Brunner Warranty Guide

Brunner & Lay’s Warranty Guide

How a Demolition Tool Breaks Rock and Concrete
When the hammer piston strikes the top of a demolition tool, its sends a compressive stress wave down to the working end of the tool. Provided the demolition 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 demolition 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 demolition tool due to leverage, will result in loss of breaker 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 demolition tool, even under correct operating conditions, create fatigue stress in the tool which can lead to the fatigue failure of a demolition 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 demolition 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 is any form of side pressure during service which creates bending

A. Using the tool as a lever
	B. Using the incorrect Driving angle
C. Attempting to break using the pull of the machine

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 include:

A. 'Free Running'- In general this is any situation where the hammer 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 demolition tool 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. Molybdenum bisulphide grease is recommended for this application at three hour intervals or as per manufacturers instructions.
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.

Demolition Tool Fatigue Failure
A demolition tool fatigue failure will generally occur approximately 4" (100mm) either side of the chuck from face or through the retainer pin flat.

Another slightly less common failure area can fall approximately 8" (200mm) from the working end, subject to nature of use.

The fracture face itself will normally exhibit a semi circular polished area with the remainder being of a rougher appearance.

The "polished" semi-circular area in the above drawing, represents the fatigue area and generally starts from a damage mark or other stress raiser on the outside of the demolition tool and spreads inwards. The fatigue area slowly widens until the stresses being applied to the demolition tool cause sudden failure of the remaining section.
Generally, the size of the fatigue area indicates the level of stress applied to the tool, i.e. the smaller the fatigue area, the higher the stress level, although it must be borne in mind that once initiation of a fatigue crack has taken place, it requires a lower stress level to cause it to grow.

Typical Failures (guide to warranty claims)
Brunner & Lay demolition tools are manufactured from high quality materials and then heat treated to produce a fatigue and wear resistant tool. Thus when a tool has apparently failed to give a satisfactory service life, a brief visual inspection can often give a quick indication of cause. Below you will find typical fractures caused by excessive bending of the demolition tool voiding warrenty.

Typical of high stress fracture, usually caused by using the machine to "pull". Warranty claims rejected.

Typical fracture caused by levering tool while buried in the burden. Warranty claims rejected.

Wear
Wear is influenced by ground conditions, but as a general guide the following applies:
Blank tools worn more than 1/3 diameter or moils and chisels worn back more than 2" (51 mm) of working end are classed as reasonable life. Warranty claim rejected.

Mushrooming; this is caused by driving the point into hard dense material for too long a period of time without penetration. This generates intense heat softening the point, thus causing it to 'mushroom'. This is not a manufacturing fault. Warranty claims rejected.