This equipment is used for automatic surfacing welding of the buyer's triple eccentric valve, using ion welding machine torch to simulate trajectory surfacing, and the trajectory is based on the simulation point of the three-dimensional drawing. weld. Equipment includes: plasma butt welding machine, cross operating machine, swinger, positioner, triple eccentric valve fixture, operating cabinet, etc.
1. Basic principles
Plasma powder welding (PlasmaPowderWelding referred to as PPW) is an advanced welding process. It is an automatic surfacing welding method that uses argon plasma arc as the heat source (transferred plasma arc is the main and non-transferred plasma arc is auxiliary), and powdered alloy is used as filler. 1 is the basic process of PPW. When combined plasma arc spray welding is used, two independent DC arc welding machines are generally used as power sources to supply the non-transferred arc and the transferred arc respectively. The negative poles of the two power supplies are connected in parallel and connected to the tungsten electrode (negative pole) of the spray gun through a cable. The positive pole of the non-transferred arc power supply is connected to the spray gun nozzle through the cable, and the positive pole of the transfer arc power supply is connected to the workpiece through the cable. The cooling water is led to the welding torch through a water-cooled cable to cool the nozzle and electrode. The argon gas enters the spray welding gun through the solenoid valve and the float flow meter. After the power is turned on, the non-transferred arc is ignited with the help of a high-frequency spark. Then, the transfer arc is ignited by the conductive channel created between the tungsten electrode and the workpiece by the non-transferred arc flame. After the transfer arc is ignited, the non-transfer arc can be retained or cut off. The transfer arc is mainly used to generate a molten pool on the surface of the workpiece. The alloy powder is continuously supplied by the powder feeder according to the required amount, and is fed into the welding gun by the powder feeding airflow (also using argon gas) and blown into the arc. The alloy powder is pre-heated in the arc column, in a molten or semi-melted state, sprayed into the molten pool of the workpiece, fully melted in the molten pool, and discharged gas and floating slag. By adjusting the transfer arc and non-transfer arc current, powder feeding amount and other process specification parameters, the molten alloy powder and the heat transferred to the workpiece can be controlled. With the relative movement of the welding gun and the workpiece, the alloy molten pool gradually solidifies, and the required alloy deposition layer is obtained on the workpiece.
2. Features
Plasma surfacing uses plasma arc as heat source and alloy powder as filler metal. Compared with other surface surfacing methods, it has the following characteristics:
(1) The productivity is high. The current deposition rate has reached 9 kg/h, which is close to the high-productivity submerged arc automatic welding, and surpasses the commonly used manual arc surfacing and oxyacetylene flame surfacing.
(2) The base material has a low dilution rate of the alloy. Due to the large number of adjustable specifications in the process, the heat input can be actively controlled; the alloy powder is pre-heated in the arc column and transitions to the molten pool in a spray shape, which has a strong impact on the arc blowing force. Buffering effect, uniform heating of the molten pool, which can control the penetration depth of the base metal and reduce the dilution rate of the base metal to the alloy. The dilution rate can be controlled in the range of 5-15%, which is close to oxyacetylene surfacing, but much lower than other methods of surfacing.
(3) The surfacing layer is formed flat and smooth, and the forming size range is wide and can be accurately controlled. By changing the specification parameters, one spray welding can control the width of 3-40 mm and the thickness of 0.25-8 mm, which is difficult to achieve with other surfacing methods. of.
(4) The quality of the surfacing layer and the process stability are good. Due to the good stability of the plasma arc, the interference of external factors (the flow of the surrounding airflow, the height of the spray welding gun from the workpiece, the slight change of the angle, etc.) affects the electrical parameters (arc voltage, Arc current) and arc stability have little influence, so that the process is easy to stabilize. The alloy powder is fully melted, with less spatter, slag and gas in the molten pool are easily removed, and it is easy to eliminate quality defects such as pores and slag inclusion in the weld layer. Due to the high temperature of the plasma arc, the heat performance is moderate. The spray welding speed is fast, and it can be melted at one time, so that the heat-affected zone of the workpiece is small. The alloy structure of the surfacing layer has fine grains, uniform hardness and chemical composition, and the quality of the spray welding layer is good.
(5) The alloy powder is easy to prepare and uses a wide range of materials. The alloy powder for surfacing welding is directly atomized into spherical powder after smelting, which is easy to prepare, unlike the filament material, which is limited by the processing technology of casting, rolling, wire drawing, and grinding. It can be formulated according to needs and smelted into various alloy powders with different compositions to obtain alloy fusion welding layers with various properties to meet the requirements for surface properties of parts under different conditions. There are many types of spray welding alloy materials, including cobalt-based, nickel-based, iron-based, and copper-based. Generally, alloys with high hardness, wear resistance, heat resistance, and corrosion resistance are difficult to make wires and surfacing with other processes. However, it is simple and easy to use plasma spray welding to make these alloys into powder.
(6) The surfacing welding process is carried out automatically, which is easy to realize mechanization and automatic operation, and reduces labor intensity.
Third, the superiority of the application in the manufacture of valve sealing surfaces
The PPW process is used to replace manual arc surfacing (or manual flame surfacing) in the manufacture of valve sealing surfaces, which can give full play to the characteristics of the PPW process and show its unique advantages. This is because the valve sealing surface is the "heart" of the valve. The manufacturing process and materials of the valve sealing surface are directly related to the quality and service life of the valve, as well as the manufacturing cost of the valve. For the valve sealing surface, a certain range of hardness and uniformity of hardness are required, good scratch resistance and certain corrosion resistance are required, and there are corresponding requirements for the composition of the alloy.
For medium-temperature, medium-pressure valves, high-pressure valves and corrosion-resistant valves with a large volume and a wide range, the sealing surface of the valve is basically manufactured by alloy surfacing. The commonly used manual arc surfacing welding, due to the high dilution rate of the base material, the single-layer surfacing welding can not meet the requirements of hardness and alloy composition, generally 2-3 layers of surfacing welding are required. The sealing surfaces of high temperature and high pressure valves and corrosion-resistant valves require surfacing welding of expensive cobalt-based or nickel-based alloys, and manual surfacing is used, which not only has low material utilization, but also difficult to guarantee quality. The manual surfacing is very poor and the mechanical cutting volume is large, which is also one of the factors that affect the manufacturing cost. The PPW process is used, and its process characteristics are just the best solution to solve many problems of manual surfacing of the valve sealing surface. Its outstanding advantages include:
1. Since the dilution rate of the base metal can be controlled, single-layer surfacing can meet the requirements of hardness uniformity and alloy composition, saving alloy consumption.
2. It is especially suitable for surfacing welding of expensive cobalt-based and nickel-based alloys. The spray welding layer is of good quality and the alloy utilization rate is high, which not only ensures the quality but also reduces the manufacturing cost of the sealing surface.
3. Because the surfacing layer is well formed and the surface is flat and smooth, the forming size can be controlled more accurately, so it is easy to cut and reduce mechanical stress.工工时。
4. Using iron-based alloy spray welding instead of manual surfacing 2Cr13 does not require annealing treatment, which saves the annealing-quenching process.
5. High production efficiency, more than 3 times that of manual surfacing.
Due to the above-mentioned advantages, the PPW process is adopted in the manufacture of the valve sealing surface, which is a high-quality, high-efficiency and low-consumption manufacturing method, which has significant social and direct economic benefits.
4. Economic analysis
For medium-temperature and medium-pressure valves with a large quantity and a wide range (the national annual output is hundreds of thousands of tons), most manufacturers currently use simple and easy manual surfacing 2Cr13. Whether the PPW process can replace the manual overlay welding of 2Cr13, the key lies in whether the sealing manufacturing cost can be reduced. The manufacturing cost of the sealing surface is mainly composed of: (1) the cost of surfacing welding material; (2) the cost of surfacing welding man-hour; (3) the machining cost of surfacing layer; (4) the cost of heat treatment. Now we analyze the economy in these four aspects.
1. Surfacing material cost
The cost of surfacing materials is mainly determined by the consumption of surfacing materials and the price of the materials. There are design requirements for the thickness and width of the surfacing layer on the sealing surface of a certain type of valve. The consumption of surfacing materials depends on the utilization rate of the surfacing alloy. The utilization rate of the surfacing alloy depends on the dilution rate of the base metal and the appearance shape. Due to the high dilution rate of the base metal of manual arc surfacing welding, it takes more than two surfacing welding to meet the requirements, so the design thickness of the surfacing layer is generally greater than 3mm. In the PPW process, the dilution rate of the base material is low, and the requirement can be met by only one welding process, and the design thickness of the surfacing layer can be reduced to 2mm. Due to poor manual surfacing formation and uneven height, it is generally thickened and widened, and the utilization rate of the alloy surfacing layer is only about 40%. The utilization rate of the PPW process alloy surfacing layer can reach 70%. Manual arc surfacing removes the coating and the electrode tip of the electrode, and the utilization rate of the material is only 70%, while the utilization rate of the PPW process alloy powder can reach 95%.
Table 1 compares the consumption of surfacing materials and material costs for the two processes. The analysis and comparison results show that although the electrode is cheaper than the alloy powder, the manual surfacing of the electrode has a low utilization rate and the weight of the material is more than 3 times that of the PPW process. Therefore, the cost of manual arc surfacing is 1.9 times that of the PPW process. This is a very staggering figure. If the total annual consumption of 2Cr13 electrodes by each valve factory is 100T, the material cost is 3.3 million yuan, with the PPW process, the iron-based alloy powder consumption is 33T, and the material cost is about 1.82 million. It saves 1.48 million.
Surfacing method, cost item, PPW process, spray welding Fe-based alloy, manual arc surfacing, 2Cr13
The effective weight of the alloy of the sealing surface surfacing layer, Kg1.51, the utilization rate of the surfacing layer alloy% 45% 70%, the weight of the surfacing layer alloy, Kg 1.433.331.43, the utilization rate of the surfacing welding material% 70% 95%, the surfacing welding Consumption of alloy material, Kg4.761.5, unit price of alloy material, RMB 3355 per kilogram, material cost, RMB 15782.5, ratio of material cost to expense 1.91
2. Cost of surfacing welding man-hour
The cost of surfacing welding man-hours depends on the production efficiency of each labor. Manual arc surfacing and PPW process surfacing only require one worker to operate. Manual arc surfacing welding requires an average of about 12Kg for each worker in a shift, while the PPW process, The amount of surfacing welding for one worker in each shift can reach 20Kg. According to the ratio of surfacing welding material consumption, if one worker in manual arc surfacing welding has 12 surfacing rams, then the PPW process can spray welding rams for 60. The efficiency is 5 times that of manual arc surfacing. If the manual electric solitary surfacing welding costs 10 yuan per piece, then the PPW process costs only 2 yuan per piece. The cost of surfacing welding man-hours is greatly reduced.
3. The machining cost of the surfacing welding layer is due to the PPW process, the spray welding layer is flat and smooth, and the amount of cutting is small. Although the hardness of the welding layer is increased, continuous cutting can be realized without cutting tools. The total machining time is lower than that of manual electric solitary piles. Welding and machining costs are reduced by about 20%.
4. Heat treatment cost
Manual electric arc surfacing welding 2Cr13, according to the manufacturing process, after the surfacing welding is completed, because the welding layer is very hard and cannot be processed, it must be processed by annealing. In order to achieve the required hardness of the sealing surface after machining, it must be subjected to high-frequency quenching and then grinding. Many valve factories do not pay attention to the quality of the sealing surface. After annealing and machining, high-frequency quenching is no longer performed, so that the sealing surface has low hardness and poor scratch resistance.
With the PPW process, the hardness of the spray welding layer is within the specified range, and it does not need to undergo heat treatment (the spray welding alloy has no hardenability), but is directly processed into a finished product, which can save power consumption and prone to quality problems. The heat treatment process. The PPW process not only improves the quality of the valve sealing surface, but also reduces the manufacturing cost.
From the above economic analysis of the manufacturing cost of the sealing surface, it can be shown that the application of the PPW process in valve manufacturing has significant advantages such as improving quality, reducing costs, and improving efficiency. If the PPW process can be comprehensively promoted in the valve manufacturing industry to replace the backward manual electric solitary surfacing welding, obvious social and corporate economic benefits will be obtained.
