Metal deforming – By deflecting successively-presented portions of work during... – With feeding of discrete articles or orienting of work...
Patent
1988-04-07
1989-06-27
Larson, Lowell A.
Metal deforming
By deflecting successively-presented portions of work during...
With feeding of discrete articles or orienting of work...
72369, B21D 912
Patent
active
048417602
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the manufacture of metallic tube bends from straight lengths of tube and particularly to the manufacture of tube bends of the type referred to in the trade as short radius bends i.e. bends the mean radius of curvature of which is short with respect to the diameter of the tube, for example those in which the mean radius of curvature of the bend is equal to 11/2times the nominal diameter of the tube.
In this specification the word tube is to be understood as including tubes and pipes.
The expressions "nominal wall thickness" and "nominal diameter" are used in the tube manufacturing industry and in the specification to mean the wall thickness and diameter by which a tube is identified. Tubes sold as of specified nominal dimensions may be of actual dimensions which differ from the nominal dimensions by maximum stated amounts known as the manufacturing tolerances.
In short radius bends such as those referred to there is such a large difference between the length of the bend at the inside of the bend and the length of the bend at the outside of the bend that simply bending a length of straight tube to the required radius does not provide an acceptable bend. A straight tube being bent in the usual manner by being bent around a curved former normally bends about its neutral axis. Thus the material at the inside of the bend is compressed longitudinally so much that it becomes too thick and often wrinkles as well while the material at the outside of the bend is stretched longitudinally so much that it becomes too thin.
Processes for the production of tube bends of such short radius and more or less constant wall thickness or other desired proportions of wall thickness are already well known.
An early known process consists of forcing at red heat a tube of smaller nominal bore than the required nominal bore of the finished bend required over a curved eccentrically expanding mandrel of circular cross section the final diameter of which is equal to the nominal bore of the bend to be made. This process is the subject of U.S. Pat. No. 1,353,714.
Tubes and tube bends are normally made to standardized dimensions and the known process and other later processes based on that early process suffer from the disadvantage that to produce bends of almost all of these standardized dimensions the smaller diameter straight tubes required must have diameters and wall thicknesses which are not standardized dimensions. Also the large amount of expansion which is performed on the tube precludes performance of the process cold because in this process the percentage expansion required exceeds the elongation that tube materials such as steel can bear in the cold state. Thus the process must be performed at forging temperature i.e. at a red heat. Also many of these known processes require separate and distinct operations to be performed on the tube so that tube bends cannot be produced consecutively as a continuous operation.
A method of and apparatus for producing tube bends from straight tube of the same diameter and wall thickness, thus obviating the need for non-standard tubes and employing a smaller percentage expansion is described in the specification of my prior GB Pat. No. 775 000, (corresponding U.S. Pat. No. 2,976,908).
In the process of GB Pat. No. 775,000 the tube section is first subjected to an inwardly radially directed compressing force which varies around the circumference of the outer surface of the tube from a maximum value at one point on the circumference to a minimum value at a point diametrally opposite and the tube, now of reduced diameter, is then subjected to an outwardly radially directed expanding force which varies around the circumference of the inner surface of the tube from a maximum at the point where the previously applied inwardly directed compressing force was a minimum to a minimum value at the point diametrally opposite where the previously applied inwardly directed compressing force was a maximum so that the original diametral dimensions are restored and subsequently or simult
REFERENCES:
patent: 1951802 (1934-03-01), Loepsinger
patent: 2441299 (1948-03-01), Taylor
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