The present invention relates to impeders that can be used in electric induction welding processes to form, for example, metal pipe or tubing from strip stock.
Impeders are used in high frequency welded pipe and tube fabrication processes. They are one or more pieces of ferrite, or other magnetic material, that is placed inside a pipe or tube within the weld area. This magnetic material accomplishes two things. It increases the electrical impedance of the inside current path of the tube, forcing the current to flow on the vee edges of the tube instead. It is this current that heats the vee edges prior to forging them together in the weld box. Secondly, it creates a low magnetic reluctance path inside the tube between the apex of the weld vee and the rear of the tube. The lower reluctance path becomes the preferred path for the magnetic field. Thus more of the magnetic field generated by the tube welder's induction coil or contacts passes through the weld vee to utilize this preferred path, and the welding current induced on the vee edges is thereby increased. U.S. Pat. No. 4,443,677 further describes the induction welding process and one type of conventional impeders.
There are many practical problems encountered with conventional impeders. The magnetic field that the impeder carries causes losses in the ferrite due to its finite resistivity and its coercivity. These losses heat the ferrite, and if heat is not removed through proper cooling, the ferrite's Curie temperature (the temperature at which a material looses its magnetic properties) can be exceeded or the binder that holds the ferrite material together can disintegrate. Ferrite is a brittle material and mechanical shock encountered during the tube fabrication processes can cause it to break into multiple pieces. When this happens the effective magnetic properties are greatly reduced. The ferrite is usually enclosed in a jacket generally made from a fiberglass type material. This helps protect the ferrite from mechanical shock and provides a means for channeling cooling water to the ferrite. When fabricating smaller diameter tube, the diameter of the ferrite must be as large as possible so that the impeder does not magnetically saturate. This results in tight clearances between the ferrite and the casing. Thus the cooling water must not contain contaminants that can plug the coolant passage between the ferrite and its casing. When this happens, the ferrite will fail almost immediately due to local over-heating. Temporary interruptions in the coolant supply can cause steam to develop inside the impeder casing. When this happens, the ferrite can temporarily exceed its Curie temperature and this can result in a section of “cold” or paste weld in the tube.
An object of the present invention is to provide an impeder with internal cooling that operates with improved efficiency.
In one aspect, the present invention is apparatus for, and method of, electric induction welding with an impeder. The impeder is formed from a high temperature impeder element disposed in a high temperature enclosure. The impeder element may be a plurality of solid wires formed from a magnetically conductive, high Curie temperature material, with each of the wires electrically isolated from all other wires. The high temperature enclosure may be formed from a suitable ceramic composition. Internal cooling may be via a closed or open cooling system where the cooling medium is circulated around the exterior of the impeder element with entry and exit passages for the cooling medium on opposite sides of the impeder. In alternate examples of the invention the impeder element may be a ferrite, or a rolled magnetically conductive sheet.
Other aspects of the invention are set forth in this specification and the appended claims.
The foregoing brief summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings exemplary forms of the invention that are presently preferred; however, the invention is not limited to the specific arrangements and instrumentalities disclosed in the following appended drawings:
a) is a longitudinal cross sectional view of one example of an impeder of the present invention that does not require internal cooling.
b) is a cross sectional view of the impeder in
a) is a longitudinal cross sectional view of one example of an impeder of the present invention with internal cooling.
b) is a cross sectional view of the impeder in
a) is a longitudinal cross sectional view of another example of an impeder of the present invention with internal cooling.
b) is a cross sectional view of the impeder in
a) is a longitudinal cross sectional view of another example of an impeder of the present invention with internal cooling.
b) is a cross sectional view of the impeder in
c) is a longitudinal cross sectional view of another example of an impeder of the present invention with internal cooling.
d) is a cross sectional view of the impeder in
Referring now to the drawings, wherein like numerals indicate like elements, there is shown in
a) and
a) and
a) and
In all examples of the invention the impeder element may be a sheet of high Curie temperature magnetic material, such as but not limited to permendur, that is rolled to form a generally cylindrical shape such as rolled sheet 42′ (shown crosshatched) in
In all examples of the invention wherein a cooling medium is used, a coolant with a high heat capacity, such as an oil-based coolant can be used to reduce the flow and pressure requirements for the cooling system. Using a return flow type impeder casing design such as that illustrated in
In all examples of the invention an optional inside cushioning liner can be disposed between the high temperature enclosure and the impeder to reduce shock transfer to the impeder material, which can extend the life of the impeder. The inside of the casing or the liner can be molded with cooling passages and/or a special texture to create turbulence in the coolant and thereby increasing the heat transfer between the ferrite and the coolant.
If a ferrite is used as the impeder, the ferrite composition can be optimized for high Curie temperature, and low coercivity and resistive losses to integrate it with the cooling system and coolant employed. High temperature binder, possibly ceramic based, can be used to prevent binder disintegration.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to various embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitations. Further, although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may effect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.
This is a divisional application of application Ser. No. 12/471,451, filed May 25, 2009, which is a divisional application of application Ser. No. 11/303,694, filed Dec. 16, 2005, which application claims the benefit of U.S. Provisional Application No. 60/637,590, filed Dec. 20, 2004, all of which applications are hereby incorporated herein by reference in their entireties.
Number | Name | Date | Kind |
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4207550 | Daikoku et al. | Jun 1980 | A |
4608471 | Vollmuth et al. | Aug 1986 | A |
4818833 | Formanack et al. | Apr 1989 | A |
5508672 | Sokai | Apr 1996 | A |
20020180284 | LeFlem et al. | Dec 2002 | A1 |
Number | Date | Country |
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60258414 | Dec 1985 | JP |
Number | Date | Country | |
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20130001219 A1 | Jan 2013 | US |
Number | Date | Country | |
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60637590 | Dec 2004 | US |
Number | Date | Country | |
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Parent | 12471451 | May 2009 | US |
Child | 13608188 | US | |
Parent | 11303694 | Dec 2005 | US |
Child | 12471451 | US |