Casting Help

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Castings that do not fill and have rounded edges at the point where the metal stopped flowing can be cause by 2 things. One, the flask temperature was not hot enough, or two, the metal was not hot enough when cast. Flask temperature should be around 800-1000 degrees when the metal is cast into the flask. Your metal should be liquid, shiny and rolling when ready to cast, most metals cast at 100 degrees over the metals melting temperature. Your metal should not be smoking, if it is smoking, then you have overheated the metal and this will lead to porosity and pitting in your casting.

Another type of incomplete castings are ones that have moon like craters with sharp edges. These castings are caused by incomplete burnout of the wax. The gasses and residue left in the flask will cause sharp edges / craters in your castings. A good way to tell if your flask is ready to cast is by checking down the sprue hole, the investment should be white and chalky and glowing orange inside the sprue hole. If there are dark spots down inside the sprue hole, then the flask is not completely burned out and needs more time. Most jewelry investments need to be burnout out at 1300 degrees F. When the flask is completely burned out, make sure the flask temperature is dropped down to 800-1000 degrees before casting.

Pitting is generally caused by dirty metal and or too much heat. The flask is too hot or the metal is too hot. Make sure you use at least 1/2 new metal when mixing with your scrap metal to cast. Make sure your scrap is completely clean and free of any residue. The larger the item you are casting, the less your flask temperature needs to be. We cast large flat items at no more than 800 degrees. Your oven temperature gauge may say 800 degrees, but a flask may be much hotter at the core of the flask. Let you flasks sit in the oven at 800 degrees for at least an hour to make sure your flask core has time to cool down from the 1300 degree burnout temperature. This is especially important on large castings and castings with smooth surfaces. Filigree and intricate items need to be cast in flask at around 1000 degrees. We do not suggest putting large flat items in same flasks as small delicate items.

Bubbles Bubbles toil and troubles. Don't you hate having a casting covered in bubbles? Bubbles are created when you mix your investment. A thinly mixed investment will cause tiny bubbles, a very thick investment will cause large bubbles. A perfectly mixed investment will cause bubbles unless you remove the bubbles from your investment or shake them loose from your wax patterns during the investing process. We suggest using a vacuum investing system. You will mix your investment and then vacuum the investment for about 60-90 seconds before pouring your investment into the flask. Then you should vacuum the flask for another 90 seconds followed up by placing the flask for a minute on a vibrating table. You need at least 30lbs of vacuum pull when investing your bowl and flask.

If you cannot afford a vacuum investing system, then at least get a vibrator to release the bubbles from the wax. There are also products available at your local jewelry supply store that you paint, spray or dip your wax pattern into before investing. These products reduce the "surface tension" that holds the bubbles onto the wax and helps release the bubbles when the investment is poured around the wax pattern.

If you live in an area that is very cold in the winter, your water from your faucet will be much colder in the winter than in the summer. Investment mixed in warm water will set up faster than investment mixed in cold water. Your investment to water ratio should always be the same and the water temperature you invest with should always be the same to insure consistent results. Use 68 degree water if possible, summer and winter and your investment will act the same all the time. This will help you get the exact ratio you need.

Bubbles can also be caused by using an old box or bag of investment. We used to by investment by the ton, sometimes when we got down to the last few boxes, we would start getting bubble problems in our castings. Even though we were doing everything exactly the same. We finally figured out that the bubbles were caused when we used the older boxes of investment. Changing to a new fresh batch of investment cleared up the bubble problems. There is usually a code on the box of investment that will let you know how "fresh" the investment is. Don't buy investment that has been sitting at the jewelry supply store for several months. If you do need to use old investment, roll the box around on the floor before using to help mix the ingredients up, that will help.

Unless you are buying a very expensive induction system (vacuum) we highly suggest using a centrifugal casting machine. You will save yourself a lot of headaches. Centrifugal machines are more forgiving, less overall problems. Just a word of advice.