H-beam steel production

H-beam steel production technology and process

Steel plays an important role in construction, manufacturing and other fields, and H-beam steel, as a common structural steel, is widely used in various industries. The surface of H-beam steel has no slope, and the upper and lower surfaces are parallel. The cross-sectional properties of H-beam steel are significantly better than traditional I-beam steel, channel steel and angle steel.

1. Types of H-beamsteel

According to the usage requirements and cross-section design characteristics, H-beam steel is usually divided into two categories: one is H-beam steel used as beam-type building components; the other is H-beam steel used as column-type (or pile-type) building components.

As a beam-shaped member, the ratio of height to leg width of H-beam steel is 2:1 to 3:1, and its specifications generally range from 100mm×50mm to 900mm×300mm.

As a columnar component, H-beam steel has a height-to-leg width ratio of 1:1, and its specifications generally range from 100mm×100mm to 400mm×400mm.

The height of H-beam steel is 80–1100㎜, the leg width is 46–454㎜, the waist thickness is 2.9–78㎜, and the unit weight is 6–1086ka/m.

2. H-beamsteel production process

The rolling methods of H-beam steel can be roughly divided into the following categories according to historical order:

(1) The rolling method using ordinary two-roller or three-roller section steel rolling mill;

(2) The rolling method using a universal rolling mill;

(3) The rolling method using multi-stand universal rolling mill.

3. Modern H-beam production methods

The multi-stand universal rolling mill is used to roll H-beam steel. This method has been widely used in the world. Specific methods include Green’s method, Sack method, J·Pop method, etc.

(1) Green’s method

The main feature of Green’s method is the use of open universal holes, in which the waist and legs are processed simultaneously. In order to effectively control the leg height and the quality of leg processing, Green believes that the vertical pressure must act on the leg end, so the compression of the leg height is carried out in a two-roller stand that is continuously rolled together with the universal stand. At present, edge rolling machines in various countries around the world mostly use Green’s method.

The process of rolling H-beam steel by Green method is roughly as follows: the ingot is rolled into shaped billet by blooming mill or two-high billet cutter, and then the shaped billet is sent to the universal roughing mill and edging machine for reciprocating continuous rolling, and the finished product is rolled into reciprocating continuous rolling in the universal finishing mill and edging machine. Green’s method only uses the horizontal roll to contact the leg end of the rolling piece (the waist does not contact the horizontal roll) during the vertical press, which can make the leg end of the rolling piece always maintain a straight. In this method, the vertical rolls are mostly cylindrical, while the two sides of the horizontal rolls are slightly inclined. In the rolling mill, the side of the horizontal rolls is about 9% inclined. In the finishing mill group, the side slope of the horizontal roll is 2% to 5%, but the side slope of the horizontal roll in the finishing mill group should be as small as possible to roll out parallel legs.

In 1908, the rolling mill built in Bethlehem Company in the United States adopted the above process, which was composed of a special-shaped bloom mill and two universal mills with a spacing of 90m immediately behind. Each universal mill consists of a universal stand and a edging machine.

Modern H-beams are also widely designed using the Green process.

(2) Sark Method

The Sark method adopts a closed universal pass, in which the leg is inclined, and a universal frame of cylindrical vertical rollers must be placed in the last line in order to finally roll out a straight leg. The vertical pressure of the Sack method is different from that of the Green method, which acts on the width of the leg, which is easy to cause the movement of the rolled piece, especially in the closed pass, which is often caused by the fluctuation of the incoming size, resulting in the protruding part of the leg end is easy to extrusion out to form an ear, affecting the quality of the finished product.

In the rough rolling universal pass of the Sack method, the horizontal roll side can adopt a large slope, which can reduce the wear of the horizontal roll, and because the vertical roll is used with taper, it can simultaneously compress the waist and leg with a large extension coefficient. This can reduce the number of rolling passes and universal racks, which is conducive to saving equipment investment.

The main process of the Sark process is: a two-high billet cutter is used to roll the ingot into shaped billet with I-shaped section, and then the shaped billet is sent to a reversible tandem mill consisting of a four-high universal frame and a two-high vertical press frame for rough rolling, and finally the finished product is rolled out on a universal frame. The horizontal roll side inclination of the rolling unit is 8%, the horizontal roll side inclination of the intermediate unit is 4%, and the leg of the rolled piece is rolled straight in the finishing universal frame, and the leg inclination of the finished I-steel is about 1.5%.

(3) Jay Popper method

The Jay Hopper method combines the advantages of the Green method and the Sack method, that is, it absorbs the two advantages of the Sack method with the inclined universal pass to obtain a large extension at one time and the Green method uses the vertical pressure pass to control the leg width. The main features of the Jepp method are that the Sacker method is used in rough rolling with oblique universal pass, and the Green method is used in finishing rolling with open universal pass. In the finishing universal rolling mill, the legs are flattened by cylindrical vertical roller and horizontal roller first, and then the vertical roller leaves and only the horizontal roller presses the leg end. Finally, the rolled pieces are fully processed by horizontal roller and vertical roller on the second finishing universal rolling mill. The process is as follows: a two-roll reversible billet cutter is used for rolling with two universal racks arranged in series. The horizontal roller of this universal rack has a 7% slope and the cone of the vertical roller is also 7%. In the finishing universal mill, because of the different varieties of I-steel, the slope of the pass is not the same, generally 1.5% ~ 9%. On the first pass of the rolled piece through the second universal frame, the leg of the rolled piece is first flattened by a cylindrical vertical roll, and then on the return pass, the neutral roll is left, and only the horizontal roll is pressed straight on the leg end. On the last universal mill, the rolled parts are fully formed with horizontal and vertical rolls.

4. H-beamsteel production process

To produce H-beam steel with good quality and low cost, it is necessary to determine a reasonable production process.

Generally, small H-beam steel mostly uses square billet, large H-beam steel mostly uses shaped billet, square billet and shaped billet can be continuous casting billet, but also can be directly supplied by the primary rolling.

After finishing and weighing, the billet is loaded into the stepping furnace and heated to 1200 ~ 1250℃. Most of the stepper furnaces use double adiabatic slide rails and axial flow burners to provide the best temperature control for different specifications of billets and save fuel.

After the billet is out of the oven, it is descaled with 1800MPa high pressure water first, and then it is sent to the billet cutting machine for rolling. The billet breaking machine is generally a two-roll reversible mill, which needs to roll about 7 to 13 lines on the billet breaking machine, and then the rolled pieces are sent to the hot saw, which is only responsible for cutting the unformed part of the head and tail.

Finally, the rolled pieces are sent to the universal roughing mill for rolling, and the general rolling is sent to the universal finishing mill after several passes, and the rolling is finally formed. At this time, the head and tail should be cut again, and the rolled pieces should be cut into a certain length according to the order requirements and then sent to the cold bed for cooling.

Due to the relatively large thickness of the H-beam steel leg and the waist thickness, if it is used flat, it is easy to cause waist waves due to the inconsistent cooling speed of the waist and leg, so it is generally used for vertical cooling. Most of them now use stepping cold beds, which can not only reduce the defects caused by the original chain hauling mechanism, but also easily control the cooling speed of steel. After cooling, the H-beam steel is sent to the straightener for straightening.

Due to the large section modulus of H-beam steel, it is generally straightened by 8-roll or 9-roll straightener, and the spacing between the straighteners is up to 200mm, and it is also necessary to supplement straightening by lying straighteners. After the steel is straightened, it is sent to the inspection table to check the size, shape and surface quality, and is marked according to the standard, and then classified according to different grades and lengths, piled and bundled before being sent to the warehouse. After restraightening the unqualified products according to the retreatable products, cut them off with cold saw or repair, weld and then check again.

In order to improve the operation rate of the mill and reduce the roll change time, most plants adopt a rapid roll change system, that is, the roll required for the next variety is assembled in advance during production. In the roll change, as long as all the original frame is pulled out and replaced with a new frame that has been installed. Each frame is equipped with an automatic electrical connection, as well as positioning connections for cooling water, thin oil and dry tubing joints and connection rods. The device is convenient and quick to disassemble, and the whole roll changing time is about 20min.

In order to effectively control the production process, modern H-beam steel plants are controlled by computers.

Generally, it is a three-level control system, the first level is used for production organization and management, and DDC control (direct digital control) is carried out by large computers. The second level is the control of the production process, that is, program control, program control computer is generally divided into two lines of control, the first line control hot rolling operation area, the first line control finishing operation area; The third stage is the control of each process, including the control of heating, rolling, sawing and other processes, which is generally controlled by microcomputers. The production information of the microcomputer reaction of each process is reflected to the respective program control machine through the intermediate computer, which is summarized and analyzed by the program control machine and reflected to the central control machine, and the central control machine issues the next adjustment and control instruction according to the production standard requirements.

In short, because of the rapid response of the computer, the product quality information can be collected and processed in time, so the computer control is the best means to control the production process.

5. H-beamsteel production process selection

In recent decades, with the progress of continuous casting technology and the improvement of on-line computer controlled rolling automation, the production process of H-beam steel is becoming more and more mature. Depending on the billet used, the pass system used and the type of mill, there are a variety of different process combinations, and there are five modern H-beam production processes to choose from.

The first production process is to use traditional steel ingot as raw material. First, the ingot is rolled into rectangular billets or billets on the blooming mill, and then these rectangular billets or billets are heated and sent to the billet cutter for rolling. There are two different pass systems, namely closed pass and open pass. In closed pass, the material deformation is uniform, but this requires more pass number and longer roll length, for this reason, closed pass is widely used in the production of medium section steel; The open pass is mainly used in the production of large section steel with larger waist width and leg width. If you want to use the closed pass rolling large section steel, you need two preforming machines in order to achieve satisfactory results in technology.

The billet is rolled into shaped billet like “dog bone” in the billet breaking machine, and then sent to the universal roughing mill composed of 1 ~ 2 universal reversible roughing mill for rolling. The rolling of the horizontal roll and the side pressing of the vertical roll of the universal rolling mill further reduce the waist thickness of the special-shaped billet and make the legs sharper and flatter. Generally, the compression of the leg thickness is greater than that of the waist thickness, which can be explained by the contact length between the rolled piece and the roll in the roll deformation zone, because the contact length between the driven vertical roll and the rolled piece is longer than the contact length between the horizontal roll and the rolled piece. In the universal finishing mill stand, the rolled piece is subjected to a small compression of the horizontal and vertical rollers, as well as the correction of the leg end by the edger.

The second production process is to adopt continuous casting rectangular billet. The difference between it and the first production process is that no blooming mill is required, and the second process can produce H-beam steel with higher yield, better finished product quality and better economic benefits than the first process. The only limitation of this process is the wide leg of the H-beam steel produced, because the thickness of the billet used is limited by the equipment conditions of the continuous casting machine. The rolling process of continuous casting billet in the section steel plant is the same as the first kind.

The third production process is the use of continuous casting special-shaped billet. Its advantage is that the use of one or a small number of continuous casting special-shaped billets can produce the full size of H-beam steel, which can be achieved by using the wide spread method on the billet machine, and its pass can be closed or open. Compared with the first two processes, this production process has a smaller number of passes. The shortcoming of this process is limited by the leg width of the special-shaped billet. The rolling process after billet opening is the same as the first two methods, which needs to be formed by universal roughing mill and universal finishing mill.

The fourth production process is the use of continuous casting slab. It is more economical to produce H-beam steel by using continuous casting slab as raw material than by using primary rolling slab and continuous casting special-shaped slab, but it needs to design a special pass on the billet. This pass is similar to the pass of a rolled rail, which is a cut wedge with a certain Angle to roll the slab to form a shaped section similar to a “dog bone”. For this purpose, the slab is first rolled vertically in the first hole to form the desired leg width, and then rolled into the next shaped hole (open or closed holes can be) to resemble a “dog bone” shaped blank. This production process is more uniform than the first three kinds of deformation, and its advantage is that only one billet machine plus universal roughing mill and universal finishing mill can produce large H-beam steel. There is also a transformation process in the preforming machine, that is, the preforming machine uses a universal slab preforming machine, and the side pressure formed by the horizontal roll and the vertical roll at a certain Angle can be directly rolled out the shaped section of “dog bone”. The latter process is the same as the first process.

The fifth production process is to use a very thin waist thickness of continuous casting shaped billet as raw material. This thin continuous casting special-shaped billet is close to the finished H-shape steel size, so it can be roughed and finished directly on the universal unit, without the need for a billet machine. In this case, the direction of increasing production is to require the continuous casting machine to have a higher casting speed and can cast a thinner shaped section. Its rolling feature is that the deformation of the whole rolling process is more uniform.