A new groove processing technology for welding equal tee
This article mainly introduces a processing method of welding equal tee‘s groove, including groove form, selection of processing method and groove processing process.
Welded tee is a common structure in boiler products, petrochemical vessels and nuclear power products. Large diameter welded tee is difficult to manufacture. In a project produced by our company, there is a new type of welded equal tee. The groove form is special, which makes the groove processing more difficult. This article briefly introduces the difficulties and solutions in the process of groove processing.
Features of product structure
The comparison between conventional welded equal tee and new welded equal tee is as follows (dark area indicates weld).
Structural characteristics of conventional welded equal tee
In the manufacture of conventional welded equal tee, the straight hole is first machined on the main pipe, and the opening diameter is equal to the inner diameter of the pipe. After that, one end of the branch pipe is processed into saddle shaped groove, and then the main pipe and branch pipe are assembled and welded.
Fig.1 Comparison of two tee structures
The advantage of conventional welding equal tee is the difficulty of groove processing
The disadvantage is that the welding workload is very large. At the same time, the heat input of welding is large, which is easy to produce large stress, which leads to large deformation of the main pipe after welding. And because of the large welding area, the possibility of welding defects is also large.
Structural characteristics of new welded equal tee
The groove form of the new type of welded tee is more complex, and the groove of main pipe and branch pipe is in the form of three-dimensional curved surface.
During the manufacture of this new type of welded tee, the groove of main pipe and branch pipe is machined by numerical control processing, and then the main pipe and branch pipe are assembled and welded.
The advantages of the new type of welding equal tee are the maximum reduction of welding work and short welding cycle. At the same time, the welding heat transfer is small, so there will be no large stress after welding forming, so the deformation of the main pipe is small. The disadvantage is that the groove structure is complex, and it is difficult to add t to the groove, so it needs to be processed by numerical control equipment.
Determination of groove processing method
The groove of this new type of welded tee is a three-dimensional curved surface shape, which cannot be accurately processed by conventional machining method. Therefore, it is considered to use CNC equipment for processing. At present, the equipment that our company can process this type of groove is CNC boring and milling machine.
Due to the slow processing speed of numerical control equipment, the cutting amount of this kind of groove processing is large. If the numerical control equipment is directly used to process the base metal, it will take a lot of time. Therefore, it is necessary to use manual gas cutting method to pretreat the base metal before CNC machining. After research and discussion, the final groove processing process is shown in Fig. 2.
FIG.2 Machining process
This process can shorten the production cycle to the greatest extent, while ensuring the groove batch, ensure the dimensional accuracy and surface finish.
Groove machining process
Preparation of groove
Groove pre-processing is the first step of the whole groove processing. The quality of pre-processing has a great impact on the subsequent groove machining, so the groove pre-processing is a crucial step in the whole process of adding I.
Determination of pre machining allowance
A certain amount of allowance is needed in the pre machining, and the determination of this allowance is also very important. If the pre machining allowance is too small, due to the large error of manual gas cutting, the gas cutting removal amount is too large, affecting the groove shape. If the pre machining allowance is too large, it will leave a large amount of work for subsequent CNC machining and affect the production cycle. After many tests, it is determined that the most reasonable allowance is 30mm, so it is decided that the allowance should be 30mm
Determination of pre machining curve
The determination of the pre-processing line will have a direct impact on the subsequent processing. In order to minimize the workload of CNC machining, it is necessary to establish a pre-processing curve similar to the groove shape. The pre-processing curve of the branch pipe and the main pipe is determined by the following methods: since the groove of the branch pipe is a single curved surface, the groove angle can be processed by manual gas cutting during the pre-processing, which can reduce a lot of machining allowance. The process of branch pipe pre machining is divided into two steps: gas cutting perpendicular to the pipe wall surface to remove the allowance, and gas cutting groove shape according to the groove angle. The processing process is shown in Fig. 3.
Fig.3 pre processing method of branch pipe
Three machining curves need to be determined during machining: the inner and outer wall curves when the allowance is removed in the first step, and the outer wall curve at the angle of gas cutting groove in the second step. According to this requirement, three pre machining curves of branch pipes are formed, which are processed according to the three curves during gas cutting in workshop.
The groove of the main pipe is composed of two curved surfaces, so it is difficult to process the groove by manual gas cutting. For the curve with the same final groove shape, only approximate curve can be selected for gas cutting. Finally, through modeling, it is decided to process according to the shape shown in Figure 4.
Fig.4 pre processing form of main pipe
According to the above modeling of the main pipe, the pre machining curve of the main pipe is generated, which is processed according to the curve in the workshop gas cutting.
Pre processing process
According to the above method, the production workshop of our company has carried out gas cutting processing on the main pipe and branch pipe respectively. The main pipe and branch pipe after gas cutting and grinding are shown in Fig.5.
Fig.5 pre processing of main pipe and branch pipe
Machining of groove
Preparation before machining
Due to the long barrel length of the main pipe, two “V” frames can be used to support the main pipe when it is processed by CNC boring and milling machine. The barrel is relatively stable and the machining accuracy can be guaranteed. However, due to the short length of the branch pipe, two “V” frames can not be used at the same time. When the single “V” frame is used to support, the workpiece vibrates greatly, which affects the machining accuracy of the groove. After study and discussion, it is decided to splice the field ends of the two branch pipes for groove processing. After the beveling machine is formed, the two branch pipes are separated by gas cutting. In this way, the length of the branch pipe can be increased, and two “V” frames are used to support, so as to improve the stability of the workpiece and ensure the machining accuracy of the groove.
Machining and forming
After gas cutting pre-processing, gas cutting surface grinding and CNC machining, the final processing and forming of the product are completely consistent with the expected model, and the groove precision can well meet the requirements of the drawing. The final forming main pipe and branch pipe are shown in Fig. 6.
Figure.6 Final groove of main pipe and branch pipe
What should buyers consider for bulk purchase of pipe tees?
- Type of pipe tee—whether welded or seamless
- Size and dimension
- Wall thickness
- Material of construction
- High pressure and temperature resistance
- Corrosion resistance etc.
This kind of processing technology can optimize the processing process, shorten the processing cycle and ensure the groove size requirements and surface finish requirements. The final processing groove size precision is high, the surface molding is good, fully meet the requirements of the drawing, and achieve the desired effect.
Through this new type of welding tee groove processing, greatly improved our company’s ability of CNC machining, especially the ability of processing special-shaped groove, and also laid a solid foundation for the processing of similar three-dimensional curved surface groove in the future.
Authors: Chang Xiaomeng, Han Xiulan
Source: China Equal Tee Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(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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