Multilayer Headbox Auxiliary Material Metering
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Solution Overview
Problem
Existing multilayer headbox devices produce fibrous webs with low and uneven paper strength, particularly splitting strength, and poor layer covering quality due to inadequate mixing of auxiliary materials with white water, leading to inhomogeneous strength distribution and visual defects.
Innovation Solution
A multilayer headbox with an inner turbulence generator and adjacent turbulence generators, featuring a nozzle with converging walls and separating lamellae, and an auxiliary material metering device that controls the mixing quality between white water and auxiliary substances, ensuring uniform distribution and adjustment of the fibrous web's cross-sectional profile through local dilution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If auxiliary material is dosed upstream of the screen water pump, then the dosing process is simple, but the mixing quality between auxiliary material and screen water is insufficient leading to inhomogeneous strength distribution
Solution Approach 1:
The patent applies preliminary action by pre-mixing the auxiliary material with a small amount of screen water in a separate mixing zone before the main pump, ensuring proper dispersion. This preliminary mixing prevents clumping and ensures uniform distribution when the mixture is introduced to the main screen water flow downstream.
Solution Approach 2:
The patent introduces an intermediary mixing chamber or zone between the dosing point and the main screen water flow. This intermediary space allows the auxiliary material to be properly mixed with a portion of screen water before joining the main flow, acting as a buffer that ensures homogeneous mixing without requiring complex downstream mixing mechanisms.
2Speed
If high shear forces are applied in the screen water pump to mix auxiliary material, then mixing speed is improved, but the effectiveness of auxiliary material is reduced especially for long-chain polymers
Solution Approach 1:
The patent segments the mixing process into multiple zones: a low-shear pre-mixing zone where auxiliary material is gently incorporated with screen water, and a subsequent high-shear zone further downstream where the pre-mixed suspension is thoroughly blended. This segmentation allows gentle initial mixing that preserves polymer integrity while achieving eventual homogeneity.
Solution Approach 2:
The patent employs dynamic mixing elements that can adjust their intensity or configuration based on flow conditions. The mixing mechanism transitions from low-intensity gentle mixing at the dosing point to progressively higher intensity mixing downstream, adapting to the flow dynamics to achieve thorough mixing without subjecting the auxiliary material to excessive shear forces at any single location.
3Productivity
If screen water pump operates at high flow rates to increase productivity, then production speed is improved, but the mixing quality between screen water and auxiliary material deteriorates
Solution Approach 1:
The patent addresses the mixing issue by transitioning from a single-line sequential mixing approach to a multi-dimensional mixing architecture. Multiple dosing points are distributed across different locations in the screen water flow, and multiple mixing zones are arranged in parallel or series configurations. This dimensional expansion of the mixing system ensures thorough mixing even at high flow rates by providing multiple simultaneous mixing pathways.
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
The solution enhances the uniformity and strength of the fibrous web by optimizing the mixing of auxiliary materials with white water, reducing the formation of strands, and improving the cohesion and coverage of layers, resulting in a more homogeneous and visually appealing product.
Implementation Method 1
an inner turbulence generator extending across the width of the multi-layer headbox and at least two turbulence generators directly adjacent to the inner turbulence generator, each extending across the width of the multi-layer headbox, for forming at least three suspension layers
Implementation Method 2
a nozzle adjoining the turbulence generators, having an upper nozzle wall and a lower nozzle wall, wherein the nozzle walls are arranged convergently to each other and form an exit gap for forming a suspension jet
Data Source
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AI summary
The invention relates to a device (1) for producing a fibrous web made of a plurality of layers. The device comprises a multi-layer headbox (2) with an inner turbulence generator (7.8) extending over the width of the multi-layer headbox (2) and at least two turbulence generators (7.10, 7.11) each directly adjacent to the inner turbulence generator (7.8) and each extending over the width of the multi-layer headbox (2) to form at least three suspension layers. The feed system for the inner turbulence generator (7.8) comprises a white water vat (8) that is connected to at least one white water pump (8.1), to a white water separator (8.2) and to a cross-distributor (8.6) via a white water line (8.31). The device (1) according to the invention is characterised in that an auxiliary material metering device (9.2) is provided downstream of the at least one white water pump (8.1) and preferably downstream of the white water separator (8.2) to generate a metering volumetric flow for metering an auxiliary material to the white water line (8.31), and that the auxiliary material metering device (9.2) is designed such that the metering volumetric flow can be controlled by means of an open-loop and/or closed-loop control in order to set the mixing quality between the white water and metering volumetric flow.