Wall Ironing Polymer Coated Can Bodies
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Solution Overview
Problem
The production of can bodies from steel sheets with polymer coatings faces issues such as excessive shear forces leading to scuffing, roughening, and potential rupture of the polymer layer during wall ironing, resulting in an unacceptable finish and risk of can body damage.
Innovation Solution
A process involving specific selection of sheet metals and wall-ironing angles, where the entry angle for the first ring is between 3.5 and 4.5° and the exit angle between 2.5 and 3.5°, using sheet metals like uncoated steel, tin coated steel, or chromium-chromium oxide coated steel, with a three-layer polymer coating system, and internal cooling, to minimize shear forces and prevent scuffing, allowing for a smooth, intact coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wall ironing is performed with conventional entry angles and external cooling, then the can body can be formed, but the polymer layer experiences excessive shear forces leading to scuffing and roughening
Solution Approach 1:
The patent applies parameter changes by optimizing the entry angle (α) to between 3.5° and 4.5° and exit angle (β) to between 2.5° and 3.5° for the first wall-ironing ring, and reducing angles for subsequent rings. These parameter modifications reduce shear forces on the polymer layer, preventing scuffing and roughening while maintaining effective wall ironing.
Solution Approach 2:
The patent replaces external mechanical cooling systems with internal cooling channels integrated into the wall-ironing rings. This substitution eliminates the need for external coolant application equipment while providing effective thermal management during the wall ironing process, reducing polymer temperature and preventing degradation.
2Temperature
If external cooling is used during wall ironing, then polymer temperature can be controlled, but operational complexity and waste increase
Solution Approach 1:
The patent merges the cooling function directly into the wall-ironing rings by integrating internal cooling channels within the ring structure. This combination eliminates the need for separate external cooling systems, reducing operational complexity while maintaining effective temperature control of the polymer layer during wall ironing.
Solution Approach 2:
The wall-ironing rings provide self-cooling through their internal channels that circulate coolant internally. This self-service cooling mechanism eliminates the need for external coolant application equipment and complex external cooling systems, simplifying the overall process while maintaining polymer temperature control.
3Shape
If high shear forces are applied during wall ironing, then the can body wall can be thin-walled, but the polymer coating ruptures
Solution Approach 1:
The patent applies parameter changes by optimizing wall-ironing ring geometry parameters including entry angle (3.5°-4.5°), exit angle (2.5°-3.5°), and land zone length (≤0.6mm). These parameter modifications distribute shear forces more uniformly, enabling the production of thin-walled can bodies while maintaining polymer coating integrity and preventing rupture.
Solution Approach 2:
The patent uses multiple wall-ironing rings with progressively smaller reduction ratios and angles. This segmentation of the wall ironing process into multiple stages with decreasing intensity allows gradual thinning of the can body wall while preventing concentrated shear forces that would cause polymer coating rupture.
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 process effectively reduces scuffing and roughening of the polymer layer, maintaining an intact coating and achieving a smooth can body finish without external coolant, reducing waste and operational complexity.
Implementation Method 1
During wall ironing the shear forces can become excessively high in the coating itself. This excessive shear results in an increase of roughness of the polymer layer.
Implementation Method 2
chromium-chromium oxide coated steel sheet produced by electroplating from a trivalent chromium electrolyte (TCCT)
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a process for the production of a can body comprising a base and a tubular body from sheet metal which is coated on at least one side with a polymer layer, in which process, firstly, a round disc is produced from the sheet metal, which disc is then deep-drawn into a cup which has a polymer layer at least on the outside, after which this cup is formed into a can body by wall ironing, the wall ironing taking place in a single stroke by moving the cup successively through a redraw die and one or more wall-ironing rings.