Design for the Environment/Metal Cleaning
This page is part of the Design for the Environment course
In repair and rebuild shops, engine pistons often need to be cleaned. Most of today’s repair industry uses chemical cleaners as a cost-effective approach to cleaning engine components, specifically pistons. However, companies fail to realize that they are inducing the production of tonnes upon tonnes of toxic waste and harmful chemicals. They get disposed of into the environment, endangering our natural habitats, and eventually our well-being. This project compares 3 cleaning methods for pistons: chemical cleaning, dry ice blasting and UV/Ozone cleaning, with the environment in mind. Each method undergoes functional analysis, streamline and economic input-output lifecycle analysis, and cost analysis. The analyses take into account environmental damage and financial costs to the company, as well any costs that may be inflicted onto society. The study concludes with a recommendation for the best cleaning method based on the overall results from all the analyses.
- 1 Background Information
- 2 Project Information
- 3 Highlights and Recommendations
- 4 Functional Analysis
- 5 Streamline Life Cycle Analysis
- 6 Economic Input-Ouput Life Cycle Analysis
- 7 Cost Analysis
- 8 References
- 9 Sources
Each method has its own unique nature of cleaning. Chemical cleaning, the baseline, is a very simple process that involves immersing the piston into a chemical bath and allowing the fluid to dissolve any surface contaminants before taking the part out. Dry ice blasting, the first design alternative, involves blasting CO2 pellets (dry ice) onto the piston surface. At impact, pellets will explode and vaporize, causing the contaminants to lift off. To utilize UV/Ozone cleaning, the second design alternative, a confined space is initially filled with ozone using a mercury lamp. UV rays are projected onto the piston, and reacts with the ozone to lift off contaminants.
The piston being cleaned is from a R18A1 engine, which is housed in the 2006 Honda Civic. The outside diameter is 80.890 mm, whereas the height is 80.93 mm . The piston is made of aluminum alloy, with a very smooth finish. The piston is assumed to have been in contact with 89-octane gasoline and motor oil prior to cleaning. Hence, we assume dirt, oils, oil deposits, salt or any other road residue a car would normally be exposed to, as well as potential rust, to be found on the piston.
Section 1 - Group 12
Joshua Tam [joshuatam]
Chulsoon Lee [chulsoonlee]
Tae Won Ha [taewonha]
Colin Liu [colin]
Highlights and Recommendations
All results, drawn from this report, seem to lead to one clear winner: UV/Ozone cleaning. From the SLCA, UV/Ozone cleaning attained the highest overall score amongst the three, with dry ice blasting being a close second. Chemical cleaners were too harmful to the environment to rank high in SLCA. However, dry ice blasting did not fair so well in the EIOLCA, where chemical cleaning, according to the results, was more environmentally friendly. Dry ice blasting and chemical cleaning were quite costly when put through cost analysis. On the other hand, UV/Ozone cleaning was superior in both the EIOLCA and cost analysis. Throughout all the analysis methods, one thing kept holding back dry ice blasting from being on top. CO2 production is just too much of an environmental concern to be taken lightly. Heavy tolls on energy are taken to produce it, which in turn renders it not preferable environmentally speaking. Practically, chemical cleaning is still the best at the moment simply because CO2 is too expensive, and that UV/Ozone cleaning does not have enough research information on it to be widely used commercially. Currently, UV/Ozone use is rarely used outside a lab environment. However, because of the results from this report, our group fully recommends that the company consider research and development into this technology.
The common function for the processes is cleaning the piston, while maintaining a very smooth finish. Naturally, the methods will be compared based on cleanliness and abrasiveness.
Chemical cleaning is a process of cleaning parts using a chemical solution. It is a relatively cheap and effective way to remove engine oil, lubricants and other organic substances from the pistions. The cleaners are a combination of various substances like builder, surfactants, sequestering agents, etc . These substances lower the surface tension of a liquid, emulsify oily and greasy soil and prevent soils from settling back on the cleaned surface.
Alkaline-based chemical cleaners are the choice pick for organic soils . The alkaline base softens water, which improves the effects of other detergent effects, and also acidic fatty soils are neutralized and thereby more easily removed. Overall, the quality of chemical cleaning for aluminum alloy parts is generally very good. The metal surfaces are cleaned very well with little or no residue soils. Lifted soils are suspended in the solution, which keeps the metal parts from being re-contaminated with dirt during removal from the baths . The degree of etching on metal surfaces as a result of chemical cleaning depends on the chemical composition of the cleaner itself. For our purpose, non-etching cleaners are chosen as to not harm the piston surfaces.
Dry Ice Blasting
Dry ice blasting is a cleaning process that uses dry ice pellets to blast off undesired layer of rust or contaminants. The dry ice pellets are loaded in to the blasting machine where they are accelerated to high velocity through a hose. When dry ice particles exit the hose and strike the coated surface, they create little explosions upon impact and lifts up undesirable material. After the process, solid dry ice particles turn gaseous and are released to the surrounding atmosphere. Dry ice blasting is very effective since it can scrape off top layers of soils. The dry ice pellets are made from CO2 which is recycled from other industrial plant’s air releases.
The process is very similar to sand blasting and soda blasting method. However, the dry ice is relatively softer than competitive mediums therefore it is less abrasive. Furthermore, phase change from solid to gas of dry ice creates a thermal shock, drawing heat from the top surface of the material. This change in temperature creates shear stresses between the top layer and the underlying layer. This shear stress initiates micro cracks between the contaminant and the part further enhancing the quality and speed of the cleaning process.
UV/Ozone cleaning is one of the dry cleaning processes utilizing the super low pressure mercury lamp that generates UV rays in two distinct wavelengths, 85% of 254nm and 15% of 187nm. UV ray at 187nm breaks down O2 to O3 and at 254nm O3 are decomposed into O2 and high energy O2- . PL16-110 from OAI is selected as an UV/Ozone surface cleaning device. The size of the chamber is approximately W6”*L6”*H10”, which provides enough space for the piston.
Widely spread in early 1980, this technique can be implemented for not only the cleaning surface of metallic materials, plastics, ceramics, and substrates, but also increasing surface “wettability” by surface modification without etching the surface .
Streamline Life Cycle Analysis
In this section, the three methods will be compared based on their SLCA scores for each process life stage. The scores range from 0 to 4, 0 having the worst impact to the environment while 4 having the least. Guidelines and scoring criteria comes from appendix of textbook "Streamlined Life Cycle Assessment" .
Resource provisioning includes all sub-processes involved with preparing the materials and resources needed for the process.
In the case of chemical cleaners, scores were low across the board due to the need for virgin materials and the fact that the base chemicals are mostly hazardous in one way or another (flammable, carcinogenic, etc). As opposed to chemical cleaning, dry ice blasting does not yield waste at the resource provisioning stage. One of the drawbacks that were found was although CO2 is recycled, it is dangerous to humans in enclosed areas and it takes extensive energy to refine and convert to dry ice pellets. When considering UV/Ozone cleaning, no virgin material is used because the device pulls the room air into the chamber for operation . As a result, no energy is consumed and no residues are produced.
A simple comparison of the scores from all three methods suggests that in order to produce chemical cleaners; a good deal of environmental damage is dealt. Both dry ice blasting and UV/Ozone cleaning relatively environmentally friendly, although dry ice blasting requires the constant recycling of CO2.
Process Implementation includes all sub-processes involved in setting up the process before operation.
Chemical cleaners received relatively high score due to the fact that the cleaning process is fairly simple and does not require complicated machinery. Equipments such as soak tubs can be made with recycled metals. In addition, very little residues are produced during implementation since only the required amount of the cleaner needs to be used with excess stored away for later. Dry ice blasting does not release significant waste during the implementation process. Various virgin materials are used to build the blasting machine; however, they are recyclable making the machine less harmful to the environment. In UV/Ozone cleaning, the comparably low rank is due to the use of mercury in the lamp and the gas waste released from the test experiments for more effective cleaning .
Comparing the scores of all three methods, chemical cleaning scores high due to the simplicity of its transport and setup, interestingly enough. Dry ice blasting and UV/Ozone cleaning lag behind in score because they require transport and setup of machines. Ozone machines require a lot of packaging because of the fragile mercury unit, which reflects the low score in solid waste.
The primary operation stage includes all sub-processes involved in performing the main function, which is cleaning the piston.
For the primary operating stage of chemical cleaning, material choice scored 0 due to the hazardous nature of the chemical cleaners. Energy is scored high due to the fact that these processes require minimum machine movement and electricity to run. After the cleaning solution reaches is maximum soil saturation point it needs to be replaced with a new batch. The waste solution is considered hazardous waste since it still contains such a high concentration of various hazardous substances. Due to this, the residues for primary process scored very low. Dry ice blasting uses electricity to run the machine for its primary operation. The main source of electricity is combustion of fossil fuel and nuclear power, contributors to green house gas (GHG) and air and radioactive pollutions. Also, the particles blown off from the part is released in to the surroundings, imposing possible danger to the workers and nearby machines. The low score for UV/Ozone cleaning is mainly due to the emission of the CO2 and O3 during cleaning process. These gases are exhausted directly to the atmosphere, but concentration of O3 is substantially diluted because most of O3 has been reacted with the contaminants before exhausted. To reduce the emission of O3 to atmosphere, O3 neutralization filter can be implemented .
Comparing the scores of all three methods, we see that using chemical cleaners are quite hazardous to the environment, making smarter to use the design alternatives. Both dry ice blasting and UV/Ozone are relatively equal in environmental friendliness, differing only in the state of waste they produce.
The secondary operation stage includes all sub-processes that do not perform the main function.
For chemical cleaners, the complementary operation is rinsing of the metal part after it has been soak cleaned. Water is used and also becomes hazardous waste after the rinse. For dry ice blasting, there is no significant trace of waste released. It is recommended to vacuum clean the work area since the blown particles could damage nearby machines. Vacuum cleaner and dry ice blasting machine both are equipped with speed controller minimizing energy consumption. As a secondary operation for UV/Ozone cleaning, the exhaustion of gases left from cleaning is required. Since the amount and concentration of the CO2 and O3 gases after primary process are not considerably high and the super low pressure mercury lamp is not required in this process.
The cleanup process for chemical cleaning, when compared to the two design alternatives, is inferior in every aspect. The waste from the rinse is hazardous. On the other hand, dry ice blasting only requires vacuuming. UV/Ozone cleaning only requires gas exhaustion after cleaning. Both cleanups do not significantly harm the environment.
End of Use
The end of use stage includes all sub-processes related to disposal, recycling and refurbishment.
Chemical cleaners score low due to the hazardous nature of the waste at the end of use stage. Specialized waste handling equipments are required and often they are made from non-recyclable plastics and rubbers. Also transportation distances for the wastes will increase since it needs to be delivered to specialize waste treatment facilities. Containers are contaminated when handing hazardous wastes and generates more hazardous waste during cleaning. Dry ice blasting machine scores lower than usual at the end of use for the process. Significant solid and gas waste is released and energy and human labor is necessary to dissemble and recycle the machine. This issue imposes one more weakness to dry ice-blasting method. Regarding UV/Ozone cleaning, the manufacturing company collects the old mercury lamp for recycling hence the scoring is high .
Comparing the scores, chemicals are more hazardous than the alternatives. Chemical cleaners are very difficult to dispose of safely, making it rank low relatively. Dry ice blasting and UV/Ozone cleaning are fairly similar at end of use, requiring the disposal of machines. The difference lies in the size of the machines, where dry ice machines are much larger than ozone machines, making UV/Ozone cleaning more preferable in this case.
Discussion of SLCA
When looking solely at these results from, we see a tremendously low score given to chemical cleaners, mainly due to its toxic nature, making it difficult to dispose of safely. Dry ice blasting and UV/Ozone cleaning, although observing a difference of one, are relatively equal when analyzed using SLCA.
Economic Input-Ouput Life Cycle Analysis
EIOLCA model on www.eiolca.net is used to analyze and compare environmental impacts and energy consumption of three methods of cleaning. To compare methods in equal and fair manner, costs of cleaning 1000 pistons are calculated for each method and are used as monetary inputs for the model.
For the chemical cleaning, “miscellaneous chemical product manufacturing” sector is chosen to represent chemical solutions used in the cleaning process. Estimating that it takes 1100lbs of chemical solutions to clean 1000 pistons and that chemical solutions cost 1.975cents for a lb, the monetary value for the chemical cleaning comes out to be in $ 14,018.22(1997 US worth). $ 14,018.22 as the monetary value, the output of the EIOLCA model is shown below.
The “air and gas compressor manufacturing” sector is used to represent the manufacture of the dry ice blasting machine itself, whereas for dry ice manufacturing, the “basic inorganic chemical manufacturing” sector is used. The monetary input for the sectors came out to be US $ 14,018.22 and US $ 66,358.59 for the dry ice cleaning. With these monetary values, air emission and energy consumption of the two sectors come out as below. It is observed that most of the environmental impact and energy consumption is contributed by dry ice manufacturing stage.
To represent UV/Ozone cleaning, two sectors were also chosen. The “fluid power cylinder and actuator manufacturing” sector represents the manufacturing of the metallic chamber and “electric lamp bulb and part manufacturing” for the super low-pressure mercury lamp. The monetary value for the UV/Ozone cleaning comes out to be US $788.50 and the results comes out as below. It is found that UV/Ozone cleaning has the lowest values in all divisions and is concluded to be the most environmental and efficient method.
The overall results for the three methods are shown above with sensitivity analysis. Dry ice blasting method ranks number one contributor on all divisions due to manufacturing of dry ice. Dry ice blasting is considered as a clean and environmentally friendly technique in the real market because there is no direct waste released during the cleaning process. However, with EIOLCA analysis, dry ice blasting is found out to be the worst cleaning method out of three because manufacturing of dry ice consumes extensive energy and releases tremendous amount of wastes and pollutants. Chemical cleaning comes in second place with fair amount of wastes, releases and energy consumption. UV/Ozone is found to be the most clean and energy efficient method
Sensitivity analysis is carried out to observe the output change when the number of pistons increases by 50%. For the chemical and dry ice blasting method, it is found that with 50% increase of piston units, the output increase nearly 50%. However, for the UV/Ozone method, the % increase went up less than 50%. With more pistons, UV/Ozone cleaning becomes more environmentally efficient. The sensitivity analysis also concludes that UV/Ozone is more environmental and energy efficient cleaning method.
Often cost tends to represent only the superficial factors, but in this cost analysis the direct and indirect costs are considered. The direct cost refers to the superficial factors such as capital, operating and disposal costs, and environmental cost is concerned as the primary factor for the indirect cost. For simplicity, there are a few assumptions and omissions made to this analysis. The cleaning process is done for 10,000 parts and increased to 15,000 parts for the sensitivity analysis to examine how the increased number of parts affects the cost. The machines required for each type of cleaning process are subject to resale after one year at the depreciated price, assuming the rate of depreciation is 40% each year, resulting elimination of disposal costs. It should be noted that the indirect cost calculated for the cost analysis contains the environmental cost in the manufacturing stage - process implementation stage - only, while the primary and secondary processes are omitted due to the broad range and high uncertainty of the amount of emission depending on the severity of the contaminants.
Discussion of Cost and Sensitivity Analysis
The numerical results of the cost and sensitivity analysis are presented as a concise table below for comparison among different types of processes.
From the table above, one of the most remarkable points is the relatively low cost of the UV/Ozone cleaning process. This is primarily due to the low capital cost for the machine and low operating cost due to the use of room air for the operation and long lifetime of the super low pressure mercury lamp . As enormously high indirect cost shows, Dry Blasting has a heavy impact on the environment and this should be considered before implementation. The sensitivity analysis shows that direct and indirect costs for dry ice blasting are nearly proportional to the units to be cleaned, but the linearity is not so evident with chemical and UV/Ozone cleaning that the rates of increase in cost are much less than the rate of increased number of parts cleaned. Even though 5000 parts are increased, UV/Ozone economically qualifies best of all three processes.
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