The pulley block is ... The pulley block

The pulley block is the mechanism by which cargo lifting is carried out. It consists of one or more groups of blocks, bent by a rope. The word "polyspast" came from the Greek polyspastion. This term is translated as "stretched by several ropes". The main function of the pulley is to increase the load capacity of the main mechanism.

In other words, this device gives a gain in strength. However, the reverse effect of using a pulley block is a reduction in the lifting speed. You can also win at speed by losing the game. However, such pulleys are used much less often. In any case, the principle of the device is the action of the lever.

Mechanism arrangement

The pulley is a lifting mechanism that allows you to obtain a force that exceeds the hoisting power of the winch by several times. In other words, this mechanism increases the carrying capacity of the device. The use of the chain hoist allows lifting heavy cargo by means of a winch with a small lifting capacity. It is important to remember that the speed of lifting heavy structures will decrease as far as the payoff in payload capacity is achieved.

Purpose of the mechanism

The pulley is necessary for lifting heavy loads with a minimum of effort. The simplest design of the chain block is arranged so that one end of the rope is fixed on the drum, and at the opposite end of the rope is a suspended load. Devices having a more complex construction include several fixed and movable rollers.

For each weight should take into account the dimensions, blocks and diameter of the rope. A load that has a large mass, when suspended on a rope, increases the load. Rapid wear is typical for this mechanism. In this case, the voltage in the cable is reduced. Therefore, two or four ropes are used to suspend a large weight. It is also possible to use a complex block structure.

Principle of operation

A person who has nothing to do with loading, the name of this mechanism will seem incomprehensible. However, in fact, the pulley block is a very simple lifting mechanism, which almost anyone can build. The principle of operation of this device is extremely simple and it is studied in school in physics lessons. Yes, and the scheme of operation of such a small "crane" is very simple.

The design of the chain block includes several groups of blocks assembled into special clips. And they alternately bend around with a rope or a rope. Even such a simple structure can be used effectively enough to increase the force applied to lower or lift loads. Also the design of a simple pulley block contains cargo blocks. They can be of the following types:

• Multi-roller or single-roller;
• Stationary or mobile.

The pulling force of the rope in this case depends entirely on the number of rope strands in the structure used.

In what areas is the device used?

The pulley block is used for lifting and moving the load in those cases when it is possible to use only the physical strength of the person and the least number of auxiliary mechanisms. Also, the pulley block is the most important component of winches, cranes and other means of mechanization.

For this reason, these devices use practical in all areas, where at least some lifting mechanisms are used: from household tasks to heavy industry.

So, by what principle does the pulley operate? The work of this device is based on the law of the lever: when you win in power you get a loss in the distance. Since this principle is very simple, it is not difficult to produce a chain block with your own hands. This requires only two single-roller blocks.

To lift a weight of a certain mass with the help of a chain block, it is necessary to exert effort, half of its weight. Do not forget about the length of the rope used. It should be twice the height to which the load will be lifted. It should be noted that the pulley blocks having the simplest device are called "two-to-one pulley blocks", since they increase the applied force by half. The construction with three blocks, respectively, gives an increase in force three times.

Multiplicity of pulley block

It should be noted that the calculation of the chain saw plays a very important role. After all, the mechanism does not work in ideal conditions. It is affected by the frictional forces that arise when the cable is moved along the pulley. Also, frictional forces occur when the roller rotates, regardless of which bearings are used in it.

To determine the tensile strength of the applied rope without taking into account friction losses, the weight of the load must be divided by the multiplicity of the pulley. It should be understood as the number of yarns holding the load. Also, friction should not be neglected. It also determines the efficiency of the pulley.

It can be reduced using blocks and ropes of high quality, as well as by high-quality execution, eliminating unnecessary overlap and bends.

For today, the circuits of pulleys are studied even in the school course of physics. With their help to make this design will not be very difficult. You also need to purchase the following items:

• Fitting;
• rope;
• Winch.

Which models of the device exist?

To create the simplest model, only one block is needed. The use of such a mechanism gives a double gain in strength. This means that for the lifting of cargo, you need to apply twice as much effort. However, the rope in this case should be twice as long. Such a chain block has a ratio of two to one. Such a design may not contain blocks of pulley block, since instead of it one can use a regular carbine.

When using two blocks at once in a chain block, it is possible to increase threefold the advantage in the applied force. There is also a safety feature that works when the rope is lowered. In this case, the two gripping units are tightened and the load is blocked.

If you add two more blocks to the previous mechanism, you get a pulley block that yields a fourfold win in force. This mechanism has four to one relationship. In this mechanism a quarter of the weight goes to the end of the rope, and the rest of the load is on the rope itself.

Complex pulley blocks

It should be noted that the transfer of effort in its pure form can not be achieved due to the appearance of a frictional force. When the rope rubs against the block, ten to twenty percent of the applied force is lost. Therefore, in a simple pulley block, in fact, the ratio will be approximately 1.8 kilograms per kilogram of lifted cargo. A 5-fold pulley block will give a gain in strength a little more than 3 times.

The above relationship indicates that it is possible to increase the number of blocks of pulley block to a certain limit, after which an opposite effect can occur. However, in order to increase the maximum ratio, it is possible to use complex pulley blocks.

This block is designed in such a way that the lifted weight does not create a load on the last block. Instead, it loads the rope that passes through the block. As a result, when 3 blocks are used, the pulley blocks 2: 1 and 3: 1 are alternately connected. In theory, this gives a sixfold gain in strength, and in practice it is 4.3 times.

How to reduce friction?

The main problem of the pulley block is that in the process of work it has to overcome the frictional forces that arise. This task can be partially solved if high-quality ropes, blocks-pulleys with smooth streams and thick lubrication are used.

Also there are additional possibilities at competent application of a design of a chain block. For example, if you use more than one carbine, and two. Due to this, the frictional force decreases, and an increase in the inflection radius occurs.