Application of the hottest Miller submerged arc we

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Application of Miller submerged arc welding technology in steel structure processing plant

by using the exclusive and proprietary balanced adjustable AC square wave technology of summit arc 1250tm welding machine of Miller electric manufacturing company, the St George structural steel processing plant not only shortened the welding time by 60%, but also improved the welding quality. There is no need to worry about too much heat input, welding deformation and reduced toughness. The weld bead is completely penetrated, and all pass the X-ray inspection (as shown in Figure 1)

northern equipment company of St George steel structure processing plant in Murray, Australia, has been established for more than 50 years, reaching the U and R levels of the American Society of Mechanical Engineers standards, and can provide users with high-quality products, reasonable prices and thoughtful and timely services. St George steel structure processing plant is famous for processing and manufacturing large and heavy weldments. Its products include wind towers, high-pressure tanks, ovens, containers, oil tanks and water tanks

Figure 1 weld bead cross section

eliminate damage

before using Miller balanced adjustable AC square wave submerged arc welding technology, St George steel processing plant has been using DC positive or negative arc welding, and single wire welding is the only welding method used in the past (as shown in Figure 2)

Figure 2 internal flange welding

single wire DC submerged arc welding limits the manufacturing capacity of the processing plant. The factory may only focus on one of the following three main variables: high cladding rate, ideal welding penetration and low heat input

DC Positive arc welding is a welding method that allows current to flow from the electrode to the workpiece. In this welding method, the workpiece needs to be preheated, and the degree of preheating is higher than that of the electrode. This welding method can form a deeper welding penetration at the weld toe and ensure a good cleaning effect. However, this method has low surfacing efficiency and high heat input, which is not suitable for high-speed welding of long welds, nor for welding easily deformed workpieces (such as oil tanks) and heat-treated materials (such as 41304140). Excessive heat input may enhance the dilution of the base metal, reduce the alloy composition ratio of the weld, and make it easier to produce cracks

DC negative arc welding can reduce the dilution of base metal and the deformation of weldments. However, because the heat flows from the steel plate to the electrode, this will lead to insufficient weld bead penetration. The surfacing rate of DC Positive arc welding is high, but the weldability is poor under low amperage current. This situation will be improved only by reducing production efficiency (as shown in Figure 3)

Figure 3 welding of four shells

therefore, the welding equipment supplier Airgas Intermountain company suggested that the St. George steel structure processing plant introduce Miller summit arc 1250 submerged arc welding machine. This "full process" submerged arc welding system is AC/DC output, the temporary load rate is 100% at 1000a/44v, and the power supply is three-phase AC power input. Most importantly, the welding machine provides a new fault handling tool for St George structural steel. The balanced adjustable square wave welding power supply can solve the common problems caused by DC submerged arc welding. For processing plants such as St George structural steel, the heat input of steel plate and electrode can be controlled by adjusting the positive and negative proportion of output waveform

this welding method can guarantee two of the following three properties, not just one. Welders can achieve greater penetration, higher cladding efficiency and smaller heat input. Miller welder maximizes the optimization of welding production for St George steel structure factory, and the best balance matching is 66% - 40% EP welding or 34% - 60% en welding

12 inch shell

when a large welding task needs to increase production, the St. George steel structure plant added four Miller summit arc 1250 submerged arc welding machine systems. The task requires a piece of long × wide × 40ft thick × 10ft × A cylinder with a diameter of 12ft (1ft=304.8mm) is made of 5/8in (1ft=12in=304.8mm) carbon steel plate. First, use a plasma cutting machine to cut the material according to the size, and then roll it into a large cylinder on the reel machine. The longitudinal joints are welded by MIG welding to form a cylindrical shell. The weld is upward, the external weld is submerged arc welded, and then the shell is turned over 180, and the internal weld is welded to ensure 100% welding penetration. This process adopts DC submerged arc welding process

however, due to the increase of welding speed requirements, technicians intend to adopt the balanced adjustable AC square wave welding process in the next processing procedure. In the next process, the flange with the specification of/2in (1in=25.4mm) should be welded with the bottom shell, and then the small flange should be welded with the other three shells. After welding, the 10ft high shell parts will be connected together to form a continuous 40ft long shell. The weld must be welded from inside to outside along the periphery of each shell. In order to ensure the completion of this task, St. George's processing plant has assembled a rack system. The above factors of this system are the factors that affect the accuracy of the metal tensile testing machine. The cylinder is placed on a tubular base, and the cylinder is rotated through a group of follow-up cam mechanisms. This system can maintain the consistency of angles between cylinders and the repeatability of welding operation (as shown in Figure 4)

Figure 4 external weld bead

such a summit arc 1250 welding machine equipment can weld both the internal welds of the shell and the external welds of the shell. Technicians have arranged a converter to allow welding operation. Two Miller HDC 1500 control systems, RAD wire feeding components, flux funnels and obt Jinan experimental machine factory can help you design test equipment to convert between 1200 welding guns. One welding part is placed on the top of the working platform to weld the outer weld (the first and last), and the other welding part is placed on the workshop floor to weld the inner weld (as shown in Figure 5). The two welding parts can swing at will and move up and down and back and forth to facilitate the accurate positioning of the welding position

Figure 5 assembly

the assembly table of roller, assembly frame and wire feeding assembly can ensure the consistency of assembly. At the same time, there are some auxiliary devices, which can eliminate the downtime during the conversion of internal and external welds. For example, move an assembly table, rotate it in place, and then carry out welding operations

save 60% of the welding time

welding the flange to the shell (as shown in Figure 6) requires welding inside and outside the cylinder (place the shell steel plate at a certain angle, and preheat the two weldments to be welded to 93 ℃). DC EP DC positive output submerged arc welding is adopted, which requires 5 passes of welding, the average welding speed is 15in/min, and the specification of welding wire is 5/32inaws EM12K. Using the same kind of welding wire, the flat computer has the ability to save the test results without time limit, and the adjustable AC square wave process. The parameters are 66% en +34% EP. The summit arc 1250 welder only needs to weld 3 times, and the average welding speed is 22in/min

Figure 6 Shell view

it takes 60min to weld a cylinder with a diameter of 12ft at a welding speed of 15in/min, and it takes at least 300min to weld the same shell using the old DC EP process. In order to ensure that the interlayer temperature is not too high, the shell still needs time to cool, so the actual operation time may be longer. The balanced adjustable square wave welding process only takes 123min, and the operation heat input is small, the weld bead is small, there is no need to wait for the weldment to cool, and the amount of flux used is small

excessive heat input will lead to various problems, such as the shrinkage of weldments during cooling. According to the regulations, the allowable tolerance of the shell is 1/4in. When using the DC welding process, if the interlayer temperature is not well controlled, the flange will far exceed the specified tolerance due to stretching, and the right angle between the flange and the shell will no longer be right and cannot be recovered

tip of the iceberg

due to the limited running time of the shell project, the technicians of St George steel 1.5875mm steel ball structure plant did not fully explore the feasibility of the new welding system. The welding system can do more than that. For example, using this process to butt two 5/8in thick steel plates, each welding can achieve 100% welding penetration, while ensuring that the width of the welding surface is only 3/4in. In this way, there is no need for beveling, so as to avoid waste of welding materials and excessive input

another technological upgrade is Miller's digital programmable HDC controller, which can preset and lock 12 sets of welding procedures. The person in charge of St George steel structure factory said that by using Miller's digital programming HDC controller, we can not only provide customers with high-quality welding, but also ensure the quality stability of the whole workflow. By setting and locking the working parameters in advance, and then applying these parameters to the workflow

in addition to saving operation time, Miller automatic submerged arc welding technology can also strengthen the production capacity of steel structure plants, thus greatly enhancing the market competitiveness of products. (end)

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