JP2010090426A - Method for pickling titanium sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for pickling a titanium sheet in which, to a pickling tank with a mixed solution of nitric acid and hydrofluoric acid as a pickling liquid, a titanium sheet is passed with both the sides thereof as the upper and lower sides, respectively, and is pickled, the upper and lower sides of the titanium sheet can be pickled almost at a uniform speed. <P>SOLUTION: When, to a pickling tank 3 with a mixed solution of nitric acid and hydrofluoric acid as a pickling liquid 2, a titanium sheet 1 is passed with both the sides thereof as the upper and lower sides 1a, 1b respectively, the pickling liquid 2 is fed from the upper and lower parts of the titanium sheet 1 during the sheet passing, the laminar flows 4, 5 of the pickling liquid 2 are formed on both the upper and lower sides 1a, 1b of the titanium sheet, respectively, and a pickling speed is uniformized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for pickling a titanium plate, and to a method for uniformly pickling both upper and lower surfaces (also referred to as front and back surfaces) of a titanium plate.

  In general, a titanium plate such as titanium or a titanium alloy is manufactured by performing hot rolling or further cold rolling as a titanium strip. Among these, in particular, titanium plates that require an appearance (aesthetics) for building materials are rarely shipped as rolled up, and are subjected to surface finishing such as descaling by annealing or pickling.

  That is, the rolled titanium plate is annealed in the atmosphere for the purpose of removing strain generated by the hot rolling and / or cold rolling and adjusting the structure to obtain desired mechanical properties. The annealed titanium plate is pickled to remove the strong oxide scale and oxygen-enriched layer formed on the surface by frictional heat during hot rolling and cutting, or annealing. Specifically, after pre-treatment such as salt bath and shot blasting to remove these scales to some extent or make them easy to remove, a mixed solution of nitric acid and hydrofluoric acid (hydrofluoric acid, hydrofluoric acid) And pickling solution containing nitric hydrofluoric acid or hydrofluoric acid).

  Such pickling finish has a beautiful appearance that can reduce the surface gloss of the titanium plate to a relatively low level and suppress the reflection of light. More versatile than vacuum annealing finish.

  When such a pickling finish titanium plate is industrially obtained, a continuous annealing pickling line is generally used. In this line, an atmospheric annealing furnace, a salt bath and a shot blast, and a pickling tank are arranged in series in the order of description. By passing a titanium plate (strip) through these devices in sequence, cold rolled pure titanium for building materials The annealing and descaling of the plate can be performed continuously.

  Soaking in a salt bath and shot blasting are performed to facilitate removal of the scale by pickling. For example, when the titanium plate after atmospheric annealing is immersed in a high-temperature salt bath of about 500 ° C. mainly composed of sodium hydroxide and sodium nitrate, a part of the scale is dissolved and cracks are caused by thermal shock. it can. This is also the case with shot blasting, where a part of the scale is mechanically peeled off, and the scale is cracked by the impact of the shot.

  After that, when both sides of the titanium plate are made to be upper and lower surfaces, and pickling is carried out in the pickling solution of nitric hydrofluoric acid (in the pickling tank), the pickling solution penetrates through the cracks to the metal, The interface between the scale and the metal is melted. As a result, the scale can be completely removed and a metallic luster can be obtained.

  Here, the upper surface of the titanium plate is a surface (hereinafter also referred to as a surface) facing the upper surface of the pickling tank in the case of passing plates with both surfaces of the titanium plate as upper and lower surfaces (upper surface and lower surface), respectively. Further, the lower surface of the titanium plate is a surface (hereinafter also referred to as a back surface) facing the bottom surface of the pickling tank in the case of passing plates with both surfaces of the titanium plate as upper and lower surfaces (upper surface and lower surface), respectively. Therefore, passing through both surfaces of the titanium plate as the upper and lower surfaces and pickling means that the titanium plate is placed in a substantially horizontal state and passed through the pickling tank.

  In such a continuous annealing pickling line, there has been a general problem of uniform glossiness between titanium plates or within the same surface of the same titanium plate, and various methods for this purpose have also been proposed. Has been.

  For example, Patent Document 1 proposes a technique for the purpose of preventing brown colored spots called so-called acid burn over the entire or local surface of a titanium plate that sometimes occurs in the pickling. For this purpose, in the continuous annealing pickling line or the like, in the pickling method for the titanium plate, the pickling solution on the surface of the titanium plate is squeezed with a ringer roll and then washed with water spray. It is described that the pickling solution in the region from entering the solution to flowing out flows in a direction perpendicular to the running direction of the titanium plate.

  Patent Document 2 proposes a technique aiming at uniform glossiness between titanium plates or in the same titanium plate in the pickling. For this purpose, in the continuous annealing pickling line or the like, when performing the pickling finish of the titanium plate or the titanium alloy plate, the pickling tank having a dipping roll is passed through a plurality of times, and the titanium plate or the titanium alloy It is described that the operation is performed so that the plate is properly reversed and passes through the pickling tank.

Furthermore, in Patent Document 3, the pickling solution locally accumulates on the surface of the titanium plate, the titanium ion concentration in that portion increases, and a difference in pickling speed occurs between adjacent plate surface localities. Techniques aimed at preventing the occurrence of uneven washing have been proposed. For this purpose, it is described that the pickling solution is sprayed onto the surface of the titanium strip in the continuous annealing pickling line or the like. More specifically, from the both sides of the titanium plate to the titanium plate in the passing plate, from the downstream side of the titanium plate to the upstream side of the titanium plate (in the direction opposite to the passing direction of the titanium plate). ), Supplying the pickling solution from a plurality of locations extending from the upstream side to the downstream side of the titanium plate.
JP-A-8-291397 JP 2000-357881 A Japanese Unexamined Patent Publication No. 63-227792

  In the above-described continuous annealing and pickling line for titanium plates, the present invention performs pickling by letting both sides of the titanium plate pass through the pickling solution of nitric hydrofluoric acid (in a pickling tank) with the upper and lower surfaces of the titanium plate as upper and lower surfaces, respectively. In addition, it has been found that there are many problems that the pickling speed is different between the upper and lower surfaces of the same titanium plate. This difference in pickling speed is a phenomenon in which the pickling speed on the upper surface side of the same titanium plate is slow, and the pickling speed on one lower surface side is fast.

  This difference in pickling speed means that the amount of titanium dissolved on the surface is different between the upper and lower surfaces of the same titanium plate. Therefore, when pickling is performed under conditions suitable for the upper surface side (front surface side) of the titanium plate having a slow pickling speed in actual operation, the lower surface side (back surface side) of the titanium plate becomes peracid pickling. That is, there is a problem that the lower surface side of the titanium plate is melted up to the base material titanium which does not need to be dissolved, and the yield of the titanium plate is lowered. On the other hand, when pickling is performed under conditions suitable for the lower surface side (back surface side) of the titanium plate having a high pickling speed in actual operation, the upper surface side of the titanium plate having the slow pickling speed (surface) However, there is still a problem of insufficient pickling.

  Therefore, in the continuous annealing pickling line of the titanium plate, there is a problem that the operation cannot be performed without sacrificing the yield of the titanium plate in order to guarantee the pickling of the upper and lower surfaces of the same titanium plate. This problem cannot be reliably solved even by using the above-described conventional technique.

  Accordingly, an object of the present invention is to provide a pickling bath in which a mixed solution of nitric acid and hydrofluoric acid is used as a pickling solution, and in which pickling is performed by passing both surfaces of the titanium plate as upper and lower surfaces, respectively. The present invention is to provide a pickling method for a titanium plate in which the pickling speed on the upper and lower surfaces of the plate is made uniform and the upper and lower surfaces of the titanium plate are pickled almost uniformly.

  As a result of intensive studies, the inventors have found that the difference in the pickling speed between the upper surface and the lower surface of the titanium plate comes from the difference in the chemical reaction at each site, leading to the completion of the present invention. The gist of the pickling method for the titanium plate of the present invention to achieve the above-described object is to pass both sides of the titanium plate as upper and lower surfaces with respect to the pickling solution containing nitric acid and hydrofluoric acid. In the pickling method, the pickling solution is supplied from both above and below the titanium plate in the plate, and the pickling solution is a laminar flow in the vicinity of the surface of the titanium plate, The laminar flow of the pickling solution that moves in the direction opposite to the moving direction is formed on the upper and lower surfaces of the titanium plate, respectively, so that the pickling speed of the upper and lower surfaces of the titanium plate is made uniform. .

  The term “laminar flow” = “laminar flow” of the pickling solution in the present invention is the same as the definition of so-called “laminar flow” in the normal fluid field. That is, it is a laminar flow having a certain thickness near the surface of the titanium plate with respect to the pickling solution that is stationary or turbulent around the titanium plate. The line is a flow substantially parallel to the titanium plate surface. In the present invention, the laminar flow is moved in the direction opposite to the moving direction of the titanium plate, and the laminar flow is formed on both upper and lower surfaces of the titanium plate.

  Here, when supplying the pickling solution to the upper and lower surfaces of the titanium plate in the through plate, respectively, from the downstream side to the upstream side of the titanium plate and over the width direction of the titanium plate. It is preferable to supply each pickling solution.

  Moreover, it is preferable that the pickling method of the said titanium plate is a pickling method applied to the pickling tank arrange | positioned in the back | latter stage of the atmospheric annealing furnace in a continuous annealing pickling line, a salt bath, and shot blasting.

  In the present invention, laminar flows of the hydrofluoric acid pickling solution are respectively formed on the upper and lower surfaces of the titanium plate so that the pickling speeds on the upper and lower surfaces of the titanium plate are made uniform.

  First, if a laminar flow of the fluoric acid pickling solution is formed on the upper surface side of the titanium plate, HNO3 (nitric acid) is consumed in the vicinity of the upper surface side of the titanium plate and the concentration is reduced as described later. ) Can be renewed and replenished with a laminar flow of fresh hydrofluoric acid pickling solution. For this reason, the relatively slow pickling speed on the upper surface side of the titanium plate can be increased.

  On the other hand, if a laminar flow of the hydrofluoric acid pickling solution is formed on the lower surface side of the titanium plate, in the vicinity of the surface on the lower surface side of the titanium plate, as described later, The trivalent Ti ion complex that causes the washing speed to be increased can be removed (diffused) from the vicinity of the lower surface of the titanium plate. For this reason, the increase in the density | concentration of Ti ion complex in pickling liquid can be suppressed, and the pickling speed | rate on the lower surface side of the said titanium plate can be made slow relatively.

  Then, the laminar flows on the upper surface side and the lower surface side of these titanium plates are formed by supplying the pickling solution independently from above and below the titanium plates, thereby ensuring both laminar flows. be able to.

  As a result, the pickling speeds on the upper and lower surfaces of the titanium plate can be made uniform.

  Embodiments of the present invention will be described in detail below. FIG. 1 is a front view of a pickling tank 3 in which both surfaces of a titanium plate 1 are passed as upper and lower surfaces 1a and 1b and pickled, and FIG. 2 is a plan view of FIG.

Pickling method:
1 and 2, the titanium plate 1 enters the pickling tank 3 from the right side of each figure, and is passed from the right side to the left side of each figure as indicated by the arrow, and the pickling tank 3 is passed from the left side of each figure. Get out. Reference numeral 2 denotes a pickling solution which is a mixed solution of nitric acid and hydrofluoric acid, 2a denotes a liquid surface of the pickling solution 2, and 9 and 10 denote feed rollers for the titanium plate 1.

  In FIGS. 1 and 2, not all lines are shown, but the pickling tank 3 in a normal continuous annealing pickling line is shown. That is, as described above, the titanium plate 1 entering the pickling tank 3 from the right side of each figure has been previously subjected to an atmospheric annealing furnace, a salt bath, and shot blasting in advance. And although not shown in figure, the titanium plate 1 which left the pickling tank 3 from the left side of each figure is normally subjected to post-treatment such as draining or rinsing to finish pickling.

  In such pickling of the titanium plate, a sufficient amount of pickling can be obtained without stirring the pickling solution 2 as described above. However, even if stirring is not performed or stirring is performed for the purpose of the prior art, the pickling speed and the pickling amount are inevitably in the upper surface (front surface) 1a and the lower surface (back surface) 1b of the titanium plate 1. Is different. This is because, as described above, the chemical reactions governed by the upper surface 1a and the lower surface 1b of the titanium plate are different.

Pickling mechanism:
This pickling mechanism will be described below. The inventors conducted a simulation test, and examined and observed in detail the reaction near the surface of the titanium plate 1 during pickling. Then, the present inventors have found that the pickling solution on the surface of the upper surface 1a of the titanium plate 1 is brown and the pickling solution on the surface of the lower surface 1b is green and the colors of the pickling solutions are clearly different from each other. It was found that the brown color of this pickling solution is caused by a large amount of NO2 originally exhibiting a brown color, and the green color of this pickling solution is caused by a large amount of trivalent Ti ions that originally exhibit a green color.

  Accordingly, the present inventors have found that the upper surface 1a and the lower surface 1b of the titanium plate 1 have a common chemical reaction, but the dominant (dominant) chemical reaction is different. That is, the chemical reaction shown below occurs in the vicinity of the titanium plate 1 during pickling, the reaction formula (1) on the upper surface 1a side, the NO2 production reaction of (2), and the reaction formula (3) on the lower surface 1b side. It is inferred that the reaction involving the trivalent Ti ion complex (4) occurs preferentially.

Chemical reaction on the upper surface 1a side of the titanium plate:
Ti + 8HNO3 → Ti (NO3) 4 + 4NO2 + 4H2 O (1)
Ti + 4HNO3 → TiO2 + 2NO2 + 2H2 O (2)
Chemical reaction on the titanium plate lower surface 1b side:
2Ti + 12HF → 3H2 + 2H3 [TiF6] (3)
2H3 [TiF6] + 2TiO2 + 6H ⁺ → 2H2 [TiF6] + 2Ti3 ⁺ + H2 O (4)

  Of course, the chemical reaction of the reaction formulas (1) and (2) also occurs on the lower surface 1 b side of the titanium plate 1. However, in addition to the continuous annealing pickling line, pickling of the titanium plate is usually performed by passing both sides of the titanium plate 1 as upper and lower surfaces 1a and 1b (titanium plate 1 substantially horizontally) and pickling. . For this reason, the upper side of the upper surface 1a of the titanium plate 1 is opened as shown in FIG. 1, and the gas NO2 generated in the reaction equations (1) and (2) is sequentially diffused upward. As a result, the NO2 production reaction of the reaction formulas (1) and (2) is further promoted.

  On the other hand, the upper side of the lower surface 1b of the titanium plate 1 is closed by the titanium plate 1 itself as shown in FIG. 1, and the gas NO2 generated in the reaction equations (1) and (2) is diffused. It becomes difficult. For this reason, since the gas NO2 stays in the vicinity of the surface of the lower surface 1b of the titanium plate 1, the NO2 generation reaction of the reaction formulas (1) and (2) is not promoted.

  On the upper surface 1a side of the titanium plate 1, the consumption of HNO3, that is, the consumption of nitric acid increases due to the promotion of the NO2 production reaction of the reaction formulas (1) and (2). As a result, the concentration of nitric acid in the pickling solution 2 in the vicinity of the surface on the upper surface 1a side is lowered. As a result of investigation by the present inventors, the concentration of HNO3 on the upper surface 1a side of the titanium plate 1 during pickling is compared with the concentration of HNO3 in the original pickling solution (bulk solution) when forced stirring is not performed. And it has fallen to about 86%. On the other hand, the concentration of HNO3 on the lower surface 1b side of the titanium plate 1 during pickling is almost the same as the HNO3 concentration of the original pickling solution (bulk solution) even when forced stirring is not performed.

  Further, while the Ti dissolution reaction of the reaction formula (1), the reaction according to the reaction formula (2), which is an oxidation reaction of Ti that does not dissolve titanium, is active in the vicinity of the upper surface 1a side surface. become. Therefore, due to the synergistic effect of these reaction formulas (1) and (2), the pickling rate on the upper surface 1a side of the titanium plate 1 decreases with time.

  On the other hand, on the lower surface 1b side of the titanium plate 1, as described above, the NO2 production reaction of the reaction formulas (1) and (2) is not accelerated, and the Ti dissolution reaction by HF of the reaction formula (3) and the reaction Dissolution of the oxide by the trivalent Ti ion complex of formula (4) is promoted. And the amount of this Ti ion complex increases, the dissolution of the oxide by this is accelerated | stimulated, and the pickling speed | rate by the side of the lower surface 1b of the titanium plate 1 increases with progress of time.

  As described above, as a result of different chemical reactions governing between the upper surface 1a and the lower surface 1b of the titanium plate 1, the pickling speed on the lower surface 1b side of the titanium plate 1 is significantly faster than that on the upper surface 1a side. As a result of the investigation by the present inventors, the pickling speed is about three times the maximum on the lower surface 1b side of the titanium plate 1 on the upper surface 1a side. Moreover, this is a unique phenomenon that occurs when both surfaces of the titanium plate 1 are passed as upper and lower surfaces 1a and 1b, respectively, and pickled using hydrofluoric acid.

  Therefore, it is a problem that cannot occur when the position and orientation of the titanium plate 1 during pickling are different, when pickling with an acid other than hydrofluoric acid, or pickling a steel plate or stainless steel.

Laminar flow of pickling solution:
In contrast to such a phenomenon specific to pickling using fluorinated nitric acid of the titanium plate 1, in the present invention, acid pickling tanks 3 are acidized on both sides of the upper surface 1a and the lower surface 1b of the titanium plate 1 in the passing plate. Wash solution 2 is forcibly supplied. Specifically, as shown in FIGS. 1 and 2, the pickling solution 2 is forcibly applied by the nozzle 7 on the upper surface 1 a side of the titanium plate 1 and the nozzles 6 a to 6 f on the lower surface 1 b side. Supply.

  Thus, the laminar flows 4 and 5 of the pickling solution 2 in the vicinity of the surface of the titanium plate 1 are opposite to the moving direction of the titanium plate 1 (left direction in FIGS. 1 and 2) (FIGS. 1 and 2). The laminar flows 4 and 5 of the pickling solution 2 moving to the right side of the titanium plate 1 are formed on the upper and lower surfaces of the upper surface 1a and the lower surface 1b of the titanium plate 1, respectively. Homogenize.

  The laminar flows 4 and 5 of the pickling solution 2 are laminar flows of the pickling solution 2 near the surface of the upper surface 1a and the lower surface 1b of the titanium plate 1, and the streamlines of the upper surface 1a and the lower surface 1b The flow is substantially parallel to the surface (of 1a and lower surface 1b). The presence of these laminar flows 4 and 5 is confirmed by actual visual inspection, or if reproduction is impossible, by reproduction (simulation) test using water instead of pickling solution, or by fluid calculation or simulation test described later. it can. Accordingly, the laminar flows 4 and 5 should be clearly distinguished from the pickling solution or the pickling solution flow that is stationary or turbulent in the pickling tank 3 around the titanium plate 1. Is possible.

Effects of laminar flow:
On the upper surface 1a side of the titanium plate 1, fresh pickling solution 2 is supplied by the laminar flow 4, and the consumption increases due to the promotion of the NO2 production reaction of the reaction formulas (1) and (2), and the concentration decreases. Nitric acid is replenished to maintain the nitric acid concentration within a certain range. Thereby, the pickling speed on the upper surface 1a side of the titanium plate 1 can be increased. In other words, a decrease in the pickling rate due to the reaction can be suppressed.

  On the other hand, on the lower surface 1b side of the titanium plate 1, the trivalent Ti ion complex is diffused from the lower surface 1b side by the laminar flow 5 of the pickling solution 2 that is forcibly supplied, and the increase in the amount of Ti ion complex is increased. It is suppressed. For this reason, the dissolution reaction of the oxide by the trivalent Ti ion complex of the reaction formula (4) and the dissolution reaction of Ti by the HF of the reaction formula (3) are suppressed. As a result, the lower surface 1b of the titanium plate 1 is suppressed. The pickling speed on the side becomes slow. In other words, an increase in pickling speed due to the reaction can be suppressed.

  What is important here is that when a laminar flow is not formed on the titanium plate, the pickling speed decreases on the upper surface 1a and the pickling speed increases on the lower surface 1b. For example, there is a difference in pickling speed between the upper surface 1a and the lower surface 1b. In the present embodiment, the nozzle 7 and the nozzles 6a to 6f are respectively provided above and below the titanium plate 1, thereby forming a stable laminar flow on both the upper surface 1a and the lower surface 1b of the titanium plate. The difference in the pickling speed of 1b is reliably suppressed.

  In order to exert such an effect, the supply amount of the pickling liquid 2 that is forcibly supplied to the upper surface 1a side of the titanium plate 1 in the passage plate is set on the upper surface side of the titanium plate 1 in the passage plate. It is preferable that the nitric acid concentration in the pickling solution 2 be an amount sufficient to be within the range of the nitric acid concentration in the pickling solution 2 on the lower surface 1 b side of the titanium plate 1. The supply amount of the pickling solution 2 is determined according to whether the amount is proper or not, and the pickled titanium is obtained by equalizing the pickling speeds on the upper and lower surfaces of the titanium plate 1 without directly measuring the amount. It can be estimated by the yield improving effect of the plate 1.

  Furthermore, the supply amount of the pickling solution 2 forcibly supplied to the lower surface 1b side of the titanium plate 1 in the passage plate increases the concentration of the Ti ion complex in the pickling solution on the lower surface 1b side of the titanium plate 1. The amount is preferably sufficient to suppress. Note that the amount of pickling solution 2 supplied is appropriate, whether the amount is appropriate or not, as in the case of the amount of pickling solution 2 supplied to the upper surface 1a of the titanium plate 1, without directly measuring the amount. It is possible to estimate by the effect of improving the yield of the pickled titanium plate 1 by making the pickling speeds of the upper and lower surfaces of the titanium plate 1 uniform.

Laminar flow velocity:
Here, the flow rates of the laminar flows 4 and 5 of the pickling solution 2 naturally differ depending on the pickling conditions, but assuming that the pickling bath 3 is in a normal continuous annealing pickling line, the flow rate is 10 cm / sec or more. It is preferable that If the flow velocity of the laminar flows 4 and 5 is too small, naturally, the influence of traveling of the titanium plate 1 on the titanium plate 1 that normally moves at a plate passing speed (traveling speed) of about 5 to 20 cm / sec. As a result, even if the laminar flows 4 and 5 are obtained instead of the laminar flows 4 and 5, the above-described laminar flows 4 and 5 are weakened.

  Due to the synergistic effect of the laminar flows 4 and 5, the pickling speed of the upper surface 1a and the lower surface 1b of the titanium plate 1 can be made uniform.

Laminar flow formation method:
In order to achieve the synergistic effect of the laminar flows 4 and 5 as described above, the flow of the laminar flows 4 and 5 is made to flow with respect to the moving direction of the titanium plate 1 (left direction in FIGS. 1 and 2) as in the present invention. Therefore, it is necessary to form it so as to move in the opposite direction (right direction in FIGS. 1 and 2). When the laminar flows 4 and 5 are formed so as to move in the same direction (left direction in FIGS. 1 and 2) as the movement direction of the titanium plate 1 (left direction in FIGS. 1 and 2), 4, 5 itself cannot be formed. That is, the relative speed difference between the flow rate of the pickling solution to be supplied and the moving speed of the titanium plate 1 is not small, and it is relatively stationary with respect to the moving titanium plate 1. The synergistic effect of the laminar flows 4 and 5 cannot be exhibited.

  However, the flow direction of the laminar flows 4 and 5 does not necessarily have to be parallel to the movement direction of the titanium plate 1 in a strict sense as shown in FIGS. Further, the streamlines do not need to be in parallel with the surface of the titanium plate 1 (the upper surface 1a and the lower surface 1b) in a strict sense. As long as the synergistic effect of the laminar flows 4 and 5 can be exhibited, the flow directions of the laminar flows 4 and 5 may be angled with respect to the moving direction of the titanium plate 1. The lines may also be angled with respect to the surface of the titanium plate 1 (upper surface 1a and lower surface 1b). However, as described later, even if the pickling solution is caused to flow in a direction perpendicular to the traveling direction of the titanium plate as described in Patent Document 1, it is opposite to the moving direction of the titanium plate 1 as in the present invention. Since the laminar flows 4 and 5 do not move in the direction, the angle of the laminar flow 4 and 5 does not include a large angle such as a direction perpendicular to the traveling direction of the titanium plate.

Pickling solution supply method:
Further, depending on the supply amount and the supply method of the pickling solution 2, the laminar flows 4 and 5 may not be obtained, or even if the laminar flows 4 and 5 are obtained, the synergistic effect of the laminar flows 4 and 5 may be weakened. There is also. For this reason, in order to surely form the laminar flows 4 and 5 of the pickling solution 2 on the upper and lower surfaces of the moving titanium plate 1, the upper and lower surfaces of the upper surface 1a and the lower surface 1b of the titanium plate 1 in the passage plate are used. The pickling solution can be forcibly supplied from the downstream side of the titanium plate 1 toward the upstream side and in the width direction of the titanium plate 1 by a pickling solution jet nozzle or the like. preferable.

  1 and 2 show specific preferred embodiments for this purpose. That is, in FIGS. 1 and 2, the upper surface 1 a of the titanium plate 1 is provided with a pickling solution jet nozzle 7 having a vertical pickling solution supply pipe 8 and a flat nozzle header. Pickling solution is supplied from the downstream side (left side in FIGS. 1 and 2) toward the upstream side (right side in FIGS. 1 and 2). Further, the nozzle 7 has a number of nozzle ports (discharge ports) 7a that open from the downstream side to the upstream side of the titanium plate 1 across the width direction of the titanium plate 1 at intervals. The pickling solution is supplied from these nozzle openings along the width direction of the titanium plate 1.

  By setting it as such an aspect, the pickling liquid 2 can be respectively supplied with respect to the upper surface 1a side of the titanium plate 1 from the downstream side toward the upstream side and over the width direction of the titanium plate 1. A sufficient laminar flow 4 can be formed over the entire width direction of the upper surface 1 a of the titanium plate 1. 1 and 2, the nozzle 7 is provided only at one location on the downstream side of the titanium plate 1, but a plurality of locations may be provided from the downstream side to the upstream side of the titanium plate 1 as necessary. .

  On the other hand, with respect to the lower surface 1b side of the titanium plate 1, the pickling solution jet nozzles 6a to 6f are respectively provided on the downstream side of the titanium plate 1 (the left side in FIGS. 1 and 2). ) Toward the upstream side (right side in FIGS. 1 and 2), the pickling solution 2 is supplied from a plurality of locations (illustrated at three locations on one side) extending from the upstream side to the downstream side of the titanium plate 1. The nozzles 6a, 6b, 6c and the nozzles 6d, 6e, 6f attached to both sides of the pickling tank 3 are spaced from the downstream side (left side in FIGS. 1 and 2) to the upstream side (FIG. 1). The pickling liquid 2 is opened toward the lower surface 1b side of the titanium plate 1 and toward the right side of the titanium plate 1.

  By setting it as such an aspect, the pickling liquid 2 can be supplied to the lower surface 1b side of the titanium plate 1 from the downstream side to the upstream side and over the width direction of the titanium plate 1, respectively. Stream 5 can be formed. 1 and 2, the number of nozzles 6 a to 6 f is selected as appropriate, and may be one on each side of the titanium plate 1 depending on conditions. Furthermore, the upper surface 1a side of the titanium plate 1 may be configured as a nozzle such as the lower surface 1b, and conversely, the lower surface 1b side of the titanium plate 1 may be configured as a nozzle such as the upper surface 1a. .

  On the other hand, when the titanium plate 1 is stationary in the pickling solution 2 or the passing speed of the titanium plate 1 is extremely slow, the titanium plate 1 can be used without using such a pickling solution jet nozzle. The laminar flows 4 and 5 of the pickling solution 2 can be formed by merely mechanically stirring the pickling solutions on the upper and lower surfaces 1a and 1b, respectively, with a rotary blade or a stirrer. In the case of a simulated pickling test in which the titanium plate 1 is stationary in the pickling solution 2 as in the examples described later, the upper and lower surfaces 1a and 1b of the titanium plate 1 are simply agitated. The formation of each laminar flow of the pickling solution 2 can be confirmed.

  However, the plate passing speed (traveling speed) in the pickling tank 3 in the actual continuous annealing pickling line is simply stirred as described above for the titanium plate 1 moving at about 5 to 20 cm / sec. Then, it is difficult to form the laminar flows 4 and 5 of the pickling solution 2 on the upper and lower surfaces of the upper surface 1a and the lower surface 1b of the titanium plate 1, respectively. By simply stirring as described above, it is difficult to form laminar flows 4 and 5 whose streamlines are substantially parallel to the surface of the titanium plate 1. Further, laminar flows 4 and 5 that move in the opposite direction to the moving direction of the titanium plate 1 over the width direction of the titanium plate 1 are effectively formed on both the upper and lower surfaces of the titanium plate 1, respectively. It is also difficult.

Target titanium plate:
In the present invention, the pickled titanium plate 1 may be pure titanium or a titanium alloy. That is, the titanium plate to be pickled in the present invention includes pure titanium and titanium alloys.

Relationship between the prior art and the laminar flow of the present invention:
The reason why the same effects as the present invention cannot be obtained by the pickling solution supply and stirring methods of the prior art will be described below.

  First, in the prior art including the above-mentioned patent documents, the present inventors have not been able to find out what disclosed the problem that the pickling speed is different between the upper and lower surfaces of the same titanium plate, which is the problem of the present invention. . The reason why this problem and countermeasures are not well known so far is presumed that the actual pickling operation itself can be carried out without any problem if the decrease in the yield of the titanium plate is inevitably or naturally approved.

  In the prior art, each purpose, the uniformity of gloss between titanium plates or within the same titanium plate surface, and the prevention of pickling unevenness caused by the difference in pickling speed between adjacent plate surface localities can be achieved. It may be. However, the prior art does not intend this problem at all, and cannot solve this problem as a result, as will be described later.

  The same applies to the steel plate pickling method in which the pickling solution is jetted from a nozzle or the like and sprayed onto the steel strip. This is because the phenomenon that the pickling speed differs between the upper and lower surfaces of the same titanium plate is a unique phenomenon that occurs when the titanium material is pickled with hydrofluoric acid, as will be described later. This is a problem that can never occur when a titanium material is pickled with an acid other than hydrofluoric acid, when a steel plate or stainless steel is pickled normally, or when pickled with hydrofluoric acid.

  Further, as described later, the phenomenon described above is caused by a unique mechanism that is sufficient to overturn the same conventional common sense that the chemical reactions governed by the front surface and the back surface of the titanium plate are different from each other. If it is found that the pickling speed is different between the front and back surfaces of the titanium plate that is treated in the same and the same way with the same pickling solution, the cause is the pickling solution or pickling reaction side. It tends to be found on the side of the material titanium plate to be pickled. Specifically, those skilled in the art will be aware of differences in scale composition and properties between the front and back surfaces of the pickled material titanium plate, or differences in surface roughness, surface composition and properties of the titanium plate. , I will definitely pay attention.

  Therefore, this problem is caused by a mechanism in which the chemical reactions governed by the front and back surfaces of the titanium plate are different from each other unless they are pursued as a phenomenon on the side of the pickling solution or pickling reaction. I don't know. Moreover, in this problem, the relationship between the conditions of the pickling treatment and how the titanium plate is pickled has not been sufficiently clarified so far in the above-described continuous annealing pickling line for titanium plates. There is also a background that there is no.

  The mechanism itself that the chemical reaction governed by the front surface and the back surface of the titanium plate is different is based on the knowledge of the present inventors as described above. In other words, in the field of pickling titanium materials with nitric acid, the phenomenon that the pickling speed is different between the upper and lower surfaces of the same titanium plate may have been recognized as an operation result. It was not known what would happen. Therefore, at least the mechanism that the chemical reaction governed by the front surface and the back surface of the titanium plate is different is not known. Therefore, even if there is no countermeasure against the phenomenon that the pickling speed is different between the upper and lower surfaces of the same titanium plate, or even if it exists, the effect inevitably had to be insufficient.

Patent Document 1:
In patent document 1, it is not the structure which supplies pickling liquid from the upper direction and the downward direction of the titanium plate in a passage plate, but the pickling liquid is applied to the surface of the titanium plate from the side by a nozzle provided at the same height as the titanium plate. Is configured to supply. Therefore, even if the pickling liquid is sufficiently supplied to one surface, the pickling liquid may not be sufficiently supplied to the other surface. In patent document 1, since it aims at making the pickling in the same surface uniform, such a thing is estimated not to be a problem, but the pickling speed of the upper surface and the lower surface of a titanium plate is made uniform. It becomes a problem in making it.

  In the above-mentioned Patent Document 1, in the continuous annealing pickling method of the titanium plate, the pickling solution in the region from when the titanium plate enters the pickling solution until it exits, in a direction perpendicular to the running direction of the titanium plate, It describes that it is made to flow at a flow rate of 10 cm / sec or more. This is because titanium ions and titanium fluoride ions existing in the vicinity of the titanium plate surface are removed as soon as possible by the “flow of the pickling solution in the lateral direction” to prevent the occurrence of acid burn.

  However, even if the pickling solution flows in a direction perpendicular to the traveling direction of the titanium plate as in Patent Document 1, it moves in the direction opposite to the moving direction of the titanium plate 1 as in the present invention. It is not laminar flow 4,5. For this reason, even if the occurrence of acid burn can be prevented, the synergistic effect of the laminar flows 4 and 5 cannot necessarily be obtained, and the pickling speed of the upper surface 1a and the lower surface 1b of the titanium plate 1 can be made uniform. Can not. The flow of pickling solution in the direction perpendicular to the running direction of the titanium plate is affected by the running of the titanium plate 1 and is accompanied by the movement of the titanium plate 1. This is because it is greatly inclined toward the traveling direction. That is, in order to obtain the laminar flows 4 and 5 that move in the opposite direction to the moving direction of the titanium plate 1 as in the present invention, as described above, the upper surface 1a and the lower surface 1b of the titanium plate 1 in the passing plate. It is necessary to supply to the upper and lower both sides of the titanium plate 1 in the direction opposite to the passing direction of the titanium plate 1 (from the downstream side to the upstream side) and across the width direction of the titanium plate 1.

Patent Document 3:
Furthermore, in Patent Document 3, from the both sides to the titanium plate in the passing plate, from the downstream side to the upstream side (in the direction opposite to the passing direction of the titanium plate), the upstream side of the titanium plate is downstream. It is described that the pickling solution is sprayed and supplied to the surface of the titanium strip from a plurality of locations on the side. Prevents pickling liquid from locally accumulating on the surface of the titanium plate, increasing the titanium ion concentration in that area, resulting in a difference in pickling speed between adjacent plate surfaces, and uneven pickling. It is to do. Also in this patent document 3, it is not the structure which supplies pickling liquid from the upper direction and the downward direction of the titanium plate in a passage plate, but the acid provided on the surface of the titanium plate from the side by the nozzle provided substantially the same height as the titanium plate. Since it is the structure which supplies a washing | cleaning liquid, the same problem as patent document 1 arises.

  That is, as in Patent Document 3, even if the pickling solution is jetted from both side surfaces toward the titanium plate surface in the passing plate, the same as in Patent Document 1, The laminar flows 4 and 5 do not move in the opposite direction to the moving direction. For this reason, even if the pickling unevenness can be prevented, the synergistic effect of the laminar flows 4 and 5 cannot necessarily be obtained, and the pickling speed of the upper surface 1a and the lower surface 1b of the titanium plate 1 is made uniform. I can't. As in Patent Document 3, even when the pickling solution is sprayed from both side surfaces toward the titanium plate surface in the passage plate, the flow of the pickling solution is affected by the running of the titanium plate 1, This is because the titanium plate 1 is greatly inclined toward the traveling direction of the titanium plate in the form of movement.

  That is, in order to make the laminar flows 4 and 5 that move in the opposite direction to the moving direction of the titanium plate 1 as in the present invention, not from both side surfaces toward the titanium plate surface in the passing plate, As described above, it is necessary to supply the pickling solution to the upper and lower surfaces of the upper surface 1a and the lower surface 1b of the titanium plate 1, respectively. Further, it is necessary to supply the titanium plate 1 in the direction opposite to the plate passing direction (from the downstream side to the upstream side) and in the width direction of the titanium plate 1.

(Reference experiment)
In order to support the operation in the actual continuous annealing pickling line, the formation of laminar flows 4 and 5 of the pickling solution 2 of the present invention and the effects of the laminar flows 4 and 5 are replaced with or carried out in the embodiment. This was confirmed by a mock test corresponding to the example.

  Specimens were picked from the actual pure titanium plate (strip) in the continuous annealing pickling line before pickling. This pure titanium plate was subjected to shot blasting with a salt bath immersion and an iron grid after annealing at 750 ° C. in an air atmosphere for 5 minutes in the continuous annealing pickling line. The pure titanium test piece was 60 mm long × 60 mm wide × 3 mm thick. Then, these two test pieces were bonded to each other on the upper and lower surfaces of the upper surface 1a and the lower surface 1b of the titanium plate 1 in the continuous annealing pickling line, and all the bonded side surfaces were sealed. Tested.

  The pickling test was performed by simulating the passing posture of a titanium plate in a continuous annealing pickling line in 250 ml of a pickling solution having a composition of 2% HF-10% HNO3 in a nitric acid solution. Both surfaces were set as upper and lower surfaces, and were left to stand horizontally and immersed at room temperature for 5 minutes.

  At this time, the forced supply of the pickling solution is simulated, stirring of the pickling solution on the upper surface side of the titanium test piece from above the titanium test piece, and pickling on the lower surface side of the test piece from below the titanium test piece. The pickling test was conducted with and without stirring the liquid. Stirring from above the titanium test piece was performed by stirring the pickling solution on the upper surface side of the titanium test piece with a stirring bar (500 rpm) provided with a cross blade at the tip (lower end) from directly above the titanium test piece. Moreover, the stirring from the lower part of a titanium test piece stirred the pickling liquid of the lower surface side of a titanium test piece with the stirrer (200 rpm) mounted in the bottom face of the pickling tank just under a titanium test piece.

  And the dissolution rate of the upper surface and the lower surface was calculated from the weight change of each of the upper and lower pure titanium test pieces of the bonded test pieces before and after pickling. In addition, the pickling solution near the upper surface and the pickling solution near the lower surface of the titanium test piece during pickling were visually observed to determine the presence or absence of laminar flow and the thickness of the laminar flow was measured. .

  The laminar thickness of this laminar flow is brown on the upper surface of the pure titanium test piece, including the above-mentioned NO2, and the flow in the vicinity of the surface on the upper surface side whose streamline is substantially parallel to the surface of the pure titanium test piece is regarded as a laminar flow. The laminar thickness was measured. In addition, the lower surface of the pure titanium test piece is green containing the above-described trivalent Ti complex, and the streamline is considered to be laminar flow in the vicinity of the lower surface side surface substantially parallel to the pure titanium test piece surface. The flow thickness was measured.

  These results are shown in Table 1. In the example of No. 1, since both surfaces (upper and lower surfaces) of the pure titanium test piece are not stirred, a laminar flow of about 0.5 mm is confirmed on both surfaces, but the pickling speed on the lower surface is the same as that on the upper surface. 2.8 times. Incidentally, this thin laminar flow is considered to be a flow of a liquid generated only by a composition change due to a portion of the pickling liquid due to the above-described chemical reaction of the pickling.

  In the example of No. 2, only the lower surface of the pure titanium test piece was stirred with a stirrer, and because of this stirring effect, the pickling solution was forcibly supplied (circulated) to the lower face of the test piece. The pickling speed of the lower surface is slow, and the pickling speed ratio of the upper and lower surfaces is smaller than that of the number 1 example. From this result, the forced supply effect of the pickling solution described above is supported. However, the pickling speed of the lower surface is still as large as 1.5 times that of the upper surface.

  On the other hand, in the example of No. 3, in addition to stirring from the lower surface of Example 2, stirring is performed from the upper surface, and by this stirring effect, the pickling solution is forcibly forced on both the upper and lower surfaces of the test piece. Each is supplied (circulated). For this reason, the pickling speed on the lower surface of the pure titanium test piece is reduced, the pickling speed on the upper face of the pure titanium test piece is increased, and the pickling speed ratio is 1.1 on the lower surface with respect to the upper surface 1. The upper and lower surfaces (front and back surfaces) of the test piece can be pickled almost uniformly.

  From these results, in order to make the pickling speed of the upper and lower surfaces (front and back surfaces) of the titanium plate uniform and perform pickling uniformly, the pickling solution is applied from both above and below the titanium plate to both the upper and lower surfaces of the titanium plate. It can be seen that it is effective to forcibly supply.

  Incidentally, in the examples of Nos. 2 and 3, when forced stirring (supply of pickling solution) was performed, a laminar flow thickness of about 50 mm was confirmed on both the upper and lower surfaces. On the other hand, when there is no forced stirring (supply of the pickling solution), the thickness of the laminar flow is only about 0.5 to 1 mm on both the upper surface and the lower surface. In the example of No. 2, the thickness of the laminar flow on the upper surface of the test piece without forced stirring (supply of pickling solution) is about 1 mm, and the thickness of the laminar flow on the upper surface of the test piece of the example of No. 1 is also thicker. This is because the flow (circulation) of the pickling solution by stirring only on the lower surface of the test piece spreads to the upper surface of the test piece.

  As described above, according to the present invention, the front and back surfaces of the titanium plate can be pickled uniformly by forcibly supplying the pickling solution from the upper and lower surfaces of the titanium plate in the pickling tank. . Therefore, this invention is suitable for the pickling method of the titanium plate in the continuous annealing pickling line which arrange | positioned the pickling tank in the back | latter stage of the process which consists of an atmospheric annealing furnace, a salt bath, and shot blasting.

It is front sectional drawing of a pickling tank which shows one embodiment of this invention pickling method. It is a top view of FIG.

Explanation of symbols

1: Titanium plate, 2: Pickling solution, 3: Pickling tank, 4, 5: Laminar flow, 6, 7: Nozzle,

Claims (3)

  In the pickling solution containing nitric acid and hydrofluoric acid, both sides of the titanium plate are passed as upper and lower surfaces and pickled, and the pickling is performed from above and below the titanium plate in the passing plate. A laminar flow of the pickling solution near the surface of the titanium plate, the laminar flow of the pickling solution moving in a direction opposite to the moving direction of the titanium plate, A pickling method for a titanium plate, characterized in that the pickling speed of the upper and lower surfaces of the titanium plate is made uniform by forming on both the upper and lower surfaces.   When supplying the pickling solution to the upper and lower surfaces of the titanium plate in the passing plate, from the downstream side of the passing direction of the titanium plate toward the upstream side, and across the width direction of the titanium plate. The pickling method for a titanium plate according to claim 1, wherein each pickling solution is supplied.   The pickling method of the said titanium plate is a pickling method applied to the pickling tank arrange | positioned in the back | latter stage of the atmospheric annealing furnace in a continuous annealing pickling line, a salt bath, and shot blasting. Pickling method for titanium plate.

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