Question 54 QMED03 - Oiler

The Correct Answer is D ### Why Option D is Correct Line shaft bearings support long shafts (line shafts) used to transmit power, often in older factory settings or power transmission systems. These bearings typically need to accommodate slight misalignment, operate reliably at moderate speeds, and be relatively easy to maintain. **Option D: Ring-oiled, babbitt-faced, spherical seat, shell** * **Babbitt-faced (or Babbitt metal):** This is a classic soft-metal alloy widely used for plain bearings (sleeve bearings) in applications like line shafts due to its excellent conformability and tolerance for minor foreign particles. * **Spherical seat (or self-aligning):** This is the critical feature. Line shafts are long and prone to sagging or thermal expansion, leading to minor misalignment between adjacent bearing supports. The spherical seat allows the bearing shell to swivel slightly within its housing, ensuring the bearing surface remains parallel to the shaft, preventing edge loading and premature failure. This self-aligning capability is essential for line shaft service. * **Ring-oiled:** This refers to a simple, reliable lubrication method common for industrial plain bearings, where a ring dips into an oil reservoir and rotates with the shaft, continuously delivering oil to the bearing surface. * **Shell:** Refers to the replaceable liner (often split) that holds the babbitt material. These characteristics perfectly describe the traditional and highly effective bearing type used specifically for supporting line shafts. *** ### Why Other Options Are Incorrect **A) Tapered roller, split type radial** * **Tapered roller bearings** are designed to handle high radial *and* high thrust loads. While they are excellent rolling-element bearings, they are typically overkill for simple radial support in a line shaft application, which experiences relatively light loads. They also tend to be less tolerant of significant misalignment compared to spherical sleeve bearings unless housed in a specialized self-aligning unit. **B) Segmental, pivoted-shoe thrust** * This describes a **Kingsbury** or **Michell** type bearing (often called tilting-pad thrust bearings). Their sole purpose is to handle extremely heavy *axial* (thrust) loads, typically found in large turbines, marine propellers, or vertical pumps. They provide virtually no radial support and are completely unsuitable for supporting the weight and radial loads of a horizontal line shaft. **C) Rigidly mounted, radial sleeve** * **Radial sleeve bearings** are indeed plain bearings suitable for radial loads, but the key issue here is **"Rigidly mounted."** A rigid mount means the bearing housing is fixed and cannot adjust its angle relative to the shaft. As noted, line shafts inherently require self-aligning capability (spherical seats) to compensate for shaft deflection and misalignment. A rigid bearing would experience severe edge loading and fail quickly in this application.