Silver soldering 12L14 Steel

[Harold Lee]

I just tried and failed to silver solder up a crankshaft made from 12L14 steel. Can this be done? My attempt ended in it looking like something was dug up by and archeologist from a old junkyard. I was using a MAPP gas torch which is all I have....

I have silver soldered many brass, copper and stainless parts but this was my first and possibly last attempt at 12L14.

Any advice would be appreciated.

Harold

 

[maverick]

Just a guess but 12L14 does contain lead which may have oxidized and contaminated the joint.
Try a test joint on regular mild steel for comparison.

 

[rkepler]

12L14 silver solders just fine in my experience. I usually use a white flux and put as much heat in it as fast as I can so the flux starts working before it ends up being burnt. It doesn't transmit the heat near as well as copper so it does take a lot longer if you're using a small torch tip - you want a large tip to apply the heat where it's needed.

 

[Deanofid]

I've had no problems hard soldering 12L14. Use white paste flux and lots of heat. Depending on the size of your crankshaft, you might need two of those torches you mentioned.
Steel will have to get to near a red heat before hard solder will flow.

 

[Mike N]

I probably wouldn't use 12L14 for a Crankshaft. (too soft & it bends easily) I use the water hardening ground rod sold by Enco. It silver solders real nice with flux applied, It makes a nice strong crankshaft.

 

[Ramon]

I've silver soldered En1a - 12L14 on many occasions without problems.

I have always used the lower melting point solder and, as has been recommended, use a fairly large flame to bring the heat up quickly. I think if the heat source is marginal and the part has to be heated for any length of time then there is the possibility of the lead to leach out and consequently cause problems.

I have to agree it's possible that En1a is not really very suitable in this instance - what kind of engine is it Harold? How big is the crankshaft?

Ramon

PS Just remembered - when I did the Nova I/C engine the cylinder head was made from En1A (leaded) and had the transfer cover put on with higher melting point solder (Can't say exactly what that was -there's been so many odd bits collected over the years) then on a second heating the boss for the intake tube put on with the lower MP. There was quite a lot of bulk in the head but definitely had no problems with it

This looks far worse than it actually did. It's a retrospective shot after it had been quenched and is already beginning to oxidise. It cleaned up very well.

Hope this helps

 

[Deanofid]

I probably wouldn't use 12L14 for a Crankshaft. (too soft & it bends easily)

I wouldn't worry about that at all. A common crankshaft material is 1018 crs. 12L14 has a higher tensile and yield strength, and a higher Rockwell hardness, to boot. It's fine for model crankshafts.

 

[Harold Lee]

Just a guess but 12L14 does contain lead which may have oxidized and contaminated the joint.
Try a test joint on regular mild steel for comparison.

Maverick - I think you are correct.... It looks like this is what happened. There might be some confusion on the board between low temp silver soldering ( around 500 degrees) and hard soldering. I found that when I heated the material to the dull red temp that the oxidation had already started and the silver solder would just bead up on the steel. I used a borax based flux and have been successfull with other materials in the past but I also know I am not an expert on this. My plan is to take a bit of CRS and try it on a test piece.

 

[Harold Lee]

I wouldn't worry about that at all. A common crankshaft material is 1018 crs. 12L14 has a higher tensile and yield strength, and a higher Rockwell hardness, to boot. It's fine for model crankshafts.

Dean - here are some pictures of my crankshaft but I have to warn you, it ain't a pretty sight. You might have to look away to keep from getting sick... Would appreciate your brutal and candid comments....

Harold

 

[Deanofid]

Maverick - I think you are correct.... It looks like this is what happened. There might be some confusion on the board between low temp silver soldering ( around 500 degrees) and hard soldering.

I'm talking about real silver brazing, what other people call hard soldering. From 1200 to 1350 degrees F. Works on 12L14 just like it should. If you're having a problem with it, it isn't the fault of the steel. First suspect is flux, then your heating technique.

Looking at your crankshaft, I don't know how clean it was to begin with, but it has to be spotless to hard solder it. It also appears to be way too big for a single mapp gas torch. I don't see anything wrong with the crankshaft itself, just going from the pics.

 

[rkepler]

That looks like the result from an acid flux (or maybe a zinc chloride) and not from a paste flux for silver brazing. A braxing flux should leave the area it covered in the right heat almost silver in color and have something of a black crystal edge that you chip off. That's all rusty and stuff, about what I'd expect from using Ruby flux.

I'd also suggest using a big-*** propane torch for this - I use a Goss with a 2" bell on the nozzle - you can't wave it around in use as it'll ignite things a couple feet away. Here's a link to the Goss page:

http://www.gossonline.com/site/torches_&_tips1.php

There are others - Sievert, etc. Anything that burns a lot of propane to generate a lot of heat (not necessarily a high temperature - they're not at all equal). Heck - a week burner wouldn't be inappropriate for that size of a job.

 

[Harold Lee]

That looks like the result from an acid flux (or maybe a zinc chloride) and not from a paste flux for silver brazing. A braxing flux should leave the area it covered in the right heat almost silver in color and have something of a black crystal edge that you chip off. That's all rusty and stuff, about what I'd expect from using Ruby flux.

>>> SNIP <<<

I'm talking about real silver brazing, what other people call hard soldering. From 1200 to 1350 degrees F. Works on 12L14 just like it should. If you're having a problem with it, it isn't the fault of the steel. First suspect is flux, then your heating technique.

Looking at your crankshaft, I don't know how clean it was to begin with, but it has to be spotless to hard solder it. It also appears to be way too big for a single mapp gas torch. I don't see anything wrong with the crankshaft itself, just going from the pics.

The flux I used was Harris Stay-Silv White Brazing Flux. Part number 40022.

I have never used it on Steel but it says it is for ferrous and non ferrous soldering. I did use two torches since the part was rather large. One was a propane and the other was a MAPP gas torch. I would sure like to figure this out since my next approach is to make it from a single chunk of steel and turn the counterweights separately. That being said, if there is something I need to learn, I'll sure stick with this method if there a a chance of getting it right. Regarding cleaning the part, I have always believed that the part be absolutely clean an in fact I used a small wire brush to clean the holes and a scotch brite wheel to clean the shaft.

Harold

 

[Rustkolector]

I have always used drill rod for crankshafts. I don't like the more corrosive nature of 12L14, but I have never had a problem like yours. I generally use a high silver content braze material that flows at about 1250F. I use a white brazing flux I get at Brownells called Ultra Flux. I don't think it is anything special. As others have said, I suspect you might be exhausting and buring the flux. This could be from too high temperature, or prolonged slow heating. The flux has a limited useful life at temperature, but it is usually quite adequate. Most white fluxes will melt and turn clear at the about 1100F. Apply heat as fast as possible up to the flux melting point, slow up heat application, watch for the flux flowing clear, begin to test temperture by touching braze to surface. When it flows maintain temperature and complete the brazing. There is no need to go any higher in temperature. You should be able to bring up the temperature within 45-60 seconds. If not, you probably need a larger torch. Once white flux turns black, it is useless, and you have to start over. I would practice on a similar sized object prior to your next attempt. You'll figure it out pretty quick.

Jeff

 

[Jasonb]

I'd also say you have exhausted the flux by taking too long to get things upto heat. On large assemblies I use Tenacity #5 or HT5 should have something similar where you are. This is made for the higher melting point silver solders and also use with stainless steel and stays active for a lot longer than the standard flux.

J

 

[Deanofid]

'

The flux I used was Harris Stay-Silv White Brazing Flux. Part number 40022.

That's the right kind of flux Harold, so you can rule that problem out. I use the same brand and type.
It works on steel as well as brass, copper, etc.

Like others have said, you need to get the heat into it in a timely manner. If you're heating it five
minutes just to get the piece hot enough to melt the silver, it's taking too long. The flux is eventually
exhausted. Looking closer at your pictures, it appears you have some beaded up silver alloy, which
means the piece wasn't hot enough, or the flux quit before the silver could flow.

Try a little experiment before you continue with your work piece; Cut a couple of smallish pieces of
your steel and hard solder them so you know what the flux looks like when it starts to flow. Try
something like a 1/2" diameter disc about 1/4" thick and a short bit of 1/4" rod to join to it. Your
torches will have enough heat to do that, and you'll know what things look like as they happen.

What silver percentage is your brazing alloy?

 

[Swede]

Already beaten to it, I thought the flux might have been incorrect, but the Harris product is good stuff. Your poor crankshaft should look NOTHING like that.

One thing with silver braze flux - I used to skimp, but no more. Now, I paint that stuff on with a popsicle stick, really put a ton of it in there, so the steel for several inches away from the heat is coated. It melts and protects the bare steel. The more flux the merrier, I say. How much flux did you use?

Exposed steel NOT to be brazed can be protected with borosilicate glass powder.

Flux exhausted is also a strong possibility.

For an assembly like that, I'd have two torches, one a regular propane torch with a spreader attachment to provide some bulk heat, and another hand help MAPP torch. You can set the assembly up so that it hangs or is otherwise exposed to a continuous soft propane flame, then work the MAPP torch at the braze area. All this assumes you don't have oxy-acetylene.

Has anyone tried using a TIG torch with perhaps the polarity reversed to heat up steel for fine silver braze work? I've been tempted to try it. I'd set the torch for DCEP (I think that's what it is... set up as if it's for aluminum, which spreads the arc) and keep the amperage low enough to avoid melting the steel. You'd get a very quick red heat in a small area. Dab in the silver braze, then move on. The TIG Argon supply would help protect the work.

 

[Harold Lee]

Guys - I think all of you hit on the problem... I think I did not have enough flux and it burnt off.... I did cut one of the journals on the small diameter and it did penetrate ok.
I think one of the issues is trying to solder two different sizes of journals on the same part without burning up the metal. I'm thinking I should try to solder in the following sequence....

Gob flux on both crank webs.
Solder the large diameter crank on one web while it is facing up. Then solder the smaller diameter (Rod bearing).

Turn the part over and solder the large diameter on the second web. Than solder the smaller diameter.

Any comments?

Thanks again for all of the help.

Harold

 

[Rustkolector]

Harold,
When I silver braze a large assembly I usually improvise using the following depending on the size of the assembly:
Largest size - put it on my propane turkey fryer heater for preheat, and braze when up to temp (wear gloves).
Medium size - put it on an old 1500 watt hot plate for preheat (don't contact the glowing elements)
Smaller size - put on on a brazing harth made of fireplace fire brick with sides and top close to object to conserve heat.
You can prop a second propane torch against the harth for added heat if needed.

I need two hands free to braze properly. I put small pieces on silver braze in the flux next to the joint. They move around during water boil off of the flux, but can be pushed back in place during heat up. Once up to brazing temp, heat the opposite side of the joint to draw the silver braze through the joint. Make sure there is some clearance in the joint (.001"-.003" to allow flow). This works well for me.

I would start heating at one end of the crankshaft and work to the other end. That way you are pushing the heat ahead of you as you progress.

Jeff

 

[Deanofid]

I've done a lot of hard soldering on many different sized pieces, and have never found that big gobs of
flux help anything. All excess flux does is make a place for the alloy to run all over the place, including
where you don't want it. You need enough only to clean the area where you actually want the sliver to flow.

 

[shred]

Swede, there are some references to 'TIG Brazing' out on the net, but I've never tried it. It seems you run the amps low and hope a lot.

I use more flux than needed, which sometimes works ok, and sometimes does not.