The type of contact surface chosen for the pulley face will impact a number of application variables within the conveyor system. Unless an alternate surface is desired, pulleys are furnished with a plain steel or mill type finish comparable to that of a standard tube or pipe. The most common contact surface modifications are those designed to increase the traction or grip between the drive pulley and the underside of the conveyor belt. In addition to providing increased traction, an alternate contact surface may be utilized to impact a pulley's wear resistance, ease of cleaning, and aesthetics.
Lagging is a term used to describe the variety of elastomers used to coat the contact surface of a conveyor pulley. The primary purpose of pulley lagging is to enhance the traction between the drive pulley and the underside of the conveyor belt by increasing the coefficient of friction between these two surfaces. The enhanced friction between pulley lagging and the conveyor belt may improve belt life by allowing lower belt tensions and reducing abrasive conditions between the pulley and belt.
Pulley lagging is specified by communicating the preferred lagging material, durometer or hardness of the material, desired thickness, and subsequent finish diameter of the pulley after applying the lagging to the face. lagged pulley surfaces may be plain wrapped (unfinished) or ground to a continuous, semismooth surface (rough ground). Proper selection of a lagging material should address the following variables:
Resistance to temperature, light, oils, fats, acids, alcohols and water, as well as compatibility with food products, are all factors that need to be considered when selecting a lagging material. Select a lagging material that is compatible with the conveyed material and has resistance to the conditions of the intended environment.
The durometer, strength, and abrasion resistance of the lagging material will impact its ability to provide traction, wear properly, and hold up to tearing, peeling, or eroding.
The type and style of lagging selected will impact the serviceability of the conveyor pulley when it requires recoating. Some styles allow for field installation of replacement lagging while others require that re-lagging services be conducted at a re-lagging facility.
The type and style of lagging selected will not only impact the coefficient of friction that is achieved between the conveyor pulley and conveyor belt, but also may impact the likelihood of reversion (see troubleshooting guide for complete explanation). Consult belt manufacturer specifications when selecting a lagging material.
The type and style of lagging selected will impact its ability to prevent sticking or adherence of foreign particulate to the surface. If ease is desired in eliminating foreign material from exposed lagged surfaces, then a lagging compound with good release properties should be considered.
The contact surface of most lagged pulleys can be modified from a rough ground finish to include several types of groove patterns. These groove patterns assist the conveyor pulley in dispersing or eliminating water and debris away from the center of the pulley, resulting in increased traction and enhanced belt tracking characteristics.
Knurling is a manufacturing process in which the surface of steel is altered by forming a pattern into the surface of the metal. The result of this process is a coarse pattern, typically diamond shaped, which gives the surface of the conveyor pulley excellent traction capabilities in most environments. However, because the surface is purposefully coarse, knurled pulleys can accelerate belt wear. Knurling is typically specified by communicating a pattern type (diamond, straight or diagonal) and level of coarseness using TPI, or Teeth per Inch as an indicator. Generally speaking, the lower the number of teeth provided per inch of surface area, the deeper the depth of groove provided, resulting in a rougher, coarser surface finish.
The construction of most conveyor pulleys allows the contact surface to be machined, ground, media treated or polished if a more consistent finish is required. A special surface finish may be desirable for:
2. Scratches or Pits
3. Need for a More Consistent Surface Finish
4. Specific Tolerances
5. Other Performance Enhancing Features
6. Ease of Cleaning / Sanitary Needs.