January 1, 2008
Protect your big ticket equipment with a properly trained and educated team of maintenance personnel.
Many aggregate producers will experience decreased profit margins because their maintenance team does not fully understand the maintenance requirements and operational parameters of the equipment with which they work. Are you one of these producers?
Cost-effective maintenance and operations techniques begin with workers who are knowledgeable about the equipment to which they are assigned. In the real world, however, the level of equipment knowledge demonstrated by many aggregate-producing plant employees is far too often found to be inadequate.
Equipment that is maintained and operated by personnel who are not properly trained will eventually suffer from escalating operating costs due to poor disassembly/assembly practices, preventive maintenance neglect, premature component wear, frequent equipment overloads, erratic use of connected horsepower, and similar faults.
Some aggregate producers make enough profit each year to offset the cost of continued and unnecessary replacement of equipment parts and lost revenue associated with equipment downtime. At best, such organizations are earning less profit then they might otherwise enjoy. At worst, they are headed for financial trouble because declining profit margins and increased competition will catch up with them.
I’ve always said that insanity consists of continually making the same repairs but expecting different results. Yet, far too many aggregate producers get caught up in this trap. Problems related to inadequate personnel training exist at nearly every aggregate production plant, regardless of size.
One of the most frustrating statements an equipment manufacturer’s field representative can hear from a customer is, “We’ve been running this crusher for “X” number of years, and we know it better then you do.”
Most factory technical representatives are diplomatic enough to ignore such comments. However, statements such as this reflect an attitude that leads to equipment neglect. Maintenance personnel who think they know everything about a certain type of equipment often create or cause unnecessary problems.
One widespread example of dangerous misinformation is a belief, held by many veteran aggregate employees, that higher lubricating oil pressure is good for some cone crushers. There have been many cases of responsible plant maintenance personnel who have taken the factory-supplied main relief valve off their cone crusher and replaced it with a main relief valve with a higher-pressure rating. The purpose of such a modification is to permit the crusher to operate at a higher lubricating oil pressure level. For reasons that are not completely clear, these employees have decided to “modify” the manufacturer’s lubrication system.
Unfortunately, such modifications can and usually will cause serious damage, or possibly even a catastrophic failure of the crusher. A cone crusher is designed to operate with countershaft box oil pressure within a particular range. For example, the Symons Cone Crusher is designed to operate at 5 to 10 psi for the 3-, 4- and 4 1/4-foot model sizes or at 5 to 15 psi for the 5 1/2- and 7-foot model sizes.
Operating a cone crusher with excessive oil pressure will cause the eccentric assembly to hydraulic (lift) during operation. This leads to decreased bearing clearance between the taper of the main shaft and the taper of the inner eccentric bushing and a mismatch (disengagement) of the gear teeth in relationship to the pinion teeth. The reduction in bearing clearance will create excessive oil temperature and can result in a burnt inner eccentric bushing, a burnt main shaft, or a broken main shaft. The mismatch of the gear and pinion teeth can lead to broken teeth.
The main relief valve limits the amount of oil pressure that can enter the crusher. The main relief valve setting is 10 psi for the 3-, 4- and 4 1/4-foot model sizes or 15 psi for the 5 1/2- and 7-foot model sizes.
A manufacturer’s design engineers establish the correct oil pressure range and main relief valve settings. This is done after careful calculations, prototype testing, and long-term field experience. The operation of the lubrication system, as designed by the manufacturer, is essential to assure proper lubrication and cooling of the cone crusher.
When operating personnel make modifications that alter the intended operation, such as installing a main relief valve of a higher pressure rating, they actually defeat the purpose of the lubrication system. The inevitable result is continuous overheating and premature failure of internal components (see Figure 1). This kind of modification is an extreme example, yet it is fairly common.
Figure 1. A properly set main relief valve is critically important.
Other well-meaning alterations are performed on rock crushers on a fairly widespread basis. For instance, it is common practice to replace the original motor sheave with one featuring a smaller diameter in order to increase the cone crusher’s operating speed. This speed change will have a major impact on internal crusher components. It will affect the temperature of the internal crusher components, the balance of the crusher, the life cycle of the crusher components, and the foundation, which supports said crusher. Keep in mind that a 20-percent increase in crusher speed will result in a 44-percent increase in unbalanced forces. This is a substantial difference!
Figure 2. Increased speed can cause the inner eccentric bushing to burn out.
Speaking of the crushers’ supporting structures, most foundations have natural frequencies above the original operating speed of the existing crusher. If the speed of the crusher is increased, it could operate close to the natural frequency of the foundation and could cause structural problems with the foundation. Additionally, as the crusher speed increases, the need for oil cooling increases due to the higher speed shearing of the oil film. A cone crusher that may have rarely, if ever, experienced an inner eccentric bushing failure may now burn this bushing nearly continuously following an increase in speed (see Figure 2).
Aggregate equipment abuse based on misinformation is frequently passed from one employee to another in the guise of on-the-job training. In a few extreme cases, poor maintenance habits and/or incorrect operational procedures become entrenched in an organization to the point that these bad habits and improper procedures are defended, and correct methods are scoffed at or resisted.
Depending upon the severity of a training gap in any given organization, the solution can be relatively simple, or extremely difficult, but in no case is it easy. To be effective, education in processing equipment maintenance and operation must be kept current and must be on-going. Aggregate producers who incorporate technical training into their annual activities have the ability to reap huge benefits, most notably increased productivity, improved product shape, increased equipment on-line availability, and decreased maintenance repair costs. All four points are very attractive to aggregate producers.
Remember this: If you think that training employees and watching them leave is expensive, try not training them at all and watching them stay!
When an aggregate producer purchases a new piece of equipment from a reputable local distributor or directly from the manufacturer, the purchase normally includes assistance during the installation and startup. The manufacturer will provide detailed installation drawings, instruction manuals, and a replacement parts book.
But in an aggregate plant, personnel changes are becoming increasingly common. A new maintenance employee or operator may be trained by a predecessor whose knowledge, or attitude, may be suspect. A familiar crusher may be replaced with an unfamiliar or used crusher that is installed by in-house personnel, with no manufacturer assistance at installation or guidance during the startup. Maintenance and operating procedures that are proper for one brand or type of equipment may be completely wrong for another. The simplest solution to such problems is continuous professional training for operating and maintenance teams who work on processing equipment.
Most equipment manufacturers are capable of providing training, and an increasing number of producers are taking advantage of it. Many producers send their middle management, supervisors, and foremen to equipment training seminars. This is a strong indication that upper management is aware of the need for training and is committed to doing something about it.
The assumption on the part of some companies is that a supervisor and foreman can attend a training session and come back and convey all of the knowledge to the rest of their crew.
Unfortunately, such an ideal transfer of technical theory and detailed procedures seldom takes place. Training seminars cover a lot of information in a short period of time. Few individuals can absorb all the knowledge much less pass it on to others in an effective manner. The principles have to be studied, and the procedures must be practiced repeatedly in the field before the personnel can gain genuine expertise. That’s why most seminars are supplemented with volumes of printed material.
Even though it is extremely beneficial to send managers, supervisors, and foremen to training sessions, this should be considered only the first step. Other employees such as lead men, oilers, maintenance planners, quality control personnel, and plant operators also need to be trained.
Among the prime candidates for training are veteran employees who have never had the chance to attend a training seminar, those who have been transferred from unrelated assignments, and new employees with no previous experience. As knowledgeable employees retire or are promoted to different assignments, competent replacements must be provided.
As mentioned earlier, most equipment manufacturers are capable of providing quality training sessions for the aggregate producer. Many manufacturers offer several training options including manufacturer training seminars conducted in the manufacturer’s home city, regional training seminars conducted in a city near a high population of related equipment, and private training seminars conducted right at the aggregate producer’s job site.
However, there are oftentimes costs associated with these sessions. Tuition fees as well as transportation and lodging for either the trainer or trainee(s) are standard expenses. While these costs are substantial, most equipment manufacturers who provide training try to keep the costs as low as possible and often operate them on a break-even basis.
The costs, however, are likely to be a wise investment for aggregate producers. It has been well documented that effective training increases employee confidence, improves employee performance, and lowers employee turnover.
It has always been my personal feeling that if you can convince the right employee to attend a well-organized, well-orchestrated technical training seminar, the attendee’s employer will possess the ability to reap huge benefits. Potential benefits include the following:
Improved awareness and knowledge of the equipment;
Increased equipment online availability;
Decreased maintenance repair costs; and
Making little rocks out of big rocks can and should be simple, economical, and even fun, but if your organization is experiencing skyrocketing operating costs due to poor maintenance and operating practices, consider yourself a prime candidate for maintenance and operations training. During a period of time when profit margins are declining and competition is increasing, cost effective maintenance and operating practices become vital.
Mark Kennedy is a senior aftermarket training instructor for Metso Minerals Industries, Inc. A 20-year veteran of the company, he has worked in the field service department both domestically and internationally, gaining valuable hands-on experience.