Chapter 9 Transmission of chains

Key points: ⑴ Failures；

⑵ Efficiency of polygon;

⑶ Lubrication methods, arrangement and tension of chain

drives.

Difficulties: Design procedure

§9.1 Characteristics and Application of chain drives

1. Characteristics

⑴ big centre distance

⑵ smaller overall than belt drive

⑶ No elastic creep,

positive Instantaneous

⑷

⑸ smaller tension required and small force acting on the shafts

⑹ can operate under adverse working conditions such as high

temperature, high humidity and oil pollution and so on.

⑺ operate only among parallel shafts

⑻ Has more noisy, more impact than belt drives

⑼ wearing lead to faulty engagement between chain and sprockets

⑽ can not be used in big variable load and sudden reverse rotation

⑾ cost is higher than V-belt drives, because complicated manufacturing

and service such as lubricating and adjusting.

2. Application

Low-speed because wearing, impact, noise. As a rule, ,

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High quality chain with small pitch, large number of teeth and effective

lubrication,

High-torque (P<100KW (<5000Kw)),

belt drive (P<20~30KW (<1000Kw)),

gear drive (P<60000KW )

,

§9.2 Types of chain drives

1. Classify

⑴ by their purpose

① Lifting/load chains, be used mainly in materials handling machinery.

② Hauling/towing chains, used for conveying machinery.

③ Power transmission chain used for transmitting mechanical energy.

⑵ by their structure

① Roller chain

② Silent chain

2. Roller chains

⑴ Components

Pins, bushings, rollers, inner side plates, outer side plates

Bushing and inner side plate, Pin and outer side plate —— tight fit

Roller and bushing, bushiing and pin —— clearance fit

Single strand, double-strand, three-strand, … quadruple-strand pt

Multiple-strand chains have same components except longer pins.

⑵ Joints

Cotter pin for even number of links and large pitch

Alligator clip for even number and small pitch

Offset link for odd number of links

⑶ Chain number

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05B、06B、08B、08A、10A、12A、16A、20A……

The digits indicate the pitch of the chain in sixteenth of an inch.

(in)

(mm)

Suffix A——A series, standard sizes

Suffix B——B series, smaller and lighter sizes

Designation:

Chain number—Number of strand × Number of links Standard number

Example: 08A—1×80 GB1243.1—83

Single strand

Multiple strand

3. Silent chain

⑴ Guide plate

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Inner guide plate better guidance for high speed and heavy-duty,

Outside guide plate for width of sprocket less than 25~30mm

⑵ Joints

① Cylindrical pin type

② Bushing type

③ Roller type

§9.3 Moving characteristics of chain drives

Chain average velocity

Speed ratio in

n

z

z121

2

2

1

On small sprocket, chain advanced speed

v v Rx 1 1 1cos cos

4

chain perpendicular speed

v v Ry 1 1 1sin sin

Similarly, on big sprocket, chain advanced speed

v v Rx 2 2 2cos cos

21 1

2

R

R

cos

cos

Instantaneous speed ratio

Only when , that is , the change ranges of and equal,

and when , , then

conclusion：Chain drives cannot move smoothly.

Efficiency of polygon:

§9.4 Appended dynamic loads of chain drives

1. Caused by periodical variable chain speed

当 180

1z时

ω↑ ， p ↑，Fd ↑

2. Caused by periodical variable angular velocity of the driven sprocket

z↓, ↓，Fd ↑

Conclusion:

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The larger speed and the larger chain pitch, the larger dynamic load.

§9-5 Force analysis of chain drives

1. Effective peripheral force

2. Centrifugal force

3. Sagging force

where a——Center distance of chain drive, mm

——Mass per chain length, ㎏/m, See table 9-1

——acceleration of gravity, m/s2

——Hanging factor when hanging value

——sag degree

——angle of gradient,°

For perpendicular installation,

For horizontal installation,

4. Tight side force Ignoring dynamic loads

5. Loose side force

§9.6 Design of roller chain drives

1. Failures

⑴ Fatigue breakage of the link plates due to the repeated application of

the tension in the tight side of the chain

⑵ Pitting on bushings or rollers surface due to the impact of the rollers

as they engage the sprocket teeth.

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⑶ Wear between pins and bushings

Wear in the joints leading to elongation of the chain and faulty

engagement with the sprockets.

⑷ Gluing/veneer failure between pins and bushings owing to poor

lubrication or high speed

⑸ Impact damage caused by overload

⑹ Static strength failure of the joint elements for heavy load and low-

speed chain drives v 0 6. m / s

⑺ Wear of the sprocket teeth

2. Rated power curves for single strand

Experiment conditions:

z1 19 ;

Lp 100 pitches;

Single strand chain mounted horizontally

Steady load

Normal working environment

Recommended lubrication way, see fig 9.12

Service life of 15 000 h;

Relative elongation of chain causing by chain wear .

Fig 9.11: Rated power curve for A series of roller chain horizontally

centered shafts

Fig 9.12: → lubrication ways

type Ⅰ Artificial regular lubrication

type Ⅱ Drop lubrication

type Ⅲ Oil-bath lubrication or splash lubrication

type Ⅳ pressure-spray lubrication

If lubrication is poor or is not applied in the recommended way, value

7

in the figure should be reduced:

⑴ When , and no lubrication, → 015 0. P

⑵ When , poor lubrication, → 0 3 0 6 0. ~ . P

⑶ When 15 7. v m / s , poor lubrication, → 015 0 3 0. ~ . P

⑷ When v 7 m / s，lubrication must be used。

4. Modified power

The real working conditions are different from experiment condition.

Where —— Working condition factor

—— factor for number of teeth of small sprocket when ,

see Table 9.3

When failure is fatigue of plates (left fatigue curve),

When failure is impact fatigue of roller or bushing

(left fatigue curve),

—— chain length factor when , see Fig. 9.13

—— multiple-strand factor when number of strands does

equal 1 , see Table 9.4

4. Design procedure

Given: Transmitted power P,

Rotational speed of sprockets n1, n2 or speed ratio i

⑴ Specify numbers of teeth of sprockets and speed ratio

① Specify number of teeth of small sprocket

, see table 9.5

For smaller sprocket at very low speed, z 1min = 7.

uniform wearing，（relatively prime odd number）：17、19、21、23、25、38、

57、95、114

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② Compute number of teeth of big sprocket

Select an integer

Generally,

③ Compute actual speed ratio

， recommending

⑵ Determining the number of the

chain links

From the belt length

formula

And ， , we gain

The centre distance is usually recommended ，if we select

，the above equation is

Even number of pitches is better.

⑶ Determining the chain pitch

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The smaller the chain pitch, the lower dynamic load; the larger the

chain pitch, the bigger the power capacity.

Large pitch less-strand chain——low-speed heavy-duty,↑a↓i

Small pitch multiple-strand chain——High-speed heavy-duty, ↓a↑i

n1 P0 chain number, p

p, v recommended lubrication way

⑷ Computing chain length and center distance

① chain length

——the number of the chain links, the chain length in pitches

② Compute real center distance

Belt centre distance

Theoretical chain center distance:

In order to ensure a suitable sag: , actual center

distance is smaller than the theoretical.

The bigger value is for adjustable center distance.

⑸ Checking chain velocity

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Fig 9-11

Fig 9-12

⑹ Force acting on the sprocket shaft

where

⑺ Static strength for low speed v 0 6. m / s

Where — calculate safety factor

—the limiting tension force for single strand, see Table 9.1

—number of strands

— Service factor, see table 9-9

§9.7 Roller chain sprockets

1. Basic parameters and principle sprocket sizes

⑴ p— chain pitch

d1—the maximum diameter of bushing

pt—the strand distance for multiple-strand

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z—number of sprocket teeth

⑵ pitch diameter of a sprocket with z teeth for a chain with a pitch of p

is

Others can be seen in table 9-3, table 9-4

2. The shape of teeth three arcs-straight line 标注 3R GB1244-85

3. The structure of sprockets

4. Sprocket materials

Wear resistant, strength

Low carbon steel, medium carbon steel,

Low carbon alloy steel, medium carbon alloy steel,

Plain carbon steel,

Cast steel, gray iron

§9.8 Lubrication, arrangement and tensioning of chain drives

1. Lubrication methods

type Ⅰ Artificial regular lubrication

type Ⅱ Drop lubrication

5~20 drops/miniter Drop lubricator

type Ⅲ Oil-bath lubrication or splash lubrication

oil-disc

type Ⅳ pressure-spray lubrication

oil-pump, oil pipe

Lubricants:

L-AN32 20#

L-AN46 30#

L-AN60 40#

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2. Arrangement

3. Tension of chain drives

Regularly adjusting by adjuster such as screw and eccentric

Automatically tensioning by springs or hangers

Supporting plates for long centre distance

Tension wheel: maybe sprocket or toothless roller with diameter closed

to that of the small sprocket.

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