RU2723494C1 - Method of rolling hollow billet on mandrel in three-shaft helical rolling mill and working roll for implementation thereof - Google Patents

Abstract

FIELD: metal forming.SUBSTANCE: group of inventions relates to metal forming, particularly, to production of seamless pipes, and can be used in rolling hollow workpieces with rolls on a mandrel in a helical rolling mill. Proposed method comprises gripping of hollow billet by rolls, deformation of hollow billet along diameter, deformation along wall, intensive deformation of wall by flange, calibration along diameter and wall. Possibility of obtaining wide-dimensioned range of obtained pipes from specified diameters of initial billet with reduction of size range of billets themselves is ensured by the fact that deformation of hollow billet along diameter is carried out with additional reduction by value ε, equal to 0.25…0.88 of total deformation. Working roll has a grip cone having a main portion adjacent to the crest and an additional portion with an inclination angle to the rolling axis of 5…15°. Roll has a rolling and calibrating cone.EFFECT: technical result consists in increase in number of deformation cycles, which promotes study of metal structure of continuously cast billet.2 cl, 4 dwg

Description

The invention relates to the field of metal forming, namely the production of seamless pipes and may be applicable when rolling hollow billets with rolls on a mandrel in a helical rolling mill.

Along with the firmware process that provides hollow billets, rolling hollow billets is an integral part of the production of seamless pipes. The prior art in this area solves the technical problem of improving the quality of seamless pipes obtained from continuously cast billets, prone to the formation of defects in the inner surface of the pipe, but does not lead to high-quality seamless pipes with a wide size assortment while reducing the size range of hollow billets.

A known method of rolling hollow billets by rolls on a floating mandrel in a three-roll helical rolling mill (SU No. 113579), including gripping a hollow workpiece, intensive wall deformation by a crest on a short floating mandrel, diameter deformation of the workpiece. The method allows to carry out the rolling process with large reductions in diameter on a floating mandrel.

In the known method, the deformation of the hollow billet at the beginning is carried out due to compression along the wall, and then - for reducing the diameter. Thus, when using this method, the reduction in diameter is limited. This is due to an increase in the ovality of the workpiece and a decrease in the stability of the rolling process with large deformations in diameter.

In addition, the use of a short floating mandrel can lead to a technical problem associated with the low wear resistance of such a mandrel. The contact of a short mandrel with a metal preheated to the rolling temperature is carried out over a short length, which leads to significant local heating and wear in the contact area.

Another technical problem is the availability of additional equipment on the output side of the mill, necessary to hold the mandrel before rolling. Due to the need to install the mandrel in the deformation zone, the setup time of the mill is increased in the pauses between the rolling of the liners, which reduces its productivity and maneuverability.

As the closest analogue to the claimed method, the selected method of rolling the sleeves on a three-roll mill for screw rolling (F.A. Danilov, A.Z. Gleiberg, V.G. Balakin "Hot rolling and pipe pressing." M .: Metallurgy, 1962 ., pp. 398-408, hereinafter referred to as the book), including the capture of a hollow billet, deformation in diameter, intense deformation of the wall with a crest, and calibration in diameter and wall. The peculiarity of the method lies in the fact that the main deformation of the hollow billet is carried out by compressing it along the wall thickness with a crest by (1.18 ... 1.25) ⋅h, where h is the height of the crest, which can be up to 90% of the original wall thickness. The size of the reduction in wall thickness depends on the size of the hollow billet. The diameter compression by the gripping cone of the roll is carried out by up to 5% in order to improve the gripping conditions and select the technological gap between the inner surface of the sleeve and the mandrel.

This method allows the production of seamless pipes with tight tolerances in geometric dimensions, as well as providing high maneuverability - the possibility of simple and quick adjustment to rolling pipes of a different diameter. Tight tolerances in geometric dimensions are characterized by high accuracy in wall thickness within ± 6.0% of the nominal diameter and within ± 0.5% of the nominal diameter size. In addition, the known method provides rolling pipes with a ratio of diameter to wall thickness (D / S) from 4 to 11.

However, the analyzed method does not allow the rolling of sleeves with high compression in diameter, thereby not providing the necessary study of the metal structure to obtain high-quality pipes obtained from continuously cast billets.

In addition, the known method involves the use of a wide size assortment of rolled billets with a fragmentation in diameter of 5-10 mm due to the fact that the reduction in diameter does not exceed 6 mm. The use of continuously cast billets is difficult because their production with a fragmentation in diameter of 5-10 mm is technologically and technically a rather complicated task.

Known work roll of a three-roll rolling mill, which has a gripping cone, a wall compression cone in front of the ridge, a comb, a rolling and calibrating cone. The roll has the following technical characteristics that limit the achievements of the technological solution indicated below. The angle of inclination of the generatrix of the gripping cone to the rolling axis is 2.5-3 °, which does not allow for additional deformation of more than 5% in diameter, while the compression cone in front of the ridge has a limited length and is designed to perform compression on the wall in order to improve conditions deformation of the workpiece on the crest of the roll. These characteristics do not allow additional diameter deformation (SG Chikalov, Production of seamless pipes from continuously cast billets / edited by A.P. Kolikov. - Volgograd: Committee on Press and Information 1999. - 416 pp.) (Chikalov S.G. Production of seamless pipes from continuously cast billets / edited by A.P. Kolikov, Volgograd: Committee on Press and Information 1999. - 416 p.).

In the above Book of F.A. Danilov, A.Z. Gleiberg, V.G. Balakin also disclosed a work roll equipped with a gripping cone, a crest rolled and calibrating sections. This technical solution is selected as the closest analogue to the proposed device.

The known work roll has a gripping cone with an angle of inclination of the generatrix to the rolling axis of not more than 3 °, which allows stable grip of the front end of the hollow billet, deformation of the wall in front of the ridge, as well as its intense deformation by the ridge. Due to the small angle of inclination of the generatrix of the gripping cone to the rolling axis, the work roll does not provide proper compression in diameter, which would lead to a reduction in the size range of the workpieces.

The group of inventions solves the technical problem of producing high-quality seamless tubes of a wide size assortment from continuously cast rolled billets on a three-roll screw rolling mill with a reduction in the size range of such billets.

The technical result provided by the method is to increase the deformation cycles that contribute to the study of the metal structure of the continuously cast billet with the possibility of obtaining a wide size assortment of the pipes obtained from the given diameters of the initial billet while reducing the size range of the billets themselves.

The technical result achieved by the device as a roll of a three-roll helical rolling mill, is to securely capture the workpiece and the ability to carry out additional deformation of the hollow workpiece in diameter.

The proposed method of rolling a hollow billet on a mandrel in a three-roll helical rolling mill involves gripping the hollow billet with rolls, deformation of the hollow billet in diameter, deformation along the wall, intense deformation of the wall with a crest, calibration in diameter and wall, while in this method, the deformation of the hollow billet with compression by a value of ε _p equal to 0.25 ... 0.88 of the total deformation.

The proposed work roll of a three-roll helical rolling mill is made with a gripping cone having a main section adjacent to the ridge, a rolling and calibrating cone, the gripping cone being made with an additional section having an inclination angle to the rolling axis of 5 ... 15 °.

In the invention-method, due to the above diameter deformation, the number of successive deformations of the workpiece by rolls of a three-roll rolling mill increases, or, in other words, the number of deformation cycles increases. This is due to the fact that the total reduction is increased. So, together with an increase in the number of deformation cycles, the workpiece metal experiences a greater number of multidirectional deformations due to the presence of compressive stresses under each roll and tensile in the gap between adjacent rolls. With a large number of deformation cycles and its multidirectional conditions under helical rolling conditions, favorable conditions are created for the development of shear deformations in the metal, which makes it possible to intensively affect its structure and mechanical properties, prevent the formation of defects on the inner surface and improve the quality of the pipes obtained. Together with the study of the structure and properties of the metal, additional compression in diameter allows the rolling process to be carried out more stable and, at the same time, makes it possible to use a continuously cast billet for a wide size assortment of the pipes obtained, while reducing the number of sizes of the used billets.

Using a work roll with an additional gripping cone having an angle of inclination of the generatrix to the rolling axis of 5 ... 15 ° allows us to stably carry out the grip of the workpiece and its deformation in diameter by the required value, in accordance with the proposed method.

The invention is illustrated by drawings:

- figure 1 shows a longitudinal section of a hollow billet and roll;

- figure 2 shows a cross section of a hollow billet and three rolls of the mill.

The deformation zone (Fig. 2) of the three-roll mill during the rolling process of the hollow billet 1 is formed by rolls 2, rotating in the same direction with a cylindrical mandrel 3.

On the roll 2, the positions indicated the following sections (Fig. 1):

- 4 - additional capture area;

- 5 - the main plot of capture;

- 6 - comb;

- 7 - wall calibrating section

- 8 - section calibrating in diameter.

When rolling, a hollow billet with an outer diameter of D _g , wall thickness S _g is set in the deformation zone, where in section 4 the rollers 3 are gripped, the workpiece is crimped in diameter by ΔD _P , and it is crimped along the wall in front of the crest.

Ridge 6 intensively compresses the wall of the workpiece due to the concentrated load that provides the best conditions for working through the workpiece.

The total absolute wall compression by sections 4 and 5 is ΔS.

The relationship between the absolute values of the compression of the workpiece in diameter, wall thickness and deformation is shown below. The total reduction in diameter ΔD and wall thickness is determined by the formula (1):

In this case, the total deformation, taking into account additional compression in diameter and wall compression ε _p is (2):

where ε _p is the additional deformation in diameter.

Then the additional deformation in diameter ε _p can be determined by the formula (3):

Thus, in order to ensure a stable grip of the hollow billet and its additional deformation on the additional section 4, which allows to efficiently work out the metal structure with the possibility of expanding the dimensional assortment of the pipes obtained, the ratio of the additional deformation in diameter to total - ε _p / ε _d should be 0.25 ... 0.88.

When ε _p / ε _{d is} less than 0.25, which is typical when rolling pipes from billets with a diameter of (220-240) mm, the additional deformation will be comparable in magnitude with the deformation by the grip area according to the prototype, i.e. less than 5%, which will not give a positive effect when using the method. The number of deformation cycles will be insufficient to develop shear deformations in the metal of the hollow billet. Small reduction in diameter of 5-10 mm will not allow to expand the dimensional assortment of the resulting pipes.

When ε _p / ε _{d is} greater than 0.88, which is typical when rolling pipes from workpieces with a diameter of (115-120) mm, the gap between the inner surface of the hollow workpiece and the mandrel will be large, this will lead to a loss of stability of gripping the hollow workpiece mandrel, runout of the mandrel about the inner surface of the pipe, which leads to "loosening" of the rear end of the hollow billet. The presence of a runout of the mandrel on the workpiece increases the dynamic loads experienced by the workpiece, which negatively affects the shape and geometric dimensions of the pipes obtained. At high dynamic loads, faceting of the resulting pipes is possible.

Here is an example of calculating the parameters of rolling by the proposed method. The total deformation is determined by the formula (2), while it must be borne in mind that the additional deformation should be (0.25 ... 0.88) of the total. The calculation results are presented in table 1 for pipes with a diameter of 80-200 mm (Chikalov SG "Production of seamless pipes from continuously cast billets" / edited by scientific editor A.P. Kolikov. - Volgograd: press and information committee. 1999 p . 299-405.). The table also presents the existing diameter of the workpiece 115-230 mm in increments of 5-10 mm, used to obtain these pipes.

As can be seen from the calculation results in table 1 (Fig. 3), depending on the diameter of the hollow preform D _g and the magnitude of the additional deformation in diameter, the total deformation of the preform can be determined by the empirical dependence (4)

The total deformation ε _d , determined by the formula (4), satisfies the above conditions of additional deformation and allows you to effectively work out the metal structure with the possibility of expanding the dimensional assortment of the pipes obtained. This is clearly noticeable if you pay attention to column 6 of table 1 (Fig. 3) "Possible range of diameters of the workpiece". In the case of additional deformation in diameter, a pipe with a diameter of 80 mm can be obtained not from a hollow billet with a diameter of 115 mm, but from billets with a diameter of 123-160 mm. In other words, the possibility of obtaining pipes from a wide diametrical dimensional assortment of billets is expanding and, conversely, obtaining a wide dimensional assortment of pipes from given diameters of a hollow billet. As shown in table 1, column 7 of the pipe with a diameter of 80-120 mm can be obtained from a hollow billet with a diameter of 160 mm. The step of the diametrical size of the workpieces when using this method is 30-40 mm instead of 5 mm.

The number of deformation cycles depends on the value of the total deformation of the workpiece in diameter and wall thickness. Since in the proposed method the total deformation increases due to additional, the number of deformation cycles will depend on its magnitude. In the process of rolling with additional compression of the hollow billet in diameter, the number of deformation cycles increases. Due to the rotational movement of the hollow billet in the deformation zone, as seen in the cross section (Fig. 2), it experiences compressive stresses under the roll and tensile stresses between the rolls. In this case, the workpiece metal is subject to a greater number of multidirectional deformations, which under the conditions of screw rolling creates favorable conditions for the development of shear deformations in the metal like equal-channel angular pressing (Loginov Yu.N. Pressing as a method as a method of intensive pressing of metals and alloys / Yu.N. Loginov - Yekaterinburg, Publishing House of the Ural University, 2016, p. 112-123.).

The study of the structure in equal-channel angular pressing is carried out due to the presence and intense influence of shear deformations (Semenova I.P., Saitova L.R., Islamgaliev R.K. and other authors of the article “Evolution of the structure of VT6 alloy subjected to equal-channel angular pressing”, journal "Physics of metals and metal science", 2005, v. 100. No. 1, pp. 77-84). In the process of screw rolling, the effect of shear deformations, by analogy with equal-channel angular pressing, carries out an intensive study of the structure. Table 1 (Fig. 3) shows the number of deformation cycles during rolling without additional deformation and with additional deformation according to the presented modes. In this case, with additional deformation, the number of deformation cycles increases by 2.5-6 times.

можно представить соотношением (5):The proposed method is carried out using work rolls, each of which is made with an additional gripping cone having an angle of inclination of the generatrix to the rolling axis (ϕ ₁ and placed in front of the gripping cone with an angle of inclination of the generatrix to the rolling axis ϕ _2. Angle ϕ ₁ should provide the necessary deformation modes while maintaining the main overall dimensions of the work roll.The relationship between the additional compression in diameter ΔD _p , the angle ϕ ₁ and the length of the cone additional capture

can be represented by the relation (5):

составляет более 350 мм, что существенно увеличивает габариты рабочего валка. В случае, когда ϕ₁ более 15°, ухудшаются условия захвата переднего торца полых заготовок, особенно при раскатке заготовок диаметром 150…230 мм. Наиболее рациональные значения угла ϕ₁ позволяющие решить поставленную задачу составляют 5…15°. Второй участок - конус захвата выполнен с углом наклона образующей к оси прокатки ϕ₂, равным 2,5°. На участке очага деформации, образованным этим конусом захвата, осуществляется выполнение условия вторичного захвата - захвата оправки внутренней поверхностью полой заготовки и деформацию перед гребнем. Угол ϕ₂ равный 2,5° обеспечивает стабильный вторичный захват и позволяет осуществлять минимальную необходимую деформацию стенки перед гребнем.According to relation (5) for large values of additional compression in diameter, for example, 60 mm, according to the condition ε _p / ε _d = 0.25 ... 0.88, with an angle ϕ ₁ less than 5 °, length

is more than 350 mm, which significantly increases the dimensions of the work roll. In the case when ϕ _{1 is} more than 15 °, the conditions for trapping the front end of the hollow billets worsen, especially when rolling blanks with a diameter of 150 ... 230 mm. The most rational values of the angle ϕ ₁ allowing to solve the problem are 5 ... 15 °. The second section - the capture cone is made with an angle of inclination of the generatrix to the rolling axis ϕ ₂ equal to 2.5 °. On the site of the deformation zone formed by this capture cone, the secondary capture condition is fulfilled - the mandrel is gripped by the inner surface of the hollow workpiece and the deformation in front of the crest. An angle ϕ _{2 of} 2.5 ° provides a stable secondary grip and allows for the minimum required wall deformation in front of the ridge.

Thus, the angle of inclination of the generatrix to the rolling axis of the additional roll grip portion of 5 ... 15 ° allows for reliable grip of the workpiece and additional deformation of the hollow workpiece in diameter.

Here is an example of modes of rolling pipes with a diameter of 80, 110, 120, 150, 160 and 200 mm with a ratio of D / S = 7 according to the proposed method from workpieces with a diameter of 160, 200 and 240 mm, using a work roll with an angle of inclination of the forming cone of compression to the axis rolling 10 °. Table 2 (Fig. 4) presents the modes of rolling by the proposed method. A pipe with a diameter of 80 mm with a wall of 13 mm can be obtained from a workpiece with a diameter of 160 mm. In this case, the compression in diameter is 50 mm, the strain in diameter is 31%, which is 0.70 of the total, this allows you to effectively increase the number of deformation cycles and work out the metal structure, while it is possible to obtain a pipe from a workpiece with a diameter of 160 mm rather than 115 mm.

Thus, we can note the technical result achieved by the rolling method:

- due to additional deformation due to the additional area of the capture of the roll, the reduction in diameter increases, the number of deformation cycles also increases, which contributes to the study of the metal structure of the continuously cast billet;

- it is possible to obtain a wide size assortment of pipes obtained from given diameters of the original billet while reducing the size range of the billets themselves;

- excludes the operation of additional rolling continuously cast billets to a smaller diameter.

The use of a work roll with an additional compression cone makes it possible to expand the possibilities of varying the compression regimes of hollow billets in diameter, to carry out a stable deformation process under rolling conditions with additional compression in diameter.

Claims (2)

1. The method of rolling a hollow billet rolls of a three-roll rolling mill screw rolling on the mandrel, including the capture of the hollow billet rolls, deformation of the hollow billet in diameter, deformation of the wall, deformation of the wall with a crest, calibration in diameter and wall, characterized in that the deformation of the hollow billet in diameter lead with additional compression by a value of ε _p equal to 0.25 ... 0.88 of the total deformation. 2. A work roll of a three-roll rolling mill of helical rolling, having a gripping cone with a main section adjacent to the ridge, a rolling and calibrating cone, characterized in that the gripping cone is made with an additional section having an inclination angle to the rolling axis of 5 ... 15 °.

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