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Shaft
Failure
It was reported
that an emergency stop was initiated at a printing
plant. At the same instant the e-stop action was
taken, a loud pop was heard on the drive side of the
machine, followed immediately by smoke and fire.
Upon
investigation, it was determined that the deck 3
Anilox roll shaft had failed. This failure
reportedly freed the gear drive (approximately 80
lbs) which took out numerous electrical and
hydraulic components as the gear drive fell to the
floor.
An overall view
of the testing debris received is shown in
Photograph A.
Photograph A
The Anilox roll
insert shaft fracture, show in Photograph B, was
cleaned in an ultrasonic bath with alcohol as the
cleaning medium for
SEM examination.
Photograph B
The fracture
mode was clearly identified as that of
metal fatigue.
An SEM map, showing the location of each SEM
examination is shown in Photograph C.
Photograph C
It should be
noted that the fracture image in Photograph C has
been rotated 90 degrees from that shown in
Photograph B. The shaft keyway has been rotated now
to the 3 o'clock position in Photograph C.
Of particular
importance was the fact that the fatigue fracture
initiation sites appeared to be at the shaft
periphery, i.e., around the outside surface. These
multiple fatigue origins correspond to the fillet
where the subject roll insert shaft changes
diameter. The mating fracture surface is shown in
Photograph D.
Photograph D
The fillet in
which the fatigue failure origins are located is
denoted with white arrows in Photograph D.
The hardness of
the previously tested shaft slice was performed.
Hardness test results confirmed the results obtained
by a previous investigator.
The chemistry of
the sample was determined of optical emission
spectroscopy (OES). The carbon and sulfur contents
were determined by LECO analysis. The results
obtained confirm that the steel conforms to AISI
1010.
Discussion
The failure of
the subject Anilox Roll Insert replacement shaft is
clearly one resulting from metal fatigue. The
subject shaft was clearly produced from low strength
(T.S. = 52 Ksi), low carbon steel.
However, the
fracture surface evaluation, visually and SEM, revealed
that the origin was on the smaller shaft OD, i.e., in
the fillet transition from the larger to the smaller
shaft.
No written
documentation of the shaft order was received or
reviewed. Materials received indicate that a
previous shaft failure had occurred and that the
subject shaft was replacement for a shaft that
failed previously. There was no indication in the
materials reviewed that the repair company was given
any engineering drawings and/or material and/or
hardness and/or strength specifications to guide
them in material/strength consideration. The shaft
in question was not immediately installed following
the previous shaft failure. Another shaft was in use
and no mention was made as to the dispensation of
that shaft. Did it fail, exhibit unusual wear, etc.
Therefore, the conditions under which the subject
shaft was installed are unknown.
The subject
failure is unusual in that the shaft fatigue
cracking began at the fillet transition between two
different diameter shafts. This indicates that the
shaft in question was being subjected to bending
stress. When the subject printing press was in
operation, these bending stresses manifest
themselves in rotational bending. That is, the
subject fatigue crack initiated in the fillet
transition at numerous locations around the smaller
shaft. It was reported that the repairing machine
ship fabricated the shaft and thus some other party
would be responsible for the installation and/or
bending stresses induced into the shaft during
installation.
Opinions
Based on the
above study, certain opinions were developed. Those
preliminary opinions were:
1. The failed
Anilox roll shaft failed by metal fatigue.
2. The fatigue
failure of the subject Anilox roll shaft initiated
in the fillet transition between two different shaft
diameters.
3. The subject
failed Anilox roll shaft was made from AISI 1010
steel and/or equivalent.
4. No specific
instructions were given to the fabricating machine
shop with regard to the strength of material
required and/or stress field or stress state that
would be experienced by the subject replacement
Anilox roll shaft.
5. No
engineering drawings were given to the fabricating
machine shop specifying the size or sharpness of the
fillet in the subject Anilox Roller shaft.
6. The subject
failure was the result of rotational bending fatigue
induced by bending stresses introduced during the
installation of the subject replacement Anilox roll
shaft. Installation of the subject Anilox roll shaft
was not provided by the fabricating machine shop.
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Dr.
R. Craig Jerner, Ph.D., PE specializes in accident
investigation and metallurgical failure analysis,
with over 30 years experience as a metallurgical
consultant and accident investigator. He has
testified as a metallurgical expert in over 250
depositions and more than 70 court appearances. If you or someone you know should need the services of Dr. Jerner and J.E.I. Metallurgical, please visit our web site at the buttons below, or e-mail Dr. Jerner --- 