Machinery and Components Adam Adgar School of Computing and Technology

Machine/Component Failures ► Major source of production downtime in most industrial plants ► Cost of production downtime is often higher than the expense involved with the repair or replacement ► Many machine/component failures can be averted, or at least the useful life can be extended ► An important part of this process is knowing the cause of the failure.

Machines ► Pumps ► Compressors ► Fans ► Conveyor belts ► Crushers ► Mills ► Gearboxes ► Rollers ► Motors

Components ► Shafts ► Bearings ► Gears ► Couplings ► Pulleys + Belts ► Sprockets + Chains ► Impeller/Vanes ► Electrical (Rotor and Stator)

Shafts ► Rotating bars which transmit force, power, and motion ► Usually circular cross section ► Torque is twisting force resisted by shaft ► Stresses on shafts Torque Tension Compression Bending Combinations

Types of Loads TENSION TORSIONBENDING COMPRESSION

Bearings ► Hydrodynamic / journal bearings Sliding action coefficient of friction high < f < ► Rolling-element / antifriction Rolling action coefficient of friction low < f < ► A device that supports, guides, and reduces the friction of motion between fixed and moving machine parts. ► Two major types:

Journal Bearings ► Shaft rotates inside a bearing bore slightly larger than the shaft diameter ► Lubricant is supplied to the annular gap ► Portion of the shaft within the bearing is called the journal. ► At rest, there is metal-to- metal contact between the journal and the bearing, along the line of contact ► Once rotation begins, a lubricant film develops between the journal and the bearing ► As speed increases, a wedge of lubricant forms, supporting the shaft away from the bearing, and preventing wear.

Rolling Element Bearings ► Make use of spherical or cylindrical rolling elements captured between inner and outer rings ► The rolling elements support the load, and transmit rotation by rolling, rather than sliding ► Friction is fairly uniform with speed hence power loss is more predictable ► Experience much less wear at slower speeds than do journal bearings Outer Race Inner Race Ball Cage or Separator Bore

Rolling Element Bearings ► There are two types of rolling element bearings Ball bearings  Point contact  High speed  Low load Roller bearings  Line contact  Low speed  High load

Gears ► Gears Wheel, disk or bar with teeth on periphery Teeth mesh with teeth on other gears Simple gears transmit power directly from one shaft to another Internal or external teeth As two engaged gears rotate together, the same number of teeth on each gear pass the line between the centres ► Types of gears Gear train Bevel gears Internal and external gears Worm gear drive

Gears ► Used in many mechanical devices ► Typically required for one (or a combination) of several different reasons: to increase or decrease the speed of rotation e.g. increase torque to reverse the direction of rotation to move rotational motion to a different axis to keep the rotation of two axes synchronized ► To create large ratios, gears are often connected together in gear trains ► Gear teeth provide advantages: Slippage between the gears is prevented. Therefore, axles connected by gears are always synchronised exactly with one another. It is possible to determine exact gear ratios by counting number of teeth in the two gears and divide one by the other, e.g. if one gear has 60 teeth and another has 20, the gear ratio when these two gears are connected together is 3:1. Slight imperfections in actual diameter and circumference of two gears don't matter. The gear ratio is controlled by the number of teeth even if the diameters are a bit off.

Couplings

► Couplings are used to make co-axial connections between two shafts ► They serve two main purposes: To allows first shaft (driver) to drive the second shaft (driven) at the same speed i.e. transmission of power To compensate for minor amounts of misalignment and random movement between the two shafts. ► Couplings are either rigid or flexible Rigid couplings require very close alignment of the shafts  Sleeve coupling  Flange coupling Flexible couplings generally ‘sandwich’ something flexible in between, or connected to, rigid flanges attached to each shaft  Toroidal coupling

Pulleys and Belts ► V belts create greater friction by wedging into the groove on the pulley hence greater torque capacity Between 70-96% efficiency ► Flat and round belts work very well require higher tension than V belts to transmit the same torque require more rigid shafts, larger bearings, etc. Up to 98% efficiency ► Toothed belts don’t slip (synchronous) hence transmit torque at a constant ratio good for applications requiring precise timing very efficient more costly than other types

Sprockets and Chains ► Compared to belts, chains can transmit more power for a given size, and can maintain more precise speed ratios. ► Like belts, chains may suffer from a shorter life than a gear drive. ► Flexibility is limited by the link-length, which can cause a non-uniform output at high speeds. ► Can be very efficient – around 98%. ► User controls the length (with master links) is a plus. ► Sprockets wear out much more frequently than pulleys

Motors

Motor Faults ► Neglect Dirt  Surface dirt causes overheating  Internal dirt degrades insulation and bearings Bad Lubrication  Too much or too frequent  Too infrequent  Mixing incompatible lubricants Poor Power Quality  Over/under voltage (especially under)  Unbalanced voltage  Single-phasing ► Misapplication Under-sizing  Service factor is not for normal use ASD Stresses  Low speed + high torque = overheating  Induced bearing currents  Standing wave phenomena Poor Ventilation  Causes overheating Coupling & Belts  Misaligned couplings or sheaves = Bearing Failures  “Soft Foot”, I.e. bad shimming

Motor Faults ► Severe Environment Hot Ambient  Requires de-rating High Altitude  Causes overheating - requires de-rating Humidity  Motors in storage (zaps insulation or bearings)  Motors with significant off time (zaps insulation)  Requires internal or ambient heating Airborne Contaminants  Damages insulation or bearings  Kills by abrasion or chemical deterioration ► Normal Wear Without unusual stresses, motors sometimes last for tens of thousands of operating hours, but will eventually succumb to...  Bearing wear  Insulation failure

Faults ► Mechanical Unbalance Misalignment Bearing Looseness Lubrication Cavitation ► Electrical Rotor Stator

Unbalance BalancedUnbalanced ► Unbalance is the force exerted on a rotor due to the difference between the centre of rotation and the centre of mass Centreline of mass Centreline of rotation

Misalignment Angular Misalignment Offset Misalignment

Bearing Faults ► Revolution around outer race ► Non-uniform radial tension of bearing ► Misalignment of outer race ► Wear of the outer race ► Cavities on the outer race ► Wear of the inner race ► Cavities on the inner race ► Wear of balls, rollers or cage ► Cavities, spallings of balls/rollers ► Complex defect ► Slip of race ► Defects of lubrication ► Causes Handling/Transportation Defects of installation/maintenance High dynamic loads from shaft  imbalance, coupling misalignment, and self- excited rotor oscillations Bearing distortion Lubrication  Lack of  Excess  Impurities  Degradation

Bearing Faults ► Defects can lead to seizure of the bearing breakage of cage Rapid or slow wear of bearing Pitting Cavities Cracks Increase in the friction coefficient

Monitoring/Diagnostic Techniques ► Many predictive maintenance technologies ► Examples include Vibration analysis Oil analysis Ultrasound Thermography Motor Current Signature Analysis

Typical Installation Motor Driven Pump VV VV P R PT A TTT

Self Study ► Read B&K Application Note on Detecting Faulty Rolling Element Bearings (pp 1-2)Application Note