By Steve Fiscor, Editor-in-Chief
With significant market share in the regions that operate the most draglines, the Columbia Steel Casting Co. knows a thing or two about dragline rigging systems. The company has recently brought two new devices to the market, Mechanically Attached Anchor Brackets and the Armor Block, and the mining business has quickly embraced both. In addition to these products, Columbia Steel is also looking at new ways to improve dragline uptime for mine operators.
The Mechanically Attached Anchor Brackets simplify bracket change out with a base that is welded to the arch once. The bracket slips onto the base and is held in place by bolts. The system eliminates additional cutting and welding on the arch. The brackets protect bolts from shear forces.
The system has been available for two years and quickly became popular with the mines. Many mines in Texas as well as Australia and Saskatchewan are using the system. In fact, some mines are ordering new buckets without anchors and welding this system on at the mine.
“Welding on arches is time consuming plus it puts a lot of heat in the arch, which is a casting, and repeated welding eventually affects the metallurgy,” said Mike Moehnke, district manager, Columbia Steel. “The miners weld these bases on once and theoretically they no longer have to weld on the arch.
“Digging and operating conditions differ from mine to mine, but traditional anchors would last eight months to two years,” Moehnke said. “When the mines decide to change the anchors, they prefer to do it when the bucket is in the shop because it’s a time-consuming process. If the anchor fails in the field, well…it’s usually a lot of downtime.” The Mechanically Attached Anchor Bracket’s universal base can be matched to a variety of arches. Both male and female versions of the bracket have been designed.
The Armor Block is new. These dump blocks have a simplified bearing arrangement that allows more efficient rebuilds, while an enclosed design protects the bearing cavity from contamination. The bearing assemblies should be easier to adjust. The bearings are greased only at build (and rebuild). The system relies on a sealed, dual-row of tapered roller bearings and has been designed for rough duty. They are larger than traditional dump blocks and hopefully they will last longer.
“We have two installations running in Texas,” Moehnke said. “We pulled one set recently to look at the sheave profile. They should be back in service soon. The big advantage with the Armor Block is the bearing setup time. Instead of being a two or three piece bearing arrangement with races, this comes as a pre-assembled kit from Timken. All of the pre-loads are set at the factory. It’s lubed when it’s assembled and sealed. Some mines are lubing dump blocks up to three times per week.”
Most of the machines in North America use a double dump-block arrangement. Wire rope is threaded from the drag socket through the dump block to the anchoring point on the arch. When the bucket dumps, the cable passes through the dump block and the teeth on the bucket drop, dumping the load. When the drag cables are pulled tight, the bucket sits flat ready for the next cut.
“The bearing itself is less expensive, even though it is larger, can carry a heavier load, and simplifies change out when the block has to be rebuilt,” Moehnke said. “Typically the bearings on the dump block would fail within six months to a year. We guaranteed the first units we placed in the field for a year. We don’t know how long they will last.” The current units in the field have only been operating for three months.
Armor Blocks are compatible with the ferrule socket system. Miners can pass a wire rope through assembled Armor Blocks. Some dump blocks must be disassembled first. Tighter sheave-sideframe mating also helps to guide the rope and prevent the ingress of dirt. The weight is similar to standard dump blocks.
The Armor Block is available in four sizes: 26, 32, 40, and 48 inches. They can also be configured in same-plane and opposite-plane designs using standardized pin lengths and diameters, with eccentric bushings at the pin holes.
“Being the world leader in chain manufacturing, we are looking internally at ways to produce the highest quality chain cost effectively and pass the savings along to customers,” Moehnke said. “Beyond chain we are also looking at standardization as a method to simplify rigging systems and parts inventories at the mine sites.”
Columbia Steel helps customers with multiple draglines standardize pin connections. “With one customer, we managed to consolidate six pins per dragline to one,” Moehnke said. “And, that’s not just pin diameter, but grip length as well.
“Over the years we have slightly modified parts and pieces for rigging packages so that pins were standardized as well as the packages,” Moehnke said. “This reduced the number of part numbers the mine had to keep in inventory. The original package for a 2570 for instance had six different pins. We reduced that to one.”
The company is now working on a new pin locking system that is totally mechanical and shrouded from the abuse that rigging items routinely endure. “Currently in North America there is a lot of welding associated with pins,” Moehnke said. “Many draglines have a 2-bolt collar-keeper arrangement with ¾-inch bolt that’s somewhat exposed. It’s a good system that works well, but the bolts break. We’re developing a system where the retaining system will be protected.
“This new pin locking system can be installed and removed with a rattle [air] gun,” Moehnke said. “As far as retainers go, it’s showing a lot of promise. We have a lot of interest from Australia. They are using fixed-pin retaining systems, which means the pin does not rotate. This has some obvious wear issues where the pins deform to a crankshaft profile. The only thing that sees rotation is the pin around the male lug in the clevis opening. With a floating pin, wear is more evenly distributed. The pin can float and we bush all parts in all location with a manganese-steel alloy. We have seen some really good pin life compared to fixed-pin arrangements.”
Some Australian dragline bucket rigging has been adopted by North American mines and the pin life was not as good as one would expect. Columbia Steel hopes the floating pin design with a more mechanical and robust retaining system will help the mines eliminate the need for hammers and welding on dragline rigging systems.