What is Belt Drive?- Types and Materials of Belt

What is belt drive?

A belt, in the context of machinery, is essentially a loop made from a flexible material that connects two or more rotating shafts usually arranged in parallel. People use belts for a few different reasons: sometimes to create motion, other times to transfer power efficiently, or even just to keep track of how different parts are moving relative to each other.

Typically, you’ll see the belt wrapped around pulleys, and depending on the setup, there might even be a twist between pulleys, which means those shafts don’t always have to be parallel.

When you’re dealing with a basic two-pulley setup, you’ve got a couple of options. The belt might simply rotate both pulleys in the same direction assuming the shafts are parallel.

But if you cross the belt, it flips the direction of the second shaft, so the driven pulley spins the opposite way compared to the driver. It’s a simple change, but it can have a big impact on how the machinery operates.

Take conveyor belts as an example they show how a belt can do more than just spin things. In that case, the belt keeps moving a load from one spot to another in a continuous loop. But belts can also tweak how fast things rotate: by pairing pulleys of different sizes, you can speed up or slow down the rotation as needed.

How much power a belt drive actually transfers depends on several factors. These include how fast the belt is moving, how tightly it’s stretched over the pulleys, how much of the small pulley is in contact with the belt (that’s called the arc of contact), and the specific working conditions the belt faces. Each of these details can make a noticeable difference in how the whole system performs.

Types of Belt Drive

Seven different types of belt drive can be found and those are:

• Open belt drive
• Closed or crossed belt drive
• Fast and loose cone pulley
• Stepped cone pulley
• Jockey pulley drive
• Quarter turn belt drive
• Compound belt drive

1. Open Belt Drive

When you have an open belt drive, you’re basically working with two parallel shafts spinning in the same direction. In this setup, the driving pulley pulls the belt along one side and then hands it off on the other.

Now, here’s something interesting: the belt on the lower side actually carries more tension than the belt on the top. That’s why we call the bottom run the “tight side,” while the belt at the top gets labeled the “slack side.”

If the shafts are spaced pretty far apart, it’s best practice to keep the tight side running along the bottom and the slack side up above. Why? Because gravity helps out here—a loose upper belt naturally sags under its own weight, which lets it hug the pulleys better, increasing the arc of contact and improving grip.

2. Closed or Crossed Belt Drive

Cross or twisted belt drives are commonly used when you need two parallel shafts to rotate in opposite directions. The way this system works is pretty straightforward the driver shaft pulls the belt from one side and then sends it over to the other side.

In this setup, you’ll notice that the bottom side of the belt carries more tension compared to the upper side. That’s why we call the bottom the “tight side,” while the upper part, where the tension drops, is often referred to as the “slack side.”

The main reason for choosing a cross belt drive is to reverse the direction of the driven shaft. However, there’s a bit of a catch: at the point where the belt actually crosses over itself, there’s a tendency for the belt surfaces to rub together. Over time, this contact can lead to significant wear and tear.

To keep wear to a minimum, it’s best to maintain as much distance as possible between the two shafts and to keep the operating speed low. More specifically, if you want to avoid trouble, make sure the distance between shafts is no more than 20 times the width of the belt (that’s what “20 B” means, with B being the belt width).

Also, try to keep the belt speed under 15 meters per second. This way, you’ll get more life out of your belt and avoid unnecessary maintenance headaches.

3. Fast and loose cone pulley

This particular belt drive arrangement comes in handy when you need to start or stop the machine shaft without interrupting the driving shaft.

Here’s how it works: the pulley that’s fixed firmly to the machine shaft is known as the “fast pulley,” and it turns at the same speed as the shaft itself. On the other hand, there’s a “loose pulley” which just spins freely on the shaft and doesn’t actually transmit any power.

Whenever there’s a need to stop the driven shaft, you simply move the belt onto the loose pulley. This is usually done using a sliding bar with belt forks, allowing for quick engagement or disengagement no need to mess with the driving shaft at all.

4. Stepped cone pulley drive

A stepped or cone pulley drive is often used when the goal is to vary the speed of the driven shaft, even though the driving shaft keeps running at a steady pace. The process is pretty straightforward: you shift the belt from one step (or groove) of the cone pulley to another.

A typical step cone pulley is made as a single piece, with several pulleys of different diameters stacked right next to each other imagine a staircase, but for pulleys. The matching set of driven pulleys is mounted upside down on the driven shaft. An endless belt connects one pair of pulleys at a time.

To change the speed, all you have to do is move the belt to a different pair of steps. The sizes of the pulleys are chosen so that the same belt can be used across all steps, making it easy to switch speeds without having to swap out parts.

5. Jockey pulley drive.

When setting up an open belt drive, there are situations where the center distance between the pulleys is short or the driven pulley itself is particularly small. In these cases, the belt doesn’t wrap very far around the driven pulley its arc of contact is limited.

This can lead to a reduction in belt tension, making it tricky to transmit power effectively. If adjusting the tension through other means isn’t possible, a common solution is to introduce an extra pulley known as a jockey pulley on the slack side of the belt.

As illustrated in the accompanying figure, this jockey pulley helps increase the arc of contact, allowing for better grip and tension where it’s needed.

This increases the arc of contact and thus stress increasing power transmission.

6. Quarter turn belt drive

Quarter-turn belt drives, often referred to as right-angle belt drives, are designed for situations where the shafts are set at right angles to each other and need to rotate in a specific direction. One important consideration with this type of setup is making sure the belt stays on the pulley.

For that reason, it’s standard practice to ensure that the pulley face is at least 1.4 times wider than the belt itself (with “b” representing the belt’s width).

In cases where it isn’t possible to position the pulley as required or if you need the system to operate with reversible speed a guide pulley can be introduced into the quarter-turn belt drive. This modification helps keep the belt in place and accommodates changes in direction when necessary.

7. Compound belt drive

A compound belt drive is used when power is passed from one shaft to another through multiple shafts.

Factors to consider before using belt drive:

• Proper shaft alignment is essential to maintain even tension throughout the belt. If the pulleys are placed too close together, the arc of contact on the smaller pulley becomes limited, which can reduce efficiency.
• On the other hand, if the pulleys are spaced too far apart, the belt places excessive weight on the shaft, leading to increased friction in the bearings—a situation best avoided.
• Long belts present their own challenges. When a belt is overly lengthy, it tends to shift from side to side during operation. This movement can cause the belt to slip off the pulley or develop twists and uneven wear.
• Another important detail is the orientation of the belt’s tight and slack sides. By positioning the tight side underneath, any sagging that occurs on the loose side actually increases the arc of contact on the pulley, improving grip and performance.
• As for flat belts, best practices suggest keeping the distance between shafts to no more than 10 meters. At the same time, you don’t want the shafts too close; ideally, the minimum spacing should be about three and a half times the diameter of the larger pulley. This balance helps ensure smooth and efficient belt operation.

Classification of Belt Drive

Belt drives are generally divided into three main categories: light drives, medium drives, and heavy drives.

• Light drives are typically found in agricultural machinery and smaller machine tools. They’re best suited for transmitting relatively low forces, especially at belt speeds that reach up to 10 meters per second.
• Medium drives come into play when there’s a need to handle moderate forces. These are commonly used in various machine tools, operating at belt speeds that exceed 10 meters per second but don’t surpass 22 meters per second.
• Heavy drives are designed for much more demanding tasks. You’ll often find them in equipment like compressors and generators, where they’re responsible for transmitting significant forces at belt speeds above 22 meters per second.

Types of Belt

There are four different types of belts:

• Round belts. Round belts are generally made of rubber.
• V belts. V belts are arguably the most widely used belts in the industry.
• Flat belts. Flat belts are also used to transmit power from one shaft to another.
• Timing/toothed belts.

There are three basic types of power transmission belting: flat belt, V belt, and synchronous belt. Misalignment is a common cause of premature belt failure. Power transmission belting has been used for more than 200 years. The first belts were flat and ran on flat pulleys.

1. Flat Belt

Flat belts serve as an efficient way to transfer power between two shafts. The mechanism behind this is pretty straightforward: power moves from one pulley to another through the friction created by the belt wrapping around the pulleys. When using flat belts, both pulleys rotate in the same direction, making the setup predictable and easy to work with.

Generally, flat belts fall into two main categories: small woven endless belts and high-strength flat belts. The woven endless types are especially handy in applications where you need to keep vibration to a minimum, mainly because the semi-elastic materials used in these belts help absorb and dampen movement.

On the other hand, high-strength flat belts are popular when there’s a need to cut down on the amount of tension required to keep the pulleys engaged. This is actually an important advantage because less tension on the belt means there’s less strain on the shaft bearings, which can help extend the lifespan of the whole system.

As for materials, high-strength flat belts are made from special abrasive-resistant compounds, which gives them the durability needed for more demanding tasks.

2. V belt

V-belts are a common choice in industrial environments like factories and workshops, especially when there’s a need to transfer significant amounts of power between two pulleys that are positioned close together.

One of the reasons they’re so widely used is because V-belts effectively address two classic issues: slippage and alignment. Thanks to their design, they’ve become the standard for power transmission in many mechanical systems.

What sets V-belts apart is their ability to offer a balanced mix of benefits. They’re known for reliable traction, efficient speed of movement, reduced stress on bearings, and a longer operational lifespan compared to some alternatives.

Typically, these belts are manufactured as endless loops, and their cross-sectional shape is generally trapezoidal an intentional design choice that helps them grip pulleys securely.

3. Circular belt

A round belt is characterized by its circular cross-section and is typically paired with pulleys that have a 60-degree V-groove. It’s worth noting that round grooves themselves are generally limited to idler pulleys, which serve mainly to guide the belt rather than transmit power unless, of course, you’re working with O-ring style belts.

When it comes to V-grooves, these are designed to transmit torque more effectively because the belt presses into the groove, generating more friction. However, round belts aren’t really built for heavy-duty tasks; their use is best reserved for applications where the torque demands are relatively modest.

In terms of availability, round belts come in pre-made lengths or can be trimmed to fit and then joined together. The connection can be made in a few different ways, whether it’s with a metal staple, a dedicated connector, adhesive, or even by welding the ends.

Historically, you’ll find that early sewing machines made clever use of leather belts, fastening them with metal staples or glue—and, for their purpose, these simple solutions worked surprisingly well.

4. Timing belt

Timing belts are a type of positive drive belt designed to maintain precise synchronization between moving parts. What sets these belts apart is the row of teeth along their surface, which mesh perfectly with the matching grooves on a toothed pulley.

When they are installed with the correct tension, timing belts operate without slipping and maintain a constant speed, making them ideal for applications that require exact timing or sequencing.

In many cases, timing belts are preferred over chains or gears, especially when minimizing noise is a priority or when regular lubrication would be inconvenient. You’ll often find timing belts in automotive camshaft systems, compact timing mechanisms, and stepper motors.

One advantage worth noting is that timing belts require the least tension compared to other belt types, yet they remain highly efficient in transmitting motion.

Selection of a belt drive:

The following are the various important factors on which the selection of belt drive depends:

• Speed ​​of driving and driven shafts,
• Speed ​​reduction ratio,
• The power to be transmitted,
• Center distance between shafts,
• positive drive requirements,
• Shaft layout,
• Location available, and 
• Service Terms.

Applications of Belt-drive:

Belt drives are used in various places:

• A belt drive is used for power transfer.
• Drive to the rotor on the rotor-spinning machine.
• The belt drive is used in Conveyor.
• Drive to drafting rollers and other rolling elements on a single delivery drawing machine.
• Drives to opening rollers, friction drums, and take-off rollers on friction spinning machine.
• Main drive on the draw-texturing machine.
• The belt drive is used in the Mill industry.
• Drive to the creel-rollers of a high-speed drawing machine.

Advantages of a belt drive

The advantages of a belt drive include:

• It is cost-effective and simple to use.
• New belt-drive efficiency can be up to 95-98 percent.
• Belt drive requires a low maintenance cost.
• Belt drives do not require a parallel shaft.
• They come with overload and jam protection
• Speeds Differences can be obtained by using a step or tapered pulleys.
• Belt drives are the most economical option when a large distance of power transmit between shafts.
• Damp out noise and vibration, Load fluctuations are shock-absorbed, increasing the machinery life
• Clutch action can be activated by releasing belt tension

Disadvantages of Belt drive

However, belt technology also comes with certain disadvantages of belt drive. These are:

• A belt drive is not suitable for small distances.
• There is a loss of performance due to high levels of slip and creep.
• A constant velocity ratio can not achieve between the drive and the driven pulley.
• It produces high noise.
• it has low mechanical efficiency.

The material used for Belts

There are five main materials that conveyor belts are made out of:

• Leather belts
• Cotton belts or Fabric belts
• Rubber belts
• Balata belts
• Plastics belts

There are five main materials that conveyor belts are made out of thermoplastics, metal, rubber, fabric, and leather. Plastics include polyester, polyvinyl chloride, silicone, and polyethylene.

The metals are stainless and carbon steel and the fabric materials are canvas or cotton. The most popular material is a rubber composite because it is flexible, resistant, smooth, and seamless.

1. Leather Belt

When it comes to flat belts, leather really stands out as the preferred material, mostly because of its unique combination of strength and durability. The highest quality leather belts are usually crafted from strips measuring between 1.2 and 1.5 meters in length, taken specifically from each side of the backbone on top-grade steer hides. This careful selection process isn’t random it’s done to ensure that the belt maintains both flexibility and resilience during use.

If you look closely at the structure of leather, you’ll notice some interesting differences between its two main sides. The hair side of the leather has a smooth, hard finish, whereas the flesh side feels much stronger to the touch.

The fibers on the hair side are oriented straight up, perpendicular to the surface, giving it a distinct texture. In contrast, the fibers on the flesh side are interconnected and run parallel to the surface, which helps give the belt its strength and toughness. So, the way the leather is cut and used really makes a difference in the performance of flat belts.

2. Cotton or Fabric Belt

Most fabric belts are crafted by folding together three or more layers of canvas or cotton duck, then securing them with stitching. Sometimes, instead of layering, these belts are woven directly into strips that have the needed width and thickness.

To make sure the belts last and hold up in tough conditions, they’re treated with linseed oil mixed with a filler. This treatment makes them waterproof and helps protect the fibers from damage.

One of the main reasons people choose cotton bands is because they’re affordable and work well in damp or humid environments. They’re also pretty low-maintenance, which is why you’ll often find them in farm machinery and belt conveyor systems.

3. Rubber belt

Rubber belts are constructed from multiple layers of fabric, all bonded together with a rubber matrix and finished with a thin outer coating of rubber. While these belts offer a high degree of flexibility, they tend to deteriorate rapidly if they come into contact with heat, oil, or grease.

A notable advantage of rubber belts is the ease with which they can be manufactured in continuous, endless forms. This characteristic makes them particularly well-suited for environments such as sawmills and paper mills, where belts are often exposed to moisture.

4. Balata belt

Balata belts share many similarities with traditional rubber belts, but there’s one key difference: instead of rubber, balata gum serves as the binding material.

This change brings some practical advantages. For instance, balata belts are naturally resistant to acids and water, and they don’t react negatively to animal oils or alkalis. That makes them a good fit for environments where chemical exposure is a concern.

However, there’s an important consideration regarding temperature. These belts shouldn’t be used in conditions above 40°C. Once you go past that point, the balata gum begins to soften and turn sticky, which can really affect performance. On a positive note, balata belts actually have about 25% more strength than rubber belts, offering a sturdier option when durability matters.

5. Plastic belt

When it comes to plastic belts, manufacturers typically use materials such as polyester, polyvinyl chloride (PVC), silicone, and polyethylene.

Each of these polymers brings its own strengths to the table like durability, flexibility, or resistance to various chemicals which makes them suitable choices for a wide range of belt applications.

FAQs.