Pressing Arrangement for Fibrous Web Dewatering
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Solution Overview
Problem
Existing press arrangements for dewatering fibrous webs face challenges in reliable web guidance and efficient dewatering, often resulting in felt markings, volume loss, and reduced rigidity, particularly during the transfer from a suction roll to a transfer belt.
Innovation Solution
The press arrangement decouples the suction roll and central roll, using a transfer press nip with a smoother, non-permeable transfer belt for safe web transfer, and incorporates steam heating to increase viscosity, along with extended press nips and a large central roll diameter to enhance dewatering efficiency, while guiding the fibrous web continuously between the former and drying unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a compact press arrangement with suction roller and transfer belt is used, then space and cost are reduced, but web transfer reliability deteriorates
Solution Approach 1:
A transfer belt acts as an intermediary element between the suction roller and the drying unit. This transfer belt is specifically designed with smooth, non-permeable surface properties that facilitate reliable web transfer while maintaining the compact press arrangement layout. The transfer belt mediates the transition of the fibrous web from the dewatering zone to the drying zone, solving the reliability issue without requiring additional space.
2Object-affected harmful factors
If felt marks are removed using a subsequent offset press, then surface quality is improved, but web volume and stiffness are reduced
Solution Approach 1:
The invention converts the potentially harmful effect of the suction roller surface into a beneficial one by using the same suction roller to both dewater the web and create a uniformly smooth surface. The smooth, non-permeable surface of the suction roller eliminates felt marks during the dewatering process itself, transforming what could be a source of surface defects into a surface-finishing mechanism. This eliminates the need for subsequent offset presses that would compromise web stiffness.
3Ease of operation
If dewatering belt remains in contact with fiber web after transfer press gap, then web guidance is simplified, but re-wetting of fiber web occurs
Solution Approach 1:
The dewatering belt is extracted from the web guidance path immediately after the transfer press gap. This separation ensures that the fibrous web does not come into contact with the porous dewatering belt surface that could cause re-wetting. The transfer belt, being smooth and non-permeable, takes over web guidance in this critical zone, maintaining both moisture control and operational simplicity through its dual function of transfer and guidance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration ensures efficient, reliable dewatering with improved web guidance, eliminating the need for subsequent offset presses and maintaining web rigidity, while optimizing dewatering performance and surface quality.
Implementation Method 1
dewatering can be further enhanced by increased viscosity resulting from heating the fiber web. For this purpose, the fiber web should be exposed to steam from a steam blower between the transfer press gap and the central roll
Implementation Method 2
a suction roller surrounded by an endlessly circulating, water-absorbing and air-permeable dewatering belt
Implementation Method 3
water-absorbing dewatering belt
Implementation Method 4
a cylindrical central roller following in the web direction, surrounded by a smooth, endlessly circulating transfer belt, which participates in the formation of at least one press gap with a press roller surrounded by an endlessly circulating, water-absorbing dewatering belt
Data Source
Figure 1
AI summary
The invention relates to a pressing arrangement for dewatering a paper, card, tissue or other fibrous web (1) in a machine for producing and/or finishing the same, with a suction roll (2) around which is looped an endlessly circulating, water-absorbing and air-permeable dewatering belt (4) and the fibrous web (1) located on the outside, and a cylindrical central roll (3) following this in the direction of web movement (5), around which is looped a smooth, endlessly circulating transfer belt (6), which roll participates with a pressing roll (17, 18), around which is looped an endlessly circulating water-absorbing dewatering belt (15, 16), in the formation of at least one pressing nip (13, 14), wherein the transfer belt (6) picks up the fibrous web (1) from the dewatering belt (4) on the suction roll (2). The arrangement intends to achieve volume-saving dewatering with as smooth a web surface as possible by the suction roll (2) forming with a transfer pressing roll (7) a transfer pressing nip (12) through which the dewatering belt (4) of the suction roll (2) and the transfer belt (6) pass together with the fibrous web (1) lying between them.