Vari-Stem Plugs work by creating a blocking effect within the drill hole by wedging the stemming material between the drill hole wall and plug. Upon detonation of the explosives, the plug is forced upward into the stemming material and "locks up." The explosive gases and energy are prevented from traveling (venting) up through the drill hole, and instead are contained within the rock mass for milliseconds longer than non-plugged blasts.
Vari-Stem offers increased fragmentation, fracturing and cap rock breakage; and reductions in fly rock, air blast, stemming ejection, dust, noise and oversized rock. These are all the direct benefits and results of containing the blast energy within the rock mass for milliseconds longer than normal.
Vari-Stem’s Patented GEAR Design:
- Prevents plug collapse in undersized holes or when forced over jagged rocks.
- Makes the plug detonator cord (tube or wire) friendly. The numerous vertical grooves on the outside diameter of the plug prevent the detonator cord from being crushed, nicked or pulled into the drill hole during insertion. (The cord will simply slip into one of the vertical grooves.)
- Gives structural strength to the plug.
- Allows a compressed hold when used in air decking.
These plugs should be inserted point-down. Using a standard loading/charge pole, simply push the plug to the ANFO or Emulsion.
Besides reducing the average rock diameter in the muck pile, Vari-Stem saves secondary breakage costs by reducing the volume of oversized cap rock. It is possible to shorten stemming heights for improved cap rock breakage. Consistent stemming heights and reduced gas emulsions are possible with the Vari-Stem in air decking.