The content of this post was originally drafted by Mark Adams at Better Engineering
The parts go in dirty and come out clean, what heck else do you need to know? As the old saying goes “there is more to the story”
In this article we will review the basics of cleaning, basic equipment components, the importance of rinsing, and how to test for cleanliness.
Basics of Cleaning
Whether you are washing parts, your car, or dishes at home, these four factors are consistent for virtually all water based cleaning applications.
Time
The longer the part is exposed to the wash or rinse solution, the better the part will clean and rinse.
Temperature
Cleaning efficacy increases as the water temperature increases, until the top operating temperature of the chemical solution is reached.
Chemical and Concentration
Chemical and concentration are selected to remove a specific contaminant from a part without harming the part material.
Impingement
In spray washers, spray impingement is defined as the pressure and volume of the spray. The distance from the spray jet/nozzle to the part is also an important factor. The closer the nozzle is to the part, the greater the spray impingement. Ultrasonics also increase impingement in immersion systems.
Equipment Basic Components
Most aqueous parts washing systems use the same basic components or circuits.
Pumping Circuit
A pump is used to spray the parts with cleaning solution, or it is used to enhance cleaning in immersion systems via spray under immersion.
Heating Circuit
Most aqueous cleaning systems use a heated solution (water and detergent) to cut oils and other organic soils. Options for heating a tank are electric, natural gas/propane, and steam. Typical operating temperatures are 130F to 190F.
Spray Bar and Nozzles
For direct spray applications, spray bars and nozzles are used to direct the cleaning solution onto the part. Depending on the part geometry, these spray bars are either fixed or oscillating to enhance cleaning.
Controls
Control types vary with the type of washing system. The controls on a single stage wash only machine can be as simple as a timer, thermostat, and toggle switches for other controls. In more complex multistage systems, PLC’s are used to control heat, cycle times, stages, show fault conditions and provide Ethernet connectively.
Sump/Tank/Process Chamber
Construction material for most applications is stainless steel either 304 or 316 for more aggressive chemistries. Mild steel should only be used in applications with very high oils. Good quality machinery uses heavier gauges of construction materials.
Rinsing is as Important as Washing
Your parts are only as clean as your last rinse. The purpose of rinsing is not to rewash the parts, but to remove detergent residue. Adding additional rinse stages will improve cleaning performance, but this will add cost and footprint. Furthermore, a fresh water or “virgin” rinse can improve overall cleanliness. A fresh rinse can come in the forms of tap, RO, or DI water. In most cases, this is the last rinse and it overflows into the previous tank. This cascading effect keeps the previous rinse tank cleaner. However, the displaced water needs to be captured or go to a drain.
How Clean Is Clean and How is Tested?
Clean is a very subjective term. It is amazing how many companies lack written cleanliness specification. Cleaning specifications vary when doing in process, vs final cleaning. There are several common techniques used to measure cleanliness.
White Glove & Cotton Swab Testing
This simple test consists of wiping the surface of the part with a clean white glove or a clean cotton swab. Once completed, the glove or swab is inspected for evidence of residuals on the part after the washing process. You must determine visually if the part is a pass or fail
Dyne Testing
Dyne Test give you a quick way to measure surface wetting or surface tension of a part. It is generally the easiest method of determining how much contaminate, such as oils, waxes, cutting fluids, etc., are on the surface of a part. A series of pens similar to a Magic Markers, or simple inks, are used to mark a flat area of a part. If Dyne ink beads up, similar to how water beads up on a newly waxed car, this is considered to be a failed test. The operator would then use the next level of inks until a test passes to give a general overview of how clean the surface of a part is.
Millipore or Gravametric Cleanliness Testing
This process involves washing a part with a solvent, either before cleaning to establish how dirty a part is, or after cleaning to determine how clean. Usually a chemical such as Acetone is used to ensure that all hard particles, such as chips, burs, metal shavings, and other similar contaminates are removed from the part. After the part has been washed down, the solution is captured in a sterile container and run through a filter system which separates out all non-soluble contaminates from the chemical that was used to wash the part. The resulting contaminates, caught in the filter system, is then analyzed under a microscope (Filtrex) to give accurate data about the amount of contaminates, the weight of contaminates, the size of contaminates, and the type of contaminates.
The content of this post was originally drafted by Mark Adams at Better Engineering