JPS6115763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for keeping steel billets, such as blooms, warm on a conveying device in a hot rolling line.

In a hot rolling line, blooms exiting a heating furnace using heavy oil or gas are usually sequentially sent by a conveying device, passed through a cable breaker, etc., and then roughly rolled in a rough rolling mill, and then sent to a continuous finishing mill.
The temperature of the bloom that leaves the heating furnace decreases over time due to radiation and convection on the conveyor, so the temperature of the bloom at the exit of the heating furnace is higher than the billet temperature required by the rolling mill by the amount of the temperature drop. It is taken out at temperature. For example, 200mm of seamless steel pipe material
When manufacturing φ round steel bars, 445mm□×7000mm
(approximately 1 ton) of bloom is taken out from the heating furnace at 1,200 to 1,250℃, transported by a conveyor, and then processed through a rough rolling mill to
It is roughly rolled to mm□×14000mm and then transported to a finishing mill using a transport device. In this case, there is a distance of approximately 250 meters from the heating furnace to just before the finishing mill, and the distance is approximately 15 to 20 meters.
200°C to 250°C during that time.
As the temperature decreases, the temperature of the steel billet immediately before the finishing mill is
It becomes 1000℃.

When the rolling mill is operating smoothly without any failures, the temperature of the bloom from the heating furnace to the rolling mill shows exactly the same time course, and the temperature at the point just before the finishing mill is always about 1000℃. Bloom can be obtained. However, if there is a malfunction in the rolling mill, the blooms on the conveying device from the heating furnace to the rolling mill must wait on the respective conveying tables until the failure is recovered. Therefore, when restarting the operation after recovery from a failure, if the bloom is directly transferred to the rolling mill, the cooling time on the transfer device will be longer due to the waiting time, and the temperature drop in the bloom will be large. For example, when the waiting time is one hour, the temperature of the bloom immediately before the finishing mill is 650°C to 700°C. At this temperature, rolling is impossible as it is well below the allowable rolling temperature (960°C just before the finishing mill). Therefore, it is necessary to reverse the rollers of the conveying device and return all the blooms on the conveying device to the heating furnace for reheating. However, since there are about 10 blooms on a 200m long conveyor, it takes a very long time to return the blooms to the heating furnace, and the rolling operation has to be stopped during that time.

This invention provides a plurality of induction heating coils on the conveyance device to heat the bloom, thereby constantly replenishing the amount of heat dissipated during conveyance or standby, and making it possible to keep the bloom at a constant temperature. . Therefore, it is not necessary to return the bloom to the heating furnace when restarting the operation after recovery from a failure, and the operating rate when restarting the operation can be increased. In addition, since the induction heating coil provides heat that balances the heat dissipated on the conveying device, it is possible to reduce the temperature taken out of the heating furnace to the temperature required for rolling the bloom in the rolling mill. and heat retention equipment.

The figures will be explained below. FIG. 1a is a block diagram showing a hot rolling line for a round bar of seamless steel pipe material. When the bloom of 445mm□×7000mm is taken out from the heating furnace 1, it is passed through the scale breaker 2 and roughly rolled to 315mm□×14000mm in the rough rolling mill 3.
Finish rolling is performed in a continuous finish rolling mill 4. The bloom is transported between these devices using a transport device 5, but the distance between the heating furnace 1 and the rough rolling mill 3 is approximately 200 mm.
m and the conveying speed is 15 m/min, the distance between rough rolling mill 3 and finishing rolling mill 4 is approximately 50 m, and the conveying speed is 30 m/min.
It is. The transportation time from the heating furnace 1 to the finishing rolling mill 4 is 15 minutes. Therefore, conventionally, the temperature at which the material is taken out from the heating furnace 1 has been set as high as 1200.degree. C., as shown in characteristic A in FIG. 1b. In this invention, as shown in FIG. 1a, five induction heating coils 6 are provided to supply the same amount of heat to the bloom as the amount of heat radiated on the conveying device 5. As a result, the result is as shown in FIG. 1b, and the temperature taken out of the heating furnace may be 1000° C., which is the same temperature as the temperature immediately before the finishing mill. In this case, one induction heating coil only needs to compensate for the heat dissipated to the next induction heating coil. The amount of heat lost from the surface of a 445mm x 7000mm bloom at 1000℃ is approximately per bloom.
1300kW (If the emissivity is 0.7, the heat dissipation per unit area is 10.5watt/cm ² , and the surface area is 1.24×10 ⁵
cm ² ), so per bloom on time average
By applying 1300kW of heat, the balance of heat can be maintained and the bloom can be kept warm on the conveyor. now,
Assume that the number of induction heating coils 6 between the heating furnace 1 and the finishing rolling mill 4 is 5, and there are 10 blooms on the conveying device 5 from the heating furnace 1 to the finishing rolling mill 4, as shown in Fig. 1a. Furthermore, the bloom passes through all the induction heating coils 6 without interruption (the rear end of the preceding bloom and the tip of the succeeding bloom pass through the heating coil without a gap), and the electrical efficiency of the induction heating coil is set at 72%. For example, each induction heating coil will have a power output of 3,600 kW (1,300 ^kW x 10/5 ÷ 0.72).

As shown in FIG. 2, the induction heating coil 6 has a structure in which it is wound so as to surround the bloom 7 passing through it.
It is divided into multiple pieces and wound. Note that the induction heating coil 7 is connected to an AC power supply device 8. In addition, 50/60 for cross sections of 445mm□ and 315mm□
Hz commercial frequency power supply is sufficient. Reference numeral 9 denotes rollers that support the bloom 7, and the rotational direction and speed of the rollers are independently controlled individually or as a group of small units. 10
is a DC motor connected to the roller 9, and the rotation direction and speed are controlled respectively. Note that the roller 9 and the DC motor 10 constitute the above-mentioned conveying device 5.

In carrying out the present invention, it is important that the bloom 7 passes through each of the induction heating coils 6 without interruption, in order to reduce the power input to the bloom 7 of the induction heating coil 6, that is, the installed capacity of the induction heating device. It's important. As shown in FIG. 3, when the blooms 7a to 7e are transferred at predetermined intervals and the number of blooms on the transfer device 5 is the same as the number of induction heating coils 6, the induction heating coil 6 is in the state 1. From state 2 to state 2, heat can be applied to the bloom, but from state 2 to state 3, heat cannot be applied because there are no blooms 7a to 7e in the heating coil 5.
Therefore, it is not desirable because it is necessary to increase the input power at the time of application by the proportion of time during which the bloom is interrupted.

By the way, FIG. 4 shows a case where the number of induction heating coils 6 is 1/2 of the number of blooms 7a to 7f, and two blooms correspond to one induction heating coil.
When the rear ends of the leading blooms 7a, 7c, and 7e pass through the induction heating coil 6, the tips of the trailing blooms 7b, 7d, and 7f follow each other without interruption as shown in state 1 to state 2. Then, when the preceding blooms 7a, 7c, and 7e pass the induction heating coil 6, only the roller 9 that conveys the preceding blooms 7a, 7c, and 7e is accelerated, and from state 2 to state 3, the next induction heating coil It is made to catch up with the heated succeeding blooms 7b, 7d, and 7f. In this case, the bloom that the bloom 7a should catch up with is not shown. When the roller 9 completely catches up and reaches state 4, the roller 9, which had been increasing its speed, returns to its normal conveying speed.

Further, FIG. 5 shows a case where the number of induction heating coils 6 is 2/3 of the number of blooms 7a to 7e, and two blooms and one bloom alternately correspond to one induction heating coil. Two consecutive preceding blooms 7
When blooms a and 7d pass through the induction heating coil 6 as shown in state 2, only the conveying roller 9 carrying blooms 7a and 7d that have passed through is accelerated, and as shown in state 3, the blooms are being heated by the next induction heating coil. reaches the rear end of bloom 7c. Therefore, the speed of the roller 9 is controlled to a normal speed. In this case bloom 7a
The bloom that should catch up is not shown. Furthermore, when the bloom 7c that has been caught up passes through the induction heating coil 6 as in state 4, this bloom 7c
Only the transport roller 9 of c is accelerated, and as in state 5, it reaches the rear end of the bloom 7b which is being heated by the next induction heating coil. Then, the roller 9 on which the bloom 7c was placed returns to its normal speed.

From state 2 in Fig. 4 to state 4, state 2 in Fig. 5
From state 3 to state 4 to state 5, until the bloom that has passed through heating coil 6 reaches the next heating coil, there is always bloom to be heated in the heating coil (therefore, In the example shown in Figure 5, it is important that the bloom position in the alternate heating coils is shifted by half a cycle. For this purpose, it is necessary that the induction heating coil is divided into a plurality of pieces on the conveying apparatus, and that the number of induction heating coils is smaller than the number of blooms on the conveying apparatus.

Next, we will discuss 1 regarding thermal insulation heating in a state where the bloom must be on standby on the conveyor when the rolling mill malfunctions.
The case where two blooms correspond to two induction heating coils will be explained with reference to FIG. When in the standby state, the preceding blooms 7a, 7c, 7e and the following blooms 7b, 7d, 7f always move at the same speed within the heating coil, reciprocating the blooms back and forth. That is, when the rear ends of the trailing blooms 7b, 7d, and 7f pass the tip of the induction heating coil 6 in state 2, the state changes from forward movement to backward movement as in state 3. Then, when the leading ends of the leading blooms 7a, 7c, and 7e pass the rear end of the induction heating coil 6 as in state 4, the reverse mode is switched to the forward mode. If the induction heating coil 6 is supplied with the same power as during normal operation of the rolling line explained in FIG. 4, the amount of heat released by the bloom and the amount of heat received from the induction heating coil are balanced, and the bloom can be kept at a constant temperature. If the rolling mill recovers during standby operation, the standby operation continues until the end of one cycle in any state.
Then, by moving to the normal operation shown in FIG. 4, switching can be performed reliably. In order to make the temperature of the bloom uniform in the conveying direction, it is preferable that the backward speed is not the same as the forward speed, but is returned to a speed about five times faster. That is, if the backward speed is increased and the warming standby is always performed in the forward state, the speed will be increased in the same state when returning, and the power will be adjusted according to the speed, so that the steady state can be quickly achieved.

Furthermore, to explain a little about standby operation when one or two blooms correspond to one induction heating coil as shown in Fig. 5, it is exactly the same that the blooms repeatedly move forward and backward, but when moving forward Or, the bloom that passes through the heating coil when reversing arrives at the front or rear induction heating coil at increased speed, and the bloom must always be present in the induction heating coil as in normal operation. be.

In addition, in the above embodiment, the same effect can be obtained even when there is no rough rolling mill.

According to this invention, when a rolling mill malfunctions, the conveying device is rotated forward or backward, and the bloom is repeatedly moved forward and backward within the induction heating coil in a constant cycle, and
By making it possible to control the speed of the conveyor and by always keeping the bloom in the induction heating coil, it is possible to keep the bloom at a constant temperature with the smallest equipment capacity, regardless of whether it is in normal operation or standby operation. be.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a hot rolling line, Fig. 2 is a configuration diagram showing the main parts of this invention, and Figs. 3 to 5 each show the relative position of the heating coil and bloom during normal operation. In the explanatory diagrams, FIG. 3 shows when the induction heating coil and bloom are in a 1:1 ratio, FIG. 4 is when the ratio is 1:2, and FIG. 5 is when the ratio is 2:3. FIG. 6 is an explanatory diagram during standby operation when the number of induction heating coils and blooms is one to two. In the figure, 1 is a heating furnace, 3 is a rough rolling mill, 4 is a finishing mill, 5 is a conveying device, 6 is an induction heating coil, and 7, 7a to 7f are blooms (steel billets).
Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A plurality of induction heating coils are distributed between a heating furnace and a rolling mill, and a number of steel pieces than the number of induction heating coils are transferred using a speed-controllable conveyance device, The steel billet is always present in each of the induction heating coils, and the steel billet is transported from the heating furnace to the rolling mill, and from the rolling mill to the heating furnace. A method for keeping a steel billet warm, characterized by controlling the temperature of the steel billet and keeping the steel billet at a predetermined temperature. 2. Claim 1, characterized in that the conveying device is controlled so that the speed of the steel billet transferred between the induction heating coils is faster than the speed of the steel billet transferred within the induction heating coil. Method of keeping steel pieces warm as described in Section 1. 3. Induction heating coils that are distributed between the heating furnace and the rolling mill to inductively heat the steel slabs, the number of the steel slabs being greater than the number of the induction heating coils so that the steel slabs are always present in each induction heating coil. A heat-retaining device for steel billets, comprising a conveying device capable of controlling the transfer speed and transferring the steel from the heating furnace to the rolling mill and from the rolling mill to the heating furnace.