Top Hammer Drilling Rig VS DTH Drilling Rig, What are the ...

Top Hammer Drilling Rig VS DTH Drilling Rig, What are the Differences Between Them?

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Drilling is an important part of mining mines. The equipment used is mainly the top hammer drilling rig or DTH drilling rig. These two are suitable for different mining operations, and the wrong use will cause huge losses. If you want to know the difference between these two rigs, keep reading.

Different Working Principle

Operation Schematic Diagram(a: top hammer drilling rig; b: DTH drilling rig)

Top Hammer Drilling Rig

The impact force of the top hammer drilling generated by the piston of the pump in the hydraulic drilling rig is transmitted to the drill bit through the shank joint and the drill rod, which is the most different from the down-the-hole drill. At the same time, the percussion system drives the drilling system to rotate. When the stress wave reaches the drill bit, the energy is transferred to the rock in the form of penetration by the drill bit. The combination of these functions can drill holes in hard rock.

However, top hammer drilling is usually used for the maximum diameter of 127mm, and the depth of the hole is less than 20M, which has high efficiency.

In Top Hammer Drilling the hammer produces a percussive force on the drill rods or tubes, which is transmitted to the drill bit. The feed device is usually attached with a hinged boom to a mobile unit. The percussive system strikes the drill rod, for example 2,000-5,000 strikes per minute, and the rotation speed can be, for example, 60-200 rounds per minute. Together these elements make it possible to drill holes in the hard rock. The excess material (cuttings) is flushed up from the bottom of the hole by means of pressurized air or water. Top hammer drills are primarily used in mining, construction and quarrying of rock material. Top hammer drilling, combined with the &#;drill and blast&#; method, makes the whole excavation process extremely efficient.

DTH Drilling Rig

The down-the-hole drill uses compressed air to drive the hammer behind the drill bit through the drill rod. The piston directly hits the drill bit, and the hammer cylinder provides a straight and stable guide for the drill bit. This keeps the effects of energy from being lost in the joints and allows deeper percussion drilling.

In addition, the impact force acts on the rock at the bottom of the hole, which is more effective and straighter than other drilling operations.

DPH drilling is more suitable for large holes in hard rock drilling, especially for rocks with a hardness of more than 200Mpa. However, for rocks below 200 MPa, not only energy will be wasted, but also the drilling efficiency will be low, which will cause serious wear on the drill bit. This is because when the hammer's piston strikes, the soft rock cannot fully absorb the impact, which severely reduces the efficiency of drilling and slagging.

In DTH drilling, the percussion mechanism &#; commonly called the hammer &#; is located directly above the drill bit. The drill pipes transmit the necessary feed force and rotation to the hammer and the bit, along with the fluid (air, water or drilling mud) used to actuate the hammer and flush the cuttings. The drill pipes are added to the drill string successively behind the hammer as the hole gets deeper.

The hammer is fully fluid actuated. It is composed of two mobile parts: a valve, controlling the flow and a piston that strikes on an impact surface directly linked to the bit. The hammer body gives straight and stable guidance of the drill bit.

Differences of Adaption 

JK410 Crawler Mounted Pneumatic Tophammer Drill Rig

Top Hammer Drilling Rig

&#;The most suitable for hole diameter between 25&#;127 mm.

&#;Generally, the hole depth is less than 25 meters.

&#;Adapt to a stable and uniform hard rock.

&#;The slag flushing medium is compressed air or water.

&#;High efficiency in shallow holes drilling, the deeper the lower efficiency.

JK650 All In One DTH Drilling Rig

Down the Hole (DTH) Drilling Rig

&#;The most suitable hole diameter is 100&#;254 mm, in special applications can be up to 2M And the minimum can be around 50 mm as well.

&#;Theoretically drilling depth is limited by back pressure only (can be up to several kilometers).

&#;Adapt to hard rock and rock formation conditions (compared to top hammer).

&#;Mainly use pressurized air for slag flushing, and sometimes air foam for special application.

&#;Highly efficient in hard rock drilling.

In summary, each drilling rig has its own advantages. When choosing the equipment, you can first look at the actual situation of your project, and decide which type of rig to choose according to the rock formations, geological formations, and working environment of the construction site.

JK Drilling is a large enterprise specialized in the development and manufacture of all kinds of DTH Drilling Equipment. The major products include All-In-One type and separate type DTH rock drilling rigs, DTH well-drilling rigs, and construction drilling rigs. 

If you need drilling rigs of high quality, please contact us!

The reason customer want to drill the hole is that drill and blast is the most efficient and economic way to break rock instead of excavating it.

Blast hole drilling equipment

• Handheld rock drills

• Top hammer drills

  •  pneumatic

  • hydraulic

• Down-The-Hole drills
• Rotary drills

  • Rotary cutting

  • Rotary crushing

  • Rotary wearing

 

 

 

 

 

 

 

 

 

 

 

 

 

FOUR ACTIONS IN A DRILLING PROCESS&#;

• ENERGY TRANSFER &#; PERCUSSION / CRUSHING

• FEEDING

• ROTATION

• FLUSHING

 

 

 

 

 

 

 

 

 

Drilling methods        

• Top Hammer
•  Down the Hole
•  Rotary

 Percussion

• Does the real job = breaking the rock.
• Produced by rock drill or hammer&#;s impact energy and frequency.
• Typically between to hits per minute.
• Compared to pneumatic drills, hydraulic drills are capable of higher percussion power and faster penetration rates.
• Percussive drill rig is built around the hammer or rock drill
• in percussive drilling rock is broken with impact energy
• Impact Force per Blow : 20 to 60 Tons
• Blow Frequency:   30 &#; 60 Blows/Sec (Top Hammer), 25 &#; 35 Blows/Sec (DTH)
• Rod/Tube diameters: 23 &#; 140 mm

 

 

 

 

 

 

 

 

 

 

Top hammer drilling principle

• When the piston hits the shank, kinetic energy in the piston creates a compressive wave in the string of drilling tools, that will cause the bit to penetrate the rock
• Piston velocity at impact &#; 10m/s but the compressive wave in the drill steel travels at a velocity of m/s (velocity of sound in steel)
• The bit is forced forward and penetrates the rock around 1.0 mm
• Part of the energy not used to penetrate the rock goes back as a tensile wave and part of it as a compressive wave

 

 

 

Want more information on DTH Drill Bits? Feel free to contact us.

 

 

 

 

 

Top hammer drilling energy and efficiency

• Example: Rock drill for TH drilling delivers 18 kW
• Energy is lost in places where the drill string diameter changes, like in joints and threads
• MF rods lost energy about 4% and rods and couplings lost energy around 6%

Efficiency 70% 60% 50% Drilling 12.6 kW 10.8 kW 9 kW Wear / Damage 5.4 kW 7.2 kW 9 kW

 

 

 

 

 

 

 

 

 

 

 

 

 

How rock breaks

• The cemented carbide buttons on the drill bit are put under load each time the piston in the hammer or rock drill strikes
• Rock penetration by percussive drilling can be divided into four phases:

  • Elastic deformation

  • Rock pulverization

  • Crack formation

  • Chipping

• All this happens of course very fast as the hammers strike at a rather high frequency, about 40 to 60 Hz (blows per second)
• How much the button penetrates at each blow depends on the type of rock and shape of the button, but typically it is in the range of 1 mm.

 Rock drill(Top hammer)and  Air hammer(DTH) configuration

 

 

 

 

 

 

 

 

 

 

Percussion pressure or power

• Too high: short steel life
• Too low: poor penetration
• Lower pressure needed when
  • Collaring
  • Hitting fractured and layered rock
  • In soft rock

Feeding

• The purpose of the feed is to maintain the drill bit in close contact against with virgin rock across the vertical plane
• To ensure maximum impact energy transfer.
• The feed force must alway be matched to the percussion pressure
• Feed pressure must be always on right level

 

 

 

 

 

 

 

Feeding pressure

• Too high:
  • Bending of steels, 

    hole deviation

  • Increased rotation resistance,

    tight couplings

  • Risk of jamming

  • Difficult collaring

• Too low:
  • Reduced penetration due to poor rock contact
  • Loose couplings, thread burning
  • Poor shank and steel life
  • Higher drifter maintenance cost
• Drilling with a very worn bit or no rotation will cause a strong compressive wave travelling back in the string of tools
• By way of distinction from a tensile wave, the compressive wave will pass through joints which in this case means, it will &#;jump&#; into rock drill and rig
• Tensile waves are more harmfull to the drill steel than compressive waves A stabilizer takes care of the returning compressive wave that otherwise will reflect back in the drill stell as a tensile wave

Rotation

• Purpose of rotation is to turn the drill bit a suitable new position for the next blow. It means the bit must rotate so the buttons on the bit are moved between each blow
• Using the button bits, the periphery is turned about 10mm between blows.
• The optimum distance generates the biggest chips or cuttings and gives the most efficient drilling.
• Rotation pressure must be kept in reasonable for avoiding overtighted threads.

 

 

 

 

 

 

 

 

 

Drill bit rotation speed

• A good indicator of optimal rotation speed is the size of drill cuttings &#; The bigger the better
• Too high:
  •  Too high: Short bit life
• Too low:
  • Low penetration rate
  • Risk of jamming steels
• Rotation pressure (=torque) is a function of feed pressure; feed force adjustments influence the rotation resistance, recommended constant rotation pressure 90-110 bar

 

 

 

 

 

 

 

 

 

 

 

Flushing

• Fuction is to:

  • Remove drill cutting from the hole bottom to the surface by air blowing or water flushing.

  • To cool a bit.

• Medium can be air, water, mist/foam.
• Bailing velocity It is derived by dividing the volume of air by the annular space available between the hole and drill-string.
• Has a direct effect on drilling efficiency.

Bailing velocity

• Bailing Velocity in fpm = Q *( 144 x 4 ) / Π( D^2 &#; d^2)
  • Where,

  • Q = Volume of air available in CFM &#; usually the FAD of compressor after adjustment for altitude

  • D = Diameter of hole

  • d = diameter of drill-rod

  • BV in fpm = feet per minute

• Recommended BV values

  • For cuttings with high or wet density : ~ fpm

  • For cuttings with average &#; low or dry density : ~ fpm

  • Generally, optimum speed: &#; fpm

Insufficient air: for Top Hammer <15 m/s, for DTH(Down The Hole)< 15m/s

• Low bit penetration rates
• Poor percussion dynamics
• Interupt drilling to clean holes
• Plugged bit flushing holes
• Stuck drill steel
• &#;Circulating&#; big chip wear

Too much air: for Top Hammer  >  30 m/s; for DTH  > 60 m/s 

• Excessive drill steel wear
• Erosion of hole collaring point
• Extra dust emissions
• Increased fuel consumption
• Correction factors

• High density rock

• Badly fractured rock (air lost in fractures &#; use water or foam to mud up hole walls)

• High altitude (low density air)

• Large chips

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