What tool is needed for rolling. Equipment and tools for rolling. Auxiliary equipment for rolling production

Rolling toolare rolls, with which ingots and other blanks are processed. Rolls are:

    smoothfor rolling sheets, strips;

    steppedfor rolling strip steel;

    brookfor obtaining long products.

The profile of the cut on the side surface of the roll is called brook... The stream of the upper and lower rolls together form caliber.

Several calibers are placed on each pair of rolls, the shape of which depends on the rolled profile. Complex rolled profiles are obtained by successive passes of metal through a series of gauges. For rails the number of calibers is 9, for beams from 9 to 13, for wire - from 15 to 19.

Depending on the rolling stage, a distinction is made between crimping calibers (reducing the section of the workpiece), rough(approximating the section of the workpiece to a given profile) and finishingor finishing(giving a given profile).

Equipmenton which the metal is rolled is called a rolling mill. The operating principle of the rolling millnext: the rolling rolls are mounted in bearings located in the frame posts. The set of rolls together with the bed is called the working stand. The work rolls are powered by a motor through a gearbox that transmits rotary motion through a gear stand and spindles.

The rolling mill also includes auxiliary machines and mechanisms that perform auxiliary operations for cutting, finishing, and transporting rolled metal.

§ 3. Classification of rolling mills

Mills are classified according to 3 main criteria:

    by appointment;

    by the number and arrangement of rolls in the working stands;

3. according to the number and location of the working stands.

By appointmentmills are divided into 2 main types:

    mills for the production of semi-finished products;

    mills for production finished products.

To the first typerelate crimping and billetstans. Crimping mills - blooming and slabbingwith a roll diameter of 800 - 1400 mm - designed for rolling ingots into large billets (blooms and slabs), which are supplied as an intermediate product for subsequent rolling into smaller billets or to obtain a finished product. Blank mills with roll diameters of 450 - 750 mm are intended for rolling blooms into smaller blanks (from 50 50 mm to 150 150 mm), which are the starting material for further rolling on section mills.

To the second type of stavesinclude:

1.rail and girder with rolls with a diameter of 750 - 900 mm for rolling

railway rails, I-beams, channels, angles

large sizes;

2. large-section with rolls with a diameter of 500 - 750 mm for rolling large-section steel (square and round from 80 to 150 mm), beams and channels 120 - 140 mm;

3. medium-section with rolls with a diameter of 350 - 500 mm for rolling medium-sized steel (square and round 40 - 80 mm), beams and channels up to 120 mm high;

4.Small-section with rolls 250 - 350 mm in diameter for rolling small section sections (square and round 8 - 40 mm), corner sections 20 20 to 50 50 mm;

5. wire mills with rolls with a diameter of 250 - 300 mm for rolling wire (rod) with a diameter of 5 - 9 mm;

6. strip (strip) mills with rolls 300 - 400 mm in diameter for rolling strips 65 - 500 mm wide and 1.5 - 10 mm thick;

7. plate mills for rolling sheets with a thickness of 4 - 60 mm;

8. hot and cold rolled sheets for sheets 0.2 - 4 mm thick and 500 - 2500 mm wide;

9. universal mills for rolling universal strips 200 - 1500 mm wide;

10. pipe mills for the production of seamless and welded pipes;

11.Special-purpose mills - wheel and tire rolling, ball rolling, etc.

As can be seen from the above classification, the main characteristic of section mills is the diameter of the work or gear rolls. If the mill has several stands, then the characteristic of the entire mill is the diameter of the rolls of the finishing stand. For example, a wire mill 250 means that the diameter of the work or gear rolls of the finishing stand is 250 mm.

By the number and arrangement of rolls in the mill's working stands distinguish:

    duo-mills - (two-roll) with two rolls in each stand located horizontally one above the other in a vertical plane.

Duo mills can have a constant direction of rotation of the rolls (non-reversible) and variable (reversible). In the latter case, the rolls periodically change the direction of rotation and the ingot or strip passes between the rolls back and forth several times; both rolls are usually driven. Reversible duo-mills are more widespread: blooming, slabbing, thick-leaf, etc.

    Trio-mills, in which three rolls are located horizontally one above the other in the same vertical plane. The strip is rolled first between the lower and middle rolls, and then with a special device (lifting and swinging tables) it rises to the split level of the middle and upper rolls and, during the return stroke, is rolled between the middle and upper rolls. The trio-mills roll section metal and sheets. Sheet trio-mills have an average non-driven roll of a slightly smaller diameter than the upper and lower ones, and on section rolls - all rolls of the same diameter.

    quarto-mills have four rolls, vertically located one above the other, two rolls of smaller diameter (middle) are working, and large (upper and lower) are supporting. Back-up rolls take up the rolling pressure and reduce the deflection of the work rolls. Quarto beams are reversible and irreversible. They are designed for rolling sheets and strips.

    multi-roll mills are six-roll, twelve-roll, dvadtsatalkovy, etc. These mills have two working rolls of small diameter, and the rest - supporting. Due to the small deflection of the work rolls, these mills are used for cold rolling of thin strips and narrow strips in coils.

    universal mills with vertical and horizontal rolls in one working stand. On these mills, the metal is crimped in width and height. Universal mills are used for rolling strips called universal steel.

By the number and location of working stands rolling mills shareon single-cell and multi-cell... The simplest type is a single stand mill. These include blooming mills, slabbing mills, heavy-plate duo and trio mills, universal mills.

Multi-stand mills have two or more working stands. The arrangement of the stands can be: linear, sequential and continuous... In these mills, each working stand or a group of 2 - 4 stands has a roll drive line.

Linear mills with the arrangement of working stands in one line are rail and structural mills and large section mills.

The most common type of modern multi-stand mills are continuous mills, in which the number of working stands is equal to the required number of passes; rolling is carried out according to the principle - one pass in each stand. The stands are located sequentially one after the other so that the strip is simultaneously in two or more stands. The rolling speed in each working stand increases as the section of the rolled strip decreases, which is achieved by changing the number of rolls revolutions with an individual drive of the rolls of each working stand, or by changing the gear ratio and the number of rolls revolutions and the diameter of the work rolls with a group drive.

Continuous mills are used as billet, bar, wire, strip (strip), sheet for cold and hot rolling. The rolling speed in these mills reaches 30 - 35 m / sec and more, due to which continuous mills have high productivity.

Rolling is called the type of pressure treatment in which the metal is plastically deformed by rotating smooth rolls or having the necessary grooves (streams). The relative position of the rolls and the workpiece, the shape and number of rolls can be different. At the same time, rolled products are obtained - finished products or blanks for subsequent processing by forging, stamping, pressing, drawing or cutting.

Rolled 75.. .80% steel melted. Rolling (Fig. 1) is longitudinal (a), transverse (b), transverse helical (c). The ingots are first fed to powerful longitudinal crimping mills: rectangular - to slabs - to produce slabs - rectangular billets, square - to blooming mills to obtain blooms - square beams with a side of 450 to 150 mm.

Figure: 1. : a - longitudinal; b - transverse; c - cross-screw

Slabs go to longitudinal rolling sheet mills with smooth rolls. Hot-rolled plate steel has a thickness from 4 to 160 mm with a tolerance of 16-18 grade. Thickness interval 4 is typical for thin sheet steel. ... 0.2 mm. Sheets less than 0.2 mm thick are called 5 thick cold rolled steel foil. ... 0.2 mm (tolerance for 12-15 grades) has a low surface roughness (Ra \u003d l, 6 ... 0.2 microns).

Blooms go to billet mills producing a billet - a square with rounded corners, going to a hot-rolled section (Figure 2) of a simple shape: square (a) with a side up to 200 mm, round (b) with a diameter of up to 250 mm, strip (c) rectangular cross-section sizes up to 200 x 60 mm, hexagonal (d), etc. - and shaped: elbows (e), T-beams (e), I-beams (g), channels (h), rails (and), etc. Accuracy of the transverse dimension of high-quality hot-rolled rolled products correspond to the 13-17th quality.


Figure: 2.: a - square; b - round; in - strip; g - hex; d - square; e - Tavr; g - I-beam; h - channel; and - rail

Periodic rental (Fig. 3, a) has a variable length area cross section and is a blank for mass and large-scale production.

Special rental , as well as periodic, is intended for the manufacture of a specific part, for example, a railway wheel (Fig. 3, b).

Figure: 3.: a - periodic; b - special

Round ingots go to the piercing mills of longitudinal rolling (Fig. 4, a), where in the billet 2, when it is compressed in rolls 1, a cavity is opened, smoothed by a plug 3. Between the main rolls, the billet is held by means of supporting rolls 4. The result is a seamless sleeve, which then on automatic (Fig. 4, b) or pilgrim mills (Fig. 4, c) is rolled into seamless pipes.

Figure: 4.

1. Main equipment of rolling production

The main equipment of the rolling production is rolling mills and rolls. A rolling mill is a technological complex of sequentially located machines and units designed for plastic deformation of metal in rolls (rolling itself), its further processing, finishing (straightening, trimming, cutting into dimensional products, etc.) and transportation.

Figure: five.

Rolling rolls (Fig. 5) are the main part of the rolling mill: they compress metal 1 and give it the required shape. The rolling roll consists of a barrel 4 (smooth or with grooves), necks 3 located on both sides of the barrel and resting on the roll bearing, clubs 2 designed to connect the roll with the spindle. Roll ends can be flat or cylindrical (with splines or keyways)

Rolls are made of bleached cast iron or alloy steel (chromium-nickel and chromium-molybdenum) and carefully ground; steel rolls are rolled. The rolls have a Brinell hardness of 150 to 800 HB. Steel rolls are either cast or forged. Forged rolls are stronger than cast rolls. Pre-stressed composite rolls are used. Currently, small-sized carbide rolls have appeared (for example, from alloys VK6, VK8, etc.). Rolls come in diameters from 3 to 1500 mm and have barrel lengths up to 5000 mm.

The necks of the rolling rolls rotate in liners made of textolite, plasticized wood of plain bearings or in roller bearings installed in the cushions of the stands. Textolite liners are lubricated and cooled with water.

Devices that provide metal deformation in rolls are called main equipment, and equipment for other technological operations is called auxiliary equipment.

The main equipment includes:

  • working stand and its assemblies and parts (rolls, bearings, pressure and balancing device, roll alignment devices in the axial direction, roll reinforcement, etc.). The defining characteristics of the working stand are the diameter and length of the roll barrel;
  • rolling mill electric motor;
  • transmission mechanisms that ensure the transmission of rotation from the engine to the work rolls (spindles, main and main couplings, gearboxes, flywheels, gear cage)

The kinematic diagram of the rolling mill is shown in Fig. 6. In the working stand between the rolls 1, located in chocks with bearings, the workpiece is rolled 2 Rotational motion is transmitted to the rolls from the main electric motor 8 through the gearbox 7 with flywheels 6, couplings 5, gear stand 4 and spindles 3

Figure: 6.

Figure: 7.: a - duo; b - varietal trio; c - leafy trio; g - quarto sheet; d - quarto for rolling rolls; e - multi-roll (six-roll); g - multi-roll (twenty-roll); h - universal; and - special

Depending on the design and arrangement of the rolls, the working stands of rolling mills are divided into six groups: duo, trio, quarto, multi-roll, universal and special design. Duo stands (two-roll) are reversible (rolling is carried out in both directions) and non-reversible (in one direction) (Fig. 7).

Cage trio (three-roll) are most often non-reversible. Rolling on such mills is carried out forward between the lower and middle rolls and backward between the upper and middle rolls.

Quarto cages (four-roll) have four rolls (Fig. 8) located one above the other, of which two work rolls are of smaller diameter and two support rolls are of a larger diameter.

Multi-roll stands have five or more rolls.

Figure: 8. : 1 - feed reel drive; 2 - rolled strip; 3 - electric motor for driving rolls; 4 - reducer; 5 - spindles; 6 - supporting rolls; 7 - work rolls; 8 - take-up reel drum

Figure: nine. Continuous rail and structural mill at the Anshan plant (PRC)

Depending on the location of the working stands, the rolling mills are subdivided into single-stand, linear, sequential, semi-continuous and continuous (Fig. 9). Continuous mills are the most perfect. Thanks to the automation, the rolling speed can reach 60 m / s.

The working stand is the main unit of the rolling mill. The metal is rolled in the stand. It consists (Figure 10) of two beds 5 with lugs (feet) 2, plates 1 on which the beds rest, installation pipes 9 connecting the beds, covers 3, rolling rolls 10, chocks of the lower 7, middle 6 and upper 4 rolls and bearings for them, a mechanism 8 for installing rolls in the vertical plane and in the axial direction and a device 11 for balancing the lower roll. In addition, there are roll reinforcement (rulers, guides, passes, etc.), devices for lubricating, cooling or heating rolls.

The bearings (cushions) contain plain bearings or rolling bearings for the roll necks. The beds are made of two types - closed and open (with a cover). Closed beds better ensure the accuracy of the rolled profile, but in such a mill it is difficult to replace rolls.But there are designs of open beds with a wedge-mounted cover (Figure 1 61), which have high reliability and, in terms of rigidity, bring the open bed closer to the closed-type beds.

Figure: ten.

Figure: eleven.

In addition to rolling stands with horizontally arranged rolls, stands are widely used, in which there are simultaneously horizontal and vertical rolls for rolling rolled metal from all sides without tilting.

For rolling mills, DC or AC motors (asynchronous and synchronous) are used. Since the number of revolutions of high-speed motors usually does not correspond to the number of revolutions of the rolls in the rolling stands, gearboxes are installed between the motors and the stands. In rolling stands, the motor torque must be distributed among several rolls. For this, gear stands are used. The torque is transmitted from the engine to the rolls by means of spindles and couplings.

2. Auxiliary and transport equipment for rolling mills

The rolled metal is finished in the mill: the ends are cut, cut into pieces of the required length, straightened, rolled wire rod into coils, rolled broadband steel into coils, etc. The finishing operations are mechanized: they are produced by auxiliary machines and mechanisms These include stationary scissors and flying, circular saws, straightening presses, winders, refrigerators, etc.

Rolled strips must be moved from one device to another. For this, special transport equipment is provided: plate, roller and scraper conveyors, roller tables, conveyors, manipulators, pushers, ejectors and pushers.

The rolls of rolling mills with their necks rest on liners made of plastic or wood plastics or rolling bearings, usually four-row, installed in the chocks of the rolling stands.

Sealed bearings or liquid friction bearings provide precise mill adjustment and relatively low energy consumption and are practically not subject to wear.Fluid friction in such bearings, even at high specific pressures in the journal (up to 25 MN / m2 and higher), is ensured by careful processing of rubbing parts and good sealing Oil is pumped into the bearing at a pressure of 0.1. ... ... 0.15 MPa, providing a friction coefficient of 0.001. ... .0,008 as for rolling bearings.

Various mechanisms are used to change and fix the position of the rolls in the vertical and axial directions and keep them in the desired position:

  • pressure devices for upper, middle, lower and vertical rolls;
  • balancing devices for upper and middle rolls;
  • devices for axial installation.

In horizontal stands, the gap between the rolls is set by moving the upper roll, and in stands with vertical rolls - by their simultaneous movement.

On various mills they are used of various kinds pushing and balancing devices. Pressure devices consist of a pressure nut and a pressure screw. In general, the design of the pressure device is determined by parameters such as speed, magnitude and number of movements per hour. So, the speed of the roll movement in different mills ranges from 0.05 to 250 mm / s, and the number of movements per hour - up to 700.

Pressure devices are of the following types:

  • with a manual drive of a pressure screw or wedge;
  • driven by an electric motor with a helical gearbox.

The balancing device ensures constant pressing of the upper pad against the pressure screw during idle, eliminates the screw clearance in the nut and thereby eliminates a possible impact (from the bottom up) at the moment the metal is captured by the rolls.

In stands with a manual pressure device at small displacements, the balancing of the upper roll is performed by rods with springs resting on the upper crossbar. For significant roll displacements, a cargo or hydraulic device is used.

Devices for axial installation of rolls on the mills allow you to move and fix the rolls not only in the vertical plane, but also in the direction of the roll axis. Axial adjustment is carried out by movement using the bolts of the cassette with an insert (Fig. 12). The pillows themselves, in this case, are fixed in the frame opening with retaining strips bolted to the frame.

Figure: 12. : 1 - pillow; 2 - bolt; 3 - cassette; 4 - roll; 5 - insert

On section mills, the rolls in the axial direction are adjusted by moving the chocks by tightening the side bolts that pass through the bed and chock flanges or through strips resting on one end in the chock and the other in the bed.There are other ways to move and fix the rolls in the axial direction.

Roll reinforcement is all types of devices and devices that are necessary to guide and hold the rolled strip in the desired position both when feeding to the rolls and when exiting the rolls:

  • introductory fittings that ensure correct feeding (rulers, funnels, boxes, passes, etc.);
  • outlet fittings, ensuring the correct exit of the strip from the rolls (ruler, line);
  • transfer devices that ensure the transfer of the strip from one stand to another, with or without turning (various tubes, helical guides, tilting rollers), bypass reinforcement, which provides automatic transfer of the strip from groove to groove both in one stand and from one stand to another

The roll reinforcement installed on the front side of the stand includes, in particular, the lead-in guides, which are a fixed continuation of the groove collars. The lead-in guides provide directional strip feed into the rolls.

When rolling, for example, an oval in a round caliber, the strip has to be continuously kept from rolling and twisting. The rulers have a corresponding profile, and they are very carefully set according to the gauge in the receiving box. Such profiled rulers are called gaps. In this case, especially difficult service conditions of the guide valve are observed, since the gaps in the process of operation come into contact with the hot metal and experience high sliding speeds. All this leads to intensive wear of the working surfaces of the passes.

The rulers are replaced with roller passes, which cause rolling friction rather than sliding friction. In fig. 13 shows the design of a box with roller passes used when rolling a circle.

Due to the difference in the diameters of the work rolls and their circumferential speeds (the number of their revolutions is equal), the rolled strip at the exit from the rolls bends towards a roll of smaller diameter. To prevent this, outlet fittings serve.

Figure: thirteen.

In order for the strip to not bend in a vertical or horizontal plane when the metal leaves the rolls and does not twist around its axis, rulers are installed on the guide bars, as well as on the front side, as well as the lower and, where necessary, the upper wiring.

Tilting of strips after leaving one stand before feeding into the next is carried out automatically by turning guides To reduce the loads, the guides are replaced by turning rolls

3. Gear stands and gearboxes

In cases where each roll is driven by an individual motor (modern blooming, slabbing and quarto plate mills), no gears are required. All other rolling mills must have gears in gear stands and gearboxes.

The gear cage consists of the main gears, the bed, bearings for the main gears (cushions filled with babbitt, rolling bearings) and a system of nozzles and pipelines that provide abundant lubrication to the rubbing parts.

The main gears have a toothed ring, journals (pins) and clubs, made in one piece from steel 40, 45 or 40X with surface hardened teeth. The gears work at high loads (often dynamic) and at high speeds. The number of teeth is taken from z \u003d 18 to z \u003d 29, chevron cutting.

The frame of the gear stand is a one-piece or two-half box, cast from modified iron or steel. During the operation of the gear stands, special attention is paid to the continuous supply of a sufficient amount of lubricant to the teeth and journals of the main gear wheels under a pressure of 0.2. ... ... 0.5 MPa.

Gearboxes between the gear stand and the electric motor are used if their installation and operating costs justify the difference in cost and operating costs of low-speed and high-speed motors.Depending on the gear ratio, the gearboxes used in rolling mills are one-, two-, and sometimes and three-stage.

Couplings and spindles of various designs are used for connecting devices that transmit torque from the engine through a gearbox and a gear stand to the rolls.

The pinion gear of the gear stand is connected to the driven shaft of the gearbox or to the motor shaft (if there is no gearbox) through a clutch, which is usually called the main one. The most widespread are gear couplings, as well as elastic or resilient couplings.

The rolls of two adjacent stands of a linear mill, as well as the main gears and work rolls in conditions of their slight movement in the vertical plane, are interconnected by couplings and spindles of the club type, which allows the spindle to work with some misalignment (1... 2 °). With significant movements of the rolls in the vertical plane, when the spindle axis makes a significant angle with the horizontal plane, the rolls are driven by articulated spindles with rolling bearings, arranged according to the Hooke hinge principle, which can transfer the rolling torque to the rolls from the gear stand when the spindles are skewed up to 10 12 °

Since the spindles weigh tens of meters in length, they are balanced using weights or springs.

4. Auxiliary equipment for rolling production

In addition to plastic deformation of metal, rolling shops carry out transportation, cutting, straightening, finishing of rolled products, etc. All these operations are functions of auxiliary equipment.

During processing, the metal moves along and across the mill, rises and falls, turns around the horizontal and vertical axes of the ingot or strip, etc. In many cases, simultaneously with the transportation of rolled products, cooling, cutting, straightening, etching, lubrication, etc.

Among the most common vehicles are ingot trucks and various types of trolleys, which provide the supply of ingots and billets from heating means to the mill. The tipping cradle is attached to the ingot truck, which, when approaching the roller table, lowers the ingot onto its first receiving rollers.

Roller tables are the main vehicle of rolling shops and are used for longitudinal and some transverse movement of metal. Roller tables are available in diameters from 150 to 600 mm, driven with a separate or group motor, non-driven The distance between the rollers depends on the length and thickness of the ingot.

Solid forged rollers are used, hollow from steel casting or pipes, as well as from cast iron.

In order to correctly direct the strip to the gauge and to correct the curved strip, the manipulators are installed (Fig. 14), and for rotation around the horizontal axis - the tilters.

Figure: fourteen. : 1 - drive hydraulic cylinder; 2 - blank; 3 - left and right rulers

To rotate the strip around its axis on the crimping mills, hook turners are used (Fig. 15). Tilting is performed by lifting one side of the strip with hooks, which in the amount of 3-4 pieces are located on one of the manipulator lines.

Figure: fifteen. : 1 - roller table roller; 2 - turnable strip; 3 - turner hook; 4 - thrust; 5 - manipulator ruler; 6 - tipper lever

There are various designs of tilters: roller, tilting rolls and helicoidal guides, tilting bushings, plate tilters, lever tilters.

On trio mills, it becomes necessary to lift the strip to feed it between the upper and middle rolls. The most widespread for this purpose are lifting and swinging tables. In case of problems when the strip is gripped by the rolls, lift-parallel tables are convenient, since they provide the strip feed perpendicular to the plane of the roll axes. If lifting tables are installed on both sides of the working stand, then they have a mechanical link (interlock) to synchronize work.

In addition to the considered transport devices, bridge and other types of cranes, slewing mechanisms, pushers and ejectors, schleppers that ensure the movement of strips parallel to their axis, refrigerators are used in rolling shops.

At the end of rolling, and sometimes at an intermediate stage of processing, the strips are cut into pieces, the front and rear ends are removed, the side edges of the sheet are cut, etc. For this purpose, scissors and saws various designs. Diagrams of the simplest scissors are shown in Fig. sixteen.

Scissors with parallel knives (Fig. 16, a) are usually used for cutting blooms, slabs, blanks in a hot state, as well as small profiles in a cold state.

In scissors with inclined knives (Fig. 16, b), most often the lower knife is horizontal, and the upper one is located at some angle (usually 2.... 6 °, but not more than 12 °) to the lower one. By design, the scissors differ depending on the direction of movement of the cutting knife and come with an upper movable knife, with a lower movable knife and with the movement of the knives in a horizontal plane.

Figure: sixteen. : a - with parallel knives; b - with an inclined knife; c - disk

Disk shears (Fig. 16, c) are used mainly for slitting sheets and strips.

Figure: 17. Diagram of Edwards flying scissors (a) and pendulum scissors (b)

Flying shears are used for cutting metal on the fly. They are installed directly behind the finishing stand of the mill or separately as an independent unit. There are several types of flying shears, which are determined by the purpose, design and nature of the movement of the knives. To cut workpieces with a section of up to 100 x 100 mm, Edwards' lever-swinging shears are used (Fig. 17, a), and for a larger section - pendulum shears (Fig. 17, b). Edwards scissors cut workpieces at strip speeds up to 4.5 m / s.

Figure: eighteen. : 1 - case; 2 - knives; 3 - spring; 4 - rollers of inclusion; 5 - axis of the hinge of the knives levers; 6 - blank

For cutting high-quality metal with a section up to 30 x 30 mm, uniaxial rotating shears are used (Fig. 18), as well as disc flying shears.

Hot-cutting saws are used to cut shaped profiles and pipes; moreover, flying saws are used in pipe-welding mills. For hot cutting of high-quality metal, saw blades cut teeth separating chips. The diameter of the discs is up to 2000 mm, the thickness is 6.. .10 mm. The peripheral speed of hot saw blades reaches 100.. .120 m / s. Common mild steel is often used as the disc material, and the teeth are heat treated. The most widespread are slide saws, there are pendulum and lever saws.

At the end of rolling, in many cases, metal straightening is required. In some cases, this operation is performed in a hot state, but usually cold rolled products are straightened. For straightening rolled products, crank presses, roller straightening and section straightening machines, and stretching straightening machines are used.

When the rolled product reaches a considerable length (small sections, wire, sheet, strip, etc.), it is wound into coils and rolls.

By design, coilers are divided into three main groups:

  • drum type (see Fig. 8);
  • roller;
  • roller-drum

Tool for rolling are rolls.

Rolling rolls (Figure 3.5) consist of a working part or a barrel 1 , bearing parts or necks 2 and connecting part 3 .

Rolling sheets and strips produced on rolls with a smooth barrel having a cylindrical, slightly convex or concave surface (3.5, and).

Section rolling produced in calibrated rolls, on the barrel of which cutouts are made 4 (3.5, b). Neckline made on one roll, called a stream.

The notches of the two rolls and the gap between them form caliber.

Caliber can be open (13.5, b) or s covered(13.5, at).

Rolls are made from cast iron, cast and forged carbon and alloy steel and hard alloys. The number of rolls, diameter and barrel length of the work roll are the main parameters of the rolling mill.

Figure: 13.5. Rolling rolls: a - with a smooth barrel; b - stream with open caliber; c - streams with a closed caliber; 1 - working part (barrel); 2 - support part (neck); 3 - connecting part; 4 - stream of the upper roll; 5 - the stream of the lower roll; 6 - caliber.

Rolling is carried out on rolling mills. Rolling mill (Fig. 13. 6 ) consists of a working stand, connecting spindles, gear stand, couplings, gearbox, flywheel, engine.

Figure: 3.6. Rolling mill: 1- working stand; 2 - connecting spindles; 3 - gear cage; 4, 7 - couplings; 5 - reducer; 6 - flywheel; 8 - engine; P is the rolling force.

Pressing.

Pressing- extrusion of metal from a closed cavity through a hole in the tool. Basic methods:

1.direct;

2.reverse.

When direct pressing (3.7, and) metal workpiece 3 extruded by a punch 2 and a press washer 5 through the die hole 4 ... When obtaining a hollow profile by direct pressing (3.7, b) the metal is squeezed out through the gap formed by the hole in the die and the needle 6 .

When back pressing the force of the press is transmitted through the punch (13.7, at) to the matrix. The matrix moves relative to the container walls. The metal of the workpiece is extruded through the die hole, forming the product 7 ... The reverse pressing of the hollow profile is carried out in the same way.

Figure: 3.7. Pressing schemes: a - direct pressing of a solid profile; b - direct pressing of a hollow profile; c - back pressing of a solid profile; 1 - container; 2 - punch; 3 - blank; 4 - matrix; 5 - press washer; 6- needle; 7 - pressed product; P is the pressing force.

When direct pressing the direction of movement of the punch and the extruded metal coincide. Distinctive feature direct pressing method is the movement of the workpiece metal relative to the container walls 1 ... Due to the friction against the walls of the container, the central metal layers are ahead of the outer ones. This phenomenon is further enhanced when the outer layers are cooled by the walls of the container. At a certain stage of pressing in the center from the side of the punch (press washer), a funnel is formed, through which surface layers contaminated with oxides and grease are drawn into the central part of the product, forming a so-called press-sink. The presence of a press bite in the product is unacceptable. Therefore, pressing at this stage is stopped, the good product is separated, and the metal remaining in the container (press residue) is sent to remelting.

When back pressing the direction of movement of the extruded metal and the punch is opposite. The relative movement of the workpiece metal and the container walls, therefore, there is practically no contact friction between the metal and the container walls.

With reverse pressing, the flow of metal is more even than with direct, due to the reduction of friction losses, the force less than pressing decreases by 25 ... 30%, the size of the press residue decreases, but the design of the working tool (matrix, punch) is more complicated during back pressing, than with direct.

Products . Compression produces:

1.Bars with a diameter of 3 ... 250 mm,

2.wire with a diameter of 1 ... 6 mm,

3.pipes with a diameter of 20 ... 600 mm with a wall thickness of 1.0 ... 1.5 mm and more,

4.solid and hollow profiles.

Alloys . Zinc, tin, lead, aluminum and aluminum alloys, magnesium and magnesium alloys, copper and copper alloys, nickel and nickel alloys, carbon and alloy steels, titanium and titanium alloys are subjected to pressing.

Equipment. When pressing, the most widespread are specialized hydraulic horizontal and vertical presses. Vertical presses with a nominal force of up to 30 MN are mainly used in the production of pipes, horizontal presses are manufactured with a nominal force of up to 100 MN.

Tool. Pressing tools include: needle, die, container, press washer (in order of temperature rise during operation). The temperature of the workpiece at the contact surface with the tool during pressing of light alloys reaches 500 ° C, copper and copper alloys - 900 ° C, steels, nickel and titanium - 1250 ° C.

For the manufacture of tools, heat-resistant die steels of the type 3X2V8, 4HVS, 5HVS, etc. ... Hard alloy inserts are sometimes used to increase the resistance of the matrices. The profile of the working part of the matrix has a great influence on the pressing force and durability of the dies. Usually, conical dies with an angle of inclination that are optimal for the given conditions are used.

Pressing is usually performed under hot deformation conditions.

The initial billet is usually a cylindrical ingot or a polyhedron obtained by continuous casting, less often a rolled billet is used.

Before pressing, the working parts of the tool are covered with technological lubricant... Apply also cladding (coating) of blanks with ductile metals.

Advantages of pressing:

1.Ability to receive solid and hollow profiles of complex cross-sectionthat cannot be obtained by other methods.

2.Press changeover the new profile is significantly fasterthan in rolling, the dimensional accuracy of the profile during pressing is higher, the surface roughness is less.

3.Ability to receive large diameter thin-walled seamless pipes with low wall thickness.

4.Capability of metal and alloy forming with reduced ductility (high-strength aluminum alloys, bronzes, heat-resistant steels and alloys, etc.).

5. Possibility high degrees of deformation (92% in cross section and more), which provides high mechanical properties, including vibration strength and fatigue resistance.

Disadvantages of pressing:

1.Significant tool wear, dies and especially needles, due to high contact stresses and temperatures, especially when pressing nickel alloys, steels and heat-resistant steels and alloys

2.The high cost of the tool.

3.Unevenness mechanical properties along the length of the pressed product due to uneven metal flow.

4. Large technological waste, especially when pressing large diameter pipes. (when direct method 12 ... 15%, with the opposite - 5 ... 6% of the workpiece weight).

Drawing.

Drawing - the process of pulling the workpiece through the gradually narrowing hole of the tool (die).

During drawing, the cross-sectional area decreases, acquiring a constant cross-section along the entire length. The application of a tensile force reduces ductility and limits the amount of deformation in a single pull.

Figure: 3.8. Drawing schemes:

a - drawing of wire, bar, solid profile;

b - drawing the pipe on the mandrel;

1- blank; 2 - drag; 3 - mandrel; 4 - clip (band); P is the pulling force.

Products . By drawing, get:

1.wire (13.8, and) with a diameter from 6 to 0.008 mm;

2.solid and hollow profiles;

3.pipes (13.8, b) with an outer diameter of 1 ... 360 mm and a wall thickness of 10 ... 0.1 mm, with precise cross-sections and low surface roughness.

The drawing blank is obtained by rolling or pressing; the workpiece should have a cross-section similar to that of the finished product.

Drawing raw materials :

1.wire -wire rod and pressed wire with a diameter of 5 ... 9 mm;

2.Bars and profiles - varietalrental and extruded profiles with a diameter of 5 ... 150 mm;

3.pipes - welded pipes with a diameter of 6 ... 200 mm, seamless rolled with a diameter of 40 ... 200 mm and pressed with a diameter of 20 ... 400 mm.

Drawing is carried out, as a rule, under conditions cold deformation... Wire drawing from tungsten, molybdenum, nichrome and zinc produced in hot.

Particular attention is paid to increasing the ductility of the original workpiece and reducing the drawing force. This is achieved by using heat treatment (annealing) to remove the hardening, high quality surface of the workpiece, the use of high-performance lubricants, optimal profile and low surface roughness of the working areas of the tool.

Equipment. Drawing mills:

1. intermittent type - chain;

2. continuous type - drum.

Tool. Carbide and diamond dies (fine wire drawing).

Alloys .

Lug benefits:

Classification of rolling mills

A rolling mill is a complex of machines and assemblies designed for plastic deformation of metal in rolls (rolling), its further processing (straightening, cutting, etc.) and transportation.

In what follows, a rolling mill will be referred to as equipment designed only for metal deformation.

Rolling mills are usually classified according to three main criteria:

  • purpose or type of products;
  • the location of the rolls in the working stand;
  • the location of the working stands.

Depending on the purpose, rolling mills are divided into the following groups.

Hot rolling mills, which include crimping, billet, rail-and-beam, large-grade, medium-grade, small-grade, wire, thick-sheet, medium-sheet, thin-sheet, broadband and strip (producing strip-billet for pipes in the form of a strip).

Cold rolling mills, including sheet mills, sheet rolling mills, as well as mills for rolling thin and thin strips.

Mills special purpose , which include wheel rolling mills, band rolling mills, mills for rolling strips and profiles of variable and periodic cross-section, etc.

According to the design and arrangement of the rolls of the working stand, rolling mills can be divided into six groups (Fig. 4.10): two-roll, three-roll, four-roll, multi-roll, universal and special design stands.

Figure: 4.10. Working stands with different roll arrangements: and - double roll stand; 6 - three-roll section stand; at - three-roll stand Lauta sheet; d - non-reversible four-roll sheet stand; d - four-roll reversible stand for rolling strip in coils; e- six-roll stand; f - twelve-roll stand; s - twenty-roll stand for rolling thin strip; and - universal two-roll stand; to - universal stand for rolling I-beams with wide parallel flanges

Double roll stands (duo) (fig.4.10, and) there are irreversible and reversible. The first type of stand has two driven rolls with a constant direction of rotation. Such stands are realized in continuous mills used for rolling billets, wire, thin strips, etc. In each stand of these mills, only one metal pass is performed in one direction. The reversing stands have two driven rolls with a variable direction of rotation, so the rolled metal passes through the rolls back and forth several times. The disadvantage of such stands is the need for energy consumption for the reverse operation, which consists in braking the rolls, and then in their acceleration in the opposite direction. Cages of this type are used in blooming, slabbing, plate mills, etc.

Three-roll stands (trio) (fig.4.10, b) - non-reversible and can be used for both section and sheet rolling. Section stands are widely used because more grooves can be placed on three rolls than on two-roll stands. The metal moves one way between the lower and middle rolls and the other way between the middle and upper rolls.

Three-roll sheet stands ( cage Laut) (fig.4.10, at) are used for rolling thick and medium sheets in the form of strips 10-20 m long. The middle roll is driven and has a smaller diameter. During rolling, it is pressed alternately against the upper and lower rolls and rotated by them due to frictional forces. Both types of mills are equipped with lifting and swinging tables for feeding workpieces between different pairs of rolls.

In the working four-roll stand (quarto) (fig.4.10, d) the rolls are located one above the other: two work rolls of a smaller diameter (medium) and two support rolls of a larger diameter, their purpose is to perceive the pressure during rolling and to reduce the deflection of the work rolls. Mills with such stands can be reversible and non-reversible. They are used for rolling thin and thick sheets and strips, armor plates, and rolls.

Cold rolling of coils is carried out on continuous non-reversing mills. In this case, a coils decoiler is installed in front of the stand, and a coiler is installed behind the stand, which creates tension on the strip and winds it onto a drum (Fig. 4.10, 0). During cold and hot rolling of coils on single-stand reversing mills, coilers are installed on both sides of the stand, and rolling occurs in one direction or the other. Sometimes during hot rolling, coilers are installed in the furnaces in front of and behind the stand.

Six-roll stands (sixth) (fig.4.10, e) with two work rolls and four backup rolls due to the rigidity of the work stand itself and less deflection of the backup rolls, they are used for cold rolling of thin strips and narrow strips in coils with precise thickness tolerances. However, the advantages of this type of stands in comparison with four-high stands are insignificant, and since their design is more complicated, they are not widely used.

Twelve- and twenty-roll (fig.4.10, f, s) stands are used for rolling foil. Due to the use of rolls of very small diameter (10-35 mm) and the high rigidity of the entire working stand and the roll system, these mills successfully carry out coil rolling of thin and thinnest strip 5-100 μm thick and 100-1 500 mm wide with a thickness tolerance of 1- 5 microns. The work rolls of such mills are driven, since they have too small a diameter; they are supported by drive rolls of larger diameter, and the latter, in turn, by support rolls. This scheme provides great strength of the entire roll system and virtually no deflection of the work rolls.

Stands with horizontal and vertical rolls are called universal. Universal stands (conventional) are used mainly as reversible two-roll stands (for example, for slabbing) (Fig. 4.10, and)or four-roll (for example, for plate mills). On these stands, metal reduction is carried out by both horizontal and vertical rolls. Vertical rolls ensure the creation of flat and smooth side edges of sheets and slabs. These rolls are usually located on one side of the working stand. In universal beam cages (Fig.4.10, to), unlike conventional rolls, vertical rolls are non-driven. These mills are used for rolling tall I-beams with wide flanges.

Special design cages used in narrow-purpose mills: wheel rolling, tire rolling, ring rolling, ball rolling, mills for rolling profiles of variable and periodic section, etc.

Depending on the location of the working stands, rolling mills are divided into five groups: single-stand, linear multi-stand, sequential, semi-continuous, continuous (Fig. 4.11).

Single-stand mills (Fig. 4.11, a) have one working stand with a roll drive line consisting of spindles, a gear stand, a reducer, couplings and a main electric motor. Single-stand reversing mills are versatile and easy to change from one program to another. The advantage of such mills is their small footprint. Disadvantage - additional expense energy and time to reverse. These mills include blooming mills, slabbing mills, three- and four-roll plate mills, and universal mills.

Working stands linear stans (fig. 4.11, 6) are located in one, two, three or more lines, and each line is powered by a separate drive, or several lines - from one electric motor. Mills of this type are irreversible; they are used as wire, high-quality, rsl-beam and thick-leaved ones.

AT consecutive stanakh (fig.4.11, at) the rolled strip passes several times through each stand, therefore the number of stands of such a mill is equal to the maximum number of passes required for the reduction of the billet with the cross section P 0 into a finished profile with a section / ^ 1 To reduce the length of the workshop and better use its area, the stands are usually arranged in several parallel rows. Mills of this group have high productivity, therefore they are widely used for rolling section sections.


Figure: 4.11. Layouts and drive of working mills: and - single-stand; b - linear; at - consistent; r - semi-continuous; d - continuous;

1-13 - working stands

Semi-continuous mills (fig. 4.11, d) consist of two groups of stands: continuous and linear. In one group of stands, the strip is rolled continuously, i.e., it can be simultaneously in two or more stands. In another group, rolling is carried out on the principle of linear and sequential mills. These mills are used for rolling fine wire and strip.

When rolling on continuous camp (fig.4.11, e) the metal is simultaneously in several stands, therefore, the speed of rotation of the rolls in the stands must be regulated and selected so that the consumption of metal per unit time in any stand is constant:

F = F 2 v 2 \u003d ... F „j n \u003d const, (4.43)

where F, F 2, F n - cross-section of the metal when leaving the first, second and last stands; x\u003e, o 2, ..., o „- strip speed at the exit from the rolls of these stands. Non-reversible continuous mills are high-performance units designed for mass rolling of the same range (size). Continuous mills are used as billet, broad-band, small-section, wire and cold coiled rolling mills for sheets and sheet metal. The roll drive of these mills can be group or individual.

For the production of rolled products in rolling shops, mills of various types and purposes are installed, which are conventionally divided into several groups.

Blank mills: blooming, slabbing, continuous blank mills. Blooming and slabbing - These are large blooming mills with rolls 800-1,500 mm in diameter, in which rolling is carried out in 11-15 passes in a reverse mode. As a rule, these are single-stand mills for the production of large billets in the form of a rectangular billet (slab) and a square billet (bloom). Blooms are single-stand, double-roll and multi-stand, reversible and continuous. The most widely used as billet mills for rolling blooms and slabs are single-stand two-roll reversible blooming mills. Depending on the diameter of the rolls, large blooming mills (1,100-1,500 mm), medium (900-1,000 mm), small blooming mills or crimping mills (800-900 mm) are conventionally distinguished. Continuous billet mills are installed directly behind the blooming mill (slabbing) and usually have two continuous groups of six stands each.

Mills for the production of finished rolled products include: section, sheet, pipe and special.

High-grade mills include large-grade, rail-and-beam, medium and small-grade. According to their purpose, they are divided into two groups: general-purpose, producing a wide assortment of high-quality products for all branches of mechanical engineering and construction, and specialized mills, intended for the production of comparatively narrow high-quality metal, used only in certain industries.

On large-section mills they produce rolled products with a circular cross-section with a diameter of more than 50 mm, as well as squares, corners, channels and other profiles of equal cross-sectional area. On medium-grade - profiles of circular cross-section with a diameter from 30 to 50 mm and other profiles of equal area. On light section millsproduce rolled products having a diameter of 10 to 30 mm, and other equal-sized profiles. These mills can also include specialized wire mills that produce round rolled products (wire rod) with a diameter of 5.0-8.0 mm.

Large-sized mills have finishing stand rolls with a diameter of 850-500 mm, medium-grade 500-350 mm, small-sized 350-250 mm and wire280-150 mm.

Rail and girder In addition to the main products (rails and beams), the mills also produce other large section sections.

TO leafy mills include mills for rolling thick-sheet and thin-sheet (coil) rolling. On strip or strip mills produce strip for pipe welding units.

TO trumpet Mills include piercing, rolling mills and cold rolling mills (CPM), as well as mills for producing welded pipes. Special mills include rolling mills for periodic roll-formed sections, ball rolling, wheel rolling, etc.

The main deforming tool of each rolling mill is rolls rotating in bearings installed in the working stands. The rolls are driven by an electric motor through intermediate transmission mechanisms and devices. The equipment that drives the rolls into rotation, as well as accepting the forces and torques arising during plastic deformation of the metal, constitutes the working line of the stand (Fig. 4.12).

11 1


Figure: 4.12. Scheme of the main line of the four-high working stand of the sheet rolling mill: 1 - working stand; 2 - universal spindles; 3 - electric motor (main drive); 4 - gear cage; 5 - reducer; 6 - motor clutch; 7 - main clutch; 8 - spring balancing device of the spindles; 9 - supporting non-driven rolls; / 0-working drive rolls; 11-

bed; 12 - slab; 13 - anchor bolt

The equipment included in the working line is divided into three main groups:

  • working stand 1 with rolls 9,10 and bed 11;
  • transmission mechanisms 2, 4-7;
  • main motor 3.

Working stand consists of two massive beds mounted on steel plates (slabs) 12, fixed to the foundation with anchor bolts. The bed of the working stand absorbs all the forces arising during metal rolling, and therefore is massive (60-120 tons and more). The bed material is cast steel. For section mills, prestressed working stands are used, in which the increase in rigidity is achieved not by increasing the mass of the bed, but with the help of special tightening mechanisms. The beds are equipped with pillows with bearings and rolls, as well as devices for moving the upper roll along the height and its axial fixation, guides for metal, etc.

Transmission mechanisms and devices depending on the purpose and design of the rolling mill, they can be different. On large mills (crimping, plate), as well as on mills that roll metal at high speed, an individual drive of the work rolls from separate electric motors is used: in this case, the transfer device is universal spindles, intermediate shafts and couplings. The rest of the mills have a common drive for the work rolls from the gear stand 4, which is a gearbox, and gear rolls play the role of gears. In this case, a motor clutch is located between the electric motor and the working stand in one line 6, gear cage 4 and universal spindles.

Spindles - these are the connecting parts due to which the torque is transmitted from the gear stand to the rolling rolls. The end parts of the spindles (heads) come in various shapes; the most widespread are spindles with universal and club heads. If the angular speed of rotation of the electric motor does not correspond to the speed of rotation of the rolls, then a reducer 5 and a main gear coupling 7 are installed in the drive line of the rolls.

Main motor The rolling mill is air-cooled, it can be AC \u200b\u200bor DC, synchronous and asynchronous. DC motors are installed on reversing mills and mills with a wide range of roll speed variation, asynchronous motors alternating current is used when the operation of the rolling mill does not require a change in the number of rolls revolutions over a wide range.

Auxiliary equipment rolling mills serves to supply metal from the heating devices to the receiving roller table of the mill (ingot cars), turn the ingot on the roller table (rotary devices), transport the metal (roller tables or conveyors), move the metal along the roll to feed it into the caliber (manipulators), turn the metal relative to its longitudinal axis (tilters), metal cooling (refrigerators), metal pickling (pickling plants), uncoiling of rolls (uncoilers), coiling of a strip into a coil or wire into a coil (coilers), metal cutting (scissors and saws), as well as for finishing metal: straightening (straightening machines and presses), training, branding, stacking, oiling, packaging, etc.

The automation of large rolling mills consists of a number of local systems assembled to control the entire course of the technological process. Automation of rolling production starts from the supply of raw material to the warehouse and from the warehouse and ending with the receipt of rolled metal at the finished product warehouse and loading it into wagons. Each system has numerous and diverse sensor devices that collect and transmit information about the course of the technological process, including the temperature of the metal, the pressure of the metal on the rolls of the mill, the parameters of the processed material, in particular, the dimensions of the rolled profile, its position and the nature of movement. All this information enters the computers of the systems, after which commands are issued to control the machines and mechanisms of the rolling mill related to the given

the machine, which unites separate systems, for the appropriate adjustment of the operation of machines and mechanisms of other sections of the mill, controlled by other systems. One of the main tasks of automation (and the most economically profitable one) is the automation of the regulation of the dimensions of the rolled profile, carried out by means of a corresponding automatic change in the space between the rolls based on the readings of a continuously operating profile size meter. Due to this, the accuracy of the profile dimensions, the quality of the metal is sharply increased, and the specific metal consumption is reduced. A particularly great effect is achieved in the production of thin sheet products.

The main tool for rolling are the rolls that perform the main rolling operation - deformation (reduction) of the metal and giving it the required cross-sectional shape. As the metal deforms, the rotating rolls take the rolling pressure and transfer this pressure to the bearings. Rolls of rolling mills are divided into two main groups: sheet and section rolls.

The rolling rolls of sheet-rolling mills have a smooth barrel (Figure 4.13, and), they are installed in a stand on two supports, which is the most common type of roll attachment.

The main parts of the roll:

  • barrel - deforming part of the roll with a diameter ABOUT and length
  • neck - has a diameter c1 w, length / w and serves as a support section for installing a roll in bearing units;
  • the end sections are intended for connection with spindles and can have different configurations depending on the spindle design (clubs, vane or cylindrical part).

Figure: 4.13. Rolling rolls: and - leafy; b - varietal

The diameter of the roll, which corresponds to the speed of exit of the roll from the rolls (excluding the advance), is rolling diameter. When rolling metal in sheet rolls, the rolling diameter is taken over a smooth barrel, and for section rolls this parameter is determined by formulas including the dimensions of the roll and the caliber. The main parameter of a sheet rolling mill is the barrel length of the rolls. This dimension is used to indicate the brand of the rolling mill. For example, the mark "broadband mill 2500" means that this mill has a smooth barrel length of 2,500 mm. This will make it possible to produce flat rolled products up to 2,500 mm wide at this mill.

The barrel of the rolls intended for hot rolling of thin sheets is made slightly concave, so that when rolling hot metal and a large heating of the middle part of the rolls, their barrel becomes cylindrical, and then the thickness of the rolled sheet will be uniform over its entire width. On the contrary, the barrel of rolls for cold rolling of thin sheets is made slightly convex: during rolling, due to the greater bending of the middle part of the rolls compared to the edges, the barrel will become cylindrical.

Varietal rolls (fig. 4.14, 6) are used for rolling section profiles. On the surface of the roll barrel there are streams corresponding to the profile of the rolled product. The grooves of two or more rolls form grooves, therefore the rolls are also called grooved. The main parameter of a section roll is its diameter, which is included in the designation of the rolling mill. For example, a blooming 250 mill is designed for section rolling and has a roll barrel diameter of 250 mm.

A roll (Figure 4.13) consists of several elements: a barrel (with a diameter?) And a length T b), which when rolling is in contact with the metal, necks (with a diameter c1 w and length / w) located on both sides of the barrel and resting on the roll bearings; the ends of the roll, serving to connect the roll with the spindle.

The main dimensions of the roll (diameter and length of the barrel) depend on the range of rolled products. The roll diameter for hot rolling ranges from 250 - 300 mm (wire rolling) to 1,000-1 400 mm (bloom and slab rolling). For cold rolling, rolls with a diameter of 5 mm (on 20-roll mills when rolling foil) to 600 mm (on four-roll mills when rolling thin strips) are used.

The quality of the rolls determines the normal operation of the mill, its productivity and the quality of rolled products. The rolls are operated under conditions of continuous abrasion by metal during rolling, under significant pressure and sometimes operate at high, rapidly changing temperatures. The rolling rolls are made of steel and cast iron. Cast-iron rolls are characterized by low strength, but at the same time they have high wear resistance, therefore they are used mainly in finishing and finishing stands, and sometimes in intermediate groups of stands. Conventional steel and cast iron rolls do not always meet the increased requirements for them, therefore, it became necessary to use cast and forged high-strength steel rolls and cast-iron rolls of increased strength. The choice of material for the rolls should take into account the type of rolling mill. For example, during hot blooming, the rolls are exposed to high pressures and temperatures. Therefore, these rolls are made from cast or forged carbon steel with high toughness. They are distinguished by good resistance to bending loads during rolling. The hardness of the rolls does not play a major role here. For cold rolling mills, it is advisable to use alloyed steel and cast iron rolls, in which the surface layer is characterized by high hardness. So, for rolls with a diameter of less than 300 mm, steels of grades 9X and 9XP are used, and for rolls with a diameter of more than 300 mm - steel 9X2, 9X2MF, 9X2V, etc. Rolls for cold rolling made of steel of all grades are subjected to heat treatment (quenching, tempering ) for special modes. The strength and hardness of the roll barrels are also increased by surface hardening. The depth of the layer of increased hardness should be in the range of 20-60 mm, which makes it possible, when the surface of the barrel is worn, to carry out a large number of regrindings and thereby extend the service life of the roll. The coefficient of friction on the surface of the rolls plays an important role in rolling. Steel rolls have an increased coefficient of friction, so they are more often used in stands with high reductions. On blooming, slabbing and billet mills, to increase the friction coefficient and, consequently, to improve the conditions for gripping the metal by rolls, surface knurling of rolls with smooth or notched rollers is used.

Rolling mills are classified by purpose, design, relative position of the main elements and other characteristics.

The predominant classification of mills is by purpose, depending on the type of rolled profiles. These are crimping mills, billet mills, rail-and-beam mills, large-section, medium-section, small-section, pipe-rolling mills, cold rolling mills, tire and wheel rolling mills and special-purpose mills.

The main value that determines the standard size of the section rolling mill is the diameter of the roll, and of the sheet mill is the length of the roll barrel, the size of which determines the possible width of the rolled sheets. For example, a 300 section mill has a roll diameter of 300 mm, and a 2000 sheet mill has a roll barrel length of 2000 mm.

Two-roll non-reversing stands (duo) (Fig. 14.1.2, a) are widely used in continuous mills for rolling billets, wire, section sections and thin strips. In each stand of such mills, only one metal pass in one direction is carried out. In double-roll reversing stands, the direction of rotation of the rolls periodically changes, and the rolled metal passes through the rolls back and forth several times. These stands are used for blooming, slabbing, plate mills, etc.

Figure: 14.1.2. Variants of arrangement of rolls in the working stand

Three-roll (trio) stands are always non-reversible, they are used in section and sheet - the Laut trio - mills, which differ from section stands by a smaller diameter of the middle non-driven roll compared to the upper and lower ones. The metal in the trio's camps moves in one direction between the lower and middle rolls, and in the opposite direction between the middle and upper rolls.

Four-roll stands (quarto) (Fig. 14.1.2, b) are very widely used when rolling thick and thin strips, armor plates.

Six-roll stands are used for cold rolling of thin and narrow strips in coils with tight thickness tolerances.

Twelve- and twenty-roll stands (Fig. 14.1.2, c) have two work rolls, the rest are support rolls and are used for rolling thin and thinnest strips and strips, especially from hard-to-form metals.

Universal mills, in addition to horizontal rolls, also have vertical rolls located on one or both sides of horizontal rolls (Figure 14.1.2, d).

The diagram of the rolling mill is shown in Fig. 14.1.3, d.

Rolling tools are rolls, which, depending on the profile being rolled, can be smooth (Figure 14.1.3, a), used for rolling sheets, strips, etc .; stepped, for example, for rolling strip steel and strand (Figure 14.1.3, b) to obtain long products. A groove is called a cut on the side surface of the roll, and the combination of two grooves of a pair of rolls forms caliber. Gauges distinguish between open and closed (Fig. 14.1.3, c). For open grooves, the roll separation line is within the caliber, and for closed grooves, outside of it. Several calibers are usually placed on each pair of grooved rolls.

Rolls consist of a barrel 1 (working part of the roll), necks 2 (trunnions) and clubs 3. The necks of the rolls rotate in bearings installed in the beds. The bed has pressure mechanisms for changing the distance between the rolls and adjusting the relative position of their axes. The set of rolling rolls with beds is called working stand 4. Torque from the electric motor 8 through the reduction gear 7 is transferred to the gear stand 6 , from the gears of which with the help of spindles 5 and the couplings are transferred to the rolls. Due to the presence of a gear stand, all rolls of the working stand are leading.