Material Handling Overhead Cranes Related

Material Handling Overhead Cranes Related

 

Material handling engineering technology is one of the weakest and most urgent fields in modern industry, but it is also one of the most potential and promising fields.

 

Material handling machinery usually includes six categories of products: lifting machinery, transportation machinery, loading and unloading machinery, storage machinery, industrial handling vehicles and hydraulic machinery.

 

In my country, the material handling machinery is used to be called lifting and transporting machinery. Due to the characteristics of various types, strong functions, and large functions, lifting machinery plays a leading role in material handling machinery, and it is also the earliest material handling machinery that uses weighing technology.

 

1. Application History of Weighing Technology in Hoisting Machinery

 

Hoisting machinery is a handling equipment that lifts, lowers and moves materials horizontally in intermittent operations. In order to make the hoisting machinery complete the weighing of the suspended materials while performing operations, people have the idea and desire to assemble a weighing device on the hoisting machinery.

 

2. Application Status of Weighing Technology in Hoisting Machinery

 

With the breakthrough of digital technology, especially the advancement of electronic weighing technology, the development of mechanization, automation, integration and intelligence of lifting machinery has been promoted.

 

Due to the continuous expansion of industrial production scale and increasing production efficiency, large-scale, high-speed and specialized hoisting machinery has the performance characteristics of automation, intelligence and informationization.

 

The application of modern weighing technology has enabled all kinds of lifting machinery to directly participate in the loading and unloading, transportation, lifting, sorting, stacking, storage and even distribution of materials in the working environment, and sometimes can directly measure, identify and track materials and management etc.

 

At present, weighing devices used on hoisting machinery can usually be divided into electronic crane scales and special weighing devices according to their functions. There are many related explanations for the widely used electronic crane scales, which will not be elaborated here. The special weighing device mainly refers to the lifting capacity limiter that has been widely used in hoisting machinery.

 

 

3. Weight Limiter

 

Noun Definition
 

The lifting weight limiter is a weighing protection device that prevents the hoisting machinery from being in danger of overloading by detecting the lifting weight. It is also called a crane overload limiter or a crane load limiter.

 

"Safety Regulations for Lifting Machinery"

 

GB6067-85 "Safety Regulations for Hoisting Machinery" stipulates that bridge cranes larger than 20t and gantry cranes larger than 10t should be installed with overload limiters;

 

Bridge and gantry cranes of other tonnages and electric hoist single-girder or double-girder cranes should be equipped with overload limiters.

 

Composition of lifting capacity limiter

 

The lifting capacity limiter is generally composed of two parts: a resistance strain gauge load cell and a weighing control instrument. The weighing sensor is used to detect the lifting weight; the weighing control instrument judges according to the lifting weight and outputs the corresponding state control signal.

 

Structural features

 

The biggest feature of the lifting capacity limiter is that it is effectively combined with the specific structure of the hoisting machinery to ensure that the load cell and weighing

 

The use of control instruments does not undermine the safety of the crane. At the same time, it should meet the functional requirements of reliable performance, convenient maintenance and high measurement accuracy.

 

According to the specific structure of the electric hoist single-girder or double-girder crane, the lifting capacity limiter usually adopts a plate ring type or a rope type load cell, and the installation position is at the fixed end of the wire rope; the weighing control instrument is usually installed in the driver's cab or Control buttons stand above.

 

According to the specific structure of the bridge and gantry cranes, the lifting capacity limiter is usually installed under the bearing seat of the crane drum with a double shear beam bridge load cell or installed on the fixed pulley shaft of the crane with a shaft load cell ; Weighing control instrument is usually installed in the driver's cab.

 

 

5. The main technical parameters
 

Scope of application: various types of cranes ranging from 0.5 to 500 tons;
Comprehensive error: ≤±5%;
Display error: ≤±3%;
Action error: ≤±3%;

 

Alarm point setting:
Pre-alarm point: 90% of the rated lifting capacity;
Delayed alarm point: 105% of the rated lifting capacity;
Immediate alarm point: 130% of the rated lifting capacity;
 

Delayed alarm time: 1-2 seconds;
Sensor overload capacity: 1.5 times;
Operating environment conditions: -10℃～+50℃ 90%RH;
Power supply voltage: 380V-15%(+10%) 50HZ
Relay contact capacity: AC380V 2A;
Sensor protection level: IP65;
Electrical control box protection grade: IP42.

 

 

6. Working Principle

 

The load cell detects the lifting weight, and the output signal is amplified by the amplifier. The amplified signal is sent to the weighing control instrument.

 

The weighing control instrument compares and judges the weight signal with the three reference weight signal settings of "pre-alarm", "delayed alarm and control" and "immediate alarm and control", and outputs the corresponding state control signal.

 

The three reference weight signal settings are respectively set at 90%, 105% and 130% of the rated load. When the weight of the hoisted load reaches 90% of the rated load, the weighing control instrument makes the buzzer sound intermittently.

 

At the moment when the crane is lifted, due to the effect of the lifting acceleration force, a temporary impact load phenomenon will be generated. In order to avoid the instantaneous false overload caused by the impact load during hoisting, the weighing control instrument has a time-delay discrimination function. At the end of the 1-2 second delay, if the overload phenomenon still exists, it is judged to be a real overload, and the weighing control instrument immediately outputs a signal to cut off the main lifting circuit of the crane, and the buzzer keeps beeping at the same time.

 

The delay of the overload signal is judged within a certain overload range. If the overload is greater than 130% of the rated load, whether it is the actual overload or the dynamic overload caused by the impact load, the weighing control instrument will output a signal to cut off the main lifting circuit of the crane, and at the same time send out an audible and visual alarm, that is, an immediate alarm control.

 

Since the output signal of the weighing control instrument only cuts off the hoisting main circuit of the crane, it will not affect the actions of the hoisting circuit for lowering and other mechanisms.