Seal Seat Research Articles

Failure and Damage of Reciprocating Lip Seals for Pneumatic Cylinders in Dry Conditions

Lip seals are components subjected to high mechanical stress and they are responsible for many out-of-service in pneumatic cylinders. The aim of this work is the development of an experimental methodology to evaluate lifetime duration and analyse failures and damages of rod lip seals for pneumatic cylinders. A dedicated test bench was designed and manufactured which reproduces actual working conditions of the seals i.e., compressed air action (seal pressurisation) and relative linear reciprocating motion. Three types of seals made of two elastomers (NBR and polyurethane) were tested; dry condition was considered to speed up the tests. The influence of geometric parameters like seal seat dimension and seal axis misalignment with respect to the rod axis, was analysed by multiple experimental tests. Results in terms of seal life duration and failure modes are presented which allow comparison of seals performance and provide a helpful tool to end-users in a proper selection of seals geometry, material and key working parameters.

Steady-State Response of a Flexibly Mounted Stator Mechanical Face Seal Subject to Dynamic Forcing of a Flexible Rotor

Mechanical face seals are constitutive components of much larger turbomachines and require consideration of the system dynamics for successful design. The dynamic interplay between the seal and rotor is intensified by recent trends toward reduced clearances, higher speeds, and more flexible rotors. Here, the “rotor” consists of the flexible shaft and the rotating seal seat. The objective here is to, for the first time, determine how the rotor affects the seal performance and vice versa. Thresholds can then be established beyond which the rotor influences the seal but not vice versa (i.e., the rotordynamics can be sent to the seal analysis as an exogenous input). To this end, a model of a flexibly mounted stator face seal is provided including the coupled dynamics of the flexible rotor. The model accounts for axial and angular deflections of the rotor and seal. Coupled rotordynamics are modeled using a lumped-parameter approach including static and dynamic rotor angular misalignments. For expediency, linearized expressions for fluid forces are used, and the resulting steady-state equations of motion are solved analytically to investigate how rotor inertia, speed, and angular misalignment influence the coupled seal dynamics. Importantly, results from the study reveal that in some operating regimes, neglecting the rotordynamics implies healthy seal operation when instead intermittent rub exists between the faces. This work also shows that when the rotor inertia is much larger than the seal inertia, the rotordynamics can be solved separately and used in the seal model as an external input.

Fatigue Failures of the 353130B Type Roller Bearings on China Railway Freight Cars

Causes are analyzed to the three shelling failures of railway 353130B type of roller bearings on China 70t grade of freight cars with K5 type of tilting bogie. These bearings are all failed in service lives less than two years, which is quit less than the overhaul inspection interval of 800, 000 km mileage of vehicles and the design life of 2, 000, 000 km mileage. The failures are all originated from the position at the outer ring inboard side nearly to the seal seat. Metallurgical observations reveal that the material chemical composition and microstructures are all in the reasonable range except for the hardness values. This implies that the manufacturing techniques may not match the requirements to lead to the reduction of fatigue strength. Elastic-plastic finite element (EPFE) analysis reveals that the position at the outer ring inboard side nearly to the seal seat is subjected to the maximum equivalent stress amplitude, which well match the situations of failures. In addition, a comparison is made to the bearing on the same axle weight freight cars But K6 type of bogie. Results reveal the maximum stress amplitude for K5 type of bogie is larger than that for K6 type of bogie. This means the bearings failures are relative to the local structures. Therefore, both the manufacturing techniques and the bogie structures should be advanced to improve the bearing service lives.

Finite Element Analysis on the Fatigue Stresses of a Railway Vehicle Roller Bearing

The distributed fatigue stresses of 353130B roller bearing of China freight car with K5 type titling bogie are investigated using an elastic-plastic finite element (FE) analysis. Policy of two steps is applied. First, an integral FE analysis is performed on adapter-bearing-axle-wheel-track interactive system. Second, local analysis is applied to the local axle-bearing-adapter part, in which on the section of axle is with the bound condition obtained from the integral analysis. Wheel contact force spectrum on a curved railway line by on-line inspection is used for the present study. Previous proposed multivariate quadratic regression approach is applied for transferring the load spectrum to the dynamic stress spectrum at a special position of the bearing. Results reveal that the rollers, innerand outer-rings of bearing are subjected to distribute axially equivalent stress amplitude. The closer to axle side, the larger the equivalent stress amplitude. The equivalent stress amplitude of outer ring at the position close to the seal seat is relative larger to that of inner ring. The results are consistency with the shell failures of the bearings in production. Availability of present study is indicated.

Leakage Flow Characteristics of Highly Effective Graphite Seal Mechanism for HTGR Core Support Blocks

The prevention of leakage flows of coolant gas is important for a thermal hydraulic design of HTGR core which consists of prismatic graphite blocks. In particular, a seal mechanism for the core support blocks is necessary because gaps between core support blocks induce leakage flows in the core. Here, a seal mechanism, which consists of graphite seal element with triangular cross section and V-shaped seal seat, has been proposed. Air flow experiments were conducted to study the leakage flow characteristics of this seal mechanism. It is shown that the present seal mechanism is highly effective in preventing leakage flows as compared with the plate-type seal mechanism. It is also found that most of the leakage flow occurs at the seal element end-gaps and the pressure loss coefficient factor of this seal mechanism can be predicted with the use of the effective flow area of the end-gaps.

Leakage flow characteristics of highly effective graphite seal mechanism for HTGR core support blocks.

The prevention of leakage flows of coolant gas is important for a thermal hydraulic design of HTGR core which consists of prismatic graphite blocks. In particular, a seal mechanism for the core support blocks is necessary because gaps between core support blocks induce leakage flows in the core. Here, a seal mechanism, which consists of graphite seal element with triangular cross section and V-shaped seal seat, has been proposed. Air flow experiments were conducted to study the leakage flow characteristics of this seal mechanism. It is shown that the present seal mechanism is highly effective in preventing leakage flows as compared with the plate-type seal mechanism. It is also found that most of the leakage flow occurs at the seal element end-gaps and the pressure loss coefficient factor of this seal mechanism can be predicted with the use of the effective flow area of the end-gaps.