Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1996-05-02
2001-02-06
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Electrical device making
C505S433000
Reexamination Certificate
active
06182351
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of producing superconductors, especially in form of tapes with a relatively high critical current density, by a mechanical deformation provided by means of a tool mechanism comprising movable clamping jaws and hinged brackets and eccentric arms connected to the clamping jaws, which are formed in such a way that the final product has a uniform thickness.
2. Background Art
It is known that high-temperature superconducting tapes can be produced by filling a mixture of metaloxide powders into a metal pipe, whereafter the pipe is deformed by being pulled into a round wire, followed by being extruded, rolled or pressed into a flat tape. Then the tape is heat-treated in such a manner that the powder is sintered to form a coherent, superconducting mass. These mechanical and thermal processes can be repeated in order to improve the superconducting properties, including the critical current density.
Metaloxide powders which can be used are, for instance, YBa
2
Cu
3
O
7
, Bi
2−x
Pb
x
Sr
2
Ca
2
Cu
3
O
y
, Tl
2
Ba
2
Ca
2
Cu
3
O
y
in polycrystalline form, in which the crystals are slightly plastic and very brittle. The metal coatings can be made of Ag or Ag-alloys which unlike the above mentioned powders, are very plastic and brittle. It is difficult to control a mechanical deformation of composite articles made of such materials, because the materials possess differing material liquidities. A ceramic, superconducting article must, however, possess predetermined structural properties in order to obtain a high critical current density. As few microcracks as possible must be present together with a high degree of texture with the superconducting Cu—O planes parallel to the current direction, and a high degree of uniformity with respect to the density, as well as a good electric interaction between the superconducting grains. It is important for obtaining these features that it be possible to control and optimize the forces having an effect on the article during the mechanical deformation.
It has been demonstrated on small lengths of tape, e.g. ones which are about 2 to 8 cm, in length that the critical current density can be improved by 3 to 4 times, provided the article after the first rolling and heat-treatment is subjected to one or more cycles involving a uniaxial force applied perpendicular to the current direction and followed by a sintering. It is, however, difficult to operate such a procedure as a continuous process, which is presumably necessary for allowing use of the articles for the production of tape-shaped wires.
During rolling of a wire into a tape, the deforming forces can be divided into a pressing force and a displacing force. During rolling, these two-forces are non-homogeneously distributed in the tape with the result that the superconducting ceramics are non-homogeneously compressed. In addition, the displacing force causes microcracks transverse to the current direction in the plane of the tape, either during the rolling or during the following sintering where possible residual tensions are released. The deformation caused by the rolling results in a higher material liquidity in the longitudinal direction than in the transverse direction of the tape. Ceramic crystals already developed can thereby be broken during succeeding rollings with the unfortunate result that microcracks may arise in the transverse direction.
Uniaxial pressing provides a very uniform power effect without noticeable displacing forces in the longitudinal direction of the wire. Such a pressing causes the material to be liquidized substantially only in the transverse direction. In addition, such a deformation reduces the formation of microcracks transverse to the current direction. Uniaxial pressing can, however, not be performed continuously.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of continuously deforming an article, but substantially without deformation in the longitudinal direction.
A method of the above type is according to the invention characterized in that the mechanical deformation is performed continuously, or stepwise continuously, and that the clamping jaws and the hinged brackets and eccentric arms connected thereto are formed such that during the deformation the same relative coordinate applies in the longitudinal direction, whereby the deformation in the longitudinal direction is negligible.
The resulting deformation method highly resembles uniaxial pressing.
A tool mechanism ensuring the above described type of deformation can be a continuously driven multi-member mechanism, but which only subjects the article to processing during a limited period of the process. The mechanism moves the clamping jaws in such a manner that only some of these clamping jaws are in contact with the article until a predetermined time and such that the pressing of the article is progressive, i.e. the processed length of the article is gradually increased. The quasi uniaxial pressing is obtained by the clamping jaws clamping on a portion of the article which has already been completely pressed while a portion not being completely pressed is subjected to the pressing. The resulting yielding of the article in its longitudinal direction is thereby minimized.
Furthermore according to the invention, the clamping jaws and the hinged brackets and eccentric arms connected thereto may be formed such that the power transmission to the clamping jaws is optimized by the angle between an eccentric arm and a hinged bracket connected thereto is close to 0° or 180° when the power transmission is maximal. Each arm is synchronously subjected to an input moment and an angular speed. In order to make the transmission of the torque as efficient as possible, the mechanism is formed in such a way that the angle of transmission of the torque is good on at least one of the arms as long as the article, e.g. the wire, is subjected to a processing by the clamping jaws. The transmission of power can be further improved by the mechanism transmitting the power from the processing into the frame in directions where the frame can be reinforced.
In addition, according to the invention, the tool mechanism may be formed in such a way that the maximum rigidity is obtained, which is obtained by the elements between the clamping jaws and the frame being made as short as possible. The elements must, however, be able to provide the desired curve.
Furthermore, according to the invention, the clamping jaws and the hinged brackets and eccentric arms connected thereto may be formed such that the largest possible length is processed per time unit. In practice, a tool mechanism is chosen which provides a moving curve for the clamping jaws presenting the longest approximately linear segment when measured in the angular turning on the input side.
REFERENCES:
patent: 3102443 (1963-09-01), Dell et al.
patent: 3575029 (1971-04-01), Weber
patent: 3577760 (1971-05-01), Franke
patent: 3583192 (1971-06-01), Kocks
patent: 3590621 (1971-07-01), Saxl
patent: 5360784 (1994-11-01), Kimura et al.
patent: 0 475 466 (1992-03-01), None
patent: 880523 (1981-11-01), None
patent: 1194520 (1985-11-01), None
patent: WO 93/14526 (1993-07-01), None
Patent Abstract of Japan, 2-183918(A), vol. 14, No. 457 (E986).
Patent Abstract of Japan, 2-192619(A), vol. 14, No. 471 (E990).
Hansen, Michael R., CADME Computer Aided Design of Mechanisms, Institute of Mechanical Engineering, Aalborg University, Ver. 1.0 Users Manual, Special Rapport Nr. 12, Apr. 1992.
Brok Kristian
Dalum Leif
Freltoft Torsten
Li Qi
Hughes S. Thomas
NKT Research Center A/S
Pillsbury Madison & Sutro LLP
LandOfFree
Method of producing superconducting tapes with a high... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing superconducting tapes with a high..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing superconducting tapes with a high... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2603270