DE372537C - Process for equalizing thermal stresses during electrical or autogenous welding and for preventing shrinkage cracks during welding repairs - Google Patents

Description

ISSUED
MARCH 29, 1923

CLASS 21 h GROUP (K 81926 vm \ 2ih?)

For difficult and complicated weld repairs on cracked machine parts the later re-tearing or the formation of new cracks is a danger that despite all care when carrying out the work can lead to failure, .90 that the person to be repaired Machine part after apparently successful execution of the work older also while the same receives new cracks, giving way can render the whole body unusable.

Large workpieces are usually heavily stressed main bodies on large machine parts, the creation of which is linked to long delivery times. So far there has been no reliable tool that can be used during or after welding occurring new cracks or the tearing again at the welds sure to prevent.

For these reasons, when carrying out such white repairs it was common to to refuse a guarantee of success.

If it is about work pieces, which do not exceed certain sizes, and which make it possible for the whole body To thermally treat before and after the welding, it is possible to carry out such welding repairs execute, taking into account the skill of the worker and the care of work performance · extraordinary high demands are made.

Such cracks are the result of thermal expansion and contraction during and after ¹ Schrwieißung.

Cast iron, from which such machine parts are usually made, suffers from the fusion thermal expansion of cracks in the neighboring parts of the workpiece, which disappears again when chasing, while when transferring the welding point in-the liquid state the thermal expansion of adjacent parts to a sprain of the Material leads, which has the consequence that material is missing after cooling, so that tensile stresses occur which cause new cracks to form. Through a previous Heating the entire workpiece in the annealing furnace maintains the same in a state of To offset thermal expansion, which compensates for a correspondingly rapid Ariheitsausführungang the thermal expansion allows. But here, too, part of this thermal expansion is possible next to) the welding point lost due to appearance, and in the correct assessment thermal expansion and shrinkage during and after welding is the ultimate art of repair welding. Despite everything However, here too, diligence and skill are not excluded.

When welding on bodies of great wall thickness, it usually happens that the deeper layers of idles material. after the weld down into the upper layers of the same has progressed into a state

the cooling shrinkage, which acts as a tensile stress, and often form There are shrinkage cracks starting from the deepest points of the welded joint, like this that the welded joint does not cope with tensile stress near completion of the weld able to follow more and tear open the whole weld again.

In the case of large machine parts, it is practically impossible to preheat the Workpiece to 'cause. Annealing furnaces cannot be considered here.

It has already been proposed that the parts of the work piece adjacent to the welding point to cool by covering them with wet cloths, which are moistened with cold water from time to time during work will.

In this process, however, the shrinkage of the material is not due to the relatively small temperature drop sufficient to compensate for the thermal expansion during welding itself '.

Also it only has one surface effect, in which the deeper layers of the material cannot or not sufficiently participate. According to the invention, these difficulties are solved in a simple manner by that in the material crossed out for making the weld there is a cooling shrinkage of the metallic parts is effected from their inner layers so that the welding is in one state the local heat shrinkage of the material which causes the temporary local cold shrinkage and the also temporary local Thermal expansion during the welding equalize each other and that the tensions and strains when the workpiece cools down canceled.

Liquid air has proven to be particularly suitable as a cooling agent. she can either be instilled into the welding joint in front of the welding point or it can be used Let it flow through suitable gutters which, as the welding progresses, slowly | in the weld joint that opens up due to the cooling tube. In the former case, the cold transfer takes place directly, whereby the liquid air evaporates, in the second case through the transfer of cold when the cooled channel material is touched with the edges of the weld joint or by cold radiation. Instead of Another suitable coolant can also be used for liquid air; but has It turned out in experiments that the cold effect of liquid air or else of cold vapors of the same, which by the evaporation pressure in the to be cooled Weld joints can be blown in, are most effective for this purpose ·.

When performing longitudinal welds on fluke iron or other sheet metal bodies the procedure can also be applied in such a way that one is on both sides of the continuous The welding point causes local heat shrinkage by means of liquid air or its cold evaporation products, which can be regulated in such a way that it reduces the local thermal expansion during the welding process able to compensate, so that thermal stresses remain avoided during and after welding.

Instead of liquid air or its evaporation products, another one can also be used Use a similarly effective coolant.

Claims (1)

Patent claim: Process for equalizing thermal stresses in electrical or autogenous Welding and to prevent shrinkage cracks in welding repairs, diaidurdh that the weld joints upstream of the welding point or also adjacent parts of the material by a coolant, in particular liquid air, in a state of cold shrinkage offset, which compensates for the local thermal expansion at the welding point during the subsequent welding.