- Excavator: All
- Wheel Loader: All
Many base edge assemblies are prematurely replaced due to development of extensive cracking in the base edges. This extensive cracking could have been prevented by maintaining a periodic inspection and repair program for developing small cracks. Weld cracks on base edges with wear protection between the adapters are often difficult to detect. However, inspection of that area when those wear parts are being replaced, should be a regular requirement.
Small weld crack at start
Inside of crack in Illustration 1
Small crack at weld start
Weld crack in Illustration 3 extending into the base edge
Typical base edge failure from type of crack in Illustrations 1 and 2.
Typical base edge failure from type of crack in Illustrations 3 and 4.
Loader and excavator base edge components are composed of hardened steel to resist high load stresses and abrasion. Components operating in a long wear life situation may eventually fail from fatigue, as will those components subjected to severe stresses. Most base edge failures begin as small cracks at the adapter weld starts. Some cracks may occur shortly after build completion due to improper weld application.
Any small crack, as shown in Illustrations 1 through 4, when detected but considered as being inconsequential and requiring no immediate repair, can eventually develop into a major failure as shown in Illustrations 5 and 6.
Often there is a tendency to repair these small cracks by just welding over the crack. However, the original welds must be gouged out completely before making a repair. Any part of the crack remaining under a "repaired weld" will propagate further along the adapter weld or deeper into the base edge until there is a complete failure similar to those failures shown in Illustrations 5 and 6.
Base edges and adapters have a high enough Carbon Equivalent to require preheating to 150° - 220° C (300° - 428° F). Before gouging out the crack to full depth, preheat the area on either side of the crack equal to three times the thickness of the base edge Illustration 7. Remove the heating source and wait at least one minute before checking for a temperature drop. Reheat the area if the temperature drops more than 10° C (50° F). Thin base edges, 25.4 mm (1.0 inch) or under, can easily overheat during welding and only minimal preheating is normally required.
Preheating adapters above 220° C (428° F) can cause loss of toughness, hardness, strength, and wear resistance. An interpass temperature up to 260° C (500° F) is acceptable as this temperature is only a temporary condition that could be reached between weld passes.
Check the preheat temperature with temperature sticks/crayons or an infrared thermometer as shown in Illustration 8. Infrared thermometers are subject to emissivity differences of various surface conditions. Infrared thermometers should be checked first against temperature sticks or crayons to verify what the corrected reading should be.
Gouged out crack
Replaced adapter weld after edge repair
Slag removal after each weld pass
If the crack propagates as the carbon arc gouging approaches the end of the crack, lance or drill the ends of the crack before continuing on. Since most base edge failures begin at the start of the adapter weld, a portion of that weld should also be removed (Illustration 9). Check for any crack remaining with dye check. Remove the dye penetrant before making a weld repair. Then use E71T-1 low hydrogen wire or E7018 stick electrode to fill in the crack with multiple passes of weld, first filling in the gouged crack area in the base edge, grinding that weld smooth with the base edge surface and then replacing the adapter weld that had been removed (Illustration 10). Always remove any slag created during each weld pass (Illustration 11).
Crack to front of edge - less chance for durable weld repair
Allow the weld repair area to slow cool in a draft free warm environment as slow cooling will help dissipate internal weld stresses.
Note: Base edges that are cracked up to the front blunt height (Illustration 12) can be repaired, but the strength of the weldment will be less than the parent metal and therefore, durability of the repair will be limited. Do not weld to the front base edge blunt height if a crack has not propagated that far.
Refer to Special Instruction, REH8015, "Loader and Excavator Bucket Base Edge Assembly Welding Requirements" for other applicable welding recommendations.