Oil wellhead device (tree) gate valve is the largest amount of oilfield dedicated gate valve in the gate valve manufacturing process, the valve body hydrostatic strength test and sealing performance test pass rate is too low (30% ~ 70%), and has long plagued the production plant. In this paper, the actual production of our plant, the crux of the above problems were analyzed and proposed solutions. 1, the improvement of rough casting process I plant gate valve sand mold cast steel blank, the valve body processing process, with the valve seat with the internal thread often appear porosity, shrinkage and other casting defects, by the macro cross-section of the valve body Analysis found that in the hot zone shown in Figure 1, there are different degrees of shrinkage phenomenon, in order to solve the above problems, we conducted several improvements to the casting test. Figure 1 1) Improve the riser system. Will be set in the valve body on both sides of the round face of the riser system to be shown in Figure 1 at the bottom of the valve body set up horizontal sprue system; 2) Sand casting mold for investment casting; 3) Top pouring method, and make the flange down. Because investment casting sand mold casting has better air permeability, faster, more uniform cooling conditions, so the organization more dense. As molten steel poured from the top, but also directly from the riser pouring, pouring riser location close to the hot section. For the casting has created a very favorable order of solidification conditions, the hot section of the timely replenishment, so after the process of improving the production of castings dense, eliminating shrinkage, shrinkage and other casting defects, the product pass rate of 99%. 2, improve the accuracy of machining and manufacturing measures The sealing effect is a key element of valve manufacturing. Sealing problem has always been the machining industry is difficult to solve the problem, in order to improve the valve manufacturing accuracy, to ensure the sealing effect of the valve, after theoretical research and production practices, summed up the following improvements. Valve body is the gate valve production in the most critical pieces of processing, due to structural requirements, the valve seat sealing surface and the center symmetry plane tilt 3o ~ 6o. For small valve body, we use horizontal lathe plus auxiliary bending plate tooling ( See Figure 2) to complete the seat tilting surface processing. But we must ensure that the bending angle (3o ~ 6o) and the body of the same process requirements. At the same time, it should be strictly to ensure high center of the machine tool and bending plate tool center coincide. Allow error control between 0.02mm ~ 0.04mm. In addition, the valve body to be considered in the processing of a compaction, positioning accuracy and reliability. As shown in Fig. 2, the heavy straight face on the main axis of the lathe should be regarded as the reference. The wedge groove and the wedge block on the vertical face of the curved plate should be used to check and press the flange face at one end of the valve body, Processing. In addition, the valve body in the process of processing, the need to turn on the lathe tooling on the rotary table 180o complete the body cavity at both ends of the processing. Slewing accuracy is guaranteed by the repeated positioning of two symmetrically distributed conical dowel holes distributed in the swivel flange. Indexing error of 0.01mm ~ 0.02mm. Figure 2 In addition, to choose the right balance with the curved plate. As we all know, the static balance of lathe curved plate tooling directly affects the lathe machining accuracy and production efficiency, so we have a lot of effort in the shape and layout of the weight of the curved plate, one is to minimize the radius of gyration of the counterweight, the second is In the layout of the inner structure of the outer circle to improve the circumferential direction of the dynamic balance performance, making the machine speed and the workpiece machining accuracy as much as possible. Finally, to ensure that the sealing process of the coordination of the various components: namely: the consistency of the valve body and the gate tilt; valve body and the body bending angle of the plate consistent; The consistency between the slope of the gate and the grinding slope. The four kinds of consistency are interrelated, mutual restraint and mutual dependence. Four kinds of consistency, we are based on the slope of the lathe curved plate, after repeated screening, grinding out of the standard slope plate, and then use the standard slope plate grinding lathe lathe with the slope tooling, good control Four consistency, increased productivity, assembly accuracy is guaranteed. In addition, should also effectively control the valve seat grinding process, to ensure that the valve seat surface flatness of not less than 100: 0.01, to ensure that the surface roughness of the surface from scratch, bump, abrasive sand unevenness of factors such as the impact of non- In order to achieve the best results after grinding, to ensure the accuracy of the seat. Through the above series of effective measures and quality control, I plant the production of wellhead valve pass rate of 98% or more.
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