Electric heating – Metal heating – Of cylinders
Patent
1994-02-03
2000-11-14
Shaw, Clifford C.
Electric heating
Metal heating
Of cylinders
21912511, B23K 9173
Patent
active
061473170
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a finned tube made of metal, particularly a heat-exchanger tube, consisting of a cylindrical tube body and a strip wrapped around it in helical fashion, the broad sides of which are roughly perpendicular to the tube surface and whose narrow side facing the tube surface is joined to the tube surface by a welded seam, as well as a process for its manufacture and a device for performing the process. The process involves at least one endless strip, forming the fins, being wrapped around a rotating tube body in roughly helical fashion and the narrow side of the strip facing the tube body being joined to the tube surface by means of a welding device.
In a familiar process of the aforementioned type (DE-PS 35 08 878), the strip forming the fin is welded to the pipe jacket on one side. In order to make effective use of larger heat exchange surfaces in this context, the welded seam to be made has to be relatively broad, this entailing the disadvantage of a need for larger amounts of welding filler and welding energy. Furthermore, this can subsequently lead to shrinkage cracks and increased corrosion. In the familiar process, the welding device is located laterally alongside the strip to be wrapped.
In another familiar process (DE-GM 91 02 944), welded seams are to be applied to both sides of the fin, so that the full width of the narrow edge of the fin is joined to the tube body. This process can only be applied if the individual fins of the wrapped strip are sufficiently far apart that the second welding device can be inserted into the gap between two fins. Apart from this, however, the same disadvantages are involved as with the first-named process.
Moreover, both of the familiar processes have the disadvantage that the application of the relatively thick welded seams permits only low working speeds.
Therefore, the invention is based on the task of developing a new manufacturing method which works in an economical and energy-saving manner with little outlay and leads to a product where the entire width of the base of the fin is optimally joined to the tube surface and the joint area displays good thermal conduction.
According to the invention, this task is solved by a process characterised in that the working end of the welding device is inserted into the free wedge-shaped space between the tube surface and the strip to be wrapped, in that the welding device is used to apply a welding bead, which runs exactly in the area of the joint between the strip and the tube surface, to the tube surface using a filler, before the narrow edge of the strip to be joined makes contact, and in that the narrow edge of the strip to be joined is pressed into the welding bead while it is still liquid.
The process pursuant to the invention can be performed with a minimum of energy and a very small amount of welding filler. Furthermore, this process is characterised by the fact that a welding speed can be used which is several times greater than that of the conventional welding process. The joint between the tube material and the welded seam can be regarded as a metallurgical bond. Depending on the boundary conditions selected, it is also possible, if necessary, to generate a metallurgical bond between the base of the fin and the welded seam. Optimum welding of this kind ensures undisturbed heat transfer between tube and fin, zones of overheating being avoided at the same time.
The welding bead to be applied to the tube surface, which need only be relatively thin, is designed to be roughly as wide as the thickness of the strip. This ensures that the welded seam reliably covers the entire width of the joint area and possibly projects slightly beyond the respective fin at the sides.
It is expedient to keep the strip to be wrapped around the tube surface under tensile strain, so that the strip is pressed into the welded seam with a certain amount of force of pressure.
However, it is also possible specifically to press the strip forming the fins into the welded seam by means of force applied in the radial directio
REFERENCES:
patent: 3246116 (1966-04-01), Anderson et al.
patent: 3436517 (1969-04-01), Pignal
patent: 3557427 (1971-01-01), Pignal
patent: 3662942 (1972-05-01), Pignal
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