In the modern world, special attention is paid to the creation and subsequent operation of various mechanisms and machines. Against this background, the achievements of current engineers make it possible to use already advanced developments, which at first glance do not seem supernatural, but at the same time show themselves perfectly in practice. One of these types of equipment, which is used today more and more often, will be discussed in this article. The name of this industrial product is slewing rotary devices (OPU). We will talk about all its features, varieties, repairs and the scope of use in more detail.
brief information
So, the rotary support device is a highly efficient mechanism, thought out to the smallest detail, designed to transfer the load from the rotary part to the directly running element. These devices were not developed today, but over the years the popularity of this unit is only growing, and it is installed not only on truck cranes and industrial units, but even on satellite dishes.
Classification
The slewing ring, like any other factory technical product, has its own classification. So, each of these devices can rotate relative to:
- Static, fixed brackets.
- Fixed columns.
- Fixed support circle.
Kinds
Ball type ball bearings are manufactured in the form of a double-row angular contact ball bearing. This device includes an outer and inner cage and two rows of balls between them. The outer ring is bolted to the swing frame and includes an upper and lower ring. The centering of the rings occurs with the help of a shoulder. An adjusting pad is also available.
Roller OPU has an indisputable advantage in comparison with the ball counterpart, which consists in a much greater carrying capacity. Roller slewing gear consists of:
- The rings are inner.
- Running frame.
- Two rings.
- Rollers.
The inner ring, due to its gear ring, is meshed with the output gear of the rotation mechanism. The rollers are located between the rings and are perpendicular to each other. The rollers moving along the tracks absorb loads that act downward, and the rollers rolling along the tracks serve as grippers, protecting the frame from spontaneous tipping. The rollers are lubricated using special grease nipples located in the ring.
Use in automotive vehicles
Consider in detail the slewing device of a truck crane. This mechanism is able to absorb loads from the weight of the rotary part of the crane and the weight of the lower / raised load. OPU is also able to withstand the strong impact of wind load and various dynamic forces.
Most often, the slewing ring of a truck crane is presented in the form of a skating circle or balls. A similar unit is used on cranes such as AK-5G, AK-5, K-32 and represents a skating circle in combination with supporting elements of a roller type. The circle is fixed at the top of the static frame, and the moving parts (supporting-roller elements) - at the bottom of the rotating platform of the machine.
Riding circle
What is this product? In fact, this is a huge ring cast from steel together with the central hub. The outer side of the circle has a special annular groove with a pair of inclined working tracks, on which the conical rollers of the supporting elements are supported. At the top of the circle is mounted the ring gear of the mechanism that provides rotation, and a gearbox of a static frame is attached to the lower edge of the hub.
Since 1960, automobile cranes began to be equipped with ball slewing devices, and the skating circle was no longer used almost completely. New GTC are special and consist of:
- Internal rotation mechanism.
- Fixed clips.
- Pairs of external movable rings (lower and upper), which are interconnected by bolts.
Between the clips are arranged in two rows of steel balls, the diameter of which is 30 mm. Differentiation of balls among themselves occurs using a special separator. Between balls and holders there is a gap regulated by a lining.
Technical Activities
Slewing-rotary devices are rotary mechanisms that oblige to pay close attention to them on the part of repair and maintenance personnel.
Each such support should be subject to periodic, thorough visual inspection. Also, you should definitely check the tightening of the connecting bolts, lubricate the rubbing parts in the internal cavity of the support and teeth.
For the first time, the degree of tightening of the bolts is checked immediately before putting the unit into operation, and the next tightening is carried out after two or three work shifts. Important: bolt tightening must be carried out diagonally in order to avoid distortion, which can lead to premature failure of the mechanism.
Operational Safety Precautions
The slewing ring can be repaired or routinely serviced not only within a variety of repair shops or other diagnostic centers, but also in the field using special mobile stations. For the safe implementation of the full scope of work, it is necessary to be guided by the "Rules of labor protection in road transport" and other regulatory technical documents.
Machinists and repairmen have the right to perform any technical actions only if they have the appropriate qualifications, documented.
Before starting maintenance work, it is necessary to fix the machine motionlessly and completely eliminate the likelihood of its spontaneous movement in any direction. You should also turn off the hydraulic, pneumatic, electrical systems and the engine, and if necessary, put up warning signs.
A few words about excavators
The rotary support device of the excavator allows it to perform the functions assigned to it. The turntable itself rotates around a vertically oriented axis in both directions at all 360 degrees.
The excavator slewing ring can be of the following types:
- Single Roller.
- Two-wheeled.
- Two-row ball.
The most widespread in our time are already ball (roller) OPU. The indisputable advantage of such mechanisms is the absence of a requirement for their centering with the help of a pin, which is necessarily installed on the roller devices in order to compensate for the horizontal force.
The rotation of the platform occurs due to the engagement of the cantilever gear and the ring gear. The gear during the operation of the excavator moves along the crown, which ultimately ensures the rotation of the platform to the desired angle. The gearing can be either external or internal.
It is also worth noting that the slewing ring enables the excavator to operate normally at various curvatures, without jamming the rotor of the machine in the trench, as well as during the rotary movements of the excavator together with the semitrailer working unit in the transport position.
Roller-type devices have one significant drawback: the presence of mandatory gaps between the rollers and the turntable leads to the fact that during the operation of the excavator the platform begins to "chat".
Tower cranes
The slewing ring of the tower crane deserves special attention. OPU on cranes of this type have such varieties:
- A bell that is worn on top of a stationary tower.
- A bell suspended on a thrust bearing.
- A shank that rests on an intermediate, auxiliary thrust bearing and held at the bottom by a bearing.
- Circle rotary ball or roller.
It should be understood that all these devices must be manufactured with high accuracy in order to avoid subsequently large distortions of the entire structure and misalignment of the surfaces, since these shortcomings are almost impossible to eliminate by any adjustment, and this, in turn, leads to jamming. In order to eliminate inaccuracies, the rotary bell is made with hinged links, which eliminates the additional loads during skewing.
As for the rotary support devices of the roller type used in wheeled and tracked lifting machines, then in tower cranes they are absolutely not applicable, because it requires the highest accuracy. Otherwise, the resulting gaps will cause a very strong swing of the tower, and this already poses a threat to the safety of personnel.
In turn, ball and roller support circles are completely devoid of this drawback. The rings of these circles are made of especially high-quality steel, and the treadmills of rolling elements are hardened. It is the minimal wear of these tracks that guarantees the minimum degree of swing of the turret towers, which rely on these circles. In addition, these turntables do not oblige them to be adjusted during operation, which, of course, is their indisputable advantage.
High-precision ring production and the use of rolling elements, the sizes of which vary within microns, make it possible to reduce the magnitude of the axial and radial clearances.
Also, in order for the slewing ring of the crane to be fully operational, it is necessary to reduce the flexibility of the running gear of the unit. The deflection of the frame should not be more than half the axial clearance, which is measured in the support circle. The upper frame of the rotating platform must also have high rigidity, so that the loads that act on it are evenly distributed over the entire length of the circle. However, at the same time, the deformation of the upper frame must exceed the same indicator of the lower frame, otherwise a very undesirable phenomenon may occur - emergency jamming of the lower row of rollers.
Industry
The slewing ring of a manipulator used, for example, in metallurgy or the chemical industry, is very similar to the construction of a truck crane. There is also a gear ring and gear, frame, load-lifting element. Most manipulators operated under the same blast furnaces or rolling mills use a hydraulic drive in which non-combustible grades of emulsions are used as the working fluid.
Satellite TV and communication
The rotary support device of the antennas serves to suspend the antenna system itself, as well as to direct the beam emitted by it to the relay satellite. OPU antennas are divided according to the mirror fixing scheme. The polar suspension is very popular, which allows you to rotate the antenna in one plane and at the same time view the visible part of the geostationary orbit.
The suspension itself moves due to the operation of an electric drive that rotates the antenna.
In general, the drive of the slewing ring device operates in quite aggressive and difficult conditions: there are large temperature differences, wind loads, and atmospheric precipitation. The linear drive of the slewing ring devices is equipped with a low-power electric motor, which is switched off in case of overheating due to the operation of a special sensor - bimetal platinum.
If we are talking about the horizon-horizon type control system, then it is appropriate to indicate that in this case the device is equipped with a gear mechanism that rotates the antenna horizontally around the polar axis over the entire length of the geostationary orbit.
Creature
The production of slewing rings is a rather complicated and laborious technological process. It obliges employees of enterprises to have appropriate skills and high qualifications.
The manufacture of slewing rings takes place in strict accordance with the required temperature conditions. So, in particular, the basis of these products is blanks from alloyed, normalized rolled products that have gone through all stages of thermal improvement. Reliability and durability of the OPU are ensured by the use of special quenching inductors.
Service
As you yourself have most likely understood, the repair of a slewing ring is an inevitable event that should be trusted by professionals.
When ball bearings are used in ball bearings, the so-called point contact occurs between all balls and raceways. Because of this, annular grooves of a spherical shape arise around the perimeter of these tracks. All this leads to the failure of the device and the need for repair operations.
This problem is eliminated as follows. Initially, the grooves that appear from the treadmills are eliminated by the boring method, and then the contact surface is hardened by a plasma-finish treatment. After that, to increase the durability of the circles of slewing rings in the tracks, roller rolling bodies, combined with ball "brothers", are installed crosswise. This position of the rolling bodies ensures the elimination of defects from the rollers by the spherical surface of the ball body.
Practice has shown that the most loaded part of the OPU is the lower movable ring, which, in turn, has different strengths over its entire cross section. For example, the ring under the rolling bodies on the HRC scale has a hardness index of 60 units, and the lower surface is 35 units. It is because of this that at peak load, the destruction begins to occur precisely from the lower surface, and this ultimately causes the deformation of the support-turntable and a decrease in its reliability and durability.
Based on the foregoing, it becomes clear that during the repair of the switchgear, particular attention is paid to the lower movable ring, which is connected to the gasket from a special high-strength material. It is allowed to use a sectional gasket, the joints of which can be located in unloaded or lightly loaded areas. The auxiliary gasket is fixed using screws or industrial types of glue.