 | | Charles Osborn
Manager, Precision Cleaning Division
PTI Industries Inc.
Enfield, CT
 |
Many companies dismiss part cleaning as an insignificant part of their manufacturing process until they experience field failures, and face a barrage of customer complaints. Many learn all too late that their highly engineered, closely toleranced device is rendered inoperable by a tiny particle. Suddenly they face a steep learning curve.
The first factor to evaluate is manpower. To many, precision cleaning and verification is a relatively new and mysterious subject. People experienced in the field are scarce. If your customer has imposed a cleanliness specification, you at least have someplace to start. It's now a matter of compliance. If not, you will need someone who is experienced in selecting an appropriate cleaning process, and verifying that it's capable.
Among the biggest questions will be: "just how clean do your parts need to be?" If you don't have the expertise, find a job shop specializing in this field. A method I've used over the years with good success is to send parts for evaluation. They can be quantitatively tested, and the existing level of cleanliness (or lack thereof) determined.
Based on the material and the geometry of the part, a cleaning process can be recommended and an experimental run made. The part is then tested to quantify the cleanliness level achieved by the selected process. You then test the functionality of the part in your application. If performance is satisfactory, the level of cleanliness and cleaning technique become the benchmark.
The next factors to be considered are equipment and process, both of which will ultimately be determined by the amount and type of contamination coupled with the material and complexity of the part. But before you go too far, determine the nature of the contaminant to see if it can be eliminated from the manufacturing process. Again, if you do not have this capability in-house, there are labs that can perform this evaluation. Even if you can reduce the contaminant, precision cleaning may still be necessary.
Vapor degreasing, pressure washing, ultrasonics, CO2 snow, and even mechanical blasting followed by a filtered rinse are common ways to achieve a high level of cleanliness. Chemistry is as important as equipment. There are many manufacturers who will tell you that their product is the best for your application. How do you choose? Work with a company that is service-oriented and willing to demonstrate the effectiveness of their products. Most have labs to do this type of development work, and of course job shops by their very nature have a wide variety of chemistries on hand.
Don't underestimate the importance of the remaining processes. Rinsing, drying, preserving, and packaging all present their own nuances. If you need spot-free parts, you will need to install a deionized water system. Drying can be the most time-consuming part of the whole operation. Options range from blowing down with shop air to vacuum bake-out ovens.
What comes next is fast becoming the most prominent factor in parts cleaning: quantitative verification of the cleaning process. There are two commonly accepted methods of obtaining cleanliness samples. One entails spraying the test part with sub-micron filtered solvent, collecting the effluent, and running it through a vacuum filter funnel to deposit any debris onto a pre-weighed or gridded filter. The second method is to sonicate the parts in solvent, remove the parts from the bath and rinse them with additional solvent, then collect and filter the effluent as in method one.
Environmental issues are important. Questions to ask include: What will you be removing from the parts, and what are you using to do it? Do you need local, state, or federal permits to store, use, and dispose of your chemistry? What about the effect of the chemistry on your employees? Investigate this area fully before committing too much time or money to equipment. |
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