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Brake Linings Wear, Starting and Braking time

brake linings wear

Brake linings wear is mainly affected by the environmental conditions in which the motor operates, by the frequency of starts, by the energy dissipated at each stop and by the torque provided by the brake. The lining temperature rises with the braking frequency and with the moment of inertia applied to the shaft. When the lining temperature raises, the lining wear increases and consequently the braking time is longer. BA series motors are designed to have continuous cooling of the braking surfaces so as to reduce brake disc wear to have a shorter braking time.

The life cycle of the brake linings can be roughly expressed by the number of brake interventions and can be approximately calculated as follows:

n = Wtot / Wb

where Wb (J) is the work done during each braking action and Wtot (J) is obtained from the table for each type of brake motor. However, it is necessary to check the brake disc wear periodically to replace the brake disc before it is completely worn. If you want to estimate the interval between two successive air gap adjustment in a specific application, note that the brake linings wear is greater than usual during the run-in (a few thousands stops).

On PV series brake motors Wtot shown in the table have to be multiplied by 0.5 and the moment of inertia have to be calculated considering the presence of the fly-wheel. The indicative number of AC brake stops NintAC between two successive air gap adjustments on a BA motor is given by the following formula:

NintAC = ErBA / Wb

while the NintDC for DC brake motors is given by : NintDC = NintAC • 0.65

100

112

132

160

180

200

225

Wtot (MJ)

537

705

952

1148

1438

2255

3290

4355

5226

rBA (MJ)

105

130

200

290

385

462

The indicative number of DC brake stops NintBM between two successive air gap adjustments on a BM motor is given by the following formula:

NintBM = ErBM / Wb

ErBM values are shown at pag. 39 (BM section).

Starting and braking time

Starting current for an asynchronous motor is always much higher than the nominal current. When the starting time is excessively long, there are electromechanical disturbances and higher temperatures on winding, damaging the motor. For information on maximum starting time allowed for each type of motor, please contact MGM. An indicative value for starting time ts (expressed in seconds) and the angle of rotation cps (expressed in radians) can be obtained as follows:

(Jmot + Japp)»n

9.55 (T - Tioad)

ta-n

ts =

19.1

Where Japp (Kgm²) is the moment of inertia referred to the motor shaft, Mload (Nm) is the opposing torque to the motor, Jmot (Kgm²) is the moment of inertia of the motor, n (RPM is the rated motor RPM), T is the average starting torque, T=(0,8+0,9)Ts (see the technical data table for Jmot, n and Ts of the selected motor).

Jtot • n tB

An indicative braking time tf (s) can be calculated as follows: tf=

9.55 (Tb ±Tload) 1000

Where:Jtot total moment of inertia at the motor shaft (Kgm²)

n motor RPM (min^-1)

Tb brake torque (Nm)

Tload resisting load torque (Nm) with + sign if matches the brake torque, or - sign if opposite.

tB brake electrical reaction time (ms)

Brake electrical reaction time tB (ms)

DC Brake (Standard)

DC Brake (Quick)

tor type

AC Brake


7	80	20
9	80	30
12	85	30
12	90	30
14	100	35

BA 71-80-90 BA 100-112 BA 132-160 BA 180-200 BA 225

The reported tB times are valid only If the motor Is connected with the brake. In case the brake Is supplied separately, the tB time has to be cut by 30 - 50%. This calculation gives an approximative indication. Please contact MGM for further information.