Braking Systems: Hoist Brakes Overview

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Questions and Answers

What effect does each 90° turn of the brake end cap have on the air gap?

Increases the air gap by approximately 0.5mm

Has no effect on the air gap

Increases the stroke length by 0.5mm

Decreases the air gap by approximately 0.5mm (correct)

Why should the brake be checked daily during the first week of operation?

To ensure compliance with operating regulations

To monitor the efficiency of the brake motor

To prevent overheating of the brake components

Because the brake lining may wear unequally until bedded in (correct)

The maximum path of rotor displacement due to wear of the brake linings is how much?

2.0mm

3.5mm (correct)

1.5mm

4.0mm

What occurs if a key shear or coupling fails in the brake system?

The load would fall (C) Signup and view all the answers

Where is the hoist brake ideally positioned?

As near to the hoist drum as possible (A) Signup and view all the answers

What is the recommended air gap maintenance limit for the brake system?

Approximately 1-1.5mm (B) Signup and view all the answers

What is the function of the torque springs in the brake system when the power is OFF?

To force the armature plate against the brake rotor and linings (B) Signup and view all the answers

What should be done to adjust the brake as the lining wears?

Remove shims (A) Signup and view all the answers

What does the sliding rotor principle utilize in an electric motor?

A conical rotor with stator windings (C) Signup and view all the answers

What happens if brake adjustment is not carried out according to instructions?

It can cause erratic motor operation (A) Signup and view all the answers

What should the air gap between the rotor and stator typically be?

0.5mm to 1.5mm (D) Signup and view all the answers

To check if brake adjustment is necessary, what should be measured?

The distance between the rotor shaft and brake end cap (A) Signup and view all the answers

What is the consequence of an increased air gap due to brake lining wear?

Insufficient magnetic force to move the rotor (B) Signup and view all the answers

Which component of force pulls the rotor into the windings?

Horizontal component (D) Signup and view all the answers

What is the main purpose of hoist brakes as per BS EN 14492-2?

To avoid unintended movements and hold the load (D) Signup and view all the answers

What should be done if the air gap exceeds 3mm?

Perform brake adjustment according to manufacturer's instructions (D) Signup and view all the answers

What is the primary design feature of the motor that uses the sliding rotor principle?

Conical rotor with angular magnetic field (C) Signup and view all the answers

In which situation must the brakes engage automatically?

When the control device returns to its neutral position (B) Signup and view all the answers

What should electric hoists prevent during a phase failure?

The load from lowering uncontrollably (D) Signup and view all the answers

What is 'single phasing'?

Loss of one phase in a three-phase system (B) Signup and view all the answers

Why are phase loss protection devices important?

To disconnect equipment when phase loss is detected (C) Signup and view all the answers

Which of the following is NOT a potential cause of a phase loss?

Increased load on hoist (C) Signup and view all the answers

What is one of the requirements for the brakes in case of a 3 phase motor?

They must engage if two phases are interrupted (A) Signup and view all the answers

How can undetected phase loss affect equipment?

It can lead to unsafe conditions and equipment failure (D) Signup and view all the answers

What is the primary function of the flywheel fitted to the motor shaft in soft travel braking?

To allow smoother acceleration and deceleration (D) Signup and view all the answers

Which component of the thrustor brake develops pressure to lift the load?

Centrifugal pump and impeller (A) Signup and view all the answers

What initiates the release of the brake shoes in a thrustor brake system?

Introduction of a 3-phase mains voltage supply (C) Signup and view all the answers

What type of motor typically drives the centrifugal pump in a thrustor brake?

AC motor (C) Signup and view all the answers

What material is used for the shoes in a thrustor brake?

High grade cast iron with linings (C) Signup and view all the answers

What is the main benefit of using compression springs in the thrustor brake?

To provide uniform pressure on the brake shoes (B) Signup and view all the answers

For checking the thrustor, what should always be referred to for accurate data?

Original Equipment Manufacturer (OEM) instructions (D) Signup and view all the answers

How is the braking pressure transmitted to the shoes in a thrustor brake?

Via a lever/tie rod mechanism (C) Signup and view all the answers

What is the primary function of the air gap in the brake system?

To maintain a specific distance between the rotor and coil (C) Signup and view all the answers

Which characteristic distinguishes the hoist brake from travel brakes?

It is a spring applied brake (B) Signup and view all the answers

Why is a fail-safe operation important in the hoist brake system?

To prevent the load from falling during power loss (D) Signup and view all the answers

What is the function of the detachable hand release mechanism?

To enable manual lowering of the load during power failure (C) Signup and view all the answers

What is the key feature of the braking characteristics for travel brakes?

They should avoid excessive braking under no load (C) Signup and view all the answers

How is the torque of the hoist brake initially set?

Pre-set during factory assembly and requires no further adjustment (B) Signup and view all the answers

What type of coil configuration is described for the hoist brake?

Stator rotor type (D) Signup and view all the answers

What is crucial to check regarding the brake rotor’s operation?

The air gap must meet manufacturer requirements (B) Signup and view all the answers

Study Notes

Hoist Brakes

BS EN 14492-2 outlines specifications for brakes used in hoisting and lowering operations.
Hoist designs must enable controlled deceleration, load retention, and prevention of unintended movements.
Brakes must automatically engage in specific situations:
- Control device returns to neutral position
- Emergency stop is activated
- External power supply is interrupted
- Power supply to the motor is interrupted in a three-phase motor when two phases fail

Failure of Power Supply

Electric hoists must prevent uncontrolled load descent during phase failures.
Phase loss typically results from blown fuses, thermal overload, broken wires, or mechanical issues.
Phase loss protection devices are cost-effective solutions that disconnect equipment when a phase is lost.

Conical Rotor Motor

Utilizes a uniquely designed conical rotor and stator windings.
The magnetic field in the motor produces two perpendicular force components: radial (rotates the rotor) and horizontal (pulls rotor into windings).

Brake Adjustment

Must follow manufacturer's instructions to ensure optimal motor performance.
Incorrect adjustments can lead to erratic motor operations due to increased air gap from worn brake linings.
Air gap should typically measure between 0.5mm and 1.5mm; must not exceed 3mm.
Daily checks recommended during the first week of operation or after lining replacement.

Adjustment Process

To adjust brakes, remove screws securing the brake end cap.
Adjusting the threaded end cap decreases air gap by approximately 0.5mm per 90° turn.
Frequent checks of rotor movement in relation to the brake lining are essential for effective braking.

Parallel Rotor Principle

Demonstrates brake function in power OFF (engaged) and power ON (released) positions.
Ensures the armature plate is pressed against the brake rotor to prevent motor shaft movement when powered off.

DC Electromagnet Brakes

Features a single disc brake that’s electro-magnetic, spring-applied with a DC coil release.
Fixed directly to the gear case or motor frame, it operates on the primary drive shaft.
Designed for easy safety checks and independent powering from motor supply for fail-safe operation during power interruptions.

Travel Brakes

Can be of disc or drum type, requiring unique characteristics differing from hoist brakes.
Braking characteristics must be finely tuned to prevent excessive braking under no load and maintain reasonable braking capacity when under maximum load.

Disc Travel Brake

Designed for soft travel braking, with reduced brake engagement and a flywheel fitted to the motor shaft for smoother acceleration and deceleration.

Thrustor Brake

Suited for heavy-duty applications, typically operates electro-hydraulically.
Utilizes a centrifugal pump and impeller to develop pressure for brake operation, influenced by motor speed.

Main Components of the Thrustor Brake

Consists of a rigid welded base, self-aligning and easily removable brake shoes, and a robust lever system for reliable braking.
Compression springs are crucial for applying pressure on the brake shoes, ensuring smooth and effective operation.
Brake release occurs by energizing a three-phase mains supply that overcomes spring force.

Checking the Thrustor

Always consult OEM instructions for correct operational parameters and maintenance guidelines to ensure safety and effectiveness during inspections.

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Description

This quiz focuses on the requirements for brakes used in hoisting and lowering movements as outlined by BS EN 14492-2. It highlights the design features that ensure load holding, deceleration of movements, and prevention of unintended movements. Test your knowledge on the critical aspects of hoist braking systems and their safety considerations.