EP2554293A1 - Pipe forging method with cast hollow block - Google Patents

Abstract

The method comprises making a tubular billet (104) with a central cavity (104a) by a primary shaping operation, mechanically machining the billet, descaling the billet using a high pressure method, coating a portion of the billet that defines the cavity with a lubricant, feeding the billet to a radial forging machine, and forging the billet into a tube by decreasing an outer diameter of the billet and a radial thickness of a wall of the billet. The primary shaping operation is electro-slag conversion or rotary casting. The method comprises making a tubular billet (104) with a central cavity (104a) by a primary shaping operation, mechanically machining the billet, descaling the billet using a high pressure method, coating a portion of the billet that defines the cavity with a lubricant, feeding the billet to a radial forging machine, and forging the billet into a tube by decreasing an outer diameter of the billet and a radial thickness of a wall of the billet. The primary shaping operation is electro-slag conversion or rotary casting. The mechanical machining removes a surface skin from the billet. The step of forging the billet is carried out using a forging mandrel (1) as an inner mold. The forging mandrel comprises a coating such as a scale coating, a ceramic coating and/or a coating with metal alloy. A base body of the forging mandrel comprises a surface profiling, where the coating is applied on the surface profiling. The surface profiling forms an undercut in an axial direction of the forging mandrel, and comprises elevations and depressions on the surface of the base body. The coating is applied: as a layer on the forging mandrel for protecting the forging mandrel against thermal and mechanical stresses; and by a thermo-chemical coating method.

Description

The invention relates to a method for forging a pipe according to the preamble of claim 1.

EP 1 814 679 A1 describes a method for producing a seamless hot-finished steel tube, in which a heated to a forming temperature block is formed by punching in a hollow block in a first forming step, wherein subsequently a finished tube is produced in the same heat in a second forming step by radial forging.

It is the object of the invention to provide a cost effective method for forging a pipe.

This object is achieved according to the invention for an initially mentioned method with the characterizing features of claim 1. By producing the hollow block with the central recess by a primary molding method, the hollow block is provided in a particularly simple and effective manner. In accordance with the principle of a primary forming, the block and the central recess required for forging the hollow block into a tube are formed in the same forming step, so that the outlay on the preparation of the hollow block is reduced.

Generally preferred, the invention relates to pipes made of an iron-based alloy, in particular steel, or even a nickel-based alloy or a titanium alloy.

In a first preferred embodiment of the invention, step a1 comprises an electroslag remelting process. For steels in particular, this provides an effective and universal method for the primary shaping of the hollow block.

Alternatively, the primary molding process may also include a centrifugal casting process. The centrifugal casting is particularly suitable for combination with a radial forging method, since a hollow block is already regularly produced with a central recess.

In a generally advantageous development of the invention, provision may be made for mechanical processing of the block to take place after step a1 and before step b in a step a2. Particularly advantageous, but not necessary, this may include the removal of a casting skin. It can be z. B. also to a homogenization of the recess, a deburring or any other suitable pre-treatment of the urgeformten hollow block prior to introduction into a radial forging device.

Generally, it is provided to carry out a heating of the hollow block after step a1 and before step b in a step a3 in order to achieve a defined forming temperature for the radial forging process. This may be particularly advantageous in alloys and structures that have a relatively narrow temperature range for forging machining.

Alternatively, it may be particularly advantageous to save energy and costs that between step a1 and step b no intermediate heating of the hollow block is made. In this case, therefore, the existing at the Urformung, regularly very high heat is used to obtain a temperature that is suitable for radial forging. In such a procedure, if necessary, a controlled cooling of the urgeformten hollow block before being introduced into the radial forging.

In a preferred embodiment of the invention, in a step a4, the desorbed hollow block is descaled before step b, preferably, but not necessarily, by a high-pressure process.

Further advantageously, it is provided that at least a portion of the recess of the hollow block is lubricated before step b by means of a lubricant. Such a lubricant may preferably be formed on the basis of glass and / or phosphate and / or graphite.

The step b of forging the hollow block into a tube while reducing an outer diameter and a wall thickness of the hollow block is generally advantageously carried out by means of a forging mandrel as an internal tool. In principle, open-die forging without a forging mandrel is conceivable, but the use of a forging mandrel is particularly effective. For the most part, the forging process will take place in such a way that the wall of the hollow block is pressed by external forging jaws against the forging mandrel arranged internally in the recess in order to effect the forming in the manner of a forging. The forging jaws can in particular be hydraulically driven, as a result of which a very controlled pressure curve is regularly achieved on the workpiece. Alternatively, however, another drive mechanism of the forging jaws may be provided, for. B. by falling weights or the like.

In a preferred development of the forging mandrel has a coating which particularly preferred, but not necessary, has a Zunderbeschichtung, a ceramic coating and / or a coating with a metal alloy applied. These coatings can be submitted individually or in combination. Under a coated metal alloy and / or hard alloy as a coating, such coatings are to be understood, which incorporated in the metal alloy and / or hard alloy hard materials, in particular ceramic nature, such as. As tungsten carbide or the like, have. Such coatings are often made by a thermal process such as plasma deposition welding, arc surfacing, or the like. The metal alloy serves to provide a sufficiently tough matrix which on the one hand provides a good and non-peeling connection with a substrate of the forging mandrel, in particular steel, and on the other hand achieves a correspondingly high hardness of the outwardly acting surface due to integrated hard material phases and / or hard material particles.

In a particularly preferred embodiment of the forging mandrel, it is provided that a main body of the forging mandrel has a surface profiling, wherein the coating is applied to the surface profiling. As a result, an additional positive connection is achieved in addition to a material flow, which particularly effectively prevents detachment of the coating from the base body. The profiling can be adapted to the shape and orientation particularly to the respective mechanical loads, z. B. to the forces caused by the respective forging jaws forces. In particular, the surface profilings form at least one undercut in an axial direction of the forging mandrel. As a result, a good fit is provided, which can also absorb very high forces acting in the direction of detachment of the coating. Particularly preferably, the surface profiling has a number of elevations and depressions on the surface of the base body.

The main body of a forging mandrel for use in a method according to the invention is preferably made of steel.

The coating of the forging mandrel protects advantageous against both thermal and mechanical loads. For example, the coating may have a targeted thermal conductivity to reduce a thermal effect on the body.

Generally, the coating can be applied by a thermo-chemical coating process.

In a generally advantageous development of a forging mandrel, internal cooling may additionally be provided, wherein the mandrel can be wetted with a coolant if required.

Further features and advantages of the invention will become apparent from the embodiment described below and in the dependent claims.

Fig. 1

zeigt ein Warmwerkzeug in Form eines Radialschmiededorns in einer Seitenansicht.

Fig. 2

zeigt die Einzelheit "Z" gemäß Fig. 1 für den noch nicht beschichteten Werkzeug-Grundkörper.

Fig. 3

zeigt die Einzelheit "Z" gemäß Fig. 1 für den jetzt beschichteten Werkzeug-Grundkörper.

Fig. 4

zeigt die Einzelheit "Z" gemäß Fig. 1 für eine alternative Ausführungsform des beschichteten Werkzeug-Grundkörper.

Fig. 5

zeigt ein erstes Schliffbild für die Einzelheit "Z" gemäß Fig. 1 durch das Warmwerkzeug; und

Fig. 6

zeigt ein zweites Schliffbild für die Einzelheit "Z" gemäß Fig. 1 durch das Warmwerkzeug.

Fig. 7

zeigt eine schematische Gesamtansicht einer Radialschmiedevorrichtung.

Hereinafter, a preferred embodiment of the invention will be described and explained in more detail with reference to the accompanying drawings.

Fig. 1

shows a hot tool in the form of a radial forging mandrel in a side view.

Fig. 2

shows the detail "Z" according to Fig. 1 for the not yet coated tool base.

Fig. 3

shows the detail "Z" according to Fig. 1 for the now coated tool body.

Fig. 4

shows the detail "Z" according to Fig. 1 for an alternative embodiment of the coated tool base.

Fig. 5

shows a first micrograph for the item "Z" according to Fig. 1 through the hot tool; and

Fig. 6

shows a second micrograph for the item "Z" according to Fig. 1 through the warm tool.

Fig. 7

shows a schematic overall view of a radial forging.

• a. Zuführen eines Hohlblocks 104 mit einer zentralen Ausnehmung 104a zu einer Radialschmiedevorrichtung 101, und
• b. Schmieden des Hohlblocks 104 zu einem Rohr unter Verringerung des Außendurchmessers und der Wandstärke des Hohlblocks 104.

The method according to the invention for forging a tube preferably comprises the following steps:

• a. Feeding a hollow block 104 with a central recess 104a to a radial forging apparatus 101, and
• b. Forging the hollow block 104 into a tube while reducing the outer diameter and wall thickness of the hollow block 104.

Previously, according to the invention, in a step a1, the hollow block 104 is produced together with its recess 104a in a primary molding process. This is preferably a centrifugal casting process or a remelting process, for example an electroslag remelting process.

After the initial forming of the block 104 with the recess 104a, if necessary, a mechanical reworking of the hollow block takes place. This may be, for example, a descaling and / or a post-processing of the recess for fine adjustment to a size and shape required for forging.

Fig. 7 shows by way of example a device for radial forging 101, at which the method can be performed. In this case, the block 104 is held in the end in a manipulator or holder 102. At the opposite end a hot tool in the form of a forging mandrel 1 is inserted into the recess 104a. At the level of the mandrel 1 access from outside Schmiedebacken 103 to the processing hollow block 104 at. The forging jaws 103 are preferably pressed by means of hydraulic drives with a defined pressure curve against the hollow block 104 in order to achieve a radially acting forging of the hollow block 104 to a tube. In an alternative embodiment, striking the forging jaws, eg via a cam mechanism, can be provided.

The hollow block 104 can be rotated and / or axially displaced by means of the manipulator 102.

It is understood that the method according to the invention can also be carried out on other radial forging devices.

In Fig. 1 the mandrel or the hot tool 1 in the form of a mandrel for the production of a seamless tube is shown schematically. The shape may vary depending on requirements and in particular be cylindrical or slightly conical. The tool 1 has a tool base body 2, which has a working area 3, which extends over a certain length in the direction of an axis a. In the working area 3, the tool 1 is provided with a coating 4 which protects the tool 1 against thermal or mechanical stress.

The whole in Fig. 1 Tool body 2 shown in the context of the present invention is an interchangeable mandrel tip, for example, releasably on a mandrel body, for example in the form of a shaft 105 (see Fig. 7 ) of the radial forging mandrel 1 can be placed. Other configurations or divisions of a replaceable mandrel tip 2 and a mandrel body 105 are possible depending on the requirements.

The exact structure of the tool as a detail in the "Z" according to Fig. 1 , ie as a section of the tool base body 2 is in the FIGS. 2 and 3 shown. As can be seen, has the radially outer surface of the tool body 2 is a surface profiling 5, which consists of a number of radially projecting elevations 6, which are arranged between thus resulting recesses 7. The elevations 6 extend in the axial direction a by an amount B, which is preferably in the range of about 250 microns to 4000 microns. The height D of the elevations 6 with respect to the recesses 7 is in a range of about 500 microns to 5000 microns. The distance A between two elevations 7 is preferably in a range of about 200 microns to 2,000 microns.

The profiling 5 is applied to the surface of the base body 2, that this is first processed smoothly and then incorporated by machining the ridge-shaped or rectangular recesses 7 in the radial section, in particular screwed, are.

After this pre-processing, the surface of the tool base 2 is provided with a coating 4, as shown in FIG Fig. 3 is shown. The total layer thickness C of the coating 4 fills out the recesses 7 and exceeds the height of the elevations 6.

Seen in the axial direction a, thus results for the material of the coating 4 as a result of the surface profiling 5 an undercut, so that the coating 4 is very firmly adhering to the base body 2 when using the tool 1.

In Fig. 4 is a preferred embodiment or to see solution. The pre-processing of the tool base body 2 is analogous to the solution according to Fig. 2 and Fig.3 made, ie it was first introduced the surface profiling 5 in the smooth machined tool body 2. The profile of the profiling corresponds to that according to Fig. 2 ,

Then, however, before applying the coating 4, a portion of the material of the base body 2 was first converted into a protective layer by using a thermo-chemical treatment process. The converted material 8 is equidistant from the profiling 5 and is indicated by dashed lines. This reduces accordingly the width of the elevations (webs) 6 and the depth of the cross-section in turn rectangular gaps, as it Fig. 4 shows.

On the thus converted material layer 8, ie on the primary or inner protective layer produced by conversion of the carrier material is applied during the conversion or subsequently the coating 4 as a second, outer layer, as it Fig. 4 for the finished tool shows. This is again done by a thermo-chemical process or for example by flame spraying or plasma spraying.

According to the in Fig. 4 As shown solution is thus created between the substrate (base body) 2 and the layer 4, a structure before or during the application or the generation of the layer 4 on the substrate 2, which manifests itself in the converted material 8.

The representations in the FIGS. 5 and 6 Examples of specific coatings can be found. The inner, more porous layer 8 and the second outer layer 4 applied thereon by conversion of the webs (elevations) 6 and filling in of gaps (depressions) 7 can be clearly seen. The inner layer 8 (converted material) consists in the present case of iron oxides and grows from the surface of the main body or the profiling. The gaps between the lands (bumps) are filled by the outer coating 4 (up).

In the embodiment according to Fig. 5 respectively. Fig. 6 the carrier material (tool base) was coated with iron oxides or material of the main body was converted into iron oxide. The carrier material is present steel. The maximum thickness of the coating on the base body is in this example about 1,000 microns.

The structured transition between the carrier material and the coating can be optimized depending on the application, so that complete peeling of the layer during use can be prevented. As a result, in particular the service life of the tool 1 can be substantially increased.

The surfaces of the coated tools, before or during use by mechanical processing, eg. B. grinding and polishing (before use) or rolling (during use), smoothed.

The smoothing of the surface reduces the friction between the tool and the workpiece (rolling stock).

LIST OF REFERENCE NUMBERS

1

Hot tool or radial forging mandrel

2

Basic tool body

3

Workspace

4

coating

5

Surface profiling

6

survey

7

deepening

8th

converted material

101

Radial forging device

102

manipulator

103

forging jaws

104

block

104a

Recess in block

105

shaft

a

axially

B

length

D

height

A

distance

C

Total layer thickness

Claims (8)

Method for producing a pipe, comprising the steps: a. Feeding a hollow block (104) having a central recess (104a) to a radial forging apparatus, and b. Forging a hollow block (104) into a tube while reducing an outer diameter and a wall thickness of the hollow block (104) m characterized by the step: a1. Producing the hollow block (104) with the central recess (104a) before step a by a primary molding process. A method according to claim 1, characterized in that step a1 comprises an electroslag remelting process. A method according to claim 1, characterized in that step a1 comprises a centrifugal casting process. Method according to one of the preceding claims, characterized by the step
a2. Mechanical processing of the hollow block (104) after step a1 and before step b; in particular comprising the removal of a casting skin. Method according to one of the preceding claims, characterized by the step
a3. Heating the hollow block (104) after step a1 and before step b. Method according to one of claims 1 to 4, characterized in that between step a1 and step b, no intermediate heating of the hollow block (104) is made. Method according to one of the preceding claims, characterized by the step
a4. Descaling the shaped hollow block (104) prior to step b, in particular by a high pressure process. Method according to one of the preceding claims, characterized by the step
a5. Lubricating at least a portion of the recess of the hollow block (104) before step b, in particular by means of a lubricant based on glass and / or phosphate and / or graphite.

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