Reaping the Rewards of Advanced Automation at Elgiloy Specialty Metals

Reaping the Rewards of Advanced Automation at Elgiloy Specialty Metals


	More than ever before, industry demands for specialty alloys require suppliers to produce cold rolled strip with tight gauge specifications, exceptional flatness, and stringent physical properties. Elgiloy Specialty Metals’ (ESM) new plant, located near Hampshire, Illinois, west of Chicago/U.S.A., was constructed to meet these demanding quality standards and incorporates annealing furnaces, tension leveler, preparation line, slitting operations, and a new 20-high rolling mill. Elgiloy, note the authors, has achieved target quality levels using an automation structure employing advanced PLC and supervisory control technology from Siemens.

ESM has provided cold rolled strip specialty alloys to the aircraft instrumentations and medical industries, as well as many other businesses requiring metal alloys with critical properties, for several decades. Strong growth in the industries requiring these exotic alloys has led to a demand for improved quality and very stringent specifications.
Recognition of this need, in addition to the increased consumption within the high technology industries, resulted in ESM embarking on an expansion involving a greenfield operation. With most customers requiring extensive historical data for the products purchased, ESM realized that a plantwide control and communications system would be essential to this new facility. In order to deliver customer orders punctually and to schedule products through the plant optimally, a cohesive plantwide control scheme was mandatory. In addition, it was acknowledged that the levels of quality required, the efficiency of equipment utilization, and the profitability of the operation would all be strongly linked to such a communications structure.

Broad project scope

Industry demands have swiftly developed toward requiring suppliers to produce strip with extremely tight gauge tolerances. In addition, the industrial business sector supplied by Elgiloy requires the strictest surface conditions, extremely flat product, and a narrow range on physical prop-erties.
To meet these objectives, it was decided that the new Elgiloy plant would incorporate several processes. Since the principal characteristics of the strip are largely formed in the rolling mill, special attention was paid to selecting this process. The minimum attainable gauge, gauge control response, and flatness were considered before choosing a 20-high mill featuring four independent columns with individual hydraulic positioning.
The rolling mill was designed to load coils onto a payoff reel and finish at either a left or a right tension reel. Each coil position has independent coil cars for loading or unloading coils. Top speed of the mill was chosen to be consistent with the production capacity target of 30,000 metric tons per year.
To support the product processing at the new facility, two annealing furnaces were also constructed. These two lines allow the annealing of material in two gauge ranges. One annealing furnace operates horizontally in a batch mode processing one coil at a time. Another annealing furnace operates vertically with a tower and in a continuous mode with strip storage at the entry and exit sections. The horizontal furnace was constructed to produce the most stringent alloy requirements in smaller lot size quantities, while the vertical furnace was installed to supply material at lowest possible cost and in larger lot size quantities. A tension leveler, preparation line, and a slitting line complete the processes needed to produce the targeted products within the facility. With regard to automation technology, it was decided that the annealing furnaces, tension leveler, prep line, and slitter would be controlled using PLCs. This hardware platform was chosen because these processes are largely controlled by sequences and advanced digital interlocking. Predefined programs for different product types are entered by the operator and then executed by the PLC logic during the processing of the coil. The rolling mill automation is far more demanding because it requires sequencing, fast digital regulation loops, and a mathematical model for proper control. In addition, intelligent sensor sub-systems are necessary for the efficient operation of a rolling mill. A layered control system consisting of supervisory process computers (HMI and process control); PLCs; realtime control processors; and smart sensors was chosen.

Plant network topology

From the earliest stages of the project, ESM planners realized that automation sophistication and proper information flow were critical to the success of the operation. Efficient production scheduling and plantwide data acquisition were acknowledged as essential components of a successful project. These aspects were given primary consideration during the initial plant design. A layered control system composed of three levels was chosen. These levels were selected based on both the speed required and the functions performed within them. The control levels are as follows:

Level 1 Realtime Process Controllers
Level 2 Supervisory Process Control with Mathematical Models
Level 2.5 Plantwide Scheduling and Data Acquisition.

The top plantwide layer was arbitrarily designated as Level 2.5. This was done in order to distinguish it from the higher enterprise resource planning applications that are conventionally associated with Level 3 and above in some models.
The plant is constructed with fiber optic backbone, which runs between each process area and the production office. All controllers or network nodes separated by more than 50 meters are connected with fiber-optic cable. All other connections within one local area of the plant or office area use copper twisted-pair wiring. Data transmission speed on all network connections is 10 Mbytes/s. Siemens SIMATIC® S5 PLCs provide sequencing and interlocking while SIMADYN® digital units handle loop control and communication. All functions are performed in realtime in the rolling mill as well as the other plant processes.

Database and information flow

When considering information flow and data availability, it was decided that information gathered at each process, as well as plant product scheduling information, should be visible to all of the individual operations. Hence, it was decided that a central database for the entire plant was the optimum choice. This database resides in the manufacturing supervisory computer (MSC) system server. All processes within the plant are connected to this central database, which then serves the human-machine interface (HMI) screens used by the operators. The rolling mill contains a separate database and HMI for control purposes. The operators at the other process lines, production planning staff and the shipping and receiving departments all have access to the plantwide data. Each of the lines is supplied with unique operating HMI screens, which display relevant data for that particular process. These screens are operated from the appropriate NT workstation. Additionally, production staff can use various screens to create work orders and schedule coils to work orders, as well as alter other coil information. Operators responsible for running the process lines are able to enter coil data and other information as each coil is processed.

Production scheduling and monitoring

After the work orders have been created at a corporate location, they are transferred to the MSC system at the Elgiloy plant via ASCII file transfer. Applications within the MSC system receive the work order files and then execute ORACLE scripts to create all of the necessary database entries. Work orders may also be created manually using the Work order Scheduling System (WSS) in the event that the link to the enterprise system is inoperative.

Fig. 1 Work order and coil scheduling screen

Work orders are created by a Production Planning System (PPS) in an enterprise level server located at the central corporate office. These work orders are designed to load the plant processes optimally while supplying the necessary customer orders in a timely fashion. The actual coils needed to allow one of the work orders to be completed are assigned at the Elgiloy plant site via the WSS located in the production office. Production office personnel are able to view the required work orders as well as the available inventory of coils using an HMI screen in the WSS. Figure 1 shows the work order and coil scheduling screen.
The coils needed to satisfy the work orders are then selected and associated with a particular work order. The required weight for the work order is displayed and decrements as each coil is assigned. The total weight assigned is displayed at the bottom of the screen. If a coil is assigned that causes the total work order weight to be exceeded, then the amount of the surplus is designated as the “rest” weight.
The coils required to satisfy the work orders created by the PPS task are shipped to the plant site in quantities and types sufficient to allow the work orders to be completed by the production office personnel. Shipments are coordi-nated so that the pool of available inventory contains sufficient candidate coils to schedule the work orders in the sequence and timeframe required by the PPS. As incoming coils are received, the primary data information (PDI) is entered on the NT workstation of the Receiving Department. As the coils are handled throughout the facility, additional information is either manually entered by process operators or automatically acquired from process controllers during processing.
After completion of all processing, mechanical inspection is performed on the material, and the operator enters this information into the database. All process data and operator-entered information can then be queried and analyzed to study vendor performance, alloy process improvements, and mechanical property refinements. Critical data required by customers is gathered and can be presented with the shipped product. The process data serves as a historical record and is retained for several months within the database in the event it is required for review at a future time. After that time, the data can be archived for long-term storage.

Data collection and communications protocols

During the many process steps through which each coil must pass, relevant data at these steps is gathered and stored in the database within the MSC system. The process controllers at each unit are responsible for gathering any cyclic data for each coil on a continuous basis. The operator NT station at each process step communicates the singular data for each coil via an HMI entry screen. Cyclic data at each process is gathered by the process controllers (i.e. PLCs) at varying rates depending on the granularity desired.
For the vertical annealing furnace, these values include

Furnace speed
Furnace zone temperatures
Control zone setpoint tempera-tures
Cooling fan speeds
Cooling gas gate positions and
Strip zone tensions,

gathered every 2 min (contrasted with every 2 s at the rolling mill). When the coil enters the process, the operator uses the workstation to enter the singular data on an HMI screen. Subsequently, he transmits this information by depressing a START button on the screen. This establishes the appropriate table entries for the coil in the database. Once the coil has been declared as started by the operator at his workstation, the cyclic data are then periodically copied into the database. After the coil has been completely treated through the process, the operator utilizes the workstation to assert that the coil is complete. This is accomplished once again by using the HMI screen at the workstation. Any final singular data is added and the STOP button is depressed. At that time, the final data items are received and the cyclic data transfer into the database is terminated. This procedure is repeated in a similar fashion at each of the processing steps, with the exception of the rolling mill, where a tracking system initiates the data transfer automatically. Communication from the rolling mill system and all of the other processing steps utilize only two protocols to send data to the MSC system. All communications between servers and the workstations or the operator displays utilize the TCP/IP protocol. Employing Layer 4 in the Open Systems Interconnect (OSI) model allows the TCP/IP protocol suite to operate with high reliability and at speeds more than sufficient for the data transfer rates encountered in these processes. A simplified network diagram can be seen in Figure 2.

Fig. 2 Communications Protocols

Communication to the database from the Level 1 controllers such as PLCs is handled in a different fashion. A simpler Layer 4 protocol, i.e. OSI, is used for these transmissions. The OSI protocol suite was developed more recently than TCP/IP and conforms to the standards set by the International Organization for Standardization (ISO). As implemented, this protocol is simpler and has fewer features than TCP/IP. However, the advantage of using these protocols is the fact that they run faster than TCP/IP and, consequently, are more suited to Level 1 platforms, which require high processing speeds. An OSI layer within the MSC server receives the data packets from the PLCs and transfers them to other applications, which use embedded SQL to store them into the database.

Rolling mill automation

Since most of the critical properties of the final product are dependent on the rolling process, a careful selection was made of the essential rolling mill features. The 20-high mill at ESM has a conventional payoff reel, a left tension reel, and a right tension reel. Coils are transported to the entry points via crane to coil cars, which feed each reel position. Unlike a normal rolling mill where the upper and lower housings are cast as one, the new Elgiloy mill has separate columns to allow greater independent movements. This capability greatly facilitates the control of strip shape.
Strip flatness is controlled using a separate shape control system. Control of flatness is accomplished by manipulating two individual control mechanisms. Using tapered intermediate rolls with lateral shifting eliminates wavy edges or center buckle. The other shape control mechanism utilized is the employment of seven bending cylinders distributed across the backup rolls. These independently controllable cylinders impart varying crown to the work rolls and are effective in eliminating quarter buckle.
The cylinders deliver positive (“crown-in”) bending to the work rolls as well as negative (“crown-out”) bending. Selection of the roll shifting position and bending pressures are chosen from pass to pass by the shape control computer.
The movement of material in the mill is detected within the Level 1 process controllers and communicated to the PCS system. From this point, the material is tracked and, if appropriate, a rolling schedule is computed. The rolling model uses information stored in the database along with adapted quantities to calculate the intended schedule of passes in the mill. After calculating the rolling schedule, the setpoint processing task dispatches this information to Level 1 for distribution to the individual regulators. During the subsequent rolling of the material, measured values are captured and sent to the PCS for use in logs, pass-to-pass adaptive learning, and transmission to the MSC system. A more detailed diagram of the data gathering and transmission to Level 2.5 can be seen in Figure 3. This diagram shows the data comprised of a header plus cyclic data.

Fig. 3 Data Transfer to Level 2.5

The header contains all the singular information on the coil taken principally from the PDI. Header data is placed in the shared memory by the setpoint processing task once the last pass has been commenced. At the end of the last pass, the final header data is stored.
Cyclic data is gathered during the rolling of the last pass into a shared memory segment. Cyclic data is gathered every 2 s during the last pass and is comprised of the following:

Thickness
Mill speed
Entry tension
Exit tension
Gap position
Forces on hydraulic cylinders.

After the end of coil, this information is transferred to the MSC system via an SQLnet connection. Upon a successful transmission, the shared memory segment is cleared in preparation for the next coil.

Finally, a neural network system was added to the mill to provide the fastest adaptation of numerous rolling variables to achieve the most repeatable process control. Adaptive learning is segmented into long-term and short-term components. Pass to pass adaptation is also performed during the rolling of the coil. After each pass, a new schedule is computed for all remaining passes.

The rewards of advanced automation

Elgiloy Specialty Metals has successfully completed the installation of a new cold rolling facility along with a plantwide control system and communications network. Positive results from the Level 2.5 system are evident in the enhanced product quality and in customer satisfaction. Products that would have been difficult to produce are routinely scheduled in addition to various new alloys. Strip surface quality and gauge performance consistently exceeds design targets. At Elgiloy Specialty Metals, a plantwide data acquisition and product scheduling system has been implemented with minimal capital investment utilizing an advanced automation structure. And the benefits derived from the system, including effective product scheduling, coil process history, and customer order tracking, speak for themselves.

Michael A. Smith, Siemens Energy & Automation, Inc., Alpharetta/U.S.A.
Stan Czuba, Elgiloy Specialty Metals, Elgin/U.S.A.