Plant-wide automation at Elgiloy Specialty Metals. Background of project. Process utilization and efficiency. Production scheduling and monitoring, страница 7

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 ransfers them to other applications, which use embedded SQL to store them into the database. Fig. 6 illustrates the interface between the various protocol layers and the application software.

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. After considering all objectives of the rolling process, as well as the economic factors, a 20-hi rolling mill with independent hydraulic columns was chosen. This mill has a conventional payoff reel, left tension reel and right tension reel (Fig. 7). Coils are transported to the entry points via crane to coil cars, which feed each reel position.

Other subsystems and features of the rolling mill are as follows:

·    Entry and exit x-rays gauges.

·    Entry and exit contact thickness gauges.

·    Entry and exit flatness rolls.

·    Inner intermediate roll shifting.

·    Backup roll bending.

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 control of strip shape. Since the entire gap positioning system of the mill is hydraulic, the position control regulator system operates at a crossover frequency of 200 radians per second Consequently, the hydraulic automatic gauge control (HAGC) system takes advantage of this speed and operates with a crossover frequency of 40 radians per second This allows production of superior gauge tolerances, while vastly reducing out of tolerance strip during transient: conditions.

Strip flatness is controlled using a separate shape control system. Control of flatness is accomplished by manipulating two individual control mechanisms. The first is the lateral shifting of the first intermediate rolls. These rolls are ground with a linear taper on the outer portion of the body. Typically, this taper may penetrate 250 mm into the roll width from the edge and would have a depth of 0.025 mm on a diameter basis. By positioning the cusp of the taper at a predefined point with respect to the strip edge, elongation of the areas near the strip edge can be controlled. Hence, wavy edges or center buckle can be eliminated. 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. These cylinders deliver positive ("crown-in") bending to the work rolls as well as negative ("crown-out") bending. The maximum force of these bending cylinders is ±50 tonnes. Selection of the roll shifting position and bending pressures are chosen from pass to pass by the shape control computer.