REDUCTION GEARBOX DESIGN
You are the designer and you have been asked to design a speed reducer that will take power from the shaft of an electric motor rotating at 1500 rpm and deliver it to a machine that is to operate at approximately 750 rpm. Assume that you have decided to use spur gears to transmit the power and you are proposing to use a single-reduction speed reducer. The power to be transmitted by the shaft is 20 KW and the input shaft is coupled to the motor shaft. Each of the shafts is supported by two ball or roller bearings that need to be specified by you with an overall reliability of 95% and a design life of 20 000 hours are desired.
The following list gives some of the important parameters for each gear: * The number of teeth, N
* The form of the teeth (involute tooth profile)
* The size of the teeth as indicated by the module, m [mm] * The face width of the teeth, F [mm]
* The pith diameter (dp) for each of the gears, [mm]
* The means of attaching the gear to its shaft (such as : keys and keyways) * The means of locating the gear axially on the shaft (collars, retaining rings, etc.) * The degree of precision of the gear teeth (you will need to decide on Qv based on the pitch line velocity V of the pair * Other geometry related to spur gears
Reduction gearboxes are used in all industries where power transmission occurs; they reduce speed and increase torque. They can be found between the prime mover (electric motor, gas, diesel or steam engine, etc.) and the driven equipment (conveyors, mills, paper machines, elevators, screws, agitators, etc.). An industrial gearbox is defined as a machine for the majority of drives requiring a reliable life and factor of safety. This project focuses on the design of a reduction gearbox that will take power from the shaft of an electric motor rotating at 1500 rpm and deliver it to a machine that is to operate at approximately 750 rpm. The gearbox will consist of 2 spurs gears in mesh, each mounted on separate shafts supported by roller and ball bearings that will have an overall reliability of 95% and a design life of 20 000 hours. The power to be transmitted by the electric motor is 20 KW. The design of the reduction gearbox will entail the following procedures: * Determining the number of teeth for each gear.
* Analysis of the forces on the gears and shafts.
* Determining the stress acting on the gear teeth and selection of appropriate material to withstand these stresses. * Drawing of shear and bending moment diagrams, free body diagrams and calculation of the reactions at the supports. * Selection of bearings for each support.
* Selection of shaft dimensions, type and design based on calculation of torque to be transmitted, speed of rotation, keyways etc. * Sizing of keys and keyways, and types of keys that will be used. * Scale drawing of entire gearbox including gears, shafts, bearings, keys and keyways, retaining rings, housing etc.
The Intended Design
With the preliminary specification, the materials will be selected to satisfy the following calculations. For the assembly, the gears will be positioned on the shaft by keys to prevent rotation and by thrust washers and retaining rings to prevent axial movement on the shaft. The retaining rings will keep the thrust washers tightly against the pinion and gear hubs hence preventing axial displacement under operation. The shafts will be simply supported by roller and ball bearings. The bearings will be pressed into the housing/casing and the oil seals will also be pressed into the housing but on the outside of the bearings. This way will enable the bearings to be lubricated by the same gearbox oil while preventing it from escaping out through the shaft ends. There will be variation in the shaft diameter to enable the bearing to keep the shafts from axially displacing while end covers will...
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