At the end of this module, you will be able to:
- Define "traction" and "tension"
- Describe the purpose of guiding and spreading devices in paper and board production processes
- List safety guidelines associated with web guiding and spreading devices
- List ways to improve traction between rolls and the sheet
- State the law of "normal entry"
- Explain how the web guiding and spreading equipment operates
- Explain how to adjust guiding and spreading equipment to address a given situation
The following key questions are answered in this module:
Which web or webs are guided and spread on a paper or board machine?
On paper and board machines, fabric loops require web guiding and spreading to keep them running correctly, and the sheet requires guiding and spreading at the dry end and winder to ensure the success of dry end and winder operations.
I've heard that guide rolls must be ""in traction"" with the sheet in order to properly guide the sheet. What does that mean?
"In traction" means that the sheet and guide roll surfaces are in contact and moving at approximately the same speed.
What is the ""law of normal entry"" for webs?
This law states that a web will seek entry to a roll at 90 degrees to the roll's axis at each point of contact. This is how a spreader roll's bow causes the web to be directed outward, toward the roll ends, when it is set up with its bow pointing downstream.
How should bowed spreader rolls be oriented?
Pointing the bow in the downstream direction utilizes the law of normal entry and spreads the web outward, but bowed rolls are sometimes rotated into or out of the web to compensate for a baggy center or slack edges.
Where are dual spreading devices used?
Dual spreading devices are sometimes used after slitters to separate the slits and then straighten their paths.
Below is a transcript of the video sample provided for this module:
Stationary spreader bars are also popular. These point into the web and have two operating principles. The first principle is minimization of strain or path length and the second is bending toward the low friction side of a slit web. One limitation of these devices is due to their stationary nature which can cause scratches or marks on the sheet surface and even cause sparks with abrasive sheets. The bent pipe spreader is popular due to its simple construction. However, because it is often crudely manufactured, its performance is often lacking. The D-bar spreader gets its name from its cross section. The main difference between the D-bar spreader and a bent pipe is that the bow curvature is adjustable using jacks.
Use the additional resources and links below to learn more about this topic: