Usage:
Introduction
This instruction gives the procedure for welding replacement sprocket rims on sprocket assemblies. Weld-on replacement rims for sprockets used on Caterpillar machines reduce costs through sprocket reconditioning. This advantage can be lost completely through use of incorrect welding procedures. Some sprockets can be rebuilt only by spoke welding. Other sprockets have a wide, uniform flange area between the ends of the spokes and the rim which permits them to be cut and welded "all the way around" in this area. Continuous welding is most practical when automatic or semi-automatic welding equipment is used.
NOTE: For some machines, adapters are available for conversion to the use of sprocket segments. If this type of reconditioning is desired, see Special Instruction SMHS7751, entitled Installation of Sprocket Segment Adapter Groups or Salvaging Segmented Sprocket Hubs.
Reference: Parts Book, Service Manual
Cutting And Beveling Of Sprocket
1. Remove the sprocket as shown in the Service Manual and place it on a welding fixture similar to the one shown, with the inside of the sprocket down. Centering cone (1) on center shaft (2), along with adjustable hub support (3), will permit quick centering for all size sprockets.
NOTE: The time needed to put a sprocket into position for welding can be greatly decreased if the fixture has a rollover feature so that the sprocket does not need to be removed at any time during the welding operation. This is especially adaptable to spoke welding.
An accumulation of any flammable substance may ignite and cause personal injury. Wipe away any spilled oil or other flammable substance before cutting with an air carbon arc torch or similar tool. |
2. Use an air carbon arc torch or similar tool to cut the rim off of the worn sprocket to dimension B from the
3. Chamfer the hub or spoke ends with an oxy/fuel torch with beveling tip to the correct joint shape as shown in the joint shapes illustrations. The joint shape is referenced in the
4. Use a grinder to assure the surfaces are clean and all slag has been removed.
Reference Dimension Locations
Joint Shapes
Procedure For Spoke Welding
NOTICE |
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Excess heat input in the spokes and the rim and/or uneven cooling of the hub and rim can cause stress concentrations that will usually cause cracks in the rim and the weld. Heat input can be controlled effectively by closely following the procedures in this instruction. |
NOTE: The repair surfaces must be clean. Remove all foreign material before welding.
1. Put the replacement rim and hub on the fixture in welding position according to dimensions B, C, D and E from the
2. Put numbers on the spokes clockwise in a sequence of 1, 9, 6, 3, 8, 5, 2, 7 and 4.
NOTE: Before welding, be sure the weld zone on the rim and hub are preheated to 149°C (300°F). The welding fixture should be located in an area free from drafts.
NOTE: Use dry, low hydrogen electrodes according to AWS Specification E7018 (available from Caterpillar [1U5232 - 3.18 mm (.125"), 1U5234 - 4.76 mm (.188")]). Do not use any electrodes that have been open to the atmosphere for more than four hours.
3. Using 3.18 mm (.125") electrodes and a setting of 120-145 Amperes, DC reverse polarity, weld one pass on spokes numbered 1, 2 and 3.
4. Clean the welds and weld one pass on the same spokes with 4.76 mm (.188") electrodes at 230-250 Amperes.
5. Using 3.18 mm (.125") electrodes and 120-145 amperes, weld one pass on spokes 4, 5, 6, 7, 8 and 9 in that order.
6. Turn the sprocket over and clean the weld joints. If the gap is too small to clean, scarf out with air carbon arc equipment.
NOTE: For minimum heat concentrations, do not weave the welds or completely fill one spoke at a time.
7. Weld spokes 1 through 9 in numerical order using 3.18 mm (.125") electrodes at 120-145 Amperes for one pass.
8. Clean and weld spokes 1 through 9 in numerical order using 4.76 mm (.188") electrodes at 230-250 Amperes for one pass.
9. Continue with 4.76 mm (.188") electrodes at 230-250 Amperes, welding one pass at a time on each spoke in numerical order, until the weld is flush.
10. Turn the sprocket over and weld one pass with 4.76 mm (.188") electrodes at 230-250 Amperes on spokes 4 through 9 in numerical order.
11. Weld one pass on each spoke in numerical order until each weld is flush.
12. Turn the sprocket on edge and weld the ends of each joint. Turn the sprocket each time so each joint being welded is in a flat position. This connects the ends of the weld beads and makes a smoother surface from the spokes to the rim.
13. During the cooling period, keep the sprocket off the floor in an area free from drafts.
14. Inspect the sprocket for dimensional accuracy after it has cooled. Although cracks are not probable, any found can be repaired by veeing out and welding with a 4.76 mm (.188") electrode.
Procedure For Continuous Welding
NOTICE |
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Excess heat input in the spokes and the rim and/or uneven cooling of the hub and rim can cause stress concentrations that will usually cause cracks in the rim and the weld. Heat input can be controlled effectively by closely following the procedures in this instruction. |
NOTE: The repair surfaces must be clean. Remove all foreign material before welding.
Automatic or semi-automatic welding equipment using the submerged arc or flux core welding wire method can be used for sprocket rim welding if a continuous weld is made. Use flux and mild steel wire (available from Caterpillar [1U5244 - 1.6 mm (.062") for flux core welding, 1U5372 - 2.0 mm (.078") for submerged arc welding and 1U5376 Flux]).
1. Put the replacement rim and hub on the fixture in welding position according to dimensions B, C, D and E from the
NOTE: Before welding, slightly preheat the weld zone on the hub and the rim to 65°C (150°F) to reduce the residual stresses and to remove contaminants such as moisture.
2. Use reverse polarity and a setting of 30 Volts and 400 Amperes to make a single continuous (360°) weld pass at a speed of 1300-1500 mm (50-60") per minute.
3. Turn the sprocket over and clean the weld joint.
4. Make a continuous weld at 150 mm (6") per minute with a setting of 33 Volts and 500 Amperes until the weld is flush.
5. Turn the sprocket over and weld until flush on this side at 150 mm (6") per minute with a setting of 33 Volts and 500 Amperes.
6. During the cooling period, keep the sprocket off the floor in an area free from drafts.
7. Inspect the sprocket for dimensional accuracy after it has cooled. Although cracks are not probable, any found can be repaired by veeing out and welding until flush.