CN117600222A - Continuous rolling method and device for steel rail continuous casting and rolling continuous straightening production line - Google Patents

Abstract

The invention discloses a continuous rolling method and a device for a steel rail continuous casting and rolling continuous straightening production line, wherein the method comprises the following steps: the continuous casting blank continuously and sequentially passes through a cogging rolling unit and a universal rolling unit to be rolled, and the blank is in an upright state and is not reversed in the rolling process; the cogging rolling unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole; the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills. The rolling scheme of the invention can be effectively applied to continuous casting and rolling continuous straightening production lines, and ensures good flatness, dimensional accuracy and surface quality of the rolled steel rail.

Description

Continuous rolling method and device for steel rail continuous casting and rolling continuous straightening production line

Technical Field

The invention relates to the technical field of rolling, in particular to a continuous rolling method and a continuous rolling device for a steel rail continuous casting and rolling continuous straightening production line.

Background

Rail rolling is an important process in rail production, and directly affects the quality and comprehensive mechanical properties of rail products. At present, rail rolling mainly comprises two modes: the two-roller grooved rolling method and the four-roller universal Kong Xingga method have the advantages that as the four sides of the steel rail in the grooved formed by the universal rollers in the four-roller universal Kong Xingga method are uniformly compressed and deformed, the processing amount is good, the quality of the obtained steel rail is better than that of the two-roller grooved rolling method, and the advantages are more outstanding than that of the two-roller grooved rolling method. The two-roll pass rolling method comprises a straight pass and a diagonal pass, and the universal Kong Xingga method comprises a semi-universal pass and a full-universal pass. At present, the production of steel rails by using a universal rolling mill and a universal rolling process method is the most commonly used technical means in the field, and the steel rails are processed and deformed by a two-roller rolling mill and a universal rolling mill in a horizontal state to obtain the final finished steel rails.

In the traditional section steel rolling technical scheme, a rolled piece shuttles in a horizontally driven roller pass, and a final section steel product is obtained by adjusting parameters such as a roller gap, a hole groove shape and the like of a roller. The universal rolling method for producing the steel rail is no exception, the steel rail is horizontally reciprocated in a universal rolling mill and an edging mill and is subjected to rolling deformation of a universal roller and an edging roller, and finally the finished product of the steel rail in a hot state is obtained.

However, in the conventional process, a series of problems such as accumulated water in the waist groove of the steel rail, asymmetric rolling deformation and the like occur due to the fact that the steel rail is rolled in a horizontal shape, and specification deviation and surface defects are caused. In addition, the traditional process rolling mill is independently arranged, and the reversible rolling mill is adopted for reciprocating rolling, so that the defects of fluctuation of product specifications and overlong arrangement of rolling lines can be caused. In addition, the rolling mill settings, hole pattern arrangement, pressure control, etc. of the rolling process affect the dimensional accuracy and flatness of the rolled product. There is therefore a need for an improved rolling scheme to improve the gauge accuracy and surface quality of the product.

Disclosure of Invention

The invention mainly aims to provide a continuous rolling method and device for a steel rail continuous casting and rolling continuous straightening production line, which are used for solving the problem that the specification accuracy and the surface quality of a steel rail rolled product are to be improved.

According to one aspect of the present invention, there is provided a continuous rolling method for a continuous casting and rolling and straightening line for steel rail, comprising:

the continuous casting blank continuously and sequentially passes through a cogging rolling unit and a universal rolling unit to be rolled, and the blank is in an upright state and is not reversed in the rolling process;

the cogging rolling unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole;

the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills, the vertical universal rolling mills adopt universal holes, and the vertical edging machines adopt edging holes.

According to one embodiment of the invention, the blooming mill train comprises 5-7 vertical two-high mills and 2-3 horizontal two-high mills.

According to one embodiment of the invention, the number of box-shaped holes is 2-4, the number of trapezoid holes is 1-2, the number of cap-shaped holes is 1-2, the number of rail-shaped deep-cut holes is 1-2, the number of rail-shaped extension holes is 0-2, and the number of rail-shaped pilot holes is 1.

According to one embodiment of the invention, the universal rolling mill train comprises 4-6 vertical universal rolling mills and 2-4 vertical edging mills; the last vertical universal rolling mill adopts a semi-universal hole, and other vertical universal rolling mills adopt full-universal holes.

According to one embodiment of the invention, for a vertical two-roll mill adopting box-shaped holes, trapezoid holes and rail-shaped pilot holes, the diameters of the rollers at two sides are equal; and/or

For a horizontal two-roll mill adopting a box-shaped hole, the diameter of a lower roll is 3-8mm larger than that of an upper roll; and/or

For a horizontal two-roll mill adopting symmetrical trapezoid holes, the diameter of a lower roll is 2-6mm larger than that of an upper roll; and/or

For a horizontal two-roll mill adopting an asymmetric trapezoid hole, if the opening of the big end side of the trapezoid hole is downward, the diameters of a lower roll and an upper roll are equal, and if the opening of the big end side of the trapezoid hole is upward, the diameter of the lower roll is 8-15mm larger than that of the upper roll; and/or

For a vertical two-roll mill and a horizontal two-roll mill adopting cap-shaped holes, the diameter of a roller at the top side of the cap is 0.8-1.2 times of the height of the cap-shaped holes compared with the diameter of a roller at the bottom side of the cap; and/or

For the vertical two-roll mill adopting the rail-shaped deep cutting hole and the rail-shaped extending hole, when adopting the straight rolling hole type, the diameter of the roller at the open side is 10-30mm smaller than that of the roller at the other side, and when adopting the inclined rolling hole type, the diameters of the rollers at the two sides are equal.

According to one embodiment of the invention, the box-shaped hole has an elongation coefficient of 1.20-1.50, the trapezoid hole has an elongation coefficient of 1.15-1.40, the cap hole has an elongation coefficient of 1.10-1.35, the rail-shaped deep cutting hole has an elongation coefficient of 1.10-1.30, and the rail-shaped pilot hole has an elongation coefficient of 1.05-1.20.

According to one embodiment of the present invention, the elongation coefficient of the last one of the universal holes is made to be 1.05-1.10, the elongation coefficient of the remaining plurality of universal holes is made to be 1.18-1.30 and decreases in sequence in the rolling direction, and the elongation coefficient of the plurality of edging holes is made to be 1.03-1.08 and decreases in sequence in the rolling direction.

According to one embodiment of the invention, for a cogging mill train, when a rail-shaped hole is used, the rail foot elongation coefficient is made larger than the rail web elongation coefficient, and the rail web elongation coefficient is made larger than the rail head elongation coefficient; and/or

For a universal rolling mill set, the rail foot elongation coefficient is greater than the rail head elongation coefficient, and the rail head elongation coefficient is greater than the rail waist elongation coefficient.

According to one embodiment of the invention, the rolling speed is determined based on the straightening speed of the downstream continuous straightening device.

According to another aspect of the present invention, there is provided a continuous rolling apparatus for a continuous casting and rolling and straightening line for steel rail, comprising: the cogging rolling mill unit and the universal rolling mill unit are sequentially arranged along the continuous rolling direction;

the cogging rolling unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole;

the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills, the vertical universal rolling mills adopt universal holes, and the vertical edging machines adopt edging holes.

In the technical scheme of the invention, the rail-shaped blank is rolled in an upright state and is not reversely rolled, so that the problems of shape and size deviation and surface defects caused by horizontal rolling and reversible reciprocating rolling are solved, and the rolling scheme of the invention can be effectively applied to a continuous casting and rolling continuous straightening production line and ensure good flatness, specification accuracy, surface quality and mechanical property of the rolled steel rail by designing and improving one or more aspects of rolling mill arrangement, hole pattern selection and arrangement, hole pattern number setting, hole pattern pressure control, hole pattern extension coefficient distribution, rolling speed setting and the like of a continuous rolling unit.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 shows a schematic view of a rolling mill layout sequence according to an exemplary embodiment of the invention;

FIG. 2 shows a schematic view of a rolling mill pass arrangement sequence according to an exemplary embodiment of the invention;

FIG. 3 shows a box-hole structure schematic diagram according to an exemplary embodiment of the invention;

FIG. 4 shows a schematic diagram of a trapezoidal aperture structure according to an exemplary embodiment of the present invention;

FIG. 5 shows a schematic diagram of a cap-shaped aperture structure according to an exemplary embodiment of the present invention;

fig. 6 illustrates a schematic view of a rail-shaped cut-depth hole structure according to an exemplary embodiment of the present invention;

FIG. 7 illustrates a schematic view of a rail-shaped extension hole structure according to an exemplary embodiment of the present invention;

FIG. 8 illustrates a schematic diagram of a rail-shaped pilot hole structure according to an exemplary embodiment of the present invention;

FIG. 9 illustrates a full universal hole pattern diagram according to an exemplary embodiment of the present invention;

FIG. 10 illustrates a schematic view of a edging hole structure, according to an exemplary embodiment of the invention;

FIG. 11 illustrates a semi-universal hole structure schematic in accordance with an exemplary embodiment of the present invention;

figure 12 shows a schematic diagram of a box-hole structure according to embodiment 1 of the invention;

FIG. 13 is a schematic view showing the structure of a trapezoid hole according to embodiment 1 of the present invention;

fig. 14 shows a schematic diagram of a cap-shaped hole structure according to embodiment 1 of the present invention;

fig. 15 shows a schematic view of a rail-shaped cut-depth hole structure according to embodiment 1 of the present invention;

fig. 16 shows a schematic view of a rail-shaped pilot hole structure according to embodiment 1 of the present invention;

FIG. 17 is a schematic diagram showing the hole pattern structure of a universal rolling mill train according to embodiment 1 of the invention;

FIG. 18 shows a schematic diagram of a semi-universal hole structure according to embodiment 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments of the present invention will be described in further detail with reference to the accompanying drawings.

It should be noted that, in the embodiments of the present invention, all the expressions "first" and "second" are used to distinguish two entities with the same name but different entities or different parameters, and it is noted that the "first" and "second" are only used for convenience of expression, and should not be construed as limiting the embodiments of the present invention, and the following embodiments are not described one by one.

As mentioned in the background section above, the inventors of the present application have recognized that conventional rolling processes suffer from the following drawbacks:

(1) In the rolling process, water is accumulated in the waist groove of the steel rail to form surface defects

Because the rail is rolled in a horizontal way, when the rail-shaped blank is rolled in a cogging mill and a universal rolling mill, medium water such as rolling mill cooling water, high-pressure water for descaling and the like can be left in a waist groove on the upper surface of the rail-shaped blank to generate accumulated water, so that the phenomenon of uneven heat dissipation on the upper surface and the lower surface of the waist of the rail is further aggravated, the temperature of the upper surface of the waist of the rail after rolling is obviously lower than that of the lower surface, thereby influencing the microstructure and the performance of the rail, the accumulated water on the waist can aggravate the oxidation of the surface of the waist to form a secondary oxide scale, and the accumulated water is pressed in or peeled off in the subsequent rolling to form a surface pit defect.

(2) The asymmetry of rolling deformation aggravates the uneven deformation of metal

In the rolling process, due to the particularity of the section of the steel rail, the axial force generated during rolling is large, the rail head is horizontally influenced by self gravity, the free falling state of the steel rail on the roller way is inclined, the head of the steel rail is inclined downwards after entering the rolling mill, the rolling force distribution is uneven up and down, the axial force is influenced to a certain extent, the universal rolling phenomenon which is originally asymmetric deformation is further deteriorated, and the final finished product size of the steel rail is influenced.

(3) Single-billet multi-frame reciprocating rolling is carried out, and the specification fluctuation is large.

The traditional process rolling mill is relatively independent, some frames are reversible rolling mills, continuous turning steel is needed for reciprocating multi-pass rolling, and the rolling gap time is increased; when the universal rolling mill is used for producing steel rails, the phenomenon of piling steel occurs at the moment of steel feeding of rolled pieces in the continuous rolling stage, and the phenomenon of tail flicking occurs at the moment of separation, and all the phenomena can cause the specification fluctuation of the steel rails; in order to ensure proper end specifications, the rolled steel rail needs to cut the end with the poor specification into the head and the tail as far as possible, so that serious material waste is caused.

(4) The pass line process is too long.

The traditional rail rolling is in the form of a universal rolling method, and consists of 7 rolling mills arranged in a mode of 1-1-2-2-1, the arrangement mode is BD1+BD2+U1E1+U2E2+UF, the frames are independently arranged, a reversible reciprocating rolling mill is adopted, the extension length and the safety distance of rolled pieces are considered among the frames, the rolling line process arrangement is longer, so that the construction investment is increased, meanwhile, the production line is prolonged, the transportation time of hot rolled pieces on a roller way is prolonged, the temperature of the rolled pieces is reduced to be large, and the cooling rate of the upper surface of the rolled pieces is further accelerated by accumulated water in grooves on the upper surface of the rolled pieces, so that the temperature symmetry distribution of the whole section of the rolled pieces is affected.

To solve the above technical problems, the present application proposes one or more embodiments as will be described below.

Referring to fig. 1 and 2, the invention provides a continuous rolling method for a continuous casting and rolling continuous straightening production line of a steel rail, which comprises the following steps:

the continuous casting blank continuously and sequentially passes through a cogging rolling unit and a universal rolling unit to be rolled, and the blank is in an upright state and is not reversed in the rolling process;

the cogging rolling mill unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling mill unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole (for example, the cogging rolling mill unit can comprise a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole which are sequentially arranged along the continuous rolling direction, or comprises a rail-shaped deep cutting hole and a rail-shaped pilot hole which are sequentially arranged along the continuous rolling direction);

the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills, the vertical universal rolling mills adopt universal holes (comprising two types of full universal holes and half universal holes), and the vertical edging machines adopt edging holes.

In the embodiment of the invention, the rolling process is always in an upright state, which can be expressed as that when the rail blank is rolled through cogging, the rail blank is in a standing state that the rail head is positioned above and the rail bottom is positioned below in the subsequent universal rolling process, the center line of the section of the steel rail extends along the vertical direction, the blank to be formed into the rail blank is also in a similar upright state in the cogging rolling process, and the blank is not turned over and does not change the posture in the whole rolling process. By rolling in the upright state, the problems that the surface defect is formed due to accumulated water in the waist groove caused by the horizontal rolling, the deformation is asymmetric, the product dimension specification is influenced and the like can be avoided. Meanwhile, in the embodiment of the invention, the blank is not reversed in the rolling process, namely, the blank is not rolled in a reciprocating and reversible manner among a plurality of rolling mills, but is always operated along a single continuous rolling direction and is rolled by the plurality of rolling mills in sequence, so that the phenomena of steel piling and tail flicking caused by the fact that the blank enters the rolling mill for many times can be avoided, the specification of the end part of a steel rail can be further influenced, and the increase of rolling clearance time caused by continuous steel turning and reciprocating multipass rolling and the production line elongation caused by the arrangement of extension length and safety distance can be avoided. In addition, the rolling scheme can be effectively adapted to a continuous casting and rolling continuous straightening production line by designing and improving one or more aspects of rolling mill arrangement, hole pattern selection and arrangement, hole pattern number setting, hole pattern pressure control, hole pattern extension coefficient distribution, rolling speed setting and the like of the continuous rolling unit, and good flatness, specification accuracy, surface quality and mechanical property of the rolled steel rail are ensured.

In the embodiment of the invention, the whole rolling process is continuous rolling and is divided into a cogging unit and a universal unit. The continuous casting billet is directly introduced into a cogging unit of a horizontal interchange hole type for rolling after induction heat compensation, and in the whole rolling process, the roll gap value of two rolling mills is adjusted to roll into a steel rail blank, so that a rail-shaped billet with a regular section is provided for a universal hole type. The cogging unit is a two-roller hole type with alternate horizontal and vertical, a rectangular billet is rolled into a rail-shaped billet, multiple passes of hole type rolling are needed, namely, the continuous rolling cogging unit with multiple frames is needed, the number of needed hole types is needed to be determined according to the section size of a casting blank, the hole types comprise box-shaped holes, trapezoid holes, cap-shaped holes and rail-shaped holes, and all the hole types are symmetrically designed. And (3) feeding the rail-shaped blank formed by rolling of the cogging mill into a compact arrangement of universal vertical rolling mill units for rolling, wherein the universal rolling mill units are formed by alternating universal roughing mill, edging mill, intermediate rolling mill, edging mill, finishing mill and the like, in the full rolling process, the roll gap value of the universal vertical rolling mill is adjusted, the rail-shaped blank is subjected to continuous finish rolling forming among the universal vertical roughing mill, the vertical edging mill and the universal vertical finishing mill, and all the universal hole patterns comprise universal holes and edging holes and are symmetrically designed.

Referring to fig. 3, there are generally three types of box hole configurations: the hole type is symmetric left and right, and the two sides are provided with side wall slopes.

Referring to fig. 4, there are two general structures of trapezoid holes, one is a half-open trapezoid hole (refer to the left view of fig. 4), the shape of which is asymmetric up, down, left and right, the small head part mainly ensures the metal amount of the rail head, the large head part ensures the metal amount of the rail bottom, and the left-right asymmetry mainly considers the control of the downward bending amount of the rolled piece. And the other is a full-opening trapezoid hole (refer to the right diagram of fig. 4), the left and right are completely symmetrical except the possibility of bending up and down asymmetrically, and the downward bending of the rolled piece is mainly regulated by the guard plate.

Referring to fig. 5, there are three general hole structures of cap-shaped hole series, the shape is bilateral symmetry, the hole groove bottom has a bulge, two sides have smaller sidewall inclination, and the upper roller has a certain convexity corresponding to the processing rail bottom.

Fig. 6 shows a schematic diagram of a rail-shaped deep-cut hole structure, and rail-shaped deep-cut hole series pass patterns, which are different in structure and need to be treated respectively. The deep hole is formed by two types of structures, namely a straight rolling hole type (as shown in fig. 6, the openings at the head and the bottom face in the same direction) and a diagonal rolling hole type (with the openings at the head and the bottom opposite in direction). The hole pattern shape is asymmetric due to the existence of the open end and the closed end. The two sides of the hole form are provided with a certain sidewall inclination so as to facilitate the repair of the groove removing head and the hole form.

Fig. 7 shows a schematic diagram of a rail-shaped extension hole structure, wherein rail-shaped extension hole series pass is the same as a deep cut hole in structure type and kind, and has a straight rolling pass and a diagonal rolling pass.

Fig. 8 shows a schematic diagram of a rail-shaped pilot hole structure, wherein the shape of the rail-shaped pilot hole is designed to be completely symmetrical left and right and is an open hole type.

Fig. 9 shows a schematic diagram of a omnipotent hole structure, wherein the omnipotent hole structure is a four-roller hole structure, the shape of the horizontal roller is bilaterally symmetrical, the upper vertical roller is provided with a groove for processing rail heads, the lower vertical roller is used for processing rail bottoms, and the surface of the lower vertical roller is flat.

Fig. 10 shows a schematic representation of the structure of the edging hole, the shape of which is designed symmetrically right and left.

Fig. 11 shows a schematic diagram of a semi-universal hole structure, wherein a finished hole or a finished hole structure in a steel rail hole type system generally selects a semi-universal hole type, the semi-universal hole type is a three-roller hole type, and the semi-universal hole type consists of two vertical rollers and a horizontal roller, and the shape of the horizontal roller is designed completely symmetrically left and right.

In some embodiments, the blooming mill train includes 5-7 vertical two-high mills and 2-3 horizontal two-high mills. In some embodiments, the number of box-shaped holes is 2-4, the number of trapezoid-shaped holes is 1-2, the number of cap-shaped holes is 1-2, the number of rail-shaped cut-deep holes is 1-2, the number of rail-shaped extension holes is 0-2, and the number of rail-shaped pilot holes is 1. Ensuring that the rail-shaped blank with proper shape and size is rolled for subsequent universal rolling.

In some embodiments, the universal rolling mill train includes 4-6 vertical universal rolling mills and 2-4 vertical edging mills; the last vertical universal rolling mill adopts a semi-universal hole, and other vertical universal rolling mills adopt full-universal holes. Ensuring that the rolled product meeting the size and shape requirements is obtained.

The pressure configuration of the hole pattern is described below.

When the box-shaped hole is arranged on the vertical rolling mill, the hole pattern is not provided with left and right side pressures, and the diameters of the left and right side rollers are equal. The lower bending caused by the dead weight is controlled by the guard. When the box-shaped Kong Zaiping rolling mill is arranged, the hole type can be matched with an upper pressure below 3-8mm, namely, the diameter of the lower roller is 3-8mm larger than that of the upper roller, and the lower bending caused by dead weight is controlled by the upper pressure.

When the trapezoid hole is arranged on the vertical rolling mill, the left side pressure and the right side pressure are not arranged in the hole pattern, and the diameters of the left side roller and the right side roller are equal. The lower bending caused by the dead weight is controlled by the guard. When the symmetric trapezoid Kong Zaiping rolling mill is arranged on the rolling mill, the hole pattern can be matched with an upper pressure below 2-6mm, namely, the diameter of the lower roller is 2-6mm larger than that of the upper roller, and the lower bending caused by dead weight is controlled by the upper pressure. When the left-right asymmetric trapezoid Kong Zaiping rolling mill is arranged on the rolling mill, if the big head side opening is downward, the pressure is not required to be arranged, namely the diameter of the lower roll is equal to that of the upper roll. When the left-right asymmetric trapezoid Kong Zaiping rolling mill is arranged, if the opening of the big end side is upward, 8-15mm of pressure is required to be arranged, namely the diameter of the lower roll and the diameter of the upper roll are 8-15mm larger.

When the cap-shaped hole is arranged on the vertical rolling mill, the left and right sides of the hole pattern are required to be provided with larger pressure so as to solve the problem of left and right bending of the steel tapping of the rolled piece. The diameter of the roller at the top of the cap is 0.8-1.2 times of the height of the cap-shaped hole compared with the diameter of the roller at the bottom of the cap, and the dead weight of the rolled piece can only be controlled by the guard plate. When the cap Kong Zaiping rolling mill is arranged, the left and right sides of the hole pattern need to be provided with larger pressure so as to solve the problem of left and right bending of the steel tapping of the rolled piece. The diameter of the roller at the top of the cap is 0.8-1.2 times of the height of the cap-shaped hole compared with the diameter of the roller at the bottom of the cap, and the dead weight of the rolled piece can only be controlled by the guard plate.

And (3) configuring rail-shaped deep cutting holes and rail-shaped extending holes. The two types of pass are two types of straight pass and inclined pass. When the straight rolling holes are arranged, a certain pressure is required to be arranged on the left roller and the right roller, and the diameter of the roller on the open side is 10-30mm smaller than that of the roller on the other side so as to control the left and right bending of the steel tapping of the rolled piece. When the oblique rolling pass is configured, the diameters of the left roller and the right roller are equal. The bending up and down is controlled by the guard.

And (3) the arrangement of the rail-shaped pilot holes. Because of the symmetrical hole type with the opening, the steel tapping bending of the rolled piece can be controlled by the diameters of the left and right rollers being equal without configuring pressure. The bending up and down is controlled by the guard.

The following describes a pressure configuration of the universal bore type.

The left and right shape and dimension of each universal hole type are symmetrical, so that the left and right bending can be controlled by the diameter of the left and right rollers being equal without arranging pressure. Meanwhile, the upper roller and the lower roller are passive vertical rollers, so that the upper and the lower bending cannot be controlled through pressure configuration, and the bending degree can be controlled only through the guard.

The left and right shape and the dimension of the universal edging hole are symmetrical, so that the left and right bending can be controlled by the diameter of the left and right rollers being equal without configuring pressure. The bending up and down is controlled by the guard.

In some embodiments, the box-shaped hole has an elongation coefficient of 1.20-1.50, the trapezoid-shaped hole has an elongation coefficient of 1.15-1.40, the cap-shaped hole has an elongation coefficient of 1.10-1.35, the rail-shaped deep-cut hole has an elongation coefficient of 1.10-1.30, and the rail-shaped pilot hole has an elongation coefficient of 1.05-1.20. In some embodiments, such that the elongation coefficient of the last master hole is 1.05-1.10, the elongation coefficients of the remaining plurality of master holes are 1.18-1.30 and decrease in sequence along the rolling direction (i.e., the closer to the finished hole pattern elongation coefficient is smaller), and the elongation coefficients of the plurality of edging holes are 1.03-1.08 and decrease in sequence along the rolling direction (i.e., the closer to the finished hole pattern elongation coefficient is smaller).

The distribution of the respective cell extension coefficients is described below.

The distribution principle of the extension coefficient of each hole is to ensure the steel tapping flatness of the rolled piece to the maximum extent.

The deformation of the trapezoid holes and the cap-shaped holes of the cogging mill set is large and uneven, the cogging mill set has the main function of ensuring the section shape required by the rail-shaped holes, and the steel tapping straightness of rolled pieces is controlled by configuring pressure for the hole patterns.

The rail-shaped deep cutting holes, rail-shaped extending holes and pilot holes of the cogging mill set control the up-down bending of the rolled piece through reasonable distribution of head and waist bottom extending coefficients, and the rail waist extending coefficients are generally larger than the rail waist extending coefficients and are generally larger than the rail head extending coefficients. The left and right bending is completed through the pressure configuration of the hole type.

The extension coefficient of each rail-shaped hole of the universal machine set is larger than the extension coefficient of the rail head according to the rail bottom extension coefficient, and the rail head extension coefficient is larger than the rail waist extension coefficient to distribute so as to fully ensure the flatness of the up-down tapping of the rolled piece and the required section shape.

In some embodiments, the rolling speed is determined based on the straightening speed of the downstream continuous straightening device. As with the speed calculation method of the rod-wire tandem mill set, the tandem rolling speed of each hole is the product of the initial rolling speed and the cumulative elongation of the hole. Different from the determination mode of the rod wire material, the method comprises the following steps: in the continuous casting and rolling continuous straightening process of the steel rail, the rolling speed of each hole needs to be determined by the rolling speed of a finished product hole, and the rolling speed of the finished product hole needs to be determined by considering the maximum speed which can be born by a straightening unit, a flaw detection unit and the like. The maximum comprehensive running speed of the rolled piece is determined by comprehensively balancing the maximum running speed of the main equipment set of the whole production line.

The invention also provides a continuous rolling device for the continuous casting and rolling continuous straightening production line of the steel rail, which comprises: the cogging rolling mill unit and the universal rolling mill unit are sequentially arranged along the continuous rolling direction; the cogging rolling unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole; the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills, the vertical universal rolling mills adopt universal holes, and the vertical edging machines adopt edging holes.

The following description is made with reference to specific examples.

Example 1

Taking the hole pattern design method of the existing standard 60kg/m steel rail as an example, the method comprises the following steps:

1. and (3) a steel rail continuous rolling process:

the whole rolling process is continuous rolling and is divided into a cogging unit and a universal unit.

1.1, directly introducing a continuous casting billet into a cogging unit with a horizontal alternative hole type for rolling after induction heat compensation, adjusting the roll gap value of two rolling mills in the whole rolling process, rolling into a steel rail blank, and providing a rail blank with a regular section for a universal hole type. The cogging unit is a two-roller hole type with alternate horizontal and vertical, a rail-shaped blank is rolled by a rectangular blank, and the two-roller hole type rolling with multiple passes is needed, namely, the continuous rolling cogging unit with multiple frames is needed, the 280 x 380mm section billet is selected as a raw material, the number of the needed hole types is 8, namely, 3 box-shaped holes, 1 trapezoid hole, 1 cap-shaped hole and 3 rail-shaped holes, and all the hole types are symmetrically designed.

1.2, rolling the rail-shaped blank formed by rolling of a cogging mill into a compact arrangement of universal vertical rolling mill units, wherein the universal rolling mill units are formed by alternating universal roughing mill units, edging mill units, middle rolling mill units, edging mill units, finishing mill units and the like, in the whole rolling process, roll gap values of the universal vertical rolling mill units are adjusted, continuous finish rolling forming is carried out on the rail-shaped blank among the universal vertical roughing mill units, the vertical edging mill units and the universal vertical finishing mill units, and universal hole patterns comprise universal holes and edging holes, in the embodiment, the number of required hole patterns is 8, namely 4 total universal holes, 3 edging holes, 1 half universal hole and all hole patterns are symmetrically designed.

The rolling mill arrangement sequence and the hole pattern arrangement sequence for continuous casting-continuous rolling-continuous straightening of the present embodiment can be referred to fig. 1 and 2, respectively.

2. Design of steel rail continuous rolling pass system

2.1 continuous rolling pass system selection:

the structure of the steel rail continuous rolling pass system comprises:

the cogging hole comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole, a rail-shaped deep cutting hole, an extension hole and a pilot hole;

the universal hole type comprises a full universal hole, a rolled edge hole and a semi-universal hole.

2.2 Structure and number of tandem rolling pass systems:

2.2.1 Box-shaped hole structure and number: referring to fig. 12, in this embodiment, box-shaped holes with convexity are selected, so as to increase the clamping of billets in the process of cogging, prevent biting and strip rolling, have symmetrical hole patterns on both sides, have sidewall slopes, and in the continuous rolling hole pattern design, the number of box-shaped holes is 3 according to the distribution of the elongation coefficient.

2.2.2 structures and number of trapezoidal holes: referring to fig. 13, in this embodiment, full-open trapezoidal holes are selected, which are completely symmetrical left and right, and the number of trapezoidal holes is selected to be 1 for transition.

2.2.3 Structure and number of cap holes: referring to fig. 14, in this embodiment, a hole pattern structure is selected in which the bottom of the hole pattern groove has a protrusion and both sides have smaller sidewall slopes, and the number of cap holes is selected to be 1, so that a near-net-shaped rail blank is provided for the rail holes.

2.2.4 Structure and number of rail-shaped deep holes: referring to fig. 15, in the present embodiment, the number of rail-shaped cut holes is selected to be 2.

2.2.5 Structure and number of Rail-shaped pilot holes: referring to fig. 16, in the present embodiment, the number of rail-shaped pilot holes is selected to be 1.

2.2.6 Structure and number of omnipotent holes: referring to fig. 17, in this embodiment, the shape and structure of the universal hole patterns in the rail hole pattern system are similar and different in size, the shape of each hole pattern horizontal roller is bilaterally symmetrical, the upper vertical roller is provided with a groove for processing rail heads, and the lower vertical roller is used for processing rail bottoms, and the surfaces of the lower vertical roller are flat. In the continuous rolling pass design, the continuous rolling pass and the edging pass are alternately arranged, and the total number of the universal holes is 4 according to the distribution of the extension coefficient.

2.2.7 Structure and number of edge rolling holes: referring to fig. 17, in this embodiment, the shape of the hole pattern structure of the edging holes in the rail hole pattern system is designed completely symmetrically left and right. In the tandem rolling pass design, the tandem rolling pass design is alternately arranged with the universal pass, and the number of the edging holes is generally designed to be 3 according to the distribution of the extension coefficient.

2.2.8 semi-universal structure and number: referring to fig. 18, in this embodiment, the finished hole in the rail hole type system is a semi-universal hole type, the shape of which is designed completely symmetrically from side to side, and in the tandem rolling hole type design, the number is selected to be 1 according to the distribution of the elongation coefficient and the quality assurance degree.

2.3 arrangement of holes for continuous Rolling

In the embodiment, the steel rail continuous rolling hole type system consists of a cogging hole type and a universal hole type, and consists of a box hole, a trapezoid hole, a cap hole, a rail-shaped deep cutting hole, an extension hole, a pilot hole, a full universal hole, a edging hole and a semi-universal hole. The cogging hole patterns are two-roller hole patterns which are arranged in a horizontal-vertical alternating manner, and the rectangular blank is formed into a symmetrical rail-shaped blank through continuous rolling. The full-universal hole pattern is a four-roller hole pattern, the edging hole pattern is a two-roller hole pattern and is vertically arranged, the half-universal hole pattern is a three-roller hole pattern, the full-universal hole pattern consists of two vertical rollers and a horizontal roller, the universal hole pattern and the edging hole pattern are alternately arranged, and rail-shaped blanks are subjected to multi-pass finish rolling forming.

2.3.1 configuration of the hole patterns for the cogging

(1) In this embodiment, when the box-shaped hole is arranged in the vertical rolling mill, the hole pattern is not arranged on the left and right side pressure, and the diameters of the left and right side rolls are equal. The lower bending caused by the dead weight is controlled by the guard. When the box-shaped Kong Zaiping rolling mill is arranged on the box-shaped Kong Zaiping rolling mill, an upper pressure of 3mm is arranged, namely, the diameter of a lower roll is 3mm larger than that of an upper roll, and lower bending caused by self weight is controlled by the upper pressure.

(2) In this embodiment, when the trapezoidal hole is arranged in the vertical rolling mill, the hole pattern is not arranged on the left and right side pressures, and the diameters of the left and right side rollers are equal. The lower bending caused by the dead weight is controlled by the guard.

(3) In the embodiment, when the cap-shaped hole is arranged on the vertical rolling mill, the left and right sides of the hole pattern are required to be provided with larger pressure so as to solve the problem of left and right bending of the steel tapping of the rolled piece. The diameter of the roller at the top of the cap is 1 time of the height of the large cap-shaped hole of the roller at the bottom of the cap, and the dead weight of the rolled piece is controlled by the guard.

(4) In the embodiment, when the rail-shaped deep cutting holes are arranged on the vertical rolling mill, the left and right sides of the hole patterns need to be provided with larger pressure so as to solve the problem of left and right bending of the steel tapping of the rolled piece. The diameter of the roller at the top of the cap is 0.8 times of the height of the large cap-shaped hole of the roller at the bottom of the cap, and the dead weight of the rolled piece is controlled by the guard plate.

(5) In the embodiment, when the rail-shaped pilot hole is arranged on the vertical rolling mill, the left and right sides of the hole pattern are required to be provided with larger pressure so as to solve the problem of left and right bending of the steel tapping of the rolled piece. The diameter of the roller at the top of the cap is 0.8 times of the height of the large cap-shaped hole of the roller at the bottom of the cap, and the dead weight of the rolled piece is controlled by the guard plate.

2.3.2 configuration of Universal hole patterns

In this embodiment, the left and right shape and dimension of each universal hole are symmetrical, so that the left and right bending can be controlled by the equal diameters of the left and right rollers without arranging pressure. Meanwhile, the upper roller and the lower roller are passive vertical rollers, so that the upper and the lower bending cannot be controlled through pressure configuration, and the bending degree can be controlled only through the guard.

In the embodiment, the left and right shapes and the sizes of each hole type of the edging machine are symmetrical, so that the left and right bending can be controlled by the diameters of the left and right rollers being equal without configuring pressure. The bending up and down is controlled by the guard.

3. Principle of continuous rolling of extension coefficient of each hole

3.1 in this embodiment, according to the hole pattern structure and the number configuration, the hole extension coefficients of the cogging mill set are distributed as follows:

3.1.1 3 box hole elongation coefficient assignments: designed as 1.28, 1.25 and 1.23 respectively;

3.1.2 1 trapezoidal aperture extension coefficient distribution: designed to be 1.25;

3.1.3 1 cap hole elongation coefficient distribution: designed to be 1.20;

3.1.4 2 rail-shaped deep cutting hole extension coefficient distribution: designed as 1.17 and 1.15;

3.1.5 1 pilot hole extension coefficient distribution: designed as 1.13;

3.2 in this embodiment, according to the hole pattern structure and the number configuration, the hole extension coefficients of the universal machine set are distributed as follows:

3.2.1 semi-universal finished hole extension coefficient is designed to be 1.075;

3.2.2 The extension coefficients of the 4 full universal holes are respectively designed to be 1.25, 1.23, 1.21 and 1.19, and the extension coefficient is smaller when the hole is closer to the finished product hole;

3.2.3 The elongation coefficients of the 3 edging holes are respectively designed to be 1.08, 1.05 and 1.03, and the elongation coefficient is smaller as the hole is closer to the finished product hole.

4. Distribution of rolling speed for each hole

As with the speed calculation method of the rod-wire tandem mill set, the tandem rolling speed of each hole is the product of the initial rolling speed and the cumulative elongation of the hole. Different from the determination mode of the rod wire material, the method comprises the following steps: in the continuous casting and rolling continuous straightening process of the steel rail, the rolling speed of each hole needs to be determined by the rolling speed of a finished product hole, and the rolling speed of the finished product hole needs to be determined by considering the maximum speed which can be born by a straightening unit, a flaw detection unit and the like. The maximum comprehensive running speed of the rolled piece is determined by comprehensively balancing the maximum running speed of a main equipment unit of the whole production line, in the embodiment, the comprehensive straightening speed is 2 m/s, the final rolling speed is 2 m/s, and the rolling speeds of the other holes are reversely pushed according to the pass extension coefficient.

5. Distribution principle of extension coefficient of each hole

The distribution principle of the extension coefficient of each hole is to ensure the steel tapping flatness of the rolled piece to the maximum extent.

The deformation of the trapezoid holes and the cap-shaped holes of the cogging mill set is large and uneven, the cogging mill set has the main function of ensuring the section shape required by the rail-shaped holes, and the steel tapping straightness of rolled pieces is controlled by configuring pressure for the hole patterns.

The rail-shaped deep cutting holes and the pilot holes of the cogging mill set control the up-down bending of the rolled piece through reasonable distribution of head-waist-bottom extension coefficients, and the rail-waist extension coefficients are generally larger than the rail-waist extension coefficients and are generally larger than the rail-head extension coefficients. The left and right bending is completed through the pressure configuration of the hole type.

The extension coefficient of each rail-shaped hole of the universal machine set is larger than the extension coefficient of the rail head according to the rail bottom extension coefficient, and the rail head extension coefficient is larger than the rail waist extension coefficient to distribute so as to fully ensure the flatness of the up-down tapping of the rolled piece and the required section shape.

In summary, the invention aims to explore a hole pattern design method for continuous rolling of a compact full-flow vertical steel rail, which not only can solve the problems of uneven stress, uneven temperature distribution and size deviation of a final finished product in the conventional horizontal rolling of the steel rail, but also can utilize a shorter production line to roll the steel rail, can effectively reduce investment cost and facilitate temperature control in the rolling process of the steel rail, realize online controlled rolling and controlled cooling of the steel rail, and can further improve microstructure uniformity and mechanical property of a section of the steel rail while ensuring the size of the final finished product.

By the technical scheme provided by the invention, the following technical effects can be realized:

(1) The steel is straight in the rolling process, the rolling piece is always in a vertical symmetrical state in the rolling process, the stress on the same plane is symmetrical and balanced in the rolling process, the influence of the temperature difference between the front end and the rear end of the rolling piece and the middle temperature is avoided, the influence of uneven cooling water of external rollers is eliminated, the influence of sinking of the gravity head of the steel on the steel rail forming is eliminated, and the steel is straight in the rolling process.

(2) The gauge precision is high, the asymmetry of the steel rail during horizontal rolling is improved, the phenomenon that the size deviation of a finished product is caused by the fact that the rolling conditions of the upper and lower rollers are asymmetric due to the tilting force generated by the influence of gravity during horizontal rolling is solved, and the size precision of the rolled steel rail is better.

(3) The surface quality is good, the frequent impact of the head and tail parts of the rolled piece with lower temperature on the roller and the guide device is reduced, the roller abrasion is reduced, and the smooth operation of the rolling mill and the transmission device thereof is facilitated; meanwhile, the steel feeding impact and tapping tail flicking are avoided, the impact of the rolled piece and a roller, a guide, an edge lining plate and the like is reduced, and the defects of bonding of oxide scales on the surface of the roller and pressing of oxide scales on the surface of the rolled piece are avoided.

(4) The wear of each hole pattern is uniform, each hole pattern is symmetrically designed, steel is discharged straightly in the rolling process, the impact of steel entering and discharging of rolled pieces on the hole patterns is reduced, and the wear of each hole pattern is uniform.

(5) The rolling load of each hole is uniform and reasonable, the elongation coefficient of each hole is uniformly distributed, the rolling reduction is uniformly distributed, and the rolling load is uniform. The rolling units are free from stack-drawing deformation, rolling pieces are always in vertical symmetrical states in the rolling process, the rolling process is continuous, the stress on the same plane is symmetrical and balanced, the rolling speed is matched with the extension coefficient, the rolling units are free from tension loss, and the rolling units are free from stack-drawing deformation.

Those of ordinary skill in the art will appreciate that: the above discussion of any embodiment is merely exemplary and is not intended to imply that the scope of the disclosure of embodiments of the invention, including the claims, is limited to such examples; combinations of features of the above embodiments or in different embodiments are also possible within the idea of an embodiment of the invention, and there are many other variations of the different aspects of the embodiments of the invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, and the like, which are made within the spirit and principles of the embodiments of the invention, are included within the scope of the embodiments of the invention.

Claims (10)

1. A continuous rolling method for a steel rail continuous casting and rolling continuous straightening production line is characterized by comprising the following steps of:

the continuous casting blank continuously and sequentially passes through a cogging rolling unit and a universal rolling unit to be rolled, and the blank is in an upright state and is not reversed in the rolling process;

the cogging rolling mill unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling mill unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole;

the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills, the vertical universal rolling mills adopt universal holes, and the vertical edging machines adopt edging holes.

2. The method of claim 1, wherein the blooming mill train comprises 5-7 vertical two-high mills and 2-3 horizontal two-high mills.

3. The method of claim 1, wherein the number of box holes is 2-4, the number of trapezoid holes is 1-2, the number of cap holes is 1-2, the number of rail-shaped cut-and-deep holes is 1-2, the number of rail-shaped extension holes is 0-2, and the number of rail-shaped pilot holes is 1.

4. The method of claim 1, wherein the universal mill train comprises 4-6 vertical universal mills and 2-4 vertical edging mills; the last vertical universal rolling mill adopts a semi-universal hole, and other vertical universal rolling mills adopt full-universal holes.

5. The method according to claim 1, characterized in that for a vertical two-roll mill with box-shaped holes, trapezoidal holes, rail-shaped pilot holes, the two-side roll diameters are made equal; and/or

For a horizontal two-roll mill adopting a box-shaped hole, the diameter of a lower roll is 3-8mm larger than that of an upper roll; and/or

For a horizontal two-roll mill adopting symmetrical trapezoid holes, the diameter of a lower roll is 2-6mm larger than that of an upper roll; and/or

For a horizontal two-roll mill adopting an asymmetric trapezoid hole, if the opening of the big end side of the trapezoid hole is downward, the diameters of a lower roll and an upper roll are equal, and if the opening of the big end side of the trapezoid hole is upward, the diameter of the lower roll is 8-15mm larger than that of the upper roll; and/or

For a vertical two-roll mill and a horizontal two-roll mill adopting cap-shaped holes, the diameter of a roller at the top side of the cap is 0.8-1.2 times of the height of the cap-shaped holes compared with the diameter of a roller at the bottom side of the cap; and/or

For the vertical two-roll mill adopting the rail-shaped deep cutting hole and the rail-shaped extending hole, when adopting the straight rolling hole type, the diameter of the roller at the open side is 10-30mm smaller than that of the roller at the other side, and when adopting the inclined rolling hole type, the diameters of the rollers at the two sides are equal.

6. The method according to claim 1, wherein the box-shaped hole has an elongation coefficient of 1.20-1.50, the trapezoid hole has an elongation coefficient of 1.15-1.40, the cap hole has an elongation coefficient of 1.10-1.35, the rail-cut deep hole has an elongation coefficient of 1.10-1.30, and the rail-pilot hole has an elongation coefficient of 1.05-1.20.

7. The method according to claim 1, wherein the elongation coefficient of the last one of the master holes is made to be 1.05-1.10, the elongation coefficient of the remaining plurality of master holes is made to be 1.18-1.30 and the elongation coefficients in the rolling direction decrease in sequence, and the elongation coefficients of the plurality of edging holes are made to be 1.03-1.08 and the elongation coefficients in the rolling direction decrease in sequence.

8. The method of claim 1, wherein for the blooming mill train, when a rail-shaped hole is employed, the rail foot elongation coefficient is made greater than the rail web elongation coefficient, and the rail web elongation coefficient is greater than the rail head elongation coefficient; and/or

For a universal rolling mill set, the rail foot elongation coefficient is greater than the rail head elongation coefficient, and the rail head elongation coefficient is greater than the rail waist elongation coefficient.

9. The method according to claim 1, characterized in that the rolling speed is determined on the basis of the straightening speed of the downstream continuous straightening device.

10. Continuous rolling device for continuous casting, rolling and continuous straightening production line of steel rail is characterized by comprising: the cogging rolling mill unit and the universal rolling mill unit are sequentially arranged along the continuous rolling direction;

the cogging rolling mill unit comprises a plurality of vertical two-roll mills and a plurality of horizontal two-roll mills which are alternately arranged along the continuous rolling direction, the hole pattern of the cogging rolling mill unit comprises a box-shaped hole, a trapezoid hole, a cap-shaped hole and a rail-shaped hole which are sequentially arranged along the continuous rolling direction, and the rail-shaped hole comprises one or more of a rail-shaped deep cutting hole, a rail-shaped extending hole and a rail-shaped pilot hole;

the universal rolling unit comprises a plurality of vertical universal rolling mills and a plurality of vertical edging machines, wherein the vertical edging machines are arranged between two adjacent vertical universal rolling mills, the vertical universal rolling mills adopt universal holes, and the vertical edging machines adopt edging holes.