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.

What are the main weaknesses of the existing UHMWPE ski base types? – Part V.

Fifth issue of the existing UHMWPE ski base types is their very low ability to bind gliding ski waxes and other gliding agents chemically.

How it works?

Chemical bonds between UHMWPE and wax-based gliding agents are very weak, chemical bonds between carbon black as main structural and reinforcement additiv in modern ski base types are extremelly weak. In other words: if applied on a ski base, wax-based gliding agents cannot rely on chemical bonds, they urgently need mechanical retention.

Mechanical retention is strongly depending 1. on available free spaces or cavities in both very top surface and in bulk material of the ski base, 2. on size and disponibility of these free spaces and cavities = they are avaibale in amorphous and transition areas only, many of them are occupied by soot and other additives), 3. on size and charakter of the wax molecules which need to get inside free spaces when base material is more flexible thanks to heat and get stuck there when base material cools down again, 4. on the level of intertwining of the molecular chain structures of both ski base material and wax-based gliding agents.

Maybe the last forth condition is the most significant one for how strong the final mechanical retention of waxes in the ski base is. At the same time this forth condition = the level of intertwining of the molecular chain structure of ski base material on the one side and ski wax substances on the other side is the most problematic and tricky one.

Why?

For wax-based gliding agents very strong dependency exist between hardness and strogness of intertwining on the one side and softness and weakness of intertwining on the other side. This very strong dependency is defined by the length and charakter of the molecular chains of wax-based gliding agents.

The longer and more branched the molecular chains of the wax-based gliding agents are, the stroger they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the stronger is their mechanical retention inside the ski base material.

The shorter and less branched the molecular chains of the wax-based gliding agents are, the weaker they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the weaker is their mechanical retention inside the ski base material.

At the same time the length and charakter of the molecular chains of wax-based gliding agents define their gliding properties.

The longer and more branched the molecular chains of the wax-based gliding agents are, the stroger they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the stronger is their mechanical retention inside the ski base material, the worse gliding properties.

The shorter and less branched the molecular chains of the wax-based gliding agents are, the weaker they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the weaker is their mechanical retention inside the ski base material, the better gliding properties.

Waxes with best gliding properties does not stick to ski base material, the better waxes stick to ski base material, the worse gliding properties they have. Good advice is better than gold.

What are the main weaknesses of the existing UHMWPE ski base types? – Part IV.

Forth issue of the existing UHMWPE ski base types is their low and uneven capacity to take and hold other substances as gliding ski waxes and agents.

How it works?

Only sintered ski base types have sufficiently long chains to create free space to take wax molecules on the very top surface and inside the bulk material.

On the very top surface we call the free spaces “flokati carpet” which are fibres or hairs several hundred nanometers long which are covering the entire ski base surface. Between these fibres is enough space for wax molecules get in and get stuck here. Most wax molecules are allocated here.

In bulk similar free cavities do exist because the bulk material consists of intertwined molecular chains. It is estimated that wax can penetrate the ski base up to 1 micrometer, thus 1000 nanometers, the deeper you go, the less wax molecules you will - however - find.

Both free spaces in flokati carpet on the very top surface and free cavities inside the bulk material are ca. tens of nanometers large which means there is enough space for wax molecules  but...

If we connect this knowledge about size and distribution of free spaces or cavities in the flokati carpet on the very top surface and in the bulk material of the ski base with the knowledge about how especially competetion skis are prepared (several basic wax layers applied as hot appoach, gliding layers applied as block waxes or powder waxes, top coats applied as liquids or sprays), we need to see / understand that the spatial capacity of free spaces and cavities which was available at the very beginning of the ski service process is consumed very fast and each new layer applied on the ski base creates more and more complex mixture than a new layer.

If we combine these types of knowledge about size and distribution of free spaces or cavities in the ski base and about competition ski service processes with the chemical interaction between PE / carbon black as main material components of the ski base on the one side with waxes and wax-based gliding agents on the other side (chemical bonds between ski base and waxes are extremely weak and waxes need to rely on mechanical retention inside the ski base) it must be absolutely clear to us that existing services processes in combination with existing ski base types cannot create any relyable / repeatable and controlable results.

Combination of the existing ski base types and existing ski service processes cannot result in relyable / repeatable and controlable gliding features on the ski base.

What are the main weaknesses of the existing UHMWPE ski base types? – Part III.

Third issue of existing UHMWPE ski base types are the fast changes of the ski base surface.

How it works?

We know that the main component of UHMWPE ski base types is PE with extremely long linear molecular chains (normaly 7 to 12 mil. g/mol) which is enriched with different additives where the most important is soot or carbon black.

Even if we speak about PE with extremely high molecular weight and about carbon black as singular material types, we need to understand that there are plenty of PEs and carbon blacks which very different and specific features.

Particular features of PE and carbon black as two main components of modern ski base types define how they interact if processed in sintration. Normally carbon black has low or no chemical interactions with PE matrix leading to pure “sitting” inside the PE matrix. This weak “sitting” of carbon black corns inside the PE matrix results in fast and easy “breaking out” of whole soot corns out of matrix, “breaking off” of soot corn parts or soot corns abrasion on the very top surface. All these processes - breaking out / breaking off / abrasion - result in quite fast microscopic changes of the very top surface. These changes are the faster and more significant, the larger and more complex the very top surface of the ski base is, i.e. complex structure patterns which enlarge the surface multiple times and create complex details accelerate these changes.

Due to very weak chemical interactions between PE matrix and carbon black the very top surface of the ski base is a subject of very fast - even if with the naked eye invisible - microscopic changes which do cause that skiers run on a new ski base surface latest in the next competition.

What are the main weaknesses of the existing UHMWPE ski base types? – Part II.

Second issue of existing UHMWPE ski base types is the ski base memory of gliding waxes.

How it works?

Only sintered ski base types have sufficiently long chains to create free space to take wax molecules on the very top surface and inside the bulk material.

On the very top surface we call the free spaces “flokati carpet” which are fibres or hairs several hundred nanometers long which are covering the entire ski base surface. Between these fibres is enough space for wax molecules get in and get stuck here. Most wax molecules are allocated here.

In bulk similar free cavities do exist because the bulk material consists of intertwined molecular chains. It is estimated that wax can penetrate the ski base up to 1 micrometer, thus 1000 nanometers, the deeper you go, the less wax molecules you will - however - find.

Both free spaces in flokati carpet on the very top surface and free cavities inside the bulk material are ca. tens of nanometers large which means there is enough space for wax molecules on the one side but there are not accessible by any mechanical cleaning process on the other side.

Wax cleaners can reach these free spaces and free cavities but to remove all wax which has entered these nano-spaces in liquid state and solidified here is hardly possible.

These wax residues which cannot be removed any more after they have entered the free nano-spaces in both flokati carpet on the very top surface and in the bulk material we call ski base memory.

What are the main weaknesses of the existing UHMWPE ski base types? – Part I.

It is well-known that competition skis are equipped with UHMWPE ski bases where PE with ultra-high molecular weight = ultra-long molecular chains is enriched with different additives, first of all carbon black.  

UHMWPE is a type of material which is difficult to be processed. The longer the molecular chains, the more problematic the process-ability. One of the few possible processes is sintration. PE in granular form is mixed with soot and other additives and sintered with help of heat and pressure to a coil which is cut to a continuous strip which is grinded and flamed

 

Here the first issue of the existing UHMWPE ski base types originates. The coil has normally a diameter of ca. 1,5 m, the steel form is cooled down from edge to centre resulting in faster cooling of outer coil areas and slower cooling of inner coil areas. Cooling speed is directly influencing the fraction of crystalline and amorphous areas or ordered and disordered molecular structure. Molecular grid arrangement (crystalline and amorphous) is directly influencing the mechanical features and ability of the ski base material to create free cavities = to take additionally applied gliding waxes.

Only amorphous and transition fraction can take additonally applied wax. Crystalline fraction cannot be entered by any wax at all.

 

Each ski base surface revealed by each grinding is an original with a unique arrangement of crystalline, amorphous and transition fractions.

Why no wax chemistry has appeared?

No-wax chemistry is a clear reaction of the wax industry on the extremely low life time of liquid waxes based on dissolved waxes. 

The life time of waxes applied on the ski base is quite low in general. Due to very weak chemical bonds between waxes and PE, waxes need to rely on mechanical retention inside the ski base. Only waxes which can penetrate the ski base – or better: free cavities in the amorphous regions – can be retained more strongly providing longer life time.

Waxes sticking to the very top surface of the ski base – with no retention inside the ski base – can last for an extremely short time.

 To make waxes penetrate the ski base, more pre-conditions need to be given:

•  ski base material needs to have free cavities to take waxes
• heat needs to be introduced to increase the mobility of ski base material and liquidize the waxes
• wax filled cavities need to shrink after cooling to retain wax mechanically

·          As you can see the standard liquid waxes where the gliding agent is dissolved in a fast-evaporating carrier do fulfil only a part of one condition needed for a strong mechanical retention = they are liquid…that’s all…

The idea that liquid waxes can penetrate the ski base material due to the liquid status does not work in reality because especially the heat induced effects are completely missing.

To replace the heat approach and keep liquid waxes application as simple as possible, alternatives have been searched for to improve the mechanical retention of liquid waxes and thus their life time.

The clear answer is no-wax chemistry = gliding agents in a carrier which helps to penetrate the ski base.

To penetrate the ski base etching or swelling approach is often used. To fix the gliding agent in and on the ski base special carriers are used which can connect with both PE and gliding agents.

No wax chemistry is the approach how to keep liquid gliding agents application simple and to achieve a reasonable life time of liquid gliding agents… With waxes it is – however – hardly possible, that’s why no-wax chemistry…

 

What is the main difference between the cheaper and more expensive liquid gliders

Normally the main difference is the life time / stability / wear resistance… in other words how long the improved gliding properties can last under given snow and weather conditions.

 

Normally the cheaper liquids last on the ski base for a much shorter time and therefore provide a much shorter improvement of gliding features.

 

Why? Most of the cheaper liquid gliders are solutions containing two main components: active ingredients dissolved in a carrier. The carrier is responsible for liquid state of the solution, enables application on the ski base in the liquid form. After application the carrier evaporates more or less fast and leaves only the solid component on the ski base.

 

The only way how this solid component sticks to the surface of the ski base is the mechanical retention in the microscopic irregularities and roughness of the ski base surfaces. The chemical bonds are extremely weak.

 

How cheaper liquid gliders can be identified?

 

·      You need to shake the bottle before you properly to mix the active ingredients with the carrier.

·      Often sponge head is used for application.

·      After application you can see a wet film on the ski base.

·      They dry quite fast (5 to 10 min.)

·      You need to brush them softly with nylon brush.

 

Normally the more expensive liquid gliders perform a bit better, but especially last longer, in other words provide the improved gliding features for a longer time.

 

Why? Most of the more expensive liquid gliders contain a component which actively disrupts the surface of the ski base in a gentle way, in other words which allows the active substances in the glider to soak or to be integrated into the ski base. In other words: more expensive gliders create their own irregularities or micro roughness for better integration into the ski base.

 

How more sophisticated liquid gliders can be identified (except for they are more expensive)?

 

·      Normally they are sprays – you spray them or apply with fleece.

·      After application they often create small bobbles on the surface.

·      They need more time to dry / be integrated (normally 25 min. to 30 min.)

·      Often they are not brushed.

Which components of the ski base are the most important

 

 

Even if specialized magazines and articles mention many different additives and ingredients used in ski bases of competition skis, finally we will find out, if we look in much more detail, that there are only two main components which influence the most important features of each ski base type, especially now after fluor ban.

 

First is the UHMWPE itself which defines the features of the matrix. The matrix itself can get touch in contact with snow surface, that’s the reason why PE is used, because currently there is no other polymer with such a low coefficient of friction and so high hydrophobicity available. With respect to other components the matrix is responsible for the wear resistance and fixation of additives.

 

For wear resistance the most important figure is the length of molecular chains, the higher the length of molecular chains, the better the wear resistance. Reaching the value of 10.000.000 the polymer can be hardly processed.

 

Additive fixation in UHMWPE is problematic. The most additives do not form strong chemical bonds with the base matrix. Additives are bound in the matrix either by very weak chemical bonds or by mechanical retention. Especial close to the surface where the contact snow and ski base surface take place especially the mechanical retention decides.

 

The most important additive used in modern ski base types is soot or carbon black. The importance is given by the amount used in the competition ski base types which reaches up to 20 % of weight fraction in Nordic skis and up to 40 % of weight fraction in Alpine skis and by the way how carbon black is fixed in the PE matrix.

 

Some carbon black is incorporated directly in the PE matrix, but most of carbon black is filling the free space or cavities between the PE corns which are sintered together using heat and pressure. Especially the second type of soot fixation is responsible for high values of E-modulus which decides how ski base changes elastically under load.

 

Wax history in the ski base

We know that the very surface of the UHMWPE ski base is created by crystalline, amorphous and transition regions. In crystalline regions no wax can penetrate, transition regions are insignificant with respect to the area, the only ski base fractions where wax can penetrate are amorphous regions.

Amorphous regions consist of disordered structure of PE molecular chains with free cavities which size is in the order of tens of nanometres. In these free cavities there is enough space for wax molecules to get in and get stuck after hot wax application.

If ski base is ironed by temperatures close or above the melting point of UHMWPE which is ca. 140 degrees C the molecular chains of UHMWPE become more flexible and the free spaces between the chains are more easily to be accessed by wax molecules. After the ski base has cooled down again, the molecular chains “freeze” again and wax molecules remain trapped in the nano-cavities.

After skiing wax removers and cleaning brushes are used. Current wax removers evaporate very slowly which means their molecules are larger and heavier than those which were used in the past. They can access the cavities and dissolve the wax, however, they cannot remove the mixture out of the cavities.

Brushes are too coarse to reach the cavities. Some amount of wax - dissolved by removers - will remain in the cavities. After wax removers evaporate, solid wax remains in the cavities. This wax will stay here, until new wax is applied and mixed with the wax history in the ski base.

Technical snow and its specific features

 Technical snow. We have already touched on this topic several times. We have already mentioned several times that technical or artificial snow, in short, so-called man-made snow, is not actually real snow. Today we will take a closer look at the specifics and unique properties of this human creation.

 

Artificial snow is produced by using a pressure pump to drive a stream of water to a sprayer, where it is broken into small water droplets of approximately 0.1 mm in size. The droplets of the broken water must not be much larger or much smaller than 0.1 mm. Larger droplets risk not freezing sufficiently, while smaller droplets risk evaporating after contact with cold air or being blown away by the wind outside the snow-covered area.

 

As soon as a droplet of sprayed water hits cold air, the temperature of which should not be higher than about -2.5 degrees C when using chemically untreated water, a kind of ice shell or ice coating first forms on the surface of the water droplet, which seals the rest of the liquid water inside. As soon as this ice shell starts to fall towards the ground, the liquid enclosed inside has approximately 1 second to freeze due to the cold air.

 

If this does not happen, it is necessary to let the artificial snow "ripen" or "freeze out" in piles on the ground, where the freezing out already occurs much more slowly and due to the insulating properties of the snow and the increasing temperatures towards the ground, part of the internal water can remain in a liquid, i.e. unfrozen, state.

 

It is this possible proportion of liquid water inside the ice grains that causes artificial snow to often be wetter or more humid than natural snow under comparable conditions.

 

The relatively small size of the so-called seed droplets of technical snow (the optimal size is about 0.1 mm) is the reason for the second characteristic property of technical snow, which is its high density and bulk density. Small droplets of dispersed water form small ice grains with an average size of 0.1 to 0.8 mm, which are also very round or rounded. These small round grains fit tightly together and leave almost no space for air between them, which greatly complicates the process of snow freezing after it hits the ground, where the access of cold ambient air ensures the complete freezing of the ice grain.

 

The last important characteristic of artificial snow is the round or spherical shape of the small grains. This third – characteristic – characteristic of artificial snow, which so significantly distinguishes it from natural snow, is caused by the opposite direction of freezing of artificial and natural snow. While natural snow grows from the core towards the surface (air moisture condenses on the germ of dirt or dust somewhere high in the clouds), artificial snow freezes from the surface to the core (when a water droplet comes into contact with cold air, a kind of ice shell is first formed, which encloses the remaining still liquid water, which then – during a short flight towards the ground – must freeze to the center or core of the grain, if this does not happen, there is a real risk that the center of the ice crystal will remain filled with liquid water).

 

Repetition is the mother of wisdom. Let us therefore repeat the basic characteristic properties of artificial snow. Artificial snow is made up of small ice grains with an average size of 0.1 to 0.8 mm. Ice grains are primarily round or rounded, without sharp edges or facets. Technical snow therefore has a high density and bulk density (shortly after production it reaches a weight of about 500 kg/m3). If technical snow is produced at higher temperatures or the broken droplets have a very short flight path in cold air before hitting the ground, it tends to be significantly wetter or moister than natural snow under similar conditions, which is caused by the liquid or unfrozen center of the ice crystals.

 

The above specification suggests that man-made snow should cause a relatively low level of abrasion or mechanical stress on the ski base. The grains are round, moist, small, without sharp edges and facets, higher humidity blocks electrostatic charge... But in fact, the opposite is true. Anyone who has even the slightest experience with servicing skis, especially cross-country skis, knows that artificial snow is enormously aggressive and abrasive and causes enormously rapid wear or even "abrasions" of even the most tenacious waxes. In other words: technical snow is much more abrasive than practically any natural snow, including aggressive and abrasive firns or angular-grained snows deep below freezing point...

 

But how can we explain this? Where does this high level of abrasion and aggressiveness come from, when technical snow should be anything other than aggressive and abrasive due to its shape, humidity and details.

 

The explanation is very simple and at the same time deeply hidden. As we mentioned above, technical snow freezes from the surface to the center. A kind of shell or ice shell first forms on the surface of the water droplet, inside which the remaining part of the liquid water remains closed. This liquid water then freezes from the surface to the center. We all know what happens if we forget a bottle of beer or wine in the freezer, which we put there for the purpose of rapid cooling and which we eventually forgot about. Yes, that's right. The beer or wine tears the packaging, usually a glass bottle. Why, liquids increase their volume when changing from liquid to solid. The force that acts on a glass beer bottle is so great that the bottle eventually breaks.

 

However, when the ice droplets of artificial snow gradually freeze, the shell or ice cover does not burst, and all the energy of the gradual increase in volume, which must fit into the same space, is reflected in the "densification" or "compaction" of the locked water in the ice grain. Yes, the molecular lattice of the frozen water changes, which is then much stronger, denser and much less subject to temperature fluctuations and melting processes.

 

Yes, that's right, the ice grains of artificial snow are ice grains of compacted water, which are enormously strong, enormously hard, enormously stable, and therefore enormously aggressive and abrasive in relation to other materials, such as ski bases. The ice grains of compacted water are also much less subject to temperature influences and melting processes, which is why technical snow can withstand even relatively high temperatures above freezing, where natural snow would have melted completely long ago.

 

As we know, a significant part of the World Cup competitions in all possible skiing disciplines are already taking place mainly or primarily on artificial or technical snow. With regard to the progressing climate changes and the retreat of the natural snow line to ever higher positions, it can be assumed that skiing on technical snow, and not only on the summit, will become an increasingly frequent and common phenomenon.

 

However, skiing on artificial snow places significantly higher demands on the chemical, but especially mechanical properties of the ski base than skiing on natural snow. In terms of the chemical properties of the base, this is mainly hydrophobicity and dirt-repellency (as we have repeatedly mentioned above, technical snow is much wetter and at the same time much dirtier), in terms of mechanical properties, this is mainly hardness, toughness and abrasion resistance (as we know, technical snow is very aggressive and abrasive and its hardness often exceeds the own hardness of the base, which is manifested by the so-called effect of plowing the base with ice crystals).

 

It is a big question whether standard hydrocarbon waxes, even supplemented with various additives, are and will be able to meet these increasing demands for hydrophobicity, dirt-repellency, but above all hardness, toughness and abrasion resistance. Perhaps the time and space have come to completely abandon wax technology, or at least supplement it with new, more promising and effective alternatives...

How does the wax stick to the ski base? - Part. III.

We know that there are main principles how waxes are connected to the ski base. Some waxes penetrate into the inside molecular structure of the ski base which is accessible for waxes only if wax is in the liquid state and ski base is more flexible due to heat. Some waxes stay on the surface and “fill” only surface imperfections and roughness where waxes are partly retained in the “open” surface structure mechanically partly connected with weak chemical bonds.

Attention: surface imperfections and roughness cannot be confused with grinded or imprinted additional structure created by stone-grinding machines or manual structuring equipment. Surface imperfections are related to flat ski base here.

If wax molecules in liquid state enter once the inside molecular structure, fill the “closed” cavities inside the molecular structure of the ski base and change back from liquid to solid state, they cannot be removed again by either chemical agents or mechanical cleaning.

What does it mean?

This means that skis which have been waxed cannot be set back to “zero” status any more even if they have been used and cleaned chemically and mechanically.

What does it mean?

This means that any wax application is reacting / is mixed / is influenced by the wax molecules which remained “locked” inside the “closed” cavities inside the molecular structure of the ski base and which become liquid again as new wax layer is ironed.

What does it mean?

This means that after the very top layer of liquids / speeders / accelerators is worn off - which normally happens within a few hundred meters or a maximum of a few kilometers (depending on the snow type), your ski will glide on a mixture of old and newly applied waxes.

Even if you see a grey or white base surface, the cavities inside the molecular structure of the ski base are filled with old wax molecules which are locked in the closed cavities.

 

How does the wax stick to the ski base? - part II.

To understand the way how the additionally applied wax sticks to the ski base, we need to go a bit deeper into the topic…

Here we do not distinguish between chemical bonds and mechanical retention in general as we did in the part I., but we concentrate on the position of the wax in or on the ski base.

If we speak about how wax sticks to sintered UHMWPE ski base types, we need to distinguish between 1. wax penetration into the inside structure in the ski base and 2. wax adhesion to the ski base surface.

1.    wax penetration into the inside structure in the ski base

If you take a piece of a new ski base strip coming directly out of production, weight it and wax it as a usual ski base (apply wax, iron, let cool down, scrap and brush excess wax) and weight it again, you will find out, the piece of ski base strip increased in weight. The weight increase will depend on the type of ski base and the amount of additives incorporated, but it will normally range between 0,6 to 3,0 mg/cm2

This wax penetrated into the ski base does not take part directly in gliding features of the ski base, it improves the gliding features indirectly only: a. it helps the wax layers on the surface to be fixed on the ski base, 2. it can restore worn wax layers on the surface under special conditions, 3. it improves general conditions of the ski base.

2.    wax adhesion to the ski base surface

On the very surface of the ski base the wax layers retain partly mechanically in fine microscopic imperfections which are filled with wax, partly with help of chemical bonds. This very top surface is the main snow – ski base interface until it wears. To increase the life time of the very top layers, ski base surface is structured which means: 1. it total surface is increased significantly, 2. surface receives a height profiles with different shapes. Especially the height profile and increased total surface promote the wax layer life time on the very top surface.

Conclusion

Wax penetration helps 1. to fix the top layers in the ski base / snow interface which decides about gliding features, 2. to prolong some gliding features after the top layer has worn off.

Wax adhesion to the very top base surface is responsible for 1. the real interface between ski base / snow interface which decides about gliding features, 2. enables a short life time of top layers only.