KEVOS® MAKEOS · Power Transmission
Silent Chain Width for a Power (Rating per Unit Width and Service Factor)
How wide must a silent (inverted-tooth) chain be to carry my power with the service factor for the drive, from the chain’s rating per inch of width at my sprocket and speed, and does the width I have chosen carry it?
Silent chain width by the rules the handbook gives with the American Chain Association ratings: horsepower capacity per inch of width = rating per inch ÷ service factor, and the chain width for a given power = power × service factor ÷ rating per inch. Here in kilowatts with the rating per 25.4 mm of width entered from the rating table for the pitch, the small sprocket teeth and its speed, giving the width needed and the capacity of the width you choose, with the lubrication type the rating table shows.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Power to transmit | kW | Power transmitted by the drive. |
| Service factor | Service factor for the driver and driven machine from the chain maker’s or handbook’s service factor table. | |
| Rating per 25.4 mm (1 in) of width from the table | kW per 25.4 mm | Power rating per inch (25.4 mm) of chain width from the rating table for the chain pitch, the number of teeth on the small sprocket and its speed (1 hp = 0.7457 kW). |
| Chain width chosen | mm | Width of the chain you intend to use, from the standard widths for the pitch. |
| Lubrication the rating table shows | choice | Type of lubrication the rating table shows at that pitch, sprocket and speed. |
| Lubrication the drive will have | choice | Type of lubrication the drive will actually have; it must be the type shown or better. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Power to transmit
- What it is
- Power the silent chain drive must transmit.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The width needed grows in proportion.
- Get it right
- Use the motor rating or the measured power of the driven machine.
What this means: Service factor
- What it is
- Service factor for the driver and the driven machine.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The width needed grows in proportion.
- Get it right
- Take it from the service factor table for the type of load and hours a day.
What this means: Rating per 25.4 mm (1 in) of width from the tab…
- What it is
- Power rating per 25.4 mm (1 in) of chain width from the rating table.
- Units and format
- Enter a number in kW per 25.4 mm: kW per 25.4 mm. The form accepts 0.000001 kW per 25.4 mm to 10000 kW per 25.4 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 9 kW per 25.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The width needed falls as the rating rises.
- Get it right
- Read it for the chain pitch, small sprocket teeth and speed; 1 hp = 0.7457 kW.
What this means: Chain width chosen
- What it is
- Width of the chain you intend to use.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 127 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the width check and the capacity reported.
- Get it right
- Choose from the standard widths for the pitch, next above the width needed.
What this means: Lubrication the rating table shows
- What it is
- Lubrication method the rating table assumes for this drive.
- Units and format
- Choose one of 3 options from the list: Type I: manual, brush or oil cup; Type II: bath or disc; Type III: circulating pump.
- Example
- The form opens with “Type II: bath or disc” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the lubrication the drive needs.
- Get it right
- It is marked on the rating table beside the rating you use.
What this means: Lubrication the drive will have
- What it is
- Lubrication method the drive will actually have in service.
- Units and format
- Choose one of 3 options from the list: Type I: manual, brush or oil cup; Type II: bath or disc; Type III: circulating pump.
- Example
- The form opens with “Type II: bath or disc” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Fails the drive if poorer than the rating assumes.
- Get it right
- Bath or disc lubrication needs an oil-tight casing; avoid greases.
Method and formulas
- Capacity per inch of width = rating per inch ÷ service factor.
- Width needed = power × service factor ÷ rating per inch (× 25.4 mm).
- Capacity of the chosen width = (width ÷ 25.4) × rating per inch ÷ service factor.
- The drive must have the lubrication type the rating shows or a better one (I < II < III).
- Example: 30 kW with a service factor of 1.4 at 9 kW per inch needs 118.53 mm of chain; the 127 mm chain carries 32.143 kW.
Limitations
- The ratings are for a life of about 15,000 hours under the conditions of the rating tables; take them from the table for your pitch, sprocket and speed.
- Chain widths come in standard steps for each pitch; choose the next standard width above the width needed.
- Sprocket sizes, chain length and centre distance are in the silent chain drive check tool.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a silent chain width for a drive
- Check the capacity of an existing silent chain
- Compare pitches for a drive by the width each needs
Who it is for
- Machine designers
- Maintenance engineers
- Drive specialists
What you get
- Capacity per 25.4 mm of width after the service factor
- Chain width needed
- Capacity of the width chosen
- Lubrication check
Interpreting the result
- If the width needed is large, a larger pitch or a faster small sprocket (more teeth) raises the rating per inch.
- The lubrication type matters as much as the width: a chain run with poorer lubrication than the rating assumes wears out early.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3475–3476. Topic reference; no source tables or recommended settings are reproduced.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Silent Chain Width for a Power (Rating per Unit Width and Service Factor) calculator