JPH11229037A - Method for cooling metallic tube and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately cool a metallic tube so that a temp. in the longitudinal direction, is uniform at the time of cooling to a prescribed target cooling temp. at a prescribed target cooling speed from high temp. at the time of control- cooling or quenching after rolling the metallic tube. SOLUTION: Both ends of the metallic the 3 are covered with caps 1 having a prescribed opening diameter, and cooling water is poured into the tube till overflowing from the opening part of the cap and the metallic tube is cooled while being held in the horizontal state and being rotated. The caps having small opening diameter are used and the poured cooling water can be poured after pre-weight the water quantity. After reaching the prescribed completing temp., the caps are removed and the water is drained. As the other way, the opening diameter in the cap or the pouring quantity of the cooling water are adjusted so as to become the prescribed cooling temp. when the cooling water completes to vaporize.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling method and a cooling apparatus for controlled cooling and quenching of a metal pipe, particularly a steel pipe.

[0002]

2. Description of the Related Art The following description describes cooling of a steel pipe as a typical example of a metal pipe. Steel pipes are used in a variety of fields for both structural and piping purposes, but high-strength, high-toughness steel pipes are desired due to demands for higher performance, resource saving, weight reduction, and high environmental resistance. . In order to achieve high strength and high toughness by reducing alloy components from the viewpoint of resource saving and high performance, quenching is performed by controlled cooling or heat treatment immediately after rolling and forming into a steel pipe.
It is effective to perform tempering. It is most economical to use water for controlled cooling and cooling during quenching, and it is often used in actual manufacturing processes. When the thickness is small, cooling from the outer surface of the tube may be used, but when the thickness is large, cooling from the inner surface of the tube is required. However, it is difficult to uniformly pour the cooling water on the inner surface of the steel pipe, and the characteristics in the circumferential direction and the length direction are non-uniform, and bending is likely to occur. In particular, as the production length becomes longer as in recent years, it has become more difficult to uniformly cool the inner surface of the tube.

For example, the following technology is disclosed as a technology for uniformly cooling the inside and outside surfaces of a pipe. JP-A-3-63
No. 29 discloses a method for uniformizing the inner surface cooling by inserting a water supply mandrel having a nozzle hole for cooling water injection into a pipe, and immersing the entire pipe in a cooling water bath to cool the pipe.

Japanese Patent Publication No. 61-4896 discloses that when jet water is blown into a metal pipe from one end and the outer surface is cooled by the jet water from a nozzle, the jet water amount or jet of the external surface is reduced toward the discharge side of the internal jet water. There is disclosed a technique for increasing the time and making up for insufficient cooling from the inner surface on the discharge side to make the cooling uniform.

[0005]

SUMMARY OF THE INVENTION The above-mentioned JP-A-3-632
No. 9 or Japanese Patent Publication No. 61-4896 is originally intended for the quenching treatment of steel pipes, and cooling water comes into contact with the entire inner surface of the steel pipe to cool it in a flowing state. The cooling rate is extremely high, and is not suitable for cooling control in which the cooling rate after rolling and the cooling end temperature are important control points.

In the method of immersing the entire steel pipe in a cooling water tank as disclosed in Japanese Patent Application Laid-Open No. Hei 3-6329, it is difficult to control the cooling rate of the inner surface of the pipe. Like the technology disclosed in
It is difficult to stop cooling at a uniform temperature in the longitudinal direction by a method of passing cooling water from the pipe end.

[0007] In order to solve the above-mentioned problems, an object of the present invention is to provide a cooling rate (or a cooling time from the start to the end of cooling) during controlled cooling after hot rolling of a metal tube or quenching of a metal tube. It is an object of the present invention to provide a cooling method and apparatus in which the cooling time) and / or the cooling end temperature are controlled to desired conditions and uniform over the entire length of the tube.

[0008]

Means for Solving the Problems As a solution to the problem of the controlled cooling, if the cooling rate is reduced, the control of the cooling rate becomes easier, and the control of the target cooling end temperature becomes easier. With the idea that the quality was stable, various tests and examinations were carried out, and the following findings (a) to (c) were obtained.

(A) If cooling water is retained in the pipe and the amount of cooling water is adjusted, the cooling rate is reduced, but control becomes easier accordingly. The cooling water amount may be obtained from the conditions of the cooling start temperature, the target cooling end temperature, the target cooling rate, and the steel pipe dimensions (hereinafter, referred to as cooling specifications) based on the cooling model.

(B) To rotate the pipe while retaining the cooling water, means for closing both ends of the pipe is required, but the cap method is the cheapest in terms of equipment cost. The cap must have openings for cooling water injection and steam discharge. (c) By adjusting the opening diameter of the cap, the amount of retained water can be adjusted.

Based on the above findings, the gist of the present invention resides in the following (1) to (6). (1) In the cooling method at the time of controlled cooling after hot rolling of the metal tube or the cooling method at the time of quenching the metal tube, both ends of the metal tube are covered with caps having openings, and cooling water is injected into the tube and retained. And cooling the metal tube while rotating the metal tube in a horizontal state.

(2) The cooling water is injected into the metal pipe at a predetermined cooling start temperature, and after reaching the target cooling end temperature, the cooling water in the pipe is discharged. Metal tube cooling method.

(3) The above (1) or (2), wherein an amount of cooling water determined based on the cooling start temperature, the target cooling end temperature, the target cooling rate and the size of the pipe is injected into the pipe.
Item 15. The method for cooling a metal tube according to item 4.

(4) Using a cap having an opening whose diameter is determined based on the cooling start temperature, the target cooling end temperature, the target cooling rate, and the dimensions of the metal tube, and injecting cooling water until overflowing from the opening. Characterized by the above
The method for cooling a metal tube according to any one of (1) to (3).

(5) In a cooling device for controlled cooling after hot rolling of a metal tube or a cooling device for quenching a metal tube, a cap having an opening covering both ends of the metal tube; A cap mounting device for mounting the cap, a cap removing device for removing the cap, a cooling water injection device for injecting a set amount of cooling water into the metal tube, and a rotating device for rotating the metal tube in a horizontal state are provided. The cooling start temperature, the target cooling end temperature, the target cooling rate, and the cooling water amount are obtained based on the pipe size, and the cooling water amount value is instructed to the cooling water injection device. A control device for providing a setting signal to each device.

(6) In a cooling device for controlled cooling after hot rolling of a metal tube, or a cooling device for quenching a metal tube,
A cap group that covers both ends of the metal tube and has a plurality of types of openings around the center, a cap of a specified type selected from the cap group, and mounted on both ends of the metal tube; , A cooling water injection device that injects cooling water into the metal pipe, a rotating device that rotates the metal pipe in a horizontal state, a given cooling start temperature, a target cooling end temperature, a target cooling speed, and a pipe The amount of cooling water is determined based on the dimensions of the cooling water, the cap mounting device is instructed to select a cap type having an opening diameter corresponding to the amount of cooling water, and a setting signal is given to each of the above devices as the metal pipe process progresses. A cooling device for a metal tube, comprising: a control device.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors conducted a test for measuring the cooling rate by heating a steel pipe, injecting cooling water into the pipe, and examining a method of cooling the inner surface of the steel pipe.

FIG. 1 is a schematic diagram showing a state of a steel pipe according to the present invention during cooling. In this figure, after covering both ends of a high-temperature steel pipe 3 with a cap 1 having an opening 2, cooling water 4 is injected from one end of the pipe. When the cooling water is injected more than the cooling water 4 overflows from the opening 2 and the steel pipe 3 is rotated by the rotating device 5, the excess cooling water 4 overflows from the opening 2, and the water level remains at the lower edge of the opening 2. .

The conventional method used for comparison is a method in which cooling water flows so as to substantially fill the inner surface of the pipe. The material of the steel tube specimen is SUS310S, tube inner diameter 100mm, wall thickness 12m
m, pipe length 450 mm. The cooling start temperature is 800 ° C,
The target cooling end temperature was 400 ° C.

In both the conventional method and the method of the present invention, the steel pipe 3 was cooled while rotating horizontally at 60 rpm while keeping the steel pipe 3 horizontal. The temperature of the steel pipe was measured by embedding a thermocouple at the center position in both the longitudinal direction and the thickness direction. Table 1 shows the test results.

[0021]

[Table 1]

As shown in the table, in the conventional method, when the cooling rate is remarkably high, for example, when the cooling start temperature is 800 ° C. and the target cooling end temperature is 500 ° C., the cooling time is only 6 seconds. If the cooling time is short, it is difficult to control the operation, and if the steel pipe is lengthened, the slight difference in the water flow start time between the inlet and outlet of the cooling water will result in a large temperature difference. Causes unevenness and variation in the characteristics.

Further, as in the conventional method, when cooling by passing water, particularly in a long steel pipe, since the cooling water has a low temperature and a high-speed turbulent flow on the water injection side, a large amount of heat is removed. Conversely, since the amount of heat removal is small, the above-mentioned cooling time is short and the temperature unevenness is further increased.

On the other hand, in the cooling method of the present invention, the cooling rate, that is, (cooling start temperature−cooling end temperature) / cooling time is about half or less of the conventional method.

When cooling water is injected into the pipe, there is a difference in cooling time between the injection side and the discharge side due to the time required for the cooling water to spread throughout the pipe. Temperature unevenness in the longitudinal direction is reduced. In addition, in the method of the present invention, the cooling water is uniformly distributed in the longitudinal direction, and the uniform heat removal contributes to the reduction in the temperature unevenness. Although the cooling rate of the method of the present invention is slightly reduced, such a decrease in the cooling rate does not cause much problem in the controlled cooling or quenching after the rolling of the steel pipe.

Table 1 shows examples of the present invention. 4 to 9 show cases where the size of the opening 2 of the cap 1 is changed. By changing the opening diameter, the amount of cooling water staying in the pipe changes, and thereby the cooling rate can be changed.

FIG. 2 is a schematic diagram showing another cooling method of the present invention. In the figure, the diameter of the opening 2 is smaller than that of FIG. 1, and the amount of the cooling water 4 is adjusted by the injection amount. Hereinafter, a method of changing the opening diameter of the cap 1 to adjust the amount of cooling water as shown in FIG. 1 is referred to as an A method, and a method of adjusting the cooling water injection amount as shown in FIG. 2 is referred to as a B method.

In FIGS. 1 and 2, the outer surface is cooled (not shown) as required. The outer surface may be cooled by a known method such as spraying cooling water from a nozzle uniformly over the entire length.

In the method A, although the control of the cooling water injection amount is not necessary to adjust the amount of the cooling water 4 retained, there is a disadvantage that various types of caps having different diameters of the opening 2 must be prepared. In the method of adjusting the cooling water amount 4 in the method B, since only one kind of cap having a relatively small opening diameter needs to be prepared, there is an advantage that cap stock can be reduced.

In the method of the present invention, when the cooling water is first injected, the cooling start temperature must be controlled. In the case of controlled cooling after rolling, the lower limit of the cooling start temperature is determined by a work standard, and in the case of quenching, the upper and lower limits are often determined. The cooling start temperature may be controlled by the temperature immediately before the cooling water is injected according to the present invention (for example, by measuring the radiation temperature of the outer surface).

In the method of the present invention, after the cooling water is initially injected, no replenishing is performed at all, and the evaporation may be left (and there may be some scattering from the opening 2 and leakage from the gap between the cap and the steel pipe). Then, in order to keep the water level in the pipe constant, cooling water may be replenished to an extent commensurate with the amount of overflow and the amount of evaporation.

In the method of the present invention, when a predetermined target cooling end temperature is reached (at the end of cooling), the cap 1 is removed and the remaining cooling water is discharged to obtain a predetermined cooling rate and a predetermined cooling end temperature. There is.

As another method of the present invention, after the cooling water is first injected, no supply is made at all, and when the cooling water 4 has completely evaporated, the initial injection amount is adjusted so that the cooling is completed. There is also a way to do it. The advantage of this method is that the cooling rate decreases as the temperature approaches the target cooling end temperature, and the target temperature can be stably achieved.

If these are combined and the cap is removed after the amount of cooling water is reduced, the cooling end timing can be controlled at a low cooling rate, so that the temperature can be controlled accurately.

In the method of the present invention, when injecting the cooling water, the cooling water may be injected by inserting a water supply mandrel into the pipe so that cooling is started under the same conditions over the entire length.

In the method of the present invention, when the cooling water is discharged after the cooling of the steel pipe 3, the cap 1 may be removed and the cooling water may be allowed to flow naturally. However, in order to make the cooling time uniform, purging with known air or steam is performed. Alternatively, the drainage may be hastened by a method such as using a steel pipe, inclining the steel pipe 3, or rapidly accelerating the steel pipe 3.

FIG. 3 is a schematic view showing another example of the cap opening shape of the method A. FIG. 3A shows a porous type in which a number of small holes 2a are formed on the same radius, and FIG. 3B shows an annular slit type formed by an annular slit 2b. In the same figure, the water level of the cooling water is small hole 2.
a or the position of the annular slit 2b, and the opening 2 is dedicated to water injection. In this case, the area of the opening 2 can be reduced,
This has the effect of reducing scattering and overflow of cooling water due to vibration during rotation of the steel pipe.

In the method A, the diameter of the opening 2 (the position of the small hole 2a from the center of the pipe or the center of the annular slit 2b in the case of a hole) is not particularly limited.
If it is in the range of 95%, it is preferable because the cooling water covering the inner bottom surface of the pipe is stable, and more preferably 20 to 9 of the inner diameter of the steel pipe.
A range of 0% is good. In the case of using a porous or annular slit type opening for cooling water injection, the opening diameter is 10 mm of the inner diameter of the steel pipe.
A range of 30% is preferred.

In the method B, the opening diameter is preferably in the range of 10 to 30% of the inner diameter of the steel pipe so that the cooling water can be easily injected and the size of the cooling water does not scatter. An example of a method for calculating the cooling water amount V (m ³ ) in the method A or the method B will be described below.

Given the dimensions of the steel pipe, the cooling start temperature T _S , the target cooling end temperature T _f , and the target cooling rate S (or the target cooling time t), the cooling water amount V can be obtained from, for example, the following empirical formula. . However, cooling conditions from the outer surface shall be constant.

V = v · L (1) v = K ₁ (1−T _f / T _s ) ^a · (1−T ₀ / T _s ) ^−b · (W / W ₀ ) ^c × (t / t) ₀ -1) ^-d (2) where, V: amount of cooling water injected into the steel pipe (m ³ ) v: amount of cooling water per unit length of the steel pipe (m ² ) L: length of the steel pipe (m) K ₁ : constant (m ² ) T _s : cooling start temperature (° C.) T _f : target cooling end temperature (° C.) T ₀ : constant (° C.) W: wall thickness of steel pipe (mm) W ₀ : constant (mm) S : Target cooling rate (° C./s) t: target cooling time (s), where t = (T _s −
T _f) / S t _0: Constant (s) a, b, c , d: positive constant (- If) B method may be set cooling water V of the cooling water injection device.

In the case of the method A, the cap opening diameter r is obtained from the geometrical arrangement of the cooling water staying at the bottom of the pipe. That is, assuming that the inner radius R of the steel pipe and the opening radius of the cap are r in the right view of FIG. It is represented by the area v, and the following equation (3) can be derived.

V = R ² cos ⁻¹ (r / R) −r (R ² −r ² ) ^1/2 (3) In this equation (3), v obtained by the above equation (2) is given. r may be obtained. Equation (3) is not a simple functional form for r, but can be obtained by a well-known numerical calculation method (giving a starting value of r and repeatedly calculating convergence). In the method A, when there is no cap stock of a type exactly corresponding to the obtained cap opening diameter r, a cap having the closest opening diameter may be selected.

In the above equation (2), when performing on-line cooling control, the cooling start temperature T _s is preferably input from a thermometer immediately before the injection of cooling water. It may be calculated from the elapsed time immediately before the injection of the cooling water. However, determining the cooling start temperature based on only the standard value (constant) without actually measuring it has a problem in quality control.

As described above, in addition to the method of calculating the amount of cooling water by the calculation formulas (1) to (3), various cooling specifications are calculated in advance by the above expression (2), and the calculation results are set as a table of the amount of cooling water. This table may be prepared, and this table may be searched according to the cooling specification given at the start of cooling.

FIG. 4 is a plan view showing an outline of the cooling device of the present invention. A steel pipe 3 is carried in from a rolling line (not shown), and caps 1 are placed at both ends by a cap mounting device 7.
Can be fitted. Next, a predetermined amount of cooling water is injected into the steel pipe 3 by the cooling water injection device 6. At this time, in the method A, a sufficient amount of cooling water to overflow from the opening 2 is injected, and in the method B, a predetermined amount of cooling water is obtained in advance by the control device 9, and a command is issued to the cooling water injection device 6, The cooling water injection device 6 measures a certain amount of cooling water and injects it into the steel pipe 3.

The cooling water amount is determined in advance by online or offline heat transfer simulation. In the method A, the control device 9 selects a cap type having a specific size from caps having several kinds of opening diameters. Command. In the method B, a command of a set value is issued to the cooling water injection device 6 with the determined cooling water amount as it is.

After the cooling water is injected, the steel pipe 3 is also cooled by the outer surface cooling device 10 while rotating on the rotating device 5.
After the elapse of the predetermined cooling time obtained by the heat transfer simulation, the cap 1 is removed from the steel pipe 3 by the cap removing device 8, and the cooling water is discharged. The cap 1 is returned to the cap mounting device 7 and reused.

The control device 9 also performs sequence control of these series of operations. That is, the control device 9 inputs the cooling specification of the steel pipe 3 from a host computer or a setting device (both not shown), inputs the temperature of the steel pipe 3 from a temperature sensor (not shown), and performs tracking (not shown). The present position of the steel pipe 3 is tracked based on a signal from the sensor, and a steel pipe conveying device (not shown), a rotation device 5, a cooling water injection device 6, a cap mounting device 7, a cap detachment idea value 8, and an outer surface cooling device. A command is given to 10 to automate the loading, cooling, and unloading of the steel pipe. The tracking and transport automation methods are well known and need not be described.

[0050]

EXAMPLE An apparatus according to the present invention was installed in an existing steel pipe cooling system, and the effect was verified. As a comparative example, cooling control by a conventional method was also performed. The material of the steel pipe of the specimen is SUS
310S, inner diameter 300 mm, wall thickness 22 mm, length 22 m.

The method of the present invention is the method A, that is, a method of changing the opening diameter of the cap. The inner surface of the conventional method (comparative example) was cooled by passing water so that the inside of the steel pipe was almost completely filled from one end of the steel pipe. The flow rate at this time was about 10 m / s. In both the present invention example and the comparative example, the outer surface was cooled by slit laminar cooling to a water amount of 1.5 m ³ / min · m.

The heating temperature of the test piece, that is, the cooling start temperature is 9
00 ° C, target cooling end temperature (thickness center temperature) 500
° C. The cooling target time of the example of the present invention was set to 18 s (cooling rate: 22 ° C./s), the cap diameter was determined for the example of the present invention based on the expressions (1) to (3), and a cap having an opening diameter of 120 mm was selected. .

On the other hand, in the comparative example, the cooling end time was determined by a heat transfer simulation under the above-mentioned water-flow cooling condition without using the cooling time as a boundary condition, and a required cooling time of 9.5 s was obtained. .

In the embodiment of the present invention, the predetermined cooling target time (18
s) After the lapse of time, the caps at both ends were removed, and the cooling water was discharged. In the comparative example, the passage of water was stopped after the elapse of a predetermined cooling time (9.5 s).

In each of the examples of the present invention and the comparative examples, after the cooling was completed, the cooling water on the inner surface of the pipe was discharged with compressed air. In both the present invention example and the comparative example, the temperature distribution of the steel pipe was measured with a radiation thermometer 10 seconds after the completion of cooling after waiting for the surface to reheat.

FIG. 5 is a graph showing the temperature distribution in the longitudinal direction after cooling is completed. From the figure, the target cooling end temperature was the expected value on average in both the present invention example and the comparative example, but in the comparative example, a large temperature difference between the inlet side and the outlet side of the cooling water (maximum 120 ° C.). Had occurred. On the other hand, in the method of the present invention, a uniform temperature distribution (a maximum temperature difference of 30 ° C.) was obtained.

In terms of the target cooling rate (target cooling time),
Although the intended cooling rate was obtained in the example of the present invention, this was not controllable in the comparative example, and the cooling rate was much higher (42 ° C./s).

[0058]

According to the present invention, it is possible to accurately control the cooling end temperature and the cooling rate in the controlled cooling after the rolling of the metal tube or in the cooling during the quenching, and to perform the cooling without the temperature unevenness in the longitudinal direction. Become.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method for cooling a steel pipe according to the present invention.

FIG. 2 is a schematic view showing another method for cooling a steel pipe according to the present invention.

FIG. 3 is a schematic view showing an example of an opening shape of a cap according to the present invention. FIG. 3 (a) is a porous type, and FIG. 3 (b) is an annular slit type.

FIG. 4 is a plan view showing an outline of a cooling device of the present invention.

FIG. 5 is a graph showing a longitudinal temperature distribution after cooling of a steel pipe is completed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cap 2 Opening 2a Small hole 2b Annular slit 3 Steel pipe 4 Cooling water 5 Rotating device 6 Cooling water injection device 7 Cap mounting device 8 Cap detaching device 9 Control device 10 External cooling device R Inner radius of steel pipe r Opening radius of cap

Claims (6)

[Claims] 1. A cooling method for controlled cooling after hot rolling of a metal tube, or a cooling method for quenching a metal tube,
A method for cooling a metal pipe, comprising covering both ends of a metal pipe with a cap having an opening, injecting and retaining cooling water in the pipe, and cooling while rotating the metal pipe in a horizontal state. 2. The metal pipe according to claim 1, wherein cooling water is injected into the pipe at a predetermined cooling start temperature of the metal pipe, and after reaching a target cooling end temperature, the cooling water in the pipe is discharged. Cooling method. 3. The metal pipe according to claim 1, wherein an amount of cooling water determined based on a cooling start temperature, a target cooling end temperature, a target cooling rate, and a size of the pipe is injected into the pipe. Cooling method. 4. A method of using a cap having an opening having a diameter determined based on a cooling start temperature, a target cooling end temperature, a target cooling rate, and a dimension of a metal tube, and injecting cooling water until the cooling water overflows from the opening. The method for cooling a metal tube according to any one of claims 1 to 3, wherein: 5. A cooling device for controlling cooling after hot rolling of a metal tube, or a cooling device for quenching a metal tube,
A cap having an opening covering both ends of the metal tube, a cap mounting device for mounting caps on both ends of the metal tube, a cap removing device for removing the cap, and a cooling water injection for injecting a set amount of cooling water into the metal tube A cooling device for rotating the metal tube in a horizontal state, a cooling water amount is determined based on a given cooling start temperature, a target cooling end temperature, a target cooling speed, and a pipe size, and the cooling water amount value is determined by the cooling water amount. A control device for instructing the injection device and providing a setting signal to each of the above devices as the cooling process of the metal tube progresses. 6. A cooling device for controlled cooling after hot rolling of a metal tube or a cooling device for quenching a metal tube, the cap group covering both ends of the metal tube and having a plurality of openings of different diameters as centers. And a cap mounting device for selecting a commanded type of cap from the cap group and mounting the cap on both ends of the metal tube, a cap removing device for removing the cap, and a cooling water injection device for injecting cooling water into the metal tube. And a rotating device for rotating the metal pipe in a horizontal state, and a given cooling start temperature, a target cooling end temperature, a target cooling rate and a cooling water amount are determined based on the pipe size, and an opening diameter corresponding to the cooling water amount is determined. A control device for instructing the cap mounting device to select a type of cap to be provided and for providing a setting signal to each device as the process of the metal tube progresses.