Application of full-position automatic welding machine for pressure pipe

Introduction : For a long time, the welding of pressure pipe of hydropower station has been using traditional, simple and heavy welding arc welding technology. Only a small number of longitudinal seams in the production field are submerged arc automatic welding technology, and the all-position automatic welding technology of pressure steel pipe is still blank. along with...

For a long time, the welding of pressure pipe of hydropower station has been using traditional, simple and heavy welding arc welding technology. Only a small number of longitudinal seams in the production field are submerged arc automatic welding technology, and the all-position automatic welding technology of pressure steel pipe is still blank. With the rapid development of hydropower construction and the continuous increase of unit parameters, the welding of large-diameter thick-walled pressure steel pipes must adopt advanced all-position automatic welding technology to meet the needs of construction and production.

The full-position automatic welding of the pressure steel pipe not only needs to realize the automatic walking of the welding trolley along the weld, the automatic conveying, the swaying, the swinging and the medium electromechanical control process of the welding wire, but also to solve the welding droplet transfer form of the welding wire and ensure the welding of the all-position welding. Sewing molding quality, especially a series of automatic control technologies for automatic adjustment of welding specifications at various positions; more importantly, the welds assembled on site have poor quality and poor construction environment, and it is difficult to meet the requirements of automated welding construction. At present, the full-position automatic welding technology of pressure steel pipe is difficult to be fully applied in the welding of large-diameter thick-walled pressure steel pipe. The main reasons are:

(1) It is difficult to achieve uniform and high precision for the installation of large-diameter thick-walled penstocks. It is required that all-position automatic welding equipment can automatically withstand the relevant process parameters according to the groove size and deviation to reduce or eliminate unevenness. The effect of parameters on the quality of the weld;

(2) The position of the weld space is constantly changing, and the welding system is required to automatically adjust the welding process parameters according to the position of the welding torch, so that the welding forming is basically the same everywhere;

(3) To realize the groove size, weld melting shape, welding specification parameters, and the adjustment of the three dimensions to ensure the quality of the weld, the automatic control technology is difficult.

Therefore, how to choose a full-position automatic welding equipment with low cost, strong adaptability, simple operation and high welding efficiency is the only way to solve the above problems. In view of the welding characteristics of the pressure pipe of the hydropower station, we developed a unique full-position automatic welding machine, and the pressure pipe in the Gudongkou Hydropower Station in Xingshan County, Hubei Province and the No. 11#14# pressure steel pipe in the second phase of the Three Gorges Project. Successful application of seam welding has been achieved.

1 Main development content and implementation plan of all-position automatic welding machine

The development of all-position automatic welding machine mainly includes two parts of mechanical and electrical control.

1.1 Mechanical design and manufacturing
The mechanical design of the whole machine includes crawling track, crawling trolley, welding torch swinging mechanism and swing adaptive groove width sensor structure design.

1.1.1 crawling track
The crawling track is composed of a stainless steel thin plate, a rack consisting of a split tooth block, and a hydrodynamic block fixed to the surface of the workpiece. The control trailer of the crawling trolley and the welding torch swings the edge of the rail by means of a pair of left and right rolling bearing pairs, so that the two can move smoothly and flexibly along the rail, and the pinion and the track on the output shaft of the driving motor in the crawling trolley are used. The racks on the rails mesh and the crawler trolleys are integrated with the torch swing control trailer through the two side links, so that the two can run reliably and smoothly on the rails, and the full-position crawling function is implemented.

1.1.2 crawling car
The crawling trolley is divided into two parts: an active driving walking trolley and a passive walking welding torch swinging control trailer. They have two pairs of 60° bearing wheel clamping rail edges on the two sides below the bottom plate, which are flexible and reliable. One of the bearing wheels on both sides of the clamping rail can be laterally moved by the screw and the slider to realize the clamping and dismounting of the trolley on the rail, so that the loading and unloading of the trolley on the rail is very convenient.

1.1.3 Torch swing mechanism
The torch swing mechanism is a mechanism for achieving lateral movement of the welding arc. The system uses a hollow thin-walled stainless steel square tube. A strip of stainless steel plate and a rack are fixed on the swing rod, and a torch clamping and a sensor fixing and adjusting mechanism are installed at the end of the swing rod. By means of the chamfered edges on the pendulum bar, the chamfered edges on both sides of the pendulum are meshed with the V-shaped rollers of the four bearing shells mounted on the vertical plate, which makes the swing very flexible, light, rigid, small, stable and reliable. A very convenient swing mechanism is removed.

1.1.4 swing adaptive groove width and welding automatic tracking dual-purpose sensor
The swing and tracking dual-purpose sensors are designed to adapt to the on-site construction conditions of hydropower stations. It is difficult to achieve uniform gaps in the circumferential groove groove assembly of large-diameter thick-walled pressure steel pipes, and it is difficult to weld the rails during full-position automatic welding. The seams are designed to be completely parallel. The sensor of the machine uses the probe to mechanically contact the sidewall of the groove to obtain the signal. This is a reliable signal acquisition method with the strongest anti-interference ability. Then the photoelectric signal is generated by the pendulum system inside the sensor, and the control circuit is controlled by the logic circuit. The torch swings the motor to the steering and staying, which realizes the function of the adaptive swing width of the welding torch.

1.2 Development of electrical control system
The perfect design function of the welder electrical control system, stable and reliable work, and good anti-interference are very important to ensure the quality of the welder. The welding machine fully considers the basic functions necessary for the all-position automatic welding machine and the functions of the same advanced welding machine at home and abroad, and develops the swing adaptive groove width and automatic tracking welding control function with its own characteristics. The main control functions of this unit are as follows:

1) Automatic and manual selection of welding torch;

2) Torch swing setting and adaptive selection;

3) adjustment of the dwell time on both sides of the welding torch;

4) Welding torch speed adjustment;

5) Welding arc motion trajectory selection;

6) Welding direction selection;

7) The welding speed is withered;

8) Set the starting direction selection under the swing working mode;

9) setting the arc correction adjustment under the swing working mode;

10) Welding control car near control and remote control.


2 Main technical parameters of the whole machine:

Car power supply: 220V 50HZ
Car crawling speed 0 ~ 450mm / min
Torch swing amplitude 0 ~ ± 40mm
Torch swing speed 250~3000mm/min
Torch swing mode 1) Straight shape; 2) Zigzag; 3) Trapezoidal; 4) Rectangular Duration of the torch on both sides 0 to 5 sec
Automatic tracking accuracy ±0.5sec
Welding torch adjustment degree of freedom 6 welded steel pipe curvature radius ≥ 1500mm
Welder weight 18.5 kg

The welding method suitable for the welding machine is not limited. CQ2 gas shielded welding, flux cored wire gas shielded welding, flux cored wire self-welding welding, MAG welding, MIG welding, TIG welding, etc. can be used as needed. Characteristic welding power supply and welding torch.

3 Engineering applications and effects
3.1 Introduction to Application Engineering
The Gudongkou Hydropower Station is located in the lower reaches of the Gufu River in Xingshan County, Hubei Province. The total installed capacity of the power station is 45,000 kW. The average annual power generation is 124 million kwh. The diameter of the pressure pipe is 5 m and the wall thickness is 16-40 mm. More than 600 m. All are made of domestic 16Mn low alloy structural steel.

The Three Gorges Project is a world-famous hydropower project with a total installed capacity of 18.2 million kW and an annual generating capacity of 84.7 billion kwh. Its pressure pipe has a diameter of 12.4 m, a wall thickness of 26 to 541 mm, and a single pipe length of 122.5 m. 16MnR low alloy structural steel and imported 600MPa grade low carbon quenched and tempered high strength steel plate.

3.2 All-position automatic welding process

3.3 Application effects
(1) The performance effects of all-position automatic welding and traditional electrode arc welding are shown in Table 2:


(2) Through the welding application of Gudongkou pressure steel pipe and the No. 11～14# pressure steel pipe of the third phase of the Three Gorges Project, the first pass rate of the longitudinal seam ultrasonic flaw detection is 99.5%, and the pass rate of the circumferential seam ultrasonic flaw detection is 98.1%. The quality of the weld appearance is 100%, which is unmatched by conventional electrode arc welding.

(3) The welding trolley adopts flexible track, the machine head swings and swings on both sides of the weld seam, and can achieve stepless speed regulation and automatic wire feeding, which is stable and reliable, and meets the basic requirements of all-position automatic welding.

(4) Due to the realization of mechanized and automated welding technology, not only the labor intensity of the welder is reduced, but also the first pass rate of the weld non-destructive flaw detection is greatly improved, and the influence of human factors is greatly reduced in the welding quality.

(5) Continuous wire feeding and high current density welding can improve work efficiency by more than one time compared with electrode arc welding.

(6) Compared with electrode arc welding, the automatic welding process has a deep penetration depth, and a smaller groove angle can be used, and the width of the heat affected zone and the residual deformation of the welding can be greatly reduced.

4 Conclusion
Based on the successful experience of similar foreign welding machines, the all-position automatic welding machine is aimed at the on-site construction characteristics of the pressure pipe of the hydropower station, the creative development; the important functions of the adaptive welding width and automatic tracking of the welding torch swing, the overall design of the welding machine Reasonable, stable and reliable work, beautiful appearance, compact and light structure, with high promotion and application value.

The successful application of all-position automatic welding technology in the longitudinal ring joint of Gudongkou pressure steel pipe and the longitudinal joint welding of No. 11~14# pressure steel pipe of the third phase of the Three Gorges Project is only the beginning of the application of automatic welding technology in the welding construction of hydropower station. The application of this equipment and technology in the annular pipe welding of the Three Gorges Project will be our next goal. The application of all-position automatic welding on the pressure steel pipe and volute of hydropower station is also the inevitable result of the development of welding construction technology.

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