The new Sandvik DD211 jumbo is a dedicated electrohydraulic development drill rig for narrow-vein applications and hard-rock conditions.

“Narrow or narrow-vein mining, as opposed to large open stopes or other mass mining operations, typically refers to the working of mineral deposits of no more than two to three metres wide,” says Johannes Välivaara, Sandvik product manager, underground development drills. “They are generally associated with a variable and often very steep dip, the angle at which the mineral deposit is inclined to the horizontal plane.”

Mines of this type are common in South America, South Africa, the former Soviet Union, the United States and Australia. Minerals typically occurring in these formations include gold, silver and diamonds, but also base metals. Ore in many narrow-vein mines, particularly in South America and Africa, has traditionally been extracted with very limited mechanization.

“There are several drivers enticing mining companies to modernize their narrow-vein operations with new technology,” Välivaara says. “Many of the easily extractable deposits have been depleted, and the remaining, less-accessible reserves call for more advanced technology.” The high demand for qualified employees presses employers to improve safety and working conditions.

“DD211 boasts advanced safety and ergonomic features that help prevent accidents and also make it easier to attract and retain a skilled workforce,” he says. “Particularly compared with manual methods, the safety upgrade is extreme. Better, safer working conditions also improve productivity.”

One of the drill’s primary safety features is its canopy, which protects the operator from both roll-over (ROPS, in compliance with ISO 3449) and falling objects (FOPS, ISO 3471). The safety canopies or cabins in many competing designs only offer one protection or the other.

Another key safety feature is the drilling module movement-prevention function. In practical terms, this means that the drilling system remains safely switched off for the duration of rod changes. This makes one of the most hazardous tasks in the process much safer for the operator. With the automatic rod changer, available as an option, the need to approach the moving parts can be eliminated almost completely.

Product safety was the top priority in the design process of the new DD211 rig.

“With this new product, Sandvik has succeeded in significantly increasing the level of safety without sacrificing the ease of use, operator comfort or drilling performance,” Välivaara says.

The key challenge in the economies of narrow-vein mining is dilution control. In other words, as little waste material as possible should be extracted along with ore. One of the main aspects in effective dilution control is not only to keep the drilling operation efficient and precise but also to carefully plan the charging and blasting, as every tonne of mined waste rock impacts on a mine’s profit.

“The new DD211 provides a high level of accuracy and control for drilling that helps the subsequent process stages to achieve maximum precision with minimized overbreak,” Välivaara says, referring to the caving-in of loose materials at the edge of an excavation.

DD211 uses the RD314 percussive rock drill optimized for hole diameters of up to 51 millimetres. The compact design, 559 millimetres long without a shank, makes it possible to use longer rods and enables multidirectional drilling in confined spaces. Rather than maximizing the power rating, Sandvik targets optimized impact energy for high precision and long tool life. High, productive penetration rates are achieved by means of a high percussion frequency of 110 Hz – more than 30 Hz higher than in the predecessor model.

The compact dimensions are an asset in narrow-vein operations. Good penetration rates thanks to higher impact frequency give good productivity. Lower impact energy means longer tool life and fewer tool changes, resulting in direct safety and productivity benefits.

“The focus on maximized impact frequency gives more accurate holes, resulting in more accurate blasting, thus less dilution and consequently better economy,” Välivaara explains.

The combination of the compact CFX feed module and the telescopic SB20NV boom with two roll-over heads particularly comes into play in the cross-cut drilling and bolting operations in formations with a steep dip.

The extended mode of the CFX module, with a rod length of 3.66 metres, enables the use of long rods for development drilling. After reaching the ore deposit, the compact telescopic feed module can again be retracted to a rod length of 1.83 metres and thus increase mobility and allow production drilling in the cramped tunnel.