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Automation
13.1 GENERAL
One of the greatest developments in HSMs since 1960 has
been the successful implementation of computer process
control tor the rapid and complex tasks in today's mills tor
better product. The operator must at all times observe the
perfomance of the mill and be in a position to take over
manual control instantly in the event of an emergency or a
computer tailure, although the latter is now becoming very
rare.
Throughout the design of the Westernport HSM computer
system, care has been taken to automate those functions
which contribute to improved coil quality or productivity,
while seeking to retain .tor the operator an interesting job
with manual control over those functions which he can do as
well as, or more satisfactorily than, the computer.
The process computer is centralised in a room· behind the
finishing mill pulpit. The computer receives signals from
various metal detectors, pyrometers, load cells and motor
instrumentation in the mill on which to base its calculations
and sends its signais to direct the equipment Today many
control actior.s can be modified simply by rewriting the
computer program whereas previously this required modifi.
cation to the wiring or equipment installed out in the mill.
The extent of computer control varies considerably between
mills. The tcllowing outlines the functions provided by the
Westernport HSM computer. The computer facility is in fact
two computers, known as SPC and /PC.
SPC (Stored Program Controller) - directS position
regulators and sequences, directS and co-ordi-
nates drives.
IPC [Integrated Process Controller) - contains all
the mathematical models describing the rolling
process control and provides values of control
settings to the SPC. It also tracks the steel's
progress throughout the mill and records associ·
ated data.
In manual operation of the mill the operator's desk settings
substitute tor the IPC. The SPC must be working tor the mill
to operate under manual or computer control.
The functions of the computer car: be grouped into:
- executive functions
- predictive functions.
13.2 EXECUTIVE FUNCTIONS
13:l.1 TRACKING
When the rolling schedule or sequence of slabs Is
prepared by the Production Planning Department's
Scheduler, a punched card representing each siab is
produced. This contains Prim:lry Data Input {PDIJ -
le, details of the slab's sequence number, its dimen-
sions, its hardness and the product dimensions and
temperature to which it must be rolled. A set of
printed sheets known as the schedule is also provided
to each pulpit operator; this gives all the data needed
tor the operator to follow the progress of each piece
through the mill and to take over manual rolling in the
rare event of JPC computer failure.
Each slab is placed on the charging table in strict
accordance with the sequence ·on the schedule. The
charging pulpit operator feeds the POl cards into a
reader and he checks that the sequence number writ·
ten on the slab is the same as that on the next PDI
card in the pack. If. so, he charges the slab into the
furnace and the computer accepts into its memory all
the POl information about that slab.
From that point on the computer at sll times knows
where that slab Is within the furnace and throuchout
the rolling train. Hot metal detectors (devices ;.,hich
sense the radiation from the hot steel). and the mill
stand load cells send signals to the computer to
enable it to follow the progress of each piece. Informa-
tion on the identity of each piece entering the activity
zone of each pulpit is displayed by digital displays to
the pulpit operator who checks that this corresponds
to the next slab on the schedule.
If a piece is removed from the rolling process, say
because it is damaged or because of mill breakdown,
the pulpit operators dial In instructions to the compu-
ter to correct its records.
When the coil reaches the weigh scale, the mass is
accepted by the computer and typed out on its records,
known as logs. ·
The control stations have small preen lights which
come on as the steel enters various zones of the
rolling train; this reassures the operator that the
computer has received the required signals.
13.2.2 AUTOMATIC OPERATIONS
The roller tables are controlled in a number of sections
or groups. The computer continually selects and con-
trols the speed and direction of each table group. The
roughing mill roll and side guide openings and rever·
sals are automatically initiated as are the descaling
sprays. The cropshear, automatic thickness control and
coiler sequencing are automatic. The coil box tor bar
coiling is also mainly automatic•.
When the bar is -detected by the hot metal detectors,
the SPC sets side guide openings, all positions and
roll and knife speeds so as to correctly coil the bar,
feed It to the cropshear and trim both the head and tail
ends of the bar by a predetermined length. The calcula-
tions take into account the speed, width, thicknes:; and
strength of the steel.
The fmishing mill automatic thickness control has been
described in Chapter 8. The system estimates the
thickness out· of each stand by comparing actual thick·
ness with desired thickness and varying the screw·
down settings accordingly. Feedback from the X-ray
thickness monitor 5 m after the last stand may be
used to vary roll settings to improve accuracy.
The downcoiler is automatically sequenced from when
the head end of the strip enters the downcoiier until
the operator stops the mandrel. This includes setting
side guid~ openings, pinch rolls, downcoiler cooling
sprays, co1ler entry gate opening and closing, and the
movement of the wrapper rolls.
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2. AUTOMATION
'13.2.3 LOGGING
Logs are typed-out collections of information on the
performance. of the mill during normal and abnonnal
running.
Engineering logs Include information on the piece of
steel being rolled, predicted and actual mill settings,
etc. Alarm logs are typed out for information on
emergencies.
Production logging includes coil quality, delays, mass.
shift and fault logs. The quality log contains identity
of the coil and the width, thickness, finishing tempera-
ture and coiling temperature performance; the metres
of product falling in two bands on each side of the
acceptable band of performance are recorded together
with the classification (prime or reject, with the
reason tor rejection) keyed in by the finishing mill
operators. The delay logs give the reason and magni-
tude of delay. Each coil's mass is logged. The shift
log Is a summary of the numbers and masses of slabs
rolled and rejected, and the prime yield each shift.
The fault log assists the engineers in the analysis of
the mill operating conditions which applied In an
emergency.
13.3 PREDICTIVE FUNCTIONS
13.3.1 FURNACE FIRING CONTROL
This Is not provided initially but may be developed
iater.
13.3..2 ROUGHING MILL AND EDGER SET-UP
For the required strip width and thickness, the compu-
ter selects values of transfer bar width and thickness
required. Using stored models. the computer calculates
the settings of sideguides, roll positions and speeds to
deliver the transfer bar at the required dimensions
with minimum heat loss. The calculation takes into
account the slab dimensions anti temperature, the bite
angle. roll separating forces, mill stretch. motor torque,
and roll diameters. The computer sends out all the
values or references to the actuators on the mill, and
Initiates the passes and reversals. Oescaling sprays
are switched on as directed by the- POl instructions
or by the operator.
A width gauge after the last finishing stand feeds back
the actual width achieved so that the computer can
be more accurate on the next similar bar.
13.3.3 FINISHING MILL SET.UP
This calculates the roll openings and speeds required
to deliver the strip at the required thickness and main-
tain a balanced flow of steel through the mill. The
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roll openings are calculated from models taking Into
account the expected roll separating force and the mill
stretch. The threading speed is set by the operator
or by the Finishing Temperature Set.Up function.
The measured roll separating force at the fil'$t stand
Is compared with the calculated value and the set-up
of the subsequent stands is varied to compensate tor
any difference. This Is repeated tor subsequent stands
to bring the head out as close as possible to the
target thickness and then the automatic thickness
control takes over to keep It as constant ·as possible
throughout the strip's length.
The computer compares the measured thickness with
the actual and upodates or adapts Its stored model for
a better resu"Jt on the next rolling of a similar product.
13.3.4 FINISHING TEMPERATURE SET-UP
This calculates the threading speed required to bring
the head end out at the required temperature. Several
calculations are made, the final one being when the
temperature of the head end of the bar (tail end when
using the coil box) is measured just after the last
roughing pass. A temperature model calculates how
much heat is lost by the time that part of the bar
reaches the finishing mill. Scaling of the bar prevents
reliable measurement near the finishing mill entry. The
set-up model takes Into account the cooling effect of
any sprays the operator has selected.
Again this model adaPts to Improve Its accuracy next
time.
13.3.5 FINISHING TEMPERATURE CONTROL
The speed of the finishing mill Is varied throug...,e:."t
the rolling .of the strip to compensate tor bar cooiing.
13.3.6 COIUNG TEMPERATURE SET·UP AND CONTROl.
Before the bar enters the finishing mill, a calculation
Is made of the number of spray banks to be turned
on on the run-out table. The number of sprays is varied
throughout the length of the strip If the measured
finishing temperature varies. Again the mode! is
adapted for a closer approach to the target tempera-
ture on the next similar Strip.
13.4 SUMMARY
Automation of the HSM is of enormous assistance in achiev-
Ing top quality product at high productivity and lowest cost.
It does not reduce operating personnel numbers but it does
handle the complex tasks with greater accuracy than is
otherwise possible at high speed.
Figure 31 summarizes the major functions.