How to Select Round Belts and O-ring Belts
Round belts and o-ring belts are light- to heavy-duty power transmission belts. These products are also called endless drive belts or endless round belts.
Round belts are solid or hollow lengths of cylindrical material. They maintain contact with belt pulleys using friction and must be stretched or elongated to operate. Round belts are commonly used in typical power transmission applications, including industrial conveying, packaging machinery, photocopiers and printers, and imaging equipment.
Round belts on a conveyor component; . Image credit: Conveyor Technologies Ltd.
In addition to providing power transmission for straight conveyors, round belts can be twisted 90 degrees (a quarter turn) to turn a shaft whose axis is rotated a quarter turn from the drive shaft. The images below show belts being used in this arrangement.
Image credit: MHE | Cumberland Conveyor
Round belts are typically constructed of polymer materials, specific types of which have different strength, elasticity, and transmission characteristics.
Buna-N, or nitrile rubber, is a synthetic rubber copolymer of acrylonitrile and butadiene. It is resistant to petroleum hydrocarbons and is therefore useful in applications involving oils, hydraulic fluids, and alcohols. Buna-N's suggested operating temperature is approximately -30° to 275° F.
Neoprene is a synthetic rubber — produced by polymerization of chloroprene — which features good chemical stability and excellent flexibility in a wide range of temperature conditions. Like nitrile rubber, it also performs well in contact with oils and chemicals. Neoprene is known to withstand damage from twisting and breakage, and can effectively operate at temperatures from -45° to 230° F.
Polyurethanes represent a diverse group of polymers exhibiting excellent elongation, recovery, and toughness characteristics. They are also flexible and abrasion-resistant.
Rubber is a natural compound with uniquely elastic properties. Rubber types include gum rubber and latex.
Round belts and o-ring belts may be reinforced by an integral cord, braid, or wire. Like a belt's primary material, all reinforcement materials offer excellent tensile strength. Different materials — such as fiberglass, Kevlar®, polyester, and steel — feature different advantages relating to environmental resistance, abrasion resistance, and electrical insulation properties.
A round belt's size specifications — cross-sectional dimensions and length — are very important to consider when selecting belts for a specific application. The image below shows a cross-section of a hollow belt, with important specifications labeled. When selecting a solid belt, only outside diameter and outside circumference are applicable.
Image credit: Durabelt
In addition to cross-sectional dimensions, a belt's overall length is also very important to consider. In order to determine a belt's necessary length, a buyer must factor in specifications about the pulleys which will accommodate the belt: the center diameter of both pulleys, center distance between pulleys, and the belt's stretch percentage. Once these dimensions are determined, they can be plugged into a belt length calculator such as this one.
Image credit: Durabelt
In more complicated power transmission applications, two round belts can be connected using a round belt connector, and example of which is shown here.
A belt's tensile strength is the maximum recommended tension during normal operation and is specified in pounds, ounces, or other measures of weight or force. Working tension is based on a belt's material characteristics and preload stretching and elongation.
Standards related to conveyors and other power transmission components typically cover round belts and o-ring belts. Typical standards include:
A-A-51644 (Round belts in engines)
BS EN 14973 (Conveyor belts for underground applications)
ISO 22721 (Conveyor belts for mining applications)