Keeping plants rolling

They loop in and around manufacturing plants, powering conveyor systems, assembly lines and a variety of machines. Some stretch for hundreds of yards (or even miles) and others reach only a few feet or less. Roller chains play a vital role in keeping industry moving.

This article offers a brief review of how roller chains operate.

Roller chains are used in power transmission designs of all kinds and in many specialized industries. They’re made up of roller links joined with pin links. The links are comprised of an inner plate, outer plate, pin, bushing and roller. Pins pass through the rollers and side plates to hold the links together.

The plate bears the tension placed on the chain. The plate needs enough strength to stand up to load and shock and often must withstand environmental factors such as dirt, oil and temperature.

The pin is subject to shearing and bending forces transmitted by the plate. Together with the bushing, it forms a load-bearing part when the chain is in use, so the pin needs high tensile and shear strength, resistance to bending and also must have sufficient endurance against shock and wear.

The bushing is also subject to shearing and bending stresses transmitted by the plate and roller, and shock loads when the chain engages the sprocket. It also requires great tensile strength against shearing and must resist shock and wear.

The roller is subject to impact load as it strikes the sprocket teeth while the chain is engaged with the sprocket. Then, the roller changes its point of contact and balance and is held between the sprocket teeth and bushing, moving on the tooth face while receiving a compression load. As a result, the roller must resist wear and still have strength against shock, fatigue and compression.

Standard configurations include single, double, triple, quadruple, quintuple or higher. A single configuration has one chain strand. A double configuration has two strands and so on. Roller chain comes in a wide variety of metal and plastic materials. Many factors, such as cost, environmental conditions, noise and heat generation influence the choice of material. Chain manufacturers can recommend the proper material and type of chain for the application.

Common features for roller chain include attachment chain, double pitch, oversized roller, rollerless, offset link, heavy-duty, self-lubricating, corrosion resistant and flexible.

Connecting links join the two ends of the chain together and come in multiple configurations. Slip-fit are the most common. The pin and link plate are slip-fit in the connecting link for ease of assembly. This type of connecting link has 20 percent to 30 percent lower fatigue strength than the chain itself.

Press-fit links utilize pitch holes in the cover plate that are smaller than the chain pins, requiring the user to press the cover plate onto the pins before installing the spring clip or cotter. This type of connection provides the greatest load carrying capacity.

Offset links are used when an odd number of chain links are required.

Roller chain is sized by pitch, which is the center-to-center distance between the pins. This is done in 1/8-inch increments, and the pitch number is found on the side bars of the chain. Some roller chain comes with a double pitch, meaning that the pitch is double that of a standard chain, but the width and roller size remains the same. Double-pitch chain can be used on standard sprockets, but double-pitch sprockets are also available. The main advantage to the double-pitch chain is that it is cheaper than standard pitch. As a result, they’re often used in applications requiring slow speeds, such as lifting pieces of equipment.

There are a number of important mechanical specifications to consider when selecting roller chain, including tensile strength, maximum allowable load and chain weight. Tensile strength is the ultimate failure tension load of a chain. The maximum allowable load is the tension the chain is rated to carry in running operation. Chain weight is specified in weight per unit length, and varies with pitch and special construction techniques.

This article originally appeared in the March '04 issue of Progressive Distributor magazine. Copyright 2004.

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