Material of HY-industry high temperature ball valve, maximum service temperature and spherical surface treatment of ball valve

(HY industry- Technical Center internal data)

 

High temperature ball valve:

The working temperature of 250 ° C or more is called a high temperature ball valve, and the ball valve sealing surface material of 250 ° C or less is usually made of PPL material. Hard seal material above 250 °C.

  • Ball valves with a working temperature of less than 250 degrees are generally used for ordinary hot water, heating water, steam systems, oil products, food, etc., and can be used when the working temperature is not higher than 250 °C.

  • The working temperature of 250 ° C or more is called high temperature ball valve should use hard sealing material, hard sealing high temperature ball valve body WCB degree can withstand 425 ° C, hardness coefficient is HRC45-58. The structure of the hard-sealed high-temperature valve is designed as a two-seat single-sided sealed hard-sealed high-temperature ball valve. The valve body is made of cast steel (WCB), the ball is 2CR13+nitrided (2CR13+stellite), and the sealing material is STL cemented carbide. The structure adopts single-side sealing: one side is sealed with graphite, and the other side is spring-loaded to face the valve seat and the ball. This design makes the valve light and light, and the sealing performance is also good. Therefore, the benefits of the product are: wear resistance, high temperature resistance, light switch, long service life.

  • Hard seal above 425 °C High temperature ball valve is a special high temperature, the material should use WC6. Special material wear-resistant hard seal high temperature ball valve. The maximum temperature can withstand 590 ° C. The valve seat on both sides of the valve uses the superalloy spring force of the spring to make the two sides of the valve seat tightly hold the ball to seal. The sealing material is made of tungsten carbide, and the spherical surface is spray welded. This hardness coefficient can be sealed with graphite between the HRC68-72 valve seat and the valve body, so the temperature can withstand 590 °C.

 

Hard seal high temperature ball valve

Benefits:

good sealing performance, high temperature resistance, wear resistance, easy opening and closing. The sealing characteristics of high temperature hard sealing ball valve are mainly metal sealing pair. The advantage is that the temperature range is wide, and the thermal expansion coefficients of various metals are not much different. Properly, it can achieve basic consistency, which is conducive to the coordination of temperature difference deformation

 

Disadvantages:

The material has high hardness and high specific pressure required for sealing. Even if the pre-tightening force is used to achieve the sealing, the sealing between the valve seat and the ball is large due to the large sealing pressure, and the friction coefficient of the metal sealing surface is higher. Large, resulting in a larger opening and closing torque of the ball valve. Therefore, high-temperature ball valves mostly use elastic sealing pairs, which have reliable performance, strong elastic compensation capability, wide temperature range, and are applicable to both floating ball valves and fixed ball valves.

 

Ball surface treatment of ball valve:

Ball valves are widely used due to their small flow resistance, wide range of pressure and temperature, good sealing performance, short opening and closing time, and non-directional installation requirements (except for one-way ball valves with special requirements).

As the opening and closing part of the ball valve, the ball plays the most important role. So what are the common surface treatment methods for our spheres?

Before we talk about the topic, we first understand several concepts: 1, electroplating; 2, cold spray; 3, thermal spray, 4, spray welding, 5, nitriding treatment.

Plating: A process in which a thin layer of other metal or alloy is plated on certain metal surfaces using electrolysis. Thereby improving corrosion resistance, wear resistance and improving aesthetics.

Cold spray:

Compressed air accelerates the metal particles to a critical speed (supersonic), and the metal particles physically deform after hitting the surface of the substrate. The metal particles collide on the surface of the substrate and adhere firmly. The metal particles are not melted during the whole process, but if the metal particles do not reach the supersonic speed, they cannot adhere. The shortcoming of cold spray is that the thickness of the sprayed layer is not high, and the surface adhesion is not well sprayed. The advantage is that the ball does not need to be heated. No deformation or internal stress is generated during the spraying process, and the thickness of the spray is well controlled. As shown in Figure 1, the cold spray schematic.

Thermal spraying:

A method in which a spray material is heated to a dissolved or semi-dissolved state by a heat source, and sprayed onto a surface of a pretreated substrate to form a coating at a certain speed. As shown in Figure 2, the thermal spray schematic.

Spray welding:

The process of spray welding is basically the same as that of thermal spraying, and the different ones add remelting procedures in the dusting process. Spray welding has a one-step spray welding method and a two-step spray welding method. One-step spray welding method is to melt one section after spraying, and spray and melt alternately, using the same spray gun. After the workpiece is preheated, spray a 0.2 mm protective layer and seal the surface to prevent oxidation. The spray is sprayed from one end, and the spray distance is 10 to 30 mm. The protective layer is locally heated to melt and begins to wet. When flowing, the powder is sprayed again, and the melting is repeated until the predetermined thickness is reached, and the surface is “mirror-surface” reflective, and then spreads forward to reach the surface completely covering the spray-welded layer.

If the thickness is insufficient once, the thickening can be repeated. One-step method is suitable for small parts or small area spray welding. The two-step spray welding method completes the spray coating and remelts it. The remelting is the key process of the two-step process and is carried out immediately after spraying. High-power soft flame with neutral flame or weak carbonized flame, the spray distance is about 20 ~ 30mm, the angle between the flame and the surface is 60 ° C ~ 75 ° C, starting from about 30 mm from the coating, properly grasp the remelting speed, will be coated The layer is heated until the coating has a “mirror” reflection and then the next part is remelted. Because the spray welding process needs remelting, when the melting point (melting temperature) of the base material (such as sphere) is lower than that of the alloy, it is not suitable for the spray welding process. Because the alloy material is remelted, if the melting point of the matrix material is lower, when the alloy reaches remelting Prior to temperature, the matrix material has melted or partially melted.

Nitriding treatment:

refers to a chemical heat treatment process in which a nitrogen atom penetrates into the surface layer of a workpiece in a certain medium at a certain temperature. The nitrided product can improve the wear resistance, fatigue resistance, corrosion resistance and high temperature resistance.

The common treatment methods for the surface of the sphere are electroplating, cold spraying, spray welding and nitriding.

The following are the surface treatment methods that engineers often encounter in their work. They are not comprehensive, but they are very useful:

1, the surface of the sphere is plated with nickel (ENP) or chrome (HCr):

  • When the spherical material is carbon steel and the valve is soft sealed, such as A105, 25, LF2, etc., the corrosion resistance of these materials is very poor, so the surface of the sphere must be treated with nickel plating (ENP) or chrome plating (HCr) to avoid spherical corrosion. , affecting the seal. When the sphere is austenitic stainless steel or other similar soft material, when the sealing ring of the ball valve is a relatively hard material such as PEEK, it is recommended that the surface of the sphere be plated with nickel (ENP) or chrome (HCr) to improve the spherical hardness to avoid the spherical surface being Scratches such as PEEK affect the seal.

  • Nickel plating (ENP) or chrome plating (HCr) plating thickness is generally 0.03mm ~ 0.05mm to meet the basic requirements, if there are special requirements, can be properly thickened;

  • The plated hardness of nickel plating (ENP) or chrome plating (HCr) is generally 600 HV to 800 HV.

2, cold spray tungsten carbide WC on the surface of the sphere:

  • Tungsten carbide is characterized by a particularly high hardness and good wear resistance. However, the disadvantage is that the melting point of tungsten carbide is particularly high, about 2870 ° C. The melting point of general metal materials is much lower than the melting point of tungsten carbide, so only the process of cold-spraying tungsten carbide WC can be used.

  • The thickness of the sprayed tungsten carbide WC is generally 0.15mm~0.18mm, which can achieve the ideal surface hardness. If special requirements, the thickness can reach 0.5mm~0.7mm, the thicker the cold spray thickness, the lower the surface adhesion. Thicker cold spray thicknesses are not recommended.

  • The surface cold-coated tungsten carbide WC hardness is generally 1050HV~1450HV, which is about 70HRC

3, spray-welded or cold-sprayed nickel-based alloy, the nickel-based alloy commonly used on the ball valve sphere is NI60, NI55.

  • NI60 and NI55 have a melting point of 1027 ° C and can be spray welded or cold sprayed.

  • The thickness of spray-welded nickel-based alloy is generally 0.5mm~0.7mm, which can meet the basic requirements. The actual maximum thickness can reach 2.5mm~3mm. For cold spray, the spray thickness is 0.15mm~0.18mm.

  • The hardness after spray welding is generally NI55: 50~55 HRC, NI60: 55~60HRC

4, spray-weld cobalt-based alloy, cobalt-based alloy is generally spray welded. Commonly used cobalt-based alloys on ball valve spheres are Stellite20, Stellite 6, Stellite 1

  • The thickness of spray-welded cobalt-based alloy is generally 0.5mm~0.7mm, which can meet the basic requirements. The actual maximum thickness can reach 2.5mm~3mm.

  • The hardness after spray welding is generally STL20:50~52HCR; STL6:38~40HCR; TL1:48~50HCR

5, Nitriding treatment:

  • The essence of nitriding treatment is to infiltrate nitrogen atoms into the surface of the workpiece. In fact, the depth of penetration is not well controlled, and the surface hardness is also unstable. In the manufacturing process of hard-sealed ball valves, the most important thing is the grinding between the seat ring and the ball. During the grinding process, the nitride layer is easily worn away. Or it is so thin that when the valve is actually used on the pipeline, the spherical surface is easily scratched by impurities in the medium, affecting the seal and even making the torque larger. Therefore, if you are not trying to ask for trouble, or if your customer will quickly replace the new valve, it is strongly recommended that the nitriding process should not be used on hard-sealed ball valves. Export products have never had a hardened, sealed ball valve. Of course, our company often has such requests from customers, mainly because of the low price, but the problems are also endless. This is all left by the customers themselves. Who will let him not listen?

HY-industry is qualified  Nickelalloy&cobalt alloy materials supplier.We have more than ten years experience in kind of High temperature ball valve&such like alloy powder production.

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