July 5, 2011
By E. Bradford Pugh
Downtime is dead time. If machines aren’t running, then you’re not making money. Anything you can do to make sure this does not happen to you and your operation is essential to your maintenance plan. Working to establish a quality plan of attack prior to needing it will decrease your costs and increase your output.
maintenance is the single most important concern that operators in the rock crushing business must deal with. It is vital to not only the life of the machine and its life expectancy, but to financial implications of the business. Having a strong working knowledge of the crusher’s parameters is vital to its success, and having a strong maintenance program detailed on the how and when to perform cleaning and maintenance will give the crusher its maximum lifespan.
All crushers have limitations. The capacity, the size of the feed, and the closed-side setting (either maximum or minimum) are just some of those limitations. You need to take into consideration the types of material being crushed and any environmental issues that could affect the crusher’s limits at any given moment. Anytime a crusher is forced to go beyond its design parameters, it can easily stress parts of the machine. When a stress like this happens, the lifespan of the machine is jeopardized and will lead to future repairs and failures. These future repairs are not only costly and increase down time and output, but could also result in permanent damage to the machine.
Doing a proper root cause analysis (RCA) on the crusher’s problems will be essential and will help determine future repairs and failures. If there is a reoccurring problem, or an operator-induced problem, identifying these can be very cost effective. An RCA not only helps in curbing the current problem, but also in forecasting the potential of an incident. Thus, preventive or other measures can be implemented well before there is a problem with the crusher. There are many different techniques and tools for conducting an analysis such as researching data, testing the operator’s skills and knowledge, and inspecting the machine and end product on a daily basis, as well as analyzing the machine placements, the environment, and the maintenance schedule. Many manufacturers would agree that most of the problems that occur with crusher maintenance could be prevented by on-site employees who are properly trained. This training should occur either one on one or in a group session and at a variety of levels, including a manufacturer-sponsored training event. Employee training should be current and recorded so the employees are credited for their new skill set. Employee training should be done on an ongoing basis so it stays fresh and current.
Rock crushers have, essentially, three types of maintenance needs: preventive maintenance (PRE or precautionary), predictive maintenance (anticipating), and reactive maintenance (responsive). Familiarize yourself with the maintenance needs of your rock crusher and make a plan for those needs. These maintenance plans may or may not come directly from the machine manufacturer.
Preventive maintenance is found in the manufacturer’s maintenance manual and should be the rule in all cases. Visually inspect all wear components such as wear liners, as well as any and all consumables. When you do not change the liners in the crusher and they become less efficient, you will be losing money because of poor or out-of-spec product. Another key problem might be that oversized or out-of-spec material is allowed to re-circulate in the closed circuit, which then increases the load on the crusher. Just remember the maintenance manual from the manufacturer should be your guide for the life of your crusher.
Predictive maintenance is the type of maintenance done while the unit is operating. Many different types of predictive tools can be used to do this type of maintenance. These include lubricating oil thermometers, lube oil pressure gauges, lubricating oil filter condition indicator devices, lube oil analysis, crusher drive motor ammeter, and daily operator crusher log sheets. By using these tools, you can determine the normal operating specs of the crusher, and this will show when things are not running properly and allow for corrective action to occur.
Reactive maintenance is the most costly type of maintenance and should be avoided at all costs. This maintenance is performed when the machine is not operating within its specifications and a determination is made that maintenance is needed. This will not only involve cost for an individual repair and/or part, but will involve the downtime of the machine. This type of maintenance can be costly; it should be seen as a last resort to the problem.
Lastly, remember that operators should always consider safety as a part of their routine. Every job you do has the potential to result in serious injury, so make sure all maintenance plans ensure safety is the top priority. Identify all hazards and make sure all operators know what their role is in the safety of maintenance procedures. Block out all components against movement and tag out equipment when necessary. Always use a “what-if scenario” to anticipate every possibility, and make sure all operators are trained in this and have a plan for each event. Most importantly, make certain the team always uses proper safety equipment and is trained in that equipment. Using a crusher maintenance program will not only save you money and time, but quite possibly a life. It’s that important. AM
Cone Crusher Guidance
Bowl float (aka: ring bounce or upper frame movement) — Most cone crushers employ a tramp iron relief (TIR) system to allow the passing of an “un-crushable” should it enter the crushing chamber. This is typically accomplished by absorption of the energy through hydraulic cylinders, accumulators, springs, or relief valves. These systems are NOT designed for continuous overloading. This is all too often seen due to misapplication of the crusher outside of its designed operating parameters, such as reduction ratio, liner configuration, excessive fines, etc. The most common problem is simply operating the crusher at too small of a closed-side setting.
Horizontal Shaft Impactor (HSI) Do’s and Don’ts
• Do check the rotor for wear after making a speed adjustment. Checking the rotor for wear will ensure that you are not over-penetrating and wearing the rotor.
• Do check for excessive horsepower draw or loss of production after making an apron (curtain) adjustment. Improper curtain settings can cause high horsepower demand and low production rates.
• Do provide well-graded input feed to the crusher. This will maximize production while minimizing wear costs.
• Do properly prep the feed when crushing recycled concrete with steel. This will reduce plugging in the chamber and blow bar breakage.
• Do monitor the wear in the crusher daily. Abrasive material, tight settings, and uncrushables can accelerate wear.
• Do make adjustments for the aprons in small increments. Smaller adjustments allow you to achieve the desired results quicker.
• Do lubricate crusher bearings daily per the manufactures recommendations. New grease keeps dirt out of the bearings and extends bearing life.
• Do flip the blow bars before they are less than 3/4-inch above the rotor. Be sure to readjust the aprons before operating the crusher.
• Don’t exceed a reduction ratio of 12:1 to 18:1. Excessive reduction ratios reduce production rates and shorten crusher life.
Vertical Shaft Impactor (VSI) Do’s and Don’ts
• Do operate the VSI with properly balanced wear liners. (Imbalance in the rotor can cause high oil temps and bearing failure.)
• Do operate the VSI with a proper lubricating oil level in the tank. (The tank allows the oil to cool and keeps condensation from forming.)
• Do operate the crusher with the anvil ring/rock shelf centered in the flow of material. (Misalignment will cause premature wear on the lid and tub.)
• Do operate the VSI at the right speed needed to balance the product gradation and wear costs. (Incorrect speed can result in higher wear rates and reduced product efficiency.)
• Do feed the crusher at full capacity to maximize production and minimize wear costs.
• Do inspect the crushing chamber daily for broken and worn parts.
• Do use a magnet on the VSI feed conveyor to to remove any tramp iron that may enter the system. (Parts broken by tramp iron can lead to catastrophic failure.)
• Don’t operate the VSI with a larger clearance than 1/2 inch between the bottom of the accelerator and the top of the pedestal skirt ring. (This can damage the pedestal.)
• Don’t operate the VSI with a gap larger than 3/8 inch from the feed tube to the top of the accelerator. (This will allow wear on the top of the accelerator and introduce shock loading into the bearings.)
• Don’t introduce water directly into the VSI. (Moisture accelerates the wear in the VSI.)
Top Maintenance Tips for Rock Crushers
Comprehensive daily inspections — Daily visual inspections will catch the majority of impending failures that could cause unnecessary and preventable down time. The pressure of business demands and operational commitments often thwarts good preventive maintenance practices. However, operations with the best, well-managed maintenance plans have proven that preventive maintenance pays over a reactive style maintenance plan. Visual inspections should be performed inside areas that can’t normally be seen such as crusher discharge areas, drive guards, and inspection covers. These inspections can identify such things as wear, build-up, and loose/missing components that could be damaged just waiting on the right “inopportune” moment to shut your plant down.
Housekeeping/material build-up — Build-up of material is nearly inevitable in the aggregate business. It will find its way in guarding, shrouds, and any horizontal surface on framework. Especially when the material is wet or sticky, it can build up in places where an operator will not normally see without further inspection. If left ignored on conveyors, it will take out rollers, head/tail pulleys, and rip belting, as well as cause tracking issues, but it won’t take long before it will cause severe damage to a cone crusher. The crusher doesn’t just have to stall out due to a plug-up to cause damage. Wear can also occur due to build-up in the crusher discharge area.
Contamination (fuel/hydraulic/oil) — Are you buying dirty fluids? In many cases, the fluids you buy may not pass a contamination analysis for particulates or even water. Bulk fluids going into your storage tanks should be pre-filtered when you get them, and again when servicing the unit/model. The days of transferring oil out of an open bucket are over. Don’t overlook fuel contamination. As emission standards push engine producers to make cleaner burning diesel engines, fuel atomization is accomplished by very high pressure injector systems. Contamination in these systems will cause extensive and expensive damage. Invest and believe in an oil analysis/preventive program.
Misapplication — Operating a crusher outside of its designed operating parameters can cause damage internally without it being readily visible. Failures can occur long after the abuse has occurred. Expect a reduced lifespan of components if a machine has been operated beyond the application for which it was designed.
Manganese wear liners wearing beyond scheduled replacement — A manganese wear liner should be considered worn out when its weight equals 40 to 60 percent of when it was new. Depending on the lifetime application, a liner may wear thin (or wear through) in certain areas before the 50-percent lifecycle has been reached. For this same reason, the liner may develop a crack or become loose before the designed liner lifespan. Daily visual inspections are critical for monitoring for loose/damaged/worn liners to prevent further damage to the crusher liner seats and retention components.
Crusher discharge/feed — The crusher will fill with material, plug, and stall if operated with the discharge belt not running. Often times, this conveyor is not visible to the operator. An operator should NEVER restart the crusher without a thorough inspection inside the discharge area and verification of damage or material trapped between the wedge plate (eccentric) and the cone head. They should turn freely of each other with consideration given to the anti-spin mechanism. There should be adequate clearance for the discharge material to exit and transition out the discharge belt. Also, it is important to keep the drop height of the feed into the crusher to a minimum distance and that it is centered. It may be necessary to install a rock box or rock ladder.
Keep daily records for trending — Keep daily written logs of as many critical items as possible. By proper written trending, preventive measures can be identified and planned before a costly failure occurs. Typical things to monitor are normal operating temperatures, lube oil flow (GPM), lube oil filter restriction, crusher coast down time from shutdown, running amps empty, and amount of oil used/added.
Cold weather start-up issues are preventable — One of the biggest benefits about roller bearings is the ability to operate at a wider temperature range. A roller bearing cone crusher’s ability to start is not limited by a “minimum operating temperature,” but is typically limited by the ability for the lubrication pump to provide sufficient minimum oil flow. This is seen as tripping of the current overload breaker for the lube pump or too low of oil flow to meet the flow trip setting and the alarm continues to sound. Common solutions are: cover the crusher opening to retain heat during shut-down periods, change to synthetic oil, and install/use an after-hours oil recirculation kit.
Use the correct lube oil — Don’t go cheap when it comes to the life-blood of a crusher. Stick to the manufacturer recommended oils and brands. There are many emerging oil manufacturers making lots of claims of higher performance, but remember, it won’t be the oil company standing behind you when you have a failure. The EP (extreme pressure) additive package specified in roller bearing cones is critical.
This article is courtesy of KPI-JCI.
E. Bradford Pugh is the marketing communication manager for Bridgestone Americas, Off Road Tire Division.