Temporary Weld Repair for Crack in Lower Jaw of Shear{6349} Caterpillar

Work Tool:

S340 (S/N: CKY1-UP)

VHS50 (S/N: BBS1-UP)

Introduction

The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.

ReferenceDisassembly and Assembly Manual, RENR4438

ReferenceOperation and Maintenance Manual, SEBU7420

Problem

Illustration 1	g01593493
Location of crack

Illustration 2	g01593338
View from inside of the jaw

Illustration 3	g01593342
View from inside of the jaw

Illustration 4	g01593459
View from outside of the jaw

A material fatigue fracture or a crack may develop. It is located at the rear bolt hole across the top of the lower jaw and into the cutting edge pocket.

Solution

Perform a temporary weld repair of the jaw in order to return the unit to service while you wait for the replacement housing assembly.

Illustration 5	g01596273
(1) Cutting edge pocket

Note: Do not attempt to perform this repair if the crack has progressed past the cutting edge pocket (1) on the inside of the jaw. The lower housing must be replaced.

Illustration 6	g01733636

Note: Order a replacement 331-2820 Lower Housing Assembly (2). In addition to ordering the housing, one 7X-2488 Bolt (3) and one 7X-2532 Bolt (4) are required.

Preparing the Metal for Welding

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Personal injury or death can result from fumes, gases and ultraviolet rays from the weld arc. Welding can cause fumes, burn skin and produce ultraviolet rays. Keep your head out of the fumes. Use ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing area. Wear eye, ear and body protection before working. 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 cause death. Read and understand the manufacturer's instructions and your employer's safety practices. Do not touch live electrical parts. See "American National Standard Z49.1, Safety in Welding and Cutting" published by the American Welding Society. American Welding Society 2501 N.W. 7th Street Miami, Florida 33125 See "OSHA Safety and Health Standards, 29 CFR 1910", available from U.S. Department of Labor. U.S. Department of Labor Washington, D.C. 20210

Use LB-26 Electrodes (AWS E7018) or equivalent electrodes. Basic welding wire ESAB OK tubrod 15.00 with a 1.2 mm (0.05 inch) diameter can also be used. The basic welding wire must be the equivalent to AWS A5.20 E71T-5 with positive polarity. The welding wire must be protected with CO2 gas.

For more welding information, consult the Caterpillar Service Welding Guide, SEBD0512.

Preparing the Metal for Welding

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Personal injury can result from flame cutting or welding on painted areas. The effect of gasses from burned paint is a hazard to the person doing the cutting or welding. Do not flame cut or weld on painted areas.

All grease, paint, and foreign objects must be removed before welding. Any of these materials will discharge gas which will cause porosity in the weld deposit. Water and rust will cause hydrogen embrittlement. Hydrogen embrittlement causes cracks in the weld deposit.

Remove foreign objects with a wire brush, a buffer, or a grinder. Shot blasting the appropriate areas will also remove foreign material.

Remove any oil or grease with a Caterpillar approved solvent.

Repair Procedure

1. Remove the cutting edges from the lower jaw of the shear.

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Illustration 7	g01596437

2. Tack weld a support plate (2) across the lower jaw in order to prevent any movement.

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Illustration 8	g01593539
(W1) Fillet weld

3. Carefully remove all traces of the crack by air arc gouging with a torch. Ensure that the full depth of the crack is removed.

4. Grind the areas that were exposed to an air carbon arc torch in Step 3. Remove all traces of carbon. The presence of traces of carbon can adversely affect the weld quality. Create a bevel that is 60 degrees on each side of the jaw. The width at the base of the groove must be sufficient enough for comfortable access of the welding torch. Refer to illustration 8.

5. Preheat the service area to a minimum temperature of 150 °C (302 °F) and a maximum temperature of 175 °C (347 °F). The preheated service area should maintain a distance of 76 mm (3 inch) from each side of the crack. Monitor the temperature by using 192-3750 Temperature Measuring Gp , or use 192-3755 Temperature Measuring Gp . Continue to measure the temperature throughout the repair process, and do not permit the temperature to drop below 125 °C (257 °F) or to exceed 175 °C (347 °F). If necessary, stop the welding process and heat the area again.

6. The weld bead should be straight. The weld bead must not exceed 5 mm (0.2 inch) wide. Remove any slag from the joint. Clean the weld area and needle peen between passes.

7. After needle peening, carefully inspect the pass for any signs of lack of penetration, porosity, or undercutting. If any such signs are found, grind out a part or the entire affected pass until the quality is acceptable before continuing with the repair process.

8. Complete the welding process. The area that has been repaired should be about 3 mm (0.12 inch) higher than the general level of the surrounding area. Remove all traces of the individual weld beads until the repaired area is completely smooth and free of stress risers. Blend all repair welds into the general surface of the structure. All transition points must have a smooth radius. Needle peen the welded area. After the welding process is completed, check the repaired area with dye.

9. Cover the repaired area with thermal blankets in order to counter the effect of any wind, and allow the structure to cool slowly to ambient temperature. The cooling should not take place at a rate more than 27 °C (80 °F) per hour.

Reference Dimensions for Bolt Hole

The following dimensions may be used to locate the bolt hole if additional machining is required for the repair.

Illustration 9	g01594313
View as seen from the inside of the jaw (A) 66.6 mm (2.6220 inch) (B) 50 mm (1.9685 inch)

Illustration 10	g01594373
Section A-A (C) Diameter 45 mm (1.7717 inch) (D) Diameter 22 mm (0.8661 inch) (E) Chamfer 45 degrees (F) 26 mm (1.0236 inch)