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Chain drives are the backbone of material handling, serving as the critical link between the drive unit (motor/gearbox) and the driven unit in a conveyor system. Unlike belt drives, they provide a positive, non-slip transmission of mechanical power, making them ideal for heavy loads and precise timing applications.
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Figure 1: Chain drives provide positive, non-slip power transmission for heavy-duty conveyors.
Chain drives can consist of single or multiple strand chains, depending on the load requirements. The chains need to be matched with the correct sprocket type and tensioned properly to prevent slippage and reduce maintenance costs.
Anatomy and Sizing
Chain is sized by the pitch, which is the center-to-center distance between the pins. In the ANSI standard, this is measured in 1/8" increments.
"The first digit(s) indicate the pitch of the chain in eighths of an inch. The last digit indicates the type."
- #40 Chain: 4/8" = 1/2" Pitch
- #60 Chain: 6/8" = 3/4" Pitch
- #80 Chain: 8/8" = 1" Pitch
Conveyor Roller Chain Design
Figure 2: A Master Link (Connecting Link) is used to close the chain loop.
Roller chains are made up of roller links joined with pin links. The roller reduces the friction between the chain and the sprocket, increasing the life of the unit.
Roller chain is ordinarily connected using a Master Link (or connecting link), which typically has one pin held by a clip. Half links (offsets) are available to increase length by a single roller, but they should be avoided if possible as they reduce strength.
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Design Rule: Even Links, Odd Teeth
To maximize the life of your sprockets and chain, follow this engineering rule:
1. Chain Links Should Be Even: This allows you to use a standard Master Link. Using an odd number of links requires an Offset Link, which is structurally weaker (often reducing load capacity by 30%).
2. Sprocket Teeth Should Be Odd: If you use a sprocket with an odd number of teeth (e.g., 17, 21), it creates a "hunting tooth" effect. This ensures that every roller contacts every tooth eventually, distributing wear evenly across the sprocket.
Double Pitch Chain
Some roller chains come with a double pitch. This means the pitch is double that of a standard chain (e.g., A2040 vs #40), but the width and roller size remain the same.
The main advantage is cost. Double pitch chain is cheaper and lighter, making it perfect for long, slow-moving conveyor applications.
Maintenance: When to Replace?
It is advisable to monitor the exact length of a drive chain. The generally accepted rule of thumb is to replace a roller chain which has elongated 1.5% to 3%. Beyond this, the chain will ride up the sprocket teeth, destroying the expensive sprockets.
The Elongation Formula:
% Wear = × 100
M - (S × P)
S × P
Where: M = Measured Length, S = Number of Links Measured, P = Pitch
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