The configuration of a conveyor pulley will impact its ability to effectively operate in a given environment. Pulley configuration should be selected based on application load requirements, environmental requirements, the intent of the pulley in the conveyor system (head/drive, tail, bend, etc.) as well as the type, amount, and characteristics of material being conveyed.
Drum Style Pulleys- contact surface is constructed from a cylindrical shell, tube or pipe allowing for continuous full contact with the conveyor belt. Drum style pulleys are commonly found in all positions on a conveyor system where the conveyed material is contained or where the risk of material buildup between the pulley contact surface and the belt is not a primary concern. Of pulley styles, drum style pulleys achieve the most conveyor belt contact and because of this, drum style pulleys are the preferred configuration choice of pulleys in drive positions.
Wing Style Pulleys – non-continuous contact surface is comprised of a series of individual wings (also called fins). This construction results in the creation of open voids that are designed to allow loose material to fall away from the contact surface. Also known as self-cleaning pulleys, wing pulleys are primarily used on the tail end of bulk handling systems where loose materials have a tendency to reside on the underside of the conveyor belt, causing damage to one or both components. Robust wing construction typically incorporates support gussets, and sometimes outer support rings, both of which act as braces for the wing members under heavier loads.
Spiral Style Pulleys – a metal strip contact surface is fixed in a spiral pattern around the circumference of a drum or wing pulley to achieve continuous contact with the conveyor belt while enhancing material removal. Spiral style pulleys are primarily used on bulk handling systems where material buildup and continuous contact with the conveyor belt are operational concerns.
Angled Wing Pulleys – wing members are angled towards the edges of the pulley to achieve continuous contact with the conveyor belt while enhancing material removal. Angled wing designs are primarily used on bulk handling systems where material buildup, cleanout and continuous contact with the conveyor belt are operational concerns. To maximize material removal, some designs feature cleanout ports to enhance this effect.
In addition to selection of a pulley style, component thicknesses must be evaluated and selected for compliance with application demands. Below are a few components that require consideration of thickness:
In many applications, if a shaft has been properly sized for an application, calculation of appropriate wall thickness does not require additional consideration. Because of its pivotal role in pulley performance, the shaft diameter will largely dictate pulley load capacity and wall thickness plays a secondary role. In these cases, use of thin wall tubing in the construction of the cylinder will be sufficient. In any case, wall thickness should be sized so the rated load of the shaft does not cause a stress in the wall of more than 10,000 psi. (SEE APPENDIX A)
The following case examples require evaluation and special consideration of wall thickness:
Stub Shafts: In cases where a stub shaft is selected as the desired hub type, wall thickness requires special consideration. With a stub shaft design, the pulley wall is responsible for accommodating the load that would normally be supported by the shaft in a through shaft design.
Surface Modifications: Pulleys that require modification of the contact surface to achieve a desired profile (V-Groove, etc), tolerance, surface finish, or runout may also need evaluation of pulley wall thickness in order to accommodate the desired modifications.
Impact Loading: Applications in which the conveyor system will be experiencing impact loads require special consideration of appropriate pulley wall thickness. In these cases, the wall of the pulley will be subject to non-uniform loads that can affect the integrity of the pulley wall.
Loose Materials: Bulk handling applications subject to an increased risk of contact by the conveyed loose materials with the pulley wall require consideration of appropriate wall thickness. The presence of material between the pulley and conveyor belt causes increased friction and/or point loading between the two surfaces leading to increased pulley wear or catastrophic failure. If the wall is not sized appropriately for the material size, this contact can lead to collapse of the pulley wall and catastrophic failure.
Disks are used for two primary purposes in the construction of conveyor pulleys; in the end of the pulley as end disks and inside the pulley as center disks. Disks are sized by pulley manufacturers to compliment the requirements of other components such as shaft diameter, hub type and wall thickness.
End Disks: If the shaft is sized properly for application loads, end disk thickness does not play a significant role in premature failure. However, choice of a thicker end disk may add an additional safety factor to the design of a conveyor pulley up to a certain point. Sizing an end disk too thick though, could prevent the shaft from flexing through the disk, leading to shaft breakage.
Center Disks: In most cases, center disks are used in the manufacture of drum style conveyor pulleys with rolled cylinders as a means of creating a common center to fabricate the wall around. Center disks contribute to the stiffness of the cylindrical portion of the pulley but should not be selected as the proper method for accomplishing increased load capacity. In small diameter pulleys, center disks are welded via holes machined in the wall of the conveyor pulley. This process creates stress concentrations, affecting the integrity of the wall which can be seen as a design disadvantage. The proper method of increasing the load capacity of a conveyor pulley is properly sizing the shaft diameter and wall thickness for the loads of the application.
Although it is possible to select customized component thicknesses for an individual application, configuration standards are often available to help simplify the selection process. These configuration options may be predesigned for application intent but do require review for compliance to application demands. Since there is no industry standard for component thicknesses, names and specifications will vary across manufacturers. Common terms include Heavy Duty, Mine Duty, Quarry Duty, Mill Duty, Extreme Duty and various Engineered Designs.