Hammer drill
A hammer drill is a work machine for drilling holes in mineral material, for example stone or concrete. The cutting edge of the drill wears down the material due to the impact pulse. To prevent the cutting edge from seizing up, the boring bar is moved after each stroke. The operation and the feed are mostly done by hand without mechanical aids. Depending on the type of drive, a distinction is made between pneumatic , electric and hydraulic rotary hammers.
General
The operation of rotary hammers is associated with a lot of noise. Only in the past 20 years has it been possible to lower the sound level to around 108 dB (A); levels of more than 125 dB (A) were previously common.
With various gear ratios (speed control) and the use of an interchangeable chuck, many rotary hammers can not only hammer drill, but also chisel or drill without impact ( e.g. for tiles, steel or wood).
Impact hammers or chisel hammers do not have a rotary drive and are therefore only suitable, for example, for chiseling, removing tiles or breaking through walls. As a rule, chisel hammers are more powerful and lighter than rotary hammers with comparable power consumption and cheaper than rotary hammers with comparable impact energy.
Working principle
In contrast to impact drills, rotary hammers have an axially movable drill with a hammer mechanism, in which the drill is not firmly clamped in the drill chuck and the drill does not move with it. The impact energy required for drilling in hard materials is generated by the so-called hammer mechanism. The types most frequently used in rotary hammers are spring hammer mechanisms or pneumatic hammer mechanisms. In both cases, a movable mass is hit on the drill, which transfers the energy to the drilling material.
The pneumatic hammer mechanism consists of a drive bearing or eccentric wheel , piston, hammer and firing pin. The drive bearing or the eccentric wheel convert the rotational movement of the drive into a stroke movement of the piston. When the piston moves backwards, a vacuum is created which pulls the club backwards. When the piston moves forward, there is overpressure between the piston and the hammer (compression), which accelerates the hammer forward. The bat flying forward hits the firing pin and releases its kinetic energy ( impact energy ). The momentum of the racket is transferred from the firing pin to the tool shank of the drill or chisel. The firing pin is essentially a precise turned part made of hardened steel, which, in addition to the transmission of impulses, also protects the inside of the machine with a sealing ring against dust and dirt. Rotary hammers are usually equipped with a safety clutch in order to prevent damage to the mechanics and, above all, a dangerous torque on the machine when the drill is blocked .
The drill must perform a rotary and axial movement at the same time. While the drill and the chuck are firmly connected to each other in impact drills , which is why the chuck has to follow the axial movement, this concept is not suitable for rotary hammers. On the one hand, the frictional tension of the drill in the chuck would be loosened by the vibration; on the other hand, a lot of kinetic energy would be lost due to the relatively large mass of the chuck. For this reason, in 1975, with SDS-Plus, a drill holder system for smaller hand tools was developed, in which the drill can freely move about 1 cm along the axis of rotation. The SDS-Max system is widespread for large hand-held hammer drills or chisel hammers .
Removal of the drilling dust
With small rotary hammers, the drilling dust is conveyed through the spiral-shaped grooves of the drill and its rotation.
In large machines, the drill dust is removed from the borehole dry or wet. Dry air purging is mainly used in opencast mining . Compressed air is fed through the hollow drill rod to the chisel and conveys the cuttings to the outside in the annular space between the drill rod and the borehole wall. In certain cases the drill dust is sucked off through the hollow drill rod (Königsborn device in the German hard coal mining, to reduce the dust pollution in the neighborhood).
Wet water flushing offers the advantages of effective chisel cooling and effective dust suppression; because of the risk of stone dust, it is used almost exclusively underground. For economic reasons, water flushing is often not used above ground because, in addition to a compressed air supply, a fresh water supply would also be necessary and the silted flushing water may have to be disposed of. Self-sufficient diesel-powered construction machines with rotary hammers usually generate their compressed air with their own compressor ; when using air purging, there is no need for a water supply.
variants
Pneumatic hammer drill
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Pneumatic rotary hammers are operated with compressed air . A piston driven by compressed air - which is controlled by means of a ball or flutter valve - strikes a hammer, which in turn strikes the insertion end of the drill rod. The drill bit sits on the drill rod, usually with a non-positive connection via a cone. The hammer is provided with a relocating device, which causes the hammer and the inserted drill rod to rotate on rebound. In this way, the cutting edge is repositioned in the relieved state. The weight of a pneumatic hammer drill is - depending on the intended use - between 10 and 50 kg, in mining it is typically around 42 kg. In addition, there is the weight of the drilling column or a carriage.
The first pneumatic rotary hammers were developed in the 1860s for tunnel construction and later for mining. The most important company producing rotary hammers was the Flottmann works in Herne.
Hydraulic hammer drill
Hydraulic rotary hammers essentially correspond in their function to pneumatic rotary hammers, but use hydraulic fluid as the drive medium. The hydraulic hammers are all in higher weight and performance classes (150 kg and more) than the pneumatic hammers and are exclusively carriage-guided.
The first hydraulic hammer drill was designed and developed in 1973 by Vigg Romell, an engineer with Atlas Copco .
Electric hammer drill
Electric rotary hammers are used wherever compressed air is not available. Compared to the pneumatic hammer, the electric version has a lower performance. Compared to the also electrically operated percussion drill , the hammer drill is characterized especially by a lower impact rate of at much higher impact energy.
history
The first "drilling machine with electro-pneumatic hammer mechanism" was built by Fein in 1914 and a patent has been applied for.
In 1932, Bosch built the first “Bosch hammer” in series. It had a twist mechanism for drilling and chiseling and already had a safety coupling. From 1967 the Hilti company also built electric rotary hammers, which helped the company gain a high level of awareness for this product.
Cordless hammer drill
Cordless rotary hammers are independent of the power supply, but due to the battery they are heavier than power packs of equal power. Furthermore, the operating time is usually very limited due to the high energy consumption.
Individual evidence
- ↑ US patent for hydraulic hammer drill. Retrieved May 29, 2012.
- ↑ Tool news / inventors. Retrieved March 17, 2012.
