aluminum animal broachs

[Stainlesmachinist]

Hi
I would like to make aluminum animal broachs and the size is about 3x1.5 inches.
I already have a few molds in rubber from before and I am going to use those
So what I will do is a experiment with one cylinder of these models
I am saying I will inject a few of these molds and make a tree,let it dry,
burn wax and place cyclinder on the floor and melt aluminum and pour
http://imageshack.us/photo/my-images/824/treeg.jpg/

My friend said that this will not work and he said I should do certifugal casting
or I should have a hole for air to go out when I am pouring the aluminum
http://imageshack.us/photo/my-images/696/tree2z.jpg/
I was also wondering if I should burn the wax before pouring the aluminum or just leave it there and pour on it

If you look here
back pin in stainles stell
is soldered and I would have to buy special solder
http://the-bestfashion.com/sober-lookin ... rooch.html

And the broach would have to be plated or painted
http://www.dalmar.net/aluminum_plating.htm
http://www.caswellplating.com/kits/
Also I am saying will this be econmiaclly feasable
How much can I charge for these things

I would like to hear opinions and I prefer not to use centrigula casing
Thanks

[Harold_V]

It is my opinion that you can't pour aluminum on wax. One reason is that the volume of wax involved is too great to be displaced by the aluminum, and the other is that hydrogen is a problem with many molten metals, including aluminum. That's the purpose in degassing. The presence of hydrocarbons will simply introduce more hydrogen, so the metal will be badly compromised. That's probably not much of an issue in this case, because you'd most likely never get a complete casting, anyway.

When wax is used, it should be completely removed, right down to traces of carbon. That's why investment casting includes a high temperature burnout operation. Even when casting gold, the presence of even traces of carbon results in porous (or incomplete) castings.

You likely can gravity cast these items, but you'd benefit from using vacuum assist.

Note that I am not an experienced foundry worker.

Harold

[hammermill]

harolds on with not poring on wax with al

if detail is imprrtant you may want to coat the pattern with silica and do what is called lost wax casting, it a bit involved

but common in the jewlery world of things.

[Rick]

You NEED to do a burn out on the investment to remove the wax and also cure the investment. But most importantly if you do not do the burn out process the water / moisture that is in the investment can explode when molten metal is poured into the mold. Also the investment needs to be at a high enough temperature so that when you pour the metal it is not themally shocked and fractures. I have not done alum investment casting (yet) but with bronze the investment temp at the time of pour is about 900 degrees F. I do not have the burn out process right in front of me but it is a step process with the temp slowly being increased up to the cure temp of the investment then brought back to the pour temp.
As far as getting the air out of the cavity, you have mentioned two ways of doing that (centifically and by using "vents") There is another way (as Harold mentioned) and that is to use vacuum around the outrside of the flask.(I use this method) The vacuum will pull the trapped air thru the investment and therfore pull the metal into all of the cavity details. If you have alot of fine details in you pattern you will need to degas the investment after you mix it and then after you pour it around the wax patterns. This is done with vacuum and will pull out all of the tiny and not so tiny air bubbles trapped in the liquid investment.

[Stainlesmachinist]

Hi Folks
Thanks for your help I appreciate it very much.
Harold has a point with vacuum casting
I have seen these machines and they are used by jewelers and it is for a good reason that jewelers buy then otherwise they would just cast without it.

http://imageshack.us/photo/my-images/696/tree2z.jpg/
I am not sure if this way the small details will come out.

But I think it is either vacuum or centrifugal casting if I want to have small details to appear in the work.

Thanks again

[steamin10]

The aluminum for this should be of higher quality with high silicon levels for fluidity. That means tight chemistry, and probably bar cert material. Only melt as much as needed.

Another thought is to have a longer vertical feed sprue, to exert some pressure on the filled cavity by nature of gravity with the weight of the metal. In sand this is a washing problem with grains coming loose, but not in investment or core mold.

[Stainlesmachinist]

Hi Big Dave
Thanks for you help
I would like to use aluminum scrap such as cans and sidings and frames.
I have read in another forum that after they remove the paint from the molten metal than they cover it with wood or charcoal than pour
I have also hear of chlorine pellets used for pools thrown in the mix when melting.

high silicon levels for fluidity

Can I mix this in the molten metal
But i don't think I should do all I have heard that if you cover the molten metal with charcoal than that will be enough

Another thought is to have a longer vertical feed sprue, to exert some pressure on the filled cavity by nature of gravity with the weight of the metal. In sand this is a washing problem with grains coming loose, but not in investment or core mold.

Can you explain this a bit I don't understand that

Thanks very much

[steamin10]

ART CASTING, for aluminum has a large following, and can be found in many places on the net. it can give more detailed info rather than me posting here. It is generally for larger pieces than what you want to do.

To change chemistry, you have to have the needed chemicals, and for aluminum small scale casting, it is in bar form where it is already in a base aluminum stock, and droped into your melt, to adjust its quantitites. This is beyond me, because I have no way to assay my scrap and melt quality, except by major SWAGS judging by what I put in. Straight silicon, can be added, as it increases fluidity, and therefor detail pickup, but the proportions are critical, as is the mixing in to your melt.

By making a deeper mold, you increase the pressure on the lower portions of the mold by gravity. To stop airation during the pour, such vertical runners are angled slightly to run down the side, to reduce the air bubbled into the stream. Degassing is most commonly done with Nitrogen, which picks the O2 for NO2 out of the ready to pour melt. This is done just after a few crumbles of Pool Tablets are immersed in a foil packet and swished with a plunger into the heat. This fluxes the heat, and brings many impurities to the surface, as dross. This is skimmed and removed. Each step is important to quality, Miss a step and quality may suffer.

I dont make jewelry, and Pewter or Jewelers metals, may be a better bet. I only do castings of aluminum for train parts, for my own amusement.

Warning! I cannot in good clear mind suggest pool tablets without, the following.
Chlorine heated in this way, is very dangerous, and the gas cast from the melt should be avoided completely. Lung damage can and will occur.

[Stainlesmachinist]

Hi Big Dave
Thanks for all that info.
I know that chlorine is bad but how about when you are doing this under a blower

[steamin10]

Rather than take my unprofessional word, you should look up the qualities of Chlorine, and Hydrogen Chloride gas. Chlorine is heavy, and without forced movement will sink in air. When it is generated by working a heat, If you are between the air stream and the vent, you will get the full benefit of being gassed. It only takes a few PPM of Chlorine to mess up your day. Ever be around a swimpool and smell Chlorine? That is less than 20 ppm, usually generated by the Chlor-amines breaking down as the Chlorine breaks down the oils and organics dissolved from dirty human bodies that shed skin cells and oils and sweat, and eventually cast the chlorine back out.

In working Aluminum, one gout of gas will result when you inoculate your melt, and it is strong enough to cause physical damage and chemical pneumonia within minutes, if you are that careless. Think WWI poison gas. Based on Chlorine it was engineered to kill and maim. To a lessor degree, you are dealing with the same chemicals, so be aware. It is easily avoided but caution must be in your process. Be smart.

[steamin10]

In the least, I would start by reading some of the archive here on casting aluminum, as there is little else, and perhaps pick up some books by Ammen and others as they have been written with a home Hobbiest in mind. While limited in value for industry, they are spot on for the home caster with limits on resources. This target is easy to follow and will get you past many, but not all of the pitfalls of small scale and garage type limits. Casting can be as easy as a ladle melting a few spoonfulls, to haveing a roaring furnace with several hundred pounds of molten metal. The process is the same, only things change very fast with small quantities. A bit of education will make your trials a lot more productive, bypassing the learning curve for failures. Eventually, getting the right practice, is your choices to follow the preached dogma of rituals, or going with your own unproven ideas, and trying to find your way out of the woods for success again. It is not that hard, if you dont violate the the basic tenents of the Alchemy involved.

Again, like any offbeat activity, here are dangers of heat, chemistry, and physical damage. So be smart, and do whatever protective measures are appropriate.

According to Murphy's law, it is not what we know, but the things we dont know that rise up to bite us, in a situation.