Dry Ice Blasting for Cathodic Coating Oxide Removal
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Solution Overview
Problem
Cathodic protective layers on hardened steel components face issues with paint adhesion and phosphating pretreatment due to the formation of thin, poorly adhering oxide layers, which are difficult to remove without damaging the underlying cathodic layer or affecting dimensional consistency.
Innovation Solution
A temporary protective layer composed of oxygen-affinity element oxides is created, with cracks and defects allowing for selective removal using dry ice blasting, which penetrates and sublimates within these cavities, removing loose particles without affecting the zinc or zinc-iron layer, thus enhancing paint adhesion and avoiding abrasive damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a temporary protective layer composed of oxygen-affinity element oxides is formed on the cathodic coating, then the cathodic layer is protected during hardening, but the protective layer complicates phosphating pretreatment and reduces paint adhesion
Solution Approach 1:
The patent removes the temporary protective layer composed of oxygen-affinity element oxides from the cathodic coating surface through dry ice blasting. This extraction eliminates the barrier that complicates phosphating pretreatment and poor paint adhesion, while the layer was previously retained only to protect the cathodic layer during hardening. The selective removal leaves the cathodic layer intact for subsequent treatments.
Solution Approach 2:
The temporary protective layer is formed in advance during the hardening process to protect the cathodic layer from oxidation and evaporation. However, the patent applies preliminary cracking of this layer through controlled heating before the final removal step, enabling subsequent easy removal without damaging the underlying cathodic coating.
2Ease of manufacture
If conventional abrasive blasting is used to remove the protective layer, then the layer can be removed, but the cathodic layer and dimensional consistency are damaged
Solution Approach 1:
The patent replaces conventional mechanical abrasive blasting with a thermal field-based removal process. Dry ice particles are used to create localized cooling and thermal shock that cracks the protective layer, followed by gentle removal methods that do not mechanically abrade the sensitive cathodic layer or alter dimensional consistency.
Solution Approach 2:
The patent utilizes the phase transition of dry ice from solid to gas to achieve layer removal. The dry ice particles sublimate upon contact with the protective layer, creating expansion forces that crack and loosen the oxide layer without mechanical abrasion. This phase change mechanism avoids the damaging mechanical action of traditional sandblasting.
3Ease of manufacture
If the protective layer is made very thin to improve paint adhesion, then paintability is improved, but the layer provides insufficient protection during hardening
Solution Approach 1:
The patent creates a dynamic system where the protective layer's thickness and integrity change over time. Initially, the layer is formed with sufficient thickness to provide protection during hardening. Through controlled heating, the layer develops cracks and becomes more susceptible to removal. Finally, the layer is completely removed to enable phosphating and painting. This dynamic evolution allows the layer to serve different functions at different stages.
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 enables effective removal of poorly adhering oxides, maintaining the integrity of the cathodic layer and ensuring good paintability, while avoiding the complexity and expense of secondary galvanizing processes.
Implementation Method 1
dry ice blasting, which penetrates and sublimates within these cavities
Implementation Method 2
sublimate, increasing in volume by up to 800 times
Implementation Method 3
The additional thermal shock due to the supercooled dry ice particles results in additional thermal stresses in the layer composed of the oxide of the oxygen-affinity element(s) and consequently promotes the removal of undesirable materials
Implementation Method 4
The flow of compressed gas used to project e.g. dry ice particles at the metal work piece to be cleaned should be preheated... The layers to be removed from the surface of the metal piece are removed by means of the mechanical action of the dry ice particles, which strike it at a high velocity and therefore have an abrasive action
Data Source
AI summary
The invention relates to a method for the production and removal of a temporary protective layer for a cathodic coating, particularly for the production of a hardened steel component with an easily paintable surface, wherein a steel sheet made of a hardenable steel alloy is subjected to a preoxidation, wherein said preoxidation forms a FeO layer with a thickness of 100 nm to 1,000 nm and subsequently a melt dip coating is conducted, wherein, during the melt dip coating, a zinc layer is applied having a thickness of 5 to 20 μm, preferably 7 to 14 μm, on each side, wherein the melt dip process and the aluminum content of the zinc bath is adjusted such that, during the melt dip coating, an aluminum content for the barrier layer results of 0.15 g/m2 to 0.8 g/m2 and the steel sheet or sheet components made therefrom is subsequently heated to a temperature above the austenitizing temperature and is then cooled at a speed greater than the critical hardening speed in order to cause hardening, wherein oxygen-affine elements are contained in the zinc bath for the melt dip coating in a concentration of 0.10 wt.-% to 15 wt.-% that, during the austenitizing on the surface of the cathodic protective layer, form a thin skin comprised of the oxide of the oxygen-affine elements and said oxide layer is blasted after hardening by irradiation of the sheet component with dry ice particles.