By Mark Shortt
Editorial Director, Design-2-Part Magazine

The need for contract cleaning, in applications ranging from industrial metal parts to critical parts for microelectronics or medical devices, continues to gain momentum in today's manufacturing environment. As the complexity of cleaning technologies has increased, so have the costs and skills required to apply them. Meanwhile, an increasing number of applications are requiring clean room environments in order to achieve, verify, and maintain specified cleanliness levels. When weighing the costs and benefits of an in-house cleaning operation against those of outsourcing, the choice is often relatively easy, especially when critical parts must be cleaned to extreme levels of verifiable cleanliness.

"For a reasonably sized ultrasonic line with one bath, two rinses, a dryer, and a programmable hoist, you're looking at approximately $65,000," says Chuck Osborn, manager of the Precision Cleaning Division of PTI Industries Inc., East Longmeadow, Massachusetts. "Automated particle counters run $40,000. Also, environmental issues surrounding waste water are a factor."

On top of these issues is the reality that effective use of an ultrasonic cleaning machine may require a host of additional investments. Besides providing capabilities such as de-ionized water and oil-free compressed air, practitioners of precision cleaning would be expected to invest in a clean room. If the magnitude of the cleaning challenge is not apparent by then, it quickly becomes obvious when factoring in costs related to regular maintenance of the machine, such as replacement of filters and disposal of effluent.

"Parts cleaning" is a diverse classification that encompasses many types of specialized parts, cleaning chemistries, and processes. In a general sense, the term refers to the gross cleaning performed during or after the manufacture of industrial parts, such as automotive, machinery, or machined metal parts. However, it is also being used increasingly for the maintenance, repair, and refurbishment (remanufacturing) of various parts, components, and instruments. For many jobs, the use of conventional parts washing or degreasing equipment is sufficient to remove machining oils, lubricants, grease, and other soluble surface debris that can be readily seen without the aid of magnification. But jobs requiring the removal of smaller particles and verification of cleanliness demand a higher level of expertise.

"Many manufacturers dismiss parts cleaning as an insignificant part of their manufacturing process until they start experiencing field failures and are faced with a barrage of warranty claims," says Osborn. "Many learn all too late that their highly engineered, closely toleranced device is rendered inoperable by a tiny particle, most likely so small that it can't be seen with the naked eye." Suddenly, the manufacturers are faced with a steep learning curve, Osborn says, referring to the myriad of issues relating to environmental regulations, equipment, chemistry, and staffing.

Although essential, much of the parts cleaning taking place in manufacturing today is either preliminary or secondary to a job shop's primary services. Metal finishing shops, for example, use various technologies to clean parts as a pre-treatment for surface finishing. Without this necessary cleaning step, coatings will fail to bond properly to the part. Other companies, such as metal stampers and precision machining firms, provide cleaning as a secondary operation to remove metal fines, stamping lubricants, or machining oils from parts that they've manufactured. While the cleaning is crucial to the quality and performance of the part, it is not the service that was outsourced to the shop.

Today, however, a steadily growing number of firms are dedicating themselves primarily to parts cleaning, and offering it as a contract service in its own right. Such companies provide cleaning that is often called "precision" for its ability to thoroughly wash or degrease parts, but they rarely handle jobs that qualify as "precision cleaning" based on type of parts cleaned or the critical nature of their applications.

This work is reserved for companies that remove contaminant particles and residues from high-tech parts, often in clean room environments. "Precision cleaning" is a general term for processes applied to parts—typically manufactured for the semiconductor, medical, and aerospace industries—that require extremely high levels of cleanliness. Not only is precision cleaning necessary to the smooth functioning of critical parts, but the consequences of failing to adequately remove contamination could be grave, in some instances leading to dangerous chemical reactions, explosions, or system malfunctions. At its highest level, precision cleaning is technically labeled "critical cleaning," a term that applies to diminutive, high-end parts used in applications such as disk drives, printed circuits, semiconductors, aviation and automotive instrumentation, telecommunications equipment, and ultra-high vacuum environments in medical and aerospace. The most critical applications require the use of sensitive analytical methods to detect the presence of contaminants so small that they cannot be seen by the naked eye.

Like parts cleaning, precision cleaning uses various cleaning chemistries and equipment, such as ultrasonic units and aqueous or semi-aqueous immersion systems. It, too, is applied for maintenance purposes, such as in the calibration of precision instruments or devices, and for repair and refurbishment. Other prime applications of precision cleaning include oxygen service components, laser optics, testing and measuring equipment, and fluid pumps, valves, fittings, and pressure gages.

"To many, precision cleaning and verification is a relatively new and mysterious technology," says Osborn. "People experienced in the field are scarce, and when you do find them, they don't come cheaply. You'll need someone who is experienced in selecting an appropriate cleaning process and verifying that it's capable. One of the biggest questions will be 'just how clean do your parts need to be and who is going to determine this?'"

But before going too far, Osborn cautions, it is best to determine the nature of the contaminant to see if it can be eliminated from the manufacturing process. The ability to successfully reduce contamination, however, is not sufficient reason to bypass precision cleaning, which may still be necessary to ensure the smooth operation of a close-tolerance mechanical assembly.

Contract precision cleaners often provide custom cleaning to suit the geometry of the parts. Various cleaning technologies are available for use, depending upon the application. Cleaning solutions include biodegradable cleaners that use oil-degrading bacteria to degrease metal parts, and chemical solvents that are subject to strict environmental regulations. Alternatives to solvent degreasers include aqueous and semi-aqueous cleaners, which are often somewhat less effective but environmentally safer.

Factors to be considered when choosing a process include the nature of the contaminant and the degree of contamination; the surface, size, and geometry of the part, and the required level of cleanliness. Options for precision cleaning are numerous, and include vapor degreasing, aqueous washing, ultrasonics, and mechanical blasting followed by a filtered rinse. Very large parts are sometimes hand-cleaned with wiping cloths and solvents.

The process of vapor degreasing uses a pure distilled solvent in conjunction with a hot wash cycle, a cold rinse cycle, and a cold spray chemical vapor rinse to remove grease and oil from parts. Because parts cleaned by this method exit the process completely dry, they do not require an additional drying stage, unlike parts cleaned by an aqueous or semi-aqueous process. In aqueous cleaning, parts are cleaned by means of an alkaline water-based soak-and-spray system. Abrasive blasting uses compressed air and an abrasive medium to remove impurities and contaminants from parts.

Vapor degreasing with chemical solvents, however, is gradually being replaced by more environmentally friendly, alternative methods of cleaning, such as ultrasonic degreasing and aqueous cleaning. Some of the newer degreasers are said to be virtually "emissionless," in that the amount of harmful solvents that they release into the atmosphere is inconsequential and within regulatory limits. In the operation of these machines, solvent is introduced into a sealed chamber that effectively limits or prevents the loss of solvents while cleaning. Solvent vapor is used in the final rinse, after which all vapors are exhausted and passed into a solvent recovery system.

Ultrasonic energy is used in many critical cleaning applications because it provides mechanical agitation that enhances the effectiveness of aqueous and semi-aqueous cleaning chemistries. Ultrasonic parts cleaning systems are known to be very effective for removing the smallest and most tenacious particles, Osborn says, particularly on parts with complex geometries. They provide a heavy-duty cleaning action that penetrates hard-to-reach areas of intricate parts, such as automotive valve bodies and transmission components with grooves and worm holes. Ultrasonics are known to effectively clean a wide range of machined stainless steel and brass parts, medical tubing, cast iron heads, valve bodies, cylinder heads, and valve covers.

"Many frequencies are available but as a rule, the finer the particles, the higher the frequency," explains Osborn. "Frequency also has an effect on how the parts survive the process. Low frequencies in the 25-Kh range can literally shatter delicate material, or, worse yet, introduce micro-cracks that cannot be seen with the naked eye."

Ultrasonic systems rely on generators that produce high-frequency electricity, which an ultrasonic transducer then converts to mechanical energy in the form of vibrating sound waves that are above the limits of human hearing. Transmission of the sound waves through the water causes the formation of cavitation bubbles, which oscillate, grow in size, and ultimately collapse and implode. Pressures generated by the implosion are sufficient to dislodge soils from the parts.

Processes that follow cleaning include rinsing, drying, preserving, and packaging, all of which "present their own little nuances," Osborn says. Options for drying of the parts, potentially the most time-consuming step, range from blowing with dry, filtered air to a vacuum oven bake procedure. Next is quantitative verification of the cleaning process, a crucial step that Osborn says is fast becoming the most prominent factor in the cleanliness industry. "Verification is the key," Osborn says. "The tighter the tolerances become in precision assemblies, the more that cleanliness becomes paramount to smooth operation."

While some contract cleaning companies perform either parts cleaning or precision cleaning, others provide, in varying proportions, both types of services. PTI's Precision Cleaning Division is one of the versatile contract cleaners that provides services ranging from the earthiest degreasing of automotive parts to critical oxygen service cleaning. In addition to precision cleaning for the aerospace, electronics, medical, and automotive industries, the multi-faceted job shop provides cleanliness testing and verification. PTI has experience in cleaning aircraft frame and engine parts, components used in space flights, medical tubing for biopsies, and automotive metering nozzles.

"We offer eight methods of precision cleaning, not just one," says Osborn, whose list includes ultrasonic cleaning, vapor degreasing, CO₂ snow cleaning, passivation, titanium cleaning, aqueous immersion, turbulent flushing, and mechanical blasting. "We also have the equipment to verify the cleanliness." The company uses computerized microscopes, balances, conductivity meters, and black lights to conduct quantitative measurements.

Osborn tells of a recent case in which a producer of silicon wafers was purchasing filtration screens for sizing of powder used in its process. The supplier of the screens had performed a rudimentary cleaning process that left parts working well at some times but not at others.

"There was no quantifiable cleanliness standard known or required," recalls Osborn. "I recommended that the end user send me several, and we performed quantifiable cleanliness testing on them to establish the existing level. We then cleaned them ultrasonically and retested them to establish the level of cleanliness achieved. The end user then tested them in their application, and all performed well. We then had a capable process that could be documented, verified, and repeated, and we've been cleaning them ever since."

Contract Precision Cleaners

Astro Pak (Downey, Calif.) is a precision cleaning contractor with more than 40 years of experience in precision cleaning, cleanliness verification, passivation technology, and protective packaging. Driven by a staff that includes licensed chemists and professional engineers, the company utilizes a variety of advanced technologies, including ultrasonic cleaning and high-pressure sprays that enable it to clean larger components more quickly and efficiently. Its proprietary Ultra Pass™ passivation system is reported to provide high chrome-to-iron ratios and increased corrosion resistance, without the high costs of disposing hazardous waste. Using environmentally "green" chemistry in its cleaning operations has the dual effect of lowering disposal costs and, in turn, customers' costs.

"Ultrasonic technology is used by many contract cleaners, as is citric passivation," says Daryl Roll, lead chemist and vice president. "Citric passivation with combined chelants meets or exceeds today's passivation standards which are typically based on older, nitric acid passivation technology. Citric passivation also avoids chemical waste disposal costs, which can be significant." Passivation chemically dissolves free iron buildup on the surface of stainless steel, reducing the risk of corrosion and making the tool or component ready for paint, epoxy, or other coatings that require a very clean surface.

"About 99.9% of all jobs we perform are driven by detailed specifications, such as MAO-110-301, a common aerospace spec used for the Space Shuttle," says Brent Ekstrand, operations manager. "There are hundreds of cleaning specifications that we must meet or exceed in order to certify that a part is clean." Ekstrand says that some specifications still refer to the older, nitric processes, which Astro Pak still provides on a regular basis.

The firm's Los Angeles facility, one of several Astro Pak processing facilities throughout the United States, is said to be among the largest contract clean rooms in the United States. An expansion at the firm's Downey facility earlier this year brought its total production clean room area—ranging from Class 100 to 1000—to 12,000 square feet. The facility includes one large degreasing tank with ultrasonics (36 x 36 x 96 inches), and two rinse tanks measuring 48 x 324 x 24 inches.

The large ultrasonic and rinse tanks give the firm the ability to process high-quantity orders, including large components, at one time. As a result, Astro Pak can offer faster turnarounds and lower prices. "We offer 24-hour turnaround and have even been able to precision clean and package parts in less than six hours," says Jerry Knepper, division plant manager. Other specialized equipment includes a high-temperature vacuum oven (48 x 48 x 48 inches) and enhanced assembly room in a class 1000 cleanroom.

Markets served by the company include the aerospace, aviation, defense, and semiconductor industries, as well as the pharmaceutical, microelectronics, and industrial sectors. The firm also provides services for government laser programs and the high-purity plumbing industry. "We're able to provide the same level of cleaning to almost any job site around the world with our mobile cleanrooms and our ability to quickly and economically construct temporary cleanrooms to suit any size project," says Knepper.

PTI's CO₂ snow cleaning system, implemented recently, is said to be effective in removing particles and light oils from delicate devices. The system generates no waste, says Chuck Osborn, and leaves parts dry when the process is complete. In the future, the company plans to couple the CO₂ snow cleaning system with a class 100 glove box for critical applications.

Acorn Industries, Inc. (Livonia, Mich.) provides both precision cleaning and industrial parts cleaning. Its precision cleaning, testing, and packaging services meet the exacting standards of industries such as aerospace, automotive, electronics, fluid power, medical devices, optical, and semiconductors, as well as the military. The company cleans many different types and sizes of parts, ranging from gaskets, filters, and syringes that are less than a centimeter in length, to flow sensors, pressure vessels, and satellite assemblies more than 10 feet long. Common types of parts that are cleaned by Acorn include those used in medical implants, surgical equipment, optical components, spacecraft components, and semiconductor manufacturing and testing. Others are used in disk drives, actuators, transmission housings, hydraulic assemblies, valves, regulators, filtration assemblies, and cryogenic equipment.

The company's cleaning facilities are said to provide cleanliness for more than 1,000 cleanliness specifications and requirements. Its cleaning services, ranging from heavy-duty degreasing to the removal of microscopic particles and molecular residues, include oxygen service, specialty gas service, low particulate (removal of particles down to 0.1 µm), and low non-volatile residue (removal of non-volatile and organic residues down to less than 0.01µg/cm²).

Kyzen Corporation (Nashville, Tenn.) provides contract cleaning services ranging from parts washing to wafer defluxing. The company employs a variety of solvent, concentrated aqueous, and semi-aqueous cleaners in its cleaning projects for the electronic assembly, semiconductor, optics, and aerospace industries. Its processes include ultrasonic batch cleaning, centrifugal batch cleaning, and vapor degreasing. Kyzen also provides spray-in-air, batch defluxing; spray under immersion, batch cleaning; atomized spray in-line cleaning; and conveyorized, in-line spray under immersion cleaning.

The company's cleaning systems are based on its proprietary technology for controlling the cleaner concentration in applications where water is added to the cleaning agent. The company has developed a closed-loop process control system (PCS) that continuously monitors the chemical concentration of the wash solution in the aqueous cleaning equipment. The PCS then automatically adjusts, as needed, the amount of chemistry or water in the wash tank in order to maintain the proper concentration. Its microprocessor-based controller actually monitors several parameters of the wash fluid, including temperature, level, and concentration. Besides eliminating the gross concentration changes associated with automatic fill systems, the PCS is said to eliminate the operator's exposure to the wash process during manual readings of concentration. It is said to be particularly suited for inline aqueous cleaners, where drag-out and frequent additions of water often lead to large changes in the wash solution concentration.

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