Salzgitter AG, Salzgitter, Germany
Interface, Salzgitter AG
In the Salzgitter AG pipe mill in Salzgitter, quality pipes, mainly for the construction of high-pressure gas, oil and water pipes have been being manufactured for years. Depending on the order, the pipes can be supplied in lengths from 9 m to a maximum of 18 m, with a diameter of 500 mm and 1 700 mm and walls of a thickness of up to 21 mm. In the pipe mill, the hot rolled strips from the hot strip rolling mill are formed in the shaping plant in a screw-like manner into a pipe shape and tack welded on the inside. The pipe is then welded simultaneously from the inside and the outside. Each one of the internal and external welding heads works with up to 1 500 A DC or AC at 30 - 38 V.
The pipes are manufactured along three production lines at Salzgitter AG
If the pipe feed is constant, the quality of the weld directly depends on the welding wire feed. The greater the feed rate of the welding wire, the smaller the arc and the corresponding weld voltage needed. Correspondingly, the setpoint of the weld voltage is electrically isolated and sent together with the setpoint of the arc control to a four-quadrant PID controller, which finally controls the feed rate of the welding wire.
The safe transmission of signals and electrical isolation of the 0-20 mA setpoint are therefore a prerequisite for the quality of the weld seam and thus for the quality of the pipes. A total of 42 MCR 3-way isolating amplifiers carry out these tasks along the three welding lines. The high rate of precision of transmission < 0.05% typ., the 3-way isolation and the narrow width of the housing played a decisive role in favor of using the isolating amplifiers in this area so determining quality.