The Structure That Does Not Actually Exist - Part No. 2

 

Dimensional Relationship Between the Groove and the Brush

The difference between the ground profile and the functional profile is clearly illustrated by the geometric relationship between the groove and the brush fibres.

Consider a symmetrical V-shaped groove with a pitch of 500 micrometres and a depth of 50 micrometres. At half its depth, it is approximately 250 micrometres wide. A steel fibre with a diameter of 120 micrometres corresponds to the groove width at a depth of approximately 38 micrometres. This model deliberately disregards elastic deformation of both the fibre and the wax and therefore represents a rather optimistic estimate of the attainable depth.

Below this level, the groove is narrower than the fibre itself. The fibre therefore cannot directly enter the bottom approximately 12 micrometres, or roughly the lower quarter of the model groove. Actual access to the bottom will also be influenced by the applied pressure, the contact angle and whether the fibre is in fact guided in the direction of the groove.

The brush therefore cannot remove wax equally from all depth levels. The peaks and the upper portions of the sidewalls are worked intensively, while an area remains in the lower part into which the fibre cannot geometrically fit.

Actual Structures Are Even More Complex

The model is based on a single regular linear V-shaped groove. Real racing structures, however, are often cross-hatched, chevron-shaped, interrupted, combined or multi-level. Multi-level patterns may contain several overlapping groove systems, so that access to one part of the profile is blocked by surrounding peaks or sidewalls.

They contain local depressions, intersections, sidewalls and tighter angles that are less accessible to the brush. The more complex the geometry, the less uniform wax removal can be expected to be.

A pitch of 500 micrometres is also only an approximate midpoint. Finer structures may have pitches of 300, 200 or 150 micrometres. Although they tend to be shallower, their cross-section narrows towards the bottom, and the diameter of a conventional steel fibre may be comparable to a significant portion of the groove’s total width. In structures with a pitch of 200 or 150 micrometres, direct contact with the lower regions may therefore be limited to a very small part of the profile or may not occur at all.

The nominal fibre diameter is not the only decisive factor. With use, the fibre tip becomes rounded and is often worn asymmetrically in the brushing direction. The actual contact geometry is therefore less capable of penetrating narrow lower regions than a simple calculation would suggest. Moreover, a worn tip does not create a single point of contact, but a broader asymmetric contact area that bears against the groove sidewalls sooner.

The fibres also work in bundles, interacting with one another, bending and deflecting. They do not always enter the grooves individually or at right angles, and in fine or multi-level structures they may pass over the upper portions without reaching the bottom. Although the flexibility of the bundle allows some adaptation to the surface, it also limits the precise guidance of individual fibres into narrow and irregular depressions.

The Brush Does More Than Remove Wax

After scraping and brushing, the wax is therefore not removed uniformly from the full depth of the structure.

The peaks and upper groove sidewalls are exposed most strongly, whereas more wax remains in the lower regions. Depending on the structure geometry, the type and wear of the brush, and the properties of the wax, the lower quarter or third—or, in fine or complex structures, an even larger portion of the original depth—may be less accessible. This is therefore not merely a passive residue of wax, but also the result of its mechanical redistribution during the preparation process.

Where the fibres can no longer penetrate deeper, they do not necessarily only remove wax. They may also act as smoothing or compacting tools: they displace the wax by shear, smooth it along the sidewalls and partly press it into inaccessible areas.

Compared with the geometry created by the stone, the functional profile is consequently shallower, more rounded and less pronounced. The peaks remain largely exposed, the transitions are softened, and the lower parts of the grooves are filled to varying degrees with residual wax.

In coarse, open and simple linear structures, the difference may be smaller. In fine, cross-hatched or multi-level structures, it may be substantially greater because their lower and lateral regions are less accessible to a conventional brush. The functional profile also continues to change with every subsequent waxing cycle, cleaning procedure and skiing session, so even after the initial break-in it is not a definitively fixed state.

Conclusion: The Ground Structure Is Only the Beginning

The central thesis is therefore confirmed: the structure created by the grinding stone and the structure that actually interacts with the snow while skiing are not identical.

The grinding machine creates only the initial geometry in the UHMWPE. Brushing, waxing, scraping, break-in and wear transform it into a functional profile whose shape results from the original grooves, the material properties, the geometry and wear of the brush fibres, the properties of the wax and other preparation procedures.

The finer, more complex and more multi-level the original structure, the greater the difference may be between the structure stored in the grinding machine’s program and the surface that ultimately glides over the snow.

Examining the structure immediately after grinding therefore captures only part of the reality. Measurements of groove pitch, depth and shape describe the geometry created by the stone, but not yet the surface after waxing, scraping, brushing and break-in. For meaningful comparisons of structures, the conditions of the subsequent preparation process should therefore be defined and reproduced as accurately as possible.

To understand how a structure functions, we must examine its condition after the complete preparation process. Otherwise, we are analysing the structure produced by the grinding machine, not the structure on which the skis actually glide. Any examination that does not take the effect of wax into account therefore reveals only part of the truth.

Hand or Rotary Brush - That Is the Question? Part. No. 1

Hand or Rotary Brush - That Is the Question?

To understand the fundamental differences between hand brushing and rotary brushing when removing excess wax from the surface of a ski base, we must first describe how wax is deposited on the base and how it interacts with the base material.

1. Three Types of Wax Reservoir in the Ski Base

After hot waxing, the wax is not present on the ski base as a single homogeneous layer. To assess the effect of brushing, it is useful to distinguish three basic reservoirs.

1.1. Macroscopic Excess Wax

The first reservoir consists of a continuous wax layer above the surface of the ski base and wax filling the ground structure.

This layer is predominantly a processing surplus. It covers the structure, may increase friction and restrict water drainage. It should therefore be removed with a plastic scraper followed by brushing.

1.2. Thin Film in the Surface Microstructure

The second reservoir consists of a very thin wax film adhering:

• to the peaks and walls of the ground structure,
• in fine grooves and surface defects,
• between UHMWPE fibrils and microscopic surface irregularities.

This layer is no longer merely a coarse excess and may contribute to the frictional and wetting properties of the ski base.

This is precisely where the difficult-to-define boundary lies between the desirable removal of excess wax and the undesirable removal of functional wax.

1.3. Wax Absorbed in the Uppermost UHMWPE Layer

The third reservoir consists of wax that, when heated, penetrated into the uppermost polymer zone of the ski base.

UHMWPE is not porous like a sponge. It is a semicrystalline polymer, and wax can penetrate primarily into its amorphous regions, interphase spaces and surface defects.

This wax cannot simply be 'brushed out' of intact polymer. It may, however, be removed together with the uppermost UHMWPE layer if the brush begins to wear it mechanically.

2. How a Fine Hand-Held Steel Brush Removes Wax

As a reference hand brush, we will assume:

• a wire diameter of approximately 0.12 mm,
• a wire length of approximately 25 mm,
• wires grouped into bundles approximately 8 mm in diameter,
• slow manual movement along the length of the ski base.

2.1. Basic Mechanism

Under pressure, the long and flexible wire bends, partially lies down in the direction of travel and slides over the surface along a relatively long path.

A hand brush therefore works predominantly by:

• slow and continuous shear,
• gradual loosening of particles,
• mechanical separation of wax from the surface,
• partial penetration into accessible parts of the structure.

It first removes loose flakes and fragments left after scraping. It then disrupts thinner wax residues by shear and gradually releases them from the walls and upper parts of the grooves.

A single stroke usually does not remove the wax completely. The first pass disrupts or shifts it, the next breaks it into smaller pieces, and subsequent strokes remove it. Hand brushing is therefore a cumulative process.

2.2. Penetration into the Structure

A 0.12 mm wire can enter only sufficiently wide and open grooves. Its actual penetration also depends on:

• the shape and depth of the structure,
• wire flexibility,
• applied pressure,
• the contact angle,
• wear of the wire tip.

A long wire has time to conform to the surface, but it often cannot reach into fine, oblique or multi-level structures.

2.3. Effect on the Individual Wax Reservoirs

A hand brush:

1. removes macroscopic excess very effectively,
2. gradually reduces the thin film in the microstructure,
3. does not directly remove absorbed wax from intact UHMWPE.

However, if the steel wire continues to contact the polymer itself, plastic deformation, micro-ploughing, removal of fibrils and a very small abrasive loss of UHMWPE may occur. Wax absorbed in the polymer may then be removed together with the polymer.

2.4. Characteristics of Hand Brushing

A hand brush is a slow and readily controllable tool. The applied pressure, number of strokes and area of action can all be adjusted continuously.

Its main weakness is non-uniformity. Hand pressure, the angle of travel and the number of contacts are not perfectly identical over the entire ski-base surface.

Why different structures need to be developed for ISANTIN?

In fact structures created with stone-grinding machines or manual rillers do not normally touch the snow surface. After the ski base is structured, it is normally cleaned chemically (to remove the cooling and greasing agent residues) and mechanically (to remove the grinding solid residues and unwanted hair) and hot waxed (to create protection film and modify ski base surface for respective snow and weather conditions).

Hot-wax-approach consists of several steps:

 1. wax is applied on the clean ski base surface (melted wax can be applied with wax applicator, solid wax can be rubbed on the ski base, wax can be melted on the iron and dropped as liquid on the ski base etc.), 

2. wax is ironed with recommended ironing temperature for recommended ironing time (normally from tip to tail with the target to make the wax penetrate to cavities inside amorphous ski base regions where wax molecules can be retained mechanically after ski base and wax cooled down to solid state), 

3. ski base with ironed wax layer is allowed to cool down for ca. 20 minutes at mediate temperature, 

4. excess wax is removed with scrapers first, from tip to tail, with sharp plastic scrapers carry-fully in flat ski base areas, 

5. after excess wax was removed from flat ski base areas, excess wax is removed out of water drainage gutter or gutters with oval plastic scrapers,

6. removing wax out of flat ski base areas with help of scrapers pushed more wax into grooves of structures which are now completely filled with excess wax which was compacted by scrapping,

7. grooves of the structure created with stone-grinding machines or manual rillers need to be restored, i.e. excess wax need to be removed out of the grooves, to remove excess wax out of the grooves brushes are used, normally fine steel or bronze brushes are used to remove excess wax out of the grooves,

8. fine steel or bronze ski brushes have normally hair 25 mm long, with bristles 0,1 mm thin which is bundled to bristle bundles with diameter of ca. 6 mm

9. if the grooves are 0,5 mm wide and ca. 0,05 mm deep (which is a middle fine structure pattern) it is quite obvious, that bristles 0,1 mm thin cannot reach the very bottom of the grooves, or in other words: remove all the excess wax out of the grooves,

10. it can be estimated that the lower 1/3 of the grooves remain filled with wax which is again compacted by the brush bristles

11. wax application makes the originally manufactured structures shallower and more rounded.

Unlike the hot-wax-approach ISANTIN covers the ski base surface with a very thin layer which is ca. 1 to 2 microns thin and thus copying the structure relief almost perfectly, in other words: after ISANTIN application the originally manufactured structure with help of stone-grinding machines or manual rillers remain more or less the same, only covered with an ultra-thin ISANTIN layer.

 

In fact the good performance of structures is tested and approved for waxed skis, not for plane = unwaxed skis which means the shallower and more rounded structure shapes after wax application are a part of the structure success.

 

If ISANTIN does not change the structures similarly to waxes, it is needed to change the structures in fabrication process = make them shallower and more rounded in stone-grinding process for ISANTIN.

How the wax application changes the ski base structure?

Especially competition skis are structured for better gliding performance. After the ski base grinding process has been highly automatised, the structuring is booming. There are various structures for any snow conditions and temperature range. Each parameter of the structure to be grinded can be set up, endless shapes, depths, pitches, angles are possible. Structures become more and more complex and highly specialized. Any detail, any parameter is important and counts...

Is it really true?

It is true that the modern grinding machines can produce almost any structure form and shape which you can even imagine. The grinding machines are extremelly precise and fast. Fine and high-quality stones are formed with diamant pins with accuracy to hundredths, pressure, feeding and revolutions can be controlled and regulated so precisely and stable that structures can be perfectly cut.

On the other side each ski base material is a bit different even if it was produced in the same production batch, but these differences are quite small.

After ski waxes - in multiple layers - have been applied on the structured ski base, a new story beginns to be written. Frist ski waxes and ski base material connect or are mixed on the molecular level to a new material which is a mixture of both wax and ski base material creating a new layer which can be called “gliding surface”. This new gliding surface is created on the molecular level chemically but in daily ski service reality it is created on macro or micro level. Thin wax layers in different forms are applied on the ski base, ironed, excess wax is scrapped off and brushed out of the structure...

Excess wax is brushed out of the structure, structure is restored by brushing, original grinded structrure is revealed again with help of brushing...

Is it really true?

Let us analyze a common case: grinded linear grooves with the pitch distance 0,5 mm which is normally called fine to middle coarse structure.

The pitch distance 0,5 mm which is 500 microns will correspond to ca. 50 microns deep structure, the ratio width / depth is ca. 10 due to technological reasons. Standard linear grooves are V-form grooves, the pitch distance between the tops amounting to 500 microns will correspond to a width amounting to few microns in the bottom (depth ca. 50 microns).

If excess wax is removed, it is first scrapped off by scrappers, later brushed out of the grooves (V-form of grooves is restored by brushing again. Which brush is used to restore the structure / grooves filled with wax?

Standardly steel or bronze brushes are used to clean the wax out of the structure. Both steel and bronze brushes consist of bundles of bristles. Bundles have normaly circle-shape with diameter ca. 5 mm. Each bundle consist of equally long and thin bristles. Standard steel and bronze brushes used to reveal structures have bristle length of ca. 20 to 25 mm and diameter of 100 microns (0,1 mm).

Let us have a look at the situation when the excess wax is brushed out of the grooves a bit more detailed: we have grooves 500 microns wide and 50 microns deep, we have brush with bundled bristles 25.000 microns long and 100 microns wide.

Conclusions: standard steel brush will remove the excess wax out of the upper half of V-shape grooves with pitch distance 500 microns. The bottom area of V-shape grooves with pitch distance 500 microns and depth 50 microns will remain “filled” with wax. In addition the bristles with the diameter of 100 microns will work as a rammer and will compact the wax inside the bottom area of the V-shape grooves resulting in shallower and more rounded groove forms.

Application of ski waxes does change the ski base structure, waxes make the structure shallower and more rounded compared to the status after fabrication.