1. Introduction
Modern steel rolling technology has brought about a qualitative change in the production process of steel bars. Steel bars produced in a rolling mill typically require cooling and hot treatments to achieve the desired effect such as strength and ductility. Cooling and heat treatments are used to control the heat distribution during the rolling process which affects properties such as grain size, pressure distributions at the surface, and cooling rate etc. This paper discusses the application of cooling and online hot treatments in steel bar rolling and surveys their prospective applications in the future.
2. Cooling for steel bar rolling
Before steel bars are rolled, the temperature of the steel has to be controlled and managed when it enters the rolling mill. Cooling of the steels is important because the temperature affects the mechanical behavior of the steel and the result of rolling. A wide range of cooling and quenching techniques are available for rolling steel bars. These techniques are categorized as follows:
a. Cooling in a bath or tank – Cooling in a bath or tank is a direct cooling technique where steel bars are immersed in a tank of cold water or some other medium. This is a simple and economical method but has the potential to induce batch to batch variations and the inline control over the process is limited.
b. Mild cooling with air – Mild cooling with air is a direct cooling technique where a constant stream of cool air is used to cool the steel bars. this technique controls the cooling rate and are comparatively economical but may not be as precise as other cooling techniques. For example, the cooling rate obtained with this technique is not stable due to the variation in the air flow rate and temperaure.
c.Laser cooling – Laser cooling is an indirect cooling technique that uses a laser beam to transfer energy to the surface of steel bars. The advantage of this technique is that it can provide a direct cooling rate and does not induce any batch to batch variation. Additionally, control over the cooling rate is better and more precise.
3. Hot Treatment for Steel Bar Rolling
In addition to cooling, during steel bar rolling, online hot treatments can also be done to achieve desired properties such as strength and ductility. Hot treatments can be done by different methods such as induction, plasma, and conduction. Each of these methods has their own advantages and disadvantages.
a. Induction heating – Induction heating is a direct heating technique that uses electromagnetic energy to heat steel bars. The advantage of this technique is that it allows for fast and efficient heating of the steel bars. However, it is difficult to control the heating rate since the electromagnetic energy is transferred to the surface of the steel bars abruptly.
b. Plasma heating – Plasma heating is a direct heating technique that uses a plasma jet to heat the steel bars. This technique has the advantage of providing a more uniform heating rate than induction and can also be used to provide precise control over the heating rate. However, the disadvantage of plasma heating is that it is expensive and difficult to control the heating rate.
c. Conduction heating – Conduction heating is an indirect heating technique that uses heat pipes to transfer heat from the surface of the steel bars. This technique is relatively inexpensive and can provide a more uniform heating rate than the other techniques. Additionally, stable and accurate control of the heating rate is possible.
4. Future application of Cooling and Hot Treatments for steel bar rolling
In the future, cooling and hot treatments for steel bar rolling will become more important as technology advances. It is expected that cooling and hot treatments will become more advanced in order to provide more precise control over the heat distribution during the rolling process. This will enable manufacturers to produce higher quality steel bars in an efficient and effective manner. Additionally, new cooling and hot treatment techniques such as the use of lasers, plasma, and specific computer software will be developed to further improve the production process.
5. Conclusion
In conclusion, there are numerous cooling and hot treatment methods available for steel bar rolling which can be used to achieve the desired effect. Looking ahead, improvements in cooling and hot treatment methods are expected to be made in order to provide more precise control over the heat distribution during the rolling process. This will enable manufacturers to produce higher quality steel bars in an efficient and effective manner.
