Domestic Highway and railway bridges have been built one after another like bamboo shoots, the finish-rolled ribbed bar, which is mainly used in the bridge column structure, has become the”Sweet Pastry” in the bridge field because of its high strength, high precision, easy connection and so on.
To keep up with the development of national bridge construction, Hongxing joint-stock company has been continuously in the bridge steel material research and development. At present, the plant successfully trial-produced 025mm and 032mm specifications of PSB785 finished rolling thread bars, surface quality and performance meet the requirements of national standards, indicating that JISCO has 785 mpa Class PSB series finish rolling thread steel batch production capacity.
“Finish-rolled rebar, also known as prestressed concrete rebar, is mainly used to prevent or delay cracks in reinforced concrete members due to external stress,” said Shi Bin, an associate engineer at the plant’s rod-rolling process, before the construction, the steel bar is stretched by external force artificially, and then the concrete is poured. When the concrete reaches the specified strength, the two ends of the steel bar are relaxed, so that the steel bar and the concrete are integrated, this can not only improve the tensile capacity of concrete under external stress but also increase the stiffness of the concrete structure.
In this process of”-pull a loose”, on the finish rolling, the mechanical properties of rebar have a very high request. The yield strength of HRB600 Steel is 600 mpa and the tensile strength is 730 mpa, but the yield strength and the tensile strength of the finish-rolled rebar must be more than 780 mpa and 980 mpa respectively. Compared with an ordinary steel bar, the shape of a finish-rolled thread bar requires no longitudinal rib, and the transverse rib must ensure the uniform arrangement of the spiral line so that the bar can be connected or anchored with nuts or anchors at any section.
“This is similar to the seamless connection between a screw and a nut. The difference is that the cross ribs of a screw are refined by a numerical control machine, while the cross ribs of finished-rolled rebar need to be rolled by a rolling mill.” Shi said that it was not easy for a large-scale mill to do such fine work. If the error exceeds 0.1 mm, there may be cases where the nut does not turn up and the threads on both sides are not on the same spiral line.
The high standard mechanical properties and strict dimensional accuracy adjust finished products become the most difficult point in the finish rolling of rebar. Because it is necessary to ensure that the finished product shape is in line with the requirements of the national standard, but also to make the finished product can smoothly screw into the nut or anchor. Before rolling, the ribbing of finished products, the processing of grooves, the assembly of the frame, the adjustment of the inlet guide and finishing tension, the alignment of the wrong grooves of the rolls, and the threads of the upper and lower rolls must be strictly controlled, neither”Wrong roll”, nor”Wrong teeth”.
According to the national standard and combined with the user’s construction technology, the project group studies the requirements of the production and quality control of the finish-rolled ribbed bar, in the composition design, the linear regression methods used to analyze the existing HRB400E and HRB500E steel grade data of the stick line, and the multi-regression fat program is obtained to design the composition of finish-rolled rebar to improve the mechanical properties of the product, the process of micro-alloying and hot-rolling is adopted to ensure the accuracy of the parameters in the process of rib-cutting, and the process of debugging is meticulous.