DE1187099B - Device and process for blueing or blackening steel or iron strip - Google Patents

Description

Device and method for blueing or blackening steel or Iron strip The invention relates to a device for blueing or blackening of steel or iron strip, which has a furnace through which the strip is continuously is pulled through at a regulated, elevated temperature. Further relates the invention to a method by which the blueing or blackening of steel or iron tape can be performed using the apparatus of the present invention can.

Various methods are known for bluing steel or iron strip. According to a known method, the metal is brought to a temperature in a belt furnace heated to about 732 ° C, with a reducing atmosphere inside the furnace is maintained. After cooling to a temperature between about 482 and At 649 ° C, the strip taken out of the oven is exposed to the open air to turn blue. It is also known to use a band-like steel or iron material in a closed Bluing space from the action of water vapor.

In both known methods, the processed material stands out often due to uneven coloring; the weight and the adhesive strength of the Oxide layers are also not always uniform, so that part of the coating can be rubbed off easily. The steam process requires one additional work by loosening the material on reels must before it is under the cover, which z. B. be a box-like tempering furnace can, is brought. Both known methods lack the possibility of the process sequence to regulate from the outset so that certain desired properties of the blue coating occur evenly everywhere.

It is also known to use metal strips, in particular steel and iron strips, to run through elongated chamber furnaces in order to expose them to the action of heat and stain the surface.

The object of the invention is to provide a device and a To create processes with which an extremely uniform blueing or blackening of the tape material is possible.

The device according to the invention has a furnace through which the Tape is continuously pulled through at a controlled elevated temperature, and it is characterized by a device for introducing an inert gas into the interior of the furnace and through a device that is released into the atmosphere of the inert Gas close to the band a gas containing free oxygen in such a regulated Quantities introduces that the oxygen reacts with the metal of the belt to form a -Oxide coating on the tape completely converts.

The inventive device thus allows the generation of a Oxide coating, which in terms of strength, uniformity and color exactly beforehand corresponds to the specified conditions.

Preferably the interior of the furnace is in flow chambers or zones divided, their temperatures by separate temperature control elements assigned to them be managed.

In a further embodiment of the invention it is provided that the furnace is made gas-tight and that at its tape inlet opening and its tape outlet opening Sealing rollers are provided between which the tape passes.

In the device according to the invention there is therefore an easily controllable one Continuous annealing takes place, which takes place at a relatively high speed, special handling, additional heating and post-treatment of scrap material completely omitted.

The bluing process for steel or iron strip runs in the method according to the invention Device preferably from such that the temperature of the belt in the vicinity the point of introduction of the free oxygen-containing gas to a value in the Range between about 400 and 566 ° C is regulated.

In the process of blackening steel or iron strip, the device according to the invention preferably used in such a way that the temperature of the strip in near the point of introduction of the free oxygen-containing gas to a value of 594 ° C or above is regulated.

In both methods, according to the invention, the gas inside the Furnace can be brought to a pressure above the pressure of the outside air.

The methods that can be carried out using the device according to the invention are extremely economical and can be regulated over a wide range. The result is flawless and uniform coatings, whereby, in contrast to the known processes, no rejects or inferior goods are created.

The invention is illustrated in the following description with reference to the drawings for example explained.

F i g. 1 is a vertical sectional view of part of a belt furnace for carrying out the method according to the invention; F i g. 2 is a sectional view according to line 11-II of FIG. 1; F i g. 3 is a top plan view of the invention Device using a belt furnace according to FIG. 1; F i g. 4 is an in enlarged side view of the device according to FIG. 3; F i G. 5. is a graph showing the changes in the weight of the oxide coating in the Compared to the volume of air introduced in accordance with one embodiment of the method according to the invention; F i g. b is a temperature-time graph.

In the embodiment of the device according to the invention shown as an example, a steel strip 10 runs around a guide roller 11 and enters a tower-like furnace 12 through a pair of entry sealing rollers or sealing rollers 13. The furnace 12 is constructed of refractory material and is supported on metal frame parts 14 . A number of parallel inner walls 15 of refractory material form a number of parallel perpendicular flow chambers or zones through which the belt 10 is passed. After entering the furnace 12, the belt 10 runs through a first chamber 16, around an oven roller 17, through a second chamber 18, around an oven roller 19, through a third chamber 20, around an oven roller 21 and through a fourth chamber 22 an oven roller 23, through a fifth chamber 24, around an oven roller 25 and through a sixth chamber 26. The belt 10 then runs around guide rollers 27 and exits the oven 12 between exit sealing rollers 28 , the tower-shaped water-cooled ducts 31 with associated rollers 30 and cooling jackets 31 'are arranged downstream; in which the belt 10 is cooled under controlled conditions and at a predetermined rate. After passing through the water-cooled channels 31, the strip 10 runs continuously between sealing rollers 32, after which it is released into the open air between rollers 33 and 34 and can be visually inspected on one or both sides. The belt 10 then enters a water-cooled channel 35 before it passes around a guide roll 36 to pressure rolls of the usual type (not shown), which pull the belt 10 continuously through the furnace 12 and the corresponding channels. The tape 10 is wound up in a known manner behind the pressure rollers.

Usual z. B. gas-fired heat radiation tubes 37 and 38 or electrical resistance heaters are provided on both sides of the continuous belt 10 in the chambers 16, 18 and 20 . In the chambers 16 and 18, the strip 10 is brought to the annealing temperature and held. The chamber 20 serves as a holding chamber in which the temperature of the strip 10 is kept essentially constant. The type of belt furnace used, the number of flow chambers, and the temperature conditions and speeds can be changed as desired.

The temperature in the flow chambers 16, 18 and 20 is monitored by mutually independent Thenmoelements 39, 39 ', 40, 40' and 41, 41 ', which are connected to a control device for the gas firing of the radiant tubes 37 and 38.

The inert furnace gas atmosphere can be formed by gas from a gas generating machine 42 (FIG. 3), e.g. B. receives natural gas from a line 43 , partially burns it and releases it through lines 44, 45, 46 into the flow chambers and possibly into the channels 31. A control valve 47 is arranged in each line 46. The lines 46 are shown in FIG. 3 from left to right with the interiors of the furnace 12 and the channels 31 through openings 48 to 53 (FIG. 1) in connection.

The flow chambers 22, 24 and 26 are used in the illustrated embodiment for a regulated initial cooling. This cooling is z. B. achieved by circulating water through cooling tubes 54, which are arranged on both sides of the belt 10 . In some cases, a baffle 55 made of refractory material can be arranged in the last chamber, chamber 26, as shown in FIG. 1. is indicated by broken lines. The cooling tubes 54 in the chamber 26 in this embodiment end at the entry side of the baffle 55, and the part of the chamber 26 below the baffle 55 is used as a reheating section, with conventional radiant tubes or electrical resistance heaters on each side of the belt 10 between the baffle 55 and the exit end of the flow chamber 26 can be used. If such a reheating section is used, the temperature to which the tape 10 therein is heated should be between 400 and 560 ° C.

To monitor the temperature of the strip 10 , a number of thermocouples 56 to 61 are in the circuit shown in FIG. 1 or at other locations within the interiors of the furnace 12. The thermocouples 56 to 61 also serve to monitor the setting values of the thermocouples 39 to 41, and they can be connected to an appropriate control device. The temperature in the channels 31 can be regulated in a similar manner depending on the particular requirements. The furnace 12 according to FIG. 1 is practically gas-tight. The interiors between the entry seal rolls 13 and the exit seal rolls 28 are usually kept at a pressure slightly above the ambient air pressure to prevent outside air from entering. A bell-shaped cover 62 provided for the channels 31 is usually closed, so that the channels 31 between the outlet sealing rollers 28 and the outlet sealing rollers 32 are also practically gas-tight.

For the blueing of the iron or steel strip 10 according to the invention, an oxygen-containing gas, for. B. air is used. In the embodiment described, the gas is compressed in a compressor. the output side of which is connected to a pipe 63 which has valves 64 on both sides of an automatically adjustable pressure control valve 65. A pressure storage tank 66 is connected to the outlet side of the pipe 63 and is provided with a drain pipe in which a valve 68 is installed, which is usually closed. An outlet pipe 69 is connected to the interior of the. Vessel 66 and includes an adjustable pressure medium valve 70. A conventional pressure gauge 71 is located on the outlet side of the valve 70 in the pipe 69 and shows the pressure at which the oxygen-containing gas into the interior of the furnace 12 is introduced. The pipe 69 is provided with branches 72 and 73, each of which contains a slide valve 74 and a needle valve 75 which are connected in series. On the exit side of each needle valve 75 is a flow meter 76 from which branch lines 72 and 73 respectively extend to the left and right sides (as seen in Figure 4) of three pairs of inlet tubes 77 and 78, respectively and 79 to dine. A valve 80 is located between each inlet pipe 77 to 79 and the branch line 72 or 73, so that each inlet pipe can be individually regulated with respect to the other inlet pipe of the same pair and with respect to the inlet pipes of the other pairs. Normally only one of the pairs 77, 78, 79 of the inlet pipes is open at a time.

The oxygen-containing gas is introduced into the furnace 12 in controlled amounts such that the oxygen completely reacts with the metal of the strip 10 to form an oxide coating on the strip.

A convenient embodiment of a pair of inlet pipes is shown in FIG. 2 showing the inlet tube 79. Each inlet tube 79 carries a cap 80 ', and its wall has a series of parallel drilled openings 81 which form nozzles for the discharge of the oxygen-containing gas to be flowed through the branch lines 72, 73. The openings 81 are preferably arranged so that they allow the gas to exit parallel to the belt 10 , so that a direct impact on the belt 10 is avoided. In general, the heat radiation tubes 38 and the cooling tubes 54 are also arranged in the relevant flow chambers 20, 22, 24 at a distance from the openings 81 of the inlet tubes 77, 78, 79. Preferably, the flow of inert furnace gas through the opening 50 is blocked when oxygen-containing gas is supplied through the inlet pipes 78 or 79 in order to keep a dilution of the gas emerging from these inlet pipes as low as possible. On the other hand, the gas emerging from the inlet tubes shows an advantageous tendency to oxidize the surface of the strip 10 which passes through the zone of the inlet tubes in question.

In a series of tests carried out with steel belts of various widths and thicknesses, good results have been obtained when the belt is fed into the furnace 12 at about 20 ° C. Zone 16 was heated to a temperature of about 538 to 788 ° C. As the strip passed through chamber or zone 18, the strip temperature was increased somewhat and in the flow chamber or zone 20 it was maintained at approximately 677 to 760 ° C. In the flow chamber or zone 22, cooling to approximately 400 to 566 ° C., preferably 427 to 538 ° C., then took place. In the flow chamber or zone 24, the strip temperature was then lowered to approximately 399 to 482 ° C. and continued cooling was such that the tape exited the exit seal rolls 32 at a temperature of about 121 to 177 ° C.

To obtain these belt temperatures, the temperature of the furnace atmosphere was used in zone 16 to about 954 to 982 ° C and in zone 18 to about 760 to Maintained 870 ° C. From zone 20 onwards, the temperature corresponded to the furnace atmosphere essentially the belt temperature, as is also the case in the FIG. 6 reproduced Diagram is indicated. The composition of the furnace atmosphere is as follows described in connection with a further series of experiments.

Oxygen-containing gas was only through in most of the experiments through the inlet pipes 78 and only in a few cases through the inlet pipes 79 fed. In general, the difference is that the oxygen-containing Gas is supplied through the inlet pipes 78 or the inlet pipes 79 therethrough, not large, but there is a slightly longer reaction time when the oxygen-containing Gas is supplied through the inlet pipes 78 therethrough. As an oxygen-containing gas air was used, at a rate of 113 to 141 dm3 / min. and under one Pressure was applied which was slightly above the pressure of the furnace atmosphere. The introduced Air was relatively dry. However, it can be used with water vapor without any harmful effects be saturated. In addition to air, any other gas can be used as an oxygen-containing gas, which does not attack the material of the tape or the coating produced on it, be used.

Such treatment resulted in a clear, dark blue colored oxide coating which appears to consist primarily of Fe .04 and was relatively uniform in weight and color and adhered excellently to the base metal of the tape 10. Samples taken from an opening 82 showed that there was no more free oxygen in the top of the chamber 24.

The table below shows the results of a series of tests with a low-alloy steel strip 10 of 530 mm in width and 0.37 mm in thickness, in which air was introduced in various amounts through the inlet pipes 78 and 79, respectively. The composition and moisture content of the furnace gas atmosphere are also given. In general, the furnace gas atmosphere initially established in furnace 12 by gas generating machine 42 is relatively dry. The furnace atmosphere gas or its constituents can be passed through a drying tunnel before they are introduced into the furnace 12 in order to lower the dew point of the furnace atmosphere to about 0 ° C. If this does not happen, the water vapor can dissociate at temperatures above about 538 ° C. This would free oxygen for a reaction with the belt 10, namely at temperatures at which an oxide coating is produced which does not have the desired properties and which adversely affects the controllability of the mode of operation according to the invention.

When introducing reactive or free oxygen into a There is a slope in the zone where the strip temperature is below about 399 ° C to stain the tape or to create unwanted light blue oxide on the tape itself or on an oxide already formed on the tape. So became a flawless dark blue oxide layer in the tests shown in the table obtained when air in the range between about 57 dm3 / min. and about 113 to 141 dm3 / min. was introduced. With larger amounts of air introduced, an oxide coating became lighter Color and lower quality preserved (see table). The decrease in speed of the tape in the oven with the same air supply led to the same effect like increasing the air supply without changing the speed of the belt.

However, if too little oxygen-containing gas or air is supplied, a dark blue oxide of very light weight is produced, which to full Protecting the metal surface is not enough.

F i g. 5 is a graph drawn with the table values, in which on the abscissa is the air flow in dm3 / min. and the change on the ordinate is applied in the weight of the oxide coating in g / m2 tape surface. The applied Points representing the supply of air through the inlet tubes 78 are denoted by 78a, and the plotted points, which the air supply through the Represent inlet pipes 79 therethrough are denoted by 79a. It shows, that the functional relationship between the weight of the oxide and the volume of air supplied in the essentially represents a parabola, which is relatively flexible in achieving the desired weight of the oxide coating.

The tests according to FIG. 5 coatings produced were unsatisfactory, if the air supply exceeds about 141 dm3! Min. lay. Heavier coatings of dark blue Oxide can, however, be generated by increasing the dwell time when the air supply is increased of the tape at a temperature in the range between about 400 and 565 ° C accordingly is increased. In general, the rate of reaction decreases in the formation of the oxide coating to the extent that the temperature approaches the upper limit of the aforementioned Temperature range shifts.

In the one shown in FIG. 6 is on the ordinate is the temperature and, on the abscissa, that of the entry of the strip at the entry seal rolls 13 plotted from elapsed time in seconds, also for a low-alloy Steel belt of about 530 mm wide and 0.37 mm thick, moving at a speed of about 53 m / min. moved forward. The plotted points are identified by the reference numerals of associated thermocouples according to FIG. 1, but designated with the addition a.

For an oven according to FIG. 1 with a 7 m high flow chamber 24, the other parts having corresponding dimensions, would have to be introduced into the interior of the plant through the pipe 44 in approximately 85 to 100 ms of furnace gas atmosphere. In such a system, satisfactory results can be achieved with belt speeds between about 24 and 68 m / min. with the lower speeds being used for thicker, larger sized tapes. The amount of air which is introduced as oxygen-containing gas through the inlet pipes 78 or 79 can then be between about 57 dm3 / min. and about 226 to 284 dm3 / min. lie.

According to the invention, a good-looking glossy black oxide coating of uniform weight can be produced on the iron or steel strip 10 by introducing an oxygen-containing gas through the inlet pipes 77. Here, the valves 80 of the inlet pipes 78 and 79 are closed. In general, the same furnace gas atmosphere, the same zone and band temperatures and the same supply of oxygen-containing gas or air are used as in the production of the dark blue oxide coating. However, the inlet tubes 77 are located at a hotter part of the furnace 12 in which the strip temperature near the inlet tubes 77 is about 594 ° C or more. The oxidation process is ended before the strip 10 leaves the flow chamber or zone 20. In general, when both the black oxide and the deep blue oxide are generated, all of the free oxygen introduced near the strip should react with the strip before the temperature reaches the area in which the black or dark blue oxide is formed.

The blackening or the formation of a black oxide coating is used for relatively flat products or z. B. for the production of shaped objects, like stovepipes. used, which is a relatively large and regular Have radius of curvature. The black oxide is stain-free and has a considerable amount Shine.

When carrying out the method according to the invention, the tape 10, when it emerges from the last channel 31 or from the channel 35, can be conveniently checked visually. If z. B. in the uniformity of the color occurs on the two sides of the tape, additional oxygen-containing gas can be supplied through one of the inlet pipes used on the lighter side of the tape by adjusting the associated needle valve 75 . The opposite setting can be used to lighten the color on one side.

If an even stronger dark blue oxide coating is desired, the reheating section is used, in which conventional heating pipes between the baffle 55 and the lower end, e.g. B. the flow chamber 26 lie. Thus, in conjunction with the inlet tubes 78 or 79, the temperature of the belt 10 is increased to at least about 400 ° C., but not above 565 ° C., a small amount of air or another oxygen-containing gas being passed through inlet tubes 55 '(FIG . 1), which are operated in the same way as the other inlet pipes.

If in the reheat section the belt temperature is above about 593 ° C and a small amount of air or some other oxygen-containing gas is introduced through the inlet pipes 55 ', an additional Blackening done. The procedure can also be performed with the inlet pipes only 55 'are executed. The oxide coating then has all the necessary properties but a lighter weight than the combined coating process.

Using the invention, tapes can be treated that consist of a wide variety of steels, for example low-alloy steel, Silicon steel or Bessemerstahl. The furnace atmosphere can deviate from the specified composition have a different composition that does not contain any crust or causes scale formation, is not explosive and practical on the oxide formed does not have a reducing effect.

Claims (6)

Claims: 1. Device for blueing or blackening steel or iron strip with an oven through which the strip is continuously drawn at a regulated elevated temperature, characterized by a device (50) for introducing an inert gas into the interior of the Furnace and a device (77, 78, 79) which introduces a free oxygen-containing gas into the atmosphere of the inert gas near the belt (10) in such controlled quantities that the oxygen reacts with the metal of the belt to form an oxide coating completely implements the tape. 2. Device according to claim l., Characterized in that the interior of the furnace is divided into zones (16, 18, 20, 22, 24) , the temperatures of which by separate temperature control elements (39, 39 ', 40, 40 ', 41, 41'). 3. Device according to claim 1 or 2, characterized in that the furnace is gas-tight and that sealing rollers (13 or 28) are provided, between which the tape passes. 4. Procedure for Bluing of steel or iron strip using a device according to one of the Claims 1 to 3, characterized in that the temperature of the strip in the Near the point of introduction of the free oxygen-containing gas to a value in the range between about 400 and 566 ° C is regulated. 5. Procedure for blackening of steel or iron strip using a device according to one of the claims 1 to 3, characterized in that the temperature of the tape in the vicinity of the insertion point of free oxygen enthalterideil gas to a value equal to or higher than 594 ° C. 6. The method according to claim 4 or 5 for blueing or blackening steel or iron strip using a device according to one of claims 1 to 3, characterized in that the gas inside the furnace is brought to a pressure above the pressure of the outside air will. Publications considered: Otto Vogel, "Handbuch der Metallbeizerei", Vol. 11 (1951), pp. 252 to 260.