Tooth deflection under cyclic loading
5.2 Modification of Gear Test-rig and its Accessories
Measurement and quantification of wear rate of the gear materials and calculation of wear volume of gear tooth for different operating speed.
The dynamic performance of the gear is tested under variable loads and speeds and the effect of temperature is ascertained. Further, the composite material spur gear was tested to evaluate its friction and wear characteristics in both adhesive and abrasive wear modes. Weight loss due to wear of the composite gear is evaluated through direct measurement under a specific load and running condition. It is observed that the adhesive wear rate significantly reduced when the cement filler loading increases. This is because shear strength and surface energy of the composite material changes while toughness and hardness of the material improve due to strengthening by cement fillers.
5.2 Modification of Gear Test-rig and its Accessories
The purpose of the dynamic test of the gear is to identify and assess the effect of temperature on the gear performance. The rise of temperature and its subsequent effect directly involves with the material performance and hence influences the working life. Because of this, it is necessary to quantify the heat loss in terms of temperature during running of the gear pair.
The gears setup with metallic bush has been shown in the Figure 5.1. Several experiments are conducted and the dynamic performance of the gear is evaluated under various loading and running conditions. Initially, a dynamic gear test-rig is modified for the experimental procedure suitable to comprehend the performance during running of the gears. The test-rig, equipped with two parallel shafts adjusted by a high-speed AC motor. The parallel shafts are then fixed by two movable self-lubricated bearing housing that allow the free rotation subjected to minimal frictional loss of the shafts. Two load cells of 13.5N and 8.5N of mild steels are employed as per the features of the test gear, gear dimensions and mechanical properties of the gear materials are shown in the Figure 5.2(a) and (b) respectively.
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(a) (b)
(c) (d)
Figure 5.1 Fabricated composite gears with bush (a) pure polypropylene, (b) 5%, (c) 10% and (d) 15% cement reinforced composite spur gears
Four variable speeds are selected in order to investigate the heat loss due to friction in terms of temperature between the gear pair during working condition. Evaluation of surface temperature in dynamic condition is aided, in line, by an Infra-Red assisted camera, IR-TCM 384. In addition, the composite spur gear material was tested to evaluate its friction and wear characteristics in both adhesive and abrasive wear modes. In dynamic condition, the gear pair runs at desired speeds with preset loading condition. Owing to the high speeds, teeth flanks i.e., surface of both the driver and driven gears come into contact very frequently, eventually, high friction takes place, results in increase of flash temperature. This induced temperature of the gear amount to fall of the performance and results in shortening of the gear life.
Chapter 5 Dynamic Performance Evaluation…
(a) (b)
Figure 5.2 Loading condition during gear running (a) 13.5N and (b) 8.5N
A high-speed AC motor (SAGAR, S.M. motor- Sl. No. 202758, type- AC/DC-CONT/ACW) of 6500 rpm, 1/12 HP capacity, 0.75 AMPs, 220 V, is used to run the gear pair as shown in the Figure 5.3(a). A rheostat (DIMMERSTAT, Sl. No. 701/9277417, input-240 V, output-0- 270 V, 2 A, Type- 2D-1P) is used to control the gear speed of the motor as shown in the Figure 5.3(b). During the test, the speed is measured using a digital non-contact tachometer (maker: Digital Promoters India Private Limited, model: DT-2001B, range: 1 to 99999 rpm).
(a) (b)
Figure 5.3 (a) AC motor used in the experiment and (b) the Rheostat
The experimental dynamic gear test-rig setup is shown in the Figure 5.4. Two parallel shafts are used and the gear meshing is supported by four bearing houses. Motor yields clockwise rotation to the driver shaft attached with the gear and corresponds to power transfer to the parallel-driven-shaft results in anti-clockwise rotation. The rheostat controls the preset motor speed for the test.
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AC motor Driver Shaft
Driven Shaft Bearing mounting
Figure 5.4 Modified gear testing setup used in the experiments
In the Figure 5.5(a) and (b), pure polypropylene and 10 wt% cement reinforced composite gear pair meshing have been illustrated. Initially, the gear pair meshing is done with the shafts using bush and set-screw arrangement.
Gear pair of 100% PP Gear pair of pure polypropylene
(a)
Gear pair of 10% CPP
Gear pair of 10% cement filled composite
(b)
Figure 5.5 (a) Pure polypropylene and (b) 10% cement filled composite test gear mesh
Chapter 5 Dynamic Performance Evaluation…
During experimentation, the IR assisted camera is fixed at two different directions along (a) transverse and (b) longitudinal direction. The ambient temperature of the laboratory remains to be 27ºC (room temperature) during experimentation. During running of the gear pair, the surface temperature rises and reaches an optimal value and this gives direct measures of the heat loss. The camera senses the emitted heat loss in terms of temperature, greater than ambient temperature and analyzed the data in accordance with the principle of infrared emissivity. The dynamic experimental conditions in different positions are shown in the Figure 5.6(a) and (b).
Bearing house IR camera Load cell
Test gear mesh
Motor
Gear testing rig Driver shaft
IR camera stand
Bearing house IR camera
Load cell
Test gear mesh
Motor
Gear testing rig Driven shaft
IR camera stand Driver shaft
(a) (b)
Figure 5.6 Dynamic gear test rig setup with accessories (a) along transverse direction and (b) longitudinal direction
The gear pair teeth meshing is an elliptical shape in dynamic condition signifies the teeth contact region where the friction wear takes place. The gear teeth meshing have been illustrated in the Figure 5.7.
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Gears meshing at idle
Meshing during running
(a) (b)
Figure 5.7 Gear pair meshing (10% cement filled composite) (a) idle longitudinal position (b) transverse position at dynamic condition