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Aqueous Parts Washers for Small Operations
Manually operated parts washers are commonly used in maintenance operations. Because aqueous parts washers use waterbased chemistries, they can be less hazardous to operate than petroleum solvent parts washers. Aqueous cleaners are less likely to cause skin problems such as dermatitis. They eliminate the slight fire risk of petroleum solvents (like mineral spirits) and can provide a better work environment by reducing the volatile organic compound (VOC) emissions and their associated odors. Aqueous parts washers, if chosen carefully and operated sensibly, can improve parts cleaning in your maintenance operation and may generate no hazardous waste.
Aqueous Cleaners
Most aqueous cleaners remove oils as fast as mineral spirits can. A few cleaners claim to remove grease faster, but most work slower than mineral spirits. Solvents used in degreasing work by diluting oils so only a thin layer of oil remains on part surfaces. As the solvent becomes saturated with oil, oil on parts will not dissolve adequately, leaving an objectionable film. Aqueous cleaners leave an oil-free surface until the cleaner is close to failure. Without a petroleum film remaining on parts, rust may be a problem; so aqueous cleaners may need to include a rust inhibitor. Because aqueous cleaners generally perform better with increased temperature, aqueous parts washers are almost always heated.
Emulsifying cleaners break oils into very fine droplets and disperse them throughout the cleaner. These cleaners are very effective when new but tend to have short lives.
Oil splitting cleaners displace oils from part surfaces but allow the oil droplets to combine and float to the surface of the cleaner. These cleaners can have very long and effective lives, but the system needs to prevent floating oils from re-contaminating parts. Sink-on-drum washers work well in this regard.
Microbes are used in some cleaner formulas to digest petroleum contaminants. Microbe and nutrient packages are added to the cleaner and circulated throughout the bath. The microbes break down the petroleum hydrocarbons and reproduce themselves in the nutrient-rich environment. This process works as long as bath conditions support the microbe colony. To successfully use microbes maintain proper solution temperature, avoid aerosol use at the parts washer and adjust microbes concentration as needed. These cleaners work best when the work load is relatively steady—long periods of inactivity can starve the microbes. Microbes used in cleaner maintenance are different from the bacteria that can grow in metal working coolant applications. Properly maintained, the end result is petroleum contaminants converted to water and carbon dioxide, without odors or degradation problems.
Water-soluble solvents, commonly terpenes, are mixed with surfactants to remain dispersed in water. They tend to be very good cleaners, particularly for removing grease. They work like emulsifying cleaners and generally have relatively short lives. It can be difficult to identify this type of cleaner—a measurable flash point (<200˚F) or significant VOC content would be indicators of aqueous solvents. Many sewer systems can accept this type of aqueous waste, but some will not, depending on their waste load and design.
Disposal
Aqueous cleaners for manual parts washing almost always have nonhazardous formulas. Determine whether the cleaner is nonhazardous by reviewing the MSDS and talking to the supplier. The following indicate if a cleaner is nonhazardous: flash point above 140˚F; pH between two and 12.5; and no hazardous ingredients or only those with high Occupational Safety Health and Administration (OSHA) permissible exposure levels (PELs) or Hazardous Materials Information Systems (HMIS) hazard ratings less than two.
A number of aqueous parts cleaning solutions are designed to operate indefinitely. Chemical additions are needed to make up for losses carried out on parts or from evaporation. While the solution does not require routine disposal, its waste includes used oil, and either sludge or filter waste.
Aqueous cleaners can pick up contaminants that turn used cleaners into hazardous waste. Oils, fluids, surface dirt and debris removed from parts may make the used cleaner hazardous. Cleaners can also pick up heavy metal contaminants, such as barium, cadmium, chrome and lead from the parts cleaned. Using carburetor cleaner, gasoline, kerosene or paint thinner near the parts washer, or on the parts going into the parts washer, can make the used cleaner hazardous. If the cleaner does not need disposal, as in the case of long-life cleaners, contamination does not matter as long as the level of contaminants remains low enough to allow proper operation of the cleaner.
The Minnesota Pollution Control Agency fact sheet Managing Aqueous Parts Washers #4.44 reviews how to assess and manage aqueous parts washer waste including oil, filters, sorbents and sludge.
Aqueous Equipment
Aqueous parts washers designed to remove or isolate oils, sludges and solids maximize the cleaning solution’s life and effectiveness. Manufacturers have different designs and procedures for doing this. Oil separation features can include oil weirs, skimming devices, oil absorbents, and microbe or enzyme-based systems. Removed oils can be combined with existing waste oil streams for disposal.
Filtration is a common feature that removes particulate matter which would cause circulation pump wear, interfere with the solution heater and degrade the cleaner. Add filtration to your current small parts washer by installing an automotive filter and relocation kit. The Iowa Waste Reduction Center has step-by-step instructions.
Look for sink designs that have easy to reach drain sumps, drain trays, oil skimmers and filtration features. These help make equipment maintenance easier, allowing more time for part cleaning.
Other washer features are useful for certain applications.
With immersion units, parts soak in a reservoir to aid in cleaning and reduce scrubbing time. Immersion chambers can use mechanical agitation to help with harder to remove soils. Ultrasonic cleaning systems use a soak chamber with transducers mounted on the sides and/or bottom. They produce high frequency sound waves that cause intense microscopic scrubbing of part surfaces, reaching blind holes and interior surface areas. This technology works well for complex parts needing precision cleaning without significant additional labor.
Cabinet Washers
Manual aqueous parts washing can be replaced with a cabinet-style aqueous parts washer when large quantities of heavily soiled parts require cleaning. Solutions are heated to higher temperatures and pressurized spray nozzles impact all the part surfaces. Cleaning labor can be significantly reduced because parts can be loaded into the cabinet, the wash cycle set on a timer and left until done.
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