What is the difference between DTH and top hammer?

Ramset 342 Dyna Drill and Chipping Hammer, shown with chipping chisel.

A rotary hammer, also called rotary hammer drill[1] is a power tool that can perform heavy-duty tasks such as drilling and chiseling hard materials.[2] It is similar to a hammer drill in that it also pounds the drill bit in and out while it is spinning. However, rotary hammers use a piston mechanism instead of a special clutch. This causes them to deliver a much more powerful hammer blow, making it possible to drill bigger holes much faster. Most rotary hammers have three settings: drill mode, hammer drill or just hammer, so they can act as a mini jackhammer.[3]

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Function

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Compared to less advanced power units known as hammer drills, rotary hammers tend to be larger and provide a bigger impact force by utilizing a technology called the "electro-pneumatic" (EP) hammering mechanism, because it is powered directly by electricity instead of a separate air compressor. Rotary hammers have two pistons &#; a drive piston, and a flying piston. An electric motor turns a crank, which moves the drive piston back and forth in a cylinder. The flying piston is at the other end of the same cylinder. The pistons do not actually touch, but the air pressure in the EP cylinder allows for a much more efficient transfer of hammering energy than springs in the cam-action style hammer drills. The majority of modern rotary hammers as well as all electric-powered chipping guns or jack-hammers all utilize this EP technology. Modern units allow the hammer and rotation functions to be used separately or in combination, i.e., hammer mode, drill mode, or both. When used in the hammer mode, the tool provides a drilling function similar to a jackhammer.[4] Rotary hammer drills have an oil filled gearbox, which allows them to operate durably despite the large forces and shocks they receive and the grit-filled environments where they are often used.

The type of work they do means that they require a "slip-clutch" which engages when the drill bit jams and sufficient torque is put onto the "slip-clutch" mechanism. This stops the violent wrenching motion that a drill without a clutch would cause when stopped suddenly from full speed, protecting the drill from damage. The slip-clutch also protects the operator, but does not always prevent injury. Some manufacturers have introduced additional technology to protect the operator. Hilti has a technology called "ATC" or "Active Torque Control"[5] which works by disengaging the drive from the motor when the tool body begins to rotate excessively through the action of a secondary magnetic clutch in addition to the standard slip-clutch. DeWALT has a related system called "CTC" or "Complete Torque Control"[6] which utilizes a two-position slip-clutch so that the operator can select the lower torque setting for greater safety.

A number of "special shanks" have been developed by various manufacturers. Over the years a fair number of these proprietary systems evolved, but the remaining shanks in use today are: SDS+, SDS-MAX, and SPLINE SHANK. These shanks were developed in order to allow for the bit to "slide" back and forth while rotating, so that the drill bit can efficiently transfer the force of the electro-pneumatic hammering mechanism to the working surface.

Use

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A rotary hammer drill used in construction

Rotary hammers can be used for "doweling" (repetitive drilling of large rebar anchor holes), and drilling through-holes in concrete and masonry walls. The hammering action helps break up the masonry so that it can be removed by the drill bit's flutes. Apart from their main function of drilling concrete, the rotary action can be switched off and use is made of just the percussive force. Chisel and point accessories are used for small chipping jobs.

Special chuck

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Worn masonry drill bit having a Slotted Drive Shaft (SDS)

Rotary hammers have such force that the usual masonry drill bits are no longer adequate. Their smooth shanks would be pounded loose from the tool's chuck in a few seconds. Rotary hammers require special bits with an SDS shank (which can stand for Slotted Drive Shaft or Special Direct System), which locks into the rotary hammer without the need for a chuck. The hammer strikes the bit directly, instead of the chuck holding the bit.

Jams

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Jams are most often caused by hitting reinforcing steel or by a worn bit. In both cases the drill must be disengaged from the bit and the jammed bit backed out of the hole with vise grips or monkey wrench. Some bits utilize a full carbide "four-cutter" head with a geometry that makes jamming less common - even when rebar is present. These full-carbide "four-cutter" bits can even, in some instances, drill through rebar, although this should be done with caution. A worn drill bit will still drill a horizontal hole, although of a slightly smaller diameter than one created when it was new. When a drill like this is used to drill holes down into a concrete slab, the flutes are so worn that they can no longer lift the dust out of the hole; the concrete dust packs up in the hole and jams the bit.

History

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Hilti had the first "electro-pneumatic" rotary hammer on the market in , the Hilti TE 17[7]

Types

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The perforating devices differ, basically, depending on the intended use, which leads to the appropriate size, weight and impact force when applied:[8]

• Relatively light electric punches (less than 10 kg) are prevalent in the construction field and the DIY market.
• Pneumatic perforators are used in mining industry and highway construction.[9]
• Hydraulic hammers demonstrate the highest performance and weight (150 kg or more).

Operation of perforating equipment is associated with much noise. Only in the last 20 years it became possible to decrease the noise level to about 100 dB(A);[10] earlier levels over 125 dB(A) were common.

References

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In the dynamic world of rock drilling, two prominent techniques have emerged as frontrunners: Down-the-Hole (DTH) drilling and Top Hammer drilling. These methods have their unique features and advantages, making them popular choices in various applications. In this article, we will delve into the intricacies of both techniques, comparing their strengths, weaknesses, and the scenarios where each excels. By the end of this read, you'll have a comprehensive understanding of whether DTH drilling or Top Hammer drilling is the superior choice for specific drilling endeavors.

 DTH Drilling - Pioneering Penetration Rates and Efficiency

Down-the-Hole (DTH) drilling is renowned for its outstanding penetration rates and efficiency, making it an ideal choice for deep-hole drilling. The DTH technique involves a pneumatic hammer that drives a drill bit down into the rock with its percussive action, chipping away at the formation. Key advantages of DTH drilling include:

1.Deep Drilling Capability: DTH drilling is particularly effective in deep-hole applications, allowing for precise and reliable drilling at significant depths.

2.Low Deviation: The straightness and accuracy of DTH drilling ensure minimal deviation, making it suitable for projects where precision is critical.

3.Versatility: DTH drilling can handle various rock types, ranging from soft to extremely hard formations, making it a versatile option for diverse geological conditions.

4.Reduced Hole Deviation: The guidance provided by the drilling rod directly attached to the bit minimizes hole deviation during the drilling process.

 Top Hammer Drilling - Optimal for Surface Applications and Smaller Holes

Top Hammer drilling, on the other hand, utilizes a percussive mechanism mounted on the top of the drill string. This method is favored for its efficiency in surface drilling and smaller-scale projects. Key advantages of Top Hammer drilling include:

1.Speed and Efficiency: Top Hammer drilling excels in surface drilling applications, offering higher drilling speeds and efficiency for shallower holes.

2.Lower Equipment Cost: As compared to DTH drilling, Top Hammer equipment generally incurs lower initial costs, making it attractive for projects with budget constraints.

3.Ideal for Cohesive Formations: Top Hammer drilling is particularly effective in cohesive rock formations, providing reliable performance in such geological conditions.

4.Ease of Maintenance: The top-mounted design of the hammer simplifies maintenance and reduces downtime, contributing to increased productivity.

The Right Choice for the Right Application

While both DTH and Top Hammer drilling techniques have their strengths, selecting the appropriate method depends on various factors, including:

1.Drilling Depth: For deep-hole drilling projects, where straightness and precision are crucial, DTH drilling emerges as the superior choice.

2.Geological Conditions: The hardness and composition of the rock formation significantly impact drilling performance. DTH drilling's adaptability to varying rock types makes it a versatile option, while Top Hammer excels in cohesive formations.

3.Project Scale: Smaller-scale surface drilling projects often benefit from the speed and cost-effectiveness of Top Hammer drilling.

4.Budget and Investment: Companies must consider their budgetary constraints and long-term investment plans when deciding between DTH and Top Hammer drilling equipment.

In conclusion, DTH drilling and Top Hammer drilling each have their niche in the world of rock drilling. DTH's efficiency in deep-hole drilling and versatility in various geological conditions position it as the preferred choice for demanding projects. Meanwhile, Top Hammer drilling's swiftness, cost-effectiveness, and suitability for cohesive formations make it a viable option for certain surface drilling applications. By understanding the nuances of these techniques and carefully evaluating project requirements, drilling professionals can make informed decisions to optimize performance and achieve exceptional results in their rock drilling endeavors.

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