A well-maintained road requires good surface material.
Getting the proper surface material may require setting up a rock-crushing operation in a central pit and hauling the crushed or pit-run material to the site. However, trucking costs can make this costly.
One solution is to use a portable windrow rock crusher. One such machine is the Rockbuster BH-1220.
The machine consists of two pieces of equipment: an agricultural tractor pulling the hammer mill crusher.
A Caterpillar 3306 turbocharged engine powers the crusher, driving four hammer shafts which are attached to 18 heavy cast hammers, each weighing 20kg.
The hammer shaft spins at 200 kilometres per hour, providing the force that enables the hammers to smash rock.
A crushing chamber, which can be hydraulically raised or lowered, encloses the hammers and is equipped with removable plates, as well as safety chains and rubber flaps that allow other nearby equipment to operate safely.
The crushing process with the BH-1220 Rockbuster is as follows:
- A Grader or rubber-tired backhoe pulls the oversized rocks and boulders from the ditch to the centre of the road to form a windrow that is approximately 1 m wide by 0.5 m high.
- Next the agricultural tractor pulls the tractor up to the windrow. The operator hydraulically lowers the crusher to the desired height, where the hammers just clear the height of the road.
- The tractor pulls the crusher over the windrow and the crushing starts. The tractor keeps a steady speed of 300 to 500 linear metres per hour. A separate set of instruments, mounted in the tractor, allows the operator to monitor the crusher's rpm, oil pressure, and water temperature.
- At the back of the machine, a consistent pile of crushed material 130 cm x 20 cm long is laid out with a crush size of 75mm (3in) minus.
- The crushed material is usually graded before more oversized material is pulled from the outside of the road to create a second windrow.
Crushing is done in three different ways: hammers strike the rocks, rocks thrash upwards in the crushing chamber, and the rock particles hit other rock particles during the crushing.
The size of the crushed material can be varied by adjusting the tractor's speed. Depending on the rock hardness, hammers can last from 6 to 15 hours and can be changed in about an hour. Crushing time varies from 2 to 5 hours per kilometre, depending on the type and size of the material being crushed and hammer wear.
Total cost of crushing varies per kilometre, based on number of windrows crushed.
