Electric heating – Metal heating – Of cylinders
Patent
1986-08-14
1988-04-05
Shaw, Clifford C.
Electric heating
Metal heating
Of cylinders
219 85, 219105, B23K 1100
Patent
active
047360844
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for heating metal elements to be joined, especially by forge welding, in which the elements are provided with surfaces to be welded and are positioned so that said surfaces constitute a narrow gap, and in which the heating takes place by means of a high frequency current supplied from a power source of alternating current.
PRIOR ART
From for example Norwegian Patent Application No. 83.3729 there is known a method for joining parts of metal by forge welding, in which the parts prior to the forge welding are heated be means of an induction coil.
In order to provide an efficient joining of said parts, it is of great importance that the heating is concentrated as much as possible in the area of the joint. If the heat is allowed to spread too far from the joint, the heating time will increase, the bending force of the parts will be reduced during the forge welding, the favourable tri-axial stress conditions will be worse and the necessity of heat treatment after the completed welding will increase.
Heating of pipe parts by means of induction heating prior to the joining of said parts, has been suggested and tested by many, but the practical application has been very limited, the heating zone having a tendency to be too long. The heat from the coil must be transfered to the metal parts closest to the coil and must spread therefrom and into the joint surfaces, a fact which entails that improper zones of the metal will be heated.
If the cross section of the material is reduced in the area of the joint for achieving higher tri-axtial tensions during the forging operation, it will be difficult to position the induction coil as close to the joint that heating will only take place in the area of the joint.
From DE Auslegeschrift No. 15 65 360 there is known a device for continuous electric welding of profiled parts. The device includes connections for two or more V-shaped gaps which are simultaneously and continuously welded in the longitudinal direction of the profiled parts by means of the same high frequency power source. However no instruction is given therein about a heating process relating to the area of a narrow gap which is kept substantially constant during the heating process.
From DE Offenlegungsschrift No. 30 07 153 there is known a method for continuous seam welding of pipes by means of high frequency welding, in which method the current is utilized in a better way by including an additional coil for the regulation of the primary high frequency current. However, the method includes the use of a sliding contact system for achieving the continuous welding of longitudinally extending seams, but this technique cannot be transferred to a butt welding of pipes and bolts, which is the case with the present invention.
From U.S. Pat. No. 2,892,914 there is known a method and an apparatus for butt welding based on induction heating, but this known technique has found no practicle application due to the fact that no concentrated heating zone can be achieved in the area of the joint. Further, no gap between the two metal parts to be joined is suggested in U.S. Pat. No. 2,892,914, let alone that the known technique suggests inclined or sloped areas bordering the gap. Due to the lack of a gap between the parts to be joined, the prior art does not allow for flushing the surfaces of the end faces to be joined.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for heating metal elements to be joined, which more rapidly and efficiently establishes a concentrated heating zone in the area contstiting the gap surfaces of the elements to be welded.
Suprisingly, it has been found that a high frequency current source can be utilized in a manner rendering a quicker and more concentrated heating zone than by induction heating.
The abovementioned object is achieved in connection with a method which is the two poles of the power source are connected galvanically to each element, respectively, close to the gap surfaces, and that
REFERENCES:
patent: 2021157 (1935-11-01), Stahl
patent: 2066668 (1937-01-01), Bennett
patent: 2542393 (1951-02-01), Chapman
patent: 2629805 (1953-02-01), Body
patent: 2805315 (1957-09-01), Chapman
patent: 3619548 (1971-11-01), Cavagnero
patent: 4241284 (1980-12-01), Rudd et al.
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