Cleaning Formula for All Cleaning Processes
For all cleaning processes, the cleaning effectiveness is dependent upon four variables. The weight or value of each variable may change from case to case. There is some ability to alter one or more variables and offset the result by changes in the other variables. For example, reduced time may be offset by higher concentration of chemicals, more aggressive agitation, or higher temperature. Thus there are a number of combinations of variables that result in effective cleaning.
Three of the four variables are accomplished through the equipment design, set up, and application.
Time - duration of the cleaning cycle
Increasing time generally favors cleaning. Excessive time may cause etching, erosion, or chemical attack. Minimizing time is generally desirable to increase production throughput.
Temperature - process temperature
Increasing temperature generally favors cleaning due to increased chemical reaction rates and increase melting/softening of soils. Excessive temperatures may exceed the chemical formulation
limit which can split the cleaner, damage parts such as plastics, cause flash drying or perhaps staining, increase evaporation rate, and use excessive heating energy.
The temperature at the part surface is more critical than bulk solution temperature; however it is more difficult to measure. In bulk processing of small parts with little solution movement, solution temperature at the surface may be very low resulting in diminishing cleaning ability. Higher velocities at the surface decrease boundary layer thickness and increase heat transfer rate to the parts and maintain the solution temperature at the surface (turbulence and agitation).
Chemical Action - concentration
The chemical action of dissolution, saponification, emulsification, removal, etc. removes soils from the part and prevents redeposition. Higher concentrations generally favor cleaning.
Higher concentrations may increase water requirements or cause chemical attacks on parts. The concentration of the soils must also be given consideration. Increasing concentrations of soils
tend to .tie up. the cleaner and reduce effectiveness or cause redeposition on parts.
Consideration of not only the cleaner and soil bulk concentration, but also the concentration of the cleaner directly in contact with the part surface. Stagnant solutions at the surface may change concentration and become saturated with soils, thus reducing effectiveness. High velocities at the surface decrease boundary layer thickness and improve mixing to keep surface conditions closer to bulk conditions (turbulence and agitation).
Mechanical Agitation - turbulence, impingement, physical scrub, etc.
Mechanical agitation may take a number of forms as described below. Increased mechanical agitation generally favors cleaning. Too much agitation may physically damage parts, causing the
cleaner to foam, or cause excessive power consumption.
Turbulence - liquid turbulence is beneficial for several reasons:
- physically assist in removing soils
- reduce boundary layer thickness to improve temperature and concentrations at the part surface
- maintain a homogeneous solution