Chain Design Matters, Construction and Components

Author : ROSIE

Update time : 2023-02-13 11:35:01

Basic functions of chains

The chain has four basic functions:

1) To transmit power.

2) To convey goods and materials.

3) To convert rotary motion into linear motion or linear motion into rotary motion. 4) To run synchronously or according to the r

The above functions seem to be very simple, but in fact the details that must be grasped for each chain are very different.

3.2 General Chain Design Matters

This chapter deals with the general design of roller chains, toothed chains, engineering steel chains and flat top chains. These matters vary according to the function of each type of chain. Special design considerations for each type of chain are dealt with in later chapters.

The following discussion is brief rather than discussing these elements in detail. This chapter is intended only to inform the reader about the factors to be considered in chain design and not to teach the reader how to design chains.

3.2.1 Tensile Loads

1. Nominal Tensile Loads

The main consideration for all types of chains is the nominal tensile load, which is the basic function required to be achieved. The nominal tensile load generally fluctuates in a cyclical pattern. For example, the chain pull generated by the nominal tensile load in a drive increases when the chain is enclosed on the driven sprocket, remains largely at a high value when passing through the tight side, decreases when enclosed on the active sprocket and remains largely at a low value when running on the loose side. Figure 3-1 shows the variation of chain tension for a chain length of 100 links with a 20-tooth sprocket drive. The nominal tensile load is the basic load in almost all chain ratings.

2. Impact load

Shock loads are caused by the characteristics of the power source and the driven equipment. They recur periodically, usually once or several times per revolution of the working shaft. They are usually to be added to the nominal tensile load. Common shock loads for most chain drives and chain conveyors are represented using a service factor.

3. Inertia loads

Inertia loads are different from shock loads. Inertial loads are loads that are caused by extraordinary, usually accidental, events to

incidental loads on the chain. They can come from the start-up of a heavy conveyor or drive system with a large inertia flywheel, or from a sudden stoppage of the conveyor or driven equipment. The designer of the drive or conveyor chain should calculate the expected starting loads and ensure that they are never greater than the chain yield strength.

4. Centrifugal tension

In high-speed drives, centrifugal forces occur when the chain runs around the sprockets. There are also centrifugal forces when the chain runs in a curved path between two sprockets. The tension caused by centrifugal forces can be added to the nominal tensile load as appropriate. Centrifugal force is one of the factors affecting the power rating of the chain drive in the high speed zone.

5. Overhang Tension

The weight of the chain at the overhanging section causes additional tension in the chain. The tension load caused by the overhanging tension must also be added to the nominal tensile load as appropriate. Overhang tension is usually a secondary factor in chain drives, but it is a major consideration in chain conveyors.

6. Polygon effect

The chain actually forms an equilateral polygon on the sprocket. This causes the chain to move up and down each time the hinge engages with the teeth of the wheel. This movement is known as the polygon effect and is illustrated in Figure 3-2. The polygon effect causes the chain speed to increase or decrease each time the hinge engages the gear teeth. Naturally, the chain tension changes slightly with each change in chain speed. The change in tensile load due to the polygon effect must also be added to the nominal tensile load together with the other tensile load fluctuations mentioned above. The change in tensile load due to the polygon effect is one of the most important influencing factors when chains are driven at high speeds.

7. Vibration

Vibration of the chain at a frequency equal to or close to the self-oscillation frequency will cause a significant increase in the tensile load of the chain.

increase. The increase in tension due to vibration can sometimes be as great as the nominal tensile load. Any tensile load caused by vibration should also be added to the nominal tensile load. If necessary, the self-oscillating frequency of the system should be calculated, as recommended in the following sections. If it is found that there is a possible vibration problem, the system should be redesigned to avoid the self-oscillation frequency.

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