Multi-layer Headbox Water Layer for Fiber Web Bulk and Strength
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Solution Overview
Problem
Existing fiber web machines struggle to enhance the internal strength of multiply products, particularly for Folding Boxboard, as prior art solutions often compromise bulk strength for internal bond strength, requiring excessive refining and bleaching.
Innovation Solution
A fiber web machine with multiple forming sections and a multi-layer headbox that uses starch in the water layer to optimize middle layer properties, allowing coarser fibers and varying refining rates, and bleaching levels between layers, while sandwiching the multi-layer web between top and back plies to maximize bulk and internal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the middle layer stock is refined to high freeness level (400-450 ml) to improve internal bond strength, then internal bond strength is improved, but refining energy consumption increases and bulk decreases
Solution Approach 1:
A water layer is introduced as an intermediary between the top and bottom pulp layers in the multi-layer headbox. This water layer acts as a bonding medium that eliminates the need for excessive refining of the middle layer stock, thereby reducing refining energy consumption while maintaining internal bond strength. The water layer penetrates the pulp structure and provides bonding without requiring high freeness levels.
Solution Approach 2:
The invention changes the freeness parameter of the middle layer stock from high (400-450 ml) to lower levels, combined with introducing a water layer with specific properties (thickness, flow rate) to compensate for the reduced refining. This parameter change reduces refining energy consumption while maintaining the required internal bond strength through the water layer's bonding effect.
2Stability of the object's composition
If the middle layer stock is bleached to reduce color difference with top ply, then color uniformity is improved, but production complexity and chemical consumption increase
Solution Approach 1:
The bleaching process is extracted or removed from the middle layer stock preparation. Instead of bleaching the middle layer to achieve color uniformity, the invention uses the water layer approach which naturally provides color uniformity without requiring chemical bleaching, thereby reducing production complexity and chemical consumption.
3Volume of stationary object
If coarser fibers are used in the middle layer to increase bulk, then bulk is improved by up to 30%, but internal bond strength decreases
Solution Approach 1:
The water layer serves as a bonding intermediary that compensates for the reduced bonding capability of coarser fibers. By introducing this water layer between the top and bottom pulp layers, the system achieves both high bulk (from coarser fibers) and maintained internal bond strength (from the water layer bonding mechanism).
Solution Approach 2:
The fiber size parameter in the middle layer is changed from fine to coarse, which increases bulk by up to 30%. The water layer parameters (thickness, flow rate, composition) are simultaneously optimized to provide the necessary bonding strength that would otherwise require fine fiber refinement, thus resolving the contradiction between bulk and internal bond strength.
4Manufacturing precision
If multiple separate headboxes are used for top ply, middle layer, and back ply, then web quality and properties are improved, but device complexity increases
Solution Approach 1:
The invention merges the headbox structures by implementing a multi-layer headbox that combines the functionality of separate headboxes for top ply, middle layer, and back ply into a single integrated unit. This multi-layer headbox ejects multiple liquid layers (pulp layers and water layer) in a coordinated manner, maintaining web quality while reducing device complexity.
Solution Approach 2:
The multi-layer headbox is designed with multi-functionality, serving as a universal device that performs the functions of multiple separate headboxes. It can eject different pulp layers with different properties and incorporate the water layer, thereby achieving the quality benefits of separate headboxes with a single multi-functional device, reducing overall system complexity.
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 significantly increases the bulk of the web by up to 30% while reducing refining energy and bleaching requirements, enhancing internal strength and reducing production costs by optimizing the middle layer's properties and using coarser fibers.
Implementation Method 1
A center diffuser of the multi-layer headbox is connected with feeding means for feeding fresh water, dilution water and/or white water
Implementation Method 2
liquid layers ejected on and conveyed by the wires are dewatered to form plies
Implementation Method 3
liquid layers ejected on and conveyed by the wires are dewatered to form plies
Implementation Method 4
The closed loops of the wire are guided such that liquid layers ejected on and conveyed by the wires are dewatered to form plies and then are merged
Data Source
Figure 1
Figure 2
Figure 3A~4
AI summary
A method of forming a multi-ply web in a fiber web machine, comprises the steps: - feeding of fresh water, dilution water, and/or white water into a central diffuser of a multi-layer headbox, - feeding pulp suspensions to respective adjacent diffusers of the central diffuser, - guiding the fresh water, dilution water, and/or white water and the different pulp suspensions through the diffuser to eject them onto a wire of a forming section, the wire forming a closed loop, - dewatering the liquid substances to form a web, - merging the web with a second web formed at a second head box ejecting pulp suspension on a wire of a second forming section, and merging the web with a third web formed at a third head box ejecting pulp suspension on a wire of a third forming section, wherein the third web is arranged on a side of the web opposite to that where the second web is arranged.