Lifting machines are designed to help a person lift something heavy to a height. Most lifting mechanisms are based on a simple block system - a pulley system. 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.

Structure of the lifting mechanism

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

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.

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.

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 of two pulleys gives approximately a twofold gain, of three - threefold, and so on. The increase in distance is calculated using the same principle. To operate a simple pulley, you need a cable twice as long as the lifting height, and if you use a set of four blocks, then the length of the cable increases in direct proportion to four times.

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, pulleys are widely used 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.

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.

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.

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.

The complex chain hoist does not belong to one or the other type. Its distinctive feature is 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.

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.

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%.

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.

Calculation of the useful action of the 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 lifting mechanism consists of several blocks. The total efficiency of a pulley block is not equal to the arithmetic sum of 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.

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 ηp for systems with different numbers of blocks at different efficiency values ​​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.

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 lifting capacity of the pulley blocks is not enough, and there is no time or opportunity to build a complex multiple lifting mechanism. 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.

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. Suitable for a homemade mechanism synthetic rope, thickness depends on the weight of the load.

The material and quality of the blocks are indicators that will provide homemade lifting devices with the calculated 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.

Step-by-step instruction for lifting loads 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.

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

Even a manual winch will make lifting the load more comfortable - you don’t 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.

In principle, even outside a construction site, the ability to build a basic pulley system for a winch in field conditions with a minimum of tools and materials 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.

It is difficult to overestimate the importance of pulley hoists in the development of modern construction and mechanical engineering. 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.

Blocks and pulleys- simple mechanisms used to lift loads either with little effort or with effort in a position convenient for the user.

Blocks and pulleys consist of two parts: a wheel with a circumferential groove (pulley) and a rope or cable. A block, as a rule, is a device consisting of one pulley in a frame with a suspension and one cable. A pulley block is a combination of pulleys and cables. The principle of its operation is similar to the operation of a lever - the gain in force affects the increase in distance with theoretical equality of the work performed.

These mechanisms can be used independently of other lifting units, such as winches, hoists, cranes, and also as their parts.

The pictures show the operating principle block and pulley:

In Fig. 1a, a load weighing W1 is lifted using a single block with a force P1 equal to the weight. In Fig. 1b, the load W2 is lifted with the simplest multiple pulley system, consisting of two blocks, with a force P2 equal to only half the weight of W2. The impact of this weight is divided equally between the branches of the cable on which pulley B2 is suspended from pulley A2 by hook C2. Consequently, in order to lift the load W2, it is sufficient to apply a force P2 equal to half the weight of W2 to the branch of the cable passing through the groove of the pulley A2; Thus, the simplest chain hoist gives a double gain in strength. Fig. 1,c explains the operation of a pulley with two pulleys, each of which has two grooves. Here the force P3 required to lift the load W3 is only a quarter of its weight. This is achieved by distributing the entire weight of W3 between the four suspension cables of block B3. Note that the multiple of the gain in strength when lifting weights is always equal to the number of cables on which the movable block B3 hangs.

Rice. 2

In the past as a cable for blocks and pulleys flexible and durable hemp rope was used. It was woven with a braid of three strands, each of which consisted of many small strands. Pulley hoists with such ropes were used wherever it was necessary to lift loads: on sea ​​vessels, V agriculture, on construction sites. The most complex of them (Fig. 2) were often used on sailing ships. There they were needed to work with sails, spar parts and other movable equipment.

Over time, hemp edges were replaced by steel cables and cables made of synthetic and mineral fibers. They are more durable and wear-resistant. Pulley hoists with steel cables and multi-groove pulleys are integral parts of the lifting mechanisms of all modern lifting equipment. Pulleys blocks usually rotate on roller bearings and all their moving surfaces are forcibly lubricated.

Has always been a priority. In this regard, a device was invented quite a long time ago, which contributed to significant relief physical labor workers involved in carrying out operations to lift or lower various objects. The name of this device is chain hoist. We will look at what this is in this article.

History of creation and definition

No one knows for sure when exactly mechanisms for moving heavy objects in space appeared and began to be used. First of all, we note: a pulley system (technical literature can also tell you what it is) is a system of blocks and ropes that can significantly simplify and speed up planned work with heavy objects.

The study of such architectural monuments as the Cheops pyramids in Egypt, the Great Wall of China and other ancient structures clearly confirms that pulleys, the purpose and design of which will be discussed below, were invented several thousand years ago. It is quite obvious that they were initially characterized by primitiveness.

general information

Let's try to study the chain hoist in as much detail as possible. What is this from a technical point of view? At its core, it is a group of blocks assembled into special cages through which either a chain or a rope passes. The simplest pulley is one block with a traction element stretched through it. This version of the scheme allows you to halve the traction force required to move the load.

Classification

Pulley hoists are divided into two large groups: power and speed. Often in practice, power analogues are used to significantly reduce the cable tension. By the way, this effort can be calculated quite simply. To do this, you will need to divide the mass of the load by the available multiplicity of the pulley. The question arises: what is multiplicity? Answer: multiplicity is the ratio of the number of branches of the organ on which the load is located to the numerical value of the branches that are already wound on the drum. This definition applies to power pulleys. As for high-speed pulleys, the multiplicity here is the value obtained by dividing the speed of the leading end of the rope by the speed of the driven end.

In high-speed pulleys, the working force is applied to the movable cage, and the load, in turn, is secured to the free end of the cable. The gain in speed during operation of this type of pulley arises due to the increase in the distance of lifting the object.

Changing the ratio

Pulley hoists (their purpose and design have remained essentially unchanged over the years of existence) allow the introduction or removal of additional blocks from the system. Due to this, the required multiplicity is obtained. If the multiplicity is even, then the free end of the rope is fixed to a stationary structural element. If the multiplicity is odd, then the same end is attached to the clip with a hook.

In power pulleys, increasing the multiplicity allows you to reduce the diameter of the rope and, accordingly, the dimensions of the drum and blocks. All this ultimately leads to a decrease in the total mass of the entire system, a decrease in But at the same time, a larger length of rope will be required.

Division by number of branches

The pulley (what it is, now you obviously understand) can be single or double, depending on the number of branches. In the first case, the flexible element moves along the axis of the drum. This option has the disadvantage that it causes an undesirable change in the load on the drum supports, and in the absence of free blocks (that is, the rope from the suspension is immediately wound onto the drum), the object will move not only vertically, but also horizontally.

The double chain hoist provides for securing both ends of the rope to the drum. An example would be a pulley for a winch. In order to avoid distortion, equalizing blocks or balancers are used. Most often, such a system is used in gantry or bridge or heavy tower cranes.

Peculiarities

Absolutely any chain hoist, the principle of operation of which is generally similar to the operation of a lever, is good because it does not require any special skills from the user, but it requires extreme caution, since, like any other, it is fraught with danger and can cause injury. In addition, the operation of pulley blocks shows that the traction elements used in their systems do not have ideal flexibility and are endowed with some rigidity. That is why the advancing branch of the rope is not able to immediately fall into the stream of a block or drum, and the running branch cannot immediately straighten out. This is best seen when using steel ropes.

Rules for chain hoists

Each manual pulley operates on the basis of the laws of physics, and therefore its operation complies with several fairly simple rules that it is advisable to familiarize yourself with.

The complex chain hoist deserves special attention. By itself, it represents a collection of simple pulley hoists, each of which pulls the other. In this way, several pulleys can be mounted together. This type is most often used during rescue operations.

In conclusion, it would be correct to say the following: the pulley system (the principle of its operation is quite easy to understand upon careful study of the issue) was, remains and, most likely, will be a faithful assistant to a person for a very long time in solving many pressing issues related to construction, installation, loading, unloading and other operations that are quite labor-intensive. The main problem, the complete elimination of which is not possible today due to, again, ideally working physical laws, is the presence of friction force in the system.

Pulley hoist- a system of movable and fixed blocks connected by a flexible connection (rope or chain), used to increase force (power pulley) or speed (high-speed pulley). Distinctive feature moving blocks is that their axis has the ability to move in space relative to the fixed blocks.

Typically used in lifting machines power pulleys, allowing to reduce the effort to lift the load, the moment from the weight of the load on the drum, the gear ratio of the mechanism, etc.

High-speed pulleys, which make it possible to increase the speed of movement of the load at low speeds of the drive element, are used much less frequently, for example, in hydraulic or pneumatic lifts.

The main parameter of the chain hoist is its multiplicity, which is understood as the ratio of the speed of movement of the movable branch of a flexible traction element to the speed of lifting the load or the ratio of the number of rope branches on which the load is suspended to the number of rope branches wound onto the drum. The multiplicity of the pulley system characterizes the gain in strength.

When choosing a chain hoist, friction losses should also be taken into account. The most best blocks used in practice lead to friction losses of at least 10% of the applied force. Thus, by making an effort 1 kg to a simple double pulley, you can lift the load in 2 × 0.9 = 1.8 kg, and when using a simple four-fold pulley, not 4 kg, as expected, and 4 × 0.9 × 0.9 × 0.9 = 2.92 kg, that is, the gain in strength will be less than 3 times, with a loss in speed of 4 times. A simple five-fold chain hoist gives a real gain of a little more than 3 times. When using carabiners instead of blocks, the friction is even greater.

List of links

1. Alexandrov M.P. Hoisting and transport machines: A textbook for mechanical engineering specialties at universities. – 6th edition, revised. – M.: Higher School, 1985. – 520 p., ill.
2. Shestopalov A. How a chain hoist works // Internet project “How Things Work”. – http://howitworks.iknowit.ru/paper1144.html.

Questions for control

1. What is the purpose of a pulley block?
2. How to determine the multiplicity of a chain hoist?
3. What is the reason for the inappropriateness of using large multiplicity pulleys?

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 win effective force with loss 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 a simple rule: how many ropes come from the load, this 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 variants of a given system are combined into one system. 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 with a large diameter or too stiff, 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 strength gain of a simple type of lifting mechanism, it is necessary to calculate the load on each branch of the rope and add them up. To calculate the gain in strength of 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.