Effective plow horizon control is necessary to cope with undulations in the coal seam. Providing the plow with the ability to follow the seam minimizes cutting of adjacent rock strata and the associated preparation costs, reduces cutting tool (bit) consumption and reduces power consumption while maximizing seam recovery. Caterpillar has developed an outrigger steering system for vertical horizon control that employs the use of hydraulic cylinders located between the gobside of the AFC and the relay bar of the shield. Extension of the cylinder promotes a downward (digging) cutting direction of the plow. Retracting the cylinder promotes an upward (climbing) direction of the plow. The steering cylinders can be controlled either manually or automatically via the Cat PMC™-R electro-hydraulic control system. A block anchorage system consisting of cylinders installed between face conveyor and shields (at the face ends) controls conveyor creep and helps maintain the proper tension in the plow chain.
- The plow is advanced in relatively small increments (cuts) compared to a shearer. This allows the horizon control system to vertically steer the plow, keeping it in the seam even when severe seam undulations are encountered. A shearer, due to its larger cutting depths and fixed position relative to the AFC, can only make gradual changes in vertical alignment. Therefore, in severely undulating conditions, the product mined with a shearer contains a higher amount of “out-of seam” dilution.
- Easy height adjustment allows plows to work smoothly through faults or undulations, minimizing the cutting of adjacent, unwanted strata.
- Coal production is maximized while preparation costs are minimized.
Variable Frequency Drive (VFD) motors allow speed to be varied between 0 and 120% of nominal while maintaining constant torque throughout a wide range of speeds. Power consumption on the motors is constantly monitored to allow load-sharing between the individual drives.
- Full utilization of available power
- Prevention of motor overheating and resultant downtime
- Reduced motor current with optimum torque during startup
- Excellent power factor (~1)
Effective overload protection is essential for fast, high-power plowing. The Cat planetary UEL overload protection system has an integrated multi-disc clutch with the pressure set to allow the clutch to slip well below the torque required to reach the breaking strength of the chain. If “clutch slip” is sensed, the gearbox torque is immediately decreased, combined with a simultaneous shutdown of the plow motors to prevent damage to the chain.
- Eliminates shock loads from all drive components
- Minimizes chain failures and maximizes component life
- Allows for a quick system restart
Caterpillar has developed an innovative shock absorber to provide added protection for the plow and chain. The elastic coupling inserted into the plow pulling sledge contains elastomers with properties that reduce the peak forces applied to the chain. This results in smoother plow operation, minimizing loads on the plow chain, the plow connectors and the drives, thereby extending their effective service life. The shock absorber is only available for the gliding (GH plow).
- Reduces wear and tear on plow, drives and chain
- Smooth plow operation extends overall service life
The key requirements for high-performance plowing are remote control, adjustable cutting depth and the ability to maintain a straight face line. These requirements are all achieved by the Cat incremental cutting system and the fully-automated plow longwall system. With conventional plows, variations in coal hardness lead to variations in cutting depth that often result in overloading of the conveyor and downstream equipment or jamming of the plow. Incremental plowing prevents these problems by keeping the depth of cut constant regardless of coal hardness or presence of rock bands. The plow makes a double cut - or a cut with double web - at each drive end, keeping the face straight at all times. Under favorable roof conditions - where the shield tip-to-face distance is not an issue - the shields are positioned in a saw tooth form: Only every 4th or 5th shield performs the “lower - advance - set” sequence during each plow pass. This minimizes the hydraulic pump capacity required for the shields and assures that plowing does not need to be halted for the purpose of advancing shields. If the roof is friable, shields can be programmed to advance more frequently, minimizing the average shield tip-to-face distance and maximizing the effective support. Also, in order to guarantee effective support of the roof, the PMC™-R electrohydraulic control system monitors pressure in the shield legs and prevents two adjacent shields from being lowered simultaneously.
- Remote operation allows highest safety and maximum productivity in low coal.
- The AFC/plow system and shield supports can be positioned exactly where they are needed (snakes, roof condition, faults etc.).
- System is self-correcting for over- or underpush, thereby maintaining a straight face regardless of conditions.
- Optimum use of installed power for maximum cutting depth for every area of the face.
- Automated Cat plow systems allow access to extended reserves in low coal seams to achieve a higher percentage of reserve recovery.
- Significantly more coal can be mined with more efficient layouts that reduce overall costs.
For Extremely Thin Seams
The base-plate plow is used for extremely low seams down to 0.6 m (24 in) with a practical minimum height of approximately 0.8 m (31.5 in). The typical maximum seam height is approximately 1.6 m (63 in).This system positions the plow chain on the gobside of the AFC, which makes it easily accessible for maintenance, a critical feature in low seam heights where working space is limited. The base-plate slides over the floor and underneath the line pans during operation. The integrated cleaning edge pushes coal from underneath the AFC back into the plow travelway. The cast plow guide is welded to the gobside of the face conveyor. Plow chains of up to 42 mm in diameter can be used, allowing the use of up to 2 × 400 kW (2 × 540 hp) installed power. Both gobside and face side pan connectors have a breaking strength of up to 2000 kN (220 tons), depending on the line pan being used.
State-of-the-Art Conveyor Technology for Underground Mining
The innovative PF plow line pans from Caterpillar define the new state of the art for underground face conveyor technology. They are based on the tried-and-tested PF3 and PF4 generations that meet all requirements regarding quality, wear resistance and conveying capacity.PF line pans form the powerful backbone of the entire conveyor system. The pioneering conveyor technology and extremely rugged pan design have been subjected to extensive testing.
Separation of Wear Parts and Structural Parts
The smart and totally new concept of segregating the different functional areas separates the wear elements from the structural elements. Extremely hard and wear-resistant materials are used for parts subject to wear, while the structural parts are made of tough, high-strength steels. The pan design allows problem-free replacement of worn-out top troughs, which delivers a lower cost of ownership during its lifetime.
- Substantially longer service life
- Considerably lower overall pan wear
Optimized Contact Surfaces
The use of the proven PF profile in the top race means maximum contact surface between the flightbar and the profile. This minimizes the surface pressure of the flightbars in snakes and undulating seams. Special shaping of the bottom race - which almost doubles the contact surface - reduces the wear of the flightbar shoulder while substantially reducing friction. Also, the curve-shaped transition at the pan ends greatly reduces the noise level during operation of the chain conveyor.
- Minimal friction
- Low wear of flightbar shoulder in the bottom race
- Minimized power losses
- Longer service life of flightbars and profiles
- Lower noise level during operation
Electronic Roof Support Control System
The modern, reliable and easy-to-operate electrohydraulic PMC™-R shield control systems are designed, manufactured and programmed by Caterpillar. Their primary function is automation of the cutting process using incremental plowing.Two configurations are possible: A control in each shield (typically used) or one control shared by three shields in cases where fewer shield functions are required. The VCU (Visualization & Control Unit) not only controls the entire longwall, but also visualizes face operations on a graphic display, including position, actual coal load on the AFC (through AFC power consumption), shield position, leg pressure, stroke and plow position. The VCU provides a face-wide network and allows remote maintenance of shield components as well as data recording and transfer of data to the surface.
Caterpillar® Global Customer Service
At Caterpillar, our relationship does not end with the sale of new equipment - it is just the beginning of a long-term partnership. We offer full life-cycle customer service with every purchase.When you invest in Cat equipment, you invest in productivity. Our global service and support packages include field service, repairs, overhauls and superior-quality OEM parts, ensuring the best long-term return on investment. Our goal is to constantly maximize customer productivity. We achieve this by remaining on the cutting edge of mining technology, providing customers with the best equipment with the lowest life-cycle costs. Cat Global Customer Service ensures that your mining equipment remains a highly productive asset.