Silver soldering/Brazing technique

[chucketn]

I have a noob question on Silversoldering/brazing. I have only silver soldered 1 part in my life. Ihave a part that press fits together with finger pressure. It's ashaft for a crank, and the other part is the flange for the crankbearing. Is this type of fit 'loose' enough for silver solder towick/wet between the parts?

Should I flux the mating surface ofboth parts before pressing together?




Chuck

 

[GWRdriver]

Hi Chuck,
These parts really do need some clearance, but not much. I would suggest making the finger-press fit into a slip-fit by relieving a bit on the shaft, but NOT so much that it allows a visible wobble of the crank or flange. Then, I would create a couple of pathways, channels, to allow solder to flow into that shaft seat. I would use a triangle or wedge needle file to put 2 or 3 shallow nicks in the bore IDs to allow the solder flow in. If you are up against a shoulder on the shaft, turn or file a clearance angle on the shoulder to allow solder to flow to the seat. Use plenty of flux and as it liquifies it will find its way in.

 

[goldstar31]

If you are wanting to do a silver soldering task after only ONE go prior to tackling what could have been hours and days of work, I would caution you to think again.

What you should be doing is learning how to silver solder and not asking how to silver solder a crankshaft- in x number of bits.

I would advise you to perhaps follow the advice which others may give but -- not on your work. Practice on something until you can 'stick the tail back on the donkey- if given the right flux'

 

[gus]

If you are wanting to do a silver soldering task after only ONE go prior to tackling what could have been hours and days of work, I would caution you to think again.

What you should be doing is learning how to silver solder and not asking how to silver solder a crankshaft- in x number of bits.

I would advise you to perhaps follow the advice which others may give but -- not on your work. Practice on something until you can 'stick the tail back on the donkey- if given the right flux'

You are right. I messed up two good parts before getting best results on a third piece.Silver Brazing can be very tricky.Brazing temperature got to be right.Tubal Cain has written a book on same subject--------Soldering and Brazing.
Brazing torches must have the power.Rod selection critical.

Gus.

 

[sunworksco]

Use the correct solder, flux and temperature. The solder will bead up like water droplets.

 

[Jasonb]

Use the correct solder, flux and temperature. The solder will bead up like water droplets.

Thats exactly the opposite to what you want and is usually the sign of a joint that has not got hot enough.

The solder should "wet" the parts and flow through the joint and form a small fillet in the internal corners though ona crankshafts it is better to have a small countersink for the fillet to form in so the job can be cleaned up without machining away the fillets. You can just see the ring of solder in teh CSK on this crank where it has been filed smooth on the inside

 

[goldstar31]

Unfortunately, the answers are coming in from various forums(?) and I am dotting about between them and losing concentration( and interest)

I have said 'practice, practice' and others have said 'wicking' and I would agree. I would, however, question achievement of the 'little globules' being wrong. If one uses silver solder paste, there will be 'little molten globules' appearing in the flux and dross and the latter will have to be removed to 'wet' the joint.

As far as the intended joint(s) are concerned, I would agree about
1. the necessary clearance between surfaces to be joined
2. I would have a little recess cut around the female part(ouch)
3. Then I would place a ring of silver solder in the recess which has already been prepared with wet flux. This wet flux is important as the torch will blow powder away.
4. The flux will turn glassy with the heat and hold the ring of solder in place.
5. As a belt and braces exercise, the fluxed extra silver solder rod should be in place to add an extra dab of solder to complete the joint.

Probably the biggest mistake in welding, brazing and welding is 'fear' and the reluctance to get in to see exactly what is happening.

 

[Jasonb]

If placing bits of solder onto the joint then applying heat you can see the solder will melt and form into small balls which is what Giovanni describes. It is only when the whole job is hot enough that these balls will flash around the joint which is a sign that all has been got upto the correct temp.

If your joint has lumpy solder and blobs sitting on teh surface then you really have not got the metal hot enough.

This is the look you should be aiming for, a nice line of solder along the whole joint where it has wetted the whole thing

And another where it has wetted both surfaces and formed a small fillet

 

[goldstar31]

'If placing bits of solder onto the joint '

I said 'a ring' of solder. this is a 'male/female' joining- and my words were to that problem- and no other.

Pedantic, maybe but so it should be.

regards

N

 

[MuellerNick]

For a plug/hole job, a fit that allows the parts to slip together just by gravity is best. File some flats around the circumference that helps the silver solder to be sucked into the narrow gap.
One thing that is often done wrong: Too slow heating up. The longer it takes, the thicker the oxide layer the flux has to break up. If you apply the flux before heating up, you only have about 30 seconds before the flux no longer works.

A steel needle helps to spread the silver solder in chamfers.

NEVER direct the flame to where you want to solder, but get the heat at the joint indirectly.


Nick

 

[Jasonb]

'If placing bits of solder onto the joint '

I said 'a ring' of solder. this is a 'male/female' joining- and my words were to that problem- and no other.

Pedantic, maybe but so it should be.

regards

N

It may have come over wrongly. I was not suggesting you were "placing bits of solder" rather than rings, I was refering to the general practice of placing pallions but the OP may not have known what this meant so "bits" was a better description" With this method the pieces of solder do tend to melt and form what could be described as "droplets of water" before the whole job gets to the right temp for the solder to flow.

Personally I tend to feed in the stick 95% of the time but will use rings or pallions if the job requires it.

J

 

[goldstar31]

Personally I tend to feed in the stick 95% of the time but will use rings or pallions if the job requires it.

J

Shhhhhhh! So do I but after all, we have been doing things a loooooooooooooong time.
To be honest I wouldn't have even bothered to to get the gas out. Probably, stick a bit of carbon from a zinc battery on one electrode of an arc welder and whey heigh. Or a spot from the mig/mag in the right place.

But this wasn't the question :hDe:

 

[gus]

Hi Jason.

Crankshaft very well done and silver brazes. For I am still shying away from same jobs as my brazing equipment is not up to mark. Have seen the professional aircon plumbers silver brazed copper pipes and they made so easy.

 

[Jasonb]

Thats a different mixture of metals that they use in the solder for air con pipes and not really suitable for our uses.

 

[goldstar31]

Gus,
it may not translate between our two Identical languages but solder in the UK is leadbased and silver solder is obviously silver and needs a higher heat.
Even lead based is a bit of a misnomer because for plumbing we- cannot use lead anymore.
You can chew off the heads of lead soldiers but you can't drink what comes out of the tap.

You can- if you lead a blameless life- live to 82( so far) with all sorts of lead paints and whatever--------------------------and it doesn't affect me-me- me- me!
So stick with a high silver solder which melts fairly easily until you a experienced, have read up the topic, got a better heat source.

Having said all that- good show!

Norman

 

[gus]

Thats a different mixture of metals that they use in the solder for air con pipes and not really suitable for our uses.

You are right. Please advise silver content for Steel. I am not very knowledgeable on Silver rods. Buy from neigbourhood weld shops but would ask for best rods for the job. Like brass to steel. Steel to steel. etc.
Plan to brush up on Silver brazing.

 

[goldstar31]

Gus,
For the time being go for a high content silver solder-- and with nerves of steel, use a strong spanner to open your pocket book.

You may need a hammer to smash your piggy bank as well, but it makes life so much easier.

Somewhat whimsically but right

Norman

 

[jasonh]

One thing that is often done wrong: Too slow heating up. The longer it takes, the thicker the oxide layer the flux has to break up. If you apply the flux before heating up, you only have about 30 seconds before the flux no longer works.
Nick

Okay Nick - I'll bite.

The way I do it (and have seen it done) is to make a paste of the flux, apply it to the joint and then have at it with the torch and the silver braze.

And I would agree- if you lay too much heat into the joint it a) oxidizes the metal and b) appears to destroy/oxidize the flux. It's a delicate art to get it right.

So - applying the flux after the preheat and slightly before the metal is probably the way to go. The question is - how are you getting the flux onto the joint?

I don't see how you could do it in the manner of rod brazing (ie on the rod) since you normally snip off as smaller piece of silver braze as will do the job.

Also - I've been using oxy-acetylene as my heat source. Certain authorities (E.g. Kozo Hiraoka) say that propane is the way to go. Any thought on that?

Straight propane seems to be a bit cold. Should I get a oxy-propane torch for my silver brazing work?

 

[rdhem2]

I don't know if this technique fits here but when possible I like to do the following. Use a spring loaded clamp to hold the part in place. Prior to this flux and put a very light coat of silver solder on the two pieces to be joined. File the solder as necessary to reassemble the parts. Reflux the joint, clamp in place. heat the surrounding area quickly with a torch until the bright flow of solder is seen at the joint. Don't DADDLE, you are done. Allow to cool. When the solder remelts the spring pressure closes the joint. This has worked well for me and usually requires little to no clean up of the joint and little to no oxidation as the heat is not allowed to get that high or dwell that long. Works great on things like soldering ramps and pistol sights. In lead soldering I've heard it refered to as sweating but not when using silver. Not a welder, just a sticker together'er.

 

[Jasonb]

Gus, the solder you have seen the aircon guys using is not a lead bearing solder with a low melting point it is a low silver content solder that has a similar melting point to the type of Silver solder we are talking about. Thes eaircon solders have 5-6% silver content and would in the US be something like the Harris Safety-silv 5

For boiler work and fabrications you want to be looking for a solder with at least 45% silver, in the US this would be Harris Safety-silv45, in the UK Easyflow No2. If you prefer the cadmium free or like us have to now use cad free then the silver content wil go up to compensate to around 55% this would be Silverflow or 455 and the international ref is IS0 17672 Ag 155.

Regarding fluxing. This is best done by mixing to a paste, apply to all surfaces you want the solder to stick to and then start heating, you don't need to preheat or apply further flux in most cases but if you do then slightly heat the end of the rod, dip it in the powder and this will coat the rod in flux which can then be fed into the joint.

I would say propane with a suitable burner is they way to go, the risk with a gas/oxy mix is that the flame is very concentrated so you end up just melting the solder onto the surface and don't get heat into all the joint. Oxy-gas can be handy on a big job where the whole thing is heated to just below melting point with a propane burner and then the oxy-gas used to work around the job.

Straight propane will melt the parts being joined let alone the solder when working with brass and copper so if definately not too cold. Its all about having a suitable size burner to get sufficient BTUs (watts) of heat not the temp the gas or gas mixture burns at.

J

EDIT

Russ your method applies to the low melting point lead bearing plumbers type solder which is silver in colour but not the silver solder we are refering to and is known as sweating the parts together and certaily works when that type of joint is needed.