An integrated steel plant is huge by any measurement. Capacity is generally more than 1 million tonnes per annum, and in many big plants, it is more than 10 million tonnes per annum. The raw materials that are consumed are also in huge quantities, be it coal (coking coal or non-coking coal depending on technology used for iron making), iron ore, limestone, dolomite, or any other raw material.
Properties of these raw materials vary greatly. Despite the mixing and refinement done at the mines before shipping to a steel plant, these are natural raw materials, and variations in properties are still present when they reach the plant. Another problem is that due to the large amount of raw materials required, these components come from many sources, and their properties will vary greatly based on where they are sourced. For example, iron ore found in one geographical area will have greatly different properties than iron ore found in some other geographical area.
Properties of incoming raw materials greatly influence the properties of intermediate and finished products as well as the process parameters at each stage of production. As a result, each of these three factors are to be measured and managed at every stage of production. At the same time, the evolution of a finished product—from its raw material and the many intermediate products along the way—is like a journey with many stops.
Any manufacturing software that is useful to an integrated steel plant should be able to meet these fundamental requirements. This aspect of numerous stops along the journey as well as the journey itself can be captured and described only if the software vendor has detailed knowledge of the processes involved in an integrated steel plant.
Stages of Production and Intermediate Products
An integrated steel plant produces either finished steel products in the form of rolled or extruded products, or semifinished products in the form of steel ingots, blooms, billets, or steel slabs from iron ore. Rolled finished products include hot and cold rolled sheets, coils, and plates. Extruded products include bars, wires, rails, channels, and many other products.
After refining iron ore, liquid or sponge iron is produced. This iron is sent to steel-melting plants, where after further refining, liquid steel is produced. This liquid steel is either sent to a continuous casting plant, or it is poured into molds and cools to make steel ingots. If sent to a continuous casting plant, the liquid steel is poured into the top of a mold whose bottom end is open and water-cooled. During passage through the mold, the liquid steel solidifies and takes the shape of the bottom end of the mold, generally forming a slab or a bloom. This solidified steel is continuously removed from the bottom of the mold at the same rate at which liquid steel is poured into it. If formed into a slab, it is then rolled to form various shapes of plates, sheets, or coils. If it is a bloom, the steel is extruded into shapes of rails, channels, wires, rods, bars, etc. In the case of cold steel ingots, they are first reheated in reheating furnaces, and then rolled to form blooms or billets. They are then extruded into finished products such as rails, bars, rods, wires, and other products. These products are then ready to be heat treated to achieve many physical properties. Some steel products are also surface treated or surface coated (such as galvanized steel sheets). Finally, these products are cut in length per customer orders, and shipped out.
For finished products to have stringent quality, intermediate products must have stringent quality throughout the plant at various stages of production. Physical and chemical properties, such as temperature, chemical composition, micro-structure, and surface finish, need to fall within acceptable norms. It is this requirement that dictates if a thorough quality control regime is maintained at every stage of production.
Such a system translates into the need to keep the product and the property data about each of its intermediate and final products. Product data needs to be recorded into the manufacturing software system.
There are a number of critical issues that must be considered when refining steel.
Raw material property variations. The chemical compositions of raw materials vary from batch to batch. Physical properties also vary. These factors greatly affect production scheduling as well as product properties, and can lead to unacceptable or unfavorable finished product quality. The software should be able to accurately record data on raw material properties so that the process parameters can be adjusted according to incoming raw material. Doing so ensures that outputted products will have quality norms according to orders.
Intermediate products property variation. Due to variation in properties of input materials, variation in processes, etc., the outputted intermediate product's can properties can have variations as well. This, again, adversely affects the properties of finished products. should be able to accurately record data on product properties so that the process parameters can be adjusted per incoming intermediate material. Again, doing so ensures that outputted products will have quality norms according to orders.
Variation in process. This refers to variation processing time, in product temperature control, product properties, etc., all of which lead to variation in the properties of finished products. The software should be able to measure the external process factors that affect product properties.
Mixed-mode manufacturing. Some of the production stages conform to flow manufacturing, some to process manufacturing, and some to mill manufacturing. The software should be good enough to incorporate all these types of manufacturing capability.
Physical state of product. Some of the intermediate products are in liquid state while some are in solid state. This results in different ways measurements can be taken of each product. The software should be able to take this fact into account.
Product yield. At each stage of production, there is a yield factor that will determine how much production of a product takes place compared to the amount of material that has gone into the product. Software for manufacturers should be able to measure product yield accurately so that the quantity of products are in line with order quantities.
Manufacturing Management Techniques
The entire manufacturing process of an integrated steel plant cannot be covered by a single manufacturing system. Some of the steps in the process come under flow manufacturing, some under process manufacturing, and final products fall under mill industry. So the steel industry is a mixed-mode manufacturing environment as a whole. This greatly affects the techniques to measure, manage, and control each intermediate product at each stage of production.
Some of the techniques include the following:
Total quality management. The most suitable technique to control quality at all levels is total quality management. In accordance with flow and process manufacturing, total quality management practices are adopted. For example, liquid steel samples are taken for testing directly from the liquid steel inside the steel furnace; production is not stopped when samples are taken. The sample is sent to the laboratory for analysis. Once analysis results are known, steps are taken to ensure the product meets the quality standards specified in the order. Thus, production staff is responsible for quality management. If samples show results that do not conform to specified norms, the production staff makes the required adjustments without stopping the production line. The software should be able to record this series of product quality data.
Flow manufacturing. Production is never planned in batch mode (even in the case of raw material processing) and production is only stopped when the shift ends. Production is reported at the end of the shift, and production figures are accumulated for the day, month, and year. The product requirements (chemical and physical properties of the product, and product quantity) are communicated during the shift or on a daily, weekly, or monthly (depending on the production run length) basis from the internal customer (described in more detail below). For example, internal orders are issued from a rolling mill to the continuous casting plant. The software should be able to record this kind of product quality data.
Internal customers. Another interesting technique is used: the concept of internal customer. This is a very useful concept that makes executives at each plant responsible to the executives of the plant to which they supply the final product. In this way, executives at upstream plants are liable for product quality, lead times, and product quantity passed on to the executives of the immediate downstream plants. The software should be capable of defining internal orders for these internal customers.
Internal customer orders. Most of the upstream plants produce intermediate products that do not have properties that can be directly derived from the ordered finished products. Therefore, the internal customer in the downstream flow of product manufacturing sets these product properties, used by the internal supplier to fulfill the internal orders.
Scrap generation. At each production stage, there is scrap generation. The internal customer sets the intermediate product quantity required, and the supplier plant sets its own product quantity, keeping in view of internal customer orders and the percentage scrap generation. The software should be able to define internal customer order quantity of intermediate products for these internal customers.
Product yield. As with scrap generation above, the internal customer sets the intermediate product quantity required, and the supplier plant sets its own product quantity, keeping in view of internal customer orders and the percentage product yield. The software should be capable of defining internal customer order quantity of intermediate products for these internal customers.
An integrated steel plant consumes huge quantities of raw materials in bulk, and the properties of these raw materials vary considerably. Variation is minimized by mixing and blending operations and then by changing process parameters, so that intermediate products' properties are as close to internal customer orders as possible. Similarly, properties of intermediate products are controlled by mixing (if intermediate products are in liquid state) and changing process parameters so that the next intermediate or final product properties downstream conform to customer order product properties.
At each stage of production, product properties should be measured and controlled using a manufacturing management software that is capable of taking into account all these factors. The need of such features in the software cannot be emphasized more.
About the Author
Ashfaque Ahmed is a seasoned consultant and business analyst in many areas related to supply chain management (SCM). He has worked with many large and medium size clients in the retail, distribution, transportation, and manufacturing industries. Ahmed is the founder of Supply Chain Management Consulting Group (http://www.scmconsultingonline.com/), and has also started a blog at http://www.learn-scm.com/. Ahmed holds a BA in engineering and an MBA in information systems. He can be reached at mailto:%email@example.com.