Usage:
772B (64W) Tractors;
773B (63W),
773D (7ER) Off-Highway Trucks;
775B (7XJ),
775D (6KR) Quarry Trucks
Reference: Service Magazine Article; June 3, 1996; Page 10, "Field Repair For Cracked Upper Strut Mount Plate."
All plates used to assemble the upper front strut to the frame assembly fore-aft beam should be inspected for cracking. Reports indicate that if stress fatigue has occurred cracking will most likely initiate at the 134-1345 Plate (not serviced). Refer to Illustrations 1 through 5.
NOTE: If your machine was successfully repaired with the above reference procedure and has no new cracking the following information is not applicable.
The following repair procedure is applicable for machines with first time cracking or for machines which were repaired with the above reference procedure and cracking is re-occurring. This repair procedure includes three phases based upon the degree of cracking. The applicable repair phase should be selected and used in place of the above referenced article. Refer to information in this article titled "Three Phase Upper Strut Repair Procedure" and Illustrations 1 through 5 for specific repair details.
Adaptable To: Effective with 773D (7ER) Off-Highway Trucks and 775D (6KR) Quarry Trucks. Adaptable to 772B (64W) Tractors; 773B (63W) Off-Highway Trucks and 775B (7XJ) Quarry Trucks.
Welding Operators Qualifications
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.
Weld Procedure
 |
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 you 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.
Weld Process
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
- 420 MPa (60 KSI) Yield Strength
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
- 420 MPa (60 KSI) Yield Strength
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.
Weld Parameters
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 plates and frame assembly 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.
Three Phase Upper Strut Repair Procedure
Before work is started, machine should be on a level surface with front wheels and struts removed. Machine should be supported at steering box and rear wheels chocked. Machine key switch should be OFF and disconnect switch should be ON. Weld ground wire should be located in weld repair area. Cover all components to protect against weld sparks.
Phase 1: Repair Procedure For Cracking On Upper Strut Rear Plate
1. Refer to Illustration 1 through 5.
NOTE: On 772B Tractors, 773B Off-Highway Trucks and 775B Quarry Trucks the 134-1345 is used on rear upper strut mount at both right and left side of machine. On 773D Off-Highway Trucks and 775D Quarry Trucks the 134-1345 Plate is used only on the right side. On 773D Off-Highway Trucks and 775D Quarry Trucks the 126-2449 Plate is used on the left side.
NOTE: When replacing either 126-2449 or 134-1345 Plate (not serviced) it is recommended to use weldable 20 mm (.78 in) thick structural steel with 550 MPa Minimum Yield. For 126-2449 Plate replacement use same repair procedure and the former plate as template.
2. If cracking is found remove the plate using either arc-air or an acetylene torch and grind area smooth.
3. Inspect 8W-7196, 2G-5594 Plate (scab plate) and surrounding area for additional cracks.
4. Install new higher strength steel rear plate. Plate should be lined up with front upper strut mount plates (scab plates) and parallel with strut support casting mounting holes. Use 7018 dry rod to tack weld, then check assembly clearance and tolerances, adjust if necessary. Finish weld the plates using dry 7018 rod. Refer to Illustration 4 for required welds.
Phase 2: Repair Procedure For Cracking On 8W-7196 Or 2G-5594 Plate (Scab Plates).
1. Refer to Illustration 1 through 5.
2. If cracking is found on either 8W-7196 or 2G-5594 Plate (not serviced), arc-air off the plate under the fore-aft beam.
NOTE: When cutting plates from frame assembly avoid any damage to the frame assembly fore-aft beams.
3. Grind area smooth and inspect for cracks that may have propagated from the upper strut mount rear plate into the frame assembly fore-aft beam.
4. If no additional cracking is found locate new scab plates to bottom of frame assembly fore-aft beam; 8W-7196 on left and 2G-5594 on right side of machine. Use dry 7018 rod to tack firmly in place, weld inside the plug holes and around outside of plate. Finish weld the plates using dry 7018 rod.
5. Install new higher strength steel rear plate. Plate should be lined up with front upper strut mount plates (scab plates) and parallel with strut support casting mounting holes. Use 7018 dry rod to tack weld, then check assembly clearance and tolerances, adjust if necessary. Finish weld the plates using dry 7018 rod. Refer to Illustration 4 for required welds.
Phase 3: Repair Procedure For Cracking On The Frame Assembly Fore-Aft Beam
Illustration 1.
Typical side view of 134-1345 Plate (not serviced).
1. Refer to Illustration 1 through 5.
2. Use magnetic-particle inspection (magna-flux) for smaller crack detections. If any cracks are found clearly mark crack and surrounding area.
3. Begin repair by removing any cracks with the grinding or carbon arc gouging method. Through section cracks should be removed with a grinder to prevent blowing through the fore-aft beam. Cracks must be completely removed to sound metal prior to welding.
4. Verify that the crack has been completely removed by magnetic-particle inspection. 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.
5. 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 (0.31 in) fillet weld volume. Slag each pass to avoid the possibility of slag inclusions.
6. Locate new scab plates to bottom of frame assembly fore-aft beam; 8W-7196 on left and 2G-5594 on right side of machine. Use dry 7018 rod to tack firmly in place, weld inside the plug holes and around outside of plate. Finish weld the plates using dry 7018 rod.
7. Install new higher strength steel rear plate. Plate should be lined up with front upper strut mount plates (scab plates) and parallel with strut support casting mounting holes. Use 7018 dry rod to tack weld, then check assembly clearance and tolerances, adjust if necessary. Finish weld the plates using dry 7018 rod.
Illustration 2.
Typical view of 8W-7196 or 2G-5594 Plates (not serviced).
Illustration 3.
Typical view of 134-1345 Plate.
Illustration 4.
Typical view of upper front strut mounting area on frame assembly. All welds indicate the welding of mild steel having a 0.30% maximum carbon content or a 0.46% maximum carbon equivalent value. A low hydrogen process is recommended (non-hardonable). Note B, provides for a process and filler metal with deep penetration capabilities to obtain 2.5 mm penetration on fillet welds and the specified penetration on groove welds.
Illustration 5.
View A-A from above Illustration. Required welds for 8W-7196 and 2G-5594 Plates. All welds indicate the welding of a hardonable steel and low alloy steels with a low hydrogen process (high strength filler metal is not required) according to the following guidelines: carbon content over 0.30%, carbon equivalent over 0.46%, an alloy or boron steel, steel requiring CVN energy of 11 J minimum at 29° C where used for ROPS. Note A, provides for a process and filler metal with deep penetration capabilities to obtain 2.5 mm penetration on fillet welds and the specified penetration on groove welds.