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).

Good training

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.