Steel Mill Question
Steel Mill Question
(OP)
Hey guys. Im a new guy here and hope y'all can help out.I work at a steel mill where we cast a slab up to 8 feet wide and then roll it down to as low as 0.187". Then we coil it up into a coil that has a width of 96" and an 'eye' of 30". The OD varies by what the customer wants, and they order in tons. The maximum weight of our coil is 90,000 pounds or 45 tons.
After we coil it up, we set it in the coil yard for a minimum of 48 hours, as we can only further process it, i.e. uncoil it and temper pass, level the material and cut to length, resulting in stacks of flat plate, when the temp of the coil is 250 deg F or lower. The coil come off the hot mill at about 1100 F. So due to natural radiant losses, we lose about 850 F in 48 hours.
Currently, our coil yard is a slag/gravel mix that we can set the coils directly on the ground. We are constantly grading the coil yard due to potholes, etc., so we have decided to pave the yard. I did a bit of homework and see that concrete starts to erode and fine cracks start at about 550 F. So our choices are to insulate the ground where we place the coils or to keep the coils off the ground a certain distance so we dont expose the surface of the crete to 550 F. How do I figure out the distance we need to keep the above described coils off the ground so as not to ruin our new concrete surface?
many many thanks for any responses.
Mark
After we coil it up, we set it in the coil yard for a minimum of 48 hours, as we can only further process it, i.e. uncoil it and temper pass, level the material and cut to length, resulting in stacks of flat plate, when the temp of the coil is 250 deg F or lower. The coil come off the hot mill at about 1100 F. So due to natural radiant losses, we lose about 850 F in 48 hours.
Currently, our coil yard is a slag/gravel mix that we can set the coils directly on the ground. We are constantly grading the coil yard due to potholes, etc., so we have decided to pave the yard. I did a bit of homework and see that concrete starts to erode and fine cracks start at about 550 F. So our choices are to insulate the ground where we place the coils or to keep the coils off the ground a certain distance so we dont expose the surface of the crete to 550 F. How do I figure out the distance we need to keep the above described coils off the ground so as not to ruin our new concrete surface?
many many thanks for any responses.
Mark





RE: Steel Mill Question
RE: Steel Mill Question
How are the rolls handled and moved?
How are they supported while waiting above the new concrete?
RE: Steel Mill Question
some back of the envelope calculation suggests a separation of 2 meters
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RE: Steel Mill Question
mark
RE: Steel Mill Question
Coils being spun while in contact with the slag/gravel mix? Forklift operators must stop doing that... [I know it's possible to not do that; one of my summer jobs between secondary and post secondary education was forklift operator
Forklifts being turned on a dime and gouging out a divot? Again, forklift operators must stop doing that...or if they can't or won't, perhaps using an articulated forklift [the kind with a knuckle joint in the middle] might eliminate the problem...
The surface you already have may well be the best choice available; I don't know that I'd be in a big hurry to go with a solid surface of any kind due to the thermal issues involved...I'm no civil engineer, but I'm wondering if it might be possible to obtain a durable enough surface by adding limestone screenings to fill in the voids, then tamping...
I ditto your safety concerns about elevated racks to support loads that heavy.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Steel Mill Question
Again, thanks everyone for some insight....
RE: Steel Mill Question
Leave a section of the gravelled area unpaved (call it 10' deep by XXX' long). Drive the forktrucks on the paved areas and park the rolls on the unpaved areas. If necessary, do this in strips, alternating paved with unpaved areas, making sure that the paved areas have enough room for the forktruck to turn in and spear the rolls. Alternately, you can have a smaller unpaved footprint by angling the rolls, dropping maybe 3' off the width (if you use a 45 degree angle) of the unpaved sections. Also, those trucks are going to be HEAVY with the roll and counterweight, make sure you check with the paving firm for how long you need to stay off of the concrete, it's usually at least one week (60% of maximum strength) but you may need to wait 4 weeks (~90% of max strength). Also, paint some "parking" stalls on the surface to try and enforce spacing and to reduce clutter in the yard.
Regards,
Matt
Quality, quantity, cost. Pick two.
RE: Steel Mill Question
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Steel Mill Question
RE: Steel Mill Question
If I understand your description, then the length (axial distance) of each coil is 8 feet, right? Use either three or four rails per coil, with the fork lift approaching each set of 3x rails from the side - perpendicular to the set of rails.
Intent is to raise the coil up off the concrete so there is no conduction of heat from the coil to the concrete, and so the coil is not damaged (scarred, scratched, dented or dirty, contaminated) by laying on the rock as it is now, but only limited areas of each coil touches the top of the 3 or 4 rails. (Check your collapse or crushing load, you only need enough rails to avoid physically damaging the outside coil layer.)
If the coil is raised, conduction is stopped (except coil-to-rail, but that has little surface area) and convection is increased under and around the coil into the air. (Assume each coil is at least 6 inches from its neighbor in the row of coils)
So, that leaves radiation as the only possible damaging heat transfer from coil outside layers to the concrete. Since the rails are supporting the 9potential) 45 tons of steel, you don't need any fancy (expensive!) barrier to stop the radiation transfer, merely a LOOSE and LIGHTWEIGHT reflective surface between the coil and the concrete. Loose is essential so the reflector can be cooled by air flow, lightweight means there is little heat transfer conductive contact between the reflective surface and the concrete below.
It won't last, but imagine a folded sheet of reflective sheetmetal between each rail, above the concrete and below the coil. The top layer of sheetmetal reflects back the heat, the bottom layer of sheetmetal separates the top layer from the concrete, the air space between the two allows cooling air to flow and cool both. Over time, the upper sheetmetal will get dirty and corroded 9darker) and so become less effective, but that may be acceptable, or may require changing every three years.
Once raised up, other forced air cooling methods may be used as well to speed up the coil cooldown rate.
RE: Steel Mill Question
If at a certain distance away, the view factor to the coil is 0.5, say, then the view factor to the surroundings will be (1-0.5)= 0.5 and so the temperature of the ground will be 0.5*1100F+0.5*68F = 584 F. You can calculate the actual distance required from the expressions on the web site given to give a more definitive answer.
Note that this excludes convection to air circulating around the coil and transient effects and probably half a dozen other things, but may give some kind of idea on how far to raise the coils.
RE: Steel Mill Question
RE: Steel Mill Question