Selection of the coupling, deviations from the alignment of...

Coupling selection

The main data for selecting a coupling are:

• nominal diameters of the shafts to be connected,

• rated torque,

• Speed ​​and operating conditions.

In the general case, the calculated torque T p is determined taking into account the influence of inertial masses by the formula:

where T n is the rated torque; J l , J 1 are the moments of inertia of the rotating masses, respectively, of the leading (input) and driven (output) shafts with the parts mounted on them, which is installed the coupling.

In the rough calculations, you can use the following:

where A p - the operating mode factor, which takes into account the operating conditions, the values ​​of which for transmissions from the electric motor are given in Table. 10.1.

Table 10.2

Coefficient of operating mode of the coupling to p

 The mechanism of the coupling design Ap Band conveyors 1.25-1.50 Conveyors, chain, screw, scraper 1.50-2.00 Fans, compressors, centrifugal pumps 1.25-2.00 Compressors and Piston Pumps 2.00-3.00 Metal cutting machines with continuous motion 1.25-1.50 with reciprocating motion 1.50-2.50 Woodworking machines 2.50-2.00 Ball mills, crushers, hammers, scissors 2.00-3.00 Cranes, elevators 3.00-4.00

In transfers from reciprocating engines, the values ​​of A p are 50-80% higher. In a simplified calculation, using the experience of designing and operating machines, take:

where A b = 1,0-1,8 - safety factor, taking into account the nature of the consequences when the coupler is out of order; A d = 1.0-1.5 is a coefficient that takes into account the nature of the transmitted load (smaller values ​​are taken at quiet load, greater values ​​are taken with shock and reverse).

10.4. Installation of coupling halves on shafts

The couplings are mounted on the cylindrical or conical ends of the shafts (Tables A.178, A.179 and A.292).

With a constant direction of rotation and moderately loaded shafts (t <15 MPa), the coupling halves are placed on the smooth cylindrical ends of the shafts for transitional plantings of the type 1R7/k6, H7! t6.

For reverse operation, as well as for heavily loaded shafts (m> 15 MPa), H1/n6 landing is used.

The installation of half couplings on the cylindrical splined ends of the shafts is used if, in calculating the keyway, the length of the landing hole is more than 1.5 * /. Landing along the centering diameter O of the splines, take Я7 // л 6.

The end clamping of the half couplings is similar to that of the inner bearing rings (Section 4.4.3.2.1).

Mounting and dismantling of the half couplings on the cylindrical ends of the shafts with interference are sufficiently technologically difficult, and when fitting the half couplings onto the conical ends, it is possible to create a significant interference in the joint and to provide a sufficiently accurate position of the coupling half relative to the shaft. Therefore, at high loads, work with jerks, impacts and in reversible operation, it is preferable to attach the coupling halves to the conical ends of the shafts, in spite of the great complexity of their manufacture. The half-coupling is placed on the tapered end of the shaft with the application of axial force, for example, by the pressure of the nut being screwed onto the threaded end of the shaft (Table A.179) through the face washer. The same nut fixes the position of the coupling on the shaft.

Shaft alignment deviations

Due to the errors in the manufacture of parts and inaccuracies in the assembly, the shafts connected by the clutch tend to have total displacements (Figure 10.19):

• angular (skew);

ah

• Axial * •.

Fig. 10.19

In Fig. 10.19: A, is the dimension determining the radial displacement of the shafts in the vertical plane; p, is the dimension determining the angular displacement of the shafts in the vertical plane; (0 | - o> 7, co ^ are the dimensions defining the axial displacement between the ends of the half couplings (or shafts).

Limit deviations of the size of? p and // e are specified in GOST 16162-78 and GOST 8592-79 at a nominal value of /; p (L e ):

• up to 250 mm - 0.5 mm;

• More than 250 to 630 mm - 1.0 mm.

Limit Deviations:

• The size P p according to GOST 16162 78 is set to 0.1 mm per 100 mm;

• size p 3 according to GOST 8592-79 for motors of normal accuracy - 0.15 mm per 100 mm.

Since the couplings of this type have a large radial and angular rigidity, their use is advisable when installing the assembled units on plates (frames) of great rigidity, and assembling the units must be done with high precision and with the use of pads.

The limiting displacement of the shafts should be taken (Figure 10.19): radial - D E = 0.10-0.15 mm; Angular - = 0.6/100 mm/mm;

axial -0 ^ = 3 mm.

The coaxiality of shafts in the vertical plane is determined by the errors in the dimensions /; p , Lo and A e , and p p , p 0 and.

The alignment of shafts in the horizontal plane is ensured when assembling by moving and rotating nodes.

The value of radial displacements in the vertical plane, if necessary, is reduced by using compensatory liners. For each paw of the electric motor put one lining thickness (5-8) mm, which are then milled or ground to the required size, or a set of two or three pads selected from a number of thicknesses (mm): 0.1; 0.2; 0.4 and 0.8.

Radial displacements in the horizontal plane are reduced by reconciling the position of the nodes on the base planes. In this case, the possible total radial displacement of the Ax axes depends on the qualification of the assemblers and on the accuracy of the instrumentation.

The use of the same thickness of pads does not compensate for deviations from the parallelism of the shaft axes in the vertical plane. Therefore, with increased accuracy of the assembly, for each paw of the electric motor, pads of different thickness are put, or with the same thickness, they are ground with a slope, and for high accuracy of assembly, shabriat.

The parallelism of shaft axes in the horizontal plane is increased by reconciling the position of the nodes on the base planes. Axial displacement is reduced if necessary by aligning the axial position of the nodes.

During the operation of drives under the action of the resulting loads, there are deformations of the hulls of the units (reducers, electric motors, etc.), as well as plates and frames. The deformation of torsion of high frames is especially significant. These deformations lead to an additional, mainly radial, displacement of the shafts and, as a consequence, to an additional load of the elastic elements of the couplings. Considering this, in the technical requirements for the installation of drives, the radial displacement of the shafts D E , reduced in comparison with the calculated one, should be set. Decrease is recommended when assembling units: on high frames - in 1,5-2,0 times; on low frames - in 1,2-1,4 times; at low cast plates - by 1.0-1.2 times.

Adjusting the accuracy of the relative position of the drive units is a laborious operation. In order not to repeat it during subsequent dismantling and installation, it is desirable to fix the position of the nodes on the plate (rams) with two control conical pins.

Pins that are put into blind holes or without access to be pinched must be threaded (internal or external) to remove when removing the drive.

Parameters of elastic sleeve-toothed couplings

Among the elastic couplings, the most flexible, thanks to the relative simplicity of the design and the convenience of replacing the elastic elements, are the flexible sleeve-to-finger couplings (MISP) (Figure 10.20).

The dimensions of these couplings, the magnitude of the transmitted moments, the limiting speeds and the permissible shaft displacements are given in Table. A.292.

They have a small compensating capacity and when connecting non-axial shafts they exert a sufficiently large force on the shafts and supports. At the same time, rubber bushes quickly fail.

If it is necessary to reduce the dimensions of the coupling in comparison with the dimensions according to GOST, it is necessary to design a non-standard coupling in which to place a greater number of elastic elements. In this case, the fingers and rings are taken as standard. placing them so that the following condition is met:

where 2 is the number of fingers; c1 0 - diameter of the hole for the elastic element; - diameter of the finger arrangement (Figure 10.2).

The outer diameter of the clutch /) is then determined from the relationship:

Fig. 10.20

The elastic elements of the special clutch are tested for collapse under the assumption of an even load distribution between the fingers:

where T to is the torque, Nmm; with/ n - the diameter of the finger, mm; - length of the elastic element, mm; th 0 - diameter of the finger arrangement, mm; and cm /) - allowable stresses of buckling, MPa.

The calculation of the stresses of crushing is conditional, since it does not take into account the true nature of stress distribution. In this case, the permissible stresses a cm p are equal to 2 MPa.

The coupling fingers, made of steel 45, are counted for bending:

where C is the clearance between the coupling halves, equal to (3-5) mm. The allowable bending stress is assumed to be:

where su t is the yield point of the material of the fingers.

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