Choice of the brake
The choice of the brake, according to the braking torque Mf necessary for a special application, depends on the knowledge of the project data. These are:
1) The total inertia Itot [kg*m2] of the rotating parts reduced with respect to the motor shaft.
2) The greatest number of motor revolutions no (rpm).
3) The maximum time allowed for braking the system tf (seconds).
4) The torque ML (Nm) acting on the system, which can be a load to be lifted up or a moment of resistance.
5) The operating frequency of the brake, or working of the brake within 1 hour m [1/h].
There are also other aspects that can determine the best performances of the brake, such as the average room temperature, the specific environment conditions (humidity, dust,etc) and the assembling position of the motor.
Warning:
in case the electromagnetic brake is requested with a special friction material to avoid the "sticking" effect, the nominal torque value declared for each brake, can be get only after the friction material running. The torque value Nm, has at the beginning a value of around less 40% of the nominal torque declared.
Functional limitations: all devices manufactured by Temporiti SrL can have serious functional limitations, in case the ambient temperature, the humidity value, the salt concentration environment exceed those specified in the "Standard Temperature and Pressure (STP)"; or there is the presence of dust, acids, oil, both in liquid and gaseous forms. In these circumstances it is absolutely necessary to contact our technical offices to identify the functional solution of the case, and prepare a maintenance plan required every 3 months, without prejudice to the limitazini of work referred to above.
Selection Criteria
In order to define the braking torque there are four frequent events:
A) lifting of a load P (N) which has with respect to the rotation axis a moment ML;
B) descent of a load P (N) which has with respect to the rotation axis a moment ML;
C) steady resisting torque ML (Nm), which is opposed to the motor rotation;
D) steady resisting torque ML (Nm), which favours the motor rotation.
We also use some expressions which are already defined, in order to check the application according to the chart and graphics reported in this catalogue:
CS safety coefficient CS ≥ 2;
ct brake operating decreasing coefficient (usually equal to 0,995);
L work per operation (Joule), or heat that the brake must dissipate during operation;
W nominal power of the motor (Watt).
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Braking torque calculation
Use the following formulae to calculate the necessary braking torque. You can obtain the wanted braking
torque multiplying the result by the safety coefficient CS, generally equal to 2.
Formula 1 (events A and C)
Formula 2 (events B and D)
Formula 3
Select from graphic 1 the brake to the nearest whole number.
Check of heat dissipation
The heat generated during brake operation will be dissipated by the brake. It’s necessary to check if this quantity of heat is compatible with the number of operations per hour that the brake must carry out. Use the following formulae to calculate the heat value (L) to dissipate:
Formula 4 (event A)
Formula 5 (event B)
Formula 6 (events C and D)
Knowing the number of operations that the brake must carry out within an hour, enter into the graphic n.1 and check that point k is under the limit curve of the selected brake. If this will not occur, check again to an higher dash.
Air-gap adjustment. Wear 0,1 mm
The maximum number of operations mmax that you can do before the adjustment of brake, may be obtained by the graph n° 2.
Enter onto the x-axis with the work to dissipate (L) and read on the intersection between the curve of the selected brake and the y-axis, the total number of operations. The time (h) for the air-gap adjustment is calculated with the following formula:
The preivous formula allows the calculation of a wear equal to 0,1 mm. The functionality of the brake is guaranteed for a max value of the air-gap of 0,7 mm (wear 0,5 mm).
Rough calculation of the braking torque
If you just know the motor power (W) and its greatest number of revolutions per minute (no), it’s possible select the necessary braking torque (Mf) with a rough calculation, using the following formula:
If it isn’t possible to check the heat dissipation, the safety coefficient CS must be selected according to the specific requested application.
Determine the load acting on the system in order to select the load application. From paragraph "Selection criteria” select the kind of load acting on the system. The four events indicated satisfy most of the frequent braking events. Choose then the formula according to the loading torque. In formula 1, ML takes energy from the loading torque, so the value Mf can be lower than ML.
Numerical example of calculation
In formula 2, ML adds energy to the loading torque, so the value Mf can be higher than ML. Calculate with formula 3 the necessary braking torque. Select in the catalogue the brake with an higher braking torque.
Determine the heat dissipation using the formulae in paragraph "Check of heat dissipation”. With the Joule value enter onto graphic 1 and check if the heat dissipation of the brake is compatible with the number of operations to carry out. With graphic 2 determine the number of operations for the air-gap adjustment.
The load belongs to class C.
From the formula 1
To formula 3
Select in our catalogue the brake model K05 with a braking torque of 35Nm.
Check then the heat dissipation of the selected brake. Calculate the work to dissipate (J) with formula 6
(as the load belongs to class C).
Check into graphic 1 if the selected brake model K05 can bear the caculated work (J) according to the number of operations to carry out. The brake can bear a work of about 28000 J, so the brake selected is correct. With the graphic 2 you can gather the number of operations to carry out before adjusting the air-gap (wear 0,1 mm).
The value obtained is 15000 which divided by the number of operations /hour to carry out, gives a value of 500 working hours. Knowing that the air-gap can reach a maximum value of 0,5 mm, you must adjust it within 2500 working hours.
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Plain Yoke Style
Crowned Yoke Style
Flanged eccentric style
