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When selecting universal joints, the models and specifications are preliminary selected on account of torques calculated through basic information. Then finding out the max aperture, the max radial dimension (rotatory space), the available RPM of corresponding models and specifications and according to standards. These factors should adapt to the working conditions of universal joints. In this way, the models and specifications of universal joints are finally determined. 
 

Here are the detailed steps to select models of universal joints. 
 

1.1 Basic Information. 

Name of driving machines, quantity of driving machines, input power, working speed, name of working machines, load category, working environment, nature of work, start frequency, the function of forward and reverse rotation, diameters and lengths of input shafts and output shafts. 

Please refer to attached table 1 for basic information. 

 

1.2 Calculation of Torques

The main parameters of universal joints are nominal torques (Tn). The nominal torques should conform to the following formula: 

T＜Tc≤Tn≤[T]＜[Tmax]＜Tmax

T refers to the theoretical torque, N·m;

Tc refers to the calculated torque, N·m; 

Tn refers to the nominal torque, N·m; 

[T] refers to the allowable torque, N·m; 

[Tmax] refers to the maximum allowable torque, N·m; 

Tmax refers to the maximum torque, N·m. 

 

1.2.1 The calculation of a universal joint’s theoretical torque. 

Formula: T=9550Pw/n. 

In this formula, Pw refers to driving power, KW; while n refers to working speed, r/min. 

 

1.2.2 The calculation of a universal joint’s calculated torque. 

Kw refers to coefficient of engine (Table 1); 

K refers to coefficient of working conditions (Table 1); 

Kz refers to coefficient of start-up (Table 1). 

Table 1

1.2.3 Special calculation methods should be applied when the following cases taking place. 

1.High-peak load. 

2.Braking (The brake wheel or the brake disc are a part of the universal joint). 

3.Axial endplay with high-frequency. 

 

Peak load

When the torque of a power-driven machine is higher than usual and moves intermittently, impulse load come into being. The rotational inertia or the system might have repetitive peak load when starting or braking universal joints. The peak load of system is the maximum load that might exist in system. In this case, torques can be calculated by the following formulas. 

a.No-reverse peak load 

Selection of torque (N.m) = peak torque of the system; 

Selection of torque (N.m) = peak power of the system (Kw) x 9950/RPM. 

 

b. Reverse peak load

Selection of torque (N.m) = 1.5 x peak torque of the system; 

Selection of torque (N.m) = 1.5 x peak power of the system (Kw) x 9950/RPM. 

 

c. Occasional peak load (No-reverse)

Within the period of universal joints’ predicated service life, the following formula should be applied if frequency of the peak torque of the system is less than 1000 times. 

Selection of torque (N.m) = 0.5 x peak torque of the system; 

Selection of torque (N.m) = 0.5 x peak power of the system (Kw) x 9950/RPM. 

For those with reverse peak load, only the step b can be applied. 

 

Braking

If the braking torque exceeds the torque of power-driven machine, one can calculate toques according to the following formula. 

Selection of torque (N.m) = braking toque x coefficient of working conditions. 

 

Axial endplay with high-frequency

If the axial endplay goes surpass 5 times per hour, then the coefficient of working conditions should plus 0.25, that is: 

Selection of torque (N.m) = power (Kw) x 9550 x (coefficient of working conditions + 0.25)/RPM. 

 

1.3 Preliminary models and specifications of universal joints

1.4 Confirming the selection

1.5 Determining models and specifications of universal joints

1.6 Product marking 

 

Examples 

 

2.1 General information

Rated motor power: 130KW

Output revolutions per minute: 37rmp

The distance between input end and output end: 2703mm

Compressed length: 2650mm

Compensated length: 100mm

Coupling type: universal joint 

Balance grade: G10

Working environment: 

Working temperatures: -30℃—120℃ 

Nature of load: Medium impact 

Surroundings: Dusty or others. 

Nature of work: Continual work. 

 

2.2 Calculation 

According to the general information, a expansion universal joint are the one used in this project. 

Calculation of models

Calculation of theoretical torques: T=9550Pw/n=9550*130/37=33554 (Nm). 

Calculation of calculated torques: Tc=T·Kw·K·Kz. 

In this case, Kw=1, K=2, Kz=1, then Tc=33554*1*2*1=67108 (Nm). 

 

2.3 Preliminary selection of universal joints models

SWC285 Universal joint, 9000Nm nominal torque. 

This type of universal joint meets requirements on torques. 

 

2.4 Confirmation 

 

2.4.1 Aperture 

For aperture is not stated in general information, it is regarded as meeting the requirements. 

 

2.4.2 Rotary Space (Compared with the conditions on site)

No limitation listed, this item is regarded as meeting the requirements. 

 

2.4.3 Allowable revolution per minute

The actual output RPM of the universal joint is relatively low, that is, 37rpm. 

This item meets the requirements. 

 

2.5 Determining models and specifications of universal joints 

The balance grade is required to be G10, therefore, universal joint SWC285*2650min+100 (expansion allowance) with balance grade G10 is the one finally determined. 

 

2.6 Product marking 

SWC285 Universal joints

SWC285*2650min+100 (expansion allowance) balance grade G10

For more information concerning universal joints, please refer to the following articles:
Basic Info for Model Selection of Universal Joints