Keeping Crushers at Work
In most mines, crushing provides the gateway to mineral recovery, and proper maintenance is the key to reliable crusher operation
By Simon Walker, European Editor
As with any piece of equipment, lubrication is one of the most importance aspects of machine maintenance. Any failure of the lubrication system can have catastrophic consequences, very quickly, as bearings and other rotating parts begin to wear, then break down or seize. In addition, damage to the wear surfaces within the crusher chamber can rapidly lead to cracking and even disintegration unless appropriate remedial work is undertaken urgently. Hence, careful inspection must be a key part of any maintenance program, as well as ensuring that lubricant levels are correct and that the lubricants themselves meet the crusher manufacturer’s specifications.
To provide an up-to-date view on the essentials of good crusher maintenance, E&MJ asked a number of the world’s leading crusher manufacturers, lubricant suppliers and wear-parts specialists for responses to a questionnaire covering a range of maintenance-related issues. From the crusher manufacturers, views and advice were provided by Daniel Svensson, FLSmidth’s global product line manager for cone crushers; Mark Kennedy, senior technical training instructor at Metso; and Mike Schultz, crushing product manager for Superior Industries. Other crusher company perspectives came from Brian Taylor, product lifecycle manager for Telsmith; Fredrik Rosdahl, global operational manager, services at Sandvik; and Eric Jones, global service director for comminution aftermarket at Weir Minerals.
Jeff High, McLanahan’s global product manager for crushing and screening, also contributed his thoughts, as did Daniel Narnhammer at Klüber Lubrication’s global competence center for mining, and Bret Jenkins, director of mining sales at Calumet Specialty Products Partners. Doug Henderson, product engineering manager at Columbia Steel Casting, provided E&MJ with his thoughts on crusher wear-part issues.
The Key Considerations
Asked what the most important aspects of mining crusher maintenance are, FLSmidth’s Svensson said, quite simply, “Safety is No.1 — it’s the most important. As manufacturers, we are always working to make maintenance easier, quicker and safer, removing high-risk tasks and designing crushers so that as much of the maintenance as possible can be done outside the machine.”
Kennedy (Metso) looked at what is needed for good maintenance practice. “Many mines will continue to experience decreased profit margins, partly because their maintenance team does not fully understand the maintenance requirements of the crushers that they are responsible for,” he said. “There are different types of crusher maintenance that must be thoroughly understood, regardless of the type of crusher being used.
“A key component in maximizing the crusher’s lifespan, preventive maintenance is the best method of keeping a crusher in good operating condition for a long period and will include scheduled checks, inspections and services at regular time intervals (daily, weekly, monthly, yearly), as recommended by the crusher manufacturer.
“Predictive maintenance — monitoring the condition of the crusher while it is in operation — uses tools such as lubricating oil temperature and pressure sensors, crusher coast downtime, no-load head spin, lube oil analysis reports, crusher drive motor power draw readings, vibration sensor readings and completed daily operator crusher log sheets. These tools can be used to help learn and understand the crusher’s normal operating condition or characteristics, against which any data that appear to be abnormal would indicate a problem and warrant closer investigation. Making a crusher repair based on an abnormal operating condition will always be considered cost-effective,” Kennedy stated, noting that if preventive and predictive maintenance is ignored, the crusher will experience poor online availability, incredibly high operating costs and a shortened life span. “Implementing a preventive and predictive maintenance program is a key factor to extending or maximizing your crusher’s life,” he said.
Aside from daily inspections, crusher maintenance used to be labor-intensive, hard work, especially when major components needed overhauling. Working in a restricted space surrounded by heavy metal is not the ideal way to achieve high-quality servicing, conditions that are even more testing when heating or flame cutting is needed. Recognizing that simplification is a key route to getting the job done quicker, safer and at lower cost, crusher manufacturers have focused on introducing technologies that help make this happen.
Kennedy summarized what has been achieved. “Manufacturers have made crusher safety a high priority in recent years. Not only have significant improvements been made to the crusher itself to make maintenance safer and easier, but there have also been lifting devices, component stands and special tooling designed and supplied with crushers in order to make all areas of crusher maintenance safer.”
High (McLanahan) noted that crushers now have lock-out pins to hold a jaw-crusher pittman or the rotor assembly of an impactor in place to prevent movement during service. Looking at cone crushers, Jones (Weir Minerals) observed that while earlier models were designed with spring packs on the outside of the machine, most manufacturers have introduced advanced hydraulic systems to raise, lower and adjust the machines safely with minimal effort.
“With current jaw-crusher designs, manufacturers have moved to hydraulic adjustments, hydraulic-tension rod nuts and a hydraulic tramping system,” he explained. “Hydraulically adjustable wedges or cylinders and hydraulic-tension rod nuts have removed the manual process of loosening/tightening the tension rods and have replaced the practice of hammering in and out toggle wedges and lifting shims in and out from the toggle area.”
Rosdahl pointed out that Sandvik can now provide tailor-made lifting tools for all of the complicated lifts needed during crusher maintenance, including internal parts and wear parts/crushing chambers. “Our design philosophy has a strong focus on service from the top, allowing access for safer lifts with overhead cranes and minimizing work in confined spaces,” he said.
Taylor (Telsmith) looked at the bigger picture: “The advent of automation has provided operators with daily reminders and trend data to assist in scheduling downtime for planned repairs.”
Primary gyratory and cone crushers use a circulating oil system to keep bearing surfaces within the crusher both lubricated and cool, while the main bearings of a jaw crusher are typically lithium-base grease-lubricated. E&MJ asked the question: “How important is it for crusher operators to use specific lubricant grades?”
All of the respondents were in complete agreement, as summarized by Klüber’s Narnhammer. “It is extremely important for crusher operators to use specific lubricant grades,” he said. “Oils and grease must provide the best bearing protection possible. Therefore, lubricant manufacturers design their products specifically for the needs of heavy mineral processing equipment. As a result, greases with high-base oil viscosities and additive packages are developed to protect from shock loads, high Hertzian pressure and high vibrations.”
Kennedy agreed. “On oil-lubricated crushers, using the correct lubricant assures proper load-bearing capability between all the bearing surfaces within the crusher,” he said. “On jaw crushers, where the bearings are typically grease-lubricated, not only is it important to use the proper grade grease, but the quantity of grease used becomes a critical factor.
“Under-greasing or over-greasing antifriction bearings has a detrimental effect on the service life of that bearing,” he warned. “Additionally, never under any circumstances would a molybdenum-based grease be used, as this type of lubricant could damage the anti-friction bearings used in a jaw crusher.”
Narnhamer asked, “Would you risk a breakdown or bearing replacement due to an incorrect lubricant purchased based on price alone? An incorrect or inferior lubricant cannot protect the bearings, isn’t pumpable at lower temperatures, does not generate the sufficient film thickness in the bearing, and thus causes high wear or energy loss. The key is proper lubricant selection.”
Timing of lubricant changes can also be important in terms of maintaining the material’s effectiveness. “For gear oils, the timing is dependent on temperatures since heat affects the oxidation of the oil,” said Jenkins (Calumet). “Grease is used as a seal as well as a barrier between two moving parts, so having the right amount of flow in the grease is paramount.”
Narnhammer added, “Since grease stays in a bearing for only a short time period, it’s lost lubrication. Mineral oil can have a life of up to a year and half, while PAO (poly-alpha-olefin)-based synthetic oils, two to three years, and polyglycol- based synthetic oils up to five years. All of these lifespans will depend on the degree of contamination, and the maintenance of the lubrication system, as well as the actual operating hours.”
And contamination, of course, can be a significant factor in how well lubricants perform, especially in hot, dusty conditions. Nonetheless, Svensson told E&MJ that he is more focused on sampling oil for signs of wear on bearings and bushings than for external material that may have found its way in to the lubrication system. Dust particles can be cleaned from the oil by filtration, which, as Narnhammer suggested, needs to be done regularly. “The filter type (filter pore size) has to be chosen correctly in consideration of the maximum achievable lubricant film thickness and the possible contamination type — which unwanted minerals are present?” he said.
Watching Wear Parts
While a crusher may do the work, its wear surfaces take the immediate pressure and force within the crushing chamber. “While doing maintenance, it is important to check on the general condition of all wear parts, looking for damage or accelerated wear,” advised Columbia Steel’s Henderson. “If wear life is tracked by weeks, months or years, it is easy to increase production or change the material being crushed, and end up with a very different life in weeks or months that may come as a surprise if you are not monitoring the wear.”
“My advice would be to change the crusher liners on time, at the right time, every time,” said Kennedy. “The biggest mistake I see mining customers make in regard to wear parts is attempting to get more life out of them than they are designed to provide. I understand that wear parts can be a significant cost of operating a crusher, but pushing liners longer than recommended generally has a detrimental effect on productivity and can lead to mechanical problems with the crusher.
“When a wear part is found to be damaged — cracked, broken or abnormally worn — or if a wear part appears to be loose, the operator should shut the crusher off immediately and report the problem. A supervisor then can assess the situation and ultimately determine if the crusher can continue to operate safely asis, or if the damaged part creates a significant safety risk to the crusher operators or of doing additional mechanical damage to the crusher.”
“If the part is damaged to the point that complete failure is likely, then it must be replaced,” confirmed Henderson. “If it has sufficient strength, can it still perform its function? If it is sound and functional, then it can probably be used but needs additional monitoring to see if the damaged area is wearing normally with time, or getting worse, or channeling more material through it and experiencing accelerated wear.”
Svensson looked at the practicalities of liner maintenance. “From a production point of view — especially with big gyratories — speed is of the essence,” he said. “Features such as hydraulic nuts to simplify removing the spider, and pans that can be lowered into the crushing chamber once the main shaft has been taken out so that whole liner rings can be lifted as one — these are the sorts of things that make liner replacement quicker and safer.
“And the same goes for cone crushers,” he went on. “Modern designs make it easier to remove and replace wear parts, without the need for hot-work permits.”
Poor Maintenance Leads to Problems
All of the respondents to E&MJ’s questions agreed with this statement. “If you don’t do the checks, you will have problems,” stated Svensson. “The sad fact is that all too often, operators don’t take their daily inspections seriously enough. It’s all about housekeeping; looking after the machine.”
“Unfortunately, preventive and predictive maintenance is either completely misunderstood, improperly performed or is just flat out neglected at many locations,” agreed Kennedy. “In addition, over the years, an alarming number of mine mechanics have simply been turned into ‘parts changers,’ tasked with changing a broken or failed part instead of identifying and eliminating the root cause of the problem.”
“Maintenance is so often something operators must do outside of their normal business of crushing and screening,” Taylor observed. “All maintenance should be completed on a regular schedule and become part of operational planning. Where mines have separate operations and maintenance crews, there must be synergies between the two teams. Operations must make time for maintenance, and they must strategize together for the overall success and longevity of the equipment.”
As for the consequences, he went on to list some of the potential results of improper maintenance: Damaged bearings and bronze sleeves, and failure of the eccentric and main shafts, as well as housings, spacers and main frames. Inadequate hydraulic system maintenance can lead to contamination, while heat tends to lead to the failure and eventual replacement of contaminated hydraulic items. Proper maintenance — such as servicing breathers and following hydraulic oil replacement guidelines — eliminates most issues.
Wear parts can also be affected if maintenance is not up to scratch and potential problems are not observed. Henderson told E&MJ that he has seen damage from tramp iron (uncrushable material like tooth points and adapters) being run through crushers. “On gyratory crushers, we sometimes see damage in the upper rows of concaves from rock breakers being run on the concaves instead of rock,” he added. Whatever the cause, damage must be evaluated quickly, and the appropriate action taken before things get worse.
As far as cone crushers are concerned, Rosdahl explained that the technology exists to help protect the crushing chamber from tramp damage, citing the example of Sandvik’s electric dump valve system, which, the company claims, can deliver the quickest tramp-iron protection currently available. Checking the hydroset pressure 200 times per second, the system instantly drops the main shaft if the pressure rises above a preset limit, while notifying the operator that the crushing chamber is opening and that the tramp material must be removed from the circuit. “An event log of all control operations enables operators to take preventative measures upstream and corrective measures downstream, helping them to avoid costly equipment damage,” he pointed out.
Improving Maintenance Practice
E&MJ asked the respondents what they could suggest for situations where they see poor maintenance practice. “Don’t hit the panic button,” advised Taylor. “It can be a bit overwhelming at first. Get a handle on all the issues, walk the plant and use the 5-L approach — Look, Listen, Log, Locate and Lubricate. Look for the obvious immediate attention items: liner wear, transfer points, missing hardware, structural issues and so on. Listen to the plant at startup, shutdown and while running. “Log all these known plant issues immediately, and make sure this log is communicated and visible so that everyone knows what needs attention in case you do have an unscheduled shutdown. “Locate and schedule the resources including your materials, components and labor needed to perform these repairs. Also locate the equipment manufacturers’ recommended lubrication and maintenance schedules. And lubricate — probably the most important part of the 5-L approach. The right lubricant, at the right time with the right amount.”
Taking things back to basics, Kennedy pointed out that cost-effective maintenance techniques begin with workers who are knowledgeable about the maintenance requirements of the crushers to which they are assigned. “The simplest solution to such problems is continuous professional training for the entire maintenance teams who work on crushing equipment. Depending upon the severity of a training gap within the organization, the solution can be relatively simple, or extremely difficult, but in no case will it be easy,” he noted.
“To be effective, education in the maintenance of crushing equipment must be kept current, and must be ongoing. Mine operators who incorporate technical training into their yearly activities have the ability to reap the benefits of increased productivity, increased crusher availability and decreased maintenance costs.”
It is, of course, in manufacturers’ interests to ensure that their customers’ machines operate as efficiently and cost-effectively as possible. As a final question, E&MJ asked the panel of experts for their views on technology developments that will help improve crusher maintenance even more in the future.
Rosdahl: “Sandvik has taken many steps already. One example is our interactive training and maintenance material on a USB stick — included in our training programs. This contains detailed information on how to service, overhaul and troubleshoot a crusher. Drawings, pictures and movie clips from real life show how the service should be performed hands-on.
“Machine connectivity is another area of interest. Connected machines that allow us to support remotely, and enhanced condition monitoring to improve predictive maintenance, will help customers in the future,” he added.
From Telsmith, Taylor concurred: “From a technology standpoint, Telsmith is integrating improved logic and data communications between functional systems like our hydraulic and lubrication components on cone crushers. Enhanced integration provides operators with additional troubleshooting or diagnostic capabilities, easier adjustments and functionality, remote access to equipment from smart devices and some automated maintenance.”
Svensson (FLSmidth): “Future crusher technology will be based on real-time data of wear parts and crucial internal parts. Machines will be linked to a cloud where all the big data can be stored and analyzed to extract the information needed to analyze machine health.”
Kennedy (Metso) added that he, too, can foresee remote monitoring or “phonehome crushers” becoming much more popular. “Most mines are operating pretty lean these days, and this may result in their inability to keep tabs on each piece of crushing equipment throughout the day as thoroughly as they should,” he said. “Remote monitoring will allow the manufacturer’s product support specialist to watch the crusher from a distant location and when an abnormality is identified, a message is immediately sent to the mine with suggestions and/or recommendations. Just about any modern crusher can be remotely monitored either by the customer themselves or by the manufacturer.”
Jones: “At Weir Minerals, we envision the advancement of wear parts to extend their wear life, increasing the time between wear parts changeout. This will increase crusher availability further and reduce downtime. We also foresee advanced conditioning monitoring technology playing a big part in the future of crushing. Conditioning monitoring systems can alert the operator to a possible failure, diagnose and change parts out before they fail. It is easier to remove a damaged part than a failed part, saving time and money.”
Calumet’s Jenkins predicted that lubricant manufacturers will focus on going above and beyond OEM’s specifications, by creating lubricants that can protect against the worst scenario, not the most common. “One millisecond of failure is failure,” he reminded E&MJ.
The last thoughts come from McLanahan’s Jeff High. “Future technology will track and give trends to alert customers of upcoming service issues and needs,” he said, before adding a few words of comfort to hard-working maintenance crews. “Robots and drones are not going to replace human beings to perform basic service needs.”