Part 2: Snowboard Base Construction

In Part One of this series I covered forces effecting movement on the snow. In this section I will cover snowboard base construction, structure theory, and snowboard base maintenance.

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Part 2: Snowboard Base Construction

PE) is a Ultra High Molecular Weight (UHMW) polyethylene" class="glossaryLink " target="_blank">Polyethylene has been used as ski and snowboard base material since it’s invention at the end of 1950s.^[1]Shimbo, M., (1960). The Mechanism of Sliding on Snow, Report of International Association of Hydrology Commission of Snow and Ice: Helsinki, Finland. p. 101-106. It is probable that the type of polyethylene was used at that time was high-density polyethylene (HDPE). The use evolved in to UHMW-PE or UHMW) is a subset of the thermoplastic polyethylene. It has extremely long chains, with a molecular mass usually between 2 and 6 million." class="glossaryLink " target="_blank">ultra high molecular weight polyethylene (UHMW-PE) or UHMW which is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene, (HMPE), or high-performance polyethylene (HPPE), it has extremely long chains, with a molecular weight between 3 and 6 million. The longer molecular chain serves to transfer load more effectively. This results in a very tough material, with the highest impact strength of any thermoplastic presently made.^[2]Stein, H. L. (1998). Ultrahigh molecular weight polyethylenes (UHMW-PE). Engineered Materials Handbook, 2, 167–171.

All modern ski and snowboard bases are made of UHMW-PE, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon." class="glossaryLink " target="_blank">hydrocarbon called polyethylene. Hydrocarbons are chemical compounds consisting entirely of hydrogen (H) and carbon (C). Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene). The length of the molecular chain determines if it is a gas, liquid or solid.

The simple structure of the molecule also gives rise to surface and chemical properties that are rare in high-performance polymers. For example, the polar groups in most polymers easily bond to water. Because olefins have no such groups, UHMW-PE does not absorb water readily, nor wet easily, which makes bonding it to other polymers difficult. This is why damage to the base is difficult to repair.

Sample Hydrocarbon Chemical Makeup

Polyethylene is a compound containing thousands of CH2’s (carbon and hydrogen). Essentially, the longer the chain of CH2’s, the higher the melting point. Because polyethylene has very long chains, its melting point is very high. To create this structure, fine particles (120-180 micron sized grains) of polyethylene are polymerized into a crystalline material by a process called sintering, which uses heat and pressure to change the original substance.

Extruded and Sintered Polyethylene

Snowboard and ski bases are made of two different processes of polyethylene; extruded and sintered. Which is best?

Base Colors

There are two general varieties of the modern UHMW-PE snowboard base: the pure UHMW-PE transparent base and the graphite black base with the amorphous carbon-black additive. The carbon bases are very similar to transparent ones and differ slightly by the molecular weight and contain the carbon-black additive. Colored polyethylene is a manufactured mix of base material colorants or additives with resin powder prior to sintering.

Graphics on the snowboard base are applied one of three ways.

Stone Grinding Base

The initial snowboard base treatment is stone ground, which is the most widely used method today.^[3]Mathia, T.G., H. Zahouani, & A. Midol, (1992). Topography, wear and sliding functions of skis. Int. J. Machine Tools Manufact, 32: p. 263–266.^[4]Moldestad, D.A., (1999). Some Aspects of Ski Base Sliding Friction and Ski Base Structure, in NTNU Department of structural engineering. Norwegian University of Science and Technology: Trondheim. p. 198.^[5]Moldestad, D.A. & S. Løset, (2003). The Ski base Structure Analyser (SSA). Modeling, identification and control, 24(1): p. 15-26.^[6]Jordan, S.E. & C.A. Brown, (2006). Comparing texture characterization parameters on their ability to differentiate ground polyethylene ski bases. Wear. 261(3-4): p. 398-409.^[7]Kuzmin, L., (2006) Investigation of the most essential factors influencing ski glide, in Departament of Applied Physics and Mechanical Engineering, Division of Computer Aided Design. Luleå University of Technology: Luleå. p. 26. Stone grinding is an accepted method of a base treatment, and snowboard factories commonly apply this method to the newly produced bases. The steel scraping method has some positive aspects^[8]Kuzmin, L., (2006) Investigation of the most essential factors influencing ski glide, in Department of Applied Physics and Mechanical Engineering, Division of Computer Aided Design. 2006, Luleå University of Technology: Luleå. p. 26.^[9]Bergersen, H., K. Bergersen, & T. Flækøy, (1994) Strukturering av Ski = Texturing of Ski (in Norwegian). SkiSport p. 60-60.^[10]Kuzmin, L. & M. Tinnsten, (2006). Dirt absorption on the ski running surface – quantification and influence on the gliding ability. Sports Engineering, p. 137-146., but this process tends cause micro-hairs in the polyethylene surface increasing friction drastically.

Stone grinding provides base structure enabling the pressure melted snow to vacate. The structure pattern is an essential parameter, which influences the snowboard glide. It is important to structure the base of snowboards because their wide imprint tends to plow more snow and the base to overcome greater amounts of friction and suction in order to glide well. ^[11]Ducret, S., et al., Friction and abrasive wear of UHWMPE sliding on ice. Wear, 2005. 258(1-4): p. 26-31. Stone grinding a snowboard base is only the initial process. Structure treatment, hot glide wax, and tuning are involved as well, otherwise the result is poor performance.^[12]Ducret, S., et al., Friction and abrasive wear of UHWMPE sliding on ice. Wear, 2005. 258(1-4): p. 26-31.^[13]Fauve, M., et al., (2005). influence of snow and weather characteristics on the gliding properties of skis, in Science and Skiing III, E. Müller, et al., Editors. Meyer & Meyer Sport. p. 401-410. The wettability of the base material can be negatively influenced from the abrasive particles of the grinding stone into the base.^[14]Yekta-Fard, M. and A.B. Ponter, (1985). Surface Treatment and its Influence on Contact Angles of Water Drops Residing on Teflon and Copper. The Journal of Adhesion p. 197-205.

I recently had the opportunity to see a demo and try out a few different Wintersteiger base grinder machines in action and talk with various ski techs about techniques they employ. The technology currently used is pretty amazing. Often employing different machines for different types of base material.

Structure

Structure is a pattern, sometimes referred to as topography, which are little grooves on the base of the snowboard. Structuring is the practice of creating a series of very small, parallel grooves on the entire surface of the snowboard base. The purpose of structuring is increased glide under different conditions of snow crystal shapes, snow hardness, snow humidity, water content, and so on. As mentioned in Part 1 of this series, snowboarding is actually riding on a micro-thin layer of water above the ice crystals. Theoretically, the proper amount of water is needed between snowboard and snow to provide optimal glide. The general rule of thumb is; the smaller the snow crystals, the finer the structure required and visa versa.

The various Wintersteiger machines are basically a high tech wet sander / wet stone grinder that can be programmed to give virtually any type of structure imaginable. Some are automated, others are manual. While the Wintersteiger machines used for base grinding look similar, there is a group which are tuned specifically for base structure.

Basically there are two types of structure; linear and broken. Structure can be fine to course (refers to structure width), or deep to shallow (refers to structure depth). Structure designs can include linear, broken linear, parallel, chevron, double wave, or a combination of them.

Below are images done under scanning electron microscopy (SEM) at 100x of different base grind methods. The SEMs are courtesy of a friend from the University of Colorado, Boulder. The first is a course base grind, the second is a medium structure base grind, and the SEM to the far right is a fine base grind structure before removing the micro hairs with a Scotch-Brite pad.

Factory Imparted Structure

The structure imparted at most snowboard factories tends to be a medium pattern structure. Coarse patterns can also be prevalent, and while this may be appropriate for wet snow commonly encountered in the coastal snowpacks, it sometimes proves too aggressive for the colder Rocky Mountain (continental) snowpacks. Drier, smaller and sharper snow crystals, which are present in colder snowpacks can lodge within the recesses of these coarser structures, which increases drag.

Basic Structure Theory

Much like a tire tread, a snowboard base needs structure to reduce drag. In cold, dry snow such as the Rocky Mountain region (20°F and below), the structure should be fine and shaped to hold minimal water for the conditions. On cold crystalline snow (10°F and below), the base should be as smooth as possible so the points of friction are minimized.

On amorphous, wet snow (20°F and above), a coarser structured snowboard base is better to minimize the points of friction. The idea is to move the free moisture away from the base and reduce suction. It is important to mention that a course structure is somewhat permanent.

Some also employ a riller to add temporary structure by hand. A riller is essentially a roller with a guide that imprints structure on to the base with pressure. Rillers, like certain base grind machines, have very specific interchangeable metal rollers with differing topography for specific conditions, and can do linear and broken structure. Rillers have an advantage in varying conditions because the structure is temporary. Typically after a few hot wax treatments the base will return to it’s original form.

Maintenance

Structure will eventually wear down. How long it lasts depends on the frequency in which you ride and also on the snow conditions. You can eyeball your base and add structure if it appears to be worn down. After any structuring, always inspect the base before waxing examining for small hairs or micro-hairs on the polyethylene surface. If present, they should be removed with Scotch-Brite™ Pro pads followed by Scotch-Brite™ Omni pads or your base will be slower than before.

 

Base Burn

You may notice a white porous white/greyish color to the base, and many assume this may be oxidization. Polyethylene does eventually oxidize, but the rate of oxidation is very slow. What is actually happening is sharp edges of snow crystals are shredding the polyethylene base where snowboard/snow friction is greatest, usually along the edges of board. This is commonly referred to as base burn.

Base burn is not burn per se, but rather the ripping of polyethylene micro-hairs from the base due to snow crystals and ice. Although there is friction involved, it is abrasion and not heat or oxidation that is causing the edge damage. Fresh snow has sharp snow crystal points. Manmade snow is also quite abrasive.

To minimize base burn, keep the base well maintained with wax. This will be covered more in the next section, but typically early abrasion is caused from not allowing the wax on the snowboard base to cool overnight. Wax needs to harden in the polyethylene pores before scraping. If the damage is slight, a good, sharp steel scraper may shave off the micro-hairs. Be careful and go light, a steel scraper can cause a lot more damage to the snowboard base, extracting even more micro-hairs. Once you have removed the surface hairs, brush the surface with a brass or copper brush. Generally, Scotch-Brite™ pads followed by Scotch-Brite™ Omni-prep pads are the best solution.

Base Repairs

As mentioned earlier, extruded bases are easier to repair than sintered because they are less dense. The closest and most widely used bond is melted polyethylene, often referred to as P-tex, but this does not provide a permanent fix to a damaged base. P-tex is a trade name for the polyethylene base material used on skis and snowboards. It was originally produced and supplied to ski manufacturers by Inter Montana Sport (IMS) of Switzerland, and, although other companies now produce polyethylene base material under different trade names, just about everyone in the ski and snowboard industry still refers to it as P-tex.

All base repair materials (ribbon, string, sticks, and candles) are made of extruded, not sintered, P-tex. Sintered P-tex cannot be heated to the melting point without changing it’s molecular structure to an extruded form. Base repair materials vary in hardness, which affects their durability when filling gouges on a snowboard base. A soft repair material wears faster than a hard one, which means that you’ll have to refill gouges more frequently if you use a drip candle versus a P-tex repair ribbon.

Try to use repair material similar in hardness to your original snowboard base. P-tex ribbon is similar in hardness to a sintered base. Repair string is more similar in hardness to an extruded base. A soft P-tex material, like a drip repair candle, is fast and easy to apply. This can be handy for travel or ‘on-the-spot’ repairs, but it will wear much quicker than surrounding base material. It will suffice for very shallow scratches, but deeper gouges can become an ongoing maintenance nightmare. If the gouge exposes any steel edge material, fiberglass or wood, as in a core shot, first melt in copolymer repair material. Copolymer is made of polyethylene and a rubber-like ingredient, and will bond to these materials. Next melt P-tex repair material over the copolymer to fill the gouge, since P-tex will bond to copolymer but not steel or fiberglass.

This covers snowboard base material and structure. In Part Three I will be covering the next step; waxing, wax structure, precautions, and health risks.

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