What is Hot Rolling?

What is Hot Rolling?

Rolling mill is a metalworking process which divided into two types: hot rolling and cold rolling. Here we will analyze the hot rolling cause we had discussed cold rolling before.

In many theory books, which called hot rolling is a metalworking process that occurs above the recrystallization temperature of the material. On the contrary, it means that below the recrystallization temperature of the metalworking process is called cold rolling.

But what is hot rolling besides of this word. Here we have the detail explanation about it. After the grains deform during processing, they recrystallize, which maintains an equiaxed microstructure and prevents the metal from work hardening. The starting material is usually large pieces of metal, like semi-finished casting products, such as slabs, blooms, and billets. If these products came from a continuous casting operation the products are usually fed directly into the rolling mills at the proper temperature. In smaller operations, the material starts at room temperature and must be heated. This is done in a gas- or oil-fired soaking pit for larger workpieces and for smaller workpieces induction heating is used. As the material is worked the temperature must be monitored to make sure it remains above the recrystallization temperature. To maintain a safety factor, finishing temperature is defined above the recrystallization temperature; this is usually 50 to 100 °C (90 to 180 °F) above the recrystallization temperature. If the temperature does drop below this temperature the material must be re-heated before more hot rolling. All of this above, just part of the hot rolling actually.

Hot rolled metals generally have little directionality in their mechanical properties and deformation induced residual stresses. However, in certain instances, non-metallic inclusions will impart some directionality and workpieces less than 20 mm (0.79 in) thick often have some directional properties. Also, non-uniformed cooling will induce a lot of residual stresses, which usually occurs in shapes that have a non-uniform cross-section, such as I-beams. While the finished product is of good quality, the surface is covered in mill scale, which is the forms at high temperatures. It is usually removed via pickling or the smooth clean surface; process, which reveals a smooth surface.  Dimensional tolerances are usually 2 to 5% of the overall dimension.

Hot rolled mill steel seems to have a wider tolerance for amount of included carbon than cold rolled, making it a bit more problematic to use as a blacksmith. Also for similar metals, hot rolled seems to typically be less costly.

Hot rolling is used mainly to produce sheet metal, rebar, wire rod or other products. In a words, hot rolling is very popular used in the steel industry.

Since 1989 Hani Tech has been always involved in design, engineering, manufacturing and installation of complete hot rolling mill plant for long products (re-bars, SBQ bars, wire rod, small and medium sections), as well as revamping and upgrading of existing plants. 

Hani Tech is the one-stop manufacturer & supplier able to design, manufacture, install and commission your hot rolling mill plant from A to Z.

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What Should The Rolling Mill Need To Pay Attention To During The Shutdown?

What Should The Rolling Mill Need To Pay Attention To During The Shutdown?

In the production process of the rolling mill, what should be noticed after the rolling mill is shut down when there is a downtime overhaul or an unexpected situation?

1. After the rolling mill stops, stop the feeding of steel, and take the gas cutting and cutting out of the online rolling parts to avoid the stress on the rolls and cause damage.

2. If the rolling mill needs long-term shutdown, the best method is to open the lubrication system to keep the main bearing lubricated, and then close it in to avoid dust and debris entering the bearing.

3. Cut off the power supply of the rolling mill and auxiliary equipment.

4. Drain the water in the cooling tube to avoid freezing the cooling water pipe when it is cold.

5. Protect the lubrication system, motor, air clutch and slow drive from dust, but not tightly sealed to avoid moisture accumulation. Use a small heater or protect the bulb to prevent moisture buildup.

6. Place bagged desiccant in all control and electrical panels to prevent moisture build-up and safely seal the control panel.

The above need to pay attention to is that the rolling mill production enterprises need to pay special attention to it. Only when the rolling mill is under maintenance, the rolling equipment can better complete the production task during the production period, improve the rolling efficiency and extend the usage time of rolling mill.

Since 1989 Hani Tech has been always involved in design, engineering, manufacturing and installation of complete hot rolling mill plant for long products (re-bars, SBQ bars, wire rod, small and medium sections), as well as revamping and upgrading of existing plants. 

Hani Tech is the one-stop manufacturer & supplier able to design, manufacture, install and commission your hot rolling mill plant from A to Z.

Please contact stella@hanrm.com for a quotation.
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Why High-Speed Wire Rod Mill Adopts Collective Transmission Mode?

Why High-Speed Wire Rod Mill Adopts Collective Transmission Mode?

In high-speed wire rod mill, the finishing mill adopts collective transmission mode, which is due to:

1) In order to shorten the excess length of the head and tail of the rolling piece caused by drawing, the structure of the rolling mill is required to be as compact as possible, so that the space between the stands is very small. Under this compact condition, it is impossible to arrange the rolling mill as a single transmission. 

2) The finishing mill of high-speed wire rod mill not only has high speed but also needs to be adjusted to different speeds according to different product specifications. If it is driven separately, the number of frames is large, and the speed required by different product specifications varies greatly in different sorties. Therefore, the required electrical control system will be very complex, and at the same time, it must have high sensitivity to adapt. 

Therefore, even if the electrical system can do it, it is difficult to maintain the micro-tension rolling relationship between the racks for all product specifications. 

3) The combined structure of collective transmission greatly improves the dynamic speed drop of the motor at the moment of biting and makes the micro-tension relationship between the stands unaffected by the electrical equipment, thus creating favorable conditions for the micro-tension rolling at high speed. 

In summary, the design of roughing mill, medium rolling mill and pre-finishing mills using AC motor drive alone, finishing mills using AC motor collective drive.

Since 1989 Hani Tech has been always involved in design, engineering, manufacturing and installation of complete hot rolling mill plant for long products (re-bars, SBQ bars, wire rod, small and medium sections), as well as revamping and upgrading of existing plants. 

Hani Tech is the one-stop manufacturer & supplier able to design, manufacture, install and commission your hot rolling mill plant from A to Z.

Please contact stella@hanrm.com for a quotation.
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Email: stella@hanrm.com   stellarollingmill@gmail.com
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What is a Rolling Mill?

The steel rolling mill is the equipment to realize the metal rolling process. Generally refers to the equipment used to complete the whole process of rolling production, including main equipment, auxiliary equipment, lifting and transportation equipment and ancillary equipment. But generally speaking, the rolling mill only refers to the main equipment.

II. Nomenclature of Rolling Mill

It is named after the type of rolled product, the type of mill and the nominal size. The principle of "nominal dimension" refers to the section mill as the pitch diameter of the herringbone gear of the gear base; the blooming mill as the nominal diameter of the roll; the strip mill as the length of the working roll body; and the steel tube mill as the maximum diameter for production. It is sometimes named after the inventor of a rolling mill (e.g. Sendzimir mill).

III. Selection of Rolling Mills

The type and dimension of finished or semi-finished rolling mill shall be selected according to the requirements of product variety, specification, quality and output, equipped with necessary auxiliary, lifting, transportation and accessory equipment, and finally balanced according to the requirements of various factors.

IV. COMPONENTS OF STEEL ROLLING MILLS

1. Work stand: composed of roll, roll bearing, frame, rail seat, roll adjustment device, upper roll balance device and roll changing device, etc.

2. Roll: It is a part that makes metal plastic deform.

3. Roll bearing: support the roll and maintain the fixed position of the roll in the frame. Roll bearings vary greatly with heavy working loads, so small coefficient of friction, sufficient strength and stiffness are required, and rolls can be easily replaced. Different types of roll bearings are used for different mills. Rolling bearings are mainly used for work rolls of strip mills because of their high rigidity and small coefficient of friction, but their small pressure-bearing capacity and large size. Sliding bearings have two types: semi-dry friction and liquid friction. Semi-dry friction roller bearings are mainly bakelite, copper and nylon bearings, which are relatively inexpensive and are mostly used in profile mills and billet openers. There are three kinds of hydrodynamic, hydrostatic and hydrostatic bearings. The advantages are small friction coefficient, large pressure-bearing capacity, high working speed and good rigidity, while the disadvantage is that the oil film thickness changes with speed. Liquid friction bearings are mostly used for support rolls in strip mills and other high-speed mills.

4. Mill stand: It is composed of two "archways" to install the roll bearing block and roll adjusting device. It needs sufficient strength and steel strength to withstand the rolling force. There are two main types of rack, closed type and open type. Closed stand is an integral frame with high strength and rigidity, mainly used for blooming mills and strip mills with high rolling force. Open frame is composed of frame body and upper cover, which is easy to change rolls. It is mainly used in cross section mills. In addition, there are no archway mills.

5. The rolling mill track base is used to install the frame and fix it on the foundation, also called the floor plate. To withstand the gravity and tipping moment of the worker base while ensuring the accuracy of the mounting dimensions of the worker base.

6. Roll adjustment device: used to adjust the roll gap so that the rolled piece can reach the required section size. Upper roll adjustment device, also known as "press-down device", has three kinds: manual, electric and hydraulic. Manual press-down devices are commonly used in profile mills and small mills. Electric press-down device includes electric motor, reducer, brake, press-down screw, press-down nut, press-down position indicator, spherical pad and pressure gauge and other components; it has low transmission efficiency, large rotating inertia of moving parts, slow reaction speed and low adjustment accuracy. Since 1970s, AGC (Automatic Thickness Control) system has been used in strip rolling mills. Hydraulic press device has been used in new strip cold, hot and thick rolling mills, which has the advantages of small thickness deviation and high product qualification.

7. Upper roll balancing device: device used for lifting upper roll and preventing impact of rolled parts when entering and leaving the roll. Forms are: spring type, multi-purpose on profile rolling mill; hammer type, commonly used on blooming mill with large roll movement; hydraulic type, multi-purpose on four-roll strip rolling mill.

In order to improve the operation rate, it is required that the roll change of the rolling mill be quick and convenient. Roll change modes are C-hook type, sleeve type, trolley type and frame type. Roll change in the first two ways is assisted by crane, while the whole frame requires two sets of frame for roll change. This method is mostly used for small mills. Car roll change is suitable for large rolling mills and facilitates automation. At present, the rapid automatic roll changing device is used on the rolling mill. It only takes 5-8 minutes to change the roll once.

8. Driving device: It consists of electric motor, reducer, gear seat and connecting shaft. The gear base distributes the drive torque to two or more rolls.

9. Auxiliary equipment includes a series of equipment for auxiliary process in rolling process. Such as raw material preparation, heating, steel turning, shearing, straightening, cooling, flaw detection, heat treatment, pickling and other equipment.

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What are Flying Shears?

What are Flying Shears?

The shearing machine for rolled pieces in transverse shearing operation is called flying shear. It is a processing equipment which can cut off iron plate, steel pipe and paper roll quickly. It is a fixed-size shearing machine for metallurgical steel rolling industry, high-speed wire and threaded steel. It is a product of modern rolling bar shearing and has the characteristics of low power consumption and low investment cost.

Flying shear is an important equipment used for shearing metal billets in iron and steel enterprises, and its performance will directly affect the production efficiency of rolling production line. There are many structural forms of flying shear mechanism. In this chapter, four-link structure is used. Through simple three-dimensional modeling of the frame, upper and lower cranks, upper and lower links, upper and lower rockers and workpieces, assembly and simulation can be carried out to obtain the shear force that the workpiece is subjected to during the shearing process and the motion track of the two cutting edges.

Flying shear is installed on the rolling mill line to cross-cut the head and tail of a rolled piece or to cut it to a fixed length. During the movement of the rolled piece, the rolled piece is cut by relative movements of the cutting edges.

The mechanism sketch of the four-link flying shear mechanism is shown in Figure 1. It consists of the upper and lower shear mechanisms with the cutting edges fixed on the connecting rods of the four-link mechanism. In practical flying shear mechanisms, the driving force is input from the lower crank. The upper crank is driven to move at the same speed by a pair of helical gears with the same number of teeth. Every revolution of the crank, the mechanism shears the work-piece once. In order to simplify the structure and facilitate the measurement of shear force, the same amount of torque is added to both cranks in Figure 1 during simulation to reduce the modeling of helical gears.

Flying shear is commonly used in steel rolling, paper and other production lines. In continuous billet or small section workshops, it is positioned at the back of the rolling mill line, cutting the rolled pieces to size or only to the head and tail. Various types of flying shears are provided in the shearing, shearing, galvanizing and tin plating units of cold and tropical steel workshops to cut the strip into fixed-scale or steel coils of specified weight. The wide use of flying shear is conducive to the rapid development of high-speed and continuous steel rolling production. Therefore, it is one of the important links in the development of steel rolling production.

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Hot Rolling Process

Hot Rolling Process

The semi-finished billet from the steel plant is rolled to make it a qualified product.

Introduction of hot polling process

Process Flow of Hot Rolling: Process Flow of Main Rolling Mill Line:

The slab is directly sent to the slab warehouse of the hot rolling workshop from the slab discharging roller table of the continuous caster in the steelmaking and continuous casting workshop, and the directly hot charged slab is sent to the furnace loading roller table of the reheating furnace for heating. 

The slab that cannot be directly hot charged is lifted into the insulation pit by the crane, and then lifted to the upper material bench by the crane after insulation, and then heated by the furnace loading roller table of the heating furnace, leaving the possibility of direct rolling. 

The continuous casting slab is transported into the slab warehouse by the continuous casting workshop through the slab loading roller table or slab unloading roller table. 

Before the slab reaches the entry point, the technical data about the slab has been sent to the computer system of the hot rolling plant by the computer system of the continuous casting workshop, and the relevant data of the slab is displayed on the monitor, so that the staff can check and receive the defect free and qualified slab. 

In addition, the cleaned slab also needs to be checked, accepted and input into the computer. The flow direction of slabs entering the slab warehouse shall be determined by the slab warehouse computer management system according to the rolling plan.

Conventional slab charging and rolling: after the slab enters the slab warehouse, the slab is stacked to the designated stacking position in the slab warehouse by the slab clamp crane according to the unified instruction of the slab warehouse control system. During rolling, according to the rolling plan, the slab is lifted out of the stack one by one by the slab clamp crane, and lifted to the slab loading bench for loading. 

The slab is weighed and checked by the weighing roller table, and then sent to the furnace loading roller table of the heating furnace. After the slab is measured and positioned, it is loaded into the heating furnace by the steel loader for heating. 

Hot charging and rolling of carbon steel insulation pit: after the slab enters the slab warehouse, the slab is stacked to the designated stacking position in the insulation pit by the slab clamp crane according to the unified instruction of the slab warehouse control system. 

During rolling, according to the rolling plan, the slab is taken out of the insulation pit one by one by the slab clamp crane, lifted to the slab loading bench for loading. The slab is weighed and checked by the weighing roller table, and then sent to the furnace loading roller table of the heating furnace. 

After the slab is measured and positioned, it is loaded into the reheating furnace by the steel loader for heating.

Direct hot charging and rolling: when the production plans of continuous casting and hot rolling match, the qualified high-temperature continuous casting slab is transported to the weighing roller table through the charging roller table of the heating furnace. 

After weighing and checking, it enters the charging roller table of the reheating furnace. 

After the slab is measured and positioned in front of the designated reheating furnace, it is loaded into the reheating furnace by the charging machine for heating. 

Some of the directly hot loaded slabs transported through the unloading roller table need to be lifted by a crane once, placed on the loading roller table and directly sent to the reheating furnace area. 

If the steel-making plant can realize the direct hot charging and the slab is transported by the feeding roller table, some crane lifting operations can be reduced. 

After the slab is sent to the heating furnace through the charging roller table of the reheating furnace, it is loaded into the heating furnace by the supporting machine. 

After heating to the set temperature, it is supported by the tapping machine according to the rolling rhythm and placed on the discharging roller table of the reheating furnace.

After the heated slab is discharged from the furnace, it is transported through the conveying roller table. After descaling by the high-pressure water descaling device, the slab is sent to the fixed width press for side pressing and fixed width as required. The maximum one-time width reduction of the fixed width press is 350mm. 

Then it is transported by the roller table into the first two high reversible roughing mill and the second four high reversible roughing mill. The slab is rolled into an intermediate slab with a thickness of about 30-60mm according to the process requirements. 

The vertical roll mill in front of each roughing mill can control the width of the intermediate billet. 

An intermediate waste billet pushing device is arranged between R2 and the flying shear to push the intermediate waste billet onto the operation side bench of the intermediate roller table. 

The intermediate billet is transported by the intermediate roller table with thermal insulation cover to the cutting head and tail of the flying shear. The thermal insulation cover is conducive to reducing the heat loss of the intermediate billet and the temperature difference between the head and tail of the belt billet.

An edge heater is set in front of the flying shear, which can reduce the temperature difference between the edge and the middle part of the intermediate billet, improve the uniformity of strip steel performance and improve the quality of rolled piece shape. 

The cutting head flying shear is equipped with an intermediate blank head and tail shape detector and a cutting optimization control system to realize optimal cutting and reduce the loss of cutting head and tail. 

The strip blank after head cutting is removed from the secondary iron oxide scale by the high-pressure water descaling device before finishing rolling, and is guided into the finishing rolling unit by the vertical roll before finishing rolling. 

The intermediate billet is rolled into 1.2 ~ 25.4mm finished strip by F1 ~ F7 four roll finishing mill.

The threading speed, acceleration, maximum rolling speed, reduction of each stand, roll shifting stroke of work roll and roll bending force of each stand of the finishing mill are calculated and set by the computer control system according to the variety and specification of rolled strip to realize the closed-loop control of strip shape. 

In order to effectively control the quality of strip steel, the rolling line detection instruments such as crown, flatness, thickness, width and temperature are set at the outlet of F7 finishing mill, and the rolling line detection instruments such as strip surface quality, width and temperature are set at the inlet of coiler. 

The strip rolled by the finishing mill is cooled from the final rolling temperature to the specified coiling temperature by the strip laminar cooling system on the output roller table. 

The cooling water volume is set and calculated by the computer according to the steel strip cooling mode and final coiling temperature.

When the coiler passes through the strip before biting into the strip, the speed of the output roller table, pinch roll, auxiliary roll and drum is ahead of the rolling speed of the final frame; 

When the strip steel is bitten by the coiler, the output roller table, pinch roll and coiler will conduct speed-up rolling synchronously with the finishing mill; 

When the tail of the strip steel leaves the end frame, the output roller table and pinch roller shall slow down, that is, lag behind the coiling speed of the coiler until the tail of the hot rolled coil.

After coiling, the steel coil is lifted out by the coil unloading trolley to the baler for bundling. Then the steel coil is transported backward by the steel coil transportation system. 

After baling, weighing and marking, it is transported to the hot-rolled steel coil finished product warehouse, cold-rolled raw material warehouse and finishing raw material warehouse respectively. 

After the steel is returned to the hot rolling and coiling warehouse for inspection, the raw materials that need to be transported to the hot rolling and coiling warehouse for inspection are sent to the hot rolling and coiling warehouse for inspection, and the finished products are sent to the hot rolling and coiling warehouse for inspection respectively.

The steel coils cooled in the steel coil warehouse shall be sent to the leveling and winding unit, steel plate cross cutting unit, cold rolling workshop or delivered according to the sales plan according to the next processing process requirements. The steel coil is transported and stacked in the way of horizontal coil. 

The transportation system for the steel coil to the steel coil warehouse or cold rolling raw material warehouse adopts the pallet transportation system, and forms a transportation network together with the transportation system of 1780 hot rolling plant, which is uniformly controlled by the computer.

From the slab entering the slab warehouse to the delivery of finished products, the whole process tracks the slab, rolled piece and coil through the rolling line material tracking system and two warehouse management system, so as to realize the automatic production control of computer.

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Low Temperature Rolling Technology of SBQ Special Steel Bar Rolling Mill

Low Temperature Rolling Technology of SBQ Special Steel Bar Rolling Mill

1. Preface

The bar rolling mill with the most advanced low temperature rolling (LTR) process built by Hani tech has been running smoothly since it was put into operation in early 2006, and has already reached full capacity, achieving good production performance and application effect. No. 1 SBQ special steel bar rollinhmill RM1 is part of the largest construction project implemented by Hani Tech in China. The project also includes the second set of Danieli "twin" bar mill RM2, which is specially used to produce ordinary steel deformed steel bars. It is arranged in the span adjacent to RM1 and installed and commissioned simultaneously with RM1 mill.

Danieli has carried out a lot of experimental research to reduce the material hardness of medium and low alloy steels, especially all steel grades that require good shear properties and are prone to cracks due to excessive hardness and stress concentration. For stainless steel production, many experimental studies have also been carried out to improve the mechanical properties of hot rolled materials for some specific purposes. In order to control the performance indexes of materials, such as hardenability and toughness, how to change the grain size and austenite transformation structure of materials has also attracted great attention.

2 . Overview of Steel Plant

The newly built No. 1 SBQ special steel bar mill RM1 (and its "twin" bar mill RM2) is an 18 stand mill with horizontal / vertical arrangement and looper control function. Two water cooling tanks are arranged between No. 14 and No. 15 racks, and a suitable distance is reserved to make the surface temperature of rolled pieces uniform. Due to this arrangement, the whole temperature drop can be controlled within 260 ℃ without affecting the product surface quality (such as local undercooling) and phase transformation. Selecting a cooling tube with high heat exchange coefficient can make the rolled piece obtain uniform cooling in the cross section. The DSC metallographic structure control system controlled by PLC can ensure that the appropriate setting parameters of the water cooling box can be obtained to make the rolled piece cool evenly in the length direction. The inlet and outlet pyrometers are used to monitor the actual temperature of rolled pieces and modify the basic parameter settings in real time when necessary.

After adopting this advanced technology, the process parameters of the heating furnace can be flexibly adjusted according to the production process needs of different steel grades or due to the long rolling cycle without changing the finish rolling temperature.

3. Product Outline

Hani Tech's SBQ special steel bar rolling mill plant has 160 billets × 160mm square billet, billet weight 2350kg. When conventional rolling is adopted, the maximum production capacity of the rolling mill is 150 t / h; When low temperature rolling is adopted, the production capacity is 100 t / h. Product is ф 16mm～ ф 60mm diameter high-quality round steel bar. The main steel grades and product specifications produced by SBQ special steel bar rolling mill of Hani Tech company.

4. Production Process

The Rolling temperature is one of the three basic rolling parameters. It will affect each stage of grain refinement in the whole process of thermal deformation.

Grain refinement and grain growth control are the main means of low temperature rolling process. It can affect the time temperature transition curve (such as the position of CCT curve), change the length of grain boundary and change the nucleation position. In particular, temperature is the most important thermodynamic parameter affecting the whole rolling process 

Formula (a) gives the influence law of temperature. It can also explain the role of the previous grain size in the grain growth process; And how all material deformation directly affects the final grain size in the low-temperature rolling process.

Tdrex=K1 × ln(——) × dck2 × eu × ek3

(a)

In the formula, K1, K2 and K3 are constants, and the value depends on the rolled steel.

The grain refinement process can be divided into different stages, although different stages may also occur at the same time. The deformation of the original grain will increase the dislocation density, and the nucleus can be formed at the boundary of the new grain. The disappearance and regeneration of new grain boundaries are closely related to the actual temperature. The formation and growth of new grains is a thermodynamic process. 

At different stages, recovery, static recrystallization and dynamic recrystallization will occur, which will affect the flow stress curve. Finally, grain growth shows a trend of minimizing grain boundary energy. The critical temperature determines the boundary between grain refinement conditions and fully recrystallized grain growth structure. With the decrease of carbon content, this effect will become more obvious. For steels such as 16mncr, the microstructure with grain refinement of more than 40% can be easily obtained.

It is very important to maintain the temperature in the whole rolling range. In particular, when the surface temperature of the rolled piece is lower than the critical temperature and the core temperature is still in the high temperature range, it is possible to form a non-uniform final structure, including grain size and phase composition. More vigorous forced cooling in a water tank will likely form a quenching and tempering layer, which will affect the final quality of the material. If the temperature difference between the material surface and the core is too large due to out of control, a non-uniform grain structure will be produced; During the final heat treatment, the mechanical properties of the material exceed the specified range.

During the test, 30 billets were rolled for each steel grade, and two different temperature ranges were used. The final cooling under these two steel grades and two different conditions is realized by natural cooling, but after the last stand rolling, two different cooling methods are adopted. Take three samples from each rolled piece. One is used for hardness testing and microstructure evaluation in rolling state; The other two are used for heat treatment test.

The cooling curve of the rolled piece on the rolling mill cooling bed affects the mechanical properties of the final material. Because once the CCT curve is determined according to the chemical composition and grain size of the steel, only the cooling route is fixed; The final organization depends on the intersection with the CCT curve. In this case, there is no need to use a cooling bed cover to delay the phase transition process.

5. Heat Treatment

During the test, especially for 60Si2Mn spring steel, many tests have been carried out to optimize the austenite transformation temperature. The amount of ferrite structure and initial grain size in the rolled material are fully considered in the test. In fact, on the one hand, the ferrite structure is suitable for cold shear without cracks in the shear process; On the other hand, it requires full attention to the austenite before quenching. If the phase structure is not handled properly, it is possible to retain the island ferrite structure after quenching, so as to reduce the mechanical properties of the final material.

The target hardness after 40Cr quenching is determined as 52hrc; The target hardness of 60Si2Mn after quenching is 60HRC. In both cases, the national standard requires oil as the quenching medium. According to the national standard, three samples need to be processed in the heat treatment furnace in the laboratory. After tempering treatment, select air cooling mode to cool the sample to room temperature.

6. Microstructure Analysis

The microstructure test results of 40Cr show that the material rolled at low temperature by LTR has very uniform ferrite / pearlite structure; The ferrite phase is more than 30%. In hot rolled products, the ferrite phase only appears near the grain boundary in the form of pre eutectic phase.

For 60Si2Mn, a higher finish rolling temperature is selected, in which the ferrite phase is more similar to the eutectic structure. In any case, if LTR low temperature rolling is compared with conventional hot rolling process, obvious difference can be seen. This is not only reflected in the grain size (from grade 9 to grade 8), but also in the distribution of microstructure. Uniform cooling can not only ensure uniform microstructure in the cross section, but also avoid coarse grains.

7. Conclusion

The SBQ special steel bar rolling  mill newly built by Hani tech company has determined the low-temperature rolling process shortly after successfully rolling the first batch of billets, so that users can produce high-quality steel conforming to GB national standards.

The finished bar not only has excellent internal and surface quality, but also achieves high dimensional machining accuracy. For low alloy steel, the low temperature rolling process shows that it can completely change the microstructure of the material within the specified range, so as to improve the mechanical properties and technical indexes of the material. To make good use of this production process, people must clearly understand what it really needs for a specific steel, how to carry out subsequent heat treatment, and what the end use of the product is.

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Metallurgical Slitting Rolling Technology

Metallurgical Slitting Rolling Technology

Whether the rolled piece can be cut is not only related to the thickness of the connecting part and the relative reduction but also closely related to the pass shape and the size of the slit rolling. In the pass design of the slitting process, the design of pre-cutting and slitting holes is particularly important, followed by the vertical box pass. The pass design of these passes is related to the success of slitting and rolling.

The pre-cut split hole is a transitional pass to ensure the smooth slitting of the split hole. Its purpose is to reduce the unevenness of the split pass, so that the splitting wedge can complete the pressing and positioning of the opposite rolling piece, and accurately distribute the rolling. The cross-sectional area of ​​the piece reduces the burden of cutting the hole as much as possible, thereby improving the stability and uniformity of the cutting. The design should have sufficient reduction, the elongation coefficient should be 1.3 to 1.4, the expansion coefficient should be about 0.6, and the height of the connecting belt should be 0.45-0.48 times the height of the hole.

The slitting hole is basically formed by the connection of a double round pass and a slitting wedge. The function of the slitting pass is that the slitting wedge continues to press down the middle of the pre-slit rolling piece, rolling out the same shape as the pass Rolled pieces, so that the thickness of the connecting strip meets the needs of tearing apart multiple rolling pieces in parallel. In the process of slitting and rolling, due to the effect of the slitting wedge, the limitation of the non-porous side wall on both sides of the rolling piece in the slitting pass, and the rolling piece has a more complex cross-sectional shape, the changes of the rolling piece are as follows: Different from conventional rolling. Its main features are as follows. Severe uneven deformation. The compression deformation at the cutting wedge is often greater than that of other parts.

Splitting deformation is no extension or small extension deformation. When slitting the rolled piece in the slitting hole, the reduction at the bottom of the groove is small, while the reduction at the slitting wedge is larger, and the metal is subjected to the action of the slitting wedge, and the horizontal component force pointing to the widthwise direction is larger. It is a forced widening deformation, so the overall extension is small and the widening is larger.

When multiple roots are divided, the cross-sections of the rolling pieces in the middle and the sides are different, and the width of the rolling pieces on both sides is large and the extension is small; the head and middle dimensions of the rolling piece are also different, and the width of the head and tail is widened. The wedge angle of the slitting hole should be reasonable. If it is too small, it will not cut cleanly or cut. If it is too small, it will cause too much clamping force on the slitting wheel and increase the load of the slitting wheel, generally 60°-65°; The rounded corner of the tip is preferably 1～1.5mm. Too sharp will accelerate the wear of the roll; the thickness of the connecting belt should be close to the gap of the roll, 1-2mm is best; the elongation coefficient is 1.08～1.15, and a certain amount is reserved. Broad room for expansion.

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Hot Rolling VS Cold Rolling

 

Hot Rolling VS Cold Rolling

Both hot rolling and cold rolling are the forming processes of section steel or steel plate. They have a great influence on the structure and properties of steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small section steel and thin plate. 

Hot Rolling

Advantages: 

It can destroy the casting structure of ingot, refine the grain size of steel and eliminate the defects of microstructure so that the structure of steel is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction so that the steel is not isotropic to a certain extent. The bubbles, cracks, and porosity formed during pouring can also be welded under the action of high temperature and pressure. 

Disadvantages: 

1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) in steel are pressed into thin sheets, resulting in stratification (interlayer). Layering deteriorates the tensile properties of steel along the thickness direction, and interlaminar tearing may occur when the weld shrinks. Local strain induced by weld shrinkage often reaches several times of yield point strain, which is much larger than that caused by the load.

2. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot rolled section steel of various sections has such residual stress. The larger the section size of general section steel, the larger the residual stress. Although the residual stress is self-balanced, it has some influence on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance. 

Cold Rolling

Cold rolling refers to the process of cold drawing, cold bending, and cold drawing of steel sheets or strips into various types of steel at room temperature.

Advantage:

With fast forming speed, high yield, and no damage to the coating, it can be made into various cross-section forms to meet the needs of service conditions. Cold rolling can make steel produce large plastic deformation, thus improving the yield point of steel. 

Disadvantage:

1. Although there is no hot plastic compression in the forming process, there are still residual stresses in the section, which will inevitably affect the overall and local buckling characteristics of steel;

2. Cold-rolled section steel generally has an open section, which makes the free torsional stiffness of the section lower. Torsion is easy to occur in bending, flexural-torsional buckling is easy to occur in compression, and torsional resistance is poor;

3. Cold-rolled formed steel has a smaller wall thickness and no thickening at the corner of the plate connection, so it has a weak ability to withstand local concentrated loads.

The main differences between hot rolling and cold rolling as following:

Local buckling of the cold-rolled section is allowed to take full advantage of the post-buckling bearing capacity of members, while local buckling of the hot-rolled section is not allowed.

The causes of residual stresses in hot rolled and cold rolled sections are different, so the distribution of residual stresses in sections is also very different. The distribution of residual stress on the section of cold-formed thin-walled steel is bending, while that on the section of hot-bonded steel or welded steel is a thin film.

The free torsional stiffness of hot-rolled section steel is higher than that of cold-rolled section steel, so the torsional resistance of hot-rolled section steel is better than that of cold-rolled section steel.

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Technical Types of Endless Rolling of Bar and Wire Rolling Mill

Technical Types of Endless Rolling of Bar and Wire Rolling Mill

Headless rolling has a series of obvious advantages, such as high production efficiency, improving dimensional accuracy by reducing the loss of cutting head and tail to improve the yield, overcoming the dimensional deviation of the head and tail of the rolling piece, reducing the impact of the head and tail of the rolling piece on the motor, transmission system, roll, guide guard and reducing accidents. It is highly praised and researched by the steel rolling workers.

At present, there are two kinds of endless rolling technology for bar and wire rolling mill :

1. EWR Headless Rolling Technology

It is to cut off the slab first, then heat it, and then weld the front and back two billets (rolled pieces) end-to-end after the furnace is discharged, or after the roughing mill, so as to realize headless rolling. The technology of endless rolling by welding is called EWR, which was developed and first applied by Japanese manufacturers. China Tanggang, Xinggang, Bagang, etc. have tried it.

EWR headless rolling technology first cut off the slab which was originally headless and tailless, and then weld it into a workpiece that is headless and tailless. This is really a helpless move to solve the speed mismatch between the caster and the rolling mill.

This process not only enjoys many advantages of endless rolling but also brings a series of difficult problems. First of all, the complexity of welding equipment and the increase of accident points affect the operation rate in the early stage of commissioning. After short-term trial use, Tang steel, Ba steel, and other manufacturers gave up their efforts to further improve the technology and returned to the original single rolling operation mode, which affected other manufacturers' views on the EWR headless rolling process, which made the later ones flinch.

2. Luna Headless Rolling Process

One is Luna headless rolling developed by Danieli company in Italy, which has been applied in Udine company in Italy. It is characterized in that the billet caster and the continuous rolling mill are directly connected in a production line, the billet is not cut off, and the direct rolling is realized after induction heating in the tunnel furnace. After rolling, it is cut to a fixed length for cooling and subsequent treatment.

Compared with the EWR process, Luna's headless rolling process avoids the embarrassment of cutting and re-welding, which is a major technological innovation in the field of bar and wire rod production and represents the future development direction of rod and wire production technology. However, the disadvantage of the Luna process is that it still needs to use a longer tunnel furnace for induction heating, and its construction cost and operation cost are high.

Generally speaking, there is still a need for further research on the endless rolling technology of bar and wire rod rolling mill.

Please contact stella@hanrm.com for a quotation.
And free send inquiry to us.
Email: stella@hanrm.com   stellarollingmill@gmail.com
Whatsapp/Wechat:+8615877652925

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Research on Energy-saving Technology of the Rolling Process

Research on Energy-saving Technology of the Rolling Process  

Steel rolling energy saving has a great impact on steel rolling production, especially in our country, the energy consumption is huge, so it is urgent to improve the energy-saving technology of production process. At present, the development of steel rolling technology in Lulei is also based on energy saving. New technology, process, and equipment of steel rolling are emerging constantly. The energy-saving effect is adjusted and the energy consumption of the process is reduced by changing the coefficient of each process in steel rolling production. This paper analyzes the energy-saving technology of the Lulei steel rolling process. 

About 12% of the total energy consumption of the whole country is the energy consumption of the iron and steel industry, while the energy consumption of steel rolling accounts for about 15% of the energy consumption of iron and steel. At the same time, due to the continuous improvement of the quality of steel, the energy consumption of steel rolling is still increasing. Based on this, energy conservation and emission reduction of the steel rolling production process are of great significance to reduce energy consumption and pollution. In terms of current energy and ecological environment, the concept of energy conservation and emission reduction must be put into practice.

Current Situation of Steel Rolling Production

China is a large country of production and manufacturing, and the iron and steel industry accounts for an important proportion. With the expansion of the iron and steel industry, energy consumption is increasing day by day. According to incomplete data, the energy consumption of the iron and steel industry accounts for about 13% of the world's total energy consumption, while the energy consumption in steel rolling production process accounts for 15% - 20% of the total energy consumption of China's iron and steel industry. With the expansion of all walks of life, the types of steel products are increasing, and the total demand is also increasing. At the same time, the rolling process is becoming more and more complex. The relevant research shows that the energy consumption of cold rolling and hot rolling processes in China is significantly higher than that of foreign steel rolling processes. Compared with foreign advanced technology, China's rolling technology, management technology, and related equipment are still relatively backward. At present, steel rolling equipment is the main energy consumption equipment in China's iron and steel production. Its energy consumption accounts for about 70% in the whole steel rolling system. Therefore, it can be seen that China's steel rolling production also contains great energy-saving potential.

Analysis of Factors Affecting Energy Consumption in the Rolling Process

1. Effect of heating temperature. The energy consumption of the rolling process mainly includes fuel energy consumption, power equipment energy consumption, and oxidation burning loss. Although there are many factors influencing the energy consumption of the rolling process in rolling production, the heating temperature is an important factor. According to the investigation, single heat consumption has a great relationship with the billet heating temperature. When the heating temperature is between 1150 ℃ and 1250 ℃, the heating temperature is between 1150 ℃ and 1250 ℃ Within the range of ℃, the unit heat consumption will decrease when the temperature drops by 10 ℃. Therefore, to properly reduce the heating temperature, not only to ensure the normal production of billet, but also to reduce energy consumption. However, there is a linear relationship between the heating temperature and the unit power consumption, but it has little effect on the power consumption, but reducing the heating temperature can still effectively save the power consumption.

2. The thermal efficiency of the rolling furnace. The heating mode and internal structure of the steel rolling furnace are also one of the main factors affecting energy consumption. A good heating mode of steel rolling furnace can effectively improve the combustion efficiency of fuel, and more heat is generated per unit fuel. In addition, the internal structure of the furnace, especially the good lining structure, can effectively improve the heat preservation effect of the furnace and reduce the heat loss.

3. Influence of steel production mode. The heating process, temperature, and time of different steel grades are different. In the process of production, the consumption of fuel is also different. If the production process of steel grades is not used properly, not only the ideal rolling effect can not be achieved, but also the consumption of additional energy is caused. This is one of the key points of energy saving in the rolling production process.

Energy-saving Technology of Lulei Steel Rolling Process

1. Wire energy-saving technology. First, the cooling technology of the air cooling line is energy-saving. The imported high-quality high-speed wire production lines all adopt the whole closed-loop cooling system. At the same time, the spinning temperature is gradually reduced, and the product performance and uniformity are improved. The total length of the air cooling line tends to be longer, and the insulation section is longer. In order to improve the cooling rate, some enterprises began to try to reduce the wind temperature, water mist cooling and other ways to improve the cooling rate. In the annealing furnace, the hot-rolled wire rod is treated by on-line solid solution treatment. After being spun into continuous coils, the hot-rolled wire rod is cooled after holding for about 5min. The equipment investment is high, the final grain size can be controlled, and the austenitic and ferritic stainless steel can be treated. The product quality is equivalent to the traditional off-line solid solution treatment. After the hot rolling wire is spun, the fan and water mist are used in the air cooling line to improve the heat exchange efficiency and increase the wire cooling rate. High-speed pulse airflow generated by the infrasonic wave is also used to cool wire rod, which can accelerate heat transfer between wire rod and surrounding air and obtain high cooling rate. The second is the collection and packaging of energy-saving products.

The collecting drum is a kind of high-speed wire that is wound in a circle and transported by an air-cooled roller table. When the coil is transported to the opening of the collecting drum through the roller table, it falls into the collecting drum in a parabolic shape at a certain initial speed and is sheathed on the nose cone held by the supporting claw in the center of the collecting drum. The packaging process is the last process of wire packing, which has a great influence on the appearance of products. When the tangent velocity at the exit of the wire rod is not equal to that at the exit of the spinneret, and the coil falling point deviates to one side, the phenomenon of uneven coil distribution and left and right position caused by the velocity can be partially offset by adjusting the claw under the spinneret. And reasonably adjust the tray running speed to strictly ensure the coiling in the drum. In this way, due to the small falling space, the coil is always in the middle of the mandrel and the cylinder wall when falling, avoiding the occurrence of a staggered layer.

2. The steel rolling process accounts for a considerable proportion of the energy consumption in the whole country, which also indicates that the steel rolling process has a great space for energy conservation, and reducing the energy consumption of the steel rolling process will surely bring China's industrial production into a new era. All in all, in order to reduce the energy consumption of steel rolling technology and achieve the purpose of energy saving, we can mainly explore new steel rolling technology, research new steel rolling technology, and replace advanced equipment from three aspects. Through the improvement of these three aspects, we can achieve the purpose of energy saving of steel rolling technology to a large extent. In addition, we should not only pay attention to these three aspects but also start from every step of the rolling process, strictly limit the energy consumption to avoid excessive loss of energy. All in all, the energy-saving of the rolling process is a necessary project now, which has a great influence on the development of the industry. All in all, in order to achieve the goal of energy saving in the rolling process, it is necessary to explore new rolling technology, innovate the rolling process, introduce more advanced rolling equipment, and do a good job in the control of energy consumption in every step of rolling. Only by strictly controlling the rolling process can the goal of energy saving in the rolling process be achieved to the maximum extent.

3. Optimize the production process. Optimization of the production process can greatly improve the production efficiency, but also save a lot of energy, improve the heat utilization of the hot billet. In the production process of steel rolling, the corresponding production process shall be set according to different steel grades, order batches, hot billet connection, and equipment conditions to give full play to the energy-saving effect of hot charging and formulate the basic principle of furnace charging. First, when a certain amount of high-grade hot billet is in the stockyard, the furnace charging shall be arranged immediately. At the same time, in the process of furnace charging, the number of continuous blocks of medium cooling and hot billet shall be as large as possible and as small as possible In addition, scientific heating time should be established to meet the production needs of different requirements of steel grades, and the connection between heating time and different grades of hot billets should be maintained.

4. Properly reduce the heating temperature of billet. The results show that reducing the heating temperature of billet to a certain extent can effectively save heat energy, electric energy, and steel oxidation loss. Generally speaking, there are three control stages in the heating furnace. The heating temperature and section temperature difference when the billet is discharged is the coupling results of the actual parameters control in each stage. In order to introduce the unknown coupling results in different stages, the heating temperature should be reduced by 30 to 40 ℃ according to different steel types and specifications. In addition, the heating time and temperature should be shortened for the hot billets with temperature more than 300 ℃, and the comprehensive energy-saving effect can be achieved by reducing the heating temperature.

5. Low temperature rolling and rolling process lubrication technology. Low temperature rolling technology is an important energy-saving measure to reduce the process energy consumption of the rolling system. Reducing the tapping temperature of the reheating furnace can reduce fuel consumption, but its deformation resistance and rolling power increase. In recent years, the practical experience of many rolling productions has proved that the energy-saving effect of reducing fuel consumption is more significant. When the temperature is 1100 ℃, the energy-saving of cooling reaches 9.6%, and when the temperature is lower, the amount of iron oxide scale is significantly reduced. The benefits of low temperature rolling on the reduction of fuel consumption and iron oxide amount can completely offset and exceed the cost of increasing rolling power 。 For many rolling mills, the use of process lubrication technology can reduce the energy consumption of rolling, especially for plate mills. The hot rolling temperature of steel is generally between 800 ℃ and 1250 ℃, and the temperature of the roll surface in the deformation zone can reach 450 ℃ - 550 ℃. Therefore, a lot of water is needed to cool the roll. Through the experiment, it can be found that the consumption of rolling power decreases by about 8% due to the reduction of the rolling force.

The energy crisis is becoming more and more serious, we must pay enough attention to the use of energy-saving technology in steel rolling production. The development form of the iron and steel industry in our country urgently requires iron and steel enterprises to use the new technology of energy-saving and consumption reduction. It is necessary to increase the research on energy-saving technology and energy-saving technology in steel rolling production, increase the investment in science and technology, save resources, meet the technical needs of modern steel rolling production to the greatest extent, reduce energy consumption, save resources, and promote the sustainable development of economy and society.


Please contact stella@hanrm.com for a quotation.
And free send inquiry to us.
Email: stella@hanrm.com   stellarollingmill@gmail.com
Whatsapp/Wechat:+8615877652925

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