temperature and comparing it to the return oil temperature.
Photos by Kevin Yanik
Cost-effective aggregate production begins with employees who are knowledgeable about the maintenance requirements and operational parameters of the cone crushers they operate. Here are some tips to maximize cone crusher maintenance.
1. Monitor lube oil temperature. A lot can be learned about a cone crusher by simply watching the supply oil temperature and comparing it to the return oil temperature. Return oil temperature should be in the range of 60 to 140 degrees, although the temperature should preferably be in the range of 100 to 130 degrees.
In addition, oil temperature should be monitored frequently throughout the shift. Once a producer learns a crusher’s normal drain line oil temperature and the normal temperature differential between supply and drain, an abnormal condition warrants an investigation.
2. Monitor lube oil pressure. It is critically important to watch the countershaft box lube oil pressure throughout each shift. Some of the things that could cause a lower-than-normal lube oil pressure include a low gallon-per-minute oil flow rate caused by a worn lube oil pump, a faulty, miss-set or stuck-open main relief valve, or having excessive bearing clearances within the crusher caused by bushing wear.
Monitoring countershaft box oil pressure each shift gives you the opportunity to learn what normal is. Once normal has been established, corrective action can be scheduled and taken based on an abnormal condition.
3. Inspect the lube oil tank return screen. An oil tank return screen – typically about 10 mesh in size – is fitted into the lube oil tank. All returning oil flows through this screen, and it’s important to note that oil is the only thing that should go through this screen.
The function of this screen is to prevent large contamination from entering the lube oil tank, and possibly being drawn into the suction line of the lube pump. Any unusual-looking debris found on this screen warrants closer investigation. The oil tank return screen should be inspected daily, or every eight hours.
installation during a company-hosted workshop.
4. Commit to an oil analysis program. Today, oil analysis has taken its place as an indispensable and valuable element of crusher predictive maintenance. There is only one thing that will wear out the inside of a rock crusher, and that is “dirty lube oil.” Clean lube oil is the most important factor affecting the service life of the internal crusher components.
Participating in an oil analysis program gives you the opportunity to watch the condition of the lubricating oil throughout its service life. An active drain line oil sample should be taken once per month, or every 200 hours of operation, and sent in for analysis.
The five main tests completed in the analysis include viscosity, oxidation, water content, particle counts, and machine-wear analysis. An oil analysis report that shows an abnormal condition gives the opportunity to investigate and correct the problem prior to failure. Remember, contaminated lube oil “kills” crushers.
5. Maintain clean crusher air breathers. The countershaft box air breather and the oil tank air breather work together to allow the crusher, oil tank and a properly pitched drain line tube to maintain atmospheric conditions. Clean air breathers assure unrestricted drainage of the lube oil and help to prevent dust infiltration through the head sealing arrangement.
Air breathers are commonly neglected components of the lubrication system. Air breathers should be inspected weekly, or every 40 hours of operation and changed or cleaned as required.
6. Monitor the crusher’s coast-down time. Coast-down time is the amount of time, in seconds, it takes the crusher sheave to come to a stop after the crusher drive motor has stopped. Coast-down time provides an example of just how free and easy the crusher is or how binding it is.
Minimum coast-down time for most mid-size to small cone crushers is around 30 seconds. Coast-down time should be documented at the end of every day. Once you learn a crusher’s normal coast-down time, a decrease from normal warrants an investigation. Common reasons for a decrease in coast-down time include crusher drive belts that are too tight or a clogged under crusher discharge area.
7. Inspect the under crusher discharge area daily. Some of the heaviest damage that can occur to a cone crusher is caused by a buildup of material below the crusher. For this reason, inspect the area under the crusher once per day.
Check for material buildup on the crusher arms and the countershaft box. This becomes particularly important if the material being processed is wet or sticky, or if the feed contains a lot of debris like tree roots. When inspecting for material buildup, also look at the condition of the mantle and bowl liner; the counterweight guard; the mainframe liners; the arm guards; and the lube oil piping.
If built-up material is found, it should be knocked down. If an abnormal condition is noticed on any of the other items inspected, corrective action should be taken to repair it.
8. Lubricate the bowl threads. Bowl threads and adjustment ring threads should be lubricated weekly, or every 40 hours of operation. The proper lubricant to use is an NLGI (National Lubricating Grease Institute) No. 1 with at least 5 percent molybdenum disulfide (by weight).
The threads should be lubricated once when the bowl is clamped tight in a crushing position, and once when the bowl clamping pressure has been released. In non-abrasive applications, you are encouraged to rotate your bowl open and closed a full revolution on a monthly basis, or every 200 hours of operation. This step helps to smear the grease over all portions of the threads.
Remember, you cannot over-grease the threads but you can certainly under-grease them. The consequence of not lubricating the threads properly is a stuck bowl.
9. Measure the bore prior to installing a new bronze bushing. Every time a bronze bushing is burned black in color, there is a possibility that the steel bore behind the bushing has become dimensionally incorrect, either pulled in small, egg shaped or distorted.
If a new bronze bushing is installed into a damaged bore, the softer bronze bushing will take the same shape as the damaged bore. This could lead to incorrect contact between the mating surfaces and a reoccurring bushing failure. Make certain to measure the steel bore with an inside micrometer prior to installing a new bushing.
If the dimensions taken show they are dimensionally incorrect or distorted, corrective action for the steel bore is required at that point. Every quarry maintenance department should have a 4-in. to 40-in. inside micrometer set on the ready.
10. Keep a daily operator’s log on every crusher. A properly interpreted daily operator’s log can help predict a problem with a crusher before a failure. Entries should be made at least once per shift, but preferably twice per shift.
The log can be used to learn the crusher’s normal operating trends. Once this has been established, red flags will pop up when something abnormal occurs.
Taking or making corrective action based on an abnormal operating condition, seen through the use of log sheets, will always lead to a cost-effective maintenance repair. But if you don’t take the time to learn and understand what the normal operational characteristics of your cone crusher are, you will never know what abnormal is until it’s too late (crusher failure).
11. Change the liners on time to maximize productivity. Pushing the crusher’s wear parts, the mantle and bowl liner too far is another common mistake.
Most cone crushers experience a decrease in the liner’s feed opening dimension late in the liner’s life. This reduction in the liner’s feed opening dimension will result in a decrease in volumetric area between the mantle and bowl liner, which, in turn, results in a decrease in crusher throughput tonnage.
A great idea is to change liners at the correct time by watching for the reduction in throughput late in the liner’s life. Consider that an excellent time to change liners is when a 10 percent loss of product occurs. The immediate increase in productivity by 10 percent will far outweigh the little gain you get in the form of extra manganese utilization.
12. Implement a preventive maintenance program. Prepare a written maintenance program that fits your plant, which includes preventive maintenance, predictive maintenance and proactive maintenance. Include specific dates when maintenance work will be done, and have management approve the plan.
13. Commit to employee training and education. It has been well documented for years that effective training and education improve employee confidence and performance. They also lower turnover. Benefits of a well-organized, well-orchestrated technical training event include:
1. Improved awareness and knowledge of equipment
2. Increased crusher on line availability
3. Decreased maintenance repair costs
4. Increased productivity
One objective that is critically important is to combine both training and education into the training program. Remember, training is teaching someone how to do something. Educating is explaining to someone why it must be done that way.
Also, remember this: If you think training employees and watching them leave your company is expensive, then try not training them at all and watching them stay.
Mark Kennedy is senior technical training instructor at Metso. He can be reached at mark.kennedy@metso.com.