What is a Flat belt pulley?
Flat belt pulleys are used in transmission systems that are driven by flat belts, typically high-speed, low-power applications in textiles, paper making, and office machinery such as computer printers. A flat pulley idler can also be used for the back side of a conventional V-belt.
When the flat belt on such a pulley is off-center and the pulley rotates, the belt quickly moves up to the largest radius at the top of the crown and stays there. The crown is important to keep the belt “tracking” stable, preventing the belt from “walking off” the edge of the pulley.
Flat belts are designed for light-duty power transmission and high-performance conveying. They are best suited for applications with smaller pulleys and large central distances. Flat belts can connect inside and outside pulleys and can come in both endless and joint construction.
Flat belts are also used for conveyors. Compared to plied belts of equal horsepower, flat belts are thinner by 25% or more, which allows flat belt pulleys to be smaller than V-belt pulleys. Flat belts are also less expensive than belts used in a serpentine belt pulley.
One safety factor is that in over-torque situations, the belt can slip, preventing damage to equipment other than the belt itself. Flat belts require flat pulleys and flat pulley idlers. They do not necessarily require grooved flat belt pulleys. Flat belt drive pulleys apply motive power to the belt.
Types of Flat belt Pulleys
Following are the various types of pulleys for flat belts:
- Cast-iron Pulleys,
- Steel Pulleys,
- Wooden Pulleys,
- Paper Pulleys, and
- Fast and loose Pulleys.
1. Cast Iron Pulleys
Pulleys are usually made of cast iron. The rim is placed on the web from the central boss or by arms or spokes. The arms may be straight or curved and the cross-section is usually elliptical. Cast iron pulleys are usually made with round rims.
When a cast pulley contracts into the mold, the arms are in a state of tension and are very liable to break. Curved arms yield rather than break. Weapons are near the hub. This slight convexity is known as a crown. The crown centers the belt on a pulley rim while in motion. The crown can be 9 mm to 300 mm in width of the face.
Cast iron pulleys can be of solid or split type. When it is necessary to mount a pulley on a shaft that is already carrying pulleys etc. or its ends are swollen, the split pulleys are easy to use. There is a clearance between the faces and the two parts are easily tightened on the shaft by a bolt. A sunk key is used for heavy drives
2. Steel pulley
Steel pulleys are made from steel sheets and have great strength and durability. These pulleys are lighter in weight (about 40 to 60% less) compared to iron pulleys of the same capacity and are designed to run at higher speeds. They present a coefficient of friction with a leather belt that is at least equal to that obtained by a cast-iron pulley.
Steel pulp is usually made in two parts that are tied together. The clamping action of the hub keeps its shaft pulley; Thus, no key is required except in the most serious service. Steel pulleys are generally equipped with interchangeable bushes with shafts of different sizes to allow their use.
3. Wooden pulley
Wood pulleys are lighter and have a higher coefficient of friction than cast iron or steel pulleys. These pulleys have 2/3 of the weight of a similarly sized cast iron pulley. They are usually made of selected maples that are placed in sections and glued together under heavy pressure. They are kept from absorbing moisture by protective coatings of shells or varnishes so that war does not occur.
These pulleys are either solid or split with an iron hub with screws or have adjustable bushes that prevent the frictional resistance between them and the shaft from being installed. These pulleys are used for motor drives in which the contact arc between the pulley face and the belt is restricted.
4. Paper Pulley
Paper pulleys are made from compressed paper fibers and are formed with metal in the center. These pulleys are commonly used for belt transmission from electric motors when the distance from the center to the center shaft is small.
5. Fast and loose pulley
Fast and loose pulleys, used on the shaft, enable the machine to be turned on or off. A fast pulley is mounted on the machine shaft, while a loose pulley operates independently.
The belt operates on a fast pulley to transmit power by the machine and is transferred to a loose pulley when the machine is not required to transmit power. In this way, stopping one machine does not interfere with other machines that run by the same line shaft.
The loose pulley is provided with a cast iron or gun-metal bushing with a collar at one end to prevent axial movement. The rim of the fast pulley is made larger than the loose pulley so that the belt runs slower on the loose pulley. The loose pulley usually has a longer hub to reduce wear and friction and requires proper lubrication.