When purchasing a new clean/rinse/dry system, one of the questions you will be asked by our engineers is the level of cleanliness required on the parts when they exit the system.  While many customers will require "zero residue" cleaning results, where no remaining contaminants of any kind remain on the parts, others may accept parts with "water spots" left on the product.  The quality of the cleaning result produced by any clean/rinse/dry system will be largely dependent upon the quality of the water in the final rinse stage just prior to the drying operation.

The cleaning system purchased for a given ultrasonic cleaning application must include enough rinsing tanks to produce the level of cleaning result required.  The greater the number of rinsing tanks, the less water that will be required to maintain adequate purity in the final rinse tanks.  Each time a basket is transferred from the ultrasonic cleaning tank to the rinsing tank, detergents are also transferred into the rinse, thereby contaminating it with detergents that will leave residues on the parts.  This is the reason why most multi-tank clean/rinse/dry systems include at least 2 rinse tanks.  The first rinse tank removes most of the detergent residues, thereby preventing it from contaminating the final rinse tank.  Less water is then required to maintain the water purity in the final rinse tank. 

Tap water will contain dissolved minerals and other materials that can create water spots on the product after drying.  During the drying process, the water evaporates, but the minerals do not, and residues remain behind on the product being cleaned.  While this is acceptable in many instances, some customers cannot accept this level of cleanliness.

If zero-residue cleaning results are required, the water used for the final rinse must be purified to reduce or eliminate dissolved minerals or other residue-creating materials.  The most common method for purifying water for ultrasonic cleaning systems is with the use of a Deionization System, which are available from Zenith Manufacturing.  These systems produce medical-quality purified water which will not leave a residue behind on the product after drying.  Deionization Systems are composed of 2 or more Water Treatment Vessels filled with Activated Carbon, and Mixed Bed Deionization Resin.  While the activated carbon will remove much of the contamination in the water by a process called "adsorption," the Mixed Bed Deionization Resin will remove any remaining ionic contamination from the water.  Additional filters and germicidal equipment is normally added to deionization systems to further purify the water, and to prevent septic odors when the system is continuously re-using the same water supply, which is called a "Closed Loop Deionization System."

Customers wishing to purchase a Closed Loop Deionization System must understand that a closed-loop system will require more maintenance than when using an existing deionized water supply.  The reason for this is that the deionization system must remove ANY and ALL detergents which are transferred into ANY rinse tank in the system.  If the part design is such that it entraps liquids, the amount of detergents which are transferred into the rinse tank, and deionization system, is considerable.  Deionization resins can only remove a certain number of "grains" of ionic material before resins need replacement.  When the resin is exhausted, it must be replaced, and exhaustion occurs much faster in a closed loop system.

Zenith clean/rinse/dry systems and deionization equipment include features which reduce the amount of detergents which will enter a closed-loop rinsing system by over 90% to drastically increase the life of deionization system resins.  In some cases, resins can last 6 months or more before requiring replacement.  If the Zenith technology is not included on a closed loop deionization system, resins may require replacement every month.  No other ultrasonic equipment manufacturers have yet changed to this technology, which will reduce operating costs and maintenance of the deionization system considerably.  For those customers who have on-site deionized water available, Zenith still adds this technology to the rinse tanks to reduce the amount of deionized water needed to keep the final rinse tank at the required level of quality.

Deionized water is measured using "resistivity," or how resistant the water is to conducting electricity.  The higher the electrical resistance of the water, the more pure the water is.  18.3 megaohms of deionized water resistance indicates electronics-grade ultra-pure water.  Although Zenith deionization systems produce such levels of water quality, this resistance is difficult to maintain in an open cleaning tank, since airborne contaminants will lower the resistance over time.  One can expect values from 3-7 megaohms on a closed-loop deionized water rinse on a continuous basis in most cases.

Another very important point to consider is contamination which does NOT change the resistance of the water.  In some applications, contaminants are added to the rinse water which do not increase the water's electrical conductance.  When this occurs, the resistivity meter will indicate that the water is pure, but parts still exit the system with residues.  In order to prevent this from occurring, Zenith salespeople have been trained to ask very specific questions about the cleaning process to determine if this potential exists.  If it does, additional filtration equipment is added to the rinse system to ensure that this contaminant is removed from the water to prevent residues.

Most multiple rinse tank systems include Reverse Cascade Overflow Capabilities.  The purest water supply is added to the FINAL rinse tank.  This rinse tank then overflows into the PRIMARY rinse tank, which then overflows to drain or into additional rinse tanks.  This technology serves 2 primary purposes; to ensure that the final rinse tank contains the purest available water supply, and to reduce water consumption since both tanks are sharing the same water supply.  The greater the number of rinse tanks, the smaller the amount of pure water that will be required to maintain adequate water quality in the final rinse.

In many cases, ultrasonic systems are added to the primary or final rinse tanks to improve rinsing.  After all, the primary function of the rinse process is to remove the detergents which are used in the ultrasonic cleaning tank.  When parts being processed have detail which may entrap detergents, ultrasonic systems can be beneficial in removing these contaminants.  However, the ultrasonic scrubbing action is greatly reduced in deionized water, since the surface tension of the water is so great that ultrasonic cavitation is difficult to produce.  Although power loss occurs in deionized water rinse tanks, the available scrubbing action is sufficient to ensure that parts are adequately rinsed.

One of the options available on Zenith clean/rinse/dry systems is the Automatic Rinse Water Quality System, which continuously monitors the water quality in the final rinse tank.  When water quality falls below acceptable values, pure water is added to the rinse tank until water quality is acceptable.  Excess water overflows into the neighboring rinse tank when multiple rinse tanks are included, or to drain if a single rinse tank is included.  This option will greatly reduce the consumption of deionized water.

Rinse Water:

• Is Responsible for Removing Detergents from Parts.
• Will Largely Determine Final Quality of the Parts being Cleaned.
• Must be Deionized or Purified to produce Zero Residue Results.
• Can be Automatically Maintained with an Automatic Water Quality Maintenance System.
• Should be Used in Multiple Cascading Overflow Tanks to Reduce Water Consumption.
• The Greater the Number of Rinse Tanks, the Less Water Consumption the System will Require.

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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