Upload
jyestha
View
238
Download
1
Embed Size (px)
Citation preview
7/31/2019 Mill - Drive Gearbox Input Pinion Shaft Failure
1/6
Problem Statement: Poor life & frequent failure of Sag Mill drive gearbox input pinion
shaft at Mines.
Observations: The above problem was studied in detail and following observations
were made:
It was reported that in last three years, total 3 input pinion shafts of the main mill
drive gearbox have failed and the failed pinion shafts gave ~12 months life (refer
plate -1 & 2).
The speed rating of the gearbox is 1470/232.59 and it was designed for a service
life factor of 1.92.
Department confirmed that each failure was reported to OEM via emails but from
OEM no satisfactory answer for the failures of input pinion shaft was given as a
result every time the failed shaft was replaced with available spare shaft and the
problem reappeared after sometime.
It was observed that all three failures of input pinion shaft took place from the
same location i.e. the position where pinion is mounted on the pinion shaft (refer
plate -2, rough sketch).
Clear beach marks (progressive lines) were observed on the fractured surface of
both failed shafts. The beach marks covers around 90% of the fractured surface
area and is an indication of unidirectional fatigue mode failure (refer plate 3 & 4).
The instantaneous zone area (final fracture area) was found very small ~10% of
the fractured surface area indicates that the designer has taken sufficient service
factor during designing. It also indicates that the failure slowly propagated across
the fatigue zone, and then very rapidly crossed the instantaneous zone (refer
plate-3&4).
It was observed that in all the failed pinion shafts, the surface of the pinion shaft
had peeled off along its circumference i.e. spalling, which is an indication of failure
due to high surface hardness. Moreover, presence of beach marks in the failed
surface (in spalling area) indicate that the failure took place in fatigue mode and
originates from the keyway fillet radius due to severe stress concentration (refer
plate - 3 & 4)
Recommendations:
Above observations suggest that the component failed due to rotating bending
fatigue under low nominal load and severe stress concentration created due to
high surface hardness (improper heat treatment) and sharp fillet radius in the
keyway at the location of failure. This aspect may be checked at OEM end.
Page 1 of 6
7/31/2019 Mill - Drive Gearbox Input Pinion Shaft Failure
2/6
Use of 42CrMo4V IS:5517, Class 4 forging material (volume hardened & tempered)
i.e. En19 could be explored, which will definitely give better fatigue life under
present operating conditions.
Include suitable fillet radius (R1 to R1.6) to avoid stress raiser and better fatigue
life in the drawing.
Page 2 of 6
7/31/2019 Mill - Drive Gearbox Input Pinion Shaft Failure
3/6
Page 3 of 6
SAG Mill Drive Gearbox Input Pinion Shaft Failure (Plate-1)
G. A. drawing of the Mill drive gearbox
Photographs of the failed input pinion shaft (Feb. 2007)
FAILURE LOCATION
INPUT PINION SHAFT
7/31/2019 Mill - Drive Gearbox Input Pinion Shaft Failure
4/6
Page 4 of 6
SAG Mill Drive Gearbox Input Pinion Shaft Failure (Plate-2)
The broken input pinion shaft (May 2008)
Rough sketch of the failed input pinion shaft
FAILURE LOCATION
7/31/2019 Mill - Drive Gearbox Input Pinion Shaft Failure
5/6
Page 5 of 6
SAG Mill Drive Gearbox Input Pinion Shaft Failure (Plate-3)
Side view of one of the failed input pinion shaft
Beach marks is a clear indication of fatiguefailure
SMALL INSTANTANEOUS ZONE AREA IS AN IDICATIONTHAT THE SHAFT FAILED UNDER NOMINAL LOAD
ORIGIN
Book photograph of a fatiguefailure
SPALLING OF THE SURFACE IS AN INDICATION OF HIGH SURFACE HARDNESS
7/31/2019 Mill - Drive Gearbox Input Pinion Shaft Failure
6/6
Page 6 of 6
Beach marks & small instantaneous area is a clear indicationof shaft failure under nominal bending fatigue mode
SAG Mill Drive Gearbox Input Pinion Shaft Failure (Plate-4)
ONCE AGAIN SPALLING OF THE SURFACE (MATEL CHIPS CAME OUT) IS ANINDICATION OF HIGH SURFACE HARDNESS OR IMPROPER HEAT TREATMET
DURING MANUFACTURING.
BEACH MARKS
ORIGIN
STANTANEOUS ZONE
Side view of second failed input pinion shaft