Comparing two identical steel samples obtained different ways, it is impossible to say for sure which one is better. But taking into account the specifics of the use of metal products (be it sheet or rod), in each specific case it is necessary to understand what properties the alloy acquires during a particular rolling of blanks (“slabs”). This is necessary not only in order to make the best choice and not overpay for products (especially if a large batch is purchased).

Sometimes the difference between hot-rolled and cold-rolled products is fundamental.

The information presented in this article will be of interest to the average consumer and will definitely help to make the right decision. But it is also worthwhile for a professional to familiarize himself with the proposed material, since it is always useful to periodically refresh his memory.

The main difference in rolling methods is the temperature at which the workpieces are processed. When hot it exceeds 920 ºC (1700 ºF). Cold rolling is carried out in a more gentle mode, and the temperature is significantly lower than the value (sometimes at room level) at which recrystallization of a particular metal (alloy) occurs.

Note

Recrystallization is a process in which equiaxed grains (granules) form and grow. Occurs with a significant increase in temperature and changes the structure of the material, which acquires different properties.

Rental features

Hot

• Metal (alloy) is easier to process, so this rolling method can produce thinner sheets or rods of smaller cross-section.
• For the manufacture of products using the hot rolling method, low-grade, cheaper steel is mainly used.
• There is a need for further processing of products, since they are often covered with scale.
• The geometry of hot-rolled samples does not differ in rigor (for example, unevenness at the corners of sheets, uneven thickness), since it is impossible to accurately calculate the limits of deformation when cooling the metal.

Calculation of the mass of hot-rolled and cold-rolled sheets according to GOST 19903-90, 19904-90:

• Reinforcing (strengthening).
• Bearing (foundation).

Cold

• This method of rolling allows you to accurately maintain the specified dimensions of products.
• The surface of the resulting samples is smoother and more even, so their subsequent processing is reduced to a minimum (and sometimes not required at all).
• Cold-rolled metal becomes harder and stronger (for bending, tensile, tearing) with a uniform structure over the entire area.
• Going into production.
• The higher quality of cold-rolled steel increases its cost.

Conclusion

If the cost of rental comes first, then preference should be given to hot. When is the determining factor appearance, strength, quality, then you should purchase cold-rolled samples.

A rolling mill is a set of equipment in which plastic deformation of metal occurs between rotating rolls. In a broader sense, it is a system of machines that performs not only rolling, but also auxiliary operations: transportation of the original billet from the warehouse to heating furnaces and to the mill rolls, transfer of rolled material from one gauge to another, turning, transportation of metal after rolling, cutting into pieces , marking or branding, editing, packaging, transfer of finished products to the warehouse, etc.

Elements of the main line of a cold rolling mill (CRM)

The main line of cold rolling mills generally consists of the same elements as hot rolling mills: working stand, frames, rolling rolls, spindles, gear stand, main clutch, gearbox, motor coupling, electric motor.

In cold rolling mills, both individual and group drives of rolls are used, both working, support and intermediate, depending on the type of mill and its assortment. The most widespread scheme is the individual drive of rolls. Its use makes it possible to reduce the number of types of electric motors and select the optimal gear ratio for NSHP stands. In the case of using an individual roll drive, there is no gear cage, and the torque from the engine is transmitted through a combined gearbox. As a rule, a 1:1 gear ratio is not used on combined gearboxes.

For high-speed SCPs, gear spindle connections with a barrel-shaped tooth profile are used. The largest skew angle at full operating torque for such a connection is 10-30° (with roll transfers up to 2°).

Also, cold rolling mills have a spindle connection consisting of two toothed bushings mounted at the end of the shafts of the combined gearbox; two clips connecting the bushings; four bushings mounted on the spindle shafts; two shafts; two coupling halves placed on the ends of the work rolls; balancing device (used only during handling of work rolls to fix them).

Toothed couplings with a barrel-shaped tooth are used as the main couplings in SHP. They consist of two bushings and two cages, connected along a connector by horizontal bolts.

The design of working stands is determined mainly by the range of strips being rolled, the nature of the work and the number of rolls. For cold rolling mills of sheet products, four-roll stands are used. The work rolls are mounted in roller bearings with tapered four-row rollers. The rolling force is perceived by the work rolls, transmitted to the barrels of the support rolls, and then to the journals of the hydraulic pump. The pads of these work rolls do not contact the pads of the support rolls, therefore elastic deformations of the work rolls in the vertical plane occur according to the beam pattern on elastic bases.

The hydraulic control unit ensures greater precision in the processing of control actions due to the elimination of backlash and elastic tightening of the pressure screw when rotating under load, which are characteristic of electromechanical control units. In addition, the GPU has low wear, high reliability and ease of maintenance. It is more compact and less metal intensive, which makes the working cage compact and increases its rigidity. The HPU, located at the top, is more convenient and 10-15% cheaper than devices located under the lower pad of the support roll.

\Typical job description Roller of a cold pipe rolling mill, 3rd class

Job Description for Roller Roller of a 3rd Class Pipe Cold Rolling Mill

Job title: Roller of a cold pipe rolling mill, 3rd class
Subdivision: _________________________

1. General Provisions:

Subordination:
• The rolling mill operator of the cold rolling mill of pipes of the 3rd category is directly subordinate to...................
• The 3rd class pipe cold rolling mill operator follows the instructions.................................................... .............

(the instructions of these employees are followed only if they do not contradict the instructions of the immediate supervisor).

Substitution:

• Roller of the cold rolling mill of pipes of the 3rd category replaces................................... .........................................
• Replaces the 3rd class pipe cold rolling mill roller...................................... .......................................

Hiring and dismissal:
The roller of a cold pipe rolling mill is appointed to the position and dismissed by the head of the department in agreement with the head of the department.

2. Qualification requirements:

Must know:

• technological process of cold rolling of pipes
• device, operating principle and rules technical operation serviced equipment
• requirements state standards for cold rolled pipes
• steel grades and their rolling properties
• pipe range
• rolling tool used
• plumbing.

3. Job responsibilities:

• Maintaining technological process rolling pipes with an outer diameter of up to 15 mm on one roller cold rolling mill for pipes.
• Camp management.
• Handling of replacement rolling tools.
• Monitoring the quality of rolled pipes and roll lubrication.
• Trimming device control.
• Handling of calibers on roller mills for cold rolling of pipes.
• Setting up the mill.
• Performing routine repairs of the mill.

page 1 Job description Roller of a cold pipe rolling mill
page 2 Job description Roller of a cold pipe rolling mill

4. Rights

• The roller of a cold pipe rolling mill has the right to give instructions and tasks to his subordinate employees on a range of issues included in his functional responsibilities.
• The roller of a cold pipe rolling mill has the right to control the implementation of production tasks and the timely execution of individual assignments by employees subordinate to him.
• The roller of a cold pipe rolling mill has the right to request and receive the necessary materials and documents related to his activities and the activities of his subordinate employees.
• The roller of a cold pipe rolling mill has the right to interact with other services of the enterprise on production and other issues included in his functional responsibilities.
• The roller of the cold pipe rolling mill has the right to get acquainted with the draft decisions of the enterprise management concerning the activities of the Division.
• The roller of a cold pipe rolling mill has the right to submit proposals for improvement of work related to the responsibilities provided for in this Job Description to the manager for consideration.
• The roller of a cold pipe rolling mill has the right to submit proposals for the consideration of the manager on encouraging distinguished workers and imposing penalties on violators of production and labor discipline.
• The roller of a cold pipe rolling mill has the right to report to the manager about all identified violations and shortcomings in connection with the work performed.

5. Responsibility

• The roller of a cold pipe rolling mill is responsible for improper performance or failure to fulfill his job responsibilities provided for by this job description - within the limits determined by the labor legislation of the Russian Federation.
• The cold pipe rolling mill operator is responsible for violating the rules and regulations governing the operation of the enterprise.
• When transferring to another job or being released from a position, the Pipe Cold Rolling Mill Roller is responsible for the proper and timely delivery of work to the person taking up the present position, and in the absence of one, to the person replacing him or directly to his supervisor.
• The roller of a pipe cold rolling mill is responsible for offenses committed in the course of his activities, within the limits determined by the current administrative, criminal and civil legislation of the Russian Federation.
• The roller of a pipe cold rolling mill is responsible for causing material damage - within the limits determined by the current labor and civil legislation of the Russian Federation.
• The cold pipe rolling mill operator is responsible for compliance with applicable instructions, orders and regulations for maintaining trade secrets and confidential information.
• The roller of a cold pipe rolling mill is responsible for compliance with internal regulations, safety regulations and fire safety regulations.

This job description has been developed in accordance with (name, number and date of document)

Head of structural

continuous mills with the number of stands 4-5-6.

Single stand multi-roll reversing mills

These mills are used for rolling small batches of sheets of a wide range, especially from hard-to-deform steel grades. The mills are easy to set up; rolling can be carried out with any number of passes. In ferrous metallurgy, quarto and 20-roll mills are most often used.

On single-stand mills, two rolling methods are used:

Sheet rolling lead to the quarto cages. The initial workpiece is a hot-rolled pickled sheet with a thickness of 3-10.5 mm; final thickness of rolled sheets up to 1.5 mm.

Rolling of rolled strips. Rolling is carried out in 20 roll mills with the diameter of the work rolls D p = 3-150 mm, barrel length L b = 60-1700 mm.

The range of such mills includes thin strips with a thickness of 0.57-0.60 mm, width up to 1700 mm. The initial workpiece is a pickled hot-rolled coil strip with a thickness of 3-4 mm. When rolling strips with a thickness of 0.002-0.10 mm the initial workpiece is a cold-rolled strip with a thickness of 0.03-1.0 mm, which has undergone “bright” annealing.

Single-stand reversing mills are equipped with coilers on the front and rear sides. Rolling is carried out in several passes, rewinding the strip from one coiler to another, with high strip tensions between the coilers and the working stand, with the mandatory use of technological lubricants to reduce the influence of friction forces on the rolling force. In Fig. Figure 33 shows a diagram of a twenty-roll cold strip rolling mill.

Rice. 33. Scheme of a twenty-roll cold rolling mill:

1 – work rolls; 2 And 3 – intermediate and support rolls; 4 – strip thickness meter; 5 And 7 – tension devices; 6 - band; 8 – winder drums

The mill has only two work rolls that deform the strip. The remaining support rolls are designed to reduce bending of the work rolls.

Continuous thin strip cold rolling mills

Continuous mills are used for significant production volumes of a relatively narrow range of strips. Modern continuous mills consist of 5-6 non-reversible quarto stands, the strip is simultaneously in all stands. Only one pass is made in each cage. Continuous mills are equipped with an unwinder on the front side and a winder on the rear.

The stock for continuous cold rolling mills is hot-rolled pre-pickled coils with a lubricated surface. Hot rolled coil strip is produced from continuous wide strip hot rolling mills. The thickness of the rolled material is, depending on the thickness of the finished product, 2-6 mm.

During cold rolling, large metal pressures occur on the rolls due to the hardening of the metal during deformation and the large influence of external friction forces. Cold rolling of coil strip is carried out with a significant tension of the strip between the stands and between the last stand and the winder with the obligatory use of technological lubricants. Strip tension provides a significant reduction in metal pressure on the rolls, which allows the strip to be rolled with high reductions for each pass and promotes tight winding of the strip onto the winder and its stable position between the rolls; the strip does not move along the roll barrel. The use of technological lubricants leads to a decrease in the influence of friction forces and a decrease in metal pressure on the rolls.

Strips with a thickness of 0.2-3.5 are rolled on 5-stand continuous mills mm, on 6 cages with a thickness of 0.18-1.0 mm. The width of strips rolled on these mills is up to 1200 mm.

On continuous mills, two rolling methods are used:

Roll rolling of strips. Each roll is rolled separately.

Endless rolling of coil strip. Adjacent rolls are butt welded before rolling.

Schemes of continuous coil rolling and endless rolling mills are shown in Fig. 34.

Rice. 34. Schemes of continuous coil mills ( A) And

infinite ( b) rolling:

1 – unwinders; 2 – working stands; 3 – winders; 4 - scissors; 5 – butt welding machine; 6 – loop-forming device; 7 – flying scissors

When rolling coils (Fig. 34, A) pickled hot-rolled coils from the warehouse are fed by crane onto a conveyor in front of the cold rolling mill, from which they are fed one at a time to the decoiler. Then the lever with the electromagnet is lowered, the magnet attracts the end of the roll, lifts it and feeds it into the feed rollers. These rollers feed the strip further into the input guide, which clamps and inserts it into the rolls of the first stand.

The rolling process begins at a low filling speed of 0.5-1.0 m/With. The strip is fed into the first stand, passed through the rolls of all stands and directed to the winder drum. When 2-3 turns of the roll are formed on the winder drum, the mill is accelerated to an operating speed of 30-40 m/With. When passing through the rollers at the rear end of the strip, the speed is again reduced. Since most of the strip is rolled at a variable speed, this leads to a change in rolling conditions, rolling force, elastic deformation of the stand, and ultimately to a change in the thickness of the strip along its length.

A significant improvement in strip quality is achieved in endless rolling mills (Fig. 34, b), on which the ends of the coils prepared for rolling are welded in the flow in front of the mill. As a result, the front end filling operations are reduced, the rolling speed is reduced only when welds pass through the rolls, and accordingly productivity increases and the metal consumption coefficient is reduced. Continuity of the process at the time of welding the ends of adjacent rolls that require stopping the strips is ensured by the presence of a loop storage 6 . When the coil welding process ends, a loop accumulation of the strip is created again; upon exiting the last stand, the strip is cut with flying shears 7 and is wound on winders 3 .

A rolling mill is a set of equipment designed to carry out plastic deformation of metal in rolls (rolling itself), as well as transport and auxiliary operations. Rolling shops or departments generally include equipment for the main line of a rolling mill, including roughing, intermediate and finishing working stands and transmission mechanisms, as well as heating furnaces, descaling systems, equipment for transportation, cutting, heat treatment, finishing, straightening, winding, marking, packaging of rolled products, etc.

The main objectives of rolling production are to obtain finished rolled products of specified sizes and shapes in the required quantities, at the lowest possible costs, with a high level of physical and mechanical properties and surface quality.

Section rolling mills are divided into single and multi-strand.

Based on the location of the rolls, the stands are divided into horizontal, vertical and universal, but according to the direction of rolling - into continuous and reversible.

Depending on the parameters of the manufactured products, section rolling mills are divided as follows.

· Mid-grade Circle up to? 75 mm;

Shaped profiles with sides up to 90 mm

· Small-grade Circle up to? 30 mm;

Shaped profiles with sides up to 40 mm

· Wire rod? 6-10 mm

In modern rolling production, increased demands are placed on obtaining products with the required properties, ensuring compactness, versatility, efficiency, maintainability and energy intensity of equipment.

Along with increasing requirements for the dimensional accuracy of rolled products and the quality of their finishing, much attention is paid to the production flexibility of equipment, the ability to quickly reconfigure to another product range, and reduce downtime associated with repairs and maintenance.

There is a tendency to cast blanks with shapes and dimensions close to the parameters of the finished product, which makes significant changes to the rolling process: the number of required passes and rolling stands is reduced with a corresponding simplification of the design, a reduction in dimensions and specific energy consumption, however, a decrease in the drawing ratio places increased demands on structure of the resulting rolled product and necessitates the widespread use of heat treatment.

Trends in the modern metal products market are manifested in a decrease in the range of sizes of finished rolled products and in a greater variety of steel grades. In any case, to obtain the highest productivity, it is necessary to ensure a minimum duration of the changeover process when switching to rolling of a different size, profile or grade of steel, as well as to reduce the duration of downtime associated with equipment maintenance.

The main types of products are construction fittings, wire rod, wire, angles, hexagons, etc.

Mills for rolling strips of ferrous and non-ferrous metals by cold rolling

Cold rolling mills for strip rolling of ferrous and non-ferrous metals are equipment for cold rolling of material using the cold deformation method. This means that the raw material is not heated in the furnace before rolling.

This rolling method is used in order to obtain a thin strip or strip with minimal thickness, a smooth shiny surface, precision cross-sectional dimensions and high homogeneity of material properties. During cold rolling, it is possible to change the mechanical properties of the metal being processed by selecting the necessary parameters of compression and temperature effects. Cold rolling of materials using the cold deformation method is widespread, and cold-rolled products are now widely used in almost all areas of our industry.

When obtaining the finished product, sometimes all the properties obtained by cold rolling are used, such as the dimensional precision of a strip with a thickness of up to max. 0.002 mm, improved strength during rolling. Sometimes, when hardening thick strips, one strives to obtain improved mechanical properties of the strip obtained by rolling. Modern developments of cold rolling mills today are much more advanced in terms of rolling speed or increasing the ability to carry axial or radial loads of bearings of various types of support and work rolls, as well as their service life. New systems have also appeared for measuring and regulating the tension of the rolled strips created between the stands, automatic regulation strip thickness and eliminating variations in thickness.

The above developments can be partially implemented on already operating cold rolling units, as a result of which the productivity of already operating mill units will be increased without any special financial costs.

The concept of “strip” has a connection with the thickness of the strip, because up to a certain point there were difficulties with rolling a wide strip of thickness? 0.2 mm, in this regard, the rolls that needed to be rolled into a strip of thickness? 0.2 mm, it was necessary to dissolve before rolling, i.e. longitudinal division into several strips. After that, the longitudinally cut strips were rolled on mills with rolls of smaller diameter and smaller barrels.

Today, with the existence of multi-roll rolling lines, where the number of rolls can reach up to 20, there is no point in longitudinally unraveling the coil, because on a multi-roll unit it is possible to roll thinner and wider strips. One must think that in the near future strips with a width of min. 1000 mm and 0.05 mm thick. And only after this the strip will be dissolved, where it will be longitudinally divided into strips of the required width. However, very thin strips, special alloys and materials will be subject to rolling on narrow strip mills.

In connection with the production of extremely thin strips, the requirements for the consistency of their thickness have become much more stringent, i.e. to its uniformity. The concept of a strip profile is interconnected with the concept of thickness variation, which refers to the average difference between the thickness of the strip in its center and the thickness within a certain distance from the edge of the strip or its edge.

It is understood that the profile of the cold-rolled strip depends on the flatness of the original stock from the hot rolling line. For example, the convex profile of a cold-rolled product almost completely replicates the profile of the source material from hot-rolled production.

Temperature effects on the strip, the rate of the deformation process, a constant gap in the deformation zone and the strip tension parameter respectively affect the variation in metal thickness along the entire length of the strip. The effect on thickness variations is not limited to this, since the precision of grinding of the back-up roll barrel is important. The design of the support unit and the configuration of the roll journal (in the form of a cylinder or cone) determine which control method is preferred when determining the dimensional accuracy achieved during grinding.

There are a number of other factors that influence differences in metal thickness along the entire length of the strip. Obviously, fluctuations in material thickness can also be caused by changes in rolling speed. And this is simply impossible to avoid, especially during the process of braking or accelerating the unit.

The friction coefficient created between the rolls and the rolled material changes, thereby causing thickness fluctuations. Consistency in rolling mode to a large extent promotes stability of strip thickness readings. Rolls must be fed into the mill with minimal interruptions. Then an almost continuous rolling process is created, which entails establishing the necessary temperature regime, affecting the profile of the rolls. Significant breaks between rolls contribute to the disruption of established conditions, their adjustment is required, and the parameters of the finished strip leave much to be desired. Variation in thickness of cold-rolled steel can be caused by poor quality of support rolls on the mill. When grinding roll barrels, it is necessary to maintain grinding accuracy, which also leads to reducing the thickness variation parameters to a minimum. Runout of the rolls in the stand can also contribute to the presence of thickness variations along the entire length of the strip.

The thickness of the rolled material and the rolling accuracy allow for a certain eccentricity of the rolls and their runout.

Invisible defects of the rolls hidden inside also lead to thickness variations. As a result, the roller can bend quite strongly under heavy load. The roll is checked for internal defects using an ultrasonic flaw detector.

Creating sufficient rigidity in the stand also helps to reduce the variation in thickness of cold-rolled steel. Rigidity can be increased by prestressing the stand, equipping the stand with a large number of rolls, rolls made of hard materials and rolls with small diameter alloys.

In order to reduce the variation in thickness of the rolled material, cold rolling mills are equipped with thickness regulators operating in automatic mode, which subsequently corrects the strip profile. There is an impact on the HPU, the bending and negative bending of the rolls, the strip tension, the methods of cooling the rolls and the rolling speed.

The composition of the rolling production equipment and the method of the rolling process determine the type of mill.

This is either a non-reversible, or, conversely, a reversible, or continuous rolling unit.

A non-reversible mill can include a mill with one stand (single stand), schematically shown in Fig. 1. The direction of rotation of the rolls does not change. The rolled strip is always fed from the coiler side, and at the exit is always transported from the decoiler. Such equipment is used for rolling sheet material or strip in rolls, when rolling can be carried out in one pass. This is typical for rolling aluminum foil or rolling on a temper rolling mill (Fig. 2).

A reversible mill can also include a mill with one stand (single stand), schematically shown in Fig. 3. The direction of rotation of the rolls changes. The strip is rolled first in one direction, then in the other, making several passes that determine the final parameters of the finished product.

A continuous mill includes a mill with multiple stands (multi-stand), schematically shown in Fig. 4. The stands on the mill follow each other, the rolling process goes on continuously, across all stands at once. Cold rolling production can consist of 6 stands (for sheet metal and thin strips) or can have up to 20 stands when rolling small sections of special steels. The direction of rotation of the rolls does not change. The rolled strip is always fed from the coiler side, and at the exit is always transported from the decoiler.

Today, all cold continuous rolling mills are equipped with rolling process regulators that operate in automatic mode and allow the process to be carried out continuously, without stopping the unit. At the moment of removing the finished roll at the exit, the next roll is being loaded at the entrance (Fig. 5).

The inlet part of such mills is equipped with a group of unwinders, consisting of 2 unwinders, a straightening and stretching machine 2, scissors 3, a welding machine 4, loop storage devices 5, which are necessary for the unit at the time of making a weld at a slow speed, and tension S-rollers 6. At the exit continuous mill 7 there are flying scissors 8 and two winders 9.

When the rolls reach a given length, flying shears, working on the guillotine principle, cut off the strip, and the end of the roll goes to the second winder. When the shears are operating, the rolling speed is 5 m/sec.

Today, combined lines consisting of a pickling line and a cold rolling mill deserve much attention.

The pickling line has a speed matched to the high material processing speed of the cold rolling line. The trawling line and the mill have a high-quality suction system for acid and emulsion vapors, which is gentle on the equipment of both lines. The strip storage can be vertical, which reduces the length of the combined line as a whole.

Combined lines have their advantages:

• · reduction in the overall composition of equipment;
• · one roll warehouse;
• · staff reduction.

Rolling mill design

Working stands of a strip rolling mill.

The requirements for cold-rolled strip are constantly becoming more stringent. This also applies to the precision parameters of the thickness, flatness of the strip and the cleanliness of its surface. These requirements form the basis for the design of rolling stand equipment, mill inlet and outlet and other auxiliary equipment.

Design changes concern the rolling stands of the mill. To create pre-stress in the stand, higher rolling forces are used, pressing devices have become hydraulic, PZhT have become more advanced, etc. The system of bending and counter-bending of the work and support rolls improves the flatness of the strip and increases the service life of the roll between grindings.

To help control the flatness of the strip, tension meters are installed on rolling units to measure the tension of the strip within its width. The HPU system plus the system of bending and anti-bending of working and support rolls, axial shift also contribute to achieving accuracy in terms of the thickness of the tape or strip.

Twin-roll mills

The rolling stand is equipped with a certain number of rolls, which subsequently determines the name of the rolling unit. Double-roll stands are suitable for rolling long profile material, narrow strips and strips, for flattening wire, and for temper rolling processes. The technology of these processes requires certain structural equipment of a stand with two rolls. The load that falls on the rolls and the speed of the rolling process determine the choice of bearings to equip the stand: rolling, sliding, roller bearings, etc. They are constantly being redesigned to last longer and reduce frictional heat loss.

Twin-roll mills can be non-reversible, reversible, or continuous. On continuous twin-roll mills, the foil is rolled and the wire is flattened. An example of such a mill is shown in Fig. 6. The composition of the equipment is quite simple: an unwinding device, a stand for rolling material and a winder.

The stand for rolling material is shown in Fig. 7. The cage is installed on the base 3. Roll cushions, the lower ones are indicated under pos. 5 and upper ones under pos. 4, are fixed together with the rollers in such a way that the pillows on the service side are fixed along the axis of the base. Using strips, which are usually fixed with bolts on the frame located on the right. The roller pads have recesses into which the slats are installed. This design firmly fixes the cushion, thus preventing its displacement along the axis and giving the cage as a whole additional rigidity.

The chock, as a single unit, mounted together with bearings, spacer sleeve, bearing cover, hydraulic clamping ring, is pulled onto the roll journal. On the drive side, the cushions are called floating, so they do not remain unfixed. The procedure for transferring rolls is thereby carried out faster, since the dismantling of the strips and fastening elements has to be done only from the maintenance side. During the rolling process, especially at high speed, the temperature balance increases, as a result of which the roll lengthens, and fastening it on both sides could lead to jamming of the roll. This situation, in turn, could lead to overloading of the bearings. The pads of the lower rolls are not installed directly on the frame, but on pads with a hardened surface 6. The lower part of the pad rests on the plane of the pad, and when the roll is bent, the bearing self-installs in the pad.

The strip enters the stand along the wiring table 7. The table is equipped with side guides mounted on rollers 9. The guides can be adjusted depending on the width of the strip or tape, for a narrower or wider tape. During transportation, the strip does not touch the guides themselves, but the rollers, which prevents wear on the guides due to constant contact with the strip. A clamping device 10 is attached to the wiring table, which fixes the strip or tape between oiled felt and wood pads. The strip is being cleaned. Before transferring the rolls, screw 11 is unscrewed, and the wiring table is freely extended beyond the frame opening, so as not to impede the removal of the roll and the cushion from the frame.

To prevent dirt from getting onto the rolled material, the rollers are cleaned by a block or scraper 12, which is pressed against the roller, collecting dirt from it.

From the stand, the strip is transported to the output of the unit, first arriving at the receiving table 13, and when supported by the pressure roller 14, it is directed to the winder of the unit. To lift the rolls in preparation for transshipment, use a screw mechanism 2.

Pressing devices of any rolling unit are used to precisely regulate the thickness of the rolled material. They can be electric or hydraulic. Since the hydraulic pressures of two-roll and four-roll rolling units are structurally almost identical, we will touch upon their description when familiarizing ourselves with the four-roll stand.

We will consider all sections of equipment that are the same for 2- and 4-high stands when describing the 4-high mill.

Four-roll mills

Today, four-roll mills are the most common rolling equipment for the production of cold-rolled materials. In the stand of a 4-high mill there are 4 rolls: two working and two supporting. The rolling process takes place between the work rolls, and the support rolls increase the rigidity in the stand, which is facilitated by different types of installation of the work rolls. Typically the support rolls are larger in diameter than the work rolls. This eliminates deflection of the work rolls. On four-roll units, usually only the work rolls are driven.

In order for the work roll to be pressed against the support roll during the non-reversible rolling mode, which eliminates the work roll from deflection, the work rolls are placed slightly ahead of the support rolls. The rolls can be positioned without axial displacement, but then the support rolls have a double-sided arrangement. How the rolls can be arranged in the stand can be seen in Fig. 8.

Optionally, depending on the technology, both rolls on a four-roll rolling unit can be controlled. It is better to make the support rolls driven rather than working. If the ratio of roll length to diameter is > 5:1, then support rolls are selected as drive rolls. On such stands, thin material is rolled, where the C or Si content is high, stainless steel, i.e. where it is necessary to create a large rolling force. We see the mill on which the drive support rolls are located in Fig. 9. In its stands, thin material with a high C or Si content, stainless steel, and high alloy alloys are rolled, and the thickness of the rolled strip can be up to 0.2 mm.

By rolling softer material with driven back-up rolls, higher reductions can be achieved.

The rolling stand frame bears the main loads present during rolling. The frames are made of cast steel. The foundation slabs for the frames are made of steel. Special clamping mechanisms connect the frames and give them additional rigidity. Support rollers are installed in the openings of the frames.

Inserts are attached to the beds, thanks to which the position of the work roll cushions and the hydraulic unit is established. The rollers lose diameter with each grinding. Therefore, below, under the support roll pads, there are mechanisms that regulate the position of the roll with a new diameter after grinding relative to the rolling line.

The upper cushions of the support rolls are equipped with rolling force meters. GNUs regulate the gap between the work rolls in the deformation zone.

Roll bearings can withstand very heavy loads. They are located in huge cushions that are installed in the frame opening. The support roller cushions contain fluid friction bearings (FB). The work roll cushions operate on roller bearings (cylindrical).

Depending on the load on the support rolls and the speed of the rolling process, bearings are selected for the support rolls. In high-performance rolling mills for rolled material with high process speed (10-15 m/s), rolling bearings will not last long. Therefore, the diameters of the support rolls are increased in order to use standard roller bearings or PZhT. PVT are more preferable:

• They are small in size
• · the diameter of the journal can be increased to 0.75 of the diameter of the support roll,
• · do not require careful maintenance like roller bearings.

Six-roll mills

In Fig. Figure 10 shows a diagram of the arrangement of the rolls of a six-roll mill with a friction drive of NS type rolls. The drive rolls in this mill are intermediate rolls. The ends of the intermediate rolls are tapered: one roll has a cone on the drive side, the other on the operator side.

The intermediate rolls can be shifted axially relative to the edges of the strip, which helps improve the flatness of the strip. The intermediate rollers rotate in different directions. At high rolling speeds, the friction coefficient becomes lower. The transverse thickness variation of the strip or strip from the NS type mill is also significantly less than on four-roll stands.

rolling mills

In Fig. 11a shows the positions of the rolls in the six-roll stand. The advantage of six-roll mills over four-roll mills is that the position of the work rolls is more fixed. Since the pads are in most cases sliding, the transfer of work rolls takes place with the least amount of time.

Flaws:

• · the number of rolls in the stand (support, working, intermediate) makes their inspection less accessible, which makes it impossible to thoroughly visually inspect their surface;
• · the difference in the diameter of the support roll and the working one is a ratio of 2.5:1;
• · the more support rolls in the stand, the more difficult it is to maintain the stand, because the support rolls must be parallel for normal operation of the rolling unit;
• Roll installation devices move four pressure screws in six-roll mills

To install the screws correctly, there are wedge devices that serve to install them and install the cushions. This ensures that the required parallelism is achieved between the support rollers located at the top and bottom.

When installing rolls, high precision is very important, because it ensures technologically normal operation of the mill. The appearance of axial forces causes malfunctions in the functioning of the main components of the rolling unit. The control rolls in a six-roll stand are the work rolls.

Rice. eleven. b shows us one of the possible designs of support rolls: the design can be solid or stacked. In this case, individual rollers (4 - 8 pieces) with supports are mounted on the axis as support rollers.

Multi-roll mills

Multi-roll rolling units are produced in Lately wider distribution, which is associated with changes in demand in the metal products market. The demand for thin high-carbon tape and tape made of stainless steel and special steels has increased. On conventional mills, these orders are not so easy to fulfill: a large number of passes and intermediate heat treatments are required.

Thanks to the use large quantity rolls of small diameter, it is possible to roll a strip or strip with a minimum thickness.

There are many benefits associated with investing in multi-roll mills:

• · reducing the weight characteristics of rolling equipment;
• · saving metal;
• Reducing the cost of equipment;
• · shop cranes of lower lifting capacity serving multi-roll mills;
• · reducing the height of the building itself during the construction of a workshop;
• · a significant reduction in investments made during the construction of a workshop for the production of cold rolled products as a whole.

And the main advantage of multi-roll mills is the production of high-quality strip or tape, since there is practically no or little transverse variation in thickness on the material.

These stands can be either non-reversible, i.e. the rollers constantly rotate in one direction or in reverse. Here, two work rolls with a small diameter are driven, all other rolls with a large diameter serve as support rolls and are idle during the rolling process. The strips rolled on such mills are quite long and are wound into coils or rolls.

To reduce the thickness tolerance and improve the surface flatness parameters in the stand, use various devices to regulate the roll profile:

• · by heating the roll barrel;
• · anti-bending of working and support rolls;
• · supplying lubricant across the entire width of the rolled material into the deformation zone itself;
• · differentiated supply of emulsion.

The thickness of the edge of the strip is always different from the thickness of the strip in the middle. On duo or quarto mills, where large diameter rolls are used and the equipment creates increased rigidity in the stand, tight product thickness tolerances are more easily met.

On multi-roll mills, for example, they roll a strip or strip 1220 mm wide with a thickness of 0.125 mm with a thickness tolerance of ±3%. In this case, the length of the strip in a roll or tape in a coil is about or more than 10,000 m.

However, multi-roll mills, especially where the number of rolls reaches 20 or more, have a number of disadvantages in comparison with duo or quarto mills, which use rolls of larger diameter. These disadvantages are as follows:

• · low rolling force in the deformation zone;
• · limited rolling speed and associated low productivity;
• · heat during rolling and the difficulty of removing heat from the stand;
• · increased complexity in the operation of the mill;
• · complex setup;
• · precision is required when preparing rolls, in particular when grinding them;
• · high energy costs associated with the operation of drive systems.

However, the choice of the type of rolling unit and its further design depends directly on the needs and demands of the market and the satisfaction of customer requests.