A method and device for controlling residual stress of a powder plasma surfacing layer of a valve face of a gas valve

Abstract

The patent discloses a residual stress control method and device for a powder plasma cladding layer of a valve face of a gas valve, and belongs to the field of welding additive manufacturing, which is used for inhibiting the residual tensile stress inside the powder plasma cladding layer of the valve face of the gas valve, and specifically is a powder plasma cladding layer pressing device for the valve face of the gas valve and a cladding residual stress control strategy. The cladding layer pressing device is composed of a valve rod clamping device, a rotary table, a valve end face pressing device and a valve face pressing device. The load applied to the gas valve is controlled during the welding process and after the welding. The cladding residual stress control strategy includes the determination of the range and flow of the cleaning area, the dynamic pressure calculation and the determination of the force application position during the cladding process and the load application after the welding.

Description

TECHNICAL FIELD

[0001] The present application provides a method and device for controlling residual stress of a powder plasma cladding layer of a valve face of a gas valve, and belongs to the field of welding additive manufacturing. The method comprises a pressurizing device and a corresponding process control strategy, and is suitable for a plasma cladding process of a sealing surface of a gas valve serving in a high-temperature and high-pressure environment. TECHNICAL BACKGROUND

[0002] During service, a gas valve is subjected to thermal shock from high-temperature and high-pressure gas in a cylinder and reciprocating mechanical shock from a valve seat, which leads to easy failure and short service life of the gas valve. Powder plasma cladding technology is a commonly used cladding method for cladding alloys of a sealing surface of a gas valve. However, when a sealing surface of a gas valve is subjected to a thermal shock test after plasma cladding, cracks often appear in the cladding layer, which leads to failure of the cladding layer to pass the severe test of a high-temperature and high-pressure environment. To solve this problem, one of the common improvement methods is to optimize the material ratio of the cladding alloy to reduce the brittleness of the material and reduce the risk of cracking. However, the adjustment of the material ratio takes a long time and is difficult to accurately control, and in addition, residual tensile stress in the cladding layer cannot be completely eliminated, which still easily leads to cracking. The residual stress in the cladding layer is mainly tensile stress caused by differences in thermal expansion and uneven shrinkage during the cooling process, and the residual tensile stress is an important reason for cracks in the service of the gas valve. Even though a heat treatment process is used after cladding to improve the residual stress, the residual tensile stress cannot be completely eliminated. Existing research has shown that the residual tensile stress in the cladding layer can be converted into compressive stress by externally applying a moderate pressure, which not only eliminates the harm of tensile stress, but also strengthens the service performance of the cladding layer. SUMMARY

[0003] In view of the problem of cracks in the cladding layer of a sealing surface of a gas valve after plasma cladding as described in the background, the present application provides a method and device for controlling residual stress of a powder plasma cladding layer of a valve face of a gas valve. During the cladding process, a certain external load is applied to the end face and the valve face of the gas valve to limit the expansion of the heating area of the heat source, so that the residual tensile stress in the cladding layer is converted into compressive stress. This method is beneficial to improving the service performance of the cladding layer of the valve face and thus improving the overall service life of the gas valve. The method comprises a powder plasma cladding layer pressurizing device of a gas valve and a cladding residual stress control strategy.

[0004] The overlay pressure device is composed of a valve stem clamping device, a rotary table, a valve end face pressure device and a valve face pressure device. The rotary table is used to fix the bottom of the valve, the valve stem clamping device is used to fix the valve stem and apply a load F1 perpendicular to the plane of the rotary table to the valve, the valve end face pressure device is used to apply a load F2 in the radial direction of the valve disc, and the valve face pressure device is used to apply a constant external load F3 in the vertical direction to the overlay.

[0005] The valve stem clamping device and the rotary table are used to fix the bottom of the valve, the valve stem is fixed by the valve stem clamping device, and the clamping device is controlled by a hydraulic system. The clamping device can rotate with the rotary table and apply a load F1 perpendicular to the plane of the rotary table to the valve.

[0006] The valve end face pressure device is adjusted by a hydraulic system arranged on the valve end face and adopts a four-petal movable structure that can be adjusted in length according to the diameter of the valve disc.

[0007] The overlay pressure device, the load F1 of the valve stem clamping device and the load F2 of the valve end face pressure device are dynamically adjusted according to the number of overlay layers.

[0008] The overlay residual stress control strategy is to apply loads to the valve overlay and the surrounding area by the pressure device to limit the excessive expansion of the welding area, which mainly includes: (1) cleaning the surface of the valve face to remove oil stains, rust and oxides; (2) applying two loads F1 and F2 to the valve by the valve stem clamping device and the valve end face pressure device during the overlay process; (3) applying a constant external load F3 to the valve by the valve face pressure device after the overlay is completed.

[0009] Considering the factors of thermal expansion, stress and the number of welding layers, the applied pressure during the overlay process can be described by the formula F0 is the initial pressure, which is set when the first layer is overlaid and has a small value to avoid excessive external force interfering with thermal expansion and material adaptability, α is the thermal expansion coefficient of the material, ΔT(n) is the temperature change of the welding area when the nth layer is overlaid, n is the number of overlaid layers, N is the total number of overlaid layers, and Fstress(n) is the additional stress caused by thermal stress. The formula Fstress(n) can be used to calculate the thermal stress based on the formula stress(n)= σ(n) · A, where σ(n) is the thermal stress generated when the nth layer is deposited, A is the area over which the pressure is applied, and the thermal stress can be estimated by the formula σ = E · α · ΔT(n), where E is the modulus of elasticity of the material, α is the coefficient of thermal expansion of the material, and ΔT(n) is the temperature change of the nth layer.

[0010] The thermal expansion compensation term (α · ΔT(n)) is one of the key factors in the deposition process. As the number of deposited layers increases, the temperature change ΔT(n) in the welded area increases, resulting in a greater thermal expansion effect. Therefore, the applied pressure gradually increases as the number of deposited layers increases to compensate for the deformation caused by thermal expansion.

[0011] As the number of deposited layers increases, more heat is accumulated, and the effect of thermal expansion becomes more pronounced in the later stages of the welding process. By introducing the ratio of the number of deposited layers n to the total number of layers N, the applied pressure can be dynamically adjusted to gradually increase as the number of deposited layers increases. As the number of deposited layers increases, the thermal stress in the welded area increases. These thermal stresses can cause deformation or cracking of the material during the deposition process. Therefore, a certain pressure needs to be applied to resist these stresses.

[0012] The present application is suitable for controlling residual stress in powder plasma deposited layers on the valve face of a gas valve. By applying an external load to the valve face and the end face of the gas valve during the deposition process, the expansion of the heated area by the heat source is limited, and the residual tensile stress in the deposited layer is converted to compressive stress. The present application not only effectively compensates for the uneven stress caused by the movement of the heat source and cooling during the deposition process, but also significantly improves the service performance of the gas valve, helps to improve the strength of the deposited layer, and improves the overall performance and service life of the gas valve. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A schematic diagram of a plasma deposition pressure device.

[0014] Figure 2 A diagram of a pressure device for the end face of a gas valve.

[0015] Figure 3 A diagram of the pressure state after deposition of a gas valve. DETAILED DESCRIPTION

[0016] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] REFERENCE Figure 1The workpiece 2 is first fixed by the tooling, the bottom of the valve is fixed by the workpiece 4, and the valve stem is fixed by the workpiece 1. The workpiece 1 is controlled by the hydraulic system, which can rotate with the workpiece 5 and apply a load F1 to the workpiece 2. A workpiece 4 is provided around the end face of the workpiece 2, which is adjusted by the hydraulic system and applies a load F2 to the valve. After the surfacing is completed, the preheated workpiece 3 is immediately pressed down to apply a constant external load F3 to the surfacing layer. Figure 2

[0018] The specific conditions of the workpiece and the implementation process are described below.

[0019] Before surfacing, the surface of the valve face is cleaned to remove oil stains, rust, oxides and other impurities to ensure good bonding between the surfacing layer and the base material. Common methods include sandblasting, chemical cleaning or mechanical polishing. According to the specific material and size of the valve, appropriate plasma arc welding parameters such as arc current, gas flow, powder feeding speed, etc. are set.

[0020] During the surfacing of the valve, a load F1 is applied to the valve perpendicular to the plane of the rotary table, a load F2 is applied to the valve disc in the radial direction by the valve end face pressing device, and the load F1 of the valve stem clamping device and the load F2 of the valve end face pressing device are dynamically adjusted with the change of the number of surfacing layers.

[0021] When surfacing the first layer, the temperature of the valve is relatively low, the thermal expansion of the welding area is small, and the applied pressing pressure is low to prevent excessive external force from interfering with the welding process.

[0022] As the number of surfacing layers increases, the thermal expansion and cooling shrinkage effect of the welding area becomes more pronounced, and the resulting stress also increases. Therefore, the pressure applied during this stage is gradually increased to a peak value to ensure that the thermal expansion of the welding area is effectively limited, thereby avoiding the formation of residual tensile stress.

[0023] After that, the load remains unchanged until the surfacing is completed. This process can be precisely controlled by the hydraulic system to ensure smooth growth of the surfacing layer during welding and effectively suppress residual stress caused by local expansion and shrinkage.

[0024] After the surfacing is completed, the preheated valve face pressing device is immediately pressed down to apply a constant external load F3 to the surfacing layer in the vertical direction. At this time, the load F2 of the valve end face pressing device remains unchanged, and the valve stem pressing device stops applying a load.

[0025] ​The valve face of the gas valve is preheated to a certain temperature before being pressed down to ensure that the residual stress of the overlaying layer caused by temperature difference is intensified. The valve face of the gas valve is further changed from a tensile stress state to a compressive stress state by applying external pressure through the valve face pressing device.

Claims

1. A method for controlling residual stress of a powder plasma surfacing layer of a valve face of a gas valve for suppressing residual tensile stress in the powder plasma surfacing layer of the valve face, characterized by, The application relates to a kind of gas valve powder plasma surfacing layer pressurizing device, load applied to the gas valve is controlled during welding and after welding, the surfacing layer pressurizing device is composed of gas valve stem clamping device, rotary table, gas valve end face pressurizing device and gas valve valve face pressurizing device, wherein the rotary table is used to fix the bottom of the gas valve, the stem clamping device fixes the valve stem of the gas valve, the hydraulic system controls the stem clamping device to be rotatable with the rotary table and can apply adjustable load F1 perpendicular to the plane of the rotary table to the gas valve; the gas valve end face pressurizing device adjusted by the hydraulic system adopts four-petal movable structure, and can apply adjustable load F2 in the radial direction of the valve disc part; The gas valve valve face pressurizing device can apply constant external load F3 in the vertical direction to the surfacing layer; The residual stress control method comprises the following steps: (1) surface cleaning of the gas valve valve face, removing oil stains, rust and oxides; (2) during the surfacing process, the load F1 and the load F2 are dynamically adjusted with the change of the number of surfacing layers, a lower pressure is applied when the first layer is surfacing, the pressure is gradually increased to the peak value with the increase of the number of surfacing layers, and then the pressure remains unchanged until the surfacing is completed; (3) after the surfacing is completed, the preheated gas valve valve face pressurizing device is immediately pressed down to apply constant external load F3 in the vertical direction to the surfacing layer, the load F2 of the gas valve end face pressurizing device remains unchanged, and the gas valve stem pressurizing device stops applying load.

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