Jackhammer

For other uses, see Jackhammer (disambiguation).

"Pneumatic hammer" redirects here. For the press, see Power hammer.

File:TVA Douglas Dam jack hammer.gif

Drilling a blast hole with a jackhammer

A jackhammer is a power tool that combines a hammer and chisel. Hand-held jackhammers are typically powered by compressed air, but some used electric motors. Larger jackhammers used on construction machinery are usually hydraulically powered. They are usually used to breakup rock, pavement, and concrete.

A jackhammer operates by driving an internal hammer up and down. The hammer is first driven down to strike the back of the bit and then back up to return the hammer to the original position to repeat the cycle. The bit usually recovers from the stroke by means of a spring. The effectiveness of the jackhammer is dependent on how much force is applied to the tool.

Terminology

The word "jackhammer" is used in North American English and Australia, while "pneumatic drill" is used colloquially elsewhere in the English speaking world, although strictly speaking a "pneumatic drill" refers to a pneumatically driven jackhammer. In Britain, the term "jackhammer" usually refers to electromechanical version of the tool.

Use

A full-sized portable jackhammer is impractical for use against walls and steep slopes, except for a very strong man, as the user would have to both support the weight of the tool, and push the tool back against the work after each blow. A technique developed by experienced workmen is a two-man team to overcome this obstacle of gravity: one man operates the hammer and the second assists by holding the hammer either on his shoulders or cradled in his arms. Both use their combined weight to push the bit into the workface. This method is commonly referred to as horizontal jackhammering.

Another method is overhead jackhammering, requiring strength conditioning and endurance to hold a smaller jackhammer, called a rivet buster, over one's head.

Types

Pneumatic

File:Aa pneumatic drill compressor front.jpg

A compressor for running a pneumatic jackhammer

A pneumatic jackhammer, also known as a pneumatic hammer, is a jackhammer that uses compressed air as the power source. The air supply usually comes from a portable air compressor driven by a diesel engine. Reciprocating compressors were formerly used. The unit comprised a reciprocating compressor driven, through a centrifugal clutch, by a diesel engine. The engine's governor provided only two speeds:

• idling, when the clutch was disengaged
• maximum, when the clutch was engaged and the compressor was running

Modern versions use rotary compressors and have more sophisticated variable governors. The unit is usually mounted on a trailer and sometimes includes an electrical generator to supply lights or electric power tools.

Electromechanical

File:Makita-demolition-breaker.jpg

A single phase demolition breaker.

This tool is useful where the work is light and inaccessible to a compressor.

Hydraulic

File:Excavator jackhammer.jpg

An excavator-mounted hydraulic jackhammer being used to break up concrete.

A hydraulic jackhammer, much larger than portable ones, may be fitted to mechanical excavators or backhoes and is widely used for roadwork, quarrying and general demolition or construction groundwork. Such tools can also be used against vertical walls (or ceilings for that matter), since the vehicles involved are massive enough and powerful enough to exert the forces involved without needing the help of gravity in operating the tool. Pneumatic or hydraulic tools are particularly likely to be used in mines where there is an explosion risk (such as underground coal mines), since they lack any high-power electrical circuitry that might cause a triggering spark.

Hydraulic breakers usually use a hydraulic motor driving a sealed pneumatic hammer system, as a hydraulic hammer would develop a low strike speed and transfer unacceptable shock loads to the pump system.

Bits

Bit types include:

• Spade - provides flat finish for concrete or edging in asphalt or dirt
• Flat tip - allows direction control or finer edge finish
• Point - general breaking
• Stake driver - drives concrete form stakes
• Scrabbler - finishes surface smooth or for cleaning prior to bonding

Health

File:Aa pneumaticdrill 01.jpg

A jackhammer with black silencer attached

The sound of the hammer blows, combined with the explosive air exhaust, makes pneumatic jackhammers dangerously loud, emitting 100 decibels at two meters. Sound-blocking earmuffs must be worn by the operator to prevent a form of hearing damage of which tinnitus is the main symptom. Most pneumatic jackhammers now have a silencer around the barrel of the tool.

Prolonged exposure to the pronounced vibration set up by the tool can lead to blood-circulation failures in the fingers, a condition known as white finger. Applying athletic tape is not effective in preventing white finger but seems to help alleviate some of its discomfort. Pneumatic drill usage can also lead to a predisposition for development of carpal tunnel syndrome.

External links

• How jackhammers workcs:Pneumatické kladivo

uk:Відбійний молоток