The Limestone Factory in Tallinn, Estonia is using the Marathon® version of Krupp Berco Bautechnik`s new HM 2300 hydraulic hammer with StartSelect to mine limestone direct from the quarry face. The hammer breaks out 240 to 300 metric tons of the rock - which has a compressive strength of 80 to 120 megapascals - per eight-hour shift.

The Limestone Factory switched from conventional blasting to mining with hydraulic hammers in 1995, a change made necessary by the construction of a residential area alongside the Tallinn-Moscow highway only 100 meters away. In addition, important gas and electricity lines are routed only a short distance from the quarry. The vibrations and other risks from blasting in this area threatened to stop quarrying operations. But using hammers to mine rock directly from the face has proved very successful: last year the company produced some 300,000 tons of limestone, two thirds of it mined by hydraulic hammers. This share will increase further in the coming years.

On-site trials of the HM 2300 Marathon® with StartSelect system convinced the Limestone Factory to buy the unit from Krupp Berco Bautechnik`s local distributor Metsatehnika AS. Krupp Berco Bautechnik GmbH premiered this model at Bauma 2001. Large numbers of the HM 2300 and the heavier HM 2600 with StartSelect system, also launched at Bauma, are now in use all over the world.

The StartSelect system offers "AutoStart" and "AutoStop" settings. In "AutoStart" mode the hammer is set to start up without contact pressure being applied to the working tool. StartSelect is supported in this case by the standard AutoControl system: in the event of idle blows, AutoControl reduces impact energy by 50 percent to protect the percussion mechanism. As soon as the tool comes up against firm resistance again, AutoControl switches back automatically to full power. Krupp Berco Bautechnik GmbH has applied to patent this system.

"AutoStart" mode is ideal for the secondary breaking of mined rock, where it can be difficult to apply the contact pressure required to start up conventional hammers. In "AutoStop" mode, contact pressure must be applied to the hammer and it cuts out automatically when the material has been broken. In quarries, for example, this setting offers advantages when mining from the face.

The HM 2300 is additionally equipped with an improved piston sealing system and new-design tie rods, two new features which further increase the hammer`s availability. Further key factors in the performance of the HM 2300 are the ContiLube® II automatic lubrication unit and the DustProtector. ContiLube® II, DustProtector and the AutoControl automatic stroke switching system are components of Krupp Berco Bautechnik`s proven Marathon® wear protection system. The HM 2300 weighs in at 3,000 kilograms and is designed for attachment to carriers in the 32 to 50 ton class.

Rock quarrying with hydraulic hammers is now an acknowledged strategy which offers considerable economic benefits in many cases. For example, rock strata of different quality can be mined selectively using hydraulic hammers. In contrast, blasting mixes the rock grades and thus reduces product purity. Direct mining from the face ensures continuous production without the lengthy interruptions required to clear the danger areas when blasting. A further advantage of hydraulic hammers is that they can perform secondary breaking on rock directly after it is mined from the face, dispensing with the expense of buying and servicing a preliminary crusher. The material can be transported straight to the downstream crushing equipment.