Pipes and tubular conduits – Spirally seamed
Reexamination Certificate
1996-02-12
2001-06-05
Gerrity, Stephen F. (Department: 3721)
Pipes and tubular conduits
Spirally seamed
C138S142000
Reexamination Certificate
active
06240972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a multi-wound metal tube prepared by winding and brazing a hoop material (metal hoop material), as well as a method and an apparatus for preparing the same.
2. Description of the Prior Art
A method of preparing a multi-wound metal tube includes a method of plastically deforming a hoop material (metal hoop material) having a copper brazing material applied over the entire surface thereof into a tubular body by a forming apparatus, melting the brazing material between walls of the multi-wound tubular body by a heating device and then coagulating the molten brazing material by a cooling device to obtain a final product. Means for melting the brazing material of the multi-wound metal tube in this method includes a method of using an electric furnace and a method of ohmic heat generation by electric current supply. The method of using the electric furnace comprises cutting a metal tube formed into a multi-wound wall structure by a forming apparatus into a predetermined length and sending the multi-wound metal tubes each of a predetermined length successively into the electric furnace and melting the brazing material, while the ohmic heat generation by electric current supply comprises supplying electric current to a tubular body by way of two electrodes spaced apart from each other in the longitudinal direction of the tubular body delivered continuously from the forming apparatus, melting the brazing material by the ohmic heat generation of the tubular body and conducting brazing continuously (refer to U.S. Pat. No. 2,746,141 and German Federal Republic Patent Specification No. 813839). However, the prior method for manufacturing the multi-wound metal tube involves the following problems.
That is, abrasion of a forming tool incorporated into the forming apparatus variation of mechanical property or size of an elongate hoop material (usually longer than 1,000 m) wound in a coiled shape sometimes causes gaps between each of multi-wound walls or peeling between inner and outer seam portions, in a wall forming step. If the multi-wound metal tube is in such a state, gaps are formed in some places which hinders adhesion of the brazing layer material between each of the wound walls even after brazing, to provide poor adhesion, as well as adhesion for seamed portions is poor, failing to provide a function as a pipeline and it can not but be discarded as failed products.
FIGS.
20
(A) and
20
(B) are photographs showing a portion of a cross-sectional structure of a multi-wound metal tube manufactured by an existent method, in which FIG.
20
(A) is a photograph showing a portion between walls and FIG.
20
(B) is an enlarged photograph for an outer seam portion. As apparent from the photographs of FIGS.
20
(A) and (B), in a multi-wound metal tube manufactured by the existent method, gaps are sometimes formed between wound walls in which a brazing layer is not present, to make adhesion poor, and a step is formed to an outer seam portion, which may result in a problem in view of the quality in a case where sealing performance is required between the outer circumferential surface of the tube and a rubber hose or on O-ring when the latter is fitted over the surface of the tube upon use.
Further, in the existent method, since there is no appropriate means for eliminating the gaps between each of the multi-wound walls caused in the forming step, materials have to be selected while considering the mechanical property, for example, spring back of the hoop material, which restricts the range for selecting the materials. Usually, a hoop material having a length of more than 100 m has been shaped as it is without correcting dimensional scattering for each of portions. Further, in view of the gaps between the multi-wound walls caused in the forming step, a great amount of the brazing material is required, to increase the cost for the brazing material such as copper and, in addition, this increases the thickness of the copper layer as the brazing material (refer to photograph in
FIG. 20B
) and there may be a worry of causing a problem of embrittlement along with increase of the copper layer, which is not preferred.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the foregoing problems in the prior art and it is an object thereof to provide a multi-wound metal tube of high quality, with excellent adhesion between multi-wound walls and for a seam portion even if dimensional scattering is present for each of portions of an elongate hoop material, by forming the material while amending the scattering by heating, or capable of extending a range for selecting the material, capable of reducing embrittlement along with increase in the amount of the brazing layer and reducing the amount of the brazing material used, as well as a method of and apparatus for manufacturing the same.
A multi-wound metal tube according to the present invention has an aspect in which an outer seam portion is filled with a brazing material to make the entire outer circumferential surface smooth, and wound walls are entirely adhered tightly without leaving gaps to each other by the brazing material.
Further, a method of manufacturing a multi-wound metal tube according to the present invention comprises pressure-welding walls of a multi-wound tubular body with each other in a radial direction while at least the outer circumference of a brazing material between the walls of the multi-wound tubular body is kept at a flowable temperature by heating and then applying cooling.
The method also has a feature of using at least one of a step for pressing the outer circumferential surface of the tubular member substantially uniformly in a radial direction from the outside for radially pressure welding walls of the multi-wound tubular body to each other, a step of pressing the inner circumferential surface of the tubular body substantially uniformly in the radial direction from the inside or a step of exerting a tensile force to the tubular body in a direction of the tubular axis.
The method has a further feature of conducting primary cooling simultaneously or as rapidly as possible after the pressure welding in the radial direction and further conducting secondary cooling.
It has a still further feature of quenching the brazing material in the flowable state approximately to a coagulation point of the brazing material by the primary cooling conducted simultaneously with or as rapidly as possible after the radial pressure welding.
It has a still further feature of applying heating by using a brazing furnace, an ohmic heating device or a high frequency heating device. Further, the ohmic heating device has a feature of using a DC power source.
Further, an apparatus for practicing the method according to the present invention comprises a forming apparatus for forming a hoop material into a multi-wound tubular body, a heating device for melting a brazing material present between walls of the multi-wound tubular body and a cooling device for coagulating the molten brazing material and cooling the tubular body, wherein the apparatus comprises at least one means for radially pressure welding walls of the multi-wound tubular body to each other in a radial direction so as to flow the brazing material between the inside of the heating device and the inlet of the cooling device.
Further, the pressure welding means comprises at least one of means for pressing the outer circumference of the tubular body substantially uniformly in the radial direction from the outside, or transfer speed varying means for exerting a tensile force on a tubular body in the direction of the tubular axis.
Further, the pressure welding means from the outside comprises one or more sets of press rolls or one or more dies.
The pressure welding means from the inside comprises a plug or mechanical pipe enlarging head incorporated for enlarging the diameter of the multi-wound tubular body.
Further, the transfer speed varying means for exerting the tensile force in the direct
Takahashi Teruhisa
Takikawa Kazunori
Casella Anthony J.
Gerrity Stephen F.
Hespos Gerald E.
Porco Michael J.
Usui Kokusai Sangyo Kaisha Limited
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