Fiber Web Calendering with Moisturizing Evaporative Cooling
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Solution Overview
Problem
Current fiber web calendering processes face challenges in achieving required surface properties and bulkiness simultaneously, leading to inefficiencies in raw material usage and production costs, particularly due to temperature-related compaction issues during the calendering of fiber webs.
Innovation Solution
The method involves partial cooling of the fiber web using a moisturizing evaporative cooling process, applying moisture and dry cool gas to evaporate and cool the web surface before calendering, maintaining the surface temperature near the wet-bulb temperature and effectively reducing the temperature difference to achieve deeper cooling without compromising material properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the fiber web is calendered at high temperature to improve surface smoothness, then the surface properties are improved, but the middle layers become overly compacted and lose bulkiness
Solution Approach 1:
The invention segments the fiber web into surface layers and middle layers, applying different temperature treatments to each. The surface layers are heated to calendering temperature (above Tg) to achieve smoothness, while the middle layers are cooled below Tg to maintain bulkiness and elasticity. This spatial segmentation of thermal treatment resolves the contradiction between surface quality and bulk preservation.
Solution Approach 2:
The invention applies local quality by creating a temperature gradient through the web thickness. The surface layers receive high temperature treatment for smoothness while the middle layers receive low temperature treatment for bulk maintenance. This localized differential temperature control allows each region to achieve its optimal property without compromising the other.
2Volume of moving object
If the fiber web is cooled to maintain bulkiness, then the middle layers retain elasticity and bulk, but the surface temperature is insufficient for effective calendering
Solution Approach 1:
The thermal treatment is segmented into surface heating and middle layer cooling operations. The surface layers are heated to calendering temperature while the middle layers are simultaneously cooled, creating distinct thermal zones that resolve the temperature contradiction between surface calendering requirements and bulk preservation requirements.
Solution Approach 2:
The invention changes the temperature parameter differentially through the web thickness. By applying positive temperature change to surfaces and negative temperature change to middle layers, the system achieves both high surface temperature for calendering and low middle layer temperature for bulk maintenance.
3Volume of moving object
If more raw material is used to increase bulkiness, then the bulk savings are improved, but the production cost increases
Solution Approach 1:
The invention changes the thermal parameters (temperature and moisture content) to control the physical state of fiber polymers. By heating surfaces above Tg for compaction and cooling middle layers below Tg for bulk maintenance, the process achieves high bulkiness with reduced raw material consumption, directly addressing the cost-bulk contradiction.
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 approach enhances smoothness and bulk savings by focusing the calendering effect on the surface, maintaining middle layers in an elastic state, thereby increasing bulkiness and reducing raw material usage while maintaining high production speeds and quality.
Implementation Method 1
partial cooling of the fiber web using a moisturizing evaporative cooling process, applying moisture and dry cool gas to evaporate and cool the web surface
Implementation Method 2
applying moisture and dry cool gas to evaporate and cool the web surface
Implementation Method 3
In calendering the web is passed into a nip, i.e. calendering nip, formed between rolls that are pressed against each other, in which nip the web becomes deformed as by the action of temperature, moisture and nip pressure
Implementation Method 4
The Tg-temperature is exceeded only at surface layers. The middle layers of the fiber web are cooled such that temperature in the middle layers remains under the Tg-temperature and the material properties of the middle layers of the fiber web remain at elastic values
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
The invention relates to a method for producing a fiber web (W), in which method the fiber web (W) is calendered in at least one calendering nip (NA) of a calender (20A). The fiber web (W) is cooled at least partially by moisturizing evaporating cooling by a moisturizing evaporating cooling unit (10) before the fiber web is calendered and that the moisture is absorbed during 10 - 500 ms. The invention also relates to a production line for producing fiber webs (W), which comprises at least a calender (20A) with at least one calendering nip (NA). The production line for fiber webs, in particular for board webs, comprises a fiber web machine (50), in particular a board machine, which comprises a head box, a wire section, a press section and a drying section, and at least one moisturizing evaporating cooling module (10), a hard nip calender (20A) with a thermo roll, which has surface temperature at least 120 °C, and a reel-up (40).