Pickling accessories

Pad or Brush?

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Electrochemical pickling is the process where both electric current and chemical solutions, basically acidic (PH below neutrality), are used to remove the residues generated during the welding process. These residues must be removed to increase the corrosion resistance of the product, increase the useful life and reduce maintenance processes.

Electrochemical pickling compared to all other pickling processes offers:

Our pickling systems, to be efficient, are:

The engine that determines these qualities is the inverter technology that gives our machines lightness, strength and the control of electrical parameters during the electrochemical process.

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Partially electrochemically cleaned weld seam

The accessories are basically of two categories:

  • Insert & Pad
  • Brush
Accessori per il decapaggio: Tampone o Pennello?

Carbon fiber brush with retractable bushing (left) – pad and relative insert (right)

These two accessories are the final part where the electrochemical reaction occurs at the weld. Here the production of:

  • Hydrogen ions, necessary to contribute to the breakdown of residues;
  • Dissolution of the metallic material due to the acid solution;
  • Development of heat, following the Joule effect of the electric current, which accelerates the reaction kinetics, favoring the detachment of the residue.

So the main characteristics that the accessories must have are:

  • Chemical inertness: they must not react with chemical solutions;
  • Resistant to high temperatures: They must not quickly lose their characteristics following the sudden increase in temperature;
  • Electrical conductivity: they must offer the least electrical resistance to increase the reaction rate and offer cleaning as quickly as possible;
  • Easy to install and adjust.

Insert & Pad

This type of accessory has two parts:

  • The insert in graphite or sintered tungsten powder;
  • The polymeric tissue pad.

The insert is a suitably shaped block to reach different welding positions which in turn gives the shape to the pad. The insert is mainly composed of graphite which is a chemically inert material and has excellent electrical properties, especially when the rise in 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 rise in temperature, gives a considerable acceleration to the cleaning process.

The pad is the area that is in contact with the surface of the stainless steel and with the welding residue. The polymeric fabric gives it high resistance to acids and withstands temperatures of around 200 ° C. The pad, containing microporosities, tends to generate a “sponge” effect that holds the electrochemical solution right in the welding area, avoiding contamination and unwanted liquid leaks. Its great tensile strength avoids tearing even in situations where the stainless steel surface is very rough, ensuring a slight abrasive action when the residue is difficult to remove.

This type is very popular for applications where the welds are linear: corner, T sections of the stainless steel, head-to-head welded pieces and all those shapes that do not require sudden changes in position but a linear movement of the torch. The insert, having an area greater than the diameter of the brush, with the same power, covers a greater area than the diameter of the brush, increasing the cleaning speed. That small abrasive action can be decisive to remove the residue quickly.

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Pad with graphite insert

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Pad with sintered tungsten insert

Brush

The brush is an agglomeration of thousands of bristles traveled by electric current and electrochemical solution.

Each bristle is made of carbon fiber. Carbon fiber is a material that has high mechanical strength, low density, thermal insulation capacity, resistance to temperature changes and the effect of chemical agents, good flame retardant properties. On the other hand, the composite material in carbon fibers is not homogeneous and often has a marked anisotropy, i.e. its mechanical characteristics have a privileged direction. In fact, it is very often used together with particular resins in such a way as to ensure maximum performance based on the orientation of the efforts. In electrochemical pickling, the use of resin would have a very negative impact as it would hinder the passage of current, a fundamental element for quickly cleaning the welded area.

Unlike the pad, the brush must be handled with care. During pickling, the bristles of the brush must strike perpendicularly against the area to be cleaned. In this way, both the liquid and the current flow correctly, increasing the reaction speed and therefore the whole cleaning process.

This avoids several factors:

  • The uneven consumption of the bristles;
  • Blocking the passage of liquid from the inlet to the welding;
  • The generation of sparks which, from a microscopic point of view, lead to the formation of micropitting, triggering undesirable corrosive processes.

This type is very popular for welded pipes, undercuts, very sharp corners, complex shapes in which the plug cannot touch and it is necessary to change the position of the torch very often. Compared to the pad, there is no small 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 to deform them elastically;
  • Constant movements in order to homogenize cleaning and facilitate the electrochemical reactions.
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Carbon fiber brush: cleaning pipes

Whatever your choice, two fundamental parameters must be kept in mind:

  • Balance of electrical power with the flow of electrolytic liquid;
  • Maintenance processes.

A greater inflow of electrolytic liquid with inadequate electrical power leads to an exaggerated waste of liquid, contaminating areas not involved in pickling. A reduction in the electrolyte flow and an increase in electrical power leads to rapid consumption of the bristles or pad.

The maintenance of accessories is a ritual that must be taken into serious consideration to extend the useful life of our accessory. At the end of the pickling process, the impurities retained inside the brush or in the pad can:

  • Obstruct the passage of electrolyte liquid;
  • To stiffen the bristles or the pad, with an immediate degradation of the mechanical characteristics;
  • Contaminate additional areas to be cleaned.

To avoid these problems it is always advisable to wash or neutralize the accessories at the end of each production cycle. In this way, on the next cycle, you can be sure of getting the job done flawlessly and quickly.

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