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Melting Lead With Only Limited Facilities

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Proud Mary

Fri Jan 11 2019, 10:18PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Does anyone have any recent practical experience with melting lead with only limited facilities that they could share with me, please?

The problem: To cast a lead block containing six channels in which GM tubes are to be inserted to form a Bruno Rossi type cosmic ray muon cascade detector.

Facilities: Either (a) my kitchen gas stove OR (b) a large Camping Gaz type butane cylinder with a burner mounted on top.

Note: I live in a retirement complex and have a very small workshop in my flat/apartment. I do not have my own garden/yard.

The metal to be melted down is assorted lead scrap, with typical surface oxidation but otherwise very clean.

I am thinking to use a stainless steel saucepan with metal lug handles (i.e. no plastic or wood fittings).

I am aware of the toxicity of lead fumes, though it can hardly be worse than half a century of soldering!

I am thinking of making a mould for my detector block from fire clay and steel tubes (for the GM tube channels) but am concerned that the fire clay might explode due to trapped air or moisture. Would the cooling lead contract around the steel tubes?

Any thoughts based on practical experience will be very welcome - Stella.

Blackcurrant

Sat Jan 12 2019, 02:02AM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

Couple of things that come to mind are

You could bake the mould first in an oven for a bit, get rid of any damp.
Make sure the mould is strong it's going to have weight pushing on the sides.
The hollow tubes may try to float up!

Cooker should be able to melt it, but I may be remembering a lead/tin mix.
If there is any rubbish in the lead it will smoke.
When you have melted the lead it may have scum on top so just skim this stuff off before pouring.
The lead will shrink while cooling so slightly overfill.
Use a pan with a pouring lip if you can.
Have your mould siting on a metal tray so if there is any spillage it's not going to get far.
If it's a lot of lead it's going to get real heavy and take ages to cool.
Try a small amount of lead first pour into a simple mould, just to see how things go.
Polycarbonate Face Screen , Welders Gauntlet. Etc

there will be a ton of stuff on youtube

klugesmith

Sat Jan 12 2019, 06:50AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Good to see you, Stella. Happy new year!

Could you skip the melting, and pack lead shot or lead wool around the tubes?

klugesmith

Sat Jan 12 2019, 04:13PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

If you use (untapered) steel tubes as cores, expect them to stay in the cast lead block forever. BC makes good point, to secure them against floatage when you pour. Could be filled with sand to seal the bottom end. Can the outer mould be a tin can or other metal box (even aluminium) that would be OK to stay with the lead block forever? Initially surrounded by loose sand or clay for safety.

You don't need to pour the whole block at once. Could do in in lifts as small as you want, melting the lead in an iron plumber's ladle, and pouring through a piece of window screen to filter out most of the dross.

2Spoons

Sun Jan 13 2019, 06:42AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

The fumes from molten lead are worse than from solder because 1) the temperature is higher and 2) Solder is only 40% Pb.
Do this either outside, or if you must use your kitchen do it under the extractor (at max).
Your mould should be hot when you pour your lead in - get it as hot as you can in your oven. Less likely to crack from thermal shock or have a steam explosion blow lead everywhere.

Conundrum

Sun Jan 13 2019, 03:05PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Can you not add some Bi to lower the melting point?
I have some here and you can source (haha) this from ye old fishing shoppe.
Though this is typically 97Bi3Sn this does not make a lot of difference and the resulting alloy is eutectic and shrink free if you get the initial proportions right.
Use some Fluxite(tm) flux to get a good result as this worked for me.

Also relevant: have some Pb "foil" from a failed roofing project if you can use it.
Guaranteed quality and very little oxidation that I can see, not sure on postage but can't see it being a major annoyance.

Re. casting etc. just be aware that fire cement *may* be OK provided it has completely cured but saucepans generally will not take the heat AT ALL especially if coated. Old iron one piece might be OK but beware of highly toxic fumes if there is any sort of non-stick coating.
This usually becomes a problem anywhere above 240C which is (I hope) well above even a hardened chef's typical food cooking temperature.
Canary, coal mine etc.

klugesmith

Sun Jan 13 2019, 06:07PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

With regard to evaporation, lead is an exceptionally nonvolatile metallic element.

Its vapor pressure _at melting point_ ranks near the bottom -- look it up. 2nd chart here:

Not in a class with gallium and indium, but many orders of magnitude lower than toxic metals known for fume hazards (cadmium and zinc).

It's more important not to be cavalier about personal protective equipment, to avoid burning yourself in an accident.
Beware of free advice on the Internet.

I like Andre's suggestion of using bismuth. Why not pure bismuth, or some prepared low-melting alloy? See what the user's manual for Cerrobend (aka Wood's metal, MP 158 degrees F), which has lots of cadmium, say about shop ventilation.
I guess lead is traditionally first choice for radiation shielding, but expect bismuth isn't far behind in those properties. Heaviest known stable isotope, if you don't count the recently discovered decay with half life greater than 1e18 years.

Conundrum

Mon Jan 14 2019, 05:48AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

I think that might be the problem. Bi is slightly radioactive.

klugesmith

Tue Jan 15 2019, 03:19AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Could not resist playing with the "slightly radioactive" numbers that I just learned about.
Natural bismuth is 100% Bi-209, long thought to be the heaviest known stable isotope.
Not until about 2003 was its alpha decay discovered, with half life of 1.9e19 years (more than a billion times the age of the universe).

For use as a radiation shield, in medicine or in Stellas' flat, bismuth might as well be nonradioactive.

Here are some unreviewed conclusions to put that in perspective.

1. The total activity of 1 kilogram of bismuth is 1/300 Bq, also known as 91 femtocuries. That's one decay every 5 minutes, somewhere within the volume.

2. Range of 3.14 MeV alpha particles is about 1.83 cm in air, and 0.00088 cm in bismuth.

3. A one-kg cube of Bi would have edge length 4.68 cm, surface area 131.5 cm^2.
The skin volume from which alpha particles might escape into air (with some energy left) contains 1.13 grams of metal, amounting to 3.8 uBq (1e-16 Ci).
About every 3 days, on average, one alpha particle would escape from somewhere on the cube.

Proud Mary

Sun Jan 20 2019, 02:01AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thanks for all your helpful suggestions, which I have thought over before replying. I'm not in a hurry, so I will build up my lead block in layers over a few weeks, so I need not have to deal with much molten metal at any one time.

There is a charity shop/thrift shop up the road, so I'll keep my eyes open for an old iron pan with a pouring lip to melt my lead, which is in good clean condition on a roll intended for roofing.

I am not worried about alpha disintegrations, as I am using big Russian GM tubes which have metal casing.

I am making two detector assemblies - Detector A with the GM tubes housed in a lead block, and Detector B (equal and opposite) detector having tubes in an identical geometric arrangement but assembled on a clear acrylic frame.

Digital signal processing will allow the tubes to be configured in many ways, and I shall be copying other peoples' circuits for this, as I am not up to designing this part of it myself.

My idea is to have a window sill observatory consisting of the cosmic ray and terrestrial radiation monitors, a VLF Sudden Ionospheric Disturbance (SID) detector fed by an aluminium hoolahoop loop antenna, a terrestrial magnetism fluxgate magnetometer (both vertical and horizontal components) detector using Speake sensors and electronics (which comes as a DIY kit from Speake & Co. 6 Firs Rd, Llanvapley, Abergavenny NP7 8SL.) and an infrasonic detector for detecting large meteor strikes into the atmosphere (and blast overpressure!!!!)

I hope, in time, to put my observatory online in real time, so my data can be compared with that of other observatories.

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