Bar Rolling Mill

Full Continuous Rolling Bar Rolling Mill Line

Bar Rolling Mill Annual Capacity: 30,0000 ∼ 50,0000 TPY

The billet is 150mm *150mm *8000mm continuous casting billet with a billet weight of 1404 kg.

Products: hot rolled round steel, ribbed steel bar.

Rolling Speed: maximum finishing speed of 16 m/s.

Specification: round steel ∅14mm~∅40mm, ribbed steel ∅12mm~∅40mm.

Steel Grades: ordinary carbon structural steel, high-quality carbon structural steel, low alloy steel, alloy steel, anchor chain steel, steel for standard parts, etc.

Production Process

Continuous Casting Billet → Reheating Furnace → Roughing Rolling Mill → 1 Flying Shear → Medium Rolling Mill → 2 Flying Shear → Finishing Mill → Step Rack Type Flying Shear  → Walking Beam Cooling Bed → Cold Shear → Inspection Collection →Bundling, Tying and Packaging → Weighing Storage

Full Continuous Rolling Technology

This bar rolling mill production line is a fully continuous bar rolling mill production line. There are 18 rolling mills in the whole rolling mill line, which are divided into roughing mills, intermediate rolling mills, and finishing mills.

Each unit is composed of six short stress rolling mills arranged alternately by horizontal rolling mills and vertical rolling mills, of which the 16th and 18th are horizontal-vertical convertible mills, and each stand is driven by a DC motor alone. The whole bar rolling mill line adopts full continuous rolling and non-twist rolling, and the roughing mill and intermediate mills adopt micro-tension rolling.

After the 12th rolling mill, vertical loopers are set up between the stands to implement tension-free rolling, thus producing high-precision products. The bar rolling mill line is controlled automatically by the computer to realize single-line continuous rolling with the maximum finishing speed of 16 m/s.

Reheating Furnace

The reheating furnace is a three-stage continuous pusher-type reheating furnace with an effective size of 8400mm *18096mm, a single row of feed, coke oven gas as fuel, and a design capacity of 80t/h.

Roughing Mill

The roughing mill consists of six flat-vertical short stress mills arranged alternately. The nominal diameter of the roll is 550 mm, and the length of the roll body is 760 mm. The range of application is 610 mm to 520 mm.

There is a crank flying shear at the exit of rough rolling mill. The maximum cross-section is 4000mm. It is used to cut the head and tail of the rolled piece after rough rolling and to break the rolled piece in case of an accident.

Intermediate Rolling Mill

The intermediate rolling mill is composed of six short stress mills arranged alternately by horizontal and vertical mills without archway. The nominal diameter of the roll is 400 mm, and the length of the roll body is 650 mm. The range of application is 430 mm to 370 mm.

There is a crank flying shear at the exit of the medium rolling mill. The maximum section of the shear is 2050 mm. It is used for cutting the head and tail of the rolled piece after medium rolling and breaking the rolled piece in case of an accident.

Finishing Mill

The finishing mill consists of three flat, one vertical and two flat-vertical convertible short stress mills without archway. The nominal diameter of the roll is 350 mm, and the length of the roll body is 650 mm. The range of application is 370 mm to 310 mm.

The finishing mill is equipped with a crank rotary changeable flying shear with a maximum shear section of 1300 mm and a length of 45 m to 72.

Bar Rolling Mill Cooling Bed

The cold bed is a stepping rack type with an area of 8m*78m, a rack spacing of 300mm/600mm, a pitch of 80mm and a working period of less than 2.8s.

Fixed Length Cold Shear

Fixed-length cold shear is upper-cut, the shear force is 5 kN, blade width is 950 mm, shear times are 10 times per minute.

Low-Temperature Rolling Technology

Low temperature rolling is to heat the billet to a temperature lower than the conventional starting rolling temperature for rolling. At present, the conventional start-up temperature of bar is 1050 ~1150 C, while the low-temperature rolling can set the start-up temperature at about 950 C. For this reason, although the rolling power consumption is increased, the comprehensive calculation is energy-saving because the energy consumption of heating furnace is greatly reduced. According to the information, low-temperature rolling can save about 20% energy.

In addition, in the process of bar continuous rolling, the temperature of the rolled piece decreases first and then rises. By reducing the start rolling temperature, a more ideal finishing rolling temperature can be obtained, which is of great benefit to improving the structure and properties of the steel.

The key problem to be considered in the implementation of low-temperature rolling is the ability of the rolling mill and motor. As long as the ability of the rolling mill and motor is enough, it is feasible to carry out low temperature rolling.

Slitting Rolling Technology

Slitting rolling can reduce rolling pass and roll consumption, save energy, expand production specifications and increase the output of small-sized products, with remarkable economic benefits. In the continuous bar rolling line of Chongqing Iron and Steel Co., the horizontal and vertical interchangeable rolling mills are adopted for the 16th and 18th stand, so that slitting rolling can be implemented. When rolling 14mm and 16mm ribbed bars, 2-slit rolling is adopted, while 3-slit rolling is used for rolling 12mm Round steel.

Surface Quenching-Hot Core Tempering Process

The surface hardening-hot core tempering process is a heat treatment process in which the rolled piece is quenched by the water-cooling device after it comes out of the finishing mill and then tempered by the residual heat of the core. The process improves the strength and toughness of steel by refining grains. Compared with microalloying strengthening process, the cost of this process is lower. The process has good flexibility in production, that is, steel with the same composition can obtain products with different properties by adjusting the water cooling device and changing the cooling intensity.

The position of water cooling device is reserved after finishing mill of continuous bar rolling line of Chongqing Iron and Steel Company. The surface quenching-hot core tempering process can be realized when conditions are ripe.

Endless rolling technology

The endless rolling technology is to weld the billet continuously on-line at the discharge side of the reheating furnace. It cancels the definition of "head and tail" of the bar and can produce products continuously and uninterruptedly. Compared with conventional rolling technology, this technology has the following advantages:

(1) The time interval between billets was canceled so that the production efficiency of the rolling mill was higher.

(2) Because there is no head and tail cutting waste of billet, the production of non-fixed length is reduced and the yield of finished product is increased.

(3) Because there is only one head in the rolling process, it can obviously reduce the longitudinal dimension and uneven performance of the rolled piece and improve the quality of the steel.