Metal deforming – By use of roller or roller-like tool-element – With non-roller metal deforming station
Reexamination Certificate
2002-12-26
2004-12-28
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
With non-roller metal deforming station
C072S208000, C072S370170
Reexamination Certificate
active
06834523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a seamless tube with a grooved inner surface preferable for a heat transfer tube to be incorporated in an air-cooled heat exchanger employed in air conditioner for home or commercial use and to a method and apparatus for producing the same. More particularly, it relates to a seamless tube with a grooved inner surface formed by a roll rolling process with excellent productivity and to a method and apparatus for producing the same.
2. Description of Related Art
As an example of a method for producing a seamless tube with a grooved inner surface, there is one using a rolling process as disclosed in JP-B No. 1991-5882. A description will be given herein below to a method for producing a seamless tube with a grooved inner surface using a roll rolling process (hereinafter referred to as a roll rolling method). As a raw material, a raw tube made of an unannealed material (H-material) is used. A grooved plug having a groove formed in the outer surface thereof is inserted into the raw tube, while a pair of rolls rotating in contact with the outer surface of the raw tube are disposed at positions corresponding to the grooved plug. The axes of rotation of the rolls are adjusted to be orthogonal to the axis of the raw tube. Each of the rolls is configured as a hollow type having a diameter larger at the center portion thereof than at the end portions thereof such that a cross-sectional configuration including the axis of rotation of the roll generally matches the configuration of the outer surface of the raw tube in a cross section orthogonal to the axis of the raw tube. By drawing the raw tube, while pressing the tube against the grooved plug by means of the rolls, the grooved plug rotates around the tube axis and the groove in the grooved plug is transferred to the inner surface of the raw tube so that a groove is formed therein.
In the roll rolling method, the grooved plug forms a groove only in a local region of the inner surface of the tube so that a load on the groove plug is smaller than in a ball rolling method. Therefore, it is also possible to form a groove parallel to the axial direction of the tube in the outer circumferential surface of the grooved plug and form a groove parallel to the axial direction of the tube in the inner surface of the tube.
However, the roll rolling method has the problem that a groove is not formed evenly in the entire inner surface of the tube. The groove is formed in the inner surface of the portion of the tube pressed by the rolls but is not formed in the inner surface of the portion of the tube not pressed by the rolls.
To solve the problem, the JP-B No. 1991-5882 discloses technology using a plurality of roll pairs each composed of two rolls such that the tube is pressed by the pairs or rolls in different directions. This allows even formation of a groove in the entire inner surface of the tube, as described in the publication.
However, the foregoing conventional technology has the following problem. In accordance with the method for producing a tube with a grooved inner surface disclosed in the JP-B No. 1991-5882, a groove is formed in the inner surface of the tube by pressing the tube in a specified direction by means of a pair of rolls and then a groove is formed in the inner surface of the tube by pressing the tube in a direction different from the foregoing specified direction by means of another pair of rolls. In this case, the following phenomenon occurs.
FIGS. 19A
to
19
C and
FIGS. 20A
to
20
C are cross-sectional views illustrating a conventional method for producing a seamless tube with a grooved inner surface, which are orthogonal to the tube axis. It is to be noted that the process steps shown in
FIGS. 19A
to
19
C and
FIGS. 20A
to
20
C are performed continuously by the same apparatus.
FIG. 19A
is a cross-sectional view showing a configuration of the tube in a cross section orthogonal to the tube axis before groove formation. As shown in
FIG. 19A
, the tube
51
before groove formation has a generally circular cross-sectional configuration and no groove is formed in an inner surface. Then, as shown in
FIG. 19B
, a grooved plug
52
is inserted into the tube
51
, while the tube
51
is pressed by a pair of rolls
53
being rotated outside the tube
1
in contact relation therewith. Consequently, the inner surface of the tube
51
is partly formed with a groove
59
, while the tube is flattened in the direction in which it is pressed, as shown in FIG.
19
C.
Next, as shown in
FIG. 20A
, a grooved plug
54
is inserted into the tube
51
, while the tube
51
is pressed by a pair of rolls
55
being rotated outside the tube
1
in contact relation therewith. The rolls
55
press the tube
51
in a direction orthogonal to the direction in which the rolls
53
press the tube
51
. Since the tube
51
has been flattened in the direction in which it is pressed by the rolls
53
, a large clearance
56
is formed between the grooved plug
54
and the tube
51
.
If the tube
51
is pressed by the rolls
55
in this state, a groove
60
is formed in the inner surface of the tube
51
, as shown in FIG.
20
B. At that time, protrusions
57
are formed at the portions of the tube
51
corresponding to the clearance between itself and the rolls
55
. If a deep groove
60
is to be formed, the protrusions
57
are increased in size. If the tube
51
formed with the protrusions
57
is then subjected to a sizing process using a die or the like, the protrusions
57
are retracted into the tube so that depressed portions
58
are formed disadvantageously. As a result, the tube
51
no more has a smooth outer surface so that the commercial value of the tube
51
is reduced significantly. In
FIG. 20C
, the grooves
59
and
60
are not depicted.
Thus, in accordance with the method for producing a seamless tube with a grooved inner surface by performing a roll rolling process using plural pairs of rolls with respect to the tube disclosed in the JP-B No. 1991-5882, it is impossible to produce a seamless tube with a grooved inner surface which has a sufficiently high quality as a commercial product.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the foregoing problem and it is therefore an object of the present invention to provide a method for producing a seamless tube with a grooved inner surface which allows a seamless tube with a grooved inner surface having a smooth outer surface and an inner surface formed with different kinds of grooves to be produced at low cost and with high productivity, while preventing the formation of the protrusions.
A method for producing a seamless tube with a grooved inner surface according to the present invention comprises the steps of: drawing a metal tube to gradually reduce a diameter of the metal tube by means of a holding die disposed externally of the metal tube and a holding plug disposed internally of the tube and engaged with the holding die; rotating a plurality of first rolls in contact with an outer surface of the metal tube with a reduced diameter such that a rotation axis of each of the first rolls is orthogonal to an axial direction of the metal tube, while disposing, at a position inside the metal tube corresponding to the first rolls, a first grooved plug formed with a grooved outer surface and coupled in relatively rotatable relation to the holding die via a first coupling shaft, and pressing the metal tube against the first grooved plug by means of the first rolls to form a first groove in a portion of an inner surface of the metal tube in a circumferential direction of the tube and thereby form a plurality of first grooved zones; performing a sizing process with respect to the metal tube formed with the first grooved zones by using a sizing device; and rotating a plurality of second rolls in contact with the outer surface of the metal tube such that a rotation axis of each of the second rolls is orthogonal to the axial direction of the metal tube and deviates from the rotat
Hinago Nobuaki
Iwamoto Hideki
Ozeki Kiyonori
Saeki Chikara
Kabushiki Kaisha Kobe Seiko Sho
Larson Lowell A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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