Cross Country Bar Mill Control

Cross Country Bar Mill Controlpermissive is missing, the operator can easily locate
 the problem using the extensive diagnostic features
Abstractprovided by the system.
This paper describes how Nucor Steel Marion, IncStand permissives are grouped and managed so that,
(former Marion Steel Company) improved Rolling Millin some cases, a countdown will begin before the
yield and productivity by 20% and 10% with less thanprocess is interrupted. This function enables operation
one million dollar investment in 2004. Three factorsto take the required action to avoid delays depending
increased mill yield: less cobbles due to a better andon the available time.
more robust master control, less amount of bars lostCascade Speed Control
during product changes due to better mill set­up, andBased on Mill Set Up parameters like delivery speed,
less waste material due to improvement in flying shearstand reduction factors, gear ratio and stand
cut precision.diameters, the speed reference set point is generated
Productivity improved as a result of increased millfor every equipment. Operation has the ability to
uptime due to less operational and maintenance delaysmodify the stand speeds in two different ways. The
as well as a secondary effect of yield improvement.first is to adjust an individual stand speed, this operation
The project included several challenges: to integrate awill modify the reduction factor of that stand and the
new coordinated control system to improve milldownstream stand in opposite direction. The other, and
availability with minimum investment and makingmost common way is to cascade the speed of all
maximum re­use of a variety of old equipment andupstream stands in order to modify only the reduction
technologies.factor of the selected stand. All automatic
Introductioncompensations like Loop Control manipulation modify
Nucor Steel Marion, Inc. is a division of Nucor Steelstand speeds in cascade mode.
meaning that they share the same business philosophy,Cobble Detection
which focuses on taking care of customers by beingThe cobble detection function provides detection of
the safest, highest quality, lowest cost, most productivehead end cobbles that occur in the mill. It utilizes HMDs
and profitable steel company in the North America.and stand loads to detect metal presence and works
Nucor Marion manufactures a full line of specialty steelon the principle that each detection should occur at
products in the specific shapes needed for thesome specific interval after the last detection. The
highway, construction and agricultural industries. Thesystem predicts the time interval based on the given
company also specializes in rebar, merchant rounds,stand speed. If metal is not detected as expected,
breakaway U­channel, small and mid­rangethen a cobble is declared.
signposts, delineators and cable barrier systems.Interstand Loop Control
In order to serve the concrete construction industry,The Finishing Mill is equipped with interstand loopers to
Nucor Marion manufactures reinforcing bar. Theassure there is no tension in the bar. The Interstand
breakaway U­channel systems for small andLoop Control algorithm was also written in the
mid­sized highway signs exceed crash impactInnovation Series Controller, which has the ability to run
standards by over 200% and they utilize new­billethigh speed tasks. The control loop achieved the great
steel that has 25% greater tensile strength and costsrobustness required in order to have a high
up to 50% less.performance and stability trough all different products
Combining these features and the current qualityand speed range. It also has the ability to learn, it saves
standards of a plant like this, there were severalthe control loop manipulation for the next bar. By doing
variables that were faced in order to provide the bestthis, the algorithm maximizes product quality by
control system from the furnace automation and billetminimizing response loop time after just a couple of
tracking through the complete revamping of thebars of the heat.
master control of the rolling mill and cooling bed.Roughing Mill Interstand Low Tension Control
Scope of the ProjectIn the Roughing Mill there are no loopers. Operation is
According to the standards of the company, theirresponsible to run each stand at the required speed,
system was required to meet the functional controlso there is no tension in the bar. This function is also
requirements through the integration of coordinatedaccomplished automatically for a wide range of
drives and control system. Overall performanceproducts. Once the Mill Set Up is accurate, the system
requirements are based on the user's business needscan sense and evaluate load fluctuation in every stand.
as they relate to production, quality, reporting andIf the system senses an increase of load in particular
system availability.stand, it would mean that the stand is pushing the
Marion Steel and AMIGE worked closely to define andmaterial into the downstream stand. In this case, the
agree on the systems that should be upgraded instand speed would be slowly and automatically
order to maximize the cost­benefit relation. Thecascaded down until the situation disappears. The
extensive knowledge of the process variables andalgorithm also works in the opposite direction as well,
best rolling practices by Marion Steel personnel wereincreasing the stand speed if the downstream stand is
enhanced with state of the art control equipment andpulling the material.
algorithms integrated in the very robust and openBar Mill Shears
architecture of the system provided by AMIGE.Clutch and Brake shear control applies to both Crop
The basic system philosophy met the followingand Flying Shear. Control is provided for Clutch Shear
requirements:where the shear drive runs continuously at the product
- Enhance performance and reduce communicationspeed plus a lead adjustable speed.
latency by customized structuring of the functionalThe shear cutting cycle is initiated by closing the
control to the mill configuration, including placing theshear's clutch to bring the blade from a parking position
functional control as close to the process and processand zero speed to cutting speed. After passing the
sensors as practical.cutting point the clutch will open and the break will
- Structure hardware and software so that each canclose, stopping the shear again in parking position. Now
be independently tested.the system will be ready for the next cycle.
- Minimize startup time by incorporating componentThe functions provided are:
simulation software into highly effective factory and- Manual normal cut. A single cutting cycle will be
field system simulations.initialized by the operator (Crop Shear and Flying
- Extensive use of structured control blocks withShear).
friendly configuration tools.- Automatic head crop. If this option is enabled, the
- Controller intelligence to directly generate diagnosticsshear will crop the bar's head at a previously specified
rather than requiring programmers to write dedicatedlength. This length is calculated using an HMD placed
software code.before the shear and mill stand tachometer pulses. An
- Encourage production and engineering personnel toautomatic trigger generated by the controller initiates
diagnose problems by extensive use of structuredthe cutting cycle (Crop Shear).
diagnostic messages available throughout the system.- Automatic tail crop. If this option is enabled, the shear
- Communicate process knowledge contained in thewill crop the beam's tail at a previously specified length.
system directly to the operators with an intelligentThis length is calculated using an HMD placed before
combination of easily selectable graphical andthe shear and mill stand tachometer pulses. An
alphanumeric screens.automatic trigger generated by the controller initiates
- Make available operating information, which allowsthe cutting cycle. (Crop Shear).
user development of planned maintenance schedules- Cut to length control. This function cuts the product
and problem anticipation.into segments according to an operator preset length.
- Minimize the quantity and type of dedicatedThe length is measured using a calibrated pulse train
communication networks and protocol.from the cut point or from the head detected by HMD
- Increased system reliability by implementing a flexible(Flying Shear).
drive system that can be applied to a variety of- Hot Bed Optimization. By predicting the tail length at
applications.HMD 2, a tail cut can be taken at the Crop Shear
System configurationwhen the diverter is deselected and this function
In order to give a brief description of how the systemenabled, with the purpose of eliminating tails at hot bed.
was originally configured, it is worth to mention that the- Continuous running for cobble cut (Crop Shear).
Rough Section had a home­made PC based system- Cobble mode: cobble cut and divert sequence for
to emulate a PLC, it also had some old Joliette analogcobble in hot bed (Flying Shear).
drives and cascade control. In addition to this, theThe symbolic diagram for the cutting cycle of the
Rough and Intermediate Sections also had someClutch and Break Shear can be appreciated in Figure
Reliance PMI drives. For the Finishing section there3.
were some ABB drives previously revamped with
Reliance Front End and AB I/O to the ABB Master
Control. A small GE 90­30 PLC controlled the coolingFigure 4: Block Diagram of the Shear System
bed.The block diagram depicted in Figure 4 shows the
New configuration was based on GE Innovation Seriesdifferent inputs and outputs of the shear system
Controller (ISC) with a unified HMI and L1 systemrequired to perform the different functions provided.
controlling all the way from the billet yard down to theThere are some characteristics of the clutch and
cooling bed. Most of the drives were reused and onlybreak shear function that are worth mentioning.
small ones in furnace, shears, pinch roll and cooling bedDepending on material speed at shear location, the
where replaced by new GE Innovation Series DCcutting cycle is as fast as a couple tenths of a second.
Drives due to economic convenience. The completeThis requires the execution rate of the controller to be
mill overview screen can be appreciated in Figure 1.in the 1 ms range. Also, the on/off control implemented
as blade position regulator is, by nature, not very
Figure 1: Mill Overview Screenaccurate in comparison to what we can achieve in
All reused drives were previously revamped bystart and stop shears. Given the mechanical system
Reliance and equipped with Automax. In order tolimitations and as There is another shear in the system,
integrate those drives into the new control systemthe Chopping Shear. It works different from the other
Reflective Memory Architecture was used. Thisshears; it is only turning at a higher linear speed than
concept provides a very fast and efficient way ofthe delivery speed. So, when the bar is diverted, it will
sharing data across distributed computer system sincebe chopped into little pieces. For this cause, it is not a
it is a high speed, real­time, deterministic network.high performance application.
With Reflective Memory each node on the networkFurnace Automation
has a local copy of shared data. Writing to theAnother very important part of the project involved
reflective memory causes the The GE Fanucfurnace automation and billet tracking. These functions
reflective memory product that uses fiber optics withwere implemented after mill start up because they
Fiber Channel technology was used in this case;were not critical to avoid mill production and new
Multibus for Automax and VME for the Innovationsystem testing. However, they provide an important
Series Controller. As a side result of this controlproductivity increase by adding reliable automatic
system upgrade, the operator control desk wassequences from the yard pusher trough the peel bar
simplified and reduced. New operator station has onlyas well as heat and billet tracking to enhance
3 PC with GE Cimplicity and smaller desk with a lotdocumentation and records.
less manual controls.Project Results
 Mill start up curve was very fast and the increase in
Mill Set­upproductivity was noticed very soon after the start up.
Product repeatability was increased by the use of aThe first production record was established as soon
database for mill set­up recipes; each product has itsas two weeks after the new system start up. Given
own recipe saved in the database for the operators tothe very wide range of products, adjustments were
use. Also operators are able to adjust the parametersmade during the first weeks of production in order to
while running the mill with a particular product and thenmake control algorithms robust and efficient given the
save it in the database as the "best practice" productdifferent mill set up conditions. This was accomplished
recipe. This was possible as a result of the integrationsatisfactorily to the point that there is no need for
of the rolling practice with the new control system, acontrol loop gain adjustments for the entire product
great effort between Marion Steel and AMIGE.range.
As set of production reports are also available, 
including mill performance and delays as seen in FigureMEXICO
2.AMI GE International
Blvd. Diaz Ordaz #402
Figure 2: Set PointsCol. Rincon de Santa Maria
Master ControlMonterrey, N.L.
By having a unified Master Control, Nucor Marion wasT. +52 (81) 1001-4050
able to improve mill availability and reduce cobbles. TheF. +52 (81) 1001-4051
Master Control is where the all the Mill parameters are 
converted into linear speed references for the stands. 
There are four main functions controlled in the MasterBRAZIL
Control: rolling modes and permissives, cascade speedAv. Das Naçones Unidas,
control and cobble detection.8501- 2 andar
Rolling Modes and PermissivesSao Paulo, SP, 05425-070
The mill modes are Ghost Rolling and Real Rolling.T. +55 11 3067 8639
Ghost Rolling feature is provided to be able to test theT. +55 11 3067 8004
availability and operation of every master and auxiliary 
equipment along the mill prior to mill start up after aARGENTINA
down time. These modes can also be switched usingBlvd. Alvarez #150
the Mill Overview screen. All the permissives areSan Nicolás,
evaluated in order to enhance the value of theProvincia de Buenos Aires
simulation. Operator screens and pulpit commands are(B2900)
fully operational while in ghost rolling mode. If anyT.