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Double Head Rotary/Rotary

MARKETS: Mining

Double head Rotary-Rotary systems are a preferred method for drilling straight, deep holes. These systems offer the driller a high level of flexibility and control to deal with varying ground conditions. In combination with a DTH system on the inner drill string, a Rotary-Rotary system is able to achieve deeper depths compared to drifter (top hammer) based systems.

  • Utilizes two independent rotary heads to separately drive the outer casing and the inner drill string
  • Uses a lower drill head to turn rotary casing equipped with a carbide casing crown. An upper rotary drill head turns the inner drill rod equipped with a down the hole hammer (DTH), drag bit, tri-cone, or an auger drill string.
  • The two rotary heads are typically mounted on separate sleds which can be adjusted independently to control the position of the inner string in relation to the casing bit.
  • The inner bit can be advanced in front of the casing bit to act as a pilot bit for the casing string or it can be retracted inside the casing crown to better contain flushing inside the casing.
  • Shock absorber (important when drilling with DTH hammers on the inner string) is mounted below the upper rotary head for the inner string and protects this rotary head from the percussive energy of the DTH hammer.
  • Elastometric elements in the shock absorber dampen the DTH vibrations protecting the internal gearing of the rotary head.

Two Independent Rotary Heads

Separately drives the outer casing and the inner drill string and are typically mounted on separate sleds which can be adjusted independently to control the position of the inner string in relation to the casing bit.

Shock Absorber

Important with DTH hammers on the inner string, its mounted below the upper rotary head and protects this rotary head from the percussive energy of the DTH hammer.

Flushing Head

Mounted above the upper drilling head
Designed to fit the specific drill head in the system

Shock Absorber

Mounts below the top rotary head and is connected to the inner drill string
Protects the rotary head from damage due to vibrations from the DTH hammer

Balanced Rod

Provides the link between the top drill head and the inner drill string
Made to the exact length required by the installed drilling head system

Casing Flange and Ejection Bell

Connects the casing to the lower rotary head
Provides an exit point for the flushing medium through the ejection bell

Inner Drill Rod

The inner drill string on dual rotary drill systems are typically API drill rods.

Casing Bit

Casing bits for dual rotary systems are ring bits with tungsten carbide inserts.
The carbide insert is typically a scraping type button form*.
*dependent on ground conditions

Inner String Bit

Typically:Down the hole hammer
May also utilize:Various rotary bits*
tri-cone bit
drag bits
*depending on ground formations

Diameter Offering

External Tube ØInternal tube Ø
108 mm, LH76.1 mmAPI 2 3/8” REG, RH
114.3 mm, LH76.1 mmAPI 2 3/8” REG, RH
133 mm, LH88.9 mmAPI 2 3/8” REG, RH
152.4 mm, LH101.6 mmAPI 3 1/2” REG, RH
177.8 mm, LH114.3 mmAPI 3 1/2” REG, RH

Casing

Standard:Male/female friction welded double-start rotary percussive casing
Also available:Rotary percussive single casing
Triple-start casing