- Wheel Loader:
- 988 (S/N: 87A1-UP)
- 988B (S/N: 50W1-UP; 62Y1-UP)
- 988F Series II (S/N: 2ZR1-UP)
- 988F (S/N: 8YG1-UP)
- 988G (S/N: BNH1-UP; 2TW1-UP)
- 988H (S/N: BXY1-UP)
- 990 Series II (S/N: BCR1-UP; 4FR1-UP)
- 990 (S/N: 7HK1-UP)
- 990H (S/N: BWX1-UP)
- 992 (S/N: 25K1-1169,1170-UP)
- 992B (S/N: 25K1-1169,1170-UP)
- 992C (S/N: 42X1-UP; 49Z1-UP)
- 992D (S/N: 7MJ1-UP)
- 992G (S/N: 7HR1-UP; AZX1-UP; ADZ1-UP)
- 992K (S/N: H4C1-UP)
- 993K (S/N: LWA1-UP; Z9K1-UP)
- 994 (S/N: 9YF1-UP)
- 994D (S/N: 3TZ1-UP)
- 994F (S/N: 4421-UP)
- 994H (S/N: DWC1-UP)
- 988B (S/N: 50W1-UP; 62Y1-UP)
Introduction
Numerous articles have been published concerning replacement of base edges in excavator and loader buckets. Due to the complexity and difficulty of replacing the larger loader base edges, special care must be taken to obtain good and durable results. This special instruction will attempt to re-emphasize the special care that must be taken in order to obtain good and durable results. A 992 system will be used in the illustrations.
Weld Information
Refer to Special Instruction, REHS1841, "General Welding Procedures" for additional information concerning welding procedures for Caterpillar products.
Welding Material
Use a flux cored wire such as AWS E71T-1 with hydrogen control and with gas shielding. E71T-1 welding wire is suitable for welding in all positions. Use wire with a diameter of 1.59 mm (0.063 inch) through 2.38 mm (0.094 inch).
Note: If the welds to be applied are in a position that is flat and horizontal, you can use AWS E70T-5 welding wire. The E70T-5 series electrodes have a lime fluoride-based slag. Weld deposits produced by these electrodes typically have impact properties and hot/cold crack resistance which is superior to the properties of the E71T-1 electrodes.
The wires should have a diffusible hydrogen specification of no more than 5 ml/100g of weld deposit. Suppliers have different recommendations for the shielding gas. Generally, the use of pure carbon dioxide is acceptable for most choices of welding wire. However, while pure carbon dioxide improves weld penetration, a mixture of 75 percent argon and 25 percent carbon dioxide is recommended for out-of-position welding. The mixture of argon and carbon dioxide also provides the following benefits: enhanced arc characteristics, less welding spatter, and improved bead wetting.
Use a wire feed track welder whenever possible in order to obtain the best quality welds. When only stick welding capability exists, be aware that the stick electrode is quickly consumed when using stick electrodes in large weldments. This condition causes many stops and starts and can result in higher concentrations of crack inducing hydrogen.
If using stick, use AWS E7018 low hydrogen electrodes for all position welding. The coating of flux on the stick electrodes absorbs moisture, therefore the coating must be kept dry. Recondition exposed electrodes by heating for 2 hours at a temperature of 260° C (500° F).
Suppliers of welding wire and electrodes make recommendations about power settings. When possible, use DC reverse polarity to obtain the deepest weld penetration. This setting is called "electrode +".
If greater ductility and superior resistance to cracking are desired, use AWS E81T1-Ni1 low nickel wire, AWS E8018-C3 low hydrogen stick electrode or an equivalent. This condition is especially true in colder climates. The wire should have a diffusible hydrogen specification of no more than 5 ml/100g of weld deposit.
Preparation for Welding
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Protect yourself and others; read and understand this warning. Fumes and gases can be dangerous to your health. Ultraviolet rays from the weld arc can injure eyes and burn skin. Electric shock can kill. Read and understand the manufacturer's instruction and your employer's safety practices. Keep your head out of the fumes. Use ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing zone and the general area. Wear correct eye, ear and body protection. Do not touch live electric parts. Refer to the American National Standard Z49.1, "Safety in Welding and Cutting" published by the American Welding Society, 2501 N.W. 7th Street, Miami, Florida 33125: OSHA Safety and Health Standards, 29 CFR 1910, available from U.S. Dept. of Labor, Washington D.C. 20210. |
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Read the instructions from the supplier and understand the instructions from the supplier. Provide fresh air circulation to the welding helmet in order to avoid any illnesses that can be caused by long-term exposure to the welding fumes. The fresh air circulation will also remove any exhaled carbon dioxide that may be trapped by the welding helmet. Use proper eye protection, ear protection, and body protection while preparing the surfaces and while you are welding on the surfaces. Use a welding helmet with a filter plate that is at least Shade-11. Auto-darkening helmets eliminate the neck-strain of "helmet flipping" while greatly increasing the accuracy of electrode placement
Before you cut on the bucket or weld on the bucket, the temperature of the bucket should be at least 24°-38° C (75°-100° F). Do not weld on surfaces that are exposed to fans. Do not weld on surfaces of the bucket that are exposed to natural cool winds. Do not lay the bucket or base edge assembly directly on the ground. An infrared thermometer has been found to be a quick, reliable, and easy to use tool for the following conditions.
- Preheating is required
- Minimum inter-pass temperatures maintained
- Maximum allowable temperatures dictated
Because emissivity may vary due to surface conditions, verify the accuracy of the thermometer. Verify the accuracy by comparing the thermometer to the temperature indicated by a temperature stick.
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| Illustration 1 | g02146375 |
An oxyacetylene torch or an air carbon arc torch may be used to cut away the base edge.
Note: An air carbon arc torch can leave an excessive amount of carbon on the cut surface that would require additional labor to remove. Residual carbon left on the cut surfaces will produce excessive slag in the weld resulting in the development of cracks.
Preparation Of The Bucket
- Refer to Illustration 2. Use a plumb and level protractor in order to establish the relationship of the existing base edge with a place on the bucket bowl. Using the plumb and level protractor allows the replacement base edge to be positioned and welded into the bucket at the proper level of flatness. Electronic versions are also available with well-defined increments.
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| Illustration 2 | g02143217 |
- Attach sets of 40 mm (1.57 inch) thick lifting eyes to the bucket as desired at the locations that are shown in Illustration 3 and Illustration 4. Apply 15 mm (0.59 inch) fillet welds in order to weld the lifting eyes to the bucket. The lifting eyes will allow the bucket to be rolled over in order to gain access to the welds on the underside.
Note: Fabricate the lifting from High Grade Structural Steel 290 MPa (42000 psi) minimum yield strength.
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| Illustration 3 | g02143218 |
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| Illustration 4 | g02143219 |
(A) 83 mm (3.27 inch) Diameter (B) 76 mm (3.00 inch) Radius (C) 63.5 mm (2.50 inch) (D) 8 mm (0.31 inch) Radius | |
- If the front bowl liner will not be replaced, tie bars must be installed. Install tie bars to support the bucket bowl and the sides when the base edge is removed. Refer to Illustration 5.
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| Illustration 5 | g02143220 |
Tie bar supports for a bucket that will not get the liner replaced | |
- If the front liner is to be replaced, burn out the welds holding the worn liner in place. Lay in the new liner plate and apply weld along the rear edge. Force the front edge of the new plate down against the bowl surface so that front edge is flush and level with the bowl surface.
- Apply a single pass weld along the front edge.
- Finish applying welds along the sides of the liner plate.
- Install tie bars inside the bowl as pictured in Illustration 5.
Removing The Base Edge
- Support the bucket so that the bucket will not roll when the existing base edge is removed.
- Locate and mark the rear most portion of the base edge.
- Refer to Illustration 6. Block under the base edge at points (J) .
If special stands are fabricated, the stands can be reused when installing the new base edge assembly. Refer to Illustration 11.
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| Illustration 6 | g02143374 |
(G) Base edge weld (H) Side bar welds | |
- Refer to Illustration 6 and Illustration 7. Use a track burner torch in order to cut through the base edge/base edge weld (G). Leave as much of the original base edge weld intact as possible.
Note: If a hand torch is used to cut through the base edge weld, use a guide plate in order to achieve a straight cut. The straightest cut will provide the best fit with the new base edge and require fewer welding passes during installation of the new base edge.
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| Illustration 7 | g02143375 |
(G) Base edge weld (F) Existing base edge assembly | |
- Refer to Illustration 6. Burn away both sidebar welds (H) at the top of the adapter straps.
- Remove the worn base edge.
- Refer to Illustration 8 and Table 1. Cut and disc grind bevels into the top and bottom bowl surfaces.
Show/hide table
Table 1 Bevel Angles For Grinding The Bowl Surfaces Sales Model Top Bevel (X) Bottom Bevel (Y) 988 25° Angle 30° Angle 990 25° Angle 30° Angle 992 25° Angle 30° Angle 993 25° Angle 30° Angle 994 35° Angle 30° Angle
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| Illustration 8 | g02143377 |
(X) Top bevel angle (Y) Bottom bevel angle | |
- Refer to Illustration 9 and Illustration 10. Grind 45 degree bevels to the bottom of the sidebars.
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| Illustration 9 | g02143378 |
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| Illustration 10 | g02143379 |
Cross-section of the bottom of the sidebar (K) 45 degree bevel angle (L) 2 mm (0.08 inch) minimum | |
- Remove all slag and burrs from the surface to be welded.
Installing The New Base Edge
- Remove all paint, rust, and moisture from the butter beaded surfaces. These butter beaded surfaces are located on the back of the new base edge assembly and the top of the corner adapters.
- Place the base edge in position on blocks or stands as pictured in Illustration 11.
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| Illustration 11 | g02143221 |
- Move the bucket into place against the base edge. Refer to Illustration 12.
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| Illustration 12 | g02143372 |
- Adjust the base edge so that the ends protrude equally from either side of the bucket by lining up marked centerlines (M) of the bowl and base edge as shown in Illustration 13.
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| Illustration 13 | g02144369 |
- Verify that the base edge is level with the bearing bores. Place a level on a straight bar laying across the bucket bores as shown in Illustration 14. Verify that the top of the base edge agrees. Adjust the blocks or stands under the base edge if necessary.
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| Illustration 14 | g02143381 |
- Check the fit between the inside bowl surface and top of the base edge as shown in Illustration 15. If parts of the bowl surface are lower than the base edge, weld a series of thick dogs (N) to the bowl. Drive wedges under the thick dogs to bring the low points flush. Refer to Illustration 16. Relocate any bowl brackets shown in Illustration 5 that might impede straightening. Apply 76 to 102 mm (3 to 4 inch) stringer welds between the bowl and base edge at the locations that the adjustments were made.
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| Illustration 15 | g02186994 |
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| Illustration 16 | g02144371 |
(N) Thick dogs temporarily welded onto the bowl | |
- If an area of the base edge top surface is below the bowl surface, apply pressure to the bottom of the base edge with a movable jack in order to make it flush with the bowl surface. Refer to Illustration 17. Apply stringer welds as described in Step 6
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| Illustration 17 | g02143376 |
- If there are large gaps between the new base edge corner adapters and bottom of the sidebars, spacer plates should be cut from Hardox 400 material that is the same thickness as the sidebars. Chamfer the bottom of the spacer plates similar to the sidebars.
- Before full length welds are applied at the rear of the base edge, verify that the base edge is level with the bucket as shown in Illustration 2 and Illustration 14. The sidebars and corner adapters should then be attached with stringer welds to keep the base edge in position. Preheat the bottom of the sidebars to 149°-232° C (300°-450° F) before welding. The butter beaded surfaces of the adapters and rear of the base edge behind the adapters do not require preheating before welding, but heating those areas to 93° C (200° F) will insure that no moisture is present. Apply stringer welds between the bottom of the sidebars and corner adapters as shown in Illustration 18.
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| Illustration 18 | g02187137 |
- Apply a full length stringer weld between the bowl and base edge to fill the gap as shown in Illustration 19.
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| Illustration 19 | g02187314 |
- Refer to Illustration 20. If hand welding, start at the center of the base edge and weld to the sides of the bucket, Apply at least three weld passes (P). Always stagger each weld start at a slightly different location. Interpass temperatures should not exceed 260° C (500° F). If using a track welder, start close to one side of the bucket and weld across to the other side. Fill in the ends by hand where the track burner could not reach. Stagger each weld pass start and stop. As always, remove the slag created during each weld pass.
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| Illustration 20 | g02144372 |
- Rotate the bucket in order to expose the underside of the bucket. Back gouge the underside of the top weld (P) at point (R) in order to provide unobstructed access to the top weld. Refer to Illustration 20 and Illustration 21.
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| Illustration 21 | g02144373 |
- Apply weld passes until the bottom groove (S) is completely filled. Stagger the starting points of the welds and remove the slag after each weld pass.
- Refer to Illustration 22. Rotate bucket upright and complete filling in the top base edge bevel groove (P) with weld.
Note: During multiple weld passes, the heat generated in the base edge may cause it to become uneven with the bowl. Periodically check the base edge and if warping starts, stop welding, rotate the bucket over and apply weld to the other side.
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| Illustration 22 | g02144374 |
- There is a possibility that the last welds being applied may run over onto the top or bottom of the base edge beyond the butter beading. If this occurs, the base edge must be preheated to a temperature of 149°-232° C (300°-450° F) before welding, regardless of the welding process being utilized. The welding should utilize the back tempering technique where the last pass of the weld does not touch the adjacent material and acts to stress relieve the previous weld pass.
- Disc grind the last pass weld, blending the weld smoothly into the base edge surface.
- Preheat the bottom of the sidebars to 149°-232° C (300°-450° F). Apply alternating bevel welds on each side of the sidebars until bevel groove (T) is filled. Refer to Illustration 23. Follow up with fillet welds that are 2 mm (0.08 inch) taller than the bevel welds. If space allows, make the width of the fillet weld 1.25 times greater than its height. Run continuous weld passes around the front of the sidebar. Do not have any starts/stops at the front of the sidebars between points (W) and (Z). Refer to Illustration 24 and Illustration 25.
Refer to Illustration 26. Always remove the slag created from all weld passes with an air peening tool.
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| Illustration 23 | g02144375 |
(T) Height of bevel groove weld (U) Height of fillet weld (U=T+2 mm (0.08 inch) (V) Base leg of fillet weld (V=1.25*U) | |
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| Illustration 24 | g02144378 |
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| Illustration 25 | g02144376 |
View A-A | |
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| Illustration 26 | g02144370 |
- Blend the sidebar welds at the front edge smoothly into the top of the adapter straps in order to eliminate stress concentrating ridges, ripples, or undercutting. Refer to Illustration 27. Round the corners and blend back along the sides of the sidebars 25-50 mm (1.0-2.0 inch). There should also be no grinding notches
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| Illustration 27 | g02144377 |
- When possible, use thermal insulating blanket material in order to allow the welds to slow cool. Slow cooling will reduce stresses and hydrogen embrittlement while maintaining toughness.
- Wait at least 24 hours before removing the support braces inside the bowl.