Talking about the spraying technology of ball valve

       In the valve spraying industry, the most common ones are plate valves and ball valves. We briefly described the spraying and grinding of valve plates before, but this time we mainly talk about the spraying process of ball valves.



The author once worked in a valve spraying company. We spray tens of thousands of sets of ball valves every year, so we have accumulated rich experience in the spraying and processing of ball valves. There are many differences in the spraying of ball valves and plate valves, mainly due to the variety of powder, process and shape of ball valve spraying, and the requirements of ball valve spraying are also different from those of plate valves. The main problems of ball valve spraying are sand holes, Cracking, peeling, pitting, low hardness, uneven coating, burrs, build-up, etc.



In ball valve spraying, we have sprayed tungsten carbide, chromium carbide, nickel-based alloy, cobalt-based alloy, Monel alloy, Hastelloy and other materials. The spraying process includes supersonic spraying, plasma spraying, surfacing, spray welding Wait, although the shape of the ball valve is round, the setting of the robot program during spraying is much more complicated than that of the flat valve. If the program is unreasonable, the thickness of the sprayed coating will be uneven, which will affect the subsequent grinding.



We focus on the common problems of spraying ball valves:



1. Trachoma



Trachoma is the most troublesome problem for all ball valve spraying plants, and a trachoma destroys a coating. Trachoma will affect the sealing performance of the ball valve. There are many reasons for the formation of trachoma. The more common ones are:



1. The surface is not cleaned after sandblasting, and there are sand grains embedded in the surface



2. The spray powder is not melted



3. Excessive carbon deposition



4. There are impurities in the powder



5. Too many coarse particles in the powder



The trachoma problem is the most difficult and common problem to solve in the spraying ball valve. The author has personally experienced many trachoma problems. The conditions of the trachoma caused by different reasons are also very different. Experienced engineers can analyze the condition of the trachoma. Causes of trachoma. The author has visited many ball valve spraying factories, without exception, there will be trachoma problems, but the strictness of everyone's control of the process determines the frequency of trachoma.



After years of exploration, we have sorted out a set of practical methods to control the occurrence of trachoma. Although it is not 100% guaranteed that there will be no trachoma, through our unremitting efforts, we have raised the pass rate of our products to more than 99%. .



2. Cracks



Cracks are also a problem that is easy to occur in spraying, and they mostly appear on products with smaller sizes and sharp edges and corners. There are two main reasons for cracks:



1. The temperature is too high



    Excessive temperature means that during the spraying process, the overall temperature or local temperature of the workpiece is kept at a very high temperature for a long time, so that the coating is very prone to cracks after spraying.



2. Excessive stress



    Some people think that the higher the temperature, the higher the stress, this understanding is inaccurate. The high stress is also related to the design of the ball valve. There are some details in the coating design of some ball valves, which leads to the concentration of stress in local areas and it is difficult to release, resulting in cracking of the coating in local areas. I have always believed that whether the coating is easy to use and durable, the design of the product should be combined with the design of the coating, otherwise it will be more prone to problems.



Three, fall off



The problem of shedding occurs rarely on ball valves, but occasionally occurs. Many customers think that the coating shedding means that the spraying is not good. This understanding is one-sided.



1. Low bonding strength of coating



Due to the uneven performance of the equipment used by many customers in the market, the spraying equipment with poor performance has a higher probability of coating falling off, and in order to reduce costs, some spraying plants recycle the corundum sand too many times, resulting in sandblasting. Quality decline, these are important reasons for coating peeling



2. The surface is not cleaned



If there is oil on the surface of the product and it is not cleaned, the coating will have a greater risk of falling off. Some spraying plants do not clean this process, and directly sandblast the product after receiving the product, resulting in oil residue and affecting the bonding strength of the coating.



3. The surface hardness of the product matrix is too high



Usually, the surface hardness of the substrate is lower than HRC50, but some products have a quenching hardness higher than HRC60, which leads to a sharp drop in bonding strength.



4. The coating is too thick



This generally exists in local places, and the probability of occurrence is not large. Usually, the thickness of the coating is suitable, not the thicker the better. When the author did experiments, he found that the thickness of the coating deposited on the tooling was up to 32 mm, but it did not fall off, and no cracks were found inside the test coating, so the thickness of the coating was not the main reason for the falling off of the coating, but in the In some special cases, the coating thickness exceeds 0.5 mm and there is a risk of peeling.



Four, pitting



Pockmark is a relatively rare problem when spraying. Although it does not affect the use at certain times, it affects the appearance. There are many reasons for the appearance of pockmarks. Usually we think it is caused by insufficient grinding, but according to the author's experience, pitting Another important reason is the powder quality problem.



5. Low hardness



As a hard seal ball valve, the hardness of the coating is very important. In the opinion of many people, the hardness of the coating will not have much effect, but through some wear experiments, it is clear that the hardness of the coating has a very direct impact on the wear resistance. Usually, the hardness of tungsten carbide coating is greater than 1100HV, but due to the relationship between equipment performance and powder quality, some coatings cannot reach such hardness. The author has measured the coating quality of some spraying plants, The hardness of sprayed tungsten carbide is only more than 800, and its wear resistance is not even as good as nickel 60.



6. Uneven coating



The uneven coating is a problem that occurs when the robot program is not properly debugged during spraying. The uneven coating will mainly cause trouble for subsequent grinding and polishing, and in severe cases, it will affect the quality of the ball valve. Experienced people know that when the ball valve is smooth on one side and rough on the other side, there will be slippage in the smooth place, resulting in uneven size and poor roundness after grinding.



7. Glitch



The main reason for the burr is that the tooling protection of the ball valve is not well done, but according to the author's many years of experience, whether the tooling protection is easy to do is related to the design of the product itself. The design of some ball valves is not combined with the coating, which makes the protection very troublesome, which not only affects the beauty of the spraying, but also seriously affects the quality of the coating. Many ball valve designers "take it for granted" during the design process, and have no actual understanding of spraying at all. They imagine spraying as the same as spray paint, just take a newspaper to cover it. This kind of taken for granted attitude not only increases the ball valve. The difficulty of spraying also increases the cost of spraying, affects the effect of the coating, and causes a lot of trouble in the follow-up.



The spraying of the ball valve seems to be very simple, but in fact there are many problems that need to be paid attention to, and for different spraying materials, different product states, shapes, including different base materials, the details that need to be paid attention to are different. We hope to work with various ball valve manufacturers to make the most suitable coating.