Fact Sheet: Cleaning Equipment for Industrial Cleaning

A pollution prevention fact sheet on Cleaning Equipment for industrial cleaning.

#10 Cleaning Equipment

When talking about solvent substitution most people immediately begin thinking of substitute solvents; some type of liquid. This line of thought bypasses some very important questions such as "Do I really need to clean?", "Why are my parts dirty?" and "Can I clean my parts without using a solvent?" It is prudent to ask these questions first.

"Dry" (Non-Liquid) Cleaning

Blast cleaners are the most popular of the non-liquid cleaning systems. Sandblasting? Not quite. New blast cleaning systems use media such as ice, steel shot, foam balls and dry ice. Although a number of these systems were developed for paint stripping, they may also be viable options for parts cleaning. A fact sheet on non-liquid cleaning is available from the Pollution Prevention Program.

Liquid Cleaning Equipment

If you must clean your parts and haven't found an appropriate 'dry' cleaning system, you should then consider non-chlorinated solvents or aqueous cleaners. Very few cleaning chemicals are volatile enough to allow vapor phase cleaning, thus most are used in wet applications. Low volatility also means that your parts will remain wet after cleaning and may require a drying step. The use of more aggressive cleaning equipment may allow you to use less aggressive chemicals. For example, a neutral aqueous solution used in a spray washer may clean as well as a more caustic solution in a soak tank, but with reduced safety and environmental concerns. Conveyor cleaning systems cost more but may offer better process control and higher throughput. Batch systems are simpler and less expensive but are more labor intensive and may require more worker exposure to cleaning chemicals.

Equipment Types

Soak Tanks

From 5 gallon buckets to 500 gallon tanks, soak tanks are simple, inexpensive and require little maintenance. Soak tanks can be made more effective by adding heat, agitation, immersion spray or ultrasonics. Soak tanks are very good for cleaning blind holes and crevasses but usually require more aggressive chemicals than spray cleaners. Oils floating on the surface of the bath can recontaminate parts as they are being removed. This may be desired as a rust inhibitor but if not, soil buildup may require continuous filtration or frequent replacement of the cleaning fluid.

Spray Washers

Spray washers are much more aggressive than soak tanks and often clean well using only water. Hand held spray wands are often used for cleaning large parts (i.e. car washes) and gloved boxes are often used for small quantities of small parts Spray cabinets and conveyor systems are used for high throughput applications. Heat, parts turntables and rotating spray nozzles can enhance cleaning. Spray washers are more expensive than soak tanks, require more maintenance and are not as good at cleaning blind holes. A flammable cleaning solution can become explosive when sprayed. Do not use low-flash-point cleaners in a spray system.

Rinsing

Rinsing can be the most important step in a cleaning system or it can be completely unnecessary. If subsequent steps involve painting or plating the parts, proper rinsing is absolutely vital. But if parts are to be inspected or rebuilt, you should seriously question the need to rinse. Many cleaning solutions will act as rust inhibitors if left on the part. If rinsing is necessary, either soak or spray can be used. A heated rinse may raise the part temperature enough to promote flash drying. A rust inhibitor can be added to the rinse to protect parts if necessary, but the rust inhibitor may also interfere with painting or plating.

Drying

Parts can be dried using hot air, infrared heat, centrifugal spinning or vacuum drying. An air knife installed before the drying step will de-water parts and expedite drying. Drying can easily be the most expensive and energy intensive step in your cleaning system so carefully evaluate the need to dry.

Cleaning Enhancers

Heat

Cleaning solutions usually work better when heated. The hotter, the better... Right? Not really. One aqueous cleaner manufacturer reports of a customer who was running an agitated soak tank at 140 F. The parts were not adequately cleaned so the customer raised the temperature to 160 F. Cleaning efficiency DECREASED. The optimum temperature for the bath turned out to be 120 F. Heating a cleaning solution can make your gas or electric meter do cartwheels. Conserve energy by covering baths, using insulated tanks, or using waste heat from other processes to heat your cleaning solution. Be careful about heating low-flash-point cleaners.

Turbulence

Addition of a pump or turbulator will improve cleaning efficiency in a soak tank. Turbulence helps to remove soils as they are dissolved or subverted, allowing the cleaner to work on the next layer. Turbulence can also help keep oils in suspension while the system is in use, reducing recontamination of parts. Spray under immersion combines the cleaning power of a spray system with the soaking action of a tank and decreases the potential explosion hazard when using flammable cleaning solutions.

Air Agitation

Air is cheap and adding an air pump and manifold to your soak tank can increase cleaning efficiency at low cost. However, air bubbling through the bath may oxidize certain types of cleaning solution (i.e. terpenes) and decrease their cleaning efficiency. Air agitation may also cause parts to oxidize.

Ultrasonics

Ultrasonics is one of the most effective types of cleaning enhancement. Ultrasonic transducers mounted on the sides of a soak tank produce high frequency sound waves in the cleaning solution. The compression and expansion of the fluid causes microscopic bubbles to form at the part surface. The formation and subsequent collapse of these micro-bubbles creates a scrubbing action and increases the reaction between cleaning solution and soil. Ultrasonic tanks typically operate in the 40 kHz range, but some operate up to 200 kHz. One manufacturer uses multiple frequencies (28 kHz - 200 kHz) to eliminate standing waves and enhance cleaning. Martin Marietta has found 20 kHz ultrasonics to be more effective than 40 kHz in some tough applications. In some applications, the ultrasonic energy alone is sufficient to clean the part using pure water.

On the down side, there is more to buy and more to break. Equipment, maintenance and energy costs can be high and will increase with the size of the tank. Cleaning large parts with ultrasonics can be exorbitantly expensive. It is essential that fixtures in the tank do not interfere with the ultrasonic energy (plastic baskets are a no-no) and air bubbles trapped in or on the part will prevent cleaning. Ultrasonics can erode the surface of parts if the system is not properly "tuned" and noise levels may be high requiring operator hearing protection. Ultrasonics will raise the temperature of the cleaning bath so care must be taken if flammable solvents are used; fire and safety codes may require the use of special equipment.

Other Considerations

System Configuration

Often a combination of cleaning steps will be most effective. For example a pre-soak tank may be followed by a spray wash, then a spray rinse and a dry step. To minimize treatment and disposal, use solution from each process step as make-up for the previous step. Thus rinse water is used to top off the spray tank, and spray solution is used to top off the pre-soak.

Separation

To minimize costs and environmental impact, it is essential that you be able to separate the cleaning solution form the soils. Without this ability, soil loading of the solution eventually will render it ineffective and the bath will need to be treated, disposed of and replaced ($$$$). When evaluating a cleaning solution, think about how it can be reused.

Many cleaners hold soils in suspension while agitated but will separate from them in a holding tank. Oils float to the surface and can be skimmed off while particles fall to the bottom allowing the cleaner solution to be reused. In an agitated soak tank, the system can be simply turned off at night and skimmed/sumped in the morning. No holding tank is necessary.

Some cleaning solutions emulsify soils at high temperatures but separate from them as the emulsion cools. This type of separation can also be done in a holding tank or during a daily shut-down of the system. If gravity separation alone does not provide sufficient contaminant removal, filtration may be necessary. New ceramic filters are available which can tolerate the chemicals and high temperatures common in cleaning systems.

Fact Sheets available in the Industrial Cleaning series:

  1. Introduction
  2. Common Pollution Prevention Opportunities
  3. Using Aqueous Cleaners
  4. Evaluating Cleaning Liquids
  5. Aqueous Cleaner Additives
  6. Terpene Cleaners
  7. Dry (Non-Solvent) Cleaning
  8. New Cleaning Solvents
  9. Hydrocarbon Cleaners
  10. Cleaning Equipment
  11. Vendors of Cleaners & Equipment

- in the Jacksonville area, call 904-448-4300
- in the Tampa area, call 813-744-6100.


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Last Updated: October 17, 1995