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Table1: Initial product results.
Figure 1 Dirty and cleaned parts.
Figure 2 ChemSpec dirty and cleaned parts.
Table 3: Visual observations for supplied parts cleaning.
Table 4: ChemSpec cleaner results.
Table2: Ultrasonic cleaning results.
Safer Detergent Chemistry Used in Ultrasonic Cleaning Eliminates Triple Acid Chemistry
Process Cleaning, Jason Marshall and Richard Adams
Ceramics Process Systems (CPS) located in Chartley, MA, worked with the Toxics Use Reduction Institute’s (TURI) Laboratory over a five-month period, July through December 2005, to explore alternative methods for removing/ cleaning- off soils present on cast aluminum composite parts. The company’s previous cleaning process involved a multi-stage immersion bath wet process—initial liquid dish soap, triple-acid etch cleaning (nitric, sulfuric, ammonium bifluoride), and multiple rinse stages.
CPS and TURI worked together and found a safer cleaning product that outperforms the previous solution. Today, CPS operators are cleaning two to three times more parts in the same amount of time, or less, and the results are better. Also, because CPS is no longer using the readily depleted, corrosive triple acid, there is much less hazardous waste, less wear on equipment, workers are better protected and the company is saving money.
Located in Chartley since 1994, CPS employs 95 people. Manufacturing metal matrix composite components for the microelectronics industry, its products are found in mobile phone base stations, computers, high-speed digital electronic and optical telecom switching systems, train motors and wind turbines. Customers using this composite material for increased product performance and reliability include Motorola, IBM, Amkor, HP and Agilent. Approximately 70 percent of its products are exported.
To manufacture the cast aluminum based parts, CPS uses unique patented and proprietary ceramic injection molding and aluminum casting processes. In order for the parts to perform correctly, soil agents need to be effectively removed from the parts.
How a Negative Situation Turned into a Positive ResultDuring a routine inspection in March 2005, the Massachusetts Department of Environmental Protection (MassDEP) found that CPS was neutralizing one waste acid bath by manually adding in and mixing sodium bicarbonate directly into the process tanks prior to placing the spent baths in a drum for final disposal by a regulated waste disposal supplier. In Massachusetts, this “elementary neutralization” is considered treatment of a hazardous waste, which made CPS noncompliant with Massachusetts Hazardous Waste Regulations. CPS’s intent was to make it safer for their operators to transfer the neutralized waste rather than the acid into drums for disposal by the waste handling supplier. The company was unaware that the change would place them in violation of the regulation.
MassDEP approved a Supplemental Environmental Project submitted by CPS that outlined a strategy to reduce the amount of acids and decrease the wastewater and hazardous waste that is generated at the facility. Besides the chemical reductions and substitutions, the $40,000 project also included the installation of filtration equipment.
To help CPS implement these improvements, the MassDEP referred CPS to the Massachusetts TURI. All three organizations help Massachusetts companies and communities find innovative, cost-effective ways to reduce toxic chemical use at the source, rather than treat wastes once produced. TURI’s Surface Solutions Laboratory (SSL) specializes in helping Massachusetts companies, free-of-charge, reduce the amount of hazardous chemicals used for surface cleaning. The lab offers companies outside of Massachusetts services for a fee.
How an Alternative Solution Was FoundSeveral issues were identified that needed to be addressed. First, the current process generated too much aqueous waste—either to hazardous waste drums (the process created an acid based aqueous hazardous waste) or the rinse water to evaporator. Additionally, the parts sometimes needed to be run through for a second or third cycle to reach the needed cleanliness level. This was causing inefficiencies.
Phase 1 Laboratory Testing—Preliminary TestingTo select possible alternative cleaning products and/or processes, the SSL used its database of testing results to generate a list of products that matched the specific cleaning needs. This database has been made available on-line at the lab’sWeb site (www.cleanersolutions.org) so that companies can begin this search on their own.
Once the parameters are entered and products screened, typically the lab selects between six to 10 cleaners for performance evaluation on the client-supplied soils. For CPS, six cleaners were identified and diluted to low-end vendor recommended concentrations using DI water in 600 ml Pyrex beakers and heated to 130° F on a Thermolyne type 2200 hot plate.
Using the supplied soil from CPS, pre-weighed aluminum coupons (matching the substrate of supplied parts) were contaminated simulating the dirty parts. The applied soil was aged for 15 to 20 minutes at 300° F using a Master Appliance Heat Gun. Final coupon preparation involved sitting overnight, followed by two hours of drying in an oven at 500° F. A second weighing was performed to determine the amount of soil applied to each coupon.
Three soiled aluminum coupons were cleaned using an immersion soak bath with minimal agitation provided by a magnetic stir-bar. Cleaning lasted for five minutes and was followed by a tap water rinse at 120° F for 15 seconds and dried using compressed air blow-off at room temperature for 30 seconds. When the coupons were completely dry, final “clean” weights were recorded. Cleaning efficiencies were calculated for each product by subtracting the final weight from the initial weight of the soil added, then dividing by the initial weight and multiplied by 100 percent. The average of three coupons was calculated and used as the cleaning efficiency for the cleaning product used to clean the coupons.
Only a few products showed signs of removing the soil from cast aluminum. Table 1 lists the products tested and the average cleaning efficiency for each product. In addition to the seven products selected, water was included as a control.
Phase 2 Laboratory Testing—Ultrasonic EvaluationBased on the conversation between SSL and CPS, ultrasonic cleaning was proposed and agreed upon as an acceptable cleaning methodology to investigate as an alternative to the current process. From the results of this trial, five of the products were selected to be tested using ultrasonic energy. The five beakers containing the diluted products were suspended in a 40 kHz ultrasonic unit filled with water heated to 120° F and then de-gassed for five minutes. All other operating conditions were kept the same except for replacing immersion soak with ultrasonic cleaning. Table 2 shows the improvement to the average cleaning efficiencies for the five cleaners.
Phase 3 Laboratory Testing—Supplied Part CleaningIntroducing ultrasonic cleaning improved the efficiency of four of the five products removing over 65 percent of the soil. These products were then used to clean several of the supplied, soiled CPS parts. Gravimetric analysis was not used during this phase of laboratory testing due to the absence of pre-measured weights before and after soiling. The parts were selected from the supplied batch of “baked” parts in order to evaluate product performance under “standard CPS” conditions. Effectiveness of the remaining four products was determined through visual analysis. Photographs were taken before and after cleaning to aid in this evaluation process. In addition, the parts were compared to the client supplied “acceptable” acid-bath cleaned parts.
One product, Product 7, a phosphoric acid based formulation, was very successful, requiring two minutes to remove the baked-on soil and brighten the parts. The two parts were cleaner than the supplied acid washed parts. In addition, the parts were almost as clean as the supplied “finished” products. A second product, Product 3, an alkaline aqueous-surfactant mixture, worked very well after five minutes of cleaning. The parts were cleaner than the acid-washed supplied parts. Table 3, lists the observations at two-, five-, 10- and 15-minute cleaning intervals. Photographs of the top-performing products are shown in Figure 1.
Additional testing was conducted on these top two alternative products for other supplied parts to determine the range of acceptable cleaning obtainable. The phosphoric acid product, Product 7, removed the unbaked contaminant from the part in the five minutes of ultrasonic cleaning. The alkaline aqueous-surfactant mix, Product 3, removed some of the contamination, but not as much as Product 7.
The top cleaner, Product 7, was evaluated at 5 and 10 percent concentrations, while maintaining all other conditions. Both diluted products did remove the “unbaked” soil on the cast aluminum. However, these dilutions required more time to achieve a sufficient level of soil removal.
Phase 4 Laboratory Testing—Pre-Pilot TestingHaving identified a potential alternative to the triple acid-washing method, CPS wanted to come to SSL to conduct testing with the identified alternatives prior to testing at their own facility. During this time, TURI requested more of Product 7 to conduct this testing. Unfortunately, the manufacturer could not be contacted as it recently went out of business so the TURI lab attempted to locate other products with similar formulations. A few products were identified and one vendor supplied a product, Product 8, for testing that consisted of phosphoric and citric acid. This product was run through many of the same performance evaluations. The product was fairly consistent in its composition with the phosphoric acid Product 7. However, the new product did not meet CPS expectations as it did not clean as well or as fast as the original alternative.
Next, the TURI lab worked with one of its platinum-level vendor partners to help formulate a potential replacement for CPS. TURI created the Vendor Partnership Program, which works with vendors for chemical cleaning formulations and manufacturers to evaluate safer and effective cleaning alternatives. Through this partnership, two new formulations from the partner’s parent company were made and supplied for testing. Following the preliminary performance review, these two products were found to be as effective as the original Product 7 results.
When CPS came to SSL to conduct testing, product performance of the two new formulations was at the previously desired level of cleaning, having removed all of the soil from the surface within a short period of time. Both products performed very well at the 20 percent concentration. Both products resulted in parts that looked as clean as the finished product samples. The 10 percent concentration needed more time to achieve effective results; however the lower concentration will result in less dragout to rinse tanks. Cleaning observations are listed in Table 4 and the cleaned parts are shown in Figure 2.
Phase 5 Onsite PilotingCPS tested the recommended formulations and found that they worked very well under their process conditions. They ran a few thousand parts through the new cleaner as part of a qualification process. The change-over to full manufacturing was simpler than other projects ongoing at the facility in relation to the supplemental environmental project rising from the Mass-DEP noncompliance status. The plan was to abandon the use of the triple acid and convert one or both ultrasonic baths to the new detergent cleaner. Additionally, CPS has installed a particulate filtration system on the detergent ultrasonic bath in order to evaluate extending bath life.
Initially the new filtration system was not adequately cleaning the bath of the soil particulates with the original particulate filter—essentially they were circulating dirty soapy water. Changing to a half micron particulate filter has resulted in the cleaning bath becoming and staying crystal clear. This is significant as they can now maintain that bath, possibly indefinitely, by simply adding more cleaning solution as the level drops. CPS plans called for running thousands more parts through this bath before making the decision to abandon the triple acid.
Phase 6 Final Adoption into ManufacturingCPS has now moved all products requiring cleaning into this new chemistry. Now that it is part of the production process they have realized the following benefits: (1) Three powerful acids were eliminated from the production process—benefiting both personnel safety and a reduction in hazardous waste; (2) productivity has increased more than three fold— the new formulation typically requires only one-pass cleaning and is faster; and (3) product quality has increased with “dirty parts” defects more than halved, resulting in much less product rework. Some outstanding issues remain regarding that of maintaining the rinse waters—which become rapidly contaminated with the cleaning formulation. They have found that in this area the chemical cleaning industry has some general guidelines, but the ultimate answer requires quite a bit of trial and error. CPS next plans to add soap and particulate filters to the rinse baths and anticipates some testing to define and refine the process.
Positive All the Way AroundAccording to CPS, changes are always a bit challenging—often finding it amazing how a simple process change can have significant consequences on product quality. By testing their parts at TURI and then on site, CPS proceeded cautiously and yet confidently in the new process. The company realizes that better products and safer processes are integral to their continuous improvement goals. This solution will not only make them compliant with regulations, but help them operate more efficiently, be kinder to the environment, protect employees and continue to be good neighbors. CPS production workers “love” the new process—they now have the flexibility to gain new training and help other departments— increasing their value to the company and breaking up the day.
Jason Marshall, is the Toxics Use Reduction Institute at the University of Massachusetts Lowell Manager of Laboratory Testing. He can be reached at (978) 934-3133. Richard Adams is the vice president of Operations and Engineering for the Ceramics Process Systems Corporation (Chartley, MA). To learn more about TURI and its Vendor Partnership Program, contact Jason or visit www.turi.org.