Teeth Failures in Ratcheting Box Wrench

Metallurgical failure analysis of a failed ratcheting box wrench was requested of J.E.I. Metallurgical, Inc., Dallas, Texas. Visual examination of the wrench revealed that a large chip had been ejected from the ratchet reverse lever. An overall view with an arrow directed toward the chipped ratched reverse lever is shown in Photograph 1 (A003).

Photograph 1  Overall view of subject ratcheting box wrench. Chipped ratchet reverse lever is denoted with an arrow.

A close-up view of the chipped ratchet reverse laver is shown in Photgraph 2 (A021). A white arrow in Photograph 2 denotes the chipped end of the ratchet reverse lever.

 
Photograph 2  Close-up view of chipped ratchet reverse lever arrow denotes chipped area on ratchet.

A microscopic view of the chipped ratchet lever is shown in Photograph 3 (B010).

 
Photograph 3  Microscopic view of chipped ratchet reverse lever. Taken with Keyence Digital Microscope (KDM) (Lens x 50)

A slightly different view of the failed end of the ratchet reverse lever showing cracking of the ratchet lever near the fractured end is shown in Photograph 4 (B017). Arrows denote transverse cracking near the fracture.

 
Photograph 4  Perspective view of the failed ratchet reverse lever. Arrows denote cracking in ratchet tooth adjacent to the ratchet lever fracture. KDM (Lens x 50)

A close-up view of another tooth in the subject wrench is shown in Photograph 5 (B029). The dark transverse area is likely an area of cracking. White arrows denote the cracking.

 
Photograph 5  Close-up view of the bar stool leg showing lack of weld penetration.

A close-up view of one end of the subject ratcheting box wrench is shown in Photograph 6 (B049). The crests (tips) of these three teeth are sheared and flattened. The sheared and flattened tooth crests are denoted with arrows.

 
Photograph 6  Close-up view of end of subject ratcheting box wrench. Sheared and flattened tips of three ratchet teeth are denoted with arrows. KDM (Lens x 5)

A close-up view of the sheared teeth shown in Photograph 6, is presented in a more highly magnified view in Photograph 7 (B039).

 
Photograph 7  Close-up view of sheared teeth shown in Photograph 6. KDM (Lens x 20)

A close-up view of the end of the subject ratcheting box wrench with another sheared ratchet ring tooth tip is shown in Photograph 8 (B048). The arrow in Photograph 8 denotes the location of the sheared tooth.

 
Photograph 8  Close-up view of end of subject ratcheting box wrench. Arrow denotes sheared ratchet ring tooth tip. KDM (Lens x 5)

A higher magnified view of the sheared ratchet ring tooth tip displayed in Photograph 8 is shown in greater detail in Photograph 9 (B042).

 
Photograph 9  More highly magnified view of sheared ratchet ring tooth shown in Photograph 8. KDM (Lens x 20)

A close-up view of an additional chipped ratchet ring tooth is shown in Photograph 10 (B035).

 
Photograph 10  Close-up view of additional chipped tooth on ratchet ring from the subject wrench. KDM (Lens x 20)

A close-up view of the failed ratchet ring tooth displayed in Photograph 10 is shown in Photograph 11 (B037).

 
Photograph 11  Close-up view of sheared teeth shown in Photograph 6. KDM (Lens x 20)

This examination is a visual (macroscopic) and microscopic examination of the subject ratcheting box wrench only. No engineering drawings or manufacturing specifications, etc. were available. The ratcheting reverse lever and several ratchet ring teeth, etc. were observed to contain chipped, fractured, and/or sheared teeth, as well as cracked contact surfaces.

Visual examination suggests that the subject wrench ratchet lever and ratchet ring were fabricated by compaction of a metal powder into the desired shape. Typically, this "green" powder metallurgical compact is then sintered, i.e., baked (heat treated) at a high temperature to bond the individual metal powder particles together, thereby giving the powder compact the strength necessary to successfully transfer the stress applied when the wrench is used.

In the matter in question, the cracking in the ratchet lever, as well as the shearing/failure of the ratcheting box wrench teeth, strongly support the conclusion that the components in the subject ratcheting box wrench were improperly fabricated, and thus did not possess sufficient strength to survive normal operational stress.

Based on visual and microscopic examination of the subject failed ratcheting box wrench, several opinions can be stated:

1) The tip of the subject ratcheting box wrench ratchet reverse lever was chipped.

2) The ratchet reverse lever also visually contained cracks and cracking adjacent to and also somewhat distant locations from the chipped end of the ratchet reverse lever.

3) The ratchet reverse lever was probably fabricated by a powder metallurgical process.

4) The ratchet reverse lever was probably inadequately sintered and therefore did not attain proper and appropriate strength.

5) Several other teeth in the ratcheting ring exhibited chipped, sheared, and failed ratchet teeth.

6) The subject ratcheting box wrench was improperly and defectively manufactured.

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