DES 40A, Winter 2016
March 14, 2016
The Bicycle’s Life Cycle: Raw Materials
The bicycle is often referred to as the most sustainable form of transportation available today. Because of this widely accepted belief, cities everywhere have begun programs to increase bicycle usage by buying thousands of bicycles for civilians to rent. However, not many people stop to consider the raw materials involved in the production process and if our consumption has a significant impact on the environment. By analyzing the life cycle of a bicycle, specifically the materials that are used to make it, we can gain a better understanding of the impact it has on our world, whether it be positive or negative. In this report I will examine the raw materials involved in the life cycle of an aluminum road bike to confirm that the benefits of cycling truly do outweigh damage that may be caused by our consumption of materials used to produce it.
The process begins with the most fundamental part of the bicycle: the frame. Today, most bicycle frames are made out of aluminum alloy, meaning that the metal has traces of silicon, iron, copper, manganese, magnesium, chromium, zinc, and titanium, but is mainly composed of aluminum (Wikipedia Foundation, Inc.). Fortunately for bike manufacturers, earth’s crust has an abundant supply of an aluminum ore called bauxite that can be easily extracted from tropical and subtropical regions by open cast mining Although open cast mining involves clearing the land of vegetation, seeds of the plants that grow on site are collected and stored in a seed bank for post-mining re-vegetation (International Aluminium Institute). Once the bauxite is shipped to Taiwan, the metal undergoes the Bayer Process to refine it. This process involves the grinding, digestion, settling, precipitation, and calcination of bauxite in order to produce alumina (Rocksandminerals.com). In the grinding step, the bauxite is processed in a grinding mill and mixed with sodium hydroxide. When bauxite undergoes digestion it essentially means the metal is put under fifty pounds per square inch of pressure and is heated to 300°F. The next step in the Bayer Process, settling, uses a series of filters to separate the alumina from the waste. While undergoing precipitation, alumina hydrate is added to the solution to help produce pure alumina particles. The final step in the Bayer Process is calcination which is a heating process used to remove the water from the alumina hydrate. After the Bayer Process finishes, the Hall-Héroult smelting process begins. In this step of the production cycle the alumina is dissolved in steel pots that are filled with a molten electrolyte composed of a compound of sodium, aluminum, and fluorine. While this refined aluminum is still molten, the other metals mentioned earlier are mixed in to make the frame stronger (Bridenbaugh, Staley, and Van Horn). The product is aluminum alloy ready to be molded into a bike frame.
To mold the aluminum alloy into a bike frame, the metal goes through a recently invented process called hydroforming. To prepare the metal for this process, the aluminum alloy is sliced into thin metal sheets and then rolled into tubes. These tubes are placed in a hydraulic press which is then filled with a fluid composed of water, lubricants, drying agents, rust preventatives, and bactericides. By filling the area around the tube with fluid, pressure is applied which can mold the metal into the desired shape (Society of Manufacturing Engineers). Once the hydroforming is complete, and all the tubes have been molded into the appropriate shapes, the tubes are welded together and smoothed with sanding, thus producing a sturdy bicycle frame.
Since aluminum is one of the most affordable materials to work with today, bike manufacturers also use this material to make the wheels. The metal goes through a process similar to the one described earlier. However, after the hydroforming process is complete, the tubes resemble the rim of a bike’s wheel rather than parts of a bike’s frame. The molded tubes are then coiled into a spring-like formation and cut downwards on one of the sides to produce four individual rims. Next, the rims are rinsed in acid to remove contaminants and the ends are welded together to form the familiar circular shape (How It’s Made). Later, the rims go through an anodization process which involves coating the surface with sulfuric acid again and running an electrical charge through them to prevent corrosion (New Zealand Institute of Chemistry). After the rims have air-dried, holes are drilled in the inner rim so the aluminum spokes can be held in place. Finally, employees perform a process called lacing the wheel which requires them to carefully insert anywhere from ten to forty-six spokes into the aluminum flange (the center of the wheel) by hand and secure them with an aluminum and steel nipple (How It’s Made). Once all the nipples have been tightened, the wheel is ready for its tires.
Making a tire begins with the collection of the primary materials in it: natural and synthetic rubber. To collect natural rubber, latex is extracted from the Hevea brasiliensis tree which is found in Southeast Asia. After making small diagonal cuts along the length of the tree, latex oozes out out of the wounds and into a cup. The process is performed once every two days and yields roughly fifty grams of rubber. Next the latex is thickened by adding formic acid. This addition to the latex transforms it into crumbs which are then washed in water, dried, and then packed into blocks wrapped in polyethylene sheets for shipment to Taiwan (Gent). On the other hand, synthetic rubber is derived from petroleum, coal, oil, natural gas, and acetylene (Columbia University Press). During the refinement process of petroleum, the gases butadiene and styrene are produced as byproducts and are then combined to form liquid latex. From here on, the latex goes through the same process as the natural rubber (How Products Are Made).
The next step in tire manufacturing is combining these materials and molding them into bike tires. Once the natural and synthetic rubbers are obtained and shipped to Indonesia, they are all melted, mixed together, and rolled into thick sheets of rubbery dough. During this process additives such as mineral oil, sulfur, and carbon black are also mixed in to increase the elasticity and durability of the tire (How It’s Made). Next the thick rubber sheets are cut into narrow strips and enter an extruder which heats and softens the rubber in order to mold it into its appropriate shape. Following this step, the rubber is cooled in water to set the shape. For the outside of the tire, more strips of rubber are cut and then reinforced with nylon mesh. The two strips are then layered over each other and placed in a mold which uses steam pressure to bind them. As a result, a firm and durable road bike tire is produced (How It’s Made).
Another crucial part of bike manufacturing is the making of the chain. Since the bike chain is made out of steel, the first step in this process is obtaining this material. Steel is made by combining coke, iron, and small amounts of limestone. The coke is made by heating coal to 1000˚C and the iron ore is mined in Australia, Brazil, or China. Both materials enter a furnace with small amounts of limestone. Then air heated to 1200°C is blown onto the materials to melt and mix them, thus producing molten steel (World Coal Association). Once the steel arrives at the KMC Chain production site in Taiwan, the metal undergoes the chain manufacturing process (KMC Chain Industrial, Co.). This process involves running steel sheets through a punch press for them to be cut into figure-eight shapes, then baking the pieces in a coal-powered oven at over 1500˚F. When the links have cooled and hardened, they are placed in a machine along with a paste made of ceramic powder, silica powder, and water to polish the links. They are then put in a basket to be washed in a series of chemicals. Unfortunately, none of the sources I found were able to identify what these chemical baths were composed of, however they did say that once the links finished this step they have a nickel Teflon surface. Next the chain is assembled by machines and then is dipped in hot oil to lubricate it. After cutting the chain to about fifty-six inches in length, it is shipped to the bike assembly site in another location in Taiwan (How Its Made).
Another material that many consumers do not consider in the life cycle of a product are the fossil fuels. In order to transport these materials to the different production sites and distribute them to the retail locations, a large quantity of fossil fuels is consumed. To get a better idea of just how much is used, I did some research and found that 225 tons of bunker fuel per day is consumed for the average cargo ship that runs at a speed of 24 knots (Rodrigue). Seeing that it takes approximately fourteen days, and 3,150 tons of fuel, for a typical cargo ship to travel from Hong Kong to California, we can expect similar results for a cargo ship from Taiwan to California (Fuller). Furthermore, when we take into consideration the fact that bike manufacturers take up a minimum of 3,150 tons of fuel to transport the bikes to its retail location, we can conclude that they can easily take up well over four thousand tons of fuel for all transportation and distribution services.
Many may think that once the bicycle reaches its retail location the consumption of raw materials ends here. However, the consumption continues when its owner puts the bike to use and is consequently bound to make repairs to maintain the bike’s condition. The most common two bicycle repairs are replacing a tire and replacing a chain. As a result, more synthetic rubber, natural rubber, and steel are used for bicycle maintenance (Breene).
The last part of a bicycle’s life cycle that consumes raw materials is the recycling process. Since aluminum is the primary material in the bike I will be focusing on the materials involved in recycling it. The process begins with the transportation of the scrap aluminum to the recycling site. There the material is shredded into small bits and de-coated of any paints or stickers by blowing hot air at 500°C through the shredded material. Next the aluminum scraps are melted in a furnace heated to 750°C (Think Cans). During this step, a mixture of different salts, namely sodium chloride and magnesium dichloride, is added to remove impurities from the molten metal (Tremblay, Desrosiers, and Levesque). Finally, the purified molten aluminum is poured into a mold, cooled with water, and transported to a new production site (Think Cans).
To conclude, the life cycle of an aluminum road bike requires a long list of materials to create, transport, maintain, and recycle it. Not to mention the quantity of fossil fuels used to transport it is high. However, when considering the fact that most transportation vehicles require the same amount of fossil fuels, if not more, to be distributed, this drawback no longer seems as great. Furthermore, since the main component of this particular bicycle is aluminum, an abundant material on earth that can be easily molded and recycled, we can confidently say that the benefits of cycling are greater than the expenses paid.
Breene, Sophia. "Beginner's Guide to the Most Common Bike Repairs." Greatist. Greatist, 9 Oct. 2012. Web. 14 Mar. 2016. <http://greatist.com/fitness/bike-repair-maintenance-guide>.
Bridenbaugh, P. R., J. T. Staley, and K. R. Van Horn. "aluminum processing." Encyclopædia Britannica Online. Encyclopædia Britannica, Inc., 2016. Web. 12 Mar. 2016. <http://www.britannica.com/technology/aluminum-processing>.
Columbia University Press. "Rubber." Infoplease. Sandbox Networks, Inc., 2012. Web. 12 Mar. 2016. <http://www.infoplease.com/encyclopedia/science/rubber-synthetic-rubber.html>.
Fuller, Thomas. "China Trade Unbalances Shipping." The New York Times. The New York Times Company, 29 Jan. 2006. Web. 14 Mar. 2016. <http://www.nytimes.com/2006/01/29/business/worldbusiness/29iht-ships.html?_r=1>.
Gent, Alan N. "Rubber." Encyclopædia Britannica Online. Encyclopædia Britannica, Inc., 2016. Web. 12 Mar. 2016. <http://www.britannica.com/science/rubber-chemical-compound>.
How It's Made. "How It's Made Bicycle Tires." YouTube. YouTube, 2 May 2015. Web. 12 Mar. 2016. <https://www.youtube.com/watch?v=gm3JJW9wjA0>.
How It's Made. "How It's Made: Aluminium Bike Wheels." YouTube. YouTube, 4 Dec. 2011. Web. 12 Mar. 2016. <https://www.youtube.com/watch?v=xYUOLGEPw9Q>.
How Its Made. "Bike Chains - How Its Made." YouTube. YouTube, 29 Sept. 2009. Web. 12 Mar. 2016. <https://www.youtube.com/watch?v=h8j5-dC6_x8>.
How Products Are Made. "Latex." How Products Are Made. Advameg, Inc., n.d. Web. 12 Mar. 2016. <http://www.madehow.com/Volume-3/Latex.html>.
International Aluminium Institute. "Mining Process." Aluminium for Future Generations. International Aluminium Institute, 2012. Web. 12 Mar. 2016. <http://bauxite.world-aluminium.org/mining/process.html>.
The International Aluminium Institute. "Processes." Aluminium for Future Generations. The International Aluminium Institute, 2012. Web. 14 Mar. 2016. <http://recycling.world-aluminium.org/resources/processes.html>.
KMC Chain Industrial, Co. "KMC ECO Solution." KMC Chain. KMC Chain Industrial, Co., 10 Feb. 2012. Web. 14 Mar. 2016. <http://www.kmcchain.com/en/eco.php>.
New Zealand Institute of Chemistry. "Anodising of Aluminum." New Zealand Institute of Chemistry. New Zealand Institute of Chemistry, n.d. Web. 12 Mar. 2016. <http://nzic.org.nz/ChemProcesses/metals/8E.pdf>.
Rocksandminerals.com. "How Aluminum is Produced." Rocksandminerals.com. N.p., 16 May 1999. Web. 12 Mar. 2016. <http://www.rocksandminerals.com/aluminum/process.htm>.
Rodrigue, Jean-Paul. "Fuel Consumption by Containership Size and Speed." Hofstra People. Dept. of Global Studies & Geography, n.d. Web. 14 Mar. 2016. <http://people.hofstra.edu/geotrans/eng/ch8en/conc8en/fuel_consumption_containerships.html>.
Society of Manufacturing Engineers. "Hydroforming_1." YouTube. YouTube, 22 Mar. 2013. Web. 12 Mar. 2016. <https://www.youtube.com/watch?v=XicB7I-gDEw>.
Think Cans. "How Cans Are Recycled." Think Cans. Think Cans, n.d. Web. 14 Mar. 2016. <http://thinkcans.net/aluminium-cans/how-cans-are-recycled#.VuZwHpMrKRt>.
Tremblay, Sylvain, Luc Desrosiers, and Daniel Levesque. "Use of a Binary Salt Flux of NaCl and MgCl2 for the Purification of aluminium or aluminium alloys, and method thereof."Google Books. Pyrotek Inc., 2 Aug. 2011. Web. 14 Mar. 2016. <http://www.google.com/patents/US7988763>.
Wikipedia Foundation, Inc. "6061 aluminium alloy." Wikipedia: The Free Encyclopedia. Wikipedia Foundation, Inc., 4 Mar. 2016. Web. 12 Mar. 2016. <https://en.wikipedia.org/wiki/6061_aluminium_alloy>.
World Coal Association. "How is Steel Produced?" World Coal Association. World Coal Association, n.d. Web. 14 Mar. 2016. <https://www.worldcoal.org/coal/uses-coal/how-steel-produced>.
15 March 2016
Embodied Energy In an Aluminum Bicycle Life Cycle
Bicycles are often perceived, as one of the greenest forms of transportation, but what most of us fail to consider is the underlying amount of energy that goes into producing a bicycle. We chose to look at the embodied energy of a bicycle to see just how sustainable they really are. Specialized Bicycles is one of the biggest bike producers in the world, ranked at the 3rd largest producer, we chose to look into the embodied energy in their first production road bike, the Allez to see where in its life cycle the embodied energy comes from. The Specialized Allez was chosen because we wanted to look at an average road bike that is mostly aluminum construction, and the Allez seemed to be a perfect example, it also worked well because specialized has recently began researching for themselves just the amount of embodied energy that goes into some of their bicycles and doing crowd research to see just what sustainability means to the consumers, and if they would be willing to pay more money for a bike that was sustainably produced. The production of almost all of today’s bicycles is done in china and Taiwan, in 2011 99% of all bicycles were produced in these countries (1). Unfortunately most bike companies do not own their own manufacturing facilities but contract out facilities to manufacture their designs, this leads to a limitation of available information.
The research done on the Specialized Allez was conducted by a team of researchers at Duke University that was backed by Specialized Bicycles to look into the sustainability of their 2014 Aluminum Allez road bike and their Carbon Fiber Roubaix road bike as well as a DT Swiss R24 wheel set and SRAM PC 1071 chain to look into the sustainability of these products (1). These products were analyzed in a cradle to gate strategy, so they looked at the energy incorporated in the production of these products from the raw material stage to the point the bicycle was packaged and ready to be shipped to a specialized factory. The goal of this report will be to discuss the findings about the Specialized Allez bicycle from this very detailed research by Duke University researchers, add additional information about individual stages where quantitative values were not given, and look at the embodied energy of the bicycle for every stage of the life cycle beyond the stages that the research paper covers to see just how sustainable bicycle production really is.
Since the Aluminum frame not only has the most mass of any bicycle component it is also the most energy intensive to produce we will focus on it first. In the research done by the Duke University team, the production of the frame consumes 1600kWh/kg or 2,380kWh per frame (1). Before production of the frame could begin the earths crust must be surface mined for bauxite from open pit mines using heavy machinery (alcoa), the mining process is an insignificant source of the total embodied energy in Aluminum. Bauxite is then refined using the Bayer process to reduce to an aluminum oxide then Hall-Héroult process to purify into pure aluminum, the most energy dominant part of this process is the smelting process in which the aluminum oxide is melted and an electrical current is applied causing the separation of oxide from the aluminum which uses 15kWh/kg (2) or 57kWh/kg for the entire primary production process (3). These processes will use a combination of electrical energy, and energy from burning coal and fossil fuels. China is also the worlds largest producer of aluminum (2) which helps reduce transportation cost to manufacturing facilities. After the primary production is complete the aluminum components then go through the various shaping and joining processes which starts with the extrusion process to make the tubes to construct the frame, butting to form the ends of the aluminum tubing, hydroforming to get the tubing into the required shapes of the frame, welding to assemble the frame, and then heat treatment to further change the physical properties of the aluminum. In addition to the frame the bicycle is composed of many other aluminum parts such as the forged stem, extrusion and hydro-formed seat post and handlebars (4) and shift/brake levers and crank sets (5). These processes use electrical energy for machinery. Once the frame is made it is then heat-treated, which according to the research done by Duke University is the most energy intensive, the ovens holds 6 frames runs at 196kW and the frames must be held at 400°F for 10 hours, assuming they get up to heat relatively quickly this equates to about 350kWh per frame. Then the quenching of the frames consumes 20kWh/frame. After heat treatment the final process to any aluminum part is painting or anodizing.
The next most used material used on the bicycle is steel, in components such as the chain, chain rings, rear cassette, cables, bearings, hardware, and stainless steel spokes. The initial production of steel begins with mining of iron ore, which like bauxite for aluminum is done with heavy machinery with the addition of explosives (6). Similar to aluminum china is also the largest producer of steel (Wikipedia). About 8% of the primary production energy of steel is from mining (7). The most energy intensive primary processing stage is the blast furnace process in which iron oxides are heated via burning of fossil fuels or charcoal, and CO2, 02, and CO are introduced to separate the oxides from the iron. Blast furnaces operate on the large range of 5.5-13kWh/kg (7). After the iron has been processed, additional processing including addition of carbon is performed to generate the steel. The primary production energy of steel is 7.2kWh/kg where as stainless steel is 23kWh/kg (3). The additional energy used to produce stainless steel is due to additional annealing required and chromium input (8). Most components are made of standard carbon steel and are stamped, such as all the sprockets, which are cold rolled, then stamped to shape. The production of the SRAM PC 1071 chain is done with a combination of extrusion to produce the rollers, and wire drawing produces the pins, both of these components then must be cut to length, the inner and outer plates are made by first rolling low alloy steel into sheets, then stamping. The stamping process causes a lot of waste and only 60% of the sheet is utilized in the stamping process, causing wasted energy in production in the excess steel. The steel is heat-treated at 4kWh/kg. The complete chain manufacturing process embodies 200kWh/kg or roughly 50kWh/chain (1). The next main component that was analyzed by Duke University was the DT Swiss front and rear wheels, which take 185kWh/kg or approximately 325kWh/wheel set. The wheel sets consist of many different parts, like drawn stainless steel for the spokes, extrusion and heat treated aluminum nipples, forged and machined aluminum hubs, and hydro formed and welded aluminum rims, along with other small assembly components, like steel axles, and bearings. All produced with machines operating on electricity. And assembled by machines to ensure correct spoke tension. (1)
The next main component of the bicycle we will focus on is the tires and tubes, which use a combination of mainly natural, synthetic, and recycled rubbers to produce. The tire also incorporates steel cable or fibers like Kevlar to get its structure, strength and puncture resistance. The tire this report will look at is the Continental Grand Prix 4000 due to its huge popularity in the road bike community. Natural rubbers used in the tire can be harvested in the form of latex from certain trees by hand where it is then taken to be processed into rubber (9) the primary production process consuming a mere 4.1kWh/kg (10). Where as the primary production energy of synthetic rubbers, which are petroleum based, consume 30.5kWh/kg (10). Carbon black though is the most energy intensive at 35kWh/kg (10). The start of the production of the actual tire starts with the combination of the natural, synthetic, and recycled rubbers, with the addition of carbon black, sulfur and mineral oil, which is then melted together and rolled into sheets where they are then cut and then heated again to get their base shape before the addition of Kevlar threads tor structure, before going into a mold oven to shape and volcanize the tire (11). Unfortunately no data was found on the embodied energy in the actual bike tire, but continental has done extensive research on the embodied energy of their car tires, if we consider the processing stage is at all similar we can use the numbers generated from the car tire to make some assumptions, from their findings the raw materials acquisition consists of 65kWh/car tire or 2.25kWh/bike tire and 29kWh/car tire for production or 1kWh/bike tire (12). This totals up to 7.5kWh for a pair of bike tires. Almost as important as the tire is the inner tube which gives it its shape during use, the most common material for inner tubes is butyl rubber which consumes 31kWh/kg in primary production production (4) and an average tube weighs about 100g. This totals to a pair of tubes having the embodied of about 6.2kWh. Shown in the appendix is a plot showing the main components that have been discussed so far and the amount of embodied energy each component has at the end of its production. As can be seen the frame is by far the most energy intensive component. Although this is partly to do with the larger weight, regardless its kWh/kg production energy is higher as well.
The next stage after all primary production is complete is the transportation phase. Specialized headquarters are based in Morgan Hill California, and since the bikes are transported by cargo ship it will also be assumed they are shipped to San Francisco Bay from their final production point in Taiwan, making a 6,500-mile ocean trip (13). They will then be transported to the specialized headquarters 75 miles away by semi truck (14), before being transported again by semi truck to a dealer anywhere in the country, which could be up to 3,000 miles away. The next stage of the bicycles life cycle is the use and maintenance stage. This stage is entirely based on the type of user; it will be assumed the bike has a relaxed life with moderate use and proper maintenance. A bicycle will use a small amount of oils and lubricants in its life to lubricate the chain, cables, and bearings to maintain optimal performance, but this is very difficult to quantitate due to the range of users. Similarly some users might ride the bike infrequently enough to never need to replace the chain and only replace the tires once or twice, we will assume the user replaces the chain once and tires and tubes 3 times. This is an additional 90kWh. But an avid rider could do this on a yearly basis.
At the end of a bicycles life it can either end up in a landfill or its components can be recycled saving large amounts of energy. The large amount of aluminum embodied in the bicycles components can be recycled for huge primary production energy savings, as pure aluminum can simply be melted down to form new ingots to then be formed into whatever shape they need for their next life. Aluminum is also infinitely recyclable, and can save as much as 95% of the production energy that would go into making an ingot from raw materials (15). Although steel is not quite as efficient to recycle it savings too are still very beneficial, the recycling of steel can save up to 74% in primary production energy (16), and the recycling of Stainless Steel can save 67% of primary production energy (17). Rubber tires are also very recyclable, and unlike steel and aluminum their recycling possibilities are even greater, with 2nd life possibilities such as rubberized asphalts tire-derived fuels, purses, and shoes, which is just to list a few (18). Recycling can greatly reduce the amount of raw materials that need to be extracted and the extra production energy that goes into making the product from raw materials.
Without actual weights for each component on the bike it becomes difficult to determine the full amount of energy that goes into making a Specialized Allez bicycle, but from what we have learned from Duke Universities research as well as our own, the total embodied energy of the main components is 2768.7kWh or 9.967GJ. And this still neglects parts like the handlebars, cranks, and other important parts to a bike. There is a lot of energy that goes into the making of a bicycle, with companies like specialized looking into potentially improving production methods to make a more sustainable bike it will be interesting to see what the future holds and if we will be seeing sustainably built bicycles on the market in the future.
Table 1: Embodied energy of major components after manufacturing
(1) Johnson, Rebecca, Alice Kodama, and Regina Willensky. The Complete Impact of Bicycle Use: Analyzing the Bicycle Impact and Initiative of the Bicycle Industry. Rep. Duke University, Specialized Bicycle Components, Apr. 2014. Web. <http://dukespace.lib.duke.edu/dspace/bitstream/handle/10161/8483/Duke_MP_Published.pdf>.
(2) "Technical Specifications" Specialized: Allez. 2014. Web. Mar. 2016.
(3) "SORA." SORA. Web. Mar. 2016.
(4) CES EduPack 2014 Sustainability & the Built Environment Edition. Cambridge: Granta Design Limited, 2014. Computer software.
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(6) "Mining Iron Ore." HowStuffWorks. HowStuffWorks.com. Web. Mar. 2016.
(7) "Energy Use In the Steel Industry." World Steel. World Steel Association, Oct. 2014. Web. 2 Feb. 2016. (8) "Stainless Steel." How Stainless Steel Is Made. Web. Mar. 2016.
(9) "Synthetic Rubber." Wikipedia. Wikimedia Foundation. Web. Mar. 2016.
(10) Buhagiar, Vinent, Dr, James Bonnici, and Simon P. Borg, Dr. Design and Testing out of an Insulating Floor Element, Composed of Recycled Rubber and Inert Demolition Waste. Rep. Ahmedabad: CEPT U, 2014. Web.
(11) "How Its Made: Bicycle Tires." Bicycle Tires. Web.
(12) Kromer, Silke, Dr, Eckhard Kreipe, Dr, Diethelm Reichenbach, Dr, and Rainer Stark, Dr. Life Cycle Assessment of a Car Tire. Rep. Continental AG, 1999. Web.
(13) "Get Quotes. Book Shipment. Track Freight." SeaRates. Web. Mar. 2016.
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(16) "Steel Recycling." Steel Recycling. Green World. Web. Mar. 2016.
(17) Johnson, Jeremiah, B.k. Reck, T. Wang, and T.e. Graedel. "The Energy Benefit of Stainless Steel Recycling." Energy Policy 36.1 (2008): 181-92. Web. 2 Feb. 2016.
(18) "The Spent Tire Initiative." Environmental Benefits. Firestone. Web. Mar. 2016.
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14 March 2016
Waste and Emissions in a Bicycle Life Cycle
Bicycles are a means of transportation that creates minimal environmental impact during its lifespan. However, the raw materials and the production process has the potential to produce both sustainable and harmful wastes. Bicycles need little maintenance after being produced, with only the chain and wheels needing to be replaced after some time. Despite people failing to take into account the production and disposal costs, bicycles as an entire product are still very eco-friendly and efficiently produced. Bicycles have many individual components, but this life cycle analysis will mainly focus on the wastes and emissions from the frame, wheels, and seat of the bicycle.
For composition, bicycles frames are made from aluminum alloys, with the most common one being 6061 aluminum alloy. The spokes of the wheels can be made with both stainless steel or aluminum, but this essay will use the latter as our model. The rubber wheel uses both synthetic and natural rubbers, with additives of oil and carbon black to give it its elastic and durable properties. The seat of the bicycle is more complex, using material like thermoplastic elastomer, foam, and hard plastic.
The refining of bauxite to alumina uses the Bayer process, where 2 to 3 tonnes of bauxite needed to produce 1 tonne of alumina. Following the Bayer process, the alumina needs to go through the Hall–Héroult process in order to become usable aluminum. The Bayer and Hall-Héroult process used in conjunction is the most efficient and economical way of producing aluminum.
In the Bayer process bauxite ore is ground up. Then, a mix of bauxite and sodium hydroxide is placed in a ‘digester’”. High temperatures up to 270°C and pressure is applied, causing reactions in the mixture. What’s left is a material called red mud, or bauxite residue, which is a thick brown paste. It contains metals such as silicon, iron, titanium, and other compounds. Elements such as scandium can be extracted from this mud. Scandium can be used in aluminium scandium alloy, which is a widely used metal in motor vehicles and other products. The leftover elements in the red mud can also be used in the production of other metals, depending on their concentration in the mud.
For the Hall-Héroult process, alumina is melted down and dissolved into molten cryolite at 950° C, and is electrolysed in a molten salt bath composed of aluminum, sodium, and fluorine. A low voltage current is directed through to electrolyze the mixture, causing aluminum to be deposited at the cathode and oxygen gas at the anode. This whole process typically takes place in a cell, where the temperature is carefully controlled through electrical resistance. “Oxidation of the carbon anode increases the electrical efficiency at a cost of consuming the carbon electrodes and producing carbon dioxide.” In order for aluminum to turn into aluminum alloy 6061 it is mixed with other elements, magnesium and silicon being two of them. For every kilogram of aluminum, approximately 1.5-2.2 kilograms of carbon dioxide are produced through this process. However, this figure does not take into account carbon dioxide production from the electricity used in this process, which would inflate the numbers further, depending on how this electricity was produced.
As for waste and emissions, aluminum can be almost entirely recycled, so the majority of emissions and wastes come from the mining and production of the metal. Recycling aluminum is “92 percent more energy efficient than making new aluminum.” Because of how efficient it is to recycle aluminum, increasing the life of aluminum by 10% decreases potential greenhouse gases by around 15%. Air emissions can come from many sources, from the mining and grinding of the bauxite to the calcination of the aluminum oxide. These processes all produce particulates, which are collected with air emission equipment. If there is enough metallic content in this dust, it can be reused to produce other materials. If it lacks particles, however, the dust is sent to the landfill. In order to offset the copious amount of airborne emissions from aluminum production, extensive gas collection and removal systems are in place to transfer the air to gas treatment facilities. As aluminum is processed, the chemical reactions also release carbon dioxide. For every tonne of aluminum produced through hydroelectric power, only 4 tonnes of carbon dioxide are released into the atmosphere. With coal, however, 21.6 tonnes of carbon dioxide are released; more than 5 times more. Other gases can include “combustion products, hydrogen chloride and metal chlorides, aluminum oxide metals and metal compounds.”
In the production process, transportation costs are minimal, as most mining sites have their processes located in close proximity. Once the aluminum is produced, however, the refined material is sent to different factories in order to become recognizable bicycle parts. In the case of Allez bicycles, “aluminum production and extrusion takes place in China” then is transported to a factory that forms the aluminum tubes and sends them to another factory to be assembled. There are transport emissions in the form of greenhouse gases when fuel is used in transportation. The majority of gases are carbon dioxide, and “relatively small amounts of methane and nitrous oxide are emitted during gas combustion.”
After the aluminum is produced, it needs to be shaped and go through a hydroforming process which uses water, lubricants, drying agents, rust preventatives, and bactericides. The aluminum is placed into molds, and sealed up. It is then subjected to a high pressure of 20,000 to 100,000 PSI internally from water in order to give the round shapes of the tube. This process uses water, which can mostly be reused, and lubricants, which can be used multiple times.
In order for the bicycle frame to be assembled, it needs to be welded. There are two gas welding processes most commonly used on aluminum and aluminum alloys, called oxyacetylene and oxyhydrogen. The gases mix with oxygen, which fuels a flame. The metal being welded is exposed to a flame in order for them to be fused together.
Bicycle tires are made from a combination of natural and synthetic rubber. Wheels are composed of mineral oil, carbon black, and 40-45% rubber, 75% of which is synthetic. Synthetic rubber can be made from from two gases called butadiene and styrene. When the two are mixed, latex occurs. Synthetic rubber goes through 4 general steps of processing: feed blending, polymerization and stripping unreacted monomers, recycle compression and purification, and finishing. The specific rubber used in this explanation is called Butyl Rubber. In the first step, a blend of 98% Isobutylene with 2% Isoprene is chilled and fed into a reactor. Then in the second step, isobutylene and small amounts of isoprene are co-polymerized with methyl chloride and a catalyst. The temperature stays at around -100 °C in order to achieve high molecular weight, and are then distilled by adding steam and hot water. The next processes remove impurities, and polymer is screened from the hot water and dried out, and are cooled. The carbon black in the tires is non-toxic, but is not biodegradable. Often, waste carbon black gets disposed in landfills, but has low emission if burned.
Bike wheel production is a meticulous process involving cutting and splicing the carcass on a building drum. Then, wire is inserted and the carcass folded. This forms the base structure of the wheel. Following this, the tread is inserted. The tire then needs to be vulcanized at temperatures of 170 degrees in a mold for 5 to 6 minutes.
For the spokes of the wheels, metal wire, in this case an aluminum alloy, is straightened and cut to length. It is then cold forged in order to increase its density. Hammers rotate around, reducing its diameter. One end is shaped into the head, while the other is rolled into a thread. It goes through one more process called flat forging, where weights of up to 250 tons are applied in order to give the spokes an aerodynamic shape, and further increasing its density. For the rim, bands of metal are laid out, flattened, and shaped into hoops. Holes are then drilled in order to allow the spokes to be threaded through. As with forming the other metal parts, there is little to no waste involved with spokes and rims, as the pieces are measured out before being cut. The only potential wastes and emissions come from the machinery and the fuels used to power them. In order to make a full wheel, the spokes must be threaded into the rim.
Emissions from the production of rubber may contain hazardous materials that negatively affect human bodies. It was found that “exposure to butadiene in the synthetic rubber industry produces a dose-related increase in the occurrence of leukemia,” while there is a marked less harmful effect in the case of styrene. In many cases for natural rubber, massive amounts of deforestation happen.
Bicycles have many positive and beneficial health aspects, and combined with the amount of greenhouse gases it cuts down on, they are quite efficient modes of transportation. Along with their ease of use and relatively low manufacturing cost, they are environmentally beneficial and deserve to be widely used.
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