JPH04218692A - Device for remelting tin electroplate steel sheet - Google Patents

Abstract

PURPOSE:To prevent the generation of a wood-grain pattern on a tin electroplated steel sheet when the sheet is remelted by adjusting the phase angle of the applied load current. CONSTITUTION:A transformer 3 (high voltage) and a transformer 4 (low voltage) are provided on the outlet side of a thyristor 7, and the output voltage on the secondary side of the transformer is changed as the load fluctuates and supplied to the load. As a result, the cutoff time of the load current is reduced by the thyristor 7.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for remelting electrolytic tinned steel sheets.

0002

[Prior Art] When manufacturing electrolytic tin-plated steel sheets (tinplate), it is impossible to obtain tinplates with a beautiful metallic luster and a beautiful surface condition by using only tin as-plated. After heating and once the tin is in a molten state,
Immediate water cooling, a so-called reflow process, is applied.

[0003] In other words, in the second half of the electrolytic tin-plated steel plate manufacturing line, the steel plate is heated directly to a temperature above the melting point of tin (232°C) for about 3 to 5 seconds using the generated Joule heat. Because a large current is applied, direct current is difficult to prevent leakage, and single-phase alternating current is used to pass current through a single steel strip. Due to equipment costs, commercial power sources (50, 60 Hz) are used as they are.

However, as the tin weight decreases,
There was a problem in that wood grain patterns were likely to occur on the surface of the manufactured tinplate. This is a pattern in which a plate-like pattern with different gloss appears alternately on the surface at a pitch of 35 to 55 mm, and this pitch is exactly 50 Hz and line speed of 240 mpm.
If you are producing at

[0005] In order to prevent the occurrence of this wood grain pattern, Japanese Patent Publication No. 61-948 and Japanese Patent Application Laid-open No. 1-177388 are disclosed. Japanese Patent Publication No. 61-918 discloses a method of treating molten tin by resistance heating in a frequency-current density relationship range in which wood grain patterns do not appear, and Japanese Patent Publication No. 1-177388 discloses a method of treating molten tin by heating the heating current or voltage in a specific rectangular waveform. However, in both cases, the aim is to shorten the time during which the heating current reaches "cutoff (zero)" as much as possible.

[0006]

[Problems to be Solved by the Invention] Generally, when remelting electrolytic tin-plated steel sheets by controlling the commercial power supply using a thyristor, etc., constant power control of the heating device is performed using the effective voltage value as shown in the following equation. This is done in ERMS [V]. ERMS = (k・ρ・L)1/2×(S)
1/2
…■ ERMS: Applied voltage to tin-plated steel sheet [V] k: Constant ρ: Specific resistance of tin-plated steel sheet [Ω・m]
L: Length of tin-plated steel plate
S: Line speed [m/S] In this case, ERMS
is determined by the steel plate size. (k and L in the formula
is constant and ρ varies). When the cross-sectional area of the steel plate is small, the voltage is high and the current is small, and when the cross-sectional area is large, the voltage is low and the current is large, and the input power is usually about 50% ma of the equipment capacity.
x (the capacity of the device is determined from maximum voltage x maximum current).

On the other hand, when the voltage is controlled using a thyristor etc. as shown in equation (2), the phase control angle α of the thyristor and the effective voltage value E
RMS has the relationship shown in Figure 3. A typical voltage waveform at this time is shown in FIG. Furthermore, since the tin-plated steel plate has almost pure electrical resistance, the current waveform shown in Figure 4
It is the same as. However, the voltage (ERMS) used for electrolytic tin plating reflow treatment is not always required to be the rated voltage because ρ changes in equation (2).
Usually only 50-80% of the rated voltage is used. Therefore, for example, if only 70% of the rated voltage is used, the power is controlled by the thyristor, so if the working voltage is constant, the voltage with the thyristor control angle α = 90° will be used as shown in Figure 3. This means that

As shown in FIG. 4, this voltage waveform shows that the instantaneous voltage is 0 for the control angle from 0° to 90°, and for the control angle from 90° to 180°.
This means that the instantaneous voltage is effectively used. Therefore, the time when the applied current is 0 is longer, and the temperature increase speed of that part of the steel plate is slowed accordingly, and a pattern with dull luster is more likely to occur. In the prior art, various devices have been devised in order to shorten the cutoff time of the heating current by the thyristor as much as possible, but there is a problem in that the device becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for remelting electrolytic tin-plated steel sheets in which the cut-off time of the heating current is made as short as possible every half cycle of the commercial power supply using a simple apparatus.

0010

[Means for Solving the Problems] The present invention solves the above-mentioned problems and is applied to an electrolytic tin-plated steel plate remelting treatment apparatus using a power conversion element, and employs the following technical means. In other words, on the output side of the power conversion element, the primary side is connected in parallel, and the secondary side generates each predetermined voltage and changes the phase of multiple load currents to be supplied by switching to the predetermined secondary voltage according to load fluctuations. This is an apparatus for remelting electrolytic tin-plated steel sheets, characterized in that it is equipped with a transformer for angle adjustment.

[0011]

[Operation] According to the present invention, when the required load voltage is low relative to the rated voltage, the phase control angle α of the thyristor becomes too large, and as a result, the time during which the heating current is cut off becomes longer and a wood grain pattern occurs. To solve this problem, if the load voltage can be low, the phase control angle α of the thyristor can be reduced by providing a transformer that outputs a predetermined low voltage and connecting the output of the transformer to the load. The same effect can be given to the heating current. That is,
It becomes possible to shorten the time during which the heating current is cut off, and the occurrence of wood grain patterns can be prevented.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an equipment system diagram of an embodiment of the present invention, and shows an example in which two transformers are used. Commercial power supply (3.3K
The effective voltage value of V) 8 is controlled by controlling the energization phase by a thyristor 7, which is a power conversion element. The voltage is stepped down to a predetermined heating voltage (for example, 230V to 160V) by the transformer 3 or 4 via the circuit breaker 5 or 6 (the rated voltage is 260V).

Here, the voltage is constant power (
In other words, it is controlled for the purpose of constant heating. When this voltage is low, the phase control angle α of the thyristor 7 becomes large as shown in Fig. 3, and in order to obtain a voltage of about 71% of the rated voltage, the phase control angle α of the thyristor 7 must be set to 90°. , the cutoff time is halved compared to that at rated voltage. Therefore, as shown in Figure 1, the output voltage ratio of two transformers is 1:1.
0.7, high voltage transformer 3 and low voltage transformer 4, respectively.
and set up. The output of the transformer is switched by a circuit breaker 5 or 6 depending on the required load voltage. An example of use at this time is shown in Figure 2. Conventionally, the phase control angle α was approximately 100° in order to obtain approximately 60% voltage, but in the present invention, the conventional low voltage control angle of 70% voltage is used. Since the side transformer is used, the above α is approximately 70°, and the heating current cut-off time is 3.
It became possible to shorten the time by 0° (1.7 ms×2/Hz in the case of 50 Hz), and it was possible to prevent the occurrence of wood grain patterns by about half. Note that the more transformers installed, the more finely the control is possible, but due to space and equipment cost constraints, the industrial limit is about two.

[0014] In the actual machine, when the line speed is 300 to 400 m, the rated voltage, current, and power are 26
0V/13400A, 3500KVA, while the voltage, current, and power normally used are 160V/11
000A (1740KVA) ~ 230V/7000A (
1610KVA).

[0015]

[Effects of the Invention] According to the present invention, by adjusting the load voltage, the time at which the heating current is cut off by the thyristor can be set within a certain value, and the time at which the heating current is cut off is set by adjusting the load voltage. It is shorter than before, and the incidence of wood grain patterns can be significantly reduced compared to before.

Furthermore, it is possible to use an inexpensive thyristor element with a low current rating, thereby reducing equipment costs.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the present invention, and is a graph of the relationship between the thyristor control angle and the effective voltage value, with the use of high-voltage and low-voltage transformers as parameters.

FIG. 3 is a graph showing the relationship between thyristor control angle and effective voltage value.

FIG. 4 is a graph showing the relationship between thyristor control angle and instantaneous voltage.

[Explanation of symbols]

1 Steel plate 2　Electrification roll 3 High voltage transformer 4 Low voltage transformer 5 High voltage circuit breaker 6 Low voltage circuit breaker 7 Thyristor 8 Commercial power supply

Claims (1)

[Claims] Claim 1: In an apparatus for remelting electrolytic tin-plated steel sheets using a power conversion element, the primary side is connected in parallel on the output side of the power conversion element, and the secondary side generates each predetermined voltage. 1. An apparatus for remelting electrolytic tin-plated steel sheets, characterized in that a plurality of transformers for adjusting the phase angle of load current are provided to switch and supply the predetermined secondary voltage according to load fluctuations.