3. How a Fine Rotary Steel Brush Removes Wax
3.1. Specific Design of a Rotary Brush
A rotary brush is functionally similar to a hand brush, but its design and mode of action differ substantially.
For SWIX and TOKO brushes, we will assume:
- a wire length of approximately 10 mm,
- a wire diameter of approximately 0.10 mm,
- an overall brush diameter of approximately 70 mm,
- an operating speed of approximately 800-1,000 rpm.
For the RED CREEK brush:
- a wire length of approximately 6 mm,
- a wire diameter of approximately 0.07 mm,
- an overall brush diameter of approximately 62 mm,
- an operating speed of around 1,000 rpm.
Despite their smaller wire diameter, the rotary-brush wires are approximately eight times stiffer than the reference 25 mm hand-brush wire because of their very short free length.
At 800-1,000 rpm, the tips of the SWIX/TOKO brush wires move at a circumferential speed of approximately 2.9-3.7 m/s.
A rotary-brush wire is therefore:
- significantly shorter,
- stiffer,
- less able to lie along the surface for an extended distance,
- loaded at a many-times higher speed.
3.2. Basic Mechanism
In a rotary brush, each wire moves along a circular path. It enters into contact with the ski base at high speed, bends briefly, shears across the surface and then springs back to its original position.
One working cycle comprises:
- a brief dynamic contact or micro-impact,
- rapid bending of the wire,
- a brief high-speed shear,
- elastic release,
- displacement or ejection of a particle.
Each individual contact is very brief, but it is immediately followed by other wires. The surface is therefore worked by a large number of short, overlapping contacts.
3.3. Wax Removal
In the first stage, the rotary brush removes very quickly:
- flakes left after scraping,
- loose wax dust,
- residues of a thicker layer,
- wax from the upper and accessible parts of the structure.
The wire disrupts, fragments or separates the wax by impact and shear. As it springs back, and under the action of centrifugal force, it may eject particles from the contact area.
A short wire can enter wide grooves. In a finer structure, however, it often acts mainly on the peaks and upper parts of the groove walls. It removes wax not in one continuous stroke, but through repeated fragmentation.
3.4. Effect on the Thin Film and UHMWPE
After the macroscopic excess has been removed, the brush continues to work on the thin wax film by the same mechanism.
The short dynamic contacts may:
- shift the film by shear,
- tear it,
- separate it from the surface,
- break it into fine particles,
- remove it progressively.
The brush does not distinguish between excess wax and functional wax.
As the film diminishes, the steel wires come increasingly into direct contact with UHMWPE at peaks, edges and fibrils. They may plastically deform it, micro-plough it, score it or detach microscopic particles from it.
This is unlikely to constitute uniform removal of a continuous layer across the entire surface. Material loss will instead be local and concentrated on the highest and most heavily loaded areas. Even very slight abrasion, however, may reach the thin wax-enriched surface zone.
3.5. Characteristics of Rotary Brushing
A rotary brush is fast, effective and generally more uniform than a hand brush.
Its defining characteristic, however, is the very rapid transition between the individual stages:
- removal of loose wax,
- opening of the structure,
- reduction of the thin functional film,
- direct contact with UHMWPE,
- possible micro-abrasion of the wax-enriched polymer layer.
A rotary brush works through a combination of micro-impact, brief shear and a very high number of repeated contacts.
Rotary brushing is faster and more uniform, but it leaves less time to stop the process at the point when the excess has been removed but the functional surface layer has not yet been significantly affected.
4. Hand or Rotary Brush - That Is the Question
Hand-held and rotary steel brushes serve the same basic purpose: to remove excess wax, open the ground structure and prepare the ski base for gliding. The way in which they achieve this result, however, is fundamentally different.
A hand brush works predominantly through slow, continuous shear by long, flexible wires. Its effect develops gradually, stroke by stroke, and the operator can continuously adjust the pressure, speed and number of repetitions. Its disadvantages are the longer working time and lower uniformity of treatment.
A rotary brush works through brief dynamic contacts by substantially shorter and stiffer wires. At a circumferential speed of several metres per second and with a high number of repeated contacts, it can remove excess wax extraordinarily quickly and uniformly. Once the excess has been removed, however, the same mechanism continues without interruption to work on the thin functional film and subsequently on the highest parts of the UHMWPE itself.
The rotary brush cannot determine whether it is currently removing:
- undesirable macroscopic excess,
- a still-desirable thin wax film,
- or the wax-enriched uppermost polymer layer itself.
The boundary between these stages is not sharp and may be crossed at different times in different areas of the ski base. The high speed of a rotary brush also significantly shortens the time available to the operator to stop the process.
From this perspective, a hand brush may be considered the safer tool. Although it is considerably slower and the result may be less uniform, it offers greater control and a wider time margin between removal of excess wax and the onset of more intensive treatment of the functional surface layer.
A rotary brush has undeniable advantages, especially in professional servicing, where speed, productivity and repeatability are decisive. These advantages, however, come at the cost of greater sensitivity to correct rotational speed, pressure, feed speed and number of passes.
The decisive question therefore cannot be merely which brush removes wax faster. More important is which tool makes it possible to stop brushing more reliably at the point when the processing excess has already been removed while the functional wax and polymer surface zone remains preserved. From this perspective, the hand brush is the more controllable tool and offers a greater tolerance for error.