Research On Tangential Split Cylinder Of Ultrahigh Pressure Die

Ultrahigh pressure equivalent is playing an increasingly important role and widely used in industrial production and scientific research, with the rapid development of the modern technology. As a core component of the ultrahigh pressure equivalent, ultrahigh pressure die has always been two aspects of development demands. One is trying to obtain a higher pressure, another one is trying to provide a larger cavity volume. Large-scale mold is the inevitable requirement of modern ultrahigh pressure equivalent development, because it not only can increase the production of synthetic products, and more important is that it can improve product quality. However, under the current technology, the problems of large-scale mold are that large size cemented carbide parts have high cost, processing and manufacturing are difficult, the quality cannot be guaranteed, and the ultimate bearing capacity of the die has also reduced.Therefore, we studied the ultrahigh pressure die with split cylinder. This structure not only can reduce the stress of the cylinder structure, but also can reduce the size of the parts significantly. On the premise of insure the bearing capacity of the die, enlarge the cavity volume and make the structure is easy to large-scale application. Split cylinder has two kinds of split type: radical split and tangential split. Tangential split cylinder has an obvious advantage in terms of ultimate bearing capacity. In this thesis, we conducted a series of research and design optimization for the tangential split ultrahigh pressure die by numerical simulation. It provides a theoretical basis and scientific reference for the design, manufacture and practical application of the split type ultrahigh pressure die.The main contents and conclusions are summarized as follows:1. Discussion on the design principle of the ultrahigh pressure die with split type cylinderSplit the cemented carbide cylinder of the ultrahigh pressure die, can eliminate the excessive circumferential tensile stress, and reduce the size of the cylinder part. There are two forms: dividing plane of the radial split is alone the radial direction of the cylinder. The tangential split is a novel split type, its dividing plane is perpendicular to the radial direction of the cylinder, and along the tangential direction of the inner cavity. We made the related theoretical analysis of the split die, deduced relevant calculation parameters and design principles, and provided a theoretical basis for the preliminary design of the die.2. Finite element modeling of the ultrahigh pressure dieFinite element model of the ultrahigh pressure die was established based on the numerical simulation software. We simulated the belt type ultrahigh pressure die, compared the stress distribution of the die on the prestress status and working status, and analyzed the stress distribution characteristics of the cylinder and the supporting rings. The result shows that circumferential tensile stress on the inner wall of the cylinder is the main reason leading to the die fracture.3. The finite element analysis and comparison of split type die and belt type dieThe stress condition of the belt type cylinder, the radial split cylinder and the tangential split cylinder was analyzed and compared. The results show that the stress values of the three structure are sequentially reduced under the same load. The radial split structure can decrease the circumferential tensile stress dramatically. The tangential split structure can completely eliminate the circumferential tensile stress and generate circumferential compressive stress. Mutual extrusion and friction effect are exist between the adjacent tangential divided bodies, and this interaction can coordinate and uniform the stress distribution of the cylinder. It can take full use of the material performance and improve the bearing capacity of the cylinder. In addition, the tangential split cylinder is the condition of three compressive stress, which is very favorable for cemented carbide material. Extreme pressure test results show that the cavity nominal pressure of the three structures is 5.75 GPa, 7.27 GPa and 8.39 GPa, respectively, when the die is crack.4. The influence of the divided blocks number to the split type dieThe results of numerical simulation show that the stress of the radial split cylinder does not change significantly with the increase in the number of the radial split blocks. For the tangential split structure, with the increase in the number of the tangential split blocks, the stress of the cylinder decreases accordingly, the distribution of the stress tends to uniform, and the ultimate bearing capacity increases. Discuss the selecting principle of the split number from several aspects. It can be summarized that the divided blocks should use less number when the size of the cylinder is small, and the divided blocks should use more number when the size of the cylinder is large. In addition, when the outer contour of the divided body is closer to the regular shape, the stress is more reasonable, the distribution is more uniform, and the capacity of load bearing, shock resistance and preventing brittle fracture is stronger.5. Structural optimization of the tangential split cylinderThe critical geometric parameters of the tangential split cylinder are optimized designing. The influence of internal height to diameter ratio, outer diameter to inside diameter ratio, total height to internal height ratio and half cone angle to the structure stress are analyzed and compared. And the best optimal values of these parameters are obtained under a certain conditions. We discussed the influence of the friction coefficient to the working cylinder. The results show that the interaction between the adjacent tangential divided bodies has a reasonable range, and it will adversely affect the stress of the cylinder when the effect is too small or too large.6. The design of ultrahigh pressure die with a large cavity using split type structureTry to design ultrahigh pressure die with a large cavity volume in the condition that the die can bear a higher ultimate pressure, based on the development trend of large-scale ultrahigh pressure equipment. The split structure is employed to decrease the size of the cemented carbide part, reduce the manufacturing difficulty and cost, improve the quality of the material, and uniform the stress of the cylinder structure. The diameter of the sample cavity is ?80mm. The cemented carbide cylinder is divided into two layers. The inner layer is tangential split structure and the outer layer is radial split structure. This method not only can significantly reduce the size of the single cemented carbide part, but also can improve the ultimate bearing capacity of the die. Therefore, the large size cylinder can withstand the working load above 7GPa. For the prestressed protection out of the split cylinder, we can use the multilayer composite supporting rings or steel wire spiral wound for preloading. The spiral wound preloaded method is more reasonable. It could decrease the general dimension of the die dramatically, and reduce the processing and assembly difficulty.