The application of plasma powder spray welding technology in valve sealing surface manufacturing

The application of plasma powder spray welding technology in valve sealing surface manufacturing

A, common valve faults and reasons in the use of the valve in the process of common faults are: 1. Stem rotation is not flexible or stuck stem rotation is not flexible or stuck, the main reasons are: packing pressure is too tight; Packing packing box is not standard; Valve stem and stem bushing use the same material or material choice is improper; Insufficient gap between stem and bushing; Valve stem bending; Thread surface roughness is not required.
First, the common failure of the valve and the cause
Common faults in the use of valves are:
1. The stem does not rotate flexibly or is stuck
Stem rotation is not flexible or stuck, the main reasons are: packing pressure too tight; Packing packing box is not standard; Valve stem and stem bushing use the same material or material choice is improper; Insufficient gap between stem and bushing; Valve stem bending; Thread surface roughness is not required.
2. The sealing surface leaks
The main reasons for sealing surface leakage are: sealing surface damage, such as indentation, abrasion, broken wire in the middle; There is dirt attached between the sealing surface or the sealing ring is not connected well.
3. The packing leaks
The reason of packing leakage is: packing pressure plate is not pressed; Insufficient packing; Packing due to poor storage and failure; The roundness of the valve stem exceeds the specified or the surface of the valve stem has scratches, lines, hair and rough defects; Packing variety, structure size or quality does not meet the requirements.
4. The connection between the valve body and the valve cover leaks
The possible causes are: uneven fastening of bolts at flange joints causes tilt of the flange, or insufficient tightening of bolts, and damage to the connecting surface of the valve body and valve cover; The gasket is damaged or does not meet the requirements; Flange joint surface is not parallel, flange machining surface is not good; Stem bushing and stem thread machining poor resulting in valve cover tilt.
5. Gate interferes with valve cover
When the gate valve is opened to the fully open state, sometimes the gate can not be fully opened, and the interference between the gate and the valve cover occurs. The reason is that the gate is not installed correctly or the geometry of the valve cover does not meet the requirements specified in the standard.
6. The ram is not tightly closed
The main reasons for this kind of situation are: the closing force is not enough; Between the valve seat and the gate into debris; Valve sealing surface is not well processed or damaged.
7. Other aspects, such as trachoma and sealing surface cracks caused by casting defects, will also affect the normal use of the valve, and corresponding measures should be taken to solve.
Two, the valve common fault solution
According to the above faults, different methods should be taken to solve them according to the actual situation. The specific solutions are shown in the table.
Third, the conclusion
To ensure the normal use of the valve, in addition to according to determine the cause of its fault occurred in the accurately and analysis, and take corresponding measures to solve it, also should strengthen the management of the valve, make daily maintenance and inspection work, such as reducing valve failure and increase integrity rate of the valve, make it play more for the port of loading and unloading production of utility.
Application of plasma powder spray welding technology in valve sealing surface manufacturing PPW process instead of manual arc surfacing (or manual flame surfacing), ** can give full play to the characteristics of PPW process, and show unique advantages. This is because the valve sealing surface is the “heart” of the valve, the valve sealing surface manufacturing process and materials are directly related to the quality and service life of the valve, but also related to the manufacturing cost of the valve. The sealing surface of the valve requires a certain hardness range and hardness uniformity, good abrasion resistance and certain corrosion resistance, and the composition of the alloy also has the corresponding requirements.
The advantages of application in valve sealing surface manufacturing
Using PPW process instead of manual arc surfacing (or manual flame surfacing) in valve sealing surface manufacturing, ** can give full play to the characteristics of PPW process, and show unique advantages. This is because the valve sealing surface is the “heart” of the valve, the valve sealing surface manufacturing process and materials are directly related to the quality and service life of the valve, but also related to the manufacturing cost of the valve. The sealing surface of the valve requires a certain hardness range and hardness uniformity, good abrasion resistance and certain corrosion resistance, and the composition of the alloy also has the corresponding requirements.
For large volume and wide range of medium temperature and pressure valves and high pressure valves, corrosion resistant valves, the sealing surface is basically made of alloy surfacing. Due to the high dilution rate of the base metal, the single-layer arc surfacing can not meet the requirements of hardness and alloy composition. Generally, 2-3 layers should be surfacing. The sealing surface of high temperature and high pressure valve and corrosion resistant valve requires the surfacing of expensive cobalt base or nickel base alloy, the use of manual surfacing, low material utilization, and quality is difficult to ensure. The manual surfacing is very poor and the amount of mechanical cutting is large, which is also one of the factors affecting the manufacturing cost. PPW process is adopted, and its process characteristics are just a good solution to solve many problems of manual surfacing of valve sealing surface:
Plasma powder spray welding technology has advantages
1, because the base metal dilution rate can be controlled, monolayer spray welding can achieve the requirements of hardness uniformity and alloy composition, save the amount of alloy.
2, especially suitable for spray welding expensive cobalt base and nickel base alloy, spray welding layer of good quality, high alloy utilization rate, not to ensure the quality and reduce the sealing surface manufacturing cost.
3, because the spray welding layer is formed well, the surface is smooth and smooth, the forming size can be controlled more accurately, so it is easy to cut and reduce the working time of mechanical processing.
4, the use of iron alloy spray welding instead of manual surfacing 2Cr13 does not need to annealing treatment, eliminating the annealing – quenching process.
5, high production efficiency, is more than 3 times of manual surfacing.
Because of the above advantages, so in the valve sealing surface manufacturing PPW process, is the quality, high efficiency, low consumption of the manufacturing method, has the highest social benefits and direct economic benefits.
Economic analysis
For large volume and wide range of medium temperature and pressure valve (the annual output of the country is hundreds of thousands of tons), at present most manufacturers use simple and easy manual surfacing 2Cr13. Whether the PPW process can replace the manual surfacing of 2Cr13 depends on whether the cost of sealing can be reduced.
The sealing surface manufacturing cost is mainly composed of:
(1) Cost of surfacing materials; (2) labor cost of surfacing; (3) Machining cost of surfacing layer; (4) Heat treatment cost, etc. Analyze economy with respect to these 4 respects now.
1. Cost of surfacing materials
The cost of surfacing materials is mainly determined by the consumption of surfacing materials and the price of materials. There are design requirements for the thickness and width of the surfacing layer on the sealing surface of a certain type of valve, and the consumption of surfacing materials depends on the utilization rate of the alloy. The utilization rate of the surfacing alloy depends on the dilution rate and appearance forming of the base metal. Due to the high dilution rate of the base metal of manual arc surfacing, it takes more than two surfacing times to meet the requirements, so the design thickness of the finished product of the surfacing layer is generally larger than 3mm. PPW process, base metal dilution rate is low, as long as the welding once will meet the requirements, the finished product design thickness of the surfacing layer can be reduced to 2mm. Due to poor manual surfacing, uneven, generally thicker and wider, the utilization rate of alloy surfacing layer * is about 40%. The utilization rate of alloy surfacing layer by PPW process can reach 70%.
Manual arc surfacing removes the electrode coating and electrode head, and the utilization rate of material is *70%, while the utilization rate of PPW alloy powder can reach 95%.
Table 1 compares the material consumption and material cost of the two surfacing processes. The analysis and comparison results show that although the electrode is cheaper than the alloy powder, due to the low utilization rate of electrode manual surfacing, the weight of materials consumed is more than 3 times that of PPW process, so the material cost of manual arc surfacing is 1.9 times that of PPW process. This is a very surprising figure. If the total 2Cr13 electrode consumed by each valve factory is 100T every year, the material cost is 3.3 million RMB. With PPW process, the iron base alloy powder consumption is 33T, and the material cost is about 1.82 million, so the material cost will be saved 1.48 million RMB.
Surfacing welding method
Cost project PPW process
Manual arc surfacing of Fe-base alloy by spray welding
2Cr13
Effective weight of alloy for surfacing of sealing face, Kg11.5
The alloy utilization rate of surfacing layer is 70%45%
Alloy weight of surfacing layer,Kg1.433.33
Surfacing material utilization rate, %95%70%
Surfacing alloy material consumption, Kg1.54.76
The unit price of alloy material is 5,533 yuan/kg
Cost of materials, 82.5157 yuan
Material cost to expense ratio 11.9
2. Labor cost of surfacing welding
The surfacing time cost depends on the production efficiency of each labor force. Both manual arc surfacing and PPW surfacing require only one worker to operate. The surfacing amount of one worker per shift for manual arc surfacing is about 12Kg on average, while that of PPW process can reach 20Kg. Manual arc surfacing if 12 RAMS are surfacing for one worker per shift, PPW process can spray weld 60 RAMS, and the production efficiency is 5 times that of manual arc surfacing. If the hourly cost of manual electric solitary surfacing is 10 yuan per piece, then the hourly cost of PPW process is 2 yuan per piece *. Time cost of surfacing welding is greatly reduced.
3. Machining cost of surfacing layer
Due to PPW process, the spray welding layer is smooth and smooth, and the cutting amount is less. Although the hardness of the welding layer is improved, continuous cutting can be achieved without cutting. The total machining time is lower than that of manual electric sole surfacing, and the machining cost is reduced by about 20%.
4. Heat treatment cost
Manual electric lone surfacing 2Cr13, according to the manufacturing process, after the surfacing is completed, the welding layer is too hard to be processed, so it can be processed by annealing treatment. After machining, in order to achieve the hardness of the sealing surface, it must be quenched at high frequency and then ground. Many valve factories do not pay attention to the quality of sealing surface, annealing mechanical processing, no longer high-frequency quenching treatment, so the sealing surface hardness is low, abrasion resistance is poor.
PPW process, spray welding layer hardness is within the range of specified requirements, do not need to go through heat treatment (spray welding alloy is not quenched), but directly processed into finished products, can save power consumption, easy to appear quality problems of heat treatment process. PPW process, not only improves the quality of valve sealing surface, but also reduces the manufacturing cost.
From the above economic analysis of sealing surface manufacturing cost, it can be shown that PPW process in valve manufacturing application has the advantages of improving quality, reducing cost, improving efficiency and so on. If the PPW process can be popularized and applied in the valve manufacturing industry to replace the backward manual electric solitary surfacing, obvious social and economic benefits will be obtained.