- March 31, 2005, Timothy J. Walker TJWalker & Assoc. Inc.
W hat is your definition of clean? What people think of as "clean enough" in their homes is staggeringly different. Hopefully, your definition for your converting operation is the same as that of your customers.
Cleanliness could be defined by particle size and frequency per area, but more often it is defined by product performance. A debris particle leaves an unsatisfied customer when it becomes a visible dimple, a coating streak, or a laminate bubble.
Some converting processes inherently are dirty. Products with mineral components, such as abrasives or roofing shingles, are difficult to contain. Paper processes are next up where fibers from breaks, sheeting, abrasion, and slitting tend to float around and are difficult to keep ahead of. The more brittle your web is, like dry paper and minerals, the more likely it will fracture into difficult-to-contain fine particles.
The cleanest converting processes are food, pharmaceutical, medical, and electronic applications. Good manufacturing practices and FDA requirements force them into a cleaner plant environment. Most of these products help their odds by using films, foils, and coated papers.
How clean is your plant? Find out by using a witness plate. Set out a microscope slide near your converting processes. After a day or a week, put a cover slide on it and go to a microscope. What do you find? A skilled microscopist can help identify what’s falling on or near your web.
For a more dramatic test, hang a sheet of clear film over your converting process. As the days go by, watch to see if it remains clean or slowly grays and blocks out the light. All the stuff that collected on your film canopy would have otherwise fallen on your web and been shipped to your customer.
Thankfully, the witness plates are a magnifier of what your customer sees. Running at 100 fpm 24/7 for a week is 1 million lineal ft; therefore, if your product is exposed to the environment for 10 ft, it would be 100,000x cleaner than the witness plate. This may give you some comfort, but it won’t satisfy the customer that gets even a single dead fly.
For a more official environmental measurement, use an automated particle-in-air counter. These electronic sniffers vacuum up air samples in a tube, pass the sample across a laser detector, and count the number of particles larger than 0.5 micron in a cubic foot of air. Clean rooms are classified from these measurements, ranging from semiconductor-manufacturing clean at class 10–100 to computer-room clean at class 100,000.
Where does all the airborne debris come from? Everything is falling apart, it’s entropy. Paint flakes off, metals oxidize, clothing loses lint and fibers, shoes and wheels track dirt in, insects bug up things, nature blows in through open doors, and we humans like to shed, too. We shed like snakes but in much smaller pieces. There a giant clean room industry based on fighting off entropy. Converters rarely need to go as far as IC chip manufacturers, but there are helpful things to learn. Does clean air guarantee a clean web? No. Converting processes in clean rooms can be a good idea, but they also commit the worst clean room sin: creating debris in the clean room. Air filtering will do little to prevent slitting and scratching debris on your product.
For a more complete cleanliness picture, run a thin, clear film through your process and look for dimples in the wound roll. Inspect the wound roll. Does it have pimples? In thin films, a single particle can create dimple and pimple impressions through tens of layers. It doesn’t take a high level of particle per square yard to make a roll look ugly.
Start collection debris samples. Cut out a sample several layers deep around the big pimples. Peel away the layers until you find the pimple-causing "tent-pole" particle and identify what it is. Compare your dimple causes to your witness plate collection. You’ll see some overlap and some new creatures. The difference will be either non-airborne particles or bonus particles sent from your roll supplier (be sure to thank them).
Cleaning up your act starts by identifying particle sources. You can’t stop it until you know what it is. Practice thinking clean thoughts, and you’ll be ready to move forward and start thinking about clean actions.
Timothy J. Walker has 20+ years of experience in web handling processes. He specializes in web handling education, process development, and production problem solving. Contact him at 651/686-5400; email@example.com; tjwa.com.