1. Field of the Invention
The present invention relates to a process and a circuit for regulating welding current and power as a function of welding speed in welding devices for continuous longitudinal-seam welding of metal bands formed into a tube.
2. Description of the Prior Art
A circuit arrangement is already known (German OS 19 00 856 corresponding to U.S. Pat. No. 3,619,554 ) in which the electrodes of a welding device are affected from a voltage source via a transformer, a control element adjusting the welding current, and a speed-dependent tachogenerator. In this case, means is provided for controlling the magnitude of the welding current as a function of the supply voltage, the electrode distance and temperature variations.
In a control circuit of this type, for DC welding, the actual welding current is continuously measured and, by means of disturbance-variable compensation, the control element is affected in the case of even very small variations, so that the welding current corresponds to the requirements in each case. The adjustment in this case can be carried out promptly, so that variations in the supply voltage, the electrode distance or temperature changes are not noticeable with regard to the welding current, but the magnitude of the welding current always takes on the value required for thorough welding of the weld in each case.
However, problems arise when higher manufacturing speeds are required and different metals or band thicknesses are used. This is because high manufacturing speeds permit the disturbing effect of the waviness of the welding current to increase, so that it is no longer assured that satisfactory welds can be produced with known control devices.
To provide a remedy in this case, it would be possible to incorporate filter elements in the control circuit, but there are limits to a significant enlargement of such filter networks because of the time constants of the control circuit. The replacement of the known control elements, for example by transistors, also does not always produce the desired effect or makes additional expenses necessary, for example, by the fact that the excess energy must be removed by means of suitable coolants, such as water or air.