Penalties for The Slab Yard Scheduling

By:
www.sitnah-aisyah.blogspot.com

There are four possible modes of scheduling the Continuous Caster, Slab Yard, Reheat Furnace and Hot Strip Mill, according to the way the continuous caster provides slabs for the hot strip mill, as well as the temperature of slabs (Dorn and Kerr, 1996a; Lee et al., 1996; Vaessen et al., 1996; Lopez et al., 1998; Cowling and Rezig, 2000; Tang et al., 2000a; Tang et al., 2001):

1. Continuous casting cold-charge rolling: in this traditional process, the
continuous caster and the hot strip mill are totally unlinked. Slabs cool down
at ambient temperature in a slabyard after they are cast. The rolling planning
and scheduling operates on the real slabs stored in the slabyard. The slabyard
is used to reconcile and maintain the coordinated production between the
continuous caster and the hot strip mill.
2. Continuous casting hot-charge rolling: in the hot-charge rolling process,
the warm slabs are held in local slabyards or in insulated chambers to cool
down for at least a minimum of five hours before being rolled. Then the
slabs are lifted from the local slabyards and charged into the heat furnace in
batches for heating based on the rolling requirements.
3. Continuous casting direct-hot-charge rolling: hot slabs coming from the
continuous caster are directly charged into the heat furnace through transfer
rails or cars in the hot state, and then the hot rolling process is undertaken.
The charge temperature varies from 700 C to 1000 C
4. Continuous casting hot-direct rolling: without being heated through the
heat furnace, hot slabs are directly sent into the hot strip mill after the edge
heater heats the slab edges. In general, slabs are kept at over 1100 C before
rolling. More direct linkage between the continuous caster and the hot strip
mill means more energy saving and shorter production lead-time.[1]


Fig 1. Slab Production Process from Continuous Caster, Slab Yard, Reheat Furnace

In the case of the system where the products of Continuous Caster need to be stored for a few days in a slab yard, the first and the second mode will have to provide a scheduling method to minimize the inventory. One way to do such scheduling system is to count on the penalties that probably occur during the operations. This is quiet a good idea and also an interesting way to schedule the slab yard since most papers only consider the slab yard as a 'static' inventory while in fact it is 'move' when slabs from the casting machine has removed into the yard, stored for five hours to weeks, and then has charged to the Reheat Furnace. Slabs are stored in piles, and each pile represents certain steel grade and dimension. It has to be done so the crane will easily remove the required slabs into the furnace without have to unpiling the slabs.

Here are some penalties for the slab yard scheduling:
1. Penalty for the change of steel grade of the adjacent slabs in a pile
2. Penalty for the change of width of the adjacent slabs in a pile
3. Penalty for the change of length of the adjacent slabs in a pile
4. Penalty for the change of thickness of the adjacent slabs in a pile

From these penalties we can understand that the arrangement of slabs in slab yard has to be done by dimensions, not by orders.

(Maaf kalo English-nya belepotan. Tulisan ini aq buat dalam rangka menyukseskan penyusunan tesisku. Walau banyak salahnya, semoga cepat selesai deh...)

[1] Ouelhadj, 2003