Melting chromed-brass bathroom fittings

[MRA]

I just cast some odds and ends using a bunch of cut up chrome-plated brass bathroom fittings. Someone present at the event (something public at a museum) remarked that he had done something similar, and the resulting metal was rock hard. I had a scratch at my results, and indeed, they seemed resistant to a hacksaw - whereas the next batch (where I was careful to find odds and ends of unplated scrap) seemed to behave more normally. I've just had a google on this, and web-people seem to think that the chrome (and underlying nickel) don't melt at brass temperatures, and just end up as flaky bits in the dross. I could believe this - there was plenty of dross, which I tried to collect using some glass in the mix - but my first impressions are, that the chromed pieces made harder metal. I wonder if anyone here has anything to add?
Thanks
Mark

 

[abby]

Over the years I have used many chrome plated brass bathroom fittings in my brass castings and the only detrimental effect that I have noticed has come to light during polishing.
In one casting I exposed almost a tiny mountain ridge of hard spots , the surrounding metal was removed by the mop leaving little peaks of silver.
Bear in mind that the amount of chrome is very small and it is plated on top of nickel so may be the hard spots were nickel ?
Anyway if the castings are to be polished I avoid plated scrap.

 

[jkimberln]

I've melted bathroom, or plumbing fixtures too, but I try to avoid plated ones. I have a relatively unlimited supply of this stuff from a plumber friend. In case of the plated ones, I boil them in muriatic acid to flash off the chrome and nickel. However, I really don't like plumbing fixtures because they have too much zinc. It is better to bite the bullet and get some silicon bronze for locomotive fittings or boiler fittings. I've reserved the scrap stuff to make blobs that will be machined down into parts, though.

 

[MRA]

The application I have (which is a bit tangential for this forum) is making bits for full-size gas, hot bulb engines etc, at an engine museum. So it's big stuff for machining - for whatever that's worth. But I know Abby (above) has made a lot of small, very detailed investment castings for model locos - so I take his comments on board too.

A friend has just put up a short video of us messing about, if you want to see

 

[jasonh]

To make my brass parts I collect and melt non-plated brass plumbing fittings. The exact original alloy is a bit of a mystery other than that it is originally cast and presumably can be re-cast. I often find the resulting part has a very tough outer layer that is hard on tools. If you can get past that layer then the material machines quite nicely. So- I wouldn't blame the chrome plating for the tough metal.

 

[dnalot]

Caswell plating sells a chrome stripper Plating Kits - Metal Strippers - Caswell Inc

Mark T

 

[MRA]

Thanks Mark, that looks interesting. Folks on the internet seem to use hydrochloric acid. And Jason - I did some more investigating today and that was my experience too - a hard skin, but a decent hacksaw blade (something I lacked at the weekend!) would go through it and once inside, it was OK. So that's great - I can continue. I was making gas valve bits for one of these. It's a really small one - so almost a model

https://www.gracesguide.co.uk/images/b/b2/Im20100829Sh-152.jpg

 

[Steamchick]

Perhaps the surface is a poor version of Nickel Brass? Much harder and used for pound coins, etc... (Legal Tender is not the cheapest source for scrap material!).
https://www.engineersedge.com/brass...and,is principally an alloy of copper and tin.
K2

 

[Richard Hed]

Caswell plating sells a chrome stripper Plating Kits - Metal Strippers - Caswell Inc

Mark T

can the chrome be electro-plated back out, do you thimpgk?

 

[dnalot]

can the chrome be electro-plated back out, do you thimpgk?

Yes, that is what I do.

 

[MRA]

That's interesting - how do you do it? I have read things online about exotic electroytes and warnings about nasty gasses coming off, but you never know with the internet.

I have used caustic soda (US - lye) with a cathode workpiece and a scrap anode, to take rust off things. I had a nice bonus once when the workpiece (bicycle forks) got accidentally galvanised when the zinc came off the scrap anode (plasterer's mesh) and stuck to them!

Nickel brass is an interesting possibility Steamchick - it looks a bit silvery (more so than the second pour I mentioned) but I was cautious about what to call it, as the melting points for chrome and nickel are a lot hotter than what I was managing in the furnace. Unless the flame playing directly on stuff poking out the top of the pot (it's wild hell in there, totally uncontrolled) melted a bit of that coating and it went into solution in the lower temp molten brass, lower down in the pot. Perhaps!

 

[creast]

I have experienced this hard skin too. Most of the plating flakes off into the dross but it is possible some alloying is taking place.
I am uncertain if this occurs due to the more rapid cooling at the mould surface causing precipitation or if it's oxidation at the same surfaces.
As you say, it is a skin effect and can be annoying but not impossible to cut.
The melting points of some constituents are not reached but that does not have to happen for some dissolution to occur as in copper additions to aluminium.

 

[Richard Hed]

I have experienced this hard skin too. Most of the plating flakes off into the dross but it is possible some alloying is taking place.
I am uncertain if this occurs due to the more rapid cooling at the mould surface causing precipitation or if it's oxidation at the same surfaces.
As you say, it is a skin effect and can be annoying but not impossible to cut.
The melting points of some constituents are not reached but that does not have to happen for some dissolution to occur as in copper additions to aluminium.

What you are saying is true. Any molten metal dissolves any other metal at least to some extent. When brazing cast iron, a tiny tiny amount of iron dissolves in the brazing material, in this case it is negligent, however, most other metals will dissolve other metals a lot more. This is how soldering copper wires or piping works. The hot solder actually dissolves a small amount of the copper into the solder making a continuous material. In the case of brazing, the hot metal gets in between the microscopic pores and adheres because of that. I'm sure there are other principles at work too, but not familiar with what they are.

With silver solder, either way could be the adhering principle. With copper, brasses, bronzes, you can expect silver solder to dissolve some surface material into the hot, liquid metal but with steel, it is a different matter. When I first silversoldered my first carbide chip to a steel bar, I actually could not believe it would hold when I used it to cut some threads. But it held very well and I have used it several times on very tough problems.

I thimpfk, but am not sure, that the guiding principle of dissolving materials is similar melting temperatures. There may be something to do with the number of chemical (co-valent, valent, whatever) bonds in the material too.

 

[the artfull-codger]

Interesting about the chrome plated taps, I've not noticed myself but often I cast brass fittings & a mixture of tap parts so not all chrome,last melt was brass rings for some vertical boilers to sit on, using tap mix, oversized lost foam & roughed out with a tipped tool then finished with hss. not a lover of lost foam but did a "quickie" to save time making a pattern for only 3 boilers.

 

[Richard Hed]

Interesting about the chrome plated taps, I've not noticed myself but often I cast brass fittings & a mixture of tap parts so not all chrome,last melt was brass rings for some vertical boilers to sit on, using tap mix, oversized lost foam & roughed out with a tipped tool then finished with hss. not a lover of lost foam but did a "quickie" to save time making a pattern for only 3 boilers.

I am a fan of lost foam, esp. for one offs.

 

[Shopgeezer]

I remember watching a video of a foundry casting engine heads using lost foam. The foam patterns were very detailed. Fairly dense looking foam. The moulds were on a moving table that rotated back and forth while the pour was happening. I assume the agitation was intended to assist gas removal from the mould. I have never tried lost foam myself but have read that outgassing as the foam melts can be a problem in casting quality. Are there tricks to this? Shaking the mould, type of foam used etc?