Chapter 9 Transmission of Chains Key Terms: chain drives pitch number of links chain plate sprocket efficiency of polygon

9.1 Characteristics and Application of Chain Drives 1.Construction 1—driven sprocket 2—chain 3—driving sprocket

Sprocket

2.Characteristic Advantages: 1) A wide range of center distance; 2) Average velocity ratio is positive; 3) High efficiency =98%; 4) Can operate under an adverse environment. Disadvantages: 1)The instantaneous velocity and speed ratio of chain are not constant, which lead to impact and noise of chain drives; 2)Wear of joints result in the faulty engagement; 3)More accurate assembly and more complicated service are required.

3.Application Good for low speed & high torque; v<15m/s, P100kW, i 8 amax=10m

9.2 Types of Chain Drivers Lifting chains Hauling chains Power transmission chains a. Roller chains b. Silent chains

1. Roller chains 1——inner side plate 4——bushing 2——outer side plate 3——pin

Strand number: single, double, multiple strands, 4

2. Pitch P 1)Pitch P is the linear distance between the centers of rollers. 2) Pitch is a critical parameter of roller chain drives, the more the pitch is, the larger the size of the chain parts and the greater the power transmitted is.

2. Number of links Lp 1) Even number of links 2) Odd number of links Best! 1) Even number of links 2) Odd number of links offset links

3. Standard roller chain (GB1243.1—83) Table 9.1: A series roller chain Mark of roller chain: 08A-187 GB1243.1-83

9.3 Moving Characteristics of Chain Drives 1. The average velocity of chain

2. The instantaneous velocity of chain

Variation of a Chain Velocity

3. The instantaneous speed ratio of chain drives

Conclusion The instantaneous velocity of the chain varies; The larger the pitch is, the less the number of teeth of sprocket is, the larger the variation of the chain speed will be; The instantaneous speed ratio varies; The uneven moving features of chain drives is named the efficiency of polygon

9.4 Appended Dynamic Loads of Chain Drives It is necessary to apply less chain pitch and much number of teeth of the sprocket.

9.6 Design of Chain Drives 1. Failure Type 1）Fatigue failure of the plates; 2）Wear in joints lead to elongation of the chain and its faulty engagement; 3）Veneer 4）Impact damage; 5）Wear of the sprocket; 6）Static break failure (v<0.6m/s).

2. Load-carry Capacity of Roller Chains 1) Limiting Power Curves, Fig. 9.10 1—good lubrication; 2—limited by fatigue failure of plates; 3—limited by impact fatigue failure of bushings and rollers; 4—limited by veneer failure of the pins and bushings; 5—applicable area; 6—bad operating condition.

2) Rated Power Curves P0, Fig.9-11 Experiment Conditions: z1=19; Lp=100; single-strand; steady load; service life=15000h; Recommended lubrication ways: Fig.9.12

Recommended Lubrication 1—artificial regular lubrication 2—drop lubrication 3—oil-bath or splash lubrication 4—pressure spay lubrication

modified power in real working conditions: P—name transmitted power; KA—working condition factor, table 9.2; Kz, K'z —factor of the number of teeth of small sprocket, table 9.3; Km—multiple-strand chain factor, table 9.4 KL—chain length factor, Fig.9.13;

3. Design Criteria 1)For general chain velocity (v0.6m/s): Rated Power Curves 2)For low chain velocity (v<0.6m/s): static strength FQ—limiting tensile load, table 9.1; m—the number of strand; Fc—centrifugal force; Ff—sagging force. KA—working condition factor, table 9.2;

4. Design Calculations and Parameter Selection 2 1 a w2 w1 D2 D1

Number of teeth of sprocket and speed ratio uneven number is best!

2) Types of chain, pitch and strand number p, P0, Fd ,v; Type of the chain: Fig.9.11

3) Distance between the sprocket axles and the chain length The number of links Lp: even number is best!

the more the number of teeth z, the much possible for the chain to shift outward upon the sprocket teeth 。

The end Thanks!