EP3017888A1 - Thermoforming tool - Google Patents

Abstract

Proposed is a hot forming tool 1 consisting of a tool body 2 with at least proportionate surface coating 4, which is obtainable by providing the base body with a raised metallic relief, which is then completely or partially oxidized and converted into a protective layer.

Description

FIELD OF THE INVENTION

The invention is in the field of manufacturing tubular metal workpieces and relates to forming tools, especially piercing mandrels, forged mandrels and billets with improved stability.

STATE OF THE ART

Seamless steel tubes are generally manufactured in three forming steps on respective rolling mills by hot forming. In a first stage, a massive steel block heated to about 1200 ° C. is shaped to form a hollow block by means of an internal tool, the piercing mandrel, on a so-called perforated piercing mill. The block is driven by means of inclined rollers on the piercer. In the second forming step, the hollow block is reduced in a longitudinal rolling process over the inner tool, a rolling rod, in diameter and wall thickness and stretched in the longitudinal direction. In the third forming step, the rolling stock is converted to the required dimensions in diameter and wall thickness, with no internal tool is usually used.

The inner tools in the first two forming stages are exposed to high temperatures and high mechanical pressures during production. In most cases, the inner tools are made of heat-resistant steel. In production, especially with longer rolling times, successive heating of the inner tool is often unavoidable. As a result of the heating, the strength of the tool decreases and the tool can then no longer withstand the mechanical loads. The tool deforms and breaks.

To achieve long service life, piercing mandrels are provided with natural scale layers. These scale layers inhibit the heat flow from the forming material into the tool and protect the tool against rapid heating and rapid loss of strength. When forming higher alloyed materials, however, the scale layer is quickly removed and thermal protection fails.

In the case of rolled rods, of course, depending on the forming process, scale or chromium-plated tools are used. Corresponding piercing mandrels are known for example from the German patent application DE10 2008 056988 A1 (SMS MEER) known. The disadvantage, however, is that the thermal insulation against the heat flow from Umformgut in the tool is low. Thus, it is especially for internal tools, which are used with reduced speed and contact length, to heating the inner tool and its failure by deformation and breakage.

The service life of the tools could be improved if the thickness of the oxide layer could be increased. Then the heat insulation would be better and with abrasive wear the protective layer would remain longer.

However, the protective layer, which is naturally formed from the base material by conversion into iron oxides, does not have high stability. It is brittle and porous and can therefore easily be destroyed by mechanical and thermal stress. Therefore, these protective layers are limited in their thickness. The limit of the layer is about 0.8 mm. The protective effect of such a layer is therefore limited accordingly. Heat therefore penetrates into the body of the tool and reduces its strength, which then leads to premature failure of the tool. For highly alloyed products, the abrasion is relatively fast, i. after a small length of rolled material for removal of the protective layer.

From the international patent application WO2011 107214 A1 (SMS MEER) are known piercing mandrels or billets for the production of seamless pipes or forging mandrels for hot forging of tubular metal workpieces having a surface profiling on which the oxide layer is applied. In this way, a better adhesion and longer life is to be achieved.

Similar tools, in which the coating consists of molybdenum, are from the EP0385439A1 (NKK CORP.).

In practice, however, the production of such profiled tools proves to be expensive, since the profiles must be cut individually into the mandrels, and also lead to material losses. The manufacturing costs of a profile increase disproportionately with the size of the wells to be introduced. A profitability and feasibility limit is reached even at a few millimeters. Another disadvantage of the profile cut into the base body is the limitation of the material to steels which are readily oxidizable. These have in particular a low chromium content and thus low hardness.

The object of the present has therefore been to provide hot forming tools with improved stability, which are free of the disadvantages described above. In particular, in comparison to the prior art, these tools should have a higher strength oxide layer which, moreover, can be applied easily and without material loss.

DESCRIPTION OF THE INVENTION

A first subject of the invention relates to a hot forming tool consisting of a tool base body with at least partial surface coating, which is obtainable by providing the base body with a raised metallic relief, which is then completely or partially oxidized and converted into a protective layer.

1. (a) den Grundkörper mit einem erhabenen metallischen Relief versieht, und
2. (b) nachfolgend das metallische Relief ganz oder teilweise oxidiert und in eine Schutzschicht umwandelt.

Another aspect of the invention comprises a method for producing a hot forming tool consisting of a tool base body with at least partial surface coating, in which one

1. (a) provides the base body with a raised metallic relief, and
2. (B) Subsequently, the metallic relief completely or partially oxidized and converted into a protective layer.

The application of a raised relief represents the opposite case to a profiling of the tool. For the purposes of the invention, therefore, material is added and not removed. Surprisingly, it was found that the relief formation in contrast to the profiling not only much easier to implement, but by completely or partially transforming the relief material itself a much harder and thus more resistant oxide layer is obtained, resulting in a significant improvement in the life of the tool. The invention also offers the possibility of varying the quality of the surface protection by selection of the relief material and of adapting the process conditions.

The economic benefits of the invention are obvious and consist, in particular, in the reduction of tooling costs in the production of steel products and the extension of the rolling time, which is usually associated with larger rolling stock lengths and reduced rejects.

TOOLS

The hot forming tools of the present invention are preferably a piercer or a forging mandrel, which are typically steel. However, the invention fundamentally also encompasses any other metallic workpiece in which the base body is to be protected against heat flow. The term metal is not limited to iron and steel, but also includes other metallic materials including metal-containing composites that are to be subjected to hot working.

However, not only for thorns, the internal tools for punching by means of oblique rolling, but also for the other internal tools used in the production of seamless steel tubes, the surface coating according to the invention can be advantageously used. In the case of the rolling rods, the internal tools in the rolling mills with a plurality of rolling mills arranged one behind the other in the second forming stage, particular care must be taken to ensure that the friction between the tool and the rolling stock is low. Therefore, the surface layer according to the invention must be ground and polished for this application. Also, an additional layer e.g. be applied from chrome on the protective layer according to the invention.

The raised relief, which is applied to the base body, can be pronounced differently, the alternative embodiments are all in principle suitable to fulfill the task fully.

In a first embodiment, the raised relief may simply be a wrapping of the base body with a wire, preferably a steel wire.

In a second embodiment, the raised relief may be a metal mesh or metal net applied to the base.

The metallic bodies applied to the surface of the tool preferably consist of a steel mesh, for example with a steel wire thickness of about 1 to about 5 mm and preferably about 1.5 mm and a mesh size of about 1 to 5 mm and in particular about 2.5 mm. Mesh size is the distance between the center lines of two adjacent fabric elements.

In a third embodiment, the raised relief may be an irregular coating as achieved by chemical or physical vapor deposition of metal.

RELIEF EDUCATION

The application of the raised relief can be done according to very different - simple and complex - method, but all solve the task of the invention fully.

In a first embodiment , the basic body is simply wrapped with a wire, preferably a metal wire.

In a second alternative embodiment , a metal mesh or a metal mesh is used instead of the wire. This can be preformed, for example by deformation to the shape of the tool and then mounted on the body. To increase the strength, it is advisable to weld the wire winding or the metal mesh to the base body.

In a third alternative embodiment , it is possible to produce the relief on the surface of the base body by chemical or physical vapor phase deposition (CVD / PVD).

The term chemical vapor deposition refers to a group of coating processes which are used inter alia in the production of microelectronic components and optical waveguides. On the heated surface of a substrate, a solid component is deposited due to a chemical reaction from the gas phase. The prerequisite for this is that volatile compounds of the layer components exist, which deposit the solid layer at a certain reaction temperature. The process of chemical vapor deposition is characterized by at least one reaction on the surface of the workpiece to be coated. At least one gaseous starting compound (starting material) and at least two reaction products - at least one of which in the solid phase - must be involved in this reaction. In order to promote surface reactions to competing gas phase reactions and thus avoid the formation of solid particles, the process is preferably carried out at reduced pressure.

Unlike CVD, the preferred PVD converts the feedstock into the gas phase. The gaseous material is then passed to the substrate to be coated, where it condenses and forms the target layer. Examples include classical evaporation methods, such as thermal evaporation, electron beam evaporation or laser beam evaporation (Pulsed Laser Deposition). For the purposes of the present invention, sputtering is preferred in which the starting material is atomized by ion bombardment and transferred into the gas phase, from which it can then be deposited again onto the base body. All these methods have in common that the material to be deposited in solid form in the most evacuated coating chamber is present. By bombardment with laser beams, magnetically deflected ions or electrons as well as by arc discharge, the target is vaporized. The amount of atoms, ions or larger clusters in the vapor varies from process to process. The vaporized material moves either ballistically or by electric fields guided through the chamber and strikes the parts to be coated, where it comes to film formation.

In order for the vapor particles to reach the components, and not be lost by scattering on the gas particles, it is necessary to work under reduced pressure. Typical working pressures are in the range of 10 ^-4 Pa to about 10 Pa. As the vapor particles propagate in a straight line, areas that are invisible from the location of the vapor source are coated at a lower coating rate. In order to produce a relief and no homogeneous coating, unlike usual is dispensed with a rotation of the substrate.

A fourth alternative embodiment for the formation of relief comprises the so-called thermal spraying. This filler materials, the so-called spray additives, inside or outside of a spray burner off, on or melted, accelerated in a gas stream in the form of spray particles and thrown onto the surface of the component to be coated. The component surface is not melted (in contrast to build-up welding) and only subjected to a low thermal load. A layer formation takes place because the spray particles flatten more or less depending on the process and material when hitting the component surface, stick primarily by mechanical clamping and layer by layer build up the spray layer. Quality features of sprayed coatings are low porosity, good adhesion to the component, freedom from cracks and homogeneous microstructure. The achieved coating properties are significantly influenced by the temperature and the speed of the spray particles at the time of their impact on the surface to be coated. The surface condition (purity, activation, temperature) also has a significant influence on quality features such as adhesion.

As an energy source for the on or melting of the spray additive used electric arc (arc spraying), plasma jet (plasma spraying), fuel-oxygen flame or fuel-oxygen high-speed flame (conventional and high-speed flame spraying), fast, preheated gases (cold gas spraying) and Laser beam (laser beam spraying). According to DIN standard EN 657, the spraying processes are classified according to these criteria.

With the aid of this method, the base body can be coated not only with metals but also with oxide-ceramic materials and carbide materials (or in general composite materials). Preferably, in this embodiment, the coating is carried out with an iron / ceramic mixture.

While the body is preferably made of steel, the requirement for the material forming the raised relief is that it be at least partially capable of forming an oxide layer. Preferably, this is iron or steel, so that an iron oxide layer, preferably scale is produced. As stated, a mixture of iron / steel and ceramics may also be used, for example in a weight ratio of about 20:80 to about 80:20.

It is understood that the relief can have a variety of forms, ranging from regular (round, square, etc.) to any free-form. Material composites can also be used, i. For example, a molybdenum fabric, which is applied to the body made of steel. The fabric element may also consist of a composite of hard chrome steel (inside) and good oxidizable steel (outside). As spacers and combustible materials can be used. It is also possible to store ceramic for better thermal insulation.

OXIDATION

The complete or partial conversion of the metallic relief into an oxide protective layer can be carried out by known processes of the prior art, for example by flame spraying, plasma spraying or by a thermochemical process.

During the oxidation of the tool with the metallic body applied to its surface, for example a steel mesh, a part of the surface of the tool base and a part of the metal relief applied to the surface are converted into oxide. At the same time an additional oxide layer is formed on all surfaces, which is typically about 500 to about 3,000 microns, and more preferably about 1,500 to about 2,500 microns. As a result, oxide is also formed in the interstices between the bodies, for example, between the tool body and the applied steel mesh and within the mesh of the steel mesh. The result is a particularly thick protective layer reinforced by internal bodies. In particular, unlike the production of depressions, the layer thickness is not limited to a few millimeters. Layer thicknesses of 10 millimeters and more can be produced without difficulty and at low cost.

INDUSTRIAL APPLICABILITY

Another object of the invention relates to the use of the new tool described in detail above, especially as a piercer, forging mandrel or roll bar for the production of seamless tubes or for hot forging tubular metal workpieces.

EXAMPLES EXAMPLE 1

On the surface of a piercer a preformed by forming to the shape of the body steel fabric was placed with a steel wire thickness of 1.5 mm and a mesh size of 2.5 mm and welded. Subsequently, the composite was subjected to a thermochemical oxidation. It was obtained a coherent gapless oxide layer of 2,500 microns thickness.

illustration 1 shows a hot tool in the form of a piercer in a side view. The tool 1 has a tool base 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 is provided with a coating 4 , which protects the tool 1 against thermal or mechanical stress.

Figures 2 and 3 show the detail "Z" in the horizontal section through the tool according to illustration 1 once for the basic material body with raised relief before and after the oxide protective layer is created ("scaling").

In Fig. 2a one recognizes the saw-shaped relief, which was created according to Example 1 by applying a wire mesh. In this case, the main body is denoted by the reference numeral 6 , the network by the reference numeral 7 . In Fig. 2b it can be seen that a part of the surface of the relief has been converted into oxide, but also between the meshes of the mesh the surface of the base has been oxidized (hatching with the reference numeral 8 ).

Figures 3a and 3b are analogous, but the relief here has no square, but a round cross-section. Here, too, it can be seen that the oxide layer (hatching) is formed in equal proportions above and below the original surface of the iron-containing body.

Claims (15)

Hot forming tool consisting of a tool body with at least proportionate surface coating, obtainable by providing the base body with a raised metallic relief, which is then completely or partially oxidized and converted into a protective layer. Tool according to claim 1, characterized in that it is a piercer, a forging mandrel or a rolling rod. Tool according to claims 1 and / or 2, characterized in that the base body made of metal, preferably made of steel. Tool according to at least one of claims 1 to 3, characterized in that the raised relief on the base body represents a wire wrap. Tool according to at least one of claims 1 to 3, characterized in that the raised relief on the base body is a metal fabric. Method for producing a hot forming tool consisting of a tool body with at least partial surface coating, in which one (a) provides the base body with a raised metallic relief, and (B) Subsequently, the metallic relief completely or partially oxidized and converted into a protective layer. A method according to claim 6, characterized in that applying the raised relief on the body by wrapping with a wire. A method according to claim 6, characterized in that applying the raised relief on the base body by wrapping with a metal fabric. A method according to claim 8, characterized in that the metal fabric is preformed by deformation to the shape of the tool and then raised to the base body. Method according to at least one of claims 7 to 9, characterized in that the wire or the metal fabric is welded to the base body. A method according to claim 6, characterized in that applying the raised relief on the body by chemical / physical vapor phase deposition. A method according to claim 6, characterized in that applying the raised relief on the body by thermal spraying. A method according to any one of claims 6 to 12, characterized in that the base body made of metal, preferably made of steel, and the material which forms the raised relief, at least partially capable of forming an oxide layer. A method according to any one of claims 6 to 13, characterized in that the complete or partial conversion of the metallic relief into an oxide protective layer by flame spraying, plasma spraying or by a thermochemical process. Use of a tool according to at least one of claims 1 to 5 for the production of seamless pipes or for hot forging tubular metal workpieces.

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