What Is Hot Rolling? What Do Slit Edge And Mill Edge Mean?

When large steel mills produce steel coils, they cannot trim the edges during rolling, and there are oxidation lines on both sides, so most of the rusty steel coils shipped out of the factory are in a rough edge state. If you want to trim the steel coils, you need to trim the edges to cut off the oxidation lines. 

1. What is hot rolling?

After a piece of steel billet is heated, it is refined through several rolling passes and corrected into a steel plate. This is called hot rolling.

Hot rolling uses slabs (mainly continuous casting billets) as raw materials, and after heating, it is made into strip steel by rough rolling units and finishing rolling units. The hot steel strip coming out of the last rolling mill of finishing rolling is cooled to the set temperature through laminar flow and is rolled into a steel strip coil by a coiler. The cooled steel strip coil is processed into steel plates, flat coils, and longitudinally cut steel strip products according to different user needs through different finishing lines (flattening, straightening, cross-cutting or longitudinal cutting, inspection, weighing, packaging and marking, etc.). To put it simply, a piece of steel billet is heated and then rolled several times, then trimmed and corrected into a steel plate. This is called hot rolling.

2. Characteristics of hot-rolled plates:

(1)Poor toughness and surface flatness, low price;

(2)The temperature of hot rolling is similar to that of forging;

(3)The hot plate is processed by hot rolling and has an oxide scale on the surface, and the thickness of the plate is different;

(4)The price and use of hot-rolled products are much wider than cold rolling;

(5)The mechanical properties of hot-rolled steel plates are far inferior to those of cold processing and forging, but they have better toughness and ductility;

(6)The surface of hot-rolled plates without electroplating is dark brown;

(7)After electroplating, it can be distinguished by the smoothness of the surface, and the smoothness of hot-rolled plates is lower.

3. What do slit edge and mill edge mean?

The trimming shear is one of the key equipment in the pickling or pickling rolling combined operation line (cold rolling for short). Its function is to trim the raw material width according to the finished product width requirements, and at the same time remove the quality defects of the raw material edge to avoid quality degradation, strip breakage, and other accidents.

The slit edge refers to the burr quality defect of the edge of the plate and strip after the raw material is processed by the trimming shear. Its harm is that the burr part is easy to cause the strip to break during the rolling process of the rolling mill; the burrs of the slit edge fall off and stick to the rollers, causing indentation defects on the surface of the cold-rolled product; the burr remaining after cold rolling affects the galvanizing quality of the strip edge and causes the strip to break in the leveler after annealing.

The factors of the quality problem of trimming burr are mainly the quality defects of hot-rolled raw materials, deviation in the calculation of the shear gap, inaccurate calibration, and shear gap jump. Reasonable control of these four items can greatly reduce the amount of burr defects.