Access Machine Case History:

METAL PRODUCTION

Customer Background:

The Elkem Plant in Alloy, WV converts North Carolina quartzite into high-quality silicon metal for use in aluminum, chemicals and electronics. Silica dust from the air from the furnaces is sold as microsilica to cement producers for use as a strengthener. The West Virginia plant is one of over a dozen Elkem installations in North America and Europe that produce silicon and related ferroalloy products. The parent company is Elkem a/s from Norway. They expanded into North America in the 1980s. Today, Elkem has three plants in the United States and one in Canada.

(Note: All Customer Background information was obtained from the News of Norway web page at www.norway.org/may96/elkem.htm.)

Plant Information:

Elkem Alloy produces silicon metal from a gravel/coal/woodchip mix in arc furnaces. The raw material is mixed in the mix house and transported to either of two furnace departments. The mix house contains raw material bins that feeds weighers, conveyor belts that transport materials from weighers to holding hoppers, and skip hoists and tram cars that transport the mix to the specific furnaces. The existing batch mix control system is adequate for the existing equipment and mix strategy but cannot be changed. The plant is bringing more furnaces on-line and adding equipment to the mix house.

Customer Needs:

• Elkem requires a pre-engineered object-based software with fully functional Management Execution System (MES) capabilities.
• Elkem requires a system that can automatically manage the batching of raw materials to the furnaces, from a library of mix orders according to the demands of the furnaces.
• The batching strategy must maximize batch throughput (maximize weigh and delivery system machinery usage), to keep as many machines as possible busy at all times.
• The system must be able to track material usage and batch history.
• The system must be expandable as necessary - weighers, bins, furnaces, etc.
• The system must be able to easily upgrade based on any new batching strategy.
• It is necessary to be able to provide statistics to the accounting department and the SPC calculations, and to import SPC control variables.

The Access Machine Solution:

The AccessWare installation of this MES product uses the new GoBatch product for Auto Batch Mix at Elkem Metals in Alloy, West Virginia. This application of AccessWare's MES GoBatch Control uses nine new Object State Machines. The batch system uses the configuration of material data plus actual system status (or state) information from the AccessPoint SCADA capability to determine the next appropriate action for production. The animated display and the linking of each Object's symbol and state are shown with AccessWare's operator interface touch screen graphics.

AccessWare provides a real-time, object oriented computer model of the Elkem system. Each device in the model, and each Batch in progress, is a software object. There are 8 different object types in the Elkem batch system: Raw Material Bins, Weighers, Conveyor Belts, Holding Hoppers, Skip Hoists, Tram Cars, Furnaces, and Batches. Device objects are provided to the system from the Object database. Batch objects are created as the need to mix a batch arises.

The software implements each object type as a state machine. In this context, a state machine consists of a set of defined states and a set of defined events. In each state, every possible type of event implies some action and, possibly, a change of state. Events may be input/output (I/O) updates indicating changing conditions of the corresponding physical devices, or time-outs, or commands from other objects (typically Batch objects). The actions taken by an object upon receiving an event may include control outputs to the plant device, or messages to other objects. In this way, each Device object exercises control over its physical counterpart, and Batch objects command the Device objects. The behavior of each type of object, and the interaction between objects in the model, implements the batching strategy employed by Elkem.

The model of the mix house and furnace departments consists of the objects configured in the Object database. As equipment is added to the mix house, or furnaces are added to the furnace departments (both of which are occurring at the Alloy plant), the control software is kept up-to-date simply by adding configurations. Not a single line of code needs to be changed to support new equipment.

Only when Elkem installs a new type of device (for instance, pocket belts to replace a skip hoist, or holding hoppers with different controls), does a new Object type needs to be implemented in the software, and objects of that type added to the Object database.

AccessPoint Software Specifics:

The status of all equipment is displayed on a pair of touch screen CRTs depicting an overview of the delivery system. Operator controls through touch screen buttons include: system mode (automatic or manual), mix order library, mix demands, manual mode control of each device (weigh and delivery system machinery), reporting, and the ability to take elements of the system in and out of service. All batching system controls are on/off toggle buttons on the touch screen.

The following is a description of the operations of the AccessPoint system:

The system has twelve raw material bins which feed into nine weigh hoppers which in turn dump into the holding and checkweigh hopper. The holding hopper then dumps one of two gates into the associated skip hoist. The hoist travels up the ramp toward the furnace department and dumps into a tram car. The position of the swivel spout directs the mix to either tram from either hoist. The tram then travels to the selected bin and dumps the mix. The mix computer scans the furnace bins to determine which bin is to be batched. Upon making this decision, the computer determines if the hoist and tram pair for this bin are in service. If all equipment is available, the computer decides which raw material bins are to be used. The weighers are tested for an empty condition and a message is printed to identify the batch in process.

The raw material feeders are started, and material can flow into the seven weighers simultaneously. Each weigher has a preliminary setpoint, a preact setpoint, and a tolerance level within which weights must remain for each material. When all weighers have completed and are within tolerance, the system checks the holding hopper for closed and empty gates before starting the belts. With the belts running, the weigher's discharge feeders are sequentially started, moving the batch into the holding hopper. When each weigher reaches the empty weight setpoint, the discharge feeder runs ten additional seconds. The conveyor belts run long enough for the material to clear before stopping. The system now looks to see if the appropriate hoist is at the home position. The holding hopper gate is opened and the batch is placed in the hoist. When the holding hopper reaches the empty setpoint, the gate is closed. The hoist is started and a tram destination is established. The remaining control of the delivery of the batch is independent of the computer.

Each weigh hopper has a high material level device to prevent overfilling. This device disables the computer outputs to the raw material feeders for the weigh hopper and provides a digital input (DI) to the computer. The computer interprets the DI to mean additional material can be added to this weigher. A chunk detector device located on belts provide a digital input to stop the belts if a large object passes underneath. When this happens, the computer will sound the alarm until acknowledged. The operator then eliminates the chunk and manually resets the switch on the detector. The discharge will automatically restart. A full complement of manual controls is enabled when the system is placed in the "HOLD" mode.

• Increased flexibility - easily able to expand the operation as needed, or change components
• Greater control over quality assurance - historical records and tracking system easily isolate problem areas
• Increase in productivity - with automated mixing of recipes, batches are completed faster and with fewer errors allowing more batches to be finished in a shorter period of time
• Touch screen capability - provides easy control and lowered training requirements.