JPH0320038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a billet heater that heats billet-shaped metal using a cylindrical induction heating coil.

[Prior art and its problems]

Billet heater coils are either cylindrical coils arranged in series and electrically connected in three phases to be voltage controlled and driven by commercial frequency wires, or single phase coils that are voltage and frequency controlled and driven by an inverter power source. There are things like that. When heating a billet with a billet heater to forge a billet, so-called uniform heating is used, in which the temperature is uniform over the entire length of the billet, and aluminum or the like is extruded using a metal extruder to produce a sash as a deformed metal bar. In some cases, tapered heating may be used in which the temperature gradually decreases toward the rear end of the billet. In the aforementioned billet heater consisting of three-phase coils, taper heating can be performed by controlling the voltage for each rectangular coil.

Conventionally, when billets are heated in large quantities using a billet heater adapted to a certain size of the billet, the desired uniform heating or tapered heating has been obtained. In the case of production, it has become common for billets to no longer have a predetermined temperature distribution. When the billet is longer than the coil, the temperature at both ends is naturally lower, but it has been found that if the billet is much shorter than the coil, the temperature at both ends becomes locally high. When we studied the temperature distribution of the billet, we focused on the magnetic flux distribution within the billet. FIG. 1 shows the magnetic flux distribution when the coil 1 uniformly heats a billet 2 shorter than a predetermined size, and FIG. 2 shows the temperature distribution of the billet 2 in the axial direction. In this case, the total length of the coil 1 is considerably longer than the total length of the billet 2 by A + B. Therefore, in the vicinity where the magnetic flux Φ enters and exits from the metal into the air, the magnetic flux Φ converges toward the coil center axis as shown in Figure 1. The induced current generated in the cross section of the billet increases in this region. As a result, the temperature at both ends of the billet becomes abnormally high as shown in FIG. This abnormal temperature can be resolved if the product is left for a certain period of time after heating, but the problem became apparent as the lead time to the next process such as extrusion was shortened to improve operational efficiency and save energy.

A similar phenomenon occurs during taper heating, and it is difficult to control the desired temperature distribution in both taper heating and uniform heating, which makes it difficult to control the desired temperature distribution, especially when applied to a metal extruder. Metal rods have a disadvantage in that there is slight variation in wall thickness in the longitudinal direction.

[Purpose of the invention]

An object of the present invention is to provide a billet heater that can control desired taper heating or uniform heating without causing abnormal temperatures at the ends of the billet even if the total length of the billet processed by one billet heater changes.

[Key points of the invention]

In a billet heater driven by a commercial frequency power source, this invention connects three cylindrical induction heating coils arranged in series in three phases, and connects each of the three coils with a transformer that can independently adjust the voltage. An intermediate tap is provided on one end of the coil for adjusting the axial length of the current-carrying part, and a stopper is provided on the other end of the coil for regulating the distance between the other end and the billet. In short, in order to shorten the lead time to the next process and prevent the abnormally high temperature at the end caused by the length of the billet from becoming defective, the coil energization length is variable and taper heating or uniform heating is used. The aim is to control the temperature distribution with high precision.

[Embodiments of the invention]

Figures 3, 4 and 5 show examples of the coil according to the present invention, in which three cylindrical induction heating coils 31, 32 and 33 are arranged in series and have three phases as shown in the figure. It is connected. The coil 31 is provided with intermediate taps 31a and 31b in addition to terminals at both ends thereof. The billet 2 is carried in from the coil 31 side and carried out to the coil 33 side by appropriate means. Both ends of billet 2 are a as shown in the figure.
By applying the same voltage to the coils 31, 32, and 33 for an appropriate period of time, the billet is heated uniformly as shown by reference numeral 4 in FIG. 4. In this case, a and b are preferably 20 to 50 mm, depending on the diameter of the billet. When it is desired to taper-heat the billet, the taps of a transformer (not shown) are switched and the applied voltages are lowered in the order of coils 33, 32, and 31, and the billet is taper-heated as shown by reference numeral 5 in FIG. Next, when a billet 2 whose length is short by c as shown by the dotted line in Fig. 3 is brought in, the tap 31b suitable for it is selected and uniform heating or tapered heating can be achieved in the manner described above. The temperature distribution is as shown by reference numeral 6 or 7 in FIG. Although FIG. 3 has intermediate taps 31a for billets of different lengths, it is possible to increase the number of taps or provide intermediate taps on the coil 33. Depending on the length of the billet, coil 31 may not be energized at all and coil 3 may
It is also possible to use only 2 and 33.

FIGS. 6 and 7 show an embodiment in which the pusher serving as the billet conveying means and the length measuring means are combined, and the billet is heated in two stages: preheating and final heating in a coil. FIG. 6 shows the billet 21 being heated or just after being heated, with the billet 21 in the final heating state and the billet 22 in the preheating state inside the coil 3, and the billet 23 on standby outside the coil. L-shaped end 81 of stopper 8
contacts the end of the billet 21 to stop the billet. The stopper 8 is biased by a cylinder 9 located outside the coil 3, and the pusher 10 is biased by a cylinder 11.

When one stage of heating is completed, the stopper 8, which is urged toward the unloading side by the cylinder 9, is gradually rotated around the axis of the cylinder 9 by a cam (not shown), and as shown in FIG. off the axis. Next, when the pusher 10 is energized by the cylinder 11 at a speed V ₁ and the billet 21 is carried out from the carry-out side at a speed V ₂ greater than V ₁ by a device (not shown), the billet 21 and the billet 22 are carried out while being relatively separated from each other. As the billet 23 moves to the side, the billet 23 that has been waiting is also carried into the coil 3. A position detecting device 12 such as a proximity switch is located near the unloading portion of the coil 3, and the pusher 10 is stopped when the end of the billet 22 comes to this position. Distance l between the initial position of the tip of the pusher 10 and the position detection device 12 and the pusher 10
The total length e+f of the billets 22 and 23 in the coil 3 is calculated from the amount of movement S. If the value of e+f is known, the third
As shown in the figure, the temperature distribution of billets 22 and 23 can be quickly controlled by selecting appropriate taps. Prior to heating, the pusher 10 is retracted and the stopper 8 comes into contact with the billet 22 to determine positions a and b within the coil of the billet as shown in FIG.

The amount of movement S of the pusher 10 described above can be detected by various known methods, and FIG. 8 is a conceptual diagram of one embodiment. S is taken out as an electrical signal from a rotary encoder 16 connected to the shaft of the sprocket wheel 13 via an arbitrary speed reducer 15.

In the length measuring means shown in FIGS. 6 to 8 described above, a part of the length measuring means is also used as the pusher 10 and the stopper 8, but it is also possible to provide a length measuring means independent of the pusher 10 and the stopper 8. However, the length measurement by the length measuring means may be performed not on the billet inside the coil but on the billet before entering the coil.

9 and 10 show another embodiment of the stopper, in which the billet 2, coil 3, stopper 8, and cylinder 9 for biasing the stopper are the same as those described above. A positioning plate 18 integral with the screw body 17 is provided opposite the other end 82 of one end 81 that contacts the billet of the stopper 8, and a screw shaft 19 that is threadedly connected to the screw body 17 is supported by a bearing 20 and is connected to the geared motor 24. is driven by. An insulating plate 26 having pins 25 arranged at equal pitches around the entire circumference is fixed to the screw shaft 19, and a proximity switch 27 is fixedly arranged opposite to the pins 25.

By driving the geared motor 24, the positioning plate 18 is supported by the linear way 28 and moved to an arbitrary position by the action of the screw body 17 screwed to the screw shaft 19, and the proximity switch 27 counts the pins 25. Accordingly, the position of the positioning plate 18 can be detected and controlled.
Thus, when the cylinder 9 urges the stopper 8 from the left to the right in FIG. 9 via the shaft 91, the stopper 8
The other end 82 abuts against the positioning plate 18 to control the stop position of the stopper 8, and as a result, the stop position of the billet 2 can be controlled by one end 81 of the stopper 8. That is, by controlling the dimension a in FIG. 3 mentioned above and controlling the dimension b in conjunction with the billet length measurement results, uniform heating or tapered heating can be performed with a highly accurate temperature distribution depending on the length of the billet. Can be done. This dimension a is controlled according to the billet dimensions, but it may be desirable for the operation of the metal extruder to intentionally increase a so that only one end of the billet on the discharge side is at a relatively high temperature. . In FIG. 9, a tip 29a of a shock absorber 29 is provided to protrude through the positioning plate 18, and absorbs the impact when the other end 82 of the stopper 8 comes into contact with the positioning plate 18.

〔Effect of the invention〕

According to this invention, even if the length of the billet changes when heating the billet, abnormally high temperatures at the ends can be avoided and arbitrary uniform heating or taper heating can be achieved with the intended accurate temperature distribution. Precise molding is possible during hot plastic processing. Accurate temperature distribution is achieved without relying on the flattening of temperature distribution due to natural cooling, which shortens the lead time to the next process and improves operational efficiency. Since the coils are not energized unnecessarily, lead time is shortened, heat loss due to cooling is reduced, and energy efficiency is improved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional billet heater, and Figure 2 is a cross-sectional view of a conventional billet heater.
The figure is a temperature distribution diagram of the billet heated as shown in FIG. Figure 3 is a temperature distribution diagram of heated billets of different lengths, Figures 6 and 7 are cross-sectional views of the length measuring means, and Figure 8 is one of the length measuring means in Figures 6 and 7. FIGS. 9 and 10 are a conceptual diagram of the detection means, which is a part of the present invention, and a plan view and a side view of the stopper. 1, 3, 31, 32, 33...Coil, 2, 2
1, 22, 23... Billet, 8... Stoppa,
10... pusher, 12... position detection device, 17
...Screw body, 18...Positioning plate, 19...Screw shaft, 27...Proximity switch.

Claims (1)

[Claims] 1 Three cylindrical induction heating coils arranged in series are connected in three phases, each of these three coils is provided with a transformer that can independently adjust the voltage, and one end of the coil is equipped with a current-carrying part. 1. A billet heater characterized in that an intermediate tap is provided for adjusting the axial length of the billet, and a stopper is provided at the other end of the coil for regulating the distance between the other end and the billet.