Rock drilling is all about power and speed. You need a lot of power to break into solid rock and high speed to repeatedly hammer away at a work site. For safety and high productivity, many of today’s machines feature remote control. This presents a challenge because the remote control must be easy to operate yet allow full functionality of the machine.
Top hammer percussive drilling — the most common method for drilling holes up to 140 mm diameter — hammers the rock with impacts transferred from the rock drill to a drill bit in the bottom or a hole. Hydraulic pressure generates the force required — pressure builds to a maximum and when released, drives an impact piston forward. When the piston strikes a chuck, it transfers its kinetic energy as a stress wave through a drill rod to the drill bit, which uses this impact energy to pulverize the rock. Obtaining the highest drilling productivity and economy requires operation of all components in the system to be highly synchronized.
When designing the hydraulic system for a rock drill rig, the operator must be given complete and independent control of the key parameters — percussion pressure, percussion frequency, feed force, and rotation — to achieve optimum drilling efficiency. When all of these parameters are optimized to suit working conditions, the drill bit has full contact with the rock and the shock wave captures maximum kinetic energy to ensure that each impact achieves high productivity.
Although the design of the machine itself accounts for much of the machine’s productivity, achieving maximum productivity to meet cost targets requires a well-engineered hydraulic system with components that can maintain high reliability even in the face of frequent heavy impacts. Furthermore, a precise remote control is needed to achieve the high synchronization necessary for maximum productivity. Remote control also provides higher visibility, controllability, and safety than machine-mounted controls. It also lends itself to data acquisition to monitor operation and aid in improving future design of machines.
Nimco Controls AB, Malmo, Sweden, developed a system to meet these criteria in drill rigs manufactured by KG Mekaniska AB, Karl Gustav, Sweden. The electrohydraulic system integrates the features of Nimco’s EasyProg CANbus-based remote-control system with its CV 2000 LS series pressure-compensated valve. As a result, drill rigs have produced optimal results over the last two years.
The electrohydraulic system consists of a variable-displacement pump with load sensing to improve energy efficiency of the system, the CV 2000 LS pressure-compensated valve, and the EasyProg CANbus system. Designers also made an effort to reduce the amount of hydraulic hose in the machine. Not surprisingly, then, the new design contains about 13 fewer hoses.
The CV 2000 LS valve can accommodate a flow of 125 lpm to each cylinder port and is designed to work with both fixed- and variable-displacement pumps. Work port flow is controlled by 12- or 24-V proportional solenoids, with manual hand lever override functions available. Pressure limiters can be fitted on each individual work port together with shock and/or anticavitation valves.
The EasyProg control is a PC-based system that can be programmed in modules; hardware can also be built in modules to suit requirements of the application. Its CANbus configuration allows for digital and analog inputs and outputs. It features an easy-to-use menu for entering all settings and standard functions. Automatic functions for drill rigs, for example, enhance the speed of parameter settings as well as ensure specific safety parameters.
The CV 2000 LS valve controls key rock drill operating functions, such as percussion pressure and frequency, rotation torque, and feed force. It also controls track drives, positioning, and a hydraulic fan drive.
The rock drill in action
To achieve the best combination of productivity and economy, the operator sets the percussion pressure and frequency, and the control sets rotational speed according to set frequency. The final setting is feed force which is set against the percussion pressure to position the drill bit close to the rock. These settings are all maintained by the CV 2000 LS valve, which has two compensators per spool section — one for each cylinder port.
Hydraulic settings are made via the EasyProg electrical remote control unit. Feed force is remotely controlled by the CV 2000 LS pressure compensator through a pilot-operated, electrically controlled proportional relief valve. This enables a continuous setting of the feed force while maintaining the possibility of a second pressure limiter working as an overpressure cutoff valve. The design enables two pressure limiters for one cylinder port and extremely fine, stable pressure control.
The valve’s compensators exhibit flat flow/pressure curves and provide a constant flow, regardless of load pressure. The frequency and rotation of the drill bit is harmonized with the precise pressure setting for the feed force. The PL-2000 pressure limiter’s distinct pressure cut-off point ensures that the correct flow is maintained throughout the entire pressure range.
The EasyProg drill rig version software has automatic setting functions to help the operator reduce initial setup time. It also contains maintenance and service frequency options that can be accessed remotely by OEMs through a GSM unit that can be connected to any mobile phone. Additional functions and portable remote control units can be integrated either by wire or by Bluetooth, which, in the new version, has a range of 100 m.
Click here to download a two-page PDF brochure on EasyProg software