Declining Ore Grades Challenge Primary Gyratories
OEMs modify machines to make them safer and easier to maintain
By Steve Fiscor, Editor-in-Chief
Miners looking to process huge amounts of ore have to strike a balance between capacity and product size. Ideally, a single, massive PG could maintain a very high capacity while providing a consistent small product size. In the real world, however, a tighter setting on the largest PGs means less ore moves through the machine volumetrically. Adding multiple machines would maintain the desired capacity levels, but it also increases capital and operating costs.
Even though the principles related to PGs have not changed much, the way the miners interact with the machines has. Obviously crushing mountains of rock takes its toll on these machines. The original equipment manufacturers (OEMs) are striving to improve maintenance methods. The safety of the people maintaining these machines is paramount. The cost of maintenance, the direct expense and the impact of downtime, is an important consideration. Technology has advanced to the point where all of the machines are delivered with software and control systems that allow them to interface with humans and other controls and machines.
The OEMs have seen demand for PGs rebound from a lull in 2009. Business was brisk prior to the global financial crisis and now demand is again returning to those 2007-2008 levels and so are the lead times for the delivery of new machines. The problem is the large castings. A single piece weighs 50 to 100 tons and only a few foundries can make these castings. All of the OEMs say to expect at least a one-year wait and, in some cases, that lead time has now grown to 16 months or greater.
As far as market share, Metso Minerals is largely viewed as the leader and it has the largest installed base of PGs, but competitive companies have made significant inroads. "Reports indicate that we had lost a little ground to some of our competitors in South America," said Ivan Pavlovic, director of mining crusher capital projects, Metso Minerals. "When markets were taking off in places like Peru and Chile, the competition gained some ground. We have since reorganized with a merger and placed more emphasis on winning back the market share we lost."
Metso has received some large orders recently. At times like these, there is a certain frenzy to get these large production projects online quickly, Pavlovic explained. "There seems to be a steady demand for all sizes of PGs and we do very well in all parts of the world," Pavlovic said. "Lead times are manageable. The lead time for larger machines are a little longer. Customers can rest assured, when their project comes online, the PG will be available. We're looking at a year right now."
PGs are big machines without a lot of differentiation between manufacturers, Pavlovic explained. "Having some special features helps, but in the end, it comes down to delivery time and price," Pavlovic said.
"For most customers, when it comes to trying to size these machines and determine the settings, it has really become a shot in the dark because of the ore grade," Pavlovic said. "The engineers rely on modeling and simulation and the models are often very good, but they do not always accurately predict grades and particle distribution.
"For mines processing large quantities of low-grade material, the semi-mobile concept has become a more important option because it allows these operations to bring production online as soon as possible," Pavlovic said. "Depending on how the systems are configured though, it's not always the most cost-effective solution."
If a mine needs to add significant capacity, the logical decision would be to install two units. "That would be easier than designing and building larger units," Pavlovic said. "What's available now is good enough, the mines should employ multiple units to increase capacity.
"For the semi-mobile installations, lowering the unbalanced forces has become a priority to reduce the dynamic forces and minimize the amount of steel used," Pavlovic said. "We have modified the machines to meet those needs."
In an effort to extend the times between liner changes, Metso has developed special alloys for the concaves. "We also have special designs where we combine rows or combine adjacent concaves to reduce the downtime involved with replacing the concaves," Pavlovic said. "We have increased the life of liners by three times that of the normal manganese liners. To further reduce the downtime, Metso has improved the method of installing concaves. We supply platforms to help the miners drop the entire liner into the crusher, rather than placing each concave individually."
Today Metso is concentrating a lot of its efforts on the maintenance aspect of these machines. Down the road, Pavlovic believes the industry will be seriously looking at a different concept, not a big departure machine-wise, but a huge improvement in the area of service and maintenance.
Balancing Capacity with Product Size
"We have seen an increase in single mine requests for multiple high-capacity machines," said Mike Wanyo, product manager-primary crushers, FLSmidth Minerals. "The overall capacities have become quite large. In the past, we were surprised when customers requested more than one machine. It is not uncommon today to receive an RFQ for two and three machines all at once."
Wanyo also believes there is a practical limit as to the ultimate size of the machines mainly from a manufacturing perspective and the fact that the mine operators need to minimize their risk by using proven technology. "There does not exist a single machine big enough to handle these large capacities, so the mines usually opt for multiple machines. In many cases, the operations were justified on a certain level of throughput. Rather than pursuing a new machine design that is not already in operation, the mine owners are staying with proven technology."
Additionally, in the last five years the end users and process designers are requiring smaller product sizes from the PG in an effort to reduce the SAG mill feed size. Prior to this, 60-in. PGs would be supplied with an 8- or 9-in. open side setting that gave a P80 in 7.5- to 8.5-in. range. Today, the engineers request a P80 of 6-in. or less. "Some are as low as 3.5 to 4 in., which is not practical for a large primary gyratory crusher. Trying to generate these small product sizes compounds the concerns with trying to produce the high hourly tonnage rates," Wanyo said. "We usually have to assess what they need and explain that some of these settings are simply not feasible for that large of the machine. If they want the capacity, they are going to have to open the settings. So the industry is returning to more historical settings on the machines mainly in an effort to reach the capacity which sacrifices a bit on product size."
On the design side, FLSmidth Minerals has been striving to improve maintenance and the ability to perform maintenance more safely. "Our greatest advancement has been the Top Service (TS) design," Wanyo said. "That allows all of the major components of the machine to be removed from the top as opposed to going under the machine through the discharge bin to take out the hydraulic cylinder or the eccentric assembly. This design has a double benefit by greatly improving the level of safety during maintenance activities and it has decreased the time required to perform them."
Additionally, FLSmidth Minerals is continually reviewing designs with its field service engineers and customers to seek areas of improvement, Wanyo said. As a result, the company is currently making changes to the head nut area on the main shaft assembly. "This may seem insignificant, but it is an important topic to the people who are involved with maintenance," Wanyo said. "These changes will also be retrofittable." Wear life in terms of grams of liner lost per ton of ore produced has not changed significantly, according to Wanyo. He said he has seen an increase in the number of miners using the concaves with alloy-material. "The wear rate is similar to that of work-hardened manganese, but if the mine has very fine and abrasive ore, the standard manganese will not work harden, but rather abrade away," Wanyo said. "Because the mines need the availability, they will install 400- to 500-Bhn alloy concaves. It doubles the life of the concaves and decreases the number of replacements per machine."
The FLSmidth Minerals theory regarding maintenance, Wanyo explained, has been: "If you cannot design the component to last longer, make it easier to replace." To meet that need, FLSmidth Minerals offers work platforms and jigs with the PGs to increase the level of safety during wear-part replacement. The platform also decreases the time it takes to perform the job. "By using the platforms, they have reduced their concave replacement times by 25%," Wanyo said. So instead of 48 hours to replace the concaves, they have reduced that to 36 hours.
As far as control systems, all of the product groups within FLSmidth Minerals are now working directly with the FLSmidth Minerals Automation division to develop and improve the control systems, Wanyo explained. "In the past three years, they have developed sub-control systems for each type of equipment," Wanyo said. "These sub-control panels can be used on individual machines and then, if FLSmidth Minerals Automation supplies the overall plant control system, the individual systems report to the higher control system. Instead of having a third party creating the control logic, the programmers are sitting in the same building as the machine designers so the control logic details can be worked out efficiently and correctly." With an overall FLSmidth Minerals Automation plant control system, FLSmidth Minerals can remotely monitor and troubleshoot all levels of plant activity from multiple global locations.
During the past few years, ThyssenKrupp has gained considerable market share in Asia and Australia. The company recently received an order for five gyratory crushers from Freeport Indonesia. Similarly, Detlef Papajewski, head of product division crushing technology, ThyssenKrupp Fördertechnik, receives similar requests to accommodate more capacity. The engineers at ThyssenKrupp are looking at ways to increase PG throughput, which would involve much larger drive sizes. "We have installed new gear sets, which allow much higher torque," Papajewski said. "We have been doing this with great success for the last few years now.
"We have also improved the overload protection between the crusher motor and the crusher," Papajewski said. "If a blockage occurs, such as shovel tooth, a hydraulic safety clutch separates the crusher from the drive train, which protects the motor."
ThyssenKrupp has been working on a number of improvements. From a maintenance aspect, they are looking at new ways to improve the oil cleaning process for the lubrication system. That extends the time between oil changes, doubling it from six months to one year. "More importantly, the system better protects the slide bearing," Papajewski said. "Particles in the lubrication could do significant damage and shorten the life of the bearing.
"Another advantage to our design is that we have separated the lubrication for the pinion assembly from the lubrication of the slide bearing," Papajewski said. "If the slide bearing has experienced troubles with particles in the return oil, this does not affect the very sensitive roller bearings found in the pinion assembly. We have a separate bath lubrication system for the pinion assembly."
ThyssenKrupp has taken a different approach to the liners. "We have been working to improve the concaves to reduce the number of rows in order to lower downtime," Papjewski said. "In some cases, when the PG is not running, the whole mine is down. We are looking at ways to reduce the downtime associated with replacing wear parts. We are also looking at ways to improve how maintenance is performed and to make it as safe as possible."
The GyroMatic control system controls all of the minimum features needed to run a ThyssenKrupp crusher in a safe manner. "We have found that, if the control is managed by a general PLC and there is a mistake in the program, it can lead to big failures on the crusher," Papajewski said. "We are supplying all of our PGs with this control software free of charge. ThyssenKrupp PGs have a separate PLC that interacts with Siemens, Allen-Bradley, etc. It minimizes programming risks and it also has a bus connection to provide all of the information to an external PLC.
"The GyroMatic also provides feedback to ThyssenKrupp in case the customer would like us to assist with any questions," Papajewski said.
Building on a Proven Design
In 2007, Sandvik signed an agreement with Earth Technica, a division of Kawasaki Heavy Industries, to license, manufacture, sell and support its line of gyratory crushers. In the 1960s, Japan's Kobe Steel became a licensee for the Allis Chalmers (AC) line of primary gyratory crushers and eventually transferred the line to Kawasaki. Through the years, Kobe Steel made many design changes before it became Earth Technica.
Shortly after Sandvik added the Earth Technica primary gyratory to its product line, the global financial crisis delayed many mining projects around the world. Sandvik did not pursue implementation of this new product aggressively, explained Vladimir Novak, product line manager gyratory crushers, Sandvik Mining & Construction. "Despite the market downturn and the general trend of projects being placed on hold, we were able to sell four primary gyratory crushers," Novak said. "One of them was placed at Tata Steel in India and has been operating for a year now. We are currently installing machines in Finland, the U.S. [Arizona], and Mauritania."
A gyratory is a gyratory, explained Novak. "With similar designs, they have almost become a commodity," Novak said. "Some areas require more attention, such as the spider bushing area. Everyone uses this hourglass shaped bushing with linear contact. It's a wear item that's not easy to access and control. If this bearing wears out, it will create more problems below in the eccentric bushing area of the crusher."
Sandvik responded with a spherical bearing for the spider bushing. "This design has a large area of contact and spreads the forces evenly," Novak said. "It is very reliable and requires almost no maintenance. Kawasaki began to use this particular design in the early 1990s. To date, not a single bushing has been replaced."
Sandvik's automation system consists of two components. The company's ASRi software controls the position of the main shaft. It tells the operators the position, open side setting, wear liner life, etc. Using the ASRi software, miners can create profiles for different crushing applications. An instrumentation monitoring system protects the crusher from overloads and pro-vides opportunities for trending data.
Most of the industry operates primary gyratories by the open-side setting. That works well most of the time, Novak explained. "If the mine cannot deliver ore to the crusher consistently, it's either working like it should or the chamber is empty," Novak said. "That can be difficult on the manganese liners. After hard working, the liners attain a hardness of more than 450 Bhn. Sliding conditions inside the chamber shave off the hardened layer and the liner wears prematurely."
For those types of conditions, Sandvik's automated system can operate the crusher by power consumption. It would close the open-side setting. The crusher would lose capacity, but the mine operator would not care at that point. The chamber would be filled. The product would be crushed to a finer consistency, which helps with downstream processes. It also eliminates the shaving action.
With tighter environmental regulations, oil spillage is a concern. One of the basic maintenance procedures is to inspect the return oil screen to see what type of debris is in the lube system. Traditionally, when the mechanic would open the valve, it spills and it's sometimes a hazardous situation. The Sandvik design is similar to a drawer in a desk, turn the bypass on, pull the drawer out, and inspect the screen. "We also have a standby lubrication system, filtration unit and pump," Novak said. "Technicians can replace the filters with no extended downtime for the crusher."
The Sandvik PG has mechanically attached concave liners for the top shell. "Once gravity-held liners are put into position, no one wants to move them," Novak said. "It's difficult to properly position gravity-held concave liners around the circumference of the top shell. The spacing on concave liners often deviates. When the upper hard manganese layer starts sliding over the soft layer, it closes the gaps between the concaves. The concaves then push out of position.
"We have mechanical fasteners that hold concaves to the top shell," Novak said. "It's not just the extra security of holding the concave to the top shell, but also guarantees proper spacing between concaves, eliminating the dangerous situation of closing gaps."
Weekly or biweekly someone has to inspect the gaps. If they are closed, someone has to climb inside the machine and trim the edges of the concaves with a torch. It's not just a mainte-nance issue, it's a safety concern. Because of the even spacing between concaves, you will not see this type of wear premature-ly. The tapered fit between shell pieces of the crusher hold the machine together. "We have 10-mm shims between spider and top shell flanges," Novak said. "If the tapers are worn, mainte-nance crews can remove the shims and reclamp the crusher and operate it for another year or so. No need to panic and repairs can be scheduled when it's convenient for the mine."
Sandvik's first PG, the unit installed at Tata Steel, replaced an FLSmidth machine of a similar size, Novak explained. "Our machine increased capacity for them by 1,000 mt/h," Novak said. "We removed the old crusher, installed an apron feeder and the new crusher in 19 days with no incidents. A normal installation takes 30 to 45 days."
Realizing the need for specialized product support, Sandvik recently created a competence center to support PGs in Milwaukee. "We will establish a global product support center and this is just the beginning," Novak said.