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Based on: Industry Standards and Best Practices

Languages: English

Sample Transcript

The forming section of a paper machine provides dewatering of the dilute stock stream that is delivered by a head box. The forming section or former, is made up of one or two endless fabric loops. Each fabric has its own set of support rolls, cleaning showers, tension system, and guidance system. The stock screen from the head box is either deposited onto a single fabric or injected between two fabrics, referred to as the inner fabric and the outer fabric. The purpose of the fabric or fabrics is to dewater and support the sheet as it forms and then carry the formed sheet to the next section of the paper machine. A properly designed, constructed, and maintained forming fabric will help the former produce a sheet that meets end product specifications at an acceptable production rate. This module will focus on the design and construction of paper machine forming fabrics and how the design variables influence overall sheet quality.

Forming Fabric Design

Training Time: 32 minutes

Paper machine forming fabrics are designed to retain as much fiber and other furnish components as possible while allowing water to drain through them as quickly as possible. These fabrics are typically produced from monofilament strands or yarns that are woven together in a pattern that can be classified by their fabric style (or weave); mesh, count, and diameter; surface topography; and air permeability. This module discusses how each of these characteristics affect final sheet quality.

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Increasing the yarn diameter reduces the open space between the yarns, which reduces the dewatering capacity of the fabric

Increasing the yarn diameter reduces the open space between the yarns, which reduces the dewatering capacity of the fabric

Significant fabric oscillation can lead to wrinkles at the fabric edges, which can cause poor sheet formation and even destroy the fabric

Significant fabric oscillation can lead to wrinkles at the fabric edges, which can cause poor sheet formation and even destroy the fabric

The air permeability test measures air flow through 20 cm2 of forming fabric using 125 Pa of pressure

The air permeability test measures air flow through 20 cm2 of forming fabric using 125 Pa of pressure

Learning Objectives

  • Identify machine direction and cross direction
  • Describe safety guidelines while working near forming fabrics
  • List the four factors that should be considered during forming fabric selection
  • Describe fabric styles (single, double, triple layer)
  • Describe mesh, count, and yarn diameter
  • Describe surface topology
  • Describe air permeability
  • State the importance of proper fabric guiding and tensioning
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Forming Fabric Design FAQs

What are the two main jobs of a forming fabric?
To retain as much fiber and other furnish components as possible, and to allow water to drain through as quickly as possible.

What are the most common fabric styles or weaves used in forming fabrics?
The most common fabric styles are single layer (one MD and one CD strand), double layer (one MD and two CD strands), double layer with support shute (one MD and three CD strands), and triple layer (two MD and three CD strands).

What is the difference between "mesh" and "count"?
Mesh refers to the number of MD yarns per inch of fabric, while count refers to the number of CD yarns per inch of fabric.

Why can't air permeability (which measures air flow) be used alone to predict the drainage capacity of a fabric?
Because it does not take into account the impact of the fibers and furnish on drainage. Surface topography and fabric construction both affect furnish retention and so can also affect the dewatering capacity of the fabric.

How can you tell if a forming fabric is misaligned?
Most forming fabrics are manufactured with a colored stripe across their width. If this stripe is not straight, this means that the fabric is skewed or misaligned.

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