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Raise Bore

Raise Bore AssemblyThe rotary drilling method of boring large diameter holes for the mining and construction industries has proven to be extremely safe and economical.  For constructing ventilation shafts, ore passes and penn stocks, raise drilling has gained worldwide acceptance as the preferred method.  MTI has developed a directional control technology for raise drilling, called the “Packed Hole Technique”, which utilizes stabilizers immediately adjacent to the bit. The design of the stabilization assembly is dependent on the accuracy required, the rock formations encountered and these key factors:

  • Clearance – the difference between stabilizer diameter and hole diameter
  • Length – the length of contact between stabilizer members and hole wall
  • Stiffness – the resistance to stabilizer member bending increases with diameter
  • Wall Support – the ability of rock being drilled to resist the side load of the stabilizers.

Once hole size, stiffness factors and directional accuracy are determined, rock formations encountered and the length of raise determine the number of stabilizers required (which may vary within a given mine). In many cases it is necessary to use as many as 10 stabilizers in the bottom hole to achieve the desired results.

It is important to keep minimum clearance between stabilizer outside diameter and the nominal pilot hole diameter. To maintain pilot hole diameter and to reduce wear rate on the stiff stabilizer column, a bit reamer stabilizer is recommended to dress the hole behind the bit.

Rotary Shouldered ConnectionsDI Series Rotary Shouldered Connections
DI Series Rotary Shouldered Connections were designed and developed for specific applications and environments.

DI-22 Connection
The DI-22 Rotary Shouldered Connection is primarily for use in underground raise drilling. It is a high torque connection which features:

  1. Deep, course threads with only the pressure flank in contact, leaving space in the threads for limited foreign matter containment during makeup.
  2. A high angle, non-pressure flank for easy stabbing.
  3. A low angle pressure flank for minimum box hoop stress.
  4. Low taper angle for minimum weight per joint.
  5. Two threads per inch on a double lead to assist in reducing the breakout to makeup ratio.
  6. Vanishing box threads to eliminate any notch effect in the critical fatigue zone area of the box member.
  7. Relief groove in the critical fatigue zone of the pin member.

All MTI thread connections are treated with Kemplating, an anti-gall protection that assists in the retention of thread lubrication. While rotary shouldered connections are designed to provide years of trouble-free service, damage in handling or makeup can ruin a connection and shorten the lifespan of the entire string. Proper application and care will ensure maximum return on investment. Refer to the MTI Maintenance Manual for recommended care and maintenance.