Why I cast my own models

[Metal Mickey]

Very impressed. I hope to build a furnace next year. Just need to find the refractory clay in the UK. Any sources welcome.......

Mike

 

[cfellows]

All

Here are some pictures of some of my casting and finished models.

Gearsguy

Gearsguy,

Are those aluminum castings or Zinc/Aluminum alloy? Just wondered if you have trouble with the aluminum flywheels being too light in weight? I've used an alloy of Zinc/Aluminum which is almost as heavy as cast iron and actually melts at a lower temperature than straight aluminum. It also machines very nicely and is very strong.

Chuck

 

[Gearsguy]

The castings are from scrap aluminum. The flywheels are quite adequate. If you look close you will see they are quite thick and have more than enough mass to run nicely. They are about 7" diameter and with only a 1" bore and only moderate compression I have no problems getting the engines running.

I did get a couple of sets made in cast iron but I haven't tried them yet. I hate turning cast iron because of the grit. Gets all over everything including me.

 

[jack404]

G'day Gearsguy

got some questions for you if thats ok?

scrap Alu do you mean alu cans? offcuts mixed or all the same??

what temps do you get them to pour ?

do you flux them or add stuff to seperate the junk ( slagging out)

do you heat the moulds?

dont want you to give away trade secrets but i cast a lot of things mainly lead for deep sea fishermen at the moment but Brass Bronze Iron but Alu i've always been told needs high voltage electricity to get structural builds ( correct crystalisation or whatever)

cheers eh

jack

 

[tel]

Yo Jack, if you want my opinion, avoid cans and extrusions like the plague - old auto heads, pistons, manifolds and even wheels are a much beter bet.

 

[Bluechip]

Hi

Tel is absolutely right. My old mate Stu., long departed, made a lot of castings in alum. and bronze/brass.

He always said if the material was cast in the first place, it would cast again. Not always so with redundant bar stock.

He had some white powder stuff he put in to improve the fluidity of the melt, but I don't remember what it was.

Dave.

 

[jack404]

i dont doubt it

but looking online does not show much but ad's for very expencive setups or business's that will do it for you

i also doubt i'll be casting anything Alu for a while thanks to my situation, when i get back to Adelaide sure,

but thats a ways off yet

but hows too is always good to have .. ya never know..

cheers folks

jack

 

[ksouers]

Jack,
I'm certainly no expert on casting aluminum but I did try some a few years ago. I did learn a few things. I melted cans and some bits of extrusions I had laying about. Also saved my chips and threw them in the mix.

Cans have almost as much slag as metal. It's all the ink/paint/varnish, whatever was in the can. It can really be tough to get rid of it, I usually ended up going through a couple refining processes to get rid of it. I'd do a melt and skim out as much slag as I could then pour into ingots. I used steel crucibles so a lot of slag end up sticking to it, as well. After a while I'd end up with a hot spot that would burn through, one time completely filling the bottom of my furnace and clogging up the jet.

When I'd melt with ingots I used a clean crucible used only for ingots. I'd still have to skim slag but not as much. After skimming I'd dip the rod in borax while it was still hot and stir the melt with it. The borax helped bring out more of the slag.

As for the castings, nothing I did came out usable. Everything had bubbles in it. I found out later that there are some tablets you can get that will remove the nitrogen and thus the bubbles.

I'd like to build another furnace and give it another go. Maybe try some bronze this time, too.

 

[Gearsguy]

Jack,

I agree with Tel, avoid cans and small bits and pieces as they produce a lot of slag. I use the thickest hunks of alu I can get. Never, never use the chips from turning or milling. Pure slag. Pistons work well as does hunks of flat and bar stock. I got fortunate a few years ago and picked up a hundred pounds of ends from a shop that produces shells for telescopic gunsights. The pieces are about 3 inches around with a 1" hole in the center and about 3-4 inches long. Fit just perfect in my 4" crucible. I usually put in one of those and then the spru from earlier melts plus other smaller scraps to fill my crucible about 3/4 full when melted. This gunsight metal when melted alone produces almost no dross. Pours and machines like a dream. Unfortunately I am almost out and not sure I can get more. I got this back when alu sold for 50 cents a pound.

I use no flux. Just melt and pour. I melt at about 1400f. That is a guess but probably not too far off. I judge how ready it is to pour by how clean my stir rod comes up from the melt. After I remove the crucible from the kiln I use a small cast iron spoon to remove any slag then pour. I keep two steel ingot molds ready to dump any left over metal. I always heat the molds and spoon by placing them near the exhaust hole to make sure they are completely dry. I also always preheat additional alu pieces that go into the pot during the melting process.

I would warn you to be very cautious about where you get scrap. Once I picked up some nice looking scrap from a motorcycle junk yard. Aluminum pieces they had separated for sending to the recycler. When I melted some of this I noticed some odd dark grey granuales form on top. I guessed that this was magnesium and knew it was a bad thing. I removed the pot and scraped this stuff off the top and dumped it in my usual spot for dross. It almost immediately lit up and burned white hot. I stepped back and away and a few seconds later it exploded and showered the spot where I had been with nasty white hot burning sparks. Not a good thing. I later figured out that this stuff had melted as it burned and flowed down to a spot where some water had accumulated and the explosion was from steam. Anyway just be careful. I always wear a hat, face shield, welders golves and heavy clothing, boots etc.

Before I got the good stuff I would often melt and pour ingots that then were used to melt for castings. This helped clean up the pour. I also found that you need to use at about 50% new metal in each melt. When I use all sprue that has been recast several times the castings become gritty and don't machine very well. I don't use a lot of extusions like window frames because they seem to create a lot of slag too. It depends how desperate I am for scrap.

Hope this answers some of your questions.

 

[jack404]

Now thats good info

cheers for that!!

printed out and put away for when i get to do it

thank you very much

jack

 

[tel]

Not only do cans and extrusions create excessive slag, they also have a much higher shrinkage rate, you need pretty hefty sprues, gates and risers to try and overcome that.

 

[Gearsguy]

Jack,

One other note. You mentioned you had been told it requires a lot of electricity to do Alu. Not so. All my melting is done using propane. Same stuff you use to BBQ. Fairly cheap and readily available. I get about 7-8 melts from a 10 gallon bottle of propane. Even commercial foundries here dont use electricity. Most use natural gas.

 

[jack404]

Cheers Gearsguy

i was meaning passing a electrical current through the molten Alu to "do something" that makes it work better or more stable or whatever

i'll be using a LPG rig i use here for a reference the outer ring burner is 16" in Dia.

i have a F52 grade crucible ( rated for 3600 deg F) that holds 32 liters of water so dont have worries that way

for lead and bronze i only use the 3 inner burners but for steel i use the fourth outer ring as well

but thanks anyway

cheers

jack

 

[tel]

Coupla pool shock tablets in the melt work as well as anything.

 

[jack404]

tel

sorry mate i dunno anything about pools

a shock tab to me is about 2" of 60/40 powergel and a number 6 safety det in the end

chuck it in a deep spot in the river and bobs your uncle

fresh trout

is a shock tablet chlorine? if so, is that wise?? chlorine is nasty stuff

need to edumacate me mate

i'm like a computer, info is best punched into me

cheers

jack

 

[tel]

;D Wrong shock tab mate!

Yep, the chlorine tabs, primary purpose is to degass the melt. What you do is break a couple up and wrap 'em in a twist of al. cooking foil - you need a little do-hickey like a short bit of pipe, with 'oles drilled into it, welded to a (say) 1/4" or so dia rod. Pop the 'bomb' in the pipe bit, plunge it to the bottom of the melt and swizzle it around for a few seconds. DO NOT stick yer 'ead over the crucible while you are doing this, nor do you use it as the basis of and breathing apparatus.

 

[xlchainsaw]

ive just come back to this forum and since i last visited the casting subject sure has taken hold. ive been busy on another forum (sorry guys) with metal casting. thought i would post a link.http://www.metalcastingzone.com/metal-casting-forum/brass-casting/molding-my-brass-flywheel-4. it seems metal casters are everywhere!

 

[T70MkIII]

I've just found this thread too. If anyone wants to build a really cheap foundry to see if they can cast (you can!) or just to do a few bits and pieces, you can do what I did.

I bought a large teracotta flowerpot and drilled a hole near the bottom of it to take 1m of 38mm steel tube for the tuyer (air blast pipe), which I angled to the side so the air would swirl around the bottom of the pot. The air came from an airless paint sprayer, but you could just about anyting handy. My first runs were with an old hairdryer. I fired it with BBQ coals and firelighters, and turned on the air 'blast' once the coals were well lit and starting to glow.

I made a crucible from a piece of 8" OD steel pipe with a welded on bottom and pouring V, with 1/4" steel bent and welded around the outside of top. I made up some scissor like tongs to grip onto the crucible under the 1/4" lip.

My first melt was a couple of pounds of pistons and soda cans, which melted beautifully within about 20mins. Yes, there was some dross, put I pulled this out with a steel rod / stiring stick. I did about 5 good pours from this foundry before the pot (which was bedded into some sand) cracked apart too much to continue to use. I'll just buy and drill a new pot when I'm ready to do some more casting.

Caution: be very respectful of molten aluminium, and have a sandbox around your foundry large enough so it can never get onto concrete (wet or dry). The water bonded into the concrete will instantly vapourise, sending chunks into the air with explosive force. How do I know? I used a ss pot as my first crucible, which pinholed causing all of my aluminium to run into the pot and down the tuyer. Of course, this catastrophically damaged the hair dryer I was using for the air, as well as the concrete. If your tuyer angles downward, you can join a near vertical pipe to it to supply the air, and just tape over the other end of the tuyer so the blast goes into the pot. The advantage of a tilted tuyer that if you get a spill in your foundry, the al will run out rather than ruining it. Not really an advantage for the easily replaceable flowerpot type foundry, however.

Gingery's "Backyard Foundry" is a great primer on building a more proper foundry than the one I describe above, and I highly recommend it. Of course, as mentioned above, there is lots of great information on the www.

 

[Bernd]

For those of you interested in home foundry techniques you might want to visit this sight if you haven't already run a cross it.

http://www.backyardmetalcasting.com/index.html

He's done a lot of experimenting.

Bernd

 

[Peralta]

It is nice to hear that you are now doing for real your old dream of learning how to cast. I guess you are sorry for the lost years why you haven't brave to learn them earlier. Well, that is life, it is better to be late than never. You can also try molding plastics that would be an improvement. Injection Molding Indiana