Patent Application
20050022571
The invention relates to a method for applying compressive and/or tractive forces on an essentially rod-shaped workpiece consisting of electrically conductive and/or magnetizable material. The invention moreover relates to a device for executing the method.
Essentially rod-shaped workpieces in the sense of this invention are such workpieces whose expansion in the axial direction clearly exceeds the dimensions in the lateral directions. This can be for example pipes, rods, bars, profile struts or flat strips.
To move such workpieces for example within the framework of a machining or manufacturing system, it is necessary to apply compressive and/or tractive forces on these workpieces. Similarly such forces are necessary especially during forming processes where the workpieces for example are pressed or pulled through molding dies to develop the profile or change the diameter. This is required e.g. when drawing pipes, wherein a pipe with a diameter D1 before the drawing process is formed by being pulled through a die or a drawing plate while shaping the material into a pipe with a smaller diameter D2 than the diameter D1. For such an operation it is necessary to apply an appropriate tractive force on the workpiece to be formed, in the example mentioned this is the pipe that is to be drawn, in order to achieve on one hand the shape and on the other hand a conveying process of the workpiece to be formed. In familiar forming systems, for example for drawing pipes, this is generally accomplished mechanically. A gripper grabs the workpiece on one end that is guided through the forming device, for example the drawing die, and is moved in the direction of traction by means of a mechanical drive, such as an electric motor. This way the tractive forces required for the forming process are generated, which can amount to for example 10 tons. Known mechanical facilities, however, have the disadvantage that a tractive element always must be attached to the rod-shaped workpiece to be formed, which is associated with considerable effort. Moreover, with such mechanical tractive elements, the speed of the drawing process is limited due to mechanics. In typical pipe drawing systems, this is, for example, a maximum of 300 m pipe material per minute. This is especially disadvantageous with so-called continuous drawing machines, where a quasi-continuous workpiece such as a wound pipe of great length is drawn continuously to be formed.
Proceeding from this prior art, it is the object of the invention to offer a method for applying compressive and/or tractive forces on an essentially rod-shaped workpiece where the use of mechanical gripping elements can be foregone. Moreover a device for executing such a method shall be provided.
To accomplish this objective, the invention suggests a method for applying compressive and/or tractive forces on an essentially rod-shaped workpiece consisting of an electrically conductive and/or magnetizable material, whereby a magnetic field is applied to the material having a gradient in the direction of the force to be applied.
By applying a magnetic field comprising a gradient pointing in the direction of the force to be applied to the rod-shaped material, a magnetic field is generated in the electrically conductive and/or magnetizable material through a flow of current initiated by induction or through an alignment of magnetic poles. Due to this induced magnetic field and the gradient of the outer magnetic field, a force that is pointed in the direction of the gradient of the outer magnetic field is applied on the rod-shaped workpiece. Depending on the alignment of the gradient of the outer magnetic field, a compressive force pointing in one direction or a tractive force pointing in the opposite direction can consequently be applied on the workpiece. Applying the forces does not take place mechanically, but purely through the interaction of the outer magnetic field with the magnetic field induced in the material of the workpiece based on this field.
Since with such a method of applying compressive and/or tractive forces mechanical motion is not required, with this method for example an advancing speed during the forming process is not limited by mechanical specifications. Consequently basically higher speeds can be reached than is the case with systems known from the state of the art.
Pursuant to a beneficial development of the invention, the magnetic field comprising a gradient can be generated by a coil arrangement subjected to current through flow, having an inhomogeneous construction. An inhomogeneous design of a coil arrangement within the meaning of this invention can be realized by a single coil having an inhomogeneous shape, for example an interior tapering down conically in the longitudinal direction of the coil, or a winding density that changes in the longitudinal direction of the coil, thus generating an inhomogeneous magnetic field. A coil arrangement consisting of several coils deviating from one another in their properties, however, should also be understood by an inhomogeneous construction of a coil arrangement. Such a coil arrangement allows a magnetic field comprising a gradient to be generated in a simple manner, whereby the coil arrangement itself is fixed in space, and the magnetic field is generated by conducting a flow of current through the coil arrangement. Such a coil arrangement requires no mechanically moving parts whatsoever; the compressive and/or tractive forces are applied on the workpiece exclusively due to the magnetic fields generated by the coil arrangement.
In accordance with another advantageous refinement of the invention, it is provided that the magnetic field comprising a gradient is generated by at least two coils that are arranged around the rod-shaped workpiece, whereby the coils are subjected to current through flow, respectively, for the generation of different magnetic fields. A coil within the meaning of the invention should hereby also be understood as individual conductive loops. Within the framework of this embodiment of the invention two coils of equivalent design can be arranged around the workpiece, axially spaced from each other, whereby for the purpose of generating different fields currents of different strengths and/or phases are conducted through the coils. When the magnetic field comprising a gradient is created with such an arrangement, it is possible, with a large number of coils and suitable control, to achieve a very exactly controlled course of the magnetic field, which enables an exactly metered application of compressive and/or tractive forces on the rod-shaped workpiece.
For the controlled application of compressive and/or tractive forces on the rod-shaped workpiece, pursuant to the method described here in an advantageous refinement of the same, the current flowing through the coils and/or the coil arrangement can be modified as a function of the time. This can occur periodically, whereby the selected frequency is preferably selected in accordance with a frequency of resonance that is designed as a function of the material properties and the dimensions of the rod-shaped workpiece. The frequency at which the most efficient conversion of electric energy into compressive and/or tractive forces occurs with the selected coil arrangement with interposition of the magnetic fields is designated as such a frequency of resonance.
In order to prevent the coil arrangement from overheating, the coils can be cooled, if necessary, pursuant to a suggestion of the invention.
Pursuant to another advantageous refinement of the invention, the rod-shaped workpiece, if it is electrically conductive, can be subjected to current through flow to support the application of compressive and/or tractive forces. By connecting the workpiece itself with an external source of power and thus supplying it by a current, apart from the magnetic field that is induced by the exterior magnetic field another magnetic field is generated around the workpiece. An amplification of the force applied to the workpiece can be attained depending on the direction of the current flow and the polarity of the exterior magnetic field.
The workpiece can be cooled in accordance with another advantageous proposal of the invention in order to prevent the workpiece from overheating due to the external magnetic field, as this can occur especially in the case of periodically alternating magnetic fields.
With the method of the invention, rod-shaped workpieces can be transported or be drawn or compressed by corresponding forming dies for the purpose of shaping them. The rod-shaped workpieces only have to consist of an electrically conductive and/or magnetizable material. Here all electrically conductive materials come into consideration, but also magnetically polarizable and/or magnetizable resins or equivalent materials.
To accomplish the aforementioned objective, the invention furthermore proposes a device for applying compressive and/or tractive forces on an essentially rod-shaped workpiece consisting of electrically conductive and/or magnetizable material, comprising a coil arrangement that can be acted by a current for creating a magnetic field comprising a gradient pointing in the direction of the force to be applied on the workpiece.
The coil arrangement here can comprise a single, inhomogeneously designed coil. However it preferably comprises at least two coils, which can be acted by a current that can be adjusted individually for each coil. Coils within the meaning of the invention should be understood not only as coils with several windings, but also individual conductor loops. Pursuant to an advantageous refinement of the invention, the individual coils are arranged concentrically around a workpiece path axially spaced from one another, along which the workpiece is to be acted upon by compressive and/or tractive forces.
Further advantages and features of the invention are disclosed to the expert from the following description of on exemplary embodiment based on the sole appended FIGURE, wherein:
With the controllable power source 7, individually different currents can be supplied to the coils 5a through 5d of the coil arrangement 5 by means of the electric lines 6a through 6d so as to create a magnetic field in the area of the coil arrangement 5 with a gradient running in the direction of the arrow 8. Such a magnetic field comprising a gradient induces a secondary magnetic field in the pipe section 3 of the pipe consisting of an electrically conductive and/or magnetizable material. Due to the interaction between the magnetic field provided with a gradient that is generated by the coils 5a through 5d and the secondary magnetic field a force is generated, which in the example shown acts in the direction of the arrow 8 on the pipe section 3 and thus on the pipe 1. The pipe 1 is drawn through the die 4 and formed with the help of this force.
The controlled power source 7 here can be operated such that the currents flowing through the coils 5a through 5d, respectively, can be varied with respect to time, whereby the currents conducted in the lines 6a through 6d each can have different amounts and/or can be out-of-phase.
With the arrangement depicted in a diagrammatic view in the exemplary embodiment, a tractive force can also be applied on the pipe for the purpose of drawing a pipe without mechanical aids. The tractive force that is required for drawing the pipe is generated solely due to the primary magnetic field that is generated with the coil arrangement and the secondary magnetic field that is induced in the electrically conductive and/or magnetizable material of the pipe. Instead of applying a tractive force on the pipe, a coil arrangement corresponding to the coil arrangement 5 could be arranged on the pipe section 2 depicted in the left of the figure, wherein the coils 5a through 5d should be switched such that a compressive force that also acts in the direction of the arrow 8 is exerted on the pipe end 2.
The embodiment shown serves only to explain the invention and is not restrictive. The coil arrangement 5 in particular can comprise a number of coils that differs from the four depicted coils 5a through 5d. Also, to reinforce the generated compressive and/or tractive force, a pipe consisting of conductive material can be connected to the power source and thus be subjected to current through flow.
| Number | Date | Country | Kind |
|---|---|---|---|
| 101-35-876.8 | Jul 2001 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP02/06297 | 10/6/2002 | WO |
