Difference between DTH(Down the Hole) Drilling and Top Hammer Drilling

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.

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Blast holedrilling 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

Drillingmethods

• 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

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, recommendedconstant 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

More articles:

• DTH(Down The Hole) Drilling Application
• General Drilling Method and Application
• DTH Drilling Care & Maintenance ' Part One
• DTH Drilling Care & Maintenance ' Part Two
• Basic DTH and Top Hammer Drilling Knowledge
• Well Drilling Method
• Rock Properties
• Rock Drillability
• How to Repair Drill Bit

Two popular drilling methods stand out: down-the-hole (DTH) drilling and Top-Hammer drilling. Each method has its own unique approach and equipment, making it essential to choose the right one for any project. Understanding the differences between these two techniques is crucial in maximizing efficiency and productivity.

DTH drilling involves a hammer drill that delivers powerful blows directly to the bit, allowing for efficient rock penetration. This method is commonly used in mining, construction, and quarrying because it can drill deep and straight holes with precision. The hammer drill in DTH drilling provides a strong impact force, making it suitable for challenging rock formations.

On the other hand, top hammer drilling utilizes a hammer drill located above ground level, delivering blows to the bit through a series of rods and tubes. This method is often preferred for smaller-scale projects or when precise hole placement is required. The hammer drill in top hammer drilling operates faster than DTH drilling, making it ideal for softer rock formations.

Selecting the right drilling method is essential for any drilling project. Different methods offer distinct advantages and disadvantages, and selecting the most appropriate one can significantly impact your project's success. Here are some key factors to consider when choosing a drilling method:

In top hammer drilling, the drill bit is directly impacted by a hammer located at the surface level, making it suitable for shallow holes with precise requirements. The equipment includes handheld rock drills or larger drill rigs with hydraulic or pneumatic hammers. On the other hand, DTH drilling involves a pneumatic hammer behind the drill bit at the bottom of the hole, allowing for deeper penetration into hard rock formations.

Want more information on Down-The-Hole Drilling Tools? Feel free to contact us.

Top hammer drills are known for providing high precision levels in shallower holes up to 150 meters deep. This makes them ideal for applications such as tunneling or bench blasting in quarries where accuracy is paramount. In contrast, DTH drills can reach depths beyond 150 meters while maintaining exceptional precision, making them suitable for tasks like borehole mining or large-scale water well installations.

Top hammer drills are commonly used in smaller-scale operations due to their ease of use and lower initial investment cost than DTH drills. They excel in applications such as road construction or small-scale mining, where quick setup times are essential. On the other hand, DTH drills are preferred for larger-scale projects requiring deep or angled holes due to their superior efficiency in specialized applications like oil exploration or geothermal well installations.

When it comes to DTH drilling equipment, the focus is on using a pneumatic hammer to drive a heavy drill bit into the rock. This method is commonly used for deeper holes and larger-diameter boreholes, making it ideal for mining and quarrying operations. DTH equipment requires a sturdy rig to handle the high air pressures needed for efficient drilling.

On the other hand, top hammer drilling equipment relies on a hydraulic or pneumatic hammer mounted above the drill bit. This method is more suitable for shallower holes and smaller-diameter boreholes, making it popular in construction and civil engineering projects. Top hammer equipment is more portable and versatile, allowing easier maneuverability in tight spaces.

When comparing the two, DTH drilling equipment offers greater power and efficiency for deep hole drilling but requires heavier machinery. On the other hand, top hammer drilling equipment provides flexibility and ease of use in smaller-scale projects but may lack the power needed for larger operations.

The advantages of DTH drilling equipment lie in its ability to handle deeper holes with precision and speed. However, its reliance on heavy machinery can make it less suitable for smaller projects or those with limited space. On the other hand, top hammer drilling equipment offers versatility and portability, making it perfect for various applications but may lack the power needed for large-scale operations.

Understanding the differences between top hammer and down-the-hole drilling methods is crucial in choosing the right equipment for specific project requirements. Both methods have unique strengths and weaknesses that must be carefully considered before making an informed decision.

When comparing the difference between top hammer and down the hole drilling methods, one of the key factors to consider is their impact on drilling speed. A hammer drill, such as the top hammer method, operates faster due to its ability to deliver rapid blows to the drill bit while maintaining constant pressure on the rock surface. On the other hand, a down the hole drill provides slower but more powerful thrusts, allowing for efficient penetration through hard rock formations.

The top hammer drill's rapid blows and constant pressure result in quicker drilling speeds, making it ideal for projects that require swift progress. Its ability to swiftly break through softer rock formations also contributes to its overall efficiency in completing drilling tasks within tight timelines. Conversely, down the hole drilling may be slower but offers greater power and precision when dealing with harder rock types.

In terms of hole quality, both drilling methods have their unique advantages. The top hammer drill creates precise and clean holes, making it suitable for applications that demand high-quality results, such as construction projects or mining operations. Meanwhile, down-the-hole drilling is known for producing straighter holes with minimal deviation, even in challenging geological conditions, ensuring excellent hole quality across various terrains.

When it comes to cost-effectiveness and return on investment, both top hammer and down the hole drilling methods have their own merits. While a higher initial investment may be required for DTH equipment due to its sophisticated technology and powerful capabilities, it offers long-term cost savings through reduced maintenance needs and enhanced durability. On the other hand, a top hammer drill may be more budget-friendly upfront but could incur higher operational costs over time due to increased wear and tear.

When considering geographical factors, the difference between top hammer and down the hole drilling becomes crucial. Top hammer drilling may be more suitable in areas with rugged terrain or limited access due to its maneuverability and ease of transportation. On the other hand, DTH drilling may be preferred in remote locations with challenging geological conditions.

In regions with varying landscapes and terrains, the choice between top hammer and down-the-hole drilling can significantly impact project success. Top hammer drills are ideal for hilly or mountainous areas where mobility is a concern, allowing for efficient maneuvering and accessibility to hard-to-reach locations. Conversely, DTH drills excel in flat or open terrains, where their powerful impact can penetrate through tough rock formations.

Rock formation is pivotal in determining whether a hammer drill or a DTH drill is more suitable for the job. Top hammer drills are effective in softer rock formations due to their precision and ability to create clean holes with minimal deviation. In contrast, DTH drills are better equipped to handle harder rock formations as they deliver high-impact force directly at the bottom of the hole.

Every drilling project has unique demands that must be considered when choosing between top hammer and down-the-hole methods. For projects requiring precise hole placement and minimal disturbance to surrounding structures, a top hammer drill may be preferred for its accuracy and controlled operation. Conversely, projects focused on deep-hole drilling or demanding higher penetration rates may benefit from utilizing a DTH drill's powerful impact force.

When it comes to maintenance, the difference between top hammer and down the hole drilling methods becomes apparent. Top hammer drills generally require more frequent maintenance due to the higher impact force on the drill bit. This can lead to increased downtime as equipment needs to be taken out of service for repairs or replacements.

Top hammer drills often need more frequent maintenance than down-the-hole drills, as the impact force on the drill bit can cause wear and tear at a faster rate. The complexity of maintenance also differs, with top hammer drills requiring more intricate care due to their design and operation. This can result in higher maintenance costs and time investments for top hammer drilling equipment.

The increased frequency and complexity of maintenance for top hammer drills can significantly impact project timelines. Downtime due to equipment maintenance or repairs can lead to delays in drilling operations, affecting overall project schedules and deadlines. It's important to consider these potential delays when choosing between top hammer and down-the-hole drilling methods for a project.

In terms of long-term durability and reliability, down-the-hole drilling equipment often holds an advantage over top hammer drills. The design of DTH equipment allows for greater durability in harsh drilling conditions, resulting in fewer breakdowns and longer operational lifespans. This enhanced reliability can contribute to cost savings over time, making down-the-hole drilling a more sustainable choice for certain projects.

When it comes to DTH drilling, Teamwhole offers a diverse line of DTH bits to cater to various drilling needs. Their range from different sizes to specific rock formations ensures you have the right tool for the job, maximizing efficiency and productivity.

Teamwhole's extensive range of DTH bits covers all bases, from small-scale projects to large-scale operations. Whether you need bits for soft or hard rock formations, their selection ensures you can find the perfect fit for your specific drilling requirements.

As technology advances in the drilling industry, it's important to embrace these advancements when selecting a drilling method. Whether it's through innovative equipment designs or improved maintenance practices, staying up-to-date with technological developments can lead to greater long-term durability and reliability in your drilling operations.

By carefully considering these aspects of top hammer vs. down the hole drilling methods when deciding, you can ensure that you're maximizing efficiency while taking advantage of technological advancements in the industry.

Contact us to discuss your requirements of PDC Drill Bit. Our experienced sales team can help you identify the options that best suit your needs.