EP2919926A1

EP2919926A1 - Method and device for producing seamless steel pipes having low eccentricity

Info

Publication number: EP2919926A1
Application number: EP13818650.7A
Authority: EP
Inventors: Hans Joachim Pehle
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-11-03
Filing date: 2013-10-26
Publication date: 2015-09-23
Also published as: DE102012022014B3; US9616475B2; CN104968447A; US20150298185A1; WO2014067514A1; RU2015120959A; CN104968447B; RU2652667C2

Abstract

The invention relates to a method for producing seamless steel pipes in a rolling train having one or more longitudinal or transverse roll stands arranged one behind the other and an internal tool that is used as a piercing mandrel or rolling bar during the rolling process. The invention provides a method by means of which the eccentricity of the rolled stock can be considerably reduced. For that purpose a movement spaced from the longitudinal axis of the rolled stock is imposed by means of a device on the longitudinal axis of the internal tool.

Description

Method and apparatus for producing seamless steel tubes with low eccentricity

description

The invention relates to a method for producing seamless steel tubes according to the preamble of claim 1. Seamless steel tubes are produced on different rolling mills. Most of such mills have in common that three forming steps are passed in succession. In a first stage (see Fig. 1 and Fig. 2), the heated rolling stock (1), for example a continuously cast steel block, is perforated with a solid cross-section

Slanting mill in which the steel block between two or more rollers (2) which are driven and perform a rotary movement (6), in a rotational movement (5) with feed in the rolling direction (la) and driven over a piercer (3]. The piercer is mounted on a mandrel bar (4), which in turn is supported on a mandrel abutment in the axial direction so that it can rotate freely about its longitudinal axis Mandrels are thereby also driven in rotational movement (7 and 8), driven by the rolling stock, whereby in the theoretical ideal case the piercer axis (10) and rolling stock axis (9) are in line, the piercer rotates centrically and produces one uniform wall thickness in the cross section of the rolling stock (see Fig. 2a)., However, since the position of the piercing mandrel in the rolling practice depends on the forces acting on it, v the mandrel axis is always more or less displaced from the center and then performs an eccentric rotational movement (11) about the rolling stock axis in the direction of mandrel rotation (see FIG. 2b).

The hollow block produced in the cross rolling mill is in a second forming stage using an internal tool, a rolling rod, in a longitudinal or

Further, the wall-thickness is reduced and the length increases accordingly. In a third forming stage, the tube is then usually rolled finished without an inner tool, wherein diameter and

Wall thickness targeted to be set according to the customer order.

replacement blade Diameter and wall thickness of the finished rolled tube must meet specified specifications, ie they must be within specified tolerances. If tolerances are not met, the product, the tube, inferior and the economic yield is low. For reasons of stability of the rolled tubes for later use in cables, components and construction elements usually negative tolerances in terms of wall thickness are required, ie the wall thickness must not fall below a specified value (minus tolerance) at any point of the tube. In order to safely comply with negative tolerances, pipes with greater wall thickness are often produced. However, this means an additional expenditure of material, so that increased

Product costs and again reduced yields. From an economic point of view, it is therefore very important to keep wall thickness deviations as small as possible.

In each of the three forming stages arise for different reasons

Wall thickness deviations, ie deviations of the actual values of the wall thickness from the specified nominal values. Wall thickness deviations differ due to different development mechanisms in their expression and size. A particularly large proportion of the wall thickness deviations of the finished rolled tube has the eccentricity (see Fig. 3). The eccentricity is shown as a wall thickness profile in the cross section of the tube with a maximum value t _m ax and a minimum value lying in cross-section t _m in. The value of the eccentricity is in the

Operating practice usually determined by (t _m ax - t _m in) / (t _m ax + tmin) x 100%.

The eccentricity arises mainly in the first forming stage and can be reduced only slightly in the two other forming stages. It is therefore particularly important for economic reasons, the formation of eccentricity in the first forming stage, the punching by means of oblique rolling, to a minimum

restrict.

The eccentricity arises during oblique rolling in that the axis of the

Mandrel parallel, possibly additionally inclined at an angle to the

Rolling stock axis shifts. This shift from the centric position is done by radially acting forces, which may have different causes. Causes can be: An uneven distribution of the temperature or the material properties

replacement blade in the cross-section of the rolling stock, an ovality of the piercer as a result of wear, a deflection of the mandrel bar, deviations from the axial orientation of rolling mill, mandrel bar guides and mandrel abutment and other. In eccentric position of the perforated mandrel axis is in the relevant cross section of the rolling stock

eccentric wall thickness profile, as shown in Fig. 3, generated

According to the current state of knowledge and technology, the problem of eccentricity is limited by the fact that the mentioned influences are kept as small as possible. Accordingly, it is ensured, for example, that the block is heated uniformly before the perforation, the rolling mill and the auxiliary equipment are exactly aligned with each other, and worn piercer spikes in time

be replaced. Under such conditions, eccentricity values of 2 to 4% can be achieved. However, it is difficult to find the influencing factors in the

To keep operating practice under control for a longer period of time. In practice, the eccentricity values are therefore usually at 5 to 10% or even higher, which causes considerable additional costs in the production

From DE 2949970 C2, a rolling mill for punching blocks with freely rotatably mounted mandrel rod is known. Mandrel and mandrel rotate at a fixed connection between piercer and mandrel bar at an angular velocity, which is imposed by the rollers. Due to this rotational movement and with the associated low relative movement between piercer and rolling stock, the wear of the piercer is kept low at least in the stationary rolling phase. However, the piercing pin axis is caused by disturbing influences, e.g. Temperature differences in the cross section of the block slightly shifted from the Walzgutmittenachse, resulting in an eccentric wall thickness distribution in the cross section of the rolled hollow block According to DE 3602523 Cl is a rolling mill for punching blocks with

driven mandrel known in which the mandrel bar before the punching process adapted to the rotational speed of the block to be punched

Rotational speed is accelerated. This ensures that even at the beginning of the hole process, the relative speed between piercer and rolling stock is low Thus, the wear of the piercer is further reduced. But even with this solution, the position of the piercing pin axis is unstable and dependent on interference. Associated with an unwanted and uninfluenced shift in the

replacement blade Lochdornachse then creates an eccentricity of the wall thickness of the generated

Hollow block.

In DE 10 2008 056988 AI a method is described, with which the

Eccentricity can be reduced significantly and reliably. In this method, the piercer is e.g. Rolling tests have been confirmed by means of an additional drive against the rotational movement of the rolling stock, and have confirmed that this eliminates a large part of the eccentricity, approximately 50%. However, this method has the disadvantage that the piercer quickly wears due to the relative movement between piercer and rolling stock and consequently acting on the surface of the piercer shear stresses also due to the relative movement errors in the

Inner surface of the rolling stock occur, which lead to rejects. Thus, the goal of cost savings with this method is achieved only very limited.

The present invention has for its object to provide a method by which the disadvantages described are avoided by the eccentricity is reliably reduced without an increased relative movement between piercer and rolling occurs, and so increased wear and internal defects can be avoided.

This object is achieved by a method with the features according to

Claim 1.

As a result of the application of this invention, the eccentricity of the rolling stock is significantly reduced, without the wear of the piercer is increased and without additional internal errors can occur.

The invention is based on the finding that the off-center rotational movement of the mandrel axis is to be regarded as a superposition of mostly two oscillations

different frequency (revolutions per time] and different amplitude (distance of the piercer axis from the rolling stock axis.) Due to the superimposition of the vibrations, the position and the distance of the mandrel axis of the change

Walzgutachse in the course of the rolling process and the rolled hollow block is accordingly a characteristic distribution of the wall thickness values over the length and the circumference of the rolling stock. In Fig. 4, the distribution of the wall thickness

replacement blade shown schematically, resulting from a rotational movement with a constant

Frequency that differs from the frequency of the rolling stock movement The lines of the same wall thickness (FIG. 4 shows by way of example the line (12) of the maximum wall thickness) form an angle α (13) with the rolling stock longitudinal axis.

If the rotational movement of the piercer axis consists of two rotational movements with different frequencies, the wall thickness values are shown as two superimposed wall thickness distributions, the two being

Wall thickness distributions different angles between the lines same

Have wall thicknesses and the rolling stock longitudinal axis.

From this finding, it is derived according to the invention that not the rotation of the piercing mandrel itself is to be changed, as described in DE 10 2008 056 988 AI, in order to influence the formation of the eccentricity, but it is to influence the rotational movement of the mandrel axis. This can be changed without changing the rotation of the mandrel, as the following application example illustrates (see Fig. 5).

The perforated mandrel shaft (14), which is a shaft which is firmly connected to the piercer, is freely rotatably mounted on the mandrel rod by means of low-friction sliding surfaces (16), which are produced for example by means of ceramic coating and graphite lubrication. The longitudinal axis of the piercer is opposite to Offset longitudinal axis of the mandrel. The offset is one or a few millimeters. The mandrel bar is with one

Provided rotary drive. Upon rotation of the mandrel rod, the position of the longitudinal axis of the piercer is influenced by means of the device described an eccentric connection of piercer and mandrel, without the rotational movement of the

Punch is changed.

Another device of an advantageous embodiment of the teaching according to the invention is shown in Fig. 6 between the piercer and mandrel is an adapter

used in which the mandrel shaft (14) by means of a ring gear on a mandrel rod fixedly connected to the hollow gear (15) rolls in this arrangement, the rotational movement (7) of the piercer produces a rotation (11) of the mandrel axis, which is opposite to the rotation of the piercer By the same arrangement can also

replacement blade the mandrel rod axis are set in a rotation which is opposite to the rotation of the mandrel bar, when it is firmly connected to the piercer

Another finding underlying the invention relates to the frequency of the imposed vibration or rotational movement of the mandrel axis. The higher the frequency compared to the frequency of the rolling-mill rotation, the greater the angle (13, see FIG. 4) between the lines of equal wall thickness and the rolling stock axis. At very high frequency compared to the frequency of the rolling goot rotation, these lines are like helical lines along the rolling stock longitudinal axis. Such an expression of

Wall thickness deviations have the advantage that due to the small axial distances of maximum value and minimum value of the wall thickness easily compensated

different wall thicknesses can take place in subsequent longitudinal rolling processes. Because if the axial distance between the large wall thickness and small wall thickness is small, both are formed simultaneously, the position of the inner tool remains stable centric and it adjusts an average wall thickness, i. the

Eccentricity is partially eliminated

This effect is taken advantage of according to a further embodiment of the invention by the mandrel axis is imposed a high frequency of rotational movement in the direction or against the Walzgut- and mandrel rotation. The imposed rotation prevents for a self-oscillation with the usual expression of

Eccentricity and generated on the other hand, a high-frequency eccentric rotation and thus an eccentricity that can be easily equalized in a downstream longitudinal rolling process.

The teaching of the invention can also be used in the second and third forming stage to effect an off-center movement of the inner tool. This movement promotes the flow of material in the circumferential direction of the rolling stock and thus leads to a compensation of wall thickness differences in the cross section of the

Rolling stock.

replacement blade Explanation of the pictures:

Fig. 1: Representation of the hole in the cross rolling mill in the longitudinal section of the rolling stock tool arrangement.

Fig. 2: Illustration of the hole in the cross rolling mill in the cross section of the rolling stock tool arrangement. (The representation of the lateral guides of the rolling stock has been omitted since they are not relevant for the described relationships.) FIG. 2a shows a centric hole process and in FIG. 2b an eccentric hole process.

Fig. 3: illustration of a Walzgutquerschnittes with eccentricity of the wall thickness T of the value of the eccentricity is determined with (t _ma x - t _m m) / t _max + t _m \) x 100%.

Fig. 4: Representation of the distribution of the wall thickness of the rolling stock on the length coordinate and circumferential coordinate of the rolling stock.

5 shows a device for producing an off-center rotary movement of the dome axis while maintaining the rotation of the dome in the direction and the rotational speed of the rolling stock.

Fig. 6: Representation of the generation of a rotational movement of the piercer

opposite rotational movement of the piercer axis by means of a rolling in the interior of a ring gear.

LIST OF REFERENCE NUMBERS

1 rolling stock

la rolling direction

2 roller

3 piercer

4 mandrel

5 rotational movement of the rolling stock

replacement blade Rotary movement of the roller

Rotational movement of the piercer

Rotary movement of the mandrel

Rolled longitudinal axis

Piercer longitudinal axis

Rotational movement of the piercer axis

Line of equal wall thickness

Angle between a line of the same wall thickness and the rolling stock axis Shaft shaft with ring gear

ring gear

sliding surface

Mandrel longitudinal axis

replacement blade

Claims

claims

1. A method for producing seamless steel tubes in a rolling mill with one or more consecutively arranged longitudinal or Schrägwalzgerüsten and used in the rolling process in the interior of the rolling stock (1)

Inner tool, designed as a rolling rod or as a mandrel rod (4) with a perforated mandrel (3) arranged thereon, wherein the rotation (7) of the inner tool about its longitudinal axis (10) is effected by the rotation (5) of the rolling stock about the rolling stock longitudinal axis ( 9), characterized in that with a device of the longitudinal axis of the inner tool movement (11) at a distance from the

Walzgutlängsachse imposed, wherein the rotational movement of the inner tool is maintained about its longitudinal axis (10) in the direction of Walzgutdrehung.

2. The method according to claim 1, characterized in that the rolling stock (1) generated rotational movement of the piercing mandrel (3) is used to generate a rotation of the mandrel rotation opposite rotational movement of the mandrel longitudinal axis.

3. The method according to claim 1, characterized in that the mandrel longitudinal axis (10) a rotational movement with a compared to the rotational movement of the rolling stock (1) high frequency is imposed.

4. Device for generating a movement (11) of the longitudinal axis of

Inside tool at a distance to the rolling stock longitudinal axis, wherein the

Rotary movement of the inner tool, designed as a rolling rod or as a mandrel rod (4) with a perforated mandrel (3) arranged on this front, around its longitudinal axis (10) is maintained in the direction of Walzgutdrehung.

replacement blade