is a laborious procedure, which requires much preparation and preliminary work, even when installing the coil. The centre of the crucible must be able to be determined accurately by means of 3 or 4 fixed points on the furnace platform. When installing the furnace coil, the coil must be installed exactly at this central point. Markings must be applied to the vertical plumb fitted in the centre of the coil at vertical spacing of 100 or 150 mm. The distance between the centre and the coil wall is now determined and documented in four directions. When installing and aligning the lining template, the exact centre, i.e. the distance from the plumb and the tamping template, must also be maintained and documented if necessary. After furnace operation, and the first cooling down of the tamping compound to approx. 40 °C, the crucible can then be measured accurately. This method also allows the identification of any lateral, excentric erosion of the tamping com- pound .A simpler method, which however does not allow the identification of excentric erosion, is the use of an excentric T-beam. The shorter T-beam is weld- ed to a holding rod at a distance of 1/3 : 2/3. The short T-beam is the measuring beam, which can be produced in 4 different lengths, or adjusted to different lengths by means of screw bolts. This gives firstly the nominal dimension and then the enlarged diameters in steps of 10-15 mm. With this measurement method, the crucible diameter can be checked immediately after total emptying.
Nominal dimensions for 12.5-t furnace
Coil diameter 1,470 mm
Crucible diameter 1,190 mm
Total wall 140 mm
min. remaining wall 95 mm
i.e. max. crucible diameter 1,280 mm
Measuring beam max. 1,260 mm
Holding rod = furnace depth + 1 m