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Roller Chain Drives

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The popularity of chain drives stems from the ability of these drives 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 these drives 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% 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% 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. One of the major weaknesses of a roller chain drive is chain wear resulting in stretching or elongation. Manufacturers recommend roller chain replacement when elongation of approximately 3% has occurred. 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 or less. 

    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%-94% 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:

    • Versatility (functional attachments can be added to convey products, trip switches, actuate levers, etc.)      
    • Ability to create any length of chain with connecting links      
    • Availability of large selection of chains and sprockets


    V-Belt Drives

    V-belt drives transmit power through friction between the belt and pulley. With efficiencies ranging from 95% to 98% at installation, V-belt drives use energy more efficiently than roller chain drives, and somewhat less efficiently than synchronous belt drives. V-belt drives are an industry standard, offering a wide range of sizes at relatively low cost, along with ease of installation and quiet operation.

    V-belts are manufactured in a variety of materials, cross-sections and reinforcement materials, and are often used singly, in matched sets or in joined configurations. They are well suited for severe duty applications, such as those involving shock loads and high starting loads. Standard V-belt drives operate best in applications of 500 RPM or greater, speed ratios of up to 6:1, and within a limited operating temperature range of -40ºF to 130ºF. Because V-belts slip when overloaded, they help protect more expensive equipment from load surges. They also allow flexibility in the positioning of the motor and the load.

    In a suitable application, the service life of a properly installed and maintained V-belt drive ranges from 20,000 to 25,000 hours.  The components of a simple V-belt drive are relatively inexpensive to purchase, install, replace and maintain. After they are installed properly and tensioned to the belt manufacturer’s recommended values, these drives require very little service, except for retensioning during the normal maintenance schedule. Due to belt slippage, V-belt drives lose up to 5% of their efficiency after installation.  V-belts stretch as they wear, making slippage worse, which can decrease efficiency by as much as 10% unless corrected by periodic retensioning. Cogged or notched V-belts can increase efficiency by 2% over standard designs.


    Synchronous Belt Drives

    Synchronous belts work on the tooth-grip principle. Round, square or modified curvilinear belt teeth mesh with grooves on sprockets to provide positive power transmission on high-torque applications with high and low speeds.

    The components of a synchronous belt drive system typically cost more initially than those of a comparable standard roller chain drive or V-belt drive. By contrast, synchronous belt drives do not have the maintenance costs associated with roller chain drives. They require no lubrication and thus no lubrication system, only basic safety guarding. While roller chain requires frequent retensioning,  and V-belts require periodic retensioning, a synchronous belt typically requires no retensioning for the life of the belt.

    To illustrate the amount of elongation that can occur in a roller chain, recommended center distance take up allowances for belt drives can be compared to center distance take up needed for a roller chain in the same length. Assuming a length of 100 inches, a roller chain, V-belt and synchronous belt can be compared as follows:

    Roller Chain

    A roller chain will elongate about 3" (or 3%) over its life, requiring about 1.5" of center distance take up.

    V-Belt

    A V-belt requires 1.5" to 2.5" of center distance take up over its life, depending upon the cross section and manufacturer.

    Synchronous Belt

    A synchronous belt typically requires only .04" of center distance take up over its life, depending upon the belt type and manufacturer.

     

    Chain and sprocket wear are significant cost factors in a roller chain drive. Synchronous belts and sprockets experience dramatically less wear. In a Gates Poly Chain® GT®2 drive system, for example, the belt will outlast a comparable roller chain on the order of 3 to 1, and the sprockets will outlast roller chain sprockets 10 to 1.

    Like roller chain drives, synchronous belt drives are sensitive to misalignment and should not be used on systems where it is inherent to the drive operation. Misalignment leads to inconsistent belt wear and premature tensile failure due to unequal tensile member loading. And while a synchronous belt like Poly Chain GT2 is resistant to abrasion, corrosion and the caustic washdown solutions used in the food handling/processing industry, it may not be suitable for certain highly corrosive environments where corrosion resistant chain may be a better alternative.

    One misconception about synchronous belts is that they are unsuitable for serpentine drives. Design engineers may think that roller chain is the only option when a load must be driven off both sides; however, double-sided synchronous rubber belts like Gates PowerGrip® GT®2 Twin Power® offer many of the same cost-saving advantages over roller chain as their single-sided cousins.

    Due to their high efficiency ratings (as high as 99% on a continuous basis in a Poly Chain GT2 drive system), synchronous belt drives can also lower energy costs compared with roller chain drives, which typically operate at 91-94% efficiency, or V-belt drives, which when properly tensioned, operate at 93-95% efficiency.