Through continuous attention to customer needs and long-term research and development investment, our new product have recently been put on the market after successful trial in local customers.Today is the second part of this topic.
About the author Dr.Juan Llano:
Deputy general manager of TSR
– Degree in Chemical Engineering. Universidad del País Vasco. Bilbao. 1981.
– Ph.D. course in Metallurgical Engineering. Universidad de Oviedo. 1989.
Part B. Roughing Stands of a Bar Mill
Author:Dr.Juan Llano
In the first stands of a bar mill, the rolls are subjected to a series of conditions that favor the appearance of thermal cracks:
– Low speed of passage of the bar
– High temperatures
– Sometimes insufficient cooling
– Sometimes unsuitable roll material.
– Residual stresses resulting from the roll manufacturing process.
The first three conditions are set by the design and operation of the mill.
• The speed of the bar in the first stands is, in general, low.
This phenomenon is much more accentuated in existing mills that have been revamped to roll larger sized billets by adding additional boxes upstream of the existing stands and whose speed has been necessary to adjust to synchronize them with the existing stands. In this case, the rotational speeds are usually particularly low.
As a general rule, passage speeds lower than 0.10 – 0.12 m / s acting on a pearlitic nodular iron roll usually generate a large number of thermal cracks.
• The temperature of the material at the exit of the oven is fixed by the characteristics of the material to be rolled, by the type of the mill and by other considerations beyond the reach of the roll manufacturer, and the roll maker must always adapt to them.
• When it comes to roll cooling, we will never tire of repeating the importance of ensure good cooling to the rolls in the mill.