Polyspast gain in strength. Lifting loads without special equipment - how to calculate and make a chain hoist with your own hands. Choosing the optimal design of the chain hoist

Polypast

TO Category:

Construction machines and their operation

Polypast

A polyspast is a system consisting of several movable and fixed blocks and a rope that sequentially envelopes all blocks. One end of the chain hoist is fixed on the holder of movable or stationary blocks, and the other - on the winch drum.

Rice. 1. Schemes of rope pulley blocks a - three-time chain hoist; b, c, d - four-, five- and six-fold pulley blocks

Rice. 2. Scheme of a double chain hoist

The number of working branches (the frequency of the chain hoist) is equal to the number of blocks when the rope escapes from the stationary block of the chain hoist, and the number of blocks of the chain hoist plus one when the rope escapes from the movable block.

Rice. 3. Reverse action chain hoist diagram

Polyspast is the simplest lifting device consisting of blocks connected by a rope. With the help of a chain hoist, you can lift the load or move it horizontally. The polyspast gives a gain in strength due to a loss in speed: how many times it is won in strength, how many times it is lost in speed.

The polyspast consists of two blocks: fixed, attached to the lifting device (beam, mast, tripod), and movable, which is attached to the load being lifted. Both blocks are connected with a rope. The rope, sequentially bending around all the rollers of the blocks, is attached at one end to the upper fixed block. Its other end is attached to the winch drum through branch blocks. If the number of working threads of the chain hoist going to the movable block is even, then the end of the rope is fixed to the upper fixed block, and if it is odd, to the lower movable one.

If the chain of the chain hoist runs not from the lower block, but from the upper one, then the upper block of the fixed block is considered to be diverting. This condition must be taken into account when calculating the chain hoists.

The polyspast is stored in two ways. According to the first method, used when equipping multi-line pulleys with large carrying capacity, the stationary block without ropes is raised to the working position and secured; the lower movable block is at the bottom. Then, a rope is sequentially passed through the grooves (grooves) of the rollers of the upper and lower blocks. The end of the rope is fixed to the upper or lower block, depending on the adopted chain hoist reeving scheme. The rope is often passed through the streams of rollers using manual lever winches, which greatly facilitates the work of reeving the chain hoist.

Recently, when equipping a multi-line pulley block, an auxiliary thin light steel rope with a diameter of 5-6'mm is used, which is manually passed through the rollers of the blocks. The end of the working rope is attached to one end of the thin rope, its second end is fixed to the winch drum. During the operation of the winch, the working rope is pulled through the rollers of the pulley blocks.

During the reeving of the chain hoist, it is necessary to ensure that the junction of the thin and thick ropes, when moving, freely passes through the rollers of the blocks.

In the second method, the pulley block is equipped at the bottom (on a boardwalk or a concrete floor), and then, in finished form, is lifted and fixed in the required place. The blocks are laid flat at a distance of 3-4 m from each other and fixed.

The rope begins to stretch from the roller from which the runaway thread comes off, leading to the winch. When the rope goes around the last roller of the block, its end is fixed to one of the blocks. After fixing the dead thread, the chain hoist is set to its original position.

In some cases, one upper fixed block or the entire chain hoist is lifted using an auxiliary single-roll block or a low-carrying capacity chain hoist. First, the auxiliary block is fixed, a rope is passed through it, to which the main block of the chain hoist is attached. The second end of the rope is fixed on a winch, with the help of which the chain hoist will be lifted. The main block of the chain hoist is fixed from the cradle or from the scaffold.

In fig. 4 shows the reeving diagrams of pulley blocks with two-, four-, five- and six-wheel blocks.

When performing rigging work, there are often cases when blocks of different carrying capacities and ropes are available. In order to choose the right rope for equipping the chain hoist, as well as a winch with the required pulling force, the rigger needs to know the calculation of the chain hoists.

The calculation of the chain hoists is reduced to determining the efforts in the chains of the chain hoists. Usually the blocks themselves do not have to be calculated, since they are calculated during the design, and each of them has a certain carrying capacity.

When rigging work, the calculation begins with finding out the carrying capacity of the available blocks, which must correspond to the weight of the load being lifted. For example, according to the scheme (Fig. 22, a) to lift a load weighing 20 tons, blocks with a lifting capacity of 20 tons are required.

Rice. 4. Schemes of re-supplying chain hoists with the number of working threads: a - six with three branching single-roll blocks, b - three, c - four, d - five, e - six, f - seven, g - eight, h - ten, and - eleven , k - twelve, S0, 1, 2, 3, 4, 5.6,7 - chain hoist threads

The suspension on which the upper block of the chain hoist is suspended is calculated for the entire load that the chain hoist lifts: the weight of two blocks, the weight of the rope, as well as the force in the runaway thread of the cargo chain hoist.

When calculating the pulley blocks, the fastening of the upper block of the chain hoist to the mechanism or device is calculated.

If we assume that both threads run vertically, then the first diverter roller is fixed to a force equal to the sum of the efforts in the 5th and 6th threads: 3.68 + 3.82 = 7.5 tf. The securing of the second branch block is calculated on the forces in the 6th and 7th threads.

Since the forces in both threads and the angle between them can be different, the force for which the block is calculated is determined according to the parallelogram rule.

Example. Pick up a chain hoist for lifting a load weighing 10 tons and a rope of the required section for hanging the chain hoist at a height of 18 m.

We select two blocks for the chain hoists. According to the table. 11 we choose a two-roll block with a lifting capacity of 10 tf for the lower movable block, and a three-roll block with a lifting capacity of 15 tf for the upper fixed block.

According to the maximum force in the 6th thread Se, we select the section of the rope. The smallest permissible safety factor of ropes k for a cargo chain hoist with a machine drive in light operating mode is 5.

Since there can be only an even number of threads, we take eight threads for suspension.

In the absence of blocks of the required carrying capacity, double chain hoists are used, for example, a double chain hoist with an equalizing roller and one or two drive winches is shown in Fig. 5.

A double chain hoist with one drive winch is calculated as a single one with the corresponding number of working threads.

A chain hoist with two drive winches is calculated as two independently operating chain hoists,

Rice. 5. Schemes of reeving double chain hoists with one (a) and two (b) drive winches: 1 - equalizing block, 2 - fixed block, 3 - movable block, 4 - traverse, 5 - suspension

A polyspast is a simple lifting device consisting of a system of movable and stationary blocks (rollers), bent around by a flexible body (usually a rope). Polyspasts are used as independent mechanisms in combination with winches and as elements of complex hoisting machines (cranes).

The blocks (rollers) of the chain hoist are placed in two clips - movable and fixed - and are sequentially bent around by one rope, to the free end or both ends of which a traction force is applied. The fixed frame of blocks (rollers) is attached to the supporting structure (mast, boom, etc.), the movable one is supplied with a load-gripping body (hook, loop, bracket).

Rice. 6. Schemes of pulley blocks a - in four lines; b - in six threads; 1 - fixed blocks; 2 - movable blocks; 3 - branch block; 4 - rope

Polyspasts are used to gain strength (less often speed). The gain in strength is the greater, the greater the multiplicity of the chain hoist, equal to the number of working branches of the rope, on which the movable holder of the chain hoist blocks is suspended.

Rice. 7. Design schemes of chain hoists

1. Determine the force 5L in the rope going to the winch when lifting a load weighing Q = 20 t with a chain hoist made according to scheme I. Blocks (rollers) of the chain hoist are installed on rolling bearings (/ j = 1.02), diverter rollers - on bronze bushings (= 1.04).

2. Determine the force 5L in the rope going to the winch when lifting a load weighing 20 tons with a chain hoist, made according to scheme II. Blocks (rollers) are taken on bronze bushings (= 1.04).

3. Determine which load Q can be lifted by a winch with a pulling force of 5L = 1.5 tf and a chain hoist made according to scheme III. Blocks (rollers) are adopted on bronze bushings.

TO Category: - Construction machines and their operation

Polyspast is a system of movable and stationary blocks connected by a flexible connection (ropes, chains) used to increase the force or speed of lifting loads. A chain hoist is used in cases where it is necessary to lift or move a heavy load with minimal effort, provide tension, etc. The simplest chain hoist consists of only one block and a rope, while it allows to halve the tractive effort required to lift the load.

Usually, power pulleys are used in lifting mechanisms, which allow to reduce the rope tension, the moment from the weight of the load on the drum and the gear ratio of the mechanism (hoists, winches). High-speed pulley blocks that allow you to get a gain in the speed of moving the load at low speeds of the drive element. They are used much less often and are used in hydraulic or pneumatic lifts, loaders, mechanisms for extending telescopic booms of cranes.

The main characteristic of the chain hoist is the multiplicity. This is the ratio of the number of branches of the flexible body on which the load is suspended to the number of branches wound on the drum (for power pulley blocks), or the ratio of the speed of the leading end of the flexible body to the driven one (for high-speed pulley blocks). Relatively speaking, the multiplicity is the theoretically calculated coefficient of gain in strength or speed when using a chain hoist. Changing the multiplicity of the chain hoist occurs by introducing or removing additional blocks from the system, while the end of the rope, with an even multiplicity, is attached to a fixed element of the structure, and with an odd multiplicity, on a hook cage.

Depending on the number of rope branches fixed on the drum of the hoisting mechanism, single (simple) and double pulley blocks can be distinguished. In single chain hoists, when winding or unwinding a flexible element due to its movement along the axis of the drum, an undesirable change in the load on the drum supports is created. Also, if there are no free blocks in the system (the rope from the hook block goes directly to the drum), the load moves not only in the vertical, but also in the horizontal plane.

To ensure a strictly vertical lifting of the load, double chain hoists are used (consisting of two single ones), in this case, both ends of the rope are fixed on the drum. To ensure the normal position of the hook suspension with uneven stretching of the flexible element of both pulleys, a balancer or equalizing blocks are used. Such pulley blocks are used mainly in bridge and gantry cranes, as well as in heavy tower cranes in order to be able to use two standard cargo winches instead of one large-sized high power, as well as to obtain two or three speeds of lifting the load.

In power pulley blocks, with an increase in the frequency ratio, ropes of reduced diameter can be used, and as a result, the diameter of the drum and blocks can be reduced, and the weight and dimensions of the system as a whole can be reduced. An increase in the frequency ratio allows to reduce the gear ratio of the gearbox, but at the same time requires a greater length of the rope and the rope capacity of the drum.

High-speed pulley blocks differ from power pulleys in that in them the labor force, usually developed by a hydraulic or pneumatic cylinder, is applied to the movable cage, and the load is suspended from the free end of the rope or chain. The gain in speed when using such a chain hoist is obtained as a result of an increase in the height of the lifting of the load.

When using pulley blocks, it should be borne in mind that the elements used in the system are not absolutely flexible bodies, but have a certain stiffness, therefore, the oncoming branch does not immediately fall into the block stream, and the running branch does not immediately straighten. This is most noticeable when using steel ropes.

Possession of a system for lifting loads using chain hoists is an important technical skill necessary for carrying out rescue and high-altitude work, organizing overhead crossings and in many other cases. This skill is essential for climbers, rescuers, industrial climbers, cavers, hikers and many others who work with ropes.

Unfortunately, in the domestic mountaineering and rescue literature it is difficult to find a clear, consistent and understandable explanation of the principles of operation of chain hoist systems and methods of working with them. Perhaps such publications exist, but I have not yet been able to find them. As a rule, the information is either fragmentary, outdated, or too complex, or both.

Even during my training to become a mountaineering instructor and a Rescue Squad badge (it was 20 years ago), I was not able to get a clear idea of ​​the basic principles of the chain hoist operation. It's just that none of the teaching instructors had a full command of this material. I had to get there myself.

Knowledge of English and foreign climbing and rescue literature helped.

I was able to get to know the most practical descriptions and techniques while studying rescue courses in Canada.

Despite the fact that at the time of training, I considered myself quite "savvy" in pulley blocks and myself had many years of experience in teaching rescue technologies for climbers and rescuers, I learned a lot of new and useful things during the courses.

I will try to put everything as simple and practical as possible.

Part one. First, a little theory.

1. Polyspast Is a lifting device consisting of several movable and stationary blocks bent around by a rope, rope or cable, allowing to lift loads with an effort several times less than the weight of the load being lifted.

1.1. Any pulley block gives a certain gain in the effort to lift the load.

Friction losses are inevitable in any moving system consisting of rope and blocks.

In this part to facilitate calculations unavoidable friction losses are not taken into account and is based on Theoretically Possible Effort Gain or abbreviated Tv(theoretical gain).

Note: Of course, in real work with chain hoists, friction cannot be neglected. More about this and about the main ways to reduce friction losses will be discussed in the next part "Practical tips for working with chain hoists"

2. The basics of building pulley blocks.

2.1. Picture 1.

If you fix a rope (cable) on a load, throw it over a block fixed at the station (hereinafter a stationary or stationary block) and pull it down, then to lift the load, you must apply an effort equal to the weight of the load.

There is no gain in effort.

In order to lift the load by 1 meter, it is necessary to stretch 1 meter of rope through the block.

This is the so-called 1: 1 scheme.

Figures 1 and 2 illustrate the following Basic Polyspast Rules:

Rule # 1.

The gain in effort is given only by MOVING rollers fixed directly on the load or on a rope coming from the load.

STATIONARY ROLLERS DO NOT GIVE AN EFFORT WINNING!

They only serve to change the direction of the rope.

Rule # 2.

How many times we win in effort - the same amount of times we lose in distance.

For example: if in the one shown in fig. 2 chain hoist 2: 1 for each meter of lifting the load upwards, 2 meters of rope must be pulled through the system, then in a 6: 1 chain hoist - 6 meters, respectively.

A practical conclusion - the "stronger" the chain hoist - the slower the load rises.

2.3. Continuing to add stationary rollers to the station and movable rollers to the load, we get the so-called simple pulley blocks of different efforts:

Examples of simple pulleys. Figures 3, 4.

2.4. Rule # 3

Calculation of the theoretical gain in effort in simple pulley blocks.

Everything here is quite simple and clear.

2.4.1. If you need to determine the TV of a ready-made chain hoist,

If the movable rollers are fixed not on the load itself, but on the rope coming from the load (as in Fig. 6), then the strands are counted from the point of the rollers fixation.

Figures 5, 6.

2.4.2. Calculation of TV when assembling a simple chain hoist.

In simple pulley blocks, each movable roller (fixed to the load) added to the system additionally gives a double TV. Additional effort FOLDING with the previous one.

Example: if we started with a 2: 1 chain hoist, then by adding another movable roller, we get 2: 1 + 2: 1 = 4: 1 By adding another roller, we get 2: 1 + 2: 1 + 2: 1 = 6: 1, etc.

Figures 7.8.

2.5 ... Depending on where the end of the cargo rope is fixed, at the station or on the load, simple pulley blocks are divided into even and odd.

2.5.1. If the end of the rope is attached to the station,

then all subsequent pulley blocks will be EVEN: 2: 1, 4: 1, 6: 1, etc.

Figure 7.

Note: Simple pulley blocks with TV more than 5: 1 in rescue practice, as a rule, are not used. This will be discussed in more detail in the second part of the article.

In addition to simple pulley blocks, so-called COMPLEX POLYSPASTS.

2.6. A complex chain hoist is a system in which one simple chain hoist pulls a simple chain hoist after another.

Thus, 2, 3 or more chain hoists can be connected.

Figure 9 shows the designs of the most common complex pulley blocks in rescue practice.

Figure 9.

2.7. Rule # 4. Calculation of TV complex pulley block.

To calculate the theoretical gain in effort when using a complex chain hoist, it is necessary multiply the meanings of the simple pulley blocks that make up it.

An example in fig. 10.2: 1 pulls for 3: 1 = 6: 1.

An example in fig. 11.3: 1 pulls for 3: 1 = 9: 1.

The calculation of the effort of each of the simple pulley blocks included in the complex is carried out according to the rule of simple pulley blocks.

The number of strands is calculated from the point of attachment of the chain hoist to the load or cargo rope coming out of another chain hoist.

Examples of in fig. 10 and 11.

Calculation of effort in a complex pulley block.

Figure 9 shows almost all the main types of chain hoists used in rescue operations.

As practice shows, these structures are quite enough for performing any tasks.

Of course, there are other, more complex, chain hoist systems. But they are rarely used in rescue practice and are not considered in this article.

All the designs of chain hoists shown above can be very easily learned at home by hanging some kind of load, say, on a horizontal bar.

To do this, it is quite enough to have a piece of rope or a cord, several carabiners (with or without rollers) and grasping (clamps).

To be continued…

Reviews(leave feedback)

question I have a purely practical question. can anyone respond. I need to raise a concrete slab of a fence under 100kg to a height of 3 meters I saw how two men installed these with their hands, but they were not strong enough. I thought that I should try it with my head :-) I bought 2 double rollers and 25m of 10mm rope in a climbing store I assembled a chain hoist with a theoretical gain I hung it 4: 1 in the garage and hung a 24kg weight for the test - it rises, of course, but not painfully easily. with his hands it is easier, in my opinion, the son planted an additional + 60 kg - he hardly rises, at the limit of his ability he sat down + 95 kg - the son could not even lift it shorter with a stove, and even approaching is not worth it, I absolutely do not understand why I see that there are cool specialists in this part, Can you tell me what the error figured out myself. noticed that under load the rollers squeal. oiled them and everything went. already installed everything I wanted

forgiveness jargon, but what is drawn is bullshit Yes, guys with physics at school you had a C. Read again rule number 1 - it is true. The winning is given only by the moving rollers. The upper, fixed roller only changes the direction of the force. One moving roller gives a win in 2 times, two moving ones - a win 4 times, three moving ones - 6 times. There cannot be an odd number of winnings at all. The famous Munter chain hoist, where supposedly winning seven times gives only four. Where in your pictures the win is nine times, in fact, it is also only four. From the practice of working as a rescuer, the calculation is as follows. Two rescuers can lift one victim without any chain hoists, of course with considerable effort and if there are good foot rests. In uncomfortable conditions, it is very difficult for three to lift one. One rescuer actually lifts one victim (about the same weight), with significant effort using a simple chain hoist with a double gain. So use pulley blocks (a good thing) sometimes you have little strength. With the help of two single rollers, you can get a win four times (plus two carabiners, a re-cord ring) and the stone can be moved if you are three or four people.

Did not impress:( To be honest, not impressed. A physics textbook and that's it. All this could be written in one paragraph. In fact, 3 things are said: Addition of force vectors, movable / fixed rollers and a cascade of pulley blocks. The simplest physics. And I was hoping to see exactly the practical part. For example: "How many carabiners and how many rollers are needed to pull a person of average weight." Or "how to move a stone of unreal weight, say a ton alone." It is in practice, taking into account the friction of the ropes, etc. After reading this article, you might think that if I pull, say, 100kg, then 5 rollers and raise the stone up. But figs for you. And 10 rollers really won't help ... Polyspasts with zhumars / cams are not described at all. We look forward to continuing.

pulley block Climbers and tourists, as a rule, do not take rollers with them - this is extra weight, and in the event of an accident or a crossing, they organize a chain hoist through carbines. Rollers, in my opinion, are the most relevant for rescuers. In the next part, as I understand it, the author will touch upon such an important problem as overcoming the friction force. It is clear that the friction losses of the rollers will be insignificant. But I would also like to know what losses arise through the bending of the carbine, since such an organization is more relevant in the real conditions of the group, incl. and for rescue operations on their own. I hope the author will touch on this point in the next part.

Polystyles are called a system formed by movable and stationary blocks, which are interconnected by cable (less often - chain) transmissions. Known back in ancient times, pulley blocks are still a device without which lifting and transport equipment cannot function. In fact, the components of this mechanism have not changed much over the millennia. Polystyles, their purpose and structure are issues that are important for the effective use of all designs of lifting mechanisms.

The device of the chain hoist and the conditions of its work

The main area of ​​application of the chain hoists is the boom mechanisms of cranes. The whole variety of pulley blocks can be reduced to two requirements: either increase the strength (power pulley blocks), or raise the speed (high-speed pulley blocks). In cranes, the former are more often used, and the latter are used in hoists. Thus, the schemes of high-speed and power pulleys are mutually inverse.

The pulley block includes the following components:

1. Blocks with fixed axles
2. Blocks with movable axles.
3. Bypass blocks.
4. Bypass drums.

All of the above elements are located mainly in a vertical arrangement, and the location of the drum depends on the presence of bypass blocks: from above, if such blocks are absent, and from below - if present.

The number of blocks with fixed axles is always one less than with movable ones. In this case, the total number of blocks determines (for power pulley blocks) the multiplicity of the increase in the total effort on the mechanism. The number of bypass blocks is determined by the dimensions of the node: with an increase in the number of such blocks, the force also increases.

Power pulley blocks, the purpose and design of which is characterized by several parameters, the most important of which is the load developed in the lifting mechanism. It increases with an increase in the calculated lifting capacity of the crane, the multiplicity of the device (the number of rope branches on which the load is suspended) and the efficiency of the unit. The efficiency takes into account the friction losses in the axial supports, as well as the losses determined by the rigidity of the rope or chain.

There can be several polystyles, then the total load on the block is proportionally reduced. Single pulley blocks are structurally simpler, but also the least effective. In them, one end is fixedly fixed on a stationary element, and the other on a drum. In this case, the deflection angle is very limited due to the danger of the rope coming off the block. The presence of a bypass block significantly improves the operating conditions of the mechanism: the load becomes symmetrical, which reduces rope wear and increases the permissible rotation speed of the blocks. The stability of the chain hoist action also depends on the distance between the bypass and main blocks. With an increase in this parameter, the reliability of the chain hoist as a functional unit increases, although its complexity also increases (due to the presence of a connecting axis).
Other chain hoist schemes used in practice are:

• Double triple, when there are three working blocks and two bypass blocks in the circuit;
• Double three-fold, equipped with an equalizing traverse. The variant is used in lifting equipment, which is operated in difficult and especially difficult conditions.

Performance characteristics of chain hoists and their choice

The following factors influence the effectiveness of the pulley blocks, their purpose and device in a particular mechanism:

1. The carrying capacity of the main mechanism, which includes these units.
2. Number of bypass blocks: with an increase in their number, friction losses increase.
3. Angles of deflection of the ropes from the middle plane of the drum.
4. Block diameters.
5. Rope diameter / chain height.
6. Rope material.
7. The nature of the supports (in rolling or plain bearings).
8. Lubrication conditions for all chain hoist axles.
9. The speed of rotation of blocks or movement of traction ropes (depending on the purpose of the device).

The greatest losses in chain hoists are associated with friction conditions. In particular, the efficiency of the considered mechanisms, which operate in plain bearings, depending on the conditions of their operation, is:

• In case of unsatisfactory lubrication and at elevated temperatures - 0.94 ... 0.54;
• With rare lubrication - 0.95 ... 0.60;
• With periodic lubrication - 0.96 ... 0.67;
• With automatic lubrication - 0.97 ... 0.74.

Smaller values ​​correspond to pulley blocks with the highest possible multiplicity. Friction losses for units that operate in rolling bearings are much lower and amount to:

• With insufficient lubrication and high operating temperatures - 0.99 ... 0.83;
• At normal operating temperatures and lubrication - 1.0 ... 0.92.

Thus, using modern antifriction coatings on the contact surface of the blocks, friction losses can be practically excluded.

The deflection angles of the rope located on the block / blocks of the chain hoist determine not only the wear of the ropes and blocks, but also the safety of the production personnel of the lifting device. This is explained by the fact that if the permissible indicators are exceeded, the rope pulling off the block is fraught with an industrial accident. This parameter is influenced by the material of the ropes, the profile of the groove of the drum, as well as the direction of winding.
The materials of the ropes are most often the types TLK-O in accordance with GOST 3079, LK-R in accordance with GOST 2688 and TC in accordance with GOST 3071. The third type has the lowest stiffness (no more than 1.7), which has a positive effect on the maximum permissible angle of deflection of the rope on the chain hoist. Accordingly, for the first two types of ropes, the rigidity reaches 2.

Normal angles of deviation from the chain hoist axis are considered angles 7.5 ... 2.5 0 (smaller values ​​are taken for maximum ratios of the block diameter to the rope diameter). In general, when designing these devices, they always try to choose this ratio in the range of values ​​12 ... 40. The permissible angle of deflection of ropes made of low-stiff materials is less: up to 6.5 ... 2 0.

GOST allows an increase in the maximum deviation, in comparison with the recommended one, by no more than 10 ... 20% (depending on the operating mode of the lifting equipment). On the equalizing block, the permissible deviation angles can increase, but not more than 1.5 times.

To reduce the angles of deflection, profile grooves are made on the pulley blocks, and the angle of their direction depends on the direction of winding. Therefore, drums in mechanisms of modern design are always made with a cross-section, suitable for both types of winding.

Re-supplying chain hoists

Stocking is a technological operation of changing the location of the main cargo blocks of the chain hoist, as well as the distances between them. The purpose of the reserve is to change the speed or height of the lifting of loads by means of a certain pattern of the passage of the ropes through the blocks of the device.

Reeving schemes are determined by the type of lifting equipment. It is known, in particular, that the mechanisms for changing the boom reach are different for a manual or electric hoist - on the one hand, and for cranes - on the other. Therefore, for winches, reeving is carried out by changing the position of the axis of the guide block, and is intended only to change the length of the boom. In cargo cranes, a reserve is used to correct the possible curvature of the movement of the load. In addition to cargo ropes, the reserve is also used for rope devices for moving the working trolley.

There are the following stock schemes:

1. Single entry, which is used for boom-type hoisting mechanisms with a jib. In this case, the hook is suspended on one thread of the rope, sequentially passed through all fixed blocks, and then wound on a drum. This way of stocking is the least efficient.
2. Double, which can be used on cranes, both with a luffing jib and a beam boom. In the first case, fixed blocks are located on the boom head, and the opposite end of the rope is fixed in the cargo winch. In the second case, one of the ends of the rope is fixed at the root of the boom, and the second is sequentially passed through the bypass drum, hook suspension blocks, boom blocks, tower head blocks and then brought to the cargo winch.
3. Fourfold used for heavy-duty mechanisms. Here one of the schemes described above is implemented, but separately for each of the blocks of the hook suspension. At the same time, two working branches of the rope are directed to the blocks of the working boom. The connection of adjacent pulleys is made through an additional fixed block, which is installed on the stand of the crane swing platform.
4. Variable, the essence of which is to change the lifting capacity of the crane. With this type of storage (it can be two or four times), a corresponding increase in the mass of the load being lifted is possible. For this, one or two movable clips are additionally installed in the movable blocks. The retention of the clips is produced by the load rope itself due to the difference in the forces that are created by the presence of the hook suspension. The change in the re-ordering rate is performed by lowering the hook suspension onto the support while the rope is being rewound.

Two- and especially four-fold reserving allows for safe lifting of the load, which is almost twice the pulling force developed by the winch. In this case, the rotation of the ropes under load is excluded, which significantly reduces their wear.

Part B

2.5. The choice of the optimal design of the chain hoist.

2.5.1 ... Each design of chain hoists, in addition to gain in effort, has other important indicators that affect the overall efficiency of its work.

General design features that improve the efficiency of the chain hoists:

The greater the working length of the chain hoist, the greater its working stroke and the distance to which the load is lifted in one working stroke.

With the same working length, the chain hoist with a large working stroke works faster.

With the same working length and working stroke, the chain hoist works faster, requiring fewer permutations.

4 . Simple 2: 1 and 3: 1 pulleys give the fastest lift with a minimum of system permutations.

Before moving on to heavy-duty chain hoists, you need to make sure that all measures are taken to combat friction in a simple chain hoist.

Often, by reducing friction losses, it is possible to continue working with a simpler chain hoist and maintain a high lifting speed.

But in general, it all depends on the specific situation in which one or another type of chain hoist should be used. Therefore, it is impossible to give unequivocal recommendations.

In order to select the optimal chain hoist for work in each specific situation, rescuers must know the main pros and cons of each system.

2.5.2. General performance characteristics of simple chain hoists

Pros of simple pulley blocks:

* Simple and straightforward to assemble and operate.

* In simple chain hoists, the working stroke is close to the working length of the chain hoist, since they are quite fully "folded" in operation - the 1st cargo roller is pulled close to the station. This is a serious plus, especially in cases where the total working length of the chain hoist is limited (for example, a short working shelf on a rock, etc.)

* It is required to move only one grasping (clamp).

* With enough people picking the rope, simple 2: 1 and 3: 1 pulleys will give the fastest ascent speed.

Cons of simple pulley blocks:

* More (in comparison with complex pulley blocks of similar efforts) the number of rollers. Consequently, the overall friction loss is large.

For this reason, simple pulley blocks are not used in rescue practice anymore.than 5: 1.And when using carabiners, it makes no sense to make a simple chain hoist more than 4: 1

* For the same total working length, simple pulleys use more rope than complex pulleys of similar forces. Fig. 18

2.5.3. General performance characteristics of complex chain hoists.

Pros of complex pulley blocks:

* With an equal number of rollers and gripping units (clamps), they allow the creation of high-effort chain hoists. For example:

3 rollers are required for a complex 6: 1 chain hoist and a simple 4: 1 chain.

4 rollers for complex chain hoist 9: 1 and simple 5: 1. Rice. 19, 20.

* Requires less rope compared to similar simple chain hoists. Fig 16.

* Compared to similar simple ones, complex pulleys give a greater actual gain in effort, since fewer rollers are involved.

For example: in a complex 4: 1 chain hoist 2 rollers work, and in a simple 4: 1 - 3 rollers.

Accordingly, in a complex pulley block, friction losses will be less, and the PV will be greater.

An example in fig. 21:

In a complex chain hoist 4: 1 (2 rollers) using rollers with a friction loss of 20% PV will be -3.24:1. In a simple chain hoist 4: 1 (3 rollers) - FV =2.95:1

Cons of complex pulley blocks:

* Harder to organize.

* Some designs of complex chain hoists require more permutations, since in order to stretch the chain hoist over the entire working length again, you need to move 2 grasping nodes (clamps)

* With the same working length, the working stroke of complex chain hoists is less than that ofsimple, since they do not fold completely at each working stroke (the roller closest to the pulling one is pulled up to the station, and the 1st cargo roller stops before reaching the station). This significantly reduces the efficiency of work, especially in cases where the total working length of the chain hoist is limited (for example, a short working shelf on a rock, etc.) It can also complicate work in the last stages of the lifting, when the load must be lifted to the working platform.

* In general, they significantly lose to simple pulley blocks in lifting speed.

Practical tips for working with complex pulleys:

* In order for a complex chain hoist to fold more fully with each working stroke, and less permutations are required, it is necessary to space the stations of simple chain hoists that are part of a complex one. Fig. 22

* The system of a complex chain hoist requires fewer permutations in work, if a simplepulley block with big pulls the pulley with an effort smaller effort.

Example on fig. 22A

A - pulley block 6: 1 (2: 1 pulls for 3: 1) In this case, it is required to rearrange 2 grasping knots.

B - another chain of chain hoists 6: 1 - 3: 1 pulls for 2: 1. Only one grasping unit (clamp) needs to be repositioned. Accordingly, the system works faster.

2.5.4. In all the above construction of chain hoists, the rope must be pulled towards the cargo station. In the mountains, on a confined area or on a wall, pulling from the bottom up can be very difficult and inconvenient. In order to pull down and turn on your weight, as well as not to tear your backs, an additional stationary roller (carabiner) is often fastened. Rice. 23.

But, according to the Rule of pulley blocks No. 1 - stationary rollers do not give a gain in effort. Friction losses in this arrangement, especially when using a carabiner, can negate all the benefits of pulling down.

b. Use complex pulley block.

Complex pulley blocks are neither simple nor complex - they are separateview.

A distinctive feature of complex chain hoists is the presence of rollers in the system moving towards the load.

This is the main advantage of complex chain hoists in cases where the station is located above the rescuers and it is necessary to pull the chain hoist down.

On Fig 25. there are two schemes of complex pulley blocks used in rescue operations.

There are other schemes, but they do not find application in rescue practice and are not considered in this article.

Note:

Diagram shown on Rice. 25 complex chain hoist 5: 1 is given in the book "School of Mountaineering. Initial training ", 1989 edition, p. 442.

The main disadvantages of complex chain hoists are similar to the disadvantages of complex chain hoists:

Complex pulley blocks do not fold completely, have a short working stroke and require many permutations at each working cycle. For example, a 5: 1 pattern requires a permutation of two grasping knots.

2.5.5. In cases where the efforts of the assembled chain hoist are not enough, and the length of the pulling rope is not enough to assemble a more powerful circuit, an additional 2: 1 chain hoist attached to the end of the rope with a grasping knot or clamp can help.

To do this, it is enough to have a short end of the rope or a re-cord folded 2-3 times, 1 roller (carabiner) and 1 grasping (clamp). Example on Rice. 26.

Also, for an additional 2: 1 chain hoist, the slack of the cargo rope can be used, as shown in the figure from the book by F. Kropf. "Rescue work in the mountains" 1975 Rice. 26A

This is one of the fastest and easiest to organize ways to increase the effort of the chain hoist - a kind of "magic wand". By adding a 2: 1 scheme to any chain hoist you will automatically get 2x theoretical gain in effort. What will it be actual winnings, depends on the situation.

The disadvantages of this scheme have already been mentioned above - this is a short working stroke and many permutations (it is necessary to rearrange two grasping ones).

However, there are situations when this method can help. For example, this method is often used in cases where some of the rescuers pulling the chain hoist are forced to switch to other tasks, and the efforts of those who remain to work on the chain hoist are not enough and the effort must be quickly increased.

2.5.6. Figure 27 shows a diagram of the so-called "built-in two".

Simple chain hoist 2: 1 is “built in” into the system of simple chain hoist 3: 1. The result is a chain hoist with TV 5: 1. This pulley block is neither simple nor complex. I could not find its exact name. The name "compound" in fig. 27 and 27A were invented by me.

Despite the small loss in TV compared to the circuit in Fig. 26 (5: 1 versus 6: 1) this system has a number of practical advantages:

* This is an even more economical method, since in addition to the rope, only one additional roller (carabiner) is required.

* In work, this method requires the permutation of only one grasping (clamp) and therefore is more efficient in work.

* Another example of this "built-in two" system is shown in rice. 27A.

A complex tackle 10: 1 works here - the tackle 2: 1 is "built" into the tackle 6: 1.

A similar system can be used when pulling out the victim alone. In such a scheme, large friction losses are inevitable and lifting is slow. But overall, the system is quite practical, works well, and allows one rescuer to work without overwork.

The guide rollers are placed in a separate station directly above the ascent (descent) point.

The station can be placed on a rock, on a tree, on a special or improvised tripod, etc. see fig. 30-37.

When ascending and descending with a build-up of ropes, guide rollers of the largest diameter are used, through which the rope with knots passes freely.

The station for the idler roller must be dimensioned for heavy loads.
rice. 29.

Benefits of using guide rollers *

In short, the competent use of HP allows rescuers to work more efficiently and safely.

Below are examples of the main benefits of using idler rollers:

* Sliding of the rope under load to the side along the edge of the working platform during the work of rescuers (it does not matter whether it is an ascent or descent, a rock or a building) extremely undesirable and dangerous by rubbing the rope!

Optimally, the rope should approach the edge at an angle of 90 °. Otherwise, the load rope will inevitably slip to the side.

The HP allows the load rope to be guided at the correct angle to the edge of the pad. Rice. 31

* When there is no suitable work platform directly above the lift or descent point, the HP allows you to position the load station for launching and retrieving away from the lift line, in a more convenient location for work.

In addition, the location of the station away from the ascent (descent) line reduces the likelihood of hitting the rescuer, the victim, the load and safety ropes by stones, etc., which can be thrown by the rescuers working at the top.

* НР makes it possible to fully or partially raise the chain hoist system over the terrain. This significantly increases the efficiency of work by reducing the friction losses of the chain hoist and its components against the terrain. This also increases the overall safety of work, since the likelihood of chafing, jamming or jamming of any component of the chain hoist is reduced.

* НР allows you to reduce or completely eliminate the friction of the load rope on the edge (bend) of the working platform. This is also a very big plus from a security point of view.

* HP can greatly facilitate the transition over the edge of the rescuer and the victim, both on the ascent and on the descent. This is one of the most difficult and time consuming moments in transportation, especially for an accompanying rescuer.

Guide rollers are extremely widely used by professionals in a variety of situations, both in the mountains and in technogenic conditions. Therefore, I want to illustrate this way of optimizing the location of the chain hoists on the ground in more detail. Rice. 30-37.

HP allows you to:

* Raise the ferry higher.

* Conveniently position the chain hoist system.

* Pull the pulley down.

* Adjust the tension of the crossing during operation.

Important! With a strong tension of the crossing, very large loads arise onextreme attachment points of the ferry. Rice. 38.

The conclusions from the above diagram are as follows:

* Over-tensioning the crossings should be avoided - this is dangerous!

For example:
When two people are simultaneously crossing a very stretched crossing (the victim and the accompanying person. Total weight ~ 200kg), due to the inevitable swinging of the crossing, peak loads on the extreme points can reach 20 KN (2000kg)and higher! This load is close to the limit of strength characteristics.climbing carabiners, guy wires and ropes (taking into account the loss of rope strength innodes).

* All ferry attachment points, including the idler roller attachment station andall its components must be extremely reliable!

To be continued…