Chain drive is a kind of transmission mode in which the movement and power of the driving sprocket with special tooth shape are transmitted to the driven sprocket with special tooth shape through the chain.
Chain drive has many advantages. Compared with belt drive, it has no elastic sliding and slipping, accurate average transmission ratio, reliable operation and high efficiency;Large transmission power, strong overload capacity, and small transmission size under the same working condition;The required tension is small, and the pressure acting on the shaft is small;It can work in high temperature, damp, dusty, polluted and other harsh environments.
The main disadvantages of chain transmission are: it can only be used for transmission between two parallel shafts;High cost, easy to wear, easy to stretch, poor transmission stability, additional dynamic load, vibration, impact and noise will be generated during operation, so it is not suitable for rapid reverse transmission.
Chinese name
Chain drive
Foreign name
chain drive
Features
Accurate power transmission with average transmission ratio
Structure
Engagement of chain and sprocket teeth
Disadvantages
High cost, easy to wear, easy to stretch, etc
Advantages
High transmission power, high transmission efficiency
Chain transmission is meshing transmission, and the average transmission ratio is accurate.It transmits power and motion by meshing the chain and sprocket teethmechanical drive。[1]
chain
Basic structure of chain drive
The chain length is expressed in the number of links.The number of chain links should preferably be even, so that when the chain is connected into a ring, the outer chain plate is just connected with the inner chain plate, and the joint can be locked with a spring clamp or a cotter pin.If the number of chain links is odd, transition chain links shall be used.When the chain is under tension, the transition link should also bear additional bending load, which should generally be avoided.Toothed chain is used for tooth shaped chain plate formed by stampingHingeThe chain shall be connected. In order to avoid chain dropping when engaging, the chain shall have a guide plate (divided into internal guide type and external guide type).The two sides of the toothed chain plate are straight edges, and the side of the chain plate meshes with the sprocket tooth profile during operation.Hinges can be made into sliding pairs or rolling pairs, and roller type can reduce friction andabrasionThe effect is better than that of bearing bush type.Compared with roller chain, toothed chain has smooth operation, low noise and high ability to withstand impact load;However, because of its complex structure, high price and heavy weight, it is not as widely used as roller chains.Toothed chain is mostly used for transmission with high speed (chain speed up to 40m/s) or high movement accuracy requirements.The national standard only specifies the maximum and minimum values of tooth surface arc radius, tooth groove arc radius and tooth groove angle of roller chain wheel tooth groove (see GB1244-85 for details).The actual end tooth shape of various sprockets shall be between the maximum and minimum tooth groove shapes.This treatment makes the design of sprocket tooth profile curve very flexible.However, the tooth shape shall ensure that the chain can enter and exit the mesh smoothly and smoothly, and facilitate processing.There are many end face profile curves that meet the above requirements.The most commonly used tooth profile is "three arcs and one straight line", that is, the end face tooth profile is composed of three arcs () and a straight line ().[1]
Sprocket
Both sides of the tooth profile of the sprocket shaft surface are in a circular arc shape to facilitate the entry and exit of the chain link.When the tooth profile is processed with standard tools, it is not necessary to draw the end tooth profile on the working drawing of the sprocket, but it is necessary to draw the tooth profile of the sprocket shaft surface to facilitate the turning of the sprocket.See the relevant design manual for the specific dimensions of the tooth profile of the shaft surface.The sprocket teeth should have sufficient contact strength and wear resistance, so the tooth surface isheat treatment。The small sprocket has more meshing times than the large sprocket, and the impact force is also large, so the materials used should generally be better than the large sprocket.Commonly used sprocket materials include carbon steel (such as Q235, Q275, 45, ZG310-570, etc.), gray cast iron (such as HT200), etc.Important chain wheels can be made of alloy steel.Small diameter sprocket can be made into solid type;The sprocket with medium diameter can be made into orifice plate;The sprocket with larger diameter can be designed as a combination. If the gear teeth fail due to wear, the gear ring can be replaced.The size of sprocket hub can refer to the pulley.[1]
Basic type
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According to different uses, chains can be divided intoLifting chain、Traction chainandDrive chainThree categories.The lifting chain is mainly used to lift heavy objects in the lifting machinery, and its working speed v ≤ 0.25m/s;The traction chain is mainly used forChain conveyorMedium moving weight, its working speed v ≤ 4m/s;The transmission chain is used to transmit motion and power in general machinery, and the normal working speed is v ≤ 15m/s.There are two types of transmission chain: tooth chain and roller chain.Toothed chain is driven by meshing the chain piece with the sprocket with a specific tooth shape. Toothed chain drive is stable and has little noise, so it is also called silent chain drive.The allowable working speed of toothed chain can reach 40m/s, but the manufacturing cost is high and the weight is large, so it is mostly used in the occasions with high speed or high movement accuracy requirements.The chain used for power transmission mainly includes sleeve roller chain and toothed chain.Sleeve roller chain is composed of inner chain plate, outer chain plate, sleeve, pin shaft and roller.The outer chain plate is fixed on the pin shaft, and the inner chain plate is fixed on the sleeve. Both the roller and the sleeve and the sleeve and the pin shaft can rotate relatively, so the engagement between the chain and the sprocket is mainly rolling friction.Sleeve roller chain can be used in single row or in combination with multiple rows, and multiple rows can transfer large power.The sleeve roller chain is lighter in weight, longer in life and lower in cost than the toothed chain.It is widely used in power transmission.Toothed chain is composed of several pairs of chain pieces with 60 ° angle on the working surface by using a pin shaft.The working surface of the chain piece meshes with the sprocket.In order to prevent the chain from falling off from the sprocket during operation, the chain is equipped with an inner guide plate or an outer guide plate.When engaging, the guide plate is inosculated with the corresponding guide groove on the sprocket.Toothed chain transmission is stable and has little noise, so it is also called silent chain, and is commonly used in high-speed transmission.The tooth shape of sleeve roller chain and toothed chain sprocket shall ensure that the chain can enter or exit the mesh freely. The impact is very small when meshing, and the contact is good when meshing.[1]
Basic characteristics
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Compared with belt transmission, chain transmission has no elastic sliding and slipping, and can maintain accurate average transmission ratio;The required tension is small, and the pressure acting on the shaft is also small, which can reduce the friction loss of the bearing;Compact structure;It can work in high temperature, greasy dirt and other harsh environmental conditions.Compared with gear drive, chain drive requires lower manufacturing and installation accuracy;The transmission structure is simple when the center distance is large.Instantaneous chain speed and instantaneous transmission ratio are not constant, so the transmission stability is poor, and there are certain impacts and noises in the work.Chain drive averagetransmission ratioAccurate, high transmission efficiency, wide range of application of distance between shafts, and can be used in the environment with high temperature and humidity;However, chain transmission can only be used as transmission between parallel shafts, and its instantaneous transmission ratio fluctuates, resulting in large transmission noise.Since the chain link is rigid, there is a polygon effect (namely, non-uniformity of motion)Kinematic characteristicsMake the instantaneous transmission ratio of chain drive change and cause additional motionloadAnd vibration must be considered when selecting chain transmission parameters.Chain drive is widely used in transportation, agriculture, light industry, mining, petrochemical and machine tool industries.[1]
main parameter
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Number of sprocket teeth
In order to improve the motion stability of chain drive and reduce dynamic load, it is better to have more teeth of small sprocket.However, the number of small sprocket teeth should not be too many, or=i will be large, which will cause the chain drive to fail earlier.After the chain works for a period of time, the wear makes the pin shaft thinner and the sleeve and roller thinner. Under the action of tensile load F, the chain pitch extends.After the chain pitch becomes longer, the pitch circle d moves to the tooth top when the chain wraps around the sprocket.Generally, the number of chain links is even to avoid the use of transition joints.In order to make the wear even and improve the service life, the number of sprocket teeth should be reciprocal with the number of chain links. If the mutual quality cannot be guaranteed, the common factor should be as small as possible.[1]
Pitch of chain
The greater the pitch of the chain, the higher the theoretical bearing capacity.However, as mentioned in the previous section, the greater the pitch, the greater the dynamic load caused by the chain speed change and the impact of the chain link meshing into the sprocket, which will reduce the chain bearing capacity and life.Therefore, the chain with small pitch should be selected as far as possible in the design, and the actual effect of selecting multi row chain with small pitch in heavy load is often better than that of selecting single row chain with large pitch.[1]
Center distance and chain length
If the center distance of the chain drive is too small, the wrap angle on the small sprocket is small, and the number of teeth of the meshing sprocket is small;If the center distance is too large, the chain will shake easily.Generally, the center distance a=(30~50) p, and the maximum center distance ≤ 80p.The chain length is expressed by the number of chain segments.According to the formula for calculating the belt length of belt transmission, the number of chain links calculated from this formula must be rounded to an integer, preferably an even number.Using the above formula, we can get the formula for calculating the center distance a from: in order to facilitate the installation of the chain and adjust the tension of the chain, the center distance should generally be designed to be adjustable;Or there shall be tensioning device.[1]
Design form
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Failure mode
The failure forms of chain drive are mainly as follows: (1) Fatigue failure of chain plate Under the repeated action of loose edge tension and tight edge tension, the chain plate will be fatigue damaged after a certain number of cycles.Under normal lubrication conditions, the fatigue strength of the chain plate is the main factor limiting the bearing capacity of the chain drive.(2) Impact fatigue failure of roller and sleeve The meshing impact of chain drive is firstly borne by roller and sleeve.Under repeated impacts and after a certain number of cycles, impact fatigue damage may occur to rollers and sleeves.This kind of failure mostly occurs in medium and high speed closed chain drives.(3) When the gluing lubrication between the pin shaft and the sleeve is improper or the speed is too high,pin shaftAnd the working surface of the sleeve.Gluing limits the ultimate speed of the chain drive.(4) Chain hingeabrasionThe chain link becomes longer after the hinge is worn, which is easy to cause tooth skipping or chain dropout.In case of open transmission, bad environmental conditions or poor lubrication and sealing, it is very easy to cause hinge wear, which sharply reduces the service life of the chain.(5) Overload pull off This kind of pull off often occurs in low speed and heavy load transmission.Under a certain service life, an expression of limiting power can be obtained from a failure form.In order to be clear, it is usually indicated by line diagram.Is the limit power curve corresponding to various failure forms under normal lubrication conditions.The shaded part is the area actually used.If the lubrication seal is poor and the working condition is bad, the wear will be very serious, and the limit power will be greatly reduced.[1]
Power Curve
The power transmitted by each model of A-series roller chain when the recommended lubrication method is used.If the lubrication is poor or the recommended lubrication method is not adopted, the value shall be reduced;When the chain speed v ≤ 1.5m/s, it will be reduced to 50%;When 1.5m/ss, it will be reduced to 25%;When v>7m/s and lubrication is not correct, the transmission is not reliable.When tensioning the device, the calculated center distance shall be reduced by 2~5mm to make the chain have a small initial sag.[1]
Common examples
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Bicycle
To increase the speed of the bicycle, the radius of the tooth disc should be increased, the radius of the flywheel should be reduced, and the radius of the rear wheel should be increased.Variable speed bicycleThis is the design.The chain drive is composed of a driving sprocket and a driven sprocket installed on a parallel shaft and a ring around the sprocketchainAs shown in Figure 1, the chain is used as the intermediate flexible part to transmit motion and power by meshing the chain with the sprocket teeth.[1]
Figure 1 Schematic Diagram of Chain Drive
Figure 1 Schematic Diagram of Chain Drive
In the chain drive, presschainThere are two types of different structures: roller chain drive and tooth chain drive:[1]
Roller chain drive
The structure of roller chain is shown in Figure 2.It is composed of inner chain plate 1, outer chain plate 2, pin shaft 3, sleeve 4 and roller 5.When the chain drive works, the roller on the sleeve rolls along the sprocket tooth profile, which can reduce the wear of the chain and sprocket teeth.[1]
Fig. 2 Chain Drive
Figure 2 Roller Chain
The chain that parallels more than one single row chain and connects it with a long pin shaft is called a multi row chain. Figure 3 shows a double row chain.The more rows of chains, the higher the bearing capacity, but the higher the manufacturing and installation accuracy requirements of chains, and the more difficult it is to make each row of chains bear uniform force, which will greatly reduce the service life of multi row chains, so the number of rows should not exceed 4 rows.When the transmission power is large, two or more double row chains or three row chains can be used.[1]
To formChain linkRing connected head to tailchain, to be connected with connectors.When the number of chain links is even, the connecting chain link is used, whose shape is the same as that of the chain link. The pin shaft and the connecting chain plate are fixed with steel wire lock pin or spring card and other locking parts at the joint;When the number of links is odd, a transition link must be added.The chain plate of the transition link is subject to additional bending moment when working, so the odd number of links should be avoided as far as possible.[1]
The distance between the centers of two adjacent pin shafts of the chain is called the chain pitch, which is expressed by p and is the main parameter of chain transmission.Roller chains have been standardized and are divided into A and B series.Series A is used for heavy load, high-speed or important transmission;B series is used for general transmission.Table 1 lists the basic parameters and dimensions of some roller chains.[1]
Toothed chain transmission table
Toothed chain transmission is realized by meshing the chain plate with a specific tooth shape with the sprocket.Toothed chain is composed of toothed chain plates connected with each other by hinges (Figure 4). The included angle between the two working sides of the chain plate is 600. The chain plates of adjacent chain links are staggered from left to right, and the chain plates are connected with pin shafts, bearing shells or rollers.According to different hinge structures, there are three types: round pin hinge type, bearing bush hinge type and roller hinge type, as shown in Figure 4.[1]
Figure 4 Chain Drive
Figure 4 Toothed Chain
Compared with roller chain, toothed chain has the advantages of stable operation, low noise, higher allowable chain speed, better ability to withstand impact load and more uniform force on gear teeth;However, the structure is complex, assembly and disassembly are difficult, the price is high, the weight is large, and the requirements for installation and maintenance are also high[1]
