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Chain transmission is based on the meshing of a chain and sprockets.
Advantages and disadvantages
The principle of engagement and the high strength of the steel chain make it possible to provide a greater load capacity of the chain drive compared to a belt drive. The absence of slipping and slipping ensures a constant gear ratio (average per revolution) and the ability to work under short-term overloads.
The gearing principle does not require pre-tensioning of the chain, which reduces the load on the supports. Chain drives can operate at smaller center distances and at larger gear ratios, and also transmit power from one drive shaft to several driven ones.
The main reason for the disadvantages of chain transmission is that the chain consists of individual rigid links located on the sprocket not in a circle, but in a polygon. This causes wear on the chain joints, noise and additional dynamic loads. Chain drives require a lubrication system.
Application area:
- at significant interaxial distances, at speeds less than 15-20 m/s, at speeds up to 35 m/s, plate chains are used (a set of plates with two tooth-like protrusions, the principle of internal gearing);
- when transmitted from one drive shaft to several driven ones;
- When gears are not applicable and belt ones are unreliable.
Compared to belt drives, chain drives are noisier, and in gearboxes they are used at low-speed speeds.
Main characteristics of chain transmission
Power
Modern chain transmissions can operate in a fairly wide range: from fractions to several thousand kilowatts. But at higher powers, the cost of transmission increases, so the most common are chain transmissions up to 100 kW.
Peripheral speed
As speed and rotational speed increase, wear, dynamic loads and noise increase.
Gear ratio:
The gear ratio of the chain drive is limited to 6 due to the increase in dimensions.
KKD transmission
Losses in a chain drive consist of friction losses in the chain hinges, on the sprocket teeth and in the shaft supports. When lubrication by immersion in a lubricant bath, mixing losses are taken into account lubricating oil. Average CCD value
Center distance and chain length
The minimum value of the center distance is limited by the minimum permissible gap between the sprockets (30...50 mm). To ensure durability, depending on the gear ratio
Types of drive chains
- Roller
- Bushing
- Serrated
All chains are standardized and manufactured at special factories.
Drive chain sprockets
Sprockets are like gears. The pitch circle passes through the centers of the chain joints.
The profile of the teeth of roller and bushing chains can be convex, straight and concave, in which only the main lower section of the profile is concave, at the top the shape is convex, and in the middle part there is a small straight transition section. The concave profile is the most common.
The quality of the profile is determined by the profile angle, which for concave and convex profiles varies according to the height of the tooth. With an increase in the profile angle, the wear of the teeth and hinges decreases, but this leads to increased impacts of the hinges when entering engagement, as well as to an increase in the tension of the idle branch of the chain.
Materials
Chains and sprockets must be resistant to wear and shock loads. Most chains and sprockets are made from carbon and alloy steels with further heat treatment (improvement, hardening).
Sprockets, as a rule, are made from steels 45, 40Х, etc., chain plates - from steels 45, 50, etc., rollers and rollers - from steels 15, 20, 20Х, etc.
Hinge parts are cemented to increase wear resistance while maintaining impact strength.
In the future, it is planned to manufacture sprockets from plastics, which will reduce dynamic loads and transmission noise.
Meshing forces
- tension forces of the leading and driven branches,
- circumferential force,
- pre-tension force,
- centrifugal force.
Kinematics and dynamics of chain drives
The movement of the driven sprocket is determined by the speed V 2, periodic changes of which are accompanied by variability in the gear ratio and additional dynamic loads. The speed V 1 is associated with transverse vibrations of the chain branches and impacts of the chain hinges on the sprocket teeth, causing additional dynamic loads.
With a decrease in the number of teeth z 1, the dynamic properties of the transmission deteriorate.
Impacts cause noise during transmission operation and are one of the reasons for circuit failure. To limit harmful influence impacts, recommendations have been developed for choosing a chain pitch depending on the transmission speed. At a certain rotation speed, the phenomenon of resonance of circuit oscillations may occur.
During operation, wear occurs on the chain hinges due to an increase in the gaps between the roller and the bushing, as a result of which the chain is stretched.
The wear life of the chain depends on the center distance, the number of teeth of the small sprocket, pressure in the joint, lubrication conditions, wear resistance of the chain material, and permissible relative wear
As the chain length increases, the service life increases. With fewer sprocket teeth, the dynamics deteriorate. An increase in the number of teeth leads to an increase in dimensions, the permissible relative clearance decreases, which is limited by the possibility of loss of engagement of the chain with the sprocket, as well as a decrease in the strength of the chain.
Thus, with an increase in the number of sprocket teeth z, the permissible relative wear of the hinges decreases, and as a result, the life of the chain before losing engagement with the sprocket decreases.
Maximum service life, taking into account strength and meshing ability, is ensured by choosing the optimal number of sprocket teeth.
Chain transmission performance criteria
The main cause of loss of performance is wear of the chain joints. The main design criterion for the wear resistance of hinges
The wear life of the chain depends on:
- on the center distance (the chain length increases and the number of chain runs per unit time decreases, i.e. the number of turns in each chain joint decreases);
- on the number of teeth of the small sprocket (with an increase in z1, the angle of rotation in the hinges decreases).
The method for practical calculation of chain transmission is given in.
chain drive, chain, sprocket, chain pitch
Calculation example of a spur gear
Calculation example spur cylindrical gear. The choice of material, calculation of permissible stresses, calculation of contact and bending strength have been carried out.
An example of solving a beam bending problem
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The task is to test the strength of a steel shaft at a given diameter, material and allowable stress. During the solution, diagrams of torques, shear stresses and twist angles are constructed. The shaft's own weight is not taken into account
An example of solving a problem of tension-compression of a rod
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Determining the speed and acceleration of a point using given equations of motion
An example of solving a problem to determine the speed and acceleration of a point using given equations of motion
§ 1. GENERAL INFORMATION
A chain drive consists of a drive and driven sprocket and a chain that surrounds the sprockets and engages with their teeth. Chain drives with several driven sprockets are also used. In addition to the main elements listed, chain transmissions include tensioning devices, lubrication devices and guards.
The chain consists of links connected by hinges, which provide mobility or "flexibility" of the chain.
Chain transmissions can be performed in a wide range of parameters.
Chain drives are widely used in agricultural and hoisting machines, oil drilling equipment, motorcycles, bicycles, and cars.
In addition to chain drives, mechanical engineering uses chain devices, i.e. chain drives with working parts (buckets, scrapers) in conveyors, elevators, excavators and other machines.
The advantages of chain drives include: 1) the possibility of use in a significant range of center distances; 2) smaller dimensions than belt drives; 3) no slipping; 4) high efficiency; 5) small forces acting on the shafts, since there is no need for a large initial tension; 6) the ability to easily replace the chain; 7) the ability to transfer movement to several sprockets.
At the same time, chain drives are not without their drawbacks: 1) they operate in the absence of fluid friction in the joints and, consequently, with their inevitable wear, which is significant due to poor lubrication and the ingress of dust and dirt; wear of the hinges leads to an increase in the pitch of the links and the length of the chain, which necessitates the use of tensioning devices; 2) they require more high precision installation of shafts than V-belt drives, and more complex maintenance - lubrication, adjustment; 3) transmissions require installation on crankcases; 4) the speed of the chain, especially with a small number of sprocket teeth, is not constant, which causes fluctuations in the gear ratio, although these fluctuations are small (see § 7).
Chains used in mechanical engineering are divided into two groups according to the nature of the work they perform: drive and traction. The chains are standardized and produced in specialized factories. The production of drive chains alone in the USSR exceeds 80 million m per year. More than 8 million cars are equipped with them annually.
Roller, bushing and toothed chains are used as drive chains. They are characterized by small steps (to reduce dynamic loads) and wear-resistant hinges (to ensure durability).
Main geometric characteristics chains are pitch and width, main power characteristic- breaking load, established experimentally. In accordance with international standards chains are used with pitches that are multiples of 25.4 mm (i.e. ~ 1 inch)
The following drive roller and bushing chains are manufactured in the USSR in accordance with GOST 13568-75*:
PRL - single-row roller of normal accuracy;
PR - high precision roller;
PRD - long-link roller;
PV - sleeve;
PRI - roller with curved plates,
as well as roller chains in accordance with GOST 21834-76* for drilling rigs (in high-speed gears).
Roller chains are chains with links, each of which is made of two plates pressed onto rollers (outer links) or bushings (inner links). The bushings are put on the shafts of the mating links and form hinges. External and internal links in the chain alternate.
The bushings, in turn, carry rollers that fit into the recesses between the teeth on the sprockets and engage with the sprockets. Thanks to the rollers, sliding friction between the chain and the sprocket is replaced by rolling friction, which reduces wear on the sprocket teeth. The plates are outlined with a contour reminiscent of the number 8 and bringing the plates closer to bodies of equal tensile strength.
The rollers (axles) of the chains are stepped or smooth.
The ends of the rollers are riveted, so the chain links are one-piece. The ends of the chain are connected by connecting links with the rollers secured with cotter pins or riveting. If it is necessary to use a chain with an odd number of links, special transition links are used, which, however, are weaker than the main ones;
Therefore, they usually tend to use chains with an even number of links.
For high loads and speeds, multi-row chains are used to avoid the use of chains with large pitches, which are unfavorable with respect to dynamic loads. They are made up of the same elements as single-row ones, only their edges have an increased length. The transmitted powers and destructive loads of multi-row circuits are almost proportional to the number of rows.
The characteristics of roller chains with increased precision PR are given in table. 1. Roller chains of normal precision PRL are standardized in the pitch range of 15.875...50.8 and are designed for a breaking load that is 10...30% less than that of lump precision chains.
Long-link roller chains of the PRD are performed in double pitch compared to conventional roller chains. Therefore, they are lighter and cheaper than regular ones. It is advisable to use them at low speeds, in particular, in agricultural engineering.
PV bushing chains are identical in design to roller chains, but do not have rollers, which reduces the cost of the chain and reduces the dimensions and weight with an increased hinge projection area. These chains are manufactured with a pitch of only 9.525 mm and are used, in particular, in motorcycles and in cars (camshaft drive). The circuits show sufficient performance.
Roller chains with curved PRI plates are assembled from identical links similar to the transition link (see Fig. 12.2, e). Due to the fact that the plates bend and therefore have increased compliance, these chains are used under dynamic loads (impacts, frequent reverses, etc.).
The designation of a roller or bushing chain indicates: type, pitch, breaking load and GOST number (for example, Chain PR-25.4-5670 GOST 13568 -75*). For multi-row chains, the number of rows is indicated at the beginning of the designation.
Toothed chains (Table 2) are chains with links made from sets of plates. Each insert has two teeth with a cavity between them to accommodate the sprocket tooth. The working (outer) surfaces of the teeth of these plates (the surfaces of contact with the sprockets are limited by planes and inclined to one another at a wedging angle a equal to 60°). With these surfaces, each link sits on two teeth of the sprocket. The sprocket teeth have a trapezoidal profile.
The plates in the links are spaced apart to the thickness of one or two plates of the mating links.
Currently, chains with rolling joints are mainly manufactured, which are standardized (GOST 13552-81*).
To form hinges, prisms with cylindrical working surfaces are inserted into the holes of the links. The prisms rest on the flats. With special profiling of the holes of the plates and the corresponding surfaces of the prisms, it is possible to obtain almost pure rolling in the hinge. There is experimental and operational data that the service life of gear chains with rolling joints is many times higher than that of chains with sliding joints.
To prevent the chain from sliding sideways from the sprockets, guide plates are provided, which are ordinary plates, but without recesses for the sprocket teeth. Use internal or side guide plates. Internal guide plates require a corresponding groove to be machined into the sprockets. They provide better direction at high speeds and are of primary use.
The advantages of toothed chains compared to roller chains are lower noise, increased kinematic accuracy and permissible speed, as well as increased reliability associated with a multi-plate design. However, they are heavier, more difficult to manufacture and more expensive. Therefore, they have limited use and are being replaced by roller chains.
Traction chains are divided into three main types: plate according to GOST 588-81*; collapsible according to GOST 589 85; round-link (normal and increased strength), respectively, according to GOST 2319-81.
Leaf chains are used to move goods at any angle to the horizontal plane in transporting machines (conveyors, elevators, escalators, etc.). They usually consist of plates of simple shape and axles with or without bushings; they are characterized
large steps, since side plates are often used to secure the conveyor belt. The speed of movement of chains of this type usually does not exceed 2...3 M/S.
Round link units They are mainly used for hanging and lifting loads.
There are special chains that transmit movement between sprockets with mutually perpendicular axes. The rollers (axes) of two adjacent links of such a chain are mutually perpendicular.
§ 3. BASIC PARAMETERS OF DRIVE CHAIN TRANSMISSIONS
The power for transmission of which chain transmissions are used varies in the range from fractions to hundreds of kilowatts, in general mechanical engineering usually up to 100 kW. Center distances of chain drives reach 8 m.
Sprocket rotation speeds and speeds are limited by the magnitude of the impact force generated between the sprocket tooth and the chain joint, wear and gear noise. The highest recommended and maximum speeds of sprocket rotation are given in table. 3. Chain speeds usually do not exceed 15 m/s, however, in transmissions with high quality chains and sprockets, effective ways lubrication reaches 35 m/s.
Average chain speed, m/s,
V=znP/(60*1000)
where z is the number of sprocket teeth; P speed of its rotation, min-1; R-
The material in this chapter is presented in accordance with GOST “Roller chains. Terms and definitions”, as well as other standards related to chain drives.
Chain drive called a mechanism that serves to convert rotational motion between parallel shafts using two rigidly attached to them gear wheels- sprockets and an endless chain put on them (Fig. 10.1).
Rice. 10.1.
Chain V general case is called a multi-link flexible link, which can be used to move loads (traction chains), suspend or lift and lower loads (load chains), to transmit motion (drive chains). In what follows we will only consider drive chains, which are used in chain drives.
The advantages of chain drives are that they allow you to transmit rotation to remote (up to 8 m) shafts, as well as drive several shafts with one chain; there is no slipping in the chain drive, and the radial load on the shafts is two times less than in a belt drive; chain transmissions have high efficiency (under favorable conditions c = 0.97...0.99), can transmit significant powers (up to several thousand kilowatts), allow chain speeds of up to 35 m/s and gear ratios of up to and = 10.
Disadvantages of chain drives are increased vibration activity and noise during operation due to pulsation of chain speed and dynamic loads; intensive wear of the hinges due to friction and lubrication difficulties; chain stretching due to wear of the hinges and elongation of the plates.
Chain drives are widely used in metal-cutting and woodworking machines, in oil, mining, transport, agricultural engineering and other industries. Chain transmissions perform as downward, so and increasing", widely known, for example, overdrive to the rear wheel of a bicycle. Responsible chain transmissions perform closed, enclosed in a rigid housing that serves as an oil bath.
The initial design characteristic of all circuits is chain pitch t, measured along the chord pitch circle stars.
Drive chains there are roller, bushing, gear and shaped-link", the first three types of chains are standardized.
Figures 10.1, 10.2 show a two-star transmission with a single-row roller chain consisting of external link I, assembled from two outer plates 1 and rollers 2, fixedly fixed in the holes of the outer plates and internal link II, consisting of two internal plates 3, bushings 4, internal plates and rollers 5 fixedly fixed in the holes, loosely attached to the bushings. The rollers, rolling over the teeth of the sprockets, reduce their wear.
The outer and inner links assembled form a rotational kinematic pair. The plates have the shape of bodies of equal resistance.
Bush chain differs from a roller chain in that it does not have rollers, and the diameter of its rollers and the length of the bushings are slightly larger, due to which, other things being equal, the average pressure in the hinges of the bushing chain is less. Bush chains are cheaper than roller chains, but their wear resistance is lower.
Roller and bushing chains can be single-row or multi-row.
Rice. 10.2.
Figure 10.3 shows a double-row roller chain, which is assembled from the elements of a single-row chain, with the exception of the rollers. The rollers of bushing and roller chains are riveted, except for the rollers connecting link1, with the help of which the ends of the chain are connected by a spring lock or cotter pins. If the number of chain steps is odd, then a transition link is used 2.
Rice. 10.3.
According to the standard, drive roller and bushing chains for machines and mechanisms are made of the following types: PRL - light series roller; PR - roller normal series; PRD - long-link roller; PRI - roller with curved plates; PV - bushing.
The number of rows of the chain is indicated by a number that is placed before the designation, for example, ZPR-25.4-170.1 - a three-row drive roller chain of the normal series with a pitch of 25.4 mm and a breaking load of 170.1 kN.
The use of multi-row chains significantly reduces the dimensions of the transmission in a plane perpendicular to the axes.
According to the standard, bushing chains are manufactured in single and double rows with a pitch of 9.525 mm; These chains are used, for example, in cars and motorcycles.
Long-link roller chains have double-pitch links, so they are lighter and cheaper than others and are used at low speeds, in particular in agricultural engineering.
Roller chains with curved plates have increased compliance (the plates bend) and therefore are used under dynamic loads, for example, frequent reverses, impacts, etc.
In addition to the above, roller drive chains for drilling rigs, which are designed to operate in high-speed gears, have been standardized; chain plates have a protective or decorative coating.
The plates of bushing and roller chains are made from steels hardened to low hardness, rollers and bushings are made from case-hardened steels, and rollers are made from both hardened to high hardness.
Toothed chains with rolling joints are manufactured according to the standard. In Figure 10.4, A three projections of the links of a type I (one-sided) toothed chain consisting of a working plate / are shown; guide plate 2, preventing the chain from slipping off the sprocket; elongated prism 3; internal prism 4; connecting prism 5; washers 6 and cotter pin 7. In Figure 10.4, b rolling joint shown 3-4. The chain plates have a tooth-like shape, the working edges of the plates are located at an angle of 60°.
Rice. 10.4.
In Figure 10.4, V shows a Type II (double-engine) toothed chain; this design is provided as standard for chains with large pitches.
Toothed chains, compared to roller chains, operate more smoothly and with less noise, provide high kinematic accuracy, and have greater reliability and load capacity. A toothed chain with the same pitch can be used over a wide power range by varying the working width (see Fig. 10.4) within significant limits. Such chains have a high efficiency (up to 0.98), are less susceptible to stretching, but their weight and cost are significantly higher than that of roller chains. It is advisable to use toothed chains at high values of transmitted power and high chain speed, which is allowed up to 35 m/s.
Example of designation of a type I timing chain with pitch t= 19.05 mm, with a breaking load of 74 kN and working width b = 45 mm: PZ-1-19.05-74-45.
Rice. 10.5.
The plates of the gear chains are made of steel 50, providing a hardness of 38...45 HRC, and the prisms are made of steel 15 or 20, followed by carburization and hardening to a hardness of 52...60 HRC.
Shaped-link chains are used at low speeds in conditions of poor lubrication and protection, in the absence of strict requirements for transmission dimensions, for example in agricultural machines. Figure 10.5 shows hook a chain that allows the links to be freely separated. The links of shaped chain chains are cast from malleable cast iron and are not further processed; The links of the hook chain can be stamped from strip steel.
Asterisks Roller and bushing chains, as well as toothed chains, are profiled and manufactured in accordance with state standards.
Figure 10.6a shows a standard sprocket tooth profile for a roller chain, where d- diameter of the pitch circle of the sprocket; t- chain pitch; D- roller diameter; sprocket cavity radius r = 0.5025/1 + 0.05 mm. In Figure 10.6, b sprocket designs for single, double and triple row chain are shown.
Rice. 10.6.
Figure 10.7 shows a standard tooth profile and sprocket section for a Type I timing chain; In the middle of the teeth there is a slot for guide plates.
The materials for the manufacture of sprockets are cast iron (gray, malleable, anti-friction, high-strength) - for sprockets with a large number of teeth and for agricultural machine chains; case-hardened steels - under dynamic loads; steels are hardenable - when working without sharp shocks and impacts. In addition, plastics and composite materials are used to make sprockets.
Rice. 10.7.
The diameter of the pitch circle of the sprocket on which the hinge axes are located
Where t- chain pitch; z- number of sprocket teeth.
Moreover, the chain itself includes numerous moving links. They are connected to each other in the form of a closed circle.
Typically, the number of teeth on a sprocket and the number of link elements in chains are determined by a mutually prime number. Thanks to this, the most uniform wear of the mechanism as a whole is ensured.
Advantages and disadvantages of chain transmission
In addition to chain drives, there are also belt drives. However, in most cases they resort to chain ones, since they have a number of important advantages:
- No slippage, as happens in belt drives under certain conditions.
- Can be provided high degree compactness of the mechanism.
- The average gear ratio is at a constant level.
- Due to the absence of such a phenomenon as pre-tension, there are no secondary loads on key components of the mechanism.
- Even if the speed drops, the power figures remain quite high.
- Chain transmissions are practically insensitive to humidity and temperature changes.
- You can quickly adapt such a transmission to almost any mechanism by adding or removing a chain link.
- If necessary, you can transmit torque to several sprockets at once using just one chain.
- It is possible to organize the transmission of torque over fairly long distances - up to 7 meters.
- Chain transmission has a high efficiency - about 98 percent.
- If necessary, failed links, the chain itself or sprockets can be quickly replaced.
However, chain drives also have certain disadvantages:
- With prolonged intensive use, the hinges in the chain links wear out, which leads to stretching of the plates and an increase in the overall length of the chain.
- The gear can be applied without the need to stop the movement during the reverse stroke.
- The chain in some types of mechanisms is quite difficult to lubricate.
- You can observe unevenness in the gear ratio and, as a consequence, unevenness in speed. Especially this effect noticeable if the sprocket does not have a large number of teeth.
All of the above should certainly be taken into account when making a choice between chain and belt types of transmissions.
What characteristics do chain drives have?
Among the most important characteristics Almost any chain transmission should be called:
- Chain pitch indicator - this parameter affects the smoothness and accuracy of movement. As this parameter decreases, the accuracy and smoothness of the move increase.
- The number of teeth on the driving and driven sprockets.
- Radii of the inscribed and circumscribed circles of stars.
- The ratio of the radii of the driving and driven sprockets. Accordingly, than larger diameter the driving sprocket in relation to the driven one, the easier it will be to transmit movement.
- The distance between the centers of the circles of the sprockets - for example, the length of the chain will depend on this.
All these points also need to be taken into account.
What does a chain drive consist of?
Chain drives are quite simple to use constructively mechanisms. However, it will not be superfluous to know what elements they consist of.
Star. Typically, chain drives are designed with only two sprockets (although there are options). One of them acts as a leader, and the second as a slave. The stability and efficiency of operation of chain transmissions will largely depend on their quality and production accuracy: compliance with the dimensions (down to the millimeter) used in the manufacture of the material.
It is worth noting that the sizes and shapes of the sprockets will be determined by the quantitative characteristics of the chains (and not vice versa, as some people think), the number of gear ratios, and the number of teeth on the smallest drive sprocket in the mechanism. Parametric and other characteristics of sprockets are determined by GOST 13576 - 81. Characteristics of sprockets for roller and bushing chains are determined by GOST 591 - 69.
Sprockets must be made of sufficiently strong and wear-resistant materials that can be used for a long time under significant mechanical loads, including shock. According to GOST, such a material can be steel grades 40, 45, 40X and other types with a hardening degree of HRC 50 - 60. Sprockets not intended for high-speed mechanisms can be made from modified types of cast iron grades SCh 15, SCh 20.
Today you can find sprockets with tooth tips made from various types plastic. Such products are characterized by a reduced degree of wear and quiet operation.
The other component of chain drives is, of course, the chain. Chains are produced at industrial production lines. Their parameters are strictly regulated by relevant standards. Today the industry can offer such types of chains as:
- Cargo - intended for raising and lowering loads and for hanging them. Such chains are usually used on various types of forklifts.
- Traction - they serve to move goods and are used in transport devices.
- Drive - serve to transmit mechanical energy from one sprocket to another. A striking example of the use of such a transmission is the most ordinary bicycle and other types of vehicles.
The main elements of a standard circuit are shown in the figure below.
Circuit classification
Since drive chains are the most common type, it makes sense to take a closer look at what types of chains exist.
Roller chains (position III in the figure) include internal and external links. Those, alternating with each other, form serial connections that are mobile relative to each other. Each link includes two plates pressed onto axial or bushing supports. The bushings are put on the link axes, forming a hinge joint. To avoid increased wear on the sprockets, a roller is usually put on the bushing, which should replace sliding friction with rolling friction.
The ends of the chain can be connected to each other:
- By means of connecting links - with an odd number of links.
- Through a transition link - with an even number of links.
If the transmission must operate in intensive mode for a long time, then a multi-row roller chain is used. This allows you to reduce the size of each sprocket and its pitch.
Roller chains can also be made with curved plates on each link (position IV in the figure). This type is used if the connection is expected to be used under conditions of high shock loads. Thanks to the special shape of the plate, the impact force is significantly dampened.
Bush chains (position V) are structurally no different from roller chains, but do not have rollers. Thanks to this, the production of such chains becomes cheaper and their weight is reduced. But this also contributes to faster wear of the teeth.
Silent toothed chains (position VI in the figure) include special plates equipped with teeth. The plates themselves have a hinged connection. Thanks to this design, it is possible to provide low level mechanism noise, as well as smooth operation. In this case, the teeth are located at an angle of 60 degrees. These types of chains are used in mechanisms with high operating speeds. Therefore, the plate should be made of hardened steel with a hardness of H RC 40 - 45. The disadvantage of such chains can be considered their relative high cost, as well as the need for special care.
Hook chains (position VII). They include links of a special shape without any additional elements.
Bushing-pin chains (position VIII in the figure) - in them the links are connected using pins. This type of chain is used in a variety of fields Agriculture and mechanical engineering.
Since any chain will stretch over time during intensive work, its tension should be periodically adjusted. This is achieved by moving one sprocket or two at once, depending on the design features adjusting mechanism. It allows, as a rule, adjustment if the chain has stretched by only one or two links. If the degree of stretching is greater, then the chain is simply replaced with a new one.
Don’t forget about timely lubrication of any chain. The duration of its work will directly depend on this. If the speed of movement of the chain is not too high - up to 4 meters per second, then lubrication is allowed using a regular manual oiler. At speeds up to 10 meters per second, a dropper oiler is used.
For deeper lubrication, the chain is immersed in a container filled with oil. The degree of chain immersion should not exceed the width of each plate.
If you have to deal with powerful high-speed mechanisms, then circulating jet lubrication using pumps is used.
When choosing one or another lubrication method, you must rely on design features each specific type of mechanism, as well as the nature of energy loss during friction. Friction losses occur due to the friction of hinge joints, plates against each other, between teeth and chain elements, and in supporting elements of the structure. In addition, there are losses due to splashing of the lubricant. True, they are significant only if lubrication is carried out by immersing the chains in lubricants and when operating at speeds close to the maximum permissible.
Application areas of chain transmission
It is noteworthy that this type transmission has been known to mankind for quite a long time. At least in theory. Studying works famous inventor and the artist Leonardo da Vinci showed that he was thinking about various options the use of chain drives in all kinds of mechanisms. In the pictures you can see prototypes of modern bicycles and many other mechanisms known today. True, it is not known for certain whether he could the great Leonardo put your ideas into practice. The industry of that time did not allow the manufacture of mechanisms with the required degree of accuracy.
For the first time in practice, it was possible to use this type of transmission only in 1832. It is worth noting that the appearance of the modern bicycle, as well as its technical and operational characteristics, was largely influenced by the fact that in 1876 the inventor Lawson came up with the idea of using a chain drive. Until then, the wheels were driven either directly through the pedals, or the rider had to push off the ground with his feet.
This type of gear in various modifications is used today extremely widely in various fields mechanical structure. Transport, industrial machine tools, agricultural units - it is not possible to list all the mechanisms in which types of chain transmission are used, without exception.
They also resort to it when the interaxle distances are sufficiently large. In these cases, the use of a belt-type transmission is impractical, and it is impossible to use gear ones due to the significant complication of the design and the increase in the mass of the mechanism. Don’t forget about the friction force, which increases in direct proportion to the number of gears in the mechanism. In the case of chain drives, as already noted, there is a rolling friction force, which is several times less than the sliding friction force.
You can also find this type of gear in technology that uses a chain as a direct working element, and not as a drive element. These, for example, include snow removal units, elevator and scraper mechanisms, and similar ones.
As a rule, chain drives are used open type, which, if necessary, are lubricated manually. In such structures there is either no moisture and dust protection at all, or it is present at a minimal level, as is the case with a bicycle.
Typically, certain types of chain transmissions are used if it is necessary to transfer powers of up to 120 kilowatts at external speeds of no more than 15 meters per second.
A little about stars
The efficiency and operating life of the entire chain mechanism will depend to a large extent on how the sprockets in the mechanism were made. This applies to both compliance with all exact dimensions and materials of manufacture.
The number of teeth is one of the most important characteristics of any sprocket.
The tension sprocket is used where it is necessary to prevent the effect of chain slack. It is usually installed on the driven parts of mechanisms.
The main parametric characteristics of sprockets are described in the relevant paragraphs of GOST 13576-81.
Chain transmissions are truly highly efficient and, moreover, economical look mechanisms. They are used in many areas of transport and mechanical engineering.
Types of chain transmission
Today you can encounter the most different classifications this type of transmission. It all depends on what specific criteria are used to classify:
- According to their purpose, transmissions can be traction, drive, or cargo.
- Complex or simple - if you classify by the total number of sprockets in the mechanism. Complex mechanisms are usually classified as those that contain more than two sprockets.
- Also, transmissions can be master and slave.
- If we classify gears based on the direction of rotation, then they can be direct and reverse.
- According to the principle of arrangement, they are closed, horizontally or vertically located.
- Also, the sprockets can be centered differently. In this case, it is customary to distinguish between horizontally located and vertically located gears, as well as at a certain angle.
- Low and high gears - according to the speed.
- Open and closed type transmissions - depending on whether they are placed in dustproof housings or not. Closed-type gears can also be placed inside a mechanism, the housing of which protects them from the penetration of dust and moisture.
- Finally, according to the method of introducing lubricant, transmissions can be manual, oil and circulating. Their specifics have already been mentioned a little above.
Each of these types is used in certain areas of technology.
The widespread use of chain drives in a wide variety of machines and mechanisms is due to the set of characteristics they provide. The main advantages of this method of energy transfer are versatility, simplicity and efficiency.
A chain drive refers to the transmission of rotational motion, which is carried out between shafts located parallel to each other using an endless chain connecting the sprockets placed on them. Like belt drives, chain drives are classified as flexible drives. However, it is capable of bending exclusively in one plane, so it can only be effectively used for parallel shafts.
Features of chain drive and its differences from belt drive
The first serious difference between the two most widespread types of transmissions - chain and belt - was indicated above. It consists in the possibility of bending the chain in only one plane and, as a result, use exclusively for shafts located parallel to each other.
Another important difference is the absence in the chain transmission of the key value of such important parameter, as the angle of the chain wrapping around the sprocket. Unlike belt transmission, it does not play such a significant role in the characteristics provided during energy transfer.
A significant factor that is a plus of the chain drive is the absence of the need to pre-tension the chain, since the operation of the mechanism is ensured by the engagement of the chain links with the teeth of the sprockets.
An important feature of chain transmission is the ability effective use for almost any center distance - both small and large. It is complemented by the ability to transmit power from one shaft to several at once. In addition, the chain transmission can be either a reduction or an increase, which is also characteristic distinctive feature this method of energy transfer.
Classification of chain drives
When classifying chain transmissions, several criteria are used. For example, according to functional purpose and the method of use in mechanical engineering and other industries, three types of chains are distinguished:
freight. The main purpose of using this type is to suspend and move various loads. In such a situation, the mechanism, as a rule, is part of some kind of lifting equipment or device, and the movement speed, mainly vertically, is no more than 0.5 m/s;
traction In this case, the chain is also used to move loads, but at a higher speed, reaching 2-4 m/s. This is explained by the fact that movement is carried out largely horizontally using mechanisms such as elevators, conveyors, escalators, etc.;
driven. The most common type of chain, usually used with a small pitch, which reduces loads and increases the service life of the product. The purpose of its use is the transfer of energy over an extremely wide range of speeds, and the gear ratio is a constant value.
It is the latter type of chains that is used in chain drives. Moreover, the word drive is often omitted when describing them, and in most of the technical and reference literature the concepts of “drive chain” and “chain in a chain drive” are largely identical.
Other classifying parameters of chain drives are:
chain type - roller, toothed or bushing;
number of rows – single and multi-row;
number of driven shafts/sprockets – two- and multi-link;
sprocket arrangement – horizontal, vertical or inclined;
option for adjusting the degree of chain slack - with a tension sprocket or a special tensioner;
design – open and closed;
influence on the speed of rotation of the shafts - increasing and decreasing.
Advantages of chain transmission
Most of the advantages of chain drives are usually considered in comparison to belt drives. This is quite logical, since these two methods of transmission rotational energy are most widely used. Some advantages of chain transmission are clearly manifested in relation to gear transmission, which is also used in practice quite often.
The main advantages of using chain transmission are:
high level strength characteristics, which allows for much more severe loads. The result is greater efficiency in a compact size;
the ability to use several driven sprockets in one mechanism at once;
the ability to transmit energy over extremely long distances, reaching up to 8 m;
relatively small (compared to a belt drive - 2 times less) level of radial load on the shafts;
high efficiency. The efficiency of the chain transmission is at the level of 90% -98%;
serious power of transmitted energy, the parameters of which reach several thousand kW;
impressive chain speed and gear ratio values of up to 35 m/s and 10, respectively;
compactness of the mechanism;
lack of such negative factor, characteristic of a belt drive, like sliding;
simple and convenient chain replacement, which is complemented by the absence of the need for serious initial tension.
Disadvantages of chain transmission
The number of obvious disadvantages of the energy transfer method under consideration is significantly less than the number of advantages listed above. However, there are disadvantages and these include:
the rather high cost of manufacturing the mechanism and its main consumable part - the chain itself;
inability to use gear when reversing without stopping it completely;
the use of chain transmission requires the almost mandatory use of crankcases;
the design of the mechanism does not always allow for convenient supply of lubricant to the hinges and chain links;
with a small number of teeth, the chain speed is inconsistent, which causes fluctuations in such an important parameter as gear ratio;
high level of noise accompanying the operation of the device;
serious requirements for correct location shafts;
the need for constant monitoring of the operation of the mechanism and its maintenance, the absence of which can lead to rapid wear.
A comparison of the disadvantages and advantages shows that when used correctly, chain transmission allows you to achieve high efficiency at a reasonable level of cost. The main thing is to wisely take advantage of the obvious advantages of this mechanism while minimizing its disadvantages.