Piercing mill mandrel at work. Pipe rolling mills - classification and design. Hot cutting line

The most widespread are piercing mills (working stands) with barrel-shaped rolls. The double-bearing fastening of rolls on such mills allows them to be used to produce sleeves not only of small sizes (diameter up to 140 mm), for rolling which mills with disk and mushroom-shaped rolls are also used, but also for sleeves of larger profiles with a maximum diameter. up to 630 mm. The piercing of large sleeves is accompanied by high pressures on the rolls and the cantilever fastening of the rolls cannot be reliable.

The design of the working stand of a piercing mill is largely determined by the specific purpose of the mill. If it is used only for the production of thick-walled sleeves, the working stand is equipped with two auxiliary idle rolls or one auxiliary roll and a fixed wire (ruler). If it is necessary to produce thin-walled sleeves at the mill, the stand has two fixed wires - rulers, tightly adjacent to the work rolls. In this case, the need for a tight fit of the rulers to the work rolls is dictated by the fact that thin-walled sleeves are characterized by low cross-sectional stability and metal can flow into the gap between the work roll and the tool, limiting transverse deformation. If this tool is an auxiliary roll, then the gap turns out to be significant; Using rulers allows you to avoid large gaps. At the same time, piercing of thick-walled sleeves, due to their high cross-sectional rigidity, can proceed successfully even with significant gaps between the working and auxiliary rolls. The use of auxiliary rolls is advisable, since this ensures less axial sliding of the metal. In addition, tool consumption is noticeably reduced, especially when rolling high-alloy steel, when the durability of the rulers is low.

An important characteristic of the working stand of a piercing mill is the ability to change the feed angle by using different inclinations of the work rolls. In the mills of the old design, this angle was not adjustable and was within the range of 4°30"-6°30". In working stands created in a later period, as a rule, regulation of the feed angle is provided. Although this complicates the design of the working stand, it is entirely justified, since it significantly increases the maneuverability of the mill, which is necessary for a wide range of pipes, both in size and steel grade.

Modern working stands of piercing mills (24) have a massive cast box-shaped frame with a removable cover. Hollow cylindrical drums with openings in which the work roll cushions are placed are placed inside the frame. The drums can rotate around an axis perpendicular to the piercing axis, thereby changing the feed angle. The drive for turning the drums can be used in different designs. In foreign designs, four setscrews are usually used to rotate the drums, resting on recesses on the drums and rotating in nuts that are inserted into the holes in the frame. After installing the drums at the required feed angle, their position is fixed with locknuts of set screws and clamping blocks, which are pressed against the surface of the drums with wedges. The feed angle is usually adjustable between 5-12°.

In domestic designs, special mechanisms are used to rotate the drums. One of these mechanisms rotates the drum by a plate chain enclosing it. The chain is driven by an electric motor through a double worm gearbox and a drive sprocket mounted on the frame cover.

In another design of the rotary mechanism, the required angle of inclination of the rolls is set from an electric motor through a worm gearbox and a cylindrical pair, the driven wheel of which is mounted directly on the drum. The drums are fixed in a given position by springs and released by a hydraulic cylinder. The drums can also be fixed using special clamps, the electric drive of which is located on the frame cover.

In domestic designs, drums can be rotated at an angle from 0 to 90°. This greatly simplifies the change of mill working rolls (transfer), since there is no need to remove the drums from the frame. Having installed the drums so that the rolls are in a vertical position, the cassettes with rolls are removed from the drums through the windows in the frame cover. In foreign structures, during transshipment, it is first necessary to remove the roof, and then remove the drums along with the rolls. The duration of transshipment in this case is 30-40 minutes longer.

The work rolls are mounted in cassettes on tapered roller bearings, placed in cups and reliably protected from scale.

Cassettes with rolls can be moved along the drum guides using pressure screws. Each roll has an independent mechanism for moving pressure screws, consisting of two helical-worm gearboxes transmitting rotation from one electric motor. The mechanisms are installed on the ends of the drums on the sides of the working cage. The simultaneous and identical movement of both rolls relative to the mill axis is ensured by synchronizing the operation of the motors of the roll installation mechanisms according to the electric shaft system. It is also possible to move each screw independently to adjust the mill. The position of the rolls relative to the mill axis is indicated on the dials.

The lower ruler is installed in a ruler holder on a stationary chair. The inlet and outlet funnels are also attached to the chair. The upper ruler is attached to a shaped crossbar, which can be moved up or down using a mechanism mounted on the bed cover. This mechanism consists of two pressure screws attached to crossbars passing through nuts mounted in the worm wheels of gearboxes, which are rotated by electric motors. Synchronization of the operation of two motors for uniform movement of the ruler is carried out using an electric shaft system. A special counter indicates on the dial the actual distance between the rulers.

When rolling thick-walled liners, instead of the upper line, a single auxiliary roll (roller) can be installed with its axis rotated in the horizontal plane at an angle of up to 7° relative to the rolling axis.

The drive of the work rolls of the piercing mill is located on the side where the workpiece is fed into them and consists of an electric motor, a gear stand and articulated spindles (25).

The gear cage is designed to distribute engine torque between the mill work rolls while simultaneously reducing the number of revolutions from the engine to the work rolls. Typically, the gear cage housing is a two-connector box. In the lower connector, a drive shaft-gear and one driven gear are placed on the rolling bearings; another driven gear is mounted in the upper slot. The gear cage housing has a through hole for installing a pneumatic cylinder for the workpiece pusher.

Each articulated spindle has two heads, one of which is tightly seated on the driven shaft of the gear cage, and the other is mounted on the work roll with a running fit. This allows you to slightly change the length of the spindles when adjusting the angle of inclination of the rolls.

When stitching workpieces dia. up to 140 mm, piercing mills with disk and mushroom-shaped rolls are used. Despite the technological advantages of piercing mills with mushroom-shaped rolls, they have not received development recently due to a number of design flaws: unregulated rolling and feeding angles, which reduces productivity and reduces flexibility in the operation of the mill; a bulky, inconvenient stand to operate, combining a gear stand and a working stand in one frame; cantilever fastening of work rolls, which greatly reduces the rigidity of the stand.

The new design of the mill with mushroom-shaped rolls developed by the Elektrostal Heavy Engineering Plant is free of these disadvantages. The main difference of this mill is the double-support mounting of the rolls and the individual drive of the rolls (26), carried out by DC motors with a power of 1750 kW each. The working cage (27) has two rotary drums into which cassettes with rolls are placed. The use of replaceable cassettes allows the use of different rolling angles within the range of 4-17°.

The drum turning mechanism consists of a motor and a worm gear mounted outside the cage, which drive a pinion shaft meshed with a ring gear mounted on the drum. Rotation of the drums provides regulation of the feed angle within the range from 4 to 15°. The rolls are changed by removing the cassettes through the windows in the bed cover. The position of the rolls relative to the rolling axis is adjusted by pressure screws, and their balancing is done by disc springs.

The design of the working stand is thus very similar to modern barrel roll stand designs, however it can provide higher liner output speeds due to both less axial slip and the use of higher peripheral roll speeds. |

Work rolls for piercing mills driven by direct or alternating current electric motors.

Recently, DC motors have been increasingly used, making it possible to regulate the rolling speed over a wide range. It is advisable to have the ability to change the piercing speed when there is a wide variety of assortments of rolled pipes, especially for steel grades that significantly differ in plastic properties and resistance to deformation.

The power of the motors of the working stands of piercing mills largely depends on the range of the mill and the rolling speed. When rolling workpieces dia. up to 150 mm engine power is 1000-1500 kW. For the latest mills designed for high roll speeds (up to 8 m/sec), the engine power is almost doubled. For mills rolling billets of larger sizes, engine power reaches 3500-4000 kW.

Piercing of a round billet or ingot is carried out at. using a mandrel that is placed on the end of a long rod. The rod is strengthened on the output side of the mill in the head of a thrust bearing, which absorbs all axial forces. Two types of mandrels are used for piercing. Cast or forged solid mandrels are put on the end of the mandrel rod and after each piercing they are removed to cool them in a bath of running water. Such mandrels are called replaceable

and only for large mandrels are devices used that partially facilitate this hard work.

Mandrels of another design (28, b) are made in the form of a hollow body and are cooled from the inside with water, which is supplied through a mandrel rod under a pressure of 98-118 I/L2 (10-12 am). During pauses between piercings, the mandrel is additionally cooled externally with water using a special shower device. Such a mandrel is removed only after it is completely worn out (after 500-600, and sometimes a much larger number of passes). Mandrels of this type, which are called non-replaceable or water-cooled, increase the productivity of the mill, and most importantly

e - allow you to fully automate the entire process, freeing yourself from heavy manual operations.

The output side of the mill (29) is equipped with a mechanism 1 for centering the mandrel holder rod 2, removing this rod from the sleeve and dispensing the sleeve from the piercing mill for subsequent processing. The release of cartridges can be lateral (a) or axial (b).

During lateral dispensing, the sleeve, after piercing, being on the rod, is slightly retracted forward until it stops. Then the rod with a non-replaceable mandrel is removed from the sleeve. For this purpose, the head of the thrust bearing 5, in which the rear end is fixed

the rod moves along guides 4, dragging the rod along with it. After the rod is removed from the sleeve, the latter is removed from the rolling axis onto the inclined grid b by circular ejectors 5, and the head of the thrust bearing together with the rod returns to the front working position.

When working on a replaceable mandrel, the latter is put on the rod at the moment its front end approaches the working stand of the mill, and the mandrel is removed after the sleeve is removed from the piercing rolls.

During axial dispensing of sleeves, the rod with a non-replaceable mandrel is always in the working position. The sleeve receives axial movement from friction rollers 7, and the head of the thrust bearing is tilted, passing the sleeve onto the receiving roller.

gang 8, the axis of which coincides with the axis of the piercing mill. After the thrust bearing head returns to its original position and jams, the piercing of the next workpiece can begin. ^

With axial dispensing of sleeves, piercing can also be carried out on a replaceable mandrel. To do this, using a special mechanism, the rod is moved back 1.5-2.0 m with the head of the thrust bearing tilted back to replace the mandrel, and then returned to B: the working position.

The head can be moved by racks, rope transmission or a pneumatic long-stroke cylinder. On large installations, movement is carried out by a special tractor (31), which is a platform moving along guides. The tractor is driven by two vertical engines.

In the working position, the head of the thrust bearing is held by a wedge mechanism mounted on the rocker. The wedge lock of the holding device is opened and closed by a pneumatic cylinder. The link in the lower part is hinged to the frame, and in the upper part it is held by a screw, by adjusting which you can change the position of the link together with the locking wedge. This changes the working position of the thrust bearing head and, consequently, the position of the rod with the mandrel relative to the work rolls. The supply of water for cooling and the correction rod is carried out through the valve mechanism and the head housing.

During axial dispensing of sleeves, the thrust-regulating mechanism (32) consists of a thrust head with a rotating spindle, a pneumatic cylinder for raising and lowering the head when passing a sleeve, a device for axial movement of the carriage necessary to regulate the position of the mandrel in the deformation zone, and, finally, a lock , fixing the head in a given position. Water is supplied through a special valve and thrust head to cool the rod and mandrel during piercing.

The rod is centered using roller centerers (33). Depending on the length of the liners produced at the mill, the number of centerers ranges from 3 to 6. Each centerer has three or four idle rollers (four-roller centerers are used when stitching large-diameter sleeves). Using a lever system and a pneumatic drive, the rollers are pressed tightly against the rod. By the time the front end of the liner approaches the clamping device, the rollers are moved apart by the amount necessary to pass the liner. The lever system is adjusted so that when the rollers are moved apart, the gap between them and the sleeve is insignificant (5-10 mm), which ensures good centering of the sleeve.

During axial dispensing, the movement of the sleeves is carried out by friction dispensing rollers, which receive rotation through cardan shafts and a gearbox from an electric motor. The rollers are brought closer and further apart by a pneumatic drive. Friction rollers are installed behind each centerer.

During lateral dispensing, the sleeves are pulled away by a driven lifting roller installed between the working cage and the first centerer.

The technological process of firmware occurs in the following sequence. The heated workpiece is rolled along an inclined grid into the receiving chute of the piercing mill and is fed by a pneumatic pusher to the stop installed in front of the rolls. Then, after the stop is retracted, the workpiece is inserted into the work rolls of the mill. The thrust is retracted only after the output side of the mill is completely prepared to receive the next sleeve, which is determined by the jamming of the thrust bearing head.

The workpiece, captured by the rollers, receives a rotational-translational motion and is stitched on a mandrel into a sleeve of the required size. When the front end of the sleeve approaches the first catcher, the latter opens to allow passage and centering of the sleeve; then, sequentially, as the sleeve approaches, other centerers open. Upon completion of the piercing in the mill with axial output of the liner, the output rollers automatically approach each other, and the sleeve is fed towards the thrust head. As soon as the rear end of the sleeve passes the first centerer, its rollers come closer and hold the rod until axial movement, since at the same time the lock of the thrust bearing head opens and the mechanism for lifting it is activated. The sleeve is transported by output rollers to the receiving roller conveyor. In some mills, axial movement is prevented by a special lever mechanism installed between the first centerer and the work rolls. This reduces the time it takes to remove the liner from the mill. After the sleeve is released onto the roller conveyor, the ejecting rollers move apart, the centering rollers clamp the rod, and the head of the thrust bearing takes its working position. As soon as it jams, an impulse is given to remove the stop on the inlet side of the mill and the next workpiece is rolled.

Axial dispensing of sleeves, adopted in domestic mills of new designs, makes it possible to reduce the time of auxiliary operations and thereby ensure the highest rate of operation of the piercing mill. The productivity of the piercing mill when rolling a workpiece dia. 140 mm in a sleeve with a cross-section of 136x16 mm and a length of 5.4 m reaches 340 pcs/h. When rolling sleeves of shorter length, the rate may be higher.

The main characteristic of pipe rolling mills is the maximum diameter of the rolled pipes. Therefore, after the name of the mill there is a number indicating the maximum diameter of the rolled pipes. For example, automatic mill 140.

Depending on the range of diameters of rolled pipes, the units are divided into three standard sizes: small - TPA-140, medium - TPA-250, large - TPA-400.

TPA-140 rolls pipes with a diameter of 70-140 mm with wall thickness 3.0-3.5 mm; on TPA-250 – pipes with a diameter of 76-250 mm with wall thickness 3.5-4.0 mm; on TPA-400 – pipes with a diameter of 159-400 mm with wall thickness 4.5-6.0 mm.

Technological production process on installations with an automatic mill

Let's consider the sequence of technological operations when rolling pipes on small automatic installations TPA-140. The equipment layout is shown in Fig. 52, technological process diagram - in Fig. 53.

The round billet is heated in a ring furnace with a rotating hearth to a temperature of 1000-1270°C. The heated billet is fed for piercing into a sleeve to a screw rolling piercing mill. The firmware diagram is shown above in Fig. 49.

The diameter of the workpiece differs from the diameter of the sleeve within 10 %. Round blank with a diameter of 70 - 150 mm obtained from pipe mills or section mills.

Before piercing, the end of the workpiece is centered with a pneumatic centering machine to reduce the difference in thickness of the sleeves. The elongation coefficient in the piercing mill, depending on the pipe size and wall thickness, is = 1.56.0.

After piercing, the sleeve is fed to the automatic machine. The working stand of automatic mills is two-roll, irreversible. 5-12 round gauges are placed along the length of the barrel. Each gauge is designed to roll only one size of pipe.

Rolling of the rough pipe occurs between rolls with grooves and a short stationary mandrel installed in the groove of the rolls. The sleeve is rolled into the pipe in two passes. The rolling diagram is shown in Fig. 54.

Rice. 52. Layout of equipment for a pipe rolling unit 140 s

automatic mill:

I – stock warehouse; II – department of pipe finishing machines; 1 – scales with a lifting capacity of 15 T; 2 – inclined grille; 3 – loading and unloading machines; 4 – heating ring furnace; 5 – correct stance; 6 – roller table; 7 – centerer; 8 – inclined grille; 9 – inclined grid for defective workpieces; 10 – automatic mill; 11 – rolling mill; 12 – sizing mill; 13 – preheating furnace; 14 – friction ejector from the furnace; 15 – reduction mill; 16 – fridge; 17 – correct stance

Rice. 53. Scheme of the technological process for pipe production

installations with automatic mills (with one firmware):

1 – heating of workpieces; 2 – centering of workpieces; 3 – firmware of blanks; 4 – rolling the sleeve into a pipe on an automatic mill; 5 – pipe rolling; 6 – pipe calibration; 7 – intermediate heating of pipes; 8 – pipe reduction; 9 – pipe cooling, 10 – pipe straightening

Rice. 54. Scheme of rolling pipes in an automatic mill:

A – rolling; b – pipe return; 1 – sleeve; 2 – top roll; 3 – bottom roll; 4 – mandrel; 5 – thrust rod; 6 – upper return roller; 7 – lower return roller; 8 – pipe

The first pass is carried out from the front side of the mill. Before rolling the upper work roll 2 and lower return roller 7 lowered down. When the liner is captured by the rollers, it is compressed in diameter and wall thickness. After the first pass, the operator wedges the upper roll, which rises upward under the action of a balancing device. At the same time, the lower return roller 7 rises up and returns the pipe to the front side of the mill (Fig. 54, b). Then the mandrel is replaced, the diameter of which is 1-2 mm greater than the first pass mandrel diameter. The second pass is carried out from the front side of the mill. Before feeding, the pipe is turned by 90°. The total elongation factor for two passes should not exceed  1.2 = 2 to avoid pipe tears. The maximum pipe length after the automatic machine is 10 - 15m.

After rolling on an automatic mill, the pipe has some ovality, different thicknesses (thickening of the wall at the points where the gauge is released), scratches may form on the inner surface of the pipe due to the adhesion of metal particles to the mandrel. To eliminate these defects, the rough pipe after the automatic mill is supplied for rolling into rolling machines (Fig. 53, 5 ). The design of rolling machines is similar to piercing mills: the pipe is rolled between two barrel-shaped rolls and a short mandrel. In rolling mills, the reduction in wall thickness is 5-10 %, the volume of metal displaced during deformation flows predominantly in the tangential direction, i.e., to increase the diameter of the pipe. Rolling mill productivity 1.5 - 2 times lower than the main mills - piercing and automatic. Therefore, to equalize the throughput of all sections, two rolling mills are installed. After rolling machines, a pipe with t600С is supplied for calibration to a continuous calibration mill 6 (Fig. 53), and then onto the refrigerator 9 and correction to the correct car 10 .

If it is necessary to reduce the diameter of the pipes, then after rolling mills the pipes are heated to a temperature of 1000 - 1150С before reduction in the oven 7 and rolled in a reducing mill 8 , from where they go to the refrigerator for cooling and subsequent editing and finishing.

TPA-250 with an automatic mill has the same equipment composition as TPA-140, with the exception of a reduction mill, which is usually not installed.

TPA-400 consists of two ring furnaces and two piercing mills. The second piercing mill is an elongator.

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In this article are described various types of sewing\ rollers, their advantages and defects, the characteristic of the is intense-deformed condition in the deformation center is resulting at an insertion on rollers various types are resulting. Besides, in the article the directing tool sewing camps is described. The comparative characteristic of Disher's disks and directing rulers is the result.

V. V. KLUBOVICH, V. A. TOMILO, BNTU, V. E. IBRAGIMOV, O. N. MASYUTINA, RUE "BMZ"

UDC 621.774.35

DESIGN FEATURES OF TOOLS FOR MANUFACTURING SEAMLESS PIPE BILLETS

The wide range of pipes predetermined the many methods, units and mills in which it is implemented. Moreover, each method is characterized by the most effective range of pipes produced. In addition, the specific requirements for pipes determine the choice of their production method.

Pipe production is constantly being improved and developed; it is characterized not only by qualitative growth, but also by significant qualitative changes in accordance with the needs of customers. The range of pipes in terms of sizes and materials is expanding, the production of pipes with specially treated external and internal surfaces (pipes for nuclear energy, instrument making), with protective and smooth coatings for main gas and oil pipelines, etc. is increasing. pipe with the appropriate properties and quality, it is necessary that a system of gauges be correctly selected and calculated to ensure that a pipe of the given size is obtained. In turn, calibrating the tools of piercing mills consists of correctly constructing the profile of the rolls, mandrels and guide tools and determining their sizes.

This article provides various types of piercing mill rolls and guide

tools, and also their comparative characteristics are given.

The following types of rolls are used in piercing mills: barrel-shaped; disk; mushroom-shaped and double-pinch rolls.

I. Barrel-shaped rolls of piercing mills are two truncated cones, folded together by large bases (Fig. 1). On such rolls there are three sections: entrance cone I; pinch t; exit cone r.

At the entrance section, the metal is prepared for piercing. The clamp is designed to smooth the transition from the input cone to the output cone. The exit cone performs transverse rolling of an already stitched pipe.

Barrel rolls are classified depending on the length of the inlet and outlet cones.

1. Rolls of the first type have the same length of the input and output cones (Fig. 2). If the length of the input cone does not provide the required quality and dimensions of the sleeves, then rolls of the second type are used.

2. In rolls of the second type, the input cone is shorter than the output one (Fig. 3).

3. In the third type of rolls there are two input cones, the first is responsible for improving the gripping conditions, the second reduces the length of the deformation zone, which leads to a reduction in defects on the outer

Rice. 1. Barrel roll of piercing mill

Rice. 2. Barrel-shaped roll of the first type piercing mill

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Rice. 3. Barrel-shaped roll of the second type piercing mill

Rice. 4. Barrel-shaped roll of the third type piercing mill

and the inner surfaces of the sleeve, therefore such rolls are used when rolling workpieces that differ slightly in diameter (Fig. 4).

Considering the axial zone of the metal in the deformation zone during piercing, it should be noted that the stress-strain state diagram here is different, since compression forces act from the rollers, and tensile forces act from the Disher disks or guide bars, as well as from the piercing side . This arrangement is not desirable, as it may cause metal destruction if critical compression is reached. Ultimately, the plasticity reserve will be completely used up, and macro-fractures will form, which leads to the formation of defects on the inside of the pipe. Therefore, an important condition for piercing is not only the creation of a favorable scheme of stress-strain state during metal deformation and the optimal ratio of transverse and longitudinal deformation, which significantly affects the possibility of destruction in the central zone of the workpiece, but also an increase in the value of critical compression.

The critical compression can be increased by changing the usual scheme of stress-strain state (along two axes - tension and one axis - compression) to a new one (along two axes - compression and one axis - tension). Such a change in the stress state pattern can be obtained by changing the slip and creating additional supporting forces. This can be realized if, along the path of the metal flow in the deformation zone, ridges are made on the rolls, which

Rice. 5. Groove calibration of rolls

These will create additional resistance to the flow of the metal, and this in turn will lead to a change in the pattern of the stressed state of the metal in the deformation zone.

The conclusions made formed the basis for new types of calibration of piercing mill rolls.

1. Groove calibration (Fig. 5) is characterized by the fact that ridges of variable height and grooves of variable width are created on the rolls. The angle of inclination of the ridge to the roll axis is 0°. The ridges are located along the entire generatrix of the roll, which leads to a decrease in tensile stress and, as a result, the scheme becomes close to the scheme with two compressive and one tensile stress, and this in turn leads to an increase in the value of the critical reduction. The groove calibration has one significant drawback, which is that it is difficult to manufacture.

2. Ring calibration (Fig. 6). The angle of inclination of the ridge to the roll axis is 900. Here the ridges have a similar effect as in the groove calibration, thereby improving the stress-strain state.

3. Screw calibration (Fig. 7). The angle of inclination of the ridges to the roll axis is in the range of 0-90°. This type of calibration makes it possible to improve the stress-strain state diagram in both the axial and tangential directions.

If workpieces with a diameter of up to 140 mm are used for piercing, piercing mills with disk and mushroom-shaped rolls are used. Rolling mills with mushroom and disc rolls produce longer liners.

Rice. 6. Ring roll calibration

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Despite the technological advantages of piercing mills with mushroom-shaped rolls, they have not received recent development due to a number of design flaws:

1) unregulated rolling and feeding angles, which reduces productivity and reduces flexibility in the operation of the mill;

2) a bulky, inconvenient to operate cage, which combines a gear and a working cage in one frame;

3) cantilever fastening of the work rolls, which greatly reduces the rigidity of the stand.

In modern production of seamless hot-deformed pipes, a type of roll is used, such as a double-pinch roll. The profile of this roll is shown in Fig. 10. The calibration of such a roll is based on the principle of crushing deformation. In this case, the roll is divided into sections in which compression is carried out, significantly less than critical, followed by passage through sections where compression is not performed. As a result, the use of rolls of this type makes it possible to improve the stability of the workpiece in the rolls, as well as reduce the thickness difference.

Rice. 8. Profile of the disk roll of the piercing mill

Rice. 7. Screw calibration of rolls

II. The profile of the disk rolls of the piercing mills is shown in Fig. 8.

Disc rolls make it possible to obtain profiles with sharp transitions; in addition, the use of double-support rolls makes it possible to significantly simplify the design of the working stand, which leads to the use of conical rolls in small-sized mills, and disk rolls in more heavily loaded large-sized mills.

III. The profile of mushroom-shaped rolls of piercing mills is shown in Fig. 9.

On such rolls, two sections are distinguished: input 1p and output (/p) cones.

Rice. 9. Profile of a mushroom-shaped roll of a piercing mill

Rice. 10. Roll profile of a piercing mill with double pinch

When calculating a system of gauges that ensure the production of a pipe of a given size, special attention must be paid to the guide tool, which forms a closed gauge in the deformation zone together with the rollers, which allows the piercing process to be carried out with increased elongation coefficients and to obtain thinner-walled sleeves. In piercing mills, guide rulers and Disher disks can be used as a guiding tool.

The rulers of the piercing mill have a rather complex shape, which is determined by the type of deformation, the amount of compression and the rise in the diameter of the sleeve compared to the diameter of the workpiece. Rulers in piercing mills are involved in the process of deformation of workpieces, so their shape must correspond to the profile of the roll so that there are no gaps between the side surfaces of the rolls and rules. Rulers also affect the transverse deformation of the metal, contributing to the ovalization of the sleeve.

In Fig. Figure 11 shows the profile of the piercing mill line.

The advantages of guide rulers are that they cover the entire area of ​​deformation, but there are also disadvantages:

1) they heat up and quickly deteriorate due to high friction with the workpiece;

2) rulers are replaced manually, which increases the risk of injury and physical stress of working personnel;

3) the cost of producing rulers is higher than that of producing disks.

To eliminate all of these shortcomings, modern production is increasingly using Disher disks as a guiding tool. The profile of Disher disks is shown in Fig. 12.

The advantages of guide discs over guide bars are as follows:

1) time for production is reduced, since there is no need to spend so much time replacing lines;

2) the disks rotate, thanks to which they have time to cool;

3) friction is significantly less than that of rulers, which increases their wear resistance;

4) the workpiece is easier to remove after rolling due to the fact that the disks are retracted in different directions.

Rice. 11. Line of piercing mill

Rice. 12. Disher disk

The disadvantage of discs is that they do not capture the entire area of ​​deformation, unlike rulers.

Replacing guide bars with guide disks is necessary for factories, since thanks to guide disks, production costs will be reduced and product output will increase. As a result of the use of guide disks, production volume will increase, the risk of injury and physical stress of personnel will decrease. Repairing and replacing guide discs is cheaper than replacing guide rulers. Their resource is also noticeably higher.

It should be noted that for the correct selection and calculation of a caliber system that ensures the production of a pipe of a given size, one should proceed from the specific production conditions, take into account the specificity of production, mechanization and automation of production, the size and shape of the deforming tool, the physical and mechanical properties of steel.

In this case, calibration must meet special requirements, ensuring:

1) obtaining sleeves with the required geometric dimensions and high quality of outer and especially inner surfaces;

2) normal and stable course of the firmware process, without violating the conditions of primary and secondary capture;

3) high mill productivity with minimal energy consumption for piercing;

4) high durability of the tool, which reduces the number of transfers and extends its service life;

5) the ability to carry out the piercing process for a wide range of liners without additional transshipment.

Literature

1. Matveev Yu. M., Vatkin Ya. L. Calibration of rolling mill tools. M.: Metallurgy, 1970.

2. Technology of rolling production / A. P. Grudev, L. F. Mashkin, M. I. Khanin M.: Metallurgy, 1994.

2015 marked 130 years since the invention and receipt of a patent for the use of a piercing mill for the production of seamless pipes.
This revolutionary discovery in technology served as a powerful impetus for the development of advanced technologies. The authors of the discovery are outstanding engineers, scientists and inventors, the Mannesman brothers.

piercing mill— two or three-roll cross-screw rolling mill for hot piercing of a deformed billet or ingot on a short, held mandrel and obtaining a thick-walled sleeve; installed in front of the rolling mills in the line of the pipe rolling unit.

elongator mill— a cross-screw rolling mill with double-cone rolls for piercing the bottom of the cup, leveling the wall along the cross section, reducing the wall thickness and lengthening the thick-walled sleeve on a short held mandrel.

(German) Reinhard Mannesmann, May 13, 1856, Remscheid - February 20, 1922, ibid.) was a German engineer, inventor and entrepreneur, best known for inventing, together with his brother Max, a method for producing seamless pipes.

He was born into the family of Reinhard Mannesmann Sr., the owner of a factory for the production of files and other tools that had existed since 1776, and, like his younger brother Max, began working in the family business. In 1884, he and his brother invented a roller piercing mill, for which they received a patent in 1885. In 1891, the brothers created a pilgrim mill that could produce seamless pipes, which was a real revolution in the pipe industry, since welded steel pipes were produced at high pressure, which was the cause of numerous accidents causing loss of life. By 1899, seamless steel pipe technology was already widespread in the German Empire, Austria-Hungary and Great Britain.
In 1890, the Mannesmanns created another innovation - the transverse rolling method, for which they received a patent on July 16, 1890 and which became another important stage in the development of the pipe industry and found application not only in pipe production, but also in architecture. The money received for both patents in the same 1890 allowed the brothers to found their own metallurgical concern, Mannesmanrören Werke, which became the largest pipe-rolling enterprise in the world at that time and, having three production sites in Germany and Austria and an authorized capital of 35,000,000 marks, was one of the ten largest German concerns.

Existing methods of metal rolling can be divided into three types depending on the direction of drawing of the workpiece being processed and the direction of the peripheral speed of the rolls:

Longitudinal rolling is characterized by the coincidence of the main direction of metal flow with the direction of movement of the deforming surfaces.
Transverse rolling is characterized by the fact that the main flow of the metal (elongation of the piece) occurs in the direction perpendicular to the movement of the deforming tool.
During transverse rolling, the rollers come closer together, compressing the workpiece to a given amount. At a certain amount of compression in the central part of the workpiece, the continuity of the metal is disrupted and a central cavity is formed
Oblique rolling occupies an intermediate position between longitudinal and transverse rolling. In this case, the elongation of the deformed metal occurs at a certain angle to the direction of movement of the deforming tool. In oblique rolling mills used in production, the angle between the direction of movement of the deforming surfaces and the direction of the main deformation is 79-85°, i.e. very close to straight. Therefore, oblique rolling is close to transverse rolling in terms of the nature of deformation.

Reinhard Mannesmann is also known for a number of inventions in other fields of technology: telephony, file production, steel carburization.

Piercing mill is a pipe rolling mill designed to produce a thick-walled hollow sleeve from a solid billet or ingot using the method of cross-helical rolling.
The piercing mill on most pipe rolling units consists of two oblique work rolls rotating in one direction, while the workpiece rotates in the other direction. To hold the workpiece between the rollers, special devices are provided (usually rulers, less often rollers). The work rolls have piercing and rolling cones, and in the middle there is a calibration belt. A mandrel is installed between the rollers along the path of movement of the resulting hollow sleeve. When the work rolls are positioned at a certain angle between their axes, rotation of the workpiece relative to its axis and at the same time its translational movement are achieved, due to which the workpiece is pushed onto the mandrel and stitched.

Piercing mill - a two- or three-roll cross-helical rolling mill for hot piercing of a deformed billet or ingot on a short, held mandrel and obtaining a thick-walled sleeve. Installed in front of rolling mills as part of injection molding machines. The piercing mill consists of a main drive with a balancing device on the input side, with a mechanism for pushing workpieces, a working stand and an output side. The mills sew blanks up to 140, 250 and 400 mm in diameter, respectively, with a weight of 0.5, 1.7 and 2.5 tons.
Piercing mill is a rolling mill used to form a longitudinal round hole in a workpiece or ingot.

The invention relates to pipe rolling production, and more precisely to cross-helical rolling piercing mills.
Currently, at all pipe rolling units in the country and abroad, two types of mills are common for producing sleeves: two-roll piercing mills and three-roll piercing mills. The main criterion for the use of a particular type of mill is the quality of the stitched sleeves in terms of geometry, the presence of internal and external membranes, variations in thickness and dimensional accuracy in diameter, curvilinearity, etc. The main advantage of a two-roll piercing mill is the relatively low thickness difference of the sleeves, the disadvantage is the presence of membranes on their inner surface. The main advantage of the three-roll piercing mill is the absence of film on the inner surface of the sleeves, the disadvantage is the increased thickness difference.
As already noted, a piercing mill for helical rolling is widely known, containing a working stand with two work rolls and a drive for rotating the rolls from a DC motor. The peculiarity of the stress-strain state at the input cone of the deformation zone of two-roll mills determines the possibility of destruction of the metal in sections up to the toe of the mandrel, which leads to the formation of defects, namely the appearance of films on the inner surface of the liners, especially with uneven heating or overheating of the workpieces. More favorable conditions for piercing, from a kinematics point of view, are possible on mills where loading takes place not at two, but at three points along the perimeter of the workpiece.
A helical rolling mill is also known, containing a working stand with three rolls symmetrically located (at an angle of 120°) relative to the rolling axis, and a group drive for rotation of the rolls.
In three-roll cross-helical piercing mills, any reduction is allowed in front of the mandrel toe without loosening in the center of the workpiece, the tendency to form internal films is reduced and the coefficient of axial slip is increased. However, since the process of piercing in three rolls is characterized by high requirements for combinations of parameters, three-roll piercing mills are used for a limited range of initial workpieces, and the difference in thickness of the sleeves is not excluded. In addition, in three-roll mills with a symmetrical deformation zone, it is still difficult to use an individual drive - more mobile, reliable and economical.
The most significant contribution to the study of the piercing process, the development of advanced methods for producing hollow sleeves and improving the design of piercing mills was made by scientists and design engineers of the Ukrainian School of Pipe Rollers P.T. Emelianenko, A.P. Chekmarev, I.A. Fomichev, M.I. Khanin, V.M. Druyan, V.F. Balakin. It is important to note that the piercing mill allows for not only transverse but also oblique rolling.

The oblique rolling process is widely used in the pipe rolling industry for the production of seamless pipes. It is used for the main operation - obtaining a hollow sleeve from a solid blank.

The deformation of the wall during oblique rolling of a hollow workpiece without a mandrel depends mainly on the amount of compression and the feed angle. Despite the fact that not all issues related to the study of the theoretical foundations of the process of producing hollow sleeves when piercing from a solid billet have been finally resolved, many practical conclusions drawn from the research and developed theoretical principles have contributed to the successful development of the domestic pipe industry.
The question of the reasons for the formation of an internal cavity has not yet found sufficiently complete coverage. Research carried out abroad by a number of authors is characterized for the most part by an almost complete absence of experimental material, and therefore the conclusions are speculative and insufficiently convincing. Experimental data are available only in the work of Siebel, who determined the stresses in a cylinder when it was compressed by two plates. Siebel came to the conclusion that the violation of metal continuity is the result of shear stresses, the magnitude of which is maximum in the center of the workpiece. This conclusion is unconvincing and is refuted by Siebel’s own experiments.

Rice. Cavity formation during cross rolling

Detailed and very valuable work on studying the processes of transverse and oblique rolling was carried out by Ukrainian scientists. The research of Ukrainian scientists and their conclusions are characterized by a fundamentally new interpretation of the issue, based on valuable experimental data, and the desire to find a comprehensive solution to the problem. Scientists Corresponding Member Academy of Sciences of Ukraine P. T. Emelianenko, Dr. tech. Sciences V.S. Smirnov, Candidates of Technical Sciences I.A. Fomichev, A.F. Lisochkin and others for the first time gave a truly scientific interpretation of the complex phenomena occurring during transverse and oblique rolling. Despite the fact that a number of issues in these works have not been finally resolved, many practical conclusions drawn on the basis of the research carried out and the theoretical principles developed contributed to the successful development of the pipe industry. Let's take a closer look at their views
P.T. Emelyanenko at one time suggested the formation of a cavity as a result of alternating stresses and continuous shifts in the central zone of the workpiece, caused by the movement of metal particles along elliptical trajectories.

Rice. Formation of caps and cracks during flashing

Due to the action of these stresses, the formation of radial cracks and flaws is observed in the core of the metal. After the appearance of cracks in the axial zone of the workpiece, transverse rolling is considered by P. T. Emelianenko as a process of continuous plastic bending. This hypothesis is very valuable, as it allowed the author to draw an important conclusion about the significant influence of the degree of ovalization of the workpiece on the formation of a cavity, which is confirmed by numerous experiments and production practice.
The phenomenon of plastic bending during oblique rolling of hollow bodies sometimes explains the appearance of cracks on the inner surface of the liners during secondary piercing.
Firmware process researcher V.S. Smirnov, based on a large number of carefully conducted experiments, developed a theory about the emergence of a cavity as a result of the action of all-round tensile stresses. The destruction of the core of the workpiece and the formation of a cavity, according to the author, is explained by the fact that the acting stresses exceed the values ​​of the brittle strength of the metal, and therefore the destruction is brittle and not ductile, as other authors believed. V.S. Smirnov’s hypothesis is original and interprets the issue in a new way. However, in this theory it is difficult to prove the possibility of creating all-round tensile stresses in the core of the workpiece under the influence of external compressive forces from the rolls.
Studying the macrostructure of samples taken from different areas of the deformation zone during piercing, I. A. Fomichev came to the conclusion that the formation of a cavity is the result of uneven deformation over the cross-section and length of the workpiece and the associated phenomenon of axial tightening. According to I. A. Fomichev, the twisting of the workpiece, which occurs in oblique rolling mills, also contributes to opening the cavity. Somewhat later, I. A. Fomichev, studying the nature of the outflow of metal during piercing, gave diagrams of radial, tangential and axial stresses. Radial tensile stresses arising due to the presence of tangential forces displacing the metal around the circumference of the workpiece, if their magnitude is large, according to the author, can lead to core ruptures. I. A. Fomichev also attaches great importance to the presence of a mandrel that excites the tightening force. Fomichev made a conclusion of great practical importance about the need to carry out the piercing process without forming a cavity before mandrel, since opening the cavity before mandrel leads to the appearance of internal films and cracks on the sleeve. The same conclusion was reached somewhat later by I.V. Dubrovsky and L.I. Matlakhov, who specifically studied the influence of the position of the mandrel in the deformation zone on the formation of internal films.

Rice. Diagram of radial tensile stresses during piercing (according to I. A. Fomichev)

It is characteristic that when rolling hollow billets, the most common is ring destruction (delamination). With a decrease in compression in the first zone of the deformation zone (before the mandrel), the resistance of the mandrel to the advance of the workpiece increases, so that under certain conditions, a decrease in compression can be not only useless, but even harmful, since this increases the number of alternating loads, increasing the tendency to open the cavity.
The amount of deformation in the second zone of the source also has a certain impact on the quality of the inner surface of the pipe. The greater this deformation, the greater the likelihood of defects, all other things being equal. This is especially clearly evident during oblique rolling of hollow workpieces made of high-alloy steel.
It should be noted that the opening of the cavity is significantly influenced by the number of work rolls. Even A.F. Lisochkin pointed out that three-roll mills in this regard are preferable to mills with two rolls. Recently, this theoretical assumption has been confirmed by direct experiments.
In the practice of pipe rolling production, piercing mills with two rolls are used. In cases where thin-walled sleeves are produced during piercing and the deformation zone must be tightly closed, the use of two-roll mills with rulers is inevitable. If piercing always produces a thick-walled sleeve, then mills with three rolls can be used. In such mills it is impossible to have a closed hearth, but when piercing thick-walled sleeves this is not necessary. In the most general case of oblique rolling in a roller mill, the axes of the rolls are inclined to the rolling axis at an angle called the rolling angle. In addition, the roller axes are skewed relative to the rolling axis. The skew angle of the rolls is called the feed angle.

Rice. Scheme of tangential and radial stresses (according to A.F. Lisochkin)

Based on the work of scientists and production practice data, the following main factors influencing the formation of a cavity can be indicated:

• decreasing the relative compression reduces the tendency to form a cavity;
• reducing the ovalization of the workpiece in the deformation zone reduces the tendency to open the cavity;
• alloy steels are more prone to cavity formation;
• As the temperature decreases, the tendency to form a cavity increases, but overheating of the steel leads to premature opening of the cavity.

Rice. Speeds when piercing in a roller mill

Kinematics of the firmware process
A round workpiece, inserted into rolls rotating in one direction, receives rotational motion due to the excited friction forces. At the same time, due to the inclined position of the rolls relative to the axis of the workpiece, it also has axial movement. Thus, each point on the surface of the workpiece moves along a helical line in the deformation zone.

The deformation zone in the piercing mill can be divided into two zones. The first zone - from the beginning of the workpiece grip to the place of the largest diameters (pinch) of the rolls - is called the piercing cone. Only at the end of this zone, when the workpiece meets the mandrel installed in the deformation zone, does an internal cavity begin to form. Further, in the second zone, the mandrel, together with the rollers, increases the cross-section of the cavity and the wall of the liner decreases. The second zone is called the rolling cone.
As the workpiece moves into the deformation zone, its cross-sectional area decreases, especially strongly from the moment the internal cavity is formed. Therefore, the speed of the workpiece in the deformation zone increases, and the speeds of the rolls change slightly or do not change at all, as in a disk mill. As a result, slipping inevitably occurs between the deformed metal and the rollers.
The sliding of the metal relative to the rolls is one of the most important factors in the process of piercing the workpiece. It affects the productivity of the installation and the quality of the resulting sleeves.
Based on numerous measurements, it has been established that the axial slip coefficient is practically in the range of 0.35–0.85. For approximate calculations, Yu. M. Matveev and Ya. L. Vatkin recommend using empirical dependencies to determine the axial slip coefficient as a function of the workpiece diameter at different piercing speeds.

Based on numerous studies, it has been established that axial slip increases:

• with an increase in the piercing speed, with an increase in the number of revolutions and, to a lesser extent, with an increase in the angle of inclination of the rolls or eccentricity;
• with increasing diameter of the workpiece;
• with a decrease in the wall thickness of the Sleeve;
• with reduced compression before mandrel;
• when the firmware temperature decreases.

  It should be noted that although the coefficient of friction between the metal and the rolls increases with decreasing temperature, the resistance of the mandrel increases more intensely, causing an increase in axial sliding.

  The slip coefficient is greatly influenced by the shape of the tool.
  The research of S.P. Granovsky, as well as the experiments of O.A. Plyatskovsky, established that over the entire length of the deformation zone, the axial speed of the workpiece is less than the speed of the rolls, i.e. metal lag occurs. There is no neutral or critical section in which the speeds of the rolls and the workpiece are equal. This position is illustrated by the measurements of S.P. Granovsky, who conducted experiments on a laboratory mill.
  The large difference in the speeds of the rolls and the workpiece at the initial moment of piercing and at the end of the process and the greatest sliding in these areas of the deformation zone lead to more intense wear of the rolls in these places, which confirms the phenomenon of uneven wear of the rolls along the length of the barrel, known from practice.
  Sliding in the tangential direction has been studied to a much lesser extent, which is explained by the difficulties in determining the tangential slip coefficient.

  

  Rice. Diagram of the deformation zone during firmware

  Each point on the surface of the workpiece-sleeve moves along a helical line.
  When determining the energy consumption for longitudinal rolling, the results of analytical calculations can be compared with values ​​established in practice. For oblique rolling, such a comparison is very difficult, since there is almost no systematic data on energy consumption in the literature. There are only data from P. T. Emelyanenko and 10. M. Matveev related to the piercing of ingots. Despite the large number of experiments carried out, a sufficiently reliable pattern of changes in energy consumption as a function of the magnitude of deformation has not yet been found.
  It has been experimentally established that extending the mandrel beyond the pinching of the rolls within certain limits leads to a slight decrease in energy consumption, and its excessive extension leads to an increase in energy consumption. It is known from experiments that energy consumption decreases with an increase in the angle of inclination of the rolls. For example, with an increase in the angle from 7 to 9°, energy consumption decreases by 20-25%, which is explained, first of all, by a decrease in machine time.
  A load diagram is presented in which three sections are clearly defined. The first section - from the moment of gripping until the deformation zone is completely filled with metal - is characterized by a gradual increase in load with a more or less obvious inflection of the curve, corresponding to the moment the metal meets the mandrel, after which the load increases more intensively. The second section corresponds to a steady-state process in which the load changes little. The third section is characterized by an increase in load at the end of the process. The beginning of the peak coincides with the moment the rear end of the workpiece hits the rolls.

  

  Rice. 51. Load diagram when piercing a workpiece

  As the piercing cone is released from the metal due to a decrease in axial slip, the feed per half-turn increases. An increased feed leads to an increase in partial compression for each half-turn, which causes an increase in the piercing power when the workpiece leaves the deformation zone. The average power and its peak value change sharply with changes in the piercing speed, piercing temperature, shape of the tool used and other technological factors. In particular, an increase in the deformation rate due to an increase in the number of revolutions or the angle of inclination of the rolls causes an increase in load. In some cases, load peaks may even limit the ability to increase the firmware speed if the engine power is insufficient.
  Thus, taking into account all of the above, we can safely say that
  that the piercing mill has become the greatest invention and an indispensable tool for the entire world metallurgy, allowing for longitudinal, transverse and oblique rolling.

The invention relates to pipe rolling production, in particular to piercing mills for cross-helical rolling. The cross-helical piercing mill contains a working stand with one barrel-shaped upper roll and two barrel-shaped lower rolls, the symmetry axes of which are shifted in a vertical plane relative to the rolling axis, and a rotation drive for the lower rolls, the upper roll is equipped with a drive located on the side opposite to the drive of the lower rolls working stand, while the pinch radius of the upper roll is determined by the formula,

The invention improves the grip of the workpiece by rollers and improves the quality of stitched sleeves. 4 ill.

The invention relates to pipe rolling production, and more precisely to cross-helical rolling piercing mills.

Currently, at all pipe rolling units in the country and abroad, two types of mills are common for producing sleeves: two-roll piercing mills and three-roll piercing mills.

The main criterion for the use of a particular type of mill is the quality of the stitched sleeves in terms of geometry, the presence of internal and external membranes, variations in thickness and dimensional accuracy in diameter, curvilinearity, etc.

The main advantage of a two-roll piercing mill is the relatively low thickness difference of the sleeves, the disadvantage is the presence of membranes on their inner surface.

The main advantage of the three-roll piercing mill is the absence of film on the inner surface of the sleeves, the disadvantage is the increased thickness difference.

The objective of this invention is to use the advantages of both types of mill and eliminate their disadvantages.

A known piercing mill for cross-helical rolling, containing a working stand with two working rolls and a drive for rotating the rolls (V.Ya. Osadchiy, A.S. Vavilin, etc. Technology and equipment for pipe production. Textbook for universities. M.: “Internet Engineering ", 2001, pp. 75-82).

The peculiarity of the stress-strain state at the input cone of the deformation zone of two-roll mills determines the possibility of destruction of the metal in sections up to the toe of the mandrel, which leads to the formation of defects, namely the appearance of films on the inner surface of the sleeves.

More favorable conditions for piercing are possible on mills where loading takes place not at two, but at three points along the perimeter of the workpiece.

A known helical rolling mill contains a working stand with three rolls symmetrically located (at an angle of 120°) relative to the rolling axis, and a group drive for rotation of the rolls (automatic certificate USSR No. 780914, B 21 B 19/02, application 21.02 .79, publ. November 23, 1980).

In three-roll cross-helical piercing mills, any reduction is allowed in front of the mandrel toe without loosening in the center of the workpiece, the tendency to form internal films is reduced and the coefficient of axial slip is increased. However, since the process of piercing in three rolls is distinguished by high requirements for combinations of parameters, three-roll piercing mills are used for a limited range of initial workpieces, and the difference in thickness of the sleeves is not excluded. In addition, in three-roll mills with a symmetrical deformation zone, it is difficult to use an individual drive - more mobile, reliable and economical.

Of the known cross-helical piercing mills, the closest in technical essence is a piercing mill containing a working stand with one upper and two lower rolls of the same shape and length, the symmetry axes of which are shifted in the vertical plane relative to the rolling axis, and a rotation drive for the lower rolls ( German patent No. 1946463, B 21 B 31/08, application 09/13/69, published 01/5/78).

The upper roll, non-driven, is a guide. The two lower rolls are working.

With this arrangement of the rolls, the rolling process is carried out with a displacement of the workpiece axis relative to the mill axis. The displacement of the workpiece axis has a beneficial effect on the stress distribution in the cross section of the workpiece, reduces the likelihood of metal destruction (cavity formation) in front of the mandrel toe and the formation of defects on sleeves and pipes (films, different thicknesses).

A disadvantage of the known design of a cross-helical rolling piercing mill is that the presence of an idle upper roll worsens the gripping conditions due to the need for additional effort to unwind this roll, which has a significant moment of inertia. It is this circumstance and the reactive friction forces that arise during a non-driven roll, directed in the direction opposite to the rolling forces, that prevent reliable gripping of the workpiece.

Another disadvantage of this piercing mill is the impossibility of rolling thin-walled sleeves, since a necessary condition for this should be a minimum gap between the lower rolls and the upper roll when rolling the entire thin-walled range of sleeves.

This, in turn, is possible only if certain relationships between the main design parameters of the deformation zone are observed.

The objective of the present invention is to create a piercing mill that improves the conditions for gripping the workpiece with rolls and improves the quality of the pierced sleeves.

This task is achieved by the fact that in a piercing mill containing a working stand with one barrel-shaped upper roll and two barrel-shaped lower rolls, the symmetry axes of which are shifted in the vertical plane relative to the rolling axis, and a rotation drive for the lower rolls, according to the invention, the upper roll is equipped with a drive located on the side of the working stand opposite to the drive of the lower rolls, while the pinch radius of the upper roll is determined by the formula

,

where R x is the pinch radius of the upper roll,

R in - pinch radius of the lower roll,

R z - radius of the workpiece being stitched,

h=0-200 mm - the displacement value of the axis of symmetry of the lower rolls relative to the rolling axis along the pinch radius.

This design of the cross-helical rolling piercing mill allows, on the one hand, to improve gripping conditions, and, on the other hand, to reduce the variation in thickness of the sleeves and the quality of their internal surface due to a more favorable stress state scheme in the presence of three drive rolls located asymmetrically relative to the rolling axis , as a result of which the advantages of all-round compression of the workpiece by three rolls and all-round stretching by the two lower rolls are taken advantage of, as in a two-roll mill.

Experiments have established that when using an upper roll with a pinch radius calculated according to the proposed formula, its contact with the lower rolls is ensured with a minimum gap, as a result of which it becomes possible to produce thin-walled liners by piercing without the appearance of defects on their surface.

To explain the invention, a specific example of the invention is given below with reference to the drawings, in which:

Fig. 1 shows a cross-helical rolling piercing mill, general top view;

figure 2 - section A-A in figure 1;

figure 3 - view B in figure 2;

Fig.4 is a diagram of the arrangement of rolls along the pinch radius.

The piercing mill for cross-helical rolling consists of a working stand 1 and a drive for rotating the rolls of the working stand.

The working cage 1 contains a frame 2, on which lower barrel-shaped rolls 5 are mounted in horizontally located drums 3 and 4 with the ability to change the position of their axis of symmetry in both horizontal and vertical planes, by the feed angle using known mechanisms. The upper barrel-shaped roll 6 is located in a drum 7 mounted in a hinged cover 8 with the ability to change the position of the symmetry axis of the roll 6 in the vertical plane and the feed angle using known mechanisms.

By changing the position of rolls 5 and 6, the piercing axis can be shifted up or down relative to the axis of symmetry of the mill.

The two lower rolls 5 and the upper roll 6 have the same shape and length.

The pinch radius R x of the upper roll 6 is determined by the formula

,

where R x is the pinch radius of the upper roll,

R in - pinch radius of the lower roll,

R z - radius of the workpiece being stitched,

h=0-200 mm - the displacement value of the axis of symmetry of the lower rolls relative to the rolling axis.

The lower rolls 5 through spindles 9 located on the input side of the mill are connected through a gearbox 10 with an electric motor 11. It is also possible to use an individual drive for each lower roll 5.

The upper roll 6 is connected through a spindle 12, located on the output side of the mill, to a gearbox 13 and an electric motor 14.

When piercing a workpiece on a piercing helical rolling mill, the main movement and shape change of the metal occurs under the influence of friction forces between the metal surface and the rollers in the deformation zone formed by two lower rolls 5 and one upper roll 6, with a displacement of the piercing axis relative to the axis of symmetry of the mill. The workpiece is fed into the deformation zone by any known method and stitched.

The displacement of the piercing axis relative to the symmetry axis of the mill creates a favorable scheme of the stress-strain state of the workpiece metal, while the minimum gap in the contact zone of the rolls eliminates distortion of the outer surface of the metal, which is especially important when producing thin-walled liners.

The proposed cross-helical rolling piercing mill, in comparison with the known ones, makes it possible to improve the conditions for gripping the workpiece and improve the quality of the liners.

Piercing mill for cross-helical rolling, containing a working stand with one barrel-shaped upper roll and two barrel-shaped lower rolls, the axes of symmetry of which are shifted in a vertical plane relative to the rolling axis, and a drive for rotation of the lower rolls, characterized in that the upper roll is equipped with a drive located in the opposite direction from the drive of the lower rolls of the working stand side, while the pinch radius of the upper roll is determined by the formula

,

where R x is the pinch radius of the upper roll;

R in - pinch radius of the lower roll;

R z - radius of the workpiece being stitched;

h=0-200 mm - the displacement value of the axis of symmetry of the lower rolls relative to the rolling axis along the pinch radius.