Talking about the spraying process of valve plate

       Last year, we mainly talked about various surface treatment processes. This year, we mainly talked about the spraying and subsequent processing technology of the following products. At present, in the domestic spraying market, the products of the valve industry are mostly used. Today, we will talk about the spraying and grinding and polishing process of the valve plate. All opinions come from the author's personal experience and analysis and judgment. If there are any mistakes or omissions, please forgive me.



Because of the work, the author has done a lot of experiments on the spraying and grinding of the valve plate. The requirements of the valve plate are very high, especially the high-pressure gas sealing valve plate. increased difficulty. Although the author always thinks that the coating color inspection is a bit excessive, but from another point of view, the color inspection has raised the standard of the valve plate to a very high level. To make high-quality coatings, the key influencing factors are powder, spraying equipment, and grinding and polishing processes. These three factors are indispensable.



Because the non-disclosure agreement was signed, the author's previous experimental data and metallographic photos could not be displayed, so he could only make some simple descriptions through words. I will gradually describe the processing flow of the valve plate from powder, equipment, grinding and polishing process, and testing methods.



powder



Powder is the foundation. Problems with the powder can directly affect the quality of the valve plate. The most direct result is that the flaw detection fails. Common problems with spray powder are as follows:



1. Powder overmelting



  Powder over-melting is often because the powder is too fine, but it is very amateurish to understand that the powder is too fine. The powders we spray on the valve plate are all agglomerated and sintered. The powder particles are actually connected by countless finer grains through the bonding phase, so the thickness of the grains also affects the powder melting. Under the scanning electron microscope, the size and number of powder grains can be clearly seen. Under the metallographic microscope, the content of oxides in the coating can be clearly seen. Usually, the high content of oxides is caused by the over-melting of the powder, and the content of oxides is harmful to the tungsten carbide coating.



2. Too many unmelted particles of powder



  The main reason for the excessive unmelted particles of the powder is that the powder has too many coarse particles and the grains of the powder are too coarse. Under the metallographic microscope, the porosity of the coating can be seen, under the scanning electron microscope, the deformation of the powder particles in the coating can be seen, and under the electron microscope, the pores of the coating can also be seen. In the case of serious porosity, the pressure test of the valve plate cannot be passed, and the flaw detection cannot be passed.



3. The stability of powder



  There are several methods of powder agglomeration and sintering. This is more complicated, so I can't describe them one by one. The stability of powder is a probabilistic event. It must be known that each powder particle is composed of countless crystal grains, and one kilogram of powder has countless powder particles. The powder is guaranteed to be stable and reliable, and we also need the joint efforts of our domestic enterprises. However, the author has been in the industry for many years, and I think that some of our domestic powders are not much worse than foreign ones.



  It is very important to choose the right powder, but there is no single cause for any problem. If the flaw detection fails, the reason for finding the powder is wrong. The author has tried the valve plate that cannot be flaw detected by the customer. After proper grinding and polishing, flaw detection just passed.



spraying equipment



The performance of the spraying equipment is an important factor in determining the quality of the coating. At present, the common equipment in the valve plate spraying industry is JP5000 and JP8000. The author has been to many valve plate spraying companies in the industry, and without exception, JP5000 and JP8000 are used.



1. Spraying parameters



  Because of the high standard of the valve plate, the spraying parameters cannot be changed frequently, and the consistency of the parameters must be guaranteed. But the problem is that JP8000 is a closed-loop control, using a mass flow controller, the parameter deviation is prone to occur during the use of the mass flow controller, especially after a period of use, such parameter deviation will inevitably occur. I often tell clients, don't believe what you see is the real value, and test the coating frequently.



2. Equipment stability



  The stability of the equipment lies in the maintenance. There will be many small problems in the equipment lacking maintenance, and each small problem may cause the instability of the coating. According to my observation, there are not many domestic enterprises that do well in equipment maintenance at present. Most of the enterprises are busy with production and neglect equipment maintenance. When the author worked in a spraying company, he formulated "three inspections before spraying and three maintenance after spraying" to ensure the stability of the equipment.



3. Equipment selection



  Some customers use equipment other than JP series to spray valve plates. I do not rule out that some equipment can also make very good valve plates. However, in the current situation, there is a lack of really excellent thermal spraying engineers in China, and the ability to operate equipment does not mean that You can operate the equipment well, and operate the equipment well, it does not mean that you can make a good product. Coating requires comprehensive technical personnel, and must select the appropriate powder according to their own equipment and formulate the appropriate process.



It is an objective fact that the author thinks that the JP series is the most suitable for valve plate spraying at present. And for a long time in the future, the valve plate spraying industry will be monopolized by JP series.



Grinding and polishing process



The grinding and polishing process is an easily overlooked link. Many people think that the valve plate flaw detection is nothing more than a powder problem and an equipment problem, but the author has done hundreds of experiments to verify the impact of grinding and polishing on the valve plate flaw detection. Because the previous experiments belong to the company's confidential, so the author will not describe too much.



Detection method



The most difficult thing for valve plate spraying companies is coloring flaw detection and pressure testing. The author of the pressure test has never personally experienced it, but the author has personally experienced coloring flaw detection and fluorescent flaw detection. Coloring inspection was originally mainly used to detect whether there are cracks in the material. In the national standard for coloring inspection, it is clearly written that "non-destructive coloring inspection is not suitable for porous materials", but our coating is actually a porous structure. It is unreasonable to use flaw detection to detect the valve plate, but then I realized that higher standards can achieve better products. Technological advances, spray operators' skills improve.



Our company has introduced surface grinder and grinding and polishing equipment this year. With years of experience and complete coating testing equipment, we can make high-quality valve plates and provide better choices for the majority of valve companies.