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Introduction to some principles of chain drive

Release time: 23-10-2018
Summary:

Chain transmission is a transmission method that transmits the motion and power of a driving sprocket with a special tooth shape to a driven sprocket with a special tooth shape through a chain. […]

Chain transmission is a transmission method that transmits the motion and power of a driving sprocket with a special tooth shape to a driven sprocket with a special tooth shape through a chain.

Chain drive has many advantages. Compared with belt drive, it has no elastic sliding and slipping phenomenon. The average transmission ratio is accurate, the work is reliable, and the efficiency is high. The transmission power is large, the overload capacity is strong, and the transmission size under the same working conditions is small. Low tightening force, small pressure on the shaft; can work in harsh environments such as high temperature, humidity, dust, pollution, etc.

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 extend, poor transmission stability, additional dynamic load, vibration, impact and noise will be generated during operation, it should not be used in rapid speeds Reverse transmission.

The chain drive is a mesh drive and the average transmission ratio is accurate. It is a mechanical transmission that utilizes the meshing of a chain with the teeth of a sprocket wheel to transmit power and motion.

Chain

The chain length is expressed by the number of links. The number of chain links is best to be even, so that when the chain is connected in a ring, the outer link plate is connected to the inner link plate, and the joint can be locked with a spring clip or a split pin. If the number of links is odd, transition links are required. When the chain is tensioned, the transitional links also have to bear additional bending loads, which should generally be avoided. Toothed chain is composed of many punched toothed chain plates connected by hinges. To avoid dropping the chain when meshing, the chain should have guide plates (divided into inner guide and outer guide). Both sides of the toothed chain plate are straight edges, and the sides of the chain plate mesh with the tooth profile of the sprocket during operation. The hinge can be made into a sliding pair or a rolling pair. The roller type can reduce friction and wear, and the effect is better than the bearing type. Compared with roller chains, toothed chains run smoothly, have low noise, and high ability to withstand impact loads; but they have complex structures, are more expensive, and are heavier, so they are not as widely used as roller chains. Toothed chains are mostly used for high-speed (chain speeds up to 40m / s) or transmissions that require high motion accuracy. The national standard only specifies the maximum and minimum values of the tooth surface arc radius, the groove arc radius, and the groove angle of the tooth groove of the roller sprocket (see GB1244-85 for details). The actual tooth profile of each sprocket should be between the largest and smallest cogging shapes. This treatment makes the sprocket tooth profile curve design very flexible. However, the tooth profile should ensure that the energy-saving chain enters and exits the mesh smoothly and is easy to process. There are many types of tooth profile curves that meet the above requirements. The most commonly used tooth profile is "three arcs and a straight line", that is, the end tooth profile is composed of three arcs () and one straight line ().

Sprockets

The two sides of the tooth profile of the sprocket shaft surface are arc-shaped, so that the chain links can enter and exit the mesh. When the tooth profile is processed with a standard tool, it is not necessary to draw the tooth profile of the end face on the sprocket work drawing, but the tooth profile of the shaft surface of the sprocket must be drawn in order to turn the sprocket hair. For the specific dimensions of the shaft tooth profile, see the relevant design manual. The sprocket teeth should have sufficient contact strength and wear resistance, so the tooth surface is mostly heat treated. The small sprocket meshes more than the large sprocket, and the impact force is greater, so the material used should generally be better than the large sprocket. Commonly used sprocket materials are carbon steel (such as Q235, Q275, 45, ZG310-570, etc.), gray cast iron (such as HT200), and so on. Important sprocket wheels can be made of alloy steel. Small diameter sprocket can be made into solid type; medium diameter sprocket can be made into perforated plate type; larger diameter sprocket can be designed as a combination type. If the gear teeth fail due to wear, the ring gear can be replaced. The dimensions of the hub part of the sprocket can refer to the pulley.