Predictive maintenance is a technique to predict the future failure point of a machine component, so that the component can be replaced, based on a plan, just before it fails. Thus, equipment downtime is minimized and the component lifetime is maximized.
Predictive Maintenance Organization
This technique involves the measurement of various parameters that show a predictable connection with the component life cycle. Examples of such parameters are as follows:
- Bearings vibration
- Temperature of the electrical connections
- Insulation resistance of the motor coil
The use of predictive maintenance is to establish, firstly, a historical perspective on the relation between the selected variable and the component life. This is accomplished by taking readings (for example, the vibration of a bearing) at regular intervals until the component fails. The figure shows a typical curve which results from plotting the variable (vibration) against time. As the curve suggests, subsequent bearings should be replaced when the vibration reaches 1.25 in / sec (31.75 mm / sec). Manufacturers of instrumentation and software for predictive maintenance may recommend ranges and values to replace the components of most equipment; this historical analysis makes it unnecessary in most applications.
Once the feasibility and advisability of conducting predictive maintenance to a machine or unit, the next step is to determine or control the physical variables that are indicative of the machine condition. The objective of this part is to review in detail the techniques commonly used in monitoring according to condition, so as they are the guidance for their overall selection. The monitoring purpose is to obtain an indication of the condition (mechanical) or health status of the machine so that it can be operated and maintained safely and economically.
For monitoring, it was understood in the beginning, such as measuring a physical variable that is considered representative of the machine condition and its comparison with values that indicate whether the machine is in good condition or damaged. With the current automation of these techniques has also extended the meaning of ‘ monitoring’ to acquisition, processing and data storage. According to the objectives to be achieved by monitoring the condition of a machine, should be distinguished between vigilance, protection, diagnosis and prediction.
- Monitoring of machines. Its purpose is to indicate when a problem exists. You must distinguish between good and bad condition, and if it is bad you should indicate how bad it is.
- Protection of machines. Its aim is to prevent catastrophic failures. A machine is protected, when the values that indicate their status reach values considered dangerous, the machine automatically stops.
- Failure diagnosis. Its aim is to define the specific problem. Its objective is to estimate how much longer could operate the machine without the risk of catastrophic failure.
In recent times there has been a tendency to apply predictive maintenance or symptomatic, that is, by vibration analysis, used oil analysis, wear control, etc..