Introduction
Output efficiency is an important issue for any steel plant manager, because poor profitability can adversely affect both steel production and production costs. In this article, the author discusses the topic of crop loss and clarifies their importance.
What are crop losses?
Output losses occur in any part of the iron and steel fabrication process when, for a particular stage, the weight of the steel product is less than the input of the steel that is being used. For example, in a cold rolling mill, if the input — often referred to as charge mass — is 100 tons of hot rolled coiled steel, and the yield is 95 tons of cold rolled steel, the yield is 95%. Another way to express the yield ratio is a ton per ton - in this case, 100 is divided by 95 or 1,053. Typical yield loss values:
- in the production of hot rolled steel (slab on hot rolled coil), 3.5%
- in the production of fittings (for harvesting in a bar), 5%
- in a seamless tube (billet to a green pipe), 8.5%.
Why do crop losses occur?
Losses of losses occur for various reasons.
- For example, during the rolling process, a break may occur, during which the steel strip leaves its normal rolling path, lands (often at speed) in the area adjacent to the stands of the rolling mill. This length of the steel bar will no longer scroll; rather, it will be processed in the form of scrap, thus reducing the yield productivity achieved on this particular shift
- Scale is often formed on a hot plate when it cools. This scale will then be removed from the surface when the stove is prepared for the next stage of the process.
- When a steel coil is created, the edge will often be cut off on the final product, resulting in a small yield loss.
- When a billet or slab is cast, it is often cut. Irregularities that occur during the casting process are also often removed.
Each of the above examples reduces the final mass of the steel product being made in comparison with the initial steel charge mass.
Why are crop losses important?
Yield losses are important for several reasons.
- First, it is important to understand the yield in order to be able to predict the output of the mill. A mini mill producing a million tons of crude steel may, for example, be able to produce 850,000 tons of finished steel if the cumulative yields from casting, hot rolling and cold rolling steel are 15%
- Secondly, crop yields are also particularly important in terms of costs. This is due to the fact that although scrap metal can usually be recycled, all labor and energy costs associated with processing the volumes of steel consumed are lost; and the value added (in terms of the final selling price) has not been reached. For some processes, the cost of yield loss may actually exceed some of the other elements of the cost of conversion (for example, the cost of consumables, electricity, or other utilities). Therefore, managing productivity of yields is an important aspect of managing the cost of steel production.
Understanding your own performance
A common way to understand crop productivity in a particular steel mill is to compare its latest productivity indicators compared to similar plants. As a rule, such plants will belong to competitors and can often be located in different countries. However, technical visits to the mills are quite common in the steel industry; and they are specifically designed so that training benefits the industry.
