EP1857193B1 - Method for hot rolling seamless pipes on an inner tool and inner tool - Google Patents

Abstract

The mandrel (5) outer circumference includes tool segments (8) of highly wear-resistant material. Between them, tool inserts (10) intervene, without gaps. The tool segments are pre-stressed axially and tangentially. They are held down radially. Cooling-, lubricating- and parting fluid is led directly into the contact region between the mandrel and the workpiece (3), via a central longitudinal bore (6) of the mandrel and radial feed bores (15). A bush (11) sets up axial pre-stressing of the segments and inserts, through its wedge-shaped contact surfaces (14). The segments are ceramic, especially a cermet. An independent claim IS INCLUDED FOR the mandrel employed.

Description

The invention relates to a method for hot rolling seamless tubes with one or more consecutively arranged longitudinal or Schrägwalzgerüsten and an inner tool used in the interior of the rolling stock in the form of a mandrel or roll bar, as by the DE 21 31 713 A1 known.

The inner tools / mandrel rods in the forming of seamless tubes are subject to high mechanical and thermal stresses depending on the manufacturing process. Accordingly, a high wear of the tool surface occurs, which leads to abrasion, adhesion and disintegration and with relatively little service life to surface damage to the forming material and the failure of the tool. Therefore, an attempt is made to use as hard, wear-resistant materials in the heavily loaded tool areas.

Usually hot working steels, but increasingly also special materials (eg hard metals, nickel-cobalt alloys, cermets) and ceramics are used for forming tools. Ceramics, cermets and other highly wear-resistant materials have the properties, which are particularly disadvantageous for this purpose, of low thermal shock resistance, low bending strength and high sensitivity to cracking when tensile stresses occur.

If you use indoor tools, eg. As rolling rods containing rings or ring segments with or without axial bias, it comes under load from the rolling to local tensile stresses, which have the occurrence of cracks and the failure of the tool result. For this reason, the use of wear-resistant materials to the tools used in the interior of the rolling stock is not yet successful.

The invention is therefore an object of the invention to provide a generic method and a generic inner tool that allow seamless tube production without the disadvantages described in the use of special materials for the inner tool.

This object is achieved by the method in claim 1 and in terms of the inner tool with the features specified in claim 4.

Advantageous and expedient embodiments of the invention are contained in the dependent claims.

According to the present invention, the occurrence of tensile stresses is avoided by distributed around the circumference tool inserts are used with which tool parts, eg. B. segments of highly wear-resistant material, are biased under high tangential compressive stresses. Thus, together with an axial preload, a stress state with high compressive stresses is generated which, when loaded by the rolling stock, leads to a three-dimensional compressive stress state and thereby makes it possible to avoid the occurrence of tensile stresses. This enables the use of wear-resistant but brittle materials on the internal tools in rolling mills of seamless tube production.

The number of tool parts or segments depends on the number of rollers, so that the mandrel / roll bar, d. H. the inner tool may have two, three or more segments, each with gapless tool inserts therebetween.

The workpiece inserts are arranged so that they are in the load case in the area without Walzgutkontakt or in the range of only low mechanical and thermal stress. During longitudinal rolling, the inner tool is aligned so that the workpiece inserts are positioned in the areas between the rollers. In the case of skew rolling, the rolling rod or the inner tool should likewise be positioned and not rotate.

Even when using special materials, such as ceramics, which have a low affinity for steel, and are wear-resistant up to operating temperatures of over 1,000 ° C, it is advantageous that a cooling, lubricating and separating agent is introduced into the contact zone tube inner tool , For this purpose, the tool body is provided with a central longitudinal bore and with radial, oblique Zuführbohrungen through which the medium is conveyed under pressure and adhering to the inner surface of the tube to the contact zone. In the case of a plurality of roll stands arranged one behind the other, each roll stand is supplied with the medium in this way. Even with skew rolling plants, the supply takes place in the same way.

Fig. 1

in einem Längsschnitt als Einzelheit einen Teilabschnitt eines Innenwerkzeugs zur Herstellung nahtloser Rohre, und zwar dargestellt im Kontaktbereich des rohrförmigen Walzguts mit einer Walze eines Walzgerüstes, und

Fig. 2

als Einzelheit einen Querschnitt des Innenwerkzeugs (Walz-/Dornstange) entlang der Linie II - II von Fig. 1.

Further details and features of the invention will become apparent from the claims and the following description of an embodiment of the invention shown schematically in the drawings. Show it:

Fig. 1

in a longitudinal section as a detail of a portion of an inner tool for producing seamless tubes, and that shown in the contact region of the tubular rolling with a roll of a rolling stand, and

Fig. 2

as a detail of a cross section of the inner tool (rolling / mandrel bar) along the line II - II of Fig. 1 ,

Before a well-known as such Kontiwalzanlage 1 for the production of seamless pipes shows the Fig. 1 in extracts, a region in which a rolling stock 3 passing through in the rolling direction 2 is in contact with a roll 4. The perforated, tubular rolling stock 3 is rolled out between successive rolls 4 of the Kontiwalzanlage 1 on an inner tool 5, designed as rolling or mandrel, the Kontiwalzanlage 1 can be advantageously operated with held inner tool 5, so that the feed path between minus 1 stand spacing to plus 1 stand distance.

The inner tool 5 consists of a central longitudinal bore 6 having a base body 7 and arranged thereon tool segments 8 of a highly wear-resistant, heat-resistant material and between them provided, as indicated by arrow 9 (see. Fig. 2 ) radially engageable tool inserts 10. The tool segments 8 and inserts 10 are taken up by a sleeve 11 enclosing the base body 7.

Through the sleeve 11, the tool segments 8 and inserts 10 are axially biased, as in FIG Fig. 1 indicated by the arrows 12. Since the tool segments 8 by the Radialanstellbarkeit (arrows 9 in Fig. 2 ) of the tool inserts 10 at the same time a tangential pressure or bias according to the in Fig. 2 registered double arrows 13, no tensile stress occurs in the tool segments 8, which is very important especially in brittle material, such as ceramic, the tool segments 8. During rolling, an all-round compressive stress is achieved. For better effectiveness when introducing the tangential and axial compressive stresses on the one hand, the sleeve 11 with the Tool segments 8 and - inserts 10 and on the other hand, the tool inserts 10 with the tool segments 8 with wedge surfaces 14 to each other.

Starting from the longitudinal bore 6 of the inner tool 5 and extending through the base body 7 and the sleeve 11, a plurality of feed bores 15 are provided radially, obliquely formed. An introduced into the longitudinal bore 6 from a supply source, not shown cooling, lubricating and separating agent is introduced via the supply holes 15 under pressure directly into the contact zone between the rolling stock 3 and the inner tool 5. There it comes to the desired adhesion to the inner circumferential surface of the rolling stock. 3

LIST OF REFERENCE NUMBERS

1

Kontiwalzanlage

2

Rolling direction (arrow)

3

rolling

4

roller

5

Inner tool (mandrel / roll bar)

6

longitudinal bore

7

body

8th

tool segments

9

Arrow (radial adjustability)

10

tool insert

11

shell

12

Arrow (axial preload)

13

Double arrow (tangential pressure / preload)

14

wedge surfaces

15

feed bore

Claims (7)

1. A method for hot-rolling seamless pipes with one or more successively arranged longitudinal rolling stands or crossrolling stands and an internal tool (5) in the form of a mandrel bar or rolling bar that is used in the interior of the rolling stock (3),
   characterized in
   that an internal tool (5) is used that features on its outer circumference several tool segments (8) of a wear-resistant material and tool inserts (10) arranged in between the tool segments in a gapless fashion, wherein the tool segments (8) and the tool inserts (10) are prestressed with tangential and axial compressive stresses by means of a sleeve (11) in such a way that the tool segments (8) adjoin the tool inserts (10) and the sleeve (11) adjoins the tool segments (8) and the tool inserts (10) with wedge surfaces (14).
2. The method according to Claim 1,
   characterized in
   that the tool inserts (10) are radially adjustable.
3. The method according to Claim 1 or 2,
   characterized in
   that a cooling, lubricating and separating means is directly conveyed into the contact region between the internal tool (5) and the rolling stock (3) via a central longitudinal bore (6) of the internal tool (5), as well as radial feed bores (15) between the longitudinal bore (6) and the tool surface.
4. An internal tool (5) that is arranged in the interior of the rolling stock (3) and preferably held with only limited feed motion for hot-rolling seamless pipes in one or more successively arranged longitudinal rolling stands or crossrolling stands in order to carry out the method according to Claim 1,
   characterized in
   that several tool segments (8) of a highly wear-resistant and heat-resistant material are provided on a base body (7) of the internal tool (5) and radially adjustable tool inserts (10) are arranged in between said tool segments;
   furthermore characterized by a sleeve (11) that axially prestresses the tool segments (8) and the tool inserts (10).
5. The internal tool according to Claim 4,
   characterized in
   that the tool segments (8) consist of a ceramic material.
6. The internal tool according to Claim 4,
   characterized in
   that the tool segments (8) consist of cermet.
7. The internal tool according to one of Claims 4 to 6,
   characterized in
   that it features a central longitudinal bore (6) and is realized with radial feed bores that extend from the central longitudinal bore up to the tool surface, wherein said feed bores directly extend into the contact region between the internal tool (5) and the rolling stock (3) and distribute a cooling, lubricating and separating means.

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