EP2692458B1 - Method and device for producing a metallic hollow block from a metallic block - Google Patents

Description

The present invention relates to a method and an apparatus for producing a metallic hollow block from a metallic block by means of a punching operation, for example by means of a piercing mandrel.

For the production of pipes, in particular of seamless pipes, it is known to punch a solid block, which serves as a starting material, and thus to produce a hollow block, which can be used directly as a pipe or can be subjected to further processing steps. In particular, in the production of steel pipes, a hollow block is produced from heated solid steel blocks in a one-stage or multi-stage, continuous rolling process and in particular a forming unit for punching blocks, for example a cross rolling mill or a punch press, usually using a punch mandrel from the solid material.

The starting material used here is usually a so-called round block. The blocks are heated in a furnace prior to punching in order to lower the yield stress and consequently the strength in the entire block so that the block material can be formed as well as possible in the subsequent punching process.

In particular, for the subsequent production of a metallic tube from the hollow block as homogeneous a wall thickness distribution of significant, very important. In the theoretical ideal case, the wall thickness at each point of the hollow block is identical. This case corresponds to an absolute eccentricity E _absolute = 0 mm and consequently also a relative eccentricity E _relative = 0%.

$$E_{\mathit{relativ}}=\frac{\left(s_{\max }-s_{\min }\right)}{\left(s_{\max }+s_{\min }\right)}*100\%$$

The eccentricity of tubular objects is defined as the distance of the centers of the outer and inner circle of the tubular object. The absolute eccentricity (in mm) or the relative eccentricity (in%) can be calculated with the following formulas (1) and (2), wherein the wall thickness of the tubular object is denoted by "s" and the indices "max" or " min "denote the maximum and minimum wall thickness of the respective cross section: $$e_{\mathit{absolutely}}=\frac{\left(s_{\mathrm{Max}}-s_{\min }\right)}{2}$$

$$e_{\mathit{relative}}=\frac{\left(s_{\mathrm{Max}}-s_{\min }\right)}{\left(s_{\mathrm{Max}}+s_{\min }\right)}*100\%$$

There is a need to keep the eccentricity of a hollow block made from a block very low.

The hitherto known technical measures for the production of hollow blocks or tubes with a small eccentricity are based on changes in the arrangement or the distances between the tools. Examples of such measures are in DE 3128055 A1 . DE 3326946 C1 . DE 4433397 C1 and EP 2067542 A1 described. Alternatively, it is proposed in the prior art to use additional or different tools. Such methods are for example in DE 473723 . US 4803861 . DE 19903974 A1 . DE 3326946 C 1 . DE 4333284 C2 and DE 4433397 C1 described. Furthermore, the machining of recesses or pilot holes on the central axis of the block is proposed. This is for example in DE 3328269 A1 . GB 1008709 . DE 2635342 C2 . US 4052874 . GB 897015 . DE 1247118 and GB 961796 described.

Finally, in the DE 31 28 055 A1 describes a mandrelless stand-up mill for seamless metal pipes, wherein the stand-up mill stands for reducing the outside diameter and correcting the wall eccentricity of seamless metal pipes from tube billets.

These measures are usually complex, costly and in many cases not sufficiently effective. Despite these technical measures, eccentricity values that are greater than 10% often result. An additional often used measure after the end of the hot forming is the subsequent separation of the zones with increased eccentricity within the tube, for example, in particular the ends of the tube. To determine that length of the pipe end with increased eccentricity, first the measurement of the eccentricity profile along the pipe and consequently increased metrological effort is required. In the extreme case, if the eccentricity values in the pipe are too great, this can mean that a large part of the pipe concerned or even the entire pipe is rejected.

The invention is therefore an object of the invention to provide a solution in which already during the production of hollow blocks, the eccentricity can be kept very low in a simple manner and reliably.

The invention is based on the finding that this object can be achieved by the strength of the block is set so that it defines the course of the perforation and in particular the alignment of a Lochungswerkzeuges in the block during the Lochungsvorgangs and possibly leads.

According to a first aspect, the object is therefore achieved by a method for producing a metallic hollow block from a heated metallic block, by means of a punching process. The method is characterized in that at least at the Anlochseite of the block in at least one temperature change zone, a local temperature change is effected and the temperature change zone is rotationally symmetrical to the central axis of the block.

As a metallic block is preferably understood according to the invention a metal block of low-alloy or non-alloy steel. However, other metals, such as aluminum, may be used. The metal block or metallic block is also referred to below as a block. As metallic Hollow block, which is also referred to below as a hollow block, is understood according to the invention an object made of a metal block, for example, in a subsequent process step as starting material for the production of metallic tubes, especially steel tubes in a single-stage or multi-stage, continuous rolling process with one or more Umformaggregaten serves. For punching the block and consequently for producing a hollow block, a forming unit is used according to the invention, for example a cross-rolling mill or a punch press. The forming unit comprises, for example, at least one piercer. If reference is made in the following to a piercer, the formulated descriptions apply correspondingly to another tool of a forming unit for punching. The punching of the block for producing the hollow block is also referred to below as punching or punching operation.

As a starting material, that is, as a metal block, a so-called round block, ie a solid cylinder with a circular cylindrical or approximately circular cylindrical cross section, can serve in the method according to the invention. However, the block may also have another, for example round or square, polygonal block cross-sectional contour. The block may be pre-formed or non-pre-formed round casting with an approximately constant diameter. The diameter of the round block may, for example, be D = 200 mm, and the mass of the block may be, for example, m = 100 to 1000 kg. The block is preferably heated in an oven, for example a rotary hearth furnace or walking beam oven, to a temperature suitable for later forming. For low alloyed or unalloyed steels, the block is heated to a temperature of, for example, T = 1300 ° C or T = 1200 ° C.

At least at the Anlochseite of the metal block is in the inventive method in at least one temperature change zone a local

Temperature change causes. As Anlochseite this side of the block and later also of the hollow block is called, at which the perforation begins.

As a zone in which a temperature change is effected, the area of the block is understood, in which the temperature change is effected. This area or this zone is therefore also referred to as a temperature change zone. The local temperature change is preferably carried out in a temperature change zone of the hole side, which comprises the end face of the block. The temperature change zone preferably extends beyond the end face of the block over a certain length in the axial longitudinal direction of the block.

The block is heated, as described above, prior to punching, for example in an oven, and is thus used as a heated block for the process. By heating the block, the yield stress and consequently the strength in the entire block is reduced so much that the block material can be reshaped as well as possible during the subsequent punching process. The aim is to produce a temperature distribution that is as homogeneous as possible in the entire block. According to the invention, a local temperature change is made.

As a local temperature change in this case a temperature change is referred to, which occurs only at a part of the block. The temperature change zone in which the temperature change occurs, therefore, has a different temperature than the other parts of the block, in particular as the adjacent to the temperature change zone parts of the block. Particularly preferably, the local temperature change occurs at least on one surface of the block. Particularly preferably, the local temperature change occurs at one or both end faces of the block. In addition, however, the local temperature change may also extend over the end face in the axial direction over part of the length of the block.

The temperature change zone in which the local temperature change is effected preferably includes only a portion of the surface of the block and more preferably extends only over part of the length of the block. In particular, the temperature change zone in which the temperature change is effected includes only a part of one of the end faces or both end faces of the block and a part of the length of the block adjacent to the respective end face. In this case, the temperature change zone extends in the part of the length of the block adjoining the end face only over part of the cross section of the block. In a temperature change zone, which lies in the end face of the block at the periphery of the end face, the temperature change zone extends for example over part of the length of the lateral surface of the block.

By the temperature change zone, which is generated according to the invention, different temperature zones are formed on the surface and also in the interior of the block, that is, areas whose temperatures differ from each other. One of the temperature zones formed corresponds to the temperature change zone, while the further or the further temperature zones are determined by an outlet temperature of the block before the temperature change. In these other temperature zones, for example, then the temperature may be present, which has exhibited the block after the initial heating.

The local temperature change is preferably effected by acting on a part of the surface of the block. The action, which will be described in more detail later, is preferably limited to a part of the end face and possibly additionally to a part of the length of the adjacent lateral surface of the block. The action is preferably an active action on the surface of the block. Thus, causing the local temperature change differs from passive temperature changes that occur, for example, by cooling in the environment.

This means that only a part of a surface of the block, preferably a part of the end face of the block is acted upon. The temperature change according to the invention thus differs from heat treatments of the block, such as heating or quenching, in which the entire surface is subjected to a temperature change.

Due to various factors, a not completely homogeneous temperature distribution in the block results, in particular in conventional methods, that is to say the temperatures within a block differ by, for example, 10 to 60 Kelvin. These temperature differences are the disadvantageous consequence of naturally never ideal homogeneous heating. Consequently, there is a principle of more or less inhomogeneous temperature distribution and consequently a principally inhomogeneous distribution of strength in the block. This inhomogeneity of the temperature distribution is different pronounced when using the hitherto known technical solutions in terms of size and type of temperature distribution. In addition, this inhomogeneity of the temperature distribution is not sufficiently precisely adjustable.

Even a very small inhomogeneity of the distribution of strength in the block but can cause significant quality defects of the tubular product. In particular, differences in strength or strength fluctuations in the face of the block as a result of the stochastic-inhomogeneous temperature distribution can strongly influence the piercing process, in particular during the first phase of the piercing process - the so-called anloch phase.

As a consequence of the inhomogeneities in the block, together with inhomogeneities of the block geometry, for example deviations from the ideal circular geometry of the block cross-section, quality defects and in particular dimensional deviations can subsequently occur in the rolling stock, in the hollow block or in the manufactured tube blank, for example in increased eccentricity.

The eccentricity is influenced by a number of physical parameters, such as the strength and thus the shape retention of a tool used for punching, in particular the piercer and its length. In addition, the eccentricity is also influenced by the properties of the block, in particular the distribution of the properties in the block. Of particular importance here are the temperature distribution and strength distribution in the block.

With the present invention, by the local temperature change of a zone of the block, which is rotationally symmetric to the central axis of the block, generates a graded and rotationally symmetric temperature distribution in at least the end face of the Anlochseite of the block. This is accompanied by a graded and rotationally symmetrical distribution of strength in at least the end face of the hole side of the block. The hollow block produced in this way has a very homogeneous wall thickness distribution and consequently a very low eccentricity compared to a conventionally produced hollow block.

In the method according to the invention, since the temperature change is effected at least at the pinhole side and preferably in the so-called pinhole zone of the cavity block, the reduction in eccentricity of the cavity block produced during the piercing process is primarily during the first phase of the piercing process, also referred to as the pinhole phase , possible. As Anlochzone according to the invention the end face on the Anlochseite of the block, as well as a to this end face, which can also be referred to as Anlochfläche, subsequent part of the length of the block referred to. The portion of the length of the block attributed to the anloch zone has a length less than the length of the block. For example, the length of the part of the block belonging to the angling zone is preferably at most 1/3 or at most 1/4 of the total length of the block.

By reducing the eccentricity of a hollow block produced in this way, there is likewise an advantageous distribution of eccentricity in the further forming steps produced therefrom up to the finished tube. The main technical disadvantage of a large eccentricity of the rolling stock or the finished tube is that the associated unilaterally small wall thicknesses in respective eccentric cross-sections lead to a one-sided, inhomogeneous, asymmetric stress distribution and in extreme cases, ie at too low wall thickness, to overuse of the relevant cross-section. Too much eccentricity means either significantly increased reworking effort or even the reject of the tubular product.

With the present invention it becomes possible, in the production of hollow blocks and in the following of precision tubes, to keep the eccentricity as low as possible, in the theoretical ideal case to identical zero ( E _relative = 0%). In conventional manufacturing practice, the demands on the eccentricity are limited to a feasible level and associated with corresponding quality classes, so that eccentricities of, for example, E _relative <10% are permitted. A typical magnitude of the relative eccentricity in the annulus zone of the block is about E _relative = 10% or greater. When passing through all stages of production after Schrägwalzlochen or hole punching the eccentricity changes within certain limits. The punching process, for example, slanting or punching, is here a forming process in pipe production, which significantly influences the eccentricity.

All currently known technical methods are fundamentally only suitable to reproducibly bring the eccentricity in the anloch zone of the block to a very small extent ( E _relative <2 to 3%). With the method according to the invention, the eccentricity can be significantly reduced in comparison to the hitherto known technical methods. The achievable magnitude of the improvement in the eccentricity is, depending on the size and course of the eccentricity in the reference hollow block, for example, factor 2 or greater.

The material strength (flow stress) of steel materials is strongly dependent on the temperature. According to the invention, therefore, the strength distribution in the block material is influenced by targeted adjustment of a temperature distribution. The dependence of the yield stress on the strain rate does not limit the effectiveness of the method according to the invention, since the strain rate in the general case remains approximately unchanged. Since changes in the change in the temperature of the material of the block and its strength, in the inventive method by the targeted temperature change in at least the end face of the Anlochseite and thus achieved temperature distribution in the end face of the block a graded, rotationally symmetric strength distribution from the outside by local Cooling and / or local heating can be generated. Preferably, in the outer annular temperature change zone of the end face (that is, the outer portion of the end face, also referred to as the outer temperature zone) of the block, a significantly lower temperature is generated than in the center zone, also referred to as the inner temperature zone, in the immediate vicinity Surrounding the central axis of the block, which may also be referred to as the main axis or center axis of the block.

As a tool and in particular internal tool of the forming unit for the piercing operation, a piercing pin can be used according to the invention. The piercer can easily penetrate into the temperature zone formed there, for example, due to an elevated temperature in the center of the end face of the Anlochseite in the inventive method. Since the temperature in this case is lower in the surrounding temperature zone and therefore the strength in the surrounding zone is higher, the piercer is automatically centered. In addition or as an alternative to heating in the middle of the end face of the hole side, therefore, the outer temperature zone surrounding an inner temperature zone of high temperature can be cooled, that is to say the temperature in this zone can be lowered. In this way, the centering effect is further enhanced.

Therefore, the distribution of strength significantly influenced by the temperature distribution improves the centering effect especially during the first phase of the punching process (that is to say in the case of so-called "pinning"), in that the block is aligned relative to the piercing mandrel via a "self-centering".

"Anchor" is understood to mean the first phase of the piercing process, that is to say the time interval from the first contact of the piercer with the block (or shortly before) to the stationary phase of the piercing process.

"Anlochzone" is the zone in the block that is punched first in the punching process, that is, the front zone of the block. Strictly speaking, this zone is not exactly geometrically defined, but represents only a relatively blurred circumscribed zone. For example, with typical block diameters of about D = 200 mm, the anloch zone comprises about the first interval length of 500 mm along the central axis of the block, starting at the front Face of the block. As an Anlochseite of the block that side of the block is referred to, in which lies the end face over which the piercer first comes into contact with the block.

"Self-centering effect" here is the effect to understand that the block during the punching process - without additional external influence - during plastic forming on the inner tool (here: piercer) even about the basic mechanical principle "Actio = Reactio" relative to the inner tool almost centric (that is, with very little lateral offset) aligns this while pinning the block.

A significant difference of the method according to the invention compared to previously known, conventional measures or approaches to reduce the eccentricity is that the centering is achieved by means of the temperature distribution and consequently with the aid of the strength properties in the block to be punched.

The essential advantage of the method according to the invention is that a precise and reproducible centering of the piercing mandrel can be achieved during the piercing process. In this way, the eccentricity of the hollow block or the tubular product compared to conventional methods or measures can be significantly reduced. By the temperature change zone, in which a temperature change is effected according to the invention is rotationally symmetrical to the central axis of the block, the centering effect is significantly supported.

By using the present invention, the eccentricity in the hollow block compared to conventional methods can be significantly reduced and thus improved, the invention has significant advantages.

With the method according to the invention, a hollow block with a very homogeneous wall thickness distribution and consequently with a very low eccentricity can be produced. In this way, the production of a hollow block can in particular be made more reproducible and very precise.

Since such a hollow block can be used for example as a precursor for a seamless tube, the inventive method for producing tubular precursors in the production of a seamless tube with very homogeneous wall thickness distribution and thus with a very low eccentricity. With the method according to the invention, a hollow block with small eccentricity variations along the hollow block can be produced, and the qualitative and quantitative variations in the courses of eccentricity between different hollow blocks produced in succession can be significantly reduced.

By preventing critical, too large eccentricities can large waste quantities or large expenses for reworking the Hollow blocks or the tubular products and the associated higher costs significantly reduced or even completely prevented.

Hollow blocks which have been produced according to the method according to the invention can also be used in particular for the production of precision tubes, since in particular the technical requirements on the geometric properties (for example on the uniformity of the wall thickness distribution and the eccentricity distribution) of precision tubes are comparatively high.

In one embodiment, the temperature change is effected in a temperature change zone that is radially spaced from the central axis of the block. This temperature change zone, which is radially spaced from the central axis of the block, can extend, for example, as far as the outer contour of the block. This embodiment is of particular advantage, since in addition to the targeted temperature change at the end face itself, a temperature change can be adjusted specifically over the length of the block. For example, in this case, the temperature change can be effected by acting on a part of the length of the lateral surface of the block, which adjoins the end face of the block.

1. a) Applizieren von flüssigen Medien, beispielsweise Wasser, vorzugsweise als zusammenhängender Wasserstrahl,
2. b) Applizieren von gasförmigen Medien, beispielsweise Wasserdampf, oder
3. c) durch Festkörperkontakt in Form beispielsweise einer Projektionsmaske.

According to one embodiment, the temperature change that is effected in at least one temperature change zone at least on the hole side of the block is a decrease in temperature. As already mentioned, an increase in strength over other temperature zones in the block is achieved by the temperature reduction and thus causes a centering and / or guidance of the piercing mandrel. Such a temperature reduction or targeted cooling of a temperature change zone of the block can be achieved, for example, by means of one or more of the following methods:

1. a) application of liquid media, for example water, preferably as a coherent water jet,
2. b) applying gaseous media, such as water vapor, or
3. c) by solid state contact in the form of, for example, a projection mask.

According to another embodiment, the temperature change zone in which the local temperature change is effected comprises the center axis of the block and the temperature change is a temperature increase. This temperature change zone is also referred to as the internal temperature zone. For example, with a block diameter of 210 mm, this temperature zone may have a diameter of 40 mm. The diameter of the inner temperature zone, which represents the temperature change zone, that is, in which the temperature is changed, according to the invention may for example be 25%, preferably 20% of the block diameter. The diameter of the, for example, axially symmetric tool (for example a piercer) which is introduced into this inner temperature zone and comes into contact with the block material in the first process phase of the piercing process can be, for example, 30 mm. The diameter of the axisymmetric tool (for example, a piercer) in that zone of the tool, which comes into contact with the block material in a later process phase of the punching process, may for example be 130 mm. The temperature near the central axis of the block, and thus in the center of the inner temperature zone, can be, for example, up to 1200 ° C. and the temperature in the outer temperature zone in the vicinity of the outer surface of the block, for example 950 ° C. These dimensions and temperatures are merely examples and therefore are not limitative of the inventive idea. The temperature difference set between the outside of the block and the central axis, that is, the difference between an inner temperature zone and an outer temperature zone may be, for example, 40%, preferably 20% of the temperature of the highest temperature temperature zone.

In the embodiment in which an inner temperature zone with increased temperature is generated, is thus at the entry point of a tool and in particular a piercer, which is usually in the center on the end face and thus comprises the central axis of the block, reduces the strength of the block material and facilitates the insertion of the tool, in particular the piercer, into the block. In addition, the temperature increase can also be chosen so large that due to this elevated temperature, the block material is melted in the temperature change zone and thus can be removed from contact with the tool, in particular the piercer, from the front side of the block.

The temperature change effected according to the invention is preferably effected by an external influence on the block. The external influence is also referred to as action. The action takes place according to the invention only on a part of the surface of the block. To act, for example, a beam can be directed to a part of the surface of the block. The beam may be a media beam or a beam of electromagnetic waves.

According to one embodiment, the local temperature change takes place by acting on a part of one of the end faces of the block. In this embodiment, the temperature change zone is formed solely by the end face of the block. When acting on a part of the end face of the block at least a further part of the end face is not directly influenced by the action. If, for example, a beam is directed onto the edge region of the end face, then the temperature change zone is formed in the edge region of the end face. In the middle of the end face, that is, in the region of the center axis of the block, however, the previously set temperature will be largely retained. By acting on a part of the end face of the block thus a temperature distribution over the end face of the block, in particular the Anlochfläche and the Anlochzone, can be adjusted exactly. Such an exact adjustment of the temperature distribution in the end face and the Anlochzone is not reproducibly adjustable in an exclusive action on the lateral surface of the block. The end face of the block, on which by acting a local temperature change is effected, may be in addition to the Anlochfläche also the through hole area.

According to a further embodiment, the local temperature change takes place by acting on a part of one of the end faces of the block and on an adjacent to this end face portion of the length of the lateral surface of the block, wherein the length of the portion of the lateral surface is less than the length of the block. In this embodiment, preferably, the edge portion of the end face of the block represents the temperature change zone. In this embodiment, the length of the temperature change zone can be increased by acting on the peripheral surface of the block rather than acting solely on a part of the end face.

According to a preferred embodiment, the temperature change zone, in which a temperature change is effected, extends over a maximum of 1/3, in particular a maximum of 1/4 of the length of the block. In this way, for example, in the Anlochzone the desired Temperaturvereilung that leads to a centering of a piercer can be adjusted, the other area of the block but still has a homogeneous temperature distribution, whereby a uniform deformation after the introduction of the piercing pin can be ensured.

According to one embodiment, a media jet is preferably directed to a part of the hole side, in particular the hole surface, and optionally additionally to a part of the through hole side, in particular the through hole surface, of the block. In this way, a targeted setting of a temperature distribution at the relevant end face of the block can be ensured. Alternatively or additionally, a part of the length of the lateral surface of the block can also be acted upon with a media jet to act on a part of the front side (or both end faces) of the block with a media jet. In particular, this admission in the Anlochzone of the block and / or in the Durchlochzone to a temperature reduction on the lateral surface can be used to achieve a guide of the tool, in particular the piercer. As an alternative to exposure to a media jet, according to the invention, a temperature change can also be effected by changing the ambient conditions. Thus, for example, a projection mask or a cooling ring can be brought before a part of the end face or arranged around part of the length of the lateral surface, so that a lowering of the temperature of the block material by means of convection is achieved.

According to a preferred embodiment, the metallic block represents a round block. In this block form, the advantages of the method according to the invention can be used particularly advantageously since in such blocks usually a hollow block is produced, which should have a homogeneous wall thickness over the circumference, to later to be processed into tubes. Thus, the temperature change zones, in which according to the invention a temperature change is to be made, in the circumferential direction of the block are constant. The setting of a desired temperature and thus a desired temperature distribution is easier to ensure in such a form of temperature change zones.

According to a preferred embodiment, the block is rotated about its own central axis at least before effecting and / or while causing the local temperature change.

Rotating the block about its central axis, which may also be referred to as the main axis or center axis of the block, prior to the piercing operation, in particular, causes the block to be centered for the subsequent temperature change and, in particular, adjustment of a temperature distribution on the face relative to the center axis of the block. In this way, then projection elements, which can also be referred to as temperature adjustment devices, aligned to the center axis of the block reliably be and generating rotationally symmetric temperature zones can be guaranteed.

Rotating the block about its central axis while effecting the local temperature change can be used, in particular, for block material which has been melted by an increase in temperature or coolant which has been applied to the end face of the end face of the block due to the centrifugal force generated during the rotation remove.

According to a preferred embodiment, the temperature change is effected by projecting at least one jet onto one of the end faces of the block, and preferably a projecting element is used for projecting, which is arranged at a distance from the block.

By "projecting" is meant in particular the transfer of a temperature distribution on the end face of the block by targeted cooling or heating from the outside (from a reference object) in, for example, orthogonal direction on the end face.

The projecting should preferably take place in the area of the front end face, that is to say the hole area, and optionally also in the area of the rear end face, that is to say the through hole area. As a projection element, a device component is designated by which at least one beam can be directed to one of the end faces of the block and transmitted. The jet may be a media jet, that is a medium such as air or water. Alternatively, it is also possible that the beam represents a beam of electromagnetic waves.

By providing the projection member spaced from the block, the block may also be moved while effecting the temperature change, for example rotated about its central axis or rotated permanently. In addition, it is the use of a spaced projection element of advantage, as this can relatively easily be moved from the position on the central axis of the block to another position after projecting and thus consequently the space is created, for example, before the piercer or other tool at this point to position the end face of the block.

Through the use of the so-called projection element, the temperature distribution and thus the strength distribution, in particular on the end face of the block, can be influenced in a targeted manner via the beam directed onto the block.

Preferably, the projection element comprises at least one nozzle element. The nozzle elements are arranged on the projection element corresponding to the temperature change zone whose temperature is to be changed by the beam. Preferably, the nozzle elements are thus arranged annularly, or the projection element comprises a single annular nozzle. The resulting annular projection is preferably centered with respect to the central axis of the block. The nozzles of the nozzle element are aligned so that they emit a beam parallel to the central axis of the block and thus also parallel to the central axis of the projection element. Thus, in particular, an annular temperature change zone at a distance from the central axis can be acted upon by the jet or the beams and, in particular, a defined reduction in the temperature in this temperature change zone can be achieved. The temperature change zone is rotationally symmetric to the central axis of the block.

According to one embodiment, at least one coolant jet, and in particular a water jet, is directed onto the end face, in particular onto a part of the end face, of the block. The jet of water can by a projection element, which is an annular element with water nozzles, on the Be directed face of the block. In addition, it is also possible to direct a jet of water on the lateral surface of the block in the region of the front side. This can be done for example by a nozzle member which is arranged annularly around the block and are directed radially inward on the nozzle.

According to a further embodiment, at least one jet, in particular an oxygen jet, is directed towards the face of the block to produce an exothermic reaction at the face and in the adjacent interior of the block. In this embodiment, the beam is preferably directed to the area around the central axis of the block. In this case, the beam can be directed to a region which lies exclusively in the central axis of the block or which additionally comprises a region around the central axis. Due to the exothermic reaction, the temperature in this temperature change zone is increased so much that the block material is melted in this temperature change zone. In order to remove the molten block material from the block, it is preferably rotated at high speeds about its central axis, so as to form a cavity open to the front (cavern), which is approximately rotationally symmetrical with respect to the central axis. This cavity serves as a pre-perforation for a punch mandrel or other tool to be inserted thereafter and thus centers the piercer or the tool. An advantage of such a method of introducing a pre-punch is that no further materials are fed to the block, which could possibly react with the block material. This is to be feared in a melting by carbon arc in the face, in which a carburization of the block material and thus increased friability is assumed.

According to an alternative embodiment, at least one electromagnetic beam, which is reflected by at least one reflector from the front side of the block, directed to the front side of the block. As a result, heating, that is, heating of the center zone of the end face (and consequently a temperature increase) in the immediate vicinity of the central axis of the block by means of a radiation reflector, which is arranged at a defined axial distance from the relevant end face of the block. Preferably, only a single radiation reflector is used to concentrate a beam on the face of the block, and in particular on the center zone of the face. The distance of the reflector from the end face is to be interpreted according to the wavelength of the electromagnetic radiation. The electromagnetic beam which is directed onto the end face is preferably a reflection of the heat radiation of the end face itself. This embodiment has the advantage that the additional provision of a medium, such as oxygen, is not required for achieving an increase in temperature at the end face. When using the heat radiation of the block to increase the temperature in at least one temperature change zone of the block, the temperature in the heated temperature change zone will generally be below the melting temperature of the block material and thus not melt it. Nevertheless, such a temperature increase, in particular in the center zone of the end face centering of the tool, in particular the piercer, and a guide of the tool, in particular the piercer, guaranteed because the temperature of the surrounding temperature zone is lower than in the center zone, which is the temperature change zone represents.

According to one embodiment, a temperature change is also effected at the through hole side of the block opposite the hole side, at least in the end face. The end face of the hole side is also referred to as the front end face. The end face of the through-hole side is also referred to as the rear end face. The temperature distribution set at the through hole side may be equal to or different from the temperature distribution at the hole side. In addition, the temperature distribution on the through-hole side of the block can be generated identically or otherwise than on the hole side of the block. For example, a temperature increase at the Anlochseite be generated by means of an oxygen jet and at the through hole side by a reflection beam of heat radiation.

Due to the change in temperature at the through-hole side, it is also possible for the end phase of the punching process to provide guidance of the piercing mandrel or another tool. Thus, a low eccentricity is ensured even in the through-hole zone, that is near the end face of the through-hole side.

According to a further aspect, the invention relates to a device for producing a metallic hollow block from a metallic block, which has a holder for the block. The device is characterized in that the device comprises at least one projection element for at least zone-wise temperature change of the block in the holder, which is directed to a part of at least one of the end sides of the block.

The holder for the block can be in one piece or in several parts. In particular, the holder may comprise rollers which engage on the lateral surface of the block and can rotate about its central axis. In addition, the holder may comprise at least one forming unit, which serves to punch the block. For this purpose, the device may comprise, for example, a cross rolling mill or a punch press. In addition, the device for producing a hollow block has at least one tool, preferably in the form of a piercer. The tool, in particular the piercer, can be designed as a separate component and, for example, together with the forming unit as a device. According to the invention, the holder for the block can be provided as an additional device to, for example, a cross rolling mill or a punch press and either integrated into it or provided separately therefrom. In the first case, it is also possible that the holder is formed by a part of, for example, the cross rolling mill or the punch press.

According to the invention, the device comprises at least one projection element, which may also be referred to as a temperature setting device, for the at least zonal temperature change of the block in the holder, which is directed to a part, that is, a partial area, at least one of the end sides of the block.

In this respect, the device according to the invention differs from a furnace, in which not a part or partial area of an end face can be specifically heated.

The projection member is preferably spaced to support the block and the block. The projection element is preferably designed so that it can be moved relative to the holder of the block. In this way, on the one hand during the adjustment of the temperature at the block a desired or defined distance can be set. On the other hand, in this embodiment, the projection element can also be removed from the holder in order, for example, to be able to guide the piercer to the block. Alternatively, it is also possible that the block is removed from the holder for punching and inserted into a forming unit, for example a cross rolling mill or a punch press, without the projection element having to be moved.

Particularly preferably, the projection element is aligned with the central axis of the block in the holder. As a result, zones which are rotationally symmetrical to the central axis can be treated in a targeted manner, and in particular the temperature in this zone or these zones can be changed.

The projection element may according to the invention, for example, represent a nozzle or a nozzle ring. Alternatively, for example, a reflector can be used as a projection element. However, it is also within the scope of the invention to use a different type of temperature-adjusting device as a projection element, as long as a temperature change or zone-wise change in temperature can be effected at least on the surface of the block by this temperature adjustment.

The projection element may comprise at least one nozzle or at least one reflector. According to the embodiment in which the projection element comprises nozzles, either a single nozzle can be used, which is preferably directed to the center of the end face, or several nozzles are used, which are arranged offset to the central axis of the block outwardly parallel to the central axis are. In the first case, a medium, for example oxygen to produce an exothermic reaction in the face of the block, can be delivered to the block through the nozzle. In the second case, for example, water or another cooling liquid can be used to lower the temperature at the zone of the end face.

If a reflector is used, the heat radiation of the block is preferably returned from the front side to the front side through this. The reflector preferably has a curved shape, whereby the rays impinging on the reflector can be concentrated by the curvature concentrated back to certain zones of the front side of the block.

The projection element can be arranged on the hole side and / or on the through hole side of the block. As arranged on one of the sides in this context, a projection member is referred to the respective side, in particular to the respective end face, objected but directed directed to this side, that can act on the respective side.

The device according to the invention is preferably designed for carrying out the method according to the invention.

Advantages and features that are described with regard to the method according to the invention apply - as far as applicable - correspondingly to the device according to the invention and vice versa. Advantages and features are therefore mentioned only once if necessary.

• Figur 1: eine schematische Ansicht einer Ausführungsform der erfindungsgemäßen Vorrichtung zum Ausführen einer Ausführungsform des erfindungsgemäßen Verfahrens;
• Figur 2: eine schematische Ansicht einer weiteren Ausführungsform der erfindungsgemäßen Vorrichtung zum Ausführen einer weiteren Ausführungsform des erfindungsgemäßen Verfahrens;
• Figur 3: eine schematische Ansicht einer weiteren Ausführungsform der erfindungsgemäßen Vorrichtung zum Ausführen einer weiteren Ausführungsform des erfindungsgemäßen Verfahrens;
• Figur 4: eine schematische Darstellung eines Blockes in einer Halterung gemäß einer Ausführungsform der erfindungsgemäßen Vorrichtung;
• Figur 5: eine schematische Darstellung des Exzentrizitätsverlaufs entlang eines gelochten Blockes nach dem Stand der Technik;
• Figur 6: schematische Darstellungen eines Blockes mit und ohne eingeführtem Lochdorn;
• Figur 7: schematische Darstellungen eines Blockes mit Lochdorn;
• Figur 8: eine schematische Darstellung der Temperaturverteilung in einer Stirnfläche des Blockes; und
• Figur 9: eine schematische Darstellung der Temperaturverteilung über die Länge des Blockes.

The invention will be described again below with reference to preferred embodiments and the accompanying drawings. Show it:

• FIG. 1 a schematic view of an embodiment of the device according to the invention for carrying out an embodiment of the method according to the invention;
• FIG. 2 a schematic view of a further embodiment of the device according to the invention for carrying out a further embodiment of the method according to the invention;
• FIG. 3 a schematic view of a further embodiment of the device according to the invention for carrying out a further embodiment of the method according to the invention;
• FIG. 4 a schematic representation of a block in a holder according to an embodiment of the device according to the invention;
• FIG. 5 a schematic representation of the Exzentrizitätsverlaufs along a perforated block according to the prior art;
• FIG. 6 : schematic representations of a block with and without inserted piercer;
• FIG. 7 : schematic representations of a block with piercer;
• FIG. 8 a schematic representation of the temperature distribution in an end face of the block; and
• FIG. 9 : a schematic representation of the temperature distribution over the length of the block.

In FIG. 1 an embodiment of the device according to the invention for carrying out an embodiment of the method according to the invention is shown. The block 1, which in the illustrated embodiment represents a round block, is held on a holder (not shown) and can be brought by this holder in a rotation about the central axis M. The direction of rotation is in FIG. 1 indicated by the arrow RED.

An embodiment of the holder that can be used to hold the block 1 is shown in FIG FIG. 4 shown schematically in two views. As is clear from this FIG. 4 In the illustrated embodiment, a roller 30 is a drive roller 300 and two further rollers 30 are guide rollers 301. The block 1 is therefore driven by the drive roller 300, whose axis of rotation or center axis MR is parallel to the central axis M of the block 1, driven and guided by the also with their central axes MR parallel to the central axis M of the block 1 lying guide rollers 301 in the rotational movement.

In the embodiment according to FIG. 1 Furthermore, a projection element 2, which can also be referred to as a temperature adjustment device, is provided. This projection element 2 in the embodiment represents an element having annularly arranged nozzles 20. However, it is also possible that the projection element 2 comprises a single annular nozzle 20. The nozzles 20 of the projection element 2 are directed to one of the end faces of the round block 1. This end face is preferably the end face of the Anlochseite 11 of the block 1, that is, that side from which the perforation takes place. The region of the length of the block 1, which adjoins this end face is also referred to as Anlochzone 13. The opposite end face is thus on the through-hole side 12th of the block 1. The through-hole side 12 denotes the side of the block on which the piercer emerges.

By the projection element 2, a coolant, for example water, is applied to the heated block 1 in the illustrated embodiment. The water jet 21 is hereby directed to a temperature change zone, which is offset from the central axis M of the block 1 on the end face of the Anlochseite 11 radially outward. Thus, those in the FIG. 1 indicated temperature zones 110 and 112 formed. The inner temperature zone 110 in this case has a higher temperature than those surrounding the outer temperature zone 112, which represents the temperature change zone.

The applied by the projection member 2 on the end face of the Anlochseite 11 coolant, especially water, is due to the rotation (RED) of the block 1 and the resulting centrifugal force in the illustrated in the figure as arrow sheets from the front side of the Anlochseite 11 transported away.

In the thus prepared block 1 can now on the Anlochseite 11 a tool that in the FIG. 6 is shown as a piercer 4 introduced. This piercer 4 is automatically centered due to the set temperature distribution and guided along the center axis M. In this embodiment results in a temperature distribution in which the temperature in the inner temperature zone 110 is higher than in the outer temperature zone 112. The temperature in the inner temperature zone 110 here corresponds substantially to the block temperature, to which the entire block before application of the method according to the invention was heated. The temperature in the outer temperature zone 112, that is, the temperature change zone, however, is reduced compared to this block temperature.

In the FIG. 2 embodiment shown differs only by the nature of the projection element 2 of the in FIG. 1 shown first embodiment. In the in FIG. 2 In the embodiment shown, oxygen is applied to the end face of the hole side 11 of the block by the projection element 2. In the illustrated embodiment, the projection element 2 is configured with an annular nozzle 20. In this embodiment, however, it is also possible, for example, to use a nozzle which is directed towards the center, that is to say the central axis M of the block 1. By the oxygen, a temperature increase is effected on the end face of the hole side 11 in the central region of the end face about the central axis M. This temperature increase is so great that the block material is melted in the region of the central axis M at the Anlochseite 11. By the rotation (RED) of the block 1 and the resulting centrifugal force, the molten block material in the in the FIG. 2 transported as arcs illustrated tracks from the front of the Anlochseite 11. This results in a recess 111, which is also referred to as cavern, in the Anlochseite 11 of the block 1. A holder 3 of the block 1 can also in the embodiment according to FIG. 2 according to the in FIG. 4 be shown embodiment provided. In addition to the formation of a depression 111, in this embodiment a temperature distribution will result where the temperature in the inner temperature zone 110, which in this case represents the temperature change zone, is higher than in the outer temperature zone 112. The temperature in the outer temperature zone 112 This corresponds essentially to the block temperature to which the entire block was heated before the application of the method according to the invention. The temperature in the inner temperature zone 110, that is, the temperature change zone, however, is increased compared to this block temperature.

In FIG. 3 a further embodiment of the device for carrying out an embodiment of the method according to the invention is shown. In this embodiment, a reflector 22 is disposed in front of the hole side 11 and the through hole side 12, respectively. The reflectors 22 are located at a distance from the End sides of the block 1 at the Anlochseite 11 and the through-hole side 12. The holder 3 of the block 1 is corresponding to the holder 3 in FIG. 4 executed. The reflectors 22 each have a concave curved shape. By this form of the reflectors 22, the heat radiation, which is discharged from the Anlochseite 11 and from the through-hole side 12, to the respective side 11, 12 is reflected back. In this case, the reflected radiation is concentrated in particular and preferably in the middle of the end face of the hole side 11 and the through-hole side 12. Thus, in this embodiment as well, a temperature distribution results wherein the temperature in the inner temperature zone 110 is higher than in the outer temperature zone 112. The temperature in the outer temperature zone 112 substantially corresponds to that block temperature to which the entire block prior to application the process of the invention has been heated. By contrast, the temperature in the inner temperature zone 110, which is the temperature change zone, is increased compared to this block temperature.

Combinations of the illustrated embodiments of the method are also possible. For example, a temperature increase in the inner temperature zone 110 and at the same time a decrease in temperature in the outer temperature zone 112 can be effected. In this case, both temperature zones 110, 112 form temperature change zones, but the temperature change in the two zones is different. In particular, in this case, the temperature change in one temperature change zone 110 is a temperature increase and the other temperature change zones 112 a decrease in temperature.

The principle underlying the invention of the method according to the invention is to project a graded and with respect to the central axis of the block rotationally symmetric temperature distribution at least on the end face of the block and thus to produce a corresponding flow stress distribution in the block - especially in the Anlochzone of the block. These temperature and Strength distribution in the block serves as quasi endogenous, centric and rotationally symmetrical guide ring, which guides the punch during the punching process centric with respect to the center axis of the block. The guidance takes place via a virtually invisible force effect over the defined strength distribution generated in the block. The temperature distribution and force effects in the block are in the FIGS. 6 to 9 shown schematically. In the FIG. 7 In this case, the force vectors acting on the piercer are schematically indicated, by which it is centered in the block. The arrows in FIG. 7 indicate the reaction force acting on the mandrel. In the FIG. 8 For example, two exemplary zonal radii R ', R "of the inner temperature zone 110 are schematically shown defining two boundaries of characteristic exemplary temperature zones on the face.

The radial course of the temperature gradient to be set can be designed differently here. In principle, it is naturally true that the guiding effect during the punching process will tend to be stronger the more the rotationally symmetric gradation of the temperature distribution is formed, that is, the larger the relevant temperature gradient in the radial direction with respect to the center axis of the block.

The central axis of the block, also called the main axis of the block or center axis of the block, is quasi the axis of symmetry in the middle zone of the block and is to be understood as a central axis without, for example, the pinched ends of the block which may arise during the manufacture of the block. Naturally, the geometry of a cylindrical block in reality is by no means ideally rotationally symmetric. For the effectiveness of the method according to the invention, this assumption of an ideal rotational symmetry of the geometry of the block, which is only approximately valid in reality, is sufficient. Strictly speaking in reality not perfect rotational symmetry of the block does not limit the effectiveness of the method according to the invention.

1. 1) Führen zu Beginn des Lochungsvorgangs mittels einer gradierten, definierten, rotationssymmetrischen Temperaturverteilung auf der Anlochseite, das heißt auf der vorderen Stirnfläche, des Blockes.
2. 2) Zentrisches Führen des Lochdorns am Ende des Lochungsvorgangs durch Erzeugen einer gradierten, definierten, rotationssymmetrischen Temperaturverteilung auf der Durchlochseite, das heißt auf der hinteren Stirnfläche, des Blockes.
3. 3) Zentrisches Führen des Lochdorns während des gesamten Lochungsvorgangs durch Erzeugen einer gradierten, definierten, rotationssymmetrischen Temperaturverteilung auf der gesamten Mantelfläche des Blockes.

By means of the temperature distribution which can be set according to the invention, the following effects can be achieved during the subsequent or simultaneous punching of the block:

1. 1) guide at the beginning of the punching process by means of a graded, defined, rotationally symmetrical temperature distribution on the Anlochseite, that is, on the front end face of the block.
2. 2) Centric guiding of the piercing mandrel at the end of the piercing process by generating a graded, defined, rotationally symmetric temperature distribution on the through-hole side, that is to say on the rear end face, of the block.
3. 3) Centric guiding the piercer during the entire punching process by generating a graded, defined, rotationally symmetric temperature distribution over the entire surface of the block.

To generate the desired, centering force on the piercer, that is, in the direction of the central axis of the block, the temperature distribution on the end face of the block and, accordingly, the distribution of the yield stress of the block material is adjusted such that the highest temperature and accordingly lowest yield stress within the block on the central axis. With a greater radial distance from the central axis, the temperature level of the temperature distribution to be set should decrease in accordance with the method according to the invention, and consequently the yield stress should in principle increase. The resulting around the central axis around the temperature zone with a higher temperature compared to the outer edge zone and consequently with a lower yield stress of the block material causes the block material to plastically deform around the piercer, so that as rotationally symmetrical material distribution and therefore possible low eccentricity of the perforated block and the most homogeneous wall thickness distribution results.

The basic mechanism here is based on the fact that the centering effect is achieved by the rotational symmetry of the graded, defined temperature distribution and consequently a corresponding strength distribution in the block to be punched. The mechanism or mode of operation is based on two significant properties, namely the rotational symmetry of the strength distribution in the block and the radial gradient on the strength distribution in the block.

In this case, the rotational symmetry of the distribution of strength in the block causes the restoring force to act in the right direction, that is to say in the radial direction, to the central axis of the block. The radial gradient of the strength distribution in the block causes the primary radially acting restoring force is sufficiently large and therefore the position correction is sufficiently fast.

In the case of a large radial gradient is achieved that even with a small deflection of the piercer, the resulting restoring force in the direction opposite to the deflection direction radially to the central axis of the block is comparatively large and thus effective. As a result, an effective and rapid correction of the position of the piercing pin is achieved.

The method according to the invention can be used both in skew rolling (as a rule with a non-driven, rotating punch mandrel, a punch mandrel rod and driven, rotating rollers) and in hole pressing (usually with purely translational movement of the driven punch mandrel).

$$D_{\mathrm{Zentrierzone}}=\mathrm{ca}\mathrm{.}1,0\mathrm{bis}3,0\times D_{\mathrm{Lochdornspitze}}$$

$$D_{\mathrm{Zentrierzone}}=\mathrm{ca}\mathrm{.}0,1\mathrm{bis}0,7\times D_{\mathrm{Block}}$$

The diameter of the high temperature temperature zone preferably becomes dependent on the diameter of the block and on the diameter of the block, the piercer or the piercer tip, for example as follows: $$D_{\mathrm{centering\; zone}}=\mathrm{ca}\mathrm{,}0.3\mathrm{to}1.2\times D_{\mathrm{piercer}}$$

$$D_{\mathrm{centering\; zone}}=\mathrm{ca}\mathrm{,}1.0\mathrm{to}3.0\times D_{\mathrm{Mandrel\; tip}}$$

$$D_{\mathrm{centering\; zone}}=\mathrm{ca}\mathrm{,}0.1\mathrm{to}0.7\times D_{\mathrm{block}}$$

With regard to the geometric properties of the block, the following should be considered. As a rule, the blocks are separated from the billet, for example by means of the separation methods warm shears or saws. As a result, depending on the separation method used, the end face of the block is generally not ideally circular, but deviates more or less slightly from the ideal circular shape.

In addition to the shape of the end face, the position of the end face is of importance, in particular in the case of a squeezing of the end face. For example, the center of the block end face - both an ideal circular and a non-ideal circular end face - lie outside the central axis of the block, that is to be offset laterally in the radial direction. For the centering of the temperature distribution to be generated is used - due to the usually not exactly circular face geometry - in the inventive method preferably the central axis of the block significantly as a reference and not the end face of the block.

• Mittels einer Rotation des Blockes, erzeugt beispielsweise über eine Antriebsrolle und eine Lagerung zur freien Rotation (siehe Figur 4).

The determination of the central axis for the centering of the block can in principle be carried out in various ways, for example optically, mechanically, with the aid of other physical effects or combinations of effects. In the method according to the invention, the centering should preferably be carried out in the following way:

• By means of a rotation of the block, generated for example via a drive roller and a bearing for free rotation (see FIG. 4 ).

In order to achieve centering, a sufficiently precise positioning of the preferably used projection element according to the invention, for example a nozzle or a reflector, relative to the block is decisive here. For this purpose, the approach to select the previously determined position of the central axis of the block as a target position for the alignment of the projection element according to the invention, makes sense. The exact position of the central axis of the block can be determined here as the center of the axes of rotation of the drive and guide rollers (see FIG. 4 ). This hereby known position of the central axis of the block then serves as input for the control or regulation for positioning the projection element according to the invention. Such a control or regulation can take place, for example, via an electronically assisted mechanical coupling of the centering elements (that is to say those drive and guide rollers) with the projection element or reflector according to the invention.

The rotational speed of the block during the centering process according to the method of the invention, for example, a speed in the interval n = 200 to 800 min ^-1 = about 3.3 to 13.3 s ^-1 are used. At such speeds, the removal of the coolant, for example, cooling water, or the molten material particles of the block can be done reliably and reliably.

The duration for the projecting process (cooling and / or heating, for example spraying with water) may be, for example, in the interval from t = 5 to 15 s.

As pressure (water pressure) for the projecting process (cooling, for example spraying with water), ie water pressure, for example, a pressure in the interval of p = about 6 to 200 bar is used.

The size of the nozzle opening (cross-sectional area, optionally circular cross-section with diameter), for example, a diameter of D = 1 to 5 mm is used.

The speed of the water during the projection process (cooling) results from the previously mentioned variables.

Naturally, the temperature field changes - even in the absence of external influence - as a result of heat conduction and heat radiation, and consequently the temperature level in the entire block decreases as the process time progresses. In order to ensure that the generated temperature field is maintained sufficiently until the block is pinned, care must be taken that the time between the end of the projecting operation and the start of the punching process does not exceed a critical limit.

For example, the time between the end of the projecting operation and the beginning of the pinning operation is t <about 20 s.

By way of example, the length of the temperature change zone in the direction of the central axis of the block in the region of its end face onto which the temperature field is to be projected
z _{temperature field} = 0 to 100 mm can be used.

In order to avoid a weakening of the temperature distribution, if descaling of the block takes place after removal of the block from the furnace, the generation of the temperature distribution ("projection") after descaling must take place.

The underlying physical processes are very complex. As an approximation, the appropriate parameters of the process (eg time duration, time points, temperature profile) can be calculated by theoretical considerations and calculated by means of numerical simulation (finite element method).

For an approximate calculation, the necessary physical quantities can be assumed here, for example, some material constants of the steel block.

• Wärmeleitung
• Wärmestrahlung

Basically in the calculation to be considered physical effects are:

• heat conduction
• thermal radiation

mit den physikalischen Größen Wärmeleitfähigkeit λ, Dichte p, spezifische Wärmekapazität c _p. Die Temperaturleitfähigkeit a hat die Einheit m²/s. Anhand der Temperaturleitfähigkeit kann überschlägig die Geschwindigkeit ermittelt werden, mit der sich eine Temperaturfront innerhalb des Objektes bewegt. Die Temperaturleitfähigkeit von Stahl beträgt ungefähr a (Stahl) = 12 bis 15 x 10^-6 m²/s.The thermal conductivity (symbol " a ") is defined as follows: $$a=\frac{\lambda }{\rho \cdot c_p}$$

with the physical quantities thermal conductivity λ, density p, specific heat capacity c _p . The thermal diffusivity a has the unit m ² / s. On the basis of the thermal conductivity, the speed at which a temperature front moves within the object can be roughly determined. The thermal diffusivity of steel is approximately a (steel) = 12 to 15 x 10 ^-6 m ² / s.

Based on the mathematical differential equations for the propagation of the temperature due to pure heat conduction in a solid (distinction between a cylindrical rod with infinitesimal small diameter and infinite length or a cylinder with finite diameter D and a finite length L) and for the change in temperature due Thermal radiation can be used to estimate the temperature change over time.

The parameters of the projecting process according to the method according to the invention have to be suitably adapted and optimized for the respective application with the respectively present boundary conditions of the production process chain.

Alternatively, or in addition to the described cooling a temperature change zone of the block, which schematically in FIG. 1 is shown, according to the invention also a so-called thermal centering can be used by heating the block and generating a centering guiding action in the block. Here, different variants (for example, as in FIG. 2 and FIG. 3 shown) of the method are used. For example, heating may be accomplished by initiating an exothermic reaction of oxygen and the metallic block material. This can be done, for example, with the in FIG. 2 be performed device shown. Alternatively, the thermal radiation of the block may be used by using a reflector to heat a portion of the block, and in particular a temperature change zone of the face of the block. This can be done, for example, with the in FIG. 3 be performed device shown.

In the first process variant, where heating is initiated by initiating an exothermic reaction of oxygen and the metal block material to effect a temperature change, the fact is utilized that iron burns in an oxygen atmosphere. The ignition temperature of steel is around 1200 ° C. The exact value of the ignition temperature of steel depends on the content of carbon and the content of other alloying or accompanying elements.

The exothermic reaction starts at the material-specific ignition temperature, which is significantly below 1200 ° C for iron. For this reason, it is possible to use the amount of heat present in the block due to the temperature level present above 1200 ° C in the block in order to realize this reaction continuously during a certain period of time. This resulting heat is transferred to the zone in the immediate vicinity of the central axis of the block. This will increase the temperature in this zone. The temperature increase in this case is so great that from the block material quantities melted by metal and oxides and centrifuged by the centrifugal forces, which act through the rotation of the block, according to the inventive method in particular radially outward. In this case, liquid metal is flushed out of the block together with oxides or ejected. The amount of heat in the remaining block is reduced only slightly and remains sufficiently high for the continuation of the course of the ongoing ignition process in the remaining block material.

Thus, with a correspondingly great heating of the relevant end face zone of the block, a cavernous cavity open to the front side, which can also be referred to as a depression, arises with an approximately rotationally paraboloidal geometry. This cavern causes a centric guide on the central axis of the block during the phase of Anlochvorgangs. This reduces lateral deflection of the piercer during the piercing process and limits lateral deflection to a very small extent.

For this purpose, for example, by means of a nozzle, which is arranged in front of the end face of the block, blasted oxygen on the end face. At a higher temperature of the block than 1200 ° C, there is a chemical reaction (here: chemical ignition) of the iron with the oxygen. Consequently, the iron melts from the hole side of the block near the center axis of the block. Due to the relatively fast, forced rotation of the block, the liquid iron is flushed out, leaving a cavernous cavity open to the face of the block with an approximately rotational paraboloidal geometry and a temperature higher than that due to the exothermic reaction Temperature previously on the face of the block.

As a time for this heating process, a period of, for example, t = 2 to 20 s can be used.

As an alternative to the previously described exothermic reaction by means of oxygen supply, a reflector (for example made of copper or aluminum, coated and water-cooled) can be used as a projection element for reflection of electromagnetic radiation ( FIG. 3 ). Such a reflector can be arranged in front of each of the two end faces of the block. The distance of the reflector from the end face is to be interpreted according to the wavelength of the electromagnetic radiation. In the FIG. 3 give z ₁ and z _{2 in} this case the axial distance of the reflectors to the end faces of the block. For a clear description of the position of the reflectors in three-dimensional space, for example, two angles (Θ ₁ , Φ ₁ ) for the reflector 1 and two angles (Θ ₂ , Φ ₂ ) for the reflector 2 can be used. The angle pairs (Θ ₁ , Φ ₁ ) and (Θ ₂ , Φ ₂ ) indicate the two angles of inclination of the axis of the reflector 1 and the reflector 2 relative to the two respective spatial axes of a Cartesian coordinate system.

The basic requirement for this effect when using such a reflector is the electromagnetic radiation that is emitted due to the high temperature ( T > 1000 ° C) from the face of the block. The operating principle of the reflector is that the reflector reflects the electromagnetic radiation radiated from the end face of the block back to this end face and consequently influences the temperature distribution on this end face.

As a result, the face of the block heats up, at those points of the face to which the reflector is aligned. Naturally, the heat - in accordance with the physical mechanisms of heat conduction and heat radiation - will continue to spread in the block and in the ambient air, and the temperature distribution will continue to change more or less negligibly. It should be noted here that a precise prediction of the temperature distribution in the block over time for the mechanism of action of the idea according to the invention is not immediately required.

With regard to the amount of the reflected electromagnetic radiation, the reflector can in this case be designed so that - with a correspondingly large amount of reflected radiation - a significant heating of the block end surface results, or - with a correspondingly small amount of reflected radiation - a slower cooling of the block end surface results.

About the contour of the reflector and the distance of the reflector from the end face of the block, a graded, defined distribution of the amount of radiation can be set or achieved. By choosing a different or changed geometric contour of the reflector, a different optical reflection effect is achieved. Depending on the desired reflection effect (ie strength of the heating of the resulting temperature distribution primarily in the face zone of the block), a suitable contour (geometry) of the reflector is to be designed and used.

This effect results in particular even without supply of oxygen and consequently without an exothermic reaction. Consequently, there is basically no formation of a cavity open on one side (cavern).

Due to the strong temperature dependence of the heat flow ∂Q / ∂t (heat radiation), which is described by the Stefan Boltzmann law, at a block temperature above 1000 ° C, the heat flow or the electromagnetic radiation (in particular the infrared radiation) is very large and increases strongly with increasing temperature. Accordingly, at such high temperatures ( T > 1000 ° C), the temperature increase in the block relative to the room temperature significantly and thus affects the temperature distribution in the block significantly. In this way, a temperature increase (in a defined, desired manner in the sense of the inventive idea) in the center zone of the end face of the block can be achieved.

(Stefan-Boltzmann-Gesetz) mit den physikalischen Größen:

• Wärmestrom (Strahlungsleistung) $\frac{\partial Q}{\partial t}$
  
  (Einheit: Joule pro Sekunde)
• Emissionsgrad ε (Werte zwischen ε = 0 für einen "perfekten Spiegel" und ε = 1 für ein "ideal schwarzes Objekt"),
• Stefan-Boltzmann-Konstante $\sigma =5,67\cdot {10}^{-8}\frac{W}{m^2{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="imgf0005.png"\; state="\{\{state\}\}">K</figure-callout>}}^4},$
  
• Oberfläche des abstrahlenden Körpers A und
• Temperatur des abstrahlenden Körpers T (in der Einheit Kelvin).

Heat flow: $$\dot{Q}=\frac{\partial Q}{\partial t}={\mathit{\epsilon \sigma AT}}^4$$

(Stefan Boltzmann law) with the physical quantities:

• Heat flow (radiant power) $\frac{\partial Q}{\partial t}$
  
  (Unit: joules per second)
• Emissivity ε (values between ε = 0 for a "perfect mirror" and ε = 1 for an "ideal black object"),
• Stefan-Boltzmann constant $\sigma =5.67\cdot {10}^{-\mathrm{8th}}\frac{W}{m^2{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="imgf0005.png"\; state="\{\{state\}\}">K</figure-callout>}}^4}.$
  
• Surface of the radiating body A and
• Temperature of the radiating body T (in the unit Kelvin).

As in FIG. 3 sketched, the reflectors are individually or jointly adjustable (that is, controllable) and optionally be controlled during the process. This adjustability with the necessary kinematic, geometric degrees of freedom (for example, the distance of the reflector from the end face of the block, respective inclination angle of the reflector axis relative to the respective spatial axes, for example to two orthogonal coordinate axes, see FIG. 3 ) can be realized by a defined positioning and storage. This possibility for defined adjustable positioning over the location and the orientation of the respective reflector allows - in combination with the contour geometry of the reflector to be selected - a defined setting of the reflectors and thus achieving a defined effect of the radiation reflection and consequently the achievement of a defined heat and Temperature distribution in the block face and in the adjacent interior of the block.

The lower the heating of the relevant end face zone of the block, the less pronounced is an optionally resulting cavernous cavity open towards the end face. With sufficiently small heating, the resulting cavity will only be negligibly small.

In FIG. 5 For example, a typical principal course of relative eccentricity along a prior art punched block is shown in simplified form. This course is the result of the statistical evaluation of a large number of rolling performed. The Y-axis indicates the eccentricity of the perforated block and the X-axis the axial coordinate in the hollow block. L here denotes the length of the hollow block.

For blocks that do not consist of low-alloyed or unalloyed steels, melting (ignition, exothermic reaction) by means of an oxygen jet is not possible or not readily possible. For this reason, a part of the method according to the invention - namely that part which involves the heating of the temperature change zone around the central axis of the block by means of oxygen jet - limited to the range of applications for blocks of low-alloy or non-alloyed steels.

The other part of the process according to the invention, which involves cooling the outer temperature-change zone of the end face of the block, however, has blocks of any metals as a possible application spectrum.

For low alloyed and / or unalloyed steels, the centering effect can be achieved by combining both projection methods, ie by cooling the block zone (primarily on the face of the block) ( FIG. 1 ) outside the central axis of the block and heating ("thermal centering" by heating) the block zone in the zone near the central axis, in particular on the end face of the block ( FIGS. 2, 3 ).

In order to avoid that the temperature is lowered too much and this would be detrimental in the subsequent rolling process after punching, the local Temperaturprojizierung (ie local cooling and / or local heating on the end face of the block to be punched) in a suitable process window to realize.

LIST OF REFERENCE NUMBERS

1

block

10

hollow block

100

perforation

11

Anlochseite

110

inner temperature zone

111

deepening

112

outer temperature zone

12

Through hole side

13

Anlochzone

2

projection element

20

jet

21

Ray of the medium

22

reflector

3

bracket

30

roll

300

capstan

301

leadership

4

piercer

M

Central axis (block / hollow block)

MR

Central axis (roll)

RED

Rotation direction (block)

r

Radius (variable)

R

Radius (block)

R '

Zone radius (temperature field)

R "

Zone radius (temperature field)

Claims (19)

1. Method for producing a hollow metallic billet (10) from a heated metallic billet (1) by a piercing operation, characterized in that at least at the hole initiation end (11) of the billet (1) in at least one temperature change zone (110, 112) a local temperature change is effected and the temperature change zone is rotationally symmetrical to the central axis (M) of the billet (1).
2. The method as in claim 1, characterized in that the temperature change is effected in a temperature change zone (112) that is spaced apart radially from the central axis (M) of the billet (1).
3. The method as in one of claims 1 and 2, characterized in that the temperature change is a decrease in temperature.
4. The method as in one of claims 1 to 3, characterized in that the temperature change zone (110) in which the local temperature change is effected encompasses the central axis (M) of the billet (1) and the temperature change is an increase in temperature.
5. The method as in one of claims 1 to 4, characterized in that the local temperature change occurs as a result of action on a portion of one of the end faces of the billet (1).
6. The method as in one of claims 1 to 5, characterized in that the local temperature change occurs as a result of action on a portion of one of the end faces of the billet (1) and a segment of the length of the circumferential surface of the billet (1), adjacent to said end face, with the length of the segment of the circumferential surface being less than the length of the billet (1).
7. The method as in one of claims 1 to 6, characterized in that the temperature change zone (110, 112) in which a temperature change is effected extends over no more than 1/3, particularly no more than 1/4, of the length of the billet (1).
8. The method as in one of claims 1 to 7, characterized in that the billet (1) is a round billet.
9. The method as in one of claims 1 to 8, characterized in that the billet (1) is rotated about the central axis (M) at least before the effectuation and/or during the effectuation of the local temperature change.
10. The method as in one of claims 1 to 9, characterized in that the temperature change is effected by projecting at least one jet (21) onto one of the end sides of the billet (1), and a projection element (2) that is spaced apart from the billet (1) is preferably used for said projection.
11. The method as in one of claims 1 to 10, characterized in that least at one water jet is directed at the end side of the billet (1).
12. The method as in one of claims 1 to 11, characterized in that least at one jet (21), particularly an oxygen jet, is directed at the end side of the billet (1) to generate an exothermic reaction at the end face or in the billet (1).
13. The method as in one of claims 1 to 12, characterized in that least at one electromagnetic beam (21) is directed at the end side of the billet (1) and is reflected from the end side by at least one reflector (22).
14. The method as in one of claims 1 to 13, characterized in that a temperature change is also effected at the hole exit end (12) of the billet (1), which is the opposite end from the hole initiation end (11).
15. A device for producing a hollow metallic billet (10) from a metallic billet (1) and comprising a piercing mandrel and a holder (3) for the billet (1), characterized in that said device includes at least one projection element (2) operative to change at least zonewise the temperature of the billet (1) in the holder (3) which is at least directed at a partial zone of at least one of the end sides of the billet (1).
16. The device as in claim 15, characterized in that the projection element (2) is aligned with the central axis (M) of the billet (1) in the holder (3).
17. The device as in one of claims 15 to 16, characterized in that the projection element (2) includes at least one nozzle (20) or at least one reflector (22).
18. The device as in one of claims 15 to 17, characterized in that the projection element (2) is disposed at the hole initiation end (11) and/or at the hole exit end (12) of the billet (1).
19. The device as in one of claims 15 to 18, characterized in that it is designed to carry out the method as in one of claims 1 to 14.

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