JP2011200879A - Method for circulating and supplying rolling oil for cold rolling, and equipment for cold rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cost-effective method for circulating and supplying rolling oil, which effectively and highly-accurately removes iron powder or scum from the large amount of emulsion used as a lubricant for cold rolling and also to provide equipment for cold rolling.SOLUTION: The equipment for cold rolling includes a circulation system for circulating rolling oil emulsion including the steps of: separating the emulsion in the system into oil and dilute emulsion through a fiber filter; and removing scum (including iron powder and water) from the separated oil by a centrifugal method.

Description

  The present invention relates to a method for cold rolling a steel strip, and more particularly, to a method for efficiently removing iron powder, scum and the like mixed in a rolling oil emulsion that is circulated and cold rolling equipment.

  In cold rolling, two performances of lubrication and cooling of the rolling roll and steel strip are important. Lubrication is a performance that lowers the coefficient of friction between the work roll and the steel strip (roll bite), reduces the rolling load, and prevents seizure between the work roll and the steel strip. Cooling is a performance necessary for preventing an excessive increase in temperature of the rolling roll and the steel strip due to frictional heat generation and processing heat generation in the roll tool.

  In order to exhibit these lubricating and cooling performances, in cold rolling of steel strip, rolling is performed while supplying rolling oil to the steel strip or roll bite, and as rolling oil, mineral oil, natural fats and oils can be used. An emulsion obtained by diluting a water-insoluble oil base oil such as a synthetic ester in water with a surfactant (hereinafter also referred to as “rolling oil emulsion”) is widely used. This emulsion is used as an O / W type (oil-in-water type) emulsion. For example, the water-insoluble oil base oil is averaged by previously mixing and stirring the water-insoluble oil base oil and water. It is made into the emulsion which contains about 1-2 mass% as an oil droplet with a particle size of about 2-30 micrometers, and is supplied to a steel strip or a roll bite. When the emulsion is supplied to the steel strip or roll bite by spraying or the like, water is removed and an oil film is formed on the steel strip surface or roll bite inlet (this phenomenon is called plate-out). By forming this oil film, the lubrication performance of the roll bite, that is, the lubrication performance such as the effect of reducing the friction coefficient and the seizure resistance is improved, and even a hard steel strip can be rolled under high pressure.

  By the way, in order to reduce the amount of the emulsion used and the amount of waste liquid, it is common to provide a circulation system of the emulsion in the cold rolling equipment and circulate and use the emulsion supplied to the steel strip and the roll bite. Here, a problem in circulating the emulsion is contamination with foreign matter in the emulsion. During cold rolling, iron powder is generated by frictional contact between the steel strip and the rolling roll. Further, this iron powder is easily taken into the oil in the emulsion, and further reacts with the emulsion to become a modified product, thereby generating a scum that is a mixture of the iron powder and the modified product. For this reason, foreign materials such as iron powder and scum are mixed in the emulsion after being supplied to the steel strip or roll bite. If these emulsions are circulated and used while these foreign materials are still mixed, the foreign materials are cold-rolled. The work environment deteriorates due to adhesion and accumulation on the rolling rolls of the equipment. In addition, foreign matter is caught in the roll bite, and surface flaws are generated in the steel strip.

Thus, when the emulsion is circulated, it is essential to provide a circulation system with a step of removing foreign matters such as iron powder and scum from the emulsion and cleaning the emulsion.
As a technique for removing foreign substances from an emulsion, for example, a technique for removing iron powder using a magnetic filter as disclosed in Patent Document 1 or a magnetic separator is known. In addition, Hoffman filters, flatbed filters and notch wire filters that remove iron powder using filter paper and filter cloth, and Schneider filters that can be precisely filtered with a filter aid are widely used. Discloses a technique in which a Hoffman filter and a Schneider filter are used in combination.

  Patent Document 3 discloses a technique in which a filtration filter and a magnetic filter are used in combination. According to this technique, particles larger than mineral oil particles in the emulsion are removed by a filtration filter, and iron powders having an average particle size of 0.5 to 1.0 μm that cannot be removed by the filtration filter can be removed by a magnetic filter.

Japanese Patent Laid-Open No. 10-192618 JP 2000-279706 A JP-A-8-243605 JP 2000-288303 A Japanese Patent Publication No. 7-34879

However, in the technology using a magnetic filter or magnetic separator, in the process of separating and removing the iron powder from the emulsion, the oil separated from the emulsion and also attached to the iron powder is removed together with the iron powder. Reduces the basic unit. In addition, the oil concentration in the emulsion is usually about 1 to 2% by mass, and the iron powder mixed in the emulsion is about 1000 to 3000 ppm by mass when converted to the iron concentration relative to the oil in the emulsion. The iron concentration is very low, about 10 to 60 ppm by mass. That is, the emulsion after being supplied to a steel strip or a roll bite is collected and stored in a large-capacity tank of about 150 to 200 m ^{3, and} about 10 to 60 mass ppm of iron from the emulsion in such a large-capacity tank. Removing powder directly is very inefficient. For this reason, there is a limit to removing iron powder from an emulsion in a large-capacity tank as described above using a magnetic filter or magnetic separator, and the iron powder is mixed in an amount of about 1000 to 2000 ppm by mass with respect to the oil. In many cases, the emulsion is recycled as it is.

  On the other hand, the Hoffman filter and the notch wire filter are for removing foreign matters using filter paper or filter cloth having a mesh size of several tens of μm, and are effective in removing enlarging scum and the like. However, the size of the iron powder mixed in the oil in the emulsion is often several μm or less, and these iron powders cannot be sufficiently removed. Further, if the opening is further reduced in order to remove these iron powders, the opening is immediately closed by a large scum or the like, so that it is difficult to efficiently remove the scum or the like.

Further, the Schneider filter is used for filtration of straight oil, and fine filtration with an opening of 1 μm or less is also possible. However, when a filter having a small opening is used as described above, oil droplets in the emulsion adjusted to a size of 2 to 30 μm aggregate and the opening is immediately closed.
Moreover, even if a filtration filter and a magnetic filter are used in combination, it has been difficult to efficiently and accurately remove iron powder from a large-capacity emulsion. Therefore, in the above-mentioned conventional technology, oil containing iron powder adheres to the surface of the steel strip after cold rolling, and the load for surface cleaning in the lower processes such as degreasing and plating is increasing. Met.

In addition, it is known that the technique of removing the iron powder by centrifugal separation using the specific gravity difference is effective in removing the iron powder mixed in the oil in the emulsion. However, in order to centrifuge a large amount of emulsion recovered and stored in a large-capacity tank of about 150 to 200 m ³ as described above, a large-scale centrifugal equipment and electric power are required. Is unrealistic because of the increased volume.

  The present invention advantageously solves the problems found in the prior art described above, and efficiently and accurately removes iron powder, scum, etc. mixed in the emulsion from a large-capacity emulsion that is circulated and used in cold rolling. It is an object of the present invention to provide a rolling oil circulation and supply method and cold rolling equipment which can be removed easily and in terms of cost.

  In order to solve the above-mentioned problems, the present inventors apply a centrifugal separation process advantageous for removing iron powder from a circulating emulsion to a cold rolling facility without causing an increase in facility cost and power cost. The means were intensively studied. As a result, it was found that it is effective to separate the emulsion into an oil component and a low-concentration emulsion by an oil-water separator using a fiber filter before sending the emulsion to be circulated to the centrifugal separator. In other words, instead of subjecting all emulsions to be circulated directly to centrifugal separation, the emulsion is separated into oil and low-concentration emulsions, and only the separated oil is subjected to centrifugal separation, thereby reducing the load on the centrifugal separator. It has been found that the iron powder can be effectively removed from the emulsion used for circulation.

The present invention has been completed based on the above findings, and the gist thereof is as follows.
(1) In a cold rolling mill circulating oil supply method for cold rolling, a circulating system for circulating the rolling oil emulsion is provided in the cold rolling equipment, and the rolling oil emulsion is circulated and used.
Separating the rolling oil emulsion in the circulation system into an oil and a low-concentration emulsion using a fiber filter;
Separating scum (including iron powder and moisture) from the separated oil by a centrifugal separation method;
A rolling oil circulation supply method in cold rolling, characterized by comprising:
(2) In the cold rolling equipment provided with a circulation system for circulating the rolling oil emulsion, the circulation system includes:
An oil-water separator having a fiber filter for separating the rolled oil emulsion into an oil and a low-concentration emulsion;
A cold rolling facility, comprising: a centrifuge for separating scum (including iron powder and moisture) from the separated oil.

  According to the present invention, when circulating a rolling oil emulsion in cold rolling, iron powder and scum are efficiently and accurately removed from the circulating oil emulsion to be circulated without causing an increase in equipment cost and power cost. It is possible to do so, and there is a remarkable effect in the industry.

It is a figure which shows an example of the cold rolling equipment provided with the circulation system which circulates a rolling oil emulsion of this invention. It is a figure which shows an example of the conventional cold rolling equipment which provided the circulation system which circulates a rolling oil emulsion. FIG. 3 is a diagram showing the relationship between the cold rolling time (hr.) And the iron concentration (mass ppm) with respect to the oil in the circulating oil emulsion to be circulated.

Hereinafter, the present invention will be described in detail.
The present invention is intended for all types of cold rolling, such as tandem rolling mills and reverse rolling mills, including commonly known cold rolling, and using emulsion as rolling oil. In addition, the material to be rolled in the present invention is a thin steel strip mainly made of an iron-based material such as ordinary steel, high carbon steel, and stainless steel.

First, the cold rolling equipment according to the present invention will be described.
An example of the cold rolling equipment provided with the circulation system which circulates the emulsion which is rolling oil is shown in FIG. The cold rolling equipment 1 includes a cold rolling mill 2 having rolling rolls (work roll 3a, backup roll 3b), emulsion supply means 4 for supplying the emulsion to the roll bite, and a circulation system 10A for circulating the emulsion. After the steel strip S is unwound from a payoff reel (not shown) and fed in the direction of the arrow in the figure, the steel strip S is rolled by a cold rolling mill 2 having a rolling roll (work roll 3a, backup roll 3b). , Wound by a tension reel (not shown).

  The circulation system 10A includes, for example, a recovery oil pan 12 and a circulation system tank 13, and the emulsion after being supplied to the roll bite from the emulsion supply means 4 is recovered by the recovery oil pan 12, and the recovered emulsion is circulated. A circulation path 11 is provided which is supplied to the emulsion supply means 4 by the pump P1 via the system tank 13 and returned. In cold rolling, the oil content of the emulsion in the circulation system tank 13 decreases due to the selective adhesion of the oil content of the emulsion to the rolled material after rolling and the fume-out phenomenon. For this reason, a replenishment tank 14 is attached to the circulation system tank 13, and the oil concentration of the emulsion in the circulation system tank 13 is set to an appropriate value by appropriately supplying new rolling oil from the supply tank 14 to the circulation system tank 13. To maintain.

  Further, as shown in FIG. 2, it is preferable to provide a known Hoffman filter 16 in the circulation path 11 between the recovery oil pan 12 and the circulation system tank 13. By providing the Hoffman filter 16, foreign matters such as enormous scum and fragments of the welded portion of the material to be rolled can be effectively removed from the emulsion recovered by the recovery oil pan 12. Further, it is preferable that the entire amount of the emulsion recovered by the recovery oil pan 12 is passed through the Hoffman filter 16 to remove foreign matters.

  In addition, since the effect of removing iron powder from the emulsion cannot be expected with the Hoffman filter 16, the circulation path 17 formed by the circulation system tank 13, the pump P2, and the magnetic filter 15 is provided as shown in FIG. Is preferred. By providing the circulation path 17 including the magnetic filter 15, iron powder can be removed from the emulsion in the circulation system tank 13. As described above, it is extremely inefficient to directly remove about 10 to 60 ppm by mass of iron powder from the emulsion in the large-capacity tank. Therefore, the magnetic filter 15 is not provided in the circulation path 11, and a circulation path 17 is separately provided as shown in FIG. 2, and a part of the emulsion in the circulation system tank 13 is sent to the circulation path 17 and processed by the magnetic filter 15. It is preferable to do.

The above-described configuration is a cold rolling mill having a conventional circulation system, but the point to be noted in the present invention is that a fiber filter that separates an emulsion into an oil and a low-concentration emulsion in addition to the conventional circulation system 10A And a centrifuge 24 for separating scum (including iron powder and moisture) from the separated oil.
As shown in FIG. 1, in the circulation system 10 of the present invention, in addition to the circulation path 11 or further the circulation path 17, for example, the emulsion in the circulation system tank 13 is subjected to oil-water separation treatment, further centrifugal separation treatment, and circulation. Circulation paths 21a, 21b, 21c returned to the system tank 13, an oil / water separator 22 and a centrifuge 24 are provided. Furthermore, between the circulation system tank 13 and the oil / water separator 22, the oil / water separator 22 separates the emulsion into an oil and a low-concentration emulsion, and then returns the low-concentration emulsion from the oil / water separator 22 to the circulation system tank 13. A path 25 is also provided.

Next, based on FIG. 1, the rolling oil circulation supply method of this invention is demonstrated.
In the circulation system 10 of the present invention, the processing steps in the circulation path 11 (and the circulation path 17) are the same as those in the prior art described above. In addition to the prior art, the point to be noted in the present invention is that the emulsion in the circulation system 10 is separated into an oil component and a low-concentration emulsion using a fiber filter provided in the oil / water separator 22, and further, from the separated oil component, This is the point of providing a step of separating scum (including iron and water) by a centrifugal separation method using the centrifugal separator 24.

  In the present invention, the emulsion recovered by the recovery oil pan 12 is freed of foreign matter such as scum that has been enlarged by the Hoffman filter 16 and is sent to the circulation system tank 13. A part of the emulsion sent to the circulation system tank 13 is sent to the circulation path 21a, and the remaining emulsion is supplied to the emulsion supply means 4 through the circulation path 11 as usual.

The emulsion sent from the circulation system tank 13 to the circulation path 21a first undergoes a process of separating the emulsion into an oil component and a low-concentration emulsion by a fiber filter. That is, the emulsion sent to the circulation path 21a is sent to the oil / water separator 22 and separated into an oil component and a low-concentration emulsion by the fiber filter of the oil / water separator 22.
In this step, it is ideal to completely separate the emulsion into oil and water, but it is difficult to completely separate the emulsion. Therefore, in the present invention, about 30 to 50% of the oil content in the emulsion is recovered by the fiber filter. That is, in this step, the emulsion is separated into 30-50% of the oil contained in the emulsion and a low-concentration emulsion in which the oil after the extraction of 30-50% is reduced in concentration. To do. The low-concentration emulsion separated by the fiber filter of the oil / water separator 22 is returned to the circulation system tank 13 through the communication path 25.

  The oil separated in the above step (30-50% of the oil contained in the emulsion) is sent to the centrifugal separator 24 by the circulation path 21b, and contains a lot of iron powder from the oil by the centrifugal separator 24. It goes through the process of removing scum. The oil from which the scum has been removed is returned to the circulation system tank 13 through the circulation path 21c. The scum and the like removed from the oil by the centrifugal separator 24 is discharged out of the system by the circulation system outside pipe 23.

As described above, the technique of removing the iron powder by centrifugation is effective in removing the iron powder mixed in the oil in the emulsion. That is, through this step, it is possible to more effectively remove the iron powder mixed in the oil in the emulsion to be circulated.
In addition, as described above, it is disadvantageous in terms of equipment costs to perform a centrifugal separation process on a large amount of emulsion. Therefore, if a large amount of emulsion delivered from the circulation system tank 13 is directly subjected to a centrifugal separation process, an increase in cost is inevitable.

  However, in the present invention, the emulsion is separated into a part (about 30 to 50%) of the oil contained in the emulsion and the low-concentration emulsion before the centrifugal separation treatment. That is, the centrifugal separator is not subjected to a centrifugal separation treatment, and only a part (about 30 to 50%) of the oil contained in the emulsion is subjected to a centrifugal separation treatment. Is reduced.

  As the fiber filter of the oil / water separator 22, for example, a fiber filter described in Patent Document 4 is preferably used. The average particle diameter of the oil droplets in the emulsion is usually about 2 to 30 μm. In the fiber filter, oil droplets smaller than the filter hole diameter are likely to pass through the filter, and oil droplets larger than the filter hole diameter are easily collected by the fiber of the filter. The oil droplets collected on the fibers gradually aggregate to form coarse oil droplets that float away from the fibers and can be easily extracted. That is, since an oil droplet having a large particle diameter is extracted from the emulsion that has passed through the fiber filter, the oil concentration in the emulsion can be reduced and the average particle diameter of the oil droplet can be reduced. In the present invention, for the fiber filter, the filter pore diameter, the filter material, the filter film thickness, and the like may be selected according to the particle size of the emulsion and the type of surfactant used at the time of emulsion preparation.

  As the centrifuge 24, a continuous centrifuge such as a decanter is preferably used. For example, a decanter described in Patent Document 5 is preferably used. The screw type decanter described in Patent Document 5 is a rotating body composed of a long cylinder supported by a horizontal rotating shaft, and a screw conveyor that is coaxially mounted therein and rotates with a slight speed difference. Centrifugal separation is performed, heavy substances are separated on the outer diameter side in the radial direction, light substances are separated on the inner diameter side in the radial direction, and each separated substance is discharged from the end of the rotating body. It is common. Note that the oil component fed after passing through the oil / water separator 22 may contain moisture. In such a case, it is preferable to prepare two decanters and separate them into three layers of moisture, scum (including iron powder) and oil.

In FIG. 1, the low concentration emulsion separated by the fiber filter of the oil / water separator 22 is shown to be returned to the circulation system tank 13 through the communication path 25, but the low concentration emulsion is separately supplied from the oil / water separator 22. A pipe (not shown) may be provided, and the cold rolling mill 2 may be supplied to a rolling mill of a specific stand that requires low lubrication.
Further, FIG. 1 shows a mode in which the oil component from which the scum containing a large amount of iron powder is removed by the centrifugal separator 24 is returned to the circulation system tank 13 by the circulation path 21c, but the iron powder and scum are removed by the centrifugal separator 24. A route (not shown) for sending the removed oil to the replenishing tank 14 may be provided separately. Furthermore, a separate pipe (not shown) is provided from the centrifugal separator 24, and the scum containing a large amount of iron powder is removed by the centrifugal separator 24 to the rolling mill of a specific stand that requires high lubrication in the cold rolling mill 2. Oil may be supplied.

In the present invention, the flow rate of the emulsion sent from the circulation system tank 13 to the circulation path 21a is various conditions such as cold rolling conditions, the capacity of the circulation system tank 13, the type of emulsion, and the processing capacity of the centrifugal separator 24. Optimized based on. For example, when the flow rate of the emulsion supplied to the roll bite is 20 to 40 m ³ / min and the volume of the circulation system tank 13 is 100 to 200 m ³ , the emulsion sent from the circulation system tank 13 to the circulation path 21a. the flow rate and 0.1 to 10 m ³ / min or so, but the flow rate of the emulsion to be sent from the circulation system tank 13 to the circulation path 17 may be 1 to 5 m ³ / min or so, of course, the present invention is not limited thereto It is not something.

As described above, in the present invention, from a large-volume emulsion to be circulated, first, a small amount of oil is extracted, and then, by removing scum containing a large amount of iron powder from the oil, a large-capacity to be circulated is used. It is possible to remove iron powder from the emulsion efficiently and with high accuracy, and to clean the emulsion to be circulated without increasing the equipment cost.
Moreover, in this invention, an oil component can be extracted from the emulsion circulated and used using a fiber filter. Therefore, in the present invention, for example, for the purpose of reducing the basic unit of the emulsion or preventing slipping due to overlubrication, the oil content in the emulsion used for lubrication can be temporarily reduced in concentration.

  Furthermore, in this invention, the iron powder mixed in the oil in an emulsion can be effectively removed by performing the centrifugation process to the oil extracted with the said fiber filter. Therefore, the oil from which the iron powder has been removed is stored in a separate tank (not shown). For example, for the purpose of suppressing heat scratches, the oil in the above-mentioned separate tank is replenished to the emulsion to be used as needed. The oil concentration can be temporarily increased. That is, according to the present invention, it is possible to control the oil content of the emulsion to be circulated as necessary.

  In order to confirm the effect of the present invention, the rolling is continuously performed for one week using the cold rolling equipment (example of the present invention) shown in FIG. 1 and the cold rolling equipment (comparative example) shown in FIG. The relationship between time and iron content in the emulsion was investigated. Each of the cold rolling mills shown in FIGS. 1 and 2 is an emulsion circulation type, 5-stand tandem type cold rolling mill. Moreover, as the material S to be rolled, ordinary steel, high-tensile steel, and stainless steel were prepared so as to have the same amount of rolling, and rolled.

As the rolling oil, an emulsion (average particle size of oil droplets: 10 μm, oil concentration: 1.0 to 1.2% by mass), which is an ester base oil and a nonionic surfactant, was used.
The capacity of the circulation system tank 13 was 200 m ³ , and the oil concentration of the emulsion in the circulation system tank 13 was adjusted to 0.8 to 1.2%. The emulsion was supplied to the roll bite of each stand at a flow rate of 35 m ³ / min, and then recovered with the recovery oil pan 12, and the total amount of the recovered emulsion was processed with the Hoffman filter 16. In addition, an emulsion having a flow rate of 4 m ³ / min was sent from the emulsion in the circulation system tank 13 to the magnetic filter 15 to perform iron powder removal treatment.

Regarding the above conditions, rolling was performed under the same conditions for both the cold rolling equipment (invention example) shown in FIG. 1 and the cold rolling equipment (comparative example) shown in FIG.
Further, in the cold rolling facility shown in FIG. 1 (example of the present invention), in addition to the above, an oil / water separator using an emulsion of a flow rate of 1 m ³ / min from a circulation system tank 13 and a polyethylene filter having a pore diameter of 7 μm The emulsion was separated into an oil and a low concentration emulsion. With this process, an average oil content of 0.005m ³ / min can be extracted, and the extracted oil content is centrifuged in a decanter (centrifugal separator 24) under the condition of 1000G (gravity acceleration) x 30s. Scum containing powder was discharged out of the circulation system. The separated low-concentration emulsion was returned to the circulation system tank 13.

  Under the above conditions, cold rolling is continuously performed for one week by the cold rolling equipment shown in FIG. 1 (example of the present invention) and the cold rolling equipment shown in FIG. 2 (comparative example), and every 8 hours. The emulsion in the circulation system tank 13 was sampled and the iron concentration contained in the oil content of the emulsion was measured. During the continuous rolling period, both the cold rolling equipment shown in FIG. 1 (example of the present invention) and the cold rolling equipment shown in FIG. 2 (comparative example) finished rolling without causing troubles during rolling. . The results of the measured iron concentration are shown in FIG.

As shown in FIG. 3, in the conventional example (circle in the figure), the iron concentration has changed from 1400 to 1800 ppm after 40 hours from the start of rolling, whereas in the example of the present invention (♦ in the figure), 40% from the start of rolling. Since then, the iron concentration has remained at a very low concentration of 500-900 ppm.
As described above, according to the present invention, the iron concentration of the emulsion to be circulated can be reduced to about 1/2 of the conventional one, thereby reducing the contamination of the steel strip and the degreasing step of the steel strip following the cold rolling. Reduction of load, improvement of rolling oil intensity, etc. can be achieved.

1… Cold rolling equipment
2… Cold rolling mill
3a… Work roll
3b… Backup roll
S… Rolled material (steel strip)
10 ... Circulation system (present invention)
10A ... Circulation system (conventional)
11… Circulation route
12… Oil pan for collection
13… Circulation system tank
14… Supply tank
15… Magnetic filter
16… Hoffman filter
17… Circulation route
21a, 21b, 21c… circulation path
22… Oil-water separator
23… Piping outside the circulation system
24… Centrifuge
25… Communication route

Claims (2)

In the cold rolling equipment, a circulation system for circulating the rolling oil emulsion is provided, and in the rolling oil circulation supply method of cold rolling using the rolling oil emulsion in circulation,
Separating the rolling oil emulsion in the circulation system into an oil and a low-concentration emulsion using a fiber filter;
Separating scum (including iron powder and moisture) from the separated oil by a centrifugal separation method;
A rolling oil circulation supply method in cold rolling, characterized by comprising: In the cold rolling equipment provided with a circulation system for circulating the rolling oil emulsion, the circulation system,
An oil-water separator having a fiber filter for separating the rolled oil emulsion into an oil and a low-concentration emulsion;
A cold rolling facility, comprising: a centrifuge for separating scum (including iron powder and moisture) from the separated oil.

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