JPS6012158B2 - Heat input control method for ERW pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat input control method for an electric resistance welded pipe, and more specifically, it performs cascade feedback control based on the welding point temperature and the secondary current of the output transformer of a high frequency power supply. This paper proposes a heat input control method with high accuracy and excellent responsiveness.

Kasumi Governor is manufactured by sequentially bending a metal strip in the width direction to make it into a cylindrical shape, heating the opposing twills on both sides with high-frequency current, passing it through a squeeze roll, applying lateral pressure, and butt welding. Ru.

In order to manufacture highly reliable lightning tubes with improved weld quality, it is essential to control the amount of heat input during welding, but in the past, operators had to control the color of the weld, the force of the flash spark, and the amount of bead excess. etc., and estimated the welding temperature from these to manually adjust the induced voltage regulator installed in the high-frequency power supply. In the case of such a method, it goes without saying that a high degree of skill is required of the operator, but stable heat input control cannot be expected, and the occurrence of defective products is unavoidable. For this reason, and in response to the demand trend of higher quality woven pipes, various automatic heat input control methods and devices have been proposed. For example, in the heat control method for exposed steel pipes disclosed in JP-A-53-140265, a welding temperature set value is obtained from a pipe manufacturing speed signal, and a welding power source is controlled based on a predicted signal obtained from this and an actual welding temperature measurement value. However, when using this method, temperature detection is delayed due to heat conduction of residual heat in the welding part (dead time in feedback control), and the
This causes a first-order delay in control due to the heat capacity of the pipe, and in other words, the response is poor, resulting in low control accuracy, making it impractical, especially in the current situation where high-speed pipe manufacturing is required. Also known is a method (Tokukan Sho 54-9147) in which a blow coil is placed on the opposite side twill or weld seam of a cylindrical steel strip, that is, an open pipe section, and detects the high-frequency current for welding. However, since the pipe is sent vibrating from side to side, the current detection level fluctuates, making it difficult to accurately capture the welding current. The present invention has been made in view of the above circumstances, and provides a heat input control method for open-welded pipes that has excellent responsiveness through combined monitoring of welding point temperature and welding current, has high control accuracy, and is resistant to external disturbances. The purpose is to provide

The heat input control method for a welded pipe according to the present invention uses means for detecting the temperature at or near the welding point and means for detecting the secondary current of the output transformer of the high frequency power supply. The present invention is characterized in that a cascade type feedback control system is configured to adjust the output of the temperature detecting means, and the output of the temperature detecting means is used as main feedback information, and the output of the secondary current detecting means is used as width feedback information.

A detailed explanation will be given below based on the drawings. The drawing is a block diagram of an electric circuit according to the method of the present invention. A commercial power source (not shown) is connected via a step-down transformer 11 to an output control circuit 12 using a thyristor. The output control circuit '2 adjusts the effective power by controlling the conduction phase angle of the thyristor, and the trigger current of each thyristor is given from the phase shifter 20. Output control circuit 1
The output of 2 is given to the anode transformer 13, where it is boosted and fed to the high frequency oscillation circuit 14.

The high-frequency oscillation circuit 14 consists of a rectifier circuit, an oscillation tube such as a magnetron, etc., and the oscillation tube output is connected to the primary wire of the output transformer 15, and the power stepped down by the transformer is transferred from the secondary wire. It is applied to the induction coil (work coil) 16 through which the open pipe 30 is inserted. Due to the high frequency current flowing through the induction coil 16, an induced current flows through the green ends of the open pipe 30 with the welding point V as the turning point. They are welded together to form a tube 32. In the method of the present invention, the secondary current of the output transformer 15 and the temperature of the welding point V (or its vicinity) are detected and used as control information, but in order to detect the secondary current, the current transformer 21 is A circuit, for example, an output lead part is interposed therein, and an infrared ray radiation thermometer 22 is provided to detect the temperature of the welded part V. Next, to explain the control system, the calculator 23 calculates the optimal welding point temperature for these conditions according to a predetermined calculation formula using inputs such as pipe size, material, pipe manufacturing speed, induction coil, etc. , which is applied to one input terminal of the differential amplifier 24 as a set reference value.

Note that when a digital circuit is used as the calculator 23, it goes without saying that the set reference value is input to the differential amplifier 24 via an A/D converter. The output of the thermometer 22 is applied to the other input terminal of the differential amplifier 24 via an isolation amplifier 25. The differential amplifier 24 outputs a signal corresponding to the difference between the two inputs, that is, the deviation between the set reference value and the actual temperature measurement value. The output of this amplifier 24 is connected to the output transformer 1 which makes it possible to reduce the above deviation to zero.
The content corresponds to the secondary current of No. 5, and is applied to one input terminal of the differential amplifier 26. The detection current of the current transformer 21 is applied to an input terminal of a differential amplifier 26 via an isolation amplifier 27. Therefore, the output of the differential amplifier 26 is a signal corresponding to the difference between the two inputs, that is, the current deviation between the current value that can eliminate the temperature deviation and the actual measured value of the secondary current. , and the phase shifter 2 changes and adjusts the conduction phase angle of the thyristor of the output control circuit 12 in the direction of zeroing the current deviation. As shown by the two-dot chain line in the figure, a current forcing setter 28 may be connected to the differential amplifier 26 to forcibly change the input from the differential amplifier 24 side. With such a configuration, it is possible to improve followability under special circumstances such as when starting up or changing the pipe manufacturing speed. As described above, the method of the present invention uses the temperature at or near the welding point V and the secondary current of the output transformer of the high frequency power supply as feedback information, and performs cascade control based on these, with the former as a measure loop and the latter as feedback information. We decided to do it as a minor loop,
The following effects are produced.

In other words, in the case of control based only on temperature, poor responsiveness due to dead time and first-order delay is unavoidable as described above, but the current control loop, that is, differential amplifier 26 single-phase shifter 20 - output control circuit 12 - output transformer There is no delay in the step response in the power supply circuit 15, current transformer 21, and isolation amplifier 27, and since there is a first-order correlation between temperature and secondary current, both responsiveness and control accuracy are greatly improved. Furthermore, when the current is not controlled, the current waveform includes ripples.

This ripple period corresponds to the rotation period of the squeeze roll, and is therefore attributed to roll eccentricity.
Even short periodic temperature fluctuations caused by this ripple can be absorbed by the current control of the present invention. Furthermore, in the present invention, since the output transformer secondary current is used as control information, the detected current level does not fluctuate unnecessarily as in the case where a blow coil is used. On the other hand, the present invention exhibits excellent effects, such as the fact that the occurrence of an arc or the like can be tracked sensitively, so that the influence of external disturbances can also be used as a control factor. Note that the present invention can be applied in exactly the same manner to the case where a contact chip is used as the high-frequency heating means.

[Brief explanation of drawings] The drawing is a block diagram of an electric circuit according to the method of the present invention.

Claims (1)

[Claims] 1. In a heat input control method for an electric resistance welded pipe manufactured by heating both opposing edges of a cylindrical bent metal strip with high-frequency current and butt-welding the edges, 2. Means for detecting temperature and output transformer of high frequency power supply
A cascade type feedback control system is configured to adjust the output of the high frequency power supply using the secondary current detecting means, and the output of the temperature detecting means is used as main feedback information, and the output of the secondary current detecting means is used as sub feedback information. A heat input control method for an electric resistance welded pipe.