- June 01, 2010, By Timothy J. Walker Contributing Editor
Does every web process need an automatic web guide? Maybe two? If I was in sales for a web guide supplier, I would say, “Of course!” and “How about three?”
Yet, even though I am not in web guide sales, my answer isn't much different. Almost every web line will benefit from at least one web guide.
In my days as a corporate web handling engineer, one of the ways I found out about all the web processes that were under development in my company was to talk to the web guide sales reps. Why this worked was somewhat unique, but it might be true at your company. First, unlike other products, most of our web guides were purchased from only one of two suppliers. Second, almost all new equipment purchases had to go through our central engineering group. So to find out what new web processes were going into my company, all I had to do was ask the web guide sales reps to whom they were talking when they visited, and I had the inside scoop on almost all of the company's new web process plans.
But not all. There are a few web processes that sneak by without automatic web guides. Some may truly need web guides but will start their lives without one (and likely get one later when they misbehave and have too much waste).
But who doesn't need an automatic web guide? It is a short list.
- Slit To Position
What is the world's best web guide? Slitting. You will never know the absolute position of a web edge better than you do immediately after a slitting knife. You don't need an automatic web guide if your input product is sufficiently wider than your final product.
If your input rolls have lateral alignment better than your target width plus a minimum trim width (both sides), you can eyeball the input roll position and trim to the final position. I recommend keeping things short and sweet after the final width and positioning trim.
The shorter the process and more attentive your operators, the more likely this will work for you. However, as you look to improve yields by reducing trim widths, you will find this guideless approach is harder and harder to do without losing your trims, and you likely will install an automatic web guide.
- Hard To Guide
If your product or process makes web guiding impossible or difficult to guide, then by default, you may not be able to guide your web even if you want to. When is guiding difficult?
If your web is stiff — a combination of thick, wide, high modulus, and short spans — it will be tough to bend or twist. (See last month's column on the force to bend a web.) Besides not having the frictional force to move your web, guiding may damage, wrinkle, yield, or break it.
Though this may mean no web guide for you, it doesn't take you off the automatic guide sales reps' radar. You may be a candidate for chase guiding in which you move your process to follow the web instead of moving the web to your process. (This may sound like holding the light bulb and turning the room, but it makes sense if your light bulb is gigantic and the room is easy to spin.)
- Easy To Guide/Too Many To Guide
If you have 100 webs, then the price of 100 automatic web guides is cost-prohibitive. Luckily, when you have 100 webs, they usually are also easy to guide.
The opposite of the hard-to-guide web — a web that is narrow, flexible, and has long spans — may be guided with the passive guiding methods of crowned roller, taper and flanged roller, or guided through dual flanges, combs, or other physical restraints. The easy, but too-many-to-guide processes include post-slitting processes (such as level winding many rolls) and processes with multiple narrow input rolls, such as paper core winding.
I don't expect this column will put any automatic web guide sales reps out of business. The automatic web guide is an important tool in many web processes, but it is nice to know when you do or don't need one.
Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 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.