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John Schaefer
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 Posted: Fri 17 Jun, 2005 10:55 am Post subject: lost wax process |
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I was wondering if anyone can tell about this process or direct me where I can go. Ive read some about it but not too much on the subject so all help will be appreciated.
Thanks
John Schaefer
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Chad Sonderberg
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| Posted: Fri 17 Jun, 2005 11:42 am Post subject: |
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There is a good description about the process in the book "The Complete Bladesmith" by Jim Hrisoulas. Its a very good book for learning about the basics of blade smithing.
The "Lost Wax" process simply involves carving the pommel and guard from a wax block (I don't remember the wax type and I'm at work so I don't have my book handy). Then casting it into a mold(I, once again, don't remember the substance name) before using the mold to cast the component.
The advantages of this process are that if an error is made while carving, one can simply heat up more wax an apply it to the area and recarve that spot. Also, the cast will have a nice finish that helps to make clean up easier.
Hope this helps!
A.C.S.
Lebend mit Ehre, Sterben Sie mit Dignität.
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Matthew Kelty
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| Posted: Fri 17 Jun, 2005 1:37 pm Post subject: |
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Most often, the wax used is a synthetic product known as Microcrystalline. It comes in varying hardnesses, as you want harder waxes for finer details, softer waxes for large, simple forms. Available at most Jewelry supply houses, try Rio Grande.
After modeling your objects, you attach wax sprues (with a tacky wax) which will serve as the places for the Wax to melt out, and later, the metal to pour in, and the air to escape.
Make sure you think about gravity, air pockets, quantity of metal needed down a certain path, and the ability to easily and completely remove the flashing as you plan the sprues.
Basically, you don't want to put a narrow sprue in a spot that is feeding a huge section of your pour, add vents on all "high" sides, and plan the sprues around areas that are easy to access and finish, but aren't in a "detailed" area. Pick the bottom, sides, ends, and back of the piece, where you can easily clean it up, but any imperfections won't detract from the overall piece.
After you've got your model sprued up, you pour investment casting around it. There are a lot of recipes for this, the Bronze casting investment I was taught was, I believe, 1 part #40 sand, 2 parts #80-#120 Sand, and 4 parts Plaster of Paris. Please reseach this for yourself, as I've only done it twice, and it was about 15 years ago.... 
After the Investment has dried (give it a couple days in a warm, dry place, as you want zero moisture), you then slowly heat it in a kiln, upside down, so as the wax melts out, and the investment is baked solid, just like pottery before it is glazed.
From here, you make your pour, and break the investment. Voila!
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Howard Waddell
Industry Professional
Location: Wisconsin, USA Joined: 18 Aug 2003
Posts: 717
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| Posted: Fri 17 Jun, 2005 1:39 pm Post subject: Re: lost wax process |
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| John Schaefer wrote: | I was wondering if anyone can tell about this process or direct me where I can go. Ive read some about it but not too much on the subject so all help will be appreciated.
Thanks
John Schaefer |
Chad gave you a good tip on Jim's book, but I will give you an idea in short form of how the process works.
The Master
Your original can be made of anything, but keep in mind that if you are trying to replicate a given piece exactly, there are percentages of shrinkage involved in each step.
Therefore, if you are trying to achieve exact dimensions, it is best to make a new master that is about 5% larger than you want the finished cast piece to be.
Starting with your original piece, you make a mold that *if* you want more than one cast piece. If you are making a one of a kind piece, your original can be used as the "investment" wax and you can skip the molding step (though this can be risky.).
The Mold
The process and materials you use to make that mold depends a lot on the characteristics of the original. Is it detailed or fairly simple? Are there undercuts or assymetries that would make it difficult to get the original and then subsequent production waxes out of the mold in one piece? If it is complex or has undercuts, you will need to make a mold of a flexible silicon (which will also need a hard backing like plaster to keep the shape true) or if it is small, a mold of vulcanized rubber (like jewelers and pewter casters use.) If there is not a lot of detail and there are no undercuts, you can use a hard silicone to make the mold (which is very durable and gives you good registration every time.)
Investment Waxes
After the mold is made from the Master, you then pour a light investment wax into the mold to get originals for casting. The investment waxes need to be cleaned up and must be as perfect and smooth as possible -- any flaw, even a small scratch, we be transferred to the final casting. It is a lot easier to clean up the investment wax than it is to clean up a piece once it is cast in bronze or steel. Remember -- the investment wax is destroyed in the process, so you need an investment wax for each individual piece you want cast.
(If you use your master as the investment wax, be prepared for heartbreak. Sometimes the process fails and then the master and all of your work is lost. That is another reason to make a mold and have the capability to make multiple copies of it.)
The foundry will take each investment wax and add wax "sprues" to it that form the pouring and venting channels in the investment flask. (sometimes multiple similar pieces will be sprued up together into a "tree" to make the casting process more economical.)
Investment Process
The foundry will first will paint the piece (to capture detail) and then submerge the piece is an investment solution. This solution has the feeling and look of crushed kitty litter. This process is a lot like slipcasting pottery.
Once the "flask" that has your wax buried inside (with a pouring channel (sprue) coming out the top) is dried, it is then put into a kiln, upside down, that burns out the investment wax and cures the flask.
You now have a clay pot that has the "negative space" representing your piece inside of it.
Pouring
Once the flask is cured, then the metal of your choice is poured into it.
Once it is cooled, the investment pot is broken away to reveal the cast piece. The sprues are cut off and you have a raw casting that must be cleaned up and polished into the final piece you envisioned.
Hope that gives you an idea.
Best,
Howy
Albion Swords Ltd
http://albion-swords.com
http://filmswords.com
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