The main disadvantage of chain transmission is. Chain transmissions - description, types, pros and cons. According to the mutual arrangement of the shafts

Lecture 10 CHAIN ​​GEARS

P lan l e c t i o n

1. General information.

2. Drive chains.

3. Features of the operation of chain drives.

4. Asterisks.

5. Forces in the branches of the chain.

6. The nature and causes of chain drive failures.

7. Calculation of transmission by a roller (sleeve) chain.

1. General information

Chain transmission (Fig. 10.1) is classified as gearing with a flexible connection. The movement is transmitted by an articulated chain 1, covering the driving 2 and driven 3 sprockets and engaging with their teeth.

Chain transmissions perform both lowering and increasing.

Advantages of chain drives:

Compared to gears, chain drives can transmit movement between shafts at significant center distances

Compared to belt drives, chain drives are more compact, transmit more power, and can be used in a wide range of applications. center distances, require significantly less pretensioning force, provide consistency gear ratio(no slipping and slipping), have high efficiency;

can transmit the movement of one chain to several driven sprockets.

Disadvantages of chain drives:

significant noise during operation due to the impact of the chain link on the tooth of the sprocket when engaging, especially with small numbers of teeth and big step, which limits the use of chain drives at high speeds;

relatively fast wear of the chain hinges (increase in the chain pitch), the need to use a lubrication system and installation in closed cases;

elongation of the chain due to wear of the hinges and its coming off the sprockets, which requires the use of tensioners;

uneven rotation of sprockets; the need for high precision transmission assembly.

Chain transmissions are used in machine tools, motorcycles, bicycles, industrial robots, drilling equipment, road construction, agricultural, printing and other machines for transmitting movement between parallel shafts over long distances, when the use of gears is impractical, and the use of belt drives is impossible. Chain transmissions with a power of up to 120 kW at peripheral speeds of up to 15 m / s have received the greatest application.

2. Drive chains

The main element of the chain transmission - the drive chain consists of individual links connected by hinges. Drive chains are used to transfer mechanical energy from one shaft to another.

The main types of standardized drive chains are roller, sleeve and toothed.

Roller drive chains. The standard provides for the following types of roller chains: drive roller chains (PR, Fig. 10.2), light series (PRL), long-link (PRD), two-, three- and four-row (2PR, 3PR, 4PR).

Links of roller chains (Fig. 10.3) consist of two rows of outer 1 and inner 2 plates. Axes 3 are pressed into the outer plates, passed through bushings 4, which, in turn, are pressed into the inner plates. The bushings are pre-fitted with freely rotating hardened rollers5. The ends of the axles after assembly are riveted to form heads that prevent the plates from falling off. With relative rotation of the links, the axle rotates in the sleeve, forming a sliding hinge. The chain is engaged with the sprocket through a roller, which, turning on the bushing, rolls over the sprocket tooth. This design equalizes tooth pressure on the sleeve and reduces wear on both the sleeve and the tooth.

The plates are outlined with a contour resembling the number 8 and providing equal strength of the plate in all sections.

Pitch P chain is the main parameter of the chain transmission. The larger the pitch, the higher the load capacity of the chain.

The pitch circle of the sprockets passes through the centers of the hinges

d = P /,

where Z is the number of sprocket teeth.

Pitch P for sprockets is measured along the chord of the dividing circle.

Roller chains are widely used. They are used at speeds of 15–30 m/s.

Bush drive chains(Fig. 10.4) are similar in design to roller ones, but do not have rollers, which reduces the cost of manufacturing the chain, reduces its weight, but significantly increases the wear of the chain bushings and sprocket teeth. Sleeve chains are used in non-critical gears at speeds of 15–35 m/s.

Sleeve and roller chains are made single-row and multi-row with the number of rows of 2-4 or more. A multi-row chain with a smaller pitch P allows you to replace a single-row chain with a larger pitch and thereby reduce the diameters of the sprockets and reduce the dynamic loads in the transmission. Multi-row chains can operate at significantly higher chain speeds. The load capacity of the chain increases almost in direct proportion to the number of rows.

The connection of the ends of the chain with an even number of its links is made by a connecting link, with an odd number - by a transitional link, which is less strong than the main ones. Therefore, chains with an even number of links are used.

Toothed drive chains(Fig. 10.5) consist of links made up of a set of plates pivotally connected to each other. Each plate has two teeth and a cavity between them to accommodate the sprocket tooth.

The number of plates determines the chain width, which in turn depends on the power to be transmitted. The working faces are the planes of the plates located at an angle of 60º. With these faces, each chain link is wedged between two sprocket teeth having a trapezoidal profile. Thanks to this, toothed chains run smoothly, with little noise, better absorb shock loads and allow speeds of 25–40 m/s.

To eliminate the lateral fall of the chain from the sprockets, guide plates are used, located in the middle or on the sides of the chain. The pitch diameter of the sprocket for toothed chains is greater than its outer diameter.

The relative rotation of the links is provided by sliding or rolling joints.

The rolling hinge ((Fig. 10.5)) consists of two prisms1 and2 with cylindrical working surfaces and a length equal to the width of the chain. Prisms rest on flats. Prism1 is fixed in the figured groove of the plate B, prism 2 - in the plate A. The prisms, when the links turn, roll over one another, providing a clean rolling. Chains with rolling joints are more expensive, but have low friction losses.

sliding hinge consists of an axis, two liners fixed in the figured grooves of the plates A and B. When the plates are rotated, the insert slides along the axis, turning in the groove of the plate. Inserts allow you to increase the contact area by 1.5 times. The hinge allows the plate to be rotated through an angle

max. Usually max = 30°.

Compared to others, toothed chains are heavier, more difficult to manufacture and more expensive.

At present, roller and bush chain transmissions are predominantly used.

Chain material. Chains must be durable and strong. Chain plates are made from steel grades 50, 40X and others, hardened to a hardness of 40–50 HRC, axles, bushings, rollers and prisms are made from case-hardened steels of grades 20, 15X and others, hardened to a hardness of 52–65 HRC. By increasing the hardness of the parts, the wear resistance of the chains can be increased.

Optimum transmission center distance taken from the chain durability condition (Fig. 10.6):

a = (30–50)P ,

where P is the chain pitch.

When the axis of the chain drive is tilted, with dividing circles d 1 and d 2, to the horizon at an angle α, the driven branch sags by the value f.

3. Features of the operation of chain drives

Variability of the instantaneous value of the gear ratio.

Speed ​​v of the chain, angular velocity 2 driven sprocket and gear ratio i =1/2 variable at constant angular velocity1 of the drive sprocket.

The movement of the hinge of the link that was last engaged with the drive sprocket determines the movement of the chain in a running gear. Each link guides the chain as the sprocket rotates one pitch and then gives way to the next link.

Consider a chain drive with a horizontal drive branch. The leading hinge on a small sprocket at some point in time is rotated relative to the vertical axis by an angle of 1 . Peripheral speed on the tooth of the drive sprocket v 1 \u003d 1 R 1, where R 1 \u003d d 1 / 2 is the radius of the chain hinges. The speed of the chain v = v 1 cos1, where 1 is the wrap angle of the leading sprocket relative to the perpendicular to the leading branch. Since when the sprocket is rotated, the angle1 changes in absolute value within (/ Z 1 - 0 - / Z 1), then the speed v of the chain when turning one

the angular step varies within (v min -v max -v min), where v min \u003d 1 R 1 cos (/ Z 1 ) and v min \u003d 1 R 1. Instantaneous angular velocity of driven sprocket

2 = v /(R 2 cos2 ),

where angle 2 on the driven sprocket varies within (/Z 2 - 0 - /Z 2).

Instantaneous transfer ratio (taking into account v = 1 R 1 cos1 )

R2cosα2

R 1 cosα1

The gear ratio of the chain drive is variable within the rotation of the sprocket by one tooth. The inconsistency of i causes uneven transmission stroke, dynamic loading due to the acceleration of the masses connected by the transmission, and transverse vibrations of the chain. The uniformity of movement is the higher, the greater the number of teeth of the sprockets (the lower the limits for changing angles1,2).

Average gear ratio. The chain travels the path S = PZ in one revolution of the sprocket. Time, s, for one revolution of the sprocket: t = 2 /1 = 60/n . Therefore, the speed v, m/s, of the chain

v \u003d S / t \u003d PZ 1 10–3 / (60 / n 1 ) \u003d PZ 2 10–3 / (60 / n 2 ),

where P is the chain pitch, mm; Z 1, n 1 and Z 2, n 2 are the number of teeth and the speed of rotation of the driving and driven sprockets, respectively, rpm.

From the equality of the chain speeds on the sprockets, it follows

i = n1 / n2 = Z2 / Z1 = R2 / R1 .

The average gear ratio i per revolution is constant. The maximum allowable value of the gear ratio of the chain drive is limited by the arc of the chain around the small sprocket and the number of hinges located on this arc. It is recommended to take the wrapping angle at least 120°, and the number of hinges on the wrapping arc - at least five. This condition can be satisfied for any interaxal distances if i< 3,5. Приi >7 center distance out of range optimal values. Therefore, usually i 6.

Hitting the chain links against the teeth of the sprockets when engaging.

The circumferential speed of the sprocket tooth at the moment preceding the entry of the chain hinge into engagement is v 1, and the vertical projection of this vector is v ". Since the previous hinge is still leading, the entire chain, including the engaging hinge, moves with speed v 1. Vertical projection of the velocity vector v 1 involved in the engagement

asterisks.

Rotation of links under load. When the sprocket is rotated by one angular step, the links connected by the leading hinge rotate by

corner. Rotation in the hinge occurs when the circumferential force is transmitted and causes wear. The angle of rotation, which determines the path of friction (wear), is smaller, the greater the number of sprocket teeth.

4. Stars

Sprockets (Fig. 10.7) of chain drives in accordance with the standard are made with a wear-resistant tooth profile. To increase the durability of the chain drive, the largest possible number of teeth of the smaller sprocket is taken. The number Z 1 of the teeth of a small sprocket for roller and sleeve chains, provided Z 1 min 13,

Z 1 \u003d 29 - 2i,

where i is the gear ratio.

The minimum allowable number of teeth of a small sprocket is taken:

at high speeds Z 1 min = 19–23; at medium –Z 1 min = 17–19; at low –Z 1 min = 13–15.

With the wear of the hinges and the increase in connection with this step, the chain tends to rise along the profile of the teeth, and the higher, the greater the number of sprocket teeth. With a large number of teeth, even with a little worn chain, as a result of radial slipping along the profile of the teeth, the chain jumps off the driven sprocket. Therefore, the maximum number of teeth of a large sprocket is limited by: Z 2 90 for a sleeve chain; Z 2 120 for a roller chain. It is preferable to take an odd number of sprocket teeth, which, in combination with an even number of chain links, contributes to its more even wear.

Sprocket material must be wear-resistant and well resist the action of shock loads. Stars are made from steel.

grades 45, 40X and others with hardening to a hardness of 45–55 HRC or case-hardened steel grades 15, 20X with hardening to a hardness of 55–60 HRC. In order to reduce the noise level and dynamic loads in transmissions with light conditions works make a gear rim of sprockets from polymer materials: fiberglass and polyamides.

5. Forces in the branches of the chain

The leading branch of the chain during transmission operation is loaded with a force F 1, consisting of a useful (circumferential) force F t and a force F 2 of the tension of the driven branch of the chain:

F1 = Ft + F2 .

Circumferential force F t N transmitted by the chain:

F t = 2 103 T/d,

where d is the pitch diameter of the sprocket, mm.

The force F 2 of the tension of the driven branch of the chain is the force F 0 of the tension from own strength gravity and force F c tension from the action of centrifugal forces:

F2 = F0 + Fc.

Tension F 0 , N from gravity with a horizontal or close to it position of the line connecting the axes of the stars:

F0 = qga2 / 8 f =1.2 qa2 / f,

where q is the mass of 1 m of the chain, kg / m; g \u003d 9.81 m / s2 is the acceleration of free fall; a is the center distance, m; f is the sagging boom of the driven branch, m (Fig. 10.6).

With a vertical position or close to it, the line of the centers of the stars

F0 = qga.

Chain tension from centrifugal forces, N,

Fc \u003d qv2,

where v is the speed of the chain, m/s.

The force F c acts on the chain links along its entire contour and causes additional wear of the hinges. Chain drives are tested for strength according to the values ​​of the breaking force given in the standard, and the tension force of the leading branch, which is calculated taking into account additional dynamic loading from the uneven movement of the chain, the driven sprocket and the masses brought to it. The tension of the driven branch of the chain F 2 is equal to the largest of the tensions F 0 or F c.

The centrifugal force does not load the shafts and supports. The calculated load F in on the chain drive shafts is slightly greater than the useful circumferential force due to the tension of the chain from its own gravity. Conditionally accept

Fv \u003d Kv Ft,

where K in is the shaft load factor; for horizontal gears, K in \u003d 1.15, for vertical gears, K in \u003d 1.05. The direction of the force F in is along the line of the centers of the stars.

6. The nature and causes of chain drive failures

Drive chains are characterized by the following main types of limit states:

wear of hinge parts due to their mutual rotation under load. Causes chain pitch to increase. As they wear, the hinges are located closer to the tops of the teeth and there is a danger of the chain jumping off the sprockets;

wear of the sprocket teeth due to relative slip and seizure in the roller-sprocket tooth interface. Leads to an increase in the sprocket pitch;

fatigue failure of chain plates due to cyclic loading. They are observed in high-speed heavily loaded gears operating in closed cases with good lubrication;

shock-fatigue destruction of thin-walled parts - rollers and bushings. These failures are due to the impact of the hinges on the teeth of the sprockets at the entrance

into engagement.

AT In a properly designed and operated chain drive, the increase in chain pitch as the joints wear outpaces the increase in sprocket pitch. Associated with this is a violation of the engagement, unacceptable sagging of the idle branch of the chain, jumping off the sprocket, rubbing against the walls of the casing or crankcase, as well as an increase in vibrations and noise. As a result, the chain is usually replaced before fatigue failure occurs. Thus, the main mode of failure of chain drives is the wear of the joints.

7. Calculation of transmission by a roller (sleeve) chain

The wear resistance of hinges is the main criterion for the performance and calculation of chain drives. Wear depends on the pressure p in the hinge and the friction path S, quantified

The transfer of energy between two or more parallel shafts, carried out by engagement with a flexible endless chain and sprockets, is called chain.

The chain drive consists of a chain and two sprockets - leading 1 (Fig. 190) and driven 2, works without slipping and is equipped with tensioning and lubricating devices.

Rice. 190

Chain drives make it possible to transmit movement between shafts in a significant range of center distances compared to gear drives; have enough high efficiency equal to 0.96 ... 0.97; have less than in a belt drive, the load on the shaft; one chain transmits rotation to several sprockets (shafts).

The disadvantages of chain drives include: some uneven travel, noise during operation, the need for careful installation and maintenance; the need to adjust the chain tension and timely lubrication; rapid wear of chain hinges; high cost; chain pulling during operation, etc.

Chain drives are most widely used in various machine tools, bicycles and motorcycles, in hoisting and transport machines, winches, in drilling equipment, in running gears of excavators and cranes, and especially in agricultural machines. So, for example, in the self-propelled grain combine C-4 there are 18 chain gears that set in motion a number of its working bodies. Chain transmissions are also often found in the textile and cotton industries.

Chain parts

Asterisks. The operation of a chain transmission largely depends on the quality of the sprockets: the accuracy of their manufacture, the quality of the surface of the teeth, material and heat treatment.

The design dimensions and shape of the sprockets depend on the parameters of the selected chain and the gear ratio, which determines the number of teeth of the smaller drive sprocket. The parameters and quality characteristics of the sprockets are established by GOST 13576-81. The sprockets of roller and sleeve chains (Fig. 191, I) are profiled in accordance with GOST 591-69.


Rice. 191

The working profile of the sprocket tooth for roller and sleeve chains is outlined by an arc corresponding to the circle. For gear chains, the working profiles of the sprocket teeth are straight. In cross section, the sprocket profile depends on the number of chain rows.

The sprocket material must be wear-resistant, capable of withstanding shock loads. Sprockets are made from steels 40, 45, 40X and others with hardening to HRC 40...50 hardness or case hardened steel 15, 20, 20X and others with hardening to HRC 50... .60 hardness. For sprockets of low-speed gears, gray or modified cast iron SCH 15, SCH 20, etc. are used.

Currently, sprockets with a ring gear made of plastics are used. These sprockets are characterized by reduced chain wear and low transmission noise.

Chains. Chains are manufactured at special factories, and their design, dimensions, materials and other indicators are regulated by standards. According to their purpose, circuits are divided into the following types:

  • cargo chains (Fig. 192, I) used for suspension, lifting and lowering loads. They are mainly used in lifting machines;
  • traction chains (Fig. 192, II), which serve to move goods in transporting vehicles;
  • drive chains used to transfer mechanical energy from one shaft to another.


Rice. 192

Let us consider in more detail the drive chains used in chain drives. There are the following types of drive chains: roller, sleeve, toothed and hook.

roller chains(Fig. 192, III) consist of alternating external and internal links, which have relative mobility. The links are made of two plates pressed onto axles (outer links) or bushings (inner links). The bushings are put on the axis of the mating links and form hinges. To reduce the wear of sprockets when running chains on them, rollers are put on the bushings, which replace sliding friction with rolling friction (Fig. 191, II and III).

The axles (rollers) of the chains are riveted and the links become one-piece. The connection of the ends of the chain is carried out: with an even number of links - a connecting link, and with an odd number - a transitional one.

At high loads and speeds, in order to reduce the pitch and diameter of the sprockets, multi-row roller chains are used.

Roller chains with curved plates (Fig. 192, IV) consist of identical links, similar to the transition link. These chains are used when the transmission is working with a shock load (reversing, jolts). The deformation of the plates contributes to the damping of shocks that occur when the chain enters into engagement with the sprocket.

Sleeve chains(Fig. 192, V) in their design do not differ from the previous ones, but do not have rollers, which leads to increased wear of the teeth. The absence of rollers reduces the cost of the chain and reduces its mass.

Sleeve chains, like roller chains, can be single-row and multi-row.

Toothed (silent) chains(Fig. 192, VI) consist of a set of plates with teeth, hinged in a certain sequence. These circuits provide smooth and quiet operation. They are used at high speeds. Tooth chains are more complex and expensive than roller chains and require special care. The working faces of the plates, which perceive pressure from the teeth of the sprocket, are the planes of the teeth, located at an angle of 60°. To ensure sufficient wear resistance, the working surfaces of the plates are hardened to a hardness of H RC 40...45.

In order to prevent the gear chains from slipping off the sprockets during operation, they are equipped with guide plates (side or internal).

Hook chains(Fig. 192, VII) consist of identical links of a special form and do not have any additional details. Connected separation of the links is carried out with a mutual inclination at an angle of approximately 60 °.

Bush-pin chains(Fig. 192, VIII) are assembled from links using pins made of StZ steel. The pins are riveted, and in the connecting links they are fixed with cotter pins. These chains are widely used in agricultural engineering.

To ensure good chain performance, the materials of its elements must be wear-resistant and durable. For plates, steel 50 and 40X is used and hardened to a hardness of HRC35 ... 45, for axles, rollers and bushings - steel 20G, 20X, etc. with a hardness of HRC54 ... 62-, for rollers - steel 60G with a hardness of HRC48 .. .55.

Due to the wear of the hinges, the chain gradually stretches. The chain tension is controlled by moving the axis of one of the sprockets, using adjusting sprockets or rollers. Typically, tensioners allow you to compensate for the elongation of the chain within two links, with a greater stretch of the chain for the link, it is removed.

The durability of the chain depends on correct application lubricants. At a chain speed (v) equal to or less than 4 m/s, periodic lubrication is used, which is carried out with a manual oiler every 6–8 hours. At v s 10 m/s, lubrication with dropper greasers is used. More perfect lubrication by dipping the chain in an oil bath. In this case, the immersion of the chain in oil should not exceed the width of the plate. In powerful high-speed gears, circulating jet lubrication from a pump is used.

mechanical transmission- a mechanism that converts the kinematic and energy parameters of the engine into required parameters movement of the working bodies of the machines and designed to coordinate the mode of operation of the engine with the mode of operation of the executive bodies.

Types of mechanical gears:

  • gear (cylindrical, conical);
  • screw (screw, worm, hypoid);
  • with flexible elements (belt, chain);
  • frictional (due to friction, used under poor working conditions).

depending on the ratio of the parameters of the input and output shafts transfers are divided into:

  • gearboxes(downshifts) - from the input shaft to the output shaft, reduce the speed and increase the torque;
  • multipliers(upshifts) - from the input shaft to the output, increase the speed and reduce the torque.

Gear- This is a mechanism or part of a mechanical transmission mechanism, which includes gears. In this case, the force from one element to another is transmitted with the help of teeth.

gears intended for:

  • transmission of rotational motion between shafts, which may have parallel, intersecting or crossing axes;
  • conversion of rotational motion into translational, and vice versa (transmission "rack-pinion").

A transmission gear with fewer teeth is called gear, the second wheel with a large number teeth is called wheel.

Gears are classified by shaft arrangement:

  • with parallel axes (cylindrical with internal and external gearing);
  • with intersecting axes (conical);
  • with cross axes (rack-pinion).

Cylindrical gears() come with external and internal gearing. Depending on the angle of inclination of the teeth, spur and helical gears are made. With an increase in the angle, the strength of helical gears increases (due to the inclination, the contact area of ​​the teeth increases, and the dimensions of the gear decrease). However, in helical gears, an additional axial force appears, directed along the shaft axis and creating an additional load on the supports. To reduce this force, the angle of inclination is limited to 8-20°. This drawback is eliminated in the chevron gear.

Picture 1 - The main types of spur gears

Figure 6 - Friction gears

Friction between elements can be dry, boundary, liquid. Fluid friction is most preferred, as it significantly increases the durability of the friction gear.

Friction gears are divided:

  • shaft arrangement:
    • with parallel shafts;
    • with intersecting shafts;
  • according to the nature of the contact:
    • with external contact;
    • with internal contact;
  • possible variation of the gear ratio:
    • unregulated;
    • adjustable (friction variator);
  • in the presence of intermediate bodies in the transmission according to the shape of the contacting bodies:
    • cylindrical;
    • conical;
    • spherical;
    • flat.

Link List

  1. Lecture 16. Mechanical transmission // Information and educational portal "Oreanda". – http://bcoreanda.com/ShowObject.aspx?ID=252 .
  2. Gear // Wikipedia. - http://en.wikipedia.org/wiki/Gear_train.
  3. Friction gear // Wikipedia. - http://ru.wikipedia.org/wiki/Friction_gear.

Questions to control

  1. What is called a mechanical transmission, their main varieties?
  2. What are gears: description, purpose, classification, advantages and disadvantages?
  3. What is the principle of operation of worm gears, their main advantages and disadvantages?
  4. What are transfers with flexible links: description, purpose, classification?
  5. What are the main advantages and disadvantages of belt drives compared to chain drives?
  6. What are friction gears: description, purpose, classification?
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General information about chain drives

Chain transmission refers to transmission gearing with a flexible connection. Power in the chain transmission is transmitted by means of a multi-link articulated chain from the leading to the driven sprocket, placed on parallel shafts.

Chain classification

Chain drives are classified according to the type of chain used. Currently, roller, sleeve and gear chains are used, which, in turn, can be single-row and multi-row.

In roller and sleeve chains, the links with the sprocket are engaged through a roller or sleeve, while the durability of the chain increases, but its weight and cost increase.

Gear chains are assembled from plates, while the design of the hinge is of great importance for the performance of the chain. The design includes a guide plate that prevents the chain from slipping off the sprocket.

Compared to sleeve chains, toothed chains run smoother and provide greater kinematic accuracy. (smooth transmission), can transmit more power, have high efficiency, but their mass and cost are much higher.

Depending on the type of chain used, the design of the chain sprockets depends. Sprockets for sleeve and roller chains are shown in fig. 2 on the left, toothed chain sprocket on the right.

Advantages of chain drives

Compared to gears:
The advantage of chain drives in comparison with gears is that they are able to transmit movement between shafts at significant center distances. (up to 8 m).

Compared to belt drives:
Compared to belt drives (by friction gears) chain drives (gearing gear) they are distinguished by compactness, the ability to transmit more power with the same dimensions, a constant gear ratio and less demanding chain pre-tensioning (sometimes there is no preload for chain drives).
In addition, chain drives work stably at small center distances between sprockets, while a belt drive can slip at small angles of wrapping the pulley with a belt.

The advantages of chain drives include high efficiency and reliability during operation under conditions of frequent starts and stops.

Disadvantages of chain drives

1. Significant noise and vibration during operation due to the impact of the chain link on the tooth of the sprocket when engaging, especially with small numbers of teeth and a large pitch (this drawback limits the use of chain drives at high speeds).

2. Relatively fast wear of the chain joints, the need for a lubrication system and installation in closed cases.

3. Elongation of the chain due to wear of the hinges and its coming off the sprockets, which requires the use of tensioners.

4. Compared to gear drives, chain drives transmit movement less smoothly and evenly.

Scope of chain drives

Chain drives are widely used in many areas of mechanical engineering, construction of agricultural and road machines, machine tool building, etc.
They are used in machine tools, motorcycles, bicycles, industrial robots, drilling equipment, lifting and transport, road construction, agricultural, printing and other machines to transmit movement between parallel shafts over long distances, when the use of gears is impractical, and belts are impossible.

Chain transmissions are most widely used for power transmission up to 120 kW at peripheral speeds up to 15 m/s.



Drive chains

The drive chain - the main element of the chain transmission - consists of individual links connected by hinges. In addition to drive, there are traction and load chains which are not considered in this section of the site.
The main types of standardized drive chains (see Fig. 1) are: roller, sleeve and toothed.
In low-speed chain drives, shaped chains (hook or pin) are also used.

Roller drive chains

Roller drive chains consist of two rows of outer 1 and domestic 2 plates (see fig. 1) . Axles are pressed into the outer plates 3 passed through bushings 4 , pressed in turn into the inner plates. The bushings are pre-fitted with freely rotating hardened rollers 5 .
The ends of the axles after assembly are riveted to form heads that prevent the plates from falling off.
With relative rotation of the links, the axle rotates in the sleeve, forming a sliding hinge.

The chain is engaged with the sprocket through a roller, which, turning on the bushing, rolls over the sprocket tooth. This design equalizes tooth pressure on the sleeve and reduces wear on both the sleeve and the tooth.

The plates are outlined with a contour resembling a number 8 and providing equal strength of the plate in all sections.
Roller chains are widely used. They are used at speeds v ≤ 15 m/s.

Driven roller chains GOST 13568-75 distinguish:

  • single row normal (ETC),
  • single-row long-link lightweight (PRD),
  • single row reinforced (PRU),
  • double row (2PR),
  • three-row (ZPR),
  • four-row (4PR),
  • with curved plates (AT).

Of the roller single-row chains, the most common are normal ETC. Long link lightweight chains DRP manufactured with reduced breaking load; allowed speed for them up to 3 m/s.
Reinforced chains PRU made of increased strength and accuracy; they are used for large and variable loads, as well as at high speeds.

Multi-row chains allow you to increase the load in proportion to the number of rows, so they are used when transmitting high powers. Roller chains with curved plates of increased compliance are used for dynamic loads (strikes, frequent reverses, etc.).

Bush drive chains

Bush drive chains are similar in design to roller chains, but do not have rollers, which reduces the cost of the chain, reduces its weight, but significantly increases the wear of the chain bushings and sprocket teeth. Sleeve chains are used in non-critical gears with v < 1 м/сек .

The sleeve single-row chain (see fig. 1) consists of inner plates 1 , pressed onto bushings 2 , freely rotating on rollers 5 , on which the outer plates are pressed 4 .
Depending on the transmitted power, the drive sleeve chains are made in single row (PV) and double row (2PV).
These chains are simple in design, have a small mass and are the cheapest, but less wear-resistant, so their use is limited to low speeds, usually up to 10 m/s.

A roller single-row chain (Fig. 1) differs from a bush chain in that on its bushings 2 install freely rotating rollers 5 . The rollers replace the sliding friction between the bushings and the teeth of the sprockets in the bush chain with rolling friction. Therefore, the wear resistance of roller chains is much higher compared to sleeve chains and, accordingly, they are used at peripheral speeds up to 20 m/s.

Sleeve and roller chains are made single-row and multi-row with the number of rows 2, 3, 4 and more. A multi-row chain with a smaller pitch t allows you to replace a single-row chain with a larger pitch and thereby reduce the diameters of the sprockets and reduce the dynamic loads in the transmission.
Multi-row chains can operate at significantly higher chain speeds. The load capacity of the chain increases almost in direct proportion to the number of rows.

The connection of the ends of the chain with an even number of its links is carried out with a connecting link, with an odd number - with a less durable transition link with curved plates. Therefore, chains with an even number of links are used.

Toothed drive chains

The toothed chain (see Fig. 1) has a set of plates in each link 1 (their number is determined by the chain width and depends on the transmitted power) with two protrusions (teeth) and with a cavity between them for the sprocket tooth. This chain is manufactured with rolling friction joints. Two prisms are installed in the holes of the plates of each hinge 2 and 3 with curved work surfaces.
One of the prisms is connected to the plates of one link, and the other - to the plates of the neighboring link, as a result of which, during the movement of the chain, the prisms roll over one another. As a result, toothed chains run smoothly, with low noise, better absorb shock loads and allow high speeds.

Gear chains with sliding friction joints are also used, but their durability is approximately two times lower than that of gear chains with rolling friction joints.

The relative rotation of the links in such chains is provided by sliding hinges.
The sliding hinge consists of an axle and two inserts fixed in the figured grooves of the plates. When the plates are rotated, the liners slide along the axes, turning in the grooves of the plates.
Inserts allow you to increase the contact area in 1,5 times.
The hinge allows the plate to rotate through an angle φ max , which usually does not exceed 30°.

To eliminate the lateral fall of the chain from the sprockets, internal (located in the middle of the chain width) or side guide plates. The guide plates are regular plates, but without the sprocket tooth notches.
For internal guide plates on the teeth of the sprocket, grooves of the corresponding profile are made.
The pitch diameter d of the sprocket for toothed chains is greater than its outer diameter.

Gear chains, due to the better conditions of engagement with the teeth of the sprockets, work with less noise, which is why they are sometimes called silent. Since the width of the toothed chains can be any (there are chains up to 1.7 m wide), they are used to transmit high power.
However, compared to roller gear chains, they are heavier, more difficult to manufacture and more expensive, so the scope of gear chains is reduced.
At present, roller and bush chain transmissions are predominantly used.

Link chains

There are two types of shaped chains (see Fig. 1): hook and pin.
hook chain consists of links of the same shape, cast from ductile iron or stamped from flat steel ZOG without additional details.
The assembly and disassembly of this chain is carried out by mutual inclination of the links at an angle 60°.

AT pin circuit cast links 1 from ductile iron are connected by cottered steel (made of St3 steel) pins 2 .

Shaped link chains are used for the transmission of small powers, at low speeds. (hook up to 3 m/s, pin up to 4 m/s), usually under conditions of imperfect lubrication and protection.
Links of shaped chains are not processed. Due to their low cost and ease of repair, shaped chains are widely used in agricultural machines.

Chain material

Chains must be durable and strong.
plates chains are made from steel grades 50, 40X 40...50HRC.
Axles, bushings, rollers and prisms – from case-hardened steel grades 20, 15X and others with hardening 52...65HRC.
By increasing the hardness of the parts, the wear resistance of the chains can be increased.

Sprockets and disks of compound sprockets are mainly made of medium carbon or alloy steel. 40, 45, 40H, 50G2, 35HGSA, 40HN hardened HRC40...50 or case hardened steel 15, 20, 15X, 20X, 12XH2 with heat treatment to hardness HRC50...60.

Sprockets of low-speed gears at chain speed v ≤ 3 m/s and the absence of dynamic loads are also made of gray or modified cast iron MF15, SC18, SC20, SC30 with surface hardness up to HB260...300.
Sprockets are used with a gear rim made of plastics (duroplast or vulkolan), which help to reduce noise and wear of chains during transmission operation.

Geometric and kinematic parameters of chain transmission

The main parameter of the chain transmission is the pitch t of the chain, i.e. the distance between the axes of the two nearest chain hinges (see Fig. 2). The larger the pitch, the higher the load capacity of the chain.

Sprocket Pitch Diameter d is determined by the formula:

d = t / ,

where z is the number of sprocket teeth.

The step t of the stars is measured along the chord of the dividing circle.

Optimum transmission center distance taken from the chain durability condition:

a = (30…50)t ,

where t is the chain pitch.

Chain length in steps:

Lp \u003d 2a / t + (z 2 + z 1) / 2 + [(z 2 - z 1) / 2π] 2 t / a,

where z 1 and z 2 are the number of sprocket teeth.

Number of teeth of small sprocket choose from the ratio

z1 = 29 – 2u.

Then z 2 = z 1 u .

The final value of the center distance:

a = t/4(L p - (z 2 + z 1)/2 + √ | 2 - 8[(z 2 - z 1) / 2π] 2 |).

Gear ratio: u \u003d ω 1 / ω 2 \u003d n 1 / n 2 \u003d z 2 / z 1.

gear ratio chain transmission cannot be defined as the ratio of the diameters of the pitch circles of the sprockets. Within one revolution of the sprocket, the gear ratio does not remain constant, so they usually talk about the average chain speed, m / s:

v = ωzt/2000π ,

where ω , z are the angular velocity and the number of sprocket teeth.



Chain transmission in its most common form consists of two wheels located at some distance from each other, called sprockets, and a chain covering them (Fig. 1, a). The rotation of the drive sprocket is converted into the rotation of the driven sprocket due to the engagement of the chain with the teeth of the sprocket. Sometimes chain drives with several driven sprockets are used. Chain transmissions operating at high loads and speeds are placed in special casings called crankcases (Fig. 1, b), which ensures constant abundant lubrication of the chain, safety and protection of the transmission from contamination and reduction of noise that occurs during its operation. Sometimes he uses chain variators, arranged according to the scheme of shoe-belt variators with sliding cones. Because chains stretch as they wear, the chain tensioner must adjust chain tension. This regulation, by analogy with belt drives, is carried out either by moving the shaft of one of the sprockets, or with the help of control sprockets or rollers.

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Advantages of chain drives compared to belt drives:
no slippage
compactness (they take up much less space in width),
lower loads on shafts and bearings (no need for high initial chain tension).

The efficiency of the chain drive is quite high, reaching the value η=0.98.

Disadvantages of chain drives:


  • elongation of the chain due to wear of its hinges and stretching of the plates, as a result of which it has a restless course;
  • the presence of variable accelerations in the elements of the chain, causing dynamic loads, the greater the higher the speed of the chain and the fewer teeth on the smaller sprocket;
  • noise at work;
  • the need for careful maintenance during its operation.

Chain drives are used at large center distances, when gears cannot be used due to bulkiness, and belt drives due to the requirements of compactness or a constant gear ratio. Depending on the design of the chains, transmissions with a power of up to 5000 kW are used at peripheral speeds of up to 30 ... 35 m / s. The most common are chain transmissions with a power of up to 100 kW at peripheral speeds of up to 15 m/s. Chain transmissions are used in transport, agricultural, construction, mining and oil machines, as well as in machine tools.

Chains in chain drives are called drive chains. Drive chains are distinguished by design:

  • sleeve, roller(GOST 13568-75),

  • jagged(GOST 13552-81)

  • shaped links.

The main geometric characteristics of the chain are the pitch, i.e. the distance between the axes of the two nearest hinges of the chain, th width, and the main power characteristic is the breaking load of the chain, which is established empirically.

Sleeve single-row chain.

Sleeve single-row chain (Fig. 2, a) consists of inner plates 1, pressed on bushings 2, freely rotating on rollers 5, on which external plates 4. Depending on the transmitted power, drive sleeve chains are made single row(PV) and two-row(2PV). These chains are simple in design, have a small mass and are the cheapest, but less wear-resistant, so their use is limited to low speeds, usually up to 10 m/s.


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Drive roller chains according to GOST 13568-75 are distinguished:

  • single-row normal (PR),
  • single-row long-link lightweight (PRD),
  • single-row reinforced (PRU),
  • two (2PR),
  • three (ZPR),
  • four-row (4PR),
  • with curved plates (PRI).

The roller single-row chain (Fig. 2, b) differs from the sleeve chain in that on its bushings 2 install freely rotating rollers 5. The rollers replace the sliding friction between the bushings and the teeth of the sprockets in the bush chain with rolling friction. Therefore, the wear resistance of roller chains is much higher compared to sleeve chains and, accordingly, they are used at peripheral speeds of up to 20 m/s. Of the single-row roller chains, the most common normal PR. Long-link lightweight PRD chains manufactured with reduced breaking load; permissible speed for them is up to 3 m/s. Reinforced PRU chains made of increased strength and accuracy; they are used for large and variable loads, as well as at high speeds.

Multi-row circuits (Fig. 2, c) allow you to increase the load in proportion to the number of rows, so they are used when transmitting large powers. Roller chains with curved plates (Fig. 2, d) of increased compliance are used for dynamic loads (impacts, frequent reverses, etc.).

Gear chain.

The gear chain (Fig. 2, e) in each link has a set plates 1(their number is determined by the width of the chain) with two protrusions (teeth) and with a cavity between them for the sprocket tooth. This chain is manufactured with rolling friction joints. In the holes of the plates of each hinge, two prisms 2 and 3 with curved work surfaces. One of the prisms is connected to the plates of one link, and the other - to the plates of the neighboring link, as a result of which, during the movement of the chain, the prisms roll over one another.

Gear chains with sliding friction joints are also used. The durability of toothed chains with rolling friction joints is approximately twice as high.

Toothed chains to prevent slipping off the sprockets and work are provided with guides plates 4, which are ordinary plates, but without recesses for sprocket teeth. These plates require the corresponding grooves on the sprockets to be machined (see Fig. 4, b).

Gear chains, due to the better conditions of engagement with the teeth of the sprockets, work with less noise, which is why they are sometimes called silent. Compared to other gear chains, they are heavier, more difficult to manufacture and more expensive, so their use is limited. Since the width of gear chains can be anything (there are chains up to 1.7 m wide), they are used to transmit large powers.

There are two types of shaped link chains: hook(Fig. 3, a) and pin(Fig. 3b). The hook chain consists of links of the same shape, cast from ductile iron or stamped from ZOG strip steel without additional parts. The assembly and disassembly of this chain is carried out by mutual inclination of the links at an angle of 60°. Molded in pin chain links 1 from ductile iron are connected by cottered steel (made of St3 steel) pins 2. Shaped link chains are used for the transmission of low power, at low speeds (hook up to 3 m/s, pin up to 4 m/s), usually in conditions of imperfect lubrication and protection. Links of shaped chains are not processed. Due to their low cost and ease of repair, shaped chains are widely used in agricultural machines.


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Lubrication of drive chains.

Lubricating the drive chains prevents them from wearing out quickly. For critical power chain drives, continuous crankcase lubrication is used, carried out at a speed of up to 8 m / s with the chain dipped in an oil bath to a depth not exceeding the width of the plate and at a higher speed - forced circulating supply of lubricant from the pump (see Fig. 1, b) . In the absence of a hermetic crankcase and a chain speed of up to 8 m / s, grease intra-hinge lubrication is used, carried out periodically after 120..180 hours by immersing the chain in a lubricant heated to liquefaction. Sometimes drip lubrication is used instead of grease. When the gear is operating intermittently with a circumferential speed of up to 4 m / s, periodic chain lubrication is also used, carried out by a manual oiler after 6 ... 8 hours.

Chain and sprocket material.

The durability of chain drives depends on the material and heat treatment of chains and sprockets.

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Elements of sleeve, roller and gear chains are made from the following materials: plates - from medium carbon or alloy steels 40, 45, 50, 30KhNZA hardened to a hardness of HRC32 ... 44, and rollers, bushings, rollers and liners - from case-hardened steels 10, 15, 20, 12KhNZA, 20KhNZA, 30KhNZA with heat treatment to hardness HRC40...65. Bush and roller chains are used, inside the steel bushings of which plastic bushings are placed, freely rotating both on the rollers and inside the steel bushings. Such chains are used when the joints operate without lubrication or with weak lubrication.

Chain sprocket designs are similar to gear wheels. Depending on the size, material and purpose, they are made whole (Fig. 4) or composite (Fig. 5).

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Sprockets for sleeve and roller chains have a small width. They are usually made of two parts - a disk with teeth and a hub, which, depending on the material and purpose, the sprockets are welded (Fig. 5, a) or connected with rivets (bolts) (Fig. 5, b). Sprockets for gear chains (see Fig. 4, b) are wide, they are made whole. Whole sprockets and disks of compound sprockets are mainly made of medium carbon or alloy steel 40, 45, 40Kh, 50G2, 35KhGSA, 40KhN with hardening HRC40...50 or hardened steel 15, 20, 15X, 20X, 12XH2 with heat treatment to hardness HRC50...60. Slow speed sprockets at chain speed v≤3 m/s and the absence of dynamic loads, they are also made of gray or modified cast iron SCH15, SCH18, SCH20, SCH30 with a surface hardness of up to HB260...300. Sprockets with a gear rim made of plastics (Duroplast or Vulkolan) are used. Vulkolan is a type of polyurethane with special properties. The design of such stars is shown in (Fig. 5, f). On the rim of the metal part of the sprocket, a dovetail-shaped groove is made, interrupted by several transverse recesses, in which a plastic ring gear is placed. The advantage of plastic sprockets over metal sprockets is reduced chain wear and transmission noise.

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