1999/05/03 Caterpillar

784B (5RK) Tractors;
785B (6HK),
789B (7EK),
793B (1HL),
793C (4AR) Off-Highway Trucks

SUPPLEMENT: JULY 5, 1999

Service Magazine SEPD0470, Article 13, Page 20, May 3, 1999; "Weld Procedure For Field Repair Of Certain Large Off-Highway Truck Differential Housings".

Disregard this article and see Service Magazine SEPD0479, Article 13, Page 19 with the same title.

--------------- END SUPPLEMENT ---------------

Description of Change: The following procedure is for fracture repair, installation of two strengthening plates and/or drain plug repair on the differential housing of the 789B Off-Highway Truck.

Fracture Repair And Plate Installation

1. Visually inspect for fractures and use 4C-4736 or 9U-6335 Liquid Penetrant Kit on surfaces where cracks are suspected.

2. Clean the area to be welded of oil, grease, paint and dirt.

3. Protect all machined surfaces from sparks or splatter produced by welding, chipping and/or grinding operations.

4. Attach the welding ground directly to the differential housing.

5. Remove any cracks with the grinding or carbon arc gouging method. Cut past the suspected end of the crack by approximately 2 inches. Through section cracks should be removed with a grinder to prevent blowing through the casting. Cracks must be completely removed to sound metal prior to welding. Verify that the crack has been completely removed. The weld groove perpetration shall include an approximate 90° angle at the root for good penetration and to minimize root defects. The side walls shall be angled at approximately 45° slope. Weld repair the prepared groove by using passes that do not exceed two times the electrode diameter. If the alternate process is selected, the welding pass size should not exceed (.31 in) fillet weld volume. Slag each pass to avoid the possibility of slag inclusions.

6. Fit a heat sink plate to the differential housing flange to prevent distortion.

Illustration 1.
Plates.

Plate Dimensions

7. Fit two strengthening plates to differential housing and tack in place.

8. Preheat area to be welded (by gas torch) to 93°C (200°F) to 204°C (400°F).

Illustration 2.
Differential Housing (Bottom View)

Illustration 3.
Rear View

9. Weld strengthening plates to differential housing as indicated by illustration.

10. Weld the fractures in the housing. Grind all welds smooth.

11. Post heat by gas torch and allow the housing to cool slowly.

12. Remove heat sink plate and back gouge the repair, weld the inside of the housing and grind smooth.

13. Visually inspect repair and use liquid penetrant kit to ensure all of the cracks have been removed.

14. Use 4C-4200 Paint to touch up welded areas.

Repair Of Drain Plug Hole

1. Clean the area to be welded of oil, grease, paint and dirt.

2. Protect all machined surfaces from sparks or splatter produced by welding, chipping and/or grinding operations.

3. Attach the welding ground directly to the differential housing.

4. Cut a 5 inch diameter hole in the drain plug area with carbon air arc and grind clean.

5. Preheat area to be welded (by gas torch) to 93°C (200°F) to 204°C (400°F).

Illustration 4.
Machined plug.

Plug Dimensions

* J. 88.90 mm (3.5 in)

* K. 50.8 mm (2 in)

* L. 69.850 mm (2.75 in)

* M. 127.0 mm (5 in)

* N. 25.4 mm (1 in)

* O. Drill and Tap - 1.5 in - 12 TPI

6. Tack the machined plug in the hole flush with bottom of the differential housing.

7. Fill level using the same weld parameters as in "Fracture Repair and Plate Installation" Step 9 (above).

NOTE: First few passes may have to be performed with stick to get to the bottom of bevel.

8. Post heat by gas torch and allow the housing to cool slowly.

9. Visually inspect repair and use liquid penetrant kit to ensure all cracks have been removed.

10. Grind clean and use 4C-4200 Paint to touch up welded areas. Adaptable To: Effective with 784B (5RK1-Up) Tractors, 785B (6HK1-Up), 789B (7EK1-Up), 793B (1HL1-Up),793C (4AR1-Up) Off-Highway Trucks

Welding Operators Requirements

All repair welding operators must be qualified for fillet and/or groove welding as outlined in the current ANSI.AWS D1.1 or D14.3 qualifications, or Caterpillar Manufacturing Practices MC1000-105. The qualification will be for the SMAW (Shielded Metal Arc Welding) process in the vertical welding positions. The alternate process for this repair is FCAW (Flux Cored Arc Welding). The welding operator must also have used the welding process within the last six months or be re-certified for this process before welding. Documentation must be maintained of the weld operators qualifications.

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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 instructions 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 gasses from your breathing zone and the general area. Wear correct eye, ear and body protection. Do no touch live electrical parts.

Refer to 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.

NOTE: Welding operator personal protection should be provided to assure that total weld fumes in the operators breathing zone does not exceed OSHA limits.

When the base metal temperature is below 0°C (32°F), the base metal shall be preheated to at least 21°C (70°F) and this minimum temperature maintained through the weld repair procedure.

NOTE: Since weld distortion is a possibility, minimizing the heat into the metal is important.

The SMAW process shall be used with E7018 (ANSI/AWS A5.1) welding electrode. The weld deposited by these electrodes will have the following minimum mechanical properties:

500 MPa (72 KSI) Tensile Strength

420 MPa (60 KSI) Yield Strength

13% Elongation

18% Reduction of Area

These are low hydrogen electrodes and must be stored in an electrode oven at 121°C (250°F) when not in use. If the electrodes get damp, scrap or recondition them to the manufacturer's specifications.

Use the direct current positive (DC reverse polarity) setting and remove the slag after every pass. The weld pass size shall not exceed two times the electrode diameter.

As an alternate process the FCAW process may be used with E71T-I (ANSI/A5.20) welding electrode and the manufacturer's specified shielding gas(es). The weld deposited by three electrodes will have the following minimum properties.

500 MPa (72 KSI) Tensile Strength

420 MPa (60 KSI) Yield Strength

13% Elongation

18% Reduction of Area

NOTE: This type of electrode has limitations if it is used to carry larger weld pass volumes in the flat welding position. Due to the fast freezing characteristics of this electrodes slag system, there is a chance of trapping evolving gases in the weld melt. Precaution should be taken by controlling weld pass size.

Welding parameters will vary due to weld position and manufacturer of the welding electrode. For 1.30 mm (.052 in) diameter electrode typical welding parameters should be:

Use the direct current electrode positive (DC reverse polarity) polarity setting and remove the slag after every pass. The weld pass size shall not exceed 8.0 mm (.31 in) fillet volume.

Clean the casting of oil, grease, paint, and dirt in the area to be welded. Attach the welding ground cable directly to the area to be welded. Protect all machined surfaces from sparks or splatter produced by the welding, chipping, and/or grinding operations.

The welds shall be free from cracks, porosity, undercut, and incomplete fusion. All weld quality shall conform to ANSI/AWS D14.3 or 1E99 specifications.