This paper describes scuffing load testing with Aluminium gears and the main objective of this work was to assess gear scuffing failure protection promoted by new lubricant formulations and comparing them with standard lubricants.

1. Design and Development of a Scuffing Load Capacity Tester for Comparison of
a Novel Plant Based Lubricant with Standard Lubricants
K. R. A. Sahthana, K. Thinesha, T. K. K. S. Pathmasiria, G. I. P. Perera a
a Department of Mechanical and Manufacturing Engineering, Faculty of Engineering,
University of Ruhuna, Hapugala, Galle, Sri Lanka.
Abstract
This paper describes scuffing load testing with Aluminium gears and the main objective of this work
was to assess gear scuffing failure protection promoted by new lubricant formulations and comparing
them with standard lubricants. Gear life is reduced due to the poor scuffing load capacity of gear oil
and it caused to reduce the efficiency of power transmission. In order to test the scuffing load carrying
capacity of Aluminium gear, back to back test rig tester was designed with use of Solidworks and
fabricated. Aluminium was chosen as the test gear material since it has a lighter weight and natural
anti-corrosive material. The main parts of the scuffing load tester include, oil sump, shafts, motor, load
application unit, test gears, temperature measurement unit, etc. The testing lubricant is poured into
the oil sump and the load is applied to the testing gear and allowed to run 20 minutes. The steps
continue with load increments until the scuffing appearance observed visually.
The developed tester was used to test the scuffing load capacity of a newly developed palm oil based
lubricant which has a viscosity of 69.3 Cst at 400
C. For comparison SAE30 engine oil also tested with
the same developed machine. Apart from this weight loss of the testing gear and temperature variation
of lubricants also measured. According to the test results, scuffing observed in Aluminium gear at 5th
and 7th
load stage for developed palm oil and SAE30 engine oil respectively. Where 5th
and 7th
stage
represent the applied torques 17.5Nm and 24.5Nm respectively. Compared to the SAE30 engine oil,
developed palm oil has lower scuffing load capacity. This variation of scuffing load capacity was caused
high depreciation of the gear tooth and increased lubricant temperature in developed palm oil
compared to SAE30 oil. However, as future works the scuffing load capacity of industrial oils (such as
H68) are to be measured and compared. The developed tester is most suitable for comparing the
different lubricant behaviors.
Key Words: Scuffing, Scuffing Load, Aluminium, Gear Lubricant
INTRODUCTION
Polishing surface can be observed before applying load between gears and scratches appeared as small
line in sliding direction of gears with increment of load. Fine marks were increased like deep grooves
in same direction with applied load, this phenomenon is called scoring. When load increased
continuously, the marks were covered all of the flank width which is ignition of scuffing[1]. The load in
which the scuffing initiation happens is known as scuffing load and it varies for each lubricant.
Lubricant create the thick film between moving parts and that are avoid metal to metal contact in
order to reduce friction, wear and heat[2][3]. Scuffing failure is strongly depending on the lubricant
properties[4][5]. The scuffing can be occurred in gear tooth flanks due to the unexpected
overloads[1][3][6]. The determination of scuffing load capacity of new lubricant gear oil is most
important to eliminate the energy losses such as vibration, high noise and heat. These are affected to
effective power transmission between rotating gears[4]. Therefore, scuffing load capacity test should
be done for new developed gear oil before used.
This study was focus on to find the scuffing load capacity of SAE 30 oil and newly developed palm oil
for Aluminium test gears. Scuffing load capacity, oil sump temperature variation and weight loss of
testing gear were determined for both lubricant oils from the testing. Gear face appearance was

2. inspected after each load stage by using photographs. Scuffing load was evaluated when observe
scuffing appearance in gear tooth face. from the test results SAE 30 and newly developed oil were
compared. The main objective of this work was to assess gear scuffing failure protection promoted by
new lubricant formulations and comparing them with standard lubricants.
METHODS
The experiments were conducted under various conditions as given in Table 1 by using Aluminium gear
back to back test rig. As an initial step pour the testing lubricant into the chamber. Applied the weights
in the hanger and switched on the tester. The tester was operated at motor rotational speed of 530
rpm and circumferential speed of 3 m/s. Defined load was applied to a pair of gears which is increased
step by step after a time period of 20minutes, under conditions of dip lubrication without cooling and
starting oil temperature of 30o
C each load stage. At the end of each load stage, the gear wheels’ tooth
faces are inspected visually. If scuffing appeared in the tooth faces, the test was terminated and the
last load stage was documented as scuffing load step. And measure the oil temperature for 5 minutes’
time interval during the test. Rotational speed of the shaft was measured by using tachometer. Mass
comparator was used for the determination of the weight loss of test gears after testing[4].
Table 1: Testing Conditions
Gear scuffing test FZG (A/3/30) *
Test gear type FZG A-type
Test material Aluminium
Speed of the motor 530 rpm
Motor rotation direction Normal
Circumferential speed 3 m/s
Maximum loading torque 50 Nm
Run duration 20 min (each load)
Loading type Step wise
Initial lubrication oil temperature 300
C
Lubrication type Dip lubrication
Oil capacity 1 L
Temperature stabilization during the run by
cooling
No
*FZG(A/3/30) stands for gear type A, peripheral speed 3 m/s and oil sump temperature 300
C.
RESULTS AND DISCUSSION
Gear Scuffing Test Results
scuffing load capacity of newly developed lube oil and SAE30 were measured by using scuffing load
test FZG (A/3/30) for Aluminium gears. Scuffing load obtained for the both oil that is shown in the
Table 2.
Table 2: Failure Load Stage for Both Oils

3. Failure Load Stage Load (N)
Torque (Nm)
SAE 30 Developed Palm Oil
1 10 3.5 3.5
2 20 7.0 7.0
3 30 10.5 10.5
4 40 14.0 14.0
5 50 17.5 17.5
6 60 21.0 _
7 70 24.5 _
From the Table 2, when SAE 30 oil was used, scuffing occurred at 24.5 Nm torque (at the 7th
stage) And
the same test undergone for developed palm oil, scuffing observed at the load stage of 5 (17.5 Nm
torque). Therefore, the scuffing occurs quickly in the newly developed palm oil. And the scuffing load
capacity is lower than the SAE 30 engine oil.
Table 3 shows the images of the wear of test gears for two gear oils at different load stages. Scratches
appear on the tooth surface for both oils in stage 2. Scratches can be identified as scratch lines (long
or short) in sliding directions of tooth faces. For SAE 30 oil, scratches improved by increasing the
applied load up to the 5th
load stage. And from 5th
stage tooth face started to scoring. Scoring marks
run in the same direction as scratches. From the photographs of the gear tooth shown in Table 3,
scoring started to happen at the 4th
stage for the new lubricant.
Next level of the wear is scuffing. Scuffing marks can be identified as single fine marks and strips. When
scuffing occurs, the area appears as dull and higher roughness than the original crisscross-grinding
pattern. Scuffing appeared at 7th
stage and 5th
stage for SAE 30 gear oil and developed palm oil
respectively. Higher scuffing appearance is observed in newly developed palm oil is higher than the
SAE 30 oil the scuffing load capacity of developed oil is lower than the SAE 30 oil.
Table 3: Symbolic modes of wears of the test gears
Load
stage
SAE 30 oil Developed palm oil
2
3

4. 4
5
7
Weight Loss of the Gear
Considering the weight loss of test gear is 3.69 g, which is higher than the newly developed lubricated
oil’s weight loss after testing, 1.9 g. Weight loss increased is meant the scuffing is higher. Therefore,
by the factor of weight loss also it can be concluded as developed palm oil’s scuffing load capacity is
lower than the SAE 30 oil.
Effect of Temperature
Depreciation of the gear tooth increased due to load increase, and this caused temperature to increase
directly proportional to applied torque. Gears could not be given the heat off and after a thermal
fatigue, thermal damages were observed on the material[8]. The oil temperature was varied with the
applied torque. The variation of the oil with the torques are graphically shown in Figure 1 for both oils.
Figure 1: Maximum Temperature vs Applied Torque
In the Figure 1, the temperature when the scuffing damage occurred was marked at the end of each
graph. Considering the graph, the maximum temperature at where the scuffing load occurred was
35.250
C and 33.250
C for developed palm oil and SAE 30 engine oil respectively. High temperature rise
was observed for developed palm oil due to lower oil viscosity compared with SAE 30. Thus a lower oil
film thickness is present in the tooth contact area. Therefore, it could be expected a risk of metal to
metal contact between gears. Thus, the scuffing risk is higher for higher temperature oils.

5. CONCLUSION
This research was based on designing a gear oil tester for measuring the scuffing load capacity for
Aluminium test gears. SAE 30 engine oil and developed palm oil were tested using the implemented
gear oil tester in order to measure the scuffing load of oils. Newly developed oil’s quality was compared
with the SAE 30 oil by measuring the scuffing load. From the visual inspection scuffing was identified
at the 5th
stage and 7th
stage for developed oil and SAE 30 engine oil respectively. By measuring the
weight losses of test gears developed oil has a larger value than SAE 30 engine oil. According to the
temperature variation of the lubricant, developed oil temperature was risen more than SAE 30 lube.
Therefore, scuffing load capacity of the developed oil is lower than the standard SAE 30 engine oil.
However, as future works the scuffing load capacity of industrial oils (such as H68) are to be measured
and compared. The developed tester is most suitable for comparing the different lubricant behaviors.
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