With excellent operating performance, hydraulic jumbos have basically replaced pneumatic rock drills in large-scale mines, hydropower projects, railway works and tunnel construction. Nevertheless, the high price and long lead time of spare parts for imported jumbos bring great difficulties to operation and maintenance. As a result, many enterprises have decommissioned their hydraulic jumbos and reverted to pneumatic rock drills.
Our company has conducted extensive investigations among end users. It is concluded that the main obstacles restricting the popularization of imported rock drilling equipment are as follows:
Mine and tunnel operators in China lack sufficient skills in equipment operation, maintenance and upkeep, which leads to failure of the main pump of the jumbo.
Dirt often enters the hydraulic system when oil hoses and fittings are replaced on site, causing damage to the main pump.
After the water seal inside the rock drill head wears out, water leaks into the oil tank via the return oil circuit. This and other factors directly degrade the cleanliness of the hydraulic system below technical specifications and damage the main pump.
The hydraulic system design of certain imported equipment is not adapted to domestic construction conditions. For instance, the suction port of the main pump on imported units is usually arranged directly at the bottom of the oil tank without a suction filter. Such design requires the end user to maintain an extremely high cleanliness level of hydraulic oil in the tank. Most domestic operators work under harsh site conditions and cannot meet this requirement. Impurities and water settled at the tank bottom are therefore sucked directly into the main pump and cause abrasive wear.
In response to the above problems, our company started the retrofit of the hydraulic system for the SIMBA H252 mining jumbo manufactured by Sweden’s ATLAS COPCO in 1998. Details are shown below:
(1) Main Pump Replacement
In accordance with local rock drilling conditions and jumbo parameters, the Rexroth A11VO main pump is selected to replace the discontinued original Rexroth A8VO58 tandem pump. This model is better suited for domestic operating conditions in China.
(2) Hydraulic System Retrofit
① A stainless steel oil tank with increased volume is adopted to improve heat dissipation and contamination control. A large-capacity self-sealing suction filter is mounted on the side of the tank, fitted with a differential pressure transmitter that triggers an alarm and shuts down the main motor.
② A ball valve for direct blowdown is installed at the tank bottom for sludge and water draining, as well as on-demand oil sampling for oil condition analysis.
③ The pneumatic pilot-controlled triple valve is replaced with an electro-hydraulically controlled triple valve (this technology has been patented by our company). This modification greatly reduces the overall failure rate of the machine.
The above upgrades make the imported jumbo better adapted to China’s site conditions and facilitate reliable operation of this advanced hydraulic drilling equipment.