Metal deforming – By use of tool acting during relative rotation between tool... – During rotation of work
Reexamination Certificate
1999-03-25
2001-10-02
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of tool acting during relative rotation between tool...
During rotation of work
Reexamination Certificate
active
06295855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to making a finned body of a high-ductility material.
More particularly, the invention relates to a method of making a finned body having a multiplicity of thin, closely spaced fins, such as a finned body having a fin density of at least one fin per millimeter, e.g. 1,5 or more fins per millimeter, and a fin height to thickness ratio of at least 5.
2. Prior Art
The invention also relates to a machine for making a finned body of this kind.
Such finned bodies find use in heat transfer structures, such as heat exchangers of the kind in which heat is transferred through the fins between a liquid or gaseous first fluid flowing in the passages defined and separated by the fins and a second fluid flowing through other passages in the finned body. The finned body often is generally cylindrical with the fins extending radially outwardly generally transversely to the axis of the body and may be made of aluminium or other light metal material of high heat conductivity.
In a known class of heat exchangers of this kind (see, for example, WO86/00395 or U.S. Pat. No. 4,923,003) the fins and the intervening gaps are dimensioned and designed such that the fluid flows in laminar fashion in the gaps or passages defined between the fins. In these heat exchangers the fins are very thin and very closely spaced: the fins may have a thickness of a few tenths of a millimeter, e.g. about 0.2 mm, and may be separated by a gap of approximately the same width, e.g. about 0.2 or 0.3 mm, and the height of the fins may be greater by one order of magnitude, e.g. about 3 mm.
As is readily appreciated, the forming of the fins on such heat exchanger bodies presents special problems, particularly where the finned body is made of a soft material, such as aluminium or some other light metal. For example, machining of such materials is often troublesome, because the material tends to stick to the machining tool and possesses poor chip breaking properties and because the surface finish tends to be poor. Moreover, because of the small fin thickness the fins easily deform or rupture under the influence of the forces to which they are subjected in the fin forming operation.
OBJECT AND SUMMARY OF THE INVENTION
A primary object of the invention is to provide a method and a machine for making a finned body of the kind indicated above.
In accordance with the invention, a method of making a finned body from a blank of a high-ductility material comprises the steps of
providing a fin-forming tool having an axis of rotation and comprising a set of flat circular spaced-apart forming discs centered on and disposed side by side at fixed intervals along said axis of rotation and in planes perpendicular thereto,
rotating the forming tool while causing it to perform cyclical movements over a surface of the blank with said planes maintained in a constant orientation and position relative to the blank, and
relatively displacing the forming tool and the blank at right angles to the axis of rotation of the forming tool to cause the peripheral portions of the forming discs during said cyclical movements of the forming tool progressively to penetrate into the blank and cause blank material to flow into the gaps separating the forming disks and form planar fins.
In the case of a tubular blank the outer surface of which is a surface of revolution, the method preferably includes mounting the blank for rotation about an axis contained in a plane which also contains the axis of rotation of the forming tool. The cyclical movement of the forming tool then is a unidirectional rotational movement in which the forming discs progressively penetrate into the outer surface layer of the body and cause the material in that layer to flow outwardly in the gaps between adjacent forming discs.
Using the method according to the invention it is possible in an economical manner to make finned bodies in which the fin dimensions and the fin density are as indicated above.
Preferably, a lubricating fluid is supplied to the points or areas where the forming discs engage the blank.
In order that the working of the blank may be smooth even if the force acting between the blank and the forming tool vary during the cyclical relative movements, e.g. as a consequence of discontinuities in the blank surface being worked, it is preferred to provide for a positive control of the transverse displacement of the forming tool relative to the blank so that the rate of displacement is not affected by variations in the resistance to the penetration of the blank by the forming discs. Such positive control can be accomplished by using a hydraulic actuator device to displace the forming tool and controlling the displacement through controlled bleeding of hydraulic fluid from the actuator device.
According to the invention, a machine for making a finned body from a blank of a high-ductility material, comprises
a blank holding device for supporting the blank,
a forming tool which is mounted for rotation about a tool axis and displacement transversely to the tool axis and comprising a set of flat circular spaced-apart forming discs centered on and disposed side by side at fixed intervals along the tool axis and in planes perpendicular thereto,
a motor for rotationally driving the forming tool,
a displacement mechanism for relatively displacing the forming tool and the blank holding device transversely to the tool axis during rotation of the forming tool to cause the forming tool to move cyclically over a surface of the blank, and
means for maintaining the forming discs in a constant orientation and axial position relative to the blank.
REFERENCES:
patent: 2143445 (1939-01-01), Le Jeune
patent: 2586011 (1952-02-01), Doelter
patent: 2645954 (1953-07-01), Pfingston
patent: 4170124 (1979-10-01), MacGregor
patent: 4612790 (1986-09-01), Przybyla et al.
patent: 274921 (1951-04-01), None
patent: 1 265 696 (1968-04-01), None
Gillbrand Per
Ohman Richard
Browdy and Neimark
Interproperty N.V.
Larson Lowell A.
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