启发式算法热轧机铝英文文献和中文翻译(3)
the same batch.
(4) Min/max heating duration: heating duration interval that
depends on the homogenization code of the batch.
With regard to preferences, a penalty must be paid if they
are not satisfied. Only one type of preferences is considered
for the furnaces, namely:
(1) Codes and products: Preferences may be expressed for a
particular furnace type, depending on the homogenizing
code and product type.
2.2. Hot rolling mill
Hot rolling considerably reduces the thickness of a metal
piece by pushing it many times through two extremely hard
cylinders or rolls that spin at high speed. As its name points
out, this operation must be done at high temperature to ease
thickness reduction. Ingots are unloaded one by one from
the furnace and are directly rolled to avoid excessive cooling.
Although a plant might have many rolling mills, a single mill
is considered in this study.
2.2.1. Alloy groups and roll life. Alloys are classified into
hardness groups from softer to harder. Here, we only have
two groups (soft and hard) but the same ideas can be
applied for more groups. Each alloy group has its own roll
wear coefficient. This constant coefficient is the average
amount of wear that a particular ingot of this alloy group
causes when it is rolled. Rolls must be changed when they
are too worn; the time between two consecutive roll
changes is called a roll life.
2.2.2. Hard and soft constraints. To meet quality
standards during rolling, some rules must be followed.
Here is the list of hard constraints that must be taken into
account by the hot rolling mill:
(1) Wear interval: Each ingot of a particular hardness group
has a wear interval within which it can be rolled. These
intervals are not disjoint in general.
The list of preferences for the hot rolling mill is the
following:
(1) Hardness transition: As much as possible, soft ingots
must be rolled before hard ones in the same roll life
because soft alloys require less damaged rolls.
(2) Width: Ingots should be processed in non-decreasing
order of width to avoid damage to the sheet edges (due
to roll deformation).
(3) Final thickness or gauge: Ingots should be rolled in
non-decreasing order of gauge. Furthermore, large
transitions between consecutive ingots should be avoided.
This is because abrupt transitions require manual
adjustments on the mill.
In practice, it is almost impossible to satisfy all preferences
because they are often contradictory. Furthermore, the
sequence on the rolling mill highly depends on the homogenization furnaces, since ingots must be heated before
they are rolled.
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