Aqueous Cleaning Technology Today

In the remanufacturing and transmission repair industry, cleaning has moved away from solvents and VOC’s to a more environmentally friendly approach with the use of aqueous cleaning detergents and parts washing technology. In this PDF slideshow, we aim to share knowledge on how aqueous cleaners are defined, the specific processes that should be taken according to your cleaning objectives, and different cleaning methods that should be implemented depending on part complexity, desired level of cleanliness, and equipment that is available to you. We hope this information will better your education on the different methods of cleaning based on your objectives as we believe that more knowledge and understanding of the aqueous cleaning technology today will better your cleaning methods and processes for tomorrow!

Aqueous Cleaning Technology Today

Aqueous cleaning technology is the use of high quality aqueous detergents that are specifically engineered for a given aqueous cleaning method and purpose that are used in conjunction with standard operating procedures.

Our focus will be on the aqueous heavy-duty production cleaning methods used in high volume transmission, torque converter, engine & heavy-duty powertrain component remanufacturing.

An aqueous cleaner is a blend of ingredients designed to enhance the cleaning ability of water.

Aqueous cleaners are cleaning solutions that are comprised of at least 90 percent water.

Aqueous cleaners may include a number of the following ingredients…

–          SURFACTANTS (SURFACE-ACTING-AGENTS)

• Improves the cleaning action of water by reducing water’s surface tension.  This allows for greater penetration or “wetting” of the cleaning liquid onto the soiled parts surface.
• In the context of cleaners, this means any chemical ingredient that lowers the surface tension or interfacial tension at liquid-gas, liquid-liquid, and liquid-solid interfaces.
• The structure of surface-active-agents used in
• Aqueous cleaners are usually oblong with one end of the molecule being hydrophobic (“water hating” )
• And the other end of the molecule being hydrophilic (“water loving”).
• Can be natural or synthetic.
• Promote the dispersion and or suspension of the greasy soils in solution.

–          DISPERSANTS

• Type of surfactant.
• Disperse or suspend solid particles in solution.
• Dispersants include water-soluble surfactants or water-soluble polymers (long-chain organic molecules).
• Are electrostatically attracted to particulates, creating a bridge between the water and the water-
• Insoluble solid particulate.

–           EMULSIFIERS

• Type of surfactant.
• Emulsify water insoluble oils into solution by
• Helping to create a liquid-liquid mixture.  

–           WETTING AGENTS

• Type of surfactant
• Lower the surface tension of water and allow the cleaning solution to “wet” surfaces and penetrate into, under and around soils and surface crevices.
• Make water “wetter”.

–           BUILDERS

• Promotes the effectiveness of cleaning by surfactants.
• Sequesters water hardness.
• They stop these metal ions from reacting with soils and other detergent ingredients to form water insoluble and difficult to clean calcium, magnesium or iron salt build-up.
• Help maintain ph.

–          CHELATING AGENTS

• Greek word meaning “claw”
• Combine themselves with disruptive calcium, magnesium and iron ions found in hard water.   These chelated hard water metal ions remain tied up in solution in a harmless state where they will not consume surfactant.
• Sequestering agent.

–          STABILIZERS

• Extend the shelf life of detergent ingredients and to maintain the uniformity of detergent blends.

–          SOLVENTS

• To enhance the removal of oily soils by disolving them
• Glycol ethers
• Ethylene
• Butyl celluosolve
• Increases VOC (volatile organic compound) levels of an aqueous detergent.

–          CORROSION INHIBITORS

• Minimize aqueous cleaners effects on metal subrates.
• Prevents the rusting or oxidation of cleaned parts
• Prevents rusting and extends the working life of the cleaning equipment if it is not made from
• Stainless steel.
• They are used for cleaning at high pH.

–          FILLERS & EXTENDERS

• Do not improve the detergency of the of the cleaner.
• Will increase the packaging and handling cost by increasing the weight of the specific package.
• Fillers and other inert powders are occasionally necessary as process aids in order to improve the free flowing characteristics of powdered detergents.

–          OTHER ADDITIVES

• Contaminant dispersants
• Anti-redisposition agents
• Brighteners
• Viscosity modifiers
• Antifoaming agents

THE AQUEOUS CLEANING PROCESS – THE MAJOR FACTORS & VARIABLES

–          CLEANING DETERGENTS & SELECTION

–          PRECLEANING HANDLING

–          CLEANING METHODS

–          CONCENTRATION

–          CONCENTRATION MANAGEMENT, REPLENISHMENT & BATH-LIFE

–          TEMPERATURE

–          CLEANING TIME

–          RINSING

–          DRYING

–          POSTCLEANING HANDLING

–          STANDARD OPERATING PROCEDURES

–          MEASURING CLEANLINESS

THE AQUEOUS CLEANING PROCESS – CLEANING DETERGENTS & SELECTION

The cleaning detergent used should be matched to the desired:

–          CLEANING METHOD

• Manual/hand – non-corrosive, high emulsifying & wetting
• Immersion soak –  high wetting & anti-redisposition
• Ultrasonic – anti-redisposition
• Spray cabinet / conveyor system – low foaming
• Power-spray pressure washers – high foaming

–          TYPES OF MATERIALS BEING CLEANED

• Ferrous  metals – cast iron & steel
• Non-ferrous  metals – aluminum, magnesium & brassGlass
  • Will it darken or turn aluminum black?
• Plastics
• Rubber
• Label removal

–          PART COMPLEXITY

• Part undercuts, blind holes, numerous cavities
• Does the cleaning detergent have the right surfactant package to “wet” the part properly?

–          TYPES OF SOILS BEING CLEANED

• Light or heavy
  • Heavy soils require heavy-duty detergents with a high concentration of cleaning ingredients and a high capacity to remove soils without having to react chemically with each individual molecule of that soil.
  • Light soils require a detergent that matches the exact type of soil in order to be able to most completely remove them.
• Organic or inorganicSynthetic oils
  • Many organic soils have limited water solubility so these types of soils are best cleaned by a high emulsifying cleaning detergents.

• Particulate matter such as road grime
• Rust
• Paint

–          CLEANING TEMPERATURES

• Cleaning detergents that incorporate emulsifying, saponifying, and dispersing agents (with high first order reaction kinetics), an increase of 18°f (10°c) will double the rate of cleaning.
• In general, cleaning solutions run at higher temperatures, result in better cleaning.

–          LEVEL OF CLEANLINESS REQUIRED

• If the part being cleaned or the manufacturing process does not require high levels or specifications for cleanliness, harsh, toxic cleaning agents can often be avoided.

–          DETERGENT QUALITY CONTROL LEVELS

• The cleaning detergent should be manufactured with appropriate quality-control procedures.
• Cleaning detergents should have lot / batch number tracking.
• CERTIFICATES OF ANALYSIS (COA’S)*
• CERTIFICATES OF COMPLIANCE (COC’S)*
  • *ADDITIONAL COST

–          HEALTH, SAFETY & ENVIRONMENTAL CONSIDERATIONS

• Human health and safety considerations include detergent toxicity, corrosivity, reactivity and flammability.
• Does the cleaning detergent present any health hazards?
• Are they corrosive?
• Does the cleaning detergent have any reactivity
• Hazards when being initially mix with water or with the soils being cleaned?
• Review the material safety data
• Sheet (MSDS) for the specific cleaning detergent.
• Can it be disposed of easily?
• Any detergent chosen should be readily disposable and biodegradable, containing no RCRA hazard classification or EPA priority pollutants designation. Otherwise, the use of hazardous cleaners may require special, expensive waste-handling treatment.
• Is it environmentally friendly?
• Considerations include ozone depletion potential, volatile organic compound (VOC) & hazardous air pollutants (HAP) content regulated by the clean air act amendments.
• Approval under anticipated future restrictions should be weighed as well.

–          ECONOMIC CONSIDERATIONS

• What is the cost per gallon?
• What is the cost per make-up?
• Is the cleaning detergent concentrated or does it contain a lot of powdered fillers or water?
• What is the bath life?
• What are the replenishment rates?
• What are the freight costs?
• What are the waste treatment or disposal costs?

THE AQUEOUS CLEANING PROCESS – PRECLEANING HANDLING

As a rule, it is important to clean parts as soon as feasible after they are soiled.

In some instances it makes sense to take parts directly from a manufacturing process and put them into a soak solution where they may be able to sit for extended periods of time prior to cleaning.

Alternatively, parts can be placed in protective packaging, dipped in a protective coating or immerse in oil or grease to keep them in a state that will not increase the burden on the cleaning process.

THE AQUEOUS CLEANING PROCESS – CLEANING METHODS

The choice of cleaning method is determined by:

–          The quantity of parts to be cleaned

–          PART configuration & SIZE

–          LEVEL OF CLEANLINESS REQUIRED

–          The budget available for equipment

Often, one or more of the following methods will be used to reach a parts desired level of cleanliness. Washing prior to ultrasonic cleaning.

The following are the predominant cleaning methods:

–          MANUAL CLEANING

• Sink-on-drum
• Aqueous parts blasters
• Typically chosen for small-volume batch cleaning.
• High levels of cleanliness can be achieved by manual cleaning, although the operator determines the consistency of cleanliness.
• For consistent manual cleaning, rigorous operator training and retraining needs to be considered.
• Well-written cleaning procedures and training procedures should be provided for—even going go so far as to certify operators in different cleaning methods with periodic recertification.   

–          IMMERSION / HOT SOAK TANK

• Usually chosen for small quantities of parts when there is sufficient time in which to clean them.
• Soaking is not labor intensive, although it is typically a slow process.
• Due to the longer times involved in soaking, there is also more time for corrosion due to interaction between the surface being cleaned and the solution used to clean it.
• Agitating soak tanks can improve cleaning cycle times.

–          ULTRASONIC

• Particularly effective on small parts with blind holes and crevices that are inaccessible by spray cleaning.
• This process is essentially soak cleaning enhanced by ultrasonic sound energy which greatly accelerates the speed of cleaning and improves the level of cleanliness.
• Ultrasound helps with dispersing and mass transfer of the cleaner and the replenishing of fresh cleaning solution to the surface of the parts being cleaned.
• Ultrasonic cleaning involves more expensive equipment and is typically suitable for somewhat larger volume batches where a higher level of cleanliness is required.

–          SPRAY-WASH SYSTEMS

• Cabinet washers
• Pass-thru washers
• Conveyor / belt washers
• Monorail washers
• Drum washers
• Spray-wash systems is the most common type of cleaning method used within the remanufacturing industry.

–          POWER-SPRAY PRESSURE WASHERS

• As volumes move up from those that may be best addressed by manual, soak or ultrasonics, it often makes sense to employ some form of spray-wash cleaning method.
• For very high-volume parts washing, a conveyor, belt or monorail system may be required.
• Spray-wash cleaning systems are very effective for parts and surfaces that are readily accessible to the spray. They are not as good at dealing with blind holes and small crevices.  With that said, cleanliness levels from cabinet spray-wash systems to conveyor spray-wash systems can vary greatly. 
• Part placement and orientation becomes a factor for part cleanliness.
• The cost of spray-wash systems can vary greatly from a few thousand-dollars for a simple cabinet washer to hundreds-of-thousands of dollars for a multi-stage conveyor or monorail spray-wash system.
• These systems are highly customizable and can be engineered to clean any part thoroughly.

–          POWER SPRAY-WASH SYSTEMS

• Designed & sized for  a general or specific cleaning task
• Spray impact pressures (PSI)
• Nozzle configuration
• Nozzle /manifold spacing & spray pattern
• Spraying distance to part
• Sump capacity
• Filtration / sludge-drag
• Oil skimming
• Equipment clean-out
• Multiple-stage systems – wash/rinse/dry

POWER-SPRAY PRESSURE WASHERS

Commonly called pressure washers, it consists of a pressurized tank with hot water and/or steam that is connected to a hand-held wand.

The wand will have a trigger to release the hot water or steam and usually has a detergent metering device or injection device to meter in detergent during spraying.

For cleaning very, very large parts (where an operator can physically move around the part, for example, vehicles or very large assemblies) it makes sense to use a power-spray wand or handheld pressure spray device to clean the parts exteriors.

THE AQUEOUS CLEANING PROCESS – CONCENTRATION

The concentration of the cleaning detergent must be optimized to many factors including:

–          Level of cleanliness desired

–          Types of materials being cleaned

–          Types of soils to be removed

–          Rate or speed of cleaning desired

–          Method of cleaning

–          Operating temperature

–          Rinsing

–          Water hardness

–          Bath-life expectations

Above a certain minimum concentration of detergent, doubling the detergent concentration may only give a 10% increase in ability to remove soil and a 25% increase in bath life.

Refer to the cleaning detergent’s technical data sheet for the recommended initial concentration.

How big is your scoop?

THE AQUEOUS CLEANING PROCESS – CONCENTRATION MANAGEMENT, REPLENISHMENT & BATH LIFE

Once the bath’s effective chemical concentration has been developed and optimized, this concentration should be monitored, maintained and recorded on a routine and regular basis for continued optimal cleaning performance.

The concentration OF THE CLEANING DETERGENT will normally decrease due to the cleaning of soils, liquid drag-out and to the replenishment of water due to evaporation.

Concentration Management can be accomplished easily with the help these monitoring methods:

–          Titration

–          pH

–          Conductivity measurement

Bath life can also be extended by physical filtration of particulates & soils, the cooling, settling and removal of sludge and the use of oil skimmers.

Continual recharging of the cleaning solution bath without proper tank drainage and cleaning will eventually lead to poor cleaning results and possible machine malfunction.

THE AQUEOUS CLEANING PROCESS – TEMPERATURE

As mentioned earlier, higher-temperature cleaning solutions result in better cleaning.

 In practice, there is typically an optimum temperature for a given combination of cleaning variables.

High temperatures are particularly important in machine/spray washing where a droplet of solution only has a split second to react with the soil before the next droplet of cleaning solution displaces it from the surface.

High cleaning temperatures also help remove soils such as wax or silicon oil that typically can only be softened at temperatures above 170°F in conjunction with a high-emulsifying cleaner.

THE AQUEOUS CLEANING PROCESS – CLEANING TIME

Cleaning time is the parts dwell time in solution that allows the cleaning detergent selected, to work in the chosen cleaning method, at a specific concentration and temperature, the time needed to overpower soils and remove them from the parts to the desired level of cleanliness.

Cleaning time allows the part to come to temperature to decrease the viscosities of grease, oils & other soils to be removed from the part.

In general, the longer the cleaning time, the more thorough the cleaning.

Many cleaning mechanisms such as emulsifying, dissolving, suspending, and penetrating are time-dependent. Up to the point where cleaning has been completed, the longer they’re employed, the more cleaning is accomplished.

Cleaning time can be DECREASED by increased agitation, more aggressive & higher detergent concentration and by increasing temperature.

If agitation, detergent, or temperature cannot be increased—perhaps because the substrate is too delicate or the proper equipment is unavailable—then one must be prepared to use longer cleaning times to achieve the desired cleanliness.

While manual cleaning may take minutes, and spray cleaning might even take seconds, soaking for hours, or even overnight, may be required to reach similar levels of cleanliness.

There are some instances when long cleaning times may promote substrate corrosion, weakening, or swelling.

The optimum cleaning time should be chosen relative to the specific substrate, temperature, cleaning method, and detergent.

THE AQUEOUS CLEANING PROCESS – RINSING

The last thing to come into contact with the cleaned surface is the rinse water.

A thorough rinse will remove soils which have been cleaned from the surface and any residue from the detergent itself.

Whatever contaminants are present in the rinse water to begin with can be present after rinsing. Therefore, the more stringent the cleaning requirement, the greater the need for rinse water purity.

The important consideration is to remove whatever contamination or residues are present to levels that will not interfere with the further use of the parts or equipment.

The use of tap, deionized or distilled water for the final rinse is part specific. 

Unfortunately, rinsing is more often than not, the forgotten step

THE AQUEOUS CLEANING PROCESS – DRYING

Drying can affect residues and corrosion since impurities from rinse water can be deposited during evaporation.

Water, particularly high-purity rinse water such as deionized water, can be corrosive to metal substrates during heated and air drying.

The use of physical removal or drying techniques or the addition of corrosion inhibitors (with the tolerance of corrosion inhibitor residues) to the rinse water can help minimize such corrosion.

THE AQUEOUS CLEANING PROCESS – POSTCLEANING HANDLING

The way in which parts and surfaces are handled after cleaning can impact their cleanliness.

For this reason it is important to consider how parts are handled and stored to ensure that the purpose of the cleaning process is maintained.

Depending on the environment, it may be advisable to make provisions for a clean storage place or conditions.

It may be appropriate to determine how long a surface or part will stay clean while stored.

Determine if PARTS need to be re-cleaned prior to use.

THE AQUEOUS CLEANING PROCESS – STANDARD OPERATING PROCEDURES

A large part of successful cleaning relies on having a sound, reproducible procedure or standard operating procedure (SOP’S).

SOP’s of course, aids in making it easier to train operators so that cleaning is consistent.

In general a good SOP should present a list of Materials and people involved, the surface being cleaned should be identified, and the major factors and variables just discussed for cleaning effectiveness should be defined.

It should also cover washer preventative maintenance.

THE AQUEOUS CLEANING PROCESS – MEASURING CLEANLINESS

Measuring cleanliness can be done at different levels depending on the technique employed.

Processes which detect cleanliness at levels as low as 0.01 grams per square centimeter include:

–          Visual to low power magnifier inspection

–          Wiping and visual inspecting

–          Water break tests

–          Surface UV fluorescence detection (Black light)

–          Tape test

The next level of cleanliness measurements detects soils at the 0.01 to .001 gram per sq. cm level.

THIS level of detection is suitable for aerospace, electrical, automotive and many surface preparation applications.

This level of detection can be achieved through:

Millipore filter measurement techniques

Surface Energy tests

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