JPH029653B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a continuous annealing line for long metal tubes,
More specifically, the present invention relates to a continuous annealing method in which a long metal tube is continuously annealed using an induction heating furnace and the annealed material is wound around a basket table.

(Prior art and problems to be solved) Long metal pipes such as thin-walled steel pipes are annealed and tempered before being used for product processing.

As for this annealing method, conventionally, the coiled material is annealed in batches in an annealing apparatus such as a roller hearth furnace while being wound into a coil shape during the pipe making process. However, in the case of long metal pipes made of materials with lower strength than steel pipes, such as thin-walled copper pipes, or long metal pipes of special shapes with grooves on the inside, it is necessary to wind up a strip of metal material. It is difficult to accumulate in a tight coil state.

That is, particular attention is paid to the winding method, for example, the annealed long tubes are sequentially stacked and wound on a drum at the same level. A winding method for manufacturing so-called level-wound coils (LWC) has been attempted, but this method increases the number of man-hours required to manufacture the LWC, lowers the yield, and increases the cost of temporary packaging and transportation of the LWC. Moreover, when LWC is annealed in a roller hearth furnace or the like, there is a problem that the tempering is different between the outer circumferential side and the inner side.

SUMMARY OF THE INVENTION An object of the present invention is to provide an annealing method that eliminates the drawbacks of the above-mentioned prior art, allows a long metal tube to be continuously annealed at high speed with good annealing characteristics, and can be wound up.

(Means for Solving the Problems) In order to achieve the above object, the inventors first installed an induction heating furnace as a line that enables continuous high-speed annealing treatment and a cooling device downstream thereof. Furthermore, the equipment is arranged to wind the annealed material under virtually no tension.
The relationship between line operating conditions and annealing characteristics was investigated. At that time, we focused on improving the winding method for annealed materials.

First, to wind up a long metal tube that is annealed material, a bending roll is installed downstream of the cooling device, and the bending roll is stroked to change the curvature and placed in a rotating basket installed on a receiving table. However, it was difficult to change the curvature of the annealed material with a bending roll.
In particular, since the annealed material is a metal tube, it is technically impossible to fit it neatly into a basket without damaging its cross-sectional shape.

Therefore, instead of using a winding method that changes the stroke of the bending roll, we changed the rotation speed of the basket table to a method that allows the material to be wound into the basket, and it was discovered that the annealed material could be neatly stored in a pancake shape. Then, the operating conditions of an induction heating annealing line employing this winding method were studied in detail, and the present invention was hereby accomplished.

That is, in the continuous annealing method for a long metal tube according to the present invention, in an annealing line in which a long metal tube is continuously annealed in an induction heating furnace and wound around a basket table, the induction While adjusting the input to the heating furnace, the rotation of the basket table is increased at a constant ratio to the line speed until the line speed reaches a steady state, and then at a predetermined period and amplitude after reaching the steady state. It is characterized by winding in a pancake-like manner.

The present invention will be explained in detail below based on examples.

(Example) Fig. 1 shows an example of the equipment arrangement of a continuous annealing line used for carrying out the present invention, and this line includes a feeding device 1, an induction heating furnace 2, a holding section 3, a cooling device 4, and a take-up device. It consists of a machine 5, a bending roll 6, and a basket table 7. A long metal tube to be annealed is supplied to an induction heating furnace 2 by a feeding device 1, heated to a predetermined temperature, passed through a holding section 3, and then cooled by a cooling device 4 using a shower or the like. The take-off machine 5 receives the annealed material from the induction heating furnace 2 and the cooling device 4 in a substantially tension-free state, and transfers the annealed material from the bending roll 6 and the basket table 7 in the front.
supply to. The bending roll 6 is for guiding the annealed material to a predetermined position on the basket table 7 without damaging its shape or the like. The basket table 7 has a basket-shaped storage container (basket) 9 placed on a rotating plate 8, and the rotating plate 8 is rotated by a drive device such as a motor (not shown).

In the above annealing line, the annealing conditions (heating temperature, cooling conditions) are determined by the material of the long metal tube to be processed, and the line speed V taking this into account is determined during the acceleration period and maximum constant speed period as shown in Figure 2. (steady state). Of course, it goes without saying that the line entering the heating period should be operated at a slow speed.

The induction heating furnace 2 needs to change its input W in accordance with the line speed V mentioned above. This input W
is usually determined by the voltage setting supplied to the induction heating coil, but it is determined by the grain size (GS) of the annealed material.
affect. For example, as shown in Figure 3,
When input W is controlled proportionally to line speed V (solid line in the figure), GS becomes large at the beginning of acceleration, and it takes a considerable amount of time to reach the optimum GS. This coarsening of GS at startup tends to increase especially as the line speed V increases, so it is undesirable to perform proportional control when the line speed V is too high, and this will lead to a decrease in yield. .

Therefore, in order to ensure annealing characteristics that do not depend on the line speed V, it is better to control the input W by setting, and as shown in Fig. 3, compared to the case of proportional control,
The input W is made low in the early stages of acceleration, and increased in the latter stages of acceleration. According to this setting control, the optimal GS of the annealed material can be obtained from the beginning of acceleration, and the GS of the annealed material is 100%.
yield is possible. Furthermore, since the start-up can be completed in a shorter time, efficiency is significantly improved.

Specifically, as shown in Fig. 4, the voltage υ during the acceleration period is divided into multiple steps, and the voltage υ= is calculated for each step as the line speed changes (V ₂ /V ₁ ) over time. υ ₀ × (V ₂ /V ₁ ) × ka
(ka: coefficient) is set, and induction heating is performed according to this input value during a predetermined period (T) of each step.

The annealed material cooled by the cooling device 4 is rolled up into a basket table, and the rotation of this basket table is adjusted in accordance with changes in the line speed V, and is put into the basket 9 in the form of a pancake. As shown in FIG. 6, the pancake shape means that the annealed material is put into the rotating basket 9 so that the winding diameter becomes smaller sequentially from the inner wall of the rotating basket 9, and when it reaches a predetermined minimum winding diameter (r), The rolls are placed toward the inner wall of the basket 9 so that the winding diameter becomes larger sequentially starting from the winding diameter r. This procedure is repeated a number of times and stacked in multiple stages in the rotating basket 9, resulting in aligned winding.

To do this, as illustrated in FIG. 5, a semicircular or arcuate curve is periodically created that decreases and increases the rotational speed N of the basket table 7 with a constant amplitude (V x kb) with respect to the line speed V. Adjust to maintain. Note that during the acceleration period, the annealed material in the basket becomes a pooled material and is difficult to move, so the rotation speed is slightly increased relative to the line speed V (V x
kc).

In this way, the annealing characteristics (elongation,
(Strength) The annealed material can be placed in the basket like a pancake under substantially no tension.

Note that the line speed, induction heating furnace input, and basket table rotation speed are set for each type of long metal tube size, and the design for each desired condition is automatically set by simply inputting the information for the material to be treated. It can also be made possible.

(Effects of the Invention) As detailed above, according to the present invention, a long metal tube can be continuously annealed by an annealing line using an induction heating furnace, so that the size of crystal grains can be optimally controlled. Moreover, since it can be wound in a pancake-like manner in a basket under substantially no tension, it is possible to wind it into a coil with good annealing characteristics (elongation, strength, etc.). Particularly when operating at a very high line speed, the start-up time of the annealing line can be shortened as much as possible, and therefore processing can be performed with high yield and high efficiency. Therefore, it is suitable for continuous annealing of long metal tubes, such as thin-walled steel tubes or internally grooved copper tubes, which are difficult to annealing and winding with conventional annealing and winding methods.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the equipment arrangement of a continuous annealing line used for carrying out the present invention, FIG. 2 is a diagram showing the speed curve of the annealing line, and FIG. 3 is a diagram showing the input curve of the induction heating furnace and the annealing material. Figure 4 shows the change in crystal grain size over time, Figure 4 shows the voltage setting of the induction heating furnace, Figure 5 shows the rotation speed curve of the basket table, and Figure 6 shows the pancake of annealed material. FIG. 3 is an explanatory diagram showing aligned winding. 1... Feeding device, 2... Induction heating furnace, 3...
Holding section, 4... Cooling device, 5... Taking machine, 6...
...bending roll, 7...basket table, 8...table, 9...basket.

Claims (1)

[Claims] 1. A long metal tube is continuously heated in an induction heating furnace,
After cooling, in the annealing line where the material is wound onto a basket table, the input to the induction heating furnace is adjusted in response to changes in line speed, and the rotation of the basket table is controlled at the line speed until the line speed reaches a steady state. A continuous annealing method for a long metal tube, which is characterized by increasing the temperature at a constant rate, and after reaching a steady state, changing the frequency and amplitude at a predetermined frequency and winding the tube in a pancake shape. 2. The method according to claim 1, wherein the induction heating furnace is subjected to setting control that changes input in steps in response to changes in line speed. 3. The input for the line speed and the rotation speed of the basket table can be set for each product size of the long metal tube to be processed, and the above conditions can be automatically set simply by inputting the product size. The method according to item 1 or 2.