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…