JPS6311681A - Pickling device for titanium strip - Google Patents

Abstract

PURPOSE:To decrease the consumption of a hydrofluoric acid and to decrease the generation of an acid burn by providing a cooler and freely liftable immersion rolls to permit the suppression of liquid temp. elevation and the change of the time for immersing a rolled strip material in the acid. CONSTITUTION:The hot rolled and cold rolled strip materials S' consisting of pure Ti and Ti alloy is immersed by the immersion rolls 1, 2' in a hydrofluoric acid pickling tank 3 in the initial period of immersion. The roll 1 is lowered down to the position of the roll 1' and the strip material S' is brought into the stage of the strip material S when the concn. of the acid decreases upon lapse of time. The uniform quantity of the thickness decrease by the pickling is obtd. by the increase in the immersion length without changing the conveying speed of the strip S. The heat of reaction of the Ti and the acid by the pickling is cooled by heat exchangers 4-7, by which the liquid temp. is maintained constant.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an apparatus for pickling titanium strips.

[Prior Art] Conventional pickling of titanium strips has been carried out by immersing the titanium strip in a nitric-fluoric acid pickling bath having a predetermined immersion length.

To explain this pickling process with reference to the drawings, Fig. 3 shows that in conventional equipment, for example, a pure titanium hot-rolled strip of a, otxl 000w is washed with an initial concentration of hydrofluoric acid of 2.0% and nitric acid of IO.
3 in a pickling tank containing 32 m3 of pickling solution at 0θ% and 30°C.
Adjust the conveying speed of the titanium strip to 4m so that it is immersed for minutes.
This graph shows the changes in liquid temperature, pickling thickness reduction amount, and effective residual hydrofluoric acid concentration when pickling is carried out at a constant rate of /min.The initial pickling thickness reduction amount is 12μ under the above conditions. . In Figure 3, A is the liquid temperature in °C, B is the pickling thickness reduction μ, C is the effective residual hydrofluoric acid concentration %, D is the elapsed time Hr, and E is the immersion time m.
Indicates in.

In such conventional pickling equipment for titanium strips, as shown in Figure 3, (1) The temperature of the liquid rises rapidly in a short period of time due to the heat of reaction between titanium and the acid solution, so it must be operated continuously for a long time. I can't.

(2) As the liquid temperature rises, the amount of thickness reduction per unit time (hereinafter referred to as pickling speed) increases, so if the immersion length is constant, the thickness reduction will occur unless the transport speed of the titanium strip is changed. The thickness increases gradually in the longitudinal direction of the titanium strip. Generally, the conveyance speed of titanium strip is determined by the annealing furnace placed on the same line as the pickling tank, so the above phenomenon occurs, i.e., the thickness of the same titanium strip material after pickling is not uniform over the entire length. There's a problem.

(3) Since the elution of titanium in the pickling solution increases, hydrofluoric acid is consumed at an accelerated rate, and the solution needs to be replenished frequently.

(4) Due to the rise in liquid temperature, the titanium strip after pickling tends to dry, and a stain pattern called "acid burn" tends to occur.

There are various problems.

[Problems to be Solved by the Invention] As explained above, the present invention has been developed as a result of intensive research and repeated consideration by the present inventor in view of the various problems of conventional pickling equipment for titanium strips. Developed a titanium strip pickling equipment that can operate for a long time, has a uniform thickness of the titanium strip after pickling, requires little replenishment of hydrofluoric acid, and can pickle titanium strips without acid burn. That's what I did.

[Means for Solving the Problems] The titanium strip pickling apparatus according to the present invention is characterized in that it is effective in pickling pure titanium and titanium alloy hot-rolled and cold-rolled strips with nitric hydrofluoric acid. , a cooling device is provided in the pickling device, and a dipping roll that can be raised and lowered is installed in the upper part of the tank.

The titanium strip pickling apparatus according to the present invention will be described in detail below.

FIG. 1 shows an example of a titanium strip pickling apparatus according to the present invention. The liquid temperature of the pickling liquid is detected by a thermocouple 8 near the bottom of the pickling tank 3 in which the liquid level is kept constant. A cooling heat exchanger 4.5.6.7 consisting of a Teflon duplex or the like having a control valve 9 for adjusting the flow rate of cooling water flowing inside the heat exchanger is installed. A pair of dipping rolls 1 and 2 are provided so as to be movable up and down while in contact with the titanium strip S by an electric motor.

In the titanium strip pickling apparatus according to the present invention having such a configuration, the temperature of the pickling liquid is controlled by the cooling device, that is, the heat exchanger 4.5.6.7, whose capacity is commensurate with the heat of reaction between titanium and acid. When held constant, the pickling rate slowly decreases as hydrofluoric acid is consumed as titanium is eluted.

Therefore, at the beginning of dipping the titanium strip, the height of either the dipping roll I' or the dipping roll 2' is increased by h to the height of the dipping roll 1 or the dipping roll 2, and as time passes, the height of either dipping roll I' or dipping roll 2' is increased by h. By lowering the immersion roll I' or immersion roll 2', for example, the titanium strip S' of the line becomes the state of the titanium strip S, and the immersion length increases (thereby, the titanium strip of the line It is possible to always obtain a uniform pickling thickness reduction amount without changing the conveyance speed of h.
The value of can be set to any value, and therefore the amount of thickness reduction by pickling can also be set to any value.

Figure 2 shows the liquid temperature in °C, the pickling thickness reduction μ, and the effective residual hydrofluoric acid when the same material as the example in Figure 3 is treated with the same speed and the same initial concentration using the titanium strip pickling apparatus according to the present invention. The concentration %, elapsed time Hr, and immersion time win are shown.

In Fig. 2, the cooling water spray regulated by the control valve 9 is flowed based on the detection of the liquid temperature by the thermocouple 8 shown in Fig. 1, and the temperature of the acid liquid is kept constant at 43°C by the heat exchanger. The initial immersion time is 1 minute, and the immersion time is gradually increased by raising and lowering the immersion roll.

As can be seen from FIG. 2, in the titanium strip pickling apparatus according to the present invention, there is little excessive dissolution of the titanium strip due to an increase in liquid temperature, that is, the pickling thickness reduction μ is small, and
It can be seen that the decrease in effective residual hydrofluoric acid concentration % is small, and therefore the time until replenishment of hydrofluoric acid can be extended.

[Effects of the Invention] As explained above, since the titanium strip pickling apparatus according to the present invention has the above configuration, the cooling device suppresses the rise in liquid temperature and maintains it at a constant value, allowing continuous pickling for a long time. In addition, the dipping roll can be raised and lowered to change the dipping time (length) according to the consumption of hydrofluoric acid, so that any uniform pickling can be carried out in the longitudinal direction of the titanium strip over a long period of time. This method has excellent effects in that it is possible to reduce the thickness, reduce the amount of hydrofluoric acid used, and reduce the occurrence of acid burn on the surface of the titanium strip.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a titanium strip pickling apparatus according to the present invention, and Fig. 2 shows the elapsed time, pickling thickness reduction, effective residual hydrofluoric acid concentration, and liquid temperature in the titanium strip pickling apparatus according to the present invention. FIG. 3 is a diagram similar to FIG. 2 of a conventional pickling device. l, 2 - dipping roll, 3 - pickling tank, 4.5.6.7 - heat exchanger, 8 - thermocouple, 9 - regulating valve. Patent Applicant Kobe Steel Co., Ltd. Agent Patent Attorney Ryo Maruki Hisako 1 Figure (9889 Self-Darkness Q LQ O-shu ○ To ,, -P 0 Yoko 3Ei

Claims (1)

[Claims] In the pickling of hot-rolled and cold-rolled strips of pure titanium and titanium alloys with nitric-fluoric acid, a cooling device is installed in the pickling equipment, and a dipping roll that can be raised and lowered is installed at the top of the tank. Features: Titanium strip pickling equipment.