Question 64 QMED04 - Boiler Technician-Watertender

The Correct Answer is B **Explanation of Correctness (Option B):** Option B describes a **ring-oiled, babbitt-faced, spherical seat, shell** bearing, which is highly characteristic of a traditional line shaft bearing assembly. 1. **Ring-oiled:** This mechanism uses a metal ring that rides on the shaft and dips into an oil reservoir, continuously lifting oil onto the shaft surface. This provides adequate lubrication for the relatively low-to-moderate speeds and continuous operation typical of line shafts. 2. **Babbitt-faced:** Babbitt metal (a soft alloy) is commonly used as a bearing surface in sleeve bearings because it conforms well, has good anti-friction properties, and can tolerate minor debris without catastrophic failure, making it ideal for the demanding environment of older factories and mills. 3. **Spherical Seat (Self-Aligning):** Line shafts often span long distances, meaning perfect alignment of all bearing supports is difficult to maintain. A spherical seat allows the bearing shell to swivel slightly within its housing, ensuring the bearing surface aligns itself perfectly with the rotating shaft axis. This self-aligning capability is crucial for long, interconnected line shafting systems. 4. **Shell:** This refers to the insert (the bearing itself), often split for ease of installation onto a continuous shaft. **Explanation of Incorrect Options:** **A) Segmental, pivoted-shoe thrust:** This describes a **Kingsbury** or similar tilting-pad bearing specifically designed to handle extremely high **axial (thrust) loads** (e.g., in steam turbines or ship propeller shafts). Line shaft bearings primarily handle **radial loads** (weight and belt tension), making this thrust-specific design inappropriate. **C) Tapered roller, split type radial:** While tapered roller bearings are excellent for handling combined radial and thrust loads, and split types exist for ease of installation, they represent a more modern, high-precision, and generally more expensive solution than the traditional sleeve bearings. More importantly, the required precision and careful mounting of roller bearings often negate the critical **self-aligning** feature inherent in line shaft design, making them less suitable than the self-aligning sleeve bearing (Option B) for the original purpose. **D) Rigidly mounted, radial sleeve:** While line shaft bearings are radial sleeve types, the term "**Rigidly mounted**" is the key flaw. Line shafting systems require **self-alignment** due to manufacturing tolerances and flexing over long spans. A rigidly mounted bearing would quickly experience edge loading and failure if the shaft deflected or the mounting settled, which is why the spherical (self-aligning) seat described in Option B is essential.