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Cojinetes de revista
Los cojinetes de revista son componentes mecánicos que respaldan y proporcionan estabilidad lateral a los ejes y ejes rotativos. Son cruciales para re…
Los cojinetes de deslizamiento se utilizan para proporcionar estabilidad lateral a los ejes y ejes giratorios.
Considere un cabrestante de cable con cojinetes de deslizamiento secos o parcialmente lubricados.
La rotación del carrete en el sentido de las agujas del reloj hace que el eje suba por la superficie interior del rodamiento hasta que se desliza y se somete a una rotación estable.
Se dibuja un diagrama de cuerpo libre del eje. Las fuerzas que actúan sobre el sistema incluyen el peso del eje, el par en el sentido de las agujas del reloj y la fuerza de reacción del rodamiento.
La fuerza de reacción no colineal es igual y opuesta al peso y actúa en un ángulo relativo a la superficie normal. Este ángulo se denomina ángulo de fricción cinética.
La línea de acción de la fuerza de reacción es siempre tangente al círculo de fricción.
La condición de equilibrio de momento alrededor del punto O produce el momento del eje.
Para un ángulo de fricción cinético pequeño, el término sinusoidal se puede aproximar a la tangente del ángulo de fricción cinético.
Como la tangente del ángulo de fricción cinética es igual al coeficiente de fricción cinética, se obtiene el momento necesario para superar la resistencia de fricción del rodamiento.
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Q1: What is the primary function of journal bearings in rotating machinery?
Journal bearings support and provide lateral stability to rotating shafts and axles while reducing friction, wear, and vibration. They work by forming a thin lubricant film between the bearing surface and the rotating shaft, which minimizes direct contact and reduces frictional forces in machinery such as engines, turbines, and pumps.
Q2: How does a shaft behave when it rotates inside a journal bearing?
As the shaft rotates clockwise, it initially rolls up the inner surface of the bearing until it slips and undergoes stable rotation. During this process, the shaft experiences forces including its weight acting downward, the applied clockwise couple representing torque, and the bearing's reaction force, which acts at an angle relative to the surface normal.
Q3: What is the angle of kinetic friction in journal bearing analysis?
The angle of kinetic friction is the angle at which the bearing's non-collinear reaction force acts relative to the surface normal. The line of action of this reaction force is always tangent to the circle of friction, which represents the locus of all possible contact points between the shaft and bearing surface.
Q4: How is the moment required to overcome bearing friction calculated?
By applying moment equilibrium about the shaft center, the required moment can be determined. For small kinetic friction angles, the sine term approximates to the tangent of the kinetic friction angle. Since the tangent of the kinetic friction angle equals the coefficient of kinetic friction, this relationship yields the moment needed to overcome the bearing's frictional resistance.
Q5: What forces are included in a free-body diagram of a journal bearing system?
A free-body diagram of a shaft in a journal bearing includes three main forces: the shaft's weight acting vertically downward, the clockwise couple representing applied torque, and the bearing's reaction force. The reaction force is equal and opposite to the weight and acts at the angle of kinetic friction relative to the surface normal.
Q6: Why is the circle of friction important in journal bearing design?
The circle of friction represents the locus of all possible contact points between the shaft and bearing surface. The reaction force's line of action is always tangent to this circle, making it essential for determining how forces distribute during rotation and for calculating the moment required to maintain stable shaft rotation.
Q7: How does lubrication affect the performance of journal bearings?
Lubrication creates a thin film between the bearing surface and rotating shaft, minimizing direct contact and significantly reducing frictional forces. This film reduces wear and vibration in the system, improving overall machinery efficiency and performance while lowering the moment required to overcome bearing friction.