At the end of this module, you will be able to:
- Identify the issues which led to the development of twin-wire formers
- Identify and describe the four basic types of twin-wire formers, including blade formers, roll formers, hybrid formers and roll/blade formers
- List advantages and disadvantages for each type of twin-wire former
- Describe the challenges presented by twin-wire formers
- Describe the advantages of twin-wire formers
The following key questions are answered in this module:
What are some benefits of twin-wire formers over Fourdrinier formers?
Twin-wire formers reduce sheet two-sidedness, wire instability, and the length of the forming section. Also, twin-wire formers double the drainage area and can run at higher speeds.
What are some potential problems presented by twin-wire formers?
Space limitations restrict the addition of more water-removal devices. Fibers can build up preferentially on the two fabric surfaces, which increases the likelihood of sheet delamination. Fabric selection is critical and there is a high potential for fabric and equipment damage because the fabrics operate in close proximity.
What is a roll former?
Roll formers are characterized by the stock jet being captured in a long nip created between two fabrics traveling together around a perforated suction forming roll.
What is a blade former?
Blade formers are characterized by a stock jet impinging into a gap between two forming fabrics which are fored together by a number of fixed blades in a vertical forming section.
What is a roll/blade former?
Roll/blade formers try to combine the advantages of roll and blade formers and avoid their problems. Two forming fabrics wrap around a perforated suction roll then there is a blade section to provide additional pulsed drainage.
Below is a transcript of the video sample provided for this module:
A twin-wire former captures the stock jet from the head box in a converging nip formed between two rolls, which are covered by two moving fabrics or wires. They are also sometimes referred to as gap formers. Twin-wire former designs have changed and evolved over the years and have developed somewhat differently for different paper and board grades. It is worth noting that the forming section of a paper or board machine, whether fourdrinier, twin-wire, or some other design has a major impact on the fundamental properties of the sheet and the runnability of the machine.
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