Paper Machine Headbox Valve Control for Homogeneous High-Viscosity Coating
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Solution Overview
Problem
Existing paper machine headboxes struggle to apply novel coating compositions with high viscosity at low shear, resulting in non-homogeneous layers in width and thickness due to mismatched speeds and angles of application.
Innovation Solution
A headbox design with a rotatable valve assembly comprising a rotatable valve body and valve case body, featuring sealing elements that adjust clearances to control the flow of coating composition, ensuring a homogeneous stream of coating composition onto a moving wet pulp substrate, suitable for high viscosity materials like microfibrillated cellulose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a traditional secondary headbox is used to apply coating composition, then the application process is simple, but the coating layer is non-homogeneous in width and thickness when the coating composition has high viscosity at low shear
Solution Approach 1:
The patent employs a rotatable valve body that can be rotated to different angular positions to dynamically adjust the clearance between the valve body and valve case body. This dynamic adjustment mechanism allows the headbox to adapt to different coating composition viscosities and flow rates, ensuring homogeneous coating application even with high viscosity materials like microfibrillated cellulose.
Solution Approach 2:
The invention changes the flow parameters of the coating composition by adjusting the rotational position of the valve body, which modifies the clearance size and consequently the flow rate and velocity profile of the coating material. This parameter adjustment enables precise control over the coating stream characteristics to achieve uniform coating layers.
2Manufacturing precision
If the speed of coating composition contact with moving wet pulp layer is not matched, then the application process is simple, but the coating layer becomes non-homogeneous
Solution Approach 1:
The rotatable valve body mechanism provides a means to adjust the coating composition flow speed in response to operational requirements. By rotating the valve body to different positions, the clearance is adjusted to match the speed of the moving wet pulp layer, ensuring homogeneous coating application without complex external control systems.
3Manufacturing precision
If the angle at which coating composition contacts moving wet pulp layer is not optimized, then the application process is simple, but the coating layer becomes non-homogeneous
Solution Approach 1:
The rotatable valve body can be rotated not only to adjust clearance but also to change the angular orientation at which the coating composition exits the headbox. This dynamic angle adjustment capability allows optimization of the contact angle between the coating stream and the moving wet pulp layer, ensuring homogeneous coating without requiring separate angle adjustment mechanisms.
4Manufacturing precision
If a headbox design is used that does not provide sufficient rigidity, then the manufacturing is simpler, but the coating layer becomes non-homogeneous due to bending propensity
Solution Approach 1:
The headbox is divided into functionally distinct segments: the stock chamber, stilling chamber, and slice chamber, connected by controlled clearances. This segmentation allows each section to be optimized for its specific function while maintaining overall structural rigidity, preventing bending that would compromise coating homogeneity.
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 design achieves a uniform coating layer with controlled thickness and width, enhancing rigidity and ensuring a stable jet of coating composition, particularly effective for microfibrillated cellulose, with improved adhesion and reduced shear stress.
Implementation Method 1
the first sealing element is at a first distance d1 from the first sealing surface on the valve case body forming a first clearance of size s1 and thereby fluidly connecting the stock chamber to the stilling chamber
Implementation Method 2
the first sealing element is in sealing contact with a first sealing surface on the valve case body, thereby forming a first seal which seals the stock chamber from the stilling chamber
Data Source
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AI summary
A headbox (1) for a paper machine, in particular a secondary headbox for applying a stream of a coating composition onto a moving wet pulp substrate in a paper machine, comprising a stock chamber (2), a stilling chamber (3), a slice chamber (4), a valve assembly for controlling the flow of coating composition from the stock chamber (2) into the stilling chamber (3) and for controlling the flow of coating composition from the stilling chamber (3) to the slice chamber (4), wherein the valve assembly comprises a rotatable valve body (5) and a valve case body (6), said rotatable valve body (5) being located within the valve case body (6), wherein said rotatable valve body (5) is rotatable into a closed state and into one or more opened states, wherein said rotatable valve body (5) comprises a first and second sealing element (7, 8) and said valve case body (6) comprises a first and second sealing surface (9, 10), wherein in an open state, the first sealing element (7) is at a first distance d1 from the first sealing surface (9) on the valve case body (6) forming a first clearance and thereby fluidly connecting the stock chamber (2) to the stilling chamber (3) and the second sealing element (8) is at a second distance d2 from the second sealing surface (10) on the valve case body (6) forming a second clearance and thereby fluidly connecting the stilling chamber (3) to the slice chamber (4), and wherein in an open state, the first clearance is larger than the second clearance.