MnM U5 Questions And Verified And Correct Answers.

Static Balance: - correct answer when its mass centerline coincides with its geometric centerline or axis of rotation. If it doesn't, the gravitational forces will produce a moment that tends to rotate the rotor when it's at rest, causing an imbalance. imbalance is a car tire. To correct static imbalance: - correct answer weights are typically added or material is removed from the rotor in such a way that the center of gravity is brought back to the rotor's axis of rotation. Not addressing static imbalance can result in - correct answer vibrations, reduced bearing life, increased energy consumption, and potential equipment damage when the machinery operates. Limitations of Static Balance - correct answer a rotor can be in static balance but still be in dynamic imbalance due to the distribution of its mass in different planes. That's why, especially for high-speed machinery, dynamic balancing is also crucial. Dynamic Imbalance: 1.Description: - correct answer In a dynamically imbalanced rotor, the mass centroids of two or more planes do not align with the rotor's rotational axis. This misalignment results in forces that create vibrations when the rotor spins. Dynamic Imbalance: 2.Effects: - correct answer 1. Excessive vibration 2. Bearing wear and premature failure 3. Structural damage to the equipment and its surroundings 4. Reduced operational efficiency5. Noise issues Dynamic Imbalance: Examples: - correct answer Consider a long shaft with discs at either end. If one disc is statically balanced but the other disc is out of balance, the entire assembly might appear balanced when inspected statically (since the center of gravity lies on the axis). However, when the assembly rotates, it will cause vibrations due to the dynamic imbalance. A propeller or fan blade that's heavier on one end and lighter on the other can introduce dynamic imbalance. Balancing of Rotating Masses: - correct answer Balancing is the process of designing (or) modifying the machinery so that imbalance is reduced to an acceptable level and eliminated completely. The following are the cases of balancing: - correct answer 1. Balancing of a single rotating mass by a single mass rotating in the same plane. 2. Balancing of a single rotating mass by two masses rotating in different planes. 3. Balancing of different masses rotating in the same plane. 4. Balancing of different masses rotating in different planes. Introduction of a Single Balancing Mass - correct answer When a machine rotates, if there is an uneven distribution of mass, it will cause a centrifugal force due to that uneven mass (often termed "disturbing mass" or "unbalanced mass"). This force can lead to vibrations, noise, and wear in the machinery.To counteract this, one might think of adding an opposite mass Condition for Static Balancing: - correct answer The net dynamic force acting on the shaft is equal to zero. This requires that the line of action of three centrifugal forces must be the same. In other words, the centre of the masses of the system must lie on the axis of rotation. Condition for Dynamic Balancing: - correct answer The net couple, due to the dynamic forces acting on the shaft, is equal to zero. In other words, the algebraic sum of the moments about any point in the plane must be zero. Balancing of single-cylinder engine: Primary Imbalance: - correct answer Caused by the piston moving up and down. As the piston moves upward, it creates an upward force, and as it moves downwards, it creates a downward force. In a single-cylinder engine, these forces are not counteracted by another piston moving in the opposite direction (as it would in multi-cylinder engines). Balancing of single-cylinder engine: Secondary Imbalance: - correct answer This results from the piston moving faster in the middle half of its stroke than it does at the top and bottom. Secondary imbalances are usually twice the frequency of primary imbalances. Balancing techniques: 1.Counterweights: - correct answer The most common method of addressing primary imbalance is by adding counterweights to the crankshaft. These weights help counteract the up-and-down movement of the piston. 2.Balance Shafts: - correct answer Some single-cylinder engines utilise a balance shaft. This shaft is equipped with specially placed weights, rotating at the same or double the speed of the crankshaft to counteract the primary and/or secondary imbalances. Bobweights: - correct answer weights are attached to the crankshaft at the rod journals. These weights mimic the weight of the rod and piston assembly. The crankshaft is then spun, and any imbalance is measured. Material is then removed or added (in the form of heavy metal) to correct any imbalances. Torsional Vibration Dampers: - correct answer Some single-cylinder engines may also employ torsional vibration dampers to help absorb and dissipate torsional vibrations. Balancing a multi-cylinder engine involves - correct answer minimizing the vibrations caused by the movement of pistons and rotating components. Unlike a single-cylinder engine, where there's only one piston generating power, multi- cylinder engines have multiple pistons firing at different times. This inherent design helps reduce vibration, but balancing is still crucial for smooth operation and longevity. multiple-cylinder engine: 1.Primary Balance: - correct answer Multi-cylinder engines inherently have some level of primary balance due to the opposing motion of pistons in different cylinders. For example, if one piston is moving up, another in a different cylinder is moving down, helping to counteract each other's forces. However, perfect balance isn't always achieved naturally. multiple-cylinder engine: Secondary Balance: - correct answer This is related to the reciprocating motion of pistons. It's about ensuring that the pistons' motion is as even as possible to reduce vibrations. Crankshaft Design: - correct answer Multi-cylinder engines typically use a crankshaft with offset crankpins. These offsets are designed to help balance out the forces generated by the pistons. Dynamic Balancing: - correct answer This involves using specialized equipment to measure the imbalance forces of the rotating assembly (crankshaft, pistons, rods, etc.) and adding or removing weight to achieve balance. Matching Components: - correct answer Ensuring that pistons, rods, and other reciprocating components are as close in weight as possible helps maintain balance. Harmonic Balancer: - correct answer This is a device attached to the front of the crankshaft that helps dampen torsional vibrations Balancer Shafts: - correct answer Some multi-cylinder engines, especially those with an inline-4 or V6 configuration, use balancer shafts. These are additional shafts with counterweights that rotate at twice the speed of the crankshaft to help cancel out imbalances. Flywheel and Clutch Balancing: - correct answer The flywheel and clutch should also be balanced to prevent vibrations. Remember, even with these balancing techniques, it's challenging to achieve perfect balance in all conditions. Factors like wear and changes in engine condition over time can affect balance. Regular mainte