attachments_01-06-2012_20-54-12 / 21

are carried out in one furnace, In the modified procedure, steel scrap is melted in a high-power arc furnace and then tapped into a ladle where it can be vacuum-degassed, stirred, reheated and given alloy additions before being cast into moulds.

By separating the two functions of melting and refining, better utilization of the equipment is obtained, since the two operations can proceed simultaneously. While one heat is being refined, the next is being melted, so that a higher output is obtained from a given size of melting unit. In addition, the refining operation can be far more closely controlled than in a conventional melting unit and, consequently, it is possible to obtain a more consistent and better quality product.

The firth brown plant

In the plant installed at Atlas Works melting takes place in a 5.2 m diameter arc furnace rated at 31.5/37.8 MVA with a nominal charge capacity of 60 tonnes, but which in practice can range between 40 tonnes minimum and 75 tonnes maximum. After melting, the steel is tapped into an austenitic steel ladle specially designed to work with the refining unit. Using this equipment, heating, alloying, vacuum degassing and refining can be carried out in any desired sequence.

The ladle is placed on a transfer car which is provided with facilities for stirring the charge at any stage of the processing cycle. Stirring is by electromagnetic induction using a 700 kVA, I Hz supply, this low frequency (one cycle per second) being obtained from a static converter. A good controllable stirring action results, giving efficient mixing of alloy additions. The stirring action also ensures a more effective separation of non-metallic matter resulting in cleaner steel. The stirring of the liquid steel combined with the reheating enables the operator to obtain the correct temperature uniformly throughout the melt and thus cast the steel at the optimum temperature. It is also possible to adjust the analysis of the steel by late additions

38

since the rapid stir ensures uniform, composition and homogeneity throughout the steel undergoing treatment.

Tap-to-tap times are of the order of 2 hours for the primary melting arc furnace and 1,5 hours or less for the ladle furnace—say 3,5 hours in all. However, Mr. Peter Fox, Firth Brown's Production Director, is already thinking in terms of thirty melts a week—depending, of course, on the type of steel being made.

Firth Brown reports that the following advantages have resulted from the installation of the new plant in the Atlas Melting Shop:

1. by separating the refining operation from that of melting, increased production has been obtained;

2. in addition, because of the greater degree of control, considerable improvements and greater consistency in regard to steel cleanness have been obtained such that quite stringent specifications can now be accepted with a high degree of confidence;

3. the greater uniformity of the molten steel, as a consequence of the ability to stir, makes for more accurate analytical control and thereby significant savings in alloys.

Production/universal lathe

The U100 production universal CNC lathe, from H.E.S. is the modern day version of an automatic production tracer lathe.

Swinging 19 5/8 in. over the bed, 7 7/8 in. in front of the slanted cross slide with an overall maximum machining diameter of 12 3/4 in., the U100 can accept a 29 in. long piece and uses CNC, a 25HP, DC spindle drive motor and either an 8 tool or 10 tool automatic index turret.

■

39