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In disc refiners (such as the Voith SDM series), the mechanical integrity of the refining zone dictates the quality of the fibre treatment and the lifespan of the equipment. The Stator Disc Holder (Stationary Head) and the Rotor Disc Holder (Rotor Head) serve as the foundational bases for the refiner plates. For the successful application of any manufactured flat refiner disc, these holders must maintain strict dimensional tolerances, absolute parallelism, and extreme metallurgical durability.
Rotor Disc Holder (Rotor Head)
Preparation and Setup
- Cleaning and Inspection: The rotor head must be completely machined, free of any debris, cutting fluids, or burrs.
- Assembly State: Depending on the strictness of the operation, the rotor head might be balanced bare, or it might be balanced as a complete assembly with the refiner plates installed (or using exact "dummy" weights) to simulate real-world operating conditions.
- Mounting: The component is securely mounted onto the spindle of a specialized dynamic balancing machine. The mounting must perfectly replicate how the rotor head will sit on the actual refiner's main shaft to ensure concentricity.
The Measurement Run (Spinning)
The balancing machine spins the rotor head up to a specific test speed. As it rotates, highly sensitive piezoelectric sensors in the machine's cradles measure the vibration forces generated by any asymmetrical weight distribution. The machine's computer calculates two crucial pieces of data:
- Amplitude: How much unbalance exists (the mass of the heavy spot).
- Phase Angle: Exactly where that heavy spot is located on the 360-degree circumference of the rotor.
Mass Correction
Once the computer identifies the exact location and amount of unbalance, the technician must correct it. For a solid steel piece like a rotor head, this is almost always done by material removal:
- Drilling/Milling: The technician drills shallow, precise holes or mills away small amounts of metal at the specific "heavy" coordinates indicated by the machine. These correction holes are typically made on the back face or the outer non-working diameter of the rotor head, never on the precision-machined mounting face where the refiner discs sit.
- Material Addition (Rare): In some industrial applications, counterweights can be welded on, but for high-precision refiner rotors subject to highly corrosive pulp slurries, material removal is the preferred and safer method.
Verification and Tolerances
The rotor is spun again to verify the correction. This iterative process is repeated until the residual unbalance falls within acceptable limits.
The final balance is measured against international standards, typically ISO 1940-1. For high-speed refiner machinery, a balance quality grade of G6.3 or even the stricter G2.5 is usually required to guarantee smooth operation and ensure the precise gap control necessary for uniform fiber treatment.
