Xiaobian today to explain to you the mirror welding technology! In fact, mirror welding is not so difficult!
1. Technical principle
Mirror welding technology is a method of placing a mirror near the position of the weld port that cannot be observed by the naked eye according to the principle of mirror imaging, and controlling the welding operation by observing the molten pool in the mirror.
Schematic diagram of mirror welding
2. Main uses
In the installation process of the tower furnace of the ultra-supercritical thermal power unit, due to the large number of component pipe rows and the small pitch of the pipe row, the local position of the welding port cannot be observed by the naked eye, which brings unexpected difficulties to the welding of the welding joint. Welding must be carried out using a special "mirror welding" welding method. This achievement through the study of mirror welding process, the development of a special mirror welding operation training program, the use of design and production of special mirror welding practice simulation frame, welding special mirror welding welders for mirror welding training, so that they can master the naked eye can not observe the welding joint welding method, to ensure the excellent internal quality of the welding port, appearance quality. At the same time, the combination welding sequence is optimized, the work efficiency is improved, the installation period of the tower furnace is shortened, and the key problem of the slow installation speed of the tower furnace is solved.
3. Key technologies
According to the principle of mirror welding and the convenience of use, in order to prevent the mirror from exploding at high temperature during the welding process, a special mirror for welding in difficult positions has been developed. Welding mirrors are made of a combination of ultra-bright stainless steel and high-strength magnets. It is connected to a strong magnet by a flexible metal hose. The mirror and metal hose are connected by a gimbal and can be rotated 360° for easy welding.
Through the study of boiler drawings, a special mirror welding practice simulation frame was designed and produced to ensure that the welder's practice environment was close to the actual welding environment.
In the actual welding process, because the pipe row pitch is too small, customized can change the angle of the welding torch 360 ° flexible argon arc welding gun, according to the specific welding position and obstacles on the spot, bend the angle between the welding torch handle and the welding nozzle, so that the welder's hand holding the gun can be placed in a position that can be controlled, so that the welding operation can be carried out smoothly.
4. Construction process
1. Preparation before welding
Weld grinding and counterpart Blunt edge size is controlled at 0.5-1.0mm, which is convenient for welders to control the welding temperature, reduce the difficulty of welder priming, and ensure that a good fusion of root welds is obtained. When the argon arc welding base adopts the internal silk method, the counterpart gap should be controlled between 2.8-3.0mm, which is convenient for observing the molten pool through the weld gap during the welding process, and prevents the root concave of the back welding position and the flat welding position due to the excessive gap. When using the applied silk method, the counterpart gap should be controlled between 2.0 and 2.5mm. For counterparts, the wrong value must not be greater than 10 percent of the wall thickness. The degree of deflection shall not be greater than 1/200.
Placement of the mirror Before starting mirror welding, first of all, the position of the mirror should be placed, generally to meet two requirements, one is to facilitate the naked eye to observe the melt pool condition of the weld through the reflection of the mirror, and the other is to not affect the position of the argon arc welding gun and the walking and swinging of the welding torch during the welding process.
Second, hit the bottom layer of welding
Spot welding Mirror welding method the position of the mouth spot welding is different from the ordinary weld, the best spot weld position is each deviated from the flat weld position of the two sides of the forty-five degrees, so that the advantage of spot welding is that in the process of argon arc welding priming, the naked eye can easily observe the weld pool through the counterpart gap of the flat weld position.
Bottom welding Welding In individual positions, the inner wire welding method can be used. The wire is fed through the groove gap on the front to the arc combustion. The welding of the bottom layer, the welding of the back welding (6 o'clock) part is the most prone to defects. At the beginning of welding, the arc is introduced from the back welding site, the welding wire is not added first, and after the root of the groove is melted, the welding wire is gently sent to the molten pool to reach the root of the groove to ensure the height of the back weld and the root fusing well.
During the welding process, the naked eye can observe the formation of the root through the counterpart gap, while observing the combustion and appearance of the arc in the mirror, and closing the arc when welding to vertical welding.
During the welding process, on the one hand, we must pay attention to the temperature of the molten pool, prevent the occurrence of weld tumors and unsoldered penetration, and do not destroy the groove lines on both sides of the weld when welding, so as to obtain a good weld line when covering the surface. On the other hand, the welder should devote himself to the mirror reflection, the curvature of the welding wire should be easy to send the wire, and the angle of the welding torch should be adjusted in time according to the arc in the mirror, so as to avoid the angle of the welding torch from overcloping and the arc is too long, to prevent the appearance of defects such as unsoldered permeability and porosity.
In the welding process, the welding joint of the back welding part must be checked with the naked eye under the illumination of the pen flashlight to ensure the quality of the argon arc welding foundation. After the argon arc welding base weld root inspection is completed, the appearance must also be strictly checked, the main content of the inspection is whether the weld and the base metal melting is good; the width of the weld in the axial direction should be as consistent as possible, creating good conditions for the welding of the filling layer and reducing the difficulty of welding the welder when welding the filling layer. In addition, the oxides generated on the surface of the weld during the welding process must be removed before filling, otherwise it is easy to produce slag.
Third, the welding of the filled layer
After the argon arc welding primer is completed, the interlayer weld is filled. First of all, choose the operation position of the welder, simulate the running trajectory of the welding torch; then fix the mirror, and adjust the angle of the mirror; the welding wire must also be combined with the specific welding position and the curvature of the weld, appropriately twisted and deformed, which is convenient for the hand to take the welding wire to choose a relatively open position, the action is flexible, it is easy to send the welding wire to the molten pool, and the welding wire can be prevented from interfering with the welder's line of sight.
In the welding process, the reflection of the arc light through the mirror is very strong, it is difficult for the welder to see the tungsten pole clearly, the welding wire is easy to collide with the tungsten pole when feeding the wire, and the shape of the tip of the tungsten pole is deformed, affecting the stability of the arc. Therefore, during the welding process, the welding wire must be close to the weld seam to prevent the collision of the welding wire with the tungsten electrode.
Fourth, the welding of the cover layer
Before welding the cover layer, first check the surface forming of the filled weld, clean the oxides attached to the weld surface, until the weld is smooth and uniform in the circumferential and axial directions, creating the best conditions for the cover surface.
When the cover layer is welded, the bevel line on both sides should be used as the reference line to maintain the straightness of the weld to obtain a good weld surface forming. Try to avoid welding joints in the mirror weld to prevent welding defects.
In the process of welder training, the initial stage is mainly to allow welders to adapt to the particularity of mirror welding, change reverse thinking, practice the cooperation and coordination of hands and brains, and practice with ordinary material pipes. After about 10 days of training, the hand and brain can achieve effective coordination, in order to basically master the welding skills of mirror welding. Because the rework of the mirror welding joint is very difficult, the lack of a high pass rate will affect the progress of the project. Therefore, the welding joints practiced by welders can only be put on the job when the appearance and internal quality can reach 100% qualification for several consecutive days.