Topics

• Introduction• Drive Chain Types• Sprockets• Sprocket Types• Chain Drive Safety • Roller Chain Installation and Maintenance

• Please read Chapter 11 in the text.

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Introduction Chains have been used for thousands of years. Chains were used on bicycles in the 1800’s Advantages of chain drives:Resistant to shock loadsCan transmit high torqueseconomical Drive Chain Function and Operation Main functions: Material handlingPower transmission

Source: http://www.osha.gov

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Chain Drive

3 Basic Parts:• Chain• Driver Sprocket• Driven

Sprocket

The Relative number of teeth between the driven sprocket and the driver sprocket determines the speed and torque of the driven shaft

Ratio of the teeth can be selected to increase or decrease speed or torque to the driven shaft

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R= Sprocket Ratio

= Number of teeth on driven sprocket

= Number of teeth on the driver sprocket

Sprocket Ratio Formula

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R= Sprocket Ratio

= Number of teeth on driven sprocket

= Number of teeth on the driver sprocket

Sprocket ratio is needed to calculate the speed and torque of chain drives

Example:Determine the sprocket ratio where = 33 teeth and = 20 teeth

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Chordal Action

The chain does not ride completely along the pitch line because each link is a rigid bar that cannot bend to follow the circular path

The chain links remain straight lines as they move around the pitch circle in chordal action

Chordal action is similar to the motion a train makes as its straight cars move through a turn in the tracks.

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The Chordal action of the chain links causes some frictional losses between sprocket and chain.

Friction occurs as each link engages the sprocket.

The roller helps reduce the frictional loss

The rising and falling of the links cause a slight speed variation in the chain drive causing the driven sprockets speed to oscillate.

The amount of oscillations depends on the number of teeth.

If #teeth > 25, oscillation is less than 1% and is disregarded.

The speed of the driven sprocket is determined by the sprocket ration. This is because the rate at which the teeth of the driven sprocket engage the chain is the same as the rate at which the driver sprocket teeth disengage the chain.

Different number of teeth constitutes different rotational speed as well as effecting the torque.

More teeth, less speed

More teeth, more torque

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= 1280 RPM

= 41 Teeth

= 12 Teeth

Chain Drive Speed Formula

Chain Drive Torque Formula

= 300 in-lbs

= 26 Teeth

= 14 Teeth

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Power is transmitted through a single strand roller chain when the driver sprocket rotates and its teeth engage the roller links, pulling the chain around it. This causes the chain to pull on the teeth of the driven sprocket, causing it to rotate.

The chain drive uses the engagement (or interlocking) of the sprocket teeth and chain to drive it.

Four common types of chains

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Roller Chain

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Rollerless Chain

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Silent Chain

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Leaf Chain

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The roller chain is the most common type of chain used in industrial chain drive systems

There are four basic types of roller chains

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Single-Strand Chain

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Multiple-Strand Chain

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Double-pitch Chain

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Offset Chain

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Components of a Roller Chain

Roller chain is made up of pin links and roller links

The links mesh with the sprockets so speed and torque can be transmitted

Roller links are similar to pin links, but are made of two side plates that are separated by bushings. The bushings support the rollers that are mounted to them

Roller links flex at the junction between links allowing rollers to freely roll reducing friction between the chain and sprocket

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The pin of the pin link passes through the bushing on the roller link to make an assembly

Roller Chain Components

Pitch

Roller Link Plates

Roller

Pin Link Plates

Pins

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Drive Chain Types• Roller Chain: most common type. ANSI numbers them such that first number is the pitch in

eighths of an inch.• Example: ANSI 50 indicates a chain of a pitch of 5/8’’ • Types of roller chains:

Multiple Strand Roller Chain: used to increase chain power capacity without increasing the pitch of the chain.

Heavy Series Roller Chain: have thick side plates, to withstand high shock loads. Identified by the letter H in the ANSI code.

Double Pitch Roller Chain: the pitch is two times longer than in standard roller chains. Self-Lubricating Roller Chain O-ring Chain: O-rings seal the lubricant in the joints.

• Engineering Chains: Offset Sidebar Chains Pintle, Mill, and Drag Chains Silent Chain: teeth are in continuous contact with sprocket, thus noise is reduced Leaf Chain Polymeric Chains Tabletop Chain.

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Sprockets

Bottom Diameter

Pitch Diameter

Outside Diameter

Length Through Bore

Face Width

Bore

Source: Drawing is in the public domain and was taken fromWikimedia Commons, Wikimedia Foundation

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Sprocket Nomenclature

Teeth (rim)

Body (plate)

Hub

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Standard Types of SprocketsA type: A plate sprocket with no hubs

B type: One hub projection (most common)

C type: The sprocket has hubs on both sides

D type: A sprocket with detachable bolts on the hubs

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Sprocket Part NumbersAmerican National Standards Institute (ANSI) maintains a standard for sprocket and chain design.

Example 1: A sprocket has the number 25A36-3/8’’ Then it is for a roller chain of a ANSI standard size of 25 and a A-style hub with 36 teeth and a bore diameter of 3/8’’.Exercise 1: A sprocket has the number 50B21-7/8’’ What is its bore diameter?What type is it, and how many teeth does it have?

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Special Sprocket TypesSplit Sprocket: to allow for installation of

halves around the shaft. Sectional Rim Sprockets: the rim is

sectioned into three parts to allow for replacement without uninstalling the sprocket.

Double Pitch SprocketShear Pin Sprockets: the hub is keyed to the

shaft, the sprocket is free to rotate on the shaft when the shear pin that couples it to the hub is broken.

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Chain Drive Selection • Drive Ratio: at most 7:1• Sprocket Size: As number of teeth increases,

variation of chain speed resulting from chordal action decreases.

• Center Distance: a good design practice is to use a center distance of about 50-80 pitches. It should not be long to avoid vibrations and pulsation.

• Idler Sprockets: a chain tightening device. Should have at least three teeth in engagement.

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Roller Chain Safety

1. Roller chain drives should be inspected after the first 100 hours of operation.

2. Regular inspections should be made once every three week intervals.

3. Chain safety guidelines: please read the guidelines on page 289 of the text.

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Roller Chain Installation and Maintenance

1. Chain installation and maintenance- Store in a dry location in lubricant- Drive interference: clean debris and built up material in between the sprocket

and chain.- Chain Case: the case is needed to protect personnel, isolate chain from

contaminant, and facilitate lubrication.- Chain and Sprocket Inspection:

1) Check for chain stretch (Chain elongation), Chain elongation should not exceed 3% (0.36’’ per foot).

2) Check side plates for misalignment, cracks, or wear.

3) Check for stiff and frozen chain joints

4) Check for corrosion in the chain drive parts.

5) Check for wobbly and loose sprockets.

6) Check for wear and scratches and changes on the teeth.

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MECH120010 Steps for Chain Installation, Alignment and Removal

1 – Mount and level the motor and driven component

2 – Inspect the Sprockets

3 – Mount the Sprockets on the shafts

4 – Mount the Chain

5 – Align the Sprockets

6 – Apply Tension to the Chain

7 – Apply lubrication to the Chain

8 – Run the Motor briefly to test the drive

9 – Recheck the chain sag

10 – Chain removal

Exercises1. You will be handed a sprocket. Measure the following?- The bore diameter- The pitch - The number of teeth- What type is the sprocket?- Compare your measurements to the ANSI number shown on

the sprocket.

2. Find the above specifications for the sprocket whose number is 60C80-5/8’’

3. What is the pitch of the chain with the specification 60?

4. What is the pitch of the silent chain specified as SC-608?

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