Model Train Journal

This is a question for our astute metallurgists:

Carey sent me a pair of boilers to be re-soldered. Inside one of them was this really shiny silver stuff that looked like bubble paper in reverse - really shiny silver and stippled.

I was guessing Cerro Bend or similar - lead always goes grey with age - so I heated it with a small propane burner tip. It quickly melted and mostly flowed out, but I had to apply enough heat so the running boards and boiler bands fell off as well. I don't think it required the same heat as solder, but it was a bit higher than the pipe bending stuff.

Any ideas as to what I was dealing with? Should I be concerned with mercury poisoning or something? There were no fumes as it poured out, and no evidence of it having adhered to the brass, like solder would have.

Not having been there to see it in person, I can reasonably guess by the description ("shiny and stippled") that it is Woods Metal (Cerrobend) or Cerrosafe. Both are alloys of bismuth, lead, tin, and cadmium.

Cerrosafe usually has a little higher melting temperature than Woods Metal, the former about 180f and the latter around 160f. The behaviour under your torch is probably because the brass heated to a far higher temperature before the slug itself got to melting temperature due to the thermal mass of the slug and the heat-conductivity of the brass.

If you think about it and there is a "next time", try boiling it instead.

sarge wrote:....(Cerrobend) or Cerrosafe. Both are alloys of bismuth, lead, tin, and cadmium.

No mercury involved! Guessing if it was poured into place probably Cerrosafe since Cerrobend very slightly expands on cooling.

If you think about it and there is a "next time", try boiling it instead.

Right. This where a yard sale crock pot becomes useful!

Thank you! Might try that on the scraps.

I haven't yet done the boiling water test, but I am reflecting on the old masters' techniques as I stick these boilers back together.

My first sort of stunning revelation is that the old masters used .020 soft brass for boiler courses, sticking the various tapers together with .010 boiler bands. Solder joints are failing, of course -

Second, both boilers were kind of wide open in the belly - probably unnecessarily so. That further weakened them.

One is a PRR L1 Mikado. There are hints of Scale Craft in the mechanism; why the builder did not use the robust Scale Craft K4 boiler is a mystery. I did a new conical section, and reinforced the other parts.

The second boiler is the same - really light gauge soft brass. It had suffered a mishap, with squashed boiler courses and dented cab roof. The neat thing about this one is the mechanism. There are castings that aim it directly at the CNW H-class Northerns. I am not inclined to reinforce this one, but with care it will look ok if its owner keeps giant hands from squeezing it.

Intriguing short projects. I might have to post a photo of the CNW mechanism.

If you remelt the scraps in boiling water, make a ladle using a tin can and a small visegrip for a handle if you don't have a metal ladle of sorts. I have a small measuring cup with a wood handle I use to melt the stuff. I just put bits in the cup then put the cup into the water in the pan.

Just dropping a slug into boiling water directly would make me nervous in case there were voids in it that might pop. Also, I'm not sure how you'd recover it to pour if it was just melted in the bottom of the pan loose.

The boiling water trick I was alluding to is how to safely heat a superstructure to get the stuff out. Immerse the superstructure, then bring to a boil; much more even heating of the brass than using a torch so soldered bits don't fall off. Of course you have to think about positioning so the stuff drains out and you can grab the dingus without scalding risk.

BTW treat it with some respect as to ventilation. Cadmium vapour is on the bad list.

In a pinch, I tried using it as a low-temp solder assembling white-metal castings to brass, a common combination in UK loco kits. It actually works alright.

sarge wrote:BTW treat it with some respect as to ventilation. Cadmium vapour is on the bad list.

Bit of an understatement there. Probably should be wearing a respirator and gloves, and not doing that boiling thing in the house.

In a pinch, I tried using it as a low-temp solder assembling white-metal castings to brass, a common combination in UK loco kits. It actually works alright.

Do let me know if you need any,

Bob,
Do you typically use a higher melting point solder when putting the major sections together? Any support rings inside? and how do you prop for alignment? I have a Scale Craft Mountain boiler that the builder allowed to droop in the middle. He must have had it supported by the smoke box and the cab.... I, understand to fix it, it will need to all come apart and that is fine... I need to learn how to do this stuff...

Here is a pic of the little beasty

Difficult to tell from the photo - is it one piece from smokebox to firebox? Is the crooked joint the firebox seam?

Yes, I use inserts - usually .032 or better -with 2-56 flathead brass screws to ensure alignment when I solder. I use straightedges and eyeballs to get the tapers aligned. I do not always get it right the first time, so sometimes the screw holes need realignment. Once in a while I get the taper wrong, and it is start over time. Firebox tapers are the last thing I do, and those are mostly eyeball. I always bolt the cab on, and study it for a week before soldering.

I use 60-40 solder for everything. I have 80 Watt, 150 Watt, and pencil torch at my workbench. Cleanliness and good flux are essential.

I did do a boiler with silver solder - the real stuff; 1100 degrees! Never again! Result was ok; you can see it in my SP Steam threads (GS-2 in 17/64, viewtopic.php?f=10&t=19746&start=15, bottom, #4410).

In the olden days, Oatey's H2O was spectacular - I could use it on dirty brass, without tinning. Can't find it, so I just use ordinary flux and cleanliness, and tin both surfaces. Even old solder needs to be cleaned and tinned.

Can you get a better photo of the sag?

Last night I discovered that Carey's L1 is 2-rail, but insulated at the hub, with insulated rods! Yuk! His solution will probably be outside third.

I'll get a better picture tonight. The smoke box is separate but the main part is one piece from there back to the firebox. Typical Scale Craft boiler, still has their big bronze casting between the tube and the firebox section. I'll get some pictures.

Hope these pictures show the sag. It isn't much, I think I can fix it.


I think I just need to make a jig to support it. I'm just wondering if I should pull it all apart or just try and heat and re align. That might work on the smoke box, but I think I'll need to get more serious on the firebox end. I feel like the cab is sitting to high, although it is partially loose. I have a couple of other boilers like this, I may try and do some practicing.

Heat it up with a torch. Firebox and cab should just drop off. You might have to pull the smokebox out. Obviously, wear welders gloves.

Any mating surface that is not shiny silver needs to be cleaned to shiny brass. I suggest a new smokebox overlay, with better rivets, but what you have is sort of standard for the area.

Tin the bare brass with a soldering iron. Assemble either in a jig or with pins. Heat with a torch, touch some solder in the joints.

Yes, cab gets lowered. Use photos to gauge - lots of them on Bing.

Thank you Bob for working on the beasts ...

Northern is a Scale Model Railways piece with operating reverse gearing hooked up to manual reverse

Mikado Alexander with double reduction gear silent drive ....

Both mid 1930's ...both outside third rail....both a mess

Thank you Bob

Cheers Carey

No, the Mike is sort of Scale Craft related, and was a 2-rail model. I will set it up for outside third, since insulating the left side main and eccentric is kind of out of the question.

Obviously I am back - 30 hours of flying in 7 days is a lot, especially in a Piper Cub. But I got to see the Columbia River Gorge, and Mounts Hood and Shasta really up close.

Glad you had a fun time up in the air ....and back safe on the ground .
Cheers Carey