A method of manufacturing a copper lengthy preparations

 

(57) Abstract:

The method relates to the field of metal forming and can be used in the production of cold-drawn products OHI copper for electrical purposes on drawing mills, equipped with machines electrocontact welding. After the butt welding of the workpiece resistance and deburring conduct local hot deformation, for example, upsetting the billet in the axial direction within the heat-affected zone of welded joint at a temperature of 810 - 870oWith prior education on preparation of local thickening with a diameter of 1.5 - 2.0 diameter of the original piece. After cooling, thickening of the gallbladder is removed by known methods. The method can improve the plastic properties of the metal in the heat-affected zone of welded joints by grinding grains of copper and use the blank of increased length. 2 Il.

The invention relates to the field of metal forming, and more particularly to the drawing production profiles for electrical purposes, of copper, and can be used for making butt resistance welding of long workpieces for which you want the area of the intersection did not differ by milling the th resistance welding, including the fixing of the ends of the workpiece in the clamping contacts of the welding machine, the make contact of the end faces of the workpieces under a small pressure, turning on the welding current, intensive heat, bringing metal to plastic state and welding under pressure precipitation [1].

It was also stated that the quality of the connection depends on the distance between the clamping contacts, surface pressure, precipitation, current density and heating duration [1, S. 174].

The disadvantage of this method is the appearance of the heat-affected zone of welded joint (hereinafter HAZ) coarse-grained structure, resulting in sharply reduced the ductility of the metal in this zone, increased breakage during wire drawing, there is a local phenomenon (HAZ) wear when using the device for the transmission of electric energy in terms of the sliding contact.

There is also known a method of butt welding resistance, comprising, along with the ones listed in previous similar characteristics, as follows: for compression parts use constant or rising towards the end of heat stress, stress relieve after switching on the welding current [1, S. 173].

A disadvantage of the known technical Gotovina and equipment standard welding machines devices to create a constant (initial stage), and then ascending to the end of heating) of the upsetting.

Closest to the invention is a method of butt resistance welding of workpieces, mainly copper wire with a diameter up to 16 mm, containing, along with the characteristics specified for the above analogues, the following: welding and simultaneous subsidence spend with amplification (thickening) in the joint, which is formed due to the landing of the metal [1, c. 173 - 174] , butt welding is carried out at a temperature of 0.7 - 0.75 melting temperature [1, c. 394]. Taking into account the melting temperature of copper, equal 1083oC, this range is 758 - 812oC.

The use of the known technical solutions, for example with the aim of obtaining long copper billets intended for further drawing (especially multiple), accompanied by the following disadvantages.

It is known that the microstructure of the heat affected zone after welding resistance in stark contrast to the microstructure of the base metal is significantly larger (8 - 10 times) grain [2]. Due to unfavorable with regard to the reduction of plasticity, coarse-grained structure, as noted above, an increasing number of cliffs front Timoti repeated stops mill and new refills), grow a waste of metal. Particularly sensitive these losses when working on the most modern multiple drawing machines - mills with slip and continuous mills. On the other hand, the effect of education on harvesting sites with significantly different grain size structure and therefore areas with significantly expands the level of mechanical properties there are three negative consequences.

First, obviously adversely decrease the mechanical strength of the wire on its different parts with large grains in the case of its use as a pendant ecoprovince (especially when the accumulation of snow and glaciers).

Secondly, uneven local wear of the wires in areas with larger grain leads to a deterioration of the conditions of transmission in the case of its use as part of a moving electrical contact, for example, the contact network of electric vehicle, especially at high speeds characteristic of modern long-range transport.

Thirdly, the frequency (periodicity) of the location of these sections of local wear varies from preparation to finished product accordingly to the ü resonance phenomenon, which, as you know sharply (dozens of times) reduces the strength of the products.

It should also be noted that the use of a heating temperature equal to 0,7 - 0,75 melting point of copper (i.e., 758 - 812oC) contributes to solving the problem of welding, but at the same time it is, despite the murky junctions, grain growth in the HAZ with all its adverse consequences described above.

The basis of the invention aims at eliminating these disadvantages, namely: to improve performance when drawing through the use of billets increased length and reduce the likelihood of breakage of the product in the drawing due to the increase of the plastic properties of the metal in the heat-affected zone of welded joint; to improve the performance characteristics of products by obtaining fine-grained structure.

This objective is achieved in that in the known method of manufacturing a copper long round billets, including flash butt welding coupling korotkomernyh blanks and deburring, according to the invention after welding and deburring conduct local hot deformation of the workpiece, for example, the draught in the axial direction within the heat-affected zone swarnava original piece, with the subsequent removal of local thickening.

The hot deformation of the workpiece, for example, precipitation in the axial direction locally, within the HAZ of the welded joint at a temperature of 810 - 870oC with formation of harvesting local thickening with a diameter of 1.5 - 2.0 diameter of the original piece (which corresponds to the degree of deformation of 0.54 to 0.92. The degree of deformation due to bulbourethral form of thickening presented in the form where F1and d1- the cross-sectional area and diameter thickening, F0and d0- same, but for the original piece) provides the necessary improvement in the structure of the HAZ by crushing grains of copper, intensively grown in the welding process. A special study of the microstructure of the HAZ after welding confirmed that the grain size in the HAZ 6 - 8 times the size of a grain outside the HAZ, i.e., in the base metal of the workpiece (in the metal state, cooled to room temperature).

The appearance in the ETVA coarse-grained structure after butt welding resistance leads to a decrease of the plastic properties of the metal in this zone. As a consequence, increasing the likelihood of breakage of the stretch rod in the drawing, the practice shows that the rod tends to obreve what's blanks, at 4 times the mill with slide and the diameter of the drums 800 mm in 14 cases (16 joints) cliffs accounted for HAZ. In addition, performance of the following service specifications of the products:

developing local wear in the case of operation as parts of the moving electrical contact (for example, the contact wires for the air network of the city and main transport), and places (areas) increased wear are heat-affected zone in the workpiece, the length of which in the finished product increases in direct proportion to the drawing ratio in the multiple drawing;

the appearance of sections of local wear of the wire reduces the stability of the process of transmission of electrical energy from the conductor to the current collector.

The local (within HAZ) hot deformation of the workpiece, for example, precipitation in the axial direction at a temperature of 810 - 870oC with the degree of deformation of 0.54 to 0.92, as shown by experimental studies, significantly, in comparison with the known technical solutions to improve the performance characteristics of products by grinding the grains in the HAZ grinding grain prints physical (including electrician, that concentrated heating surface area and sediment provide high plastic and electrical properties of welded joints. In [2] also noted that when welding copper is often necessary in the prior and concomitant heating of the base metal with the purpose to alleviate significant thermal strains and stresses, and to improve performance when drawing through the use of billets increased length and reduce the likelihood of breakage of the product in the drawing. A violation of these limits results:

when the deformation of the metal at a temperature below 810oC to below the lower limit of the desired deformation (0,54) because of the low power capabilities of the serial welding machine with which it's performed, and heating and plastic deformation, resulting in failure to obtain the necessary grinding of grain and increase the ductility of the metal in the HAZ, in addition, to increase efforts precipitation in connection with increasing the deformation resistance of the metal at lower temperatures;

when the deformation of the metal at temperatures above 870oC - to increase the likelihood of undesirable grain growth [2] and to intensify the process of scaling due to bliss the heating of the workpiece;

when upsetting to the degree of deformation below the lower limit of 0.54 to insufficient working of metal and to insufficient grinding grain HAZ;

when upsetting to the degree of deformation above the upper limit of 0.92 to unjustified increase in the volume of metal that goes on the thickening of the blank during its precipitation and the need to increase costs for subsequent removal of this volume, as well as to increase efforts precipitation.

Thus the implementation of the method of manufacturing a copper long round billets offered by way provides improved performance when drawing and improvement of the performance characteristics of products.

In Fig. 1 shows the workpiece after welding and deburring; Fig. 2 - procurement after conducting its local hot deformation draught in the axial direction.

The method is as follows.

After conducting contact docking welding korotkomernyh hot-rolled or hot-pressed billets and deburring long workpiece 1 without pre-cooling (no cooling of the workpiece after welding is equivalent to the preliminary heating HAZ, very polisemico.) establish and fix in clamping contact of the welding machine, which was carried out by welding. Then spend electrocontact heating billets carried out in the mode of annealing. Annealing mode included in the construction of the welding machine. Heat lead on the length of the workpiece corresponding to the length (along the longitudinal axis) HAZ 3, i.e., the length of about two diameters of the workpiece. Heating billets lead to a temperature of 800 to 870oC. Achievement of regulated temperature interval periodically monitor bayonet thermocouple. Upon reaching this temperature, carry out the local axial upsetting of the billet in its length corresponding to the length of HAZ 3, i.e., length, approximately equal to two diameters of the workpiece. Settling for a specified length provide installation screw terminals of the welding machine at a distance corresponding to the length of the HAZ.

In the process of local heating of the workpiece is regulated temperature reaches a first region of the welded joint 2 (centre HAZ), HAZ region 3 on both sides of the joint 2 are reduced in comparison with the center temperature. The corresponding temperature gradient on both sides of the junction (810 - 870oC in the center of the HAZ-650 - 680oC on the periphery HAZ) results in uneven fact deformation of the ptx2">

After cooling, thickening 4 it is removed by known methods. To determine the effectiveness of the proposed method and find the interval of heating temperature and the degree of deformation HAZ, providing a stable process of grinding grain to improve the ductility of the metal, experiments were carried out with the experimental-industrial batch of copper billets with a diameter of 16 mm welding machine rolling-drawing mill VSP-5 Kamensk-Ural plant processing non-ferrous metals. Preliminary experiments it was found that the temperature difference in the center of the HAZ and on its periphery is 140 - 160oC. Because it is known [4] that the lower temperature limit of the hot processing of copper is 650oC, we concluded that the lowest temperature in the center of the HAZ should be 650 + 160 = 810oC. was defined as the lower limit of the heating temperature of the metal, is fixed in the center of the HAZ. The case of the upper limit of the operating temperature range equal to 870oC above. Next were tested modes of treatment HAZ with the following basic parameters:

the heating temperature in the center of the HAZ,oC: 920, 870, 820, 770, 720;

the diameter Bulavinov thickening of the workpiece in centre to the diameter of the original piece: 2,09; 2,00; 1,88; 1,69; 1,50; 1,44; 1,38; the degree of deformation in this case amounted to, respectively,: 0,98; 0,92; 0,84; 0,70; 0,54; 0,49; 0,43.

Analysis of the results obtained at the local sediment HAZ billet in the axial direction in the above conditions showed the following.

Precipitate at temperatures of metal in the center of the HAZ equal to 770 and 720oC, results in Bulavinov thickening the diameter of 22.5 and 21.7 mm, respectively, i.e., not reached the lower limit of the required relationship of diameters equal to 1.5. The grain size in the HAZ when it exceeds the size of the grains in the base metal of the workpiece 4 to 5 times. It was noted above that the grain size in the HAZ after welding without the use of the proposed method of processing exceeds the grain size outside the HAZ (i.e. mostly metal) 6 - 8 times.

The precipitate at a temperature in the centre of the HAZ, equal 920oC, results in Bulavinov thickening the diameter of 33.4 mm, i.e., to exceed the upper limit of the ratio of the diameters of 2.0. The grain size in the HAZ exceeded the size of the grains in the base metal 2 to 3 times; the surface of the metal (by visual assessment) is covered with a more substantial layer of scale than when heated to a temperature above 870oC.

When heated to temperatures in the center of C is Smurov grains in the base metal (up to 1.5 times maximum).

When upsetting to the degree of deformation, equal of 0.49 and 0.43 (diameter thickening is 23 and 22 mm, respectively) grain size in HAZ exceeded the size of the grain outside the HAZ 5 to 6 times.

When upsetting to the degree of deformation equal to 0.98, the diameter bulbourethral thickening amounted to 33.5 mm, which exceeded the upper value of the interval 24 - 32 mm and has generated increased metal consumption and increased costs if you then remove too much metal.

Sediment with degrees of deformation HAZ equal 0,54; 0,70; is 0.84 and 0.92, has provided fine-grained structure, little different from the metal structure outside the HAZ.

In General, experimental test pilot batches of copper billets with a diameter of 16 mm showed that the axial sludge heat-affected zone of welded joint, carried out outside the regulated temperature and deformation modes hot working, does not give positive results.

Drawing industrial parties lengthy preparations, obtained by the proposed method compliance with regulatory regimes, a drawing machine with slip confirmed the complete absence of cliffs extending our products therm zones the invention compared with the known technical solution, is to improve performance when drawing and improvement of the performance characteristics of products.

Performance is improved when the drawing is achieved through the use of billets increased length and reduce the likelihood of breakage of the product when being drawn through improved plastic properties of the metal in the heat-affected zone of welded joint.

Improvement of the performance characteristics of the products is ensured by improving the structure by crushing grains of copper in the heat-affected zone of welded joint.

The invention can be used in the manufacture of cold-drawn copper products for electrical purposes on drawing mills, equipped with machines electrocontact welding.

A method of manufacturing a copper lengthy preparations of circular cross section for drawing, including contact butt welding korotkomernyh blanks and deburring, wherein after welding and deburring conduct local hot deformation, for example, upsetting the billet in the axial direction within the heat-affected zone of welded joint at a temperature of 810 - 870oWith prior education on preparation of local thickening of diameter 1

 

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