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Double Disc Refiner

A double-disc refiner (DDR) is a high-efficiency machine used in the pulp and paper industry to mechanically treat fibers. By subjecting pulp to the action of rotating discs, it modifies fiber characteristics to improve the strength, smoothness, and quality of the final paper product

Design and working principle

The working principle of a permanent magnet (PM) motor-driven double disc refiner combines high-efficiency electromagnetic drive technology with mechanical pulp refining. It operates by using a synchronous motor to rotate a central disc between two stationary discs, creating two refining chambers where pulp fibers are mechanically processed.


1.  Drive Principle (Permanent Magnet Motor)

The refiner is powered by a Permanent Magnet Synchronous Motor (PMSM), which provides higher efficiency and more precise speed control compared to traditional induction motors. 

  • Magnetic Interaction: The motor's stator windings generate a rotating magnetic field when energized with three-phase AC. This field interacts with the constant magnetic field of the rotor's permanent magnets, creating torque.
  • Synchronous Operation: The rotor "chases" the stator's magnetic field, rotating at the exact same speed (synchronous speed). This allows for highly accurate pulping control.
  • Variable Speed Control: Using a Variable Frequency Drive (VFD), the motor's speed and torque can be adjusted to meet specific refining requirements, such as fiber length or freeness. 

2. Refining Principle (Double Disc Mechanism)

The mechanical refining occurs within the refiner chamber, which typically houses three main discs: 

  • Dual Chambers: The assembly consists of two stationary discs (stators) fixed to the housing and one double-sided rotating disc (rotor) mounted on the main shaft.
  • Fiber Treatment: Pulp is pumped into the center and flows through the narrow gaps between the rotating and stationary discs. The mechanical action of the disc "teeth" causes fiber swelling, internal fibrillation, and the release of microfibrils, which are essential for paper strength.
  • Gap Adjustment: An automatic feeding mechanism (often a worm gear or hydraulic system) moves the movable pedestal to precisely adjust the refining gap between the discs, controlling the degree of refining. 

3. Integrated Control and Safety

Modern PM double disc refiners are often integrated with DCS (Distributed Control Systems) for automated operation: 

  • Sensors: Real-time monitoring of vibration, temperature, and plate wear ensures stable operation.
  • Auto-protection: The system includes automatic "no-load" positioning during startup and shutdown to prevent disc damage.
  • Energy Efficiency: The use of PM motors reduces no-load energy consumption and eliminates the need for external rotor magnetization current, lowering overall power usage. 

Features and Benefits

  • Fiber Treatment: It increases the "beating degree" (Schopper Riegler or °SR) and wet weight of pulp, improving fiber-to-fiber bonding.
  • Versatile Material Processing: It handles various raw materials including virgin chemical wood pulp, mechanical pulp, recycled waste paper, and long-fiber pulps like cotton or hemp.
  • Pulping Stages: Primarily used in the stock preparation or beating section for continuous refining
  • Dual Grinding Zones: The machine features a central rotating disc (rotor) that moves between two fixed discs (stators), creating two distinct refining areas.
  • Refiner Plates: The discs are equipped with replaceable refiner plates featuring specific bar patterns to suit different fiber types and paper grades.
  • Gap Adjustment: Modern units utilize electromechanical or gear-motor devices to precisely control the gap between discs, ensuring stable refining quality.

Specification

 DDR MODEL DDR20 DDR26 DDR34 DDR42 DDR52
 Plate diameter inch 20-24 26-32 34-40 42-48 52-58
 Motor Power KW 315 500 900 1700 3000
 Speed Range RPM 530-1200 470-1000 420-750 325-600 300-600

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Doube Disc Refiner

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