Introduction: A low-tech method of creating the centrifugal force needed to create precise castings in some metals. In this centrifugal system, the operator becomes the machine- the person supplies the power.
» Process: Make a sling keeping in mind that it doesn't have to be anything faaancy. This technique is possible for flask a big as 3X3. In order to keep the molten metal from dribbling into the mold cavity as it melts, the sprues must be small enough that the surface tension ofo the metal prevents it from entering the sprue openings through the fore of gravity.
When the flask is ready, set the sling caster onto a heat proof surface such as fire brick and check the area all around and overhead to be sure the swinging action will not be impeded. Set the flask into the center of the sling's pad. If using large models, clamp the holddown lid into place by screwing the bolts down the threaded rods.
Set the metal into the neck of the flask and melt it with a torch, adding flux a couple times. When th emetal is completely molten, stand close to the sline, raise it high enough to straighten out the cable or rods, and slowly sway it ba ck and forth a few times to get the feel of it. Keep the torch on the metal while this is going on.
Remove the torch and simultaneously snap the sling overhead in a broad circle. Speed is important as a constant pressure, in this case not noly to force the metal into the mold, but also to keep the hot flask from dropping on the head. After a few minutes of swinging, gradually slow down the swing and allow the sling to come back to vertical position. When the button has lost its red color the flask can be quenched.
A simple sling machine can be made of a couple pieces of pipe that telescope together. Weld the cross bar to the outer tube and configue some way to attach a counter weight. Wrap a piece of rope sround the column and pull it when the metal is molten. This will cause the pipe to spin and force the metal into the mold as the flask is pulled into a horizontal position. The machine must be securely fastened to a solid base.
