The use of a movable block gives a double gain in force, the use of a stationary block allows you to change the direction of the applied force. In practice, combinations of movable and fixed blocks are used. Moreover, each moving block allows you to halve the applied force or double the speed of moving the load. Fixed blocks are used to connect movable blocks into a single system. Such a system of movable and fixed blocks is called a pulley block.

Definition

A pulley block is a system of movable and fixed 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 pulley system consists of just one block and a rope, and at the same time it allows you to halve the traction force required to lift a load.

Figure 1. Each moving block in the pulley gives a double gain in strength or speed

Typically, lifting mechanisms use power pulleys to reduce the tension of the rope, the moment from the weight of the load on the drum and the gear ratio of the mechanism (hoist, winch). High-speed pulleys, which make it possible to obtain a gain in the speed of movement of the load at low speeds of the drive element, are used much less frequently. They are used in hydraulic or pneumatic lifts, loaders, and telescopic boom extension mechanisms of cranes.

The main characteristic of the pulley is the multiplicity. This is the ratio of the number of branches of the flexible organ on which the load is suspended to the number of branches wound on the drum (for power pulleys), or the ratio of the speed of the leading end of the flexible body to the driven end (for high-speed pulleys). Relatively speaking, the multiplicity is a theoretically calculated coefficient of gain in strength or speed when using a chain hoist. Changing the multiplicity of the pulley system 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 structural element, and with an odd multiplicity - on the hook clip.

Figure 2. Rope fastening with even and odd multiplicity of pulley system

The gain in force when using a pulley with $n$ movable and $n$ fixed blocks is determined by the formula: $P=2Fn$, where $P$ is the weight of the load, $F$ is the force applied at the input of the pulley, $n$ - number of moving blocks.

Depending on the number of rope branches attached to the drum of the lifting mechanism, single (simple) and double pulley hoists can be distinguished. IN single pulley 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 suspension block directly passes to the drum), the load moves not only in the vertical, but also in the horizontal plane.

Figure 3. Single and double pulleys

To ensure strictly vertical lifting of the load, double pulleys (consisting of two single ones) are used; in this case, both ends of the rope are fixed to the drum. To ensure the normal position of the hook suspension in case of uneven stretching of the flexible element of both pulleys, a balancer or equalizing blocks are used.

Figure 4. Methods to ensure vertical lifting of the load

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

When using pulleys, it should be taken into account that the elements used in the system are not absolutely flexible bodies, but have a certain rigidity, so the oncoming branch does not immediately fall into the stream of the block, and the running branch does not straighten out immediately. This is most noticeable when using steel ropes.

Question: why do construction cranes have a hook that carries the load, not attached to the end of the cable, but to the holder of the moving block?

Answer: to ensure vertical lifting of the load.

Fig. 5 shows a power chain hoist, in which there are several moving blocks, and only one fixed one. Determine how much weight can be lifted by applying a force of $F$ = 200 N to a stationary block?

Figure 5

Each of the moving blocks of the power pulley doubles the applied force. The weight that a power polypaste of the third degree can lift (without taking into account corrections for frictional forces and cable rigidity) is determined by the formula:

Answer: The chain hoist can lift a load weighing 800 N.

Lifting machines are designed to help a person lift something heavy to a height. Most lifting mechanisms are based on simple system blocks - chain hoist. It was known to Archimedes, but now many people do not know about this brilliant invention. Remembering your physics course, find out how such a mechanism works, its structure and scope. Having understood the classification, you can begin to calculate. For everything to work out, here are instructions for constructing a simple model.

Block system - theory

The invention of the chain hoist gave a huge impetus to the development of civilizations. The block system helped build huge structures, many of which have survived to this day and puzzle modern builders. Shipbuilding also improved, and people were able to travel great distances. It's time to figure out what it is - a chain hoist and find out where it can be used today.

Simplicity and efficiency of the mechanism

Structure of the lifting mechanism

A classic chain hoist is a mechanism that consists of two main elements: a pulley; flexible connection

The simplest scheme: 1 – movable block, 2 – fixed, 3 – rope

A pulley is a metal wheel that has a special groove for a cable along its outer edge. An ordinary cable or rope can be used as a flexible connection. If the load is heavy enough, ropes made of synthetic fibers or steel ropes and even chains are used. To ensure that the pulley rotates easily, without jumping or jamming, roller bearings are used. All elements that move are lubricated.

One pulley is called a block. A pulley block is a system of blocks for lifting loads. The blocks in the lifting mechanism can be stationary (rigidly fixed) and movable (when the axis changes position during operation). One part of the pulley is attached to a fixed support, the other to the load. Movable rollers are located on the load side.

Fixed block

The role of the stationary block is to change the direction of movement of the rope and the action of the applied force. The role of the mobile is to gain strength.

Movable block

How it works - what's the secret?

The operating principle of a pulley block is similar to a lever: the force that needs to be applied becomes several times smaller, while the work is performed in the same volume. The role of the lever is played by the cable. In the operation of a chain hoist, the gain in strength is important, so the resulting loss in distance is not taken into account.

Depending on the design of the pulley, the gain in strength may vary. The simplest mechanism from two pulleys it gives approximately a twofold gain, from three - threefold, and so on. The increase in distance is calculated using the same principle. For work simple chain hoist you need a cable twice as long as the lifting height, and if you use a complex of four blocks, then the length of the cable increases in direct proportion to four times.

Operating principle of the block system

In what areas is the block system used?

A chain hoist is a faithful assistant in a warehouse, in production, and in the transport sector. It is used wherever force needs to be used to move all kinds of loads. The system is widely used in construction.

Despite the fact that most of the heavy work is performed by construction equipment (cranes), the chain hoist has found a place in the design of load-handling mechanisms. The block system (pulley block) is a component of such lifting mechanisms as a winch, hoist, and construction equipment (various types of cranes, bulldozer, excavator).

In addition to the construction industry, pulley hoists received wide application in organizing rescue operations. The principle of operation remains the same, but the design is slightly modified. Rescue equipment is made of durable rope and carabiners are used. For devices of this purpose, it is important that the entire system is quickly assembled and does not require additional mechanisms.

Pulley hoist as part of a crane hook

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Classification of models according to different characteristics

There are many executions of one idea - a system of blocks connected by rope. They are differentiated depending on the method of application and design features. Get to know different types lifts, find out what their purpose is and how the device differs.

Classification depending on the complexity of the mechanism

Depending on the complexity of the mechanism, simple ones are distinguished; complex; complex chain hoists.

Example of even models

A simple chain hoist is a system of series-connected rollers. All movable and fixed blocks, as well as the load itself, are combined by one cable. Even and odd simple pulleys are differentiated.

Even lifting mechanisms are those whose end of the cable is attached to a fixed support - a station. All combinations in this case will be considered even. And if the end of the rope is attached directly to the load or the place where the force is applied, this structure and all its derivatives will be called odd.

Odd chain hoist diagram

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A complex pulley system can be called a pulley system. In this case, not individual blocks are connected in series, but entire combinations that can be used on their own. Roughly speaking, in this case one mechanism sets in motion another similar one.

Combining a two-fold and six-fold simple chain hoist gives a complex six-fold version

The complex chain hoist does not belong to one or the other type. His distinguishing feature– rollers moving towards the load. The complex model can include both simple and complex chain hoists.

Classification according to the purpose of the lift

Depending on what they want to get when using a chain hoist, they are divided into:

Power;

Express.

A – power version, B – high-speed

The power option is used more often. As the name suggests, its task is to ensure a gain in strength. Since significant gains require equally significant losses in distance, losses in speed are also inevitable. For example, for a 4:1 system, when lifting a load one meter, you need to pull 4 meters of cable, which slows down the work.

The high-speed chain hoist, by its principle, is a reverse power design. It does not give a gain in strength, its goal is speed. Used to speed up work at the expense of the applied effort.

Multiplicity is the main characteristic.

The main indicator that people pay attention to when organizing cargo lifting is the multiplicity of the pulley. This parameter conventionally indicates how many times the mechanism allows you to win in strength. In fact, the multiplicity shows how many branches of the rope the weight of the load is distributed over.

Kinematic ratio

The multiplicity is divided into kinematic (equal to the number of kinks in the rope) and force, which is calculated taking into account the cable’s overcoming the friction force and the non-ideal efficiency of the rollers. The reference books contain tables that display the dependence of the power factor on the kinematic factor at different block efficiencies.

As can be seen from the table, the force multiplicity differs significantly from the kinematic one. With a low roller efficiency (94%), the actual gain in strength of a 7:1 pulley will be less than the gain of a six-fold pulley with a block efficiency of 96%.

Schemes of pulleys of different multiplicities

How to make calculations for a chain hoist

Despite the fact that theoretically the design of a pulley hoist is extremely simple, in practice it is not always clear how to lift a load using blocks. How to understand what multiplicity is needed, how to find out the efficiency of the lift and each block separately. In order to find answers to these questions, you need to perform calculations.

Calculation of a separate block

The calculation of the chain hoist must be performed due to the fact that the working conditions are far from ideal. The mechanism is subject to frictional forces as a result of the movement of the cable along the pulley, as a result of the rotation of the roller itself, no matter what bearings are used.

In addition, flexible and pliable rope is rarely used on a construction site or as part of construction equipment. Steel rope or chain has much greater rigidity. Since bending such a cable when running against a block requires additional force, it must also be taken into account.

For the calculation, the moment equation for the pulley relative to the axis is derived:

SrunR = SrunR + q SrunR + Nfr (1)

Formula 1 shows the moments of such forces:

– Srun – force from the side of the escape rope;

– Srun – force from the oncoming rope;

– q Srun – force for bending/unbending the rope, taking into account its rigidity q;

– Nf – friction force in the block, taking into account the friction coefficient f.

To determine the moment, all forces are multiplied by the arm - the radius of the block R or the radius of the sleeve r.

The force of the approaching and escaping cable arises as a result of the interaction and friction of the rope threads. Since the force for bending/extension of the cable is significantly less than the others, when calculating the effect on the block axis, this value is often neglected:

N = 2 Srun×sinα (2)

In this equation:

– N – impact on the pulley axis;

– Srun – force from the oncoming rope (taken to be approximately equal to Srun;

– α – angle of deviation from the axis.

Pull block block

Calculation useful action block

As you know, efficiency is the efficiency factor, that is, how effective the work performed was. It is calculated as the ratio of work completed and work expended. In the case of a pulley block, the formula is applied:

ηb = Srun/ Srun = 1/(1 + q + 2fsinα×d/D) (3)

In the equation:

– 3 ηb – block efficiency;

– d and D – respectively, the diameter of the bushing and the pulley itself;

– q – rigidity coefficient of flexible connection (rope); f – friction coefficient;

– α – angle of deviation from the axis.

From this formula it can be seen that the efficiency is affected by the structure of the block (through the f coefficient), its size (through the d/D ratio) and the rope material (q coefficient). The maximum efficiency value can be achieved using bronze bushings and rolling bearings (up to 98%). Sliding bearings will provide up to 96% efficiency.

The diagram shows all the forces S on different branches of the rope

The lifting mechanism consists of several blocks. Total Efficiency of pulley block not equal arithmetic sum all individual components. For the calculation, they use a much more complex formula, or rather, a system of equations, where all forces are expressed through the value of the primary S0 and the efficiency of the mechanism:

– S1=ηп S0;

– S2=(ηп)2 S0; (- 4)

S3=(ηп)3 S0; ….

– Sn=(ηп)n S0.

Efficiency of a chain hoist at different magnifications

Since the efficiency value is always less than 1, with each new block and equation in the system, the value of Sn will rapidly decrease. The total efficiency of the pulley will depend not only on ηb, but also on the number of these blocks - the multiplicity of the system. Using the table, you can find ηп for systems with different numbers of blocks at different meanings Efficiency of each.

How to make a lift with your own hands

In construction during installation work It is not always possible to fit a crane. Then the question arises of how to lift the load with a rope. And here a simple chain hoist finds its application. To make it and fully operate, you need to make calculations, drawings, and choose the right rope and blocks.

Different schemes simple and complex lifts

Preparation of the base - diagram and drawing

Before you start building a chain hoist with your own hands, you need to carefully study the drawings and choose a suitable scheme for yourself. You should rely on how it will be more convenient for you to place the structure, what blocks and cable are available.

It happens that the load-carrying capacity of the pulley blocks is not enough, and constructing a complex multiple lifting mechanism there is no time and opportunity. Then double chain hoists are used, which are a combination of two single ones. This device can also lift the load so that it moves strictly vertically, without distortions.

Drawings of a dual model in different variations

How to choose a rope and block

The most important role in building a chain hoist with your own hands is played by the rope. It is important that it does not stretch. Such ropes are called static. Stretching and deformation of a flexible connection causes serious losses in work efficiency. For a homemade mechanism, a synthetic cable is suitable; the thickness depends on the weight of the load.

The material and quality of the blocks are indicators that will provide homemade lifting devices design load capacity. Depending on the bearings that are installed in the block, its efficiency changes and this is already taken into account in the calculations.

But how can you lift a load to a height with your own hands and not drop it? To protect the load from possible reverse movement, you can install a special locking block that allows the rope to move only in one direction - the desired direction.

Roller along which the rope moves

Step-by-step instructions for lifting a load through a block

When the rope and blocks are ready, the diagram has been selected, and the calculations have been made, you can begin assembly. For a simple double pulley you will need:

– roller – 2 pcs.;

– bearings;

– bushing – 2 pcs.;

– clip for the block – 2 pcs.;

- rope; hook for hanging cargo;

– slings – if they are needed for installation.

Carabiners are used for quick connection

Step-by-step lifting of the load to a height is carried out as follows:

1. Connect the rollers, bushing and bearings. They combine all this into a clip. Get a block.

2. The rope is launched into the first block;

3. The frame with this block is rigidly attached to a fixed support (reinforced concrete beam, pillar, wall, specially mounted extension, etc.);

4. Then the end of the rope is passed through the second block (movable).

5. A hook is attached to the clip.

6. The free end of the rope is fixed.

7. Sling the load being lifted and connect it to the pulley.

The homemade lifting mechanism is ready to use and will provide double the strength benefits. Now, to raise the load to a height, just pull the end of the rope. By bending around both rollers, the rope will lift the load without much effort.

Is it possible to combine a chain hoist and a winch?

If to homemade mechanism, which you will build according to these instructions, attach an electric winch, you will get a real crane, made by yourself. Now you don’t have to strain at all to lift the load; the winch will do everything for you.

Even hand winch will make lifting the load more comfortable - no need to rub your hands on the rope and worry about the rope slipping out of your hands. In any case, turning the winch handle is much easier.

Pulley hoist for winch

In principle, even outside the construction site, the ability to hiking conditions With a minimum of tools and materials, building a basic pulley for a winch is a very useful skill. It will be especially appreciated by motorists who are lucky enough to get their car stuck somewhere in an impassable place. A hastily made pulley will significantly increase the performance of the winch.

Overestimate the importance of the chain hoist in development modern construction and mechanical engineering is difficult. Everyone should understand the principle of operation and visually imagine its design. Now you are not afraid of situations when you need to lift a load, but there is no special equipment. A few pulleys, a rope and ingenuity will allow you to do this without using a crane.

A person is not very strong for lifting large loads, but he has come up with many mechanisms that simplify this process, and in this article we will discuss pulleys: the purpose and design of such systems, and we will also try to make the simplest version of such a device with our own hands.

A cargo pulley is a system consisting of ropes and blocks, thanks to which you can gain effective strength while losing in length. The principle is quite simple. In length we lose exactly as many times as we win in strength. Thanks to this golden rule of mechanics, large masses can be built without much effort. Which, in principle, is not so critical. Let's give an example. Now you have won 8 times in strength, and you will have to stretch a rope 8 meters long to lift the object to a height of 1 meter.

The use of such devices will cost you less than renting a crane, and besides, you can control the gain in strength yourself. The pulley has two different sides: one of them is fixed, which is attached to the support, and the other is movable, which clings to the load itself. The gain in strength occurs thanks to the movable blocks, which are mounted on the movable side of the pulley. The fixed part serves only to change the trajectory of the rope itself.

Types of pulleys are distinguished by complexity, parity and multiplicity. In terms of complexity, there are simple and complex mechanisms, and the multiplicity means a multiplication of force, that is, if the multiplicity is 4, then theoretically you gain 4 times in strength. Also rarely, but still used, a high-speed pulley block is used; this type gives a gain in the speed of moving loads at a very low speed of the drive elements.

Let's first consider a simple assembly pulley. It can be obtained by adding blocks to a support and a load. To get an odd mechanism, you need to secure the end of the rope to a moving point of the load, and to get an even one, we fasten the rope to a support. When adding a block, we get +2 to strength, and a moving point gives +1, respectively. For example, to get a pulley for a winch with a multiplicity of 2, you need to secure the end of the rope to a support and use one block that is attached to the load. And we will have an even type of device.

The operating principle of a chain hoist with a multiplicity of 3 looks different. Here the end of the rope is attached to the load, and two rollers are used, one of which we attach to the support, and the other to the load. This type of mechanism gives a gain in strength of 3 times, this is an odd option. To understand what the gain in strength will be, you can use simple rule: how many ropes come from the load, such is our gain in strength. Typically, pulleys with a hook are used, on which, in fact, the load is attached; it is a mistake to think that it is just a block and a rope.

Now we will find out how a complex type chain hoist works. This name refers to a mechanism where several simple options of this cargo device, they pull each other. The gain in strength of such constructions is calculated by multiplying their multiplicities. For example, we pull one mechanism with a multiplicity of 4, and another with a multiplicity of 2, then the theoretical gain in force will be equal to 8. All of the above calculations take place only for ideal systems that have no friction force, but in practice things are different .

In each of the blocks there is a small loss in power due to friction, since it is still spent on overcoming the friction force. In order to reduce friction, it is necessary to remember: the larger the bend radius of the rope, the less frictional force will be. It is best to use rollers with a larger radius where possible. When using carabiners, you should make a block of identical options, but rollers are much more effective than carabiners, since the loss on them is 5-30%, but on carabiners it is up to 50%. It is also useful to know that the most effective block must be located closer to the load to obtain maximum effect.

How do we calculate the real gain in strength? To do this, we need to know the efficiency of the units used. Efficiency is expressed by numbers from 0 to 1, and if we use a rope large diameter or too hard, then the efficiency of the blocks will be significantly lower than indicated by the manufacturer. This means that it is necessary to take this into account and adjust the efficiency of the blocks. To calculate the actual gain in strength simple type lifting mechanism, it is necessary to calculate the load on each branch of the rope and fold them. To calculate the gain in strength complex types it is necessary to multiply the real forces of the simple ones of which it consists.

You should also not forget about the friction of the rope, since its branches can twist among themselves, and the rollers under heavy loads can converge and pinch the rope. To prevent this from happening, the blocks should be spaced relative to each other, for example, you can use a circuit board between them. You should also purchase only static ropes that do not stretch, since dynamic ones give a serious loss in strength. To assemble the mechanism, either a separate or a cargo rope can be used, attached to the load independently of the lifting device.

The advantage of using a separate rope is that you can quickly assemble or prepare a lifting structure in advance. You can also use its entire length, this also makes it easier to pass knots. One of the disadvantages is that there is no possibility of automatic fixation of the lifted load. The advantages of a cargo rope are that automatic fixation of the lifted object is possible, and there is no need for a separate rope. The important thing about the disadvantages is that it is difficult to pass through the knots during operation, and you also have to spend a cargo rope on the mechanism itself.

Let's talk about the reverse motion, which is inevitable, since it can occur when the rope is caught, or at the moment of removing the load, or when stopping to rest. To prevent backlash from occurring, it is necessary to use blocks that allow the rope to pass in only one direction. At the same time, we organize the structure so that the blocking roller is attached first from the object being lifted. Thanks to this, we not only avoid backtracking, but also allow us to secure the load while unloading or simply rearranging the blocks.

If you are using a separate rope, the locking roller is attached last from the load being lifted, and the locking roller should be highly effective.

Now a little about attaching the lifting mechanism to the cargo rope. It’s rare that we have the right length of rope at hand to secure the moving part of the block. Here are several types of mechanism mounting. The first method is using grasping knots, which are knitted from cords with a diameter of 7-8 mm, in 3-5 turns. This method, as practice has shown, is the most effective, since a gripping knot made of 8 mm cord on a rope with a diameter of 11 mm begins to slide only under a load of 10-13 kN. At the same time, at first it does not deform the rope, but after some time, it melts the braid and sticks to it, beginning to play the role of a fuse.

Another way is to use a clamp general purpose. Time has shown that it can be used on icy and wet ropes. It begins to crawl only with a load of 6-7 kN and slightly injures the rope. Another method is to use a personal clamp, but it is not recommended, since it begins to creep with a force of 4 kN and at the same time tears the braid, or can even bite the rope. These are all industrial designs and their application, but we will try to create a homemade chain hoist.

Blocks are used to change the direction of traction when lifting and moving small weights or when tightening gear, as well as for founding hoists. The block consists of a wooden, metal or molded plastic housing, inside of which one or more metal pulleys are loosely mounted on an axis called a dowel. The blocks come in one-, two-, three- and multi-pulley types. The block body has partitions that separate one pulley from the other. The outer surfaces of the outermost partitions are called cheeks.

Rice. 1. Gorden.

The simplest design is a single-pulley block. A cable passed through such a block, fixed motionless, is called a gorden (Fig. 1). The arbor allows you to change the direction of thrust when lifting and moving a load, but does not provide a gain in strength, so it is used for lifting small weights. Single-pulley blocks with halyards passed through them are used to hoist flags and pennants, signal lights and signs.

Wooden and plastic blocks are used only when working with vegetable and synthetic cables. Most marine equipment uses metal blocks.

Rice. 2. Metal blocks.

Double-pulley metal block (Fig. 2, A) consists of a body 3, two steel or cast iron pulleys 4, bushings 5 with lubrication groove or with bearing, dowel 6, shackles 7 , mounting bolts 1 and pendants 2.

To equip the block, the cable must be passed between the cheeks of the block and placed in the pulley bale. Equipment simple block inconvenient, since you have to thread the cable from the end. Therefore, on ships they use single-pulley blocks with a folding cheek - rosin blocks (Fig. 2, b). The folding jaw allows you to insert the middle of the cable into such a block.

To prevent excessive bending of the cable passing through the pulley of the block, the dimensions of the block must correspond to the thickness of the cable. Pulley diameter metal block should be at least 10 - 15 diameters of a steel cable, and a wooden one - 2 times the circumference of a vegetable or synthetic cable.

The blocks must be periodically disassembled, cleaned of dirt and rust, and lubricated rubbing parts. If cracks or significant wear of the dowel or pulley are detected, the block should be replaced. Units that are not in use must be thoroughly lubricated and stored in a dry place in a suspended state.

Hoists are devices that allow you not only to change the direction of traction, but also to gain strength when lifting and moving heavy objects, when tightening gear and in other cases. According to their design, hoists are divided into ordinary and mechanical.

Ordinary hoists consist of two blocks, through the pulleys of which a cable called a rope is passed. One end of the shovel, attached to the block, is called the main end, the other, coming out of the block, to which an external traction force is applied, is called the running end. One block of hoists, fixed, is secured in place through a suspension. The other block is called movable, since during operation it rises along with the load or moves in the direction of tightening the gear. According to the number of pulleys in both blocks, hoists are divided into two-, three-, four- and multi-pulley.

Rice. 3. Ordinary two-pulley hoists.

The simplest are double-pulley hoists, based on a lopar between two single-pulley blocks. Such hoists can be based in two ways: the running end of the lopar comes off the stationary one (Fig. 3, A) or from a mobile one (Fig. 3, b) block. Let's consider the gain in force when lifting a load with a mass T will be in both cases.

In the first case, the mass of the load is distributed over two branches of the lopar coming out of the lower, movable block, and in the second - over all three branches. Therefore, to hold a load weighing T in the first and second cases, efforts must be made to the running ends of the lopars F 1 And F2, equal to 1/2 respectively T and 1/3 T. This means that the gain in strength is equal to the number of loaded branches of the Lapp or the total number of pulleys in both blocks in the first case and the total number of pulleys plus one in the second. Thus, indicating the total number of pulleys in both blocks P, we obtain formulas expressing the dependence of the force applied to the running end of the lopar to hold the load suspended, and the total number of pulleys in both blocks:

F 1 =m/n; F 2 =m / (n+1)

To lift the load to the running end of the lopar, additional effort is required to overcome the friction forces arising in the hoists. It is practically believed that the effort to overcome the frictional forces in each pulley of hoists based on vegetable or flexible steel cable, constitutes 10 and 5% of the mass of the lifted load, respectively.

Rice. 4. Ordinary multi-pulley hoists.

Ordinary hoists are used on ships various designs and load capacity. To tighten gear, three-pulley grip hoists are used (Fig. 4, A). Along with them, hoists are used, based between two blocks with the same number of pulleys - gintsy (Fig. 4, b). The armament of heavy booms includes multi-pulley hoists having blocks with pulleys on ball bearings - gini (Fig. 4, V).

The methods for founding hoists depend on the number of pulleys in the blocks (Fig. 5). They are always founded with the root end of the lapar clockwise for right-hand descent cables and counterclockwise for left-hand descent cables. The hoists are based on the deck, placing one block opposite the other at some distance with the pendants outward. For the base of double-pulley hoists (Fig. 5, A) behind fixed block take the one that has a device for attaching the root end of the lapar. The root end is passed through the pulley of the stationary block, then through the pulley of the movable one and attached to the stationary block.

Rice. 5. Methods for founding hoists.

When founding three-pulley hoists (Fig. 5, b) a two-pulley block is taken to be a fixed block, and a single-pulley block is taken to be a movable block. The root end is passed through the lower (closest to the deck) pulley of the two-pulley block, through the single-pulley pulley, then through the upper pulley of the two-pulley and attached to the single-pulley block.

When founding four-pulley hoists (Fig. 5, V), consisting of two two-pulley blocks, the root end is passed sequentially, first through the lower pulleys of the fixed and movable blocks, then through the upper pulleys of these blocks, after which the root end is brought to the fixed block and secured to it.

The base between two three-pulley blocks of six-pulley guineas (Fig. 5, G) is carried out with the root end of the lopar according to the scheme: the middle pulley of the fixed block - the lower pulley of the movable - the lower pulley of the fixed - the middle pulley of the movable - the upper pulley of the fixed - the upper pulley of the movable - to the attachment point on the fixed block. This wiring diagram for the root end of the paddle prevents the blocks from skewing while lifting the load.

In all cases, after passing the root end of the lapar through all the pulleys of both blocks, it is sealed with a fire and a thimble, with which it is attached to the butt on the corresponding block.

Mechanical hoists allow you to obtain multiple gains in strength, the ability to smoothly lift the load and keep it automatically locked in any position.

Rice. 6. Mechanical differential hoists.

Mechanical differential hoists are widely used on ships (Fig. 8). The suspension of such hoists contains a fixed block cage, which consists of two rigidly connected pulleys of different diameters with a diameter ratio of 7:8 or 11:12. The suspension with the block is attached to a fixed support or to the traverse of a trolley moving along a suspended rail. The lower (movable) single-pulley block is also placed in a cage that has a hook for hanging the load. The closed operating chain sequentially covers the small pulley of the fixed block, the pulley of the movable and the large pulley of the fixed block. Lifting of the load is ensured by turning the large pulley of the stationary block by applying a traction force to the branch of the working chain running from this pulley.

When lifting heavy loads with differential hoists, a 16-fold (with a ratio of the diameters of the fixed block pulleys of 7:8) and 24-fold (with a ratio of these diameters of 11:12) theoretical (without taking into account friction) gain in strength is obtained.

Ordinary hoists that are not in use are stored in a dry, ventilated area in a suspended state. All rubbing parts of the blocks are well lubricated. After finishing work with portable hoists, they are carefully folded, preventing the hoist from becoming tangled. When working with ordinary hoists, try to avoid sudden jerks, which can lead to breakage of the paddle or damage to the blocks. If, upon inspection of the blocks, significant wear of the dowels, hooks, brackets or butts is discovered, such blocks are replaced and the hoists are re-founded.

Mechanical hoists are kept clean, rubbing parts are regularly lubricated, and their serviceability is monitored.

Weight lifting mechanism

First letter "b"

Second letter "l"

Third letter "o"

The last letter of the letter is "k"

Answer for the clue "Mechanism for lifting weights", 4 letters:
block

Alternative crossword questions for the word block

Union of states public organizations or groups for joint action

Volleyball defense

Volleyball defense or Russian poet

French writer (1884-1947, "Sibilla", "Spain! Spain!", "Toulon")

Defense technique in sports

Famous Russian poet Alexander

Technique in martial arts

Definition of the word block in dictionaries

Explanatory dictionary of the Russian language. D.N. Ushakov The meaning of the word in the dictionary Explanatory Dictionary of the Russian Language. D.N. Ushakov
block, m. (English block) (fur.). Simple machine for lifting weights using a rope (chain, belt) thrown over a wheel fixed at a height with a groove around its circumference. Pick up something. block.

Explanatory Dictionary of the Living Great Russian Language, Dal Vladimir The meaning of the word in the dictionary Explanatory Dictionary of the Living Great Russian Language, Dal Vladimir
m. Morsk. gate, veksha, vekoshka; block with opening and roller; two wooden cheeks, between which a circle, roller, ayushka (pulley) with a groove (kip) along the edge is inserted on the axis (dowel), for pulling tackle and ropes through it. In our everyday life it is also called a roller block...

Wikipedia Meaning of the word in the Wikipedia dictionary
Block is a surname of Jewish-German origin. Known carriers: Blok - Russian noble family. Block, Abraham van den (1572-1628) - Renaissance architect and sculptor of the Free City of Danzig. Block, Adrien (c. 1567-1627) - Dutch merchant,...

Examples of the use of the word block in literature.

When he realized that all the water from pure condensate tanks and from chemical water treatment was switched to emergency block, he immediately reported to Fomin in the bunker that he would shut down the reactor.

He was running around block, mainly along the deaerator shelf, in order to cut off the left two deaerator tanks, from which water flowed to the destroyed emergency feed pump.

Zemskov, who had just conscientiously bypassed the emergency block and heavily irradiated.

Suspension possible blocks with 80 mm rockets, machine guns or grenade launchers, as well as 2 or 4 aerial bombs with a total weight of 500 kg.

Berezhkov came to the idea that a modern aircraft engine requires block cylinders, such a design was seen in his imagination, he even expressed it in sketches, and now, looking at this motor that arrived from America, disassembled in the ADVI assembly hall, Berezhkov again felt as if someone from a foreign country had snatched and carried out his plan.