WO2001032960A2

WO2001032960A2 - Machine for localised cleaning with electrolytic and/or ultrasound cell, for pickling and/or polishing

Info

Publication number: WO2001032960A2
Application number: PCT/IB2000/001583
Authority: WO
Inventors: Richard Sigrist
Original assignee: EDK Research AG
Current assignee: EDK Research AG
Priority date: 1999-11-04
Filing date: 2000-11-02
Publication date: 2001-05-10
Anticipated expiration: 2002-05-04
Also published as: CA2389659C; DE20019118U1; JP4623905B2; KR20020070977A; DE60034477T2; CN1217032C; ITMO990244A1; KR100729466B1; EP1230431A2; ATE360106T1; CN1409776A; ES2284536T3; CA2389659A1; JP2003514118A; US20070062030A1; EP1230431B1; IT1311147B1; US7803258B2; DE60034477D1; WO2001032960A3

Abstract

Machine for localised cleaning, including pickling acid or a composition/mixture of chemical elements with pickling action that is applied by hand or by mechanical instruments to the surface (5; 46; 64; 73) that is to be treated and also contains acid held in a limited quantity in the work position by a cell (1; 25; 35; 48; 65; 74) in material that will withstand the corrosive action of the acid; the cell is of the same volume (7; 47) as the acid used, i.e. it completely fills it with acid and reduces the volume to the volume of the acid contained in the perimeter of the cell projected on the surface to be treated; the acid is activated by the action of a device (11; 68) that activates pickling in its own device. Different constructional forms with electrolytic and/or ultrasound action are described together with aspiration and separation of fumes.

Description

MACHINE FOR LOCALISED CLEANING WITH ELECTROLYTIC AND/OR ULTRASOUND CELL, FOR PICKLING AND/OR POLISHING

The invention concerns : a machine for localised clean- ing with electrolytic and/or ultrasound cell for pickling and/or polishing, and also a machine that is used to clean metal parts on which previous processes have left scabs, halos and in general dirt on the metal surfaces; it is very useful for cleaning welding beads . The prior art comprises machines that are designed to clean surfaces by means of abrasive tools and which are characterised therein that the metal surface to be cleaned, pickled and/or polished is scoured by abrasives that can be applied to the tool head or be dissolved in porous elements . United States patent US-A-4206028 combines with the abrasive action either electrochemical pickling by a suitable agent placed between the aforementioned head and the surface to be treated through which a direct current with a positive pole is passed, which agent is applied to the surface to be treated whilst the negative pole is applied to the aforementioned tool head, or else ultrasound is used that is supplied by an emitter and sonotrode that are separate from the aforementioned tool or head; if necessary the head is used in combination with alternating current and/or with a liquid that applies electrolyte to the surface to be treated , thereby exploiting inversion of polarity.

Furthermore, a similar prior-art device that has been known for many years has not found practical application because of the difficulty in using the instruments employed and because of the impossibility of defining the working environment of the electrochemical agent or ultrasound, although the supply is in the aforementioned head or tool of the electrolytic liquid, which is bonded but occurs together with the abrasive material . - -

In addition, the prior art includes US patent US-A- 4772367 , which comprises a head for cleaning the inside of pipes, in which a branched electrode is placed near the outer surface of the head to create electrochemical action by means of the electrolyte that is supplied inside the head and the aforementioned surface: a dielectric coating enables the electrolyte to remain in position near the surface: the dielectric coating is not in contact with the surface, but remains a cavity to enable the electrolyte to flow away through the pipe .

However, the aforementioned head for pipes illustrates the disadvantages of the electrochemical cleaning technology specified in United States patent US-A-5964990 that is characterised therein that the dielectric coating is also interposed with materials that are highly resistant to heat, which makes it impossible to prevent time being lost due to the dielectric coating' s becoming worn and the disadvantage of the electrolyte's being removed from the surface to be treated as mentioned in all the previous exam- pies remains .

Finally, the prior-art includes the manual method of chemical cleaning of the metal surfaces with pickling agents in the form of concentrated gel which are manually placed by the operator on the cleaning area and are left for a period of time ranging from a few minutes to several hours for the reaction to take place and are then washed off so that the entire agent is lost by being washed through the drainage point so that that the workplace has to be equipped with waste-water treatment systems to pre- vent pollution of the external environment.

There is considerable scope for improvement of the prior art by means of a device that cleans metal surfaces that is highly efficient and does not have the disadvan- tages of the prior art. - -

The foregoing remarks show that it is necessary to solve the technical problem of finding a type of electrolytic and/or ultrasound cleaning machine that ensures high pickling performance, ease of use, low consumption of pickling agent, low operating power, which the user can subject at will to heavy or light service and which efficiently prevents pollution of the workplace and of the environment .

The invention solves the aforementioned technical problem by adopting: a localised cleaning machine that comprises pickling acid or a composition/mixture of chemical elements that act as a pickling acid that is applied manually or by mechanical application instruments to the sur- face to be treated and which is characterised therein that the acid is held in a limited quantity in the work position by a cell in material that withstands the corrosive effect of the acid; this cell is of the same volume as the acid used, in other words by completely filling it with acid or by reducing its volume to the volume of the acid on the perimeter of the cell that is projected onto the surface to be treated ; and this acid is activated by the action of a device that activates the acid's pickling action in its own right. Adopting, in a further and preferred embodiment: at the edge of the aforementioned cell near the surface to be treated , a peripheral seal for the edge against the aforementioned surface to be treated .

Adopting, in a further embodiment: the aforementioned activating device consists of a generator of electric current, one pole of which is connected to the material of the surface to be treated whilst the other pole is connected to an electrode in material that conducts electricity located inside the cell and is not in direct contact with the surface to be treated but only via its pickling acid; this electric current generates in the cell the electrolytic action between the aforementioned surface and the electrode.

Adopting, in a further embodiment: the aforementioned activating device consists of an ultrasound generator applied to a metal sonotrode, one end of which is located inside the aforementioned cell; the action of the ultrasound vigorously activates the acid ' s pickling action . Adopting, in a further embodiment: the electrode also acts as a sonotrode, or vice versa; the pickling acid inside the cell is subjected to both electrolytic and ultrasonic action.

Adopting, in a further and preferred embodiment: the electrode and/or sonotrode is/are made mobile inside the cell in order to adapt the volume to the volume of acid that the cell contains.

Adopting, in a further embodiment: the electrode is fitted with an indentation with prongs in order to increase the surface of the electrode that comes into con- tact with the pickling acid, on the facing surface within the aforementioned electrolytic cell .

Adopting, in a further embodiment: the electrode is fitted with an added plate that improves conductivity in combination with the pickling acid on the facing surface within the aforementioned electrolytic cell .

Adopting, in a further embodiment: the electrode is fitted with an indentation with prongs on an added plate that improves conductivity in combination with the pickling acid in order to increase the surface of the elec- trode that comes into contact with the pickling acid, on the facing surface within the electrolytic cell .

Adopting, in a further embodiment: the seal at the edge of the cell in contact with the surface to be treated, consisting of a ring with a circular cross-section that is housed in a ring-shaped seat around the edge. Adopting, in a further embodiment: the seal along the edge of the cell in contact with the surface to be treated that consists of a ring with at least one lip that faces the surface and is housed in the ring-shaped seat around the edge .

Adopting, in a further embodiment: the seal along the edge of the cell that comes into contact with the surface to be treated and which consists of a ring-shaped suction cup facing the surface to be treated that is connected by means of conduits and pipes to a vacuum aspiration system. Adopting, in a further embodiment: in the aforementioned electrode and/or sonotrode there is at least one diaphragm valve for the release of fumes generated during pickling; at the same time the cell too has holes to allow the fumes to escape .

Adopting, in a further and preferred embodiment: near the cell a device for aspirating the fumes leaving the cell .

Adopting, in a further embodiment: a series of vents connected to the system for aspirating and scrubbing the aspirated polluting fumes.

Adopting, in a further and preferred embodiment: a hood, with a bottom edge near the edge of the cell, connected to the system for aspirating and scrubbing the as- pirated polluting fumes .

Adopting, in a further embodiment: a ring seal with a pair of lips, the cavity between them being connected to the system for aspirating and scrubbing the aspirated polluting fumes . Adopting, in a further and preferred embodiment: a separator between the pickling acid and the aforementioned aspirating and scrubbing system; the aspirated liquid or gelatinous part in the case of gel is separated from the fumes in the aforementioned separator before the fumes are scrubbed. Adopting, in a further embodiment: a ring-shaped cell with seal rings that are the same as the external /internal diameter and that are near the internal /external diameter of the surface of the pipe/round bar to be treated; a de- livery and a return line for the pickling acid to be supplied the cell, together with an electric cable connected to the electrode.

Adopting, in a final embodiment: the aforementioned cell fitted with two series of radially arranged delivery or return holes for the pickling acid; these holes are arranged axially and/or at angles to one another.

This invention provides the following advantages: the cleaning machine is much more effective than prior-art ma- chines; a limited area of the surface to be treated is cleaned that faces the cell volume; the energy required to activate acid pickling is much less than is required for manual operations or for electrolytic cleaning carried out in immersion tanks; the scope of the cleaning machine is not restricted by buffer replacement or by other manual tasks such as the distribution and washing of the pickling gel; ultrasound can also be used with pickling acid in the cell to clean surfaces that are not conductors of electricity; the combined use of electrolytic cleaning power and mechanical ultrasound cleaning power enables cleaning capacity to be greatly increased and therefore enables cleaning costs to be greatly reduced.

Some purely illustrative embodiments of implementing the invention are shown as mere examples in the attached drawings: Fig. 1 is a section drawing of an electrolytic cleaning cell according to the invention; Fig. 2 is a section drawing of a mechanical ultrasound cleaning cell; Fig. 3 is a section drawing of an electrolytic cleaning cell with vents to aspirate the fumes created; Fig. 4 is a WO 01/32960 - 7 - PCT/IBOO/015

section drawing of a mechanical ultrasound cleaning cell, that is fitted with a hood for aspirating the fumes and excess pickling acid; Fig. 5 is a section drawing of an electrolytic cleaning cell, that is fitted with a ring- shaped suction cup that is fixed to the surface to be treated and with a hood for aspirating the fumes; Fig. 6 is a section drawing of a combined electrolytic and ultrasound cleaning cell that is fitted with a ring-shaped suction cup that is fixed to the surface to be treated and with vents for aspirating the fumes; Fig. 7 is a section drawing of an electrolytic cleaning cell that is fitted with a double-lipped seal and a system for aspirating the fumes and the excess electrolyte from the cavity between the two lips; Fig. 8 is a section drawing of a combined electrolytic and ultrasound cleaning cell that is fitted with a single-lip seal and a hood for aspirating fumes and the excess electrolyte; Fig. 9 is a section drawing of a combined electrolytic and ultrasound cleaning cell for cleaning corner welding beads and is fitted with vents for aspirating fumes; Fig. 10 is a drawing of the separator that separates the fumes from the electrolyte that is aspirated downstream of a cleaning cell; Fig. 11 is a section drawing of an ring-shaped electrolytic cleaning cell of the same diameter as the external diameter of pipes or round bars; Fig 12 is a section drawing of a circumferential electrolytic cleaning cell for cleaning the internal diameter of pipes .

The following are shown: 1, Figure 1 is the cell in stiff dielectric heat-resistant material , preferably in highly resistant plastic, within which a metal electrode 2 is located with peripheral seal rings 3 ; 4 is a pipe inside the electrode in material that is resistant to the pickling acid and which acts as an electrolyte: the bottom edge of the cell that comes into contact with the surface to be treated 5 is fitted with a seal ring 6 to be defined, a volume 7 within which cleaning takes place; 8 is a plate in metal with higher electrical conductivity, fitted with prongs 9 that penetrate the electrolyte in area 7 in order to increase the surface that is in contact with the electrode and the electrolyte; 10, Fig. 2 is the hollow sonotrode that is made to vibrate by the ultrasound generator 11; 12 is a small pipe cladding the interior of the sonotrode that withstands the pickling acid and which is supplied with acid by means of the pipe 13; 15 Fig. 3 are the vents formed in a hollow spout 16, that are located to the top of and near the aforementioned electrode 2 that aspirate the fumes that escape laterally from the cell seal 6; with 18, Fig. 4 is a sonotrode to which a hood 19 is applied, the bottom edge 20 of which is near the surface to be treated 5 : the fumes and the excess pickling acid that escape f om seal 6 are aspirated by the air sucked into the cavity 21, the air is connected to the aspiration system by the conduit 22. The following are also shown: 25, Fig. 5 shows a cell with a ring-shaped suction cup 26 at its bottom edge; 27 shows conduits inside the cell that creates the vacuum by means of a vacuum system that is not illustrated and to which the conduits are connected by pipes 28; 29 is the electrode located in the cell that is fitted with diaphragm valves 30 to enable the fumes to go through and the pickling acid to be retained in the aforementioned volume 7; 31 shows vent holes in the body of the cell 25; 33, Figure 6 shows a sonotrode that also functions as an elec- trode which is fitted with the aforementioned diaphragm valves near the internal surface of volume 7 that enable the fumes to escape that were generated during cleaning of surface 5; 35, Fig. 7, shows a cell with holes 36, to aspirate fumes and excess pickling acid from the cavity 37 through the ring-shaped lips 38 with which the edge of the cell is fitted; 39 is a connecting sheath for aspiration between the aforementioned holes 36 and the vents 15 of the hollow spout 16; M is the cell transfer movement that is allowed by the aforementioned lips; 41, Fig. 8 is a sonotrode that also functions as an electrode, fitted near the internal surface of volume 7 of the cell 1 of a plate 42 in metal with higher electrical conductivity; 43 is a ring-shaped bottom lip for the seal of cell 1 to mark off volume 7. Finally, 45, Fig. 9 shows corner welding between two walls 46 requiring cleaning; 47 is the cleaning volume of the cell 48 between the bottom surface 49 of the elec- trode-sonotrode 50 and the flat boundary walls 51 of the cell to which the electrode-sonotrode is sealed; 52 is the prongs that penetrate the electrolyte in the volume 47 to increase the contact surface between the electrode and the electrolyte; 54, Figure 10, is the delivery pipe of the pickling acid and, where it exists, the electrode that acts as an electrolyte; 55 is the pickling acid pump; 56 is a cleaning cell of the type previously seen with a system for aspirating excess acid; A are the returning air routes for conveying the acid G to the conduit 57 connected to the separator 58, which is fitted with diaphragms 59 with staggered holes 60; F is the air and fumes that the fan 62 separates and pushes towards a further scrubbing filter; 64, Fig. 11 is the external surface of the pipe on which the rung-shaped cell 65 is concentric, which is fitted with ring-shaped lips 66 and the toroidal electrode 67 that is in electrical contact with the electric cable 68; 69 shows two series of holes of the electrode, each of which is connected with a ring-shaped delivery and return chamber 70 of the pickling acid, which return chamber acts as an electrolyte: a pair of conduits 71 delivers and returns to the separator 58; T is the work motion between the ring cell 65 and the pipe; 73, Figure 12, is the in- ternal surface of the pipe to be cleaned within which the circumferential cell is located; 74, I is its mobile movement during insertion and L is the extraction stroke, either or both being work movements; 75 shows a chamber created in the body 76 of the cell for supplying a series of holes 69 of the aforementioned toroidal electrode 67, the chamber is closed by the plug 77; 78 is a ring that completes the cell, is rigidly fitted to the body, and guides the cell from the exterior of the pipe by means of the bored rod 79.

Localised cleaning machine occurs as follows . The cell is filled in some manner with pickling acid, which is also an excellent electrolyte because of its electrochemical properties, also by means of a brush if the acid is in gel form, the cell is then placed in contact with the surface 5 to be cleaned and cleaning is started. If there is just one electrode 2, as in Fig. 1, a direct or alternating electric current is passed through the acid. As with the prior art, the different currents applied generate a high level of energy if the anode ( + ) is applied to the surface 5 and the cathode (-) is applied to the electrode, vice versa much less energy is obtained and this tends to polish the surface to be treated 5; finally with alternat- ing current the effect lies between the aforementioned two. If there is just one sonotrode 10, as in Fig. 2, the acid is disturbed mechanically by the agitation caused by the ultrasound and the resulting pickling is much greater than the mere depositing of gel achieved by the prior art . Finally, after cleaning the point, the operator moves the cell and repeats the aforementioned operations .

The aforementioned single cell cannot be used with liquid pickling acid so the acid must be supplied by a pump 55, which may operate intermittently or continuously, from separator 58 or from a storage tank, if the small amount required can be lost. Moreover, it is very useful to maintain this supply at high levels and to collect excess pickling acid, also in gel form, together with the fumes generated by cleaning the surface, by means of hood 19 or aspiration into the cavity 37 through the ring-shaped lips 38; the recirculation of the pickling acid generated in the ring-shaped cell 65 and circumferential cell 74 serves the same purpose, i.e. to replace the acid that becomes overheated during operations and gives off polluting fumes and takes with it the dirt removed from the surface. If the acid is not or cannot be fully recirculated, aspiration of the fumes that have escaped from the cell through the vents located on the hollow spout is nevertheless effective, also via the diaphragm valves . The simultaneous action in the cell of electrolytic and ultrasound cleaning greatly increases the effectiveness of cleaning. As all the Figs, of constructional forms show, except for those showing the internal or external diameters of the pipes or round bars, the two effects of elec- trolytic and ultrasound cleaning can be combined because they are applied to the pickling acid contained in the volume 7, 47 of the cell by the same organ with the dual function of electrode and sonotrode.

Both the electrolytic and ultrasound treatment of the acid are enhanced by the possibility of reducing volume 7 of the cell 1, 25 or 35 to very low levels, by making the electrode 2, 29 or the sonotrode 10, 18, 41 run along its body to the surface to be treated 5, this movement is made possible by the presence of the seal ring 3 between the aforementioned cell and the electrode; another way of increasing electrolytic action is to point a plate 8, 42 in metal with very high conductivity or which is polarised towards the surface to be treated of the electrode pointing towards volume 7, 47 of the cell or to also or as an alternative fit the end of the electrode with prongs 9, 52 that increase the area of the surface that is in contact with the pickling acid.

The ring-shaped suction cup 26 on the edge of the cell ensures secure positioning and a secure seal on the sur- face to be treated 5 : the cell must therefore be fitted with diaphragm valves 30 to enable fumes to escape whilst in the case of a ring seal 6 or a lip seal 43 the fumes and the excess pickling acid escape normally. Finally, the lips 38 or the single lip 43, 66 enable the cell to be moved even during operation .

The body of the cells is in stiff dielectric material that is heat resistant and preferably in highly resistant plastic whilst the material of the electrode and/or sonotrode is metal and may be clad in a layer that is resist- ant to the action of the pickling acid in the supply conduit and/or be clad by the aforementioned highly conductive plate 8, 42 in the surface facing the cell volume 1, 25, 35, 65 and 74.

In the practical embodiment, the details may be different from those indicated, but be technically equivalent and still fall within the scope of this invention.

The cell can thus be made from non-insulating material but have an insulating cladding, similarly, the edge of the electrode 48 in the cell of Fig. 9 may be protected in the same way near the walls 46 of the surface to be treated from short circuits between it and the aforementioned walls .

Finally, much less economically, the cell material may not be resistant to corrosion from the pickling acid: the cell will have a much shorter life than the cells in material that is resistant to acid corrosion; or the cell may be protected by a layer in material that is resistant to acid corrosion, as described above for non-insulated mate- rial .

Claims

1. Machine for localised cleaning, containing pickling acid or a composition/mixture of chemical elements with the effect of pickling acid, applied manually or by mechanical feed instruments to the surface to be treated (5; 46; 64; 73) , characterised therein that the acid is kept in a limited quantity in the work position by a cell (1; 25; 35; 48; 65; 74) in material that resists the corrosive action of the acid; the volume of this cell (7; 47) is made to match that of the acid used, i.e. by completely filling it with acid or by reducing the volume to the volume of the acid within the perimeter of the cell, which acid is projected onto the surface to be treated; this ac- id is activated by a device that activates the acid's pickling action in its own right.

2. Machine for localised cleaning according to the previous claim, characterised therein that at the edge of the aforementioned cell near the surface to be treated there is a peripheral seal (6; 26; 38; 43; 66) of the edge against the aforementioned surface.

3. Machine for localised cleaning according to one of the previous claims, characterised therein that the aforementioned activating device consists of a generator of electric current, one pole of which is connected to the material of the surface to be treated whilst the other pole (68) is connected to an electrode (2; 29; 41; 50; 67) in material that conducts electricity located inside the cell and is not in direct contact with the surface to be treated but only via its pickling acid; this electric current generates in the cell the electrolytic action between the aforementioned surface and the electrode.

4. Machine for localised cleaning according to one of the previous claims 1 or 2 , characterised therein that the aforementioned activating device consists of an ultrasound generator (11) applied to a metal sonotrode (10; 18; 33; 41; 50) , one end of which is located inside the aforementioned cell; the action of the ultrasound vigorously activates the acid' s pickling action.

5. Machine for localised cleaning according to one of the previous claims 3 or 4 characterised therein that the electrode also acts as a sonotrode, or vice versa: the pickling acid inside the cell (1; 25; 35; 48) is subjected to both electrolytic and ultrasonic action.

6. Machine for localised cleaning according to one of the previous claims from 3 to 5 characterised therein that the electrode and/ or sonotrode (2; 10; 18; 29; 33; 41) is /are made mobile inside the cell in order to adapt the volume to the volume of acid that the cell contains .

7. Machine for localised cleaning according to one of the previous claims 3 or 5 characterised therein that the electrode (50) is fitted with an indentation with prongs (52) in order to increase the surface of the electrode that comes into contact with the pickling acid, on the facing surface (49) within the aforementioned electrolytic cell (48) .

8. Machine for localised cleaning according to one of the previous claims 3 or 5 characterised therein that the electrode (41) is fitted with an added plate (42) that improves conductivity in combination with the pickling acid on the facing surface within the aforementioned electrolytic cell .

9. Machine for localised cleaning according to one of the previous claims 3 or 5 characterised therein that the electrode (2) is fitted with an indentation with prongs (9) on an added plate (8) that improves conductivity in combination with the pickling acid in order to increase the surface of the electrode that comes into contact with the pickling acid, on the facing surface within the electrolytic cell (1) .

10. Machine for localised cleaning according to one of the previous claims from 2 to 6 that is characterised therein by a seal at the edge of the cell in contact with the surface to be treated (5; 46) , consisting of a ring with a circular cross-section (6) that is housed in a ring-shaped seat around the edge.

11. Machine for localised cleaning according to one of the previous claims from 2 to 6 that is characterised therein that the seal along the edge of the cell (1; 35) in contact with the surface to be treated (5) consists of a ring with at least one lip (38; 43) that faces the surface and is housed in the ring-shaped seat around the edge .

12. Machine for localised cleaning according to one of the previous claims from 2 to 6 that is characterised therein that the seal on the edge of the cell (25) that is in contact with the surface to be treated (5) consists of a ring-shaped suction cup (26) facing the surface to be treated that is connected by means of conduits (27) and pipes (28) to a vacuum aspiration system.

13. Machine for localised cleaning according to one of the previous claims from 2 to 6 or 12 that is characterised therein that in the aforementioned electrode and/or sonotrode (29; 33; 50) there is at least one diaphragm valve (30) for the release of fumes generated during pickling; at the same time the cell (25; 48) too has holes to allow the fumes to escape.

5 14. Machine for localised cleaning according to one of the previous claims from 2 to 6 that is characterised therein that near the cell there is a device (15; 16; 19; 36; 39; 62) for aspirating the fumes leaving the cell.

10 15. Machine for localised cleaning according to the previous claim 14 that is characterised therein that there is a series of vents (15; 16) connected to the system for aspirating and scrubbing the aspirated polluting fumes .

15 16. Machine for localised cleaning according to the previous claim 14 that is characterised therein that a hood (19) , with a bottom edge near the edge of the aforementioned cell, is connected to the system for aspirating and scrubbing the aspirated polluting fumes .

20

17. Machine for localised cleaning according to the previous claim 14 in combination with claim 11 that is characterised therein that a ring seal with a pair of lips

(38) and the cavity (37) between them are connected (36; 25 39; 15; 16) to the system for aspirating and scrubbing the aspirated polluting fumes.

18. Machine for localised cleaning according to one of the previous claims from 16 to 17 that is characterised

30 therein that a separator (58; 60; 61) is located between the pickling acid and the aforementioned system for aspirating (62) and scrubbing the aspirated polluting fumes; the liquid aspirated or gelatinous part in the case of gel is separated from the fumes in the aforementioned separa-

35 tor before the fumes are scrubbed.

19. Machine for localised cleaning according to the previous claim 3 that is characterised therein that there is a ring-shaped cell (65; 74) with seal rings (66) on the external /internal diameter that are near the internal /ex- ternal diameter of the surface (64; 73) of the pipe/round bar to be treated and that there is a delivery and a return line (70; 71; 75) for the pickling acid designed to supply the cell, together with an electric cable (68) connected to its electrode (67) .

20. Machine for localised cleaning according to the previous claim 19 that is characterised therein that the aforementioned cell (65; 74) is fitted with two series (69) of radial delivery or return holes for the pickling acid; these holes being shifted axially and/or at angles in relation to the others .