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Research Progress on preparation technology and technology of copper elbow

Copper pipes are generally used in the field of air conditioning and refrigeration, mainly in two aspects: one is the evaporator and condenser of air conditioning and refrigeration, and the other is the connecting pipe fittings of air conditioning. No matter what purpose the copper pipe is used for, it has an inseparable function, that is, the channel of refrigerant. The copper elbow is mainly used on the connecting pipe of evaporator and condenser to connect the bent internal thread copper pipe and aluminum foil. Nowadays, in order to enhance the service life and experience of copper pipes, some enterprises put forward higher requirements for the thickness and tooth shape of copper pipes. In order to reduce the production cost, the production trend of small elbow gradually tends to the new style of small diameter, thin pipe wall and thin and high teeth. The size of copper elbow is lower than that in the past, which leads to defects such as “U” flat and too thin outer pipe wall in the bending process. These problems will lead to cracking of outer pipe wall and wrinkling of inner pipe wall. Therefore, exploring the causes of copper elbow defects and bending process plays an important role in improving the stability of copper elbow production. Not only that, for the production plant, it can greatly improve the yield of copper elbow.

Defect analysis of copper elbow

Effect of tensile stress on defects of copper elbow

When bending deformation occurs, the copper elbow will follow the principle of constant plastic deformation volume, resulting in compression and tension on the inner and outer pipe walls of the copper pipe. When the copper elbow deforms under the action of external force, the outer pipe wall will produce tensile stress, which will make the pipe wall thinner and crack the outer pipe wall of the copper pipe. When the inner pipe wall of the copper elbow is subjected to compressive stress, the pipe wall will become thicker, resulting in wrinkle defects on the inner pipe wall of the copper elbow [1]. When the external tensile stress and internal compressive stress are generated at the same time and the resultant force of the copper pipe is compressed, the transverse diameter of the copper pipe will increase, and the shape of the copper pipe will change from circular to oval, as shown in Figure 1.
In the process of bending deformation of copper elbow, there is a change process of maximum equivalent stress. In the bending process of copper elbow, the maximum equivalent stress is located on the outside of copper pipe and will displace with the degree of bending.

This shows that cracks are easy to occur on the outer wall of the copper elbow, and the location of the cracks will change with the bending degree of the copper pipe. The above is the influence of tensile stress on the defects of copper elbow.

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Figure. 1 copper elbow

Effect of angle on defects of copper elbow

The change of angle will also have a certain impact on the copper elbow. Different bending angles of copper elbow will produce different quality effects. When the bending angle of copper elbow is 180 °, the range of the maximum equivalent stress value generated by the copper elbow is the largest. Therefore, the cracking of the outer pipe wall is most likely to occur at this time, and the crack will expand from outside to inside. When the bending angle of the copper elbow is 45 °, a particle will be generated at the bending point, which will show a spiral moving track. When the bending angle of copper elbow increases to 90 °, the helical displacement of the particle moves from the outside to the inside of the copper tube. The spiral movement of particles will lead to multiple particles in the copper pipe. After the number of particles increases, the phenomenon of particle accumulation will occur in the copper pipe, resulting in the thickening and folding of the copper pipe wall. When the bending angle of the copper elbow is between 135 ° ~ 180 °, the particle spiral motion at the bending disappears, which shows that the angle at which the copper elbow is most prone to folding is 0 ° ~ 90 ° [2].
This result can provide an effective reference for the progress of copper elbow manufacturing process in China, and can promote the development of copper pipe manufacturing process in China to a certain extent.

Bending forming principle and classification of copper elbow

Classification of bending forming of copper elbow

In China’s pipe field, there are many pipe bending methods, which are classified according to different pipe materials, specifications and bending limits. According to the bending shape, there are rectangular tube bending, irregular section tube bending and circular tube bending; According to the bending method, there are welded pipe bending and seamless pipe bending; According to bending materials, there are copper pipe, steel pipe, titanium alloy pipe bending, etc; According to whether the copper pipe is bent with filler, it can be divided into coreless bending and cored bending; According to the difficulty of pipe, it can be divided into large curvature and small curvature bending; According to whether the copper pipe needs to be heated during bending, it can be divided into room temperature cold bending and heating bending; According to the bending mode, it can be divided into pure bending, pull bending, bending, push bending, press bending, roll bending, etc. [3]. In general, the bending method of cold processing can meet the bending needs of pipes. For pipes with small batch and certain length, manual bending is generally adopted, and special bending equipment is used for mass pipe production. For some pipes with severe work hardening, in order to improve the plasticity of the pipe and deform to the maximum, heating bending is generally used to achieve this purpose. In order to reduce the problem of abnormal cross-section of the pipe, the fillable pipe can be filled with filler or mandrel during bending, which can effectively reduce the defects of abnormal cross-section of the pipe [4].

Analysis of bending forming principle of small elbow

Pipe plastic forming is to produce pipe parts after secondary processing by means of plastic processing with pipe as blank material. It is classified as the technical category of deep processing in China. Pipe bending is the process of bending blank pipes through different shaping means. Pipe bending has certain bending principles in terms of shape, bending angle and bending radius, as shown in Figure 2. Generally, the bending deformation of the pipe is realized through the action of external force. When the copper elbow is bent, due to the action of tangential tensile stress, the outer pipe wall will produce a certain elongation deformation; The inner pipe wall is subjected to tangential compressive stress to produce shortening deformation [5].

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Fig.2 principle structure diagram of bending forming of small elbow
When the bending deformation process of copper elbow is completed, the tensile stress is compressed to the compressive stress direction, resulting in bending deformation of copper pipe. With the progress of bending, the degree of deformation is increasing, and the pipe bending will produce the transformation from elastic deformation to plastic deformation. The whole deformation process consists of three stages: elastic deformation stage, elastic-plastic deformation stage and plastic deformation. It is a progressive deformation process.

Technical research progress of copper elbow

Bending process of copper elbow

The bending process of different pipes is different. In the bending process of copper elbow, the position of mandrel used for bending needs to remain unchanged after it is fixed. One end of the blank pipe is fixed by the anti wrinkle block and the upper pressing plate, and the other end is held by the pressing block and the bending grinder. When the bending angle meets the established requirements, the bending process of the copper elbow is basically completed [6]. Due to the strong plasticity of copper, the bending process is generally cold working at room temperature. As a kind of copper pipe, copper elbow is generally used for bending processing, even for cold processing at room temperature. The main molds are bending die, mandrel, rotary pressing block and pressure die [7]. The preparation process of copper elbow is affected by many factors. It is necessary to strictly follow the processing conditions and methods, follow the established bending rules and bending angles, and improve the level of copper elbow bending process.

Analysis on bending process of copper elbow

The bending process of small elbow is affected by many factors, such as, stress field, strain field, wall thickness change, section distortion and so on. The forming characteristics of the pipe produced by bending during the bending of copper elbow make it easy to have the phenomena of too thin outer pipe wall, too thick inner pipe wall and abnormal section in the bending process, and even lead to bending cracking and instability folding of pipe wall [8]. The defects of these copper elbows affect the use effect to a great extent. As an important link in the production process of copper elbow, we should pay great attention to the bending process of copper elbow. During the bending process, with the continuous enhancement of the bending degree, when a reasonable balance point is found, the deformation degree of the inner and outer pipe walls of the copper elbow will gradually become stable and coordinated, which will make the tensile stress and compressive stress on the inner and outer pipe walls of the copper pipe tend to be reasonable, and the thickness of the inner and outer pipe walls of the copper elbow tend to be reasonable [9].


The current application field of copper elbow in China is mainly in air conditioning and refrigeration. The main production enterprise is copper coil processing enterprise, which is directly used in the process flow of copper coil processing enterprise. Copper coil processing enterprises mainly serve air conditioning processing enterprises and their supporting manufacturers. Through the research on the preparation process of copper elbow, it can effectively improve the production efficiency of the factory, reduce labor costs, reduce costs and increase efficiency for production enterprises, and greatly reduce the scrap rate of copper elbow. Improving the production and preparation process level of copper elbow can not only improve the income for production enterprises, but also better meet the needs of the market for high-quality copper elbow. Therefore, it is of great significance to study the preparation process of copper elbow. This paper focuses on the analysis of various indexes of copper elbow, and compares the differences of bending process between different pipes in detail. By comparing different pipes, it is found that the manufacturing process level of copper elbow is affected by many factors, such as stress distribution, copper pipe, bending process and so on. We should proceed from reality, specifically analyze and master the influence of different factors on the manufacturing process of copper elbow, further optimize the preparation process of copper elbow, and produce excellent copper elbow to meet the needs of the market.

Authors: Hu Chunhui, Zhao Sensen

Source: China Copper Elbows Manufacturer – Yaang Pipe Industry Co., Limited (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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