Strength analysis and optimization for both the cylinder and the anvil of a BELT-type ultra-high-pressure apparatus by FEM

Abstract

BELT-type ultra-high-pressure apparatus has been used widely to synthesize diamond and CBN. Because of the critical service conditions in the chamber (6 GPa pressure and 1500°C temperature), cracks are very likely to appear in both the cylinder and the anvil of the BELT, resulting in a short working life. FEM-analysis models of both the cylinder and the anvil are presented, which have been verified by comparison of the press tonnage between practice and models. In accordance with the FEM-analysis results, the maximum principal stress within the cylinder is either the maximum axial stress near to the outer surface or the maximum tangential stress near to the inner surface, depending on the magnitude of the pre-stress acting on the outer cylindrical surface by shrink rings. It is the maximum principal stress which causes the brittle failure of the cylinder. The function of the shrink rings is of double character: the positive side is that they can decrease greatly the maximum tangential stress, whilst the negative side is that they can increase slightly the maximum axial stress. The influence of the shrink rings on the anvil is limited. It is the ultra-high compressive stress which causes the failure of the anvil. The influence of thermal stress on both the cylinder and the anvil is limited. An optimization method is presented also, by means of which the maximum axial stress within the cylinder can be decreased by about 46%, therefore enabling the working life of the BELT to be extended greatly.