In this paper, an analytical procedure is developed for evaluating the filament loading, constrained elastic deformation, and overall stiffness of a circular brush, Filament deformation is computed on the basis of a large displacement mechanics analysis in conjunction with kinematic constraints for a flat, rigid workpart with smooth surface finish. Numerical results are reported which examine the relationship between workpart penetration, brush stiffness, and force distribution characteristics of the workpart contact zone.

Brush seals have proven to be an attractive alternative to labyrinth seals for turbomachinery applications. This innovation in seal technology utilizes both the high temperature capability of special-alloy wire and the flexural adaptability of fibers to accommodate a wide range of operating conditions that are encountered during service. The effectiveness of the seal is principally derived from the bristles ability to endure forces imparted by both the fluid and shaft, and yet maintain contact between the filament tips and the surface of the rotor. Consequently, contact forces generated along the interface of the fiber tip and rotor are an important consideration for both the design and performance of the rotor-seal assembly. This paper focuses on evaluating brush seal forces that arise along the surface of the rotor due to the dimensional disparity or interference between the rotor-fiber. Filament tip contact forces are computed on the basis of an in-plane, large deformation mechanics analysis of a cantilever beam, and validation of the model is assessed by using an electronic balance for measuring the shear and normal force exerted by a bristle tip onto a flat, hardened surface. Formulation of the mechanics problem is briefly reviewed, and includes the effect of Coulombic friction at the interface of the fiber tip and rotor. Filament contact force is used as a basis for computing bearing stress along the fiber-rotor interface. Results are reported for a range of brush seal design parameters in order to provide a better understanding of the role that seal geometry, friction, and bristle flexural rigidity play in generating rotor contact force.

In this paper, a mechanics formulation is outlined and used for evaluating the steady-state, large deflection of a slender member subjected to displacement-dependent centrifugal load. The problem is examined within the context of rotating filamentary cup brushes that are used in surface finishing operations. Several parameters which are closely related to the machining performance and service life of cup brushes are identified and reported, including filament tip spatial distribution and orientation, filament stress, and the steady-state configuration of the working surface of the cup brush during free rotation. Numerical results indicate that filament inertia forces can lead to significant fiber displacement and stress and thus, must be included as an integral part of the design of rotary cup brushes.

This paper addresses the contact problem associated with the filament/workpart interaction that arises during brushing processes. A discretized model of a filament within the brushing tool is developed by employing Lagrange’s equations in conjunction with special constraint equations that are appropriate for the impact and impending large displacement of a flexible fiber whose tip traverses a flat, rigid surface. This formulation leads to the identification of five nondimensional parameters which fully characterize the filament/workpart contact problem. A damping mechanism is also included which can be used for modeling complex filament interactions that arise during the actual brushing operation. Special consideration is given to examining the initial filament/workpart impact and the subsequent forces that are generated along the contact region. Initial velocity of the filament is determined by employing an inelastic impact mechanics analysis. Time-varying transient response of the filament is then obtained by employing a predictor-corrector technique in conjunction with a finite difference method. Overall brush force is computed by a superposition of filament contact forces exerted onto the workpart surface. Numerical results are reported and compared with experimentally obtained data for an actual brush/workpart system.

In this paper the role which workpart geometry plays in the stiffness properties and contact zone characteristics of circular filamentary brushes is investigated. The problem is examined by employing a recently developed mechanics-based procedure for evaluating large filament deformation, in conjunction with appropriate kinematic constraints for filament tip contact with a smooth, rigid workpart of prescribed constant curvature. Numerical examples for a circular filamentary brush system are presented and discussed for the purpose of illustrating the basic nature of brush stiffness response characteristics for a range of prescribed constant-curvature workpart surfaces.