Scheme of a chain hoist with a multiplicity of 4. Lifting loads without special equipment - how to calculate and make a chain hoist with your own hands. Is it possible to combine a chain hoist and a winch
Polyspast - this is a lifting device, consisting of several movable and fixed blocks enveloped by a rope, rope or cable, which allows lifting loads with an effort several times less than the weight of the load being lifted.
Any chain hoist gives a certain gain in effort to lift the load. In any mobile system consisting of a rope and blocks, friction losses are inevitable. In this part, for ease of calculation, inevitable frictional losses are not taken into account and the theoretically possible gain in effort, or abbreviated TB theoretical gain, is taken as the basis.
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"
Basics of building chain hoists
If you fix the rope (cable) on the load, throw it over the block fixed at the station (hereinafter referred to as the stationary or fixed block) and pull it down, then to lift the load, you must apply a force equal to the mass 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.
The rope (cable) is fixed at the station and passed through the block on the load. With this scheme, to lift the load, an effort is needed 2 times less than its mass. Effort win 2:1. The roller moves up with the load. In order to lift the load by 1 meter, it is necessary to stretch 2 meters of rope through the roller.
This is a diagram of the simplest chain hoist 2: 1
Figures No. 1 and 2 illustrate the following Basic Rules of Polyspasts:
Rule number 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 serve only to change the direction of movement of the rope and WIN IN EFFORT DO NOT GIVE.
Rule number 2.
How many times we win in effort - the same number 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 up, 2 meters of rope must be pulled through the system, then in the chain hoist 6: 1 - respectively 6 meters. The practical conclusion is that the “stronger” the chain hoist, the slower the load rises.
Continuing to add stationary rollers to the station and movable rollers to the load, we get the so-called simple chain hoists of different forces:
Examples of simple chain hoists Fig. 3, 4.
Rule #3
Calculation of the theoretical gain in effort in simple chain hoists. Everything here is quite simple and clear.
If it is necessary to determine the TV of an already finished chain hoist, then you need to count the number of strands of rope going up from the load. 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 attachment of the rollers. Figures 5, 6.
Bold
Calculation of TV when assembling a simple chain hoist
In simple chain hoists, each movable roller (fixed on the load) added to the system additionally gives a double TV. The incremental effort DOES add up to the previous one.
Example: if we started with a chain hoist 2:1, then by adding another movable roller, we get 2:1 + 2:1 = 4:1; By adding one more roller, we get 2:1 + 2:1+2:1= 6:1, etc.
Figures 7.8.
Depending on where the end of the cargo rope is fixed (at the station or on the load), simple chain hoists are divided into even and odd.
If the end of the rope is fixed at the station, then all subsequent chain hoists will be EVEN: 2:1, 4:1, 6:1, etc. Figure 7
If the end of the load rope is fixed on the load, then ODD chain hoists will be obtained: 3:1, 5:1, etc. Figure 8
In addition to simple chain hoists, the so-called COMPLEX chain hoists are also widely used in rescue work.
Complex chain hoist
A complex chain hoist is a system in which one simple chain hoist pulls another simple chain hoist. Thus, 2, 3 or more chain hoists can be connected.
Figure 9 shows the designs of the most commonly used complex chain hoists in rescue practice.
Rule number 4. Calculation of TV complex chain hoist.
To calculate the theoretical gain in effort when using a complex chain hoist, it is necessary to multiply the values of simple chain hoists that it consists of. 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 that make up the complex one is carried out according to the rule of simple pulley blocks. The number of strands is counted from the point of attachment of the chain hoist to the load or cargo rope coming out of another chain hoist. Examples in fig. 10 and 11.
Figure 9 shows almost all the main types of chain hoists used in rescue operations. As practice shows, in most cases, these structures are quite enough to perform any tasks. Further in the text, several more options will be shown.
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 pulley blocks 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 cord, several carabiners (with or without rollers) and grasping (clamps). I highly recommend it to all those who are going to work with real chain hoists. From my own experience and the experience of my students, I know that after such training, there are much fewer errors and confusion in real conditions.
Complex chain hoists
Complex chain hoists are neither simple nor complex - this is a separate type.
A distinctive feature of complex chain hoists is the presence in the system of rollers 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.
Figure 12. shows two schemes of complex chain hoists used in rescue work. There are other schemes, but they are not used in rescue practice and are not considered in this article.
If it is necessary to obtain a large gain in strength for lifting or horizontal movement of heavy loads, chain hoists are used - systems of movable and fixed blocks, combined in common clips and connected by a rope.
Polyspast - This is a lifting device, consisting of
several movable and fixed blocks of fire-
beaten with a rope, rope or cable, allowing
capable of lifting loads with a force several times
less than the weight of the load being lifted.
They are an integral part of many lifting mechanisms with a flexible working body.
Polyspasts represent a system of two clips:
Mobile,
And motionless
each of which consists of one or more blocks wrapped around by a rope. At one end, the rope is fixed on a movable or fixed clip, and its last branch in the chain hoist is wound directly through the outlet block onto the drum.
Fig.59. Polyspast:
but - wrapped around by a rope; b - wrapped around by a chain.
The chain hoist is used to gain in strength, which is achieved by the fact that the load applied to the movable block is balanced by the efforts of all working threads of the rope.
There are two types of polyspasts:
■ with a traction rope running off the movable block,
Fig.60. Polyspast with a traction rope running from a movable block.
■ and with a traction rope running from a fixed block.
Fig.61. Polyspast with a traction rope running
to the moving block.
The first chain hoists are used in gantry and portal cranes, the second - in construction machines with winches located below the level of the axis of fixed blocks.
Fig.62. Numbering of threads in the chain hoist.
The main parameter of the chain hoist is its multiplicity (gear ratio) i , equal to the ratio V to rope travel to speed V g lifting load or equal to the number of branches of the rope n , perceiving the weight of the load G
Or (9)
Polyspasts are characterized by a multiplicity, which depends on the number of blocks in the clips and is determined by the number of rope branches on which the load is suspended.
Polyspast multiplicity - the number of chain hoist threads for which
movable clip is suspended.
The multiplicity shows how many times the force required to lift the load is less than the specified mass of the load. Since the number of branches of the chain hoist, on which the mass of the lifted load is distributed, is numerically equal to the multiplicity of the chain hoist, we can recommend the following simple method for determining it. If the chain hoist is mentally cut by a plane that intersects all the branches of the rope that goes around the blocks, then the multiplicity of the chain hoist will be numerically equal to the number of ropes crossed by the plane. The greater the multiplicity of the chain hoist i, the less effort R, which must be developed by a winch to lift a given load G, and the greater the speed of the rope wound on the drum, which provides a given speed of lifting the load.
Fig.63. The procedure for determining the multiplicity of the chain hoist.
Any chain hoist gives a certain gain in effort to lift the load. In any mobile system consisting of a rope and blocks, friction losses are inevitable. In this part, to facilitate the calculations, the inevitable friction losses.
They are an integral part of many lifting mechanisms with a flexible working body. The purpose of the chain hoist is to reduce the rope tension, which helps to reduce the load moment. Polyspasts represent a system of two clips: movable and fixed, each of which consists of one or more blocks, enveloped by a rope. One end of the rope is hooked on a movable or fixed clip, and its last branch in the chain hoist is wound directly through the outlet block onto the drum. The load is suspended in a movable cage. Polyspasts are characterized by a multiplicity, which depends on the number of blocks in the clips and is determined by the number of rope branches on which the load is suspended.
Fig.64. Polyspasty:
1 - movable clip; 2 - fixed clip; 3 - drum
winches; 4 - lifting device.
Fig.65. Davit beam with chain hoist for descent
on the water and lifting boats aboard.
To lift loads on truck cranes, two-, three- and four-fold chain hoists are used (reeves with a multiplicity of 2, 3 and 4).
Fig.66. Polyspasty:
but- double; b - quadruple.
Quadruple chain hoists are most widely used on automobile parks. Their design depends on the location of the load limiter and the installation location of the movable blocks of the chain hoist. If the load limiter is installed on a swivel frame (KS-2561D), the jib rope is attached to the limiter lever, it wraps around two movable, fixed and deflecting blocks and is directed to the jib winch. The fixed blocks are installed on the head of the two-legged rack, and the movable blocks are mounted on the head of the boom or a movable traverse connected by braces to the boom.
Fig.67. Double and triple chain hoists on truck cranes.
Use of chain hoists:
Fig.68. Rope block system of crawler crane
with tower-boom equipment:
1, 3, 6 - safety rods of the gooseneck; 2 - tower safety rod;
4 – cargo chain hoist; 5 - goose traction; 7, 11 - pulley pulley changes you-
summer gander; 8 - gander pulley block; 9, 12 - pulley pulley of the tower; 10 - poly-
save the towers.
Fig.69. Grab:
1 - grab with bucket; 2 - tong grab; 3 - multi-jaw grab.
Fig.70. Typical hydrokinematic scheme
automobile crane of the fourth dimensional
groups with a load capacity of 20 tons.
If we could create a chain hoist in which there was no friction in the blocks, then for such a chain hoist the coefficient i would always be equal to the number of working threads of the chain hoist ( then the traction force in the winch rope, if friction forces are not taken into account, is equal to the force in one working thread
where P is the traction force in the winch rope;
G is the load applied to the movable pulley block;
i- number of working threads.
Number i- is called the polyspast multiplicity.
The greater the multiplicity of the chain hoist, the less the load on each of its working threads and, therefore, the less the pulling force of the winch.).
To simplify the calculation, the value of the coefficient i for a chain hoist with a different number of working threads and outlet blocks, it was calculated in advance (Table 1).
- Block Promalp double: 2 pcs.
- Carabiner Height 513: 3 pcs.
- Rope Promtex 10 mm: 100 m
- Write a constructive review about a product that you have had or has with a post on any social network. And we will give you a coupon that allows you to get a 5% discount on one item from a future order. Write five reviews and we will give you five such coupons.
You can ask a question about the product in this form.
Our managers will receive this question and will try to answer your e-mail or by calling the phone number you specified.
- in our catalog for individuals and legal entities is available for purchase both at retail in our store and wholesale in our department of work with corporate clients.
Buy in bulk
Bulk prices
Bulk prices
We offer wholesale prices for regular customers with whom we have established partnerships and for legal entities for which we have a separate office and warehouse. A commercial offer can be obtained by sending us a request through the feedback form. You can also use the electronic catalog system of the online store by adding the desired products to the basket and placing an order. Our managers will process it, if necessary, advise you on the specifics and expediency of buying this or that equipment and transfer it to the wholesale department for further processing.
- Purchases for a total amount of 10 thousand rubles - 5% discount
- Purchases for a total amount of 30 thousand rubles - 10% discount
- Purchase for a total amount of 90 thousand rubles - 15% discount
- Purchase for a total amount of 150 thousand rubles - 20% discount
It makes sense to use such a chain hoist when lifting loads weighing up to 700 kg. Very good quality bearings and large pulleys at a relatively low cost of blocks make this chain hoist one of the most justified and reasonable options. The only disadvantage of such a kit is a rather high weight.
The working length of the chain hoist is 20 meters, but can be changed according to your requirement.
Kit contents
The chain hoist is a lifting structure that was invented back in the time of the great thinker Archimedes. Now it is impossible to establish exactly who this genius was, but the already mentioned philosopher also put his hand to the development of this construction. Otherwise, it is also called the system of blocks, because of the main purpose and the counterweights available at that time, in the form of limestone blocks.
Blocks and chain hoists, the purpose and arrangement of which now for an ordinary person who is accustomed to high technology, looks rather primitive. But it is worth considering the fact that it was thanks to this mechanism that great historical buildings were built, such as the pyramids, the Pantheon, the Colosseum and the like. But the technology did not remain on the pages of textbooks, but continued its development, adapting to emerging technology and the needs of people.
Description and arrangement of chain hoists
The design itself is a device for lifting loads using special connection blocks and ropes between them. Using the lever rule and the force of friction, the structure comes into action increasing the force or speed of lifting an object. There are different types of chain hoists, which differ in the number of blocks, cable connections, load capacity and other configurations.
The system, in turn, consists of movable and fixed elements, along which ropes are drawn, creating tension and ensuring the transportation of cargo. The fixed element is the main structure that is attached to the vehicle or static bar, and the movable element is attached to the load. Therefore, the first must be able to withstand a lot of pressure, and the second to evenly distribute it.
The lower or movable block is usually equipped with a special mount, in the form of a hook, a powerful magnet, a carabiner, and so on. The upper block has special rollers along which the rope is carried and the pressure exerted on each rope individually depends on the number of rollers. And this means that the appropriate number of rollers and working branches are required to lift large heavy loads.
The video tells and demonstrates how the chain hoist works, and also reveals its advantages
Purpose
Given the fact that this invention is more than two thousand years old, it has been used to perform an unimaginable amount of work and tasks. Often this is the construction industry, where chain hoists are used in cranes, winches and the like. Also, the mechanism was used on ships, for lowering and raising lifeboats. It was used for some time in the first prototypes of the elevator, before the advent of hydraulic and electric drives.
Pulleys, purpose and device, their multiplicity changed and found application in sports, namely, in rock climbing and other extreme activities at high altitudes. Also, for a long time, rescue teams in mountainous areas were equipped with devices to pull victims out of hard-to-reach places. You can often find the use of blocks in electrical wiring, or rather, to create tension in the cable network.
Varieties of chain hoists
All pulley blocks can be divided into two categories:
- power;
- high-speed.
Based on the name, the purpose of each species is determined and based. The first is the most common and is used to lift loads, exactly as it was invented. The high-speed option is a modified design, where great efforts are directed to increase the speed of transportation. According to this principle, cable cars are created at ski resorts.
In addition, the difference lies in the number of rollers and working branches, as well as other modifications. An electric drive and a stopper can be connected to the structure. Another difference lies in the material of the rope, because it can be represented as:
- ropes;
- metal rope;
- iron chain;
- electric cable.
In construction engineering, the second option is most often used, due to the strength of the material. Rope ropes are used most often in tourism, rescue operations and so on. The use of an iron chain is very rare; these are narrowly focused varieties for certain jobs.
lift with at home
Sometimes in everyday life there is a need to lift a heavy load, but not all people have the opportunity to fit a construction crane to the threshold, from which they have to get out. And here the system of blocks can just come to the rescue. Polyspasts, the purpose and arrangement of which may seem rather difficult to design, but with proper preparation, creating such a design at home will not be a problem. Everything is done in four stages:
- Calculations. They are made taking into account your goals and objectives, namely, the parameters of the working room, the presence of restrictions in it, the weight of the cargo and the distance over which you need to transport. It is necessary to fix all these data for drawing up a drawing and choosing a design.
- Creating a drawing. If there is no experience in this matter, then it is better to turn to a person with experience and engineering education, who can reduce the time to create a model on paper. If there is nowhere to get help, then it is better to turn to the Internet and see the working drawings of the basic structures. Each of the types will be effective in certain conditions, the measurements of which you will make earlier.
- Selection of materials. The selection should begin already at the first stages, namely, starting from the things you already have and those that can be purchased. It depends on your drawing and calculations what parts will be needed and what material is better to use. Buy according to your budget and with a reserve for further use. It’s not worth saving much, otherwise the design can fail at the most crucial moment.
- Design. This step is the easiest of all, because here you just need to follow the plan and do it right.
With a certain skill and preparedness, a very solid working model can be obtained, which will not be inferior to building counterparts. But if the tasks are not too ambitious, then this will not require strong costs. For reliability, you can use ready-made parts from construction chain hoists in the creation.
Conclusion
Pulley blocks are simple in design, but their purpose is important, because thanks to them it is possible to carry out the most complex lifting manipulations. Construction of buildings, installation of electric cable lines, installation of a funicular or rescue operation, in any of these situations, the system of blocks can guarantee the reliability of execution.
Polyspast(from the Greek polyspastos - pulled by many ropes) is a lifting device that works on the principle of a lever and is designed to move various loads, both vertically and horizontally, or to pull a bowstring, for example, crossings.
Any chain hoist gives a certain gain in effort to lift the load.
The degree of increase in the applied traction force in the chain hoist is called the gear ratio or multiplicity of the chain hoist and is indicated by the Latin letter "I".
Structurally, the chain hoist consists of two types of blocks:
- motionless attached to the anchor station (beam, mast, tripod, etc.);
- And mobile that are attached to the load being lifted.
The blocks are interconnected by a rope (rope, cable, chain, etc.), which, sequentially bending around all the rollers of the blocks, at one end usually is attached to a fixed block (upper when lifting loads), and its other end (traction) is directed through the outlet blocks to the place of application of force (physical or mechanical).
The roller of the fixed block, from which the end of the rope runs, is considered to be a diverting roller. The lower pulley block, as a rule, has a cargo hook (or connecting element: carabiner, shackle, etc.), to which the load being lifted is suspended. And the top one - for which the chain hoist itself is suspended (see Fig. 1).
Rice. 1. Pulley block in general form (a), in the tightened state with a hook on the blocks (b) and in the tightened state with earrings on the blocks (c)
Legend:
1 - movable block;
2 - rope;
3 - block fixed;
4 - traction rope;
5 - earring;
6 - hook.
The main advantage of the chain hoist is that it allows you to get a significant gain in strength. Therefore, the use of chain hoists is advisable in cases where the pulling force of the available traction means is less than the effort required to lift or move the object.
As for the gain in effort, it is given only by movable blocks fixed directly on the load or on a rope coming from the load. Fixed (stationary) blocks serve only to change the direction of the rope and do not give a gain in effort.
For example, pulley blocks 3:1 and 4:1 can be obtained with the following options (see Fig. 2):
Rice. 2. Schemes of chain hoists
The speed and path traveled by the object being moved decrease (in relation to the speed and path traveled by the traction end of the cable) in direct proportion to the increase in force, i.e. how many times you win in effort, how many times you lose in distance, and the “stronger” chain hoist - so it is “slower”.
Based on this chain hoists are divided into power (direct) and high-speed (reverse). The former are the most commonly used, so we will talk about them below.
As for the design features, the chain hoist can be configured in a wide variety of combinations of the corresponding components (movable and fixed blocks, ropes, anchors, clamps, auxiliary clamps, brakes for smooth removal of loaded systems). Due to this feature chain hoists according to the structural device are differentiated into simple and complex:
- in simple chain hoist all blocks are wrapped around by one cable;
- in complex- several simple chain hoists are connected in series, i.e. one simple chain hoist pulls another simple chain hoist, etc. In them, the last block loads not the load being lifted, but the rope passing through the block. That is, there is a serial connection of chain hoists (for example, the connection of chain hoists 2: 1 and 3: 1 - theoretically provides an increase in effort by 6 times).
Depending on where the end of the cargo rope is fixed (at the station or on the load), simple chain hoists are divided into even and odd. If the end of the rope is fixed at the station, then all subsequent chain hoists will be even (2:1, 4:1, 6:1, etc.). If the end of the cargo rope is fixed on the load, then odd chain hoists will be obtained (3: 1, 5: 1, etc.).
Complex chain hoists, which are neither simple nor complex, are singled out as a separate type. Their distinctive feature is the presence in the system of block-rollers moving towards the load. This is the main advantage of complex chain hoists in cases where the station is located higher and it is necessary to pull the chain hoist down. There are other schemes as well.
The process of calculating the theoretical gain in effort in chain hoists is quite simple and is based on the following rules, according to which:
- each movable roller (fixed on the load) added to the system gives a twofold theoretical gain in strength;
- with a simple chain hoist, the additional effort is added to the previous one;
- when using a complex chain hoist, it is necessary to multiply the values \u200b\u200bof the simple chain hoists that it consists of.
At the same time, the calculation of the effort of each of the simple pulley blocks that make up the complex one is made according to the rule of simple pulley blocks. The number of strands is considered from the point of attachment of the chain hoist to the load or cargo rope coming out of another chain hoist.
Consider the most commonly used chain hoist systems, emphasizing that there are other, more complex, chain hoist systems, but rarely used.
The figure below shows the most popular schemes of simple and complex chain hoists, shown in natural and schematic form (see Fig. 3, 4 and 5).
Rice. 3. Schemes of simple chain hoists of various configurations
Rice. 4. Schemes of complex chain hoists of various configurations
Rice. 5. Conditional schemes of simple and complex chain hoists of various configurations
The selection process of the chain hoist has certain features. Initially, the chain hoist scheme is selected based on the parameters of the moving object (mainly its gravity) and the traction capabilities of the subject of this process (the physical capabilities of a person or the parameters of the equipment used).
In any mobile system consisting of rope and blocks, friction losses are inevitable. Theoretically, it is possible to add stationary blocks to the station and movable blocks to the load indefinitely in order to obtain simple chain hoists of various forces. However, in practice this is hindered by the force of friction. Due to the force of friction, a pure transmission of force is impossible, and due to friction losses, the efficiency of the chain hoist can be significantly lower than theoretically possible. And the increase in the number of blocks has a certain limit, beyond which the opposite effect is possible. Thus, from the foregoing, we can conclude that the main problem of the chain hoist is to overcome the friction force. The main solution to the problem of friction is the use of high-quality block rollers on ball bearings with large diameter strands and soft ropes. It is known that the efficiency for blocks supported by plain bearings η=0.95÷0.96; for blocks on rolling bearings η=0.97÷0.98.
And when using the construction of a chain hoist without rollers, for example, put two carbines next to each other instead of one. Due to this, the bending radius of the rope increases and the friction force decreases.
TM "CROC",
August 2015
