Rebuilding Wheel Tractor-Scraper Hitches, Brackets, and Scraper Kingbolt Housings{7100} Caterpillar

Rebuilding Wheel Tractor-Scraper Hitches, Brackets, and Scraper Kingbolt Housings{7100}

Usage:

621B (45P, 31V, 35V, 36V, 73V);
623B (61E, 46P);
627B (14S, 15S, 32V, 33V),
(34V, 37V, 38V, 56V)

Introduction

This Special Instruction lists the key dimensions for rebuilding wheel tractor-scraper hitches, brackets, and scraper kingbolt housings. Repair is encouraged to reduce replacement cost. Each item should be evaluated to determine the need for repair or replacement. All dimensions listed are dimensions used for manufacturing and assembling a new machine.

Show/hide table

NOTICE

Do not weld on cushion hitch "H" link or steering link assemblies. These items have been heat treated; welding will soften the material and shorten its service life.

Reference: Service Manual and Parts Book

Cleaning Procedure

All foreign material like oil, grease, water, paint, rust, dirt and scale, must be removed before the welding operation. These materials discharge gas when they come in contact with heat. This gas can cause porosity (very small bubbles of gas or air) in the weld deposit. Water or rust can cause a condition known as "hydrogen embrittlement" the result of which is cracks in the weld deposit.

Remove oil and grease with solvent. Remove paint, rust, dirt and scale with a brush or glass beads.

Cracks

No cracks are permissible, external or internal. If external cracks are suspected the part should be thoroughly cleaned and Magnafluxed.

X-Ray or Ultrasonic methods are ideal to check for internal cracks. However, these methods are more involved and require a special shop to perform the checks.

The cracks that are repairable should be cut or ground out approximately 6 mm (0.25") deeper than the original crack whenever possible. Fill the hole with weld.

Bores

A dial bore gauge on a boring bar is recommended for measuring bores, and perpendicular surfaces to the bores.

The vertical and horizontal bores should be in line within 0.13 mm (.005"). However, if the bores are 508 mm (20") or more apart 0.25 mm (.010") would be acceptable.

Approximately 0.76 mm (.030") to 1.0 mm (.040") fore and aft is permissible in the area where the hitch is pinned to the tractor.

As this clearance increases to 1.27 mm (.050") or 1.5 mm (.060") a repair should be scheduled as soon as possible to prevent damage to component parts.

Bores out-of-round should be treated as worn out and should be checked for cracks.

Preheat

If the surrounding temperature is less than 16°C (60°F), the bores and flanges on the hitches, brackets and kingbolt housings should be preheated to 260°C (500°F) prior to welding to prevent cracks. If the welding process is completed in a reasonable time no additional preheating should be required. To ensure a good weld, the material around the weld area should be 230 ± 10°C (450 ± 50°F) during the welding process on the part being repaired.

Heat Treatment

No heat treatment is required on these parts after the welding has been completed.

Voltage, Current, and Polarity

The voltage, current and polarity used has a specific effect on the weld deposit.

The voltage controls the shape and size of the weld bead. The weld bead becomes flatter as the voltage is increased.

The current (or amperage) controls the rate of weld deposit. The higher the amperage, the higher the rate of deposit. A high rate is desired because it decreases the amount of time needed for rebuilding. The use of high amperage to get high deposit rates is limited because of the heat factor. As the amperage goes up, so does the heat input. The type of current can be either direct (DC) or alternating (AC). DC is generally used.

The polarity basically controls the penetration (depth) of the weld. If the electrode is positive (reverse polarity), there is more penetration. Normally, welding is done with direct current and electrode positive (DCEP).