Foundry work & casting. Introduction.

Bramblebush Workroom Project

Foundry Work & Casting
A compendium of miscellaneous information

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Introduction

We have gathered together a series of related posts from the ArtMetal mail list which centers around the process of foundry work and casting.

The format being used is very informal and will consist of edited posts with the relevant information extracted. References will also be made to the archives of interviews extracted from our Thursday night chat sessions.

Taken as a whole, we feel that this project will contain a wealth of information that has been generously contributed by a variety of folks. We wish to thank everyone for their submissions.

Chris Ray - editor


Jan. 4, 1999 -  (Editor's note: this thread had already begun between John Dach and Glen Carliss so we'll simply start with the messages as John had passed along to us).


Jan. 4, 1999 - >>(snip) I only do sand casting and have a McEngelvan B-16 furnace. I >>stick with a #11 crucible because I also do everything myself, including >>pouring. Thirty pounds of molten bronze is about the maximum I want to deal >>with by myself. (snip)

>>I want to break into ceramic shell in the worst way! I have a sculptor friend, >>Eric Parks, who is begging me to get set up. But I have no first hand >>experience.

>Shell can be very easy and not too expensive to try. R&R have a "kit" of a 5 gal pail of coloidal silica and a couple of bags of sand (was about $150 acouple of years ago and prices havn't really gone up much for their products). Biggest expense is the mixer system. Either on 7-24 of on a timer 5 min on/5 min off (Grainger timer is about $120).

Then some sort of motor, slower speed for the agitation but higher speed needed to mix the mew materials, so I use a 90 Volt, vairable speed, DC motor from Graingers (1/2 Hp was about $400-500 a couple of years ago but if you go to a 55 galbarrel, you will be better off with a 3/4 hourse unit).

Lastly is a mixing prop, I first used a large Jiffy Mixer prop (about $75) but have since gone to a IDACO ss 6 inch prop. Lasts longer, mixes better and is in the long run, MMUUCCHH cheaper than the Jiffy, which I had to rebuild every 6 months or so.

Lastly, you need an area to apply the sand to the wetted wax/shelland a place to dry the unit. >> I have read about it, understand the process, but need some first >>hand experience before I will commit to the equipment and supplies. One of the >>nice things about sand casting is that you can come back to it after a couple >>weeks and jump right in.

The burnout phase of ceramic shell is probably the >>biggest mystery and stumbling block to me. >This is the best part of ceramic shell.... The shelled wax is heated (many ways to do this, if interested let me know) to remove the wax.

Then theshell is heated to about 1800+++--- (big range here) for about 15 minutes (another big range here time wise) to vitrify the shell materials. When cool (or whenever you want to go to the next step) any drain holes, cracks or whatever are filled with a purchased ceramic goo or a mix of the slurry and the sand. The shells can be stored at this point or readies for filling.

When casting, the shells are usually heated to between 600 and 1500, even 1800 and then cast. The casting temp varies with the foundry and the particular casting, but the temps are pretty flexable (at least for me they are,,,,,, no pyrometer in the shell kiln!!!).

The slurry can be left to settle and when ready to use it again, remixed. Slurry is good for at least 1 year (mmine have been staying good for 3-4 years), it just cannot get down to 35F or lower as the silica starts to precipate in a one way reaction.

Shell does allow for VERY EASY hollow casting comparied to sand, but sand sure does have the benefit of speed if it is needed. Costs too....>

>>Well, I could go on for hours. Thanks for reaching out and contacting me. I >>look forward to sharing our mutual passion for metal manipulation.

John Dach and Glen Corliss


Jan. 4, 1999 ->>I've got a bunch of fire brick and a couple kick monster propane burners >>(250,000 BTU) that I have been thinking about using in some fashion to do the >>initial wax melting and firing of the ceramic shell. Does this sound feasible? >>I've got Young and Fennell's Methods for Modern Sculptors but they never say, >>"Just wing it!"

>IMHO the 250,000 burners are overkill. You do want to heat the shell/wax FAST so the first wax to get hot (next to the shell) gets liquid and it needs to do so over most all of the inside surface of the shell so as it melts, it can "get out" and not crack the shell (the wax really expands as it gets hot).

I use a venture burner from a ceramic kiln o the end of a 2.5 foot piece of pipe with a ball valve at the back end. I hand the shell on Nicrome wire, and start at the bottom (cup) and heat the shell/melt the wax from the cup upward. I also grind wax "vents" in the shell where I think< there is a good potential of the wax heating in an area but not having an escape route without the hole. Has worked GREAT.

These holes are filled after the initial firing with the ceramic goo or shell slurry/sand mix. I also put in a small piece of rolled up gause so as not to get the repair material into the casting area. This too has worked GREAT. I use a small die grinder with a cutoff wheel to make the drain holes. <

>>So, what exactly do you use for your melting and firing? Do you catch and >>recycle the wax? What is the largest (size-wise) shell you work with?

>I catch the wax in a half 55 gal barrel. When I get a bunch, tip the barrel over, heat it with the tourch and the wax drops out. I remelt this to clean it (has sand, other stuff in it) and the sprue wax I use is softer so I have to add a fair amount of hard wax to this to reuse it).

Size is limited to how much one can lift. I limit my pieces to about 40 or 50 lbs (wax and wet shell/sand weight) which meand avout 3 feet high and 8-10 inches in diameter (this is definately an approximation as each piece is so different). I will not hesitate to cut the wax of a large piece to get handable sizes and weld them back together in the bronze. This is pretty< much the practice in the industry for monumentals and the like. Also my slurry tank opening is a limiting factor, as well as my fluidized sand bed.

Many foundries just use big tables with raised edges to sand the dipped pieces, but I do like the fluidized bed as it is so fast and for me easy.

>>As far as cores are concerned, I use the CO2 method. The process involves >>mixing sodium silicate into your core sand. Sodium silicate is about the >>consistency of molasses so when you are done you have a sand mixture that is >>relatively cohesive. Once you have formed it into shape you pass carbon >>dioxide through the core and it hardens instantly. That is a very simplified >>explanation but it is not much more complicated than that.

You can also use >>the CO2 process for a facing of intricate work like grills or use it as a >>complete free form mold without the traditional flask used in sand casting. It >>is a very inexpensive way to get into core making without the need for a core >>oven or nasty core binder chemicals.

John Dach and Glen Corliss