Gears overload

Gear overload is another leading cause of failure. In some instances, the overload is constant, which is an indication that the gearbox is not suitable for the application. In other cases, the overload is intermittent and only occurs when the speed changes or when specific production demands cause a momentary spike in the torsional load requirement of the gearbox. 

In many eases, the gear manufaeturer is provided with only the design horsepower of the maehine. Aetual transmitted loads ean be mueh higher due to the proximity of torsional or lateral eritieal speeds. Surge in eentri-fugal eompressors ean eause severe overload and result in failures. 

The main causes of failure in gear couplings are wear or surface fatigue caused by lack of lubricant, incorrect lubrication, or excessive surface stresses. Component fracture caused by overload or fatigue is generally of secondary importance. 

Axial or propeller blade fatis are eithet Irelt or gear driven. Some drivers are variable speed tnoiors. and some fatis have variable pitch blades. Iti s iecial circumstances, steam turbine, gas or gasolitie etigine drivers are used. Geais should be carefully specilied to avoid overload and should be special ) sealed to prevent moisture entering the case. 

The three most likely types of operational service misuse are overloading, incorrect lubrication and the presence of contaminants. Overloading is primarily due to the use of too small or too weak a gear unit, and this may be the result of false economy (installing an available unit for an application beyond its capacity) or failure to cater for the effects of shock loads in calculations of power rating. 

Likewise, process machinery shall also be examined for materials of construction, in-built safety features such as internal safety valves (e.g. gear pumps), limit switches for overload, over hoisting for hoists, tripping of drive motor in case of jamming of lobes of twin lobe blowers due to dust, etc. 

Screw conveyors can be used for feeding solid powders at a controlled rate corresponding to the RPM of the shaft. The drive can be throngh a gear box and Variable Frequency Drive (VFD)-operated motor if there are chances of overloading the motor when material gets crashed or stuck in the fins. An instantaneous trip relay should also be provided for such condition. 

Safety gear. All passenger lifts must be fitted with safety gear which will arrest and support a fully loaded car in the event of suspension rope failure. The safety gear linkages, attachments, ropes etc. should be carefully checked for security and freedom of movement at each examination. The safety gear must also be tested every four years. Control equipment and the overload protection devices. 

In order to prevent overloading of the installed electric motors, one should be geared to the maximum power consumption. Since the modification of the power requirement is essentially determined by the work done on compression, the maximum of the compression achievement also represents the maximum of the power consumption. This can be derived from Eq. (3.21) ... 

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