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Recycling Alone is not Enough

 

Here is the energy budget life cycle of one treated rotor versus its equivalent untreated.

Energy Used, Treated vs. Untreated (BTU's)

*Does not include transportation and machining.

There are three strategies for dealing with used brake rotors:

  • Send them to the landfill.

  • Send them to be recycled.

  • Use cryogenically treated rotors, then send them to be recycled.

Send them to the landfill.

Obviously sending them to landfill is not environmentally friendly. Rotors are made of cast iron, which is easily recycled. The mining and smelting of iron ore alone is energy intensive.  To create a ton of pig iron, you start with 2 tons of ore, 1 ton of coke and a half ton of limestone. The fire consumes 5 tons of air.  Sending rotors to land fill loses the energy of the mining operation and the casting operation.

 

 

Send them to be recycled

So it is environmentally friendly to send used brake rotors for recycling. But recycling them results in the use of energy and can cause pollution. 

 

There is a more environmentally friendly option. Cryogenically treating rotors results in getting three or more times the use of the rotor before it has to be recycled. Let's take a look at the environmental results.

To recycle a rotor, it is melted. A common rotor for a full size car weighs about 24 pounds. Of course, you just don't melt a rotor, you melt a whole bunch of scrap metal, usually in a device called a copula. The energy use of a copula works out to about 800 kilo watt hours/metric tonne. If you do the math, this works out to about 9 Kilo Watt hours/24 pound rotor, which works out to about 31,000 BTU's per rotor. 

 

But there's more. Gates, runners and risers in the mold require about 50% more metal than what is just in the brake rotor. So that makes the BTU's for the casting 46,500. Also, when the metal is melted, a percentage is lost due to reacting with the atmosphere and creating dross or iron oxide. This is about 7%. So this represents another 3,255 BTU's that are used to heat enough metal to replace the lost metal. So to recast a brake rotor involves about 49,755 BTU's of energy used, not counting what it takes to get it to the recycling plant nor the energy used to machine the resulting casting.

Use cryogenically treated rotors, then send them to be recycled.

Let's look at what happens when you cryogenically treat a rotor. It takes about 8.2 liters of liquid nitrogen to process a rotor in our medium size machine. (It is less in our biggest machine) Air Liquide tells us that to make that amount of liquid nitrogen would take about 2460 BTU. The heating cycle in the machine also takes about 1000 BTU electrical usage per rotor in the machine, for 3460 BTU. The treated rotor will last about three times the life of the untreated rotor.

By the way, the nitrogen used does not pollute the atmosphere. It was taken from the atmosphere in the air separation process used to liquefy it, so it is just being released back from where it came. The atmosphere is about 79% nitrogen to begin with.

Reduced Heavy Metal Pollution

Another advantage is that brake pads tend to last two to three times as long on treated rotor. Brake pads contain copper which is worn off them and deposited along the road way where it makes its way into the sewer systems and into rivers. Copper pollution is a major problem, especially along the coast lines where it does considerable damage to water life. We can cut this pollution source considerably.