Mining companies have been traditionally slow in accepting or adopting new tech nology for predictive maintenance. I helped with the installation of such technology at the first planning and scheduling of maintenance programs. That was more than 20 years ago, and I know there are still some mining operations that don’t plan and sche dule maintenance. Maintenance is a service, so it’s difficult to put a value on it. If a piece of equipment is doing a job adequately, supervisors are seldom interested in how well it’s operating, just as long as it is ope rating. It may be that the mining industry has dragged its feet in accepting new maintenance ideas because the higher echelons are dominated by production-type people. They want to get the tons out, because a mine’s life depends on the tons. Maintenance is just a necessary evil. But a well-managed preventive maintenance program ensures higher availability of equipment with fewer failures and emergencies. Constant monitoring and inspections of equip ment as well as lubrication and ser vicing on a preplanned schedule help to identify problems while machines are running. And now, with the improvements in predictive mainte nance systems and in instruments using new technology, detecting and isolating problems are much easier. Predicting failure is more scientific.
A commitment to a program is not straightforward and is better made with expert advice. The following gives a brief description of some of the new systems. Vibration-monitoring instruments are used to indicate changes in vibration levels of machines. A base level measurement is taken when the machine is running well. Any recorded changes from this base level measurement can indicate trouble ahead. Several different instruments, some rather advanced and others less so, have been developed for vibration- monitoring. The basic manual system incorporates a hand-held vibration meter and a portable analyser for diagnosing problems found with the meter. More advanced is the small micro-processor data-collector and a central data storage/analyser or micro- computer, which provide information on each machine’s mechanical condition. No matter what system you choose, formal training is a must.
Another modern maintenance tool uses thermography infra-red radiation, which has a wavelength that is slightly longer than visible light at the red end of the spectrum. Thermography in volves non-contact infra-red instruments that see and measure radiant energy and convert it into brightly colored heat pictures that indicate abnormal warmth. Images can be recorded by photography or video and serve as a baseline measurement of faults and defects for comparison with future scans. One particular use is locating hot spots in electrical systems created by high current flow across poor connections and terminations of cables, busbars, pot heads and bushings. Typically, an electrical survey is performed bi-annually by a technician with an understanding of the power distribution network and trained in the interpretation of the thermographs.
Other periodic thermal surveys are used in assessing the thermal performance of buildings and to detect roof leaks by the temperature difference at the roof surface caused by wet insulation. Overheating of mechanical components such as motor bearings, couplings, refractory linings and boilers can also be checked. In addition to surveys, temperature readings can be taken at any time with infra-red thermometers. These are hand-held, non- contact, and will record accurate temperature readings from a distance. Ultrasound Detection
Ultrasound is a short wave signal and in most equipment can be isolated easily. When emitted, it is loudest closest to the problem source. This is because it needs greater amplitude to travel the same distance as a low- frequency sound, a characteristic which provides easy detection by instruments designed for ultrasonic testing. Detectors are used as scanners for gas and current leaks, or as metal rod contacts when physical connection is required as a waveguide. Instruments are usually battery- operated for portability and the user has a stethoscope and an analog meter which displays the signal strength. Diagnosis of vacuum and pressure leaks, faulty valves and steamtraps are provided fast. The testing is especially useful in detecting potential bearing failure. Good bearings emit ultrasound and the intensity increases as they wear. The sound of a current jumping a gap indicates loose connections and defective switches and relays in electric systems. Wear Particle Analysis
Wear particle analysis is used to analyse and trend wear on machine components. Lubricant samples ex tracted on a fixed schedule are sent to a laboratory for analysis. The wear in the machine is shown by the color, shape, quantity and makeup of the wear particles in the sample. Recom mendations are then made for main tenance based on what is found.
A predictive maintenance program for an overall plant can be installed from scratch, but it is more likely to be an extension of an existing preven tive maintenance system. Realizing the benefits of the first installation, people will want to try the next stage. From the lessons learned they will know that the first essentials are to start slowly with the simplest technology. After the decision is made on the particular technique, the procedure is very similar to that used when preventive maintenance is being initiated. The plant and equipment are selected and the what, how, and when to measure is determined. An extra requirement is the setting of standards to which measurements are compared.
There are predictive maintenance systems that are immediately available without the preliminaries re quired for semi-manual plantwide systems. The application of a fully automated system for a mobile production machine is described in the November 1987 issue of The Northern Miner Magazine. It was developed by Advanced Electronic Systems in Markham, Ont.
The vital components of each machine are monitored with 70-odd sensors and transducers and the help of an on-board computer. Flashing alarm lights inform the operator when something is wrong. Additional soft ware is being developed to allow operators to do their own trouble- shooting. After entering poor machine performance into the system, they will be told, in plain English, the diagnosed problem.
Breakdown maintenance used to be common practice in the mining indus try. Then preventive maintenance techniques were discovered and people found it was possible to prevent pieces of equipment from failing before they reached the end of their planned lives. Recently we reached another milestone for improved main tenance — the emergence of the new techniques described above. In time, these techniques for prediction of equipment failure will be common place in all programs. Keith Bowley is a Toronto-based main tenance consultant.
Be the first to comment on "Maintenance PREDICTING PROBLEMS"