Aqueous Ultrasonic Cleaning System Processing Stages

Zenith Manufacturing specializes in the manufacturing of ultrasonic cleaning systems which utilize water-based cleaning fluids rather than hazardous and expensive solvents.  Aqueous cleaning systems typically include 3 distinct processes; ultrasonic cleaning to remove the contaminants, rinsing to remove the detergents, and drying to remove the rinse water, and are capable of producing absolute zero-residue cleaning results when the system has been designed for such a purpose.

When looking at ultrasonic cleaning systems in this web site, consider that some systems, such as our Table-top Systems or Single-tank Consoles include ONLY the ultrasonic cleaning tank.  When considering these systems, customers must have existing rinsing and drying means for the process since these processes are are not included.

If your process requires rinsing and/or drying processes, a Multi-tank Ultrasonic Cleaning System will be required.  Baskets must be transferred from tank-to-tank, either manually by hand, or with optional Automation Systems.  Zenith offers multi-tank cleaners with 2 or more tanks to suit any customer requirement.  A common 2-tank design includes ultrasonic cleaning, heated rinsing, and a compressed air blow-off drying system.  4-tank designs normally include ultrasonic cleaning, 2 rinsing stages, and a drying tank.  For zero-residue cleaning applications, at least 2 rinsing stages are recommended.

Determining the Number of Ultrasonic Cleaning Tanks Required

In most cases, a single ultrasonic cleaning tank can address the application in question.  However, there are instances where 2 ultrasonic tanks may be preferred.  For example, if a great deal of contaminant is present, such as heavy deposits of buffing compounds, or if 2 different cleaning agents will be used for different parts, 2 or more ultrasonic cleaning tanks may be required.  95% of multi-tank cleaning systems delivered include only a single ultrasonic cleaning tank.

Determining the Number of Rinse Tanks Required

Zenith normally recommends at least 2 rinse tanks designed with Reverse Cascade Overflow Capabilities.  This rinse tank design reduces the amount of water consumed, while simultaneously ensuring that the final rinse tank contains the purest available water supply.  Fresh water enters the FINAL rinse tank first.  This tank then overflows into the FIRST rinse tank before overflowing to drain.  To automatically control the consumption of water, Zenith also offers Automatic Rinse Water Quality Maintenance Systems which automatically monitor the quality of water in the final rinse tank, and adds fresh water when water quality falls below acceptable levels.

When you consider how a multi-stage clean/rinse/dry system operates, it is easy to understand why 2 or more rinsing tanks are recommended.  First, a basket is lowered into a heated detergent bath and ultrasonically cleaned.  Next, this batch of parts is moved to the Primary Rinsing Tank.  However, detergents which are present on the parts and on the basket are also transferred into the Primary Rinse Tank.  Detergent levels in the Primary Rinse Tank continue to rise as baskets are processed.  Under these conditions, it is easy to see why single rinse tank systems are not very popular.  In essence, you are rinsing in low-concentration cleaning fluid, which will produce an unacceptable cleaning result with parts that are covered with detergent residues unless fresh water is constantly added to the rinse tank to reduce detergent concentrations.

Multi-tank cleaning systems which include 2 rinse tanks will produce zero-residue cleaning results when the rinse system is connected to a deionized water supply.  Although a 3-stage rinse will not improve this performance, it will reduce the water consumption of the rinse system.  The decision regarding the number of rinse tanks to be purchased should consider the monetary budget for the system, the volume of parts being cleaned, and the part's design.  If the parts will tend to entrap cleaning fluids from the cleaning tank, 3 rinse tanks may be the better option.

Ultrasonic Rinse Operations

Ultrasonic rinse operations may be required for operations when parts being cleaned include metal folds or other detail which may entrap cleaning fluids.  The addition of ultrasonic components on the rinse tank will ensure that these areas are adequately rinsed.  However, most ultrasonic cleaning systems sold by Zenith do NOT include ultrasonic rinse operations, even when zero-residue cleaning is required.  In most cases, oscillation of the product in the rinse tank will completely remove detergents from the parts.

One must also  consider that the scrubbing action produced by the ultrasonic cleaning system in deionized (purified) water is less powerful than that produced in the ultrasonic cleaning tank.  Cavitation is the process by which all ultrasonic cleaners operate, and requires the momentary separation of fluid molecules to produce a cavity.  The surface tension of deionized water is so great that this separation is more difficult.  As such, the scrubbing action produced is less evenly distributed and less powerful.

Drying Tanks

The drying operation of a multi-stage ultrasonic cleaning process is typically the "bottleneck" of the entire operation.  Under optimum conditions, an ultrasonic cleaning system can remove contaminants from a batch of parts in under 5 minutes.  Rinse values for each rinse tank included are typically 1-3 minutes.  However, depending upon the design of the product, drying time values can range from 10-15 minutes.  Therefore, if a single drying tank is included in the system, product will exit the system every 10-15 minutes.

When the volume of product being cleaned demands more throughput, a 2nd drying tank can be included to double the output of the cleaning system, or air knives can be installed to remove large puddles of water which increase required drying times.  Zenith installs high-volume blowers and adjustable fresh air intake to maximize the performance of the drying operation.

Zenith's VORTEX Centrifugal Ultrasonic Cleaning System specifically addresses this issue by including centrifugal rotation in the drying tank to remove 95% of the water from the product in less than 30 seconds.  The balance is typically dried in less than 5 minutes.  This system also includes centrifugal rotation cycles immediately prior to basket transfer, which virtually eliminates detergent drag-out into the rinse, thereby drastically reducing water consumption and part quality, since most of the rinse water is removed from the product before it has a chance to dry on the surface and leave a residue behind.

Detergent Considerations

While selecting the appropriate ultrasonic frequency and power for a given application is the most important consideration when designing and ultrasonic cleaner, selecting the proper detergents for use in ultrasonic cleaning systems is the 2nd most important consideration.  Detergents must be chemically compatible with the parts being cleaned, and the stainless steel which the tank is manufactured of.  More importantly, the detergent selected must be able to reduce the bond between the contaminant and the surface of the product being cleaned to a level which allows the available ultrasonic power to break it free from the surface.

Different detergents also play a role in the distribution of the ultrasonic scrubbing action produced, the degassing time required, and the force behind the scrubbing action.  Some cleaning fluids will actually reduce the performance of the ultrasonic scrubbing action.  However, the cleaning fluid itself may overcome this loss of ultrasonic effectiveness when its properties include an improved ability to reduce the contaminant-to-part bond. 

Longevity of the cleaning fluids must also be considered.  The longer the cleaning agent lasts, the less it will cost to operate the system.  For oil and coolant removal applications, cleaning agents are specifically selected based on its longevity, and cleaning performance.  Some detergents are considered emulsifiers, in which oils do not float to the surface of the fluid, but are rather held in suspension by the fluid itself.  Some chemistries are considered separators, where oils will float on the surface of the fluid.  

Each type of cleaning agent has its benefits and drawbacks.  While a benefit of an emulsifier is its improved ability to remove the contaminant, the fluids do not typically last as long.  Once the fluid is saturated with contaminants, it will fail to clean the product adequately.  Separating chemistries do not clean as well as emulsifying chemistries in most cases, but may be adequate for a given application.  Since the contaminants are not absorbed by the cleaning fluid, longevity is drastically increased, and fluid bath life can be as long as 3 or more months with appropriate fluid maintenance.  However, one must consider that the contaminant is present on the fluid surface, and may re-deposit onto the parts when they are removed from the bath.  To reduce this possibility, systems using these chemistries may include overflow weirs and surface spargers to continuously or intermittently overflow the surface of the fluid, thereby preventing re-deposition.

Disposal of the cleaning agents must also be considered during the selection process.  While some customers may pay for waste management firms to cart the material away in drum quantities, others decide to purchase Wastewater Evaporators to greatly reduce the amount of waste which requires traditional disposal.  Since most ultrasonic cleaning baths are 92-95% water, evaporation of this water will reduce the amount of material which requires disposal by that amount.  Other methods for waste disposal include neutralization and filtration of the cleaning fluid until it meets acceptable local guidelines for dumping in facility sewer drains.  In either case, Zenith can assist you to determining the best methods for waste disposal for your application.

Selecting the Best Ultrasonic Frequency for the Application

Selecting the appropriate ultrasonic operating frequency is the most important consideration to ensure success.  Frequencies must be selected based on the weight of the batch of parts, contaminant which requires removal, material of part construction, and the amount of detail in the design of the part. 

As a general guideline, heavier parts will require lower frequencies.  For example, when cleaning a 2000lb plastic injection mold, frequencies from 25-40kHz are most common.  Lighter batches under 150-250 pounds are most commonly addressed with higher frequencies, such as 40kHz or 80kHz.  Parts which include significant detail in the design may require higher frequencies to ensure that the scrubbing action produced consistently cleans these areas.  Aluminum components require the use of higher frequencies to prevent damage to the surface of the product itself.

For specific information regarding each available ultrasonic frequency, see our Ultrasonic Frequency Selection page.

Optional Equipment

Ultrasonic cleaning systems are typically purchased with optional equipment which may include Particulate Filtration, Pump Drain Systems, Ultrasonic Timers, Automatic Rinse Water Quality Maintenance, Oscillation Systems, Automation, Closed loop Deionization, and others. 

Particulate filtration includes the components necessary to filter particles of contaminant which are removed from the parts being cleaned.  Systems include a flow pump, filter housings which contain filter cartridges or bags which trap the contaminants, pressure gauges to indicate when the filter housings require servicing, and plumbing to connect the system to the tank being filtered.  When considering a filtration system, 2 different types of filter housings are available; a Bag Filter Housing, and Cartridge Filter Housing. 

Cartridge filter housings tend to trap less contaminant, and are used for most installations.  The system utilizes disposable filter cartridges which are removed and replaced during maintenance operations.  However, when the contaminants on the parts are excessive, a Bag Filter Housing may be required, as it has an improved ability to trap MORE contaminant before requiring servicing.  Rather than using a disposable filter cartridge, a filter bag is installed in these systems which can be washed and re-used in many cases, and the time required between maintenance operations is also extended.

Pump Drain Systems are used to drain the contents of each liquid-bearing tank to a location of choice using control switches.  The pump drain option is usually added to systems which do not have a convenient drain location near the cleaning system, or for those customer who wish to pump the liquids to overhead waste lines.  Zenith pump drain systems include valves and positive displacement pumps to ensure that the pump can adequately and fully drain the tanks without producing "vapor lock."

Ultrasonic Timers are used to automatically time the duration of the ultrasonic cleaning cycle.  Operators press a button to start the sequence, and the system will automatically deactivate once the process is complete.  Timers indicate both set-point and actual timer values.

Automatic Rinse Water Quality Maintenance Systems are purchased when the customer wishes to automatically maintain the quality of rinse water in the final rinse tank to ensure that parts are rinsed in water which is known to produce the desired result.  Systems include digital water quality meters, and stainless steel gate valves for the ultimate in reliability.

Oscillation Systems may be added to an ultrasonic cleaning system when parts include detail which may entrap contaminants, preventing its removal.  Oscillation will serve to flush the part, freeing these contaminants from entrapment areas.  Oscillation may also be used to prevent damage to sensitive components, such as highly-polished aluminum components, and others.

Automation Systems are purchased to reduce the amount of labor required to operate a multi-stage cleaning process.  Rather than having to transfer parts manually from tank-to-tank, an automation system performs all basket transfers fully automatically.  Automation systems include the TRANSTAR Pick & Place Robotic System, the ULTRAMATIC HV, the VORTEX, and others.  See our Automation Systems page for details on each design.

Deionization Systems are used to produce pure water which will not leave residues of any kind on parts being cleaned.  However, some facilities do not have available deionized water, or would like to re-use the same rinse water continuously, adding only water which is lost through evaporation or drag-out into the drying tank.  Zenith offers deionization systems to provide our customers with the ability to produce zero-residue results even if deionized water is not available.

Choose your Cleaning System Design:

By the time you have finished reading the above information, you are ready to make educated decisions regarding the type of system which may be required. 

If one tank is required, a Table-top or Single-tank Cleaning System will suit your needs.  If more than one tank is required, a Multi-tank Cleaning System will satisfy your needs. 

If parts are heavy, or are contaminated with highly-bonded soils, lower ultrasonic frequencies will be needed.  If parts are lighter and include fine detail, or are sensitive to ultrasonic attack, higher frequencies will work best.

If you require zero-residue cleaning results, at least 2 rinse tanks will be needed, and the system must be connected to deionized water or water treated by Reverse Osmosis.

If drying is required, 1 or more drying tanks will also be required.  Typically, system throughput is determined by the speed of the drying operation, since drying typically requires more time than cleaning and rinsing combined.

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Zenith Mfg. & Chemical Corp.
85 Oak St.
Norwood, NJ  07648-0412
800-432-SONIC (7664)
201-768-6999
sales@zenith-ultrasonics.com