Rebar is produced by small rolling mills. The main types of small rolling mills are: continuous, semi-continuous and row.
At present, most of the new and in-use small rolling mills in the world are fully continuous. Today's popular rebar mills are general-purpose high-speed rolling rebar mills and 4-slice high-production rebar mills.
The billet used in the continuous small rolling mill is generally continuous casting billet, the side length is generally 130~160mm, the length is generally about 6~12 meters, and the single billet weight is 1.5~3 tons.
At present, new technologies such as stepping heating furnace, high-pressure water descaling, low-temperature rolling, and endless rolling are mostly used in bar rolling. Rough rolling and intermediate rolling are developing towards adapting to large billets and improving rolling accuracy. The machine is mainly to improve the accuracy and speed.
The production process of the rolling mill is as follows:
Heating furnace→roughing mill→intermediate rolling mill→finishing mill→water cooling device→cooling bed→cold shearing→automatic counting device→baling machine→unloading stand
Second, the characteristics and quality of rebar
1. Classification of rebar
There are two commonly used classification methods for rebar:
The first is to classify by geometric shape, and to classify or type according to the cross-sectional shape of the transverse rib and the spacing of the ribs. For example, in the British Standard (BS4449), the rebar is divided into type I and type II. This classification mainly reflects the gripping performance of the rebar.
The second is based on the performance classification (grade), for example, in the Chinese standard (GB1499.2-2007), the rebar is divided into 3 grades according to the strength grade (yield point/tensile strength);
In the Japanese Industrial Standard (JI SG3112), the rebar is divided into 5 types according to the comprehensive performance; in the British Standard (BS4461), several grades of the performance test of the rebar are also specified.
In addition, rebars can be classified according to their uses, such as ordinary steel bars for reinforced concrete and heat-treated steel bars for reinforced concrete.
2. Specification and quality of rebar
The ordering principle of rebar is generally based on the requirements of the grip performance required by the engineering design, and the mechanical process performance or mechanical strength index is the main factor.
The specification requirements of rebar should be listed in the import and export trade contract. Generally, it should include the standard grade, the nominal diameter of the steel bar, the quality, the specified length and the allowable difference of the above indicators.
The standard recommends rebar series with nominal diameters of 8, 10, 12, 16, 20, and 40mm.
①Surface quality. Relevant national standards stipulate the surface quality of rebar, which requires that the ends should be cut straight, and the surface should not have cracks, scars and folds, and there should be no harmful defects in use.
②Allowable value of external dimension deviation.
The requirements for the bending degree of the rebar and the geometric shape of the rebar are specified in the relevant national standards. Some national standards stipulate that the bending degree of straight steel bars is not more than 6mm/m, and the total bending degree is not more than 0.6% of the total length of the steel bars.