Electrochemical marking on stainless steel
The process, called electro-marking, allows to reproduce faithfully on any metal any decorative pictures or shapes imprinted on suitable marking screen made by polymeric material, allowing to partially mask the entire surface of the treated sample. Swab electrolysis consists in an anode device soaked by suitable electrolyte. This electrode is electrically connected to the metal surface, considered as cathode. One could say that “you bring the galvanic bath on the object to be treated”. This process is also referred to as the Dalic process (name of the company that introduced the process). It was introduced to industries to solve problems of:
- Fretting corrosion;
- Friction coefficient between the mechanical parts;
- Electric conducibility;
- Corrosion processes;
- Extreme temperature conditions;
- Corrosion agents.
These problems occur in all industries, especially when large metal parts are to be handled that can not be immersed in electrolysis tanks or complex pieces where the manipulation is very delicate.
The Nitty-Gritty method is realized by an electrical source called Multimark capable of establishing a potential difference (in alternating current) between the sample and a torch. The latter is slid on te marking screen that is in contact with the treated metal.
This results in an electrochemical system in which the first electrode is the sample and the torch is the second electrode. The latter is covered in the end by a pad capable of absorbing and retaining an appropriate electrolyte; the felt is positioned between the torch and the sample. When the torch moves over the marking material, the electrical circuit is closed by the electrolyte soaked into the pad. The marking screen allows an appropriate distribution of the electrolyte, allowing it to effectively fill the design that you want to impress and reach the surface efficiently. This factor contributes to the competitiveness of the technique with the classic screen printing methods traditionally used for steel decoration, witnessed and expressed by a number of examples of possible applications: ovens and hobs, nameplates, fire extinguishers and other applications, etc…
Nameplates attached to the machine
Decorative electrochemical marking on a sword
Electrochemical marking on stainless steel oven
During marking, you do not have to be stuck with the pad and the contact piece otherwise is likely to have burns. To obtain constant thicknesses, it is best to work with maximum motion irregularities, avoiding linearity. Since the current intensity is the function of the relationship between the anode and the cathode, it is necessary to operate with the maximum possible surface of the pad in order to decrease the treatment times. Please note that the device causes locally significant overheating by Joule effect. For this reason, cooling systems must be adopted when the marking area is of considerable size. The anode must be insoluble, otherwise it will be consumed very quickly, and must maintain its geometric shape to confer a constant coating on the entire marking surface. It must also be cheap and easy to process.
Corrosion Test on different stainless steel
From the previous image it is noted that, after an accelerated corrosion test, the marked zone has a much higher corrosion resistance (pitting) than the metal base. This particularity is due to the presence of a compact layer of protective oxides. These oxides are made of nickel, chrome and ferrous and guarantee a compact and solid coating against the various types of corrosion. In the field of corrosion protection, swab electrolysis has a particular interest. The swing movement on the metal surface eliminates the risk of pitting corrosion and gas occlusions, ensuring the coating ventilation. All of these advantages lead to the elimination of hydrogen embrittlement on high-strength metals such as those used in landing gears.
Fretting corrosion can be effectively fought by electro-marking because it is possible to create ternary alloy coatings that, for example, protect the steels used in the naval field, enhancing the useful life of the pieces strongly solicited.