The popularity of chain drives stems from their ability to transmit high torque levels in a small package, at relatively low cost, while utilizing readily available stock components. While initial costs of standard roller chain drives can be quite low, the cost of maintaining them can be substantial. Proper maintenance is essential for optimal roller chain drive performance and includes the following cost factors:

• Lubrication
• Alignment
• Tension
• Drive component replacement

According to chain industry estimates, roller chain drives operating without lubrication wear approximately 300 times faster than comparable drives that are properly lubricated. And yet, roller chain manufacturers estimate that 90 to 95 percent of all installed drives are either improperly lubricated or not lubricated at all. Determining the type of lubrication method needed is a major design consideration with cost implications of its own. An oil-retaining chain housing, for example, can represent up to 75 percent of total chain drive system cost. In addition to lubrication, proper sprocket alignment and chain tensioning are critical to increasing roller chain life.

Another maintenance factor with cost implications is drive component replacement. A major weakness of a roller chain drive is chain wear, which results in stretching or elongation. Manufacturers recommend roller chain replacement when elongation of approximately 3 percent occurs. Most roller chain manufacturers also recommend replacing sprockets with each new roller chain because the metal-to-metal contact generates severe sprocket wear.

Power rating tables published within the roller chain industry are based on a theoretical design life of 15,000 hours, assuming proper drive design, alignment, lubrication, maintenance, etc. But in a typical operating environment, actual drive life rarely approaches the ideal. Unlubricated roller chain drives operating under harsh conditions can be as short-lived as 100 hours.

The cost of the maintenance requirements noted above, added to the initial cost, approximates the true cost of a standard roller chain drive. However, beyond the cost of lubricant and drive component replacement is the labor expense of frequent retensioning, which requires shutting down the drive, resulting in production downtime. Also, standard roller chain drives operate at 91 to 94 percent efficiency, depending on the application, so energy costs must be taken into account.

Maintenance and energy costs notwithstanding, roller chain drives offer designers and users some advantages over V-belt or synchronous belt drive systems:

1. Versatility (functional attachments can be added to convey products, trip switches, actuate levers, etc.)

2. The ability to create any length of chain with connecting links

3. The availability of a large selection of chains and sprockets