Thermal gouging is an essential part of welding fabrication. Used for rapid removal of unwanted metal, the material is locally heated and molten metal ejected – usually by blowing it away. Normal oxyfuel gas or arc processes can be used to produce rapid melting and metal removal. However, to produce a groove of specific dimensions, particularly regarding depth and width, the welder must exercise careful control of the gouging operation. If this does not happen, an erratic and badly-serrated groove will result.
Thermal processes, operations and metals which may be gouged or otherwise shaped:
|Thermal process|| |
Oxyfuel gas flame
|Grooving Washing Chamfering||Low carbon steels, carbon manganese steels (structural), pressure vessel steels (carbon not over 0.35%), low alloy steels (less than 5%Cr) cast iron (if preheated to 400-450 deg.C)|
|Manual metal arc|| |
|Grooving Chamfering||Low carbon steels carbon manganese steels (structural), pressure vessel steels, low alloy steels, stainless steels, cast iron, nickel-based alloys|
Air carbon arc
|Low carbon steels carbon manganese steels (structural), pressure vessel steels, low and high al- loy steels, cast iron, nickel-based alloys, copper and|
copper alloys, copper/nickel alloys, aluminium
|Chamfering Grooving Washing|| |
Aluminium, stainless steels
Note: All processes are capable of cutting/severing operations. Preheat may or may not be required on some metals prior to gouging
It should be emphasised that because gouging relies on molten metal being forcibly ejected, often over quite large distances, the welder must take appropriate precau- tions to protect himself, other workers and his equipment. Sensible precautions in- clude protective clothing for the welder, shielding inside a specially-enclosed booth or screens, adequate fume extraction, and removal of all combustible material from the immediate area.
Thermal gouging was developed primarily for removal of metal from the reverse side of welded joints, removal of tack welds, temporary welds, and weld imperfections. Figure 1 illustrates the value of typical back-gouging applications carried out on arc welded joints., while Fig. 2 shows imperfection removal in preparation for weld repair.
Fig.1 Typical back-gouging applications carried out on arc welded joints
Fig. 2 Imperfection removal in preparation for weld repair
The gouging process has proved to be so successful that it is used for a wide spec- trum of applications in engineering industries :
Thermal gouging is also suitable for efficient removal of temporary welded attachments such as brackets, strongbacks, lifting lugs and redundant tack welds, during various stages of fabrication and construction work.
Gouging operations can be carried out using the following thermal processes: