INTRODUCTION:

Electromagnetic brakes electrically released and spring set to achieve ‘fail safe’ operation. i.e. in the event of power failure, the brake applies automatically eliminating the rise of potential damage. However, in certain applications, on power failure, it may be necessary to release the brake manually for a short time. The manual release attachment on BCH brakes has been designed for this purpose. An important feature is that it is self resetting. i.e. the brake stays released just as long as manual force is applied, but sets immediately on removal of the force.

S.M BRAKES:

In this brake the magnet coil is separately placed between the inner and outer armatures. When the coil is energized, the armatures are attracted each other until their pole faces seal. The movement of the armature moves the shoes away from the wheel. The inner armature moves the inner shoes and the outer armature moves the outer shoe. When the coil is de-energized, the compression spring forces the armature apart which presses the shoes against the wheel.

Note the when the brake is properly adjusted for proper stroke; the torque adjuster washer face stands clear for the armature surface. As the lining wears, this clearance decreases. If the adjustment is neglected, the brake operation become sluggish and when the torque adjustor washer touches the armature surface the torque drops rapidly reaching zero when the clearance is used up. The clearance dimension is not measurable value but depends upon proper adjustment of individual brake.

COMPONENTS IN S.M BRAKE:
1. Lock nut
2. Compression spring
3. Lock nut
4. Pull rod
5. Spring
6. Wedge adjusting bolt
7. Adjusting wedge
8. Armature (inner)
9. Pin
10. Armature (outer)
11. Dust cover
12. Sounding pin
13. Torque adjusting nut
14. Coil
15. Shoe lever (inner)
16. Base
17. Brake wheel
18. Shoe lining
19. Shoe lever (outer)
20. Clamp
21. Cap screw
22. Shoe complete
23. Armature setting bolt

MATERIALS USED:

Brake lining -- ferodo ZA1
Bonding compound -- brake lining cement
Braking plate -- mild steel
Methods to attach friction linings to brake shoes:-
Riveting, Brass set screws and bolts, bonding, Ferodo ferobond.

WORKING OF ELECTRO HYDRAULIC THRUSTER BRAKE

Mill duties CRANE CONTROL makes thrustor brake are suitable for 400/440 Volts, 3 Phase AC supply for a wide range of drum sizes from 100mm to 600mm DIA. The braking pressure to the shoes is transmitted from the springs by means of an extremely rigid and simple Lever/ Tie rod mechanism. Since these brakes are in normally closed position, the release of the brake shoes is effected by energizing the 3 phase electro hydraulic thrustor which over comes the spring force and the shoes are moved clear off the drum by lever / arm linkage system so that the drum is free to rotate without any friction.
The angle of the brake shoe being 70 degree makes the replacement and maintenance of the brake shoes easy at site. The design of the brake is such that as the lining keeps wearing out due to normal operation of the brake, the thrustor stroke adjusts itself on its own to achieve the rated torque. The Crane Control make electro - hydraulic thrustor, which forms part of the brake is a self-contained unit and comprises of a centrifugal pump and impeller driven by an electric motor. When the power is given to the thrustor unit the impeller spins in oil and develops a pressure head, which is impressed upon the piston. Since the piston is connected to the arm of the brake the arm is pushed upwards and the brake opens up. When specified, break drum or brake drum coupling both pin bush type and flexible geared type can be supplied along with the brakes.


WORKING OF THRUSTOR:-

Electro hydraulic thrustors are linear actuators that incorporate motors and closed-loop hydraulic systems for the actuation and operation of brakes, levers, dampers and safety devices for industrial equipment. An actuation is the mechanism by which an artificial intelligence agent acts upon an environment. Actuators are a subdivision of transducers. They are devices which transform an input signal (mainly an electrical signal) into motion. Electrical motors, pneumatic actuators, electro hydraulic actuators, hydraulic pistons, relays, comb drive, piezoelectric actuators, thermal bimorphs, digital micro mirror devices, and electro active polymers are some examples of actuators. An electro hydraulic actuator uses an electrical power supply but operates the valve hydraulically, providing the responsive actuation required without the risk of damage to either valve or actuator. Electro hydraulic thrustors are generally used in safety devices for industries.

Electro hydraulic thrustors are commonly seen in electro hydraulic brakes. Electro hydraulic brakes (EHB) detect a driver's braking intention by means of sensors and transmit it in optimized form to the braking system. By depressing the brake pedal with an electro hydraulic brake system, the appropriate command is transmitted electronically to the electronic controller of the hydraulic unit. This process determines the optimum braking pressure and actuates the brake calipers hydraulically. Electro hydraulic actuators are actually cylinders engineered for feedback and control systems. An electro hydraulic cylinder is designed to use a low pressure hydraulic oil source (typically turbine lube oil) to provide the linear actuation force to operate steam turbine control valves or valve racks. Electro hydraulic cylinders have a modular design, which allow them to be custom configured to the specific application’s force and stroke requirements. Standard bore diameters and strokes are also available for electro hydraulic cylinders. Electro hydraulic thrustors are designed and manufactured to meet most industry specifications.
Electro hydraulic thrustors are used in many applications. An electro hydraulic thrustor can be used in brakes, levers, dampers, and safety devices. Electro hydraulic thrustors should adhere to the American National Standards Institute (ANSI) and American Society of Mechanical Engineers (ASME) standards.

PARTS IN THRUSTOR BRAKES:
1. Connecting rod
2. Connecting rod pin
3. Brake arm
4. Brake shoe
5. Base plate
6. Base plate pin
7. Thrustor top pin
8. Eldro thruster
9. Spring tube
10. Torque arm
11. Thruster bottom pin

SOP FOR MAINTANACE IN BRAKES:

1. Brake drum wear on the surface shouldn’t exceed 10% of its original
2. Brake lining needs replacement when it wears exceeds at centre ½ and at end 2/3 of its original thickness.
3. Electro magnetic brakes needs frequent adjustment of the shoe gap on the brake drum.
4. Shoe Travel: in the open position (with the electro magnet switched on) is checked with a feeder gauge and should be nearly equal on both sides.
5. When working on brake, loads must be prevented from imparting a torque to the shaft.
6. Disconnect the power supply before working on the motors.
7. The motor must not be operated with open terminal box.
8. When starting three phase brake motors the brake is released and the shaft is axially displaced.
9. Only use flexible coupling.

PRECAUTIONS TO BE TAKEN:

1. The brakes should be used only for the duty cycle specified or ordered.

2. The maximum number of operations per hour is 720. The temperature of the drum during working of brake should not exceed 200 degrees c.

3. The lining should be replaced if their thickness is reduced to less the half the original thickness.

4. The thrustor stroke should be maintained as specified in the name plate of the thrustor.

5. The working of the main spring should correspond to that given in the name plate for the specified torque.

6. Their should be no cracked or damaged parts especially in the spring and bracket.

7. Do not apply oil or grease in brake lining or brake drum.

WEEKLY MAINTANANCE:

Check brake linings for wear, check linkage and adjustments to ensure brake is not rubbing the brake drum during operation. Grease linkage pins. When crane is first out into operation adjust brakes every day of first week.

QUATERLY MAINTANANCE:
All brake assembly will be checked for loose connection, earthing connection, linings for wear, leakages and adjustments to ensure brake is not rubbing the brake drum during operation.