Method for producing bimetallic material

Abstract: The invention relates to a method for producing bimetallic material in a continuously operated extrusion machine (3), in which method the bimetallic components (1, 2) are fed together into the extrusion zone. According to the invention, the bimetallic material (1, 2) to be extruded is made to flow in an essentially laminar fashion throughout the extrusion, and the bimetallic material (1, 2) is made to be discharged from the extrusion machine (3) in an essentially radial direction with respect to the outer circumference of the feeding device (4) of the extrusion machine.

Description: The present invention relates to a method for producing bimetallic material of a superconductor material in a continuous process, so that the number of working steps in the process can be essentially reduced. In this connection, bimetallic material means a metal product formed of two metal components, where the components are either metals as such or metal alloys. Among such bimetallic materials, let us point out for instance a metal product formed of copper and of columbic titanium filaments contained therein used as superconductor. A superconductor which is high in copper and low in columbic titanium can be produced for instance as a channel conductor, where the columbic titanium serving as the superconductor is joined to a groove in the copper profile by means of soldering. When this type of channel conductor is wished to be insulated, the insulation is generally carried out by means of an enamelling process. In enamelling, the processing temperature of the channel conductor rises above the soldering temperature, in which case the soldering joint breaks open and the conductor is destroyed. A superconductor which is high in copper and low in columbic titanium can also be produced as a monolithic conductor, where columbic titanium is first packed inside the copper, and the ready-made superconductor is obtained as a final product from a production line including several working steps and heat treatments. From the point of view of the outcome, the multi-step production process is necessary for the columbic titanium only; when produced like this, copper is part of the conductor and passes there along at all stages. As for the production costs and unit length, a monolithic conductor is not so desirable as a channel conductor, but a monolithic conductor can be insulated in the enamelling process without damaging the conductor. In continuous extrusion, there is often applied a method described in the GB patent 1,370,894, called the Conform method. In this method the material to be extruded is conducted into a groove formed on the outer circumference of a wheel-like member. While the wheel turns around its axis, the material to be extruded enters into contact with a co-operating shoe structure essentially filling the groove, so that the motion of the material to be extruded is changed in relation to the wheel-like member. Thus the material is rendered to be extruded in the proceeding direction thereof, prior to the shoe structure or through an extrusion aperture provided in the shoe. By means of the Conform method, there can advantageously be extruded essentially long pieces with different shapes in cross-section. The JP patent application 55042139 relates to a production of composite deformed bar. The production is carried out in a continuously operated extrusion machine where an aluminium wire and a steel strip are introduced together, in overlapped form, into a container corresponding passage formed between a grooved wheel and a shoe block. The both metals extruded are pulled into the passage, and the aluminium wire tends to be delayed until reaching the die corresponding part. Thus, the both metals are pressure-welded firmly in the boundary surface. According to JP patent application the extruded bar is removed from the continuous extrusion machine mainly in the tangential direction; only the excess of the aluminium material is removed in the radial direction. The working degree by extrusion is thus very low and also the temperature is substantially low based on the temperature required for aluminium. The JP patent application 56041015 relates to a continuous manufacture of a composite rod by extruding the composite material through a die. The soft coating material as aluminium is fed into a hollow groove and at the same time the hard strip as stainless steel sheet is sent into the cavity formed by a circumferential end plane of the roll and the hollow groove under the condition that the strip material is tight pressed to the circumferential end plane of the roll. The composite material is pushed into a space in the depth of the cavity by the friction force between the composite material and the wall surface of the hollow groove, and hereby, the soft coating material is pressure welded to one side of the hard strip material. The JP patent application 55042139 and the JP patent application 56041015 relate to the continuous extrusion process where the coating material is welded to one side of a sheet or strip material. The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve an improved and more economical in costs method for producing bimetallic material in continuous extrusion where one bimetallic component is located centrally as a core material. The essential novel features of the invention are apparent from the appended claims. According to the invention, the bimetallic material to be produced is extruded in a continuously operated extrusion machine, such as a Conform machine, so that the material flows in an essentially laminar fashion throughout the working process. Moreover, the bimetallic material is removed from the continuous extrusion machine essentially in the radial direction. The bimetallic material is a superconductor material which is for instance high in copper and low in columbic titanium, and it is advantageously obtained the length of the state-of-the-art channel conductor and the insulation capacity of the monolithic conductor. In order to feed bimetallic material to be extruded into a continuously operated extrusion machine, the bimetallic component with a larger volume, e.g. copper, is advantageously worked into a grooved profile, and the bimetallic component with a smaller volume, e.g. columbic titanium, is inserted in the groove of said profile. The obtained- unit of bimetallic components to be extruded-is-fed onto the wheel-like feed member of a continuously operated extrusion machine, the outer circumference of said wheel being advantageously provided with a groove. When the bimetallic material to be extruded is a superconductor material that is high in copper and low in columbic titanium, the mixing of the different bimetallic components must be prevented. Consequently, the bimetallic blank obtained from the feed member of a continuously operated extrusion machine is conducted into extrusion, so that the bimetallic material flows in an essentially laminar fashion throughout the extrusion process. Moreover, because the components of the bimetallic material are in mutual contact already at the feeding stage, the extruded bimetallic material can be removed from the extrusion machine in an essentially radial direction with respect to the wheel-like feeding device of the extrusion machine. According to the invention, the co-operating shoe structure essentially filling the groove of the feed member in a continuously operated extrusion machine, as well as the extrusion member containing the extrusion aperture, are advantageously designed so that there is obtained an essentially laminar flow of the material to be extruded for the duration of the whole extrusion process. In order to create the laminar flow, the channel leading to the extrusion aperture provided in the extrusion member must, at least as for the first wall in the feeding direction of the material to be extruded, be designed so that the radius of curvature at the beginning of the channel wall is at least 70 percentages, advantageously 80 - 90 percentages, of the largest diameter of the extrusion aperture, when the aperture is for example oval-shaped, or of the diameter of the extrusion aperture, when the aperture is round. Moreover, the co-operating shoe member essentially filling the groove of the feed member of the extrusion machine is designed so that the co-operating shoe forms an essentially concentric circular curve with the first wall in the feeding direction of the material of the channel leading to the extrusion aperture. The co-operating shoe can also be rendered in the desired shape so that the material to be extruded as such forms a non-flowing area in front of the co-operating shoe, and at the border surface of the non-flowing and flowing areas the non-flowing area forms, in the feeding direction of the material of the channel leading to the extrusion aperture, an essentially concentric circular curve with the first wall, advantageously for a section corresponding a central angle of 40 degrees at maximum, when starting from the changing point of the flow and seen in the feeding direction of the material. When applying the method according to the invention for producing bimetallic material, the bimetallic component with a smaller volume, e.g. columbic titanium, is located centrally as the desired core material, surrounded by a jacket made of the material with a larger volume, e.g. copper. In the method according to the invention, this kind of production of the bimetallic material is carried out in a one-step continuous process, while the extrusion ratio is such that the extrusion temperature is at least 600° C. The invention is explained in more detail below, with reference to the appended drawing illustrating a preferred embodiment of the invention. According to the figure, the different components 1 and 2 of the desired bimetallic material are fed into the feeding device 4 of a continuously operated extrusion machine 3. The component 1 is formed as a grooved profile, and the component 2 is inserted in the groove thereof. The feeding device 4 is essentially wheel-like, and the components 1 and 2 are together fed into the groove provided on the outer circumference of the feeding device 4. The feeding device 4 transfers a bimetallic blank 5 containing the components 1 and 2 to the extrusion zone. In the extrusion zone, a co-operating shoe member 6 filling the groove of the feeding device 4 guides the bimetallic blank to the extrusion aperture 7. In order to make the bimetallic blank 5 to proceed in a laminar fashion in the different steps of the extrusion, the first wall 9 in the feeding direction of the extrusion member 8 is rounded, so that the radius of curvature of the wall 9 is 80 percentages of the diameter of the extrusion aperture 7. Likewise, in order to make the bimetallic material to proceed in a laminar fashion, in front of the co-operating shoe 6 there is formed, of at least part of the material to be extruded, a non-flowing area 10, the border surface 11 with the flowing material whereof forms an essentially concentric circular curve with the wall 9 for the section that corresponds to a central angle α of about 35 degrees, when starting from the point of change of the flow and seen in the feeding direction of the material. Advantageously the border surface 11 extends from the groove on the outer circumference of the feeding device 4 to the wall 12 of the extrusion machine. The extruded, ready-made bimetallic material is discharged from the continuously operated extrusion machine 3 in an essentially radial direction with respect to the wheel of the feeding device 4.

Claims: A method for producing bimetallic material of a superconductor material in a continuously operated extrusion machine (3) in one step, in which method the bimetallic components (1,2) are fed together into the extrusion zone, and the bimetallic material (1,2) is made to discharge from the extrusion machine (3) in an essentially radial direction with respect to the outer circumference of the feeding device (4) of the extrusion machine, and in which method the component (1) with a larger volume is formed as a grooved profile and the component (2) with a smaller volume is inserted in the groove thereof in order that the bimetallic material (1,2) to be extruded is made to flow in an essentially laminar fashion throughout the extrusion, so that the bimetallic component (2) with a smaller volume is located centrally and surrounded by a jacket made of the material (1) with a larger volume. A method according to claim 1, characterised in that in order to achieve an essentially laminar flow, as the counter surface (11) for the co-operating shoe (6) of the extrusion machine there is formed, together with the wall (9) which is essentially first in the feeding direction of the extrusion member, an essentially concentric circular curve extending advantageously for a section corresponding to a central angle (α) of 40 degrees at maximum, when starting from the point of change of the flow and seen in the feeding direction of the components (1, 2). A method according to claim 2, characterised in that the counter surface of the co-operating shoe (6) is formed of at least part of the material to be extruded. A method according to any of the preceding claims, characterized in that the first wall (9) in the feeding direction of the extrusion member (8) is rounded so that the radius of curvature of the wall (9) is at least 70 percentages, advantageously 80 - 90 percentages of the largest diameter of the extrusion aperture (7). A method according to any of the preceding claims, characterised in that the extrusion temperature is at least 600° C. A method according to any of the preceding claims, characterised in that the material with a larger volume is copper.

Inventors: VOITTO VANHATALO, VOITTO,VANHATALO
Applicants: OUTOKUMPU COPPER PRODUCTS OY
Application year: 1997
Main classification: B21C23
IPC codes: B21C23