If you ever peer inside the drive of a conveyor, hoist or palletizer, you will notice a myriad of mechanical parts all moving as an interconnected system. These power transmission components are the devices that drive materials handling equipment.

Unfortunately, too many managers don't notice such devices until the power transmission parts wear out and the equipment stops running. Recognizing some of the basic power transmission components, how they drive equipment and how they can fail are important steps to keeping materials handling equipment up and running.

A bearing reduces friction by allowing parts to easily roll over each other. Without bearings, machine parts would constantly wear out.

Bearings incorporate an inner and outer metal ring with metal balls or rollers usually housed securely inside. They are connected to shafts, which are straight rotating rods forcing other parts of a power transmission drive to move. Shafts are held together with a small cylindrical mechanism called a coupling.

The two types of bearings are plain and anti-friction. A plain bearing has a revolving round element sliding inside a stationary element. Plain bearings generally support light loads on low-speed equipment.

More commonly used in materials handing equipment is the anti-friction bearing, which comes in two designs. One has a spherical shape (commonly called a ball bearing) while the other has a cylindrical shape (often called a roller bearing). In both types, one or two rows of the bearings fit between an inner and outer ring of the structure. Typically, ball bearings handle a lighter load than roller types, but both are well suited to high-speed applications.

Bearing maintenance begins with proper lubrication. A lubricant reduces sliding friction by creating a protective layer between the ball or rollers and the outer ring. Oil lubricants are generally suited to high-speed, high-temperature applications, but are difficult to keep inside the bearing housing. A grease lubricant, usually used for low- to moderate-speed applications, easily stays inside the housing, making it ideal for sanitary applications.

Gears are another common power transmission component. The teeth of these circular devices fit into the teeth of an adjoining gear, synchronizing the two and preventing slippage. In addition to transmitting power, they change speed and the direction of rotation. Most importantly, they reduce a motor's output speed while increasing torque, the force producing the rotary motion. This function is called gear reduction.

There are several types of gears- spur, helical, bevel, hypoid and worm- that are classified by the shape of the teeth and angle at which the gear is mounted to a shaft.

The gear type used depends on the application speed or load. For instance, spur gears, which have straight teeth, are generally used on equipment operating at moderate speeds, such as a hoist. Helical gears, however, have angled teeth, making them more efficient at higher speeds. And worm gears with their spiral-shaped teeth resembling a screw, are ideal for producing large gear reductions.

A set of gears connected to shafts and bearings is often enclosed in a sealed metal housing called a gearbox or speed reducer. Despite the protection of a gearbox, misuse and poor maintenance can result in serious gear-drive failures such as broken gear teeth and lost bearing rollers. To avoid failures, check lubricant levels every six months or at 2,500 operating hours, and match the speed reducer load capacity to the motor's horsepower. For example, a motor delivers maximum torque upon starting. If a motor's capacity or horsepower is too high for the gearbox, the motor will overpower the gears and eventually deteriorate the gear's teeth.

Power transmission belts are as useful in driving equipment as gears. Easy to install and maintain and relatively inexpensive, belts operate with little noise and without lubrication while providing shock load dampening.

The three basic types-V, synchronous and flat-are characterized by the belt's shape and use inside a power transmission drive.

V-belts, which are generally inexpensive and available in many sizes, operate over a wide horsepower range and at speeds up to 6,500 feet per minute.

Synchronous belts, like gears, have notches that fit into the grooves of a drive's pulley. They are ideal for applications where precise positioning and constant speed are required, such as in sortation machines and various conveyors.

Flat belts, which are made from reinforced, rubberized fabric, can operate at speeds over 20,000 feet per minute. However, they require more maintenance compared to the other two types of belts.

Power transmission belts will not have long service lives though if their tension is improper, are misaligned or operate at inappropriate speeds or loads. Belt failures occur due to slippage, cracks and breaks, and overheated belt drives. Belt tension should be readjusted periodically based on manufacturer's specifications. The temperature in the warehouse also affects a belt's performance and service life. Most belts that are correctly tensioned, aligned and operated at suitable horsepower rates run for approximately 25,000 hours in ambient temperatures of 85 degrees. But when operated at significantly higher temperatures, belts have a drastically reduced service life.

Power Transmission 101

Want to learn more about the fundamentals of power transmission?

Take a seat and open your textbook. The Power Transmission Distributors Association (PTDA) has published the 3rd edition of its informative handbook. This indispensable educational tool, reference source and resource manual illustrates the basics and applications of power transmission components from bearings to belt drives, gears to motors. Written for entry-level individuals in an easy-to-read format, the handbook has 14 definitive chapters with charts, diagrams, drawings and photos and includes maintenance and diagnostic tips as well as application and selection criteria and standards. An accompanying workbook and answer guide also provides true/false, multiple choice and short answer questions on each chapter. Power Transmission Distributors Association $34.95 for members, $43.70 for non-members.

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