Casting a Mould 4

[edstimator]

So the part that I am trying to make is a dry cast concrete corbel.
That is my ultimate goal. I'm choosing dry cast concrete because once you are set up you can make parts continuosly and basically at your own speed. This as opposed to wet cast where one would have to cycle in and out of a set of moulds.
Ok so that's the part, now I need a mould.
A Aluminum mould would be bad ass as a 4 piece block mould.
Possibly three pieces but due to some undercutting I'm thinking four.
So now how to get the mould? Do I contract a foundry?
We have one very nearby. OOOOORRRRR do i build a furnace and make my own. (I tried plastic already and that was a failure due to material degrade issues)
So? any thoughts?

 

[MikeHalloran]

Aluminum plate, machined and bolted with a little sealant.

OR

Really thick aluminum plate, with cavities by CNC milling.




Mike Halloran
Pembroke Pines, FL, USA

 

[edstimator]

Hey Mike, thanks for the input butthe part Ian making is wuite ornate and needs to be cast. The mould need to have this same detail so casting it is really the only option. It is confusing but I need to cast a mould so I can use that mould to dry cast other parts. I need like three hundred or so of these parts so the mould has to be quite durable to withstand the abuse of the sand being compacted into it.
I have done sone research and a cheap home made foundry with charcoal fits the bill and is almost free to make so I think I am going to go for it and cast my own

 

[CastMetal]

Making a 3-4 part aluminum mold on a CNC machine will be the most efficient way to get what you are looking for. A competent CNC operator with a decent CAM software can machine in finer details than you are likely to get with a backyard sandcasting setup. Going this route would likely cost over 2000$ depending on size and just how "ornate" this corbel is but certainly has fewer headaches.

If you are making a mold at home I assume you plan to use an existing version of the corbel as a form for a sandcasting mold? Or the corbel itself coated with a ceramic spray as the casting surface for the aluminum mold (I don't know how well concrete withstands a quick burst of heat from 1100*F metal)? Sounds like an interesting backyard project, best of luck.

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

 

[blacksmith37]

Had you considered zinc; much easier to cast at a lower temp? Used by the auto industry for short life dies/molds.

 

[berkshire]

What ever metal you use, make sure that concrete is completely dry, before, you pour molten metal of any type around it.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Compositepro]

Aluminum will corrode, even if the concrete is dry. Cement dust is very caustic and absorbs humidity from the air.

 

[edstimator]

compositpro, you are absolutely right and I thank you for bringing that up. I may have to paint the mould before casting the part.
Dry cast concrete is sort of a misnomer. It is moist sand and cement mixture and not trulu dry. The mould is of course open on one side and after it is packed with this mixture the aluminum mould is unbolted and the part is released not unlike a sandcastle.
After the concrete cures (sometimes in a steamroom) the process is complete. The moulds are not hot or anything and at the point where you are casting parts there is no danger save for smashing your fingers as you tamp down the sand and cement mixture.

As for cnc, that's for all you guys that just happen to have a $200,000.00 machine in there garage. I have a router and a hammer.
OK, I've got more than that but I'm trying to make a point.

Expanding on that for a minute and slightly off the subject I've notice that a few of you blokes totally live up to the tagline of smart questions for smart people who are even smarter than you or however that goes. I mean some of you dudes are just ridiculously smart. My point is that I am not generally thought of by people who know me as fitting that description and if I am intruding into your world of really really smart people just let me know. I'm not trying to pose as one of yas, but even the really stupid answers on this forum are light years ahead of most of the other sites. I'm hoping to learn something from you guys and so far so good. As long as wikipedia holds out and doesn't crash I'm good. Just wanted to hang out for a while with someone smarter than myself. Hope you guys don't mind. I'll try not to dumb down the site too much.

 

[edstimator]

The thing about drycast concrete is that after it has cured and all it ends up having what has been described as a sugar cube finish. This is not a finish that is conducive to fine detail such as hair or fingerprints but those details can be captured in wetcast concrete. I am choosing drycast because I can start and stop at any time without wasting material. Think of the plastic mould of a castle. You can make one or twenty sand castles with a mixture of wet sand. just pack the mould, turn out the part and let it cure.

I am somewhat of an expert on wetcasting but have never cast a dry cast part in my life. I don't like to read fiction books and I don't make silly artsy things so when I ran into this problem of how to turn out hundreds? of these corbells for my house at a dirt cheap price I thought of this method and I am very excited to try this. Rubber moulds dont work well unfortunately because the are flexible and my plastic moulds just sucked because apparently I am just too impatient to let the paint dry on the mother part. I have been thinking about making a blast furnace for a while now so I finally came up with a reason so I'm going to go ahead and do it.

And finally, what is the advantage of zinc over aluminum and assuming I chose zink, where would I source this. I don't need specifics, I mean I can google that but would I go to scrap metal or a supplier or what? Scrap aluminum is everywhere. Unless the advantage is great, and I don't know so I'm asking, whouldn't it be a better choice? I am going at this furnace thing with the intent of building a perfectly fine furnace for no money except one bag of cement. I think I have everything else and of higher quality than I've seen online.

And thanks again for the responses. Can't promise to take every suggestion but I do promise to think about what you are suggesting and I appreciate the time you spend giving advice. It is generous to offer it and it is appreciated.

 

[edstimator]

I started making my furnace and going quite well actually. Took the carcass fromm an oven for the container, five gallon bucket to make the inside of the furnace and cement and pearlite mixture for the refractory. I took a burner from a stove and will be using that for the air supply. I have a hvlp compressor that I will be utilizing for the air supply so I think that will work quite well. I ran out of Pearlite so I need another bag to make the lid but it should be done tonight.

 

[blacksmith37]

You may be able to get Zn pretty cheap. A secondary smelter (scrap melter) that handles auto scrap. Many parts , especially older cars, door handles, carburators, fuel pumps ,etc are Zn.These are melted to give a large ingot of non-spec Zn, which I think would work for your mold. Alternatively you could get virgin ingots ( "prime western" seems to be the main grade).

 

[edstimator]

Hey Blacksmith, you may be on to something and as soon as I get my furnace up and running I will try just that. I'm finding out that you need to have a blacksmith shop set up to make all the tools you need or be prepared to shell out some coin. I think the ladle tongs and pouring irons are kindof important as you obviously don't want to be sloshing molten metal around like it is soup. Safety first and all that. Seriously concerned about foot protection. Would you say that speacial shoes are in order or no big deal?

 

[MikeHalloran]

Shoe covers of metal or leather sound like a real good idea.


Mike Halloran
Pembroke Pines, FL, USA

 

[edstimator]

I guess it all comes down to how well you like your feet eh? I'm kinda partial to mine but I think even counting that i've got a phobia of dumping liquid aluminum on my foot.

 

[berkshire]

Check out this site , they may have what you need.
Look at spats.
B.E.

http://www.themanstoreonline.com/Aluminized-Clothing-Welders-Clothing-s/104.htm

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[edstimator]

that looks perfect. Minimum order requirements suck but I will look for them somewhere else to avoid that. thanks for the tip though

 

[CastMetal]

If you are going to make a habit of pouring liquid metal a pair of foundry boots (slip on steel toe boots) may be in order. I have seen a pair of lace-up boots that got aluminum spilled on them, guy couldn't get them off in time, not pretty.

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

 

[edstimator]

Castmetal, yeah, that visual right there is what I'm not looking for.
As stated earlier I have a phobia about that so thanks for feeding the monster Bwahaha

 

[edstimator]

OK, well I think I just hit the jackpot on this one. I called a local foundry that will basically teach me how to make a mold and then they will cast it for me into the mold that I make. The best of both worlds as it is the tooling and pattern making that is expensive and being a heavy duty woodworking guy, I think I have a pretty good idea how to make a pattern. Guess it pays to talk to the pros but it took a while to figure out that he was willing to do this. More than willing actually, apparently a lot of clients do this so same ole same ole for him.
So I just learned something
hope anyone reading this did also.
Think I will let this thread die a natural death and move on
gd luk