CMRT CMRT Mechanical Systems and Alignment 2

Question 1

What is the difference between static (residual) unbalance and dynamic unbalance in a rotating component?

Accepted Answer

Static unbalance is a single heavy spot in one plane, while dynamic unbalance involves heavy spots in two or more planes that create a couple

Answer

Static unbalance is a mass imbalance in a single axial plane causing the shaft to bow, while dynamic unbalance involves imbalance in two or more planes that creates a rocking couple during rotation.

Question 2

What is the purpose of a keyway and key in a shaft-hub connection?

Accepted Answer

To transmit torque between the shaft and the hub by providing a positive mechanical drive

Answer

A key inserted into matching keyways on both the shaft and hub creates a positive mechanical connection that transmits torque while preventing relative rotation between the two components.

Question 3

What does 'interference fit' (press fit) mean when installing a bearing or coupling hub on a shaft?

Accepted Answer

The hub or bearing bore is slightly smaller than the shaft diameter, requiring force or heating to assemble

Answer

An interference fit (press fit) means the bore is smaller than the shaft diameter so the component must be pressed or thermally expanded for installation, creating a tight grip that transmits loads without slipping.

Question 4

Which seal type is most appropriate for preventing lubrication leakage from a rotating shaft in a pump or motor?

Accepted Answer

Mechanical face seal (mechanical seal)

Answer

Mechanical face seals (mechanical seals) use two precision-lapped faces — one rotating and one stationary — pressed together to create a dynamic seal around a rotating shaft.

Question 5

What is the primary function of a flexible disc coupling in a high-speed turbine-generator set?

Accepted Answer

To transmit torque while accommodating small amounts of angular and axial misalignment without requiring lubrication

Answer

Disc couplings transmit torque through thin flexible metal disc packs that accommodate angular and axial misalignment without lubrication, making them ideal for high-speed, high-power turbine applications.

(CMRT) Certified Maintenance and Reliability Technician Practice Test

(CMRT) Certified Maintenance and Reliability Technician Practice Test

CMRT CMRT Mechanical Systems and Alignment 2