All questions of Design of Machine Elements for Mechanical Engineering Exam

Function of Cage in Ball Bearing

The cage, also known as the ball bearing retainer or separator, is an essential component of a ball bearing. It is a device that separates and maintains a fixed distance between the balls, allowing them to roll smoothly and evenly within the bearing raceways. The function of the cage in a ball bearing is to:

1. Maintain the Balls at a Fixed Distance Apart:
The primary function of the cage in a ball bearing is to hold the balls at a fixed distance from each other. It ensures that the balls are evenly spaced and distributed around the bearing raceways. By keeping the balls in a specific arrangement, the cage prevents any contact or collision between them, which could lead to increased friction, wear, and damage.

2. Prevent Ball Slippage:
The cage also plays a crucial role in preventing the balls from slipping or sliding. It provides a confined space for the balls to roll within, guiding their movement and preventing them from tangling or getting displaced. This ensures that the balls maintain their intended positions and do not deviate from the proper load distribution, allowing for efficient and smooth operation of the bearing.

3. Reduce Friction:
While the primary function of the cage is not to reduce friction, it indirectly contributes to minimizing friction within the ball bearing. By maintaining a fixed distance between the balls, the cage helps to distribute the applied load evenly across the bearing raceways. This reduces excessive contact, friction, and wear between the balls and the raceways, resulting in smoother rotation and improved efficiency of the bearing.

4. Retain Lubricant:
The cage also helps to retain the lubricant within the bearing. It acts as a barrier, preventing the lubricant from flowing out of the bearing and ensuring that it remains in contact with the rolling elements. The lubricant plays a critical role in reducing friction, dissipating heat, and preventing corrosion within the bearing. By retaining the lubricant, the cage helps to maintain the optimal operating conditions and prolong the lifespan of the ball bearing.

In summary, the cage in a ball bearing functions to maintain the balls at a fixed distance apart, prevent ball slippage, reduce friction, and retain the lubricant. It plays a vital role in ensuring the smooth operation, longevity, and efficiency of the bearing.

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Positive Clutch: Dog clutch

A positive clutch is a type of clutch that transmits power from the engine to the transmission without any slippage. In other words, the clutch is fully engaged and the power is transmitted without any loss. The following are the types of positive clutches:

Centrifugal Clutch:
The centrifugal clutch is a type of positive clutch that uses centrifugal force to engage the clutch. It is commonly used in small engines such as go-karts, lawn mowers, and chainsaws.

Single Plate Clutch:
The single plate clutch is a type of positive clutch that has only one friction plate. It is commonly used in cars and trucks.

Cone Clutch:
The cone clutch is a type of positive clutch that uses conical friction surfaces to engage the clutch. It is commonly used in industrial machinery.

Dog Clutch:
The dog clutch is a type of positive clutch that uses two or more pairs of teeth to engage the clutch. It is commonly used in manual transmissions and racing cars. The teeth on the clutch engage with corresponding slots in the transmission gears, providing a positive and instantaneous engagement.

In summary, the dog clutch is the only positive clutch among the given options. It provides instantaneous and positive engagement, making it suitable for high-performance applications.

Frictional torque in a disc or plate clutch compared to a flat collar bearing

Introduction:
A clutch is a mechanical device used to transmit torque from one shaft to another shaft, typically in an automotive system. One type of clutch is the disc or plate clutch, which consists of a set of friction plates that are pressed together to transmit torque. On the other hand, a flat collar bearing is a type of bearing that supports a rotating shaft with a flat collar. Both the disc or plate clutch and the flat collar bearing rely on friction to transmit torque. In this context, let's compare the frictional torque transmitted by a disc or plate clutch to that of a flat collar bearing.

Frictional torque in a disc or plate clutch:
- A disc or plate clutch consists of a set of friction plates, typically made of a high-friction material such as organic or metallic material.
- When the clutch is engaged, the friction plates are pressed together, creating frictional contact.
- The frictional torque in a disc or plate clutch is generated by the frictional forces between the contacting surfaces of the plates.
- The frictional torque is proportional to the normal force between the plates and the coefficient of friction between the contacting surfaces.
- The frictional torque can be calculated using the equation: T = μ * R * F, where T is the torque, μ is the coefficient of friction, R is the effective radius of the contact surface, and F is the normal force.

Frictional torque in a flat collar bearing:
- A flat collar bearing consists of a flat collar that supports a rotating shaft.
- The frictional torque in a flat collar bearing is also generated by the frictional forces between the contacting surfaces of the collar and the shaft.
- The frictional torque is proportional to the normal force between the collar and the shaft and the coefficient of friction between the contacting surfaces.
- The frictional torque can be calculated using the equation: T = μ * R * F, where T is the torque, μ is the coefficient of friction, R is the effective radius of the contact surface, and F is the normal force.

Comparison:
- From the above explanations, it is clear that the frictional torque in both a disc or plate clutch and a flat collar bearing can be calculated using the same equation: T = μ * R * F.
- The factors affecting the frictional torque, such as the coefficient of friction, effective radius, and normal force, are similar for both the clutch and the bearing.
- Therefore, the frictional torque transmitted by a disc or plate clutch is the same as that of a flat collar bearing.

Conclusion:
The frictional torque transmitted by a disc or plate clutch is the same as that of a flat collar bearing. Both the clutch and the bearing rely on friction to transmit torque, and the factors affecting the frictional torque are similar for both.

Trapezoidal thread

A trapezoidal thread is a type of thread commonly used in mechanical engineering applications. It is characterized by its trapezoidal shape, with both the thread flanks and the top being inclined at a certain angle.

Characteristics of Trapezoidal Threads

- Trapezoidal threads have a relatively large thread angle, typically 30 degrees. This angle allows for a larger contact area between the mating threads, resulting in increased load-carrying capacity and improved resistance to wear.

- The flanks of trapezoidal threads are inclined at the thread angle, which provides self-locking characteristics. This means that the thread can resist axial forces and prevent unintended loosening or tightening of the threaded components.

- Trapezoidal threads have a flat top, which allows for efficient transfer of torque between the threaded components. This makes them suitable for applications that require high torque transmission, such as power transmission systems.

Comparison with Other Thread Types

- Acme threads: Acme threads are similar to trapezoidal threads in terms of their trapezoidal shape and self-locking characteristics. However, the thread angle of Acme threads is typically 29 degrees instead of 30 degrees for trapezoidal threads. Both thread types are commonly used in power transmission and linear motion systems.

- Square threads: Square threads have a square-shaped profile, with both the flanks and the top being perpendicular to the thread axis. Unlike trapezoidal threads, square threads do not have self-locking characteristics. They are commonly used in applications that require high efficiency in power transmission, such as lead screws.

- Buttress threads: Buttress threads have an asymmetrical shape, with one flank being inclined at a large angle and the other flank being perpendicular to the thread axis. They are primarily used in applications that require high load-carrying capacity in one direction, such as jack screws and vise mechanisms.

Conclusion

In conclusion, trapezoidal threads are a type of thread commonly used in mechanical engineering applications. They are characterized by their trapezoidal shape, self-locking characteristics, and efficient torque transmission. While other thread types such as Acme, square, and buttress threads also have their own advantages and applications, the correct answer to the given question is that trapezoidal threads are specifically associated with the trapezoidal shape.