There are four basic variables that, combined, establish the success or failure of any industrial cleaning process. The variables are Time, Temperature, Chemistry and Agitation. Although there may be additional variables – things like fixture design and variations in the process prior to cleaning – which can have major impact and, in fact, make or break the overall process, these four are the biggies when it comes right down cleaning stuff. They are “knobs” that the process technician responsible for the process has available to tweak.
Time is important because it determines how long any process step has to do its job. Chemical processes, dissolution, and temperature stabilization are among the things that are affected by time. In general, longer times will produce better results but this is not an absolute. There are cases when excess time may actually be detrimental to the process and may even cause part damage.
Temperature is the most important variable in a majority of cleaning processes. Amazingly, a temperature variation of as little as a few degrees Fahrenheit may be the difference between success and failure. This is because temperature has a cascading effect and may change the characteristics of the contaminant, the activity of the chemistry and have any number of other effects which may not be intuitively expected. Temperature is also a major factor in the effectiveness of ultrasonic activity.
Chemistry selection and concentration are both process variables. In cases where the chemistry is mandated, of course, concentration is left as the only chemical variable.
Agitation is the impetus that gets everything together. Be it spraying, physical agitation, turbulation, ultrasonics or whatever, agitation or mechanical motion of some sort is mandatory for success as we’ve discussed before.
The success of the process requires a careful balance of the above variables which have effects that often interact. For example, a shortcoming in temperature may be overcome by increasing time, chemical concentration or agitation. Weak chemistry may be overcome by increasing time, temperature or agitation. The required process time might be reduced by increasing temperature, chemical concentration or agitation. The lack of agitation is a little more difficult to overcome by boosting any of the other three. If that part of the system is not functioning, the process is probably down.
On the other side of the coin, it must be noted that there is usually a limit to the ability to compensate using one variable vs. another. Temperature, for example, has certain limits that are not process related. Increasing temperature beyond that recommended by the manufacturer may cause chemistry to break down and become ineffective. Cases where emulsifiers separate and float to the surface at elevated temperatures are one good example of this. There are other cases where elevated temperature may damage the part being cleaned rendering it scrap. In ultrasonic processes, increasing time excessively may result in damage to the part through the effect of cavitation erosion or “burning.” This is especially true on soft metals including aluminum and brass.
Although the process technician should be aware if he interaction of the variables of the process he should also be cognizant of the fact that certain limits do exist and assure that they are obeyed. In future blogs I will discuss some of these interactions and limits in greater detail and include some practical examples.