Blocks designed to maintain and change the direction of movement of a rope with a diameter dk... Blocks are subdivided into movable, the axis of which moves in space, and fixed. A type of fixed blocks is an equalizing block, which does not rotate when lifting and lowering a load, but serves to equalize the length of unevenly stretching rope branches in a double pulley block.
Rope blocks are made of steel by casting, welding or stamping. For cast blocks, steel with mechanical properties not worse than steel is used 45L-11, for stamped ones - no worse than steel 45 , and for welded - no worse than steel Art 3.
The profile of the block stream must ensure unhindered entry and exit of the rope and have the largest area of contact with it (the largest surface area of the stream). Based on this, it is recommended that the ratio of the main block sizes be taken as shown in Figure 3.10.
Blocks must have a device (bracket) that prevents the rope from leaving the block stream. The gap between the specified device and the flange of the block should be no more than 20% of the rope diameter.
Drums designed for winding a flexible traction element (rope or chain). They are made of cast iron (cast) or steel (cast or welded).
To reduce the specific pressure between the rope and the drum and prevent friction of the rope against an adjacent turn, helical grooves are made on the drum surface with a pitch 
mm. If one branch is wound on the drum (single chain hoist), it has grooves in only one direction. With two branches (double chain hoist), the grooves are in the right and left directions.
The design of the drums should provide for the placement of parts for fastening the rope to the drum, which can be carried out using overhead strips, clamping strips or a wedge (Figure 3.9).
Minimum drum diameters D, blocks D bl, and equalizing blocks D ur.bl. along the center line bent by steel ropes, determined by the formulas:
With increasing ratio D / d k the durability of the rope increases as the contact and bending stresses decrease.
The drum diameter obtained according to the formula (3.9) D should be rounded up to a value from the series: 160; 200; 250; 320; 400; 450; 500; 560; 630; 710; 800; 900 and 1000 mm.
Coefficient change is allowed h 1, but not more than two steps in the classification group up or down (Table 3.7) with appropriate compensation by changing the value Z p(Table 3.6) for that number of steps up or down. Drums for single-layer rope winding must have grooves cut along the helical line (Fig. 3.11). For grab cranes with single-layer winding of a rope onto a drum and for special cranes, during the operation of which jerks and weakening of the rope are possible, the drums must be equipped with a device (rope-laying device) that ensures the correct laying of the rope or control of the position of the rope on the drum.
Smooth drums are used in cases where, for structural reasons, multilayer winding of a rope onto a drum is necessary, as well as when winding a chain on a drum (Fig. 3.12) Smooth drums and grooved drums intended for multilayer rope winding must have flanges on both sides of the drum. The ribs of the rope drums must rise above the top layer of the wound rope by at least two of its diameters, and for chains - at least by the width of the chain link.
The length of the drum, which determines its rope capacity, should be such that at the lowest location of the load-gripping body (hook, etc.), at least 1.5 turns of the rope or chain remain wound on the drum, not counting the turns under the clamping device. Taking into account flanges and turns for fastening the rope, the total length of the drum when winding is:
· on one branch of the rope
|
|
The most common electric bridge, slewing, jib, metallurgical and other cranes have a lot in common in the lubrication system, but depending on different operating conditions, they have their own characteristics.
Lubrication of the crane gearboxes of the lifting mechanism and the mechanisms for the movement of the bridge and bogie is usually carried out by means of an oil bath. Since the gears in crane gearboxes work in harsh conditions, with shock loads, frequent switching on and off, they use more viscous and oily oils compared to conventional machine tool gearboxes. When filling crane gearboxes with oil, it is recommended to follow the instructions given in table 21.
Table 21
Lubrication of crane gearboxes depending on the lifting capacity and operating modes of the crane
Oil change and gearbox flushing is done once every 4-6 months and is usually timed to planned repairs or inspecting the crane. For metallurgical cranes, the oil life is reduced to 2-3 months. Before opening the gearboxes, remove dust from their covers to prevent it from getting into the oil. The oil level in the gearbox must not be lower than the control mark of the oil gauge; in its absence, it is recommended to fill the oil no higher than the level reaching 3-5 cm to the bottom of the lower shaft, but not lower than the level that ensures the full height of the teeth of the lower gear is immersed in oil. Gearboxes must be free of oil leaks. Particularly unacceptable is it getting on trolleys, crane bridge deck and rails, as well as on brake pulleys, pads and belts. If leaks are found, they are immediately repaired.
Lubrication of bearings of crane gearboxes of old designs, where the bearings of the high-speed first shaft of the gearbox have ring lubrication, when operating under normal temperature conditions, is carried out by filling them with industrial oil 20 once every 3 months, refilling is done once every 3-5 days. In conditions of high temperatures and dustiness, these bearings are poured monthly with industrial oil 50, topping up is carried out 2-3 times a week.
Plain bearings in gearboxes with cap grease fittings are lubricated at normal temperature with US-2 or USs-2 solid oil by turning the grease fitting cover 1-2 turns 1-2 times per shift. At elevated temperatures, they are lubricated with constantin UT-1 or UTs-1 by turning the lid of the oiler by 1-2 turns up to 2-3 times per shift.
In gearboxes of modern cranes, rolling bearings are usually installed, which at normal temperatures should be filled with US-2 solid oil once every 4-6 months, and for metallurgical cranes with 1-13 grease or UT-1 constantin at each repair. Grease is added on a monthly basis through cap or grease fittings supplied to these bearings. If gearboxes contain rolling bearings with grease, pay special attention to the serviceability of the seals and do not allow grease to leak out of the bearing housing or be flushed out by leaked oil from the gearbox bath.
On some cranes, a pump is installed in the gearboxes that supplies oil to the bearings. In this case, caring for them is reduced to monitoring the presence and quality of oil and the correct operation of the pump.
Bridge mechanisms for heavy-duty electric cranes, especially metallurgical ones, are currently produced with centralized lubrication systems from automatic or manual lubrication stations. In this case, lubrication is carried out according to the operating instructions for these systems. The automatic centralized lubrication system ensures a reliable supply of lubricant to all lubrication points, including remote and hard-to-reach ones. This saves maintenance time, which is especially important for continuously operating cranes, and significantly reduces the consumption of lubricants.
In older cranes, lubrication of the travel wheel bushings of the transmission shaft slide bearings is usually carried out through cap nipples, grease nipples or from central lubrication units. Lubrication of cranes operating at normal temperatures, for example, in mechanical assembly shops, is performed with US-2 or USs-2 solid oil by turning the lids of the grease fittings by 1-2 turns or filling the grease fittings with a syringe 1-2 times per shift. Lubrication of forging, foundry, trough-filling and other metallurgical cranes is carried out with contalin UT-1 or UTs-1 by turning the grease nipple caps by 2 turns or filling the grease nipples 2-3 times per shift. Remote points, wheel bushings and parts and assemblies that are directly exposed to high temperatures should be lubricated with particular care. The rolling bearings of the axle travel mechanisms are lubricated similarly to the rolling bearings of crane gearboxes.
Low-temperature greases CIATIM-201, NK-30, No. 21, GOI-54, etc. are used as greases for cranes operating outdoors in winter.
In the bogie travel mechanism, gears and gearbox bearings, travel wheel bearings are lubricated in the same way as the corresponding components of the axle travel mechanism. Since the bogie is constantly moving along the bridge, it is especially important here to prevent oil leaks from the gearboxes onto the deck and rails.
In the load lifting mechanism, gearboxes and bearings of the load drum are lubricated similarly to the same units of the bridge and bogie movement mechanism. Since the lifting mechanism works more intensely than other crane mechanisms, it is recommended to lubricate its assemblies more often. Lubrication of rolling and sliding bearings, hook yoke axles is carried out with US-2 solid oil, at high temperatures with constantin by filling through grease fittings or plugs located at the ends of the block axes. For cranes operating at normal temperatures, lubricant is supplied 2-3 times a week, and for metallurgical cranes - at least 1 time per shift. Cage hook ball bearings are filled at normal temperatures with US-2 solid oil once every 3-6 months, in metallurgical cranes - with constalin or 1-13 grease once a month.
In order to avoid rapid wear, open gear drives are lubricated: in light duty cranes with light duty and at normal temperature - with half-tar once every 5 days, with medium lifting capacity and medium duty at elevated temperatures - with graphite ointment once every 5 days and heavy metallurgical cranes 2 times a week - graphite ointment, prepared by mixing 90% constalin and 10% graphite powder, when heated not higher than 110 °. Remove old grease before applying grease.
The lubrication of the electric motors is shown below. Drum controller bearings are lubricated with US-2 or US-3 solid oil, croutons, segments and ratchet wheels - with a thin layer of US-2 solid oil or technical vaseline. The hinge joints of the contactors are lubricated with industrial oil 30. The parts of the limit switches are systematically lubricated, at least once every 10 days, with the same oil or solid oil US-2, depending on design features node. Lubrication of the fingers of the current collector rollers is carried out with de-energized trolley wires once a week with solid oil US-2, and at high temperatures with constantin UT-1.
To avoid accidents, lubrication of cranes should be carried out only in the de-energized state of all crane mechanisms on its landing site. The daily supply of lubricants in clean containers (separate for each grade) should be kept in a closed box on the crane bridge. In view of the danger for crane operators, as well as the presence of a large number of hard-to-reach lubrication points on cranes, it is especially insistent to transfer all units to centralized and automatic lubrication.
n1.doc
(EPI MISIS)
Faculty: _______________________________
Department: __________________________________
Speciality: ____________________________
Group: ___________________________________
Settlement and graphic work
at the rate _________________________________
Topic: Load lifting mechanism
Completed by: ___________________
Checked by: Associate Professor A.A. Maltsev
Protection rated ________________________________________________
"_______" _____________________ 2008
Elektrostal 2008
Electrostal Polytechnic Institute
Moscow State Institute of Steel and Alloys
(University of Technology)
(EPI MISIS)
Department of TPM
EXERCISE
To perform RGR
Group student _________________________________________
1. Project topic: Load lifting mechanism
2
1 - electric motor
2 - clutch with brake
3 - reducer
4 - drum
5 - hook suspension
... Initial data: Kinematic diagram of the lifting mechanism (Fig. 1)
Carrying capacity Q = 10 t
Lifting height H = 20 m
Load lifting speed V = 0.1 m / s
Working mode group 6M
Fig. 1. Lifting mechanism diagram
3. List of issues to be developed:
Examine the design of an electric winch. Calculate the lifting mechanism: select the rope; choose a hook suspension; calculate the drum; choose an electric motor; choose a gearbox; choose a clutch with a brake pulley; choose a brake.
P.
Introduction 5
1. Steel rope 6
2. Hook hanger 7
3. Drum 8
4. Electric motor 9
5. Gearbox 10
6. Flexible coupling with brake pulley 11
7. Shoe brake 12
Literature 13
Appendix 14
Introduction
In an electric reversing hoist winch (Fig. 2), the motor 9 rotates the drum 2 through the elastic coupling 4 and the gears of the spur gearbox. It is characterized by a rigid kinematic connection between the drum and the engine, in which the direction of rotation of the drum is regulated by changing the direction of rotation (reversing) of the engine.
Fig. 2. Winch
The rigid connection of the drum with the engine is carried out by the gear drive of the reducer 3.
Start and reversal of the engine is carried out by electric starting equipment: drum controller 7, magnetic starters 8, pad contactors, etc. This equipment is installed on the frame 1 or at a place remote from the winch.
1.Steel rope
Weight of the lifted load, (1)
where g= 9.81 m / s 2 - acceleration of gravity.
For pulley blocks with a multiplicity of not more than four, it is permissible to determine the efficiency by the formula
, (2)
where ? bl= 0.98 - unit efficiency, ? = 2 - the frequency of the chain hoist.
The maximum tension of the rope branch when lifting a load is determined by the formula
,
(3)
where ? = 1 - coefficient for a single chain hoist.
Breaking strength of the rope
, (4)
where K = 6.0 is the safety factor:
Operation mode group ………………… .. 2M 3M 4M 5M 6M
Safety factor K …… .... 5.0 5.0 5.5 6.0 6.0
We select in accordance with GOST 2688-80 (Table 1) a steel wire rope with a diameter of d k = 22.5 mm (Fig. 3) double cross lay LK-R 6Ch19 (1 + 6 + 6/6) + 1o.s. Explanation: LC - linear contact of the wires between the layers in the strands; P - different diameters of the wires in the outer layer of the strand; 6 - six-strand rope; 19 - the number of wires in one strand; 1o.s. - one organic core.
Fig. 3. Rope
2.Hook suspension
The hook suspension (Fig. 4) consists of a hook 1, a traverse 2, a support bearing 3, a special nut 4 for attaching the hook to the traverse, cage cheeks 5, movable blocks of the chain hoist 6 and the axle of fastening blocks 7.
Fig. 4. Hook suspension
We select a hook suspension with a lifting capacity of 10 tons (Table 2).
Crane hooks with a cylindrical shank are manufactured by hot stamping with subsequent machining shank. According to the highest carrying capacity, the hooks are divided into numbers from 1 to 26, and according to the length of the shank - into types A and B: A - with a short shank, B - with a long shank.
3. Drum
The drum diameter is determined by the formula, (5)
where e = 30 - coefficient:
Operation mode group ………………………… 2M 3M 4M 5M 6M
Coefficient e …………………………………. 20 20 25 30 30
The drum will be wound in one layer.
Let the working length of the drum L 0 = 600 mm, then the number of working turns on a smooth drum
. (6)
Drum rope capacity
The length of the rope wound on the drum at a given lifting height
, ( 8)
which is less than the rope capacity of the drum.
The drum is made from a cast billet or from a pipe. Flanges are welded to the pipe, to which the bottom with the hubs with the shaft pressed into them is screwed (Fig. 5).
Fig. 5. Drum
4.Electric motor
Hoist efficiency, (9)
where? m = 0.98 - coupling efficiency; ? ed = 0.97 - gearbox efficiency; ? bar = 0.99 - efficiency of the drum bearings; ? floor = 0.96 - the efficiency of the chain hoist.
Required motor power when lifting a load
.
(10)
We select the crane electric motor MTKF 312-8 (Fig. 6) with the following technical characteristics (Table 3) and dimensions (Table 4):
power N dv, kW …………………………………………………………… 11.0
rotation frequency n dv, rpm …………………………………. ……………… .. 700
output shaft diameter, mm ………………………………………………… 50
Fig. 6. Crane electric motor
Bearing elements - body with horizontal ribbing and end shields are cast from ductile iron. The cable is connected to the winding of the phase rotors through the holes in the bearing shields, and the terminal box is located at the top, which provides power supply from either side of the motor. The fan is made of aluminum alloy, the casing is steel.
5.Reducer
Drum rotation frequency
.
(11)
Required gear ratio
.
(12)
Estimated torque on the low-speed shaft of the gearbox
. (13)
We select a two-stage gearbox Ts2-500 (Fig. 7) with the following technical characteristics (Table 5) and dimensions (Table 6):
torque on the low-speed shaft, Nm …………. ……………. 18000
ratio u ed ……………………………..………………. 100
Fig. 7. Reducer
6.Elastic clutch with brake pulley
Estimated torque on the high-speed shaft of the gearbox
.
(14)
The elastic sleeve-finger clutch softens shocks and shocks in the drive and prevents dangerous vibrations. It consists of two half-couplings set on shafts, interconnected by fingers with rubber rings or bushings put on them (Fig. 8). 
Fig. 8. Elastic coupling
We choose an elastic sleeve-finger coupling MUVP-7 (GOST 21424-75) (Table? 7). The clutch is made with a brake pulley.
7. Shoe brake
The calculated braking torque is determined by the formula, (15)
where TO T= 2, 5 - braking safety factor:
Operation mode group …………… 1M 2M 3M 4M 5M 6M
Braking coefficient ……… .. 1.5 1.5 1.5 1.75 2.0 2.5
According to the magnitude of the braking torque, taking into account the diameter and width of the brake pulley, the TKG-160 shoe brake is selected (Table 8).
The shoe brake (Fig. 9) consists of a frame 1, two pivots Z and 6 with pads 2 and 7, the working surfaces of which are lined with a friction tape, rods with a clamp 5 and an opening device with an electro-hydraulic pusher 8.
Fig. 9. Shoe brake
Literature
Hoisting machines: Textbook for universities in the specialty "Hoisting and transporting machines and equipment" / M.P. Alexandrov, L.N. Kolobov, N.A. Lobov and others - M .: Mechanical Engineering, 1986. - 400s.
Volkov D.P., Krikun V.Ya. Construction machines and means of small-scale mechanization - M .: Masterstvo, 2002. - 480s.
Fidelev A.S. Hoisting-and-transport machines - Publishing association "Vishcha Shkola", 1975. - 220s.
Lifting and transporting machines. Atlas of structures, ed. M.P. Alexandrova, D.N. Reshetova, M .: Mechanical Engineering, 1987 - 122s. 3.
Guidelines for course design / V.T. Torshin, E.D. Zaitsev, M.I. Grinshpun, V.A.Kozlov, I.V. - MISiS, 2001 .-- 29p.
Lectures of Associate Professor A.A. Maltsev.
Application
table 1Steel ropes LK-R 6Ch19 (1 + 6 + 6/6) +1 o.s. (GOST 2688-80)
| diameter Rope, mm | discontinuous Effort, N | diameter Rope, mm | discontinuous Effort, N | diameter Rope, mm | discontinuous Effort, N |
| 3,6 | 8780 | 11,0 | 83200 | 28,0 | 525000 |
| 3,8 | 9930 | 12,0 | 95000 | 30,5 | 629000 |
| 4,1 | 11550 | 13,0 | 107500 | 32,0 | 654500 |
| 4,5 | 13300 | 14,0 | 131000 | 33,5 | 718000 |
| 4,8 | 15200 | 15,0 | 152000 | 37,0 | 854000 |
| 5,1 | 17200 | 16,5 | 184500 | 39,5 | 977000 |
| 5,6 | 20950 | 18,0 | 220000 | 42,0 | 1110000 |
| 6,2 | 25500 | 19,5 | 253000 | 44,5 | 1225000 |
| 6,9 | 31800 | 21,0 | 294500 | 47,5 | 1435000 |
| 7,6 | 38000 | 22,5 | 333000 | 51,0 | 1625000 |
| 8,3 | 46100 | 24,0 | 380000 | 56,0 | 1980000 |
| 9,1 | 55000 | 25,5 | 430000 | ||
| 9,6 | 64650 | 27,0 | 483500 |
table 2
Hook hangers
| Carrying capacity, t | Number of blocks | Block diameter, mm | Hook number |
| 3,2 | 1 | 320 | 12A |
| 5 | 2 | 400 | 14A |
| 10 | 3 | 360 | 17A |
| 12,5 | 3 | 500 | 18A |
| 16 | 3 | 400 | 19B |
| 20 | 4 | 500 | 20A |
| 25 | 3 | 400 | 21B |
| 32 | 3 | 400 | 22B |
| 32 | 4 | 610 | 22A |
| 50 | 5 | 700 | 24B |
table 3
Technical characteristics of crane electric motors
| engine's type | power, kWt | Rotation frequency, rpm |
| DMTKF 011-6 | 1,4 | 875 |
| DMTKF 012-6 | 2,2 | 880 |
| DMTKF 111-6 | 3,5 | 900 |
| DMTKF 112-6 | 5,0 | 910 |
| MTKI 160 L8 | 7,0 | 680 |
| MTKF 311-8 | 7,5 | 690 |
| MTKI 160 L6 | 10,0 | 915 |
| MTKF 312-8 | 11,0 | 700 |
| MTKF 411-8 | 15,0 | 695 |
| MTKF 412-8 | 22,0 | 700 |
| MTKN 511-8 | 30,0 | 700 |
| MTKN 512-8 | 37,0 | 700 |
| MTKN 512-6 | 55,0 | 925 |
table 4
Dimensions of crane electric motors
| engine's type | l1 | l10 | l31 | l33 | b10 | b11 | H | H31 | d | b | h |
| DMTKF 011-6 | 60 | 140 | 70 | 407 | 140 | 188 | 112 | 320 | 28 | 8 | 31 |
| DMTKF 012-6 | 60 | 159 | 70 | 442 | 159 | 210 | 112 | 320 | 28 | 8 | 31 |
| DMTKF 111-6 | 80 | 190 | 140 | 713 | 220 | 290 | 132 | 342 | 35 | 10 | 38 |
| DMTKF 112-6 | 80 | 235 | 135 | 574 | 220 | 290 | 132 | 342 | 35 | 10 | 38 |
| MTKI 160 L | 140 | 254 | 108 | 910 | 254 | 320 | 160 | 410 | 60 | 12 | 45 |
| MTKF 311 | 110 | 260 | 155 | 637 | 280 | 350 | 180 | 444 | 50 | 14 | 53,5 |
| MTKF 312 | 110 | 320 | 170 | 712 | 280 | 350 | 180 | 444 | 50 | 14 | 53,5 |
| MTKF 411 | 140 | 335 | 175 | 749 | 330 | 440 | 225 | 527 | 65 | 18 | 66,4 |
| MTKF 412 | 140 | 420 | 165 | 824 | 330 | 440 | 225 | 527 | 65 | 18 | 66,4 |
| MTKN 511 | 140 | 310 | 251 | 945 | 380 | 500 | 250 | 570 | 70 | 18 | 71,4 |
| MTKN 512 | 140 | 390 | 271 | 1054 | 380 | 500 | 250 | 570 | 70 | 18 | 71,4 |
table 5
Gearbox specifications
| Gear unit size | Ratio | Torque on the low-speed shaft, Nm |
| Ts2-250 | 8, 10, | 2500 |
| Ts2-300 | 3400 |
|
| Ts2-350 | 5800 |
|
| Ts2-400 | 8000 |
|
| Ts2-500 | 18000 |
|
| Ts2-650 | 33500 |
|
| Ts2-750 | 47500 |
|
| Ts2-1000 | 128000 |
Depending on the requirements for lubricants, components of crane mechanisms are divided into the following main groups: gearboxes and gear couplings, open gears, rolling and sliding bearings, flanges of traveling wheels, rails and guides, ropes.
The gearbox is suitable for transmission oils. Essential features transmission oils according to GOST 23652-79 - their all-season nature, long service life and high load capacity.
For rolling bearings, multigrade greases with good anti-corrosion properties and long service life are preferred.
The ribs of the travel wheels are lubricated with graphite rods (TU 32CT 558-74).
Press grease C. GOST 4366-76 - grease for bearings, open gears, guides.
To lubricate the rope, wire rope grease is used according to TU 38-1-1-67.
Graphite grease GOST 333-80 is used to lubricate the flanges of travel wheels and ropes.
Lubricants must be free of foreign matter.
Safety engineering
Only persons who are at least 18 years of age must be allowed to operate the crane, who have the appropriate certificate and have passed a medical examination for the suitability of working on the crane.
Before starting work, the driver must check technical condition the main mechanisms and assemblies of the crane (brakes, hooks, ropes, blocks, metal structures of the crane) and the correct operation of safety devices.
The operation of electric hoists and their supervision must be carried out in accordance with the "Rules for the construction and safe operation hoisting cranes ".
Supervision of electric hoists is imposed by the order of the administration on a certain person of technical personnel with appropriate qualifications and experience, who is responsible for the good condition of electric hoists and their safe operation.
The voltage in the mains must not be lower than the current standards, otherwise the electric hoist, brake and magnetic starters will not work normally.
It is not allowed to lift loads exceeding the rated carrying capacity, as well as exceeding the specified in technical characteristics operating mode and operation of electric hoists in conditions that do not allow their use.
When operating the electric hoist, the worker should be on the side of the open part of the drum.
The load must not be suspended in such a way that an unacceptable load on the hook tip is obtained. In such cases, the hook may bend noticeably.
Pulling loads with an electric hoist with an oblique tension of the ropes, tearing off attached objects, as well as the production of work unusual for it with the help of an electric hoist is prohibited.
The GGTN rules, as well as the CMEA 725-77 standard, on hoisting cranes with an electric drive provide for the installation of limit switches for automatic stopping:
crane, if its speed can exceed 0.533 m / s (according to the CMEA-0.5 m / s standard);
lifting mechanism of the load gripper before approaching the stop.
When lifting a load, do not move the hook holder to the limit switch.
The limit switch is an emergency stop. It is not permitted to use it as a permanent automatic stop.
It is absolutely necessary to check the correct operation of the limit switch at the beginning of each shift.
The limit switch of the travel mechanism is set so that at the moment the current is turned off, the distance from the buffer to the stops is at least half of the braking distance. Limit switches are installed in the electrical circuit so that when they are opened, the circuit is preserved for the reverse movement of the mechanism.
The limit switch of the lifting mechanism is installed so that after stopping the load gripper, the gap between it and the stop on the trolley is at least 200 mm. For this purpose, switches of the KU 703 type are used, which has a two-armed lever.
Lifting mechanisms
A schematic diagram of the lifting mechanism is shown in Fig. 115. Typically, these mechanisms consist of a toothed cylindrical or worm gear coupled with an electric motor. The output shaft of the gearbox is connected to the drum.
As a motor coupling, an elastic finger coupling MUVP (mechanical engineering standard MN 2096-61) or a gear coupling (GOST 5006-55) is often used.
For mechanisms for lifting the load, which have a non-separable kinematic connection between the drum and the motor, one of the half-couplings connecting the motor with the gearbox can be used as a brake pulley. If this clutch is elastic (MUVP, spring, etc.), then as a brake pulley, according to the rules of Gosgortekhnadzor, it is permissible to use only the half-clutch located on the gearbox shaft. In this case, the elastic elements of the clutch when braking are freed from the action of the load moment, as a result of which their service life increases.
Rice. 1. Diagram of a lifting mechanism with a mechanical drive
Rice. 2. Couplings with a brake pulley:
a - MUVP coupling; b - gear clutch
For mechanisms with frictional or cam clutches (usually this is the case of driving several mechanisms from one engine, for example, automobile cranes, etc.), the brake pulley must be fastened directly to the drum or mounted on a shaft that has a rigid kinematic connection with the drum.
According to the rules of Gosgortekhnadzor, the mechanisms for lifting the load and changing the boom outreach are performed in such a way that the lowering of the load or boom is possible only with the engine. The mechanisms of hoisting machines, equipped with cam, frictional or other types of devices, for switching the ranges of speeds of working movements are arranged so that spontaneous engagement or disengagement of the mechanism is impossible. With the winch for lifting the load and the boom, in addition, the possibility of switching the speed under load is excluded, as well as the shutdown of the winch mechanism without first applying the brake. The use of friction and cam engagement clutches on mechanisms designed to lift people, molten or hot metal, poisonous and explosive substances is not allowed.
The peculiarities of connecting the drum with the gearbox have a significant impact on the design and performance of the hoist mechanism. There are several options for performing this node. The first option is a scheme with the installation of the drum shaft on two independent supports and the connection of the drum shaft with the gearbox shaft by means of a coupling. Since the drum supports are independent of the gearbox, some errors may occur during assembly. That's why coupling is compensating. It is very convenient to use for this purpose an elongated gear coupling, which allows a significant relative displacement of the connected shafts, which simplifies the process of mounting the mechanism. Connections made according to this scheme are distinguished by their reliability in operation, ease of installation and maintenance of the mechanism, but they have relatively large dimensions.
Reducing the dimensions can lead to the use of two- and three-bearing shafts of the lifting mechanism, in which the drum shaft is simultaneously the output shaft of the gearbox. The two-bearing shaft is very heavy. In addition, inaccuracy in the installation of a separate drum support leads to a violation of the accuracy of the gearing in the gearbox. A three-bearing shaft is very sensitive to mounting inaccuracies. In both cases, separate assembly and running-in of the gearbox becomes impossible, which violates the principle of creating a block design. Therefore, these two schemes are not widely used.
In some designs, the torque is transmitted to the drum using an open gear pair. In this case, the gear wheel can be fixed on the drum shaft or mounted directly on the drum, then the drum axis will work only for bending. Since gears are usually placed in closed cases to increase their reliability and durability, these schemes are not widely used and are used only in manual and special mechanisms (for example, in two-drum drives of casting cranes).
To obtain the static definability of the shafts and create a block and compact design, it is most rational to install one of the drum axis supports inside the gearbox output shaft console. The structural implementation of this unit is shown in Fig. 4. The end of the output shaft of the reducer is made in the form of a half of a toothed coupling; the second half of the coupling is attached to the drum. in this case, both the gearbox shaft and the drum axis are mounted on two supports. The drum axis works only for bending.
Rice. 3. Diagrams of connection of a drum with a gearbox
In modern cranes, gearboxes mounted directly on the driven shaft are increasingly used. At the same time, it eliminates the laborious work of aligning the installation and centering the gearbox, and compresses the requirements for manufacturing accuracy and the rigidity of the mechanism frame. Mounted gearboxes are especially advisable when using flanged motors, since then all adjustment work is completely eliminated.
Rice. 4. Typical design of the connection of the drum with the shaft of the gearbox using a gear coupling
The design of the lifting mechanism is significantly influenced by the frequency of the chain hoist. The choice of the frequency of the chain hoist is made on the basis of a constructive analysis of the selected scheme of the mechanism. In cranes where the rope is wound on a drum without passing through the guide blocks (for example, in overhead cranes), double chain hoists are used to ensure a strictly vertical lifting of the load. In cranes, where the rope passes through the guide blocks before being wound onto the drum, double chain hoists are usually not used (with the exception of some designs of jib cranes) and single chain hoists are used with a multiplicity higher than that of double ones.
In lifting mechanisms, the suspension of the load on one branch of the rope is used only in cranes with low lifting capacity (up to 1-3 tons). In jib (portal) cranes with a large lifting height, a suspension on one branch is used with a lifting capacity of 5 and even 10 tons. With a lifting capacity of up to 25 tons, two-, three- and four-fold pulley blocks are usually used. And with even higher carrying capacities, the frequency of the chain hoist reaches 12.
Polyspasts with an odd multiplicity can cause a misalignment of the hook suspension, therefore, pulley blocks with an even multiplicity are more preferable to use. The unification of lifting mechanisms for cranes of various lifting capacities is achieved by changing the multiplicity of the chain hoist to obtain approximately the same torque from the load and the required power of the electric motor. This makes it possible to use the same electric motors, gearboxes, drums, blocks, ropes, brakes, etc., in cranes of various carrying capacities.
Pneumatic hoisting mechanisms are widely used. For work in an explosive environment, such hoists are produced with chains made of special steel, which does not cause the formation of sparks, and with bronze load hooks. Pneumatic piston lifts can be with vertical or horizontal arrangement of the working cylinder. The air pressure in such hoists is used in the range from 2 to 12 am, their carrying capacity is from 10 kg to 5 t / the diameter of the working cylinders is from 30 to 300 mm; lifting height from 50 to 2000 mm. The lift has a double-acting cylinder. The control is carried out using a two-button distributor connected to the cylinder by two air ducts. The lifting speed is infinitely variable; in any position of the hook, the lift can be stopped. Depending on the lifting capacity and the diameter of the air duct, the lifting speed is 0.1-0.5 m / s.
Rice. 5. Pneumatic lifts
The cantilever hoist is designed to withstand bending and overturning moments. The lifting console is rigidly fixed on an additional full-turn guide tube moving along the outer surface of the pneumatic cylinder; the guide tube is connected to the piston rod. The trolley for the suspension of the lift is double-rail. The arrangement of pneumatic lifts using deflecting rollers and pulleys is shown in Fig. 5, c.
The lifting height of the hook of the hoist shown in fig. 5, c, is twice the piston stroke. Significant lifting heights with minimum overall dimensions the lift is achieved according to a scheme with a horizontal arrangement of the working cylinder. The horizontal movement of the stem is converted by deflection rollers into vertical movement of the hook. With increased cleanliness of the working surfaces of the cylinder and piston and with good quality and the design of seals, the efficiency of pneumatic piston lifters reaches 0.9 - 0.93. With a built-in chain hoist, the lifting height of such hoists can reach up to 9 m.
In cranes equipped with a load electromagnet, the lifting mechanism must also have a special cable drum for a flexible cable that supplies electricity to the magnet. The cable drum is located on a separate shaft and is driven from the cargo drum shaft using a chain or gear drive. From the mains, the current is supplied to the rotating drum by means of a slip-contact slip ring.
The lifting mechanisms of stacker cranes are carried out using rope or chain loading bodies. The greatest application is received by rope hoisting mechanisms, in which normal units and elements of other types of hoisting machines are widely used. Very often, electric hoists with a micro drive are used as a lifting mechanism, which ensures accurate load placement in the rack cells.
The advantage of chain hoists is their compactness. The disadvantage of chain hoist mechanisms is the relatively high cost of the chain and the difficulty of placing its idle branch.
In stacker cranes with control from the cabin, which rises together with the load gripper, ropes are usually used as a more reliable flexible load body or the drive for lifting the load is carried out by a chain, and the drive for lifting the cabin is carried out by a cable. At low heights of lifting the load with a stacker crane, use chain mechanisms lifting mechanisms equipped with hydraulic cylinders, similar to the lifting mechanisms of forklift trucks. In this case, the hydraulic cylinder is located vertically on the crane column and the cylinder plunger, rising upward, is equipped with two movable blocks, through which two load plate chains are thrown, attached to the load carriage.
Rice. 6. The lifting mechanism of the magnetic hook carriage
The clamshell winches of two-rope grabs have two drums - one for the hoisting rope, the other for the closing rope. Working with a two-rope grab requires separate work with each drum. So, when scooping up the load, the closing rope is wound on the drum, and the hoisting rope has some slack even when the grab is deepened. When lifting and lowering the grab, both drums rotate together. When the hanging grab is opened, the drum of the lifting rope is stationary, and the drum of the closing rope rotates downhill. When opening a rising or falling grab, it is necessary to rotate the malfunctioning drums, but at different speeds.
Clamshell winches are divided into two groups - single-engine and twin-engine. Single-motor winches have a motor, kinematically rigidly connected to the shaft of the closing drum. The drum of the hoisting rope is connected to the engine by means of a rigid connection, which is switched off as required by means of a frictional connection. The disengagement of the rigid connection of the lifting drum is carried out using a clutch controlled clutch. The drum can be held stationary when the brake is closed. When scooping, the brake is closed, the drum 6 is stationary, the clutch is open and the clutch slips.
At the end of scooping, the lifting drum begins to rotate to lift under the action of the friction clutch, while the brake is open. To open the grab, the brake closes and stops the drum, and the drum of the closing rope works towards the descent. Subsequent lifting or lowering of the open grab requires the brake to be released and the clutch engaged, since otherwise the jaws will spontaneously close by turning the weak friction clutch, which serves solely to automate the transition from digging to lifting. It creates the minimum tension in the hoisting rope necessary to eliminate slack and overcome the inertia of the drum mass. Excessive tension on the hoisting rope adversely affects the scooping process. A significant disadvantage of a single-engine winch is the impossibility of combining movements (opening - closing the jaws) on the go.
Rice. 7. Single motor grab winch:
a - a diagram of the mechanism; b - change in the force in the ropes during operation
When using the winch according to the above diagram, the load on the ropes is very uneven. When the filled grapple is moving, the weight of the load Q and the grapple G itself is carried by the fully closing rope, while the hoisting rope is almost unloaded. When lifting or lowering an empty grab, the main load is taken up by the hoisting rope, and the closing rope is unloaded.
Rice. 8. Twin-motor grab winch with independent drums:
a - mechanism exema; b - the change in the force in the ropes in the process of work; 1 - closing rope; 2 - hoisting rope
A common disadvantage of single-engine winches is the presence of quick-wear clutches and clutches; they are mainly used with low productivity and load capacity. The main application is found for twin-engine winches, which can carry out any combination of operations, which significantly increases the productivity of the crane. The control of twin-engine winches is simpler and safer, however, the total power of both motors of the twin-engine winch is 20-50% more than the power of the Motor of the single-engine winch. The most widely used as Twin-engine winches are clamshell winches consisting of two single-type normal crane single-drum winches with independent electric motors. One winch is for the hoisting rope and the other for the trailing rope. When scooping up the load, the motor of the closing winch is running, which at the end of scooping is loaded with the full weight of the loaded grab. The hoist motor is turned off and the hoist's brake is released to maintain the slack in the hoisting rope. Then the motor of the hoisting winch is switched on, the speeds and loads are leveled and the loaded grab is lifted with practically the same effort of the hoisting and closing ropes. Since the overload of the closing motor at the end of the scooping process is short-lived, both motors with a certain margin take the same power, equal to 0.6 of the total power required to lift a loaded grab. Such winches are very simple in design and quite simple to operate.
Rice. 9. Twin-engine clamshell planetary winch
Clamshell twin-engine winches with planetary connection between drums are also widely used. One of the schemes of such winches is shown in Fig. 9. This winch has two motors of different power. The lifting motor is rigidly connected to the lifting drum and the planetary gear ring. The closing motor drives the sun wheel of the planetary gear. The closing drum receives rotation through a gear connected by a planetary carrier, on which the planetary gear axles sit. When scooping up a load, the engine is inhibited. Only the engine is running, rotating the closing drum through the wheel and carrier. The satellites roll on a fixed frame. When lifting or lowering the grapple, the engine is braked and the engine runs, rotating both drums at the same speed. At the same time, the toothed ring rotates and the satellites roll along the stationary wheel, driving the carrier and the closing drum. To open or open the jaws on the move, while the engine is running, the engine is turned on, accelerating or slowing down the rotation of the carrier, and therefore the closing drum.
The power of the lifting motor is selected equal to the required lifting power of the loaded grab; the power of the closing motor is equal to 0.5 lifting power at a rope speed during scooping equal to the lifting speed of the grab. The total power is equal to 1.5 lifting power. The engine brake is calculated as for the full weight hoist of a laden grapple. The engine brake is calculated only for 50% of the weight of the loaded grab, as a result of which, when switching from the scooping process to lifting the loaded grab after the engine 5 is turned off, the rope tensions are equalized due to brake slippage. Since the magnitude of the braking torque can be unstable, the calculations usually do not take into account the possibility of equalizing the tension of the ropes and with a certain margin assume the distribution of the load between the ropes the same as in a single-engine winch.
Rice. 10. Diagram of a multi-speed lifting mechanism with a planetary clutch
In many cases, in mechanisms for lifting hoisting machines, it is necessary to change the speed of lifting and lowering the load, depending on the nature of the operation being performed and on the size of the load. This need has given rise to the emergence of multi-speed cargo lifting mechanisms.
So, in the mechanism for lifting an overhead crane with a lifting capacity of 15 tons, two speeds are achieved by using two drive motors and a planetary clutch. The drum of the lifting mechanism rotates from the main electric motor through a two-stage helical gearbox, and when operating at low speed from auxiliary engine which is connected to the drum through the rotor of the main motor, a planetary gear clutch and a single-stage helical gearbox. The mechanism has three brakes: the main engine has a brake, the auxiliary engine has a brake 9 and a brake on the rim of the planetary clutch.
When operating at normal speed, the auxiliary motor brake is closed and the other brakes are opened. When operating at low set speed, the auxiliary motor is activated, the outer rim of the planetary clutch is braked and the brakes are released. If the planetary clutch brake does not open during operation of the main electric motor due to some malfunction and the outer rim of the clutch remains braked, the rotor of the auxiliary motor rotates at an increased speed, which can cause damage to the motor. To prevent this danger, the mechanism is equipped with two centrifugal switches. The switch opens the control circuit at double the speed of the rotor of the main electric motor and stops the mechanism in case of failure of the planetary clutch or a malfunction of its brake during operation at low speed from the auxiliary electric motor. The switch opens the control circuit when the auxiliary motor doubles the rotor speed and stops the hoist mechanism in the event of a brake failure when operating at high speed from the main motor.
The planetary clutch carrier is connected to the rear end of the main motor rotor shaft. On the carrier axles, two satellites are fixed, which are in engagement with the sun wheel and a toothed ring fixed in the body. The body is bolted to the brake pulley. The shaft of the sun wheel is connected to the output shaft of the helical gearbox, the high-speed shaft of which is connected to the shaft of the auxiliary motor.
When the auxiliary motor is turned on, rotation is transmitted through the sun wheel and satellites to the carrier, which drives the main motor shaft, gearbox and drum in rotation. In this case, the brake is closed and the planetary clutch ring gear is stationary. When operating from the main engine, rotation is transferred to the carrier, and from it to the satellites. The sun wheel 6 remains stationary because the auxiliary motor brake is closed and the motor is not turned on. The satellites roll on the sun wheel and rotate the ring gear. The planetary clutch brake is open and its rim rotates freely.
The described system provides landing speeds equal to 0.65 m / min at the main hoisting speed equal to 8 m / min. The use of planetary gears allows you to create mechanisms that are particularly compact.
In fig. 12 shows a kinematic diagram of a multi-speed crane lifting mechanism, which provides two lifting speeds and three lowering speeds, which makes it possible to accurately set the elements mounted by the crane.
Rice. 11. Planetary clutch
In fig. 13 shows a section through the drum of this mechanism with an integrated planetary gearbox. The mechanism consists of two motors of the same power with a squirrel-cage rotor, two two-stage gearboxes and a drum with a planetary gear built into it. The drum shaft is split, which makes it possible to vary the speed of rotation of the drum over a wide range.
When one of the engines is turned on, for example, the engine and the brake is open (while the engine is stationary and the brake is closed), the gear, rotating with the shaft, rotates the gear in engagement with it, which, in turn, is in mesh with the gear. The gear runs around the gear, which remains stationary as the motor and shaft do not rotate. In this case, the drum rotates at a speed provided by the gear ratio of the reducer and the planetary gear 3-11.
Rice. 12. Diagram of the multi-speed lifting mechanism tower crane MSK 5/20
When both electric motors are turned on so that the gears rotate in one direction, the drum rotation speed will increase in proportion to the gear ratio of the gearbox. When the electric motors, and therefore the gears, rotate in different directions, the rotation speed of the drum decreases.
Thus, when lowering the load, the lowest landing speed is obtained when both engines are turned on in different directions; the highest speed is when both motors are turned on in the same direction and the average speed is when one of the motors is turned on. When lifting a load, two speeds are used - the first when one engine is running and the second when both motors are running in the same direction.
In electric hoists, a so-called microdrive is often used, which ensures low landing speeds. In fig. 14 shows the microdrive of the TE-VNIIPTMASH hoist lifting mechanism. The hoist has a main motor built into the drum, which provides lifting of the load at a speed of 8 m / min. To obtain micro-speeds (equal for hoists with a carrying capacity of 1 and 2, 3, 5 tons, respectively, 1, 0.6, 0.5 m / min), the hoist is supplied with a microdrive consisting of a low-power AOL type motor connected through a gear pair and an electromagnetic disc clutch clutch with the high-speed shaft of the lifting mechanism. When the main motor is turned on, the micro-drive shaft rotates with no load, and the gear pair 2 remains stationary. When the microdrive motor is turned on, the electromagnetic clutch is simultaneously turned on and rotation is transmitted from the micromotor through the gear pair to the gearbox shaft of the lifting mechanism.
Rice. 13. Drum with built-in planetary gearbox
Rice. 14. Microwire hoist TE-VNIIPTMASH
In elevator lifting mechanisms, winches with traction sheaves are currently used, in which there is no rigid connection of the cab and counterweight with the leading element of the lifting mechanism - traction sheave. The traction force in the ropes is created by friction between the rope and the walls of the pulley grooves. The design of elevators of this type is characterized by small dimensions, simplicity, increased operational safety and significantly great opportunities unification, since the same winch can be used for buildings of various storeys.
In gearless winches, the traction pulley and the brake pulley are located on the rotor shaft of a low-speed electric motor direct current operating on the so-called generator-engine system. Due to the absence mechanical transmission the design of the gearless winch turns out to be more compact, despite the fact that the low-speed electric motor has significantly big sizes than a conventional electric motor of the same power. However, the gearless drive includes other electrical machines and devices that are not in the gear drive. Thanks to electrical regulation, gearless winches allow for smooth, stepless speed change in a wide range, which increases the smoothness of starting and stopping, stopping accuracy and reduces noise and vibration. They are widely used at cab speeds of 2 m / s and above. For lower speeds, gear winches are lighter and more economical.
According to the methods of regulating the speed of movement of the cabs, necessary for the implementation of a smooth start and a smooth, precise stop, winches with electrical and mechanical control are distinguished. Electrical speed control by system generator-engine, carried out by changing the voltage supplied to the electric motor, provides smooth regulation in a wide range of speed variation, but it is very complicated and expensive.
Mechanical speed control is used in gear-type winches at cab speeds up to 2-2.5 m / s, and is carried out using a special additional micro-drive.
TO Category: - Lifting and transporting machines
