Need help choosing a Rock Drill? Choosing a Rock Drill
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The 1st step in choosing the right steel and bits for your rock drill and application would be to determine the shank configuration on your drill.
The smallest common pneumatic drills are a variation of the CP9 and use a one piece bit/drill steel combination called a Whirly Bit.
When you move to the bigger hand held drills, there are only 3 common shank sizes. 7/8 x 3 ¼', 7/8 x 4 ¼' and 1 x 4 ¼'. These measurements refer to the diameter of the hex steel (measured across the flats) and the length above the retaining collar. The larger sinker drills will usually run the larger steel but it is not uncommon to have a 55lb drill which is set up for a 7/8 x 3 ¼' shank. You must know which shank configuration you have prior to ordering your drill steel.
These bits are actually the bit and the drill steel all in one piece. The shank which goes into the drill, the body of the steel, and a silver brazed carbide tip. The body of the drill steel is actually smaller than the bit to allow cuttings to travel up and out of the hole. Even a 1' shanked 60# class drill can be used to drill a hole smaller than 1' to a limited depth.
H thread is probably the most commonly used contractors thread due to its versatility and availability. The male thread on the steel is about 1' diameter and about 3/4' long. The steel is typically stocked from 12' to 120' long in all 3 shank configurations. The bits range from 1 3/8' up to 3' diameter in full carbide cross (most common), 1 3/8' to 2' in shallow carbide cross, 1 3/8' to 2 1/4' in button bit bits and 1 3/8' to 2 -5/8' diameter in an all steel bit.
H thread drill steel is usually made from a high carbon steel. It is usually forged, machined, and heat treated to have a wear resistant exterior while retaining a slightly softer core to handle and transfer impact energy. It is a shoulder drive steel which means the skirt of the bit tightens up to the forged/machined shoulder on the steel. The percussive energy is transferred though the steel and skirt of the bit to face ' shattering the material in front of it.
While H thread steel is the most common contractors thread - it does have its inherent weaknesses. The shoulder drive dictates that the bit must remain tight against the shoulder of the steel. If it becomes loose from the shoulder ' all of the drills forces are going very small threads on the bit and steel ' and they will quickly fail. Keep constant down pressure and do not allow the drill to bounce in the hole and H thread should work very well in most hard rock drilling applications.
This bit has 4 large silver brazed carbide inserts that hold up extremely well in production hard rock drilling applications. They hold there gauge well and can be sharpened if they get too dull to be effective.
The economy bit costs a little less than the Full Carbide bit but has a fraction of the tungsten carbide insert. They can sometimes be more 'economical' in some situations. (small jobs, very abrasive material, drilling in conditions prone to bit failures)
The button bit costs a little more than the Full Carbide cross bit. It has multiple carbide buttons pressed into the face of the bit and may appear to be dull and ineffective at first glance. However, keep in mind, how a percussive rock drills works. Larger hand drills can deliver enough impact energy to make these bits far superior to a cross bit in speed and longevity in the right conditions.
These cross bits are forged and hardened and are the least expensive options. Without the carbide component you can expect a relatively short lifespan especially in abrasive conditions.
Tapered drill steel was/is primarily used in underground mining on jackleg drills. 12 degree taper is more prevalent in Canada and 11 degree is more prevalent in the US and Central America. The female tapered bit pushes on to the male tapered drill steel. Once mated ' they can be separated by means of a bit knocker when the bit is worn out.
Some contractors have adopted it - as the steel is produced in larger volumes and is easier to manufacture therefore it can be less expensive. However, it was made for production mining and is limited in scope. The drill steels normal shank configuration is 7/8 x 4 ¼ and the range of bits is limited. Crowder Supply stocks shallow cross bits from 1' through 2', button bits 1 3/8 ' 1 1/2 'and 11 degree steel in 18' through 12' increments. Failure to maintain steady down pressure may result in losing the bit in the hole.
100 rope (1' rope, R25) and 125 rope (1 ¼'rope, R32) are used extensively in underground production mining applications. Many contractors have turned to this type of steel to deliver a longer life, especially in more demanding conditions or when consistently drilling 2 ½' plus diameter holes. The drill steel is normally carburized which is a process of infusing the steel with carbon elements in a furnace. This gives the steel an extremely hard casing while maintaining a lower hardness inside to transfer the impact shockwave. The thread is larger/longer and will bottom out inside the rock bit. This combination is more forgiving in tough drilling conditions. Crowder Supply manufactures a large variety of steel and bit adaptors for larger track drills but it is seldom necessary to move beyond these two threads with hand drills.
Rope thread steels also give you the ability to run drill strings by using extension steels. This gives you the option to drill a deeper hole or to drill longer holes in confined spaces.
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Rapid economic development has promoted the development of construction engineering fields such as mining, energy construction, foundation engineering construction, and traffic road development. Therefore, the market demand for rock drilling tools is also showing a growing trend, which prompts products to have higher development requirements in terms of category, performance, and quality. To produce more and better products, rock drilling tool manufacturers are also constantly developing new products and processes, and there are rich types of rock drilling tools.
From the article 'What are rock drilling tools', we can learn that according to the type of rock drilling machinery used in geotechnical drilling engineering, there are six types of rock drilling tools: top hammer rock drilling tools, DTH drilling tools, roller cone drilling tools, raise drilling tools, mechanical cutting drilling tools, and geological exploration drilling tools. But this is just a classification of rock drilling tools. We all know that the most basic definition of rock drilling tools is that they are made of brazing steel and other materials (such as cemented carbide) to drill rock and they are also the collective name of rock drill bits, drill rods, coupling sleeves, shank adapters and other products, which constitute the rock drilling tools and are also the core products of rock drilling tools.
It is the part that directly breaks the rock mass and is used to rotate and break the rock through the impact of the blade and button in various solid rocks to form rock holes with different diameters. It mainly can be divided into taper bit, thread bit, and DTH bit.
A. Taper bit: It can be divided into chisel bit, cross bit, and tapered button bit.
a. Chisel bit: It has a relatively simple manufacturing process, convenient regrinding, reliable work, and strong adaptability to rock mass performance. It is often used with light internal combustion, electric, pneumatic, and hydraulic rock drills to drill rock holes with a diameter of less than 50mm in various types of rock.
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b. Cross bit: It is the main variety in the international chip series drill bit. The diameter of the drill bit is in the range of 29-48mm, and it has strong adaptability to rock drilling conditions and is almost not limited by the rock drilling type and rock mass.
c.Tapered button bit: It is a kind of drill bit used in combination with the pneumatic rock drill and the tapered rod. After connecting with the drill rod, the drilling operation is carried out.
B. Threaded bit: Because of its reliable connection, It can transmit large torque, and it is convenient to extend the drill rod, so it is mostly used on drill stands or drilling rigs to drill large and deep rock holes. The specifications commonly used in various countries are R22, R25, R28, R32, R38, T38, T45, and T51.
C. DTH bit: The commonly used diameter of the DTH drill bit is 65~130mm, DTH rock drilling rig is used in medium and large aperture open-pit rock drilling projects. The down-the-hole drill bit has stable rock drilling performance and is easy to use and grind.
Note: When using a hand-held or leg-type light rock drill and a small-diameter drill bit for shallow hole drilling, it is mostly equipped with tapered drilling tools. When the diameter of the drill bit is large, and the drill frame and rock drilling rig are used underground or in the open for medium and deep rock drilling, threaded drilling tools are used.
The drill rod is a structural part that supports the drill bit to transmit the impact stress and torque of the rock drill. It mainly can be divided into integral drill rod, quarry drill rod, tapered drill rod, and threaded extension rod.
A. Integral drill rod: A drilling tool made by integrating the drill bit, drill rod, and drill tail. Features: It eliminates the energy loss at the connection of the tapered rock drilling tools and the phenomenon of drill bit loss, which improves work efficiency; each integral drill has a specific length and drill diameter. When the hole depth exceeds its length, it needs to be replaced by a longer drill rod; when the head alloy sheet is normal retirement, it can be cut and used as a conical drill.
B. Quarrying drill rod: This kind of drill rod is the main application in small hole operations in the quarrying industry. The diameter of the drill bit of the quarrying drill rod may be smaller than the diameter of the rod.
C. Tapered drill rod: Such drill rod is connected with the rock drill using a forged drill shoulder and shank adapter. The tapered drill rod is the most widely used of all types of drill rods. Hollow hexagonal drill rods belong to the category of small cross-section drill rods. 19mm, 22mm, 25mm, and 28mm are more commonly used internationally.
Although the tapered drill rod is bearing the effects of impact, torsion, and bending stress at the same time during drilling, it is mainly axial impact stress. Since the drill rod is a slender rod, the bending stress generated in drilling is also very harmful to it.
D. Threaded extension rod: It is a hollow circular or hollow hexagonal drill rod with threads at both ends or one end of the rod. It is the main component of the threaded extension drill tools. One end of the extension drill rod is connected with the shank and the rock drill through the coupling sleeve and the other end is directly connected with the drill bit. The threaded extension drill rod can be connected with a shank adapter and drill bit in single or multiple pieces. It has a wide range of applications. High speed, less loss of impact energy transfer, high rock drilling efficiency, easy to realize mechanized drilling, improved drilling conditions, and other advantages. Therefore, the proportion of threaded extension rods in rock drilling tools has been rising. That is to say, it has the largest variety, the most complete specifications, the largest quantity, and the best economic benefits among all the drilling tools. Threaded extension rods are divided into shank rods, extension rods, trolley drill rods, and speed rods.
a. Shank rod: It is a threaded connection drill rod with a nominal diameter of the thread larger than the hollow steel rod. During processing, the end must be forged and upset before thread processing. During drilling, the reduction in the weight of the drill rod is beneficial to the improvement of drilling efficiency.
b. Extension rod: Threaded drill rod with a threaded connection at both ends, nominal diameter of the thread is equal to the nominal diameter of the hollow steel rod body or the distance between the opposite sides.
c. Trolley drill rod: It is a threaded extension drill rod with one end of the nominal diameter of the thread larger than or equal to hollow steel and the other end equal to or smaller than hollow steel. Its main structural feature is that the nominal diameters of the two threads are inconsistent. When drilling, the larger end is connected with the shank, and the other end is connected with the drill bit.
d. MF rod: This is a round or hexagonal threaded extension drill rod with an internal thread at one end and an external thread at the other end. This threaded extension drill rod is known as the MF drill rod abroad. Because the Speed rod integrates the coupling sleeve and the drill rod, the weight of the matching drill tool is lower, it shortens the thread connection length, and the impact energy loss at threaded joints is reduced. The connection, change' loading, and unloading of the drill rod are more convenient. The drilling speed is accelerated, and the rock drilling efficiency is greatly improved.
The coupling sleeve is an indispensable accessory in the drilling tools. It is applicable to connect drill rod to drill rod, and drill rod to shank with an internal thread. During the drilling process, the coupling sleeve is in the joint part of the matching rock drilling tools and is subject to the corrosion effects of stress such as axial tension and compression, bending and torsion, contact, and friction. Therefore, it is vital to rationally select the steel used for the coupling sleeve and optimize its geometric structure and manufacturing process. The coupling sleeve uses its thread to connect two or more drill rods or shank rods on the same axis, transmits the impact function of the rock drill, and achieves the purpose of drilling rock holes. It also acts as a stress wave propagation carrier like the drill rod.
Coupling sleeves are classified according to geometric structure, including straight-through coupling sleeves, middle-stop-type coupling sleeves, and reducing coupling sleeves; according to thread structure, there are wave thread, compound thread, trapezoidal thread, etc.
As a modern component for supporting rock drilling tools, the shank adapter is natal with the development of drilling technology and rock drilling conditions. The shank rod used in this rock drilling process is the prototype of the development of the shank adapter.
Shank adapters are classified by water supply methods, including straight-through water supply and side water supply; by the structure and shape of drill lugs, there are double-wing, three-wing, four-wing, five-wing, six-wing, eight-wing, ten-wing, etc.; by thread structure classification, there are the wave, compound, trapezoidal thread and so on.
When choosing rock drilling tools, comprehensive consideration should be made according to the specific geological conditions, construction requirements, and cost budget. Various rock drilling tools have different advantages, disadvantages, and applicable scopes. Selecting the right tool is crucial for improving construction efficiency and reducing costs.
At the same time, when using rock drilling tools, please note the following points:
Rock drilling tools are an important tool for rock drilling and blasting, and also an important symbol of social civilization. Moderate resource extraction through rock drilling tools can widen a larger living space, improve the living environment of human beings and build more energy bases, and various social, economic, and political factors also promote the rapid development of tunneling, shaft boring, and underground construction process technology worldwide. Therefore, with the advancement of rock drilling technology and rock drilling machinery, the development of rock drilling tools increasingly accelerates. I believe that the types of rock drilling tools will be abundant according to the continuous changes in market demand. Let us wait and see.
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