Pick Peat!

Skate wheels have to deal with some pretty rough treatment, including hard impacts, and gripping or skidding over concrete under your full weight.   Additionally, skaters have different needs for different surfaces and skating styles. 

For example, a vert or park skater will want very hard wheels.  They roll fast on the smooth concrete and wood ramps in a skatepark, and slide more easily than soft wheels, making it easier to do tricks.  On the other hand, street skaters sometimes want slightly softer wheels to help absorb the roughness of asphalt, and to get more traction on the road.  Hard wheels are louder, soft wheels are quieter.  There are a lot of trade offs, and almost every skater has a different take on it.

Urethane (a.k.a. polyurethane) is almost perfect for the job — it’s inexpensive, easy to work with, incredibly tough, and the softness can be easily adjusted.  Most other plastics just aren’t up for the task, or are so exotic they’d be too expensive.

The process of manufacturing a wheel is pretty straight forward:

• Several polyurethanes and other ingredients (like colors and curing agents) are mixed and melted together, according to a recipe.  The combination of different polyurethanes is what gives a wheel it’s characteristic hardness and durability, so a wheel manufacturer will have several different recipes for the different styles of wheel they produce.
• The hot mix is injected into a mold, and hardens as it “cures.”  It’s kind of like baking a cake: the curing process is a chemical reaction that happens when all the ingredients interact and cook together. 
• When the wheel is done curing, it’s put on a lathe that trims it down and finishes the surfaces:  the seat for the ball bearings, the smooth sidewalls, and the lightly textured rolling surface.
• Finally, graphics are applied to the wheel to dress it up a bit.

Tada!  A urethane skate wheel is born!

So, what about recycling?  

If you’re an environmentally conscious skater, this is a problem.  Most skaters will replace their wheels after they’ve worn down a few milimeters — wheels don’t always wear evenly, and they’re unpleasant to ride when they develop a flat spot.   The end result is that you end up with a pretty big chunk of urethane that isn’t useful anymore … and wouldn’t it be nice if it could get recycled into other skate wheels?

There are a few forms of recycling, but in most cases it’s just too expensive to do.

Complete recycling of the urethane in a wheel requires it to be broken down into reusable chemicals, which is quite difficult.  It’s like unbaking a cake:  because urethane wheels are cured, the ingredients have been changed at a molecular level.  If you attempt to melt a wheel down, you’ll change the chemical structure and it won’t be reusable for skate wheels.  In fact, you’re more likely to burn the urethane than melt it if you try it on your own.

There are other ways to recycle urethane, though. In some cases, it can be cut up for use in fish habitats, used in asphalt, other other “green” disposal forms.

One of the cooler recycling programs I’ve seen takes an old wheel, cuts it down, and uses it as the core for another wheel.  It’s like a retread truck tire (where they just wrap a new rubber tread around an old, worn down tire).  There’s still waste in the lathing process, but it’s about as direct of a recycling program as you can get.

There you go:  why we use urethane, and why we have a hard time recycling it.

The chemistry of urethanes is a continually growing and improving science.  There are people who are working right now on solving this problem, and I’m excited to see the day when the recycling question is easily answered.