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 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:

1. No slippage, as happens in belt drives under certain conditions.
2. Can be provided high degree compactness of the mechanism.
3. The average gear ratio is at a constant level.
4. Due to the absence of such a phenomenon as pre-tension, there are no secondary loads on key components of the mechanism.
5. Even if the speed drops, the power figures remain quite high.
6. Chain transmissions are practically insensitive to humidity and temperature changes.
7. You can quickly adapt such a transmission to almost any mechanism by adding or removing a chain link.
8. If necessary, you can transmit torque to several sprockets at once using just one chain.
9. It is possible to organize the transmission of torque over fairly long distances - up to 7 meters.
10. Chain transmission has a high efficiency - about 98 percent.
11. If necessary, failed links, the chain itself or sprockets can be quickly replaced.

However, chain drives also have certain disadvantages:

1. With prolonged intensive use, the hinges in the chain links wear out, which leads to stretching of the plates and an increase in total length chains.
2. The gear can be applied without the need to stop the movement during the reverse stroke.
3. The chain in some types of mechanisms is quite difficult to lubricate.
4. You can observe unevenness in the gear ratio and, as a consequence, unevenness in speed. Especially this effect noticeable if the asterisk does not have a large number 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 of almost any chain transmissions are:

1. Chain pitch indicator - this parameter affects the smoothness and accuracy of movement. When decreasing this parameter accuracy and smoothness increases.
2. The number of teeth on the driving and driven sprockets.
3. Radii of the inscribed and circumscribed circles of stars.
4. 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.
5. 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 fairly simple mechanisms in terms of design. 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 long time be operated 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 on industrial production lines. Their parameters are strictly regulated by relevant standards. Today the industry can offer such types of chains as:

1. Cargo - intended for raising and lowering loads and for hanging them. Such chains are usually used on various kinds forklifts.
2. Traction - they serve to move goods and are used in transport devices.
3. Drive - serve to transmit mechanical energy from one sprocket to another. A striking example of the use of such a transfer is the most regular bike 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 mobile relative to each other serial connections. 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:

1. By means of connecting links - with an odd number of links.
2. 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 ensure a low noise level of the mechanism, 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 the most different areas 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 of the adjustment 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 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 some time. By at least, in theory. A study of the works of the famous inventor and 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 equipment, agricultural units - list all, without exception, mechanisms in which varieties are used chain transmission, is not possible.

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 that is several times greater less strength sliding friction.

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 a truly highly efficient and, at the same time, economical type of mechanism. They are used in many areas of transport and mechanical engineering.

Types of chain transmission

Today you can encounter a variety of classifications of this type of transmission. It all depends on what specific criteria are used to classify:

1. According to their purpose, transmissions can be traction, drive, or cargo.
2. Complex or simple - if classified according to total number sprockets in the mechanism. Complex mechanisms are usually classified as those that contain more than two sprockets.
3. Also, transmissions can be master and slave.
4. If we classify gears based on the direction of rotation, then they can be direct and reverse.
5. According to the principle of arrangement, they can be closed, horizontally or vertically located.
6. 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.
7. Low and high gears - according to the speed.
8. 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.
9. 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 simplest chain drive (Fig. 3) consists of two sprockets (1 and 2), each attached to its own shaft, the smaller of which is most often the driving one, and an enclosing chain 3, composed of many rigid links that can rotate relative to each other friend.

Chain drives found wide application in machines for general industrial use.

Chain drives are widely used in various lifting (for example, multi-bucket elevators) and transport devices. The use of chain drives in these cases simplifies the design of machine components, increases their reliability and productivity. These devices use circuits of a wide variety of design types.

Chain transmissions are used both for reduction (reducing speed during transmission) rotational movement, and for its multiplication (increasing speed).

Advantages of chain drives: 1. Possibility of transmitting motion over fairly large distances (up to 8 m). 2. The ability to transmit movement by one chain to several shafts. 3. No slippage, and therefore stability of the gear ratio with reduced lateral load on the shafts and their supports. 4. Relatively high efficiency (0.96...0.98 with sufficient lubrication).

Disadvantages of chain drives: 1. Increased noise and vibration activity during operation due to pulsation of chain speed and resulting dynamic loads. 2. Intensive wear of chain hinges due to impact interaction with the sprocket cavity, sliding friction in the hinge itself and difficulty in lubrication. 3. Chain stretching (increasing the pitch between the link hinges) due to wear of the hinges and elongation of the plates. 4. Relatively high cost.

Classification:

Circuits according to their intended purpose can be divided into:

1. traction chains designed to move loads along a horizontal or inclined surface;

2. load chains designed for lifting loads;

3. drive chains designed to transmit motion, most often rotational, in chain drives.

The most widely used drive chains are roller, bushing and toothed chains. These three types of chains are standardized.

8. Gears, diagrams, purpose, advantages, disadvantages, classification.

Gear- a three-link mechanism, including two movable links interacting with each other through a higher gear kinematic pair and forming lower (rotational or translational) kinematic pairs with the third fixed link

Rice. 1. Types of gears

The smaller gear involved in meshing is usually called gear, more – gear wheel, a gear link that makes a linear movement is called a gear rack (Fig. 1, j).

Rice. 2. Gear diagram and its parameters

The purpose of a gear transmission is to transmit motion (most often rotational) with the transformation of parameters, and sometimes its type (rack and pinion transmission). Rotary gears are the most common in technology (Fig. 5). They are characterized by transmitted powers from microwatts (quartz mechanism wristwatch) up to tens of thousands of kilowatts (large ball mills, crushers, kilns) at peripheral speeds of up to 150 m/s.

Advantages of gears:

1. High reliability of operation in a wide range of loads and speeds.

2. Great resource.

3. Small dimensions.

4 High efficiency.

5. Relatively low loads on shafts and bearings.

6. Constancy of the gear ratio.

7. Easy to maintain.

Disadvantages of gears:

1. Difficulty in manufacturing and repair (requires high-precision specialized equipment).

2. Regarding high level noise, especially at high speeds.

3. Irrational use of teeth - usually no more than two teeth of each of the meshing wheels are simultaneously involved in the operation of the transmission.

Gear classification:

1. By gear ratio:

1.1. with gear ratio u >1 – reducing (reducers - most gears);

1.2. with gear ratio u<1 – мультиплицирующие (мультипликаторы).

2. According to the relative position of the shafts:

2.1. with parallel shafts - spur gears

2.2. with intersecting shaft axes - bevel gears

(bevel gears with an angle of 90 degrees between the shaft axes are called orthogonal);

2.3. with intersecting shaft axes - worm, screw (Fig. 5, i), hypoid;

2.4. with motion conversion – rack and pinion

3. According to the location of the teeth relative to the generatrix of the wheel surface:

3.1. straight teeth - the longitudinal axis of the tooth is parallel to the generatrix of the wheel surface;

3.2. helical - the longitudinal axis of the tooth is directed at an angle to the generatrix of the wheel surface;

3.3. chevron - the tooth is made in the form of two helical wheels with an opposing inclination of the tooth axes;

3.4. with a circular tooth - the axis of the tooth is made in a circle relative to the generatrix of the wheel surface.

4. According to the shape of the interlocking links:

4.1. with external gearing - the teeth are directed with their tops away from the axis of rotation of the wheel;

4.2. with internal gearing - the teeth of one of the meshing wheels are directed with their vertices towards the axis of rotation of the wheel;

4.3. rack and pinion gearing - one of the wheels is replaced by a straight toothed rack;

4.4. with non-round wheels.

5. According to the shape of the working tooth profile:

5.1. involute - the working profile of the tooth is outlined along the involute of a circle (a line described by a point of a straight line rolling without sliding around a circle);

5.2. cycloidal - the working profile of the tooth is outlined along a circular cycloid (a line described by a point on a circle rolling without sliding along another circle);

5.3. lantern (a type of cycloidal) - the teeth of one of the wheels that engage are replaced by cylindrical pins - lanterns;

5.4. with a circular tooth profile (Novikov gearing) – the working tooth profiles are formed by circular arcs of almost identical radii.

6. According to the relative mobility of the geometric axes of gear wheels:

6.1. with fixed wheel axles - ordinary gears (Fig. 5);

6.2. with movable axles of some wheels - planetary gears.

7. According to the rigidity of the gear ring of the wheels that engage:

7.1. with wheels of unchangeable shape (with a rigid crown);

7.2. including wheels with a crown of changing shape (flexible).

8. According to the circumferential (tangential) speed of the teeth:

8.1. low-speed (Vз< 3 м/с);

8.2. medium speed (3< Vз < 15 м/с);

8.3. high-speed (Vз > 15 m/s).

9. By design:

9.1. open (unframed);

9.2. closed (cased).

The most widely used are reducing gears of rotational motion, including in multi-purpose tracked and wheeled vehicles (gearboxes, final drives, drives various devices). Therefore, the further presentation, unless specifically mentioned, concerns only rotational motion transmissions.

§ 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 drives include tensioners, 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 elements (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 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 higher accuracy of shaft installation 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. Release only drive chains 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, the main power characteristic is the breaking load, established experimentally. According to 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 when high speeds and have their main application.

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 gears with chains and sprockets high quality at effective ways lubrication reaches 35 m/s.

Average chain speed, m/s,

V=znP/(60*1000)

where z is the number of sprocket teeth; n speed of its rotation, min-1; R-

A chain drive is a transmission in which energy between several parallel shafts is produced by a coupling using a flexible chain and sprockets. It consists of a chain and two sprockets. One sprocket is leading, and the other is driven. The chain transmission operates without slipping and is provided with tensioning and lubrication devices.

A chain drive makes it possible to transmit movement between shafts over a larger range of center distances compared to a gear drive. The efficiency of the chain drive is 0.96...0.97. It has less impact on the shaft, which makes it different from a belt drive. One chain transmits speed to several sprockets for chain drives.

Types and scope of application of chain drives

Chain drives are classified into several categories, which differ in their design features and the principle of functional action. Depending on the type of chains, transmission devices are divided into roller, bushing and gear. According to the number of rows of chains on mechanisms supplying force for movement, there are single-row and multi-row. Depending on the number of driven sprocket elements, there are two-link and multi-link mechanisms. According to the location of sprockets for chain drives, devices are divided into horizontal, inclined, and vertical.

The negative qualities of transmission mechanisms include: jerky movement, increased noise during work processes, the need for carefully maintained assembly and regular maintenance according to established parameters, constant adjustment of the tension of the chain device and lubrication of mechanical connections on time, rapid susceptibility to the shock-absorbing effects of hinges chain attachment, high cost of the device, chain stretching during use, etc.

Chain drives have gained great popularity in a variety of machine tools, bicycle and motorcycle equipment, in machines lifting loads, winches, in drilling rigs, in units of cranes, and exclusively in agricultural machines. For example, the S-4 self-propelled grain combine has 18 chain drives that drive its many operating mechanisms. Chain transmission mechanisms have also become widespread in light industry enterprises.

Main parameters of chain transmissions

The functioning of a chain-type device that changes the transmitting force depends on the characteristics of the sprocket components: the correctness of their production, the hardening of the surface of the teeth, metal and the quality of processing. The dimensions and shapes of the sprockets are made according to the values ​​of the selected chain and gear ratio, which determines the number of teeth of the smaller drive sprocket. The gear ratio of a chain drive changes during operation and is calculated similarly to the gear ratio of a cylindrical drive. Assembly of the chain drive is limited to installing and securing the sprockets on the shafts, putting on the chain and adjusting it.

When calculating a chain drive, you must refrain from obtuse angles between the line that matches the centers of the stars and the horizontal line. The leading branch is usually placed on top. In gears with large elevation angles, it is necessary not to forget about tensioning devices. Chain transmissions, due to the inevitable stretching of chain links due to wear and collapse in the hinges, usually require the ability to regulate their tension.

Initial tension is only important in vertical transfer actions. In horizontal and inclined transmission processes, the connection of the chain device with the sprocket elements is guaranteed by the tension from the force of gravity of a particular chain link, and the sag of the chain connection must be optimal within the initially listed boundaries.

View: this article has been read 14944 times

Pdf Select language... Russian Ukrainian English

Brief overview

The entire material is downloaded above, after selecting the language

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.

Scope of application:

• 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 gear drives are not applicable and belt drives are unreliable.

Compared to belt drives, chain drives are noisier, and in gearboxes they are used at low 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 chain transmissions up to 100 kW are most common.

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 of the lubricating oil are taken into account. 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 the harmful effects of 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 in terms of strength and engagement is ensured by selecting 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
An example of calculating a spur 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
In the example, diagrams of transverse forces and bending moments were constructed, a dangerous section was found and an I-beam was selected. The problem analyzed the construction of diagrams using differential dependencies, carried out comparative analysis different cross sections of the beam.

An example of solving a shaft torsion problem
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
The task is to test the strength of a steel bar at specified permissible stresses. During the solution, diagrams of longitudinal forces are constructed, normal stress and movements. The rod's own weight is not taken into account

Application of the theorem on conservation of kinetic energy
An example of solving a problem using the theorem on the conservation of kinetic energy of a mechanical system

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