MXPA98008506A - Descascarillado of metali surfaces - Google Patents

Abstract

The surface of a metal body is peeled off by subjecting the body to electrolysis in an electrolyte bath, and also to ultrasonic agitation. Electrolysis involves applying an electric potential of pulses to the metallic body while the metallic body is present in the bath, and the ultrasonic agitation is carried out while the body is still wet after the electrolysis.

Description

DISCARDING OF METALLIC SURFACES Field of the Invention The present invention relates to the removal of the oxide layer from the surfaces of metal bodies, such as steel, in the form of wires, and steel rods and the like. BACKGROUND When mild steel is airborne at a temperature in the range of 575 to 1370 ° C, it results in a surface incrustation in the form of an oxide layer (or thermal layer) on the steel surface. Before the steel wires can be hardened or the surface treated (such as by tinning or galvanizing), such an oxide layer must be removed. Currently, the most common method for removing the thermal layer is "stripping" the wire in (5 to 40%) dilute mineral acid, such as sulfuric acid or hydrochloric acid. Similar pickling methods are used for the removal of surface contaminants from other metals (such as bronze). This method of pickling has several disadvantages including slow speed (pickling periods of up to several minutes), the possibility that the hydrogen released during pickling will disperse in the metal and cause brittleness, and the rapid consumption of acid through the dissolution. of the layer (with simultaneous production of high concentrations of water-soluble heavy metal salts), causing a significant emission problem. Electrolytic pickling was introduced for the first time in the thirties, and originally the objective was to use electrolysis as a way to improve conventional acid pickling techniques. Consequently, the electrolytes used always tend to be derived from the main mineral acids used during conventional pickling processes (hydrochloric and sulfuric acid). In electrolytic pickling, an applied electrical potential causes a current to flow between a deoxidizing solution and a metal surface. The current may be anodic or cathodic and will typically be of a density of 1 to 200 amps dm ~ 2. Initially, the electrolytic pickling was introduced in order to make the acidic pickling faster and more efficient, and therefore the deoxidizing solutions used changed very little. However, recently the advantages of decreasing the temperature and acid concentration were fully recognized. Electrolytic pickling has several advantages over acid pickling, mainly shorter pickling periods, reduced brittleness due to hydrogen absorption, and removal of the thermal layer without dissolution, with the consequent lower consumption of the deoxidizing solution and less contaminated emanation of heavy metal. Another significant advantage in using an electrolytic process over more traditional methods is that the incorporated reactions are much more controllable. A review of the use of electrolysis is provided in "Wire Journal International," June 1985, pages 62-67. An example of the use of electrolytic pickling is described in GB 1571308, in which the process is followed by ultrasonic rinsing. A process that incorporates electrolysis and simultaneous ultrasonic agitation is described in SU 916618; that is, to be used in an electroplating process. The pickling period is minimized when the layer is porous or cracked (either initially or by subsequent pickling). The pickling period can also be reduced by stirring the pickling liquid, since this can soften the insoluble layer and increase the speed at which the solution on the surface of the layer is supplied. Another type of surface layer for metals such as steel is a solid lubricant, such as graphite. Graphite is an effective matrix lubricant for wire tempering, but subsequent removal of a solid graphite layer compacted from a metal surface is difficult. The currently most preferred method is generally to treat jet by wet firing or acid stripping. SUMMARY OF THE INVENTION According to the present invention there is provided a process for dehusking the surface of a metal body, in which said metallic body is subjected to electrolysis in an electrolyte bath and also to ultrasonic agitation, electrolysis comprising the application of an electric pulse potential to the metallic body, while the latter is present in the bath, taking out ultrasonic agitation while the body is still wet. The body may still be wet from the electrolyte or from another suitable intermediate solution. It is advantageous that the body is not allowed to dry before ultrasonic agitation, since the drying hardens the layer and hinders successful descaling. The electrolysis and the ultrasonic agitation can be carried out simultaneously, or the electrolysis can be followed by a separate step of ultrasonic agitation. Typically, the process is carried out with the electrolytic bath in a substantially neutral pH. Typically, the process is used for the removal of the acid layer from the steel, which is typically in a wire, rod or other continuously formed form. Preferably, the electric pulse potential has a current density that is in the range of 0.1 to 10 amp cm 2, more preferably in the range of 0.5 to 5 amp cm -2, according to a first embodiment of the present invention. invention, the electrolysis is carried out in a substantially aggressive electrolytic bath (which is a bath containing anions of a highly ionized acid, such as chloride, sulfate, nitrate or the like). Preferably, the aggressive bath comprises a solution of an sulfate or alkali metal chloride or ammonium In such salts, the alkali metal is typically sodium It is preferred that the electrical potential is predominantly anodic, with the anodic pulse duty cycle preferably being at least 67% (such as at least 75%) It is particularly preferred that the anodic pulse service cycle be at least 90% According to a second embodiment of the present invention, the process is carried out on an electro lyito substantially non-aggressive. Preferably, the non-aggressive electrolyte comprises a solution of an alkali metal or ammonium tripolyphosphate.; typically, the alkali metal is sodium. The electrical potential may be predominantly anodic or cathodic, typically with an anode pulse duty cycle of 5 to 95% such as 45 to 75%. It is advantageous to use a tripolyphosphate electrolyte, because the oxide layer removed from the surface of the metal body using the process according to the invention, is left as a solid in the electrolytic solution and can easily be removed by filtration, thereby allowing so much that the electrolyte solution is reused. The phosphate also forms a protective layer on the cleaned surface, which inhibits corrosion. BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of an exemplary process and apparatus, according to the invention; Figure 2 is a schematic illustration of a waveform of the typical pulsed current used for the electrolytic current in a process according to the invention (preferably in the first embodiment of the invention); Figure 3 is a graph showing the cleaning periods for the removal of oxide from the carbon steel wire with thermal layer as a function of pH and the current density in a process according to the first embodiment of the invention; Figure 4 is a graph showing the cleaning periods for the removal of oxide from the carbon steel wire with thermal layer as a function of pH and the current density in a process, without being according to the invention, not incorporating the ultrasonic treatment; Figure 5 is a three-dimensional plane showing the cleaning periods for the same wire in 10% of the aqueous NaCl solution at 65 ° C, as a function of frequency and anodic service cycle; Figure 6 is a graph showing the percentage of layer (graphite) that remains on the surface of the wire, as a function of time, for current densities of 0.5 and 2.5 amps cm "2, according to the first mode of the present invention: Figure 7 is a graph showing the period for cleaning as a function of the current density at the pH's of 0, 1 and 7, respectively; Figure 8 is a graph showing the influence of the anodic service cycle on period-dependent cleaning at a pH of 7, with a current density of the percentage of layer (graphite) remaining on the surface of the wire, as a function of time, for current densities of 1 amp cm "2; Figure 9 is a three-dimensional surface plane of the peeling period as a function of the current density and temperature in a neutral sodium chloride solution, with a cycle of 95% anode service Figure 10 is a three-dimensional surface plane of the peeling period as a function of the current density and pH in a sodium chloride solution with an 95% anode duty cycle and interleaved ultrasound Figure 11 is a three-dimensional surface plane of the peeling period as a function of the current and temperature density in a neutral sodium chloride solution with a cycle 95% anode service and interleaved ultrasound; Figure 12 is a three-dimensional surface plane of the peeling period for the removal of the graphite layer as a function of the anodic service cycle and frequency at 60 ° C in neutral sodium sulfate with a current density of 1 Acm. " Figure 13 is a three-dimensional surface plane of the peeling period for the removal of the graphite layer as a function of the current density and pH at 60 ° C in sodium sulfate with an anode service cycle of 95% and interleaved ultrasound Figure 14 is a three-dimensional surface plane of the peeling period for the removal of the graphite layer as a function of the current density and pH at 60 ° C and 1 Hz in sodium sulfate with a cycle of 95% anode service and continuous ultrasound Figure 15 is a three-dimensional surface plane of the peeling period for the thermal oxide layer as a function of the anode duty cycle and frequency 60 ° C and 1 Hz in 10% of the sodium tripolyphosphate solution at pH 7 and 1.6 Acm "2 of current density; Figure 16 is a three-dimensional surface plane of the descaling period again for the thermal oxide layer as a function of the current density and pH at 60 ° C and 1 Hz in 10% of the sodium tripolyphosphate solution with a 95% anodic service cycle and interleaved ultrasound; Figure 17 is a three-dimensional representation of the descaling period (again for the thermal oxide layer) against the concentration of the electrolyte and the temperature of the solution, with data collected under the conditions of pH 7, 1 Hz to 95% of the cycle of anodic service; and Figure 18 is a two-dimensional plot of the peeling period (again for the thermal oxide layer) against the anode duty cycle at 1 Hz frequency (for which the cleaning conditions were pH 7 adjusted using orthophosphoric acid, 60 ° C, 10% sodium tripolyphosphate, the Si-Mn wire samples being high carbon, pickled and subsequently deoxidized in the air and at 900 ° C for several periods). DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, a computer 1 is shown which is operatively connected to a voltage waveform controller 11 to generate a voltage waveform with an amplitude not greater than ± one volt. This voltage waveform was used to control the electroplate 2, which passes a current of amplitude of proportion between the respective electrodes, 3 and 4. The electrode 3 (in the wire form) is the sample to be cleaned, and the electrode 4 is a graphite carbon counter electrode. Both electrodes were mounted in a glass for analysis of electrolyte 6, which in turn was placed in an ultrasonic bath 7 containing water 10. The bath itself was thermostatically controlled in order to maintain a constant temperature. During the test, the exposed area of the electrode 3 is immersed in the electrolyte 6. A capillary tube of Luggin 8 was placed in contact with the electrode 3, so that a reference electrode 9 could be used to measure the potential of the electrode 3. This data of the potential is sent back to the Data Acquisition card on computer 1, and they are recorded continuously. The electrolytic current was applied to the cell, using a pulsating alternative current (a typical waveform is shown schematically in Figure 2). Experimental Method The cleaning of the combined electrolytic-ultrasonic surface of the wires was carried out using the cleaning cell apparatus shown schematically in Figure 1. The wire 3 to be cleaned was suspended in a volume of the electrolyte 6 contained within a thermostatic ultrasonic stirring bath 7. The electrolytic current was passed between the electrode wire 3 and a graphite counter electrode 4; in all cases the wire area of the electrode exposed to the electrolyte was determined, in order to calculate the current density of the surface. The flow of the electrolytic current was established using a voltage controlled by a current source (galvanostat) 2, which in turn was driven by means of the voltage waveform controller 11. The electrolytic current passed through the cleaning cell it was usually found in the form of a pulsating alternating current and a waveform of the typical current is shown schematically in Figure 2. The ultrasonic agitation was carried out both continuously and simultaneously with the electrolytic current (referred to as simultaneous electrolysis-ultrasonication) or intermittently and in alternation with periods of electrolysis (referred to as electrolysis-interspersed ultrasonication): the object of these procedures was to determine whether or not one could detect any of the synergistic effects in the case of electrolysis and ultrasound applied simultaneously. The progress of cleaning was followed by periodic removal of the wire sample and visual examination of the surface. Two types of surface cleanup estimates were made: 1. Whether or not the oxide layer has been completely removed from the surface: in this case the only recorded amount was the "period to clean". 2. The fraction of the surface oxide layer that remains in the period; in this case the fraction of the surface covered with the oxide layer was estimated by looking through a millimeter grid and the "% of the remaining oxide layer" was recorded as a function of time. In both cases above, "time" is the total time by which the electrolytic current flows on the surface of the sample. In the experiments involving electrolysis-interspersed ultrasonication, the electrolytic current was interrupted and followed by a period of ultrasonication to immediately remove any softened oxide layer before the visual evaluation of surface cleanliness. Unless stated otherwise, all experiments were conducted with a square wave electrolytic waveform of 1Hz (1 cycle per second), that is, with an anode duty cycle (as defined with reference to FIG. 2) of 0.5. EXAMPLE 1 Thermal Oxide Layer (Aqueous Sodium Chloride) Figure 3 shows the cleaning periods for the removal of oxide from the carbon steel wire with thermal scale in 10% of the aqueous sodium sulfate solution at 65 ° C as a function of pH and current density. Figure 4 shows the cleaning periods for the same system subjected to ultrasonic electrolysis. Figure 5 shows the cleaning periods for the same wire in 10% of the aqueous sodium chloride solution at 65 ° C as a function of frequency and anode duty cycle (the duty cycle shown as a percentage figure). ); the identical cleaning periods were measured by the same system subjected to electrolysis-ultrasound interspersed. When using electrolysis-ultrasound intercalated under neutral conditions (pH7) at 65 ° C, with a current density of 2 amp cm "2 and an anodic service cycle of 95%, the cleaning is completed in approximately twenty seconds. from Figures 3 and 4 that the cleaning period in the sulfate medium is reduced with the increase of the current density and the reduction of the pH, the cleaning periods in pH3 were immeasurably long (> 30 minutes). Figures 3 and 4 also show that there is a synergistic effect between ultrasound and electrolysis, in which the cleaning periods were approximately 30% shorter in the case of simultaneous electrolysis-ultrasonication.

It can be seen from FIG. 5 that the cleaning periods in the chloride medium are effectively independent of the frequency of the electrolytic current but are markedly reduced with the increase in the anodic service cycle. The observation that there are negligible differences in the cleaning periods for the cases of ultrasonic-electrolysis intercalated and simultaneous in neutral chloride implies that there is little or no synergistic effect between ultrasound and electrolysis under these conditions. It was found that making the electrolyte completely anodic (ie, c.d.) resulted in increasing the cleaning period along with significant amounts of anodic chlorine evolution due to electrolysis of the chloride; however, pressing the d.c current (without any medium cycle) gave a marginal improvement over the c.a. of faster pulses with little evolution of chlorine. It was concluded from these findings that: 1. The stage that determines the speed for the removal of the oxide layer was the anodic dissolution of the implicit metal. 2. That the competing reaction (evolution of anodic chlorine) was discouraged by the electrolysis of c.a. or c.d. of pulse possibly by means of a depassivation of the metallic surface during the zero current or the cathodic part of the cycle. (In the present, "passivation" means the coverage of the metal surface with an oxide layer, developed electrolytically resistant to dissolution.)) The ultrasound alone has no effect. ) The removal of the oxide layer, which leaves a «Metal surface, clean satin texture, it is possible using electrolysis of c.d. Anodic and ultrasound combined in aqueous sodium sulfate solutions at pH < 3.) The removal of the oxide layer, which leaves a metal surface, clean of satin texture, is possible using electrolysis of c.d. Anodic and ultrasound combined in aqueous sodium chloride solutions at pH 7 but with significant evolution of anodic chlorine. ) The pulsation of the electrolytic current provides a significantly faster cleaning than the method of c.d. and greatly reduces the amount of chlorine incorporated in aqueous sodium chloride. ) Electrolysis alone softens the oxide layer but does not remove it. ) Rust detachment appears to occur through the anodic dissolution of a thin layer of the implicit metal. EXAMPLE 2 Lubricant extracted from graphite (aqueous sodium sulfate) The following results were obtained from the carbon steel wire extracted from graphite in 10% aqueous sodium sulfate solution at 50 ° C. Figure 6 shows the percentage of incrustation (graphite) that remains on the surface of the wire as a function of time, for current densities of 0.5 and 2.5 amps cm "2, with and without simultaneous ultrasound Figure 7 shows the period for cleaning as a function of the current density at pH 0.1 and 7, and Figure 8 shows the influence of the anodic service cycle on the cleaning curve that depends on the period at pH 7 with a current density of 1 amp cm "2. Under neutral conditions (pH 7) at 50 ° C, with a current density of 2 amp cm "2 and an anodic service cycle of 95%, cleaning was completed in approximately ten seconds. Forms of cleaning curves are different for the cases of electrolysis-simultaneous ultrasonication and electrolysis-ultrasonication interspersed, there is no significant influence of simultaneous ultrasonication in the period for cleaning (see also figure 7). 7 reveals that the removal of graphite is achieved more quickly at lower pH but that the influence of pH is reduced at higher current densities. Figure 8 shows that the cleaning speeds increase markedly with the increase in the anodic service cycle; however, it was also found that making the electrolyte completely anodic, ie, c.d., resulted in large increases in the cleaning period along with significant amounts of anodic oxide evolution due to electrolysis in water. The additional results of the descaling of the graphite layer are illustrated in Figures 9 to 14. It was concluded from the results described above that: 1. The stage that determines the speed for the removal of graphite was the anodic dissolution of the implicit metal . 2. That the competing reaction (evolution of anodic oxygen) is discouraged by the electrolysis of c.a. of pulse, possibly by a depassivation of the metal surface during the half cathode cycle.eNG 3) The ultrasound alone, has no effect. 4) The electrolysis of c.d. Anodic and ultrasound combined in solutions of aqueous sodium chloride resulted in the partial removal of the graphite, leaving a metal surface highly pitted, with significant evolution of the concomitant chlorine.

) The electrolysis of c.d. Anodic and ultrasound combined in solutions of aqueous sodium sulfate resulted in the removal of the graphite, leaving a clean metallic surface with a satin texture, with significant evolution of the concomitant oxygen. 6) The pulsation of the electrolytic current in aqueous sodium sulphate solutions, with alternating cathodic and anodic half cycles, provide a significantly faster cleaning than the c.d. without any significant evolution of concomitant oxygen. 7) Electrolysis alone softens the graphite layer but does not remove it. 8) The detachment of the graphite seems to occur by the anodic dissolution of a thin layer of the implicit metal. Example 3 Thermal oxide layer (tripolyphosphate or sodium) A 10% sodium tripolyphosphate bath adjusted to pH 7 and raised to 60 ° C was established. The current density for each sample was 1.6 Acm "2, which represents 1 lh of exposed metal surface for descaling.The electrical properties varied methodically, the anodic service cycle was adjusted from 5 to 95% and the frequency The pulse rate varied from 0.3 to 1000 Hz. The peeling periods obtained were compiled and installed in a three-dimensional graph shown in Figure 15. Optimal conditions appear to be obtained with an anode duty cycle of 45-75% and frequencies of 0.3 to 100 Hz. For this particular set of conditions, the fastest cleaning periods are achieved in an anodic service cycle of 75% and in the lower frequency of 0.3 to 1 Hz. Figure 16 shows a three-dimensional plane of the results compiled from a 10% of the bath of sodium tripolyphosphate raised to 60 ° C and the potentiostado was established in an anodic service cycle of 95% with a frequency of 1 Hz. The acidity of the solution The ion varied from pH 3 to 12 and the current density was adjusted systematically from 0.5 to 2.5 Acm "2. Orthophosphoric acid was used to adjust the pH. The lower peeling periods were clearly obtained at much higher current densities and at a lower pH value of 3. At pH 2, where the solution is very alkaline, dehulling becomes slower and inefficient with cleaning periods that reach values of several minutes as the current density decreases below 2 Acm. "2 Under neutral conditions (pH 7), peeling periods are acceptably rapid, only a few seconds slower than under more acidic pH conditions 3. Figure 17 shows a three-dimensional representation of the results of the peeling period against the temperature of the solution and the concentration of tripolyphosphate.The concentration of tripolyphosphate varied from 1-15% and the temperature of the bath was adjusted to 20-60 °. C. The pH value was kept constant at 7 and the anodic service cycle was fixed at 95% with a frequency of 1 Hz. Figure 18 summarizes vi The results obtained in the descaling periods using sodium tripolyphosphate with the variation of the thickness of the thermal oxide layer. An oven was allowed to reach the temperature of 900 ° C before being filled with argon gas. The samples were spread on a ceramic capsule, separated from each other, and subsequently left in the oven for 15 minutes to allow it to reach 900 ° C. Subsequently, the furnace was completely flooded with a fast air stream for a period of 20 seconds and the samples were allowed to oxidize for 1-60 minutes. Once sealed for the required period of time, the capsule was removed from the oven and placed in a ceramic fiber mesh to be cooled by air at room temperature. The samples were allowed to oxidize 1, 5, 10, 15, 30, 45, and 60 minutes, to ensure a considerable increase in the thickness obtained from the layer. Using 10% of the electrolyte bath of sodium tripolyphosphate adjusted to pH 7 with orthophosphoric acid, the cleaning solution was raised to 60 ° C and exposed to ultrasound for a minimum period of 15 minutes before experimentation. The electrical properties were set at IA and the pulse of the current was fixed at 1 Hz. The anodic service cycle varied between 5-95% and proved its efficiency for the descaling of the wire of various thicknesses of the oxide. A general trend is evident with the peeling periods at their lower values when 5% of the anodic service cycle is used, regardless of the thickness of the layer. The samples oxidized in air for a period of 1 to 15 minutes show very similar cleaning period requirements. As the oxidation periods of the samples increase from 3 to 60 minutes, a significant increase in the cleaning periods is suddenly observed. The optimum descaling conditions for the fastest descaling of the metal samples were obtained in high electrolyte concentrations (10-15%) and high temperatures of 50-60 ° C

Claims (17)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. A process for dehusking the surface of a metal body, in which said metal body is subjected to electrolysis in a bath of an electrolyte and also to ultrasonic agitation, characterized in that said electrolysis comprises the application of an electric pulse potential to said metallic body while said metal body is present in said bath, and said ultrasonic agitation is carried out while said body is still wet.
2. 2. A process according to claim 1, characterized in that said electrolysis and said ultrasonic agitation are executed simultaneously.
3. 3. A process according to claim 1, characterized in that said electrolysis is followed by a separate ultrasonic agitation step.
4. 4. A process according to any of claims 1 to 3, characterized in that said electrolyte bath is at a substantially neutral pH.
5. 5. A process according to any of claims 1 to 4, characterized in that said metal is steel.
6. 6. A process according to any of claims 1 to 5, characterized in that said body comprises a continuously formed article. A process according to any of claims 1 to 6, characterized in that said electric pulse potential has a current density in the range of 0.1 to 10 amp cm "2. A process according to claim 7, characterized in that said density Current is in the range of 0.5 to 5 amp cm "2. 9. A process according to any of claims 1 to 8, characterized in that said bath of the electrolyte is substantially aggressive. 10. A process according to claim 9, characterized in that said aggressive bath comprises a solution of an alkali metal or ammonium chloride, nitrate or sulfate. 11. A process according to claim 10, characterized in that said alkali metal is sodium. 12. A process according to any of claims 9 to 11, characterized in that said electric potential is applied predominantly in anodic pulses. 13. A process according to claim 12, characterized in that said electric potential has an anode duty cycle of at least 67%. 14. A process according to claim 13, characterized in that said service cycle is at least 75%. 15. A process according to any of claims 1 to 8, characterized in that said electrolyte bath is substantially non-aggressive. 16. A process according to claim 15, characterized in that said bath comprises a solution of an alkali metal or ammonium tripolyphosphate. 1
7. 7. A process according to claim 16, characterized in that said alkali metal is sodium.