A method for surface treatment of a steel belt

Abstract

The invention relates to a method for surface treatment of a steel belt (6). The method comprises continuously feeding of the steel belt through a liquid bath (3) in a tank (2). The liquid bath (3) contains an alkali based oxidizing agent, and the tank (2) has a first opening (5), through which first opening the steel belt (6) is fed into the tank (2), and a second opening (8) opposite to the first opening, through which second opening the steel belt (6) is fed out of the tank (2). The method further comprises feeding of the steel belt (6) through the liquid bath (3) in the tank (2) while maintaining one and the same feeding direction (17) of the steel belt (6).

Description

[0001] A method for surface treatment of a steel belt

[0002] TECHNICAL FIELD

[0003] The invention relates to a method and an arrangement for surface treatment of a steel belt.

[0004] BACKGROUND

[0005] Steel belts are usually oxidized in furnaces where a gas is introduced to achieve the desired atmosphere. The steel belt is placed in the furnace in a coiled state with spacers between the turns of the steel belt coil.

[0006] Such a process requires a lot of work and does not always provide consistent quality.

[0007] SUMMARY

[0008] An objective of the invention is to provide a method for surface treatment of a steel belt, by which method a steel belt can be oxidized in a rational way without using a furnace.

[0009] The objective is achieved by a method for surface treatment of a steel belt, which method comprises continuously feeding of the steel belt through a liquid bath in a tank, wherein the liquid bath contains an alkali based oxidizing agent, and the tank has a first opening, through which first opening the steel belt is fed into the tank, and a second opening opposite to the first opening, through which second opening the steel belt is fed out of the tank, and which method further comprises feeding of the steel belt through the liquid bath in the tank while maintaining one and the same feeding direction of the steel belt.

[0010] The invention is based on the insight that by such a method, a steel belt can be oxidized when the steel belt is uncoiled, without bending or folding the steel belt which otherwise could cause cracking in the surface of the steel belt. Hereby, surface treatment of relatively long steel belts for various industrial applications can be effectively performed.

[0011] The liquid bath is preferably an alkaline solution providing blackening or black oxidation of the steel belt when the steel belt is fed through the liquid bath in the tank. Such an oxidation process results in a thin layer of black oxide, i.e. magnetite (FesCU), on the surface of the steel belt The alkaline solution can contain for example sodium hydroxide (NaOH), sodium nitrate (NaNOs) and / or sodium nitrite (NaNO2). The liquid in the tank suitably has a temperature in the range 60-150°C, preferably 80-120°C. A temperature at a lower end of the range can be used for carbon steels, and a temperature at an upper end of the range can be used for alloy steels and high alloy steels such as stainless steels.

[0012] Although it depends on the characteristics of the liquid bath and the steel belt material, a feed speed of the steel belt when the steel belt is fed through the liquid bath in the tank can often be in the range 0.05-0.5 m / min, preferably 0.1 -0.3 m / min.

[0013] According to one embodiment, the method comprises keeping a liquid level in the tank above an upper side of the steel belt when the steel belt is fed through the liquid bath in the tank. Hereby, it can be secured that the entire surface of the steel belt is exposed to the liquid in the tank for achieving an even oxidation along the surface of the steel belt.

[0014] According to a further embodiment, the method comprises keeping a predetermined liquid level in the tank by providing additional liquid to the tank compensating for leakage of liquid from the tank via the first opening and / or the second opening when the steel belt is fed through the liquid bath in the tank. Hereby, a relatively stable liquid level in the tank can be maintained and a lowest allowed liquid level can be secured without using an unnecessarily large tank and starting with an unnecessarily high liquid level in the tank.

[0015] According to a further embodiment, the method comprises collecting and using liquid that has leaked from the tank via the first opening and / or second opening as at least part of the additional liquid. Hereby, the liquid can be reused and only a small amount or no new liquid has to be added for maintaining the requisite liquid level in the tank.

[0016] According to a further embodiment, the method comprises providing the additional liquid continuously from above in a downward direction towards an upper side of the steel belt when the steel belt is fed through the liquid bath in the tank. Hereby, in addition to maintain the liquid level, due to a stirring and flushing effect caused by the additional liquid, the steel belt is exposed to the liquid in a way improving the oxidation of the surface of the steel belt. According to a further embodiment, the method comprises, before the steel belt is fed through the liquid bath in the tank, cleaning the steel belt by an alkaline cleaner. Hereby, the surface can be cleaned from dirt and grease and be prepared for oxidation. Such an alkaline cleaner or detergent can be based on for example a sodium hydroxide or potassium hydroxide.

[0017] According to a further embodiment, the method comprises, before the steel belt is fed through the liquid bath in the tank, feeding the steel belt through an activation bath, preferably using an acidic solution as the activation bath. Hereby, the steel belt is prepared for the following oxidation in the liquid of the tank, by removal of oxides and an increased activity of the surface.

[0018] The acidic solution can contain for example sodium bisulfate (NaHSO4) and sulfonic acid (HS(=O)2(OH)).

[0019] According to a further embodiment, the method comprises, after the steel belt has been fed through the liquid bath in the tank, cooling the steel belt by oil. Hereby, at the same time as the steel belt is cooled, a post-treatment of the surface is performed. Oil will penetrate the pores of the steel belt surface making the steel belt prepared for various industrial processes, such as for example food manufacturing processes. Preferably, an oil for food industry according to ISO 21469 standard is used.

[0020] According to another aspect of the invention, a further objective is to provide an arrangement for surface treatment of a steel belt, by which arrangement a steel belt can be oxidized in rational way without using a furnace.

[0021] This objective is achieved by an arrangement for surface treatment of a steel belt, wherein the arrangement comprises a tank and a liquid bath in the tank, wherein the liquid bath contains an alkali based oxidizing agent, and the tank has a first wall portion with a first opening, for enabling the steel belt to be fed into the tank through the first opening, and a second wall portion with a second opening opposite to the first opening, for enabling the steel belt to be fed out of the tank through the second opening. The invention is based on the insight that by such an arrangement, a steei belt can be fed through the tank and be oxidized when the steel belt is uncoiled, without bending or folding the steel belt which otherwise could cause cracking in the surface of the steel belt. Hereby, surface treatment of relatively long steel belts for various industrial applications can be effectively performed.

[0022] The liquid bath in the tank is preferably an alkaline solution for providing a black oxidation of the steel belt when the steel belt is fed through the liquid bath in the tank.

[0023] According to one embodiment, the arrangement comprises a collection receptacle for receiving liquid that has leaked from the tank via the first opening and / or second opening, and a pipe loop extending between the collection receptacle and the tank, and a pump for pumping the liquid from the collection receptacle to the tank via the pipe loop. Hereby, the liquid can be reused and only a small amount or no new liquid has to be added for maintaining the desired liquid level in the tank.

[0024] According to a further embodiment of the arrangement, an end portion of the pipe loop constituting an inlet to the tank is arranged at a level above the first opening and the second opening. Hereby, when entering the tank, the liquid pumped from the collection receptacle can flow via the inlet into the tank from above in a downward direction and cause a stirring and flushing effect that improves the oxidation of the surface of the steel belt.

[0025] According to a further embodiment, the arrangement has a heating element for heating the liquid. Hereby, the liquid can be heated to a suitable temperature for the oxidation process.

[0026] Further advantages and advantageous features of the invention are disclosed in the following description and in the claims.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings:

[0029] Fig. 1A is a flow chart illustrating a method for surface treatment of a steel belt,

[0030] Fig. 1 B is a schematical side view of an arrangement for surface treatment of a steel belt, and a steel belt,

[0031] Fig. 2A is a perspective view showing a part of the arrangement for oxidation of the steel belt, and

[0032] Fig. 2B is a cross section view along A-A in Fig. 2A.

[0033] DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0034] Fig. 1A shows a flow chart illustrating an example embodiment of a method for surface treatment of a steel belt.

[0035] The method can be applied to a steel belt, which steel belt suitably has been rolled and machined to the desired dimensions. The steel belt can be made of different types of carbon steel, alloy steel or high alloy steel such as stainless steel.

[0036] The steel belt is suitably a relatively thin metal sheet. For example, the thickness of the steel belt can be a few millimetres and the width can be hundreds of millimetres. The length of the steel belt can be several meters. The dimensions are of course adapted to the current application where the steel belt is to be used. As an example only, the width of the steel belt can be in the range 400-1500 mm, for example 850 mm, and the thickness of the steel belt can be in the range 0.8-1.4 mm, for example 1.2 mm.

[0037] The method suitably comprises cleaning 100 of the steel belt by an alkaline cleaner. In this way, the steel belt is cleaned from dirt and grease before performing an oxidation of the steel belt.

[0038] The method comprises continuously feeding of the steel belt through a liquid bath in a tank. The liquid bath contains an alkali based oxidizing agent. An oxidation 200 of the steel belt is performed, suitably with an alkaline solution used as the liquid bath, providing a black oxidation of the steel belt when the steel belt is fed through the liquid bath in the tank. In addition, water is suitably periodically added to the bath, with proper controls to prevent a steam explosion.

[0039] The tank has a first opening, through which first opening the steel belt is fed into the tank, and a second opening opposite to the first opening, through which second opening the steel belt is fed out of the tank. The method further comprises feeding of the steel belt through the liquid bath in the tank while maintaining one and the same feeding direction of the steel belt. In other words, the steel belt does not need to change feeding direction to be immersed in the liquid bath, since the steel belt is fed into and out of the tank at level such that the steel belt is fed through the liquid bath.

[0040] After the steel belt has been fed through the liquid bath in the tank, the method suitably comprises cooling 300 of the steel belt by oil.

[0041] Further, the method suitably comprises, before the steel belt is fed through the liquid bath in the tank, and after any cleaning 100, feeding of the steel belt through an activation bath. Activation 150 of the surface of the steel belt prepares the steel belt for the following oxidation 200.

[0042] Fig. 2A is a perspective view showing an arrangement for surface treatment of a steel belt, and a steel belt being oxidized. The method will now be described more in detail together with the arrangement for surface treatment of a steel belt, with reference to Figs. 2A and 2B.

[0043] In the following, the oxidation 200 and the components for performing the oxidation will be described more in detail. It should be stressed however that similar equipment can be used for one or more of other method steps, i.e. for cleaning, activation and / or cooling. See also Fig. 1 B, which is a schematical side view illustrating the arrangement also including equipment for cleaning 100, activation 150 and cooling 300.

[0044] The arrangement 1 comprises a tank 2 and a liquid bath 3 in the tank 2. The size of the tank 2 is adapted to the steel belt to be oxidized. For example, the width of the tank 2 can be in the range 0.5-2 m corresponding to the width of the steel belt, and the length of the tank can be in the range 1-10 m.

[0045] The liquid bath 3 contains an alkali based oxidizing agent. The tank 2 can be open at the top or provided with a lid. The tank 2 has a first wall portion 4 with a first opening 5, for enabling the steel belt 6 to be fed into the tank 2 through the first opening 5, and a second wall portion 7 with a second opening 8 opposite to the first opening 5, for enabling the steel belt 6 to be fed out of the tank 2 through the second opening 8.

[0046] The first opening 5 is preferably an inlet slot which suitably is horizontally arranged. The inlet slot 5 has dimensions which are substantially the same as or only slightly greater than the dimensions of the cross section of the steel belt 6. In other words, the height of the inlet slot 5 is slightly greater than the thickness 9 of the steel belt 6 and the width of the inlet slot 5 is slightly greater than the width 10 of the steel belt 6. See Fig. 2B showing a cross section view along A-A in Fig. 2A.

[0047] In the same way, the second opening 8 is preferably an outlet slot which is suitably horizontally arranged. The outlet slot 8 has dimensions which are substantially the same as or only slightly greater than the dimensions of the cross section of the steel belt 6, i.e. the height of the outlet slot 8 is slightly greater than the thickness 9 of the steel belt 6 and the width of the outlet slot 8 is slightly greater than the width 10 of the steel belt 6.

[0048] By adapting the dimensions of the first opening 5 and the second opening 8 to the current steel belt dimensions, the leakage of liquid out of the tank 2 via the first opening 5 and the second opening 8 can be minimized. In the example embodiment illustrated in Fig. 2A, the arrangement 1 comprises a collection receptacle 11 for receiving liquid that has leaked from the tank 2 via the first opening 5 and / or second opening 8, and a pipe loop 12 extending between the collection receptacle 11 and the tank 2, and a pump 13 for pumping the liquid from the collection receptacle 11 to the tank 2 via the pipe loop 12.

[0049] As also illustrated in Fig. 2B, an end portion 14 of the pipe loop 12 constituting an inlet 15 to the tank 2 is suitably arranged at a level H above the first opening 5 and the second opening 8. In the example embodiment illustrated in Figs. 2A and 2B, the inlet 15 to the tank 2 is the same as an outlet of the pipe loop 12. Further, the inlet 15 is preferably arranged at the top of the tank 2 or above the tank 2 such that the liquid entering the tank 2 via the inlet 15 can flow into the tank from above in a downward direction 19. In case the tank 2 is provided with a lid, the lid can have an opening corresponding to the pipe dimension of the end portion 14. Optionally, the end portion 14 and the lid can be connected or integrated with each other.

[0050] Further, the arrangement 1 suitably has a heating element 16 for heating the liquid used in the tank 2. As schematically illustrated in Fig. 2A, the heating element 16 can be arranged in the collection receptacle 11 to heat the liquid. The heating element 16 can be an electrical heating element, such as a resistive heater converting electrical energy into heat. For example, an immersion heater or similar. The liquid in the tank 2 suitably has a temperature in the range of 60-150°C, preferably 80-120°C.

[0051] In Fig. 2A, the steel belt 6 is fed from right to left. The direction of motion of the steel belt 6 is indicated by an arrow 17. Thus, the steel belt 6 is moving in the longitudinal direction of the steel belt 6. The feeding of the steel belt 6 can be performed by one or more driving rolls powered for moving the steel belt 6, and idling rolls, and control rolls arranged for guiding the steel belt 6. The feeding equipment is known by the skilled person in the art and is not shown in the figures.

[0052] The steel belt 6 is fed into the tank 2 through the first opening 5 of the first wall portion 4 and out of the tank 2 through the second opening 8 of the second wall portion 7. The first wall portion 4 and the second wall portion 7 are arranged opposite to each other as end portions of the tank 2. The first opening 5 and the second opening 8 are suitably arranged at the same height such that the steel belt 6 can be substantially horizontal when being fed through the liquid bath of the tank 2.

[0053] The feed speed of the steel belt 6 when the steel belt 6 is fed through the liquid bath 3 in the tank 2, is preferably constant. The feed speed can be in the range of 0.05-0.5 m / min, preferably 0.1-0.3 m / min, for example approximately 0.2 meter per minute.

[0054] The liquid level 18 in the tank 2 is preferably kept above an upper side 20 of the steel belt 6 when the steel belt 6 is fed through the liquid bath 3 in the tank 2, such that the part of the steel belt 6 being in the tank 2 is exposed to the liquid over the entire surface of the steel belt 6. In the example embodiment illustrated in Fig. 2A, a predetermined liquid level in the tank 2 is kept by providing additional liquid to the tank compensating for leakage of liquid from the tank 2 via the first opening 5 and / or the second opening 8 when the steel belt 6 is fed through the liquid bath 3 in the tank 2. Liquid that has leaked from the tank 2 via the first opening 5 and / or second opening 8 is collected and used as at least part of the additional liquid. Optionally, new additional liquid can also be added if required.

[0055] The liquid which has leaked from the tank 2 reaches the collection receptacle 11 , and is then pumped back to the tank 2 via the pipe loop 12 by means of the pump 13. Although other solutions are possible, the tank 2 can be arranged inside the collection receptacle 11, for example on the bottom of the collection receptacle 11, to enable the liquid to be collected.

[0056] The additional liquid is added continuously from above in the downward direction 19 towards the upper side 20 of the steel belt 6 when the steel belt 6 is fed through the liquid bath 3 in the tank 2. The inlet 15 of the tank (which also is the outlet of the pipe loop 12) is preferably arranged above the steel belt 6, and above the first opening 5 and the second opening 8, at a distance 21 in the vertical direction from the steel belt 6 (and from the first opening 5 and the second opening 8). See Fig. 2B.

[0057] The vertical distance 21 can be in the interval 5-30 cm, preferably 10-20 cm. At the same time, by adjusting the liquid level 18 to be just above the upper side 20 of the steel belt 6, the incoming liquid will have a drop height of approximately the same size as the vertical distance 21.

[0058] Although in the example embodiment illustrated in Fig. 2A, there is only one pipe loop 12 with one nozzle or outlet, two or more such pipe loops and / or a plurality of outlets could be arranged above the steel belt 6 depending on the width of the steel belt and the length of the steel belt being in the liquid bath. Hereby, a stirring and flushing effect that improves the oxidation of the surface of the steel belt can be achieved over the entire upper side 20 of the steel belt which creates conditions for an evenly distributed oxidation on the surface of the steel belt 6.

[0059] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1. A method for surface treatment of a steel belt (6), the method comprising continuously feeding of the steel belt through a liquid bath (3) in a tank (2), the liquid bath containing an alkali based oxidizing agent, the tank (2) having a first opening (5), through which first opening the steel belt (6) is fed into the tank (2), and a second opening (8) opposite to the first opening, through which second opening the steel belt (6) is fed out of the tank (2), and the method further comprising feeding of the steel belt (6) through the liquid bath (3) in the tank (2) while maintaining one and the same feeding direction (17) of the steel belt (6).

2. A method according to claim 1 , characterized by keeping a liquid level (18) in the tank (2) above an upper side (20) of the steel belt (6) when the steel belt is fed through the liquid bath (3) in the tank (2).

3. A method according to claim 1 or 2, characterized by keeping a predetermined liquid level (18) in the tank (2) by providing additional liquid to the tank compensating for leakage of liquid from the tank via the first opening (5) and / or the second opening (8) when the steel belt (6) is fed through the liquid bath (3) in the tank (2).

4. A method according to claim 3, characterized by collecting and using liquid that has leaked from the tank (2) via the first opening (5) and / or second opening (8) as at least part of the additional liquid.

5. A method according to claim 3 or 4, characterized by providing the additional liquid continuously from above in a downward direction (19) towards an upper side (20) of the steel belt (6) when the steel belt is fed through the liquid bath (3) in the tank (2).

6. A method according to any preceding claim, characterized by using an alkaline solution as the liquid bath (3) in the tank (2), providing a black oxidation of the steel belt (6) when the steel belt is fed through the liquid bath (3) in the tank (2).

7. A method according to any preceding claim, wherein a feed speed of the steel belt (6) when the steel belt is fed through the liquid bath (3) in the tank (2), is in the range of 0.05-0.5 m / min, preferably 0.1 -0.3 m / min.

8. A method according to any preceding claim, wherein the liquid (3) in the tank (2) has a temperature in the range of 60-150°C, preferably 80-120°C.

9. A method according to any preceding claim, characterized by before the steel belt (6) is fed through the liquid bath (3) in the tank (2), cleaning the steel belt (6) by an alkaline cleaner.

10. A method according to any preceding claim, characterized by before the steel belt (6) is fed through the liquid bath (3) in the tank (2), feeding the steel belt (6) through an activation bath.

11. A method according to claim 9 and 10, characterized by after the steel belt (6) has been cleaned and before the steel belt (6) is fed through the liquid bath (3) in the tank (2), feeding the steel belt (6) through the activation bath.

12. A method according to claim 10 or 11, characterized by using an acidic solution as the activation bath.

13. A method according to any preceding claim, characterized by after the steel belt (6) has been fed through the liquid bath (3) in the tank (2), cooling the steel belt (6) by oil.

14. An arrangement (1) for surface treatment of a steel belt (6), the arrangement comprising a tank (2) and a liquid bath (3) in the tank, the liquid bath (3) containing an alkali based oxidizing agent, wherein the tank (2) has a first wall portion (4) with a first opening (5), for enabling the steel belt (6) to be fed into the tank (2) through the first opening, and a second wall portion (7) with a second opening (8) opposite to the first opening, for enabling the steel belt (6) to be fed out of the tank (2) through the second opening.

15. An arrangement according to claim 14, characterized in that the arrangement (1) comprises a collection receptacle (11) for receiving liquid that has leaked from the tank (2) via the first opening (5) and / or second opening (8), and a pipe loop (12) extending between the collection receptacle (11) and the tank (2), and a pump (13) for pumping the liquid from the collection receptacle (11) to the tank (2) via the pipe loop.

16. An arrangement according to claim 15, characterized in that an end portion (14) of the pipe loop (12) constituting an inlet (15) to the tank (2) is arranged at a level above the first opening (5) and the second opening (8).

17. An arrangement according to any of claims 14-16, characterized in that the liquid bath (3) in the tank (2) is an alkaline solution for providing a black oxidation of the steel belt (6) when the steel belt is fed through the liquid bath (3) in the tank (2).

18. An arrangement according to any of claims 14-17, characterized in that the arrangement (1) has a heating element (16) for heating the liquid.

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