Plied Type Construction
Plied conveyor belts consist of covers, one or more fabric plies/carcasses, and skim coats.
The cover is constructed of rubber or other polymers and is designed to protect the fabric plies/carcasses against potential damage from the material being conveyed and other unforeseen hazards. In many cases, there is a bottom cover that comes in contact with the pulleys and idlers. The inclusion of a cover is designed to protect the carcass against possible wear that could eventually damage the belt’s integrity.
The fabric plies or carcass is the load- carrying member of the belt components. The plies provide strength against impact, a medium for fastener holding, and protection against rips and tears. There are three types of materials used in the construction of the plies: polyester, nylon, and steel.
Polyester provides the best resistance to stretch. In addition, polyester plies tend not to shrink and trough well on the carrying idlers. Unfortunately, belts made from all polyester are relatively inflexible and are more likely to experience rips, tears, and punctures. For this reason, polyester belts are poor at supporting mechanical fasteners in rugged applications and should be considered for vulcanization.
Nylon fibers have an excellent memory, thus making them an excellent carcass for harsh applications. Nylon carcasses are more likely to stretch than polyester belts, but technology has advanced to the point where the percentage variations are negligible.
The nylon carcass holds up well to high impacts and is excellent at withstanding the pressures of trapped material between the belt and pulleys. Not only does the nylon carcass trough well, but it has superior mechanical fastener retention.
In higher pounds per inch of width (PIW) rated belts, a combination of polyester and nylon is used. In this type of carcass construction, the polyester is used as the warp cord, while the nylon is used as the weft or fill. Accordingly, the polyester allows for a higher tension longitudinally, while the nylon provides greater fastener retention and trapped material pliability.
There are two basic types of steel belts: the steel mesh carcass and the steel cable belt. While the steel mesh carcass is rare, the steel cable belt is very popular in long overland systems where a very heavy-duty conveying surface is needed.
Between the plies is the skim coat. The skim is rubber or another polymer, which provides load support, adhesion between the fabric plies, and helps absorb impact.
Heavy belts are rated according to fabric weight and cover thickness. For example, a three-ply 330 PIW, ¼ x 1 belt is broken down as follows:
1. Three ply 330 PIW tells us that there are three separate plies/carcasses, of 110 PIW (pounds per inch of width) each.
2. The ¼ x 1 tells us that the top cover polymer is ¼” thick and the bottom cover is 1/16” thick.
Because there are many different belt selections for most applications, please consult your belt supplier for specific nomenclature and belting recommendations.
Lightweight Construction
Lightweight conveyor belts come in many types and styles. Lightweight belting can be plied or have an integral woven fabric. Like the heavy-duty plied belts, a plied lightweight belt is rated by each ply fabric’s PIW. Similarly, a woven carcass belt’s load-carrying capacity is also measured in PIW. Lightweight belt applications range from food processing, distribution centers, and airport luggage handling, to postal and high- tech parts movement.
In most cases, a lightweight belt is selected for its profile and polymer qualities over its load-carrying capacity. Top cover profiles such as “roughtops,” “pebbletops,” and “meatcleats” are just a few of the hundreds of examples of what is available. Lightweight belting manufacturers design their profiles to meet a large cross-section of applications. Therefore, it is sometimes difficult to find a perfect match for the application, but the probability of finding a suitable substitute is high.
Polymer material is the other consideration in lightweight belting selections. Application parameters strongly dictate which polymer to use in a conveyor system. Again, manufacturers purposely manufacture specific profiles with application-relevant polymers. These combinations are a result of years of application experience.
Rubber Compounds (for Various Applications)
Every conveyor belt manufacturer touts their rubber compound as superior compared to other brands. The Rubber Manufacturers’ Association (RMA) has classified compounds into different types and grades so that consumers are able to ensure they are getting the right rubber for their application.
Some of the specific RMA grades are as follows:
Grade I (RMA 1): “Superior resistance to abrasion, cutting, gouging, and tearing caused by the impact of large material. Recommended for transporting large, heavy lump ores, quartz, trap rock, granite, glass bullet, scrap, ballast, and similar heavy-duty applications.”
Grade II (RMA II): “Excellent for continuous abrasion and good resistance to cutting and gouging, recommended for conveying sand and gravel, limestone, crushed rock, slag, coke, coal, cement rock, potash, trona, salt, and other abrasives”
In addition to the RMA standards, each belting manufacturer makes available specialty compounds to meet specific application demands. These requirements range from oil resistance to heat and fire resistance.
SOR (Super Oil Resistant): “Highly resists mineral oil and most other oils that cause swelling and sponginess. Recommended for handling animal or vegetable fats, oily metals, etc.”
MOR (Moderate Oil Resistant): “Recommended for specialized service such as waste disposal, sewage, sludge, and oil-treated materials.”
Fire Resistant (MSHA): “Meets U.S.A. Mine Safety and Health Administration requirements. Designed for service in coal, potash, salt, and other underground mining where fire-resistant belts are mandatory.”
SCORF (Static Conductive Oil & Fire Resistant): “Specially compounded for the oily effect of grains. This is static conductive and flame resistant; meets MSHA requirements.”