CAD modelling of couplings to extend reliability.

Eftimie, Lucian ; Tierean, Mircea ; Baltes, Liana 等

1. INTRODUCTION

Gear couplings are as usual, industrial assemblies used to transmit torque of rotating movement and to compensate angular and radial misalignments of the connected end shafts (figure 1). There is a wide range of application for high torque or high speed rotation, used in steel processing, rubber, paper, plastic industries, water and wind power stations, transport and conveyor equipment, or mining applications.

2. APPLICATION FOR GEAR COUPLING HUB

It must be used a compact design and reliable solution to avoid the single-point basic design. It is better to use a line contact, but it is very difficult to configure the tooth shape to reach this requirement.

Basic design means involute type teeth, connected as shown in Fig. 1, as a general design assembly made using CATIA V5 software. The connected teeth allow a relative axial movement made by friction of the side connected surfaces of the teeth. The involute is used because the precise machining technology. The clearance between the connected teeth surface manage the angular flexion of this assembly (Alaci et al., 2008).

Using the CAD design--CATIA V5 software, the teeth shape can be generated and modified to accept the angular flexion of the connection.

The contact angle can be extended up to [+ or -] 5[degrees] rotation of the axis, and the contact line is realised on more than 70% length. It is necessary to use nitride steel and a quenched tempered body of the tooth, to realise enough strength (McGinnity et al., 2005).

Firstly, it is necessary to generate the tooth involute shape using specific relations and parameters as shown in figure 2.

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Using the extrusion command of the CATIA software, we generate a curve tooth--figure 3--to allow the rotation of the hub.

Now there are starting the technical problems, because this fact can be possible for minimum clearance, only if we modify the cross-section of the tooth, as shown in figure 4.

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Starting from the top of the tooth, we sketch--see figure 4--the tilting curve as a circle to allow the oscillation on the horizontal contact teeth an we make a pocket to remove material along the involute. The result is a space surface from the same family of involute.

Using specific parameters, we choose the dimension of the top and bottom of the tooth, generating a slice of the future gear--figure 5 and figure 6.

The slice will be repeated as a circular pattern, completing the gear.

General design will be made to obtain the gear hub assembly in respect to the inner and outer dimensions to realize a good connection to the end shaft.

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The connection of the relative teeth will allow the minimum clearance and the necessary oscillation of the assembly in the same time with linear contact--figure 8 (Landry, 2002).

It can be observed that the cross section of the teeth is identical to the medium plane cross section of the involute (Patras-Ciceu et al., 2008).

That means that the contact curve line can be repeated step by step on other two cross sections, symmetrical aligned to the medium plane. That is the situation which allows maximum angular misalignment. Machining of the surface can be made by automatic four axis CNC vertical centre machine Fadal 4020. The surfaces must be smooth and the clearance can be diminished up to 0.02 mm.

3. CONCLUSION

Using CAD design, we provide engineered solutions to achieve better reliability during the gear coupling function.

The backlash between the connected teeth is diminished and optimised to reach the required thickness of the filled oil film. The torque is transmitted mostly by involute surface rolling, minimising the faces sliding friction. The reliability of the coupling is increasing caused by this change of surface contact, similar to ball contact inside a bearing. To obtain a reliable contact of this connected faces it is necessary to increase the hardness of the surface concomitant with body strengths. It means to use nitride alloyed steels hardened and tempered before the surface thermo-chemical treatment. The surface space model will be precisely machined using CAM technology.

4. REFERENCES

Alaci, S.; Amarandei, D.; Ciornei, F.C. & Patras-Ciceu, S. (2008) Simulation of gear rack generation of involute spur gears, Annals of the Oradea University. Fascicle of Management and Technological Engineering, volume VII (XVII), p. 1172-1180

Landry, J. (2002) Backlash vs. lost motion, Design News for Mechanical and Design Engineers, http://www.designnews.com

McGinnity, M. & Mancuso, J. (2005) New pump coupling reduces effects of torque, misalignment and unbalance, World pumps, May, p. 34-37

Patras-Ciceu, S.; Ciornei, F.C. & Alaci, S. (2008) The surface temperature in sliding contacts of gear working flanks, part 1--Analytical solutions, Annals of the Oradea University. Fascicle of Management and Technological Engineering, volume VII (XVII), p. 502-505

CATIA documentation V5R17 2007