Wall-flow filter coating uniformity via pre-wetting and pressure reversal
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Solution Overview
Problem
Existing wall-flow filters face issues with coating gradients and increased back pressure due to catalytically active materials, leading to uneven filtration efficiency and pressure loss, which are not adequately addressed by current coating techniques.
Innovation Solution
A method involving pre-wetting the wall-flow filter with a liquid, such as water, to reduce viscosity and prevent clogging, combined with a coating suspension applied under pressure with subsequent reversal to remove excess, ensuring a more uniform and homogeneous coating distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a coating suspension is applied to the wall-flow filter without pre-wetting, then the catalytic coating is deposited, but the coating becomes uneven with significant gradients and increased back pressure
Solution Approach 1:
The wall-flow filter is pre-wetted with water before applying the coating suspension. This preliminary action saturates the porous walls, preventing excessive absorption of the coating suspension and ensuring more uniform coating distribution along the flow channels, thereby reducing coating gradients and back pressure.
Solution Approach 2:
The patent changes the physical state of the porous walls by transforming them from a dry state to a saturated state through pre-wetting. This parameter change (moisture content) controls the absorption characteristics of the walls, leading to more uniform coating deposition and reduced back pressure.
2Manufacturing precision
If the coating suspension is applied from below using pressure difference, then the coating is deposited into the channels, but excess coating remains and creates clogging and uneven distribution
Solution Approach 1:
The patent employs periodic reversal of the pressure difference direction. First, pressure is applied from below to push the coating suspension into the channels. Then, the pressure direction is reversed to withdraw excess coating. This periodic action ensures thorough coating penetration while removing surplus material, preventing clogging and achieving uniform distribution.
Solution Approach 2:
The patent extracts the harmful excess coating suspension from the system by reversing the pressure difference. This removal action separates the useful coated filter from the harmful excess coating that would otherwise cause clogging and uneven distribution.
3Ease of manufacture
If the porous walls are left dry before coating, then the coating suspension can be applied freely, but the walls absorb too much coating creating gradients and increasing back pressure
Solution Approach 1:
The porous walls are pre-saturated with water before coating application. This preliminary action controls the absorption capacity of the walls, preventing them from taking up excessive coating suspension and ensuring more uniform coating distribution throughout the channels.
Solution Approach 2:
The moisture content parameter of the porous walls is changed from dry to saturated state. This parameter modification regulates the coating absorption behavior, leading to uniform coating distribution while maintaining ease of application.
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 results in a more uniform coating with reduced gradient and lower back pressure, enhancing filtration efficiency and catalytic performance while minimizing waste and maintaining coating suspension properties.
Implementation Method 1
The inner walls of the wall-flow filter are at least partially pre-moistened with a liquid, in particular with water, such that the open pores of the wall are filled with the liquid
Implementation Method 2
applying a coating suspension to the wall-flow filter
Data Source
AI summary
The present invention relates to a method for coating wall-flow filters. It also relates to correspondingly produced wall-flow filters and to their use in exhaust gas cleaning.