Blast furnace rebuild programme
Recently, as part of a complete blast furnace rebuild programme for Dofasco Inc., a fully integrated steel producer from raw materials through to coated steel sheet, in Canada, Metalock machined fifteen hearth shell bores to accommodate tapered tuyere cooler holders. the Metalock Engineering Group secured the contract on a competitive basis.
The first operation for the Metalock team was to assemble a drill jig on the inside and outside faces of No 1 tuyere holder to drill and tap four equi-spaced holes 0.625 inch diameter x 1 inch deep on a 38.5 inch PCD (16mm by 25mm deep on a 978mm PCD). These holes were used to mount a boring bar assembly, with inner and outer bearing supports, to machine the tapered cooler holder bores. To position the boring bar assembly accurately, a telescope was fitted to the outer end and the bar aligned visually with the furnace central datum and a datum point on the opposite inner shell through a central hole in the bar. Being equi-spaced around the shell circumference at 24 degree intervals, the tuyeres were not diametrically opposite each other.
Purpose-designed boring machines
Two purpose-designed boring machines, built by the Metalock Engineering Group, incorporated hydraulic drive gearboxes and a toolpost assembly that traversed along linear rails set at an angle of 7 degrees to produce the taper required through each of the fifteen 5.187 inch (132mm) thick tuyere bosses. Then the faces and the inner diameter of the bore was machined to 31.921 inches (811mm). The outer bore was stepped by a further 0.125 inches (3mm) to provide relief for the cooler holder and give a diameter of 33.980 inches(863mm).
Using two identical machines each working on adjacent cooler holders simultaneously, Metalock was able to substantially speed up the machining process. Work continued round the clock using three men per shift to complete the schedule on time.
