Secondary breaking in surface mines and quarries occurs where oversize rocks are produced from a primary blast that need to be reduced to a manageable size for loading and crushing. In practice most hard-rock surface mines and quarries would expect to re-blast or break up to 5% of their rock after effective primary blasting.

secondary breaking (before)

secondary breaking (after)

There are hidden costs associated with ‘oversize resulting from a mass blast using conventional explosives:

• the oversized rocks are an obstacle to productive load and haul activity
• they cannot be dealt with cost effectively due to size and get in the way
• are normally left to be charged in the next mass blast, which often creates new oversize, thus the obstacles are perpetuated
• oversize impacts negatively upon production unless dealt with in the on-going production cycle
• tramming equipment over distances out the pit in order to use conventional explosives must be avoided; Wear and tear on final drives and tracks is a significant hidden cost.

Using Nonex cartridges for secondary breaking during load and haul activity is feasible, safe and productive; overall productivity is significantly enhanced.. Most open cast sites have large excavators, some of which have outlived their productive life, but make excellent support tools in the secondary breaking process. Material handling support for drilling, putting the oversize into manageable rows provides easy access to the rock and enhances safety. The same excavator loads the broken rock for removal

Secondary Breaking Options

Nonex offers a wide range, from 3-10g ‘rock poppers used for splitting oversize to fit the crusher jaws, drilled electrically, and from 20g up in steps of 20g to 250g drilling diameter 40mm using hand-held rock drills, using a rig to drill diameter 64-76mm holes charge weights in the diameter 60mm range from 200 – 500g charge weights, which also prove effective in the Nonex equivalent of a ‘mass’ breaking application. The common denominator provided by Nonex, non-explosive, non-detonating technology is controlled, precision breaking; no shockwave, minimal to 100% fly rock control and the capacity to produce the desired particle size for handling and crushing, which is what every pit manager wants.

Frequently, the Nonex way is also the most cost effective way. Nonex is often used in combination with an excavator mounted hydraulic hammer. Nonex is used to drill and break large oversize >1m3 and particularly large ‘elastic’ rock, which resists hydraulic breaking. Rocks < 1m3 and brittle rock,(nonelastic) break easily, then an hydraulic hammer which doesn’t need drilled holes is more cost effective. The combination is usually ideal.