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Things they dont tell ya when you start casting. :)

Posted: Sun May 20, 2018 1:14 am
by Lazz
Being a noob at casting Im sure I missed sources of information. Youtube and google have answers... but ya gotta know which questions to ask before some answers mean anything....
But the next guy can ready this here and maybe find a few answers for some of the questions I didnt know to ask until I tried to cast ...

PLEASE if the people who cast often or well have suggestions I will gladly listen...

1) How much sand should I start with?

This stuff isnt cheap. I looked and found a guy selling 35 pounds for $59 with free shipping. How much area does 35 pounds cover....
The 35 pounds fills a large flat rate box. .46 of a cubic foot. The seller was fast to ship and as noob I was happy with his product.
My starting project is a flat plate 9" x 5 1/2" with 1" tall bumps. So I built a flask a 12" X 9" x 6" plenty of sand with 35 pounds but the sprue and riser were rather close to the edges...

2) Is a steel crucible a good option for aluminum?

Speaking with the experience of 5 times firing up the furnace I can say it only leaked 3 of the 5 times....
I got the furnace at an estate sale with a steel crucible and a few other tools for nearly nothing.... I have no idea how many times the previous owner used this stuff... it may have been used for years...

3) How much should you panic when the crucible leaks and covers the floor of the furnace with molten metal?

Panic level low..... Aluminum doesnt stick to concrete products very well... If does creep into voids that make things hard to remove when the aluminum solidifies...
My 3 leaks were different.
The first I noticed the crucible had been fuller.... As the aluminum level lowered I got the ideal something was wrong...That time I pulled the burner and dumped the furnace. The next leak got noticed when I pulled the crucible to pour muffins... The third time I poked the hole for the leak while mining for dross.
When I had some molten aluminum on the floor of the furnace I just left my 3 foot long 5/16 dowel in the pool and pulled it and the aluminum out the next day after things cooled off.

4) What is that stuff floating on the molten aluminum?

Dross is a good name for nasty floating junk. When scooping dross out of the crucible go all the way to the bottom now and then. My second cast attempt failed cause the top of the crucible was nice clean aluminium and the bottom half was dross...

A good tip for dross is, flux will make it easy to remove.... I used table salt and lite salt. My experience says it helps to flux with salts, but not which is better or in what volumes.
Experts feel free to chime in here.

5) How soon can the petrobond sand be reused?

As a noob I shook out the first casting attempt and saw a couple things I wanted to improve on... I learned the burnt sand isnt good against the pattern. It will not stay in place very well... it needs some sort of processing.
Sand holds the heat... A long time... That stuff was hot. Having pulled the cast aluminum and laid it on top of the sand the casting cooled faster than the sand.

6) How is petrobond like a trip to the beach?

In minutes there is sand everywhere.

Feel free to add to this...

Re: Things they dont tell ya when you start casting. :)

Posted: Sun May 20, 2018 1:53 am
by Harold_V
While I have a keen interest in foundry work, my casting experiences have been limited to pouring precious metals (primarily silver and gold).
That said, the reason I made mention of precious metals is that if there's one thing I learned from refining, it's that molten metals are fierce solvents of other metals. Give that some thought as you consider the use of a steel "crucible". Just as sugar dissolves in water, metals dissolve in molten metals, even when the temperature of the molten metal is well below the melting point of the one which has not melted. That's the reason why solder from wave soldering machines must be changed ----it gets "contaminated" with gold and, possibly, silver. That's what happens with your aluminum and steel ---and why your vessel sprung a leak. Buy a proper crucible. They're not all that expensive when you consider the huge number of heats you can get from one when melting aluminum.

If you prefer to use one made of steel, line it with a refractory. Washes are available that coat the surface so there's not intimate contact of the molten aluminum with the housing in which it's melted. That prevents the aluminum from being contaminated with iron, which destroys the properties of the material you wish to cast.

There's likely to be a few who chime in and suggest that they melt aluminum in steel all the time. Yeah, it works. Never said it didn't, but it's a serious compromise as it destroys the properties of aluminum. It's not for me to say that they're doing something wrong, for I have no idea what they expect from their endeavors.

Steamin10 has experience in this arena. With a little luck, he'll see this thread and add his comments.


Re: Things they dont tell ya when you start casting. :)

Posted: Sun May 20, 2018 2:57 am
by choprboy
Lazz wrote:
Sun May 20, 2018 1:14 am
2) Is a steel crucible a good option for aluminum?
No... Lots of people use it, but unless you need to do something special/oversize/etc., I wouldn't use one repeatedly. Iron actively dissolves in aluminum, meaning you contaminate the charge and erode away the crucible. Additionally, the steel exterior will flake in the foundry.
4) What is that stuff floating on the molten aluminum?
Dross is it. I have heard table salt works OK, but I haven't used it. I far prefer real aluminum drossing flux, something like Asbury #770 which has a mixture of salts including sodium chloride (table salt, NaCl), potassium chloride (KCl), and sodium fluorosilicate (Na2SiF6). Place a charge of flux into a small paper packet, place the packet on the end of a rod (wire clipped or cupped end), and plunge it to the bottom of the crucible. The dross quickly changes into a dry ash that floats to the surface with very little residual aluminum, easy to skim off.

Re: Things they dont tell ya when you start casting. :)

Posted: Sun May 20, 2018 3:29 am
by steamin10
First off, there is nothing safe about casting or any of its attributes. High heat, explosive fuel gas, molten metals, poison gasses and heavy metal poisoning. It is a venture not to be taken lightly. Like any other activity, steps can be taken to minimize the risks, and use uncommon sense to limit exposure to danger. So, if you are willing to take that tiger by the tail, and fire up the equipment, then please read on.

I cant add much to the truth of the matter of contamination by iron/steel in aluminum. Clean scrap ina crucible is the best start on the road to success. The more paint, oil and crud added, well, garbage in, garbage out. Like melting pop cans for the metal, is a waste of resources. Way too much plastic (the spray in liner) and paint for the pitance of metal involved. The best material for casting is what was a casting before. Extrusions have trace metals that do not work for you. The handy BBQ grill the neighbor threw out is not the best either, it being a high zinc content, for die casting. There are something like 1100 commercial grades of aluminum alloy, and about 150 are most common to our use. Recycle aluminum bar is what most foundries use, and keep a small supply of additions to get where they want in the material. Silicon is one such addition that strengthens aluminum and makes it fluid for detail casting. Iron has the property of making aluminum pasty to the point it wont even flow becoming a blob in the vessel. Iron cannot be removed, it would have to be reprocessed in an arc furnace. Dross and cleaning of aluminum is tricky, most use HTH or similar pool tablets broken up into a fine grains and a tablespoon or so swished into the melt brings out oxides and junk. Chlorine is the active ingredient, and that is dangerous for your lungs.

While it is fun to think you are recycling metal into something useful, the quality of the metal must be there to start with, and any errors in handling and thinking will reduce your success accordingly. When you get brave enough the idea of casting brass or bronze will come across your bench. It is a whole nother ball game as it works different, and gets gassy, or casts zinc fume that will make you ill beyond belief if you are unaware.

Having been down this road with all the failures and getting lost in the woods, I recommend METAL CASTING, by C. W . Amen. It will take you past the basics and prevent you from making all the dumb mistakes that a noob is prone to make and lesson the pain of failure.

Casting metals is basic to repair and construction,, and has been for millennia. Since it is well known, you can apply that knowledge at most any level you chose.The trick is to have a feeling for what works, and what does not. Dont try to re-invent the wheel, read and follow the path and lore of casting and you can do many things that will amaze even you.

Re: Things they dont tell ya when you start casting. :)

Posted: Sun May 20, 2018 10:11 am
by NP317
As part of teaching Manufacturing Process at the Univ. of Washington, Seattle, WA, I taught simple aluminum casting foundry processes to our Mechanical Engineering students.
We were fortunate to have an induction furnace. Safer for such teaching, 'cause no open flames.

I always used a refractory-lined crucible.
I always poured the metals into the sand/flasks on a bed of sand (a large floor-level "sand box"), NEVER on concrete, which can explode from vaporizing the water in the surface.
In 11 years of casting in front of students, we never had a crucible leak, or exploding metal!
Yes, some flasks leaked at the joint due to improper production, but no harm done.
My take.

Re: Things they dont tell ya when you start casting. :)

Posted: Sun May 20, 2018 11:25 pm
by steamin10
Sand:I have tried to make contact with the marketer mentioned and he did not reply to me. He is literally in my back yard but a few miles South of me, perfect forsaving shipping charges, and alrger quantities of material. No answer, Dead end. I cannot force a reply. Sooo...

There is a formulae put out by a university that copies Petrobond. Starting with clean filter sand for a swim pool, synthetic outboard oil is added with a bit of Isopropol rubbing alcahol to make it sticky, and the mess is first flipped by shovel on the floor, and then walked on, to squish it past itself, and rolled again with a shovel until smooth. The red color comes from the clay/red oxide added to keep brass from skinning into the cavity. One of my experiences was to cast a perfect pour of the shape of the pocket with the bronze surrounding the void. Quite surprising and useless. Dont be in too much of a hurry when you cast anything. Aluminum can be mush for a period of time and your enthusiasm in pulling a hot part can effect the grains structure of the metal and actually bend a too hot casting out of shape. Thin sections can warp easily or crack with low hot strength. Brass is notorious for being hot short, and thumping a hot piece on the floor can easily destroy it. Bronzes are much tougher, and contain no zinc. Either one can be gassy by the nature of the copper that is the base metal. Copper and silver oxidize quite redily and are a problem if not handled correctly. Pouring pure copper takes special techniques for success, but you should not have the need, as brass compounds are more forgiving.

If the sand is tooo hot, spread it out, and let the air circulate. If it is smoking, keep it piled, till it stops, then cool it off. Dont addd water or anything until it is cool enough to be bath warm, then mix/ mull /stomp it, to work the grains again. Petro will respond to an oz of alky if it loses it tack. A fist ball should have some strength to avoid crumbling, and should lump when packed. Baby powder is all that is needed for parting and mold release. A slick painted pattern will benefit from some automotive paste wax, and then lightly dusted. If pouring heavy brass some weights on the cope will keep it from floating with the metal pushing up. I use junk rotors from autos for this purpose. and they can be tossed outside to the elements without worry. They are scrap.

A screen box with 1/4 inch hardware cloth is good enough to remove bits and junk, and refine the sand down into uniform texture. Working about 1/3 of your used volume each time will keep you with fine sand for facing the pattern, and the floor sand being the backup/filler to speed the job. Dont waste time on being too perfect, it is the end result we need. I hope this basic primer is a help to organizing your mind in the process that will shorten the learning curve.

Re: Things they dont tell ya when you start casting. :)

Posted: Mon May 21, 2018 9:27 am
by Lazz
1/4 hardware cloth, the window screen I tried wasnt real effective....... There will be one of those for the next attempt.
Thank you...

Re: Things they dont tell ya when you start casting. :)

Posted: Mon May 21, 2018 9:32 pm
by steamin10
Window screen is too fine, as you have seen. The traditional riddle, is like a round hatbox, and is shaken and thumped with the palm in operation for hand work. It will sift enough fines onto the pattern to tighten the surface when it is rammed up. A simple box of 1x4 with a screened bottom is ample for most needs. A hand made rammer with a point on one end and a blocky flat end on the other is used to gently tamp the sands around your pattern. Over fill the cope and drag by several inches and ram it down. when you have compacted the mold, I use a small length of angle iron to screed off the excess and roll or cut in the gates and spouts. Before pulling the mold, use a coat hanger to run a few air vents into the rammed up mold and then strip. This is all basic, and pardon me if I am singing to the choir, but as they say, the devil is in the details. Further surface smoothness can be achieved if you mix some alcohol and pure graphite into a wash and spray a bit on your open mold. It is then set afire to flash off and close the mold. This is standard for iron casting and gives a finer finish, petro has shown me my fingerprints on the surface of castings at times and needs no wash for the most part, the reproduction is so good in detail. Casting in petrobond is the cheepest, most sure and accurate way to get fine detail, without resorting to waxes and hard molds.

Use a commercial crucible. Buy one for each type of metal, and dont cross them. Buy a pouring shank and use it. Handling a hot vessel with plyers by the edge is asking for disaster. The vessels when at high heat are spooky soft , like rubber and are damaged easily with rough handling. I pour over a sheet of 3/4 inch plywood. Any spills just smoke and cool out. Pig molds of a cast iron material, like a muffin pan, or corn bread form, is handy to pig your excess material into, or just some finger bars in some casting sand. I have some box molds of channel iron that make a small brick. DONT LET THEM RUST. They will blow when molten aluminum is run in. So wear a ball cap at minimum, if you do get a pop, it doesnt mess up your hair. Ask me how I know about concrete blows too. Who says casting is boring?

Re: Things they dont tell ya when you start casting. :)

Posted: Sat Jun 09, 2018 11:47 am
by Michael_Moore
There are lots of good books on foundry practice, if you want to go in serious depth get a copy of Campbell's "Complete Casting Handbook". He's the inventor of the Cosworth casting process.

A friend and I have done a bit of foundry work with aluminum. The parts have been more complicated, like the air-cooled cylinder for his two stroke single vintage race bike that took about 200 hours of pattern making time on his part.

We decided that doing foundry projects was going to be a lot less aggro if we bought supplies from a local foundry supply company. This means ingots of A356, real foundry chemicals/binders/sands/filters/safety gear etc. Sure you can use kitty litter and table salt and old motor oil and drink cans as ingredients, but our goal was to get some good castings that were of a quality to be used on a race bike. Why mess around with "maybe this will work, maybe it won't" stuff that might see all your efforts come to naught?

You may be casting in your back yard, but that doesn't mean you can't work like a professional, and maybe have a better chance of getting professional results.

If you just want to play with fire/molten metal on the cheap, then do the cheap stuff. If your goal is to make usable parts consider spending a bit more money, and maybe making it easier to get those parts.


Re: Things they dont tell ya when you start casting. :)

Posted: Tue Jul 03, 2018 1:47 pm
by Lazz
Since Im in my 60's playing with fire and molten metal is low on my wanna do list.... right next to hemorrhoids.... The last thing I need in my life is a mishap with fire for the wife to worry or complain about.

I do want to have the ability to replace missing or broken machine parts.
Amazon provided a couple crucibles and a thermometer , ebay offered up the petrobond.
And my dont throw it away past means I have a small collection of broken cast aluminum parts.

Dont forget Im in Phoenix... it can be called warm here this time of year.Casting has taken a back seat to the things that keep me in the cool...

At the moment the ratio is 7 fails and 4 successes.
6 of the fails are for the same item.... Im thinkin it may have been injected... its about 1/8" thick 5" X 7" with folds on the edges. I cant seem to get the metal to flow to all the edges. Maybe with more experience.

Having failed 6 times in a row I went with a totally different project. I tried a lost foam casting for a larger item.... and promptly found an error in my volume math... :) Making it 7 fails in a row!

The last 4 casting all went well.
The corrected volume lost foam casting went better than I ever expected.
Next a couple couplings came out great.

My latest castings are for hand wheels. I did a count and found a need for at least 6 more. That means I should do at least 12 . Yesterday I bought some oven bake clay to help with the irregular parting line.

Right now Im wondering if I should postpone continuing the handwheel project until I find the time to construct a proper molding bench. Now as I look in my work area I see little dribbles of sand every where. So ramming up on top of the table saw, doing a shake out in a wheel barrow. All those tasks spread small piles of sand. Im thinkin a bench with sand storage and with a nice adjustable rack on top to ram up stuff and shake out . That would also fix the problem about over filling the flask while ramming up.

I would like to thank everyone for the responses and suggestions.......

As I live my retirement I wonder how did I have time to do anything when I worked?

Re: Things they dont tell ya when you start casting. :)

Posted: Tue Jul 03, 2018 4:48 pm
by Harold_V
Lazz wrote:
Tue Jul 03, 2018 1:47 pm
As I live my retirement I wonder how did I have time to do anything when I worked?
For me, the answer is simple. I didn't do anything but work (I was self employed). My interests pretty much sat on the back burner.
I've been retired for 24 years now, and I still am not caught up with my projects.

I'm happy to report the above. It is my opinion that a retired guy must have a reason to get out of bed. I've known a few who retired at age 65, only to die shortly thereafter. In most of those cases, death came to those with little to no interests outside of their jobs.


Re: Things they dont tell ya when you start casting. :)

Posted: Tue Jul 03, 2018 7:00 pm
by 10KPete
Lazz, you might like the moulding bench Mr.Pete made: