5.3 Roller Chains, Sprocket Alignment & Lubrication

ANSI Roller Chain Size Designations & Anatomy

Industrial roller chains provide positive, non-slip power transmission over wide center distances. In North America, precision steel roller chains are manufactured in compliance with ANSI B29.1 standards.

ANSI Size Coding Standard

ANSI chain numbers use a systematic multi-digit code:

• First Digit(s): Indicates chain pitch in 1/8 inch increments.
  • #40 Chain: 4/8 in = 1/2 in (12.7 mm) pitch
  • #50 Chain: 5/8 in (15.875 mm) pitch
  • #60 Chain: 6/8 in = 3/4 in (19.05 mm) pitch
  • #80 Chain: 8/8 in = 1.0 in (25.4 mm) pitch
  • #100 Chain: 10/8 in = 1-1/4 in (31.75 mm) pitch
• Second Digit: Indicates chain construction type:
  • 0: Standard roller chain construction
  • 1: Lightweight chain series
  • 5: Rollerless (bushing) chain series
• Suffix H (Heavy Series): Indicates extra-thick side link plates (e.g., #80H has the link plate thickness of a #100 chain on a #80 pitch), increasing fatigue resistance.
• Strand Suffix: Multi-strand chains use hyphens (e.g., #60-2 for double-strand, #80-4 for quadruple-strand).

Roller Chain Assembly Breakdown
       +--------------------------------------------+
       |  Outer Pin Link   |   Inner Roller Link    |
       +-------------------+------------------------+
       | Pins press-fit    | Bushings press-fit     |
       | into outer plates | into inner link plates |
       |                   | Rollers spin free      |
       +--------------------------------------------+

Master Link Spring Clip Orientation

Connecting (master) links join chain ends. On spring-clip master links used in single-direction drives:

CRITICAL INSTALLATION RULE: The closed curved end of the spring clip MUST point in the direction of chain travel. If installed backwards, the open split prongs can catch on machine guards or sprocket teeth, stripping the clip and dropping the chain.

Sprocket Kinematics & Chordal Action

Unlike smooth belt sheaves, a sprocket operates as a polygon rather than a true circle. When a roller chain engages a sprocket, the chain links seat along flat chordal lengths between tooth pockets.

Chordal Action (Polygon Effect)

As the sprocket rotates at uniform angular velocity, the effective radius where the chain pin engages fluctuates between:

• Maximum Pitch Radius (R): $R = \frac{P}{2 \cdot \sin(180^\circ / N)}$
• Minimum Chordal Radius (r): $r = R \cdot \cos(180^\circ / N)$

Where P is chain pitch and N is sprocket tooth count.

Chordal Action (Polygon Effect) Diagram
                  Max Radius (R)  ---> Outer Pitch Circle
                     / \
                    /   \  <--- Flat Chordal Link
                   /     \
                  +-------+  ---> Min Radius (r = R * cos(180/N))
                 Center of Sprocket

This radius variation causes the linear velocity of the chain to fluctuate continuously during rotation according to the ratio:

$\frac{V_{\min}}{V_{\max}} = \cos\left(\frac{180^\circ}{N}\right)$

Operational Impact of Low Tooth Counts (N < 19):

• High Chordal Vibration: Causes severe cyclical shock loads across the driveline.
• Impact Noise: Rollers strike the bottom of sprocket tooth gullets with high velocity.
• Mitigation: Millwrights should select driver sprockets with at least 19 to 21 teeth for medium-to-high speed drives, and use an odd number of teeth to establish a hunting tooth pattern that distributes tooth wear evenly.

Sprocket Shaft Alignment & Chain Wear Elongation

Sprocket Alignment

Sprocket alignment requires verifying two conditions:

1. Shaft Parallelism: Driver and driven shafts must be parallel in both horizontal and vertical planes.
2. Axial Coplanar Alignment: Sprocket tooth faces must lie in the exact same axial plane.

Coplanar Sprocket Face Alignment
   Driver Sprocket              Driven Sprocket
   +-------------+              +-------------+
   |  Sprocket   |  <---------  |  Sprocket   |  <-- Precision Straightedge
   +-------------+  Alignment   +-------------+      Touches 4 Points

Chain Elongation Wear Limits

Roller chain "stretch" is not caused by metal plate stretching under tension. It is caused entirely by frictional wear between the articulating pin outer surface and the bushing inner bore.

As pin material wears away, the pitch length of each individual link increases. To measure elongation:

1. Shut down and lock out the drive.
2. Pull the upper strand of chain tight.
3. Measure the span distance (M) over 12 to 24 pitches using a precision steel tape or chain wear gauge.
4. Compare measured length M to nominal un-worn length L (L = Number of Pitches × P).

$\% \text{Elongation} = \left( \frac{M - L}{L} \right) \cdot 100$

Chain Wear Elongation Limits
- Standard Drives: Replace chain when elongation reaches 3.0%
- Fixed-Center / Cut-Tooth Drives: Replace chain when elongation reaches 1.5%

Sprocket Destruction Hazard: Operating a chain elongated beyond 3% forces rollers to climb high onto the sprocket tooth tips. This quickly wears hook-shaped profiles into sprocket teeth, destroying the sprockets.

Industrial Chain Lubrication Regimes

Proper lubrication reduces pin-bushing friction, flushes out wear particles, dissipates frictional heat, and cushions roller-tooth impact. Oil must be directed onto the edges of the link plates on the lower slack strand, allowing centrifugal force and capillary action to draw oil into the internal pin-bushing joints.

Lubricant Application Point
   Top Strand (Tension Side)    =========================>
   Sprocket                                              Sprocket
   Bottom Strand (Slack Side)   ====[ OIL APPLIED HERE ]====>
                                    Apply between inner
                                    & outer link plates!

Standard Lubrication Delivery Regimes (ANSI / ISO)

Lubricant Selection Rules

Millwrights must specify high-quality non-detergent petroleum oils (typically ISO VG 68 to ISO VG 220 depending on ambient temperature).

CRITICAL RULE: Heavy grease or tacky open-gear compounds must NEVER be applied to high-speed roller chains. Heavy grease cannot penetrate the tight clearances (0.025 to 0.05 mm) between pins and bushings, trapping abrasive dirt on outer rollers while allowing internal joints to run dry and seize.