| Pitch p, mm | Drive sprocket speed, rpm | ||||||||
| 12,7 | 7,1 | 7,3 | 7,6 | 7,9 | 8,2 | 8,5 | 8,8 | 9,4 | |
| 15,875 | 7,2 | 7,4 | 7,8 | 8,2 | 8,6 | 8,9 | 9,3 | 10,1 | 10,8 |
| 19,05 | 7,2 | 7,8 | 8,4 | 8,9 | 9,4 | 9,7 | 10,8 | 11,7 | |
| 25,4 | 7,3 | 7,8 | 8,3 | 8,9 | 9,5 | 10,2 | 10,8 | 13,3 | |
| 31,75 | 7,4 | 7,8 | 8,6 | 9,4 | 10,2 | 11,8 | 13,4 | - | |
| 38,1 | 7,5 | 8,9 | 9,8 | 10,8 | 11,8 | 12,7 | - | - | |
| 44,45 | 7,6 | 8,1 | 9,2 | 10,3 | 11,4 | 12,5 | - | - | - |
| 50,8 | 7,7 | 8,3 | 9,5 | 10,8 | - | - | - | - |
2.4. Design of roller chain sprockets
Sprockets are made of steels 40 and 45 according to GOST 1050-88 or 40L and 45L according to GOST 977-88 with hardening up to 40 ... 50 HRC e. The design of the sprocket is developed taking into account the standard for the profile of the teeth and the cross section of the rim in accordance with GOST 591-69.
The cross-sectional shape of the rim is selected depending on the ratio of the thickness of the disc FROM and rim diameter D e. With a relatively large disk thickness FROM and D e £ 200 mm use a solid disk or a disk with holes to save metal. At D e > 200 mm, it is recommended to use a composite structure.
The position of the hub relative to the disk with the rim is taken for design reasons. When the sprocket is installed cantilevered at the output end of the shaft, it should be located as close as possible to the support in order to reduce the bending moment.
The design of a single-row roller chain sprocket is made according to the following recommendations.
Tooth width, mm:
The sprocket tooth can be made with a bevel (Fig. 2.3, a) or rounded (Fig. 2.3, b);
Bevel angle g = 20 o, tooth chamfer f » 0.2b;
Radius of curvature of the tooth (largest);
Distance from the top of the tooth to the line of the centers of the rounding arcs;
rounding radius r 4 \u003d 1.6 mm with a chain pitch p £ 35 mm, r 4 \u003d 2.5 mm with a chain pitch p\u003e 35 mm;
The length of the largest chord, for sprockets without displacement of the centers of the arcs of the troughs, mm:
| , |
with the displacement of the centers of the arcs of the depressions:
Thickness, mm:;
Groove diameter, mm: .
Inner diameter, mm:
where [ t] = 20 MPa - allowable stress during torsion;
Outer diameter, mm:
Length, mm: ;
- keyway dimensions: width b and depth t2 we choose in accordance with the inner diameter of the hub from table 2.7, the length of the key is taken constructively from the values of the standard range by 5 ... 10 mm less than the length of the hub.
Table 2.7
Prism keys (GOST 23360 - 78)
| Shaft diameter d, mm | Key section | Groove depth | Chamfer, mm | Length l, mm | ||
| b, mm | h, mm | Vala t1, mm | Hubs t2, mm | |||
| Over 12 to 17 Over 17 to 22 | 3,5 | 2,3 2,8 | 0,25…0,4 | 10…56 14…70 | ||
| Over 22 to 30 | 3,3 | 0,4…0,6 | 18…90 | |||
| Over 30 to 38 Over 38 to 44 | 3,3 | 22…110 28…140 | ||||
| Over 44 to 50 Over 50 to 58 Over 58 to 65 | 5,5 | 3,8 4,3 4,4 | 36…160 45…180 50…200 | |||
| Over 65 to 75 | 7,5 | 4,9 | 56…220 | |||
| Over 75 to 85 Over 85 to 95 | 5,4 | 0,6…0,8 | 63…250 70…280 |
Notes: 1. Key lengths l choose from the following row: 10, 12, 14, 16, 18, 20, 22, 25, 28, 32, 36, 40, 45, 50, 56, 63, 70, 80, 90, 100, 110, 125, 140 , 160, 180, 200, 220, 250. 2. An example of key designation with dimensions b = 16 mm, h = 10 mm, l = 50 mm: Key 16´10´50 GOST 23360 - 78.
2.5. Development of a working drawing of a roller chain sprocket
Working drawings of drive roller chain sprockets must be made in accordance with the requirements of ESKD and GOST 591 standards.
On the image of the asterisk (Fig. 2.3) indicate:
Sprocket tooth width;
Crown width (for a multi-row sprocket);
Radius of curvature of the tooth (in the axial plane);
Distance from the top of the tooth to the line of centers of arcs of curvature (in the axial plane);
Rim diameter (largest);
The radius of curvature at the border of the rim (if necessary);
The diameter of the circle of the protrusions;
The surface roughness of the tooth profile, the end surfaces of the teeth, the surface of the protrusions and the roughness of the surfaces of the rounding of the teeth (in the axial plane).
In the drawing, the stars in the upper right corner place the parameter table. The dimensions of the table columns, as well as the dimensions that determine the location of the table on the drawing field, are shown in fig. 2.4.
The sprocket ring gear parameter table consists of three parts, which are separated from each other by solid main lines:
the first part is the basic data (for manufacturing);
The second part is data for control; the third part is reference data.
In the first part of the parameter table are given:
Number of sprocket teeth z;
Mating circuit parameters: pitch R and roller diameter d3;
Tooth profile according to GOST 591 with the inscription: "With offset" or "Without offset" (centers of the arcs of the depressions);
Accuracy group according to GOST 591.
In the second part of the parameter table are given:
The size of the diameter of the circle of the depressions D i and limit deviations (for sprockets with an even number of teeth) or the size of the largest chord L x and limit deviations (for sprockets with an odd number of teeth);
Book title Next page>>§ 8. Safety requirements for hoisting and transport machines and mechanisms.
Ropes and chains for lifting machines. Safety factor of pull ropes.
When calculating the most important parts of hoisting machines and ropes, a large margin of safety is taken.
Ropes and chains- the most critical parts of lifting mechanisms. Methods for securing the ends of the ropes are given in the instructions supplied with the equipment. Cargo, boom, cable, bearing and traction steel wire ropes are checked by calculation before installation on a hoisting machine:
where k - safety factor; P - breaking force of the rope (accepted according to GOST), N; S - the maximum tension of the rope branch (excluding dynamic loads), N.
The tension of steel pull ropes depends on the number of branches and their angle of inclination to the vertical (Fig. 117). The smallest safety factor for some types of ropes is given in table. 38.
Rice. 117. Variation of stresses in ropes and permissible load depending on the angle between rope branches
Table 38
The calculation is carried out according to the formula
The safety factor of pull ropes with hooks, rings or earrings at the ends is assumed to be at least 6. If more than 10% of the wires in a pull rope break in one strand, the entire rope is rejected, no splices are allowed.
The safety factor for welded chains is selected in the range from 3 to 9 depending on the type and purpose of the chain and the type of drive. If the chain links are worn more than 10% of their original diameter (chain gauge), the chain operation is not allowed.
The diameter of a steel rope depends on the diameter of the drum or block it wraps around and is of great importance for ensuring its wear resistance.
where D is the diameter of the drum or block, measured along the bottom of the groove, mm; d - rope diameter, mm; e - coefficient depending on the type of hoisting machine and its mode of operation, having a value from 16 to 30.
steel ropes- a critical element of the hoisting machine, and their condition requires constant monitoring. Steel ropes are rejected according to the number of wire breaks in the length of one lay stride. The lay pitch is determined along the longitudinal line of the rope surface; it is equal to the distance at which the number of strands in the section of the rope fits. For multi-strand ropes having strands in the inner and outer layers, the count of the strands is made based on the number of strands in the outer layer.
The rejection of the ropes is carried out according to the following criteria, given in table. 39.
Table 39
Ropes of hoisting machines intended for lifting people, as well as for transporting molten or red-hot metal, acids, explosives, flammable or poisonous substances, are rejected with half the number of wire breaks in one lay step than indicated in Table. 39.
With surface wear of the rope or corrosion of the wires, their number at the lay step decreases as a sign of rejection (Table 40).
Table 40
In case of wear or corrosion of the rope wires that have reached 40% or more of their original diameter, as well as when a broken strand is detected, the rope is rejected.
When using a welded chain, the diameter of the drum or block is taken: for manual hoisting machines - at least 20 times the chain caliber, and with a machine drive - at least 30 times the chain caliber. When using a sprocket, welded calibrated and leaf chains must be in simultaneous full engagement with at least two sprocket teeth.
3.4.7.1. Lamellar chains used as cargo chains must comply with the requirements of GOST 191-82 and GOST 588-81.
3.4.7.2. Welded and stamped chains used as cargo and for the manufacture of slings must comply with the requirements of TU 12.0173856.015-88.
3.4.7.3. The safety factor of leaf chains used in hoisting machines must be at least 5 with a machine drive and at least 3 with a manual one.
3.4.7.4. The safety factor of welded and stamped cargo chains and chains for slings must not be less than that specified in the documentation.
3.4.7.5. The rejection of chain slings is carried out in accordance with the Rules for the Construction and Safe Operation of Hoisting Cranes.
3.4.7.6. Splicing of chains is allowed by electric or forge welding of new inserted links or by using special connecting links. After splicing, the chain is inspected and load tested in accordance with the documentation.
3.4.7.7. Chains used on hoisting machines and for the manufacture of slings are accompanied by a manufacturer's certificate of their testing in accordance with the requirements of the state standard by which they are manufactured.
3.4.7.8. In the absence of the specified certificate, a chain sample is tested to determine the breaking load and check for compliance with the dimensions of the state standard.
3.4.8. Safety requirements for ropes and cords
from vegetable and synthetic fibers
3.4.8.1. Hemp ropes are allowed to be used for the manufacture of slings. In this case, the safety factor must be at least 8.
Hemp ropes must comply with the requirements of GOST 30055-93.
3.4.8.2. When rigging, in addition to these ropes, sisal and nylon ropes can be used - according to GOST 30055-93, ropes - according to GOST 1868-88.
3.4.8.3. Ropes, cords and ropes used for the manufacture of slings and for rigging must be provided with tags (labels), which must indicate the inventory number, permissible load capacity and the date of the next test.
3.4.8.4. Ropes and cords that are not provided with passports, before use, and also periodically at least 1 time in 6 months, must be subjected to a technical examination, including inspection and testing with a record of this in the Journal of Accounting and Inspection of Slings.
3.4.8.5. For work in dry rooms, it is recommended to use white ropes, which have great strength, but quickly collapse under the influence of moisture. For work in conditions of high or variable humidity, impregnated ropes or ropes made of synthetic fibers are recommended.
3.4.8.6. Ropes and cords should be stored in closed dry rooms, protected from direct sunlight, oil, gasoline, kerosene and other solvents, suspended or on wooden racks at a distance of at least 1 m from heating appliances.
3.4.8.7. The ends of the ropes, if they are not used for tying loads, must be equipped with thimbles, staples and other lifting devices.
3.4.8.8. The possibility and conditions for the use of slings made of synthetic and plant materials are established by the organization using such slings.
Specifications must be developed for the calculation, manufacture, testing and rejection of these slings.
3.4.8.9. When inspecting the ropes, it is necessary to pay attention to the absence of rot, burning, mold, knots, fraying, dents, tears, cuts and other defects. Each turn of the rope should be clearly distinguished, the twist should be uniform.
Hemp ropes used for guying should not have frayed or mashed strands.
3.4.8.10. With satisfactory results of the inspection, static tests of the rope with a load twice the allowable working load, with an exposure time of 10 minutes, should be carried out.
3.4.8.11. During operation, ropes and cords should be inspected every 10 days. To ensure safety, the permissible working load on ropes and cords should be reduced in accordance with the results of strength tests obtained during the technical examination.
3.4.8.12. Registration, date and results of technical examinations and inspections of ropes, cords and ropes should be reflected in the Logbook for accounting and inspection of slings.
Answer. Must be at least 5 for machine drive and at least 3 for manual drive (clause 3.4.7.3).
Question 132. In what way is chain splicing allowed?
Answer. Allowed by electric or forge welding of new inserted links or by using special connecting links. After splicing, the chain is inspected and tested by load in accordance with the documentation (clause 3.4.7.6).
Question 133. What is the use of hemp ropes for?
Answer. It is allowed to use for the manufacture of slings. In this case, the safety factor must be at least 8 (clause 3.4.8.1).
Question 134
Answer. The inventory number, permissible carrying capacity and the date of the next test must be indicated (clause 3.4.8.3).
Question 136. What should be paid attention to when inspecting ropes?
Answer. It is necessary to pay attention to the absence of rot, burning, mold, knots, fraying, dents, tears, cuts and other defects. Each turn of the rope should be clearly distinguished, the twist should be uniform. Hemp ropes used for guying should not have frayed or macerated strands (clause 3.4.8.9).
Question 137. During what periods should ropes and cords be inspected during operation?
Answer. Should be inspected every 10 days (clause 3.4.8.11).
Question 138
Answer. Designed to work on wooden and wooden poles with reinforced concrete stepsons of power transmission and communication lines, on reinforced concrete poles of overhead power lines (VL) 0.4-10 and 35 kV, as well as on cylindrical reinforced concrete poles with a diameter of 250 mm VL 10 kV (clause 3.5 .one).
Question 139
Answer. Service life 5 years (p. 3.5.12).
Question 140. When are claws and manholes subjected to static tests?
Answer. They are tested at least once every 6 months (clause 3.5.16).
Question 141. What should be the mass of the belt?
Answer. Should be no more than 2.1 kg (clause 4.1.7).
Question 142. What dynamic load should the belt withstand?
Answer. Must withstand the load arising from the fall of a load weighing 100 kg from a height equal to two lengths of the sling (halyard) (clause 4.1.9).
Question 143
Answer. Should it be made of steel rope or chain?
Question 144
Answer. They are used to ensure the safety of an employee when ascending and descending along vertical and inclined (more than 75 ° to the horizon) planes (clause 4.3.1).
Question 145. What is the principle of operation of the catcher and the system as a whole?
Answer. When the worker falls under his weight through the belt-sling system, the body of the safety device rotates, and the safety rope is pinched between the movable and stationary cams, locking the safety device on the safety rope and keeping the worker from moving down (clause 4.3.3).
Question 146. For what purposes should helmets be used?
Answer. Should be used to protect the worker's head from mechanical damage from objects falling from above or in collision with structural and other elements, to protect against water, electrical shock, such when working at height on construction, installation, dismantling, repair, adjustment and other work (p. 4.5.1).
Question 147. What should helmets provide?
Answer. Should provide the maximum transmitted force at a nominal impact energy of 50 J, not more than 5 kN (500 kgf) - for helmets of the first quality category and not more than 4.5 kN (450 kgf) - for helmets of the highest quality category (clause 4.5.3).
Question 148. What colors are the helmet casings produced in?
Answer. Available in four colors:
white - for management staff, heads of workshops, sections, employees of the labor protection service, state inspectors of supervisory and control bodies;
red - for foremen, foremen, engineering and technical workers, chief mechanics and chief power engineers;
yellow and orange - for workers and junior service personnel (clause 4.5.6).
Question 149. What marking does each helmet have?
Answer. Has the following markings:
in the middle of the upper part of the visor of the helmet, the name of the helmet - "Builder" should be applied by casting;
on the inside of the visor or body by casting or molding should be applied: the trademark of the manufacturer, the designation of the standard, the size of the helmet, the date of issue (month, year) (clause 4.5.16).
Question 150. What is the warranty period for storage and operation of helmets?
Answer. The warranty period is 2 years from the date of manufacture (clause 4.5.21).
Question 151. What safety devices should have mechanisms and equipment with a mechanical drive?
Answer. Must have automatic start interlocks that are easily accessible and clearly recognizable to the operator by emergency stop devices. Hazardous moving parts must be guarded (clause 5.1.4).
Question 152. What are the requirements for wrenches?
Answer. Wrench gaps must match the size of the nuts or bolt heads and not have cracks or nicks. It is not allowed to increase the levers of wrenches that are not designed to work with an increased leverage (clause 5.2.10).
Question 153
Answer. They must be provided with gloves with anti-vibration padding on the side of the palm (clause 5.3.6).
Question 154. What voltage should an electrified hand tool be used for?
Answer. It should be used, as a rule, for a voltage not exceeding 42 V. The body of a class I electrified hand tool (at a voltage above 42 V, not having double insulation) must be grounded (zeroed) (clause 5.4.1).
Question 155. Who is allowed to work with a hand-held electrified tool?
Answer. Persons at least 18 years of age who have undergone special training, have passed the appropriate exam and have an entry about this in their labor protection certificate (clause 5.4.6) are allowed.
Question 156. What should a hand pyrotechnic instrument have?
Answer. Should have:
protective device or screen;
a device that protects against an accidental shot;
a device that prevents a shot if the nozzle of the pistol is not resting on the working surface (clause 5.5.2).
Question 157. Who is allowed to work with the use of hand pyrotechnic tools?
Answer. Workers trained in its safe use are allowed (clause 5.5.7).
Question 158
Answer. Allowed employees are at least 18 years of age, who have worked in the organization for at least 1 year, have a qualification of at least the third category, have completed a training course according to an approved program, have passed the exams of the qualification commission and received a certificate for the right to work with a manual piston-type pyrotechnic tool (clause 5.5. ten).
Question 159. Who should have a certificate for the right to manage work with a manual pyrotechnic tool?
Answer. Must have foremen, foremen, mechanics and other specialists associated with the operation of this tool, who must take a course in the program for specialists and receive a certificate for the right to manage these works (clause 5.5.11).
Question 160
Answer. Should get:
work permit for the right to perform work;
pyrotechnic tool;
cartridges (no more than the established norm);
personal protective equipment (hard hat, earmuffs, protective shield, leather gloves or mittens) (clause 5.5.12).
Tasks 81-90
Calculate a vertical bucket elevator with a capacity of Q, intended for transportation of bulk density material r, medium size aWith to the height H. The elevator is installed in an open area.
Select the initial data for solving the problem from Table 5.
Table 5
task number | Q, t/h | r, t/m3 | aWith, mm | Conveyed material |
|
clay dry |
|||||
Pyrite flotation |
|||||
Lump sulfur |
|||||
Sand dry |
|||||
Limestone |
|||||
Chalk crushed |
|||||
Dry ash |
|||||
Bauxite crushed |
Guidelines:, p.216 ... 218, example 12.
Guidelines for the implementation of practical work
Practical work No. 1
Selection of steel ropes and chains, pulleys, sprockets and drums.
1. Selection of steel ropes and chains .
The exact calculation of ropes, welded and plate chains, due to the uneven distribution of stresses, is very difficult. Therefore, their calculation is carried out according to the norms of Gosgortekhnadzor.
Ropes and chains are selected according to GOST in accordance with the ratio:
FR£ FR.m
where FR.m- breaking force of the rope (chain), taken according to the tables
relevant GOSTs for ropes (chains);
FR- estimated breaking force of the rope (chain), determined by
Fp =FmOh· n,
where n- safety factor, taken according to Pra-
forks of Gosgortekhnadzor, depending on the purpose of the rope and
mode of operation of the mechanism. Its meaning for nk ropes and chains
nц are given in Table P1 and P2.
FmOh- maximum working force of the rope branch (chain):
Fmax =G/zhn, kN,
Here G- cargo weight, kN;
z- the number of branches of the rope (chain) on which the load is suspended;
hn- Efficiency of the chain hoist (Table P3).
The number of branches of the rope on which the load is suspended is:
z = u · a ,
where a- the number of branches wound on the drum. For simple (one
narny) chain hoist a= 1, and for the double a = 2;
u- polyspast multiplicity.
According to the value of the breaking force FR from the condition FR£ FR.m
according to the GOST tables, we select the dimensions of the rope (chain).
Example 1 Choose a rope for the lifting mechanism of an overhead crane with a lifting capacity G= 200 kN. Lifting height H= 8m. Mode of operation - easy (PV = 15%). Polyspast double multiplicity u= 4.
Initial data:
G= 200 kN - the weight of the lifted load;
H\u003d 8m - the height of the load;
Mode of operation - easy (PV = 15%);
a= 2 - the number of branches wound on the drum;
u\u003d 4 - the multiplicity of the chain hoist.
Maximum working force of one branch of the rope:
Fmax =G/zhn= 200/ 8 0.97 = 25.8 kN,
where z=u· a= 4 2 = 8 - the number of branches on which the load is suspended;
hn- efficiency of the chain hoist, according to the table. P3 at u= 4 for pulley block with bearing
nick rolling hn= 0.97 Estimated breaking force: Fp =FmOh· nto= 5 25.8 = 129 kN,
where nto– rope safety factor, for a crane with a machine
drive for light duty nto= 5 (Table A1).
According to GOST 2688-80 (Table P5), we select a rope of the LK type - R 6x19 + 1 o. With. with breaking force FR.m. = 130 kN at ultimate strength Gin= 1470 MPa, rope diameter dto= 16.5 mm. Actual Rope Safety Factor:
nf =FR.m. · z· hn/G= 130 8 0.97/200 = 5.04 > nto = 5,
Therefore, the selected rope is suitable.
Example 2 Choose a welded calibrated chain for a manual hoist with a load capacity G= 25 kN. Polyspast multiplicity u= 2 (polyspast simple).
Initial data:
G= 25 kN - lifting capacity of the hoist;
u\u003d 2 - the multiplicity of the chain hoist;
a= 1 - simple chain hoist.
Fmax =G/zhb= 25/2 0.96 = 13 kN,
where z=u· a= 2 1 = 2 - the number of branches on which the load is suspended;
hb\u003d 0.96 - efficiency of the chain block. Estimated breaking force: Fp =FmOh· nc= 3 13 = 39 kN,
where nc- chain safety factor, for welded calibrated
chains with manual drive nc= 3 (Table A2).
According to table P6, we select a welded calibrated chain with a breaking force FR.m. = 40 kN, in which the diameter of the bar dc= 10 mm, internal length (pitch) of the chain t= 28 mm, link width AT= 34 mm.
Actual margin of safety:
nf =FR.m. · z· hn/G= 40 2 0.96/25 = 3.1 > nc= 3.
The selected chain is suitable.
Example 3 Select a load leaf chain for a machine-driven hoist with a lifting capacity of G= 30 kN. The load is suspended on two branches ( z = 2).
Initial data:
G= 30 kN - the weight of the lifted load;
z= 2 - the number of branches on which the load is suspended.
Maximum working force of one branch of the chain:
Fmah =G/zhsv= 30/2 0.96 = 15.6 kN,
where hsv\u003d 0.96 - sprocket efficiency.
Estimated breaking force: Fp =FmOh· nc= 5 15.6 = 78 kN,
where nc- safety factor of the chain, for a lamellar chain with
machine driven nc= 5 (Table A2).
According to table P7, we accept a chain with a breaking force FR.m. = 80 kN, which has a step t= 40 mm, plate thickness S= 3 mm, plate width h= 60 mm, number of plates in one chain link n= 4, diameter of the middle part of the roller d= 14 mm, roll neck diameter d1 = 11 mm, roller length in= 59 mm.
Actual margin of safety:
nf =FR.m. · z· hn/G= 80 2 0.96/30 = 5.12 > nc= 5.
The selected chain is suitable.
2. Calculation of blocks, stars and drums.
The minimum allowable diameter of the block (drum) along the bottom of the stream (groove) is determined according to the standards of Gosgortekhnadzor:
Db³ (e - 1)dto, mm
where e- coefficient depending on the type of mechanism and mode of operation, you
taken according to the normative data of the Rules of Gosgortekhnadzor
(Table A4);
dto- rope diameter, mm.
Block sizes are normalized.
The diameter of the block (drum) for welded non-calibrated chains is determined by the ratios:
for manual mechanisms Db³ 20 dc;
for machine-driven mechanisms Db³ 30 dc;
where dc- the diameter of the steel bar from which the chain is made.
The diameter of the starting circle of the sprocket for a welded calibrated chain (the diameter along the axis of the bar from which the chain is made) is determined by the formula:
Dn. about. = t/sin 90° /z, mm
where t- internal length of the chain link (chain pitch), mm;
z- the number of sockets on the sprocket, accept z³ 6.
The diameter of the starting circle of the sprocket for the leaf chain is determined
are calculated according to the formula:
Dn. about. = t/sin 180° /z, mm
where t- chain pitch, mm;
z- number of sprocket teeth, take z³ 6.
Rope drums are used with a single-layer and multi-layer winding, with a smooth surface and with a screw thread on the surface of the shell, with one-sided and two-sided winding of the rope.
The diameter of the drum, as well as the diameter of the block, is determined according to the Rules of Gosgortekhnadzor:
Db³ (e - 1)dto, mm.
The length of the drum with two-sided winding of the rope is determined by the formula:
and with one-sided winding:
https://pandia.ru/text/78/506/images/image005_7.png" width="124" height="32 src=">,
where z- the number of working turns of the rope;
https://pandia.ru/text/78/506/images/image007_5.png" width="18" height="23 src=">,
Where b- the distance between the axes of the streams of the extreme blocks, is taken according to table P8;
hmin- the distance between the axes of the drum and the axis of the blocks in the uppermost position;
Permissible angle of deviation of the rope branch running onto the drum from the vertical position, = 4 ... 6 °.
The wall thickness of the drums can be determined from the condition of compressive strength:
https://pandia.ru/text/78/506/images/image009_4.png" width="48" height="29"> - allowable compressive stress, Pa, when calculating take:
80MPa for cast iron C4 15-32;
100MPa for steels 25L and 35L;
110MPa for steels St3 and St5.
For cast drums, the wall thickness can be determined by empirical formulas:
for cast iron drums https://pandia.ru/text/78/506/images/image010_1.png" width="26" height="25 src=">= 0.01 dB+3 mm, and then perform a compression test. Should be:
https://pandia.ru/text/78/506/images/image012_2.png" width="204" height="72"> mm
where t\u003d 28 mm - internal link length (pitch) of the chain;
z 6 - the number of nests on the block (asterisk), we accept z=10.
Example 5 According to example 3, determine the diameter of the initial circle of the sprocket.
Sprocket Pitch Circle Diameter
mm,
where t\u003d 40 mm - chain pitch;
z 6 - the number of teeth of the sprocket, we accept z=10.
Example 6 Determine the main dimensions of the cast iron drum according to the example 1..png" width="156 height=44" height="44">, mm
where dk= 16.5 mm - rope diameter;
e- coefficient depending on the type of mechanism and operating mode, for cranes with a machine drive in light duty e=20 (Table A4)
dB\u003d (20-1) ∙ 16.5 \u003d 313.5 mm, we take the value of the drum diameter from the normal series dB\u003d 320 mm (Table A8).
Determine the length of the drum. Drum with double-sided cutting. The working length of one half of the drum is determined by the formula:
mm
where t- pitch of turns, for a drum with grooves
t=dk+(2…3)=16.5+(2…3)=(18.5…19.5) mm, accept t= 19 mm;
zo\u003d 1.5 ... 2 - the number of spare turns of the rope, we accept zo=2 turns;
zp- the number of working turns of the rope
https://pandia.ru/text/78/506/images/image019_0.png" width="210 height=36" height="36"> mm
Full drum length:
Lb=2(lp+l3)+lo, mm,
Where l3- the length of the drum required for fastening the rope;
https://pandia.ru/text/78/506/images/image022_0.png" width="16" height="15">=4-6° - the permissible angle of deviation of the rope branch running onto the drum from the vertical position, we accept = 6°.
l0=200-2∙4/80∙tg6°=99.1mm
accept l0=100 mm.
Thus, the total length of the drum
lb\u003d 2 (608 + 60) + 100 \u003d 1436 mm, we accept
lb=1440 mm = 1.44 m
The wall thickness of the drum is determined by the formula:
https://pandia.ru/text/78/506/images/image024_0.png" width="47 height=19" height="19">mm.
The wall thickness of the cast drum must be at least 12 mm.
Practical work No. 2
Calculation of winches and lifting mechanisms of hoists with manual and electric drives according to specified conditions.
1. Calculation of winches with manual drive
sequence of calculation of a winch with a manual drive.
1) Select a load suspension scheme (without a chain hoist or with a chain hoist).
2) According to the given load capacity, select a rope.
3) Determine the main dimensions of the drum and blocks.
4) Determine the moment of resistance on the drum shaft from the weight of the load Ts and the moment on the shaft of the handle, created by the force of the worker Tr.
Moment of resistance from the weight of the load
N∙ m,
where Fmax- maximum working force in the rope branch, N; dB- diameter of the drum, m.
The moment on the shaft of the handle:
N∙m,
where pp- the effort of one worker, is accepted
pp=100…300 N
n– Number of workers;
https://pandia.ru/text/78/506/images/image001_21.png" width="15" height="17 src=">.png" width="80 height=48" height="48">
where η – winch efficiency.
6) Calculate open gears and shafts (the method of their calculation was studied in the section "Machine parts" of the subject "Technical mechanics").
7) Determine the main dimensions of the handle. The handle rod diameter is determined from the bending strength condition:
m,
where l1- the length of the handle rod, is taken l1=200…250 mm for one worker and l1=400…500 mm for two workers;
https://pandia.ru/text/78/506/images/image029_1.png" width="29" height="23 src=">=(60…80) MPa=(60…80)∙106Pa.
The thickness of the handle in the dangerous section is calculated on the combined action of bending and torsion:
 | ||
The width of the handle is taken equal to
where G- lifting capacity of the winch, kN;
Vp- the circumferential speed of the drive handle is usually taken
Vp=50...60 m/min.
Example 7 Calculate the lifting mechanism of a hand winch designed to lift a load with a weight G= 15 kN per height H= 30m. Number of workers n=2. winch efficiency h=0.8. The drum surface is smooth, the number of layers of rope winding on the drum m=2. Polyspast multiplicity u=2. Polyspast simple ( a=1).
Initial data:
G\u003d 15kN - weight of the lifted load;
H\u003d 10m - the height of the load;
n=2 - the number of workers;
h\u003d 0.8 - winch efficiency;
m=2 - the number of layers of rope winding on the drum;
drum surface is smooth;
u\u003d 2 - multiplicity of the chain hoist;
a=1 - the number of branches wound on the drum.
Rope selection.
Maximum working force in one rope strand:
Fmax= 15/2×0.99=7.6 kN,
where z=u×a= 2 - the number of branches on which the load hangs;
The efficiency of the chain hoist according to the table. P3 for chain hoist with multiplicity u=2 on rolling bearings 0.99.
Estimated breaking force:
fp=nk× Fmax\u003d 5.5 × 7.6 \u003d 41.8 kN,
where nto- safety factor of the rope, for a cargo winch with a manual drive nto=5.5 (Table P1).
According to GOST 26.88-80 (Table P5), we select a rope of the LK-R type 6x19 + 1 o. With. with breaking force fp.m.= 45.45 kN at tensile strength 1764 MPa, rope diameter dto=9.1 mm.
Actual Rope Safety Factor:
nf =Fr.m. ·z hn/G = 45.45 2 0.99/15 = 6 > nto = 5,5.
Determination of the main dimensions of the drum.
Minimum allowable drum diameter:
dB ³ ( e– 1)dk, mm
where e- coefficient depending on the type of mechanism and mode of operation, for
manual cargo winches e=12 (Table A4);
dk- rope diameter, mm, then
dB³ (12 – 1)9.1=100.1mm
We accept from the normal range dB=160mm (Table P8).
The working length of the drum with multi-layer winding of the rope is determined by the formula:
where t – winding pitch, for a smooth drum ; t= dk=9.81 mm ;
Lk – rope length excluding spare turns
Lk=H∙u=30∙2=60m
Full length of the drum with one-sided winding
lb= lR+ lin+ lh,
where lb=(1,5…2)∙ t- the length of the drum required for spare turns ,
lb=(1,5…2)∙9,81=13,65…18,2 mm ,
accept lb=18 mm
lh – the length of the drum required to secure the rope
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