Free-Jet Nozzle Coating to Overcome Boundary Layer Air
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Solution Overview
Problem
Existing methods for applying treatment substances like starch to paper or paperboard webs at high speeds are limited by the negative influence of boundary layer air, leading to uneven distribution and potential nozzle blockages, especially when using high solids content starch.
Innovation Solution
A method and apparatus that utilize a gravitationally induced jet curvature with a free jet nozzle positioned above the roll, enhancing the jet impulse to effectively remove boundary layer air, allowing for higher solids content and faster application speeds by aligning the nozzle to create a parabolic jet that directs the impulse force in the moving direction of the roll.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a free jet applicator is used to apply treatment substance to a moving substrate at high speeds, then productivity is improved, but the boundary layer air creates negative influence leading to uneven distribution and potential nozzle blockages
Solution Approach 1:
The boundary layer air is removed in advance from the impingement zone using a suction device positioned upstream of the nozzle, creating a favorable flow condition before the treatment substance is applied. This preliminary action prevents air interference during the coating process, enabling high-speed application while maintaining coating uniformity and preventing nozzle blockages.
2Quantity of substance
If high solids content starch is used to compensate for strength loss in recovered paper, then the treatment substance quantity is improved, but starch particles adhere to nozzles causing streaking and blockages
Solution Approach 1:
The suction device removes boundary layer air from the impingement zone before the starch suspension is applied, creating a controlled flow environment that prevents air-starch interaction and nozzle blockages. This allows high solids content starch (up to 35%) to be applied without adhering to nozzle surfaces, eliminating streaking and maintaining continuous operation.
Solution Approach 2:
The suction device acts as an intermediary that controls the flow conditions between the starch suspension and the substrate. By creating a low-pressure zone that draws away boundary layer air, it mediates the interaction between the high solids content starch and the coating surface, preventing adhesion and blockages while maintaining coating quality.
3Device complexity
If the nozzle is positioned close to the roll surface for direct application, then the device complexity is reduced, but the jet impulse is insufficient to remove boundary layer air at high speeds
Solution Approach 1:
The suction device serves as an intermediary that enables the nozzle to be positioned closer to the roll surface by actively removing the boundary layer air. This creates a favorable flow condition that compensates for the reduced jet impulse distance, allowing high-speed application while maintaining coating quality and preventing air interference.
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 reduces the impact of boundary layer air, ensuring stable and uniform application of treatment substances at speeds up to 2000 m/min with higher solids content, preventing splashing and blockages, and maintaining coating quality.
Implementation Method 1
a free jet applicator with a free jet nozzle (1.1, 1.2) with an outlet gap (B) for applying the treatment medium in the form of a machine-width, film-like jet (2.1, 2.2) to a moving substrate
Implementation Method 2
enhancing the jet impulse to effectively remove boundary layer air, allowing for higher solids content and faster application speeds by aligning the nozzle to create a parabolic jet that directs the impulse force in the moving direction of the roll
Implementation Method 3
The intensity of the jet impulse at the impingement line (A) is increased by a gravitational acceleration of the jet (2.2)
Data Source
AI summary
Method and apparatus for applying a treatment substance to a running paper or board web comprising an applicator with at least one free-jet nozzle having an outlet gap for applying the treatment substance, being a machine-width, film-like jet, to a moving substrate, in particular at least one applicator roll which transfers the treatment substance to the paper or board web in a treatment nip defined by the at least one applicator roll with a counter element, wherein the free-jet nozzle is positioned at an angle to the moving substrate in such a way that an angle φ to the perpendicular of an impingement line of the coating on the moving substrate is between 5° and 85°, and the intensity of the jet impulse at the impingement line is increased by a gravitational acceleration of the jet caused by an adjustable effective height H from the outlet gap of the free-jet nozzle, and a jet curvature along a path length is modulated via the angle φ.