Calculation and Practical Application of Chain Drives

I. Selection and Calculation of Chain Drives (Key Focus)

The selection logic is Working backward from the load to the motor , determine the parameters step by step in the following order.

1. Determine the basic parameters

Assume a typical operating condition:

• Load weight: m = 500 kg
• Conveying speed: v = 0.3 m/s
• Operating condition: Steady-state operation, motor-driven
• Gear ratio: 1:1 (or given)

2. Tensile Force Calculation

The primary force that a chain must overcome when pulling a load is friction:

• (F) : Tension ( N )
• (mu) : Coefficient of friction (ultra-high-molecular-weight polyethylene is commonly used for chain guides, (\mu \approx 0.1) )
• (m) : Load mass ( kilogram )
• (g) : Gravitational acceleration, take (9.8 \text{ m/s}^2)

Example Calculation F=0.1×500×9.8=490 N

Note: If the chain itself has a substantial mass, it should also be included in the total mass.

3. Power Calculation

Power required by the load:

P = F · v P = 490 × 0.3 = 147 W This is Load power , not the motor power. Subsequent considerations will also include transmission efficiency and relevant coefficients.

4. Sprocket Speed Calculation

Given linear velocity (v) and the pitch diameter of the sprocket (D) ：

• (n) : Rotational speed ( r/min )
• (D) : Pitch circle diameter ( m )
• (v) : Linear velocity ( m/s )

Without a reducer, the sprocket speed = Motor output speed.
The calculation is based on the smaller sprocket.

5. Correction of Power Calculation

When selecting a chain, you must consult the table using the corrected power:

• (PC) : Corrected power ( kW )
• (P) : Transmitted power ( kW )
• (f1) : Operating condition factor
• (f2) : Number of teeth coefficient

Operating condition coefficient (f1) Select Reference

Motor-driven, with no more than daily starts 2 Use the smaller value under these conditions, and the larger value when the internal combustion engine is driven and starts frequently.

Number of teeth coefficient f2

With 17 Based on the tooth, f2=1.5 . The fewer the number of teeth, the larger the coefficient. Refer to the handbook or selection charts for specific values.

6. Power Correction for Multi-Row Chains

If a double‑row or triple‑row chain is selected, the load‑carrying capacity of a single‑row chain must be multiplied by a corresponding factor:

7. Safety Factor Verification

For conveyor chains or lifting chains, a tensile strength verification is also required:

• Fmin Breakage: Minimum breaking load of the chain (refer to the manual)
• Coefficient 0.15 The corresponding safety factor is approximately 6 times

8. Summary of the Selection Process

1. Determine the load and speed. → Calculate the tensile force (F)
2. Calculate the load power (P = F \ v)
3. Determine the sprocket rotational speed. (n)
4. Select the operating condition coefficient. (f_1) and the number-of-teeth coefficient (f_2)
5. Calculate the corrected power (P_c = P \ f_1 \ f_2)
6. Check the selection chart or table. : with (P_c) As the vertical axis, (n) Use the horizontal axis to determine the chain model (e.g., 08A、 10A etc.)
7. Verification Tension : Ensure Chain breaking load
8. Determine the number of sprocket teeth. : Prioritize selection 17 Above the teeth, odd-numbered teeth take priority.

II. Machining of Sprockets and Drawing Annotations (Practical Section)

1. Hole Machining and Tolerances

Commercially available sprockets may be unperforated or pre‑drilled, and typically require custom machining.

Processing sequence : First machine the hole positions. → Re-machined keyway
Bore–shaft fit : The bore diameter should be similar to the shaft diameter.
Common Tolerances ：

• Hole Tolerance: h7 (Commonly used)
• Shaft tolerance: g6 (In general), select when under heavy load.  k6

2. Keyway Dimensions and Tolerances

With shaft diameter 35 mm For example:

• Consult the manual to determine the key specifications: 10 × 8
• Keyway width: Obtained from the table   3.3 mm
• Keyway width tolerance: Typically adopted as  js9

3. Symmetry Annotation

The symmetry tolerance is determined from the handbook based on the datum dimension.
Example: Baseline dimension 10 mm At that time, symmetry tolerance   0.01 mm

4. Key Points for Engineering Drawing Annotation

• The diameter dimension must be fully annotated; it cannot be indicated by the radius alone.
• Roughness: Sprockets are typically marked.   3.2 μm , Special requirements may be indicated.   1.6 μm
• Common fit tolerances for sprocket shafts  N9

5. Special Requirements for Plate Chain Conveyors

• Sprockets are usually Paired configuration , using a buried installation method
• The keyway position of the sprocket assembly must… Relatively coincident with the roller center , otherwise it will not synchronize
• When marking, use the tooth center or roller center as the datum.

III. Chain Lubrication

Chain lubrication method is selected based on the linear speed:

• Low speed: Manual periodic lubrication
• Medium speed: Oil-drop lubrication
• High-speed: oil-bath or oil-spray lubrication

IV. Common Issues and Challenges

1. Polygon effect What is it?
When the chain wraps around the sprocket, it does not follow a perfect circular path but instead traces a polygonal trajectory, resulting in fluctuations in instantaneous velocity. The fewer the number of teeth on the sprocket, the more pronounced this effect becomes.

2. Why can’t chains be selected using the same criteria as gears?
Chain selection is System Design , the motor, sprockets, and operating conditions must be considered as an integrated system; the chain should not be selected in isolation.

3. What should you do if power and RPM data are unavailable?
First, review the foundational theories from the earlier stages, working backward from the load. Power and rotational speed are the cornerstones of equipment selection—both are indispensable.