Silver soldering advice needed

[picclock]

Hi

I'm silver soldering a shaped pad onto the outside of a cylinder to thicken the wall thickness for a fitting thread. Unlike most of the silver soldering I've done I need to preserve the inside of the cylinder, preventing oxidation. I would also for aesthetic reasons like to minimise any silver solder running over the outside of the cylinder. Both parts are steel.

My current plan is to stuff the cylinder full of charcoal and clamp a couple of plates over the ends, as this should cause an oxygen reducing atmosphere, preventing oxidation. For the outside I intend to plaster it with soap dissolved into a thick goo.

Normally I would just go ahead and take a chance but its one of those jobs that I really don't want to screw up.

Its quite a large part (45mm diameter) so I am planning on using two heat guns to get it up to temperature fairly quickly.

I have silver soldered a few bits and pieces but would not consider myself an expert in the field. needless to say the parts will be clean, have minimal gap, and be correctly fluxed. I intend to hold the parts together with binding wire and/or a clamp.

I'd appreciate any comments or improvements to my intended technique, or any other help in general.

Best Regards

picclock

 

[Ken I]

Picklock - I'd probably justclose off the ends and flush propane through it to a vent - with a burner nozzle attatched - keep the nozzle burning during the process after first flushing with propane (butane, MAPP whatever) before applying heat.

Keep it burning during cool down as well so you dont "contract" air in and cause a bang.

Like in a real reduction atmosphere furnace - all leak and vent points are kept aflame to prevent explosions (sounds daft doesn't it).

You could also pack it with sand (or charcoal) just to keep the explosive volume down - but at that size I wouldn't be too concerned.

I think the charcoal might cause some colouration at the hot zone by contact carbon absorption - maybe a trial run of a piece of gash tube to check first.

2c

Ken

 

[gbritnell]

I have never tried this so take it for what it is. They make a Boron powder that's used as a coating when heat treating. I bought some from a gun supplier many years ago. I use it when I make piston rings. You heat the part up, coat it with the powder and then when it gets to red heat it protects the item from oxidization. It's like what the flux does for silver soldering. You could clean up your part in preparation to soldering, coat with flux, bring up the heat until it can be coated internally with the Boron powder then brought up to full silver soldering temperature. I don't know what type of gasses come off of the Boron powder but I know a person has to be careful of not breathing the dust when using it, skin contact also.
Another option would be to coat the entire bore with silver solder flux. Did you ever notice that when you were silver soldering the areas that didn't oxidize were the areas that had flux on them?
Just a thought.
gbritnell

 

[Springbok]

Wow
Some of these suggestions sound like suicide missions to me.

Have a safe lovely day in the workshop

 

[Mainer]

Here's an idea for you: cut a piece of stainless steel shim stock such that when rolled into a tube it just fits in the cylinder and springs out against the cylinder walls. That should keep oxygen away from the surface and prevent discoloration...maybe. I've never tried this stunt, so if you decide to try it, an initial "proof of concept" experiment would be prudent.

 

[RonGinger]

Remember the little bottles of 'white out' or 'liquid paper' that were used to correct typewriter mistakes? I have used that to paint on a surface where I didnt want silver solder to flow. The little brush in the cap works great. I clean and flux the parts first, then paint on a stripe to stop the solder flowing.

I has worked for me, maybe not for the inside of the big cyclinder, but around the edges of the fitting.

 

[Ken I]

Wow
Some of these suggestions sound like suicide missions to me.

Have a safe lovely day in the workshop

Yeah - I know it sounds wild - but if you've ever worked with a full sized reduction atmosphere furnace (with several cubic feet of red hot propane inside) they are quite safe.
The weird thing is the ignition flames at the door - you open the door and a great gout of flame belches upwards - the air entering the oven pushes the flame front inwards as the gas consumes the oxygen - when you close the door it simply uses up the remaining air. It becomes dangerous if you don't light it off.
These things can and do explode - normally during start up and particularly during shutdown (The Plessey Swindon works outside London blew its roof off during a power failure many years ago.)

A 45mm cylinder is never going to make a bigger bang than a firecracker - worst case scenario - but then perhaps not for the faint hearted.

Ken

 

[steamer]

When heat treating piston ring via the Trimble method, the procedure has you making a steel annealing crucible to put the rings in. One of the other things put in is a piece of brown paper bag. The point of which is to burn up and consume the air inside so the rings don't oxidize during annealing.

The annealing temperature is the range we're talking about for silver solder....

So perhaps the charcoal bit will work....I would experiment with the paper thing and the charcoal thing, or any of the other things on a seperate piece before you commit your work piece.

Good Luck!

Dave

 

[Swede]

I've used KeepBryte, which is that borosilicate glass powder, for years with total success to prevent oxidation.

But it's a mess. What I prefer is the stainless foil method. I ran a batch of rings using Trimble's method, and they came out bright and free of scale using the stainless foil.

The jig was prepped and also degreased. The foil envelope was prepared, and sealed except for one tiny hole. Into that, I squirted argon from my TIG welder, enough to displace the O2 in the foil pack. It was then quickly sealed. Once out of the furnace and cooled down, the rings were as bright as if I hadn't even heated them. I did also put some brown paper in there, and it turned to charcoal... helped scavenge what oxygen remained.

So if there's a choice, SS foil works great. Otherwise, it's keepbryte all over the part until it forms that protective, glassy slag. Flux also works, but there's usually a bit of an acidic action with flux as they are designed to clean and remove oxidation under heat. KeepBryte doesn't do that.

 

[Mosey]

After silver soldering stainless steel, how do you remove the black oxidized burnt flux, etc., and other crud on the surface?
and, how do you keep the flux from spreading over the surface where you don't want the solder to flow?

 

[picclock]

Hi Mosey

I think you should have started a new topic with that question. Oxide removal is best done with a 'pickle', usually an acidic solution that the part is immersed in. I've used citric acid which is user friendly and seems to work OK - maybe 1-2 hours in a warm solution of 20gms citric acid powder to a pint of water or so.

Not sure how too stop the flux spreading and have always found removal a pain. I use Tenacity 5 flux. Best way seems to be to dunk the part in cold water whilst its still at 300C or so then remove any flux by abrasive mechanical means. I have a part in front of me that I brazed today. The part is minimally fabricated, so that although location points exits for machine alignment, the rest of the machining can be done after brazing, removing most of the traces of flux and other discolouration which have occurred.

If anyone knows of a better method of flux removal I would be very glad to hear it.

Best Regards

picclock

 

[kwoodhands]

I use hydrochloric acid to remove flux. Takes ten minutes or so but must be washed off repeatedly.This acid is mixed ten parts water to one part acid for a pickle.Will cause rust very quickly on Ferris metals. I once left a small part on a table after pickling without rinsing it off with water. The next day I had a rusted hunk of junk.
I have used this as a pickle for copper,brass, steel, not stainless though. I haven't ever had the occasion to hard solder stainless.
I like the idea of citrus acid.I did use it once and it worked fine. I might use it all the time from now on. I pickled three small parts in citric acid for 3 or 4 hours. Looked clean to me, then proceeded to hard solder the pieces with no trouble.
Because I only used the citric acid one time on small parts ,I hesitate to recommend it for all hard soldering.
mike

 

[Blogwitch]

Mike,

For purely safety reasons, I wouldn't recommend anything other than citric acid for pickling, anything stronger in the wrong hands could be asking for real trouble.

I had to anneal a gold ring a couple of weeks back to allow me to stretch it a lot, and I didn't want any oxide coating left on it at all, so I used the recommended method. Cover the whole part in flux paste before and during heating. Not one bit of oxidation anywhere. I use Tenacity 5 flux mixed with water and a tiny drop of washing up liquid, it just washes off completely afterwards in running warm water.

That should work on your bore.

To prevent solder going everywhere, draw around the area with a graphite or lead pencil fairly thickly, the solder shouldn't go past it. Also instead of stick feeding, use pallions, and roughly work out how much silver solder is required in the joint. It never fails for me.


John

 

[picclock]

@ John

>> roughly work out how much silver solder is required in the joint.

I've always used pallions for the small amount of brazing I've done, couldn't get on just feeding the joint as insufficient thermal inertia to keep small parts hot enough while applying solder. I never seem to be able to judge the correct amount. Once I didn't use enough, and although the joint was mechanically sound, the fact that one corner of the joint was not brazed looked very odd and made a mess of the part. Now I tend to overdo it and try to allow any excess an escape path that can be machined later.

So how do you judge how much silver solder to use ?

Will definitely try the pencil trick next time, many thanks for that.

Best Regards

picclock

 

[Blogwitch]

If I am doing say a boiler insert, or a pipe fitting, I would just use one wrap around circle of 0.5mm silver solder wire the same diameter as the part.

For the job you are contemplating, I would actually use 0.003" sheet silver solder foil, the same size as the part I am putting onto the outside and sandwich it in between the two parts. That would give a solder thickness of about 0.002" and a small fillet around the outside of the joint.

If I only had rod solder of say 1/16" diameter, I would 'persuade' it between a hammer and a hard place until it was almost paper thin, then use it like the foil above.

It is rather difficult to explain how to do it without actually being there, but I hope what I have said will give you some sort of guidance.

We are lucky in the UK that we can easily get our silver solders in all shapes and sizes and heat ranges, the same goes for our fluxes. In fact it wasn't too long ago that I bought myself 10ft x 3" wide x 0.003" foil for a very reasonable price (about 25 pounds), and 0.5mm wire is available from lots of places, I usually get mine from Blackgates Engineering at around 1 pound per metre.

John

 

[Jasonb]

Tenacity No5 or HT5 is a harder flux to remove, if you are not doing stainless steel or need its higher & longer heating properties then just use Easyflow or EF flux which washes off easily. One thing that helps remove HT5 is caustic soda.

Another tip to stop solder going where you don't want it is to use Tipex type writer correction fluid, the solven based one.

J

 

[picclock]

@ Jasonb

HT5 flux - I'll give the caustic soda route a try. The pesky stuff always seems to run over the most awkward parts of the job. I'm not sure if I have tippex around (long time since I used a typewriter ;D) but it sounds like it might be easier to apply than a pencil.

I think I also tend to overheat my joints which may make the flux more difficult to remove. The reason is that I am always concerned about cold areas which I may have missed. I work mainly with steel which is a poorer conductor of heat than brass or copper.

Many Thanks

picclock

 

[Jasonb]

This is when the Tipex does what a pencil can't. To accurately hold these parts while being soldered they wer placed on dowels set into a bit of plate, obviously don't want them ending up soldered to the jig so it was coated in tipex

After soldering

And cleaned up

J

 

[Mosey]

I've been told that Titex (Whiteout) is highly toxic when heated. Phosphorus gas! So, how about yellow ochre to prevent solder flowing too far?
and, I've read now about anti-flux?
Anyone know what these are?

 

[Jasonb]

Would that be more toxic than the cadmium in the solder?