This article will take an in-depth look at belt conveyors.
The article will bring more understanding on topics such as:
This chapter will cover the basics of belt conveyors and their various components.
A belt conveyor is a system designed to transport or move items such as materials, goods, or even people from one point to another. Unlike other conveying methods that use chains, spirals, or hydraulics, belt conveyors utilize a belt to move the items. This system consists of a loop of flexible material stretched between rollers, which are driven by an electric motor.
Since the items being transported can differ significantly, the belt material used in the conveyor system also varies. Typically, it is made from polymers or rubber, depending on the specific requirements of the application.
A standard belt conveyor system includes a head pulley, tail pulley, idler rollers, the belt itself, and the frame.
The head pulley is connected to the actuator and the electric motor, providing the pulling force that drives the conveyor. Located at the discharge end where the conveyor offloads its materials, the head pulley is crucial for system operation. To enhance traction, the outer surface of the head pulley is often covered with a rough jacket known as a legging.
The head pulley usually has the largest diameter of all the pulleys. Sometimes a system can have multiple pulleys that act as drive pulleys. The pulley at the discharge end, is a drive roller usually with the biggest diameter, and will be identified as the head pulley.
The tail pulley is situated at the loading end of the belt conveyor. It often has a wing shape to help clean the belt by directing materials away from the support members.
In a basic belt conveyor setup, the tail pulley is typically mounted on guides with slots to adjust the belt’s tension. In other conveyor systems, as we will explore, tensioning is managed by a separate component known as the take-up roller.
Idler rollers are positioned along the length of the belt to support both the belt and its load, prevent sagging, ensure proper alignment, and remove carryback (material that sticks to the belt).
While idler rollers can perform all of these functions or just one, their primary role in any conveyor system is to support the belt.
Various types of idler rollers are designed for specific functions, as outlined below:
Troughing idlers consist of three rollers arranged to create a "trough" shape for the belt. These idlers are positioned on the side of the conveyor that carries the load. The central idler is fixed, while the two end idlers can be adjusted to modify the angle and depth of the trough.
These idlers help reduce spillages and maintain a consistent cross-sectional area along the length of the belt conveyor, which is crucial for stability.
This idler features rubber disks spaced along the roller's axis. The rollers at the extreme ends are positioned closer together to support the belt edges, which are more susceptible to tearing. The spaced disks help dislodge any carryback or leftover material, reducing buildup on the underside of the belt. This buildup is a common cause of mistracking, where the belt shifts to one side and causes misalignment.
In some cases, the disks are arranged in a helical pattern, resembling a screw, and the idler is referred to as a rubber screw idler roller. Despite the different design, its function remains the same. An example of a screw idler roller is shown below.
The screw idler can also be constructed from a rubber helix. Screw idlers are particularly useful in situations where a scraper for removing carryback isn't practical, such as on mobile belt conveyors.
Trainer idlers ensure the belt runs straight and counteract mistracking. They feature a central pivot that redirects the roller back to the center if the belt drifts to one side. Additionally, they include two guide rollers to help guide the belt.
When setting up a belt conveyor, the belt itself is often the most intricate component. Its tension and strength are crucial, as the belt endures significant stress during loading and transporting materials.
The increasing demand for longer conveyor lengths has spurred research into new materials, though this often comes with significant costs. Stronger belts that comply with environmentally friendly regulations can be prohibitively expensive, sometimes making the costs difficult to justify. Conversely, opting for a more economical approach can lead to belt failure and higher operating costs. Typically, the cost of the belt should be less than 50% of the total cost of the belt conveyor.
A belt is comprised of components such as:
Since this is the skeleton of the belt, it has to provide the tensile strength needed to move the belt and the lateral stiffness for supporting the load. It must also be capable of absorbing loading impact. The belt is a loop so it has to be joined; this is known as splicing. Because some of the splicing methods require the use of bolts and fasteners, the carcass must be able to provide an adequate and firm base for these fasteners.
The carcass of a belt is typically constructed from steel cord or textile ply. Textile ply consists of fibers such as aramid, polyamide, and polyester. A single-ply carcass may also be PVC-coated. Carcasses can be built up to six layers thick and often include edge protection, which is essential for bulk conveyor belts.
The covers of a belt are made from flexible materials such as rubber or PVC and are exposed to weather elements and the working environment. It is important to carefully select the covers based on their intended use. Considerations typically include flame resistance, low-temperature resistance, grease and oil resistance, anti-static properties, and food-grade suitability.
The carrying side of the conveyor is designed based on the load, angle of inclination, and overall use of the belt. It may feature special configurations such as corrugated, smooth, or cleated surfaces to suit different requirements.
In applications such as scrap conveyors in CNC machines, steel belt conveyors are used because they are more durable and resistant to wear compared to conventional materials.
In the food processing industry, PVC, PU, and PE belts are utilized to preserve food quality and minimize contamination.
Plastic belts, while relatively new, are gaining popularity due to their numerous advantages. They are easy to clean, have a wide temperature range, and exhibit excellent anti-viscosity properties. Additionally, they are resistant to acids, alkaline substances, and saltwater.
The frame of a conveyor system varies based on factors such as loading, operational height, and the distance to be covered. It can range from a simple cantilever setup to more complex trusses for handling larger loads. For simple and lightweight operations, aluminum extrusions are also commonly used.
The frame design is a crucial aspect of conveyor construction. An improperly designed frame can lead to:
Additional accessories, such as walkways and lighting, can be mounted on the frame, as shown above. Lighting installations often require sheds and guards to protect the material. Loading and discharge chutes may also be added. Understanding these potential add-ons is crucial to prevent uncalculated overloading.
This chapter will cover the various types of belt conveyors, including:
In this type of conveyor belt, the surface just beneath the belt consists of a series of closely stacked rollers. This arrangement minimizes belt sagging.
These conveyors are suitable for both long and short-distance conveying. In some cases, they can be so short that they use only two rollers for the entire system.
When utilizing gravity for loading, a roller bed conveyor is an excellent choice. Manual loading can cause damage to the rollers due to the internal bearings they typically have. These bearings, combined with the generally smooth surface of the rollers, significantly reduce friction, making conveying easier.
Roller bed belt conveyors are primarily used for hand sorting, assembling, transporting, and inspection tasks. Examples include:
The flat belt conveyor is one of the most commonly used types of conveyors. It is typically employed to transport items within a facility. Internal conveyance relies on a series of powered rollers or pulleys to move the belt.
The belts used in flat belt conveyors can range from fabrics and polymers to natural rubbers, making them versatile for transporting various materials. They are also easy to align, with the tail pulley typically mounted to allow for adjustments. Generally, flat belt conveyors operate at low speeds.
Applications of flat belt conveyors include:
Unlike flat belt conveyors, which use a continuous flexible belt, modular belt conveyors employ a series of interlocking rigid pieces, typically made from plastic or metal. They function similarly to a bicycle chain.
This design provides significant advantages over flexible belt conveyors, including greater durability and the ability to operate across a wide range of temperatures and pH levels.
When a section of a modular belt becomes damaged, it is easy to replace just that section, unlike flexible belts, which require replacement of the entire belt. Modular belts can navigate corners, straight lines, inclines, and declines using only one motor.
While other conveyors can also perform these tasks, they often involve increased complexity and cost. Modular belt conveyors are particularly advantageous for applications requiring unusual dimensions, such as widths greater than lengths.
Due to their non-metallic nature, ease of cleaning, and porosity to gases and liquids, modular belt conveyors are suitable for applications including:
Cleated belt conveyors are designed with barriers or cleats that segment the belt into distinct sections. These cleats help to prevent particles and materials from rolling back or falling off the conveyor, particularly during inclines and declines.
The cleats come in various shapes and sizes, including:
This cleat stands at a 90-degree angle to the belt, providing support and flexibility for delicate items. It is ideally suited for light-duty applications, including handling small parts, packaged goods, and food products.
Due to its orientation, this cleat effectively resists leverage forces and can scoop granules while holding them against gravity. It is suitable for handling light to medium-weight granules.
These cleats, typically less than 5 cm in height, function similarly to a trough. Their design allows them to transport heavy or bulky materials effectively, as the short cleat height can endure high impacts.
These cleats assist in draining liquids after washing items like vegetables and fruits. Lugs and pegs provide a cost-effective method for conveying items that don’t require full-length support, such as large cartons or rods. They can also selectively move products that exceed a desired size and secure individual items in place.
Additional applications of cleated belt conveyors include:
This conveyor features a pre-fabricated curved frame designed to transport items around tight corners. It is ideal for situations with limited space where space-saving winding conveyors are needed. The curves can accommodate angles of up to 180 degrees.
Modular plastics with interlocking segments are used when the conveyor has a straight run before curving. Flat flexible belts are utilized if the conveyor primarily consists of curved sections.
Incline conveyors require tighter tension force, higher torque, and traction on the belt surface to prevent items from falling off the belt conveyor. Thus, they will incorporate a gear motor, a center drive, and a take up. The belt must also have a rough surface to allow for greater traction.
Similar to cleated conveyors, these conveyors are designed to transport items up a gradient while preventing them from falling off. They can also enhance the gravitational flow of fluids.
In the pharmaceutical and food industries, stringent sterilization and washing procedures are required to comply with health and safety guidelines. Washdown and sanitary conveyors are specifically designed to handle these sanitary processes. Typically, these conveyors use flat belts that are relatively thin to accommodate the cleaning requirements.
Sanitary wash-down belt conveyors are designed to handle items exposed to extreme temperatures, such as those from freezers or furnaces. They can also operate in hot oil or glaze. Due to their robustness in greasy environments, they are sometimes used to offload oil drums and crates from ships.
A troughing belt conveyor is not a separate type of conveyor but rather a feature that can be incorporated into various types of conveyors.
It uses a belt that takes on a trough-like shape due to the troughing idler rollers positioned underneath it.
The troughing idler rollers feature a central roller with a horizontal axis of rotation, while the two outer (wing) rollers are angled upward, typically at around 25 degrees. Troughing occurs only with the top idler rollers and not with the bottom ones.
Excessive troughing angles can cause permanent damage to the belt. If the belt is curved at steeper angles, it may retain a cup shape, making it difficult to clean and track, and potentially damaging the belt carcass. This can also decrease the surface contact with the idler rollers, ultimately reducing the efficiency of the belt conveyor system.
Trough belts generally operate in a single plane, either horizontal or at inclines of up to 25 degrees. The belt must have a sufficiently large radius to ensure full contact with all the rollers in the troughing idler. If the troughing angle is too steep, the belt may fail to make contact with the center idler roller, which can compromise the belt's structural integrity and reduce the overall efficiency of the conveyor system.
Magnetic belt conveyors are designed to position and control ferrous metal pieces and parts. They utilize ferrite or neodymium magnets to transport materials and are especially useful for handling small parts that might not fit on traditional belt conveyors. While they operate similarly to conventional belt conveyors, their distinguishing feature is the use of magnets to exploit the magnetic properties of materials.
The magnets on a magnetic belt conveyor are positioned along the conveyor bed with sufficient strength to counteract gravity. The size of the materials has little effect on the conveyor’s performance, as the magnet strength can be adjusted to meet varying conditions and requirements.
Magnetic Belt Conveyors - Magnetic belt conveyors are the most prevalent type of magnetic conveyor due to their ease of construction and operation. They are equipped with a magnetized sheet metal belt featuring either permanent magnets or a series of electromagnets that attract ferrous materials to the conveyor belt.
Besides the presence of magnets, magnetic belt conveyors function like traditional belt conveyors. They are used for moving cans, parts, ore, and other magnetic materials, and can handle products vertically, up inclines, and even upside down.
Magnetic Separator Belt Conveyors - Magnetic separator belt conveyors are designed specifically to separate ore from loose dust and debris. As material travels along the belt, non-magnetic materials fall off to the side, while magnetic materials adhere to the belt. These conveyors are available in dry and wet types. The dry type does not require the material to be wet for separation, while the wet type does.
Key parameters to consider when designing a conveyor belt include:
To select the appropriate motor, it is essential to first determine the effective pulling force required for the conveyor.
For a simple horizontal conveyor, the effective pulling force is determined using the following formula:
Fu=µR · g(m+ mb+ mR)
Where:
Fu=Effective pulling force
µR =Friction Coefficient when running over roller
g = Acceleration due to gravity
m =Mass of goods conveyed on the whole length of the conveyor
mb =Mass of Belt
mR =Mass of all rotating rollers minus mass of drive roller
For an inclined conveyor system, the effective pulling force is calculated using the following formula:
Fu=µR · g · (m + mb+ mR) + g · m · sina
Where
Fu =Effective Pulling Force
µR =Friction Coefficient when running over roller
g = acceleration due to gravity
m = mass of goods conveyed on the whole length of the conveyor
mb =Mass of Belt
mR =Mass of all rotating rollers minus mass of drive roller
a =Angle of inclination
Once the pulling force is established, calculating the required torque becomes straightforward, which in turn helps in selecting the appropriate motor and gearbox.
The conveyor speed is calculated by multiplying the circumference of the drive pulley by the number of revolutions per unit time.
Vc=D · F
Vc =Speed of conveyor belt in ms-1
D =Diameter of drive pulley in meters.
F =Revolutions of drive pulley per second
Take-up is a crucial component for maintaining and achieving optimal belt tension, which significantly contributes to the process and its mechanical stability.
A properly tensioned belt will wear evenly, contain material uniformly in the trough, and run centrally over the idlers.
All conveyors will experience some degree of stretch in their length and width. Typically, a new belt will stretch up to an additional 2 percent of its original length. This added length creates slack in the belt, which must be taken up to maintain optimal tension.
The degree of stretch increases with the length of the conveyor. For example, a 2-meter long conveyor may stretch 40 mm, whereas a 200-meter long conveyor could experience up to 4 meters of slack.
Take-up mechanisms are also advantageous during maintenance. By releasing the take-up, personnel can perform maintenance more easily.
Various take-up configurations each offer distinct advantages and disadvantages. Common types of belt conveyor take-ups include the gravity take-up, screw take-up, and horizontal take-up.
The screw take-up configuration uses mechanical force to take up all the slack in the belt. It achieves it by adjusting a threaded rod that is attached to one of the rollers, especially the tail roller. This threaded rod will be on each side of the roller so it can also work as an alignment procedure. Since this is a hands-on manual approach, screw take-up is often called manual take-up.
Another type is the top angle take-up. While it is popular, it requires a large and heavy tail frame to be effective, and the guards also need to be substantial.
Screw take-ups are an inexpensive and efficient method for controlling belt tension in relatively short conveyors and are a common and straightforward choice for many applications.
Screw take-ups are generally unsuitable for managing the stretch in conveyors longer than 100 meters. In such cases, a gravity take-up system is the more effective solution for maintaining belt tension.
A gravity take-up assembly consists of three rollers: two are bend rollers, and one is a gravity or sliding roller that continuously manages belt tension. A counterweight attached to the gravity take-up roller exerts downward force on the belt, maintaining tension through gravity. The bend rollers guide the belt slack around the gravity take-up roller.
The complete take-up assembly is mounted at the bottom of the conveyor frame, ensuring consistent belt tension. This self-tensioning mechanism allows the take-up to adapt easily to sudden changes in tension or load.
The gravity take-up method effectively maintains proper belt tension and prevents damage from sudden spikes in load or tension. Because gravity tensioners are self-adjusting, they require less maintenance compared to screw take-ups. Maintenance is typically needed only when the belt reaches the end of its lifespan, at which point the take-up assembly may be at its maximum travel distance. In such cases, the belt may need replacement or repair. Gravity take-up systems are also known as automatic take-ups due to their self-adjusting nature.
Maintenance for gravity take-up systems is typically required when the belt reaches the end of its useful life, which occurs when it has stretched enough for the assembly to reach its maximum travel distance. At this point, the conveyor belt may need to be replaced or cut and vulcanized. Gravity take-up systems are often referred to as automatic take-ups because they adjust themselves automatically.
The horizontal take-up serves as an alternative to the gravity take-up, especially in situations where space is constrained.
This take-up operates similarly to the gravity take-up, but instead of being positioned below the belt, the assembly is mounted vertically behind the tail roller. This configuration is particularly advantageous when the conveyor is installed on a slope or in locations where there is insufficient space underneath the conveyor.
Unlike the gravity take-up, the horizontal take-up does not extend below the conveyor. Instead, it uses a system of cables and pulleys to tension the belt with a weight box. Cables connected to the tail pulley move along a carriage, enabling the take-up to be adjusted in and out to maintain proper tension.
This chapter will cover the applications and benefits of belt conveyors, as well as common issues encountered with belt conveyors, their causes, and the impact of environmental factors on their performance.
Conveyor belts are used in various industries for a multitude of applications, including:
Other conveyor applications are:
Pulleys play a crucial role in belt conveyors by providing drive tension and altering the direction of the belt's movement. Belt conveyor pulleys are categorized into several types, including drive, tension, motorized, snub, wing, and bend pulleys. These pulleys can come with various surfaces, such as smooth, rubber-coated, or cast rubber.
Motorized pulleys serve as the driving mechanism for belt conveyor systems. They feature a sealed motor and a protective exterior drum, which the motor drives. This drum provides the necessary traction to move the conveyor belt. Motorized pulleys come in various configurations to accommodate the diverse needs of conveyor systems.
The drive pulley, or head pulley, is responsible for supplying traction to the conveyor belt. It typically has a surface coated with chevrons or diamonds to enhance friction between the belt and the pulley, ensuring effective movement. Drive pulleys can be single or double-sided and may have one or two drives, depending on the size and requirements of the conveyor system.
Bend pulleys are used to redirect the belt conveyor, creating a continuous loop. They function as the tail roller in a tensioning device and help change the belt's direction. Bend pulleys resemble return pulleys but are designed with a smaller diameter.
A tension pulley, also known as a return pulley, creates tension in the conveyor belt, increasing the force exerted on it. These solid pulleys are built to withstand significant forces and can be placed anywhere along the belt, although they are most effective when positioned close to the drive pulley.
The snub pulley works in conjunction with the drive pulley to increase the contact area between the belt and the drive pulley. By enhancing friction, snub pulleys are ideal for conveyor systems that require high drive power or operate under contaminated conditions.
Wing pulleys are designed to clear material from the return belt and continuously clean themselves. They offer excellent traction and come in various types, including spiral, heavy-duty, and herringbone.
Magnetic pulleys are integral to magnetic conveyor belts, used to separate ferrous materials from non-ferrous ones. Constructed from steel and enclosed with permanent magnets, these pulleys effectively remove both large and small ferrous debris.
A crowned head pulley features a cylindrical middle with tapered ends to ensure stable operation of the conveyor belt. By guiding the belt back to the center, crowned head pulleys improve stability and are typically used with flat belt drives.
Belt conveyors are widely recognized for their convenience and efficiency in moving, sorting, packing, and shipping goods and products. Having been in use for many years in various forms, they have significantly improved supply chain efficiency.
Belt conveyors offer several advantages, including:
Despite their advantages, belt conveyors are complex systems that require careful monitoring and management. Key concerns to address include:
Possible causes of these issues include:
Potential causes of this issue include:
Possible reasons for this include:
This can be attributed to factors such as:
Factors such as water, petroleum products, chemicals, heat, sunlight, and cold can all impact the performance and lifespan of a belt conveyor.
The effects and causes of these factors can be categorized as follows:
A belt conveyor is a system designed to transport or move physical items like materials, goods, even people from one point to another. Unlike other conveying means that employ chains, spirals, hydraulics, etc., belt conveyors will move the items using a belt. It is critical to be cognizant of the design considerations and applications of various belt conveyors depending on the intended use.
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