It is steel that must be used for building components above medium-sized. General rebar specifications shall include standard brand, nominal diameter, nominal weight, specified length and allowable deviation of the above indicators. Generally speaking, deformed steel bars are produced by small rolling mills.
New processes such as walking beam heating furnace, high-pressure water descaling, low-temperature rolling and endless rolling are mostly used for bar rolling. Next, let’s have a look with Xiaobian!
Deformed steel bar specifications shall include standard brand (type code), nominal diameter, nominal weight (mass), specified length and allowable deviation of the above indicators.
Deformed steel bar series with nominal diameters of 6, 8, 10, 12, 16, 20, 25, 32, 40 and 50mm are recommended in Chinese standards. The supply length is divided into fixed length and double length.
The selection range of fixed length of deformed steel bars exported from China is 6 ~ 12M, and that of deformed steel bars produced in Japan is 3.5 ~ 10m; If there are no requirements specified in the contract, the length of domestic screw thread steel is usually 9m and 12m.
① Surface quality. The surface quality of deformed steel bar is specified in relevant standards. It is required that the end shall be cut straight, and the surface shall be free of cracks, scabs and folds, harmful defects in use, etc.
② Allowable deviation of overall dimension. The requirements for the bending degree of deformed bar and the geometry of reinforcement are specified in relevant standards.
Specification, dimension and outline of deformed steel bar:
The nominal diameter range of reinforcement is 6 ~ 50mm, and the nominal diameter of reinforcement recommended in the standard is 6, 8, 10, 12, 16, 20, 25, 32, 40 and 50mm.
The design principle of transverse rib of ribbed reinforcement shall comply with the following provisions:
Included angle between transverse rib and reinforcement axis β It shall not be less than 45 degrees. When the included angle is not more than 70 degrees, the direction of the transverse rib on the opposite two sides of the reinforcement shall be opposite.
The nominal spacing l of transverse ribs shall not be greater than 0.7 times the nominal diameter of reinforcement.
Included angle between side of transverse rib and reinforcement surface α Not less than 45 degrees.
The sum of the gaps (including the width of longitudinal ribs) between the ends of transverse ribs on two adjacent sides of the reinforcement shall not be greater than 20% of the nominal perimeter of the reinforcement.
When the nominal diameter of reinforcement is not more than 12mm, the relative rib area shall not be less than 0.055; When the nominal diameter is 14mm and 16mm, the relative rib area shall not be less than 0.060; When the nominal diameter is greater than 16mm, the relative rib area shall not be less than 0.065. Refer to Appendix C for the calculation of relative rib area.
Rebar is produced by small rolling mills. Popular rebar rolling mills include general high-speed rolling rebar mill and 4-SLITTING high-yield rebar mill.
The production process of deformed steel bar is stepping heating furnace → roughing mill → medium mill → finishing mill → water cooling device → cooling bed → cold shear → automatic counting device → baler → unloading.
The billet used for continuous small rolling mill is generally continuous casting billet, with side length of 130 ~ 160mm, length of about 6 ~ 12M, and single weight of 1.5 ~ 3T.
The rolling lines are mostly arranged in the form of horizontal interchange, so as to realize no torsion rolling of the whole line. According to different blank specifications and finished product sizes, there are 18, 20, 22 and 24 small rolling mills, and 18 are the mainstream.
New processes such as step heating furnace, high-pressure water descaling, low-temperature rolling and endless rolling are mostly used for bar rolling. Rough rolling and medium rolling are developed to adapt to large billets and improve rolling accuracy. The finishing mill is mainly to improve accuracy and speed (up to 18m / s).
Product specifications are generally ф 10-40mm, also available ф 6-32mm or ф 12-50mm. The steel grades produced are low, medium and high carbon steel and low alloy steel which are widely needed in the market; The maximum rolling speed is 18m / s.
Rebar is the surface ribbed reinforcement, also known as ribbed reinforcement, usually with two longitudinal ribs and transverse ribs evenly distributed along the length direction.
The shape of transverse rib is spiral, herringbone and crescent. Expressed in millimeters of nominal diameter.
The nominal diameter of ribbed reinforcement is equivalent to the nominal diameter of plain round reinforcement with equal cross section. The nominal diameter of reinforcement is 8-50mm, and the recommended diameters are 8, 12, 16, 20, 25, 32 and 40mm. Ribbed reinforcement mainly bears tensile stress in concrete.
Due to the action of ribs, ribbed reinforcement has great bonding ability with concrete, so it can better bear the action of external forces. Ribbed steel bars are widely used in various building structures, especially large, heavy, light thin-walled and high-rise building structures.
Rebar is produced by small rolling mill. The main types of small rolling mill are continuous, semi continuous and horizontal. At present, most of the newly-built and in use small continuous mills in the world.
Nowadays, the popular steel bar rolling mills include general high-speed rolling steel bar rolling mill and 4 cutting high-yield steel bar rolling mill.
The billet used for continuous small rolling mill is generally continuous casting billet, with side length of 130 ~ 160mm, length of about 6 ~ 12M, and single weight of 1.5 ~ 3T.
The rolling lines are mostly arranged in the form of horizontal interchange, so as to realize no torsion rolling of the whole line. According to different blank specifications and finished product sizes, there are 18, 20, 22 and 24 small rolling mills, and 18 are the mainstream.
At present, new processes such as step heating furnace, high-pressure water descaling, low-temperature rolling and endless rolling are mostly used for bar rolling. Rough rolling and medium rolling are developing to adapt to large billets and improve rolling accuracy.
Finishing mills mainly improve accuracy and speed (up to 18m / s). Product specifications are generally ф 10-40mm, also available ф 6-32mm or ф 12-50mm. The steel grades produced are low, medium and high carbon steel and low alloy steel which are widely needed in the market; The maximum rolling speed is 18m / s. The production process is as follows:
Walking beam heating furnace → roughing mill → intermediate mill → finishing mill → water cooling device → cooling bed → cold shear → automatic counting device → baler → unloading bench
one is to classify by geometry, which is to classify or type according to the cross-sectional shape of cross ribs and the spacing of ribs, For example, in British Standard (bs4449), deformed steel bars are divided into type I and type II. This classification mainly reflects the grip performance of deformed steel bars.
Second, according to the performance classification (grade), for example, in Chinese standard (gb1499.2-2007), deformed steel bars are divided into three grades according to the strength grade (yield point / tensile strength); Japanese industrial standard (Ji sg3112), rebar is divided into five categories according to comprehensive properties;
British Standard (bs4461) also stipulates several grades of rebar performance test. In addition, rebar can also be classified according to purpose, such as ordinary rebar for reinforced concrete and heat-treated rebar for reinforced concrete.
According to the national standard, the grade of hot-rolled ribbed steel bar for reinforced concrete in China is composed of HRB and the minimum yield point of grade. H. R and B are the English first letters of hot rolled, ribbed and bars respectively. Hot rolled ribbed bars are divided into three grades: HRB335 (old brand 20MnSi), HRB400 (old brand 20MnSiV, 20MnSiNb and 20mnti) and HRB500.
Rebar is widely used in civil engineering construction such as houses, bridges and roads. From public facilities such as expressways, railways, bridges, culverts, tunnels, flood control and dams to the foundation, beams, columns, walls and plates of housing buildings, threaded steel is an indispensable structural material.
With the deepening of China’s urbanization and the vigorous development of infrastructure construction and real estate, there is a strong demand for rebar.
Reinforced concrete structure is still the main structural form of buildings in China at present and for a long time in the future. Therefore, it can be expected that the demand and output of rebar will remain at a high level.
According to statistics, the steel consumption of China’s construction industry accounts for about 50% of the total steel consumption. As one of the industries with large resource consumption, in order to achieve sustainable development, the construction industry must adjust the consumption structure of building materials, vigorously apply high-strength reinforcement and high-performance concrete, and take the road of energy-saving development.
If we can improve the strength grade of the currently used reinforcement and concrete, it can bring great savings to the society.
According to the calculation, if the strength of the main stressed reinforcement of reinforced concrete can be increased to 400-500n / mm2 according to the requirements of the specification, about 10% of the current steel consumption can be saved.
