WO2021058044A1

WO2021058044A1 - Automated pickling time selection

Info

Publication number: WO2021058044A1
Application number: PCT/DE2019/100853
Authority: WO
Inventors: Martin PEESEL; Friedrich-Werner Siedentop
Original assignee: Siedentop Gmbh
Priority date: 2019-09-26
Filing date: 2019-09-26
Publication date: 2021-04-01
Also published as: EP4034873A1

Abstract

The invention relates to a pickling method for pickling workpieces made from steel, particularly stainless steel, in batch operation, in which a pickling agent containing hydrofluoric acid is sprayed from a pickling agent tank onto the workpieces accommodated in a pickling booth. An appropriate pickling time (t_B) must be chosen to achieve a desired pickling effect on the surfaces of the workpieces to be pickled. The method is characterized in that the temperature of the pickling agent (T_B) is measured and the appropriate pickling time (t_B) is determined therefrom. The invention also relates to a pickling plant for pickling workpieces made from steel, particularly stainless steel, in batch operation, in which a pickling agent containing hydrofluoric acid is sprayed from a pickling agent tank onto the workpieces accommodated in a pickling booth. An appropriate pickling time must be selected to achieve a desired pickling effect on the surfaces of the workpieces to be pickled. The pickling plant is characterized in that a first temperature sensor is provided for determining the temperature of the pickling agent in the pickling agent tank or in a feed line to spray nozzles in the pickling booth, a second temperature sensor is provided for determining the temperature of the workpieces to be pickled, and a third temperature sensor is provided for determining the temperature of the ambient air in the pickling booth, the first, second and third temperature sensors being operatively connected to an evaluation and control unit to determine or to calculate the appropriate pickling time.

Description

Automated pickling time selection

The invention relates to a pickling process for pickling workpieces made of steel, in particular stainless steel, in batch operation, in which a pickling agent containing hydrofluoric acid is sprayed from a pickling agent tank onto the workpieces held in a pickling cabin, with a desired

Pickling effect on the surfaces of the workpieces to be pickled, a suitable pickling time (t _B ) must be selected. The invention also relates to a pickling system for pickling workpieces made of steel, in particular stainless steel, in batch operation, in which a pickling agent containing hydrofluoric acid is sprayed from a pickling agent tank onto the workpieces held in a pickling cabin, with for

A suitable pickling time must be selected to achieve a desired pickling effect on the surfaces of the workpieces to be pickled.

Pickling processes and systems in which the workpieces to be pickled are placed in a pickling cabin in batch operation and are sprayed with a pickling agent containing hydrofluoric acid with the pickling cabin closed, are known, for example, from EP 1 477583 B1. The pickling agent containing hydrofluoric acid is fed from the pickling agent tank to the spray nozzles in the pickling booth by means of a controllable pump. The pickling agent is then sprayed onto the workpieces to be pickled and runs down the workpieces due to gravity, where a corresponding collecting basin for returning the pickling agent to the pickling agent tank is arranged in the pickling cabin.

Pickling is known when processing metals, especially precious metals, such as so-called VA steel (stainless steel), since a metal oxide layer or scale layer is often formed on its surface, which affects both the appearance and the possible further processing of the material . In the case of stainless steel, this undesirable layer adheres very firmly to the surface, so that aggressive acids are used for pickling. A common pickling acid mixture is nitric acid and hydrofluoric acid, which is used in aqueous solution. In this so-called spray pickling process, the amount of acid used can be significantly reduced by fine spraying, so that the necessary permits for such systems can be obtained more easily. It is also known from EP 1 477 583 B1 to use pickling agents made solely from hydrofluoric acid in aqueous solution, that is to say to dispense with the addition of nitric acid. This makes it easier to comply with environmental protection regulations.

The problem with such pickling plants, however, is the precise determination of the pickling time, that is to say the exposure time of the pickling agent sprayed on during the pickling time. So far, the pickling time for such spray pickling processes has been selected by the plant operator based on empirical values. It is important that the oxides are completely removed during the pickling process in order to remove all discoloration of the edge zones and tarnishing from the workpiece surface. A material removal of approx. 1 to 3 pm is achieved. After a successful pickling process, the stainless steel surface is completely bare and no longer shows any discoloration or residue. This pure surface is then protected again in the atmosphere by oxidizing the chromium particles on the surface of the stainless steel.

If, however, a pickling time that is too short is selected, unwanted discoloration of the edge zones and tarnishing or other residues can remain on the surface, so that the finished workpiece does not have the desired surface quality and purity. If, on the other hand, the pickling time is chosen too long, there is likely to be an undesirably high material removal and, in addition, too long a process time and thus a reduced material throughput at the pickling plant.

The object of the invention is therefore to design a known pickling process or such a pickling plant in such a way that a suitable pickling time is selected automatically. This object is achieved with a pickling process according to claim 1 and a pickling plant according to claim 11.

If the temperature of the pickling agent (T _B ) is measured and the suitable pickling time (t _B ) is determined from this, a direct, automated assignment of the suitable pickling time is determined from the most important parameter for the pickling time to be selected, namely the temperature of the pickling agent to be sprayed on. For example, a fixed pickling time is assigned to each pickling temperature or to each pickling temperature range, for example in degree increments. This can be done via an evaluation and control unit in which suitable pickling times are stored for the temperature ranges or a corresponding algorithm is available from which the suitable pickling time is determined.

Furthermore, the temperature of the workpieces to be pickled is preferably measured when they are placed in the pickling cabin and the suitable pickling time is derived from this. This makes it possible for a correction value to be added to or subtracted from the pickling time in the event of greater temperature differences between the workpieces to be pickled in the pickling booth and the temperature of the pickling agent.

In a further embodiment of the invention it is provided that the temperature of the ambient air in the pickling cabin is measured and the suitable pickling time is derived from this. Since the pickling booth also contains a considerable volume of air, especially for large, bulky workpieces, this should also be taken into account when calculating the pickling time. If there are major differences between the temperature of the ambient air and the temperature of the pickling agent, corresponding correction amounts must be added to or deducted from the pickling time. For example, in a very cold environment, when placing the workpieces to be pickled, for example from the outdoor area of a factory into the pickling cabin, both the workpieces to be pickled by spraying with the possibly heated pickling agent and those in the pickling cabin during loading with the to be bitten Workpieces exchanged and cooled ambient air must be warmed up. Accordingly, the sprayed pickling agent cools down considerably, so that a significant increase in the pickling time is necessary.

If the weight of the workpieces to be pickled when placed in the pickling booth is measured and taken into account when calculating the pickling time, the total heat capacity of the workpieces to be pickled in the pickling booth can also be used when calculating the pickling time to be selected, especially in connection with the correspondingly measured Temperatures for the workpieces to be pickled and the pickling agent used can be determined.

Because the hydrofluoric acid concentration of the pickling agent is measured and taken into account when calculating the pickling time, an increase in the concentration of the pickling agent can occur when the pickling agent is diluted, for example due to the entry of moisture from wet workpieces to be pickled or particularly moist ambient air (precipitation) or with partial evaporation be taken into account when calculating the pickling time. With a higher hydrofluoric acid concentration of the pickling agent, the pickling time is automatically reduced, while with a lower hydrofluoric acid concentration the pickling time is extended.

If the material of the workpieces to be pickled is determined when it is placed in the pickling booth and taken into account when calculating the pickling time, the material of the workpieces to be pickled can be checked using measurements, thus ensuring a quality control of the respective pickling order and an adjustment of the pickling time to the respective material can be automated . For example, a stainless steel with the material number 1.4301 can be processed with a shorter pickling time than, for example, a material 1.4429. For measuring the respective material, material analysis devices are known which are designed, for example, as laser pistols and which determine the material using optical evaluation methods. Because the wall thickness of the workpieces to be pickled is determined when they are placed in the pickling cabin and is taken into account when calculating the pickling time, the pickling time can also be adapted to the material thickness of the workpieces to be pickled, since thin-walled workpieces are very large in relation to their weight The surface will quickly adapt to the ambient temperature and the temperature of the pickling agent and very massive workpieces, in which the temperature of the workpiece on its surface will only slowly adapt to the temperature of the environment and the temperature of the pickling agent, are taken into account. In connection with the weight of the workpieces to be pickled and the material determined and the thermal conductivity coefficients derived therefrom, model calculations or analytical equations for temperature adjustment on the surface can be derived and used to calculate the pickling time.

A pickling factor is determined and taken into account when calculating the pickling time so that the individual wishes of the respective customer can also be taken into account when selecting the automatic pickling time. The pickling factor indicates, as it were, whether normal pickling, strong pickling or removal pickling is desired by the customer. The automatically determined pickling time is adjusted accordingly, taking into account the selected pickling factor.

In a further embodiment according to the method, the pickling time (t _B ) to be used in hours (h) is _{calculated using the formula t B} (h) = V ^* F _t ^* F _H F ^* F _w ^* F _B , the factors being defined as follows:

V quality factor for the material quality with

V = 2 with a conventional pickling time of 30 min,

V = 4 for 60 min conventional pickling time,

V = 6 at 90 min conventional pickling time,

V = 8 with a conventional pickling time of 120 min;

F _t factor temperature with F _t = 4 at T _tot = 0 ° C, F _t = 2 at T _tot = 10 ° C,

F _t = 1 at T _tot = 20 ° C,

F _t _ges = 0.5 at T = 30 ° C, wherein Tges ⁼ (Tw + TR + TB) / 3, with

T _w = temperature of the workpieces to be pickled,

T _R = temperature of the ambient air in the pickling cabin, T _B = temperature of the pickling

F _H F factor hydrofluoric acid with

F _H F = 3 at 1% hydrofluoric acid concentration in the pickle,

F _H F = 2.2 at 2% hydrofluoric acid concentration in the pickle,

F _H F = 1.6 at 3% hydrofluoric acid concentration in the pickle,

F _H F = 1.2 at 4% hydrofluoric acid concentration in the pickle,

F _H F = 1 at 5% hydrofluoric acid concentration in the pickle,

F _H F = 0.9 at 6% hydrofluoric acid concentration in the pickle,

F _w wall thickness factor

F _w = 0.8 with 1 mm wall thickness of the workpiece,

F _w = 0.9 with 2 mm wall thickness of the workpiece,

F _w = 1.0 with 3 mm wall thickness of the workpiece,

F _w = 1.1 with 4 mm wall thickness of the workpiece,

F _w = 1.2 with 5 mm wall thickness of the workpiece,

F _w = 1.3 with 6 mm wall thickness of the workpiece,

F _w = 1.4 with 7 mm wall thickness of the workpiece,

F _w = 1.5 with 8 mm wall thickness of the workpiece,

F _B Pickling type factor

F _B = 0.5 for light pickling,

F _B = 1.0 for normal pickling,

F _B = 1.5 for intensive pickling,

F _B = 2.0 for pickling.

The pickling time is based on the measured values for the material thickness of the workpiece to be pickled, the measured temperatures of the pickling agent, the ambient air in the pickling cabin and the pickling agent temperature with the corresponding factors derived from the measured values are calculated as the pickling time to be applied in hours. When assigning the factors to the measured values, extrapolation is made for intermediate values.

The fact that hydrogen peroxide is metered into the pickling agent tank after measuring the solids content provides automatic redox measurement and metering for adding hydrogen peroxide to the pickling agent.

The pickling system according to the invention contains at least three temperature sensors, namely a first temperature sensor for determining the temperature of the pickling agent in the pickling agent tank or in a feed line to the spray nozzles in the pickling cabin, a second temperature sensor for determining the temperature of the workpieces to be pickled and a third temperature sensor for determining the temperature the ambient air in the pickling booth, the first, second and third temperature sensors being operatively connected to an evaluation and control unit in order to determine or calculate the suitable pickling time. In this way, the essential temperature-related influences on the pickling result can be taken into account using a relatively simple sensor system with a connected evaluation and control unit, and the appropriate pickling time can be determined from this.

To determine the weight of the workpieces to be pickled, a scale is provided in the feed of the workpieces to be pickled. The workpieces to be pickled can for example be hung on or on mobile racks, in which case these mobile racks, which remain in the pickling booth, also have to be measured accordingly.

To measure the hydrofluoric acid concentration of the pickling agent, an analysis device for measuring the hydrofluoric acid concentration of the pickling agent is arranged in the pickling agent tank or in a feed line to spray nozzles in the pickling cabin.

An exemplary embodiment of the invention is described in detail below. In the exemplary embodiment, a stainless steel workpiece made of 2 mm stainless steel sheet of the quality 1.4301 is processed with a hydrofluoric acid pickle in a pickling cabin by spray pickling. The pickling time required for this workpiece is calculated according to the invention using the formula according to claim 9. For a stainless steel sheet of quality 1.4301, a pickling time of 30 minutes is usually used according to a conventional choice based on experience with pickling agents. Accordingly, the quality factor has to be assigned 2.

The temperature of the workpiece is T _W = 10 ° C. after a corresponding temperature measurement. For example, the temperature is automatically recorded with an infrared surface temperature measuring device when the workpiece to be pickled is placed in the pickling cabin. The room air temperature is T _R = 15 ° C, which is recorded by a room temperature sensor. Furthermore, the dressing agent temperature, measured in the dressing agent storage tank with an acid-proof temperature sensor in the liquid, is T _B = 20 ° C. The average temperature value results from this as T _tot = 15 ^° C. and thus as the temperature to be assumed for the selection of the temperature factor F _T = 1.5.

As already mentioned at the beginning, the concentration of hydrofluoric acid in the pickling agent is 4%, which results in a hydrofluoric acid factor F _HF = 1.2. As described at the beginning, the material thickness is included in the calculation with 2 mm and thus with a factor of wall thickness F _{w = 0.9.} In addition, a normal pickling is selected from the desired pickling type according to the pickling type factor F _b = 1. This selection can be automatically transferred to the system control via the order data for the workpiece to be pickled.

A total pickling time of t _B = 3.24 h is thus calculated.

Accordingly, the workpiece to be pickled is hooked into the pickling cabin and pickled for 3% hours under the aforementioned conditions. Due to the values measured and transferred to the system control, the pickling result always corresponds to the desired degree of pickling and is also below different boundary conditions, in particular other temperatures, a slightly lower or higher hydrofluoric acid concentration in the pickling agent and the like are always comparable. Due to the measured boundary conditions and the correspondingly assigned factors, the correct pickling time can always be used. It is preferred that the measured values are transmitted directly to a control unit in which the calculation mode and the associated factors are stored, so that the correct pickling time is always carried out automatically on the pickling device.

Claims

PATENT CLAIMS

1. Pickling process for pickling workpieces made of steel, in particular stainless steel, in batch operation, in which a pickling agent containing hydrofluoric acid is sprayed from a pickling agent tank onto the workpieces held in a pickling cabin, with a suitable pickling effect to achieve a desired pickling effect on the surfaces of the workpieces to be pickled Pickling time (t _B ) is to be selected, characterized in that the temperature of the pickling agent (T _B ) is measured and the suitable pickling time (t _B ) is determined from this.

2. Pickling process according to claim 1, characterized in that the temperature of the workpieces (T _w ) to be pickled is measured when they are placed in the pickling cabin and the suitable pickling time is derived from this.

3. Pickling process according to claim 1 or 2, characterized in that the temperature of the ambient air in the pickling cabin is measured and the suitable pickling time is derived therefrom.

4. Pickling process according to claim 1, 2 or 3, characterized in that the weight of the workpieces to be pickled is measured when they are placed in the pickling cabin and is taken into account when calculating the pickling time.

5. Pickling process according to one of the preceding claims, characterized in that the hydrofluoric acid concentration of the pickling agent is measured and taken into account when calculating the pickling time.

6. Pickling method according to one of the preceding claims, characterized in that the material of the workpieces to be pickled when Setting in the pickling booth is determined and taken into account when calculating the pickling time.

7. Pickling process according to one of the preceding claims, characterized in that the wall thickness of the workpieces to be pickled is determined when placing in the pickling cabin and when calculating the

Pickling time is taken into account.

8. Pickling process according to one of the preceding claims, characterized in that a pickling factor is determined and taken into account when calculating the pickling time.

9. Pickling process according to one of the preceding claims, characterized in that the pickling time (t _B ) in hours (h) is _{calculated with the formula t B} (h) = V * F _t * FHF * Fw * F _B , the factors are defined as follows:

V quality factor for the material quality with

V = 2 with a conventional pickling time of 30 min,

V = 4 for 60 min conventional pickling time,

V = 6 at 90 min conventional pickling time,

V = 8 with a conventional pickling time of 120 min;

F _t factor temperature with F _t = 4 at T _tot = 0 ° C,

F _t = 2 at T _tot = 10 ° C,

F _t = 1 at T _tot = 20 ° C,

F _t = 0.5 at T _tot = 30 ° C, where T _tot ⁼ (Tw + T _R + T _B ) / 3, with

T _w = temperature of the workpieces to be pickled,

F _H F factor hydrofluoric acid with

F _H F = 3 at 1% hydrofluoric acid concentration in the pickle, F _H F = 2.2 at 2% hydrofluoric acid concentration in the pickle,

F _H F = 1.6 at 3% hydrofluoric acid concentration in the pickle,

F _H F = 1.2 at 4% hydrofluoric acid concentration in the pickle,

F _H F = 1 at 5% hydrofluoric acid concentration in the pickle,

F _H F = 0.9 at 6% hydrofluoric acid concentration in the pickle,

F _w wall thickness factor

F _w = 0.8 with 1 mm wall thickness of the workpiece,

F _w = 0.9 with 2 mm wall thickness of the workpiece,

F _w = 1.0 with 3 mm wall thickness of the workpiece,

F _w = 1.1 with 4 mm wall thickness of the workpiece,

F _w = 1.2 with 5 mm wall thickness of the workpiece,

F _w = 1.3 with 6 mm wall thickness of the workpiece,

F _w = 1.4 with 7 mm wall thickness of the workpiece,

F _w = 1.5 with 8 mm wall thickness of the workpiece,

F _B Pickling type factor

F _B = 0.5 for light pickling,

F _B = 1.0 for normal pickling,

F _B = 1.5 for intensive pickling,

F _B = 2.0 for pickling.

10. Pickling process according to one of the preceding claims, characterized in that hydrogen peroxide is _{metered into the pickling agent tank after measuring the Fe 3} content.

11. Pickling plant for pickling workpieces made of steel, especially stainless steel, in batch operation, in which a pickling agent containing hydrofluoric acid is sprayed from a pickling agent tank onto the workpieces held in a pickling cabin, with a suitable pickling effect to achieve a desired pickling effect on the surfaces of the workpieces to be pickled Pickling time is to be selected, characterized in that a first temperature sensor for determining the temperature of the pickling agent in the pickling agent tank or in a supply line to Spray nozzles are provided in the pickling cabin, a second temperature sensor for determining the temperature of the workpieces to be pickled and a third temperature sensor for determining the temperature of the ambient air in the pickling cabin, the first, second and third temperature sensors having an evaluation and

Control unit are operatively connected to determine or calculate the appropriate pickling time.

12. Pickling plant according to claim 11, characterized in that a scale for determining the weight of the workpieces to be pickled is arranged near the pickling booth.

13. Pickling plant according to claim 11 or 12, characterized in that an analysis device for measuring the hydrofluoric acid concentration of the pickling agent is arranged in the pickling agent tank or in a feed line to spray nozzles in the pickling cabin.

14. Pickling plant according to claim 11, 12 or 13, characterized in that a material analysis device for determining the material of the workpieces to be pickled is arranged near the pickling cabin.

15. Pickling plant according to claim 11, 12, 13 or 14, characterized in that for metering hydrogen peroxide into the pickling agent, a measuring and metering device with a hydrogen peroxide storage tank is assigned to the pickling agent tank.