Aqueous Cleaning Systems Offer Economical, Ecological Benefits
The challenge has been to find cleaning systems that are both cost-effective and ecologically friendly
By Doug Kaufman
As concern for the environment and worker safety has increased over the years, attention paid to the cleaning processes used in engine rebuilding facilities has sharpened as well.
No matter what size the shop, engine components are dirty and need to be cleaned. There are numerous ways to clean parts, of course, and no method has been developed that works best for all of them.
Cleaning is a time consuming, expensive process for most rebuilders. According to Engine Builder's most recent Machine Shop Market Profile, rebuilders say they spend 13 percent of their total production time in cleaning. When the cost of equipment, chemicals, labor, maintenance and disposal costs are considered, some experts estimate that up to one-third of a shop's overhead costs go to cleaning expenses.
Additionally, rebuilders and their communities are more aware than ever of the impact cleaning has on the environment. The challenge has been to find cleaning systems that are both cost-effective and ecologically friendly. Concerns about solvents are many: volatile organic compounds (VOC) that contribute to smog formation may be toxic when inhaled; solvents evaporate quickly, making worker exposure difficult to control and monitor; and legal restrictions dictate how and where you can dispose of waste.
For these reasons, aqueous cleaning has gained a solid foothold in today's engine rebuilding facility. According the U.S. Environmental Protection Agency (EPA) aqueous cleaners are defined as "water-based cleaners that contain less than 5 percent (50 grams per liter) of VOCs." There are many different aqueous solutions available for effective cleaning of cast-iron and aluminum parts.
According to the aqueous-cleaning equipment manufacturers, water-based detergents and washer systems clean just as effectively as solvents - provided the equipment and cleaning solutions are maintained properly.
Aqueous cleaning is fast, too. A typical wash and rinse cycle may only take 10 to 15 minutes compared to hours of soaking in caustic or a solvent tank. Automated spray washers and flow-through systems mean you can load the parts, push a button and walk away, eliminating the need for a lot of manual scrubbing and brushing. This frees up time for other tasks such as billable labor for machine work or assembly work and helps boost overall shop productivity and profitability.
Here is an overview of the basic types of aqueous cleaning systems in use.
o Manual system. In essence, this is a sink on a drum that recirculates a heated water-based solution. A filtered stream of 100°-115° F aqueous cleaning solution flushes away dirt and oil as parts are cleaned with the familiar brush on the end of a hose.
Experts say many of these drum and sink tanks are also being converted to bio-remediation systems. A bio-remediation system is a water-based solution that contains microbes, which are live organisms that eat oil.
When the Exxon Valdez struck a rock in 1989 and spilled millions of gallons of crude oil on the Alaskan shores of Prince William Sound, oil-eating microbes were put to work to help clean up the mess. The same approach is used in bioremediation to break down and digest oils and other hydrocarbons. Oil-eating microbes transform the grease and other gunk into water and carbon dioxide.
The process is relatively slow and it requires maintaining the water temperature within a certain range, usually no hotter than 110° to 120° F, and replenishing the microbes regularly.
o Immersion system. This is a less labor-intensive method in which parts are - simply enough - immersed in a cleaning solution. Within the immersion cleaner's tank a lift platform agitates up and down during the cleaning process. This type of system can also be used as a soak tank.
In addition to a lift platform, a recirculating pump can be added to provide more turbulence to the tank. This moves the cleaning solution around in a circle inside the tank, creating additional scrubbing action.
Immersion washers are very effective on intricate parts - those with blind holes, channels, etc. The agitation process forces the cleaning solution into all the tight areas of the engine part.
o Jet washer or cabinet washer. Essentially, this is an industrial-strength dishwasher. Jet washers use a pattern of spray nozzles that spray cleaning solution with detergents under some pressure (typically 40-60 psi) onto the parts.
The combination of water pressure impinging against the surface, and the secondary action of the water and detergent dispersing and rinsing away the contaminants does an effective job on most automotive parts.
The disadvantage of the spray cabinet washer is actually the advantage of the immersion washer, explain experts. The jet washer's spray pattern cleans what it hits very well. But it can't get into tight areas - blind holes, for example - and if it can't get in there, it can't clean.
There are several different types of spray cabinets. Front loading cabinet washers typically have spray bars underneath the basket, on top of the basket and on the sides to provide full coverage of the spray. Another type of cabinet washer is the top-loading kind. The advantage to this design is that you can use an overhead crane to load it.
Spray washers or jet washers generally use V-jet nozzles and some type of stationary manifold system to direct water at parts sitting on a turntable inside a cabinet. On some washers, the parts are stationary and the nozzles rotate to vary the spray pattern.
High-pressure spray cabinets add increased cleaning capabilities. They require manual operation and blast out about 400-600 psi of pressure. This gives a high degree of impingement with an aqueous cleaning solution to clean even parts with blind, tight areas.
Spray washers and power washers come in a variety of sizes and configurations, with prices ranging from $6,000 up to $50,000 or more.
o Ultrasonic washers are very effective, used primarily for removing carbon and burned on oils. The process is particularly effective in cleaning blind holes and geometrically complex parts.
Ultrasonics is the science of sound waves above the frequency normally considered audible for humans (above 18 Kilohertz). When vibrations at these high frequencies are introduced into liquids, areas of extremely high vacuum and extremely high pressure are generated alternately at any given point in the liquid as the sound waves pass. Under the influence of vacuum, the liquid is literally torn apart to create what is called a cavitation bubble. As positive pressure replaces the vacuum which formed the cavitation bubble, it collapses in implosion resulting in high pressure shock waves which do the work we ascribe to ultrasonics.
The result: Energetic disturbances generated by the implosions of countless cavitation bubbles. These perform the cleaning task by providing micro-agitation throughout the liquid volume.
The Solution Is The Solution
The most attention in aqueous cleaning over the past several years, say industry spokespersons, has been paid to the chemical and waste disposal areas. While the actual process of aqueous cleaning hasn't changed dramatically, what goes into - and comes out of - the wash water is more important than ever.
With aqueous-based cleaning processes, choosing the "right" detergent and/or chemical for the application is very important. The same equipment may clean very differently when different detergents are used. Some cleaning products are formulated for specific types of applications like aluminum or cast iron, while others are "general-purpose" cleaners. The best advice here is to follow the equipment suppliers' recommendations for chemical usage.
Several manufacturers recommend using a milder or less aggressive cleaner on aluminum because some products designed for cleaning ferrous metals can etch or discolor aluminum making it difficult to achieve a bright like-new finish. Yes, this usually means you'll need to invest in separate processes for cast iron and aluminum cleaning, because manufacturers say no single product cleans everything equally well.
Using different cleaning solutions for aluminum and cast iron can complicate the cleaning process, so some rebuilders set up separate cleaning lines for each type of metal. Many rebuilders also use different cleaning techniques for different metals, using a spray washer for aluminum and an oven for cleaning cast iron blocks and heads. Others may use an oven to bake off grease and oil, and a spray washer, rather than a shot blaster to clean off the scale and ash left by the oven. Spray washers also seem to be a popular choice for final cleaning to removing oils and residue after parts have been machined.
Some aqueous-cleaning equipment manufacturers sell their own brand of detergent and/or chemicals while others do not. Most equipment suppliers do provide a list of recommended products for their washers. Spray washers that operate at lower pressures and rely more on the surfactant action of the detergent to clean parts will be more sensitive to the type of cleaner used and the concentration of cleaner in the solution than equipment which operates at higher pressures and relies more on the force of the water to loosen and remove dirt.
For water to clean effectively, it usually needs heat. The hotter the better - to a point. The recommended temperature range will vary according to the type of equipment and chemicals used, and may range from 105° up to 190° F. Many spray washers operate best in the 140° to 180° F range. If the water temperature is too hot, though, water loss due to evaporation may become a problem requiring more make-up water to maintain the cleaning solution. Some equipment suppliers recommend a slightly lower water temperature when cleaning aluminum while others do not.
Maintenance includes adding make-up water as needed to compensate for water which is lost during cleaning operations and to evaporation, adding detergent and other chemicals such as rust inhibitors to maintain the proper balance in the solution, replacing or cleaning filters and oil skimmers as needed to slow the buildup of contaminants, and periodically removing sludge and other solid matter that accumulates in the bottom of the cleaning equipment.
The key to successfully cleaning parts with most aqueous-based processes is keeping the water clean. Clean water is especially important in spray washers because dirty water can clog spray nozzles, reducing the overall cleaning effectiveness of the process. Spray washers and power washers depend mostly on the force of the water striking the surface to loosen and wash away dirt and grease, but many also rely on the detergent or other chemicals to complete the job.
The other key is to get rid of the dirty water in a safe manner. As the cleaning solution becomes dirty, it must eventually be treated or disposed of and replaced. That's one of the drawbacks of any type of liquid cleaning process, be it water or solvent-based. Filters and skimmers can prolong the life of the solution, but cannot do so indefinitely unless other means are employed to treat and restore the solution.
Dirty water poses fewer environmental dangers than solvents, but it depends on the contaminants that are in the water. Heavy metals such as lead, cadmium and chromium are the main concerns. Heavy metal contamination can be minimized by removing bearings and plated parts prior to washing. But if the water contains significant amounts of these contaminants, it may have to be disposed of as hazardous waste. For this reason, waste water should always be tested to determine what's in it and whether or not special handling is required.
New methods of wastewater processing have been developed that literally remove the waste product from the solution. The water is then typically clean enough to return to the cleaning equipment, recycled or disposed of in the sewer. The removed waste can often simply be landfilled, although depending on the chemicals remaining other methods of disposal may be more suitable.
For contact information about and direct links to suppliers of aqueous and ultrasonic cleaning equipment, utilize the Engine Builder Buyers Guide, available on this Web site.