"White Layer Flaking" of Transfer Gears in Off-Highway Trucks and Tractors{3159} Caterpillar

Off-Highway Truck/Tractor: All

Introduction

© 2013 Caterpillar All Rights Reserved. This guideline is for the use of Cat Dealers only. Unauthorized use of this document or the proprietary processes therein without permission may be violation of intellectual property law.

This Reuse and Salvage Guideline contains the necessary information in order to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar dealers and customers to benefit from cost reductions. Every effort has been made in order to provide the most current information that is known to Caterpillar. Continuing improvement and advancement of product design might have caused changes to your product which are not included in this publication. This Reuse and Salvage Guideline must be used with the latest technical information that is available from Caterpillar.

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Canceled Part Numbers and Replaced Part Numbers

This document may include canceled part numbers and replaced part numbers. Use NPR on SIS for information about canceled part numbers and replaced part numbers. NPR will provide the current part numbers for replaced parts.

Important Safety Information

Illustration 1	g02139237

Follow all safety warnings. Most accidents that involve product operation, maintenance, or repair are caused by failure to observe safety warnings. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs. Personnel must be properly trained in order to perform maintenance, repair, or operate any machine. Safety precautions and warnings are provided this instruction and on Caterpillar products. These warnings should be observed before performing any procedures. Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The warnings in this publication and on the product are not all inclusive.

The hazards are identified by the "Safety Alert Symbol" which is followed by a "Signal Word" such as "DANGER", "WARNING" or "CAUTION". The "WARNING" Safety Alert Symbol is shown in Illustration 2.

Illustration 2	g00008666

This safety alert symbol means:

Pay Attention!

Become Alert!

Your Safety is Involved.

The message that appears under the safety alert symbol explains the hazard.

Operations that may cause product damage are identified by "NOTICE" labels on the product and in this publication.

Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The safety information in this document and the safety information on the machine are not all inclusive. Determine that the tools, procedures, work methods, and operating techniques are safe. Determine that the operation, lubrication, maintenance, and repair procedures will not damage the machine. Also, determine that the operation, lubrication, maintenance, and repair procedures will not make the machine unsafe.

The information, the specifications, and the illustrations that exist in this guideline are based on information which was available at the time of publication. The specifications, torques, pressures, measurements, adjustments, illustrations, and other items can change at any time. These changes can affect the service that is given to the product. Obtain the complete, most current information before you start any job. Caterpillar dealers can supply the most current information.

Summary

This guideline for reusable parts contains reuse information for transfer gears used in Off-Highway Trucks and Tractors. Included is an explanation of the condition, "white layer flaking" and illustrations of reusable and nonreusable conditions.

Conditions for "White Layer Flaking"

Some Off-Highway Trucks and Tractors use transfer gears with nitride hardened teeth. These gears will have a light gray or steel gray appearance. Nitride hardened parts develop a hardened case 0.13 to 0.30 mm (0.005 to 0.012 inch) thick. A by-product of the nitride hardening process is a brittle skin which is up to 0.025 mm (0.0010 inch) thick. The skin is removed from some gears during a final grind or polish operation.

Transfer gear teeth, however, do not undergo such processing. During normal operation, the teeth can develop a harmless condition in which the thin skin chips off, leaving scars. This is called "white layer flaking" (refer to Illustration 3 and Illustration 4). Any amount of this flaking is acceptable. White layer flaking has a different appearance than either frosting or pitting. White layer flaking has a white appearance and can be felt with the fingernail. Frosting has a gray appearance and in many cases looks and feels like stain. Gears should be reused if only showing white layer flaking and/or frosting. Pitting has a V-shape appearance and can be seen without magnification. Since pitting is indicative of surface damage that will progress, pitted gears are not to be reused. (Refer to Illustration 1).

Illustration 3	g02328355
(1) White layer flaking (2) Frosting

Use again the surfaces of the gear teeth, that have "white layer flaking" and become frosted (Both conditions are acceptable). Any amount of "white layer flaking" or frosting is acceptable as long as pitting is not visible.

Illustration 4	g02328393
Close-up of "white layer flaking"

Use again

Illustration 5	g02328415
(2) Frosting (3) Small pits

Surfaces of the gear teeth have become frosted, which is acceptable. However small pits are also present which makes this gear unusable.

Do not use again.