Introduction
Pure and simple, conveyors transport material. From the perspective of the economy, conveyors perform the redundant tasks historically done by animals, people, handcarts, wagons, and trucks. From conveying integrated circuits only a few inches, to millions of tons of dirt over many miles, conveyor systems are the backbone of global product handling. This article examines the types of conveyors, conveyor components, and relevant terminology.
Advantages of Conveyors
History shows us that conveyors have been in use since the late 18th century (or earlier!), when they hauled bulk agricultural goods. These conveyors freed resources to conduct other, more skilled tasks. There are many advantages of conveyor usage over other forms of material transportation:
- Operates in all weather conditions
- High tonnage per hour
- Low cost to tonnage ratio
- Mobility
- Length easily shortened
- Length easily extended
- Adaptable to terrain requirements
- Low degradation of material during transport
- Capable of multiple gathering points
- Capable of multiple discharge points
- Meets environmental requirements
- Safety
Leather, canvas, and non-reinforced rubber were used as the conveying surface until World War II. During the War years, rubber and cotton became rationed items, thus forcing manufacturers to develop other materials for use in conveyor systems. Synthetic material was used in place of rubber and cotton, and quickly became the inspiration for future developments.
Conveyor Profiles
There are many different types of conveyor systems, and each possesses a profile fitting the application. Accordingly, each profile may have its advantages and disadvantages; however, the application dictates the profile. Some of the common profiles are: Straight Incline, Convex Curve, and Concave.
Straight Incline: A “straight” conveyor profile does not include a concave or convex ascent or descent. The figure below illustrates the straight conveyor profile. Although both profiles are straight, the possibility of an elevation change is not precluded, as found in a “straight incline.” In most cases, there will be a combination of straight and incline, which leads to the next two types of profiles.
Convex Curve: A “convex curve” profile uses one or more convex-shaped curves. The convex curve forces the conveyor belt over the transition, thus ensuring solid seating to the idlers even when the belt does not contain material.
Concave: The “concave curve” profile uses one or more concave-shaped curves (see the figure). The concave curve tracks in the idlers well when loaded, but can lift off the conveyor when empty and proper tensioning precautions have not been made. Conveyor belts only track well when they are in contact with all rollers of each idler. Consequently, conveyor belts on concave profile systems tend to track poorly. Design considerations should include plans for appropriate tensioning and starting practices.
Types of Conveyors
Depending on the design and application conditionsm conveyors can be of mainly 5 types: Light duty, Heavy duty, Bucket conveyor, Table top conveyors, and Wire belt
Light Duty Conveyors
A light-duty conveyor system consists of a carrying surface (usually a lightweight conveyor belt), a support structure, and a drive pulley. Although not always required, many lightweight conveyor systems have an end pulley, take-up pulley, or a combination end/take-up pulley. Components differ by conveyor type. Listed are various types of common systems, all of which are designated by their carrying support type. Slider Bed conveyors consist of a flat bed (constructed of steel, although other materials may be used) to support the conveying surface, and a drive pulley. Very popular in lightly loaded conveying applications, the slider bed generates a high coefficient of friction. Advantages of a slider bed are cost and easy construction, coupled with full belt load support. In the case of food applications where the system has a tendency to get wet, suction between the belt and bed may stall the conveyor.
Slider Bar conveyors consist of a group of parallel bars (usually constructed of steel, although other materials may be used) to support the conveying surface, and a drive pulley. Like the slider bed, the slider bar conveyor is designed for light loads. Inexpensive and easy to construct, the slider bar conveyor has a much lower coefficient of friction and is ideal for wet applications.
Roller Bed conveyors consist of multiple shaft-supported “free rolling” canisters (usually constructed of steel, although other materials may be used) aligned perpendicular to the conveying surface, and one drive pulley. More expensive to build and operate, the roller bed conveyor has a very low coefficient of friction.
Roller bed conveyors can generate high decibel ratings when combined with hundreds or thousands of other rollers in an indoor environment. The noise comes from the low-precision, non-caged, rolling element bearings. The hollow rollers accentuate this noise.
Live Roller conveyors are identical to the roller conveyor; however, the difference is that instead of using a drive pulley to move the conveying surface, each roller is powered to rotate, thus moving the material. Roller rotation is generated either by a conveyor belt riding underneath the rollers or by each roller being driven by its own drive belt. Live roller conveyors are relatively expensive compared to a slide bed or slider bar system. Maintenance costs are higher as well, but live roller systems tend to be quieter, and overall longevity is greater. This is due to the conveyor belt’s driven style design. With this design, the rollers only rotate when a product is passed along the top. In doing so, the weight of the box, or bag, pushes down the spring-loaded roller, which in turn makes contact with the moving conveyor belt below. When the box or bag has passed, the spring-loaded roller disengages the belt and stops rolling. In effect, less maintenance is required, thus lowering operation costs. In addition, decibel ratings decrease because fewer rollers are rotating.
Heavy Duty
A heavy-duty conveyor system consists of a carrying surface (usually a multiplied heavy duty conveyor belt), a support structure, and a drive pulley. Unlike most lightweight conveyor systems, heavy-duty systems need an end and take-up pulley. Heavy-duty systems are easily recognized by their heavy construction and idler belt support units.
Bucket Elevators
Bucket elevator systems move material vertically (or at high inclines), by using a bucket affixed to a conveyor belt, cable, or chain. Bucket elevators are highly specialized and components vary by application.
Folding belt conveyor systems fall into the heavy-duty category. The folding belt system is identical to a conventional system, with the exception of belt construction. In a folding system, the belt has the capability to fold over the material being conveyed, thus encapsulating the material. Folding belts are very expensive and are usually used in applications where the terrain is severe or the potential loss of material is high.
Tabletop Conveyors
The term “tabletop conveyors” refers mainly to the type of conveying surface. The construction of a tabletop type conveyor consists of the carrying surface (usually some type of interlocking chain), drive pulley sprockets, and support idler sprockets.
A tabletop belt is similar to a conventional roller chain. Made from many different types of materials, the tabletop belt consists of multiple flat links interconnected with pins. This type of construction makes codifications and repairs much more economical than that of a conventional conveyor belt. It also allows the user to change belt widths with little effort or major equipment redesign. Similar to the wire belt, the tabletop belt is good for applications where liquid drainage is required.
Wire Belts
A wire belt conveyor system also refers to the conveying surface. Light to heavy gauge wire is interlinked to form the carrying surface, called a wire belt. System construction consists of the wire belt, support surface, a drive pulley, a tail pulley, and a take-up mechanism. Wire belts are used in rugged applications where polymers will not work, or where the cost of special materials becomes cost-prohibitive. Construction consists of links and pins. The wire links are assembled side by side, aligned, and held in place by the links. Because the wire belt is made of steel, it is capable of withstanding heat and cold, as well as water and chemicals. They are also advantageous when drainage is required.
