Deburring method of thread head of threaded coupling

In order to eliminate the burr defect of the first thread in the process of thread machining, the causes of burr and common elimination methods in the process of thread machining are analyzed. Combined with the production practice, several methods of deburring the first thread of threaded coupling are put forward, and the mechanical deburring method is optimized through experiments. Mechanical deburring can improve work efficiency, reduce labor intensity and safety risk, and improve the threading quality of threaded coupling.
The first thread burr of threaded coupling is directly related to the material, processing technology and process of threaded coupling. In the processing process of threaded coupling, the change of processing technology process of threaded coupling and the treatment method after comb thread processing are also the main reasons affecting the first thread burr. The first thread burr of threaded coupling has an impact on the overall efficiency, cost, quality and tool consumption of threaded coupling. In this study, the emergence of burr and the methods to eliminate burr in the thread processing process of common threaded couplings are analyzed, several common methods to remove burr of threaded couplings are put forward and optimized, which fundamentally improves the production efficiency of the threading machine of threaded couplings, reduces the labor intensity, and achieves the purpose of removing the first thread burr of threaded couplings.

Causes and removal methods of first thread burr of threaded coupling

Causes of first thread burr of threaded coupling

In the processing of threaded coupling, the general processing process is shown in figure.1. Firstly, the a end of the threaded coupling shall be machined to ensure that the end face is flush, which is also the datum plane for machining the B surface, and the external chamfer shall be turned in this process; Rough turning and boring shall be carried out after end face machining, because the boring diameter of round buckle threaded coupling needs to be turned separately, so as to reduce the cutting amount of the blade, and then carry out boring and fine turning. In this process, some machining allowance will be reserved for thread turning to avoid excessive cutting amount of flat top or comb turning; Thread processing is carried out after boring and fine turning. Because the initial thread belongs to incomplete thread, the first thread burr (sometimes accumulated cutting tumor) occurs; After the processing of side a is completed, start to process side B at the other end of the threaded coupling. The steps are the same as above until the processing of the whole threaded coupling is finally completed.

Fig.1 Schematic diagram of thread processing flow of threaded coupling
It can be seen from the processing flow of threaded coupling that some chamfered workpieces are prone to burr areas (corners or processing extrusion). Chamfering can remove burr and avoid corner or burr hurting people. However, the thread first buckle burr of threaded coupling is a common defect in the thread processing process of threaded coupling, which can not be removed by chamfering basically. The burr produced by the first thread will affect the service performance of the thread of the threaded pipe collar and the matching of the thread, which is mainly reflected in the damage to the pipe thread in the process of loading and unloading, which is easy to cause sticking, etc. On the whole, the removal of the first buckle burr can only be completely eliminated by subsequent treatment, including machining removal or other removal methods.

Common deburring methods

The first burr (as shown in figure.2) is an inevitable defect in the product processing process. Generally, the burr can only be removed after the processing process is completed. However, by changing the processing flow, reasonably selecting cutting tools and cutting specifications, the burr can also be controlled to a certain extent in the production process, so as to avoid burr or small burr, so as to improve the processing quality of threaded coupling and reduce the processing cost.
At present, many threading machines for threaded pipe couplings in the industry are not equipped with equipment or facilities with deburring function, and with the increase of equipment investment years, the equipment accuracy continues to decrease. Some deburring equipment also has the problems of reduced accuracy or poor deburring effect, which is easy to produce burr inversion or incomplete deburring. At present, when the finished products of threaded couplings are accepted in major oil fields, the first thread burr will be checked, and the existence of burr also has certain adverse factors on the service performance of threads. Therefore, the threading machine posts of threaded couplings are mostly deburred by manual grinding, which not only has high labor intensity, but also has the risk of incomplete grinding or damaging the complete thread.

Fig.2 photo of thread head burr of threaded coupling

First thread burr elimination method of threaded coupling

Principle and method of deburring

Burr removal is to remove the thorns or flash generated at the cutting intersection of the machined parts of the threaded coupling. Although the first thread burr of threaded coupling is small, it directly affects the thread connection performance of threaded coupling. With the attention of machining industries to deburring, there are more and more deburring methods. For example, burr grinding methods are divided into manual grinding and mechanical grinding. At present, burr robot instead of manual grinding has also become popular. In the deburring and grinding process of threaded coupling, manual grinding generally adopts tools such as grinding wheel, finishing plate and thousand blade wheel to realize the purpose of deburring and removal.
The deburring tool bar and blade are mostly used for deburring in machining. However, due to the difference of equipment and production and processing technology of different manufacturers, the deburring sequence or blade installation position are different; In the threading machining process of threaded coupling, special wool bayonet is usually used for removal. In addition, end face blade or boring blade is also used for burr removal, or sand blasting, phosphating and other methods are used. However, due to various reasons, the burr removal effect is quite different.

Manual burr removal method

Manual deburring generally exists in the products of threaded couplings with low degree of equipment automation or high requirements for first thread burr. Usually, file, sandpaper, grinding wheel, finishing plate, thousand blade wheel, etc. are used for removal. Pneumatic tools are used to drive the grinding wheel, finishing plate and thousand blade wheel to remove more, so as to finally achieve the purpose of burr removal. According to the different removal tools and sizes of threaded couplings, the manual deburring of a threaded coupling generally takes 1 ~ 3min. This method has low production efficiency, high labor intensity of operators and poor deburring effect.

Figure.3 common refinishing pieces for manual grinding

Mechanical deburring method

Burr removal method I of wool bayonet

Install a deburring arbor on the spare station of the threading machine turret of the threaded coupling, as shown in Fig.4. This kind of deburring tool bar can change the blade clamping angle according to different product requirements to meet the deburring requirements of different types and angles, and then add the deburring program in the processing program. The function of deburring is realized by machining. When removing burrs through the burr cutter bar, it is best to carry out program simulation and calculation on software or drawing paper, and adjust the appropriate cutting angle, otherwise it is easy to produce burr inversion or unsatisfactory removal effect, as shown in figure.5. There are three processes for deburring with deburring blade.

Fig.4 deburring tool bar

Fig.5 Schematic diagram of near deburring

• Process 1: point turning is adopted near the deburring position, that is, the wool bayonet blade is quickly close to the thread first buckle position of the threaded coupling, and the knife is quickly deburred. The edge surface of the burr blade is adopted near the deburring position, and the contact point is in the center of the edge surface of the burr blade. This method requires further exploration of the burr blade close to the allowance, which is generally recommended to be controlled at 0.05 ~ 0.15mm, so as to avoid the occurrence of unable removal or thread topping.
• Process 2: face turning is adopted near the deburring position, that is, the edge surface of the burr blade is used to go close to the initial chamfer of the thread. This method can also be used as the correction of the initial chamfer angle of the thread. The burr is removed quickly by the wool bayonet and the back knife. At this time, it must be ensured that the blade angle is the same as the initial chamfer of the thread to avoid knife marks or shoulders caused by the initial chamfer of the thread.
• Process 3: remove the burr by turning, restart the fine turning and boring steps, and turn until the initial chamfer of the thread. This method uses the tool tip of the burr blade, which belongs to finish machining, which can ensure the accuracy of the boring diameter and boring depth, and ensure the quality of deburring. The disadvantage is that it takes a long time.

For the of threaded couplings of different steel grades, it is necessary to select appropriate turning specifications to ensure the removal quality; The adjustment of assembly accuracy and angle of wool bayonet also needs to be standardized. According to the processing characteristics of different equipment, the process personnel need to constantly explore and practice according to the processing parameters of on-site equipment, and fix the deburring parameters of different steel grades and button threaded couplings, which can be adjusted in a small range by the on-site operators according to the specifications.

Burr removal method II of wool bayonet

Due to the number of spare stations of the turret of the threading machine of the threaded coupling or based on the influence of processing efficiency, some manufacturers use the blade to be integrated on one arbor. This method reduces the cost of the arbor, saves the replacement time of the turret and improves the processing efficiency. The method of integrating multiple blades on a cutter bar has been well applied in many industries, and the technology is relatively mature. In addition to the production process of small-size threaded coupling, it is not easy to integrate due to the inner hole diameter of threaded coupling, it can meet the production demand.
The machining procedure and deburring method of the integrated tool bar are basically the same as those described in 2.3. It only needs to be designed on the integration of the tool bar and consider the angle and space problems. Moreover, for the deburring process, the wool bayonet has little or no force, and the rigidity requirement of the tool bar is not high.

Deburring methods of other blades

In addition to the above deburring methods, for example, in the threading equipment of some threaded couplings, the boring cutter bar is also used to carry out the step of boring and finishing machining again after thread machining (as shown in Fig.6), which is equivalent to turning the initial chamfer of the thread again with the boring cutter, so as to achieve the effect of deburring. However, as the tool with the largest tool consumption in the processing of threaded couplings, Its cutting edge is easy to wear, which is easy to cause burr inversion or incomplete burr removal in the processing process.

Fig.6 schematic diagram of deburring with boring cutter

Other deburring methods

• (1) Chemical solution deburring method: it adopts chemical solution deburring technology, generally using soaking process. This method is not applied in pipe processing industry temporarily, and is widely used in other industries.
• (2) Sand blasting deburring: in the production process of psl-2 products, sand blasting is generally required. After sand blasting, burrs can be effectively removed and the product quality can be improved to a certain extent. However, at present, the sand blasting efficiency is relatively low, and the internal thread cleaning in the later stage of the product is more troublesome, so an additional cleaning process needs to be added before phosphating.

Conclusion

At present, the burr of the hoop thread machining machine has become a bottleneck of the hoop thread machining, which affects the thread machining efficiency of the hoop. At present, the method of manual grinding and deburring not only causes unnecessary manual waste, but also is not conducive to promoting the lean management of manufacturers and reducing cost and increasing efficiency. This study summarizes a variety of burr removal methods, which provides reference ideas for manufacturers. At present, the method of mechanical deburring is gradually popularized and applied in the processing enterprises of casing thread hoops, and a relatively mature process has been formed, which can ensure the stability of product quality.
Author: YANG Bingbing,TONG Nannan,GUO Peng,ZHANG Qiang,LI Liuwu,FAN Zhenxing,PENG Jianjun,LI Xu

Source: China Pipe Coupling Manufacturer – Yaang Pipe Industry (www.epowermetals.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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Reference:

• [1] Jiang Xinping, Cheng Chang. Case based course of mechanical design and application [M]. Beijing: Higher Education Press, 2015
• [2] Zhang Jianzhong. Fundamentals of mechanical design [M]. Beijing: Higher Education Press, 2007
• [3] Wang Haifeng, Zhang Xinmin. Modification of burr removal device in HFW630 welded pipe production line [J]. Welded pipe, 2009, 32 (11): 43-45
• [4] Cheng Daxian. Mechanical design manual (3rd Edition) [M]. Beijing: Chemical Industry Press, 1993
• [5] Yang Xiaorong. CNC transformation of lathe [M]. Shanghai: Shanghai Science and Technology Press, 2007
• [6] Li Feng, Li Zhimin. Application and maintenance of CNC machine tool system [M]. Beijing: Chemical Industry Press, 2008
• [7] Liu Caibao. Programming and operation of CNC lathe [M]. Beijing: Chemical Industry Press, 2009
• [8] Song Zhifang. Development status and future prospect of tool materials [J]. Industry and science and Technology Forum, 2013 (12): 129-130
• [9] Cui Zhongqi, Qin Yaochun. Metallography and heat treatment [M]. Beijing: China Machine Press, 2011
• [10] Li Guoqiang. Research on two kinds of deburring tooling [J]. Mechanical management development, 2020 (4): 44-45
• [11] Niu Chengjie, Zhang Meimei, Wang Xianlin. Selection of internal burr removal tools for friction welding of petroleum drill pipe [J]. Steel pipe, 2015 (6): 54-58
• [12] Chen Feifei. Analysis on burr removal method of thread chamfer in NC machining [J]. Heilongjiang Science and technology information, 2020 (3): 51-53
• [13] He Peng. Analysis, control and removal of burrs [J]. China Equipment Engineering, 2019 (10): 232-233
• [14] Han Xiang. Brief discussion on burr status and removal methods [J]. Shandong youth, 2015 (10): 99-100
• [15] Cao Zhenzhong. Overview of burr removal technology for mechanical parts [J]. Science and informatization, 2018 (31): 135