- October 08, 2013, Timothy J. Walker
A simple question with a not so simple answer. Let's start by narrowing down the culprits.
If the web moves off centerline, there are a limited number of reasons this happens.
1. Roller misalignment
2. Roller diameter variations
3. Web bagginess
4. Nip pressure variations
5. External forces
Mechanism #1, roller misalignment and the parallel entry rule (see in my next blog!) are extremely important concepts to understanding webs and web handling. The parallel entry rule describes what the ideal web will do between misaligned roller if there is sufficient traction to bend the web. Without sufficient traction, the web behavior on misaligned roller is less predictable.
Mechanisms #2 through #4 are all dependent on the parallel entry rule. Therefore, which way a diameter variation, baggy web, and uneven nip will shift a web is also a function of traction.
Mechanism #5 (or external forces) includes the sundry possible interactions of the web to elements of the outside world, whether solid, liquid, or gas, including interaction with people, equipment, attached parts, air flow, or coatings.
But what's this Parallel Entry Rule? Nothing but the most important rule in web handling, that's all! Tune in for more with my next blog post.