Information on metallurgy, casting and foundry work

[redneckalbertan]

You mention the zinc burning off as a white vapor.

I know it has been mentioned else where in this site and Dave has mentioned being careful with heavy metals accumulating in the body. Your mention of the zinc burning off brought to mind metal fume fever.
http://en.wikipedia.org/wiki/Metal_fume_fever
Nasty thing, be careful to limit intake of zinc. You will know in short order if you have not. I had the privledge of getting it after welding galvanized pipe a while back. Not something that I would wish on my enemies.

[steamin10]

C Pipes: I was speaking to the thermal shock of a dead cold vessel being thrown into the path of a good hot running furnace. I think it risks cracking the vessel. Myself, I prefer to 'Pilot fire' the furnace for a few minutes to warm up the brick and my empty vessel, as I believe the warming of the brick saves some deterioration of the furnace walls. My home built aluminum furnace has shed the 1/2 inch inner coating, and shows the firebricks that are the mainstay of the layed up liner. They have not changed in so many years, but I dont push them hard until the blower, and gas valve are opend fully. A few minutes warm the furnace and my vessel, and then I charge the cold scrap by tongs, (ok I cheat and toss in small parts.. and miss once in a while) but never spalsh if I add when the heat starts to lower level by melting down. (my home made aluminum furnace is actually Propane and responds across a range of gas settings, and is unblown. It will not run up to brass temperatures, as the oriface for the double venturi burner will not admit enough gas for the BTU load.)

As far as Making your pattern and having your gland material, it ignores many hours of preparation that has gone before. Consider if you called the foundry, and told them to have a 4 lb bar of such and such, can you have it by Tuesday? Good luck. It is the reason so many commercial foundries will simply not deal with hobbiests, who tend to be unresonably naive about getting something cast. IMHO, if I were to supply working parts to the hobby, my focus would be getting the patterns to perform, and then turn it over to the everyday experts, for production. Understand that with enough refinement to your equipment, they cannot do much more than any home shop guy that mirrors industry. Think of it as a home lab, and you have final control with quality, and they cant pass off bad shrinks, or porosity, from slipping practice, or the attitude that 'its only a hobby guy'. There are pitfalls, in an imperfect world. I take the quality enhancement, making modifications right where I see it, (development) as the core of what I need, and my hands on direction. ( Am I King in my world? um, more like Emporer).

Ugh! When I say a 10% addition of zinc, that is a Swag on many times melted brass. This is where I am relying on color of the bar revert, as loss of the zinc will darken the alloy as more copper becomes evident. Go to the book table and see that #44 compostion has but .5% pb, and any adjustments are to bring the copper down to master levels of 83-87%. Zinc is 14-17%. That is why I have a sample board that is polished for brass, and can compare visually while I work to tighten my scrappy standard. Its why pouring a button underwater, can give me a great read on what you have.

Now I have to throw out there, I have been talking about BRASS. When we add Tin, now we have bronze, and that entails a list of diferent metals in the alloys and require controls to keep the alloys true in compostion, to match the tasks demanded. Gunmetal is a bronze used for bushings on copper boilers, and is good for many heated parts, because of its strength, and ability to silver solder well. #63 is the general utility alloy, Cu 86-89%, Sn 9-11%, Zn 0.25%, Pb 1 - 2.5%, Phos 0.25. At 30Kpsi it is strong, and willl not shed zinc and weaken at threads, because there isnt any to speak of.

Now that I floated one in the punch bowl, you can see why a pro using bar metal is the way to go for consistancy in the technical world. I have no way at all, to truly assay my feed stock or what I create in the crucible, which is always the major caviat for the home guy. This is why I say to measure everything by weight, and explore the tables for close alloys and their properties, to educate my guess for where I want to be. ( There is reported to be a Star Trekky gun, like a heatgun, that scrap yards use to determine approximate metal composition for non-ferrous metals. I have no knowledge of this device)

So far, I dont make many critical parts, so a thumbs up SWAG is good for my use. Your milage will vary according to your attitude and how skilled you are at making good estimates on the technical side of building things. Thats why all this is much more than just making lead soldiers in a mold. Weren't those fun? Worry Warts would have a COW if those were on the market today. Remember the toothpaste in the lead tube? A lot went down the drain so I could get my new Generals in line.

I hope this helped with your questions. It is my view.

[rrnut-2]

C Pipes: I was speaking to the thermal shock of a dead cold vessel being thrown into the path of a good hot running furnace. I think it risks cracking the vessel. Myself, I prefer to 'Pilot fire' the furnace for a few minutes to warm up the brick and my empty vessel, as I believe the warming of the brick saves some deterioration of the furnace walls. My home built aluminum furnace has shed the 1/2 inch inner coating, and shows the firebricks that are the mainstay of the layed up liner. They have not changed in so many years, but I dont push them hard until the blower, and gas valve are opend fully. A few minutes warm the furnace and my vessel, and then I charge the cold scrap by tongs, (ok I cheat and toss in small parts.. and miss once in a while) but never spalsh if I add when the heat starts to lower level by melting down. (my home made aluminum furnace is actually Propane and responds across a range of gas settings, and is unblown. It will not run up to brass temperatures, as the oriface for the double venturi burner will not admit enough gas for the BTU load.)

Even in the foundry that I worked in, the induction furnaces were heated very slowly (idled at 30kw) for about 1 - 2 hours before going to full power 250kw. Full power on a cold furnace was looking for disaster. The furnace would fail once the melt was molten with metal going everywhere.

Jim B

[steamin10]

Um , we are talking apple to oranges here, as it should be obvious that my furnace walls only one brick thick, will heat faster than something with almost two feet of monolithic refractory. My brick will move at the seams, a monolith will virtually explode at the hot surface. Cracks in linings are ineveitable, but forced deterioration is just dumb. Still a little time to heat things within reason I believe to be a benefit. Crucibles are expensive, and losing one to shock or a floor drop is tragic to me, but not world ending, having dropped one because I used some offset pliers to pick it up. Ya cant fix stupid, and is one of the reasons I am adament about certain things. If there is a way to ork things up and run it in the ditch, I probabaly have the map to show where I did it. Learn, adapt, overcome. The more you know, the less mistakes you will make. Adapt proven knowledge, and shorten the learning curve. Dont try to reinvent the wheel if you dont have to, casting has been done for thousands of years. It should be near brainless to those that watch Star Trek, (Or was it McGyver?) We have so many advantages.

[Pipescs]

Short deviation on another subject.

Crucibles:

When I started out I was a total beginner and still have much to learn.

In my early attempts to get the Artful Bodgers Waste Oil Furnace running I purchased a set of Crucibles from the Budget Casting Supply on line.

Now that I am looking back at their site I see I may be using something that is not meant to be.

I purchased 3 A-8 Crucibles. They are listed as Part# 5082 Size A8 Type Clay Shape A Price $35.50

http://www.budgetcastingsupply.com/Crucibles.php

Looking at their site I now see all the others are listed as Graphite-Clay. These were just Clay.

Is this ok to use at Brass and Bronze melting heat or am I living on the edge?

[Harold_V]

I have considerable experience with clay melting devices, as I used clay dishes for torch melting small amounts of gold and silver.
Clay, as well as clay/graphite, is sensitive to moisture. Rapid heating of such a vessel when it has not been properly seasoned will generally result in a cracked vessel. One is advised to heat them slowly, so any moisture contained within can evaporate slowly.

It's not clear to me that the crucible in question is just clay. If it has a gray color, or even black, it's my opinion that it is most likely graphite/clay. It is less expensive than a bilge type because it's easier to make, although it may well also contain less than desirable material in its making. I can't say, as I don't know that to be the case.

If you hope to use the safest crucible, buy a silicon carbide. They don't suffer from fracturing by moisture the way graphite/clay types do. They cost more, but if handled with care, they may be worth the extra cost.

Avoid fluxing when you have that option. Flux is always hard on a melting vessel, as well as the furnace. Because it was necessary to flux recovered silver (in the refining process), I got only eight heats per crucible before there was damage beyond reason. The crucible, below the metal line, would be in perfect condition, while the walls above the metal line were virtually gone---removed by the required flux (borax). I'd stop using them when they'd spring a hole in the side. I went through a lot of #8 crucibles!

Harold

[steamin10]

Thanks for the notables Harold, as all my crucbles are bilge style and silicon carbide. Other than the dropped disaster from my stupid handling, I have not worn one out yet, altho there is significant thinning to several, ( I have 6 of varying sizes, 2 each for Al, Brass, Bronze, as I dont mix metals).

I had two clay graphite, that were used and abused, and they got me started, but failed in wall thickness rather early. I had a 2 gallon cast iron cookpot that I abandoned early, as I found that Aluminum was being destroyed chmically by the iron of the pot. After working hard all day melting cans and storm windows, I did not get a single cast of truck frames. When the 100lb propane tank ran out of pressure I pigged a blobby mass of stuff that resembled aluminum, but would not even move unless you mashed it with something. That set about learning that the iron in the pot dissolved into the aluminum and ruined the fluidity, along with the loss of crucial Silicon, essential for detail. Between the two, I was dead meat, the metal would not fill the mold or conform to minor details, so it was misrun and partials, all the day long. (Thats what I call being lost in the woods!) It took me a while to believe in the facts I read, ( I can do anything so why dont it work like in the book?) And a real crucible, made all the diference without a heat failure in the next handfull of sessions. Ok, stop beating me, I learned, somebody has already done this.

I wish I had more history to share. Taxes, kids, jobs, and life get in the way of this stuff. I only have 40 hrs a day. (REALLY?)

[Harold_V]

On the subject of borax---a necessary evil for the non-ferrous foundry.

In refining, I used borax for various operations, and came to understand that one size does not fit all.

Borax is available in several states of condition. The five and ten mole borax contain considerable water (although it appears to be dry), and is fluffy and hard to melt as a result. It is easily blown from the container in which it is placed, and froths up upon melting.

By sharp contrast, anhydrous borax is a more solid material, much heavier, and melts without issue, to a tranquil covering. For the ultimate condition, one can procure borax glass, which is borax that has been melted. It is clear of color, although it appears white. Either of the two (glass or anhydrous) offer acceptable performance in a furnace, whereas the five and ten mole tend to be troublesome. That would include laundry grade borax. Avoid them if at all possible.

There's a lot more to be learned in regards to fluxing. Thick flux can be thinned by the addition of fluorspar. Soda ash, too, can be added, but I would advise against either of them unless there is a distinct need, as they are extremely hard on crucibles.

What some folks tend to ignore is the fact that molten metals are strong solvents of other metals. That fact is used to advantage in assaying, whereby litharge (lead oxide) is used to oxidize samples, then the resulting lead absorbs (collects) traces of values in the specimen, which it does by dissolution. It does so even though it may be well below the melting point of these elements.

I made mention because it's well known that melting aluminum in an unprotected (refractory lined) iron vessel is an open invitation to problems, as you discovered. Compound that with the fact that you melted aluminum that is known to be low, or lacking, in silicon, your failures were ensured. The good news is, you now know that in ways that others do not. Failures are often better teachers than success.

Harold

[steamin10]

Indeed a failure is only one way it doesnt work, so what does? It is part of the process.

In brass founding, glass over a small amount of flux does wonders in not aging the crucibal. While the glass can be a stringy mess, and I am told borosilicate glass is better, It serves well to conserve the brass without heavy aging of the crucible. It just leaves a bit of ring where it sat. The borosilicate glass (firehole covers) is softer and less demanding, as beer bottle glass is thick and sticky for a cover. It sure is cheep tho, and lessons the need for flux to reduce oxygen exposure, and zinc loss.

[rrnut-2]

Um , we are talking apple to oranges here, as it should be obvious that my furnace walls only one brick thick, will heat faster than something with almost two feet of monolithic refractory. My brick will move at the seams, a monolith will virtually explode at the hot surface. Cracks in linings are ineveitable, but forced .

No, these linings are about two inches thick and in some cases, the crucibles are ceramic pots that are about 1" thick.

Jim B

[steamin10]

OK, I probably have not seen that style of furnace. Still thermal shock is the issue best avoided.

Hi-cycle or frequency induction furnaces are prefered now because of the properties and 'activating' the metal in the vessel by the magnetic currents imposed. (self stiring)

[RCW]

Hi-cycle or frequency induction furnaces are prefered now because of the properties and 'activating' the metal in the vessel by the magnetic currents imposed. (self stiring)

Anyone got a picture of the above furnaces? Or a free sample ;-}