Firecracker Welding (German:
Elin Hafergut Process) was invented by Georg Hafergut around 1938 in Austria and was subsequently modified. In this process,
up to 2 m long flux-coated stick electrodes were melted automatically without mechanical equipment. The electrode was placed along its length on the seam forming the opposite pole, clamped
to the power source at its bare end and an arc was struck the opposite end, which then burned along the length of the electrode.
This arc welding process did not require any special manual skill on and was the only one working with a horizontal electrode at the time of its invention. However, it had originally so many disadvantages that it did not gain much practical significance.
The electrode sometimes buckled upwards because it was bent by the ohmic resistance of its core, the arc burned inconsistantly and went out again and again, the penetration was only slight.
Firecracker welding: On the left the arrangement for V-joints and on the right for single or double-sided simultaneous welding of fillet welds. A
cavity is to be left between the workpiece, electrode and cover bar by forming suitable grooves in the latter, to absorb the slag produced during melting.
Hafergut improved the process by placing a profiled copper bar, which was well clamped to the workpiece, over the flux-coated rod electrode shown in the illustration.
Other metals were not suitable for the production of the cover rail. As shown in the illustration, the rail could be provided with grooves of different radii at all four corners in order to be
able to use it for different electrodes with 2 to 10 mm diameter.
A paper strip, e.g. made of packing paper, clamped between the electrode and the workpiece improved the welding result and operational safety. This arrangement not only improved fusion penetration but also ensured a uniform flow of the melt and slag due to the closed channel. This kept the arc length constant so that seams could be produced with a uniformity otherwise only achievable by automatic welding machines.
The left part of the figure illustrates the arrangement for V-seams, the right part the arrangement for single or double-sided simultaneous welding of fillet welds. A cavity should be left between the workpiece, electrode and cover bar by suitable grooving in the latter, which can absorb the slag produced during melting.
If possible, the beam should be turned during welding so that the flat position (PA).
When working with direct current, polarity and current intensity are approximately the same as for manual electric welding. In practice, however, alternating current has proved to be the best choice, because the unfavourable deflection of the arc due to the blowing effect is lowest here.
Since the electrodes cannot be loaded with higher current than in manual welding, this method was only economical if a welder could operate several welding points simultaneously using suitable equipment. It was only of importance where bulk goods were welded whose seams were not accessible for manual electric welding.
R.M. Evans and R.P. Meister of Batelle Columbus Laboratories carried out a comprehensive study in 1975 for the Bethlehem Steel corporation and under the support of the U. S. Maritime. Horizontal fillet and groove welds were made successfully, both with single or multi pass beads. The conclusions can be summarised as follows:
The conduction of further studies have been proposed in 1975 as follows: