Questions about lost wax casting

[44-henry]

Can anyone tell me if it would be a bad idea to use soft lead solder, instead of wax, for the sprue for the lost wax casting process. I have had my fill of breaking delicate homemade wax wire sprues and am wondering if lead solder might not be a more durable option. I'm playing around with the steam casting technique where a damp sponge is used create steam to force the molten silver into the mold cavity and it requires four rather delicate wires to act as feeders to the mold. I have lots of good wax for patterns left over from when our department did this process years ago, but I don't have any of the sprue wire that the below mentioned website suggests using and I'm too impatient to wait for the stuff to arrive. I'll probably end up trying it, but I am just curious if anyone has gone down this path already before. I figure since the mold is going to be subject to a burnout and firing past somewhat past 1000 degrees the lead tin mix should melt out and vaporize with the wax, any comments? There is an interesting tutorial on this process at http://www.myheap.com/book/chapter-08A/dnorris/Lesson_01.php

[Dave B]

At what temp does lead vaporize? I think this sound like a bad Idea. I know there are various types of waxes with diffent strengths and srink rates. I dont think the lead will vaporize enough to guarantee a complete removeal from the cavity. Not to mention the health risks and legal ramifications. If the EPA  got wind of it. I checked a web site that says lead vaporizes at 1800 degrees or so. The wax is the way to go in my book. Use your lead for round balls.

[Jim Chambers]

If you don't want to use wax, have you ever tried plastic.  Some casters have better results getting fine detail using plastic instead of wax.  Most cheap plastic spoons, forks, and knives will dissolve in xylene and can be used instead of wax.

[Acer Saccharum]

You may get lead oxides that could interfere with your casting, above and beyond the health risks. I think what you want is sticky wax for your sprues. beeswax is too brittle.

Sometimes you get a real burning desire to get something done, and you don't have the right stuff. You are most often better off to wait to make things as right as you can instead of doing the job half right. I know all about this, having screwed up many projects. Then you have to get over the failure and start all over. You will benefit the most by giving your project what it needs.

Sources of sticky wax:
Gesswein sells it.
http://www.gesswein.com/
Rio Grande
https://www.riogrande.com/home/
-or-
How about the red wax that comes on Gouda cheese? or the fake wax lips you buy at the candy store?

[davec2]

44 henry,

I do a hundred or more centrifugal castings a week in gold and silver.  Steam casting is a very effective method of making small castings , although, I find vacuum casting easier and more accurate.  Nonetheless, you will always need a mold and the process for making that mold is almost universally the same.  A huge part of successful casting is knowing where and how to attach sprues and, if required, vents.  Using lead is a bad idea.  I'm not one particularly frightened by lead toxicity (unless of course you are talking about the kind of "lead poisoning" that a fired bullet represents) but even the most minute amounts of lead in silver or gold will destroy the alloy.  Gold becomes so brittle when contaminated with even trace amounts of lead that you can crumble the casting in your hand.

If you are having trouble keeping the pattern on the sprues, your sprues are too small.  Use wax wire (comes on spools) of sufficient gage to support the pattern as it is invested and to provide sufficient flow area for the molten metal.  The number of sprues, the size, and the location are critical to get the casting to come out successfully and without porosity.  As the casting chills, there must be sufficient liquid metal to draw from as the casting solidifies.  That means that the thickest part of the casting should be the attach point for the main sprue and the sprue should be of sufficient size so that it does not solidify before the casting does.  Otherwise, you will get a lot of porosity or shrink back at the attach point.

If the sprue can be inserted directly into the pattern and set up on the investment sprue former so that there is a straight shot out of the mold, you can use a piece of welding rod or even a nail.  For example, I recently made a small sterling silver cannon charm.  To make the pattern, I dipped a piece of 1/8 inch diameter weld wire in wax until I had sufficient wax to turn on a lathe a small cannon barrel (1 " long) on the end of the wire.  (The wire protruded from the cannon muzzle).  I put the free end of the wire into wax on the top of the sprue former with the cannon barrel pattern standing straight up on this wire sprue.  When the investment had set up, I pulled the rubber sprue former off the casting ring and the end of the wire was exposed sticking out of the bottom of the investment.  I pulled the wire out of the mold with a pair of pliers, burned out the remaining wax and cast the charm.  As a boy, I used to make perfect castings of insects by mounting them on a pin, investing them this way, and casting through the hole left when I removed the pin.

As mentioned by others, you can sometimes use plastic for sprues.  However, be advised that most plastics require a burn out at much higher temperatures to be completely removed.  Also, some plastics will expand quite a bit as they are heated and they can crack a delicate mold before they burn out.

Hope this helps.  I would also heed Acres advice about getting the gear you need.  The references he sites also carry the spools of wax wire (made specifically for casting sprues) in several gages.

Merry Christmas

[jerrywh]

Rio Grande jewelers supply has a wax called platiwax. Very tough. Like Dave says , I have never had trouble with wax in any way except fo excess shrinkage on large patterns.
  I would never think of using lead. It will not vaporize at burnout temperatures. But I don't want it in my furnaces. Like dave says very small amounts will ruin gold and silver.
  PS lead vaporizes around 3150 fer.  I think.

[44-henry]

Thanks for all the info, I'll be ordering some wax wire in the morning. What methods are you guys using to cast some of the larger pieces using this process?

[jerrywh]

When I cast I use a vacuum table. And I invest all my patterns in large stainless steel flasks made of stainless pipe or regular large steel square tubing. My flasks are burned out at the rate recommended by the makers of the investment. I mostly use Kerr Satin cast or Ultravest investment. I buy it in 100 pound boxes. It will come with a sheet giving recommended burnout procedures.
 For large flasks I pour with a flask temp of about 550 to 750 fer.  It is very important to have enough sprue weight to force the metal into the molds if you want very precise and intricate reproduction of the art work on items. On items without engravings or art work it is not as important.
 There is much that cannot be learned from books or any other way than just trail and error. It is a hard and expensive way to learn , Especially if you are casting silver or gold.
  Do not let anybody talk you into using silicon bronze.
  Electric furnaces are not as good for burnout as gas furnaces are. The wax fumes are very hard on the elements. The furmace must be set up to have a drain of some sort for the majotity of the wax to escape as it drains from the flasks.