Question 32

The Correct Answer is B. Precision manufactured roller bearings are designed to minimize friction and handle various operating conditions effectively. **Why option B ("They are well adapted to variable speed operation.") is correct:** Precision roller bearings are inherently suited for a wide range of operating speeds, including variable speed environments, due to several key characteristics: 1. **Low Starting and Running Friction:** Precision manufacturing ensures smooth, geometrically accurate surfaces and tightly controlled internal clearances. This results in very low friction (especially compared to plain/sleeve bearings), meaning they generate minimal heat across a range of speeds. 2. **Standardized Lubrication:** While proper lubrication is crucial, modern roller bearings are designed to operate effectively with standard lubricants (grease or oil) across a wide range of speeds and loads, provided the correct viscosity is selected. 3. **High Rotational Accuracy:** The precise manufacturing processes ensure minimal vibration and runout, which are essential for stable operation whether the speed is low, moderate, or high. **Why the other options are incorrect:** * **A) They have a relatively high power loss due to friction.** This is incorrect. One of the primary advantages of precision roller bearings (antifriction bearings) is their **low** friction and, consequently, very low power loss compared to plain (sleeve) bearings, especially during starting and running. * **C) Their lubrication is complicated and requires constant attention.** This is incorrect. While lubrication is essential, precision roller bearings are often sealed or shielded and packed with grease for life, or utilize simple, standardized circulating oil systems. Modern designs aim to make lubrication predictable and low-maintenance, not complicated or requiring constant attention. * **D) They are not capable of maintaining alignment over long periods of time.** This is incorrect. Precision roller bearings are specifically designed to maintain rigid and precise shaft alignment and positional stability under load for extended operational periods, provided the mounting is correct and the bearing is properly rated for the application.