The preferred Welding process for repair of earthmoving equipment is GMAW Gas Metal Arc Welding or what is commonly known as MIG welding or, FCAW Flux Cored Arc Welding. If these welding processes are not available or not practical, SMAW is the process you will have to use.
Considerations for Repair of Cracked or Defective Welds
- * Selection of material and welding procedure.
- * The welding repair process has to be selected with regard to base material cleanliness and the environmental conditions (indoors or outdoors).
- * Develop a weld procedure that will include welding process, welding parameters, filler metal, welding sequence, and any other specific information concerning the welding joint technique.
- * Weld repair process, use DC, reverse polarity (i.e. electrode is positive (+), ground is negative (-) for either GMAW, FCAW or SMAW.
- * Before welding of arc-airing, the area to be repaired must be at least 21° C (70° F), and the surface must be dry and free of moisture, paint and grease.
- * This can be accomplished by acclimating in a heated workshop or preheating.
- * Don't let surfaces get above comfortable hand temperature to prevent distortion to bore surfaces. Bores can be cooled with compressed air to help prevent overheating.
- * Protect finish bores and surfaces from spatter when welding or air arcing.
NOTE: - in proximity of finished bores and diameters.
- * Note about grounding - ground connection must be located where welding current will not arc through critical surfaces. (e.g. roller bearings, duo-cone seals, polished shaft/rods, etc) and locate ground as close to work as possible to eliminate arc blow. Turn tractor disconnect key to off position before welding or air arcing.
- * Remove flaw or crack completely using air arc method or by grinding. It is critical that flaw is completely removed or the repair could fail. Refer to "Crack Preparation" in this section.
- * Use dye penetrant to confirm removal of flaw.
- * Grind area that was air arced to remove slag and carbon pickup.
- * Reweld area where flaw was removed.
- * Remove spatter from welded area and grind toes of welds to a smooth transition. (see Figure 35).
- * Hammer peening the welds to improve the residual stress state.
- * The welding repair process has to be selected with regard to base material cleanliness and the environmental conditions (indoors or outdoors).
In general, a weld repair will have, at best, the same fatigue life as the original detail. However, a repair made under difficult circumstances (poor access, out of position, outdoors, etc.) may have a shorter life.
Crack Preparation
- 1. Cracks must be completely removed with an air carbon arc torch or similar tool.
- 2. When a crack is removed with an air carbon arc tool, make sure the procedure does not cover up the cracks. A dye-penetrant can be used to check if the crack is completely removed down to a solid metal.
NOTE: All slag or foreign material must be removed from the crack before a check is made with a dye-penetrant.
Figure 35 - Four types of welds and four joint configurations are used.
- 2. When a crack is removed with an air carbon arc tool, make sure the procedure does not cover up the cracks. A dye-penetrant can be used to check if the crack is completely removed down to a solid metal.
Local Grinding
Toe grinding is normally done to improve the fatigue properties of the weldment by reducing the stress concentration at the weld toe detail. The grinding procedure should produce a smooth concave profile as shown in Figure 36. Toe grinding can be assumed to improve the fatigue strength of the weldment by 30% (a factor of 2.2 over the life of the weldment).
Figure 36 - Toe grinding detail to improve fatigue life.