Cleaning after lapping presents various problems. Polar as well as nonpolar soilings need to beremoved. For this, a technology is applied that combines high cleaning quality with environmental protection.
The cleaning of surfaces has become an important part of the manufacturing process. Generally, non-chlorinated, organic solvents are used to remove nonpolar soilings (e.g. mineral oils) while water-based detergents are suitable for removing polar soilings (e.g. salts). For this purpose, Amsonic (Biel, Switzerland) offers two technologies: the automated cleaning systems CleanLine and EgaClean.
The Cleaning of Parts after the Lapping Processes
Vallotech, a company located in Vallorbe, Switzerland, is a subcontractor to the automotive industry that produces cast polymer parts in phenoplast used for automobile fuel pumps. After the lapping process (an abrasive process to get a good surface finish), these parts are soiled with mineral oil, petroleum, particles and additives. The parts’ geometry and the high drag in of soiling require a cleaning process that is efficient and constant in quality. The company’s previous Amsonic water-based cleaning machine produced a high volume of effluent because the detergent was always rapidly saturated with oil. In December 2006, this multi tank cleaning unit was replaced by an EgaClean 4200, an A3 solvent cleaning system (isoparaffin, non-halogenated solvent) by Amsonic. The new system was a development of Amsonic representing the next generation of cleaning machines (without water detergent) used in the case of soils of oil and grease.
Particle Soiling
Polar soilings, e.g. salts, are preferably removed with water-based detergents. These salts are residues from water-based cooling emulsions that are used during the mechanical processing. As the proportion of oil remaining on the parts after the lapping process is minimal, the used water-based detergent is not soiled too heavily.A large proportion of oil would influence the cleaning process and require the application of oil separators.
Particle soiling is a critical factor in connection with new generation diesel injection nozzles as they feature very small boreholes. It is crucial to completely remove these particles. The cleaning concept applied for this purpose includes an ultrasonic immersion cleaning process using a water-based detergent that is especially adapted to the respective material and soiling. Amsonic’s CleanLine cleaning procedure consists of the following process steps: • Ultrasonic cleaning—three minutes • Ultrasonic cleaning—three minutes (For #1 and #2 the process is continuous, so that approximately six baskets are running in line, every five minutes one basket comes out (from drying)) • Rinsing—three minutes • Rinsing with DI water—three minutes • Passivation—three minutes • Hot air drying—five minutes • Vacuum drying—three minutes
The machine processes 12 cleaning baskets per hour. This particular application uses Amsonic’s WetEx vacuum drying process which was developed in collaboration with the Fraunhofer Institute in Brunswick (Germany). It guarantees a perfect, stainless drying even in tapped blind holes. For each charge, the control software automatically produces a data sheet to confirm the adherence to the cleaning process and parameters, thus allowing information on process steps, functions (e.g. ultrasonics, basket rotation etc.) and the DI water quality to be saved and printed.
Machine Capacity
Thanks to the bulk cleaning instead of positioned parts on a rack, one person can be used for other productive tasks in the company. The savings of the Amsonic machine are also in waste water, detergent costs and energy (see Table 2). The parts are controlled 100 percent after cleaning. This control shows a drastic improvement compared with the ultrasonic water cleaning. This is mainly due to the fact that the solvent is continuously distilled, which ensures a constant cleaning quality. The replacement of the water-based machine from Amsonic purchased in 1990 by the new Amsonic technology is a step in the environmental protection and improved productivity.
Table 1 shows what features and technical specifications (CE and ATEX conformity) are included on the EgaClean 4200. The standard cleaning program consists of the following process steps: 1. Working tank (pre-cleaning) ultrasonics 2. Micro filtration 3. Clean tank (distillate) ultrasonics 4. Flooding 5. Vapor phase 6. Drying
Cycle time is approximately 14 minutes. The solvent is heated to approximately 65°C (149°F) under vacuum (100 mbar). The movement of the cleaning baskets is programmable (oscillating, rotating or static).
Economic Efficiency and Environmental Protection
In principle, the solvent is not replaced periodically. The periodical replacement of the solvent would mean supplementary cost. Because there is no need to replace the solvent, it achieves a “perfect” distillation, allowing users to get a constantly clean solvent. With per- or trichloroethylene, the solvent has to be replaced periodically to avoid it from becoming acidic. This cannot happen in the A3 system, as the solvent has no atom (chlor for instance), leading to the formation of acid. Distillation losses amount to approximately 5 to 10 percent of the oil drag in (see Table 2).
In comparison with cleaning machines based on chlorinated solvents, the Amsonic EgaClean features an outstanding ecological balance. The A3 technology has therefore managed to achieve a broad market share and is an alternative to cleaning with per- or trichloroethylene.
The complete recycling of the solvent guarantees a constant cleaning quality and a high economic efficiency of the process. This technology is also applied to clean parts prior to galvanic processes such as PVD and CVD coating.
All types of class A3 solvents can be used in the EgaClean. Isoparaffin is applied in case of soiling by mineral oil. In the electronics industry, however, modified alcohols are applied because of their optimal suitability for the cleaning of printed circuit boards after soldering processes. With regards to cleaning quality, the values shown in Table 3 can be achieved.
To conclude, it should be said that, cleaning technologies have to be applied systematically. Water-based cleaning processes are particularly suitable for the removal of polar soilings and in cases of low oil drag in. They assure a very high degree of cleanliness. If the material to be cleaned is subject to corrosion, certain precautions have to be taken in connection with this cleaning method, e.g. corrosion inhibitors have to be used in detergents and rinsing tanks.
Nonpolar soilings, e.g. cutting oils, are preferably removed with A3 solvent based processes. This technology is nontoxic and offers a good protection against corrosion. Consequently, there is no universally valid cleaning solution and the coaction of soiling and material has to be reviewed carefully before choosing the one or the other technology.
Jean-François Fallot is a consultant with Amsonic SA (Biel, Switzerland) and has specialized in cleaning and surface treatment for 30 years. For more information on Amsonic SA, call +41 32 344 35 00 or visit the Web site at www.amsonic.com.
Despite enhancements to manufacturing technology, there are still issues today that can cause programs to fail. These failures can cause lost time, scrapped parts, damaged machines and even injured operators.
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