Polymer Coated Steel Substrate Eliminating Yield Point Elongation
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Solution Overview
Problem
Polymer-coated steel substrates for packaging applications often exhibit yield point elongation and Lüders' lines due to accelerated ageing at elevated temperatures, which are aesthetically unattractive and can lead to discontinuous yielding, making them unsuitable for finished products.
Innovation Solution
A process involving the electrodepositing of a tin layer on steel substrates, followed by diffusion-annealing to form an FeSn alloy layer and subsequent polymer coating, with a stretching operation through temper rolling or stretcher-levelling to eliminate yield point elongation and improve mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the substrate is heated to elevated temperatures during polymer coating, then the polymer coating process can be completed, but yield point elongation returns and Lüders' lines develop
Solution Approach 1:
The substrate undergoes temper rolling before the polymer coating process to eliminate yield point elongation. This preliminary action ensures that when the substrate is later heated during coating, the detrimental Lüders' lines do not form because the dislocation structure has already been modified by the prior plastic deformation and recovery process
Solution Approach 2:
The invention changes the mechanical parameters of the substrate through temper rolling (applying controlled plastic deformation followed by recovery) to alter the stress-strain behavior. This parameter change prevents the return of yield point elongation even when temperature increases during the subsequent coating process
2Reliability
If the substrate is temper rolled before coating, then yield point elongation is eliminated, but the coating process becomes more complex
Solution Approach 1:
The temper rolling operation is integrated into the existing coating line workflow, combining the mechanical treatment and coating processes in a unified production sequence. This merging allows the additional temper rolling step to be incorporated without requiring separate standalone equipment or disrupting the overall process flow
3Object-affected harmful factors
If a Cr—CrOx coating layer is applied, then corrosion protection is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The Cr—CrOx coating layer serves as an intermediary barrier between the steel substrate and the corrosive environment. This intermediate layer provides corrosion protection while being compatible with the existing polymer coating process, acting as a mediator that protects the substrate without requiring fundamental changes to the manufacturing system
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 process results in a polymer-coated steel substrate that is substantially free from yield point elongation, preventing Lüders' lines and enhancing bulk mechanical properties, while also providing corrosion protection and improved adhesion for organic coatings.
Implementation Method 1
annealing the tin-coated steel substrate at a temperature Ta of at least 513° C. for an annealing time ta to convert the tin layer into an iron-tin alloy layer
Implementation Method 2
electrodepositing a tin layer on one or both sides of the single-reduced or double-reduced steel substrate
Data Source
AI summary
This relates to a coated substrate for packaging applications and a method for producing the coated substrate.