Cranes can be seen at any construction site. It is there that they extend their powerful paws. Movable machines, like the crane shown in the picture, they can extend their hydraulically operated telescopic boom up to 130 feet and lift 45 tons of construction materials with ease.
By removing the moving part of the boom inside, such a crane is made the size of an ordinary truck and simply goes further where it is needed. The winch mechanism controls the cable lowered from the boom. A load is attached to this cable with a hook. When the winch begins to wind the cable, the load rises. The system of multiple pulleys and cables between the hook and the boom reduces the effort that must be applied to the winch in order to lift the load.
To balance a heavy load
When cranes lift heavy loads, they rely on cantilever beams or stabilizers to keep from tipping over. Each such beam acts as the fulcrum of the balance beam. With its help, the load being lifted is balanced by the weight of the crane itself. Retractable support beam legs are made of steel, aluminum or nylon. Each leg can be individually raised and lowered until the crane is in the desired position.
Lowering and lowering the boom
Two hydraulic cylinders control the movement of the boom. One cylinder raises and lowers the boom, while the other lengthens and shortens it.
Hook, rope and truck crane block
Block with a hook with a lifting capacity of 20 tons
7 pass block
Watching the crane. On-board computers monitor the operation of the crane: the weight of the load, the angle of elevation and length of the boom, the angle of the crane itself and, in some models, even the speed of the wind.
Truck Crane Load Moment Diagram
The upper diagram shows that the more the boom is extended in the horizontal direction, the less load the crane can carry without the risk of tipping over.
Many years ago, lifting equipment was one of the main achievements of technology. But today, when advanced technologies and modern materials are being actively introduced, it is gradually becoming more traditional. Currently, there are a large number of companies that supply both various lifting equipment and a wide range of construction and industrial equipment.
Lifting equipment: terminology
The term "lift" today is understood as a special technique that is able to function continuously or intermittently. Equipment such as cranes, elevators, etc., has the main purpose - the movement of various loads by a carrier moving along a high-strength vertical guide or along rail tracks.
Lifting equipment today is represented by several varieties. The most common and most frequently used in almost all industrial areas are cargo lifts. In them, the device for moving the load is attached to the envelope of the winch, wound on a drum, or a traction sheave. Load-lifting cranes work mainly on electric drives, as well as on hydraulic ones.
Jib cranes
In the construction industry, console lifts are the most popular and in demand, which became possible due to the simplicity of their design and low cost. They are made in the form of mast racks without railings, relative to which platforms are placed in a cantilevered manner.
The safe operation of cranes depends largely on the type chosen correctly. It is worth noting that console-type equipment is divided into:
- Column crane. It is a stationary column along which cargo is lifted; it is widely used in machine-building production.
- Wall-mounted crane. It differs from the first option in that it consists of a wall truss, along which the trolley moves. Installation method - stationary. The main advantage is the ability to work in small spaces. As a rule, this type of crane is installed in order to reduce the load on bridge hoists.
Bridge electric mine crane
There are also mine cranes, which, unlike cantilever cranes, have a special device for protecting people, in which lifting cabins or platforms move along the guide. Basically, this technique is used in the mining industry. Overhead cranes are designed for lowering / lifting large-sized objects. Thanks to a certain method of delivering goods, this type of equipment can significantly reduce costs, especially in comparison with an inclined shaft and a motor ramp. Compliance with safety rules when working with such cranes allows you to minimize the risk. The main advantage of this type of equipment is the fast and relatively safe transportation of heavy loads.
Gantry cranes
This equipment moves along special paths, the number of which can vary from 1 to 3. The width of the knees is 6 m, 10.5 m, 15.3 m. The length of the boom can reach up to 100 meters. This type of crane is widely used in the shipbuilding industry, both in sea and river ports. Also, this equipment is used in floating docks and shipyards. Their specialization is quite narrow, it is used only for work in open areas.
Subdivided into subspecies:
- mounting (KPM) - carrying capacity up to 300 tons;
- reloading (checkpoint) - designed for weight from 5 to 40 tons;
- dock (efficiency) - is used to work with cargo, the weight of which does not exceed 30 tons.
The design of the equipment is a portal with a swivel boom, which moves along the crane runways. Special hooks and grabs are used to lift loads.
Operation of cranes
Before starting work on cranes, it is necessary to study the safety rules. All companies provide training. Some points may vary depending on the type of equipment, but the general essence of this documentation is the following points:
- work with electrical equipment;
- study and principle of operation of the main components of the crane (trolley, gallery, etc.);
- control method;
- braking coefficient, etc.
Features of choice
There are a number of important factors to consider when choosing a material handling hoist for construction. This is the method of fastening, load capacity and many others. Additionally, various load-handling devices and devices are also used. In addition, you should take into account the frequency of lifting loads and calculate the approximate number of turns on and off the crane. Using the obtained data, it is possible to choose a lift taking into account the weight of the transported cargo. It is important to know the rules for the operation of cranes and their design features. This will secure and greatly facilitate the process of moving heavy objects.
) is a self-propelled hoist with a side boom for lifting, transporting and installing pipes. The base machine for a pipe-laying crane is usually a crawler tractor.
Picture 1 - Pipe-laying crane
- truck crane mounted on a truck chassis;
- pneumatic wheel crane mounted on a pneumatic wheel chassis;
- short-base crane mounted on a short-base chassis;
- a crane on a special chassis mounted on a special automobile-type chassis;
- crawler crane mounted on a crawler undercarriage.
Picture 10 - Jib crane
Figure 11 - Classification of jib cranes by type of undercarriage: a) truck crane; b) crawler crane; c) a crane on a special chassis; d) pneumatic wheel crane; 1 - arrow; 2 – hydraulic cylinder; 3 - platform; 4 - turntable; 5 - running frame; 6 - outrigger; 7 - tower-boom equipment; 8 - goose; 9 - drawers
All jib cranes have their own source of energy (power plant) - a diesel engine, so they can work where there is no electricity.
The boom of such cranes is hinged on a turntable, which is placed on the undercarriage with the help of a turntable. Crane mechanisms are placed on the turntable: the mechanism for lifting the load, the mechanism for changing the departure, the turning mechanism. Heavy duty cranes can be equipped with main and auxiliary lifting mechanisms.
Automobile cranes, cranes on a special chassis, short-base cranes are the most mobile, they move along roads in a transport position, but can only lift cargo on outriggers.
Caterpillar and pneumatic wheeled cranes can move around the construction site with a load on the hook, while the lifting capacity of pneumatic wheeled cranes is approximately 2 times less than on outriggers.
Jib cranes are distinguished by:
- according to the execution of the boom equipment:
- with flexible suspension of boom equipment;
- with a rigid suspension of boom equipment.
- by type of drive mechanisms:
- with electric drive mechanisms;
- with hydraulic drive mechanisms.
The jib of flex-suspension cranes is held and tilted by ropes. In this case, a lattice boom is used. To increase the service area, the boom is supplied with a jib.
The boom of rigid suspension cranes is held and tilted by hydraulic cylinders. In this case, a telescopic boom is used, consisting of a main section and two to four retractable sections. Changing the reach of cranes with a rigid suspension is carried out by changing the angle of the boom, as well as by extending the boom sections (telescope).
Caterpillar and pneumatic wheel cranes usually have an electric drive of mechanisms and flexible suspension of boom equipment. The hydraulic drive of the mechanisms and the rigid suspension of the boom equipment have truck cranes, short-base cranes and cranes on a special truck-type chassis.
Picture 13 - Jib crane
Figure 17 - Main parameters of cranes
All models of general purpose self-propelled jib cranes manufactured in the Russian Federation are assigned an index, the block diagram of which is shown in. The first two letters of the KS index designate a self-propelled jib crane; the four main digits of the index sequentially indicate: the size group (load capacity in tons), the type of undercarriage, the method of suspension of the boom equipment and the serial number of this crane model.
Ten size groups cranes are indicated respectively by the numbers 1 ... 10.
Chassis type indicated by the numbers 1 ... 9, and the number 1 indicates a caterpillar device (G), 2 - widened caterpillar (GU), 3 - pneumatic wheel (P), 4 - special automobile-type chassis (Sh), 5 - chassis of a standard truck (A) , 6 - chassis of a serial tractor (Tr), 7 - trailed undercarriage (Pr), 8 and 9 - reserve.
Boom equipment suspension method indicated by the numbers 6 or 7, indicating respectively a flexible or rigid suspension.
The last digit of the index (numbers 1…9) denotes serial number of the model crane.
The additional letter following the digital index (A, B, C, etc.) indicates ordinal modernization of this crane, subsequent letters (HL, T or TV) - type of special climatic version machines: HL - northern, T - tropical, TV - for work in the humid tropics.
For example, index KS-4561АХЛ designates: a self-propelled jib crane, the fourth size group (with a lifting capacity of 16 tons), on a standard truck chassis, with a flexible suspension of boom equipment, the first model that has undergone the first modernization, in the northern version.
5. How does the lifting capacity of the crane depend on the outreach?
The lifting capacity of boom-type cranes depends on the reach inversely proportionally. The crane has the maximum load capacity at the smallest reach, and with an increase in the reach, its load capacity decreases. When working with a crane, it is important to understand this relationship in order to avoid overloading the crane.
For a crane, the load characteristic is the most important. It is the load characteristic that clearly demonstrates the ability of the crane to lift the load of the required mass. Passport lifting capacity is the value of the mass of cargo lifted by a crane in the most favorable conditions. For jib cranes, for example, such a condition is the minimum reach of the boom. The load cannot adjust to the crane and can often be located anywhere within the working area. So, to represent the real potential of a lifting machine, some kind of visualization tool is needed. Such a tool is the load characteristic.
Load characteristic- this is a graph, along the ordinate axis of which the load capacity of the crane is plotted, and along the abscissa axis - the value of the parameter that affects this load capacity.
Consider the load characteristics of the DEK-251 crawler crane (), which has a maximum lifting capacity of 25 tons at an outreach of 5 m. With an increase in the outreach, the crane’s lifting capacity decreases, therefore, with the largest outreach for this boom equipment (14 m), the crane can lift only 4 tons.
Figure 19 - Load characteristics of the crawler crane DEK-251
6. Forces acting on the crane
The crane is subject to:
- cargo weight,
- inertia force, F in, which occurs when the speed of lifting and lowering the load changes.
The slope of the work platform also reduces the stability of the crane. Overturning forces create overturning moment relative to the rollover edge (). The overturning moment created by the load is equal to the product of the mass of the load Q on the shoulder b: M def = Q × b. Obviously, with an increase in overhang, the leverage increases. b consequently, the overturning moment increases.
7. What keeps the crane from tipping over?
The jib crane is a free-standing machine that is kept from tipping over by its own weight. G. The mass of the crane creates a restoring moment equal to the product of the mass of the crane G on the shoulder A ().
The stability of the crane is increased by increasing the mass of the crane with a counterweight, which is mounted at the rear of the turntable.
The second way to increase the stability of the jib crane is to install outriggers. The crane places outriggers, as a person spreads his legs wider to increase stability, while increasing the shoulder A, respectively, the shoulder decreases b.
8. What causes cranes to lose stability and tip over?
Possible causes of overturning cranes:
- the lifting capacity of the crane is exceeded at the given reach;
- the rules for installing a jib crane were violated (outriggers were not installed, installation on freshly poured soil, etc.);
- rail crane way is faulty;
- the crane operates at a wind speed that exceeds that indicated in its passport;
- tower or other rail crane is not installed on anti-theft devices.
All cranes are designed with a margin of stability, so the overturning of the crane is always the result of a gross violation of safety rules.
The overturning of the crane can occur due to the fault of the slinger in the event of slinging a load that exceeds the lifting capacity of the crane at a given reach.
9. How is the rail crane way arranged?
For tower, gantry and other rail cranes, a rail track is laid on a prepared subgrade with drainage grooves. The crane track () consists of a ballast layer, wooden or reinforced concrete sleepers and rails. The rails are attached to wooden sleepers with crutches or travel screws, and to reinforced concrete sleepers - with bolts and nuts. At the joints, the rails are connected by overlays.
Figure 21 - Crane track: 1 - groove; 2 - ballast layer; 3 - sleeper; 4 - rail; 5 - ruler; 6 - dead end stop; 7 - overlay; 8 - jumper
Dead ends are installed at the ends of the track to prevent the crane from derailing. Switching bars are fixed in front of dead ends, designed to automatically stop the mechanism of movement of the crane.
Crane operation is not allowed with the following malfunctions of the crane tracks:
- cracks and punctures of the rail;
- absence, destruction or incomplete set of fasteners;
- fracture, transverse cracks, rot in wooden sleepers;
- solid girdle cracks, exposure of reinforcement in reinforced concrete sleepers;
- absence or malfunction of dead-end stops;
- faulty grounding of the crane track.
10. What is protective earthing? How does it protect a person?
Protective earth- this is a deliberate connection of the body of the electrical installation with a grounding device. Grounding is necessary to protect the operating personnel, since in the event of a violation of the insulation of parts of the electrical installation that are energized, the body of the electrical installation is also energized.
11. How is the crane earthed?
At rail cranes, the crane track () is grounded. All rails are connected with steel jumpers by welding. The crane way is connected to the grounding conductors by at least two grounding conductors. Grounding conductors are steel pipes or corners driven into the ground.
Electric jib cranes must be grounded when connected to an external electrical network. To do this, the neutral wire of the supply cable is connected to the crane body.
In the event of a malfunction or lack of grounding, the slinger, touching any part of the crane, may be under the influence of an electric current.
In the event of a fire on the crane, the slinger must turn off the power supply. It is also necessary to de-energize the electrical equipment when a person gets under the influence of electric current.
The knife switch (circuit breaker) is located at the point where the crane is connected to the electrical network.
12. What devices and safety devices ensure the safety of cranes?
Crane safety devices and devices include:
- load limiter;
- limiters of working movements for automatic stop of lifting mechanisms of the load-handling body in its extreme upper and lower extreme positions, change of departure, movement of rail cranes and their cargo carts;
- limiters of working movements for automatic shutdown of crane mechanisms at a safe distance from the wires of power lines (installed on jib cranes);
- crane operation parameter recorder;
- coordinate protection to prevent collision with obstacles in cramped working conditions (installed on jib and tower cranes);
- sound signal;
- load capacity indicator corresponding to the reach;
- inclinometer - an indicator of the angle of inclination of the crane (installed on jib cranes);
- anemometer - a wind speed indicator that automatically turns on a sound signal when a wind speed is reached that is dangerous for the operation of the crane (installed on tower, portal and gantry cranes);
- anti-theft devices (installed on cranes moving along a crane track in the open air), rail grips and wedge stops are used as anti-theft devices.
All jib-type cranes are equipped with a load limiter (load moment), which automatically turns off the lifting and departure mechanisms.
Shutdown occurs when a load is lifted, the mass of which exceeds the carrying capacity for a given departure:
- more than 15% - for portal cranes and tower cranes with a load moment up to 20 t-m inclusive;
- more than 10% - for jib cranes and tower cranes with a load moment of more than 20 t-m.
Bridge-type cranes are equipped with a load limiter if their overload is possible according to the production technology. The load limiter of such cranes should not allow an overload of more than 25%.
After the load limiter has been triggered, the load can be lowered and the reach reduced.
Modern jib cranes with a rigid suspension of jib equipment have a load capacity indicator, which is located in the crane operator's cab. In this case, the slinger must clarify the lifting capacity of the crane at a given reach from the crane operator.
) is designed to automatically stop the mechanism in the uppermost position of the load gripping body. The limiter is a limit switch, the electrical contacts of which are closed under the weight of a small load. Moving upward, the hook suspension lifts the load, opens the electrical contacts of the limit switch, as a result of which the engine of the lifting mechanism is turned off. The lifting device must stop at a distance of at least 200 mm to the stop. After the automatic stop of the mechanism during lifting, it can be switched on for lowering.
Figure 23 - Load lifting mechanism limiter: 1 - hook suspension; 2 - cargo; 3 - limit switch; 4 - arrow
13. The main components and mechanisms of lifting machines
- engineering and technical worker (ITR) for supervision of the safe operation of cranes;
- Engineer responsible for the maintenance of cranes in good condition;
- person responsible for the safe operation of cranes.
Figure 27 - Specialists responsible for cranes
18. What is the procedure for appointing a person responsible for the safe operation of cranes?
In the workshop, at the construction site or other site of crane work in each shift, a person responsible for the safe performance of work by cranes must be appointed by order from among the foremen, foremen, heads of workshops, sections. In warehouses of materials and other areas of work, warehouse managers and foremen can be appointed as persons responsible for the safe performance of work by cranes, in agreement with the bodies of Rostekhnadzor.
Responsibility for ensuring the safe performance of work with cranes at each work site during each shift should be assigned to only one employee. The names of these persons must be indicated on a sign posted at a permanent work site.
The person responsible for the safe performance of work with cranes is the direct supervisor of the slinger.
19. What are the main responsibilities of the person responsible for the safe operation of cranes?
The person responsible for the safe performance of work with cranes is obliged to:
- organize the conduct of work by cranes in accordance with safety rules, the project for the production of works, technical specifications and technological regulations;
- prevent untrained and uncertified personnel from servicing cranes, determine the required number of slingers, as well as the need to appoint signalmen;
- instruct crane operators and slingers on the safe performance of the work ahead;
- provide slingers with distinctive signs and protective equipment, as well as means and devices for the safe performance of work;
- not allow the use of unmarked, faulty or non-corresponding to the nature and weight of the cargo removable load-handling devices and containers;
- monitor the fulfillment by crane operators and slingers of production instructions, projects for the production of work and technological regulations.
20. What rights does the person responsible for the safe performance of work with cranes have?
The person responsible for the safe performance of work with cranes has the right to:
- suspend slingers and crane operators who violate production instructions from performing work using cranes;
- raise a question before the administration of the enterprise about the punishment of slingers and crane operators who violate production instructions.
21. What is the responsibility of the person responsible for the safe operation of cranes?
The person responsible for the safe performance of work with cranes is responsible in accordance with applicable law:
- for committed violations of the Rules and job description, regardless of whether or not it led to an accident or an accident;
- violation of production instructions by crane operators and slingers;
- issuance of instructions or orders forcing subordinate employees to violate the Rules and production instructions;
- unauthorized resumption of work by cranes that were forcibly stopped by the bodies of Rostekhnadzor and engineering and technical personnel for supervision of the safe operation of hoisting machines;
- failure to take measures to eliminate violations of the Rules and instructions.
Depending on the consequences, the person responsible for the safe operation of cranes may be subject to disciplinary liability (Labor Code), administrative liability (Code of Administrative Offenses) and criminal liability (Criminal Code).
Crane lifting capacity- this is their main characteristic, and it is determined by the maximum weight of the load that it can lift, while maintaining good stability and structural strength. For jib cranes, the maximum lifting capacity corresponds to the smallest reach of the boom - as the reach increases, the lifting capacity decreases. Therefore, for self-propelled cranes, the lifting capacity at the minimum reach is almost several times greater than at the maximum.
To improve the stability of the crane, sites are planned in advance and roads are prepared. It is strictly forbidden to operate a crane on terrain with a slope, even a slight one. If you neglect this requirement, the irreparable may happen, and in this case it will be the least of the troubles. The maximum allowable slope must be indicated in the technical passport. You can increase stability with the help of outriggers.
Also, the carrying capacity is largely determined by the cargo moment - this is the product of the mass of the cargo and the amount of departure in meters. It is measured in tonometers. For example, the load moment of a crane is 16 ton meters. At the smallest outreach, the carrying capacity is one ton, at the smallest - 2, with an outreach of 16 meters, the largest and 8 - the smallest. With these parameters, the load moment will be the same - 2 * 8 and 1 * 16. We get the desired 16 tonometers.
The length of the boom departure is determined by the distance between the center of the axis of the head block and the axis of the heel of the arrow. Hook outreach - the distance between the axis of rotation of the boom, passing vertically through the center of the portal or support trolley and the vertical axis, which goes through the center of gravity of the load and is aligned with the center of the hook cage.
Main parameters of cranes
The main characteristics and parameters of cranes include carrying capacity, boom length, cargo moment, hook lifting height, boom travel angle, departure change time, speed of lowering or lifting the load, speed of rotation, movement, power of the power plant, operating mode and overall dimensions.
But the main parameter is considered to be the load capacity, it is what they pay attention to when they want to buy a crane or rent it. It should be noted that the load capacity is understood not only as the mass of the load being lifted, but also as the mass of the load-handling devices and devices.
It is possible to slightly increase this parameter when using the support or bracing of the arrow. The most common are the following methods of bracing - a brace with several branches and braces, the branches of which are equipped with chain hoists - this ensures the normal rotation of the boom and the possibility of departure. During unmooring, the boom block is somewhat loosened, so that the entire load falls on the moored brace. Thus, it is possible to increase the carrying capacity by one and a half to two times.
A crane is an indispensable assistant in many industries. The need for it arises when it is necessary to move goods vertically or the load is so heavy that it is not possible to remove or load it into a car or railway transport manually.
First, let's look at the GPC chassis.
There are purely narrowly directed cranes. Such as railway. Their main purpose is to load and unload trains. Sometimes they are used to organize warehouses near railway tracks. In rare cases, to eliminate blockages and build all the same railway tracks.
Stationary cranes. They are used by large enterprises where it is necessary to constantly move goods from place to place. These include any ports and large warehouses with constantly changing saturation. Those. the resource of the crane will be exhausted before it becomes necessary to rearrange it. is a bright representative of this type of cranes.
Truck mounted cranes. Extremely high mobility, extremely low carrying capacity - for these qualities they are loved by most construction and residential enterprises. In these organizations, simple work directly affects the cost of work and loads are usually not so heavy.
Cranes on their own. These cranes are able to move not due to the engine of the car or train on which they are installed, but, as they say, on their own two feet. These cranes are used when it is not necessary to install a stationary high-capacity crane covering the entire job site, and it is not financially feasible to install several cranes. These cranes are mainly used on construction sites where there is almost no need for such a crane to travel.
Crane support structure
The support structure determines the basic operating height of the crane. For truck cranes, this is the height of the car itself. For the tower, it is called "support structure". For an overhead crane, this value exceeds the height of the load.
Carrying structure of cranes.
For a tower crane, this is an arrow. For some cranes, the boom changes size, for some, the place where the load is applied to the boom changes. At an overhead crane, this is called a girder. The boom/beam with the load securing point can be connected with ropes, chains, etc. All this together allows you to position the load in space.
In everyday communication, a load-handling body is a nozzle on a crane. Something that grabs and holds a load. Modern cranes are usually equipped with all possible grips for any job. You only need to choose the one you need. For example:
