Wedgewire Screen Cylinder Coating to Minimize Overspray Wear
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Solution Overview
Problem
Existing screen cylinders for pulp screening face issues with wear-resistant coatings being applied inconsistently, leading to overspray and inadequate coating on desired areas, which affects performance and efficiency.
Innovation Solution
A screen cylinder design with optimized wedgewire bars and a controlled application process using high-velocity thermal spraying, where the bars' shape and spray nozzle angle variation ensure the coating is applied only on desired locations, minimizing overspray and maximizing thickness on wear-prone areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroplating process is used to apply chrome coating, then wear resistance is improved, but coating consistency deteriorates due to variability in current flow, temperature, and chemical strength
Solution Approach 1:
The patent replaces the electroplating process (electrical/chemical system) with a mechanical spray coating system. The spray system applies coating material mechanically through controlled atomization and deposition, eliminating dependence on electrical current flow, bath temperature, and chemical strength variations that plague electroplating. This substitution provides more consistent and controllable coating application.
Solution Approach 2:
The patent changes the fundamental parameters of the coating application process by transitioning from electrochemical deposition to mechanical spray deposition. This allows independent control of coating thickness, composition, and distribution through spray parameters (pressure, angle, distance, speed) rather than being constrained by electrochemical reaction parameters, thereby achieving better coating consistency.
2Productivity
If high-velocity spray coating is used, then coating speed is improved, but overspray increases causing coating to be applied to undesirable locations
Solution Approach 1:
The patent employs a movable spray nozzle system that dynamically adjusts its position, angle, and movement speed during the coating process. The nozzle can move along the screen cylinder surface and adjust its orientation in real-time, allowing the high-velocity spray to be precisely directed only at the intended coating areas (inflow surfaces and ridges) while avoiding adjacent slots and surfaces, thus maintaining high productivity without excessive overspray.
Solution Approach 2:
The patent applies coating with locally optimized spray parameters for different areas of the screen cylinder. The spray nozzle delivers coating material with varying intensity and direction tailored to each specific location - ensuring adequate coverage on inflow surfaces and ridges while preventing deposition in slots and on side surfaces. This localized control enables high-speed coating without harmful overspray.
3Reliability
If spray coating is applied to maximize thickness on inflow surface, then wear resistance is improved, but coating may extend into slots causing flow restrictions
Solution Approach 1:
The patent uses the ridge structure as an intermediary element that separates the coating application zone from the slot area. The ridge acts as a physical barrier and deposition target, allowing the spray coating to achieve maximum thickness on the inflow surface and ridge itself while the ridge geometry prevents coating material from extending into the slots. This intermediary structure resolves the conflict between achieving thick protective coating and maintaining unobstructed flow paths.
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 wear resistance and longevity of screen cylinders by ensuring consistent and targeted coating application, reducing wear and maintaining optimal hydrodynamic conditions for efficient pulp screening.
Implementation Method 1
high-velocity thermal spraying
Data Source
AI summary
A screen cylinder includes a cylindrical screening media having an inflow side and an outflow side. The screening media is formed of a plurality of circumferentially spaced an axially extending wedgewire bars, which have an inflow surface facing the inflow side. The axially extending wedgewire bars have a profile shape optimized to apply a spray on wear resistant coating on their inflow surface.