EP2991780B1 - Piercing mandrel having an improved service life for producing seamless tubes - Google Patents

Description

The invention relates to a piercer for punching heated round blocks made of metal for the production of seamless tubes, comprising a piercing lug nose and a perforated mandrel body, which is connectable to a mandrel.

It is well known that seamless tubes are made by a process in which cylindrically shaped and heated in a rotary hearth furnace starting material, so-called round blocks, is formed in a cross-rolling mill using an axially fixed internal tool consisting of piercer and mandrel to a tubular hollow block.

To form a seamless hollow block tube, the block, after being picked up by the cross rolling mill, is transported helically through the cross rolling mill and thus over the axially stationary inner tool and, in the course of the process, is drawn to form a seamless tube. The hole is created by driving the round block through the inclined rollers and pressing it over a piercer. The perforated mandrel itself usually has a diameter increasing steadily from the tip.

The usually consisting of a high-temperature tool steel piercer has in addition to the actual punching the task of any material tears to re-weld, to smooth the inner surface of the resulting hollow block and to bring its wall thickness as uniform as possible to the desired level.

Since the piercer has to do its work under the influence of rolling heat, it is stressed to the utmost and has only a limited life. Since the invention of the cross rolling process, efforts have been made to extend the life of the mandrels in order to save costs and improve the quality of the rolled tubes. If the service life of the piercer, also called rolling mandrel, approaches its end, the piercer can lose its shape and receive a damaged surface or material welds. This also means a deterioration of the tube quality, in particular by errors on the inner surface of the hollow block and a non-uniform wall thickness.

Particularly problematic in this case are difficult to form tube materials, such as chromium-containing materials, with more than 5 wt.% Chromium, the thermic and mechanical stress particularly the mandrel and in particular the mandrel tip so that it has wear traces already after a few holes, which quickly leads to defective changes in geometry of the dome and thus lead to internal errors and geometry deviations on the hollow block.

Over time, many measures have been proposed to reduce heat input into the mandrel and increase tool life. Examples include the execution of the piercer tips made of particularly heat-resistant materials such. As technical ceramics, the coating of the piercer surface with filler metals, a controlled oxidation of the surface, frequent replacement of the mandrels in conjunction with Wasserspritz- or immersion cooling, and internal cooling of the piercers with water through the mandrel through. An overview of the state of the art give the Japanese disclosure JP 03204106 A , the German patent DE 196 36 321 C1 and the European patent application EP 2 404 680 A1 ,

In order to improve the service life of the piercer and to avoid internal defects on the hollow block, has been according to the European published patent application EP 2 404 680 A1 trying to achieve an improved geometry of the piercer tip in conjunction with an iron oxide coating improved lifetime of the piercer. At the same time, it is proposed to avoid friction-induced surface defects on the perforated mandrel by spraying a cooling lubricant through the mandrel tip into the resulting hollow block. For this purpose, the cooling lubricant is passed through the main body of the piercer over obliquely extending into the piercer tip outlet openings in the hollow block. For this purpose, the piercer tip consists of a cylindrical portion and a hemispherical tip, wherein the outlet openings are arranged in the transition region between the cylindrical portion and piercer main body. A disadvantage is the still insufficient cooling of the piercer tip itself and the oblique position of the outlet openings for the coolant at the piercer tip, on the one hand consuming to produce, on the other hand, a closure during the piercing process by contacting with the material of the round block not yet reliably prevented. Another disadvantage is the one-piece design of the piercer, which requires a replacement of the complete piercer when worn.

In order to reduce the costs for the exchange of worn thorns, was further in the German patent application DE 100 24 246 A1 proposed to form the piercer two-part with a lug nose and a perforated mandrel body connectable thereto and to increase the service life, according to the thermal and mechanical stresses, mandrel nose and body made of different materials and replace only the piercer tip if necessary. The disadvantage here is that the mandrel tip is uncooled and the life is still insufficient, especially in difficult to deform materials.

Also is from the European patent specification EP 1 961 497 B1 another piercer of a piercing mill known. This piercer shows a piercer nose on a piercer body. The piercer nose widens conically in the direction of the perforated mandrel main body.

Furthermore, from the patent US 1 374 369 A a piercer with a piercer main body and a spherical piercer nose known. In the patent US 2 261 937 A a two-part piercer nose is shown, which has a hexagonal screw head-shaped tip and a conically widening in the direction of a piercer main body cap. In the patent US 2 197 098 A is a piercing mandrel with a perforated mandrel main body and with a widening in the direction of the piercer main body punch nose shown in different versions. At a end facing a mandrel rod, the perforated mandrel main body tapers.

All of these measures were not yet suitable to effectively reduce the thermal and mechanical stress of the piercing mandrels during oblique rolling so that, from an economic and qualitative point of view, sufficiently long service lives could be achieved, in particular in the case of difficultly deformable materials.

The invention is based on the object, the service life of the piercer when punching round blocks of metal, in particular of higher alloyed, difficult to deform Steel materials, by means of oblique rolling, taking into account a qualitative improvement of the inner surface of the perforated round block and to reduce tooling costs to increase.

This object is achieved by a piercer, comprising a piercer nose and a perforated mandrel body, which is connectable to a mandrel, which is characterized in that the piercer nose is formed conically tapering in the longitudinal extent to the piercing mandrel main body in the outer diameter. Surprisingly, it has been found in experiments that a significant increase in the service life of the piercing mandrel could be achieved by simultaneously improving the inner surface of the hollow block by the conical geometry of the mandrel nose or the nose cap.

In this case, it is particularly advantageous that the perforated-mandrel nose is formed from a nose core connected to the perforated-mandrel main body and a nose-cap connected over and detachably connected to the nose-core. Due to the detachable connection of nose cap and nose core a simple and cost-effective replacement is realized in case of wear, because not the complete piercer or the lug nose with the consuming introduced Kühlmittelzufluss- and drain lines but only the most affected by wear, easy to produce nose cap must be replaced ,

It is of particular constructive advantage that the mandrel nose for cooling the mandrel nose or the nose core for cooling the nose cap and for lubricating the piercer to a leading through the perforated mandrel main body to the mandrel nose or the nose core supply line for cooling lubricant and at least one through the mandrel nose or the nose core the coolant is connected back again leading drain line and arranged at the end of the drain line in the transition region of piercer nose and piercer main body an outlet for the cooling lubricant from the piercer. In combination with the inverted conical geometry of the mandrel nose or the nose cap, a significant increase in service life of the piercing mandrel can be achieved while improving the inner surface of the hollow block, as clogging of exactly in This area arranged outlet opening and thus a reduced or even completely interrupted cooling is effectively avoided.

Of particular importance for the increase in service life of the perforated mandrel or the mandrel nose, especially when punching steels difficult to deform with more than 5.0 wt.% Chromium, has the special geometric design of the mandrel nose or the nose cap, wherein the diameter tapers conically towards the mandrel main body , Conversely, is conical. Since the diameter of the mandrel base body increases starting from the nose-side end, in the transition region of the mandrel nose or the nose cap and mandrel main body, a "gusset" significantly enlarged in comparison to known piercer spines, in which the outlet opening for the cooling lubricant is preferably arranged radially.

During the hole is thereby ensured that the outlet opening for the cooling lubricant can not come into contact with the material of the round block to be punched, so that clogging of precisely arranged in this area outlet opening and thus a reduced or even completely interrupted cooling is effectively avoided ,

In experiments it has also been found that by this inversely conical geometry of the mandrel nose or the nose cap and the preferably radial arrangement of the outlet opening in the gusset of the transition region of mandrel nose and mandrel body closure of the outlet opening is effectively avoided, so that sufficient cooling and lubrication of the piercing pin and especially the most stressed nose cap is always guaranteed.

In order to reliably realize this effect, the following conditions should be met for the geometry of the mandrel nose or the nose cap: The length L of the mandrel nose or the nose cap is determined depending on the block diameter DB to be rolled and the nose diameter DN at the nose-side end of the mandrel nose or the nose cap, such that the condition 0.10 × DB ≦ L ≦ 3 × DN is satisfied.

Compliance with this condition is necessary in order to have a minimum volume and a minimum cross section for the mandrel nose or the nose cap available, since the cooling of the cap according to the invention can not completely prevent a warming of this.

The radius at the nose-side end of the mandrel nose or the nose cap should advantageously have a value of r ≥3.0 mm in order to avoid load peaks at this transition and thus premature wear.

The necessary for the reverse conical design of the lug nose or the nose cap angle α should be between 2 ° and 10 ° to form a sufficiently large gusset and thus to achieve the effect of increasing the service life of the piercing pin according to the invention.

A radial arrangement of the outlet opening in the transition region of mandrel nose and mandrel main body is advantageous because their production can be much easier compared to known, oblique bores introduced. Advantageously, the outlet opening is formed as an annular gap to ensure a uniform lubrication over the circumference of the piercing pin.

In order to ensure a sufficiently large flow of cooling lubricant through the nose core to the inside of the nose cap, a sufficiently large axial distance between the front end of the nose core and the inside of the nose cap is provided. The inflow line of the cooling lubricant preferably extends centrally through the piercer to the front end of the nose core. The preferably several outflow lines through the nose core lead up to the outlet opening from the piercer in the transition region of mandrel nose and mandrel body and are preferably arranged radially around the inflow line. Depending on the diameter of the nose core and the required flow rate of cooling lubricant, for example, four, six or eight drain lines may be arranged in the nose core.

In a further improved embodiment of the invention it is provided that the nose core is detachably connected to the mandrel main body, so that if necessary, only the mandrel body needs to be replaced and not in addition the nose core, with channels for cooling lubricant inflow and outflow.

The connection of nose core and mandrel body can be made according to the invention either by means of a screw or for easier mounting and dismounting, advantageously by means of a bayonet closure.

To further increase the service life of the piercing mandrel is provided in an advantageous embodiment of the invention, either only the mandrel nose or the entire piercer with a heat input into the mandrel-reducing coating, e.g. an iron oxide coating. Alternatively or additionally, lug nose and body can also consist of different materials, which take into account the different stresses during punching.

• Figur 1 eine schematische Darstellung des Lochungsprozesses in einem Kegelschrägwalzwerk mit einem erfindungsgemäßen Lochdorn,
• Figur 2 den erfindungsgemäßer Lochdorn in vergrößerter schematischer Darstellung und
• Figur 3 Schnittdarstellungen einer Lochdornnase.

Further features, advantages and details of the invention will become apparent from the following description of the embodiments shown in the appendix. Show it:

• FIG. 1 a schematic representation of the Lochungsprozesses in a cone slanting mill with a piercer according to the invention,
• FIG. 2 the inventive piercer in an enlarged schematic representation and
• FIG. 3 Sectional views of a piercer nose.

In FIG. 1 schematically a cone slanting mill is shown, which transforms a solid block of steel by means of a piercing mandrel according to the invention to form a hollow block pipe.

The cone slanting mill 1 consists of two work rolls 2, 2 ', which transform the solid block 3 into a hollow block pipe 6 via an internal tool consisting of a piercer 4 according to the invention and a mandrel bar 5. In reverse direction of the work rolls 2, 2 'of the block 3 and the hollow block tube 6 is moved helically over the axially fixed inner tool.

According to the invention, the perforated mandrel 4 consists of a perforated mandrel main body 4.1 to which a mandrel nose 4.2 is connected. The diameter of the perforated mandrel main body 4.1 increases continuously starting from the nose-side end up to a maximum value which determines the inner diameter of the hollow block tube 6. According to the invention, the mandrel nose 4.2 has a conically tapering diameter to the perforated mandrel main body 4.1, with a gusset 7 forming in the transition region between mandrel main body 4.1 and piercer nose 4.2 to the resulting hollow block tube 6, which does not come into contact with the material of the hollow block tube 6 during piercing.

Not shown here is exactly in this gusset or in the transition region arranged outlet opening for the cooling lubricant and the cooling of the piercing pin.

FIG. 2 shows geometric details of the piercer 4 according to the invention in an enlarged schematic representation.

The mandrel nose 4.2 is conically tapered towards the piercer main body 4.1, wherein an angle α between 2 ° and 10 ° is maintained. The angle α is enclosed between the outer surface of the piercer nose 4.2 and an imaginary straight line which runs parallel to a longitudinal axis of the piercer 4 and the outer surface of the piercer nose 4.2 is tangent in the region of its largest diameter DN. The piercer nose 4.2 has a length L which depends on the diameter of the block 3 to be punched (DB) and the largest diameter of the mandrel nose 4.2 (DN), the condition 0.10 x DB ≦ L ≦ 3 x DN being maintained , Furthermore, the mandrel nose 4.2 at the front end has a radius r, which is at least 3 mm.

FIG. 3 shows schematically the formation of the piercer nose 4.2 in a longitudinal section (left part of the picture) and in a cross section (right part of the picture). In this example, perforated mandrel body 4.1 and mandrel nose 4.2 are shown in a one-piece, so not releasable design because of the simpler presentation. The following description can be analogously transferred to a detachable version.

It can be seen in the left-hand part of the drawing that the piercer nose 4.2 according to the invention consists of a nose core 4.2a and a nose cap 4.2b mounted thereon. To realize a sufficiently large flow of cooling lubricant through the piercer nose 4.2, an axial distance "x" between the front end of the nose core 4.2a and the inside of the nose cap 4.2b is provided. In order to maintain the necessary axial distance during the piercing operation, the connection is designed as a conical seat 10, wherein the nose cap 4.2b and nose core 4.2a are clamped to one another via the axial pressure exerted on the nose cap 4.2b during punching.

The inflow line of the cooling lubricant 8 to the nose cap 4.2b extends centrally through the piercer 4 to the front end of the nose core 4.2a. Evident are also through the nose core 4.2a passing drain lines 9, which extend up to the annular gap formed as the outlet opening 11 in the transition region of piercer nose 4.2 and mandrel body 4.1.

In the right part of the picture FIG. 3 shown cross-section through the mandrel nose 4.2 are four radially around the supply line 8 circularly arranged drain lines 9 can be seen.

LIST OF REFERENCE NUMBERS

1

Cone piercing mill

2, 2 '

strippers

3

solid block

4

piercer

4.1

Piercer body

4.2

Piercer nose

4.2a

nose core

4.2b

nose cap

5

mandrel

6

Hollow block tube

7

gore

8th

Inlet line for cooling lubricant

9

Drain pipe for cooling lubricant

10

conical seat

11

outlet opening

DB

Diameter block

DN

Diameter nose

L

Length of the piercer nose

r

Radius nose cap

α

angle

Claims (16)

1. Piercing mandrel (4) for piercing heated round blocks (3) of metal for the production of seamless pipes (6), having a piercing mandrel nose (4.2) and a piercing mandrel main body (4.1) which can be connected to a mandrel bar (5), characterised in that the outer diameter of the piercing mandrel nose (4.2) is formed in a conically tapering manner in the longitudinal extension towards the piercing mandrel main body (4.1).
2. Piercing mandrel as claimed in claim 1, characterised in that the piercing mandrel nose (4.2) is formed from a nose core (4.2a), which is connected to the piercing mandrel main body (4.1), and from a nose cap (4.2b) which is placed thereover and is detachably connected to the nose core (4.2a).
3. Piercing mandrel as claimed in claim 2, characterised in that the piercing mandrel nose (4.2) for cooling the piercing mandrel nose (4.2) or the nose core (4.2a) for cooling the nose cap (4.2b) and for lubricating the piercing mandrel (4) is connected to a supply line (8) for cooling lubricant, which passes through the piercing mandrel main body (4.1) as far as through the piercing mandrel nose (4.2) or the nose core (4.2a), and is connected to at least one discharge line (9), which then guides the cooling lubricant back through the piercing mandrel nose (4.2) or the nose core (4.2a), and at the end of the discharge line (9) in the transition region of the piercing mandrel nose (4.2) and piercing mandrel main body (4.1) there is disposed an outlet opening (11) to let the cooling lubricant issue out of the piercing mandrel (4).
4. Piercing mandrel as claimed in claim 3, characterised in that the outlet opening (11) for the cooling lubricant extends in a radial direction with respect to the longitudinal axis of the piercing mandrel (4).
5. Piercing mandrel as claimed in claim 3 or 4, characterised in that the outlet opening (11) is formed as an annular gap between the piercing mandrel nose (4.2) and the piercing mandrel main body (4.1).
6. Piercing mandrel as claimed in any one of claims 3 to 5, characterised in that the supply line (8) of the cooling lubricant extends centrally through the piercing mandrel (4) as far as the face-side end of the nose core (4.2a).
7. Piercing mandrel as claimed in claims 1 to 6, characterised in that the length L of the piercing mandrel nose (4.2) satisfies the requirement 0.10 x DB ≤ L ≤ 3 x DN, wherein DB is the diameter of the round block (3) to be pierced and DN is the diameter of the front end of the piercing mandrel nose (4.2).
8. Piercing mandrel as claimed in any one of claims 1 to 7, characterised in that the radius at the front end of the piercing mandrel nose (4.2) is at least 3 mm.
9. Piercing mandrel as claimed in any one of claims 1 to 8, characterised in that the angle α of the conical tapering of the piercing mandrel nose (4.2) satisfies the requirement 2° ≤ α ≤ 10°.
10. Piercing mandrel as claimed in any one of claims 2 to 9, characterised in that the nose core (4.2a) and the nose cap (4.2b) are connected via a cone seat which itself becomes jammed under axial pressure.
11. Piercing mandrel as claimed in any one of claims 1 to 10, characterised in that the piercing mandrel nose (4.2) and the piercing mandrel main body (4.1) are detachably connected together.
12. Piercing mandrel as claimed in any one of claims 1 to 11, characterised in that the piercing mandrel nose (4.2) and the piercing mandrel main body (4.1) are connected together by means of a screw-connection.
13. Piercing mandrel as claimed in any one of claims 1 to 12, characterised in that the piercing mandrel nose (4.2) and the piercing mandrel main body (4.1) are connected together by means of a bayonet fitting.
14. Piercing mandrel as claimed in any one of claims 1 to 13, characterised in that the piercing mandrel nose (4.2) and the piercing mandrel main body (4.1) consist of different metallic materials.
15. Piercing mandrel as claimed in any one of claims 1 to 14, characterised in that the piercing mandrel nose (4.2) and/or the piercing mandrel main body (4.1) are provided with a coating which reduces heat introduction into the piercing mandrel (4).
16. Piercing mandrel as claimed in claim 15, characterised in that the coating is a iron oxide coating.

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