Effect of Rotational Speed On The Performance of Unreinforced and
Effect of Rotational Speed On The Performance of Unreinforced and
Effect of Rotational Speed On The Performance of Unreinforced and
& Design
Materials and Design 28 (2007) 765–772
www.elsevier.com/locate/matdes
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
Abstract
Polymer gears used in power and motion transmission work under different loads and speeds. Mechanical properties of the polymers
are severely influenced by the loading rate compared with the metals. The gear rotational speed decides the loading frequency of the
polymer gear tooth, which influences the temperature generated and thereby the strength of the material. Performance of polymer base
gears at different gear rotational speeds is reported in this paper. Injection molded unreinforced Nylon 6 and 20% short glass fiber rein-
forced Nylon 6 spur gears were tested at various speeds and torque levels in a power absorption type gear test rig. Gear rotational speed
affects the performance of gears made of both the materials at high running speeds and high test torques and not in low speeds and tor-
que levels. On-line measurement of test gear surface temperature and failure analysis was done to understand the failure mechanisms. At
all the investigated gear speeds, glass fiber reinforced Nylon 6 gears shows superior performance over unreinforced Nylon 6 gears due its
superior mechanical strength and resistance to thermal deformation.
Ó 2006 Elsevier Ltd. All rights reserved.
0261-3069/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.matdes.2005.12.002
766 S. Senthilvelan, R. Gnanamoorthy / Materials and Design 28 (2007) 765–772
temperature correction factor in the design is discussed precision wire cut electric discharge machine considering
[15]. Hooke et al. [16] measured the surface temperature the shrinkage. The gear data and location of the injec-
of acetal gears during testing and correlated with gear tion-molding gate in gear are shown in Fig. 1. Detail com-
wear. A methodology was proposed to predict the gear puter aided simulation studies of gear molding were
temperature. conducted for finding out the best gate location and are
Machine elements like gears experience both gear tooth described elsewhere [25]. Molded gears were dried at
fatigue and contact loading during service. Gear tooth fati- 313 K for 30 min to remove the moisture content. Test
gue loading causes hysteresis heating of the tooth. The heat polymer base spur gears were mated against the hobbed
generation in conventional fatigue loading is studied by standard stainless steel spur gear (AISI SS316).
many investigators [17–22]. Rittel [17] investigated the heat
generation during cyclic compressive loading on polycar- 3. Gear test rig and testing procedure
bonate and polymethylmethacrylate specimens. Both the
materials are heated up during cyclic loading and the 3.1. Test rig details
amount of heat generation depends upon the frequency
and amplitude of loading. The failure mode of both the Fig. 2 shows the schematic of the in-house developed
material is influenced by the temperature rise and distribu- gear test rig used for conducting performance tests. In this
tion. An increase in temperature during fatigue testing was test rig, the test gear is driven using a DC motor and can be
observed in glass fiber reinforced polyester resin tensile fati- run at any speed up to 1500 rpm. Test gear mates with an
gue specimens loaded at different frequencies [19]. Temper- identical standard gear, which is connected to the DC gen-
ature, frequency and loading type were found to affect the erator. The required test torque is introduced by loading
fatigue performance of different polymers [20]. Chen et al. the rheostat connected to the generator. Various features
[23] identified pitch line velocity as one of the factors, of developed test rig are discussed elsewhere [26]. Severe
which affect the fatigue strength of Nylon gears. No work wear of the gear tooth is one of the gear failure modes,
has been performed to understand the influence of gear which leads to a gradual increase in sound and vibration
rotational speed on surface temperature of gear and gear of the unit. In the gear test rig, the vibration level of the
performance. bearing block, gear tooth surface temperature and sound
This paper discusses the effect of gear rotational speed level of the system are monitored. When any one of mon-
on the performance of injection molded Nylon 6 and glass itoring sensor indicated an abnormal value, the tests were
fiber reinforced Nylon 6 spur gears. Test gears were run at terminated and the gears were inspected. Speed sensors
different rotational speeds and the performance is dis- and digital counter are suitably placed to monitor the speed
cussed. Failure mechanisms at different rotational speeds and number of cycles run, respectively. Detail methodology
are investigated using optical microscope. followed for test gears condition monitoring is discussed
elsewhere [27].
2. Gear materials and processing
3.2. Gear test procedure
Commercially available Nylon 6 and 20% glass fiber
reinforced Nylon 6 granules were used for injection mold- Gear tests were conducted at different torque levels, 0.8,
ing the test gears used in the current investigations. The 1.5, 2, 2.5 and 3 Nm. The corresponding gear tooth bend-
mechanical and thermal properties of the test materials ing stresses computed using Lewis equation [28] are 8, 15,
are shown in Table 1 [24]. The strength, modulus and ther- 20, 25 and 30 MPa, respectively. Tests were conducted at
mal conductivity of glass fiber reinforced material are supe- four gear rotational speeds, 600, 800, 1000 and 1200 rpm
rior compared to that of unreinforced material. The under unlubricated dry conditions. Rotational speed of
granules were preheated at 353 K for 4 h prior to injection the test gear is gradually increased to the test speed and
molding to remove the moisture content. Test gears were maintained constant throughout the test. Tests were con-
made using an injection molding machine (Macfield) at tinuously run until the gear failure is observed or until 5
the molding pressure of 125 MPa and melt temperature millions of cycles run whichever is earlier. At least three
of 513 K. Gear profile in the molding die was cut using a specimens were tested at each torque level. All the gear
Table 1
Properties of Nylon 6 and 20% glass fiber reinforced Nylon 6 material [24]
Unreinforced Nylon 6 20% Glass fiber reinforced Nylon 6 ASTM Standard
Flexural strength (MPa) 110 193 D790
Flexural modulus (MPa) 2965 6206 D790
Elongation at yield (%) 18.5 6.57 D638
Deflection temperature at 1.82 MPa (°C) 71 243 D648
Thermal conductivity (W/m K) 0.3 0.42 C177
S. Senthilvelan, R. Gnanamoorthy / Materials and Design 28 (2007) 765–772 767
800
300
200
100
0
0 0.5 1 1.5 2 2.5 3 3.5
Applied Torque (Nm)
Fig. 3. Effect of applied torque and gear rotational speed on the tooth
loading rate.
Fig. 4. Gear tooth surface temperature of unreinforced Nylon 6 gears Fig. 6. Variation of the gear tooth surface temperature of unreinforced
tested at different speeds at 8 MPa gear tooth bending stress. Nylon 6 gear tested at 1200 rpm at different stress levels.
S. Senthilvelan, R. Gnanamoorthy / Materials and Design 28 (2007) 765–772 769
Fig. 9. (a–f) Failure morphology of glass fiber reinforced Nylon 6 gears tested.
S. Senthilvelan, R. Gnanamoorthy / Materials and Design 28 (2007) 765–772 771
35 Acknowledgments
600 rpm 800 rpm
30
Tooth bending stress (MPa)
1000 rpm 1200 rpm Authors acknowledge the financial support provided by
25 the Robotics and Manufacturing Division, Department of
20 Science and Technology, India.
15
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