DE1621558B2 - - Google Patents

Description

have an approximately equally thick layer of scale) to be descaled, it is not necessary for each to make an analysis of the individual object to be immersed in the pickling bath. Suffice it from one take a sample from such a batch and determine the iron content.

The routine analysis required only occasionally in the method according to the invention is by far not as complex as the analysis of the descaling bath according to German patent specification 1 078 404, which must be continuously examined with great care to avoid corrosion of the container and the desired effect is achieved. The method according to the invention is also much safer to handle, since the addition of sodium oxide is not required.

example

A bundle of wire rod of 350 kg, a wire thickness of 6 mm and a scale content of about 10 kg / t is placed in a molten bath made of NaOH / KOH with a hydride content of 0.9 ° / ₀ , based on NaOH / KOH, at 240 ° C Immersed for 30 minutes with gentle swirling. The bundle is then quenched in water at room temperature and rinsed free of alkali.

The bundle is then shaken on a vibrating table, the loose layers trickling off and the bare metal surface comes to light.

In a comparative experiment was found analytically that the remote reduced scale is practically after 2 hrs pickling of the wire rod used in the above example to 100 ° / ₀ of iron. In contrast, the analysis of the removed reduced scale pickling after half an hour according to the above example gives only an iron content of 71 ° / _0th

The required pickling time was determined as follows:

Several pieces of approximately the same size of the wire to be pickled are cut off from the bundle and balanced.

The following weights resulted:
Piece 1 = 10.6 g,
Piece 2 = 10.2 g,
Piece 3 = 9.8 g,
Piece 4 = 12.7 g,
Piece 5 = 10.9 g,
Piece 6 = 11.3 g.

These pieces are suspended from a binding wire and immersed in the pickling bath for different lengths of time as follows:

Piece 2 = 15 minutes,
Piece 3 = 30 minutes,
Piece 4 = 1 hour,
Piece 5 = 1.5 hours,
Piece 6 = 2 hours,
Wire piece 1 remains untreated.

After the appropriate pickling times, the samples were carefully removed from the pickling bath and allowed to cool in the air. Now all the samples a beaker of 100 cm were immersed ³ 20 ° / ₀ aqueous hydrochloric acid including piece 1 in each. 1% of the total solution of the hydrochloric acid was provided with an inhibitor consisting of hexamethylenetetramine and butynediol in a molar ratio of 1: 1 and had an inhibition value of about 95 ⁰ J ₀ .

ίο The Surface coating from the pieces of wire, largely only the oxides due to the inhibitor go into solution.

The solution is then filtered. 10 cm ^{3 of} the filtrate are placed in a 100 ml volumetric flask, the _{pH is adjusted to 4 with NH 4} OH ₃ , 1 g of hydroxylammonium chloride and 30 cm ^{3 of} a 10% aqueous α, α-dipyridil solution are added and H _{2 is added} O filled up to 100 cm ^3. After about 10 minutes, the absorbance is measured in a photometer and evaluated using calibration curves.

Result

The solution by piece of wire

No. 1 contained 0.0082% Fe,
No. 2 contained 0.0039% Fe,

No. 3 contained 0.0022% Fe,

No. 4 contained 0.0015% Fe,
No. 5 contained 0.00009% Fe,

No. 6 contained 0.00011% Fe.

Since the Fe content of the solutions of wire pieces 5 and 6 with respect to the wire weight approximates are the same and hardly any iron can be detected in the solutions, the descaling of Wire piece No. 5 with a pickling time of 1.5 hours is considered quantitative.

Based on the Fe content of the solution or the scale content of piece of wire no. 1 results in

Piece 2 = 15 minutes of pickling a 50% descaling,

Piece 3 = 30 minutes of pickling a 71% descaling,

Piece 4 = 1 hour pickling an 85% descaling,

Piece 5 = 1.5 hours of pickling, 100% descaling,

Piece 6 = 2 hours of pickling, 100% descaling.

Tables 1 and 2 show the various immersion times that are used in the case of the invention Process for descaling a heavily scaled wire rod with a diameter of 6 mm and a Scale content of 1.5 percent by weight can be used, with the pickling bath according to Table 1

a eutectic caustic soda-caustic potash melt and according to Table 2 a caustic soda melt with varying sodium hydride content were used.

Table 1
Pickling bath: Eutectic caustic soda / caustic potash melt Table 2
Pickling bath: Caustic soda melt

temperature _^0/0 NaH Tinder Diving Pickling of
Pickling bath in the
Pickling bath layer thickness Time (° / o) Re-
duction ( ⁰ Q (mm) (Min.) 240 0.3 0.3 30th 50 240 0.3 0.3 60 70 240 0.3 0.3 85 80 240 0.9 0.3 15th 50 240 0.9 0.3 30th 70 240 0.9 0.3 50 80 240 5.0 0.3 5 50 240 5.0 0.3 12th 70 240 5.0 0.3 20th 80

temperature »/ Ο NaH Tinder Diving Pickling 3 des
Pickling bath in the
Pickling bath layer thickness Time % Re
duction ( ⁰ Q (mm) (Min.) 380 0.3 0.3 35 50 380 0.3 0.3 55 70 380 0.3 0.3 80 80 380 0.9 0.3 12th 50 380 0.9 0.3 25th 70 380 0.9 0.3 45 80 15 380 5.0 0.3 4th 50 380 5.0 0.3 10 70 380 5.0 0.3 15th 80

The thickness of the scale corresponds to a heavily scaled wire rod with a diameter of 6 mm and a scale content of 1.5 percent by weight.

Claims (1)

1 2 leaves. This goal is achieved in that the Claim: Melt apart from alkali oxide and alkali hydride, for example 0.2 to 10 weight percent iron in the form of a Process for removing scale from strongly oxidic dissolved compounds are added, scaled metal surfaces by pickling in 5 This known process, however, has the disadvantage of 0.3 to 5 percent by weight of sodium hydride that it is very expensive and difficult to handle. The descaling bath must be continuously analyzed with great care at temperatures above the melting temperature and adjusted to a certain mixture, subsequent quenching of the iron and sodium oxide content, pickled goods in a water bath and consequently corrosion the container is avoided and the subsequent mechanical treatment, thereby achieving the desired effect,
characterized in that the pickling time for the subject of the invention is now a process Schmelzbadbehandlung, up to the 50 to 80 ° / ₀ of are reduced to remove scale from heavily oxidised scale analytically in a loading metal surfaces by dressing in a 0.3 to known way on samples at a given bath 15 5 weight percent of sodium hydride containing alkali temperature and given bath composition lischen melt bath at temperatures above the determined and then the pickling material is immersed in a known manner in the alkaline melt bath quenching the pickled material during the melting temperature of the mixture, subsequent determined pickling time. bath and subsequent mechanical treatment, 20 in which the disadvantages of the known methods are avoided in that the pickling time for the Molten bath treatment, up to the 50 to 80% of the Zunders are reduced, analytically in a manner known per se on samples at a given bath temperature and It is known that unreduced scale is determined based on a given bath composition and thereafter Metal surfaces adhere. In this way it is possible to strengthen the pickling material during the determined pickling time Layers of scale or rust from unheated metal-alkaline molten bath in a manner known per se surfaces is removed by mechanical treatment. distant. For example, you can with the help of a sand that in the procedure according to the invention, Clean surfaces cleanly by blasting or bending unheated metal wire in which the scale is imperfectly reduced. In this case, however, it is possible, even with a single treatment - without frequently damaging the metal surface in such a way that anodic or cathodic aftertreatment - this method cannot be used with many materials on the scale of heavily scaled metal surfaces. Another disadvantage of removing all of these from such was surprising, because mechanical cleaning is the fact that, as is well known, the unreduced scale cannot be removed without wrapped objects, such as B. wire bundles or other, z. B. can only be removed by shaking on a vibrating table, spirals, for cleaning and rewinding. It therefore seemed completely absurd, only need, which is difficult with larger wire diameters and 50 to 80 ° / ₀ of the scale to reduce, as angenommanchen metal qualities also hurts. had to be ensured that the still on the metal surface To avoid these disadvantages, it has already been proposed that the remaining non-reduced layer of scale would adhere firmly to the metal surface with scale or rust. Over-metal objects by dipping in a caustic soda - surprisingly this is not the case,
and / or caustic potash molten bath with a sodium ■ The method has the further advantage that the pickling hydride content of 0.3 to 5 ° / _{0 is} pickled and then the scale or rust layer only partially penetrates the reduced scale mechanical 45 needs to penetrate, whereby naturally the hydride treatment of the surface of the metals is depleted compared to the previous cleaning. This method is e.g. B. in "Steel and Iron", the procedure is reduced accordingly. That has been described by 84 (1964), pp. 1865 to 1872, and the pickling partly to metal or lower oxides, one can infer from this publication that reduced scale or rust layer adheres after the scale must be completely reduced because 5 ° quenching so loosely on the metal surface that, as is known, unreduced scale adheres firmly to metal surfaces, easily removed by mechanical treatment. which can be compared to the electrical In many cases, mechanical treatment is sufficient treatment, which is another benefit. Not depending on the shape of the pickled metal objects, so that the objects are used with various mecha-reduced scale by subsequent electrical 55 niche processes. For example, vibrating devices are suitable for bundles and - initially anodic, then catho spirals as a result of polarity reversal, while dische - treatment in an alkaline bath of large objects with pressurized water and the metal surfaces must be removed. After being cleaned with compressed air or brushing,
This method does not succeed, however, strongly. The method according to the invention also has the scaled objects due to one-time pickling and the advantage of saving time in the work flow Anodic and cathodic treatment can be designed to be satisfactory and much more rational. That putting to clean. In this case, therefore, the problem must be met especially with heavily scaled metal cleaning processes repeated several times. Objects particularly noticeable, as is well known but this makes the process uneconomical. the required pickling time from the thickness of the scale layer In the German patent specification 1 078 404, a 65 is dependent. Since in practice mostly larger Process for the complete reduction of scale beaten with the aim of producing a reduced tinder batch (which can be heated under the same conditions which are easily deformed or annealed away from the material and which as a result