Generally speaking, quarry equipment includes the following machinery:
* pneumatic steel drillers (for vertical, horizontal or inclined drilling, manual or mounted on special devices), mostly diameter 34 mm.
The different quarrying machines have different functions which have to be evaluated according to the following factors:
* type of rocks (hard, soft, abrasive, etc.)
Quarry management has to decide from case to case the optimal proceeding method.
The main quarrying methods are drilling and diamond wire cutting. In many cases also chain cutting is used but only for marble or travertine.
As for tool costs, drilling on marble is about 0,25 USD, on granite about 1 USD per drilled linear meter. Consumption of diesel fuel by the compressor is about 7 l of diesel per hour, for each hammer. That means about 0,15 l of diesel for each hp per working hour of the compressor. The drilling speed depends on the type of rock. In principle it ranges form 50 to 80 cm/min with the new generation of pneumatic hammers.
Depending on the splitting aptitude of the material, the spacing of holes ranges between 15 and 30 cm. For obtaining 1 sqm of surface, there are roughly 6 linear meter of perforation required.
Afterwards the drilled faces have to be separated by means of blasting. Normally PTNE (detonating cord) of 8-12 g/m of pentrite is used. Two drilled faces of a block or a bench can be blasted simultaneously, the other 4 faces must be free otherwise the block will be destroyed together with part of the deposit.
As alternative to pneumatic drilling, also hydraulic drilling is used. This method is extremely efficient but can not be achieved by manual equipment or simple devices as in case of pneumatic drilling. Hydraulic drillers have to be mounted on tractors, excavators, front loaders or other heavy devices which are very expensive. Therefore hydraulic drilling is mainly used where labour is expensive.
Wire cutting has become quite popular in the last 20 years in marble quarries and in the last 10 years in granite quarries. A diamond wire saw can work without operator. The first modern wire saws for granite used to have mechanical speed variators which wore out quickly, however, and were energy consuming (about 30% of the absorbed energy was consumed by the mechanical variator itself). The last generation machines now have inverter motors which change the cutting speed by varying the frequency. In this way all the absorbed energy is directly transmitted to the diamond wire (the fly-wheel is mounted on the motor-shaft itself).
Quarry wire saws can be used for large primary cuts (up to 300 sqm) as well as for small bench cuts. As for machine capacity, you may consider that the installed machine power in hp, times 3, gives the maximum cut in sqm on marble and times 4 on granite. For example, a marble quarry saw with 45 hp installed power can cut a bench of up to 45 x 3 = 135 sqm. Although granite is much harder than marble, granite cuts can be much larger. This is due to the fact that cutting on marble lets the wire easily penetrate into the material and therefore the friction becomes high. On granite the wire penetrates very slowly and so there is less friction (but the cut proceeds slowlier).
The cost of the only quarry equipment (drillers, splitting devices, saws, tools and consumables) for a small granite quarry is 200.000 - 250.000 USD.
Wire costs are about 100 USD per meter for marble wire and 150 USD for granite wire. Some local suppliers are cheaper. Wire life for marble is up to 70 sqm, for granite up to 15 sqm per linear m of wire, depending on hardness and abrasiveness of the materials. Production per linear meter is between 1 and 3 sqm/h for granite and between 5 and approx. 15 sqm/h for softer material.
As for chain cutting, the best conditions are in case of quarries with a large front where the machine can continuously cut the bottom of the bench horizontally. In that case no time is lost in repositioning rails. After the bottom cut, there can be done vertical holes (slim driller) which end up into the bottom slot left by the chain and thus the job can be finished in short time by wire cutting. On Botticino our chain is cutting at a speed of 4,5 cm/min which corresponds to about 8,6 m²/h (chain length 3,2 m, Kennametal K34-04 tools). Tools costs and greasing are about 2 $ per sqm.
Handling is another important quarry operation. Quarried blocks have to be ranged, lifted, transported, etc. The easiest way to do this is with a front-loader. But, apart from the purchasing cost of that machine (300.000 - 500.000 $ according to the required performance), also the operating and maintenance costs are very high. Such machines need 30 - 40 liters of diesel per hour and maintenance is about 10 $ per hour. Therefore these machines should be employed only in case there are no alternatives. If the quarry is restricted to a limited area, a much cheaper solution could be a Derrick crane which has a boom between 40 and 70 meters, lifting capacity 20 - 50 t and a rotation of 220 degrees. Its purchasing cost is just a fraction of the cost for a front-loader with similar lifting capacity and its operating costs are close to nil.
The ideal situation would be if the quarry could deliver well squared commercial blocks to the processing plant, thus saving costs in transportation and further time consuming operations. For this purpose a stationary diamond saw in the quarry could be useful, in order to cut the unshaped block faces before transportation.
As already mentioned, a good quarry management is capable of finding the right compromise between the different cutting and handling methods in order to get the maximum profit at the fastest production time and at minimum costs.
All mentioned costs and prices are approximate and for the Italian Market.
As a simplified example for the calculation of cutting costs, we want to consider the production of a standard granite block, hardness class 2, dimensions W = 1,20 m, L = 3,00 m, H = 1,60 m (= 5.76 m3). We will consider that 80% of quarrying is done by drilling and 20% with diamond wire cut. Furthermore we consider that the calculation has to be done on half of the faces as the other half has to be accounted for the next block. The total surface of the block is about 20 sqm. We therefore consider 10 sqm for our calculation:
8 sqm (= 80%) are obtained by drilling.
2 sqm (= 20%) are obtained by cutting.
Just as a matter of example, we consider 1 sqm surface obtained by 6 linear meters of perforation. Therefore the 8 sqm obtained by drilling correspond to 8 x 6 = 48 linear meters of perforation. At a speed of 0.50 m/min, the net time needed for drilling is 96 min (1.6 hours). At a perforation cost of 1$/m, cost for steel tools is about 48$.
The compressor needs about 1.6 h x 7 l/h = 11 liters of diesel which cost about 10$ (at 0.85$/l). Total cost of steel tools and fuel is 48 + 10 = 58$ for 8 sqm, equivalent to 7.25 $/sqm. The actual drilling cost is higher, because of the idle time (about 50%).
As for wire cut, the surface is 2 sqm. A medium size saw could be of about 30 kW. Wire production is about 2 sqm/h. Wire life is about 10 sqm/m. Energy about 0.05 $ per kWh (in Italy). The machine needs 1 h for cutting the 2 sqm. Tool cost is 150$ / 10sqm x 2sqm = 30$ and energy cost is 0.05$/kWh x 30kW x 1 h = 1,5$ for 1 hour machine operation. Total cost for tools and energy for cutting the block with diamond wire is 31.5$. This correspond to 31.5$ / 2sqm = 16$/sqm of sawing. 1 operator for short time required.
The above mentioned cut is double as expensive for a quarry yield of 50% or three times as much if the quarry yield is 33%.
Total theoretical net costs for our block are about 58$ for drilling and 31$ for sawing = about 90$. This corresponds to about 9$/sqm. As our block has got 5,76 cubic meters, the cost per cubic meter is about 16$.
On top of it there have to be added all other expenses (opening of the quarry, labour, machine depreciation, maintenance, spare parts, material splitting and handling, transportation, quarry yield, idle time, etc).