ABSTRACT: In recent years, with the constant updating of air-conditioning industry standards, copper pipe processing enterprises continue to optimize technology, energy efficiency and quality improvement more prominent. This technology mainly studies and designs a kind of intelligent finishing annealing integrated technology and equipment for high precision inner grooved copper tubes. The mechanical uniformity of copper tubes is greatly improved by adopting the eddy current heating technology which is formed by medium frequency induction, it effectively solves the problem that the residual stress in the process of finishing and rewinding of hard tubes causes the expansion of copper tubes during annealing, and solves the problem that the existing inner-threaded copper tubes have high scrap rate and low yield rate in use, the production efficiency of copper pipe production enterprises and copper pipe application enterprises is greatly improved, the production cost is reduced, and the product quality is guaranteed. The research and development of this technology has realized the integration of finishing, rewinding and annealing processes, optimized the process flow and product performance, and innovated the copper tube processing technology and equipment at home and abroad.

Key words: Copper Tube with internal thread; finishing and winding; Annealing; Copper Tube Expansion; residual stress

By Zhou Lixing

Document id: A ARTICLE ID: 1002-5065(2020)08-0166-21. The research content of a new type of copper tube processing technology is based on the traditional processing technology adopted by the domestic and foreign enterprises at present, which is the continuous casting and rolling process, the process is as follows: Raw material-horizontal continuous casting-milling surface-planetary rolling-coupling-drawing-on-line annealing-internal thread forming-finishing rewinding-final annealing-cutting and packaging. This technology discards the existing finishing rewinding and final annealing processes, the process flow is as follows: Raw material-horizontal continuous casting-milling-planetary rolling-coupling-drawing-on-line annealing-internal thread forming-finishing annealing-cutting and packaging. The main research contents of this technology are the integration of finishing and annealing of semi-finished rifled tubes, the change of layout of rifled tubes during finishing and annealing, the effective elimination of residual stress and the uniform performance of copper tubes:

(1) the intelligent integrated process technology of hard tube finishing, rewinding and annealing packaging is developed. In order to reduce the waste of labor, material, capital and handling in the production process, the project has shortened and integrated the copper pipe processing process, and designed the main technology and equipment, including the copper pipe laying system, on-line clamping system, COPPER TUBE surface cleaning system, horizontal and vertical straightening system, heating and annealing system, inspection ink-jet system, cooling system, passivation system, drying system, receiving and crimping system, feeding and packaging system and inner surface nitrogen blowing system.

(2) develop the equipment technology of high efficiency annealing and finishing rewinding from bottom to top, and apply the medium frequency induction eddy current heating technology in this project. In order to solve the problem that the copper tubes were laid out from the inner side to the outer side in the traditional process technology, and then annealed and softened, which resulted in the copper tubes not being laid freely in the use of the terminal, in this project, copper tubes are annealed directly by induction through the medium frequency induction coil and Eddy current generated by the coil. It is not necessary to coil into the annealing furnace, the arrangement of the wires is arranged from the bottom layer to the top layer of the net, and the gap between the copper tubes is reduced, thus reducing the amount of compensation for using the terminal wiring.

(3) a set of integrated process management system of intelligent finishing and annealing for high precision copper tubes has been developed. This project through the equipment process design and practice, clear in this project each working section has the function, and to its completion, at the same time, for different copper pipe specifications, after this equipment system, its performance uniformity can be effectively guaranteed, and according to different specifications, set the corresponding finishing line program, so that the specifications of the equipment system can adapt to the effectiveness of process execution can be guaranteed. This project makes a special packaging program, so that the copper tube can be directly packed after discharge, reducing the packaging site and material turnover site.

2. Frequently asked questions

(1) in the welding process, welders in order to ensure the quality of welding, so that welding materials can better penetrate into the gap between the pipe and fittings, at the same time require that the fittings mouth must be horizontal up. However, it is found that more than 30% of the pipes are over 2m in length, as shown in Fig. 1, the height of the welding seam which needs to be welded will exceed the height of the constructors, and it is difficult to carry out the welding process. The experimental results show that the flame temperature is as high as 2500 °c ~ 3000 °C when the gas welding temperature is 0.05 MPA at the acetylene meter and 0.5 MPA at the oxygen meter, and the flame temperature becomes soft when the red copper tube is heated to 600 °C ~ 700 °C. If the diameter of the pipe to be welded is tilted due to the height problem, the positioning of the pipe and fittings will become soft under the high action to be detached.

(2) because of the limited installation conditions in a certain area, it is difficult to meet the welding process requirements of some pipelines. For example, the distance between piping and fittings is small, and the distance between welds is actually only 30 mm. After the first weld is completed, when the second weld is welded, the temperature of the first weld will reach 890 °c of the welding melting point because of the small spacing, thus the first weld appears melting defect.

3. A new processing technology of Red Copper Tube is shown in Fig. 2.

4. A new type of red copper pipe processing technology is focused on solving the problem because the copper pipe processing in the normal production process is carried out in the hard state process, the residual stress can not be eliminated, and the copper pipe is densely arranged from the inner side to the outer side, the gap between copper tubes is small, and after annealing, the residual stress is eliminated, the coil material expands, and the gap between copper tubes is further reduced The traditional finishing process is separated from the finished product annealing and listed as two processes, which results in an increase in personnel, a long material turnover time, a long waiting time, and an increase in the probability of bump in the copper pipe transportation process, affect the use of copper pipe performance.

5. Conclusion this project technology is mainly applied to copper coil processing enterprises, directly applied to copper coil processing enterprises in the process flow, for air conditioning processing enterprises and supporting manufacturers, compared with existing copper coil processing enterprises, production cycle can be reduced by about 1 day, capital consumption can be reduced by one day, the process of material handling process can be reduced, at the same time, can reduce team 6 people per shift, improve production efficiency, reduce labor costs. At the same time, the winding mode of the original copper coil pipe has been changed in the use of air-conditioning enterprises, and the wiring mode of the copper pipe has also been changed from the original precise and regular inner wiring to the loose coil type, the gap between the copper tubes increases, and the wiring mode is from the upper layer to the lower layer, which reduces the number of frequent changes in the copper tubes during the original internal wiring process and the scrap rate caused by it, and the results of this study can increase the weight of single coil, reduce the use of air-conditioning enterprises in the process of changing the frequency, greatly improve the efficiency of air-conditioning processing enterprises, reduce the rejection rate of copper pipe. 

Source: Chinanews.com by Zhou Lixing

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