1. Technical Field
This invention relates to drive and idler pulleys generally used in belted conveyor systems and, in particular, to a conveyor pulley with helical grooving formed in the surface of the pulley.
2. Description of the Related Art
In operation, the typical belted conveyor system uses a multiplicity of both drive and idler rollers or pulleys. Generally speaking, the drive rollers or pulleys are the means by which force is applied to the belts within the system, thereby causing movement of the belts as they carry various materials throughout the system. The idler rollers or pulleys are generally used to provide support for the belts in the system. The idler pulleys are also generally capable of being adjusted in such a manner as to increase or decrease the tension of the belts within the system, thereby enhancing the ability of the drive pulleys to move the belt and to reduce belt wear.
For the purpose of the present description, the terms "pulley" and "roller" may be used interchangeably. In general, however, the term "pulley" will be employed with the understanding that the term also embraces "rollers."
Conveyor pulleys can be covered with an multitude of materials that are attached by various methods. This covering, referred to as lagging, is used to: (1) increase the coefficient of friction between the conveyor pulley and the belt, (2) reduce the wear on the conveyor pulley face and the conveyor belt, (3) effect a self-cleaning action on the surface of the belt and pulley, and (4) improve the tracking of the belt. The most commonly used lagging is made of elastomeric compounds, which are bonded and cured by vulcanization, to the pulley core and extend around the pulley. Other common methods of attaching the lagging materials to the pulley include bolting, painting, cementing, and spraying. Lagging thickness can vary from a few thousandths of an inch, as with sprayed-on coatings, to a considerable thickness, as with some solid rubber vulcanized coatings.
In belted conveyor systems, belt slippage, caused by insufficient energy transfer between the drive and idler pulleys and the belts, reduces the operational performance of the belts. Additionally, material accumulation on the surface of the drive or idler pulleys or the belt surface has a detrimental effect on the tracking capability of the belt and often increases slippage between the pulleys and the belt.
Some prior art conveyor pulleys have attempted to solve the mis-tracking problem by crowning the face of the pulley. Crowning, as that term is generally understood in the art, refers to the shape or diameter profile of the pulley. However, in belted conveyor systems, in which a single pulley member supports one or more individual belts, it has been found that multiple crowned rollers do not aid in the tracking of the belts. In fact, a multiple crowned roller has been found to be detrimental to tracking, where the belt width is relatively narrow (less than about 12 inches) and the transverse stiffness of the belt is greater than the longitudinal stiffness of the belt, and where the longitudinal modulus of elasticity of the belt is considered high relative to the actual operating tension of the particular application.
All of the above referenced problems, i.e. tracking, traction, and trash accumulation, result in inefficient operation of belted conveyor systems. In a worst case scenario, operations must be stopped while belts are cleaned, repaired or replaced at great expense to the user of the belted conveyor system. There is therefore a continuing need for a conveyor pulley which can more effectively deal with the above-referenced problems.