- February 01, 2008, By Timothy J. Walker Contributing Editor
A new year often brings new budgets and thoughts about new equipment. If you are lucky enough to be handed a project to buy new converting equipment, take some time not only to think about the “value adding” process involved (coating, printing, etc.) but also about the backbone of any converting line: the web handling process.
If you haven't figured out by now from reading my columns, I'm a process guy. More specifically, my career at 3M was mostly in the role of process development. So though I never had the lead role as new equipment project manager or equipment designer, I often was involved in providing the process specification for new equipment.
Also, in my role over the years as a process problem solver, I've seen many equipment designs that I don't like because they make a process more sensitive to web handling and winding defects. Here are some tips on what to consider when ordering new converting equipment for any web handling process.
Step 1 | Process Flow Diagram
What are the key process steps and their web handling needs? I think about web handling in the same order I cover the web handling process fundamentals in classes: web properties, tension control, rollers and traction, guiding, wrinkling/anti-wrinkling, winding and unwinding.
Step 2 | Tensioning
What are the mechanical properties of your webs? Think about the extreme cases of high tension (wide, thick, stiff) and low tension (narrow, thin, stretchy). A good starting point is to set tension at 10%-20% of the web yield or break point, whether in pounds per width or percent elongation.
Step 3 | Process Tensions
What special tension considerations are needed in your different process steps? Consider noisy tension at unwinding, smooth speed and high tension at coating, low tension in heating films, and taper tension for winding. Break down a tension control plan from the process needs, including number of zones, preferred tension feedback by zone, and drive roller traction preferences. (I like to avoid nipped drive rollers). Include the proposed tension control plan in the specification to allow an apples-to-apples comparison of supplier quotes.
Step 4 | Speeds
Include maximum speed and desired accel/decel rates as well as the need for emergency stopping. This will allow the control engineers to size the motors.
Step 5 | Rollers
Specify roller surface to meet your traction needs, especially at high-speed, large-diameter, low-tension conditions. Specify bearings, support, and alignment design. Specify roller straightness, deflection under load, diameter tolerance, and alignment needs.
Step 6 | Guiding
Specify a web guiding plan: Where do you need it; what accuracy; what type of guide is preferred; and what type of detector is preferred? Specify brands of web guides if you have one or two preferred suppliers and want to avoid having to learn four different systems and spares. Get rollers on the web guides that match the rest of your process.
Step 7 | Wrinkling
Specify any special locations that may need anti-wrinkle or spreading rollers and what kind are preferred.
Step 8 | Unwind/Wind
Specify core material and geometry; preferred core support (shafted vs. shaftless, core grabbing mechanism); splicing type and roll transfer needs; and preferred roll loading and handling plan. Include a performance spec on auto roll transfers and some winding quality features (such as edge alignment).
This isn't everything, but it's a start. Add to this list cleanliness, footprint, cost considerations, check-out plans, and start-up support, and you've got a good start. Feel free to send me your tips.
Web handling expert Tim Walker, president of TJWalker+Assoc., has 20+ years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; firstname.lastname@example.org; www.webhandling.com.