not answer as are a very friendly couple and go out of their way to help I always enjoy meeting and chatting to them at our BSSME Thornbury show..
I made my hearth from a bit of sheet steel and lined it with firebricks the type that are used in open
log/coal fires and obtainable in most decent builders merchants. OK a bit Heath Robinson but very efficient. As everyone has suggested heat, clean flux and clean workpiece are essential for a sound joint. There are numerious Threads, Books, and articles on this subject.

Have a nice day in the workshop

Bob

Damn I used the enter key instead of Shift Enter for single spaceing.

As folk have described, fire-bricks can be used to form a mini-furnace to reflect heat back to the onject being soldered but another option is to use ceramic wool as the lining of your mini-furnace - it's got a lower specific heat capacity so heats up faster.

Hi all,

Just a quick word on the use of refractory bricks, There are two main types. There are the hard, dense firebrick and the lighter more porous white type.

The former is used in ovens, furnaces, fireplaces etc and have a high thermal mass and absorb and hold lots of heat, hence the use in furnaces, pizza ovens etc where they are held at high heat for long periods, the bricks acting as a heat store and help keep a constant temperature. The latter have a lower thermal mass and will reflect more heat back into the job and are better for short heat and cooling cycles as less heat is absorbed and hence less wasted plus the cycle is faster  I fact you can hold one end while heating the other to red heat and keeping it at that heat quite comrotably. They are used in pottery kilns for that reason, i.e. they reflect heat into the pottery and not absorb so much, but cool relatively quickly to allow the pottery to be removed in as short a time as possible. They will however not withstand rough handling as they break easily but this is sometimes an advantage when small pieces are needed to pack round an oddly shaped workpiece.

If you can get them, these lighter, white refractories are much better for our uses when silver soldering or making a small muffle for heat treatment than the harder firebrick.  The difference was made very apparent to me early in my engineering career when designing furnaces for different purposes (from heat treatment ovens to blast furnace equipment) at companies in the late 60s.

Regards

Terry

Edited By Terryd on 30/05/2012 08:27:04

The lightweight bricks can be cut very easily to specific sizes or shapes with just about any saw.

They will even accept a logitudinal cut so you end up with two slabs - although I'll repeat the caveat about care in handling.

These bricks can be sourced from suppliers of refractory materials to industry. As I live in South Wales this is not difficult but others may have to look further afield and cope with a minimum order value.

For most practical purposes Celcon lightweight blocks (dry) make excellent and cheap alternatives to the "proper" white ones.

If you are relying upon the reflected heat to ensure you can solder, your heat input from the torch is too low. The reflected heat assists in stopping unnecessary loss away from the job, but I have seen many a good job soldered without any blocks at all, just with adequate heating input.

Edited By KWIL on 30/05/2012 10:54:06

Hi Kwil,

If you are not using reflectyed heat you are wasting a substantial proportion of your fuel and using a much larger torch than is really neccessary. Largest isn't always the best. Refected heat used intelligently can make sure that all parts are heated adequately all round and not just at the seat of the flame. It also prevents overheating of the flux locally by concentrating too much heat in the flame area causing the problems that the initial poster has been experienceing.

But then again I'm only a novice having only started silver soldering copper fabrications in 1972 - what do I know?

Regards

Terry

Having seen Kwil's silver soldering first hand I'd say less than he knows

J