The electrochemical pickling is that process in which both electric current and chemical solutions, basically acidic (PH below neutral), are used to remove residues generated during the welding process. These residues must be removed to increase the corrosion resistance of the part, increase service life, and lower maintenance requirements.
Electrochemical pickling compared with all other pickling processes offers:
- The use of less aggressive and harmful substances for the operator.;
- Immediate result;
- Targeted application where needed. Without waste and contamination;
- Clean and protected surface: Substantial increase in corrosion resistance and lowering the probability of brittle fracture.
Our pickling systems, in order to perform well, are:
- Lightweight and sturdy;
- Electrically performing;
- Equipped with sturdy and durable accessories.
The motor that determines these qualities is the inverter technology which gives our machines lightness, robustness and control of electrical parameters during the electrochemical process.
Accessories basically fall into two categories:
- Insert & Pad;
- Brush.
These two accessories are the final part of the machine where the electrochemical reaction takes place at the weld. Here the production of:
- Hydrogen ions, which are needed to help break down residues;
- Dissolution of metal material due to acidic solution;
- Development of heat, as a result of the Joule effect of the electric current, which accelerates the reaction kinetics, promoting detachment of the residue.
So the main characteristics that the accessories must possess are:
- Chemical inertness: must not react with chemical solutions;
- Resistant to high temperatures: They must not lose their characteristics rapidly as a result of the sudden increase in temperature;
- Electrical conductivity: they must offer the lowest electrical resistance to increase the speed of reaction and offer the fastest possible cleaning;
- Easy to install and adjust
Insert & Pad
This type of accessory has two parts:
- The graphite insert or sintered tungsten powder;
- The polymer fabric pad.
The insert is a block shaped appropriately to achieve different solder positions, which in turn gives the pad its shape. The insert is composed mainly of graphite, which is a chemically inert material and has excellent electrical properties, especially when rising temperature comes into play. In fact, when the temperature rises, this material lowers its electrical resistance, facilitating the cleaning process. This ability, combined with the temperature rise, gives a not inconsiderable acceleration to the cleaning process.
The pad is the area that is in contact with the stainless steel surface and the residue to be removed. The polymer fabric imparts high resistance to acids and withstands temperatures around 200°C. The pad, containing microporosities, tends to generate a “sponge” effect that retains the electrochemical solution right in the weld area, preventing contamination and unwanted liquid spillage. Its high tensile strength avoids tearing even in situations where the stainless steel surface is very rough, providing a mild abrasive action when the residue is difficult to remove.
This type is popular for applications where welds are linear: parts welded at an angle, with a T-section, head-to-head, and all those shapes that do not require sudden changes in position but a linear movement of the torch. The insert, having a larger area than the diameter of the brush, with the same power, covers a larger area than the diameter of the brush, increasing cleaning speed. That small abrasive action can be decisive in removing residue quickly.
Brush
The brush is an agglomeration of thousands of bristles run through with electric current and electrochemical solution.
Each bristle is made of carbon fiber. Carbon fiber is a material that possesses high mechanical strength, low density, thermal insulation ability, resistance to temperature changes and the effect of chemicals, good fire retardant properties. In contrast, carbon fiber composite material is non-homogeneous and often has a pronounced anisotropy, that is, its mechanical properties have a preferred direction. In fact, it is very often used together with special resins in such a way as to ensure maximum performance according to the orientation of stresses. In electrochemical pickling the use of resin would have a very negative impact as it would hinder the passage of current, which is essential to quickly clean the welded area.
Unlike the pad, the brush must be handled with care. During pickling, the bristles of the brush should bump perpendicularly against the area to be cleaned. In this way, both the liquid and the current flow properly, increasing the reaction speed and thus the whole cleaning process.
In this way, several factors are avoided:
- The uneven consumption of the bristles;
- Blocking the passage of liquid from the inlet to the area to be cleaned;
- The generation of sparks that, from the microscopic point of view, lead to the formation of micropitting, triggering corrosive processes undesirable.
This type is very popular for welded pipes, undercuts, very sharp corners, complex shapes in which the pad fails to touch and it is necessary to change the position of the torch very often. Compared to the pad, there is not that little abrasive action, so you have to take advantage of the electrochemical process by following a few simple rules:
- Keep the bristles perpendicular to the welding area, avoiding elastic deformation;
- Constant movements so as to homogenize cleaning and facilitate electrochemical reaction.
Whatever your choice, two basic parameters must be kept in mind:
- Balancing electrical power with electrolyte liquid flow;
- Maintenance processes.
Increased electrolyte flow with inadequate electrical power leads to exaggerated liquid waste, contaminating area not interested in pickling. A reduction in electrolyte flow and an increase in electrical power results in rapid consumption of the bristles or pad.
Accessory maintenance is a ritual that must be taken seriously to extend the useful life of our accessory. At the end of the pickling process, impurities retained inside the brush or in the pad can:
- Obstruct the passage of electrolyte liquid;
- Stiffen the bristles or pad, with immediate degradation of mechanical properties;
- Contaminate additional areas to be cleaned.
To avoid these inconveniences, it is always advisable to wash or neutralize the accessories at the end of each production cycle. This way, at the next cycle, you can be sure to perform the job flawlessly and quickly.
