01-20-2009, 05:33 PM
Josh, you show a "broiler house" on your plan - should this perhaps be a "boiler house"? 
One of the benefits of a continuous caster is that it eliminates several operations in the steelmaking process, cutting down on facilities, associated equipment and labour. The plant where I worked cast both slabs and billets, using the same caster (although not at the same time). Slabs varied in width from, if I recall correctly, about 57" up to at least 80", and lengths varied from a minimum of 175" up to about 40' - the thickness was always just under 10". Billlets were cast in two "strands" at the same time and were generally the same thickness and about 25" wide, and, I'm guessing, about 15' long. Slabs went, for most grades, to #2 Conditioning, where they were, in some cases, slit lengthwise into two slabs (this was destined for the Strip Mill, which was only capable on rolling fairly narrow slabs). After slitting, and, for slabs that weren't slit, all were visually inspected for defects, and some or all, depending on the grade, would be "scarfed" with very large hand-held torches - this was to allow better inspection of the surface for cracks, and also to remove defects, such as scrap inclusions, etc. The large, un-slit slabs were sent to another plant, where there was a strip mill capable of rolling coils up to 80" wide. Certain grades of slabs were conditioned, then sent to the Plate Mill, where they would be torch-cut into shorter lengths, then rolled as plates, which, again depending on the grade, could be used in shipbuilding, railway cars (particularly hoppers), pipe, pressure tanks, or military tanks.
Billets underwent a similar process, and, like slabs, were re-heated, then rolled into various sizes for further processing.
A continuous caster eliminates the ingot moulds, and their stools, buggies, handling, and preparation, along with the stripper cranes that remove the moulds. The slabbing mill is also eliminated, with its soaking pits (for re-heating ingots for rolling), roller stands (for turning the ingots into slabs), shears (for cutting off the head- and tail-crops and for cutting slabs to ordered lengths), and slab handling equipment. Waste is reduced, as casting is continuous - there's scrap at the front end of the "strand", and no more (if things are working properly) until the caster is shut down for maintenance or to change the slab mould over to billet moulds. Every ingot, when rolled into a slab, has scrap at both ends of the slab. Quality control is also more precise - with ingots and billets, additions of various elements and compounds was done manually - shovels-full of this or that, and "a few bags of such-and-such" tossed in. With a caster, these are done with machinery controlled, nowadays, by computers.
When steel is cast into moulds, as ingots, it has to sit in the mould a specified time, depending on the grade, the type of ingot, and the size of the ingot, before the mould can be removed. This is to allow it to harden sufficiently for the stripping process. The minimum time, at least at our plant, was an hour and a half, but most were longer, up to four hours. Of course, as the steel hardens, it's also getting colder. When the ingot finally gets to the soaking pits, it will take proportionately longer to re-heat it to rolling temperature (about 2350 degrees F. for most grades).
Cast slabs, on the other hand, are solidifying as they pass from the bottom of the mould, and, by the time the strand reaches the torch cutting operation, it's solidified right through. Since it needs, in most cases, to be conditioned before further processing, it may be sent to a slab yard, where it's allowed to cool. When the slabs have been conditioned, and move on for further processing (usually some form of rolling) they still have to be reheated. However, a 25 ton slab can be re-heated much more quickly than can a 25 ton ingot, as the slab is both thinner than the ingot and has a much larger surface area through which to absorb the heat. It's easy to see why continuous casters are much more common than the older processes.
Wayne
One of the benefits of a continuous caster is that it eliminates several operations in the steelmaking process, cutting down on facilities, associated equipment and labour. The plant where I worked cast both slabs and billets, using the same caster (although not at the same time). Slabs varied in width from, if I recall correctly, about 57" up to at least 80", and lengths varied from a minimum of 175" up to about 40' - the thickness was always just under 10". Billlets were cast in two "strands" at the same time and were generally the same thickness and about 25" wide, and, I'm guessing, about 15' long. Slabs went, for most grades, to #2 Conditioning, where they were, in some cases, slit lengthwise into two slabs (this was destined for the Strip Mill, which was only capable on rolling fairly narrow slabs). After slitting, and, for slabs that weren't slit, all were visually inspected for defects, and some or all, depending on the grade, would be "scarfed" with very large hand-held torches - this was to allow better inspection of the surface for cracks, and also to remove defects, such as scrap inclusions, etc. The large, un-slit slabs were sent to another plant, where there was a strip mill capable of rolling coils up to 80" wide. Certain grades of slabs were conditioned, then sent to the Plate Mill, where they would be torch-cut into shorter lengths, then rolled as plates, which, again depending on the grade, could be used in shipbuilding, railway cars (particularly hoppers), pipe, pressure tanks, or military tanks.
Billets underwent a similar process, and, like slabs, were re-heated, then rolled into various sizes for further processing.
A continuous caster eliminates the ingot moulds, and their stools, buggies, handling, and preparation, along with the stripper cranes that remove the moulds. The slabbing mill is also eliminated, with its soaking pits (for re-heating ingots for rolling), roller stands (for turning the ingots into slabs), shears (for cutting off the head- and tail-crops and for cutting slabs to ordered lengths), and slab handling equipment. Waste is reduced, as casting is continuous - there's scrap at the front end of the "strand", and no more (if things are working properly) until the caster is shut down for maintenance or to change the slab mould over to billet moulds. Every ingot, when rolled into a slab, has scrap at both ends of the slab. Quality control is also more precise - with ingots and billets, additions of various elements and compounds was done manually - shovels-full of this or that, and "a few bags of such-and-such" tossed in. With a caster, these are done with machinery controlled, nowadays, by computers.
When steel is cast into moulds, as ingots, it has to sit in the mould a specified time, depending on the grade, the type of ingot, and the size of the ingot, before the mould can be removed. This is to allow it to harden sufficiently for the stripping process. The minimum time, at least at our plant, was an hour and a half, but most were longer, up to four hours. Of course, as the steel hardens, it's also getting colder. When the ingot finally gets to the soaking pits, it will take proportionately longer to re-heat it to rolling temperature (about 2350 degrees F. for most grades).
Cast slabs, on the other hand, are solidifying as they pass from the bottom of the mould, and, by the time the strand reaches the torch cutting operation, it's solidified right through. Since it needs, in most cases, to be conditioned before further processing, it may be sent to a slab yard, where it's allowed to cool. When the slabs have been conditioned, and move on for further processing (usually some form of rolling) they still have to be reheated. However, a 25 ton slab can be re-heated much more quickly than can a 25 ton ingot, as the slab is both thinner than the ingot and has a much larger surface area through which to absorb the heat. It's easy to see why continuous casters are much more common than the older processes.
Wayne