Newbie Question

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johnny

Newbie Question

Post by johnny »

I went to the Cabin Fever Expo in York PA last weekend and saw lots of steam engines and kits. Most had familiar looking castings, but some had really smooth, highly detailed castings with a surface like unpolished marble. What is the difference in the processes that make these castings? Any good Casting 101 books out there that give the basics on the subject? Thanks,
Johnny
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Harold_V
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Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Newbie Question

Post by Harold_V »

Johnny,
The finish you speak of is a result of the chosen casting process, which is likely to be investment casting. It is commonly referred to as the lost wax process. A wax pattern is created in a mold or it can be carved or otherwise sculpted, which is then put in a flask that is filled with investment (investment closely resembles plaster of Paris.) The wax is then burned out in an oven and the metal poured in the mold while it's still hot. It yields exceptional detail, with a very smooth surface. There's more to it than this, spruing and treeing are a part of the process, which explains how the wax gets out and the metal gets in.

The wax process can also be used in other ways; shell molding is an example. The wax is coated with a refractory material by dipping in a slurry several times, then treated about the same way the investment mold is. This system lends itself to larger items.

Very good sand castings can be poured if enough care is used in the molding process and fine grained sand used, but it falls short of equaling the quality and precision of investment casting. The surface is generally not nearly as smooth as investment surfaces are.

A good example of investment casting can be found in a lot of jewelry. It is used extensively by jewelers, who carve or otherwise build up a wax model, which is then invested and cast. Rings and other pieces of jewelry are made in this fashion, as are most dental pieces such as bridges and metal crowns for teeth.

If you'd like to read about the investment casting process, a jewlelry supply house is a great place to go for books because of its wide spead use in that industry. Check the yellow pages in your phone book.

Hope this helps~

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

Re: Newbie Question

Post by johnny »

Harold,
Thank you. That was very helpful.
Johnny
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