Multi-Wall Pipe Brazing with Cyanide-Free Nickel-Solder Coating
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Solution Overview
Problem
The existing methods for producing multi-walled pipes using electroplating for solder layer adhesion on steel strips are economically inefficient and require toxic cyanide, leading to poor adhesion and quality issues.
Innovation Solution
A cyanide-free electroplating process using nickel and solder layers applied in cells with constant electrolyte flow rates, specifically radial cells or gravitel cells, with high current densities and balanced electrolyte mixtures to ensure strong adhesion and quality, replacing cyanide with nickel as an adhesion promoter and using copper-rich solder layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroplating with cyanide is used to coat steel strip with solder layer, then adhesion of solder layer is improved, but harmful factors (toxicity) increase
Solution Approach 1:
A nickel intermediate layer is introduced between the steel strip and the solder layer. This nickel layer acts as an adhesion promoter that eliminates the need for cyanide in the electroplating process, thereby maintaining good solder adhesion while removing the toxic harmful factor
Solution Approach 2:
The chemical composition parameters of the electrolyte bath are changed by replacing cyanide-containing solutions with cyanide-free formulations. The process uses controlled current densities (10-50 A/dm² for nickel, 5-20 A/dm² for solder) and specific electrolyte compositions to achieve proper coating adhesion without toxic additives
2Object-affected harmful factors
If cyanide-free electroplating processes are used to avoid toxicity, then harmful factors are reduced, but adhesion of solder layer deteriorates
Solution Approach 1:
The nickel intermediate layer serves as a mediator that enables effective adhesion between steel and solder in cyanide-free processes. The nickel layer provides a surface that promotes strong bonding to both the steel substrate and the solder coating, compensating for the absence of cyanide
Solution Approach 2:
Specific electroplating parameters are optimized for cyanide-free operation: nickel layer thickness of 5-50 μm applied at current densities of 10-50 A/dm², followed by solder layer deposition at 5-20 A/dm². These parameter changes ensure adequate adhesion without cyanide
3Productivity
If conventional electroplating processes are used for large-area coating, then productivity is improved, but adhesion quality deteriorates without cyanide
Solution Approach 1:
The nickel intermediate layer enables continuous high-speed electroplating of large steel strips (250-1500 mm width) without cyanide, maintaining both productivity and adhesion quality through its promoter function
Solution Approach 2:
The process uses controlled current densities and electrolyte compositions that enable uniform coating across large areas at high production speeds, achieving both efficiency and quality in cyanide-free operation
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 achieves robust and high-quality multi-walled pipes with improved adhesion and reduced brittleness, enhancing the anti-corrosion properties and allowing for economical production without the use of cyanide.
Implementation Method 1
the at least one starting nickel layer and preferably also the at least one starting solder layer is or are applied by means of electroplating
Implementation Method 2
At least one electrolyte bath is expediently used during the electroplating of the at least one starting nickel layer and/or the at least one starting solder layer
Implementation Method 3
the copper is melted by heating the multi-walled tube, whereby the rolled-up walls of the tube are soldered together
Implementation Method 4
the copper is melted by heating the multi-walled tube, whereby the rolled-up walls of the tube are soldered together and thus result in a high-quality material connection
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a method for producing multi-walled pipes and the multi-walled pipes produced therefrom. A steel strip forms a steel starting layer (8) of a metal strip, on which a nickel starting layer is applied at least on one side. A solder starting layer (9) is applied to one nickel starting layer or one of the two or both nickel starting layers. The multi-walled tubes (1) are formed from the metal strip or from sections of the metal strip by means of rolling. The walls of the tubes are brazed by heating.