Free-Jet Starch Coating Against Air Boundary Layer Instability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing free-jet coating systems are limited by the air boundary layer at higher production speeds, leading to instability and uneven distribution of starch on paper or cardboard webs, which restricts production speeds and solids content, especially in the production of packaging papers like testliner and corrugated medium.
Innovation Solution
A method and device that positions the nozzle above the roller, utilizing gravity-induced momentum and a parabolic jet shape to enhance the jet's momentum, positioning an air barrier scraper to combat the air boundary layer, and adjusting the jet's angle and height to ensure effective application at higher speeds and solids contents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the production speed is increased, then productivity is improved, but the air boundary layer becomes more significant causing jet instability and uneven starch distribution
Solution Approach 1:
The air barrier scraper is positioned upstream of the impact zone to preemptively remove the air boundary layer before the starch jet reaches the roller surface. This preliminary action prevents the air boundary layer from interfering with jet stability during high-speed operation, allowing consistent coating even at elevated production speeds.
Solution Approach 2:
The harmful air boundary layer is extracted or removed from the coating zone using the air barrier scraper. By taking out this interfering element before it can affect the starch jet, the system maintains jet stability and coating uniformity despite increased production speeds.
2Manufacturing precision
If the solids content of starch is increased, then coating quality is improved, but starch particles adhere to nozzles causing streaking and blockages
Solution Approach 1:
The air barrier scraper removes the air boundary layer before the starch jet impacts the roller, preventing premature adhesion and splashing. This preliminary action ensures that even high-solids-content starch is applied uniformly without causing nozzle blockages or streaking, maintaining both coating quality and nozzle reliability.
3Manufacturing precision
If the jet impact velocity is increased, then coating coverage is improved, but the curtain rebounds and tearing occurs
Solution Approach 1:
The air barrier scraper removes the air boundary layer that would otherwise cause curtain rebound and tearing. By extracting this interfering element, the system can use higher jet impact velocities for better coverage without experiencing the harmful rebound effect, thus maintaining curtain stability.
Solution Approach 2:
The air barrier scraper applies preliminary counter-action by removing the air boundary layer before it can cause curtain rebound. This preventive measure allows the starch curtain to impact the roller effectively without rebounding or tearing, even at high velocities.
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 method and device enable stable coating at higher speeds and increased solids content, preventing splashing and ensuring uniform distribution of starch, thus overcoming the limitations of traditional free-jet coating systems.
Implementation Method 1
the intensity of the jet pulse at the impact line is increased by a gravity-induced acceleration of the jet
Implementation Method 2
the air boundary layer that can reach the application unit and negatively affect the application result
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Method and apparatus for applying at least one liquid or pasty coating medium to a moving substrate by means of a free-jet coating unit, wherein the substrate is, in the case of direct application, the surface of a paper, cardboard or other fibrous web and, in the case of indirect application, the surface of a transfer element, in particular an application roller (4, 5), which transfers the coating medium to the surface of the fibrous web (9), in particular in a treatment nip (N), and the free-jet coating unit has at least one free-jet nozzle (1.1, 1.2) having a discharge gap (B) for releasing a medium jet (2.1, 2.2), which applies the medium jet (2.1, 2.2) in a film-like manner to the surface of the substrate and achieves a desired width of a coating layer there in an impact position (12), wherein a device for adjusting the intensity of the jet pulse of the medium jet (2.1, 2.2) is provided.2) is arranged in the impact position (12), wherein the device is designed as a positioning system for position and angular displacements (11, 13, 18) of the free jet nozzle (1.1, 1.2) relative to the ground, wherein a reference direction for describing the instantaneous position and angular position of the free jet nozzle (1.1, 1.2) relative to the impact position (12) is given by the gravitational field.