8/12/2019 Analisis_Sintomatico_Reductores

1/3

PREDICTIVE MAINTENANCE: MONITORING THE HEALTH OF GEAR

DRIVES

Threat of equipment failure and unplanned downtime haunts all maintenance supervisors. The bestway to avoid costly repair, rebuild or replacement jobs for any piece of equipment is to prevent

trouble before it occurs. Predictive maintenance, the methodical analysis of the most likely sourcesof trouble, provides the best insurance against equipment failures.

In the case of gear drives, predictive maintenance primarily concerns itself with measured changesin vibration, noise, temperature and oil.

Vibration

Vibration levels of new gear drives vary due to the statistical nature of the factors that influence the

vibrations. The initial vibration level tends to remain unchanged for a long period of time. Ascomponents start to wear or fail, the vibration level rises.

Two methods used to determine vibration performance of the equipment are trending anddiagnostics. Both methods are widely used in grain processing mills, refineries, power plants and

other process industries where continuous operation of gear drives is critical.

Trending monitors vibration over time using accelerometers or velocity pick-ups. Monitors

continuously measure vibration levels, while hand-held instruments periodically analyze vibration. As

a safety precaution to avoid catastrophic failure, continuous monitors feature preset safety shutdownlevels.

Diagnostic equipment measures the frequency content of vibration. The overall vibration level is

broken down into individual frequency components. These separate readings are then linked tospecific pieces of equipment, such as bearings or a pump. When trend readings indicate increasing

vibration levels, diagnostic equipment is used to better evaluate the need for corrective action onspecific components.

Guidance for defining typical vibration levels for commercial gear drives is given in AGMA standards.

Sound

Performing sound analysis is easier than vibration analysis, but because it is one step removed fromthe trouble source it should be part of a more extensive predictive maintenance routine.

An operator who is familiar with a piece of equipment may be able to detect a subtle change in the

level or type of noise coming from the gearbox. However, the use of instruments helps quantifynoise characteristics and variance over time.

Sound is accurately diagnosed through the use of frequency measurement devices. For example, if agear mesh is starting to wear the amplitude of the sound at the mesh frequency tends to increase.

An increase in gear mesh frequency may indicate a wear problem. On the other hand, a bearing

generates different frequency and has its own signals to suggest wear.

Sound by itself does not necessarily mean the beginning of a failure pattern. The sound must be

traced to a particular component and then compared to its normal sound level.

8/12/2019 Analisis_Sintomatico_Reductores

2/3

Temperature

Monitoring the operating temperature of gear drives is common practice. Variations in operating

temperature may indicate trouble. To prevent temperature variations, set a maximum tolerationtemperature and have an alarm sound when the temperature reaches the threshold. It is not

unusual for the alarm to sound because a bearing or the lubricant is failing.

Temperature fluctuations are diagnosed by sensors that are placed inside the gear housing and areconnected to a gauge or other readout apparatus on the outside of the gearbox. The two types ofsensors are Thermocouples and Resistance Temperature Devices (RTD).

A Thermocouple contains two dissimilar wires bonded together producing an electrical current with

temperature change. A RTD relies on material that changes resistance with temperature. Astemperature changes, the corresponding resistance change is sensed in electrical readout circuits.

Both sensor systems measure the skin temperature of the gear housing, the outer race of bearing,

bulk oil or other areas where proper temperature is essential. Both systems are reliable.

Thermocouples and resistance temperature devices (RTD) can measure the skin temperature of thegear housing, the outer race of bearing, bulk oil or other areas where proper temperature is

essential.

Oil Analysis

Oil samples are an excellent way of detecting trouble before it affects the performance of theequipment. Samples should be taken in accordance with the equipment manufacturer's

recommendations and test results compared to the lube manufacturer's specifications.

Collecting oil samples from the top central area of the oil reservoir immediately after shutting downthe machine ensures freshly circulate, evenly distributed oil. The plant or an independent testing

laboratory then analyzes the sample.

8/12/2019 Analisis_Sintomatico_Reductores

3/3

Oil samples are an excellent way to detect the source of trouble before it affects the performance of

the equipment. Collect a sample from the top central area of the oil reservoir immediately aftershutting down the machine.

Oil analysis targets three principal factors: changes in viscosity, the amount of water in the oil, and

the presence of foreign particles.

An oil sample showing viscosity levels rising about the proper range indicated deterioration. Thepresence of sludge denotes oil breakdown. An excess amount of water contributes to ruse, loss of

lubrication and eventual component breakdown. The analysis also takes a close look at contaminantsin the oil. The composition of these help identify whether contaminants are entering the gearbox

from the outside, or if some part within the gearbox is wearing out. Machine wear is inevitable. But,

by following these predictive maintenance guidelines on a regular basis, wear can be monitored andcostly, unplanned downtime avoided.