At the end of this module, you will be able to:
- Identify typical guidelines for working around the forming section of a paper or board machine
- Describe the purpose of a forming fabric
- Explain how fabric tension specifications are determined
- List some problems associated with improper wire tension
- Identify the purpose of fabric guiding system components, including the guide palm, autoguide and manual guide
- Explain the basic principle of fabric guiding
The following key questions are answered in this module:
In addition to furnish retention and dewatering capacity, what else is required of a forming fabric?
The forming fabric must be able to withstand the wear caused by stationary elements and vacuum devices on the former.
Relatively high fabric tension is desirable because it improves drainage and reduces slippage on driven rolls. However, what happens if the tension is too high?
Excessive fabric tension can reduce drainage capacity by narrowing the openings in the fabric, damage the wire seam, or cause roll deflections and warping, which can lead to ridges in the fabric.
What is the problem with low fabric tension?
Very low fabric tension can cause slippage at the driven forming section rolls, and wire flexing at the gravity foils and vacuum boxes. This can lead to wire abrasion, and guiding and speed control issues.
What is the purpose of seam straightening?
A skewed seam or colored stripe on the forming fabric indicates a misalignment in the forming section. Straightening the seam evens out the fabric tension, which evens out the dewatering capacity of the fabric across the machine.
What is the basic principle of fabric guiding?
The fabric will move or ""steer"" toward the end of the roll that it contacts first.
Below is a transcript of the video sample provided for this module:
The tensioning system is responsible for keeping the forming fabric tension constant on the Fourdrinier. Fabric tension is important because it impacts fabric wear, dewatering, and sheet formation. If fabric tension is not monitored and kept close to its recommended setting, there are undesirable consequences. Relatively high tension is desirable because it improves drainage. However, excessive wire tension actually reduces the size of the openings in the wire mesh and restricts water drainage. Poor drainage during sheet formation can lead to holes and other defects in the sheet.
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