Paddle Feeder and Rotary Plough Feeder are types of feeders used for extracting loose bulk material from stockpiles, track hoppers, bunkers and silos and feeding it at a controlled rate onto a conveyor system.
In a coal handling plant, these feeders provide controlled extraction of coal from the track hopper and transfer it to the downstream conveying system.
Paddle Feeder Working Principle
A paddle feeder works by mechanically extracting coal from a track hopper and discharging it onto a belt conveyor at a controlled rate. The rotating paddle wheel penetrates the coal, helps break material bridges, and supports continuous coal.
How Does a Paddle Feeder Extract Coal?
The method of coal extraction depends largely on the flowability of the bulk material.
For free-flowing material, only the bulk material within the angle of repose tends to discharge from the track hopper onto the conveying system below, such as a belt conveyor. As material is discharged, fresh material flows downward under gravity to replace the material that has been removed.
However, cohesive or difficult-flowing bulk materials may not flow freely under gravity alone. In such conditions, bridges or arches can form above the discharge opening, restricting the flow of material.
The discharge paddle therefore penetrates deeper into the bulk material and mechanically extracts it. The required penetration depends on the flowability and internal friction of the material.
Sufficient paddle penetration is necessary to continuously break the bridges formed within the bulk material. This allows the vertical pressure of the material above to contribute to continuous discharge and helps maintain a steady flow onto the conveyor.
Main Components of Paddle Feeder / Rotary Plough Feeder
1. Paddle Drive
The paddle drive is the main mechanism responsible for rotating the paddle wheel. In the arrangement described here, the paddle drive consists of a hydraulic motor, hydraulic power pack and planetary gearbox.
The output shaft of the planetary gearbox is connected to the paddle assembly.
An overload protection arrangement is provided to protect the drive from excessive torque. A sensing probe fitted to the output shaft provides pulse signals to a proximity switch. If the pulse count falls below the preset value, indicating that the paddle wheel may be jammed or rotating abnormally slowly, the protection system can trip the paddle and travel drives.
The exact protection settings should be maintained according to the equipment manufacturer’s recommended values.
Working of the Hydraulic Paddle Drive
When the electric motor of the hydraulic power pack is started, the hydraulic pump circulates oil through the hydraulic circuit and returns it to the reservoir through the directional control valve, oil cooler and return-line filter.
When the solenoid of the directional control valve is energized, pressurized oil is directed to the hydraulic motor. The hydraulic motor rotates and drives the planetary gearbox and paddle assembly.
The hydraulic system pressure is monitored through the pressure gauge. Paddle speed can be controlled through the hydraulic pump and flow-control arrangement, depending on the equipment design.
2. Travel Drives
The travel drive moves the paddle feeder along its runway.
Typically, each pair of wheels is driven by a geared motor with an integral brake and torque arm arrangement. Two geared motors are used for the travel drive in the equipment arrangement described here.
The travel drives are reversible and synchronously operated so that the machine can move in either direction while maintaining proper alignment.
3. Cable Reeling Drum (CRD)
The Cable Reeling Drum (CRD) supplies electrical power to the moving paddle feeder through a flexible cable.
The cable is wound onto and unwound from the drum as the machine travels along the runway.
The CRD helps maintain a continuous electrical connection between the stationary power supply point and the travelling machine.
Paddle Feeder Operating Sequence
Correct starting and stopping sequence is important for reliable operation.
Starting
Start the paddle drive first → allow the paddle wheel to reach the required speed → then start the travel drive.
Starting the paddle before travelling allows the paddle wheel to establish proper rotation before it enters or moves through the coal.
Stopping
Stop the travel drive first → then stop the paddle drive.
This sequence prevents the machine from remaining stationary while the paddle is still working under material load.
Freewheeling and Obstruction Handling
Large boulders, stones or other rigid foreign material entering the hopper can cause the paddle wheel to experience excessive resistance.
If the available torque is sufficient, the paddle wheel may overcome the obstruction and continue operating. If the obstruction cannot be cleared within the allowable torque, the freewheeling/protection circuit can operate to protect the paddle drive and travel system.
What Should Be Done?
If the machine trips because of an obstruction:
- Select the appropriate maintenance mode according to the plant procedure.
- Reverse the paddle wheel using the approved operating procedure.
- Inch the machine backward if required.
- Identify and clear the obstruction safely.
- Remove large boulders or foreign material manually only after ensuring the equipment is safely isolated.
- Restart the equipment according to the normal operating sequence.
Never attempt to manually remove an obstruction while the paddle feeder is capable of starting or rotating. Follow the plant’s isolation, PTW and LOTO requirements.
Preventive Maintenance of Paddle Feeder
Preventive maintenance is important because the paddle feeder operates continuously in a dusty, abrasive coal-handling environment.
During preventive maintenance, the following components and conditions should be checked.
| No. | Equipment / Area | Important Checks |
|---|---|---|
| 1 | Long Travel Drive | Oil leakage, gearbox oil level and condition, wheel condition, rail clamp and stopper condition |
| 2 | Hydraulic Power Pack | Tank condition, oil level, gauge glass, breather/silica gel, oil cooler fan, hoses and hydraulic lines |
| 3 | Paddle Wheel Assembly | Hydraulic motor, planetary gearbox, paddle/blade and liner condition |
| 4 | Chain & Sprocket | Chain condition, lubrication, sprocket condition and guards |
| 5 | Coupling | Coupling condition and alignment |
| 6 | Dust Suppression System | Nozzles, tank, hoses and pump condition |
| 7 | PCRD & CCRD | Drum condition and guide roller condition |
| 8 | Gearbox | Lubrication, oil level and leakage |
| 9 | Oil Cooling System | Hydraulic oil hoses, cooler/radiator and fan condition |
| 10 | Foundation Bolts | Tightness and physical condition |
| 11 | Housekeeping | Coal accumulation, oil spillage and general cleanliness |
| 12 | Waste Management | Removal and proper disposal of scrap and maintenance waste |
Important Parameters to Monitor During Operation
Operators should continuously observe the condition of the feeder rather than relying only on protection trips.
Important parameters and observations include:
- Paddle motor/hydraulic drive condition
- Hydraulic system pressure
- Paddle speed
- Travel movement
- Motor current, where applicable
- Gearbox temperature
- Bearing condition
- Abnormal vibration
- Abnormal noise
- Coal flow
- Paddle/blade condition
- Coal choking or bridging
- Hydraulic oil leakage
- Cable reeling drum operation
A change in hydraulic pressure, paddle speed, noise or vibration can provide an early indication of a developing mechanical or material-flow problem.
Common Problems in Paddle Feeder
Some common operating and maintenance problems include:
Paddle or Blade Wear
Continuous contact with abrasive coal and stones can wear the paddle blades and liners. Excessive wear can affect the ability of the feeder to extract material effectively.
Paddle Jamming
Oversized coal, stones, boulders or tramp material can become lodged around the paddle wheel and increase the required torque.
Hydraulic System Problems
Low hydraulic pressure, oil leakage, contaminated oil, restricted filters or hydraulic motor problems can affect paddle speed and extraction capacity.
Gearbox Problems
Abnormal noise, overheating, oil leakage or increased vibration can indicate developing gearbox problems.
Travel Drive Problems
Unequal travel-drive performance can result in misalignment, abnormal wheel loading or difficulty in moving the feeder.
Material Bridging
Cohesive or wet coal can form a bridge or arch above the discharge opening, restricting material flow. Proper paddle penetration and suitable operating conditions are important to maintain continuous extraction.
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