Design of packing cup interference fit value of hypercompressors for low density polyethylene production
Da LEI1(), Xuehong LI1, Yun LI1, Xiwen REN2
1. School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an 710049, China 2. Shenyang Yuanda Compressor Co., Ltd., Shenyang 110027, China
The hypercompressor is one of the core facilities in low density polyethylene production, with a discharge pressure of approximately 300 MPa. A packing cup is the basic unit of cylinder packing, assembled by the interference fit between an inner cup and an outer cup. Because the shrink-fitting prestresses the packing cup, serious design is needed to gain a favorable stress state, for example, a tri-axial compressive stress state. The traditional method of designing the interference fit value for packing cups depends on the shrink-fit theory for thick-walled cylinder subject to internal and external pressure. According to the traditional method, critical points are at the inner radii of the inner and external cup. In this study, the finite element method (FEM) has been implemented to determine a more accurate stress level of packing cups. Different critical points have been found at the edge of lapped sealing surfaces between two adjacent packing cups. The maximum Von Mises equivalent stress in a packing cup increases after a decline with the rise of the interference fit value. The maximum equivalent stress initially occurs at the bore of the inner cup, then at the edge of lapped mating surfaces, and finally at the bore of the outer cup, as the interference radius increases. The traditional method neglects the influence of axial preloading on the interference mating pressure. As a result, it predicts a lower equivalent stress at the bore of the external cup. A higher interference fit value accepted by the traditional method may not be feasible as it might already make packing cups yield at the edge of mating surfaces or the bore of the external cup. Along with fatigue analysis, the feasible range of interference fit value has been modified by utilizing FEM. The modified range tends to be narrower and safer than the one derived from the traditional method, after getting rid of shrink-fit values that could result in yielding in a real packing cup.
雷达, 李雪红, 李云, 任希文. 用于生产低密度聚乙烯的超高压压缩机填料盘的过盈量设计[J]. Frontiers in Energy, 2019, 13(1): 107-113.
Da LEI, Xuehong LI, Yun LI, Xiwen REN. Design of packing cup interference fit value of hypercompressors for low density polyethylene production. Front. Energy, 2019, 13(1): 107-113.
Throughout the inner cup and at the bore of the outer cup
Equivalent alternating stress
Lapped sealing surfaces, lube oil hole, sealing ring groove.
Lapped sealing surface, lube oil hole, sealing ring groove
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