Method and device for controlling residual stress of powder plasma surfacing layer of valve face of air valve

Abstract

The invention discloses a method and a device for controlling residual stress of a powder plasma surfacing layer of an air valve face, belongs to the field of welding additive manufacturing, is used for inhibiting residual tensile stress in the powder plasma surfacing layer of the air valve face, and particularly relates to a pressurizing device for the powder plasma surfacing layer of the air valve and a surfacing residual stress control strategy. The surfacing layer pressurizing device is composed of an air valve rod clamping device, a rotary table, an air valve end face pressurizing device and an air valve face pressurizing device, and loads applied to an air valve are controlled in the welding process and after welding. The surfacing layer residual stress control strategy comprises the steps of range and process determination of a cleaning area, dynamic pressure calculation in the surfacing process and after-welding load application and force application position determination.

Description

Technical Field

[0001] The present invention proposes a method and device for controlling residual stress of a powder plasma surfacing layer on a gas valve surface, which belongs to the field of welding additive manufacturing. The method and device specifically include a pressurizing device combined with a corresponding process control strategy, and is suitable for the plasma surfacing process of a gas valve sealing surface serving under high temperature and high pressure environments. Technical Background

[0002] During the service process, the valve is subjected to the thermal shock from the high temperature and high pressure gas in the cylinder and the reciprocating mechanical shock from the valve seat for a long time, which makes the valve easy to fail and have a short service life. Powder plasma cladding technology is a common cladding method for cladding alloys on the valve sealing surface. However, when the valve sealing surface is subjected to thermal shock test after plasma cladding, cracks often appear in the cladding layer, which makes it unable to pass the harsh test of high temperature and high pressure environment. To address this problem, one of the common improvement methods is to reduce the brittleness of the material and reduce the risk of cracking by optimizing the material ratio of the cladding alloy. However, the research time for adjusting the material ratio is long and difficult to control accurately. In addition, the residual tensile stress in the cladding layer cannot be completely eliminated, which still easily leads to cracking. The residual stress inside the cladding layer is mainly the tensile stress caused by the difference in thermal expansion of the material and the uneven contraction during the cooling process. The residual tensile stress is an important reason for the cracks in the valve service. Even if the heat treatment process is used to improve the residual stress after cladding, the residual tensile stress cannot be completely eliminated. Studies have shown that the residual tensile stress inside the weld overlay layer can be converted into compressive stress by applying moderate external pressure. This method can not only eliminate the harm of tensile stress, but also enhance the service performance of the weld layer. Summary of the invention

[0003] In response to the problem of cracks in the cladding layer after plasma cladding on the valve sealing surface described in the background technology, this patent proposes a method and device for controlling the residual stress of the powder plasma cladding layer on the valve surface. During the cladding process, a certain external load is applied to the valve end face and the valve face to limit the expansion of the heat source heating area, so that the residual tensile stress in the cladding layer is converted into compressive stress. This method is conducive to improving the service performance of the valve surface cladding layer, thereby increasing the overall life of the valve. Specifically, it includes a gas valve powder plasma cladding layer pressurization device and a cladding residual stress control strategy.

[0004] The cladding layer pressurizing device consists of a valve stem clamping device, a turntable, a valve end face pressurizing device and a valve face pressurizing device, which controls the load applied to the valve during and after welding, wherein the turntable is used to fix the bottom of the valve, the valve stem clamping device fixes the valve stem and applies a load F1 perpendicular to the turntable plane to the valve, the valve end face pressurizing device applies a load F2 in the radial direction of the valve disc, and the valve face pressurizing device applies a constant external load F3 in a vertical direction to the cladding layer.

[0005] The valve stem clamping device and the turntable are used to fix the bottom of the valve. The valve stem of the valve is fixed by the valve stem clamping device. The valve stem clamping device is controlled by a hydraulic system. On the one hand, the clamping device can rotate with the turntable, and on the other hand, it can apply a load F1 perpendicular to the turntable plane to the valve.

[0006] The air valve end face pressurizing device is adjusted by a hydraulic system arranged on the air valve end face and adopts a four-petal movable structure, which can be telescopically adjusted according to the different diameters of the air valve disc.

[0007] The load F1 of the cladding layer pressurizing device, the valve stem clamping device and the load F2 of the valve end face pressurizing device are dynamically adjusted as the number of cladding layers changes.

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

[0009] Taking into account factors such as thermal expansion, stress, and number of weld layers, the pressure applied during cladding can be expressed as To describe, F0 is the initial pressure, which is set when surfacing the first layer. Its value is small 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 in the welding area when surfacing the nth layer. n is the number of surfacing layers, N is the total number of surfacing layers, and Fstress(n) is the additional stress caused by thermal stress. The formula based on thermal stress F stress(n)=σ(n)·A, σ(n) is the thermal stress generated during the nth layer of cladding, A is the area of ​​applied pressure, and the thermal stress can be estimated by the formula σ=E·α·ΔT(n), where E is the elastic modulus of the material, α is the thermal expansion coefficient of the material, and ΔT(n) is the temperature change of the nth layer of cladding.

[0010] The thermal expansion compensation term (α·ΔT(n)) is one of the key factors in the cladding process. As the number of cladding layers increases, the temperature change ΔT(n) in the welding area will gradually increase, resulting in a greater thermal expansion effect. Therefore, the applied pressure should be gradually increased with the increase in the number of cladding layers to compensate for the deformation caused by thermal expansion.

[0011] The effect of thermal expansion is more pronounced in the later stages of the welding process, as the number of weld layers increases, leading to more heat accumulation. By introducing the ratio of the number of layers n to the total number of layers N, the applied pressure can be dynamically adjusted to increase gradually with the number of weld layers. As the number of weld layers increases, the thermal stresses in the weld area gradually increase. These thermal stresses may cause deformation or cracks in the material during the weld process. Therefore, a certain amount of pressure needs to be applied to resist these stresses.

[0012] The present invention is suitable for controlling the residual stress of the powder plasma cladding layer on the valve face of the gas valve. During the cladding process, a certain external load can be applied to the end face and 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. The present invention can not only effectively compensate for the stress unevenness caused by the movement and cooling of the heat source during the cladding process, but also significantly improve the service performance of the gas valve, help to improve the strength of the cladding layer, and improve the overall performance and service life of the gas valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of plasma surfacing pressurization device.

[0014] Figure 2 This is a diagram of the air valve end face pressurizing device.

[0015] Figure 3 This is a diagram of the pressurized state of the gas valve after surfacing. DETAILED DESCRIPTION

[0016] The present invention is described in detail below with reference to the accompanying drawings and specific implementation modes.

[0017] refer to Figure 1The cladding layer pressurizing device in this specific embodiment is introduced. First, the workpiece 2 is fixed by the tooling, the bottom of the gas valve is fixed by the workpiece 4, and the valve stem of the gas valve is fixed by the workpiece 1. The workpiece 1 is controlled by the hydraulic system. On the one hand, it can rotate with the workpiece 5, and on the other hand, it can apply a load F1 to the workpiece 2. A structure adjusted by the hydraulic system is set around the end surface of the workpiece 2. Figure 2 The workpiece 4 shown applies a load F2 to the gas valve. After the cladding is completed, the preheated workpiece 3 is immediately pressed down to apply a constant external load F3 to the cladding layer.

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

[0019] Before cladding, first clean the valve surface to remove impurities such as oil, rust, oxides, etc. to ensure a good bond between the cladding layer and the base material. Common methods include sandblasting, chemical cleaning or mechanical grinding. According to the specific material and size of the valve, set the appropriate plasma arc welding parameters, such as arc current, gas flow, powder feeding speed, etc.

[0020] During the gas valve cladding process, a load F1 perpendicular to the turntable plane is applied to the gas valve, and a load F2 is applied in the radial direction of the gas valve disc through the gas valve end face pressurizing device. The load F1 of the gas valve stem clamping device and the load F2 of the gas valve end face pressurizing device are dynamically adjusted as the number of cladding layers changes.

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

[0022] As the number of cladding layers increases, the thermal expansion and cooling contraction effects of the weld area become more obvious, and the stress generated also increases. Therefore, at this stage, the applied pressure is gradually increased to the peak value to ensure that the thermal expansion of the weld area is effectively limited, thereby avoiding the formation of residual tensile stress.

[0023] The load remains constant until the cladding is completed. This process can be precisely controlled by the hydraulic system to ensure the smooth growth of the cladding layer during welding and effectively suppress residual stress caused by local expansion and contraction.

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

[0025] The valve face pressurizing device is preheated to a certain temperature before pressing down to ensure that the residual stress of the cladding layer caused by the temperature difference is aggravated. The valve face pressurizing device further transforms the cladding area from a tensile stress state to a compressive stress state by applying external pressure.

Claims

1. A method and device for controlling residual stress of a powder plasma cladding layer on a valve face, which are used to suppress the residual tensile stress inside the powder plasma cladding layer on the valve face. The method and device are characterized by including a valve powder plasma cladding layer pressurizing device and a cladding residual stress control strategy. The cladding layer pressurizing device is composed of a valve stem clamping device, a turntable, a valve end face pressurizing device and a valve face pressurizing device. The load applied to the valve is controlled during and after welding. The cladding layer residual stress control strategy includes cleaning area control, cladding process and load application control after welding.

2. A method and device for controlling residual stress of a gas valve surface powder plasma cladding layer according to claim 1, characterized in that The valve powder plasma cladding layer pressurizing device, wherein the turntable is used to fix the bottom of the valve, the valve stem clamping device fixes the valve stem of the valve, the hydraulic system controls the valve stem clamping device to rotate with the turntable and can apply an adjustable load F1 perpendicular to the turntable plane to the valve; the valve end face pressurizing device adjusted by the hydraulic system adopts a four-petal movable structure, which can apply an adjustable load F2 in the radial direction of the valve disc; The valve face pressurizing device can apply a constant external load F3 in a vertical direction to the cladding layer.

3. A method and device for controlling residual stress of a gas valve surface powder plasma cladding layer according to claim 1, characterized in that The described surfacing residual stress control strategy includes three major steps: (1) cleaning the valve face to remove oil, rust and oxides; (2) during the surfacing process, F1 and F2 are dynamically adjusted as the number of surfacing layers changes. A lower pressure is applied during the first surfacing layer. As the number of surfacing layers increases, the pressure gradually increases to a peak value, and then the pressure remains unchanged until the surfacing is completed; (3) after the surfacing is completed, the preheated valve face pressurizing device is immediately pressed down to apply a constant external load F3 in the vertical direction to the surfacing layer, the load F2 of the valve end face pressurizing device remains unchanged, and the valve stem pressurizing device stops applying the load.

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