How a Hydraulic Breaker Tool Breaks Rock and Concrete

When the hydraulic hammer piston strikes the top of a hammer tool, it sends a compressive stress wave down to the working end of the tool.  Provided the hammer tool is in contact with the rock or concrete which requires breaking, it is this compressive stress wave which fractures the rock.Immediately following  the compressive stress wave,a tensile stress wave is formed due to the hammer position lifting from the top of the hydraulic hammer tool.  This cycle of compressive and tensile stresses flowing down the tool is repeated for each hammer blow.
Obviously, anything that interferes with the ‘strength’ of the compressive  stress  wave during  service,  for example ‘free running’ or bending of the hydraulic rock hammer chisel due to leverage, will result in loss of hammer efficiency of up to 80% and possible  fatigue  failure  of the tool itself.

Cause and Effect of Fatigue

The continuous cycle of compressive  and tensile stresses in the hydraulic breaker tool, even under correct operating conditions, create fatigue stress in the tool which can lead to the fatigue failure of a hydraulic breaker tool before it is worn out.  Again, anything which interferes with the cycle of compressive and tensile stresses will also increase the level of fatigue stress being applied to the hydraulic rock breaker tool and thus increase the risk of early fatigue failure of the tool.
1.  The main cause of increased fatigue stress in a demolition tool

A. excessive bending or levering of the demolition tool

B. using the hydrauli breaker chisel as an anchor to pull the machine

C. incorrect driving angel

All these are detrimental to the life of a demolition tool and should be avoided.

2. Other causes of increased fatigue stress in a demolition tool(hydraulic breaker chisel ) include:

A.  ‘Blank striking’
In general this is any situation where the hydraulic breaker piston strikes the top of the demolition tool, but the working end is not in proper contact with the rock or concrete to be broken.  This includes jobs where the tool slides off the work and also when break-through of thin concrete slabs or boulders occurs.

B. Cold
Low temperature causes a hydraulic hammer chisel to be more susceptible to fatigue failure. Tools should be warmed before use.

C. Mechanical and thermal damage
Any form of damage to the surface of a demolition tool renders it more liable to suffer fatigue failure.  Thus all care must be exercised to prevent accidental gouging, or contact welding (‘galling’ or ‘pick-up’) due to contact between the tool and chuck bushings through the lack of lubrication or excessive bending.

D. Lubrication
Care must be taken to avoid metal to metal contact that, as a result of galling or pick-up, could cause deep damage marks which, in turn, lead to the formation of fatigue cracks and eventual failure of the demolition tool.  Ensure that the shank of the demolition tool is well lubricated before locating in the machine.

E. Corrosion
A rusty demolition tool is more likely to suffer fatigue failure, thus keep tools well greased and sheltered from the weather when not in use.