Electromagnetic brakes maintenance
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Inspecting hoisting brakes for proper functioning is a key element of a proper periodic inspection and important to ensure that the load does not drop unexpectedly creating a potentially fatal safety hazard.
 
Hoists must have two braking functions, Holding and Controlled Lowering. The holding brake maintains the load in a stationary position when the load is suspended and no power is applied to the motor. The controlled braking function must ensure that the load does not overhaul or overspeed the motor when the load is being lowered.
 
Many older style hoists use a friction type brake for the holding brake and a mechanical (Westin Style or other) brake for the controlled lowering. Newer style hoists often use the friction brake for both the holding and controlled lowering and provide a brake that is capable of 150% of full load hoisting torque. There are other braking setups employing newer or older technologies, however virtually all are based off a friction type brake for the holding the load.
 
The following should be checked during routine maintenance:
  • Brake shoe lining wear
  • Drum wear and corrosion
  • Spring tensioner for wear and corrosion
  • Spring adjustment bolts for wear and corrosion
  • Electro magnet foe correct adjustment
  • Lubrication of linkages
  • Note that there should be no oil or grease on the brake shoe linings or the drum

 

Brake failure and cause:

1. The brake wheel cannot be stopped (weight slides down) Cause of failure:

  • The hinge of the lever is stuck.

  • The brake wheel and friction plate have oil on them.

  • Solenoid core does not have enough travel.

  • Severe wear on brake wheel or friction plate.

  • Loose and damaged mainspring.

  • Lose lock nut, loose tie rod.

  • The hydraulic push brake impeller does not rotate properly.

Remedy:

  • Clear the jam fault

  • Oil Cleaning

  • Adjusting the Brake

  • Replacing Friction Blades

  • Replacing Friction Blades

  • Tighten the lock nut.

  • Overhaul of propulsion mechanism and electrical parts

2. Brake does not release Cause of failure.

  • Burned out solenoid coil

  • Disconnect the wire to the solenoid

  • The friction pad sticks to the brake wheel.

  • The movable hinge is stuck

  • Excessive force in the mainspring or too much counterweight

  • Bend the brake top lever, does not push the electromagnet (on the hydraulic push rod brake)

  • Improper use of fluids

  • Impeller jamming

  • Voltage is less than 85% of rated voltage, electromagnet suction force is insufficient

Exclusion Method:

  • Replacement

  • Connect the wires

  • Cleaning with kerosene

  • Eliminate jamming, lubrication

  • Adjusting the mainspring force

  • Top bar straightening or replacing the top bar.

  • Changing the fluid according to the working environment temperature

  • Adjusting the actuator mechanism and checking the electrical parts

  • Identify and troubleshoot the causes of voltage drop

3. The brake is hot, the friction plate smells burnt and wears out quickly. Cause of failure.

  • The brake shoes are not evenly and completely disengaged from the brake wheel after the brake is released, resulting in friction.

  • The gap between the two brake shoes and the brake wheel is uneven or too small.

  • Short-stroke brake auxiliary spring is damaged or bent.

  • The working surface of the brake wheel is rough.

Elimination method:

  • Adjustment gap

  • Replace or repair the auxiliary spring

  • Turn the surface of the brake wheel as required

4. The brake easily leaves the adjustment position, and the braking torque is not stable enough. Cause of failure

  • Adjustment nut and back nut not tightened

  • Thread damage

Exclusion Method:

  • Tighten the nut

  • Replacement

5. Electromagnet is hot or loud. Cause of failure.

  • Excessive mainspring force

  • The lever system is jammed

  • The armature and the core are not correctly positioned.

Exclusion Method:

  • Adjust to the right size

  • Eliminate causes of seizure, lubrication

  • Scrape the laminated surface