Crucible withdrawal devices were developed in order to circumvent the patent for the crucible removal device. In this case an approx 20 mm thick steel plate with a 30 – 50 mm hole is inserted centrally below the crucible. To withdraw the crucible, a hole is then drilled in the crucible bottom, a rod fed through the hole from inside the crucible, and the rod fixed in place below the withdrawal plate by means of a nut or wedge. The crucible is then withdrawn with the aid of a crane, although the crab must not be in the centre of the jib when lifting, since this method of working is not without risk. When applying a lifting force of approx. 10 t, the crucible is released suddenly, and the weight of the crucible now hanging from the crane hook is in this example only 3 t. This procedure with the sudden change of load can cause the crane to “buck”.
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