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formation of mill scale on steel plate,What is Mill Scale on Steel Plate? Mill scale is a thin layer that forms on the surface of steel plates during the manuf

What is Mill Scale on Steel Plate?

Mill scale is a thin layer that forms on the surface of steel plates during the manufacturing process. It occurs mainly due to the high - temperature oxidation of iron when the steel is being hot - rolled. When the steel is heated to high temperatures in the rolling mill, the iron on the surface reacts with oxygen in the air. This reaction creates a layer of oxides, which is what we call mill scale.

How Does Mill Scale Form?

As the steel plate is heated in the mill, the iron atoms on the surface become more active. The oxygen molecules in the air then bond with these iron atoms. The reaction can be represented simply as: (4Fe + 3O_{2}rightarrow2Fe_{2}O_{3}). However, the composition of mill scale is not just pure (Fe_{2}O_{3}), but also contains other iron oxides like (FeO) and (Fe_{3}O_{4}). The layer forms very quickly as the steel is being processed at high speeds in the mill.

The Appearance of Mill Scale

Mill scale usually has a bluish - black or dark gray color. It is relatively thin, but it can cover the entire surface of the steel plate. It has a somewhat flaky or scaly texture, which is why it is named "mill scale". The appearance can vary depending on factors such as the temperature during formation, the composition of the steel, and the amount of oxygen available during the process.

Impact on Steel Quality

While mill scale can provide a certain level of protection against further corrosion in the short term, it also has some negative impacts. For example, if the mill scale is not removed properly before further processing such as painting or welding, it can cause problems. In welding, the mill scale can cause inclusions in the weld, reducing the strength and quality of the joint. In painting, it can prevent the paint from adhering properly to the steel surface, leading to premature peeling and reduced protection against corrosion.

Removal of Mill Scale

There are several methods to remove mill scale from steel plates. One common method is pickling, which involves using an acid solution to dissolve the mill scale. Another method is abrasive blasting, where high - pressure air or water is used to blast abrasive particles onto the surface to remove the scale. Mechanical methods like grinding or wire brushing can also be used, especially for small - scale or localized removal.

Questions and Answers

Question 1: What are the main factors affecting the formation of mill scale on steel plate?Answer: The main factors include the high - temperature during hot - rolling, the amount of oxygen present in the air during the process, and the composition of the steel itself.

Question 2: Why is it important to remove mill scale from steel plates?Answer: It is important because if not removed, it can cause problems in further processing such as welding (causing inclusions) and painting (preventing proper adhesion), and thus affect the overall quality and performance of the steel product.