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Lubrication in the cement industry offers some unique challenges. It’s not so much the type of equipment that is the issue but the environment in which the machinery is operating, which can vary from season to season depending on the plant’s location.
This factor must be carefully considered when selecting and applying lubricants, as oils and greases that work well in almost identical equipment might not be as effective in the conditions this industry must often face.
Typically, a cement plant is located adjacent to or very near a quarry. Raw material must be transported from the quarry into the cement plant and eventually into large storage hoppers. The mode of transportation is generally via conveyors, with the most common types being belt conveyors.
Even if raw material is brought into the cement plant from a source some distance away, there will still be numerous conveyors throughout the plant.
These conveyors usually are driven by electric motors, some of which will be large due to the power required to pull the belts. The larger types have grease nipples that require infrequent greasing. There will also be greased bearings on both the drive end and non-drive end as well as on tension rolls in between.
Many different types of greases are used successfully in these applications. The specific grease employed is not as important as the frequency of the greasing, which can help to keep dust out of the races and prevent rapid wear rates. Since conveyors are often outside and open to all weather conditions, it is not uncommon to choose a water-resistant grease to inhibit water ingress.
In these applications, greasing is seldom performed frequently enough because of the distances between the bearings and the height at which they are located above the ground. A lack of labor availability can add to this problem.
The use of greasing systems in which a centrally located reservoir feeds numerous points through piping may be considered. However, the pipe runs could potentially be quite long, requiring a number of these types of systems.
The other alternative would be a single-point grease lubricator that attaches directly to each bearing. These lubricators can be set to expel grease over variable amounts of time to suit the application and bearing size.
They can also significantly reduce the amount of labor required to individually grease the bearings as well as help to alleviate the ingress of contaminants by applying constant pressure on the bearing.
Of course, the total cost of utilizing these types of lubricators throughout a plant must be weighed against the amount of labor involved. In addition, keep in mind that these systems must be inspected on a regular schedule to ensure they are working properly. No automatic lubrication system should ever be implemented on a “fit and forget” approach.
Conveyors typically are driven by different types of reduction gearboxes, including worm gearboxes, to allow the electric motor to sit adjacent to the conveyor and not protrude excessively. In these instances, a simple oil with the appropriate viscosity can be used. The lubricant does not necessarily need to possess extreme-pressure properties.
Gearboxes and bearings are also found in numerous crushers within the infeed section of the quarry. These components must cope with the same issues as conveyors in terms of dust. Centralized greasing systems are commonly used here, since the bearings are located close to each other, ensuring that the pipe runs are not too long and the grease reservoir can easily be housed inside.
These gearboxes generally are quite large and have a substantial oil capacity. The gear teeth often experience high shock loading, so extreme-pressure gear oil is frequently used for this reason.
Crusher gearboxes benefit greatly from regular oil analysis and condition monitoring. The small oil sample required does not affect the overall oil level, and the information gained from the subsequent analysis can save a considerable amount of money in avoiding unplanned downtime and the associated costs of lost production.
There are many different types of open gears associated with cement plants, along with different lubricants and application methods. The main requirement for these open gears is that the lubricant be able to adhere for the entire revolution of the driven gear in order to offer the needed protection.
This lubrication requirement occurs when the driving pinion is mating. Therefore, the best lubricants for these applications are sprayed onto the teeth just before the pinion and driven gear mate. The spray pattern is critical for the coverage of the mating teeth to be sufficient.
Normally, the lubricant is sprayed directly from a barrel due to the quantity required. The lubricant may also need a certain degree of heat resistance and must not melt away.
Both greases and thick oils with tackifier additives can be used, as long as they can be sprayed. They must also have the proper load-carrying ability to withstand the potentially high loads that will be experienced. Conventional greases are not suitable, since they do not possess these attributes. Be sure to inspect the gear teeth on occasion to check for uneven wear, which could indicate ineffective lubricant coverage.
Rotary kilns have their own lubrication challenges for both bearings and gearboxes due to their slow rotation, high loads and thermal transfer of process heat. It is common for gearbox oil to be used in a circulation system utilizing both heat transfer systems and filtration. The oil is often synthetic, but this is not always necessary if the flow rate is adequate and the heat transfer system is efficient.
The inherent frictional properties of certain types of synthetic lubricants may be advantageous, as might the high viscosity index. However, the selection of a synthetic grease likely will be more important than the selection of a synthetic oil for the gearbox, as greased bearings will not provide the same cooling effects.
In most cement plants, slow-moving conveyors, sometimes called clinker conveyors, transport material directly from the kilns. These conveyors typically are constructed of metal and consist of a series of buckets that are hinged together. They are often carried by wheels on guide rails with a grease nipple in the center. Because of the adverse operating conditions, i.e., dusty and hot, they will require frequent greasing.
Centralized greasing systems will not work in this type of application due to the constant movement of the wheels. A system must be installed that travels with the buckets for a short distance, with greasing probes automatically projected into the grease nipple. This type of automatic system works well, but it must be checked on a regular basis because of the many moving parts and associated sensors.
Large cement plants frequently have a limited lubricant stock in order to keep lubricant application as simple as possible. While this approach can be somewhat effective, specialized lubricants should be considered in certain applications. Their increased initial cost can lead to larger savings in the long run as a result of the equipment’s longevity and reduced downtime. Consideration should also be given to the use of synthetic gear lubricants in larger geared drives, as their potential energy savings can be significant.
Although every cement plant operates differently and will have its own existing lubrication strategies, preferences, historical problems, maintenance requirements, management structure and available workforce, optimum solutions can be identified regarding the lubricants selected, the equipment utilized to apply those lubricants and the maintenance regime.
All of these elements can then be combined with appropriate condition monitoring techniques. By coordinating both lubrication and condition monitoring strategies with your maintenance regimes, you can ensure that your cement plant operates more efficiently and cost effectively.