A cast roll and method of using the same

Abstract

The application discloses a casting and rolling roller and a use method thereof, and solves the common problem that cracks appear on a slab due to water cooling of the casting and rolling roller by an external nozzle in the prior art. The casting and rolling roller is provided with a center hole and a bypass hole for cooling water flow, the center hole and the bypass hole are both through arrangement, the center hole is coincident with an axis of the casting and rolling roller, the bypass hole is provided with a plurality of bypass holes, the axes of the plurality of bypass holes are parallel to the center hole and are uniformly arranged outside the center hole, a distance between a center axis of the bypass hole and an outer circumferential surface of the casting and rolling roller is L, and a ratio of a radius of the casting and rolling roller to the L is 5.5-6.2. The slab after rolling reduction of the casting and rolling roller provided by the application is free of cracks and meets the rolling reduction requirement, and the casting and rolling roller has a long service life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of continuous casting, and particularly relates to a casting-rolling roller and a use method thereof. BACKGROUND

[0002] The casting-rolling roller is a main device for implementing single-pass large reduction on a slab in a secondary cooling zone of continuous casting, and is usually separately installed in a certain sector at a solidification end of a continuous casting machine. The casting-rolling roller is different from a sector casting roller 300 (see Figure 1 ) of the continuous casting machine. The casting-rolling roller has a large roller diameter and is similar to a rolling roller. Since there is a large temperature difference between a surface and a thickness center of the slab in the continuous casting process, the temperature difference in the solidification end region can reach more than 400 DEG C. By using the natural temperature advantage, a single-point large reduction (greater than or equal to 10 mm) is implemented on the slab at the solidification end of the secondary cooling zone through the casting-rolling roller with a large roller diameter, so that the reduction force can efficiently penetrate into the center of the slab, and the center shrinkage porosity defect of the slab can be greatly improved. The light reduction and the large reduction principles and working modes of the sector casting roller 300 of the continuous casting machine are different. The light reduction is continuously implemented in multiple sectors along with the solidification of the slab, and is mainly used to solve the center element segregation problem in the solidification process of the slab. The light reduction is small, and the total reduction is only 0.5-1 mm / m and 4-9 mm. The large reduction is mainly used to solve the center shrinkage porosity defect of the slab, and the light reduction is mainly used to solve the center element segregation.

[0003] The roller diameter of the casting-rolling roller is greater than or equal to 500 mm, which is much larger than the roller diameter of the sector casting roller of the slab continuous casting machine. In addition, the single-point large reduction of the casting-rolling roller on the slab is greater than or equal to 10 mm. When the slab passes through the casting-rolling roller, the heat of the slab is transferred to the casting-rolling roller, so that the casting-rolling roller is heated. In addition, under the action of high load, the strength and service life of the casting-rolling roller are seriously affected.

[0004] At present, please refer to Figure 1 , a nozzle 400 is usually used to spray cooling water to cool the casting-rolling roller. In the continuous casting process, the casting-rolling roller and the slab surface are continuously in contact under large reduction, and a large amount of external cooling water is accumulated on the slab surface, which causes the local surface of the slab to be supercooled into the high-temperature brittle zone of the steel, and causes the surface crack defect of the slab when the large reduction is implemented. SUMMARY

[0005] According to the temperature field and stress field simulation of the casting-rolling roller with different cooling modes, the casting-rolling roller and the use method thereof are obtained, which can not only ensure the efficient cooling of the large roller diameter casting-rolling, but also solve the problem of the surface crack of the slab.

[0006] In a first aspect of the application, a casting-rolling roller is provided. The casting-rolling roller is provided with a center hole and a bypass hole for cooling water flow. The center hole and the bypass hole are both provided through. The center hole coincides with the axis of the casting-rolling roller. The bypass hole is provided with a plurality of bypass holes. The axes of the plurality of bypass holes are parallel to the center hole and uniformly arranged outside the center hole.

[0007] The distance between the center axis of the bypass hole and the outer circumferential surface of the casting roll is L, and the ratio of the radius of the casting roll to the L is 5.5-6.2.

[0008] In some embodiments, the ratio of the radius of the casting roll to the radius of the bypass hole is 18.6-19.5.

[0009] In some embodiments, the ratio of the radius of the casting roll to the number of the bypass holes is 40.9-65.

[0010] In some embodiments, the ratio of the radius of the casting roll to the radius of the center hole is 15.6-16.5.

[0011] The distance between the center axis of the bypass hole and the outer circumferential surface of the casting roll is L, and the ratio of the radius of the casting roll to the L is 5.5-6.2.

[0012] In some embodiments, the diameter of the casting roll is 500-1500 mm.

[0013] In some embodiments, the diameter of the casting roll is 500 mm, the radius of the bypass hole is 13 mm, the radius of the center hole is 15 mm, and the number of the bypass holes is 6.

[0014] In some embodiments, the distance between the center axis of the bypass hole and the outer circumferential surface of the casting roll is 45 mm.

[0015] In the second aspect of the present application, a method for using the casting roll of the first aspect is provided, wherein when the casting roll is used to cast a slab with a large reduction of ≥10 mm, cooling water is supplied to the center hole and the bypass hole, wherein the cooling water in the center hole and the bypass hole flows in the same direction, the flow rate of the cooling water in the center hole is 50-300 L / min, and the total flow rate of the cooling water in the bypass hole is 200-1000 L / min.

[0016] In some embodiments, the flow rates of the cooling water in the plurality of bypass holes are the same.

[0017] According to the casting roll and the method for using the same provided in the embodiments of the present application, the casting roll is provided with a center hole and a plurality of bypass holes, the center hole and the bypass holes are both used for cooling water flow, the center hole is throughly arranged, the axis of the center hole coincides with the axis of the casting roll, the bypass holes are throughly arranged, the axes of the plurality of bypass holes are parallel to the center hole and uniformly surround the center hole, the distance between the center axis of the bypass hole and the outer circumferential surface of the casting roll, i.e., the roll surface, is L, and the ratio of the radius of the casting roll to the L is 5.5-6.2.

[0018] The center hole and the bypass hole are arranged through, so that the cooling water in the center hole and the bypass hole can cool the inside of the cast-rolling roller, reduce the temperature of the cast-rolling roller, and make the cast-rolling roller have high strength and be not easy to deform when the slab passes, so as to ensure that large reduction is realized on the slab. The ratio of the radius of the cast-rolling roller to the L is controlled to be 5.5-6.2, so that the roller surface temperature of the cast-rolling roller is more uniform, and thus the strength uniformity of the cast-rolling roller is better, and the fatigue life is higher.

[0019] Compared with the roller surface cooling of the cast-rolling roller by the nozzle in the prior art, the internal cooling channel cooling is adopted in the application, the cooling water is not splashed on the slab, the roller surface temperature of the cast-rolling roller is low and uniform, the surface quality of the slab is high, and there is no crack. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 An assembly view of a cast-rolling roller and a nozzle in the related art is shown.

[0021] Figure 2 An end surface view of the cast-rolling roller in the embodiment of the application is shown.

[0022] Figures 3-6 A simulation temperature cloud chart of different moments in one rotation period of the cast-rolling roller in the large reduction process in embodiment 1 is shown.

[0023] BRIEF DESCRIPTION OF DRAWINGS:

[0024] 100-cast-rolling roller, 110-center hole, 120-bypass hole, 200-slab, 300-cast roller, 400-nozzle. DETAILED DESCRIPTION

[0025] In order for those skilled in the art to which the present application belongs to more clearly understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] In the first aspect of the present application, a cast-rolling roller is provided, which does not need to adopt external water cooling, so that the surface quality of the slab is not affected, and at the same time, the cast-rolling roller has higher temperature uniformity, so as to ensure high temperature strength and realize large reduction on the slab.

[0027] Please refer to Figures 1-2The casting roll 100 provided in this embodiment of the application is provided with a central hole 110 and a bypass hole 120. Both the central hole 110 and the bypass hole 120 are used for the flow of cooling water. The cooling water can cool the casting roll 100 and reduce the temperature of the casting roll 100, so that the casting roll 100 still has high strength and is not easily deformed when the slab 200 passes through it, so as to ensure that the slab 200 is subjected to large reduction.

[0028] A central hole 110 is provided, coinciding with the axis of the casting roll 100, so that cooling water absorbs the heat transferred to the axis of the casting roll 100, thus cooling the center of the casting roll 100. Multiple bypass holes 120 are provided, for example, five, six, or ten. The axes of the multiple bypass holes 120 are parallel to the central hole 110 and evenly distributed around it. That is, the axes of the multiple bypass holes 120 are located on the same circumferential surface centered on the axis of the casting roll 100. Cooling water flowing through the bypass holes 120 can cool the portion of the casting roll 100 near its outer circumference, resulting in a low and uniform temperature of the roll surface where the casting roll 100 contacts the slab 200.

[0029] The distance between the central axis of the bypass hole 120 and the outer circumferential surface of the casting roll 100, i.e., the roll surface, is L. The ratio of the radius of the casting roll 100 to L is 5.5 to 6.2, such as 5.6, 5.7, 5.8, 5.9, 6.0, and 6.1. This ratio can be called the distance coefficient. The distance coefficient is controlled at 5.5 to 6.2 to ensure the cooling intensity of the roll surface and keep the roll surface temperature ≤200℃. If the distance coefficient is too large, the cooling of the roll surface is weak and the roll surface wears quickly. If the distance coefficient is too small, the cooling intensity of the roll surface is large, but the internal cooling intensity of the casting roll is weak, which affects the overall service life of the casting roll 100.

[0030] In some embodiments, the ratio of the radius of the cast roll 100 to the radius of the bypass hole 120 is 18.6 to 19.5, such as 18.7, 18.9, 19.2, and 19.4. This ratio can be called the circumferential cooling coefficient. Controlling the circumferential cooling coefficient to 18.6 to 19.5 ensures the overall cooling intensity and rigidity of the cast roll. If the circumferential cooling coefficient is too large, the structural rigidity of the cast roll 100 will decrease, and there is a risk of breakage under large reduction. If the circumferential cooling coefficient is too small, the cooling intensity will be insufficient, and the service life of the cast roll 100 cannot be guaranteed.

[0031] In some embodiments, the ratio of the radius of the cast roll 100 to the number of bypass holes 120 is 40.9–65, for example, 41, 43, 45, 47, 49, 50, 52, 54, 55, 58, 60, 62, and 64. This ratio can be called the circumferential distribution coefficient. Controlling the circumferential distribution coefficient to 40.9–65 and the appropriate number of bypass holes 120 ensures the overall circumferential cooling intensity and uniformity of the roll, thereby improving the service life of the cast roll 100. During the design of the cast roll 100, the diameter of the cast roll 100 is determined first. If the circumferential distribution coefficient is too large, it means that the diameter of the cast roll 100 is very large, and / or, the number of bypass holes 120 is too small, resulting in weak cooling intensity and a higher operating temperature of the cast roll 100. This reduces the structural rigidity of the cast roll 100, thereby reducing its service life. If the circumferential distribution coefficient is too small, it means that the diameter of the casting roll 100 is very small, and / or the number of bypass holes 120 is too large. The cooling intensity is good, the working temperature of the casting roll 100 is low, and the temperature uniformity is good. However, if the number of bypass holes 120 is too large, the rigidity of the casting roll 100 will be reduced in the structure, thereby reducing the service life of the casting roll 100.

[0032] In some embodiments, the ratio of the radius of the casting roll 100 to the radius of the center hole 110 is 15.6 to 16.5, such as 15.7, 15.9, 16.1, 16.2, 16.3, and 16.4. This ratio can be called the center cooling coefficient. Controlling the center cooling coefficient to 15.6 to 16.5 improves the cooling intensity and temperature uniformity of the casting roll 100. If the center cooling coefficient is too large, it means the radius of the casting roll 100 is large, and / or the radius of the center hole 100 is small, which reduces the cooling effect of the casting roll 100, resulting in higher temperatures during operation and reduced rigidity. If the center cooling coefficient is too small, it means the radius of the casting roll 100 is small, and / or the radius of the center hole 100 is large, which structurally reduces the rigidity of the casting roll 100, thereby reducing its service life.

[0033] In some embodiments, the distance between the central axis of the bypass hole 120 and the outer peripheral surface of the casting roll 100 is L, and the ratio of the radius of the casting roll 100 to L is 5.5 to 6, such as 5.6, 5.7, 5.8 and 5.9. This ratio can be called the distance coefficient. Controlling the distance coefficient to 5.5 to 6 can improve the cooling effect and temperature uniformity, thereby increasing the service life of the casting roll 100.

[0034] In some embodiments, the diameter of the casting roll 100 is 500mm to 1500mm, such as 600mm, 700mm, 800mm, or 1200mm. Generally, the diameter of the casting roll 100 is very large, and its temperature uniformity is very low.

[0035] In some embodiments, the diameter of the casting roll 100 is 500 mm, the radius of the bypass hole 120 is 13 mm, the radius of the center hole 110 is 15 mm, and the number of bypass holes 120 is 6. In some embodiments, the distance between the central axis of the bypass hole 120 and the outer peripheral surface of the casting roll 100 can be 45 mm.

[0036] A second aspect of this application provides a method of using a casting roll 100 according to any embodiment of the first aspect. The method includes: when the casting roll 100 applies a large reduction of ≥10mm to the slab 200, cooling water is introduced into the center hole 110 and the bypass hole 120, wherein the cooling water in the center hole 110 and the bypass hole 120 flows in the same direction, the cooling water flow rate in the center hole 110 is 50-300L / min, and the total cooling water flow rate in the bypass hole 120 is 200-1000L / min.

[0037] The cooling water flows in the same direction in the center hole 110 and the bypass hole 120. That is, the water inlet end of the center hole 110 and the water inlet end of the bypass hole 120 are both located on one side of the casting roll 100 along the axial direction, and the water outlet end of the center hole 110 and the water outlet end of the bypass hole 120 are both located on the other side of the casting roll 100 along the axial direction, which facilitates the installation of water tank mechanisms for water inlet and outlet.

[0038] The cooling water flow rate in the center hole 110 and the bypass hole 120 should be appropriate. The heat flux value increases with the increase of the cooling water flow rate, but when the cooling water flow rate increases to a certain amount, the heat flux value basically stops increasing and the heat transfer efficiency approaches its limit. Increasing the cooling water flow rate further is a waste of resources. Insufficient cooling water flow rate will result in insufficient cooling intensity, which will lead to insufficient cooling of the roller, affecting its rigidity and service life.

[0039] The casting roll 100 provided in this application embodiment is suitable for slabs 200 with a thickness of 250 to 600 mm, and the single-point reduction of the casting roll 100 on the casting slab is ≥10 mm.

[0040] The following describes in further detail the casting roll 100 provided by the present invention and its usage method with reference to embodiments.

[0041] Example 1:

[0042] In the secondary cooling zone of continuous casting, a 500mm diameter casting roll 100 is used to apply a single-point 10mm reduction to a 250mm thick slab 200. The dimensions of the center hole 110 and the bypass hole 120 of the casting roll 100 are as follows:

[0043] 1) The radius of the bypass hole 120 is 13mm (the radius of the casting roll 100 is R=250mm, and the circumferential cooling coefficient A is taken as 19.5).

[0044] 2) The radius of the center hole 110 is 15mm (R=250mm, the center cooling coefficient B is taken as 16.5).

[0045] 3) There are 6 bypass holes (R = 250 mm, circumferential distribution coefficient C is 40.9).

[0046] 4) The distance between the axis of the bypass hole 120 and the surface of the casting roll 100 is 45mm (R=250mm, distance coefficient D is 5.5).

[0047] In the implementation of the above scheme, the cooling water flow rate of the central hole 110 is 50L / min, the total flow rate of the bypass hole 120 is 200L / min, the cooling water flow rate of each bypass hole 120 is the same, the temperature inside the casting roll 100 during the large reduction process is below 150℃, the maximum temperature difference is 31℃, the service life of the large reduction casting roll 100 is 3 million tons of steel, and the service life is long; the 10mm reduction is stable and smooth, and the surface cracking rate of the slab 200 is 0.

[0048] Example 2:

[0049] In the secondary cooling zone of continuous casting, a casting roll 100 with a diameter of 900mm is used to apply a single-point 30mm reduction to a 400mm thick slab 200. The dimensions of the center hole 110 and the bypass hole 120 of the casting roll 100 are as follows:

[0050] 1) The radius of the bypass hole 120 is 24mm (the radius of the casting roll 100 is R=450mm, and the circumferential cooling coefficient A is taken as 19).

[0051] 2) The radius of the center hole 110 is 28mm (R=450mm, the center cooling coefficient B is taken as 16).

[0052] 3) There are 9 bypass holes (R = 450 mm, circumferential distribution coefficient C is 50).

[0053] 4) The distance between the axis of the bypass hole 120 and the surface of the casting roll 100 is 75mm (R=450mm, distance coefficient D is 6).

[0054] In the implementation of the above scheme, the cooling water flow rate of the central hole 110 is 150L / min, the total flow rate of the bypass hole 120 is 600L / min, the cooling water flow rate of each bypass hole 120 is the same, the temperature inside the casting roll 100 during the large reduction process is below 200℃, the maximum temperature difference is 35℃, the service life of the large reduction casting roll 100 is 2.6 million tons, which is long; the 20mm reduction is stable and smooth, and the surface cracking rate of the slab 200 is 0.

[0055] Example 3:

[0056] The secondary cooling zone of continuous casting uses a 1500mm diameter casting roll 100 to apply a single-point 50mm reduction to a 600mm thick slab 200. The casting roll 100 adopts a cooling design with internal circumferential water passages and a central shaft water passage.

[0057] 1) The radius of the circumferential water passage is 40mm (the radius of the cast roll 100 is R=750mm, and the circumferential cooling coefficient A is taken as 18.6).

[0058] 2) The radius of the central shaft water hole is 48mm (R=750mm, and the central cooling coefficient B is 15.6).

[0059] 3) There are 12 circumferential water holes (R = 750 mm, circumferential distribution coefficient C is 65).

[0060] 4) The distance between the axis of the bypass hole 120 and the surface of the casting roll 100 is 121mm (R=750mm, distance coefficient D is 6.2).

[0061] In the implementation of the above scheme, the cooling water flow rate of the central hole 110 is 300L / min, the flow rate of the bypass hole 120 is 1000L / min, the cooling water flow rate of each bypass hole 120 is the same, the temperature inside the casting roll 100 during the large reduction process is below 200℃, the maximum temperature difference is 38℃, the service life of the large reduction casting roll 100 is 2 million tons, and the service life is long; the 50mm reduction is stable and smooth, and the surface cracking rate of the slab 200 is 0.

[0062] Comparative Example 1

[0063] Comparative Example 1 uses water spray cooling on the surface of the casting roll 100. The diameter of the casting roll 100 is the same as that of Example 1, the reduction amount is the same as that of Example 1, the service life of the casting roll 100 is about 500,000 tons, and the crack rate of the continuous casting slab 200 after large reduction is 35%.

[0064] Comparative Example 2

[0065] Comparative Example 2 uses a water spray cooling method on the surface of the casting roll 100. The diameter of the casting roll 100 is the same as that of Example 2, and the reduction amount is the same as that of Example 2. Compared with the external water cooling method of the roll, the life of the casting roll 100 is about 300,000 tons, and the crack rate of the continuous casting slab 200 after large reduction is 50%.

[0066] Comparative Example 3

[0067] Comparative Example 3 uses a water spray cooling method on the surface of the casting roll 100. The diameter of the casting roll 100 is the same as that of Example 3, and the reduction is the same as that of Example 3. Compared with the external water cooling method of the roll, the life of the casting roll 100 is about 300,000 tons, and the crack rate of the continuous casting slab 200 after large reduction is 60%.

[0068] The casting roll 100 provided in this application has at least the following advantages:

[0069] (1) The casting roll 100 adopts a cooling method of internal circumferential bypass hole 120 + center hole 110, which fundamentally solves the problem of cooling water accumulation on the surface of the billet caused by external cooling method and eliminates the crack defects of the billet.

[0070] (2) By limiting the size, number and position of cooling water holes of casting roll 100 with different roll diameters, the temperature of casting roll 100 is reduced, the uniformity of temperature on the circumferential surface of casting roll 100 is improved, the rigidity of casting roll 100 is maintained, and the metallurgical function of large reduction of slab 200≥10mm is realized. This achieves efficient cooling and long service life of casting roll 100 in the continuous casting large reduction process.

[0071] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0072] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0073] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0074] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0075] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A casting roll, characterized in that, The casting roll is provided with a central hole and a bypass hole for cooling water to flow through. The central hole and the bypass hole are both through the central hole. The central hole coincides with the axis of the casting roll. There are multiple bypass holes. The axes of the multiple bypass holes are parallel to the central hole and are evenly arranged around the central hole. Wherein, the distance between the central axis of the bypass hole and the outer circumference of the casting roll is L, and the ratio of the radius of the casting roll to L is 5.5 to 6.

2.

2. The casting roll according to claim 1, characterized in that, The ratio of the radius of the casting roll to the radius of the bypass hole is 18.6 to 19.

5.

3. The casting roll according to claim 2, characterized in that, The ratio of the radius of the casting roll to the number of bypass holes is 40.9 to 65.

4. The casting roll according to any one of claims 1-3, characterized in that, The ratio of the radius of the casting roll to the radius of the center hole is 15.6 to 16.

5.

5. The casting roll according to claim 4, characterized in that, The distance between the central axis of the bypass hole and the outer circumference of the casting roll is L, and the ratio of the radius of the casting roll to L is 5.5 to 6.

6. The casting roll according to any one of claims 1-3, characterized in that, The diameter of the casting roll is 500mm to 1500mm.

7. The casting roll according to any one of claims 1-3, characterized in that, The diameter of the casting roll is 500mm, the radius of the bypass hole is 13mm, the radius of the center hole is 15mm, and the number of bypass holes is 6.

8. The casting roll according to claim 7, characterized in that, The distance between the central axis of the bypass hole and the outer circumferential surface of the casting roll is 45mm.

9. A method of using the casting roll according to any one of claims 1-8, characterized in that, When the casting roll applies a reduction of ≥10mm to the continuously cast slab in a single pass, cooling water is introduced into the center hole and the bypass hole. The cooling water in the center hole and the bypass hole flows in the same direction. The cooling water flow rate in the center hole is 50L / min to 300L / min, and the total cooling water flow rate in the bypass hole is 200L / min to 1000L / min.

10. The method of using the casting roll according to claim 9, characterized in that, The cooling water flow rate is the same in all of the bypass holes.

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