Parameters of asynchronous motors

	Rated power P_r, kW	Synchronous rotational speed n_s, rpm

	Type designation	S,%	Type designation	S,%	Type designation	S,%
0.55	63В2	8.5	71A4	7.3	71B6
0.75	71А2	5.9	71B4	7.5	80A6	8.4
1.1	71В2	6.3	80A4	5.4	80B6	8.0
1.5	80А2	4.2	80B4	5.8	90L6	6.4
2.2	80В2	4.3	90L4	5.1	100L6	5.1
3.0	90L2	4.3	100S4	4.4	112MA6	4.7
4.0	100S2	3.3	100L4	4.7	112MB6	5.1
5.5	100L2	3.4	112M4	3.7	132S6	3.3
7.5	112M2	2.5	132S4	3.0	132M6	3.2
11.0	132M2	2.3	132M4	2.8	160S6	2.7
	160S2	2.1	160S4	2.3	160M6	2.6
18.5	160M2	2.1	160M4	2.2	180M6	2.7
	180S2	2.0	180S4	2.0	200M6	2.8
	180M2	1.9	180M4	1.9	200L6	2.1

For our mechanical drive we select 4A132S6 Induction Motor
(P_r = 5.5 kW, n_s = 1500 rpm).

1.5. Determine the motor rated rotational speed n_r

where S is relative speed loss that is determined according to table 1.2. In our case S = 3.3 %. After substituting corresponding magnitudes we obtain

1.6. Determine the output rotational speed

1.7. Determine the total velocity ratio of the mechanical drive

1.8. Distribute the total velocity ratio between mechanical drive steps.

The total velocity ratio can be found by the formula

u = u_red × u_cd,

where u_red is the speed reducer velocity ratio; u_cd is the chain drive velocity ratio.

First, determine the velocity ratio of the speed reducer.

For straight spur gears, helical spur gears and bevel gears speed reducers the velocity ratio should be chosen from the following standard series u_red =1.25;1.4;1.6;1.8;2;2.24;2.5;2.8;3.15;3.55;4;4.5;5;5.6.

For worm gear speed reducers u_red is taken from the following standard series u_red = 8;10;12.5;16;20;25;31.5;40;50;63;80.

In our case we have helical spur gears speed reducer. Let us take u_red=u_hsg = 4.

Determine the velocity ratio of the open drive. In our case it is chain drive

Obtained value of the velocity ratio of the open drive should satisfy to the following condition. For chain drives u_cd is to be ranged from 1.5 to 4, for belt drives u_bd is to be ranged from 2 to 4, for straight spur gears u_ssg is to be ranged from 2 to 5. If this condition is not satisfied we take the other value of u_red from the standard series.

1.9. Determine the rotational speed of all shafts

n ₁ = n_r = 967 rpm;

Obtained magnitude of n ₃ must be equal to n_out calculated according to p. 1.6. Error ε must be not more than 1%. In our case ε=0.09%.

1.10. Determine the angular velocity of all mechanical drive shafts

1.11. Determine the power at mechanical drive shafts.

Calculation is carried out for P_inp, determined in p.1.3.

P ₁ = P_inp× h _c× h _b = 4.767×0.996×0.99 = 4.7 kW;

P ₂ = P ₁ × h _hsg× h _b = 4.7×0.97×0.99 = 4.514 kW;

P ₃ = P ₂ × h _cd× h _b = 4.514×0.94×0.99 = 4.201 kW;

Obtained magnitude of P ₃ must be equal to P_out calculated according to the p.1.1. Error should not be greater than 1%. In our case ε=0.02%.

1.12. Determine the torques at all shafts.

Checking.

The output torque T_out can also be found as

Determine the error. It should be less than 1%.

2. Analysis of allowable stresses

Let us analyze the speed reducer of the mechanical drive when: n^p = 967 rpm; n^g = 241.75 rpm.

We will begin from the selection of the material of gears and determination of their allowable contact and bending stresses.

2.1. Select the material of toothed wheels.

The main material of toothed wheels is carbon or alloy steels. Depending on material’s hardness toothed wheels are subdivided into two groups:

- toothed wheels with surface hardness ;

- toothed wheels with surface hardness .

For general purpose speed reducers the following alternatives are possible:

1. A pinion and a gear are produced from identical carbon or alloy steel, such as Steel 45 (0.45C), Steel 40X (0.40C-Cr), Steel 40XH (0.40C-Cr-Ni). Heat treatment of both the gear and the pinion is martempering. The pinion hardness is ranged from 269 to 302 BHN and the gear hardness is ranged from 235 to 262 BHN.

2. A pinion and a gear are produced from identical alloy steel, such as Steel 40X (0.40C-Cr), Steel 40XH (0.40C-Cr-Ni), Steel 35XM (0.35C-Cr-Mo). Heat treatment of the gear is martempering to hardness ranged from 269 to 302 BHN. Heat treatment of the pinion is martempering and surface (induction) hardening to hardness ranged from 45 to 50 HRC.

Toothed wheels of the straight spur gears and helical spur gears are recommended to produce according to the 1st alternative. If we deal with bevel gears we can use either the 1st or the 2nd alternative.

2.2. Determine the mean magnitude of the hardness of the gear and the pinion:

- for the pinion

- for the gear

In our case a pinion and a gear are produced from identical alloy steel of grade Steel 40XH and we use the 1st alternative (heat treatment of the gear is martempering to hardness ranged from 235 to 262 BHN; heat treatment of the pinion is martempering to hardness ranged from 269 to 302 BHN):

BHN; BHN.