Braking torque

The braking torque of the shoe brakes may diminish with the number of operations. The heat of braking wears out the brake linings. The extent of fading will depend upon the braking torque to deeelerate the heavy loads nid frequeney of its operations. They mtiy also need replaeement of the brake linings, similar to an automotive vehiele. 

The brakes should be suitable to counter at least the torque developed by the motor. They must therefore develop at least this amount of torque. To find the least braking torque, the brake drums must be able to develop, in either of the above typies of mechanical brakes, the torque shown in equation (1.10) may be used i.e. 

Figure 6.56 Typical braking torque curves for a wound rotor for different external resistances but same excitation current...

Tex = braking torque of the external brakes, if provided otherwise it may be considered to be zero Tj, = locked rotor (starting) torque of the motor k2 = factor to account for the average braking torque. This may be considered to be 1.3-1.7 (consult the manufacturer for a more accurate value)... 

Figure 6.58 Obtaining d.c. voltage through a bridge rectifier Figure 6.59 Braking torque during d.c. electric braking...

Static controls and braking of motors 6/163 T(, = braking torque in mkg... 

Tb = average braking torque between running speed and the final speed... 

Remarks When the brake torque of the hand brake cannot meet the brake requirement, the thickness of the brake shoe gasket shall be tested. If it is less than the minimum value of brake show gasket, the brake shoe shall be replaced, minimum thickness 1.0mm... 

Where much larger braking torques are required the tendency is to use the larger brake units. These will produce a braking force of 320kN at a 1mm air gap. 

Design braking torque per brake stand and per control system 4 840 kNm 4 840 kNm... 

In the mid-1960 s, GEC of the UK produced their high pressure hydraulic applied and released brakes. All of these applied the braking torque to the winders drums via calhpers of varying geometric configurations, lined with a friction material acting on brake drums or brake paths. 

About 2kV/mm is required to produce 8kPa of shear stress at a few hundred s shear rate and a two wheel braking torque of 16 Nm. The draw back to further adaptronic application is the 20 to 80 ms time constant of shear stress to voltage and possibly the Wiesenberg effect arising due to rotation of the polymer at high shear rate. 

Fig. 6.80. Typical braking torque versus current for direct-shear brake...

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