JP7587145B2 - Rolling lubrication method and rolling lubrication device in cold rolling - Google Patents

Description

The present invention relates to a rolling lubrication method and rolling lubrication device for cold rolling.

In cold rolling, lubricating oil (rolling oil) is generally supplied to the steel plate and work rolls at the entry side of the rolling stand in the rolling mill to maintain the coefficient of friction between the steel plate and the work rolls within an appropriate range in order to stabilize the rolling operation, improve the shape and surface quality of the product, prevent seizure and slippage, and extend the life of the work rolls.

On the other hand, it is known that the amount of rolling oil introduced into the roll bite (the processing area where the steel plate and the work roll are in contact) changes depending on factors such as the surface roughness of the steel plate and the work roll, and the temperature. Such a change in the amount of rolling oil introduced leads to a change in the coefficient of friction between the steel plate and the work roll, which may cause problems such as gauge hunting (plate thickness fluctuation) and chattering (abnormal vibration of the rolling mill) due to load fluctuation between the steel plate and the work roll. Therefore, in order to realize stable rolling operations, it is important to control the coefficient of friction between the steel plate and the work roll within an appropriate range and suppress the fluctuation of the friction coefficient. In order to control the coefficient of friction between the steel plate and the work roll within an appropriate range, it is necessary to detect whether the rolling oil is being supplied to the steel plate and the work roll in an appropriate amount.

In this regard, several prior art techniques for detecting oils, lubricants, etc. are known. For example, Patent Document 1 describes a method for detecting contamination of oil or lubricants in manufactured products, which includes the steps of adding a fluorescent taggant to the oil or lubricant contained in a processing machine for the product, transporting the product through an infrared detection device, irradiating the product with infrared light from the detection device as the product passes through the detection device, and detecting the infrared light emitted from the irradiated product.

For example, U.S. Patent No. 5,399,433 proposes a fluorescent lubricant that is applied to an object as a liquid and dries to form a solid coating to provide lubricity to the part and enable the part's position to be determined when the part is used in low light conditions.

Patent Document 3 describes a coating-type water-based lubricant film-forming agent for metal plastic processing, which contains an aqueous base component and, in some cases, a lubricant component, and is characterized by further containing an aqueous fluorescent dye. Furthermore, Patent Document 3 describes that such a lubricant film-forming agent ensures uniform dispersion of the fluorescent material before and after coating, and also ensures uniform dispersion of the fluorescent material in the film before and after plastic processing, so that the adhesion of the lubricant film can be easily investigated at the processing site by simply irradiating it with ultraviolet light and measuring the luminescence.

JP 2017-161530 A JP 2003-313577 A JP 2007-277468 A

Patent Documents 1 to 3 propose using fluorescent substances to detect the oil and lubricating film they contain, but do not adequately measure or analyze the detected oil, etc., quantitatively, and do not teach or suggest in any way that the proposed technical matters can be applied to the rolling lubrication process of steel sheets.

The present invention has been made in view of the above, and its purpose is to provide a rolling lubrication method and rolling lubrication device for cold rolling that can achieve improved rolling lubrication through a novel configuration.

The present invention which achieves the above object is as follows.
(1) A step of supplying rolling oil containing a fluorescent substance to a steel plate and a work roll from an inlet side of a rolling mill;
measuring a fluorescence intensity from rolling oil present on a surface of the steel sheet using a fluorescence microscope arranged on the delivery side of the rolling mill;
calculating a distribution of the oil film thickness h on the steel sheet based on the measured fluorescence intensity and a previously determined relationship between the fluorescence intensity and the oil film thickness of the rolling oil;
The oil film thickness h and the following formula 1:
h _b =0.5×√(R _roll ² +R _strip ² )...Formula 1
(where R _roll and R _strip are the arithmetic mean roughnesses of the surfaces of the work roll and the steel sheet to be rolled, respectively) based on the boundary lubrication threshold value h _b defined by the above formula, calculating the ratio of the area where h < h _b to the entire area photographed by the fluorescence microscope as the contact ratio α;
From the contact ratio α and the boundary friction coefficient μ _b specific to the steel plate, the following formula 2:
μ = α × μ _b ... Equation 2
A rolling lubrication method in cold rolling, comprising a control step of controlling a friction coefficient μ between the steel plate and the work rolls, the friction coefficient μ being calculated by the above formula (1), within a predetermined range.
(2) The method according to (1) above, characterized in that the control step is carried out by adjusting the supply amount or concentration of the rolling oil.
(3) The method according to (1) or (2) above, characterized in that the fluorescent microscope travels at the same speed as the steel sheet on the delivery side of the rolling mill.
(4) A rolling mill equipped with work rolls for rolling steel plates;
a supply device disposed on an inlet side of the rolling mill for supplying rolling oil containing a fluorescent substance to the steel plate and the work rolls;
A rolling lubrication device for cold rolling, comprising: a fluorescent microscope arranged on the exit side of the rolling mill; and a control device for controlling the supply of rolling oil from the supply device based on a signal from the fluorescent microscope.

According to the rolling lubrication method and rolling lubrication device in cold rolling of the present invention, the contact state between the steel sheet inside the roll bite and the work roll can be properly evaluated by measuring the fluorescence intensity emitted from the fluorescent substance contained in the rolling oil present on the steel sheet after rolling. By properly evaluating the contact state between the steel sheet inside the roll bite and the work roll, the friction coefficient between them can be determined. Therefore, according to the rolling lubrication method and rolling lubrication device in cold rolling of the present invention, the supply of rolling oil can be adjusted so that the friction coefficient is controlled within a predetermined range, and it is possible to realize stable rolling operation in cold rolling without causing rolling defects such as seizure, slip, gauge hunting, and chattering. In addition, even under a situation where the type of steel used in cold rolling is changed and adjustments to achieve stable rolling operation normally take time and cause a decrease in yield, it is possible to realize stable rolling operation more quickly while suppressing a decrease in yield compared to the case of conventional cold rolling without controlling the supply of rolling oil.

FIG. 1 is a schematic diagram showing a rolling lubrication device in cold rolling according to an embodiment of the present invention. 1 is a graph showing the experimentally determined relationship between fluorescence intensity and rolling oil film thickness at an exposure time of 0.5 seconds. FIG. 2 is a diagram showing a schematic diagram of the composite roughness of a work roll and a steel sheet surface. FIG. 1 shows the area of the boundary lubrication region calculated based on signals from a fluorescent microscope.

<Rolling lubrication method in cold rolling>
A rolling lubrication method in cold rolling according to an embodiment of the present invention includes:
A step of supplying rolling oil containing a fluorescent substance to a steel plate and a work roll from an inlet side of a rolling mill;
measuring a fluorescence intensity from rolling oil present on a surface of the steel sheet using a fluorescence microscope arranged on the delivery side of the rolling mill;
calculating a distribution of the oil film thickness h on the steel sheet based on the measured fluorescence intensity and a previously determined relationship between the fluorescence intensity and the oil film thickness of the rolling oil;
The oil film thickness h and the following formula 1:
h _b =0.5×√(R _roll ² +R _strip ² )...Formula 1
(where R _roll and R _strip are the arithmetic mean roughnesses of the surfaces of the work roll and the steel sheet to be rolled, respectively) based on the boundary lubrication threshold value h _b defined by the above formula, calculating the ratio of the area where h < h _b to the entire area photographed by the fluorescence microscope as the contact ratio α;
From the contact ratio α and the boundary friction coefficient μ _b specific to the steel plate, the following formula 2:
μ = α × μ _b ... Equation 2
The method includes a control step of controlling the coefficient of friction μ between the steel plate and the work roll, which is calculated by the above formula (1), within a predetermined range.

As mentioned above, in cold rolling, in order to maintain the coefficient of friction between the steel sheet and the work rolls within an appropriate range, rolling oil is generally supplied to the steel sheet and the work rolls at the entry side of the rolling stand in the rolling mill. In relation to this, for example, if the amount of rolling oil supplied is small, the coefficient of friction increases, and the steel sheet and the work rolls come into direct contact with each other, which may cause so-called seizure or an increase in the rolling load. On the other hand, if the amount of rolling oil supplied is large, the coefficient of friction decreases, and the steel sheet may slip against the work rolls, which is called slippage, or chattering (abnormal vibration of the rolling mill). Any of these phenomena caused by an excess or deficiency of rolling oil can cause defects on the surface of the steel sheet or a deterioration in quality. Therefore, in order to control the coefficient of friction between the steel sheet and the work rolls inside the roll bite within a desired range and realize stable rolling operations, it is important to appropriately adjust the amount of rolling oil supplied.

However, as mentioned above, it is known that the amount of rolling oil introduced into the roll bite changes depending on factors such as the surface roughness of the steel plate and work rolls, and temperature, and it is generally not easy to determine the appropriate amount of rolling oil to supply. On the other hand, changes in the amount of rolling oil introduced into the roll bite can lead to fluctuations in the coefficient of friction between the steel plate and the work rolls, which can in turn cause problems such as gauge hunting and chattering due to load fluctuations between the steel plate and the work rolls.

Therefore, the inventors have focused on a fluorescent substance, which is a substance that converts external energy into light, and have investigated the use of the fluorescent intensity (brightness) emitted from the fluorescent substance in the rolling oil supplied to the steel sheet and the work rolls to control the supply of the rolling oil. As a result, the inventors have found that the contact state between the steel sheet and the work rolls inside the roll bite can be properly evaluated by measuring the fluorescent intensity emitted from the fluorescent substance contained in the rolling oil present on the steel sheet after rolling. By properly evaluating the contact state between the steel sheet and the work rolls inside the roll bite, the friction coefficient between them can be determined. Therefore, the supply of the rolling oil can be adjusted so that the friction coefficient is controlled within a predetermined range, and thus, in cold rolling, stable rolling operation can be realized without causing rolling defects such as seizure, slip, gauge hunting, and chattering. In addition, even in situations where the type of steel used in cold rolling is changed and adjustments to achieve stable rolling operations would normally take time and result in a decrease in yield, it is possible to achieve stable rolling operations more quickly while suppressing the decrease in yield compared to conventional cold rolling where the supply of rolling oil is not controlled.

The rolling lubrication method for cold rolling according to an embodiment of the present invention will be described in more detail below with reference to the drawings. However, these descriptions are intended to merely exemplify preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments.

Figure 1 is a schematic diagram showing a rolling lubrication device in cold rolling according to an embodiment of the present invention. Referring to Figure 1, the rolling lubrication device 10 in cold rolling according to an embodiment of the present invention includes a rolling mill 4 having a work roll 2 for rolling a steel sheet 1, a supply device 5 arranged on the entry side of the rolling mill 4 for supplying rolling oil containing a fluorescent substance to the steel sheet 1 and the work roll 2, a fluorescent microscope 6 arranged on the exit side of the rolling mill 4, and a control device 7 for controlling the supply of rolling oil from the supply device 5 based on a signal from the fluorescent microscope 6, and the control device 7 is electrically connected to the supply device 5 and the fluorescent microscope 6. The rolling mill 4 may further include a backup roll 3 for supporting the work roll 2 as shown in Figure 1. In Figure 1, for ease of understanding, a rolling mill consisting of only one rolling stand is shown as the rolling mill 4, but the rolling mill 4 is not necessarily limited to such a rolling mill, and may be a tandem type rolling mill consisting of multiple rolling stands. Furthermore, if the rolling mill 4 is composed of multiple rolling stands, the supply device 5 and the fluorescent microscope 6 may be disposed at the entry and exit sides of each rolling stand, respectively, or may be disposed at only the entry and exit sides of some of the rolling stands.

To explain more specifically with reference to FIG. 1, in the rolling lubrication method using the rolling lubrication device 10 in cold rolling, first, rolling oil containing a fluorescent substance is supplied from the entry side of the rolling mill 4 to the steel sheet 1 and the work rolls 2 by the supply device 5. Next, the steel sheet 1 is rolled and passed through the exit side of the rolling mill 4, and the fluorescence intensity from the rolling oil present on the surface of the steel sheet 1 is measured using a fluorescent microscope 6 arranged on the exit side of the rolling mill 4. Here, when the fluorescence intensity is measured with the same exposure time, the value increases as the oil film thickness increases, so the relationship between the fluorescence intensity and the oil film thickness of the rolling oil can be experimentally obtained in advance in the form of a calibration curve or a relational equation. Based on the relationship between the fluorescence intensity and the oil film thickness of the rolling oil thus experimentally obtained in advance and the fluorescence intensity measured in the actual cold rolling process, the control device 7 calculates the distribution of the oil film thickness h on the steel sheet 1.

Next, the distribution of the oil film thickness h obtained is compared with the boundary lubrication threshold value _hb, which will be described in detail later, in the control device 7. Here, on the rolled steel sheet 1, there is a region called fluid lubrication, where a comparatively large amount of rolling oil is present, and a region called boundary lubrication, where rolling oil is not present at all or is not sufficiently present, and the boundary between them is the boundary lubrication threshold value _hb . Therefore, by comparing the distribution of the oil film thickness h with the boundary lubrication threshold value _hb , the area where h< _hb is regarded as the area of the boundary lubrication region where rolling oil is not present at all or is not sufficiently present, that is, the area where the steel sheet 1 and the work roll 2 contact, and the value can be calculated. The area of the boundary lubrication region obtained in this way is converted into a ratio to the total area photographed by the fluorescent microscope 6, and the contact rate α between the steel sheet 1 and the work roll 2 is calculated.

On the other hand, since the steel sheet 1 has an inherent boundary friction coefficient μ _b , the control device 7 calculates the friction coefficient μ between the steel sheet 1 and the work roll 2 inside the roll bite from the previously obtained contact ratio α and the boundary friction coefficient μ _b . Finally, the control device 7 judges whether the calculated friction coefficient μ is within a predetermined range. Then, when the calculated friction coefficient μ is small, the control device 7 controls the friction coefficient μ to be large by reducing the supply amount of rolling oil from the supply device 5. On the other hand, when the calculated friction coefficient μ is large, the control device 7 controls the friction coefficient μ to be small by increasing the supply amount of rolling oil from the supply device 5. By performing such control of the supply of rolling oil, it is possible to realize stable rolling operation in cold rolling without causing rolling defects such as seizure, slip, and gauge hunting and chattering. Also, compared to the case of conventional cold rolling in which such control of the supply of rolling oil is not performed, it is possible to realize stable rolling operation earlier while suppressing a decrease in yield. Hereinafter, each step of the rolling lubrication method in cold rolling according to the embodiment of the present invention will be described in more detail.

[Rolling oil supply process]
In the rolling lubrication method for cold rolling according to the embodiment of the present invention, first, rolling oil containing a fluorescent substance is supplied to the steel sheet and the work rolls from the entry side of the rolling mill. By using the rolling oil containing a fluorescent substance, the contact state between the steel sheet and the work rolls in the roll bite can be appropriately evaluated based on the fluorescence intensity emitted from the fluorescent substance in the rolling oil present on the steel sheet after rolling.

[Fluorescent material]
The above-mentioned fluorescent material may be any material known to those skilled in the art that can convert external energy into light, and is not particularly limited. Examples of the fluorescent material include CdTe/CdSe, CdS(Se)/CdTe, CdS(Se)/ZnTe, CuInS(Se)/ZnS(Se), Cu(GaIn)S(Se)/ZnS(Se), ZnTe/CdS(Se), GaSb/GaAs, GaAs/GaSb, Ge/Si, and Si/Ge. , PbSe/PbTe, PbTe/PbSe, CdTe, CdSe, ZnTe, CuInS, CuGaS, Cu(Ga,In)S, CuGaSnS(Se), CuGaS(Se), CuSnS(Se), ZnS, CuInSe, CuGaSe, ZnSe, ZnTe, GaSb, GaAs, Ge, Si, PbSe, PbTe, PbTe, and PbSe.

The particle size of the fluorescent substance may be any particle size within a range that does not inhibit the function of the rolling oil, and is not particularly limited, but may generally be 1 to 100 nm, for example 1 to 50 nm. Similarly, the concentration of the fluorescent substance in the rolling oil may be appropriately selected within a range that does not inhibit the function of the rolling oil, and is not particularly limited, but may generally be 0.01 to 0.50 mg/ml, for example 0.05 to 0.30 mg/ml. The rolling oil containing the above fluorescent substance is supplied to the steel plate and work rolls from the entry side of the rolling mill using any appropriate supply device, for example a supply nozzle. When the rolling mill is a tandem type rolling mill consisting of multiple rolling stands, the rolling oil may be supplied to the steel plate and work rolls from the entry side of each rolling stand, or the rolling oil may be supplied to the steel plate and work rolls only from the entry side of some of the rolling stands.

For example, if the rolling mill is a tandem type rolling mill consisting of multiple rolling stands, the reduction ratio may differ between each rolling stand. In such a case, the rolling load differs between each rolling stand, and in rolling stands with a large rolling load load, there is generally a tendency for rolling oil to be oversupplied. From this perspective, for example, in the case of a tandem type rolling mill, the rolling oil supply control according to the present invention may be performed only in some rolling stands where the rolling load load is large and therefore appropriate rolling oil supply control is particularly required.

[Steel plate]
The rolling lubrication method according to the embodiment of the present invention can be applied to any steel plate having different chemical compositions and properties, such as ultra-low carbon steel (so-called IF steel) and steel plate made of DP steel composed of a composite structure of a soft ferrite phase and a hard martensite phase, and can achieve the same effect for any steel plate having such an arbitrary chemical composition. The thickness of the steel plate may be any thickness suitable for cold rolling, and is not particularly limited, but may generally be 1.0 to 4.0 mm, for example 1.0 to 3.0 mm.

When steel sheets with different properties such as chemical composition and tensile strength are cold-rolled in the same rolling equipment, the appropriate supply amount of rolling oil changes depending on the steel type when switching the steel type, so it may take time to adjust to achieve stable rolling operation. In such a case, not only does it take time, but it may be necessary to discard the products manufactured during that time, which may lead to a decrease in yield. However, according to the rolling lubrication method of the embodiment of the present invention, even if the steel type is changed, it is possible to quickly and relatively easily calculate the friction coefficient μ between the steel sheet inside the roll bite and the work roll from information such as the relationship between the fluorescence intensity and the oil film thickness of the rolling oil previously obtained for the steel type, the arithmetic mean roughness of the surface of the steel sheet made of the steel type, and the boundary friction coefficient μ _b specific to the steel sheet. Therefore, according to this rolling lubrication method, even if the steel type to be cold-rolled is changed, it is possible to realize stable rolling operation earlier while suppressing a decrease in yield compared to the case of conventional cold rolling.

[Fluorescence Intensity Measurement Step]
Next, the steel sheet is rolled and passed through the exit side of the rolling mill, and the fluorescence intensity from the rolling oil present on the surface of the steel sheet is measured using a fluorescent microscope arranged at the exit side of the rolling mill. In order to ensure an appropriate exposure time and obtain sufficient fluorescence intensity, it is preferable that the fluorescent microscope runs at the same speed as the steel sheet at the exit side of the rolling mill, for example, as shown by an arrow in relation to the fluorescent microscope 6 in FIG. 1. By running at the same speed as the steel sheet at the exit side of the rolling mill, the relative speed with respect to the steel sheet can be set to zero, so that an appropriate exposure time can be ensured at the measurement position. Such a running speed may generally be 2000 m/min or less, for example, 480 to 1800 m/min (8 to 30 m/sec) or 600 to 1200 m/min (10 to 20 m/sec). In addition, the exposure time may be selected as any appropriate time depending on the performance of the fluorescent microscope, and is not particularly limited, but may generally be 0.05 to 1.0 seconds, for example, 0.1 to 0.5 seconds. In addition, since the fluorescence intensity increases as the exposure time becomes longer, the exposure time of the fluorescence microscope placed on the exit side of the rolling mill needs to be the same as the fluorescence intensity experimentally determined in advance, which will be explained later.

Measurements using a fluorescent microscope are preferably performed on the center of the width of the steel sheet. This is because the rolling oil may cling irregularly to the ends of the width of the steel sheet, which may prevent stable measurements. In addition, multiple fluorescent microscopes may be placed on the exit side of the rolling mill to measure the fluorescence intensity. The size of the field of view that can be observed using a fluorescent microscope is generally several tens of μm x several tens of μm, for example, about 50 μm x 50 μm. For this reason, by monitoring the contact state between the steel sheet and the work roll inside the roll bite using multiple fluorescent microscopes and reflecting the measurement results in the supply control of the rolling oil, it is possible to achieve more accurate control. As the fluorescent microscope, any appropriate fluorescent microscope known to those skilled in the art can be used, and is not particularly limited, but for example, an epi-illumination fluorescent microscope or a confocal laser microscope equipped with a detector such as a photomultiplier tube can be used.

[Oil film thickness distribution calculation process]
Next, the distribution of the oil film thickness h on the steel sheet is calculated based on the fluorescence intensity measured in the previous step and the previously determined relationship between the fluorescence intensity and the oil film thickness of the rolling oil. As mentioned above, when measured with the same exposure time, the fluorescence intensity increases as the oil film thickness increases, so the relationship between the fluorescence intensity and the oil film thickness of the rolling oil can be experimentally determined in advance in the form of a calibration curve or a relational equation.

Figure 2 is a graph showing the relationship between the experimentally determined fluorescence intensity and the rolling oil film thickness at an exposure time of 0.5 seconds. In Figure 2, the fluorescence intensity obtained when samples in which oil films of 0 to 2.4 μm were formed on steel pieces were measured with a fluorescence microscope at an exposure time of 0.5 seconds is plotted. From the results in Figure 2, it can be seen that when the exposure time is constant, the fluorescence intensity measured by the fluorescence microscope increases as the oil film thickness increases, that is, the fluorescence intensity shows a certain correlation with the oil film thickness. Therefore, by experimentally determining the relationship between the fluorescence intensity and the oil film thickness in advance in the form of a calibration curve or a relational equation with the same exposure time as the fluorescence microscope placed at the exit side of the rolling machine in the actual cold rolling process, it is possible to calculate the distribution of the oil film thickness h on the steel sheet after rolling from the fluorescence intensity measured in the actual cold rolling process.

[Calculation process of contact rate α]
Next, the contact ratio α is calculated by comparing the distribution of the oil film thickness h obtained with the boundary lubrication threshold value _hb . As mentioned above, on a rolled steel sheet, there are an area called fluid lubrication where a relatively large amount of rolling oil is present, and an area called boundary lubrication where no rolling oil is present or is not present sufficiently, and the boundary between them is the boundary lubrication threshold value _hb .

In the cold rolling process, since the steel plate and the work rolls each have a certain surface roughness, it is known that the amount of rolling oil introduced into the roll bite is affected and changed due to such surface roughness. When the surface roughness of such a steel plate and work roll is taken into consideration, the amount of rolling oil introduced into the roll bite is affected by the effect of being captured in the recesses on the steel plate and work roll surfaces rather than the hydrodynamic effect, and the boundary lubrication threshold value _hb in the boundary lubrication region is determined almost entirely by this effect. More specifically, the boundary lubrication threshold value _hb is expressed by the following formula 1:
h _b =0.5×√(R _roll ² +R _strip ² )...Formula 1
(wherein R _roll and R _strip are the arithmetic mean roughnesses of the surfaces of the work roll and the steel sheet used in rolling, respectively), it is 1/2 of the composite roughness of the root mean square roughnesses of the work roll and the steel sheet surfaces (see, for example, Akira Shodoshima, "Analysis and Measurement of Oil Film Thickness Taking into Account Surface Roughness-Research on Friction and Lubrication in Cold Rolling V-", Journal of the JSTP, vol. 36, no. 414 (1995-7), pp. 737-742).

To explain in more detail, first, the composite roughness of the work roll and the steel sheet can be expressed by √(R _roll ² +R _strip ² ) (wherein R _roll and R _strip are the arithmetic mean roughness of the surfaces of the work roll and the steel sheet used for rolling, respectively), and FIG. 3 is a diagram showing this in schematic form. Referring to FIG. 3, the arithmetic mean roughness R _roll of the surface of the work roll 2 and the arithmetic mean roughness R _strip of the surface of the steel sheet 1 shown in FIG. 3(a) can be converted to the composite roughness of the work roll 2 and the steel sheet 1 expressed by √(R _roll ² +R _strip ² ) by combining them with the surface of the steel sheet 1 by making the surface of the work roll 2 mirror-finished as shown in FIG. 3(b). The boundary lubrication threshold value h _b , which is the boundary between fluid lubrication and boundary lubrication, depends on the amount of rolling oil captured in the recesses of such composite roughness, and more specifically, is 1/2 of the composite roughness.

In this step, the distribution of the oil film thickness h calculated in the previous step is compared with the boundary lubrication threshold value _hb , and the area where h< _hb is considered to be the area of the boundary lubrication region where no rolling oil is present or is not present sufficiently, that is, the area where the steel sheet and the work roll contact, and the value can be calculated. The area of the boundary lubrication region thus obtained can be converted into a ratio to the total area photographed by the fluorescent microscope, and the contact ratio α between the steel sheet and the work roll can be calculated. When the entire area is the boundary lubrication region, that is, when the entire area is h< _hb , the contact ratio α is 1, whereas when the entire area is the hydrodynamic lubrication region, that is, when the entire area is h> _hb , the contact ratio α is 0.

Figure 4 shows the area of the boundary lubrication region calculated based on the signal from the fluorescence microscope. The darker areas indicate areas where the amount of rolling oil is small, forming boundary friction regions. The total area in Figure 4 corresponds to the total area photographed by the fluorescence microscope, and therefore, in the example of Figure 4, the contact ratio α can be calculated to be 0.654 by image processing.

[Control process of friction coefficient μ]
Next, the contact ratio α and the boundary friction coefficient _μb specific to the steel plate are calculated using the following formula 2:
μ = α × μ _b ... Equation 2
The friction coefficient μ between the steel sheet and the work roll inside the roll bite is calculated by the above equation. Here, the boundary friction coefficient μ _b is a friction coefficient specific to the steel sheet and can be measured in advance by a friction test such as a Bowden test. For example, in the case of general steel, the boundary friction coefficient μ _b is about 0.160 to about 0.200.

Finally, it is judged whether the calculated friction coefficient μ is within a predetermined range, more specifically, within a preferable range for realizing stable rolling operation without rolling defects such as slippage, chattering, seizure, and increased rolling load. The preferable range of the friction coefficient μ varies depending on the chemical composition and characteristics of the steel plate, and even the rolling mill used, so it is necessary to determine the appropriate range of the friction coefficient μ during actual rolling operation for each steel type and rolling equipment used. Therefore, although it is not possible to specify a preferable range of the friction coefficient μ that can be applied to any steel plate and rolling mill, it is generally preferable to control the friction coefficient μ within the range of 0.040 to 0.070, and more preferably within the range of 0.045 to 0.065. For example, if the calculated friction coefficient μ is smaller than 0.040, slippage and chattering may occur or may occur, so in order to prevent these, the friction coefficient μ is controlled to be 0.040 or more by reducing the amount or concentration of rolling oil supplied from the entry side of the rolling mill. On the other hand, if the calculated friction coefficient μ is greater than 0.070, there is a risk of seizure or an increase in rolling load, so to prevent these, the friction coefficient μ is controlled to be 0.070 or less by increasing the amount or concentration of rolling oil supplied from the entry side of the rolling mill.

<Rolling lubrication device for cold rolling>
The rolling lubrication device in cold rolling according to an embodiment of the present invention is
A rolling mill having work rolls for rolling steel sheets;
a supply device disposed on an inlet side of the rolling mill for supplying rolling oil containing a fluorescent substance to the steel plate and the work rolls;
The rolling mill is characterized by comprising a fluorescent microscope disposed on the exit side of the rolling mill, and a control device for controlling the supply of rolling oil from the supply device based on a signal from the fluorescent microscope.

[Rolling mill]
The rolling mill according to the embodiment of the present invention may be any rolling mill equipped with work rolls for rolling steel sheets, and may be, for example, a rolling mill consisting of only one rolling stand as shown in Fig. 1, or a rolling mill of a tandem type consisting of multiple rolling stands. The work rolls may have any suitable diameter, and may be, for example, a diameter of 300 to 1000 mm, and may be, for example, a diameter of 400 to 600 mm, but is not particularly limited thereto. The rolling mill may also be equipped with backup rolls for supporting the work rolls as shown in Fig. 1.

[Supply device]
According to an embodiment of the present invention, a supply device is disposed at the entry side of a rolling mill, and rolling oil containing a fluorescent substance is supplied to the steel sheet and the work rolls by the supply device. By using rolling oil containing a fluorescent substance, the contact state between the steel sheet and the work rolls inside the roll bite can be appropriately evaluated based on the fluorescence intensity emitted from the fluorescent substance in the rolling oil present on the steel sheet after rolling. Such a supply device may be, for example, one equipped with one or more supply nozzles along the width direction of the steel sheet. In addition, when the rolling mill is composed of multiple rolling stands, the supply device may be disposed at the entry side of each rolling stand, or may be disposed only at the entry side of some of the rolling stands. In addition, the fluorescent substance may be a substance described in relation to the rolling lubrication method.

[Fluorescence microscope]
According to an embodiment of the present invention, a fluorescent microscope is disposed on the delivery side of a rolling mill, and the fluorescent intensity from the rolling oil present on the surface of the steel sheet after rolling is measured by the fluorescent microscope. As described above, any appropriate fluorescent microscope known to those skilled in the art can be used as the fluorescent microscope, and is not particularly limited, but for example, an epi-illumination fluorescent microscope or a confocal laser microscope equipped with a detector such as a photomultiplier tube, etc. can be used.

When multiple rolling oil supply devices are arranged on the entry side of the rolling mill along the width direction of the steel sheet, multiple fluorescent microscopes may be arranged on the exit side of the rolling mill accordingly. As described above, the size of the field of view that can be observed by the fluorescent microscope is generally several tens of μm x several tens of μm, for example, about 50 μm x 50 μm. For this reason, by monitoring the contact state between the steel sheet inside the roll bite and the work roll using multiple fluorescent microscopes and reflecting the measurement results in the supply control of the rolling oil, it is possible to realize more accurate control. In addition, when the rolling mill is composed of multiple rolling stands, the fluorescent microscope may be arranged on the exit side of each rolling stand, or may be arranged only on the exit side of some of the rolling stands. By arranging the supply device and the fluorescent microscope on the entry side and exit side of not only one rolling stand but also multiple or all rolling stands, the rolling lubrication method according to the embodiment of the present invention can be implemented for these multiple rolling stands, making it possible to realize more stable rolling operations.

As explained in relation to the rolling lubrication method, in order to ensure an appropriate exposure time and obtain sufficient fluorescence intensity, it is preferable for the fluorescent microscope to run at the same speed as the steel plate at the exit of the rolling mill. Therefore, in order to enable such running of the fluorescent microscope, for example, a rail several meters long, for example 1 to 5 m or 2 to 4 m, may be provided above the exit of the rolling mill, more specifically the exit of the rolling stand, and the fluorescent microscope may be installed on the rail, so that the fluorescent microscope runs at the same speed as the steel plate at the exit of the rolling mill.

[Control device]
The control device is equipped with an electronic circuit or computer that performs calculations based on a predetermined program, and is electrically connected to a supply device at the entry side of the rolling mill and a fluorescent microscope at the exit side of the rolling mill. In the rolling lubrication device according to the embodiment of the present invention, the control device calculates the distribution of the oil film thickness h on the steel sheet after rolling based on a signal from the fluorescent microscope and a relationship between the fluorescence intensity and the oil film thickness of the rolling oil obtained in advance, and calculates the area of the boundary lubrication region by comparing the oil film thickness h with a boundary lubrication threshold _hb , and calculates the contact ratio α between the steel sheet and the work roll inside the roll bite by converting it into a ratio to the total area photographed by the fluorescent microscope. Next, the control device calculates the friction coefficient μ between the steel sheet and the work roll inside the roll bite from the obtained contact ratio α, and finally judges whether the calculated friction coefficient μ is within a predetermined range or not, and adjusts the amount of rolling oil supplied from the supply device if the friction coefficient μ is not within the predetermined range.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

In the following examples, cold rolling of different steel types was carried out using the rolling lubrication method and rolling lubrication device for cold rolling according to the present invention, and the time required to achieve stable rolling operations when the steel type was changed was investigated.

[Example]
In cold rolling using the same rolling lubrication apparatus as that shown in Fig. 1 except that a tandem type rolling mill equipped with five rolling stands was used, a test was carried out in which the steel type was changed from an extremely low carbon steel (IF steel) having a tensile strength of 440 MPa to a dual phase steel (DP steel) having a tensile strength of 590 MPa. In general, the rolling load is large, and in order to reduce this, the rolling oil supply amount for the third rolling stand (the third rolling stand from the upstream side) tends to be excessively supplied, so a supply nozzle and a fluorescent microscope were arranged at the entrance and exit sides of the third rolling stand, respectively.

The rolling oil supplied from the supply nozzle contained CuInS/ZnS manufactured by NN-LABS as a fluorescent substance at a concentration of 0.2 mg/ml. The fluorescent microscope was installed on a rail of about 2 m provided above the exit of the third rolling stand so that it could photograph the center of the width direction of the steel plate, and it ran at the same speed as the steel plate at the exit of the third rolling stand for a distance of 2 m above the rail so that it could photograph the steel plate at zero relative speed. The exposure time with the fluorescent microscope was 0.2 seconds. The diameter of the work roll of the third rolling stand was 460 mm, and for both the 440 MPa class IF steel and the 590 MPa class DP steel steel plates, the entry side thickness of the third rolling stand was 1.5 mm, the exit side thickness was 1.2 mm, and the plate width was 1000 mm. The rolling speed was 600 m/min (10 m/sec).

The range of the appropriate friction coefficient μ for 590 MPa class DP steel in which rolling defects such as slippage and chattering do not occur was investigated in a preliminary actual machine test, and the range was 0.040 to 0.070. On the other hand, the boundary friction coefficient μ _b specific to 590 MPa class DP steel was measured in advance using a Bowden tester, and the boundary friction coefficient μ _b of the DP steel was 0.180. Considering these preliminary test results, the range of contact ratio required to control the friction coefficient μ within the range of 0.040 to 0.070 can be calculated backwards from Equation 2 as α = μ / μ _b ≒ 0.222 to 0.389. On the other hand, when the average roughness R _roll of the work roll surface and the average surface roughness R _strip of the steel sheet surface were measured, they were 0.318 and 0.278, respectively. Therefore, the boundary lubrication threshold h _b was calculated to be 0.211 from Equation 1. These data obtained in advance are summarized in Table 1 below.

Based on the data obtained from these preliminary experiments, the cold rolling process was changed from a 440 MPa class IF steel sheet to a 590 MPa class DP steel sheet, and the distribution of the oil film thickness h on the steel sheet at the exit of the third rolling stand was calculated based on the fluorescence intensity obtained from the fluorescence microscope arranged at the exit of the third rolling stand and the relationship between the fluorescence intensity and the oil film thickness of the rolling oil as shown in Figure 2. Next, the area where the oil film thickness h is smaller than the boundary lubrication threshold value h _b = 0.211 was calculated and converted into the ratio (contact ratio α) to the total area photographed by the fluorescence microscope. Next, the amount of rolling oil supplied was adjusted so that the friction coefficient μ between the steel sheet and the work roll calculated from the contact ratio α by Equation 2 was controlled within the range of 0.040 to 0.070, in other words, so that the contact ratio α was controlled within the range of 0.222 to 0.389.

As a result, even when the 440 MPa class IF steel was changed to the 590 MPa class DP steel, the contact ratio α was controlled within the range of 0.222 to 0.389 in the very short time of about 7 seconds, that is, the friction coefficient μ between the steel plate and the work roll was controlled within the range of 0.040 to 0.070 in the very short time of about 7 seconds, and stable rolling operations without rolling defects such as slipping and chattering were realized. Therefore, the length of the product (the length of the steel plate to be discarded) required to realize stable rolling operations could be kept to about 70 m (10 m/sec x about 7 seconds = about 70 m), and the yield was greatly improved compared to the comparative example described below.

[Comparative Example]
When changing the steel type from 440 MPa class IF steel to 590 MPa class DP steel, the rolling lubrication method according to the present invention using a fluorescent microscope was not applied, and the supply amount of rolling oil was adjusted while visually observing the occurrence of rolling defects such as slipping and chattering. As a result, it took about 20 seconds to realize a stable rolling operation without these rolling defects. Therefore, the length of the product (the length of the steel plate to be discarded) required to realize a stable rolling operation was about 200 m (10 m/sec x about 20 sec = about 200 m), which was nearly three times the length of the steel plate to be discarded compared to the example according to the present invention.

REFERENCE SIGNS LIST 1 Steel plate 2 Work roll 3 Backup roll 4 Rolling mill 5 Supply device 6 Fluorescence microscope 7 Control device 10 Rolling lubrication device in cold rolling

Claims (3)

A step of supplying rolling oil containing a fluorescent substance to a steel plate and a work roll from an inlet side of a rolling mill;
measuring a fluorescence intensity from rolling oil present on a surface of the steel sheet using a fluorescence microscope arranged on the delivery side of the rolling mill;
calculating a distribution of the oil film thickness h on the steel sheet based on the measured fluorescence intensity and a previously determined relationship between the fluorescence intensity and the oil film thickness of the rolling oil;
The oil film thickness h and the following formula 1:
h _b =0.5×√(R _roll ² +R _strip ² )...Formula 1
(where R _roll and R _strip are the arithmetic mean roughnesses of the surfaces of the work roll and the steel sheet to be rolled, respectively) based on the boundary lubrication threshold value h _b defined by the above formula, calculating the ratio of the area where h < h _b to the entire area photographed by the fluorescence microscope as the contact ratio α;
From the contact ratio α and the boundary friction coefficient μ _b specific to the steel plate, the following formula 2:
μ = α × μ _b ... Equation 2
A rolling lubrication method in cold rolling, comprising a control step of controlling a friction coefficient μ between the steel plate and the work rolls, the friction coefficient μ being calculated by the above formula (1), within a predetermined range. The method according to claim 1, characterized in that the control step is performed by adjusting the supply amount or concentration of the rolling oil. The method according to claim 1 or 2, characterized in that the fluorescent microscope travels at the same speed as the steel sheet at the exit of the rolling mill.

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