You’ve probably seen those amazing people on TV who can pull cars with their hair and drag trains with their teeth. But did you know science can make you strong, too?
If you need to lift huge weights, don’t strain your back: use the power of science, and an amazing device called a pulley. Let’s take a closer look at how they work!
What is a pulley?
A pulley is a simple wooden or metallic machine that uses a wheel and rope to lift heavy loads. Nowadays, plastic pulleys are also available in the market to carry small loads. This can be rotated freely about an axis passing through its center.
It can change the direction of a force, which makes it much easier for people to lift anything. With this, you can pull down on one end to lift the 10 kgs and one-meter high object.
The main element of a pulley system is a rope, cable, belt, or chain. Pulleys are fixed on the shaft, and the shaft moves other pulleys; these are called “Driver Pulleys”.
The pulleys moved by the driver pulley are called “Follower Pulleys”. Pulleys are available in small and large sizes.
We can easily increase or decrease the speed of power transmission in terms of gears and shafts by using large and small pulleys.
Parts of a Pulley
The following are the parts of a pulley:
- Face
- Hub
- Arms
- Bore
#1. Face.
The part containing the periphery of the pulley is called the Face. It extends somewhat from the center and is descending from the sides. The protruding middle part is called the Crown. The face is either plain, or a “V” groove is built on it.
#2. Hub.
The hub is a central part of a pulley, which has a bore for the shaft. There are three types:
a) Solid Hub: It is only a shaft of one particular size that is fitted. For shafts of different sizes, it is used with different bores.
b) Slotted Hub: It is slotted from one side, which is tightened with a nut and bolt after fitting the shaft. It is also made in one piece. It can be used with shafts of different diameters.
c) Split Hub: This type of hub is made in two parts. For fitting these two parts on the shafts two nuts and bolts are used. Their faces are made of two pieces. These can be used for big and small shafts of the same type.
#3. Arms.
The joining parts that join the face and hub of the pulley are called Arms. Their number is according to the diameter of the pulley and its use. It may be made with four, six, or eight.
#4. Bore.
The hole in the hub is called the bore. A key way is to cut in the hole, with the key shaft and pulley locked.
Types of Pulleys
For different machines and jobs, the following types of pulleys are used:
1. Fixed Pulley.
A fixed pulley has its wheel mounted securely to a stationary support, such as a ceiling or frame. When the rope is pulled, the pulley simply changes the direction of the applied force without reducing the effort needed to lift the object.
This type doesn’t provide a mechanical advantage in terms of force multiplication but is invaluable for redirecting force, allowing the user to pull down while the load moves up. Fixed pulleys are common in flagpoles, window blinds, and simple lifting setups.
2. Moving Pulley.
Unlike fixed pulleys, a moving pulley attaches directly to the load. The rope runs through the pulley, and one end is anchored while the other is pulled. This arrangement reduces the effort required to lift the load by effectively sharing the load between the rope and the pulley support.
The force needed to lift the load is halved, providing a mechanical advantage of two. Moving pulleys are widely used in construction cranes and elevators for heavier lifting tasks. However, the disadvantages are increased rope length and slower lifting speed.
3. Compound Pulley.
A compound pulley system combines fixed and moving pulleys to amplify the mechanical advantage while also changing the direction of force. By arranging multiple pulleys, the compound system allows lifting heavy loads with much less effort.
The ropes run through several pulleys, distributing the weight and reducing the required input force dramatically. Compound pulleys are fundamental in applications that demand both ease of use and efficiency, such as theater rigging and heavy machinery.
4. Block and Tackle Pulley.
One of the most efficient systems, the block and tackle, consists of multiple fixed and moving pulleys mounted on two blocks. Each pulley in the system is connected by rope, drastically reducing the force needed to lift a heavy load.
This arrangement also allows for smooth, controlled lifting of substantial weights and is common in maritime settings, large construction projects, and industrial hoisting equipment. The mechanical advantage depends on the number of pulleys used.
5. Cone Pulley.
Cone pulleys are characterized by several pulley wheels of decreasing diameter stacked together in a conical shape. This design enables the user to change the speed and force ratio by moving the belt to different-sized wheels.
The cone pulley is prevalent in machinery that requires variable speeds, such as lathes and bicycles with multiple gears. It allows seamless adjustment without changing gears manually.
6. Swivel Eye Pulley.
A swivel eye pulley incorporates a mount that can rotate, providing flexibility when lifting loads that need to change direction or angle during operation. This dynamic rotation helps prevent twisting of the rope or cable and is especially useful in applications requiring frequent orientation changes.
They are commonly used with fiber, nylon, or wire ropes in rigging, rescue operations, and theater equipment.
7. Fixed Eye Pulley.
With a fixed eye pulley, the attachment point (eye) is stationary. Such pulleys are used in systems where stable attachment is critical, often configured with multiple pulleys to reduce effort effectively.
Fixed eye pulleys are chosen for conveyor belts, lifting apparatus, and scenarios where rotation of the mount is unnecessary or unwanted.
Examples of Pulleys
- Elevators: Utilize a pulley system to move the car up and down the shaft.
- Wells: Traditional wells use a pulley to draw water with a bucket.
- Cranes: Heavy-duty construction cranes use complex pulley systems to lift heavy materials.
- Flagpoles: Pulleys are used to raise and lower flags.
- Blinds: Window blinds use a pulley mechanism to adjust the height.
- Theatres Curtains: Stage curtains use pulleys to open and close smoothly.
- Garage Doors: Overhead garage doors often use pulleys to ease opening and closing.
- Exercise Machines: Gym equipment, like lat pulldown machines use pulleys for resistance training.
- Clotheslines: Some clotheslines use pulleys to extend the line for hanging clothes.
- Bicycles: The derailleur system in bicycles uses pulleys to guide the chain.
- Rock Climbing: Pulleys are used in belaying systems for safety.
- Sailing Boats: Rigging on sailboats uses multiple pulleys to manage the sails.
- Fishing Rods: Some fishing rods use pulleys to manage heavy lines.
- Theatre Fly Systems: Used to move scenery and lighting on stage.
- Window Washers: Suspended platforms for cleaning skyscrapers use pulley systems for movement.
Pulley Examples in Real Life
- Cable Cars: Use pulleys to transport people up and down steep inclines.
- Construction Hoists: Pulleys lift materials to higher floors in building projects.
- Winches: Use pulleys to pull in or let out cables, often used in towing and off-roading.
- Ski Lifts: Pulleys are essential in moving chairs up and down the slopes.
- Elevator Doors: Use small pulleys to open and close automatically.
- Zip Lines: Use pulleys to glide riders from one end to the other.
- Bucket Elevators: Use pulleys to transport materials vertically in industrial settings.
- Boat Lifts: Use pulleys to hoist boats out of the water for maintenance or storage.
- Awnings: Pulleys extend and retract awnings over windows and patios.
- Rescue Systems: Firefighters and rescue teams use pulley systems to lower or lift people safely.
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. 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 overtorque 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.
A flat pulley idler can also be used for the back side of a conventional V-belt. Flat belt drive pulleys apply motive power to the belt.
Types of Flat Belt Pulleys
The major parts of flat belt pulleys in various industries include:
- Fast and loose pulley
- Paper Pulley
- Wooden pulley
- Steel pulley
- Cast Iron Pulleys
1. Fast and loose pulley.
The machine can be switched on or off thanks to fast and loose pulleys on the shaft. A free pulley runs on its own, whereas a fast pulley is fixed to the machine shaft.
When the machine is not needed to transmit power, the belt switches to a loose pulley. The belt is initially driven by a fast pulley. This prevents other machines that share a line shaft from being impacted when one machine is stopped.Bottom of Form
To stop axial movement, a cast iron or gun-metal bushing with a collar at one end is connected to the loose pulley. To make the belt move more slowly on the loose pulley, the fast pulley’s rim is made bigger than the loose pulleys. The loose pulley has to be well lubricated and often has a longer hub to minimize wear and friction.
2. Paper Pulley.
When the distance between the center and the center shaft is small, paper pulleys which are composed of compressed paper fibres with metal in the center are frequently used for belt gearboxes from electric motors.
3. Wooden pulley.
When compared to cast iron or steel pulleys, wood pulleys are lighter and have a higher coefficient of friction; they weigh two-thirds as much as a similarly sized cast iron pulley and are typically made of selected maples that are glued together under intense pressure. Protective shell or varnish coatings prevent them from absorbing moisture, preventing war.
Wood pulleys can be solid or split with an iron hub that is fastened with screws, or they can have movable bushes that reduce the frictional resistance between them and the shaft. These pulleys are used in motor drives where the contact arc between the pulley face and the belt is limited.
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4. Steel pulley.
Steel sheets are used to make steel pulleys, which are incredibly strong and resilient. Compared to iron pulleys of the same capacity, these pulleys are made to run at higher speeds and weigh between 40 and 60 percent less.
They exhibit a coefficient of friction with a leather belt that is at least as high as that which a cast-iron pulley can generate.
Typically, two pieces of steel pulp are joined together. Especially in most cases, it is a key necessity because the clamping action of the hub retains its shaft pulley. In order for steel pulleys to be used, they generally come with interchangeable bushes with shafts of different lengths.
5. Cast Iron Pulleys.
Cast iron is usually used to make pulleys. The main boss, arms, or spokes are used to position the rim on the web. The cross-section is usually elliptical, and the arms can be either straight or curved. Typically, cast iron pulleys have circular rims.
The arms of a cast pulley are under stress and are prone to breaking when it shrinks into the casting. Instead of breaking, curved arms give. Near the hub are weapons. We call this little convexity a crown. When moving, the belt is centred on a pulley rim by the crown. The length of the crown can range from 9 mm to 300 mm.
There are two types of cast iron pulleys: split and solid. Split pulleys are simple to use when mounting a pulley on a shaft that already has pulleys, etc., or when the ends of the shaft are swollen. The faces are spaced apart, and a bolt may be used to simply tighten the two pieces on the shaft. Heavy drives are used with a buried key.
Uses of Pulley
Pulleys are versatile tools widely used in various applications:
- Lifting Heavy Loads: Commonly used in construction sites, cranes, and elevators to lift and move heavy materials.
- Theater Productions: Employed to move scenery, curtains, and other stage equipment.
- Exercise Equipment: Incorporated into gym machines to provide adjustable resistance for strength training.
- Sailing and Boating: Utilized in rigging systems to raise and lower sails, and to control the movement of sails.
- Garage Doors: Integrated into mechanisms to ease the opening and closing of heavy garage doors.
- Wells: Used to draw water by lifting buckets with minimal effort.
- Rescue Operations: Implemented in pulley systems for hoisting individuals or equipment in rescue missions.
- Industrial Machines: Found in conveyor systems, manufacturing equipment, and other machinery to transmit power and control movements.
Advantages of the Pulley System
- Pulleys reduce the amount of force which is required to lift heavy objects.
- They can also change the direction of the force.
- Pulleys are pretty easy to assemble.
- They are cost-effective.
- The use of pulleys helps maintain a safe distance between the operator and the weight, which avoids mishappenings.
- They are low-maintenance. The moving parts of the pulley system require little or no lubrication after installation.
Disadvantages of the Pulley System
- The main disadvantage of pulleys is that they require a large space to increase their mechanical advantage.
- The risk of slipping and breaking ropes, belts, or chains is high when they move over wheels without grooves.
- Ropes get weaker with continuous use and break at any time. If the ropes are installed inside the pulley system, they should be checked regularly or often to avoid machine breakage.
- The wheels, belts, ropes, or chains require constant maintenance and regular checkups.
- A single fixed wheel pulley with a rope or belt is hard to lift heavy objects; however, pushing objects downwards is quite easy. Man’s force will be applied to lift things.
- The main advantage of a simple pulley system is that it can slip because they use friction for transferring motion.
- Another disadvantage of the pulley is that they require large space to operate and install.
- Pulley systems are not always reliable or suitable for high-power transfer.
- Multiple pulleys, wheels, and extra ropes are required to lift a heavy object or support the weight, and it costs a lot.
Closing It Up
As we discussed above, a pulley is a wheel with grooved rims that works to change the direction of the force exerted on the rope and is used to lift heavy weights. There are many pulleys and their functions also differ from each other.