Heading work Calculation of boom departure mechanism of KB0-7507 tower crane -

Contents

Introduction

2. Tower cranes

3. Load grippers

3.1 Hooks

3.2. Loops

4. Elements of load and traction devices

4.1. Polyspasts

4.2. Drums

4.3. Blocks

5. Brakes. General requirements. Classification of braking

devices. General characteristic

5.1. Block brakes

5.2. Tape brakes

5.3. Brakes with axial pressing

6. Mechanisms of cargo lifting and boom departure

6.1. Cargo lifting mechanisms diagrams

6.2. Mechanisms of boom departure change

7. Mechanisms of movement

7.1. Designs of drive mechanisms

wheels

8. Calculation of boom departure mechanism

9. Reducer

9.1. Cylindrical crane gearboxes

9.2.Chervical gearboxes

Conclusion

List of literature used

Introduction

Tower cranes, being universal mounting machines, are used for the installation of tall and extended structures where boom self-propelled caterpillar and pneumatic wheeled cranes can be used.

The main advantages of tower cranes:

1) the boom is high attached to the crane tower, usually above the elevation of the mounted structures, which allows them to be supplied to any point of the served territory in any sequence;

2) heavy lifting capacity at large boom sorties;

3) ease of crane movement;

4) clear arrangement of the installation site.

The disadvantages of tower cranes are the duration and labor intensity of installation and dismantling, the difficulty of transporting them from site to site and the high cost of tracks. All this significantly increases the cost of operating the crane and reduces the useful time of its operation. Modern models of tower cranes provide for the transportation of cranes with the least dismantling of units and the possibility of quick installation and dismantling without the use of additional mechanisms.

Tower cranes have become widespread in construction.

By purpose, tower cranes are divided into:

a) cranes with light capacity up to 5 tons for maintenance of low-rise civil engineering;

b) cranes of medium capacity with lifting capacity from 5 to 25 g for maintenance of multi-storey civil and industrial construction;

c) high-capacity cranes with a carrying capacity of 25-75 tons, and sometimes up to 100 tons for the installation of prefabricated structural elements in hydraulic engineering and industrial construction.

In hydraulic construction, low-power tower cranes are used to service auxiliary work; cranes of medium capacity are used mainly as concrete laying cranes for supply of concrete mixture by buckets to concreting units during erection of cast-in-situ concrete structures; high-capacity cranes are used as installation cranes when erecting structures from precast reinforced concrete.

Mounting heavy-duty tower cranes are especially effective for servicing the construction of low-pressure hydraulic units with a weight of prefabricated elements of up to 70-80 tons and even 100 tons; they move on both sides of the structure.

Brakes. General requirements

Classification of braking devices

The mechanisms of lifting machines must be equipped with reliable braking devices. In lifting mechanisms providing for cargo stopping and holding it in suspended condition with preset braking margin, and in mechanisms of movement and turning - braking till complete stop at preset length of braking track. The brakes of lifting and transportation machines increase the safety of these machines and their performance.

In order to increase the intensity of the mechanism, the braking period should be as short as possible, however, during abrupt braking, the drive elements are subjected to high dynamic loads, causing disruption of connections, increased wear of couplings, bearings, running and gear wheels. During the movement of lifting and transport machines, sharp braking can lead to slipping of running wheels, splashing of liquid metal transported in buckets, swinging of transported cargo, vibration of metal structures and other undesirable phenomena, which should be taken into account when determining the braking moment and calculating the elements of lifting and transport machines.

Braking of electrically driven mechanisms can be carried out both electrically and mechanically. With electric braking, it is possible to significantly reduce the speed by the time the brake is closed. However, even in this case, the mechanical brake remains the only means of stopping the mechanism when the power supply is stopped. Therefore, the calculation of mechanical brakes in any case must be carried out according to the full value of the braking torque.

To determine the braking torque, the following shall be known:

1) the nature and mode of operation of the mechanism;

2) design and design data of the mechanism: mass of the transported load, masses of individual elements, moments of inertia of the elements of the mechanism, speed of movement, gear ratios and efficiency of gears, etc.;

3) the position of the brake in the kinematic scheme of the mechanism (the value of the braking moment varies depending on the gear ratio from the working member, for example, the drum, to the brake shaft);

torque acting on the brake shaft at the brake -

burning and determined taking into account losses in the elements of the mechanism;

brake shaft speed;

when some brake designs are used, it is also necessary to know the direction of rotation of the brake pulley.

Braking devices of lifting and transportation machines are classified according to the following features:

by design of working elements: on shoe brakes - with working element in the form of shoe rubbing on external or internal surface of brake drum (pulley); ribbons - with a working element in the form of a flexible tape rubbing along the brake drum; disk - with the working element in the form of a whole ring disk or separate segment blocks and conical - with the working element in the form of

cones. The last two types of brakes are usually combined into one group with the closing force acting along the brake axis - axially pressed brakes;

according to the principle of action: on automatic brakes (with electromagnetic, electrohydraulic or electromechanical drive, as well as closed by the weight of the transported cargo, etc.), which are closed regardless of the will of the maintenance personnel at the same time as the engine of the mechanism on which the brake is installed, and controlled brakes, which are closed or opened by the maintenance personnel when acting on the control;

By purpose: stop brakes, which stop the mechanism, and release brakes and speed regulators, which limit the speed of movement within certain limits and act during the entire period of operation of the corresponding mechanism;

4) by the nature of the force that controls the brake: on normally closed brakes, the closure of which is created by a permanently active force (from a spring, the weight of a special closing load, etc.), and the opening that occurs simultaneously with the actuation of the mechanism drive - when the brake control force is applied (when the drive is turned off, the brake is automatically closed); normally open brakes, which are opened by means of a permanent opening force and closed when the brake control force is applied; combined brakes operating under normal conditions as normally open brakes and under emergency conditions as brakes normally closed by an external closing force.

All brakes, regardless of their design, are subject to the following basic requirements: sufficient braking torque for the given operating conditions; fast closing and opening; strength and durability of brake elements; simplicity of construction, which determines low cost of manufacture; ease of inspection, regulation and replacement of worn parts; stability of control ensuring reliability of braking device operation; minimum wear of friction elements; minimum dimensions and mass; limited temperature at friction surface not exceeding limit temperature for given friction material.

The brake pulley is typically mounted on a high speed shaft of the mechanism where the lowest torque is applied and therefore a low braking torque is required. In this case, one of the half-couplings of the connection of the engine with the reduction gear can be used as a brake pulley. If the mechanism is applied! clutch with damping device (bushing, spring, etc.), then the half-coupling located on the gear shaft should be used as a brake pulley.

Mechanisms of movement

Movement mechanisms serve to move cargo in horizontal plane. There are two types of fundamentally different schemes of movement mechanisms. Mechanisms with driven running wheels are located directly on the object to be moved (on the crane trolley or bridge); mechanisms with rope or chain tie-rod are located separately from the object being moved and are connected to it by means of flexible element (rope, chain).

Reducer

9.1. Cylindrical crane gearboxes

Gearbox is an independent assembly unit connected to the electric motor and the working machine by couplings or open gears.

The gearbox serves to reduce the speed and increase the torque. Gear or worm gears fixed on shafts are arranged in housing. Shafts rest on bearings arranged in housing sockets.

Type of reduction gear is determined by gear composition and position of shafts rotation axes in space. To denote transmissions, capital letters of the Russian alphabet are used according to a simple mnemonic rule: C - cylindrical, P - planetary, K - conical, Ch - worm, G - globoid, B - wave. The number of identical transmissions is indicated by a number. Shaft axes located in horizontal plane are not marked. If all shafts are located in the same vertical plane, then the index B is added to the type symbol. If the axis of the high-speed shaft is vertical, then the index B is added, and to the slow-speed shaft, respectively, T.

Motor - gearboxes are indicated by the addition of the letter M. For example, MC2CV means a gearbox motor with a two-stage coaxial cylindrical gear, where the horizontal axes of rotation of the shafts are located in the same vertical plane, here B is not an index, so it is written next to the capital letter.

The gearbox type designation consists of its type and the main parameter of its slow-moving stage. For cylindrical, worm globoid transmission, the main parameter is the axial distance; planetary - carrier radius, conical - diameter of wheel dividing cone base, wave - inner mounting diameter of flexible wheel in undeformed state.

Gear ratio of gearbox, version of shaft ends assembly and shape are taken under design.

Version of cylindrical gear box assembly and shaft end shape as per GOST 2037374; worm reducers - as per TU 2.056.21883, and conical - cylindrical reducers - GOST 2037380.

The main energy characteristic of the reduction gear is the rated torque TN, which is the permissible torque on its slow-moving shaft.

New reducers have smooth bases of housings with recessed legs, and covers have horizontal surfaces of upper parts, which serve as technological bases (Fig. 1).

The new gearbox enclosures have the following advantages:

1. The volume of oil has been increased, which increases its shelf life.

2. The possibility of excluding flanges as the main source of flatness.

3. High stiffness of the base and pliable cover of the body, which improves vibroacoustic properties.

4. Less warping during aging, which eliminates oil leakage;

5. Reduction of failures by about 30% due to increased strength of recessed legs.

6. Simple drainage of accumulated oil from spraying from bearing units.

7. Possibility to increase accuracy of shaft axes location.

8. Easy external processing.

9. Absence of counterbore for heads of tightening screws of the housing with the base.

10. Provision of technical aesthetics requirements.

Cylindrical pairs of cylindrical reducers are made according to unfolded narrow, unfolded or coaxial scheme with one or two power flows.

The most widespread is the expanded scheme due to the rational unification of the parts of the reduction gear box. For example, gears, wheels, and shafts can be used to make several types of gearboxes. When using helical gears, it is recommended to choose the gear tooth direction - left, for the wheel - right in all stages of the reduction gear for unification. These recommendations are justified for large-scale and mass production, since the unification of parts leads to a decrease in cost. However, in single and small-scale production, it is advisable at the first stage to take the direction of the gear teeth - left, and the gear of the second stage - right. This is due to the fact that the axial forces on the intermediate shaft are partially balanced, thereby reducing the axial load on the supports.

When arranging the reduction gear, it is recommended to position the gears on the driving and driven shafts further from the output ends of the shafts in order to ensure a more even loading of the supports with radial force.

It is advisable to use the expanded scheme up to = 630... 800 mm. The gearbox, designed according to an expanded scheme, is of an elongated shape. The weight of such a reduction gear is about 20% more than that of a reduction gear designed according to a bifurcated scheme.

In a bifurcated scheme, a high-speed or slow-speed stage is bifurcated into two oblique gears with an opposite tooth direction, forming in fact a chevron gear with spaced half-arms. A more rational scheme with a bifurcated high-speed stage is considered, since it doubles the nomenclature of less loaded parts, simplifies the intermediate shaft, it can be made like a shaft, it becomes possible to make the high-speed shaft "floating," this is preferable than to make the intermediate or slow-moving shaft "floating" with a bifurcated slow-speed stage.

In the coaxial scheme, the axis of the high-speed shaft coincides with the axis of the slow-speed shaft, this makes it possible to assemble technical devices in the axial direction. Reduction gear made according to coaxial scheme has weight, dimensions and cost the same as reduction gear made according to unfolded scheme. In the coaxial reduction gear, therefore, the high-speed stage of the reduction gear is underloaded and accordingly more powerful. Coaxial gearboxes are very convenient for use in machines with a re-short-term mode of operation. The disadvantage of coaxial gearboxes includes some complication of the structure of the support of the high-speed and slow-speed shaft located inside the gearbox.

The most compact among gearboxes with fixed shafts are multithreaded gearboxes, in which the power flow branches from the gear of the high-speed stage into a number of flows and, passing through the intermediate shafts, passes to the wheel of the slow-speed stage, from where it is removed taking into account engine power losses.

Multithreaded gearboxes are close to planetary gearboxes, however, the gear ratios of planetary gearboxes are much higher, so multithreaded gearboxes have limited use. They are used in case of necessity of symmetrical arrangement of drive relative to its longitudinal axis.

Conical-cylindrical gearboxes are a set of conical gearbox with single-stage cylindrical, which reflects all the advantages and disadvantages of these gearboxes.

Since conical gears have lower load capacity and therefore larger dimensions, it is recommended to make the high speed stage conical in order to reduce the overall dimensions of the drive. However, it should be borne in mind that conical gears are very sensitive to mounting and manufacturing errors, especially at high speed gearbox stages. In order to reduce the influence of installation errors, it is allowed to use conical transmission on intermediate and slow-moving stages of the drive. If an increase in the size of the conical transmission is not a decisive factor in the design of the drive, then a slow-moving drive stage can be made conical.

A feature of conical cylindrical reducers is that the tooth direction of the oblique cylindrical pair should be chosen so that the axial forces on the intermediate shafts are subtracted.

The operation of bevel gears is influenced by radial loads acting on the output end of the shaft, since a large radial load causes deformation of the shaft and, accordingly, disruption of the engagement of the bevel pair. Therefore, in cases where a pulley or sprocket is located on the end portion of the bevel gear shaft, which creates a large radial load during operation, it is recommended to provide a device for unloading the shaft from the radial load.

9.2. Worm gears

Worm reducers are made with cylindrical and globoid worm, with archimedean, involute, convalute and concave profile of worm. Globoid gearboxes are characterized by high load capacity and higher efficiency due to more engaging pairs of teeth and better lubrication conditions. The main drawback of worm gears is the low efficiency, especially in self-braking worm gears with a cylindrical worm. Therefore, worm gears are used when operating in repeated short-term modes.

Two-stage worm gears are very rarely used, since they have a very low efficiency and a high manufacturing cost. Two-stage reduction gears are made with either two cylindrical or one globoid and one cylindrical worms. Two-stage globoid gearboxes are practically not used, due to the difficulty of double adjustment of engagements. In the two-stage worm reduction gear, the length of the intermediate shaft increases, and therefore its rigidity decreases while simultaneously increasing the temperature deformations of the shaft. To increase the efficiency of the drive at high gear ratios, it is recommended to use worm-cylinder and cylinder-rack reduction gears. Worm-cylinder reduction gears have the smallest width of the drive and the minimum dimensions of the reduction gear at large gear ratios.

Worm gearboxes make it possible to carry out a large gear ratio from 8 to 80 in one stage. Due to the high vibration acoustic parameters, elevators and machines of the food industry are equipped with worm gears. However, due to the low efficiency and less life than gear gears, they are rarely used in continuous machines.

The layout capabilities of the worm gear are determined by the position of the worm pair in space. A conventional worm gear with a lower position of the worm is indicated by the assembly diagram - 51, with an upper worm - 52, with a vertical position of the worm - 53, the lateral position of the worm in the horizontal plane and the vertical position of the wheel shaft is indicated - 56.

Two-stage worm, worm - cylindrical, cylindrical - worm reducers usually belong to special reducers. They have the following significant disadvantages:

1. Complexity of adjustment of worm pair and bearings.

2. The durability of the worm pair, namely the worm wheel, is much less than that of the gears.

3. Tendency to jam the worm pair when normal contact is disturbed.

Conclusion

Even in the distant past, levers and blocks, polyspasts and ropes, toothed and worm gears, ropes, which are still widely used in cranes, were known. But the main components, assemblies and parts of cranes with centuries have undergone fundamental changes or have already been re-designed today according to fundamentally new schemes. Thus, the tower crane seemed to combine the distant past and advanced present, traditions with the most recent achievements of scientific and technological progress. The transition from old to new took place, of course, gradually, over many hundreds of years. At first, instead of lever lifts, cranes with a non-rotating cantilever appeared, movable cranes, tower cranes with a non-rotating tower, later they were replaced by the current cranes with a rotary, and even folding tower, modified by the departure of the hook.

Today, more than 200 thousand installation cranes, 164 thousand excavators, 43.6 thousand bulldozers, many loaders, scrapers, tractors and other construction equipment are used at the country's construction sites. In each generation of cranes, people carefully selected the best, those useful qualities and properties that were passed on to the next generations. And today at construction sites you meet tower cranes of a wide variety of structures, having great mobility and carrying capacity, increased speeds of working movements and lifting height of weights, which require a short time for installation and dismantling.

Tower cranes are used less often in the reconstruction of workshops than in the construction of new objects. This is due to an increase in specific costs for the installation of crane tracks, the installation and dismantling of the crane, with an increased constriction of the installation zone, which limits the possibility of delivering the crane to the construction site. However, the vertical nature of the crane tower and the high height of the boom suspension allow you to move the mounted structures above the existing ones and place them even in narrow corridors formed by existing buildings.

The field of application of tower cranes can be expanded using various combined systems and devices. The simplest example of this is the simultaneous operation of two tower cranes or tower and any other crane for lifting cargo exceeding the lifting capacity of each crane separately.

You can significantly increase the lifting capacity of the tower crane by turning it into a goat by rigid coupling of the booms of the two tower cranes or by resting the crane boom on an additional temporary support.

An effective way to improve the structures of tower cranes and adapt them to work on reconstructed and dispersed objects is to transfer them to a rail-free course (pneumatic, caterpillar or walking). For installation works performed in constrained conditions, rail-free tower cranes having an boom with a cargo trolley can find the most use. With a sufficiently large departure, such a crane can work for a long time in one parking lot, due to which the main disadvantage of rail-free travel - the impossibility of moving with the load - is not significant. Other modernization methods are possible to expand the application of tower cranes.

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