Advantages of Belt Drives
The prevalent types of power transmission drive components used in industrial applications today include chains, gears and belts. From large rock crushers to tiny sewing machines, the variety of applications is wide. Selecting the best type of drive for a particular application is key to providing optimal performance.
While the range of applications with belts in the distant past was limited by their horsepower capacity, continuous development has resulted in products that today can compete with metal components such as gears and chains in very high torque and horsepower applications. Belts also offer the added feature of acting as a "safety fuse" in the drive system. In a peak torque or drive blockage situation, the belt (often the least expensive component of the drive) will break, sacrificing itself rather than the breakage of much more expensive components (shafts, etc.) in the system.
Belts have some major advantages over metal drive components:
- Quiet - Less noise generated than metal components;
- Clean - no lubricants, grease or oil to contaminate the environment or product;
- Less weight - drives designed with belts can weigh significantly less;
- Economical - can be significantly less expensive than a drive designed with metal components;
- Compactness - Belt drives can often be designed using less space than other drive components.
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Major Types of Power Transmission Belt
There are two major types of power transmission drive belts. They come in many different sizes and constructions but can be broken down into these two groups:
- V-Belt;
- Synchronous Belt (also commonly referred to as timing belt).
V-belt is a friction device and works on the principle of the wedge. It relies on tension to create friction on the sidewall of the sheave to transmit power. V-belts allow slippage which can be desirable and intended in drive design. For example, in a mower deck, the belt must slip rather than break the belt or bend a shaft when the blade contacts a rock or a stump.
A synchronous or timing belt is a positive engagement device. It is a highly efficient system of power transmission. It combines the advantages of mechanical and flexible components without the disadvantages. All synchronous belts operate on the positive engagement principle, the same principle as chains, moulded belt teeth meshing with sprocket teeth. Synchronous belts wrap around the sprocket using flexion and not by rotation of articulated parts as do chains. This eliminates one of the causes of wear and noise. Synchronous belt does not allow slippage as there are drives where synchronicity is a necessity and any slippage can cause damage. For example, the valve train of an internal combustion engine. If the drive does not maintain synchronous operation the piston can contact and damage the valves.
V-Belts: Applications & Advantages
V-Belts are available in a wide variety of cross section sizes and construction types allowing them to be an option in drives ranging from low to high horsepower. They can also be used in sets of multiple belts arranged side-by-side for use on very high-horsepower drives. There are generally two construction types available, wrapped and raw edge. Wrapped belts have an envelope of fabric that entirely covers the external surface of the belt. Wrapped construction should be used where maximum slippage capability is desirable.
Raw edge construction does not have fabric on the sides of the belt that engages the sheave, and has cogs, also referred to as notches, on the bottom section of the belt for additional flexibility to wrap around small sheaves. Raw edge construction belts do not slip as easily as wrapped belts due to the exposed rubber on their sidewalls. Raw edge belts are used where higher horsepower capability is necessary while still requiring some slippage in peak torque conditions. Raw edge belts can be a very cost-effective upgrade to a system resulting in a significant efficiency increase due to their reduced slippage versus a V-belt and the fact that they can be installed on the existing pulleys without any need to make component changes to the drive.
Advantages of V-Belts
- Lower noise
- Less cost
- Allows some slippage - can act as a safety fuse
Use a V-Belt Drive where:
- Some slippage is desirable;
- Low noise is required;
- The most economical drive is requested.
Synchronous Belts: Applications & Advantages
Like V-Belts, synchronous belts are available in a wide variety of sizes and construction that allows them to be an option on almost any drive. All synchronous belts are somewhat similar in their construction, the difference is in the type of belt body compound, tooth profile, and tensile cords used. They are available in either rubber or polyurethane construction. The choice of rubber or polyurethane depends on the type of application. For example, in production environments such as the food industry where cleanliness is a priority a polyurethane belt may be used as it has less tendency to shed material than a rubber-based construction.
Conversely, for very high temperature applications a rubber belt will be chosen due to its much higher heat capabilities. Synchronous belts also require a very low installation tension in comparison with v-belts which exerts much less stress on drive components such as shafts and bearings. Tooth profiles are chosen based on various conditions. For example, where precise registration is required, a tooth profile that has minimum play or clearance between the belt tooth and pulley groove may be chosen. On a very high torque drive, a parabolic curvilinear shape tooth profile will be desirable due to its capability to transmit high power and torque while minimizing the chance of the belt tooth jumping out of the sprocket and jeopardizing synchronization. Synchronous belts also require less tensioning maintenance than V-belts. While V-belts must be periodically checked to ensure correct tension is maintained, synchronous belts tend to remain at the correct tension long after the initial belt installation.
Advantages of Synchronous Belts
- Exact shaft synchronization
- Elimination of slippage and resulting speed loss common to v-belts
- Low installation tension means less stress on shafts and bearings
- Less maintenance
- Higher Drive Efficiency
Use a Synchronous Belt where:
- There are high torque and low RPM requirements;
- Compact drive layout is necessary;
- Synchronous transmission between shafts is a must;
- High precision positioning of shafts (minimal backlash);
- High mechanical drive efficiency and energy savings required;
- Low maintenance is a priority;
- Low noise requirements (compared to chain, gears).