In any friction-driven conveyor system, the most fundamental concept is the relationship between the Tight Side Tension (T 1 ) and the Slack Side Tension (T 2 ) . If you get this ratio wrong, your drive pulley will slip, your belt will wear out prematurely, or your take-up counterweight will be too light to maintain traction. In this guide, we will use CEMA standard calculations to determine the correct tensions and take-up weight. Table of Contents 1. The Basics: T1 vs T2 2. Euler’s Equation (The Grip Formula) 3. Worked Example: Calculating Tensions 4. Take-Up Units: Gravity vs Screw 5. Common Failure Modes Advertisement 1. The Basics: T1 vs T2 Imagine a conveyor belt running over a drive pulley. The motor pulls the belt, creating a tension differential: T 1 (Tight Side): The tension pulling the loaded belt toward the drive pulley. This is the highest tension point in the system. ...
Figure 1: Roller chains provide positive, non-slip engagement for heavy-duty power transmission.
A chain is a power transmission element made as a series of pin-connected links. Unlike belts, chains provide a positive engagement (no slip) and can transmit massive tensile forces. When transmitting power between rotating shafts, the chain engages mating toothed wheels called sprockets.
The most common type is the Roller Chain. A hardened steel roller on each pin allows the chain to roll seamlessly into the sprocket teeth, reducing friction and wear significantly compared to older bushing chains.
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1. Decoding the Numbers: ANSI Standard Sizes
Standard roller chains (ANSI B29.1) are designated by a number system that tells an engineer the pitch instantly.
Rule of Thumb: The digits (excluding the final zero) indicate the pitch in eighths of an inch.
Figure 2: The anatomy of a chain link. Proper lubrication must penetrate between the pin and bushing.
- No. 40: 4/8" = 1/2 inch pitch
- No. 80: 8/8" = 1.0 inch pitch
- No. 200: 20/8" = 2.5 inch pitch
Common Suffix Codes:
- H (Heavy): Thicker side plates for higher fatigue resistance (e.g., 60H).
- SS (Stainless): For food processing or corrosive environments.
- C (Double Pitch): Extended pitch used for long conveyor runs to save weight.
2. Power Ratings & Multi-Strand Factors
Chain ratings consider three specific failure modes:
- Plate Fatigue: Failure due to cyclic tension load.
- Roller Impact: Failure from engaging teeth at high speeds.
- Galling: Micro-welding of the Pin/Bushing due to lack of lubrication.
The Multi-Strand Myth:
Adding a second strand does not double the capacity. Because load is never perfectly shared across the width of the chain, you must use these derating multipliers:
Adding a second strand does not double the capacity. Because load is never perfectly shared across the width of the chain, you must use these derating multipliers:
| Strands | Load Multiplier |
|---|---|
| 2-Strand | 1.7x |
| 3-Strand | 2.5x |
| 4-Strand | 3.3x |
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3. The #1 Enemy: Chain Elongation (Stretch)
Chains do not actually "stretch" like a rubber band. They get longer because the Pins and Bushings wear down, creating sloppy clearances at each pitch.
Figure 3: Elongation occurs at the pin/bushing interface.
Maintenance Rule: When a chain elongates by 3% (or 1.5% for fixed centers), it must be replaced. If not, the mismatched pitch will grind the sprocket teeth into "hook" shapes, destroying your expensive sprockets.
4. Design Guidelines Checklist
- Minimum Teeth: Use at least 17 teeth. Fewer teeth cause "Chordal Action" (the polygonal effect), resulting in significant vibration and noise.
- Wrap Angle: Ensure a minimum 120° wrap on the small sprocket to distribute load.
- Tensioning: Chains need slack! The slack span should have a sag of 2-4% of the center distance. Never tension a chain tight like a V-belt.
- Lubrication:
- Slow Speed: Manual drip or brush (SAE 30 oil).
- High Speed: Oil bath or pressure spray is mandatory to remove heat.
5. Reference & Further Reading
Robert L. Mott, Machine Elements in Mechanical Design
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