Discussion on the Safety Performance of the Crane Brakes

1. Crane Brake Out of Control Causing Casualties

Mar 9^th, 2003. Dahua Hydropower Plant in construction work contracted Zuojiang plant maintenance works, press workplan turn reincarnation installation. Held classes before the meeting, conduct operations before working arrangements and safety technical tests, relevant staff is ready to begin work. Good runner cone in the lifting, try hanging the overall runner after the same, 10:28 began to machine pit lifting, 10:30 when turning crane to the machine pit and decentralization approximately 3m, the bridge is suddenly out of control, turning accelerate whereabouts. In this process, the bridge machine brakes burst, gear box gear crack, the rope pull off, turning off to the machine pit.

Preliminary cause of the accident analysis for the bridge machine when lifting off the file was decentralized, causing the bridge machine out of control.

2. Crane Brake Unreasonable Manner

It is understood that the vast majority of crane brakes, all wheel brakes, gate or braking when needed by the electromagnet suction, discharge or pump start and stop, the braking force of the spring pressed or released. And now when lifting work, especially when lifting large weights, often with a number of staff in charge of guardianship on the crane, which aims at lifting off stalls occur, the slip hook accident, have to use a crowbar and other tools. In the “3.9” incident, the staff responsible for monitoring the bridge machine has taken such measures, but did not achieve the appropriate role, but it crack occurred because the brake, brake debris flying out of major accidents resulting in casualties guardianship. Why pay a painful price casualties failed to reduce the extent of damage accident it?

First, the mechanical work of staff responsible for monitoring the use of crowbars and other tools to increase brake shoe pressure on the brake drum, so as to achieve the purpose of the working methods of the emergency brake is debatable. When the crane lifting large weights yet occurred off the file, slide the hook accident, starter motor, drive shaft with the acceleration of the weight of the decline will produce runaway speed, brake wheel drive shaft also will produce a powerful radial.  Therefore, I think the staff use crowbars and other tools to increase brake shoe pressure on the brake drum, so as to achieve the purpose of the working methods of the emergency brake is not desirable. Secondly, the brake on the transmission shaft provided only inadequate. So how to reduce accident losses arising from off the file crane because of it? I believe that the ship lift the braking mode can learn from.

3. Improvement of the safety performance of the crane brakes

In Yantan vertical ship lift into the water brake mode as an example, its weight in ship compartment 1430t, with heavy concrete weight 1100t, main hoist brake in the form of hydraulic disc brakes, including two sets of operating brake and safety brake system. Shiplift when action is required, safety brakes each first gate, gate emperor in place to enhance the motor output torque up to a certain operating brake gate, ship lift starts running; if necessary stop working with the main hoist motor brake first. The whole process reliable and secure, reliable verified in running the installation and commissioning of ship lift and in the past few years.

3.1 Hydraulic disc brakes

And hub brakes compared to hydraulic disc brakes with braking principle is simple, reliable, and fast closing response characteristic.

3.2 Increase safety brake

To increase security here brake means a brake set with reference to the vertical ship lift, part of the increase in the spool brake disc brake disc and placed in the appropriate array proper position, so that they become completely independent set of safety brake.

1. The custodial staff of human liberation operation, reducing the risk of being hurt;
2. To enhance the safety and reliability of the crane operation, when the crane accident can effectively prevent the expansion of the accident. Popular, that is to happen if the crane off the file, slide the hook accidents, even in the starter motor, drive shaft, brake work, the case of the gear box are damaged, the safety brake drum parts can be effectively closing the brake, stop hanging.
3. Required by the gearbox on some special overhead cranes to switch high and low profile, simply closing brake safety brake, ensure that the reel is to hold fast to the safety brake, make the appropriate safety brake to prevent.

3.3 Control System Requirements

Request, if the safety brake is also frequent moves, it will affect the lifting operation requirements, therefore, the control system should be designed to meet the requirements of the following operating conditions:

1. Normal operation. Before each crane start, crane driver presses the start button, automatic safety brake gate after gate signal to the console in place to allow the crane to work. During the crane work, elevating brake work by the operating brake is completed, the safety brake and the normally open. End of the lifting operation, operating brake switch on the brake, the crane driver after checking the same, leaving the operation of the stage, cut off the crane power supply, security lock brake closing, end of the work;
2. Cranes working condition when the failure occurred. When a fault occurs, press the emergency brake button crane driver, operating brake immediately closing the brake, safety brake closing delay 2 ~ 5s brake to prevent accidents;
3. Crane working condition occurs when damage accidents. When the accident occurred, according to the emergency brake button crane driver, crane control power supply is disconnected, the operating brake and safety brake immediately lost power switch on the brake, to prevent accidents;
4. In exceptional circumstances (such as crane suddenly lost power systems), operating brake and safety brake should also make emergency brake closing. Or the safety brake is set to normally open safety brakes, safety brakes usually remain fully open state, the crane lifting brake work by the operating brake is completed, the safety brake as a protective reserve. Time when the crane accident or malfunction and operating brake needs an overhaul, loosen the brake switch work upshift and downshift, the safety brake was put into use.

Other conditions can also be requested, by setting the electrical part and a separate adjustment.