Entry Level Casting.

Home enthusiasts discuss their Foundry & Casting work.

Moderator: Harold_V

User avatar
steamin10
Posts: 6712
Joined: Sun Jun 08, 2003 11:52 pm
Location: NW Indiana. Close to Lake Michigan S. tip

Re: Entry Level Casting.

Post by steamin10 » Fri Jan 10, 2014 8:58 pm

I wont tell you to forget shell molding, but it is a bit more complicated than natural green sand or Oil sands for molding on pattern boards. For working in brass and aluminum, I would advise you to move straight for Oil sands, as they are completly recyclable, and can be used for a very long time before needing freshening up. There are at least two home brew oil sand formulae on the web, that was created by the University of Colorado, if I remember right. I bought the components for Petrobond, at a supply house in Chicago, where I just drove in and hauled out my sand.

Again, read and get a feel for what is needed, at bare minimum, before you spend dollar one. You can make it expensive, but really much of it can be had nearly free. Starting with 200lbs of beach sand, and getting the oil and Alchahol mixed up in half of it is a good first step. Lead and aluminum cna get you started rather quickly on making stuff. Flasks built of wood, and bolts for pins are easy to make, so you see, you can create your own fairly well. I have professional steel flasks, and equipment, but they were bought at auctions for pennies on the dollar.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

Harold_V
Posts: 17597
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Entry Level Casting.

Post by Harold_V » Fri Jan 10, 2014 11:53 pm

I'm with Big Dave.

Shell molding is an excellent method to cast, but it requires supplies that don't lend themselves well to not being used constantly. There's also the issue of having to make a mold to create the required waxes, which, in turn, must be burned out, so in the long haul, unless you intend to cast on a continuing basis, oil tempered sand is really the best possible choice so long as you limit your castings to non-ferrous (melting iron is difficult with a crucible furnace, and impossible with steel).

Back to the issue of waxes, an injector would be required, plus a dewaxing device, as well as a burnout oven. Again, a great way to make precision castings, but very equipment intensive.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

jkimberln
Posts: 85
Joined: Sat Dec 05, 2009 10:32 am
Location: Richmond, California

Re: Entry Level Casting.

Post by jkimberln » Sat Jan 11, 2014 9:43 pm

Harold, shell molding doesn't require wax patterns, no burnout, etc. Shell molding is where you drop a resin bound sand mix on a heated aluminum pattern, jolt it, then roll it over to empty off the uncured sand. Then the shell is removed. Two shells are placed together either in a frame backed by sand or by being clamped along the edges, if small, then poured.

It is true, though, that you need a jolt-rollover machine to do shell molding properly. It is really for production work.

My first job as foundry control chemist back in 1963 was at a shell molding foundry pouring 110 tpd white iron. While we also used green sand, shell molding was better since it supposedly guaranteed a casting accurate to 0.020". The application dictated the molding method.

JerryK

Harold_V
Posts: 17597
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Entry Level Casting.

Post by Harold_V » Sat Jan 11, 2014 11:52 pm

Thanks for the update on shell molding, Jerry. I've not seen that system, although I also have quite limited exposure to the foundry business.

The process I described was the one used by a company in Utah (where I used to reside), whereby a wax pattern was dip coated with a slurry, then coated in sand. The process was repeated until the shell was adequate to support the molten metal. After drying, the wax was then burned out, and the object cast. If there was a question about the shell's ability to support the molten metal, the shell itself was surrounded by dry foundry sand prior to pouring. I considered this a modified investment casting technique, which I assumed to have been the shell molding process, as that's all that remained after the burnout. It was a rather labor intensive process, although very precise, as you alluded.

Early in my machining career, I machined some small aluminum castings (roughly two inches by three inches), used as a chassis for electronic gear. Features were cast with .005" tolerance, which was within the limits of the process in use. Call it what you wish---this type of casting is really nice.

The process you described would be equally unfriendly for the home foundry. Much like using the furan process for sand. Some things are simply best left to industry.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
steamin10
Posts: 6712
Joined: Sun Jun 08, 2003 11:52 pm
Location: NW Indiana. Close to Lake Michigan S. tip

Re: Entry Level Casting.

Post by steamin10 » Sun Jan 12, 2014 11:24 am

HV. Your asessment of core molding is the same as mine with the wax mandrel pattern and burnout.

At Blaw knox the process of striiking Furan based sand into a heated mold and turning it out, was refered to as coremold. It was the same process for making the keyed cores for castings, but upgraded or use changed for molding more complex shapes to be attched to the mold for intricate shapes that did not mold well otherwise. Like the idler trunions for bearings near the front slope of the M-60 we produced, or the Hull ports for the torsion bars in the suspension. Many were simply 'heads' that fed critical areas to make sure that hot tears and thinning did not occur in the main castings. Two halves would be Glued with core glue, for the pocket. These were removed after shakout, and was part of the revert to the furnace. I have no doubt such a system could be used to produce other types of parts.

These were generally heavy cast aluminum placed on a heated table with two guys shovelling furan based sand into the shapes, and striking them level, and after only about a minute they were turned out on a belt, that carried them through a heater, where they slid off onto a table and then were hand stacked on pallets, being just a bit doughy but hard enough to handle. These guys could make about 200 per hour with 4 molds. The largest ones we made with this process were the ventilated armor doors on the rear of the hull. ( these were CNC milled and ate tooling with the nickle based armor castings.) all the V-shaped vents were cast in, and only the mounting edge and boltups were machined.

The problem with any such system is it gets very hungry for materials, and founding with resin sands has it own problems with recovery, burnoff, and such investment in equipment that is auxilary to productiion, only raising costs.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

jpfalt
Posts: 982
Joined: Sun Jan 05, 2003 12:55 pm

Re: Entry Level Casting.

Post by jpfalt » Sun Jan 12, 2014 1:22 pm

http://imgur.com/gallery/zr6T2

(Actually pretty good technical practices other than possible heavy metal poisoning from the hot dogs)

jpfalt
Posts: 982
Joined: Sun Jan 05, 2003 12:55 pm

Re: Entry Level Casting.

Post by jpfalt » Sun Jan 12, 2014 1:34 pm

On iron contamination:

I have used steel crucibles for melting aluminum and a very small amount of iron dissolves during the melt. One pass through the process doesn't hurt the aluminum quality, however I have been told that after about three remelts in an iron crucible will begin to affect the ductility and grain size of the casting.

I limit the amount of my own scrap and haven't seen adverse results. If you are concerned about iron contamination, commercial casters will use a wash of refractory material (such as graphite mixed with alcohol) in the crucible before melting the aluminum to limit the steel/aluminum contact.

Most of my alloy issues come from zinc in die cast aluminum. Die cast aluminum usually has between 9 and 12 percent zinc and the sand cast sections have to be limited to about 1/4 inch or the grain size in the casting gets huge and the casting becomes weak and brittle. I once poured a 6" round billet out of aluminum die castings with 9% zinc and when I cut into it, the metal grain size was nearly 1" across at the center of the slug and was useless for much more than spacers or dead weights.

drmico60
Posts: 22
Joined: Wed Oct 03, 2012 8:05 am
Location: United Kingdom
Contact:

Re: Entry Level Casting.

Post by drmico60 » Sun Jan 12, 2014 2:15 pm

It is actually quite easy and inexpensive to get into casting aluminium. I think my initial investment to build a furnace and get going was circa £20 (US$ 30). Most of my castings have been done using the lost foam technique. This is a quick and easy method for one off castings.
I have written up a few pages on casting on my website that may be of interest, see
http://mikesworkshop.weebly.com/foundry.html
Mike

wildun
Posts: 32
Joined: Fri Sep 13, 2013 7:13 pm
Location: Auckland, New Zealand.

Re: Entry Level Casting.

Post by wildun » Sun Jan 12, 2014 5:18 pm

steamin10 wrote:I wont tell you to forget shell molding, but it is a bit more complicated than natural green sand or Oil sands for molding on pattern boards. Flasks built of wood, and bolts for pins are easy to make, so you see, you can create your own fairly well. I have professional steel flasks, and equipment, but they were bought at auctions for pennies on the dollar.
STEAMIN.& Co.
I see there has been a flurry of posts since the last time I looked and (as everywhere) there is a tendancy for 'Shell Moulding' to be confused with 'Lost Wax Investment Casting', this is understandable as the lost wax casting is also (technically speaking) shell moulding.
Of course I am not totally familiar with this, but I have made a few metal (cast iron) coreboxes and patterns in the past for this and have gone to the foundry and watched the pouring procedure - I was very impressed with the process.
As someone here says it is more of a commercial scale thing than a home foundry thing - I acknowledge that and take it on board.

The process is basically as described by someone here earlier, it consists of resin sand being sprinkled by various means onto hot metal patterns (or into coreboxes), which bakes the sand to the pattern in a thin 'biscuit'. These patterns/coreboxes are of course made in two halves and when the 'biscuits' are seperated from the patterns, they can be easily reassembled minus the pattern and are then ready for the pouring. Any necessary additions such as sprues/risers/coreprints etc. could of course be designed into the patterns.
I'm told they can also be buried in loose dry sand to keep them in position and to support them during pouring.

The foundry where all this took place normally cast bathroom fittings but were also producing bronze fluid valve castings for my employers, - a very interesting time!

Getting back to the home foundry, I have a lot to learn still, but I'll get there.
I have Tubal Cain's videos to guide me with the simple oilsand method which should get me going at home - one step at a time I guess!

PS. please understand that our spelling of some words is not the same as the American spelling, bear with me! - then of course there's - biscuits? cookies? :)

Cheers,
Will.

User avatar
steamin10
Posts: 6712
Joined: Sun Jun 08, 2003 11:52 pm
Location: NW Indiana. Close to Lake Michigan S. tip

Re: Entry Level Casting.

Post by steamin10 » Sun Jan 12, 2014 6:12 pm

At risk of being in the shooting gallery here, I have to say this:

In casting speak, you have to understand that the names of 'Shell mold' and 'lost Wax investment', or simply 'investment casting', denote completely diferent processes, so the names have a meaning in themselves.

I will challenge any day of the week the idea that melting aluminum in the presence of iron is ok. It changes the metal as soon as the aluminum begins to disolve the iron into solution. It is only a matter of time before enough iron content changes the physical properties. Home guys use washes for separation, I dont know of any foundry that uses iron crucibles. They use pouring ladles of lined brick, or tilting furnaces, without any iron exposed to the melt. Bilge crucibles are sometimes used for hand pouring from a larger vessel, still no iron. A crucible is not that large an expense, to be ignored against metal quality.

I used a large dutch oven for melts for a coupla years, and learned the hard way, it just doesn't work well. I bid you peace.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

wildun
Posts: 32
Joined: Fri Sep 13, 2013 7:13 pm
Location: Auckland, New Zealand.

Re: Entry Level Casting.

Post by wildun » Sun Jan 12, 2014 11:14 pm

steamin10 wrote:At risk of being in the shooting gallery here, I have to say this:

In casting speak, you have to understand that the names of 'Shell mold' and 'lost Wax investment', or simply 'investment casting', denote completely diferent processes, so the names have a meaning in themselves.


STEAMIN,
You are not in any firing line with me!
I do agree with you there and understand these different processes (mainly in theory though).
Here, I was just referring to the fact that the one thing they have in common was a thin 'ceramic shell' which breaks down when heated and burnt out by the molten metal. Only one of them is called 'shell moulding' - ie the one with the permanent re-usable metal patterns and coreboxes.

As for the other stuff, you are most probably correct.

Cheers,
Will.

User avatar
steamin10
Posts: 6712
Joined: Sun Jun 08, 2003 11:52 pm
Location: NW Indiana. Close to Lake Michigan S. tip

Re: Entry Level Casting.

Post by steamin10 » Mon Jan 13, 2014 12:23 am

As I know it, Shell molding is a wax process where the wax mandrel with the needed parts are in a tree, is dipped in a ciramic slurry, and then an air fluidized sand box to coat the slurry goop, and the dipping process is repeated as often as needed to build up a shell. This shell is then hung upside down in a burnout furnace, where the shell not only dries but bakes the ciramic hard, and dewaxes. These shells are normally poured hot, and do not heat shock. It was developed to cast fine details and dimensions, and give superior finish on the as cast parts over any other method. It uses less material in the long run for the molding (the shells) but the slurry has a relatively short life, and is lost easily if not correctly handled.

It is quite diferent from coremold setups, where disposable molds are made, and destroyed. In more complicated items, these coremold pieces are assembled or 'racked' into a larger part, so that many peices can build one unit of relatively complex shapes, to be poured and shakeout as a unit. Like a louver door, or a larger water turbine, where each blade may be assembled as a separate piece. It takes the name from the use of coremold material from start to finish.

In the last year of BlawKnox, they went to a dry sand vacuum process. They went to a plastic sheet over the form, and poured dry sand over it, where it was formerly resin sand. 3 inch hoses were connected to a vacuum manifold, and the peices (cope and drag) were stacked and poured under vacuum. When the molds were removed from the pouring pit, the outer flask was removed and the sugar sand just ran out, and the casting was sent to the heat treat ovens, after the pouring heads and sprues were removed. This had the advantage of no smoke or firey shakeouts, or fumes from the binder/catylist, and no reclaim problems breaking (grinding) down sand for re-use.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

Post Reply