Course project on machine parts

Contents

Introduction

1 Selection of electric motor

2 Calculation of belt transmission

3 Material selection and allowable stress calculation

4 Calculation of gears

4.1 High speed stage

4.2 Slow-moving stage

5 Structural dimensions of the gearbox housing and cover

6 Shaft strength check

6.1 Gearbox drive shaft calculation

6.2 Calculation of gearbox intermediate shaft

6.3 Calculation of gearbox driven shaft

7 Selection of bearings

7.1 Selection of bearings for the drive shaft

7.2 Selection of bearings for intermediate shaft

7.3 Selection of bearings for driven shaft

8 Calculation of key connections

9 Coupling selection and calculation

10 Selection of lubricant for gears and bearings

11 Assembly, adjustment and disassembly of reduction gear box

Literature

Introduction

A reduction gear is a mechanism consisting of geared or worm gears (wheels) made in the form of a separate unit and serving to transfer rotation from the shaft of the engine to the shaft of the working machine.

The purpose of the reduction gear is to reduce the angular speed and, accordingly, increase the rotational torque of the driven shaft compared to the driving one.

The reduction gear consists of a body (cast iron or welded steel), in which the transmission elements are placed - gears, shafts, bearings, etc. In some cases, other auxiliary devices are also placed in the housing.

Gearboxes are classified according to the following main features: gear type (toothed, worm or gear-worm);

number of stages (single-stage, two-stage, etc.);

to type of cogwheels (cylindrical, conic, konicheskotsilindrichesky, etc.);

relative location of gear box shafts in space (horizontal, vertical);

peculiarities of kinematic scheme (unfolded, coaxial, with bifurcated stage, etc.).

Two-stage cylindrical reduction gears.

The most common are two-stage horizontal gearboxes made according to an expanded scheme. These gearboxes are simple, but due to the asymmetric arrangement of the wheels on the shafts, the concentration of load along the length of the tooth increases. Therefore, rigid shafts should be used in these gearboxes.

Selection of lubricant for gears and bearings

Since we have a general-purpose gearbox and the circumferential speed does not exceed 12.5 m/s, we accept a crankcase lubrication system in which oil is poured into the gearbox housing so that the rims of the gears are immersed in it. When they rotate, the oil is carried away by the teeth, sprayed, falls on the inner walls of the body, from where it flows into the lower part of the body. Inside the housing, a suspension of oil particles is formed in the air, which covers the surface of the parts located inside the housing.

As per [7] we determine that oil with kinematic viscosity of 28· 106 m2/s is required to lubricate the reduction gear box at circumferential speed of 2... 5 m/s and contact voltages up to 60 MPa. accept oil I-G-46 GOST 17479487 for lubrication of gear transmission.

Lubrication of rolling bearings will be carried out from the reduction gear case as a result of oil spraying with a gear wheel. For this purpose, bearing cavities are made open inside the housing.

During operation of the transmissions, wear products gradually contaminate the oil. Over time, it ages, its properties deteriorate. Therefore, the oil poured into the gearbox housing is periodically changed. To replace oil in the housing, a drain hole is provided, which is closed by a plug with a conical thread.

To monitor the oil level in the housing, we install a viewing window.

During long-term operation due to air heating, the pressure inside the housing increases. This leads to oil leaking through seals and joints. To avoid this, the interior of the housing is communicated with the external environment by installing a perfume in its upper part.

Gearbox assembly, adjustment and disassembly

Keys are pressed into shafts. Press gears on the intermediate shaft. Install remote bushings and press bearings. The assembled shaft is installed in the housing. In the slots of the housing we install bearing covers with adjusting screws wrapped in them. Adjusting washers are installed between bearings and covers.

Press the gear wheel on the slow-moving shaft, install the remote bushing and press the bearings, put on a through cover with a cuff pressed into it. All this is done in accordance with the gearbox assembly drawing. The assembled shaft is installed in the gearbox housing so that the bearing covers fall into the slots of the housing.

Press pins into the housing and lubricate the plane of the housing flange to sealants.

Install the housing cover and tighten it with tightening bolts.

We adjust the shaft bearings by pressing or squeezing the adjustment screws so that the shaft rotates freely by hand, without jamming. The manhole cover is open. We rotate the shaft by the wheel.

Install the sleeve assembled with the driving shaft into the socket of the sleeve. We do not yet install adjustment gaskets between the sleeve flange and the reduction gear box housing. We achieve such a position of the sleeve and the conical wheel so that the outer end sections of the conical gear and the wheels coincide. If it is necessary to change the position of the wheel (in order not to disturb the adjustment of the bearings), turn the adjustment screws by the same angle. In this position, the probe measures the clearance between the sleeve flange and the housing. Remove the sleeve and install adjustment gaskets under the flange. The thickness of the gasket set must be equal to the measured gap. We put the glass in place. Put the bearing cover on the shaft with the cuff pressed into it and press the sleeve with screws to the housing.

In the middle of the tooth, we apply a small spot of paint and turn behind the shaft. If the paint spot crushed by the teeth is asymmetric with respect to the middle of the tooth, it is necessary to adjust the engagement by moving the gear along the axis. Movement is performed by adjusting screws depending on spot position. In order not to disturb the adjustment of the bearings, the screws must be moved the same distance (that is, as far as we push one screw, we must push the second one as well).

Wrap the drain plug into the housing and pour the required amount of oil through the hatch. Oil should appear in the inspection window.

Close the hatch with a cover, install a gasket under it.

Disassembly of reduction gear box is performed in sequence, reverse assembly, preliminary oil drain.