Barrick Gold Corporation maintains 27 operating mines and boasts the largest gold and copper reserves in the industry. Barrick is targeting its 2009 gold production at an approximate 7.6 million ounces and copper production at 400 million pounds. Its Goldstrike property, located near Elko, Nevada, is the company’s largest gold producing operation with an output exceeding 1.65 million ounces annually and an employee roster topping 1,300 workers. Treating ore from one open pit and two underground operations, the Goldstrike mine combines two processing facilities – an autoclave circuit, which treats non-carbonaceous sulfide (refractory) ore; and the roaster, which treats carbonaceous ore.

Idler Rightsizing
Mark Morfin is the wetmill crusher maintenance supervisor for Barrick Goldstrike’s autoclave facility. From initial material feed to final stockpiling, his challenge is maximizing uptime, which is no small feat for a 24/7 operation with a processing capacity of more than 12,000 tons per day from its gyrosphere crushing circuit and 7,000 tons per day from its jaw crushing circuit. As such, Morfin welcomes the right solutions from equipment and component suppliers – ones that will increase efficiency and reduce maintenance requirements while decreasing costly downtime.

For example, he says that a recommendation from Superior conveyor components distributor CIR of Sparks, Nevada, resulted in a significant decrease in maintenance downtime in replacing failed idlers. After consulting with Superior engineers, Morfin switched out his previous brand of CEMA D idlers and upsized to Superior CEMA E idlers on a 60-inch by 150-foot-long belt conveyor which draws material from underneath the gyrosphere crusher. “This belt takes a big beating. The ore is minus-4 ½-inch material, loaded a foot deep. So that’s a lot of weight,” says Morfin. He adds that he is pleased with the new idlers, particularly because they feature a sealed bearing that requires no greasing, and an ability to retrofit to competitor frames or to previous Superior frames.

Downtime Eliminated
Prior to the installation of the Superior CEMA E idlers, Morfin says they would have to shut down the crushing circuit at least once a week just to change out rolls or entire idlers on the heavy duty conveyor. “From just days to a week or two, we were wearing them out. They would start to make noise and then seize up long before the actual roll would wear. It was always a bearing failure,” he says. After upsizing to the CEMA E idler, Morfin says that this downtime is eliminated and he gets the same desired wear life from the CEMA E idler on the heavy duty conveyor as he would get from a CEMA D idler on his smaller systems.

Number Crunching
Selecting the right idler for an application involves much more than mere calculations. “In running the numbers on an application such as the one at Goldstrike, it may indeed be within the CEMA D idler range. But you must also factor in the amount of vibration and impact load, which is what will really change those numbers,” says Jarrod Felton, chief engineer of standard products for Superior Industries. “In this application, the belt is operating from the primary crusher, so there could be significant vibration just from the crusher depending upon how it’s mounted,” he says.

According to the CEMA manual, the main influences in idler selection are belt weight, material weight, idler load rating, belt sag, idler life, belt rating and belt tension. And, proper idler roll diameter, size of bearing, and shaft selection is based upon the load carried, belt speed and operating conditions.

Bullet Proof Bearing Protection
However, in addition to all of the aforementioned parameters, Felton points to the importance of seal design. “What is often ignored is that bearings may fail due to the load, but they may also fail due to contamination – or a combination of both. This is why seal design and technology is so important,” says Felton.

The new Superior Industries CEMA E idler used at Goldstrike is engineered with 40-millimeter precision-sealed ball bearings, which eliminate maintenance labor and grease expenditures while also extending bearing life. Its SpinGuard® seal design technology features improved contact seals that result in less seal drag; triple labryrinth seals that increase the distance that contaminants must travel; and grease fills that easily trap contaminants. The idler is also designed to eliminate pinch points between the end stand and the outside roll, as the pinch points in typical idlers allow foreign materials to lodge within them, causing the roll to seize up.

Bottom line, Felton says there may often be a little trial and error in idler specification. “You just have to take your best shot. However, sticking with the same manufacturer and the same high quality sealing technology as you upsize will ensure that you gain that longer life from bearings with a higher load rating. And, if you have a high enough load rating, you will have little worry. Overkill is less expensive than finding out that the idler is not sufficient enough for the load. While there are other products available to handle impact in the loading areas – such as impact idlers or impact beds – upsizing idlers works well too,” he says.