Vinaora Nivo SliderVinaora Nivo SliderVinaora Nivo Slider

Slegar Observations

Rate this item

5.0/5 rating (4 votes)

on

Monday, 12 September 2011.
Slegar Observations
Super User

Read

317541
Important observations

The following observations  are based on careful studies  supported by lengthy experience and by thorough tests of the phenomena which may occur between the ski sole and the snow. We hope  that these observations will contribute to stimulate new ideas and to open new roads: it is only with knowledge of these phenomena that it will be possible to improve and resolve problems connected to the gliding of the skis.

As everyone knows the ski slides on the snow’s surface thanks to the fusion of snow crystals created by the sliding itself. Under the sole, at the contact points, the temperature exceeds zero degrees even when the temperature of the snow is much lower and therefore melts the snow crystals;  all this occurs in a fraction of a second and at a superficial level, immediately thereafter the particles of water become solid returning to the initial temperature.

This phenomenon is easily ascertained. Certainly  many of you may have observed on very cold days the  lines of the skis left on the snow can dazzle as if they were mirrors when reflecting the sun. So what happened?  Simply what we described above: by sliding we provoked the fusion of snow crystals and then the successive transformation into minute particles of ice which precisely  have the property of reflecting the light.

This first consideration makes one understand how the ski sole, making friction with the harshness of the snow, provokes the  above described effect. In other words, friction is produced between the surface of the sole and the surface of the snow, provoking an increase of the temperature and the consequent fusion of the snow crystals.

The ski sole finds itself  sliding not on the snow crystals, which being very hard would oppose the sliding of the ski, but in the instance of the fusion, on a microscopic veil of water which forms only on the contact points,  gradually as the ski advances.

Provoking friction between the surface of the sole and the surface of the snow to be able to slide more effectively at first seems to be a paradox. It goes to say  that in order to have the maximum output the coefficient of  friction must be as balanced as possible in relation to the morphology of the snow and to the meteorological conditions.

In the field of  friction in general the ski represents the exception.  In mechanics and in other sectors this kind of phenomenon is not found, because in these sectors it is the materials that have the lowest coefficient of friction that determine the maximum sliding.

As a counter-check of what is sustained various tests were effected. Amongst these the most significant test compared  the sliding of two pairs of identical skis within mechanical parameters, but different with different soles: one with a Teflon (ptfe) sole and the other with normal sole in sinterized polyethylene. The plastic material with the  friction coefficient of that is absolutely the lowest among all the existent plastic materials is Teflon (ptfe).  Teflon is non-stick and water repellent and hence   is used in various sectors to resolve friction problems.

The photocell test showed instead that the skis with polyethylene soles are always the fastest. The sole in Teflon with a much lower friction coefficient  in respect to those in polyethylene, are unable to create sufficient friction on the snow crystals to allow fusion.  We can therefore deduce that the sliding provoked by effect of the fusion of snow crystals is greater with soles in polyethylene, in respect to the dry sliding on snow crystals with Teflon (ptfe) soles with the lowest  friction coefficient. The Teflon soles only give good sliding results if the snow is very wet.

 

 

Imprints:

On the basis of what has been previously sustained it goes to say that imprints also hold a very important role in the sliding of the skis. This argument will be dealt with very briefly without entering into typically tecnical particulars, remaining rather with the general principles.

The principal purpose of the imprint is that of contributing to produce more or less friction between the surface of the sole and the surface of the snow needed to increase the temperature and provoke the fusion of crystals. The various types of imprints permit  the modification of the coefficient of friction of the soles. For equal depth (which must always be extremely limited), the imprint with very close groves will give a higher coefficient of friction and will produce more “heat” and is therefore more adapted to colder snow. On the contrary the imprint with the grooves more spaced will give a lower coefficint of friction, producing less “heat” and is therefore more adapted to less cold snow.

In the light of what has been said on the cause-effect between friction and sliding it will be simpler to choose the right type of imprint and the preparation of the soles.

Paraffin:

It may seem strange but paraffins also contribute to create friction between the surface of the snow and the paraffined sole.

The same general rules apply to paraffin as for the imprint on the sole, but here the components and the variables at stake are multiple.

It is possible to do a small test at home to understand how paraffin modifies the surface of the sole: it is sufficient to rub a little paraffin on one ski sole only and to then buff it with a cloth, leaving the other ski untouched. Place the skis horizontally with the soles up and then place an object on the sole without paraffin (for example a cell phone). Try to tilt the ski until you find the point that makes the object slide down. Next put the object on the paraffined ski and do the same test. The object does not readily slide down the ski, hence the  paraffin modifies and obstructs the sliding of the object.

This phenomenon doesn’t occur on snow, instead the opposite happens. The paraffin with it’s coefficient of friction contributes to the increase in temperature, hence the consequent fusion of snow crystals and as a final result better sliding.

It has happened particularly on very cold days and in conditions with little humidity, that one is  unable to make the skis slide correctly and one finds oneself in what feels like sand instead of snow. The cause of this condition is a combination of very low snow temperatures and very dry air. In these weather conditions the snow crystals are very hard and pointed and the sole tries with great difficulty to slide on these grains of very cold snow without however being able to obtain any satisfactory fusion. The sliding occurs for the most part in dry conditions, the ice grains slide under the sole in virtue of it’s sliding coefficient, but it is  really the coefficient low friction that cause the lack of sliding and the sole alone is not able to provoke sufficient friction to obtain the fusion of snow crystals.

Soft paraffins create the greatest friction, but in these extreme conditions it is not possible to use them because the hard, pointed snow crystals get stuck into the paraffin making sliding extremely difficult. Therefore it is necessary to use very hard paraffins with formulas capable of causing sufficient friction on the snow crystals to increase the temperature and the consequent fusion.

Also being studied are soles with particular inserts in a special elastomeric. The number of these inserts vary based on the coefficient of friction one wants to obtain and in relation to the temperature of the snow needed to provoke a correct and minute increase of the temperature and the consequent fusion of the snow crystals.

In conclusion therefore, it is possible to affirm that the best lubricant for the sliding of the ski is the microscopic veil of water that forms for an instant in myriads of points of contact with the surface of the sole, that in a continuous “kindling” transforms the ice to water;  all that we apply and do to the soles is nothing but a means of obtaining the RIGHT quantity of this precious natural lubricant water.

 

Gian Tessari

 

 SLEGAR SKI snc

Via dell’artigianato, 118

36012 Asiago (VI) Italia

Phone: +39/0424/462499

Fax: +39/0424/462360

www.slegar.com

email: This email address is being protected from spambots. You need JavaScript enabled to view it.

 

 

 

 

 

Social Bookmarks

Comments (0)

Leave a comment

You are commenting as guest.