September 27, 2003

By: Mark Harris
Website: http://www.bearing-n-bearings.com

Self-adjusting elastomeric chain/belt tensioners maintain drive bearing efficiency and reduce wear

Lovejoy ROSTA SE Series Elastomeric Tensioners provide automatic, continuous tensioning of chains and belts in mechanical power-transmission systems. Employing pre-loaded rubber torsion elements, SE Series models not only maintain drive efficiency without manual adjustment, they also absorb shock loads and vibrations. As a result, they extend chain/belt life by as much as 30 percent while minimizing wear of drive bearings and shafts.

The SE Series includes seven standard model sizes, as well as special high-temperature, oil-resistant, and stainless steel designs. With rubber elements set within a wide range of pre-load conditions, these self-adjusting tensioners generate and maintain prescribed deflection forces of 3½-1,124 lbs.

Unlike fixed and adjustable tensioners, Lovejoy ROSTA self-adjusting elastomeric models keep belts and chains taut continuously. Rubber torsional elements, under pre-load in the tensioner body, force the tensioning arm to automatically adjust for routine chain/belt stretch. This eliminates uneven drive surges and power losses created by otherwise sagging, slipping and slapping chains and belts. It also eliminates the need for frequent manual adjustments to re-tension the drive.

With the recommended angle of pre-tension, SE Series units generate prescribed deflection forces with the capability to absorb vibration and shock loads. SE Series units are most efficient when pre-tensioned to approximately 20°. A torsion angle scale on the element housing allows visual monitoring of chain/belt stretch. This enables users to quickly gauge when chains and belts need replacement, before drive efficiency drops and tensioning problems develop.

Unlike steel springs in other self-adjusting tensioners, ROSTA elastomeric torsion elements are not susceptible to breakage or wear. Standard elements provide optimal performance in temperatures from -40°F to +180°F and are unaffected by mud, dirt, water, and sunlight. With no metal-to-metal contact, they run silently and do not require lubrication.

Lovejoy ROSTA tensioners mount with a single bolt, providing 360° positioning flexibility on almost any drive frame. For "blind" frame structures, where standard through-bolt mounting is not possible, special SE-F models feature mounting bolts that tighten from the front. Where space restrictions dictate the use of a smaller tensioner body, a "hard" idler mounting hole -- located slightly closer to the arm/housing joint -- can be used to yield approximately 25 percent more force than the "normal" position.

In addition to standard models, the SE Series includes three design modifications for specific operating conditions. High-temperature SE-W models employ special heat-resistant rubber elastomers for systems subject to +180°F to +250°F temperatures, such as diesel engines and industrial driers. Oil-resistant SE-G models feature neoprene synthetic elastomers and zinc-plated housings for oil bath applications (gear boxes, crank cases) and those running in heavy oil mist; SE-G models can be used in temperatures from 0°F to +200°F. Corrosion-resistant SE-I models are constructed of stainless steel for food, chemical, pharmaceutical and other applications requiring complete corrosion resistance.

SE Series model sizes are designed for power-transmission systems using ANSI chain sizes from single-strand 25 to double-strand 240 and triple-strand 200; v-belt sizes A-E and 3L-5L; and flat belts of widths 1-6 inches.

Lovejoy offers a full range of bolt-mounted ROSTA idlers to support power-transmission chains, v-belts and flat belts. These include single- and double-strand chain sprockets; a flat belt or quiet chain pulley; v-belt pulleys; belt rollers; and heavy-duty plastic chain riders. All but the stationary rider feature permanently lubricated ball bearings for long life. Idler bolts included with all Lovejoy ROSTA tensioners also accommodate most standard industry brands of sprockets and pulleys.

Lovejoy ROSTA SE Series models also can serve as elastic spring devices for belt scrapers, cleaning brushes, brake bars, limit stops, conveyor shock absorbers, hold-down and guide rollers, and many other applications requiring maintenance-free, automatic tensioning.

Lovejoy has been a pioneer in the development and manufacturing of power transmission components since patenting the jaw coupling in 1927. Today, Lovejoy offers a full range of elastomeric, metal and specialty couplings and is an important supplier of universal joints, chain/belt tensioners, motor bases and variable-speed pulleys. The company's broad line of products is available through a worldwide network of PT distributors, supported by 20 sales offices and seven regional warehouses across North America and Europe.

About The Author:

Mark Harris is a successful author and regular contributor to http://www.bearing-n-bearings.com.  Keep things running smoothly with ball bearings, roller bearings, ball thrust bearings and tapered bearings.