CN117483475A

CN117483475A - Small-diameter thin-wall copper and copper alloy pipe and manufacturing method thereof

Info

Publication number: CN117483475A
Application number: CN202210885077.6A
Authority: CN
Inventors: 祁威
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-07-26
Filing date: 2022-07-26
Publication date: 2024-02-02

Abstract

The invention provides a small-diameter thin-wall copper and copper alloy pipe and a manufacturing method thereof, wherein the manufacturing method comprises the following steps of pipe blank manufacturing: continuously extruding by adopting a continuous extruder to prepare a tube blank with the outer diameter phi 25-phi 80mm and the wall thickness of 1.5-5 mm; drawing: continuously and directly drawing the tube blank for at least one pass and coiling and drawing for multiple passes until the tube blank reaches the size of a finished product, wherein the total wall reduction of drawing is not less than 60%; annealing: and annealing the copper and copper alloy tube drawn to the finished size by adopting on-line induction annealing or nitrogen protection atmosphere annealing furnace annealing. The manufacturing method combines continuous extrusion with drawing and annealing of the later pass for the first time, and simultaneously carries out new setting on the outer diameter and the wall thickness of the continuous extruded copper and copper alloy pipe, thereby not only retaining the advantages of continuous extrusion, but also overcoming the defects of continuous extrusion on processing small-diameter thin-wall pipes.

Description

Small-diameter thin-wall copper and copper alloy pipe and manufacturing method thereof

Technical Field

The invention relates to a method for manufacturing small-diameter thin-wall copper and copper alloy pipes and the copper and copper alloy pipes manufactured by the method, belonging to the field of nonferrous metal pipe processing and manufacturing.

Background

The copper and copper alloy pipes with the outer diameter smaller than 16mm and the wall thickness not larger than 1.0mm are called small-diameter thin-wall copper and copper alloy pipes in industry, and the small-diameter thin-wall copper and copper alloy pipes are mainly used for heat transfer pipes and connecting pipes of air conditioner heat exchangers. The annual usage of the refrigeration air conditioning industry exceeds 100 ten thousand tons. The modern small-diameter thin-wall copper and copper alloy pipe manufacturing factories mainly use a casting and rolling method of horizontal continuous casting and planetary rolling to produce the small-diameter thin-wall copper and copper alloy pipe. Compared with the prior art, the casting and rolling method has the advantages of short flow, high efficiency, large yield and low cost, and the method replaces the traditional technology and is a representation of technical progress. However, casting and rolling also have some problems: the horizontal continuous casting technology has high requirements, difficult quality control and poor control, furnace leakage accidents can occur, and explosion is easily generated when continuous casting cooling water contacts with molten copper water, so that personal injury and property loss are caused; the planetary rolling mill has the advantages of complex structure, high failure rate, high operation and maintenance difficulty and high cost; the casting and rolling method is only suitable for large-scale production of single variety of small-diameter thin-wall copper pipes, the yield of a single line is more than 2 ten thousand tons/year, and more small and medium enterprises are production scales with the yield of 2000-5000 tons/year, so that the technology is difficult to meet the demands of the enterprises.

Continuous extrusion is a relatively new extrusion method developed in the twentieth century 70-80. The most successful application of this method in the field of pipe manufacture is the manufacture of pure aluminum pipe. The round aluminum bars are used as raw materials, the extrusion wheels continuously rotate to generate friction force to continuously press the single aluminum bar into the extrusion chamber for extrusion of the aluminum pipe by the split-die bridge, and aluminum metal entering the extrusion chamber is split and welded to be extruded into the aluminum pipe. The whole extrusion process is simple, continuous, efficient and low in cost, and is completed in one step by a continuous extruder from raw materials to finished products, and drawing and annealing in the later step are not needed. The continuous extruded pure aluminum tube can be used in large quantities on a refrigerator heat exchanger with great success. The section of the continuously extruded pipe is provided with welding seams generated by the split dies, a plurality of split bridges are provided with a plurality of welding seams, the extrusion with the welding seams is commonly called as seamed extrusion in the industry, and the pipe is called as a seamed pipe. The problem of continuous extrusion is that it is not able to provide a sufficiently large extrusion force and extrusion ratio as in the case of a horizontal extruder, various problems occur in the case of an aluminum alloy material such as 3003, 6063 and the like, which has a slightly large extrusion deformation resistance, the extruded product has coarse grains, the weld seam strength is insufficient to produce flaring cracking, and the tube bending and expanding process produces an outer surface "orange peel" rough surface and the like. The continuous extrusion method is still unable to manufacture aluminum alloy pipes for air conditioner heat exchangers and automobile pipe fittings up to the present day, and the application of the continuous extrusion method is greatly limited.

UKAEA (british atomic energy administration), BWE, honton, et al, 1980-2000, have continuously filed several patents for manufacturing copper tubes by extrusion using a continuous extruder, which give specific structures of the extrusion die, the size distribution ratio of the runners, the extrusion temperature, and the regulating structure … … for ensuring stable entry of copper tubes into the extrusion chamber. See patent CN1148354, continuous extrusion apparatus for details; CN1376093, copper tubing and WO2004076087, CONTINUOUS EXTRUSION APPARATUS (continuous extrusion apparatus).

The method for manufacturing the copper pipe by adopting the continuous extrusion machine extrusion is a very good technical scheme, and compared with the casting and rolling method, the method has the advantages of shorter flow, higher efficiency and lower cost. The copper rod purchased in the market is formed into a copper pipe through one pass of a continuous extrusion machine, and the single-line productivity of the continuous extrusion machine can be from 2000 tons/year to 10000 tons/year from small to large. And compared with a planetary rolling mill, the continuous extrusion machine has simpler structure and more convenient operation and maintenance. The continuous extruder can be used for replacing the extrusion wheel and the die, and copper bars, copper bars and other copper profiles can be manufactured. This technology, if successful, is most likely to be the dominant copper tube manufacturing technology. Unfortunately, the above patent publication does not have further subsequent achievements, and the study conducted by uk corporation fails to reach industrial application.

The inventor has seen the potential of this method and made extensive research and experiments in recent years, and has found that when the size of the extruded copper tube is too small, the extrusion working condition becomes bad, and the service life of the die is insufficient, which is also the main reason for the failure of the technical development in the present year. The foregoing uk company has been desiring to directly extrude finished small diameter copper tubing from experience that has been used to succeed in continuously extruding aluminum tubing when developing continuously extruded copper tubing in the 1980-2000 s. The method has the advantages that the processing procedure of the copper pipe in the subsequent pass can be saved, the efficiency can be greatly improved, and the cost can be reduced. The data that can be found show that the copper tube sizes they had originally extruded include Φ6x1 and Φ20x2, see "recent development of the British CONFORM continuous extrusion technology" by light alloy processing technology 1990.1. In addition, from the patents CN1376093a and copper pipe filed by BWE company, it can be seen that the structure of the die is designed specifically for extruding small diameter pipes. However, these attempts by uk have eventually failed.

To successfully extrude a finished tube with a continuous extruder, it is very difficult to solve all technical problems in this process. The biggest technical problem of the seamed pipe is that the mechanical property of the welding seam is poorer than that of the matrix, and the extrusion pressure and the extrusion temperature in the extrusion chamber are increased to improve the mechanical property of the welding seam. Finished copper tubes used in the refrigeration industry are typically small diameter thin wall tubes, the size of the dies used to extrude such tubes can be small, and deformation temperatures exceeding 750 ℃ are required in the extrusion chamber, see patent CN1376093a. Even now, this extrusion temperature is an extremely stringent consideration for any hot die steel. In addition, the extrusion force is large, and the specific pressure acting on a small unit area of the die is large. The severe extrusion conditions of high temperature and high pressure can greatly reduce the service life of the die, thereby eventually leading to failure of the technique.

It is the success of continuous extrusion in pure aluminum tube processing and the failure of the above-described processing of copper and copper alloy tubes, especially small diameter thin wall copper and copper alloy tubes, that results in the formation of an inherent concept to those skilled in the art: continuous extrusion cannot be used to produce small diameter thin wall copper and copper alloy tubes. However, through the studies of the present inventors, unexpected and surprising findings have been found.

In the 90 s of the twentieth century, a technology for seamless welding of pipes has appeared in the steel pipe industry in China. Welded pipes in the steel pipe industry are not identical to the slotted pipes produced by the slotted extrusion previously mentioned in this patent. The welded steel pipe is produced through high frequency welding after the steel belt is formed in a pipe welder. The welded seam of the welded pipe is formed by butt welding two sides of a steel belt with molten metal, and only one welded seam is arranged on the circumference of the welded pipe of the steel pipe. The weld joint and the heat affected zone near the weld joint are all greatly different from the matrix in geometric dimension, mechanical property and grain structure due to the difference of heated temperatures during welding the pipe, and the weld joint and the heat affected zone near the weld joint are weak parts of the welded pipe. The so-called seamless welding of pipes is in fact a process for strengthening the weld. Firstly, removing burrs of inner and outer welding seams by using inner and outer scrapers, and then, carrying out thermal tension reducing on welded pipes by using a ten-odd frame steel pipe tension reducing mill. The welded pipe is heated to 920-950 ℃ and rolled under the large reduction of a plurality of frames, the matrix, the welding line and the heat affected zone of the welded pipe are simultaneously subjected to hot rolling under the large reduction, and the structures of the matrix, the welding line and the heat affected zone become the same dynamic recrystallization hot working structure. The weld joint and the heat affected zone of the welded pipe subjected to the seamless processing are the same as the base body in terms of geometric dimension, mechanical property and grain structure, and the welded pipe can reach the use standard and performance of the seamless pipe, and can be seen in the HFW welded pipe seamless processing of pages P51-53 in the 34 rd coil of the welded pipe and the analysis of the welded pipe seamless processing mode of pages P8-12 in the 4 th coil of the welded pipe in the 22 nd coil of the welded pipe.

In addition, the present inventors have been working on the development of composite tubes, one of which is to clad aluminum alloy tubes with strips of different aluminum alloys, and then completely compound two layers of metals or alloys together by means of continuous multi-pass drawing and annealing to make a composite tube. The two aluminum alloys can be metallurgically bonded at the joint surface of the whole pipe in the whole length, manufacturers cannot separate the metallurgically bonded two aluminum alloys, and the composite layer cannot be separated in the processes of pipe expanding, pipe bending and the like. The specific method can be seen in patent CN107262550B, and a manufacturing method of the aluminum-aluminum composite pipe.

The technique of seamless welded pipe tells us that the longitudinal weld joint can be strengthened, and the high-temperature high-reduction rolling can lead the weld joint to have the same mechanical property and grain structure as the matrix. But hot working is not suitable for copper materials and high Wen Fahei oxidation of copper is difficult to remove in the later pass, but large process volume distortion of cold working may be a suitable choice. The technology of the composite pipe can compound two different metals or alloys in a large area, the reinforcement of a welding seam can be regarded as an intermetallic compound, if the welding seam is not good or even only the metal on two sides of the welding seam is attached, the cold working and annealing of the large deformation of the technology of the composite pipe can also generate the effect of the composite pipe, and the metallurgical bonding can be generated on the metal on two sides of the welding seam only by enough processing amount of the pipe, the organization and performance of the welding seam can be reinforced, and even the performance of the matrix of the pipe can be exceeded.

Along the above thought, the manufacturing method of the invention is obtained through multiple tests, has unexpected good effects, can not only keep the advantage of continuous extrusion, but also overcome the defects caused by welded seams, and can manufacture small-diameter thin-wall copper and copper alloy tubes with multiple specifications, multiple varieties and excellent quality by using the existing equipment at low cost.

Disclosure of Invention

In order to solve at least one of the technical problems, the invention provides a manufacturing method of small-diameter thin-wall copper and copper alloy pipes, which combines continuous extrusion with drawing and annealing in the subsequent pass for the first time, and simultaneously sets the outer diameter and the wall thickness of the continuous extrusion copper and copper alloy pipes newly, so that the advantages of the continuous extrusion processing method are maintained, the defects of the continuous extrusion method in processing the small-diameter thin-wall copper and copper alloy pipes are overcome, and the manufacturing method is organically combined with the drawing and annealing in the subsequent pass, so that qualified small-diameter thin-wall copper and copper alloy pipes with different specifications can be manufactured efficiently and at low cost, and the defects of the prior art are overcome.

The invention provides a manufacturing method of small-diameter thin-wall copper and copper alloy tubes with the outer diameter smaller than 16mm and the wall thickness smaller than 1.0mm, which comprises the following steps:

S10, manufacturing a tube blank: continuously extruding by adopting a continuous extruder to prepare a copper and copper alloy pipe blank with the outer diameter of phi 25-phi 80mm and the wall thickness of 1.5-5 mm;

s20, drawing: performing at least one-pass continuous direct drawing and multi-pass disc drawing on the copper and copper alloy pipe blank until the copper and copper alloy pipe is in a finished product size, wherein the total wall reduction of drawing is not less than 60%;

s30, annealing: and annealing the copper and copper alloy tube drawn to the finished size by adopting an on-line induction annealing or nitrogen protection atmosphere annealing furnace annealing mode.

Preferably, in the step S10, a copper and copper alloy pipe blank with an outer diameter of phi 40-phi 60mm and a wall thickness of 2-4mm is manufactured.

Preferably, in the step S20, 2-4 passes of continuous direct drawing are performed.

Preferably, two winders are arranged at the outlet of the continuous extrusion machine, one is used for continuously extruding and winding, and the other is used for continuously and directly drawing and uncoiling, and the winders are alternately recycled.

Preferably, for the copper alloy pipe, the pipe blank extruded by the continuous extrusion machine is a long straight pipe blank, and the long straight pipe blank and the straight pipe are stored and enter continuous straight drawing without winding.

Preferably, in the step S20, continuous direct drawing is used when the outer diameter of the copper and copper alloy tube is phi 30mm or more, and disk drawing is used when the outer diameter of the copper and copper alloy tube is phi 30mm or less.

Preferably, in the step S20, the total wall reduction of the drawing is greater than 80%.

Preferably, in any of the above technical solutions, after the step S30, the method further includes the following steps,

s40, inner surface spinning: and (3) spinning the copper and copper alloy pipe obtained after annealing in the step (S30) by using an internal thread copper pipe.

S50, annealing again: and (5) annealing the copper and copper alloy tube subjected to the spinning processing of the internal thread copper tube in the step S40 again.

Preferably, in any of the above technical solutions, before the step S10, the method further includes a step S1 of cleaning the surface of the raw material: the surface of the raw material before entering the continuous extrusion machine is cleaned to remove greasy dirt, oxide, water and other dirt.

The invention also provides a copper and copper alloy pipe, which is manufactured by adopting the manufacturing method of the small-diameter thin-wall copper and copper alloy pipe according to any technical scheme. The copper and copper alloy pipe can be used for manufacturing air conditioner heat exchangers, and the flaring, the pipe expansion, the bent pipe and the like are not damaged, so that the quality is excellent, and the requirements of the pipe for the air conditioner heat exchanger are met.

The general technical route of the invention is to adopt two technological methods to butt-joint and finish the processing of the small-diameter thin-wall copper and copper alloy pipe. The first is the manufacture of a tube blank: the tube blank with increased size is manufactured by adopting a continuous extrusion method, so that the severe extrusion working condition in an extrusion chamber can be improved, and the stability of continuous extrusion and the service life of a die are increased; the second is the reinforcement of the weld joint: the weld joint of the tube blank is reinforced by adopting a multi-pass cold drawing and annealing method, so that the tube blank has the same metallographic structure and mechanical property as the matrix. The two methods are combined to form a technical scheme which can be practically applied to manufacture small-diameter thin-wall copper and copper alloy tubes.

The present invention increases the gauge size of the continuously extruded copper and copper alloy tubing, i.e., tube stock, as compared to the prior art of directly continuously extruding copper tubing to finished dimensions, which is seemingly simple but extremely important. Firstly, the specification and the size of the extruded copper and copper alloy pipes are increased, and the service life of the extrusion die can be greatly prolonged; and secondly, enough reducing and wall-reducing space can be reserved for strengthening the welding seam of the copper and copper alloy pipe, so that the defect at the welding seam can be eliminated.

For a continuous extrusion machine, a small-diameter thin-wall pipe is difficult to extrude, the size of a continuous extrusion die for the small-diameter thin-wall pipe is small, the annular section of the pipe wall of an inner die and an outer die of the extrusion die is also small, the extrusion pressure in an extrusion chamber is increased when the wall thickness is thinner as the diameter is smaller, the deformation resistance of an extrusion material is increased, and the temperature rise of deformation is increased. Therefore, under the working condition, the die can bear large extrusion pressure at high temperature, the specific pressure acting on the unit area of the die can be large, and the service life of the die can be greatly prolonged. The invention increases the size of the continuous extrusion copper pipe blank and designs the size in a medium size range, so that the extrusion die has a stress area and a heat dissipation area which are several times to tens of times larger than those of the prior art, therefore, the extrusion pressure in the extrusion chamber can be greatly reduced relative to the extrusion small diameter due to the increase of the size of the extrusion pipe blank, the deformation resistance in the die cavity can be greatly reduced, the fluidity of metal in the die cavity is smoother, the thermal deformation temperature rise of extrusion can be relatively reduced, and the service life of the extrusion die and the stability of the continuous extrusion copper and copper alloy pipe can be greatly prolonged due to the reduction of stress and temperature.

The diameter of the tube blank is limited in the range of 25-80mm and the wall thickness is 1.5-5mm, because the tube blank is too large in diameter, too many drawing passes are difficult to be wound and unwound, and too small in diameter, too thin and insufficient in reducing wall space. Although the sizes of the extruded tube blanks are different in different final product sizes and different production capacities, the tube blanks with large final product sizes and the equipment with large production capacities are selected from tube blanks with large diameters and thick production capacities, and the tube blanks with small sizes are selected from small and thin tube blanks. At present, for the refrigeration air conditioner, the main stream product of the copper and copper alloy pipe is characterized in that the outer diameter is smaller than 16mm, the wall thickness is between 0.25 and 1mm, for the factory with the capacity of more than 5000 tons/year, the diameter of the tube blank manufactured by the copper and copper alloy pipe continuous extrusion machine is between 40 and 60mm, the wall thickness is between 2 and 4mm, the size range of the tube blank is more suitable for continuous extrusion processing of the tube blank, and the reinforcement of the welding seam of the copper and copper alloy pipe in the subsequent pass is also facilitated, so that the method is a preferable scheme.

The size of the tube blank is increased, the extrusion pressure and temperature in the extrusion chamber can be reduced, the service life of the die is prolonged, and the side effect is that the extrusion under the working condition can not enable the welding seam of the tube blank to reach the same strength as the tube substrate. The invention aims to solve the performance deficiency, and adopts a method that the welded seam is reinforced by the subsequent pass. Because the welding seam is always the weak position of the pipe blank obtained by seam extrusion, the metals at the two sides of the welding seam are only partially welded and even only attached, and thus the winding and unwinding of the pipe blank after extrusion are very important. Both the pre-bending of the continuous extruder winding and the subsequent unwinding of the drawing machine can cause damage to the seam which is poorly welded. The larger the diameter of the winding basket is to reduce such damage, the better: a basket of 3-6m diameter is a good choice, too large would affect the logistics transportation of the factory. In addition, continuous upper winding can be considered, a double upper winding machine similar to a planetary rolling mill is arranged at the outlet of the continuous extrusion machine, one winding machine is used for continuous extrusion, and the other winding machine is used for unwinding of a continuous direct drawing machine for alternate recycling. A manufacturing plant with large production scale can adopt a configuration of a plurality of continuous extruders and a set of continuous direct drawing machines. For the copper alloy pipe blank difficult to weld, the extruded pipe blank can be considered to be subjected to overlength straight pipe stock, so that the welding seam damage caused by the winding and unwinding process of the continuous extruder and the drawing machine is avoided.

In order to solve the problem that the welding seam strength of the continuous extrusion copper and copper alloy pipe cannot meet the use requirement, the invention refers to the working principles of seamless welded pipe and composite pipe, and adopts a method for strengthening the welding seam after extrusion: the defects and defects at the welded seam are overcome by purposefully carrying out multi-pass cold drawing processing and annealing on large-specification copper and copper alloy pipe blanks subjected to continuous extrusion, wherein the defects and defects at the welded seam are overcome by strengthening, the welded seam and a matrix structure are changed from a hot processing structure after extrusion into a cold processing structure at the same time during the multi-pass cold drawing processing with large wall reduction, and then the two are changed into a recrystallization structure of complete phase copper by annealing, so that the performances of the welded seam and the matrix are consistent.

The cold working of the pipe can be carried out by various methods, and the reducing and wall-reducing of the pipe can be finished by cold rolling, cold drawing, continuous spinning and the like. The cold pilger rolling should be the best one in terms of the weld strengthening effect on the extruded tubing of the present invention. The rolling mill is a high reduction rolling mill, a pipe can be rolled from phi 100x12 to phi 40x2 in one pass, the wall reduction of only the pass is more than 80%, the forming area of the rolling mill is very long, and the defect elimination at welding joints can be greatly beneficial. However, this rolling mill is a periodical rolling mill, has low efficiency and low yield, is only used for processing copper alloy pipes and difficult-to-deform aluminum alloy pipes, and is not suitable for cold working according to the invention.

The existing copper tube factories serving for refrigeration and air conditioning finish the machining of the geometric dimension of the finished product of the tube by a cold drawing method, and the main stream copper tube factories are to draw the tube blank with the diameter of 50x2.5 after being rolled by a planetary rolling mill by a straight drawing machine and then draw the tube blank by a coiling drawing machine. The drawing process of the existing copper pipe factory is only used for processing the pipe into the size required by a user, and has no other functions. The invention combines the equipment of the existing copper pipe factory with the continuous extrusion process, strengthens the weld joint of the extruded pipe blank, solves the problem which cannot be solved all the time in the prior art by the simplest and most familiar way, and has the advantages of minimum change and maximum effect.

The cold drawing of copper and copper alloy pipes is carried out by adopting a drawing mode of a movable core head, and each pass of drawing can lead the pipe to generate the deformation of reducing diameter and reducing wall, so that the hot working structure of the extruded copper pipe blank is gradually changed into a cold working structure. The change from the hot working structure to the cold working structure of the pipe changes at the same time at the base body and the weld joint of the pipe, and the more the drawing passes, the larger the cold working deformation of the pipe, the more the grains of the pipe are broken, and the harder the pipe. Beyond a certain draw wall reduction, the grain structure at the weld joint and the tube base becomes the exactly same cold work structure.

In the drawing forming area, the pipe is axially stressed by unidirectional tension and radially stressed by bidirectional compression. The compressive stress in two directions causes the drawn pipe to be subjected to strong compressive stress at the matrix and the weld joint of 360 DEG circumference in the drawing deformation zone, and the compressive stress becomes larger and larger along with the drawing hardening of the pipe, so that any crack defects on the whole circumference of the pipe generate metallurgical bonding trend. The drawing of each pass can increase a certain metallurgical bonding degree, so that small deformation accumulation is realized, and when the drawing passes and drawing wall reduction amount reach a certain degree, weld seams in the tube, crack defects in the tube and the like can generate an effect similar to the metallurgical bonding of double-layer metal of the composite tube. In theory, as long as the drawing wall reduction amount is large enough and the drawing passes are large enough, defects such as welding seams in the pipe, cracks in the pipe and the like can be enhanced, and even if some pipes with poor welding seam quality are extruded, the welding seams can reach the metallurgical bonding level.

The drawing of the pipe is carried out, and the wall reduction and the diameter reduction are matched with each other. A large number of practices prove that the wall reducing amount of pipe drawing plays a greater role in strengthening the welding seam. To achieve a stable weld strengthening effect, 60% of the total wall reduction is the most basic, below which the strengthening effect is unstable. The larger the total wall reduction, the better the reinforcing effect of the welded seam. A total wall reduction of more than 80% will have a very good strengthening effect.

The combination of continuous straight drawing with small pipe diameter and disk drawing with large pipe diameter is necessary because the pipe blank with large diameter and thick wall thickness is drawn to be made into the pipe with small diameter and thin wall thickness. If the extruded large-pipe-diameter thick-wall pipe blank is directly drawn by a coiling and pulling machine, the pipe is crushed and defects are caused when the coiling and pulling machine presses a material ring to arrange wires. Most importantly, for some pipes with poor weld joints, the pipe is wound on a large disc of a disc drawing machine under great tension when the coil pipe is drawn, and the weld joints of the pipe can generate the possibility of bending and cracking. Even if the weld joint does not have a macroscopic cracking, there is a tendency to crack. The degree of metallurgical bonding increased in the deformation zone of the drawing die during each drawing pass of the pipe is counteracted by the tendency of bending and cracking of the large disc, so that the effect of accumulating the metallurgical bonding with small deformation of each drawing pass is poor, and finally the weld joint strengthening is failed. Theoretically, the strengthening effect of 100% of the whole-process continuous straight-pull butt weld joint is the best. And the production efficiency, the size of the tube blank and the product quality are taken into consideration, and continuous direct drawing of at least one pass is necessary. For the pipe with the outer diameter of 40-60mm after extrusion, 2-4-pass direct drawing is a proper choice. The extruded tube blank is firstly subjected to continuous direct drawing, the welded seam is primarily strengthened, and then the tube blank is drawn by a disc drawing machine, so that the strengthening effect of the welded seam is the best, and the production efficiency is the highest. Therefore, the outside diameter of the common pipe is straight-pulled at the phi of 30mm or more, and is disc-pulled at the phi of 30mm or less, which is a good choice.

Annealing is an important process for processing small-diameter thin-wall copper and copper alloy pipes, and the cold-working structure of the copper and copper alloy pipes can be changed into a recrystallized soft structure by heating and annealing, so that the plasticity and toughness of the pipes can be recovered, the strength of the pipes can be reduced, and users of the annealed pipes can use the pipes. The annealing of the copper tube is generally in an on-line induction annealing or nitrogen protection atmosphere annealing furnace. The invention gives new functions to annealing without changing the existing copper pipe annealing process and flow: in the present invention, drawing and annealing are two equally important steps of weld seam strengthening. According to the invention, the annealed pipe is a pipe obtained by drawing a continuously extruded seamed pipe blank by a large drawing amount, metals at two sides of a welded seam are strengthened by cold working by a large drawing amount, the base body and the welded seam of the pipe are softened and recrystallized at the same time in an annealing process, the annealed pipe base body and the welded seam have identical recrystallized grain structures, the welded seam and the base body have identical mechanical properties, and the welded seam of the pipe is fully strengthened. After the continuously extruded copper and copper alloy pipe blank is reinforced by the butt welding joint by the method, the state and the performance of the seamless copper and copper alloy pipe can be completely achieved.

For the common light pipe with smooth inner surface, the weld joint is strengthened to the step S30, but for the internally threaded copper and copper alloy pipe, the inner surface is processed into uniform fine teeth by a spinning method after the step S30, and finally finished product annealing is carried out. After the tube is drawn, the internal thread is spun and annealed once more than the light tube, the structure of the tube has two processes from hardening to softening, the welded seam is further strengthened, and the degree of strengthening is very high, which cannot be achieved by the seamless technology of the welded tube of the steel tube.

In summary, the manufacturing method of the present invention has the following advantages in terms of production:

1. the manufacturing method provided by the invention is simple, easy and safe.

Although the prior art patent describes continuous extrusion of copper tubing, this method has not been practical and has proven to be a failure for small diameter thin wall copper and copper alloy tubing. In contrast, the method of continuous extrusion, drawing with large wall reduction and annealing provided by the invention not only maintains the advantages of the continuous extrusion process, but also overcomes the defect of insufficient strength at the welded seam after continuous extrusion, and has very magic technical effects. After the welding seam is reinforced by the method, the welding seam has the same grain structure and the same mechanical property as the matrix, and the problems of flaring cracking, bending cracking and the like caused by insufficient welding seam strength of the continuous extrusion copper and copper alloy pipes are completely solved. The method eliminates the most complex horizontal continuous casting and planetary rolling mill casting and rolling method in the existing main flow small-diameter thin-wall copper and copper alloy pipe manufacturing technology, is simple, easy and safe, and can be the next generation main flow method for processing the small-diameter thin-wall copper and copper alloy pipe.

2. Low manufacturing cost and good quality of finished products.

The invention can adopt the up-leading copper rod or the continuous casting and rolling copper rod which are sold in the market as raw materials, the raw materials are extruded into tube blanks through a continuous extruder, a disc of copper rod can be used up to connect the subsequent copper rod in butt welding by adopting a cold welding machine, and the extrusion can continuously run all the time as long as the problem of an extruder die does not occur, and the weight of a single blank can reach several tons. The commercial copper rod is a raw material of the electric wire and the cable, the material composition meets the electric wire quality, the market supply is large, the quality is good, and the cost is low. The high-quality raw materials are the guarantee of high-quality products, for example, the purchasing of the upward copper rod can be used for manufacturing the high-requirement oxygen-free copper pipe with low cost, and the high-requirement oxygen-free copper pipe is difficult to realize in the prior art.

3. The productivity is suitable for wide-range production and can be produced in multiple varieties.

The single machine capacity of continuous extruders with different sizes can be from 2000 to 10000 tons/year, and the capacity is particularly suitable for enterprises with different scales to select. The prior art has large capacity and complicated technology, and is hardly accepted by common small and medium enterprises. The invention greatly reduces the technical threshold for processing small-diameter thin-wall copper and copper alloy pipes, and is suitable for large, medium and small users to select the production technology provided by the invention; the invention also provides wide market space for copper pipe equipment manufacturers; in addition, a plurality of wire and cable factories all use continuous extrusion machines to produce copper bars, etc., and only need to change the mould to extrude the copper tube blank, thereby being capable of producing small-diameter thin-wall copper and copper alloy tubes, and greatly improving the market competitiveness of enterprises in various production.

4. Familiar technical procedures and existing equipment, without additional purchase of equipment and training personnel

The invention selects the most familiar technical route and process equipment combination in the existing copper pipe processing industry to solve the problem, and gives a new function to drawing annealing to enable the continuous extrusion copper pipe technology to obtain unexpected effect, so that a copper pipe continuous extrusion technology which has failed once and is very good is practically applied, and enterprises can directly apply the copper pipe continuous extrusion technology without additionally purchasing equipment and training industrial workers.

The foregoing and/or additional aspects and advantages of the present invention will become apparent and may be learned by practice of the embodiments as set forth hereinafter.

Drawings

FIG. 1 is a photograph of a cross section of a copper tube billet extruded from a continuous extrusion machine;

FIG. 2 is a schematic drawing force diagram of a drawing deformation zone of a pipe, wherein FIG. 2-1 is a schematic drawing deformation zone diagram, and FIG. 2-2 is a schematic drawing force diagram of any small metal in the drawing deformation zone;

FIG. 3 is a schematic drawing of the stress on the section of the tube drawing deformation zone, wherein FIG. 3-1 is a schematic drawing of the stress on the section of the welded seam, and FIG. 3-2 is a schematic drawing of the stress on the section of the layered defect of the tube wall;

FIG. 4, a continuous straight pull schematic;

FIG. 5, a schematic drawing of a disk pull;

FIG. 6 is a photograph of metallographic structure of a continuously extruded copper pipe blank, wherein FIGS. 6-1 and 6-2 are photographs of metallographic structure of a base body, and FIGS. 6-3 and 6-4 are photographs of metallographic structure of welded joints;

FIG. 7 is a photograph of a transverse cross-sectional metallographic structure of a base body after the first 4-pass drawing of the copper pipe, wherein FIGS. 7-1, 7-2, 7-3 and 7-4 are photographs of transverse cross-sectional metallographic structures of base bodies after the first 1 st to 4-pass drawing, respectively;

FIG. 8 is a photograph of a longitudinal cross-sectional metallographic structure of a base body after the first 4-pass drawing of the copper pipe, wherein FIGS. 8-1, 8-2, 8-3 and 8-4 are photographs of a longitudinal cross-sectional metallographic structure of a base body after the first 1 st to 4-pass drawing, respectively;

fig. 9 is a photograph of a weld joint metallographic structure after the first 4-pass drawing of the copper tube, wherein fig. 9-1, 9-2, 9-3, 9-4 are photographs of weld joint metallographic structures after the 1 st to 4 th passes drawing, respectively;

fig. 10 is a photograph of a metallographic structure and a weld seam metallographic structure of a base body after 4-pass drawing and annealing of a copper pipe, wherein fig. 10-1 and 10-2 are photographs of a transverse metallographic structure and a longitudinal metallographic structure of the base body after annealing, and fig. 10-3 and 10-4 are photographs of a weld seam metallographic structure after annealing;

fig. 11 is a comparison photograph of the results of the flaring test before and after the weld joint strengthening, wherein fig. 11-1 is a photograph of the results of the flaring test of a continuous extrusion copper pipe blank, fig. 11-2 is a photograph of the results of the flaring test of a hard pipe after the 4 th pass drawing, and fig. 11-3 is a photograph of the results of the flaring test of a soft pipe after the 4 th pass drawing and annealing.

The correspondence between the reference numerals and the component names in fig. 1 to 11 is:

1. an outer mold; 2. an inner mold; 3. continuous direct drawing machine; 4. a large disc of a disc puller; 5. an uncoiler;

A. welding seams; B. delamination defects of the pipe wall; F. drawing force; f. drawing the compressive stress of the deformation area; fa. Compressive stress; fb. Compressive stress; m, drawing deformation area; K. a small piece of metal; δ1, the wall thickness of the pipe before drawing; delta 2, wall thickness of the drawn pipe; δ10, wall thickness of the tube blank; delta 20, wall thickness of the finished pipe; o, coiling the pulled pipe; p, coiling the tube before pulling; the U and disk pulling direction; v, uncoiling direction.

Detailed Description

In order that the above objects, features and advantages of the invention may be more clearly understood, a description of specific embodiments according to the invention will be given below with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the embodiments of the present application and the features in the embodiments may be combined with each other.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those described herein, and therefore the scope of the present invention is not limited to the specific embodiments disclosed below.

In one aspect of the invention, a method for manufacturing small-diameter thin-wall copper and copper alloy tubes with an outer diameter smaller than 16mm and a wall thickness not larger than 1.0mm is provided, which comprises the following steps:

The manufacturing method combines continuous extrusion with drawing and annealing of the later pass for the first time, and simultaneously carries out new setting on the outer diameter and the wall thickness of the continuous extrusion copper and copper alloy pipe, thereby not only retaining the advantages of the continuous extrusion processing method, but also overcoming the defects of the continuous extrusion method on processing small-diameter thin-wall copper and copper alloy pipes.

In some embodiments of the present invention, in the step S10, a copper and copper alloy tube blank having an outer diameter Φ40- Φ60mm and a wall thickness of 2-4mm is produced. The external diameter of the continuous extrusion tube blank is set to phi 40-phi 60mm, the wall thickness is 2-4mm, the success rate of continuous extrusion can be well ensured, the cold drawing processing of the subsequent pass can have enough diameter reduction and wall reduction, the reinforcement of drawing and annealing butt welding seams and the processing of the tube size can be well realized, and the continuous extrusion tube blank is a preferable scheme of the invention.

Preferably, in the step S20, 2-4 passes of continuous direct drawing are performed. Although the invention can be realized by continuous direct drawing of one pass, the reinforcement effect on welded seams is better by adopting continuous direct drawing of 2-4 passes, which is a preferable scheme.

Preferably, two winders are arranged at the outlet of the continuous extrusion machine, one is used for continuously extruding and winding, and the other is used for continuously and directly drawing and uncoiling, and the winders are alternately recycled. A coiling machine with a basket diameter of 3-6m is arranged at the outlet of the continuous extrusion machine, and the extrusion welding seam is always a weak position of the extruded tube blank, so that the welding seam is possibly only partially welded or even attached, and the coiling and uncoiling of the extruded copper tube blank are very important. The wound pre-bending and the subsequent drawing uncoiling can damage the welding seam which is not well welded, so that the larger the diameter of the winding basket is, the better the winding basket is. A basket of 3-6m diameter is a good choice, too large would affect the logistics transportation of the factory. The continuous upper winding can also be considered, a double upper winding machine similar to a planetary rolling mill is arranged at the outlet of the continuous extrusion machine, one winding machine is used for continuous extrusion, and the other winding machine is used for unwinding of a continuous direct drawing machine and is used in an alternating and circulating way.

Preferably, for some copper alloy pipes with high welding difficulty, the pipe blank extruded by the continuous extrusion machine is a long straight pipe blank, and the long straight pipe blank and the straight pipe are stored and enter continuous straight drawing without winding. By adopting the preferred embodiment, the welding seam damage caused by the winding and unwinding process can be avoided, and the quality of the finished product is further ensured.

Preferably, in the step S20, continuous direct drawing is used when the outer diameter of the copper and copper alloy tube is phi 30mm or more, and disk drawing is used when the outer diameter of the copper and copper alloy tube is phi 30mm or less. The extruded tube blank is drawn by a continuous direct drawing and then a coiling and drawing machine, so that the strengthening effect of the process arrangement on welding seams is the most reasonable and the production efficiency is the highest.

Preferably, in the step S20, the total wall reduction of the drawing is greater than 80%. The larger the total wall reduction amount is, the better the strengthening effect of the welding seam is, and the more than 80% of the total wall reduction amount has a very good strengthening effect.

Further embodiments of the present invention, based on the above embodiments, further comprise the following step after the step S30,

s40, inner surface spinning: carrying out spinning processing on the copper and copper alloy pipe obtained after annealing in the step S30;

For a common pipe with a smooth inner surface, the weld is strengthened to the end of step S30, which can be manufactured by using any of the above examples. However, for the internal thread copper pipe, the internal thread copper pipe needs to be manufactured by adopting the embodiment, namely, the copper pipe needs to be processed into fine teeth with uniform inner surfaces by a spinning method, and finally, finished product annealing is carried out. The internal thread spinning processing and the annealing more than the light pipe are adopted, two processes are adopted from the hardening to the softening of the structure of the pipe, the welded seam is further strengthened, the degree of the strengthening is that the seamless technology of the welded pipe of the steel pipe can not be achieved, and the effect is very good.

Preferably, the step S10 is preceded by a step S1 of cleaning the surface of the raw material: the surface of the raw material before entering the continuous extrusion machine is cleaned to remove greasy dirt, oxide, water and other dirt. The welding seam is absolutely clean during continuous extrusion, dirt, oxide skin and the like are not mixed in, and the inside of the extrusion chamber is kept absolutely clean, so that raw materials are subjected to surface cleaning treatment, water, oil or other dirt cannot be mixed in the extrusion chamber, and the bonding surface of two metals is absolutely ensured to be the bonding between fresh metals, so that the quality of a finished product can be ensured.

In another aspect, embodiments of the present invention provide a copper and copper alloy tube manufactured by the method for manufacturing a small diameter thin wall copper and copper alloy tube according to any of the embodiments above.

The copper and copper alloy pipes manufactured by the method provided by the embodiment of the invention have very good reinforcement of the welded seam, the performance and the metallographic structure of the welded seam are basically consistent with those of a matrix, the welded seam can be used in the air conditioner refrigeration industry, the quality of the pipes is not affected by pipe bending, pipe expanding and the like in use, the variety and the specification of the pipes are various, the cost is reduced, and the diversified requirements of users are met.

The invention will be further described with reference to the accompanying drawings for a further understanding of the invention.

FIG. 1 is a photograph of a cross section of a tube blank of a phi 45x3 copper tube extruded by a continuous extrusion machine, the positions indicated by the left and right black arrows being the positions of the weld joints. In the embodiment, two copper rods are adopted to feed the continuous extrusion machine, the extrusion wheel rotates to directly press the two copper rods into the extrusion chamber through respective flow channels for continuous extrusion, two strands of metal in the extrusion chamber are converged and extruded into a copper pipe blank through the extrusion die, and two welding seams are formed on the section of the extruded copper pipe blank by the two strands of metal.

Compared with the prior art, the embodiment increases the size of the continuous extrusion tube blank, namely the size of the extrusion die, so that the deformation resistance and the deformation temperature of metal in the extrusion chamber are reduced. The temperature in the extrusion chamber is measured to be lower than 650 ℃, and various hot die steels and high-temperature alloys can be used stably in the temperature range and have long service lives. The extrusion pressure, the extrusion force on the unit area of the die and the extrusion temperature are reduced simultaneously, so that the severe working condition in the extrusion chamber is greatly improved, and the stability of continuously extruding the copper pipe blank is improved. But the extrusion pressure and temperature must not be too low to allow only a portion of the two metals to contact and bond within the weld joint, and another portion to leave a gap without contact. The post-pass reinforcement of this phenomenon cannot improve the strength of the welded seam and must be avoided. In the present invention, it is very important to control the quality of the weld seam, and the subsequent reinforcement can only be accomplished on the basis of a high quality weld seam. To control the quality of the weld, first, the extrusion speed, extrusion temperature and extrusion pressure are controlled to maintain these parameters within reasonable ranges. Secondly, the weld joint needs to be absolutely clean, and dirt, oxide skin and the like cannot be mixed in. The weld joint must not have significant cracks, defects, oxidation, etc. During extrusion, the extrusion chamber is kept clean absolutely, raw materials such as copper rods and the like are subjected to surface cleaning treatment, water, oil or other dirt cannot be mixed into the extrusion chamber, and the bonding surface of two metals is ensured to be bonding between fresh metals absolutely. However, despite these measures, the weld seam is still the weakest point on the circumference of the tube blank, and the tensile strength and elongation at the weld seam are low compared to the matrix. Through tests, 100% of extruded tube blanks can generate flaring cracking at welding seams, the flaring rate during the cracking is generally not more than 10%, and a photograph of the flaring cracking of the continuous extruded tube blanks is shown in fig. 11-1.

Fig. 2 is a schematic drawing force diagram of a tube drawing deformation zone, and fig. 3 is a schematic drawing force diagram of a section of the tube drawing deformation zone.

The drawing force F of the drawing machine (not shown in the drawing) in fig. 2-1 draws the pipe in the arrow direction, the outer mold 1 outside the pipe and the inner mold 2 inside the pipe (i.e., the floating core) determine the outer diameter and the wall thickness of the outlet of the pipe, and the outer mold 2 gives the compressive stress F of the pipe in the drawing deformation area M, which is the compressive stress F of the drawing deformation area. If the wall thickness of the pipe before drawing in each pass is delta 1 and the wall thickness of the pipe after drawing is delta 2, [ (delta 1-delta 2)/delta 1] x100% is the wall reduction rate of the pass. If the wall thickness of the tube blank made by the continuous extrusion machine is delta 10 and the wall thickness of the finished tube is delta 20, [ (delta 10-delta 20)/delta 10] x100% is the total wall reduction rate, and the larger the total wall reduction rate is, the larger the drawing deformation of the tube is. It can be seen from fig. 2-2 that any small piece of metal K in the drawing deformation zone M is subjected to unidirectional tensile stress and bidirectional compressive stress. The Y direction is tensile stress, the X, Z direction is compressive stress, and the drawing force F overcomes the drawing resistance between the outer die 1 and the inner die 2 to finish drawing the pipe. In fig. 3-1, a represents a weld line of copper pipes, and is represented by a thick black solid line. The weld joint is perpendicular to the pipe wall direction. Since the inner pipe is subjected to X, Z bi-directional compressive stress in the drawing deformation zone, the metal at the weld seam in fig. 3-1 is strongly extruded by the compressive stress fa during drawing, and the compressive stress fa is greater as the wall reduction amount of the pipe drawing is greater. Each pass of drawing produces the same extrusion effect on the weld joint. If the initial continuous extrusion tube blank has poor welding effect, the welding seams are only partial welding seams or only bonding seams, and as long as the welding seams are clean and have no mixed dirt, the extrusion effect accumulation generated by drawing the wall reduction in enough passes can lead the welding seams with poor welding seams to generate the effect similar to the compounding effect of the compound tube, the welding seams can generate complete metallurgical bonding, and the welding seams are strengthened. The weld seam strength can reach or even exceed the matrix strength.

The drawing of the pipe can strengthen not only the welded seam, but also the defects in the pipe. B in fig. 3-2 represents delamination defects of the tube wall in bold black lines. When a continuous extrusion machine extrudes a copper pipe blank, unstable metal flow in the die may also cause such defects in the pipe blank matrix or weld joints. The compressive stress fb formed by drawing acts on the two sides of the layered metal during drawing, and the accumulation of multi-pass extrusion can also realize metallurgical bonding of the layered metal.

Fig. 4 is a schematic continuous drawing diagram, reference numeral 3 in fig. 4 is a continuous drawing machine, the drawing machine has two types, namely a crawler type drawing machine and a cam type drawing machine, when the drawing machine is used for drawing, a mold of the drawing machine is used for holding the outer surface of a pipe to carry out continuous linear drawing, the center line of the outer mold 1, the center line of the continuous drawing machine 3 and the drawing center line are the same straight line, the drawing force F is used for drawing along the arrow direction, and the pipe after drawing is wound by a winding machine (not shown in the drawing machine) without tension at the outlet end of the continuous drawing machine 3. The continuous direct drawing stress is reasonable, the drawing process does not have a bending process with tension, even if the weld joint quality of the tube blank is poor, the continuous direct drawing can not damage the weld joint quality, and theoretically, the continuous direct drawing has the best effect on strengthening the weld joint. The continuous direct drawing machine can be used for single drawing, or can be used for connecting 2-3 machines in series to form two continuous drawing and three continuous drawing. The continuous drawing is efficient, the wall reducing amount is large, 2-3 continuous drawing can generate more deformation heat in the drawing die forming area, and the high temperature, large deformation amount and large compressive stress can greatly increase the welding seam strengthening effect.

Fig. 5 is a schematic drawing of a disk pull. The coiled and pulled pipe O is wound on the large coil 4 of the coiling machine for a plurality of circles during drawing, the large coil 4 of the coiling machine is coiled and pulled in the direction of an arrow U, and the coiled and pulled pipe O wound on the large coil 4 of the coiling machine and the large coil 4 of the coiling machine are coiled tightly to provide drawing force F for the pipe; the other sides of the outer die 1 and the inner die 2 are provided with uncoilers 5, and the uncoilers 5 rotate and unwind along the arrow V direction. Because the drawing force F is large, the coiled pipe O wound on the large disk 4 of the coiling machine bears large tension in a bending state, if the quality of the welded seam of the pipe is problematic, the bending with tension can damage the quality of the welded seam of the pipe, and in the worst case, the pipe wound on the large disk 4 of the coiling machine can be directly cracked at the welded seam when being drawn. The larger the diameter of the pipe is, the thicker the wall thickness is, the larger tension is applied to the pipe O wound on the large disc 4 of the disc drawing machine, and the bending of the large-diameter pipe can cause larger damage to the welded seam, so the disc drawing machine is not suitable for reinforcing the welded seam of the large-diameter pipe.

The conclusion from a number of experiments was: for the tubes with the diameter of 30mm and above, the continuous direct drawing is used, and the disc drawing is used for the tubes with the diameter of less than 30mm, which is a good choice. The continuous direct drawing machine has low speed, high pulling force and reasonable stress. The continuous direct drawing machine is used for drawing to primarily strengthen the welded seam, the pipe diameter and the wall thickness are drawn to be small, then the pipe diameter and the wall thickness are drawn by the disc drawing machine with higher speed, and the advantages of the two drawing devices are combined, so that the quality and the efficiency can be considered.

Fig. 6 to 10 are metallographic photographs of copper pipes manufactured by the embodiment of the manufacturing method of the present invention.

In the embodiment, a continuous extruder is adopted to continuously extrude a phi 45x3 red copper pipe blank, and the metallographic structure of the copper pipe blank which is continuously extruded is shown in figure 6. Wherein, FIGS. 6-1 and 6-2 are the metallographic structures of the substrates, and FIGS. 6-3 and 6-4 are the metallographic structures of the welded joints. It can be seen from fig. 6 that the matrix of the continuously extruded tube blank is a fully dynamic recrystallized thermally processed structure, which has good workability. The continuous extrusion weld seam is shown by arrows in fig. 6-3 and 6-4, so that the boundary line of the weld seam is clear, the metallographic structure in the weld seam is obviously different from that of the matrix, grains at two sides of the weld seam do not mutually diffuse, the bonding effect of the weld seam is poor, and metals at two sides of the weld seam are layered. And then carrying out a flaring test on the phi 45x3 red copper pipe blank which is continuously extruded, wherein the cracking rate is 100%, and the position of the flaring cracking is 100% at the welding seam of the pipe blank, as shown in fig. 11-1.

For the subsequent pass of drawing strengthening, the embodiment of the invention draws copper tubes with 3 sizes: the 1 st is that a phi 45x3 extruded tube blank is subjected to 2-pass direct drawing and 2-pass disc drawing, and the total number of the copper tubes is 4 to phi 20.5x1; 2 nd is an air-conditioning connecting pipe from phi 45x3 extruded tube blank to phi 12.7x0.7-phi 6.35x0.5 through 2-pass direct drawing and 4-6-pass disc drawing; and 3 rd is that the phi 45x3 extruded tube blank is drawn to phi 9.52x0.30 by 2 times of straight drawing and 8-9 times of disc drawing, and then is spun and annealed by an internal thread copper tube to form the internal thread copper tube with phi 7x0.26. The copper pipe with the 1 st size is used for detecting the strengthening performance of the welding seam, and because the copper pipe is larger than the other 2 sizes, if the strengthening effect of the welding seam with the diameter of 20.5x1 is good, the copper pipe can bear a standard pipe expanding test, the smaller-size pipe can have better strengthening effect, and the copper pipes with the 2 nd and 3 rd sizes are products which are practically used in industrial mass. The specific strengthening effect can be seen from fig. 7 to 10:

FIG. 7 is a photograph of a transverse cross-sectional metallographic structure of a substrate after the first 4-pass drawing, wherein FIGS. 7-1, 7-2, 7-3, and 7-4 are photographs of transverse cross-sectional metallographic structures of a substrate after the first 1 st to the 4 th pass drawing, respectively. Fig. 8 is a photograph of a longitudinal section metallographic structure of a substrate after the first 4-pass drawing, wherein fig. 8-1, 8-2, 8-3, 8-4 are photographs of longitudinal section metallographic structures of a substrate after the 1 st to 4 th passes drawing, respectively. Fig. 9 is a photograph of a weld seam metallographic structure after the first 4-pass drawing, wherein fig. 9-1, 9-2, 9-3, 9-4 are photographs of weld seam metallographic structures after the 1 st to 4 th passes drawing, respectively. Fig. 10 is a photograph of a metallographic structure and a weld seam metallographic structure of a base body after drawing and annealing in the 4 th pass, wherein fig. 10-1 and 10-2 are transverse and longitudinal metallographic structures of the base body after annealing, and fig. 10-3 and 10-4 are weld seam metallographic structures after annealing.

The photographs of fig. 6-10 show, from a metallic microscopic perspective, the process of the present invention for modifying the metallographic structure of a continuous extrusion copper and copper alloy tube blank substrate and weld seam:

it can be seen from fig. 6, 7 and 8 that the tube base and weld joint are simultaneously work hardened after the pass-by-pass drawing, and the tube gradually changes from a soft state to a hard state in the as-machined state. The more drawing passes, the greater the wall reduction, and the more severe the hardening of the pipe. The drawing copper pipe matrix transverse section crystal grain in fig. 7 is crushed and thinned in a pass-by-pass manner, the longitudinal matrix crystal grain in fig. 8 is elongated and thinned in a pass-by-pass manner, the crystal grain structures at two sides of the weld joint in fig. 9 are crushed and thinned by strong bidirectional compressive stress in a drawing deformation area and simultaneously generate a mutual extrusion effect, the extrusion effect is changed in quality by the accumulation of drawing in multiple passes, and experiments show that when the total wall reduction amount of drawing is not less than 60%, the crystal grain structures at two sides of the weld joint are subjected to so-called metallurgical bonding. It can be seen from fig. 7 that as the drawing pass increases, the boundary and shape of the weld become increasingly blurred, and the metallographic structure in the weld becomes increasingly convergent with the matrix structure, indicating that the metallographic structure in the weld can be effectively changed by cold drawing.

FIG. 10 shows a photograph of the annealed metallographic structure, and it can be seen that the weld seam and the substrate are the same recrystallized structure, the weld seam boundary is very fuzzy, only one incomplete weld seam is found at the arrow of FIG. 10-3, the weld seam is not found in the whole section of 10-4, and the position of the weld seam is difficult to find in the metallographic photograph of more than 70% of the sample. After the drawing and annealing strengthening are carried out, the welding seam of the continuous extrusion copper pipe is fully strengthened. The effect of the drawing strengthening weld joint is very obvious, and even the phenomenon that the strength of the weld joint exceeds that of a matrix can occur. Experimental statistics are given in table 1.

TABLE 1

The test data in table 1 are test data obtained by drawing different times after continuously extruding a copper pipe blank, annealing copper pipe systems with different sizes to a length of 50mm, and then performing flaring test one by one, wherein flaring is performed according to national standard (GB/T17791-2017 copper and copper alloy seamless pipes for air conditioning and refrigeration equipment). The oil press of sample number 1 flares, and other samples are manually flared. Sample number 1 is a tube blank after continuous extrusion, and the cracking rate of the welded seam expanded tube is 100%; sample number 2 is the tubing after 2 nd pass drawing, test number 3 is the tubing after 4 th pass drawing. As can be seen from Table 1, sample No. 2 drawn in 2 passes showed a weld cracking rate of only 25% although the wall reduction rate was only 43%, indicating that the effect of drawing and annealing strengthening was very remarkable from the 2 nd pass. With the increase of the drawing pass, the total wall reduction rate of sample numbers 3-5 exceeds 60%, and the weld joint cracking rate is zero. The above results also indicate that the reinforcing effect of the weld joint gradually increases with the increase of the drawing pass and the wall reduction, and that the reinforcing effect is stable when the total wall reduction exceeds 60%, and the larger the wall reduction ratio, the better the reinforcing effect.

Fig. 11 is a graph comparing the results of the flaring test before and after weld seam strengthening. Fig. 11-1 is a photograph showing the result of a continuous extrusion copper pipe blank flaring test, fig. 11-2 is a photograph showing the result of a hard pipe flaring test after 4 th pass drawing, and fig. 11-3 is a photograph showing the result of a soft pipe standard flaring test after 4 th pass drawing annealing. The contrast of the three pictures is strong. The continuous extrusion copper pipe blank with phi 45x3 is cracked at the weld joint by 100% through a flaring test, and the flaring rate during the cracking is generally not more than 10%, and fig. 11-1 shows that the weld joint strength of the continuous extrusion copper pipe blank is obviously lower than that of the base body. In fig. 11-2, a copper tube in a hard state is drawn into a copper tube of Φ20.5x1 in 4 passes, but can withstand a hard state flaring of 30% flaring rate, and the result is completely beyond expectations. Although the hard flaring test is not very standard, national standard or user use standard should be to carry out flaring test on soft copper pipe, but this can demonstrate that the method provided by the invention is extremely effective to strengthen the welded seam performance of the seamed copper pipe after continuous extrusion, and the hard flaring with 30% flaring rate can be achieved by only 4-pass drawing, so that the good strengthening effect is completely unexpected. Based on the above, the inventor makes further tests, the phi 20.5x1 hard state pipe is continuously flared to crack, 100 patterns are made, the position of the crack is detected, 76% of the crack positions are found to be not at the welding seam, and the fact that most of the welding seam strength exceeds the strength of the matrix at the moment is shown, and the welding seam is completely reinforced. Fig. 11-3 are photographs showing the results of soft-state flaring test of the tube after drawing and annealing in the 4 th pass, the soft-state tube expansion effect is better, and all indexes reach and exceed the requirements, as shown in table 1.

In summary, the method for manufacturing the small-diameter thin-wall copper and copper alloy tube provided by the invention combines continuous extrusion with drawing and annealing in the later pass for the first time, and simultaneously carries out new setting on the outer diameter and the wall thickness of the continuous extrusion copper and copper alloy tube, so that the advantages of the continuous extrusion processing method are maintained, the defects of the continuous extrusion method in processing the small-diameter thin-wall copper and copper alloy tube are overcome, and the method can be used for manufacturing qualified small-diameter thin-wall copper and copper alloy tubes with different specifications efficiently and at low cost by organically combining with the drawing and annealing in the later pass, and overcomes the defects of high technical level, difficult quality control, potential safety hazard, high maintenance difficulty, high cost, single variety and high yield requirement in the prior art in producing the small-diameter thin-wall copper and copper alloy tube by continuous extrusion of finished small-diameter thin-wall copper and copper alloy tubes and cast rolling. The prepared small-diameter thin-wall copper and copper alloy pipe has very good reinforcement of welded seam, has basically consistent performance and metallographic structure with the matrix, can be used in the air conditioner refrigeration industry, can be used for bending pipes, expanding pipes, flaring and the like without influencing the quality of the pipe, has various pipe varieties and specification sizes, can reduce the cost and meets the diversified needs of users. Overcomes the defects of the prior art and realizes the aim of the invention of the patent.

In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "front", "rear", "inner", "middle", "outer", etc., are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or unit referred to must have a specific direction, be constructed and operated in a specific direction, and thus should not be construed as limiting the present invention.

In the description of the present specification, the terms "one embodiment," "some embodiments," "particular embodiments," and the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent copper replacement, improvement, etc. made within the spirit and principles of the present invention should be included in the scope of the present invention.

Claims

1. The manufacturing method of the small-diameter thin-wall copper and copper alloy pipe with the outer diameter smaller than 16mm and the wall thickness not larger than 1.0mm is characterized by comprising the following steps:

2. The method for manufacturing the small-diameter thin-wall copper and copper alloy pipe according to claim 1, wherein the method comprises the following steps:

in the step S10, a copper and copper alloy pipe blank with the outer diameter of phi 40-phi 60mm and the wall thickness of 2-4mm is manufactured.

3. The method for manufacturing the small-diameter thin-wall copper and copper alloy pipe according to claim 1, wherein the method comprises the following steps:

in the step S20, 2-4 times of continuous direct drawing is carried out.

4. The method for manufacturing the small-diameter thin-wall copper and copper alloy pipe according to claim 1, wherein the method comprises the following steps:

Two winding machines are arranged at the outlet of the continuous extrusion machine, one winding machine is used for continuous extrusion, and the other winding machine is used for continuous direct drawing and unwinding, and is used in an alternating and circulating way.

5. The method for manufacturing the small-diameter thin-wall copper and copper alloy pipe according to claim 1, wherein the method comprises the following steps:

for the copper alloy pipe, the pipe blank extruded by the continuous extruder is a long straight pipe blank, and the long straight pipe blank and the straight pipe are stored and enter continuous straight drawing without winding.

6. The method for manufacturing the small-diameter thin-wall copper and copper alloy pipe according to claim 1, wherein the method comprises the following steps:

in the step S20, continuous direct drawing is adopted when the outer diameter of the copper and copper alloy pipe is phi 30mm or more, and disk drawing is adopted when the outer diameter of the copper and copper alloy pipe is phi 30mm or less.

7. The method for manufacturing the small-diameter thin-wall copper and copper alloy pipe according to claim 1, wherein the method comprises the following steps:

in the step S20, the total wall reduction amount of the drawing is more than 80%.

8. The method for manufacturing small diameter thin wall copper and copper alloy pipe according to any one of claims 1 to 7, wherein: after said step S30 further steps are included,

9. The method for manufacturing small diameter thin wall copper and copper alloy pipe according to any one of claims 1 to 7, wherein:

the step S10 is preceded by a step S1 of cleaning the surface of the raw material: the surface of the raw material before entering the continuous extrusion machine is cleaned to remove greasy dirt, oxide, water and other dirt.

10. A copper and copper alloy tube, characterized in that: a method for manufacturing a small diameter thin wall copper and copper alloy pipe according to any one of claims 1 to 9.