GEMCO Brake Systems Application Guide: Crane trolley braking torque

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GEMCO Brake Systems Application Guide:

Index

Brake summary & key features

Typical description &
applications hydraulic brakes

Typical description &
applications electric brakes

Selecting brake torque based
on motor data

Crane hoist braking torque

Crane trolley braking torque

Selecting brake size based
on load data

Overhauling load torque

Brake thermal capacity

Overhauling loads

Hydraulic brake selection for
bridge cranes

Hydraulic brake torque ratings
& thermal capacities

DC magnetic shoe brake torque
ratings & thermal capacities

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Brake Systems Application Guide

CRANE TROLLEY BRAKING TORQUE
Crane trolley brakes are typically sized with a torque rating less than the motor's full load torque (service factor less than 1.0) to provide a longer stopping time or a "soft stop." Overhead crane trolley brakes are minimized to prevent sway of the hook and load. Typical service factor is 50% for "soft stopping."

SELECTING BRAKE SIZE BASED ON LOAD DATA
For applications where high inertial loads exist or where a specific stopping time or distance is required, the brake should be selected based on the total inertia of the load. Total system inertia reflected to the brake shaft can be expressed as follows:

	WK_T²	=	WK_B²+ WK_M²+ WK_L²
where:	WK_T²	=	Total reflected inertia to brake (lb-ft²)
	WK_B²	=	Inertia of brake wheel (lb-ft²)
	WK_M²	=	Inertia of motor rotor (lb-ft²)
	WK_L²	=	Equivalent inertia of load reflected to brake shaft (lb-ft²)

The following formulas apply when calculating inertia of systems with different rotational speeds or linear moving loads to brake shaft speeds.

Rotary Motion:

	WK_b²	=	WK_L² (N_L/ N_B)²
where:	WK_b²	=	Inertia of rotation load reflected to brake shaft (lb-ft²)
	WK_L²	=	Inertia of rotating load (lb-ft²)
	N_L	=	Shaft speed at load (RPM)
	N_B	=	Shaft speed at brake (RPM)

Horizontal Linear Motion:

where:	WK_W²	=	Equivalent inertia of moving load reflected to brake shaft (lb-ft²)
	W	=	Weight of linear load (lb)
	V	=	Linear velocity of load (ft/mm)
	N_B	=	Shaft speed at brake (RPM)

With the total system inertia calculated, the required average dynamic torque for a desired stopping time can be calculated using the following formula:

where:	T_d	=	Average dynamic braking torque (lb-ft)
	WK_T²	=	Total inertia reflected to brake (lb-ft²)
	N_B	=	Shaft speed at brake (RPM)
	t	=	Desired stopping time (sec.)
	308	=	Constant

To determine stopping time for a given brake torque this formula can be rewritten as follows:

For some brake styles the time required until the brake lining makes contact with the wheel may be significant. Time required to stop is then as follows:

where:

t₁

= Time between signal and moment when brake torque is
actually applied (sec.)

For linear applications, the dynamic braking torque can be calculated directly using the following formula:

where:	T_d	=	Average dynamic braking torque (lb-ft)
	W	=	Total weight of linear moving load (lb.)
	V	=	Linear velocity of load (ft/sec.)
	g	=	Gravitational acceleration constant (32.2 ft/sec²)
	t	=	Desired stopping time (sec.)
	r	=	Length of movement arm or wheel radius (ft.)

This formula is applicable on crane trolley or crane bridge brakes.