In this presentation, we will look at the short- and long-term benefits of belt and molded chain driven systems. Low noise, reduced backlash, simple installation, and low repair cost are just a few of the positive aspects of these systems. While not every application is right for a belt driven system, there are times when it is without question the best option.
The goal of this webinar is to provide another tool to designers and anyone working in power transmission. Different applications call for different solutions and knowing more about belts and molded chain can help optimize a drive design.
Key Takeaways (jump to a section)
Questions to Ask When Designing a Belt Drive System
The right drive configuration can save on costs, improve productivity and reduce downtime and maintenance in power transmission applications. Here are some things to consider when designing a drive system:
Total Cost of Ownership
- What is the cost to purchase, & replacement cost?
- How critical is this drive to the customer's application?
- How often do they expect to do maintenance on the system?
- What is the expected life of the product the drive is going into?
- How easy will it be to perform maintenance once the product is fully assembled?
- What is the expected lead time?
Performance (defining the precision and accuracy required for the system)
- How fast are drive input & output expected to be?
- What are the torque requirements for the application?
- What noise &/or vibration considerations are needed for the end product?
Noise is very important to define upfront. Sound can be transmitted in many different ways, and it's easier and more cost effective to design with this in mind versus determining a system is too loud once installed.
Space Considerations
- What is the envelope size?
- Are there weight restrictions?
- What is the center distance & layout?
- Any other factors that influence the space in which the drive will go?
Special consideration is given to the locations of fasteners, not only for the drive system, but also for any components that will be hidden once it's installed.
Environmental Concerns
- What is the operating temperature range?
- Will foreign contaminants (shavings, dust, chemicals) be present near the operation site?
- What about static buildup & discharge during drive operation?
- Will it operate in ozone rich environments & other special considerations?
- Any regulatory requirements such as those for food processing?
These factors are critical in determining the enclosure type that will be needed for the drive. They also limit what materials can be used throughout the system.
Reliability and service further define the aspects from the total cost of ownership:
- Is a customer's expectation that the drive will make it one year beyond the warranty period?
- Or do they have a brand reputation to uphold that is significantly different than this?
- What is their expected level of quality?
Installation
- When does the drive need to be installed?
- What tools will be needed to install this?
- Are there any special skills required?
As you can see, many of these factors go hand-in-hand with other design aspects already considered.
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Common Drive Designs
Now that we gathered the information needed to select a drive design, what general solutions do we look at? Here’s a review of the most common drive products and Berg solutions that extend the drive system's life.
Roller Chain Drives
The first common drive option is roller chain, which transmits loads in tension to and from sprocket teeth. Roller chain drives have been around for many years and are well proven, provided they are properly maintained.
Roller chains are ideal for applications with high reduction ratios and high load capacities and are nearly as efficient as a gear drive. They also tend to be resistant to environmental effects as they are unaffected by sun, heat, moisture and oil, and can also be made from corrosion-resistant materials.
Some concerns with roller chains are that they can be noisy, especially when not tensioned correctly. When used at higher speeds, a constant lubrication source needs to be present as the change in direction around the sprocket can fling the lubrication away from the rolling elements of the chain, resulting in sliding wear.
Also, roller chains can be sensitive to alignment of the sprockets. Care must be taken to ensure that these are within the chain manufacturer's allowance for optimum life and performance of the drive.
Roller Chain Design Characteristics
Torque
- Allows for relatively high power transmission
- Comparable efficiency to spur gears (up to 91-98%)
Installation
- Some misalignment allowed, but at the cost of negative performance
- Simple setup with standard components
Space Limitations
- Center distance can be modified easily if needed
- Best for low-to-medium center distances
Speed
- Best for lower-speed applications due to noise
- Similar ratio options to spur gears
Operating Environments
- Metal chain doesn't deteriorate due to sun, heat & oil
- Corrosion resistant
- Requires consistent lubrication
Backlash
- Improper tensioning can lead to backlash
- Low backlash when installed properly
Shock loads
- Higher load capacity than other belts, but lower than gears
Maintenance & Life Cycle
- Regular lubrication required
- Medium life expectancy
Flex-E-Pitch: Roller Chain Alternative
Berg has designed a number of drop-in roller chain replacement materials under the Flex-E-Pitch product line to address some of these concerns. These are directly interchangeable with the corresponding roller chain. No need to change the sprockets in the system. The polyurethane overmolded material provides a quieter system while reducing inertia due to the weight of the chain. This material also eliminates the need for lubrication as there are no moving joints with the Flex-E-Pitch roller chain alternative. This system is best used in applications where the tensile load with the chain is less than 75 pounds.
The entire product line offers many different sizes and load capabilities. We'll be happy to select the appropriate model for your application. This system can easily be designed for no backlash without the requirement for special sprockets or other difficult considerations.
Flex-E-Pitch Features
Design
- Interchangeable with metal roller chain
- Molded polyurethane over a stainless steel cable
Benefits
- Quieter, smoother & lighter than roller chain
- Lower inertia
- No lubrication required
- Minimal backlash
Applications
- Ultimate tensile strength: 100-300 lbs
- Recommended operating load: 25-75 lbs
Gear Drives
Next, are gear drives: what we consider to be the most torque dense option for drive systems. That is, the ability to transmit the most torque for the given space of the drive system. Gear drives alter speed, torque and/or direction of rotating shafts, and are most commonly used in power transmission applications.
Most of this was covered in our gear drive design guide, but some things to consider when looking at the gear design include the gear type—for example, spurs, helicals, bevels or worms. Be sure to understand the advantages of each and what is right for the drive.
Next is the tooth strength. When doing so, please consider both running and any shock loads that might be put into the system. Third are the sizing of the gears and any materials that are being used. Typically, as size decreases, the material requirements will increase.
Next would be the rating system and any safety factors. How much safety factor do you truly need to meet the design goals? And finally, any of the backlash requirements. Please be sure to be realistic here. Decreasing backlash can greatly increase cost. Gears have some drawbacks, including lubrication and noise, especially as the speed (both input and output) increases.
Gear Drive Design Characteristics
Torque
- Gears provide the highest torque capacity
Installation
- Expert installation is generally required for loose gears
- Gearboxes provide a “plug & play” option at a higher cost
Space Limitations
- Center distance is determined by the gearset in most cases
- Not ideal for large center distances
Speed
- Different types of gears can be utilized based on the speeds required in the application
Operating Environments
- Full enclosures may be needed for an optimal gear drive
Backlash
- Zero backlash is unobtainable with gears
- Backlash can be minimized at the cost of performance or $$$
Shock Loads
- Gears can be designed to hold up to large shock loads
Maintenance & Life Cycle
- Gears tend to last longer than other components in a power transmission system when designed & installed correctly
Flex-E-Gear: Gear Drive Alternative
Berg has a number of options to help directly counter some of the issues with gear drives. Our Flex-E-Gear line of belts is designed to work with spur gears. These belts can handle operating loads of up to 25 pounds with a maximum speed of about 375 feet per minute. Because the gear teeth are not interfacing with one another, these are virtually silent running.
These belts are a great choice when spacing is an issue, but torque multiplication is not needed. We have seen several cases where customers are using five, six or even as many as ten gears to provide spacing around a feature, but there was no multiplication of torque or speed. This significantly increased the amount of backlash in the system, whereas using the belts this could have been eliminated and would have been easier to assemble and maintain.
Flex-E-Gear Features
Design
- Operates on standard sprocket gears
- Molded polyurethane over a stainless steel cable
Benefits
- Sprockets have the ability to mate with spur gears
- Pitches correspond with standard gear pitches
Applications
- Ultimate tensile strength: 30-100 lbs
- Can handle operating loads up to 8-25 lbs
Timing Belt Drives
Timing belts are flat belts with evenly spaced or pitched teeth, and provide a positive no-slip engagement when matched with the grooves in the pulleys.
If you are a car person, you are likely familiar with these for controlling the camshaft timing relative to the crankshaft. These have high accuracy, good torque carrying capability and are generally quiet running. They do not require lubrication. This is a big plus when designing the system because for fast-moving systems in small areas, it can be difficult to add an oil pump for chains and gears.
However, timing belts are also susceptible to the application environment. Heat, chemicals and oils can cause the rapid breakdown of the material.
Timing Belt Design Characteristics
Torque
- High accuracy: force transmitting spine
- Torque capabilities not as high as metallic chain or gearing
Installation
- Belts must be properly tensioned
- Good alignment is required
Space Limitations
- Custom lengths or number of pitches
- Freedom of shaft placement
Speed
- Wide range of allowable speeds
Operating Environments
- Material degrades with higher temperatures or contact with motor oil
- Lubrication not needed
Backlash
- Naturally flexible & accurate
- Movements reflect & repeat the accuracy of the mold at every cycle
- Negligible backlash
Shock Loads
- Lower shock load capability
Maintenance & Life Cycle
- No lubrication required
- Timing systems utilize idlers or pulleys & tensioners
- Life generally shorter than gears or chains
Flex-E-Grip: Timing Belt Alternative
Berg offers a line of timing belts called FlexE-Grip that are designed as a substitute for traditional timing belts. These belts have a stainless steel core that gives high strength and low stretch.
One key feature of these is that they are specially designed to not need flanges on the sides of the pulleys. The center rib of the belt with the pulleys will ensure that these track straight and have low wear. This is very helpful should the belt need to be replaced in the field. It can be very difficult to get the old belt over these flanges.
Flex-E-Grip Features
Design
- Designed as a substitute for traditional timing belts with an increased tensile strength
- Same size as rubber type belts
Benefits
- “No walk” feature eliminates the need for pulley flanges
- Stainless steel center core for superior strength & stretch characteristics
- Significantly stronger than conventional timing belts
Applications
- Can be used in smaller applications - pulleys need not be made wider than the belts
- Ultimate tensile strength: 20-125 lbs
Min-E-Pitch: Timing Belt Alternative
Another timing belt alternative Berg offers are Min-E-Pitch belts. This is a specially designed line of belts that has a circular pitch based on pi, making it easier to have the right number of pitches for the application and having lower requirements for tensioning. Also, due to the center rib design of this belt, it's possible to twist them such that power can be transmitted 90 degrees to the driven shaft.
Min-E-Pitch Features
Design
- Molded on a pitch distance equal to one twentieth of Pi (𝛑)
Benefits
- Series forms with two & three spines to add strength & flexibility
- Transmits power to mating shafts 90° to each other
Applications
- Ideal for low-speed, low-load standard timing chain replacement
- Operating pitch of 1/20 that can work in circular dimensions
- Ultimate tensile strength: 50-120 lbs
V-Belt Drives
V-belts are designed to transmit power via pulleys, sheaves or sprockets, and are identified by their trapezoidal shape.
If you have owned a car, you are likely already familiar with v-belts. These are popular choices for lower-torque, higher-speed applications and have the advantage that if the torque gets too high, the belt can slip. For example, the characteristic squealing noise emitted from under the hood when the air conditioning clutch freezes. V-belts have very little backlash because the belt is in constant contact with the pulley.
Additionally, with no teeth, there is very little wear of the belt system. While these require little maintenance, v-belts need to be periodically replaced due to the heat generated within the belt from the speed and flexing causing degradation of the belt. Also, any oil can be absorbed by the belt, significantly decreasing the torque capability.
V-Belt Design Characteristics
Torque
- Grooves around the circumference of the pulley guide & gain traction; allows for slip in case of overload
- Can achieve a 98% transmission efficiency
- Best for low-torque applications
Installation
- Alignment is less important
- Improper tension will render system useless
Space Limitations
- Wide range of center distances & diameters allowable
Speed
- Typically operate between 1500-6000 ft/min, with 4500 ft/min the ideal capacity for standard
Operating Environments
- Approx. temperature limit of 140°F
- Can be purposely made to slip as an overload protection device
Backlash
- Belt that is in constant contact with pulley causes no backlash
- Minimal wear on belt due to no teeth engagement with the sprocket
- Slippage will result in backlash
Shock Loads
- Possibility of slippage provides protection against shock loads
Maintenance & Life Cycle
- Minimal maintenance with no lubrication
- Life cycle depends greatly on load & environment
Pow-R-Vee: V-Belt Alternative
Berg offers a line of v-belt substitutes called Pow-R-Vee. These belts are specially molded in segments to allow for greater flexibility and increased misalignment capability of the sheaves.
Pow-R-Vee is also made from a special polymeric material that is highly resistant to abrasive wear and is more tolerant of dusty environments. As with most of our belts, these can be spliced to almost any length, allowing the user to keep a spool of material on hand and make to any length needed for the application.
Pow-R-Vee Features
Design
- Molded plastic series of v-belt
- Tolerates greater variation in the angle of the sheave groove
- Flexibility allows for increased misalignment of the driving & driven sheave
Benefits
- Can be spliced to size in the field, reducing machinery downtime
- Greater transverse flexibility
Applications
- Can be spliced to size the right instrument or equipment
- Ultimate tensile strength: 50-350 lbs
Flex-E-Belt Series
Berg's Flex-E-Belt series was designed as a problem solver for when it was not possible to get proper alignment between the sprockets in the system. This belt allows for up to seven degrees of misalignment between the sprockets without loss of motion, and is capable of a 90-degree offset of the input and output shafts.
The center rib design of the belt, reinforced by either stainless steel or Kevlar, allows for high flexibility and strength, with ultimate tensile strength of 20-50 lbs.
This belt is also ideal for replacing low reduction ratio gearboxes, especially where the center distance between the shafts is too great to make bevel or helical gears an option.
Flex-E-Belt Features
Design
- Designed to accommodate sprocket misalignment
Benefits
- Deviations of up to 7° are withstood without loss of motion
- Accommodates 90° sprocket offset
Applications
- Ideal for applications with center distances too large for bevel & crosses helical gears
- Ultimate tensile strength: 20-50 lbs
Molded Belts
Molded belts are a unique design of molded polyurethane over stainless steel cable, offering a strong, flexible, quiet and lube-free system.
Berg offers a line of belts that can take the place of other belts, chains and even gears. These are offered with either a stainless steel or Kevlar backbone, giving high strength as well as high flexibility.
The engineered polymer material is designed to give trouble-free service with resistance to wear, chemicals and corrosion. Additionally, they require no lubrication and very little maintenance in the correct applications.
Molded Belts Design Characteristics
Torque
- Relatively good torque transmitting capability when compared to other non-metallic belts & chains
- Torque capabilities not as high as metallic chain or gears
Installation
- Belts must be properly tensioned
- Good alignment is required
Space Limitations
- Custom lengths or number of pitches
- Freedom of axis placement
Speed
- Linear speed no greater than 2000 FPM
Operating Environments
- Absence of metal-to-metal contact allows for noise-free functioning
- Rust proof
- Fabrication & materials result in a lighter assembly
Backlash
- Lack of moving joints is naturally flexible & accurate
- Movements reflect & repeat the accuracy of the mold at every cycle
- Negligible backlash
Shock Loads
- Flexible material allows for some shock load resistance
Maintenance & Life Cycle
- No lubrication required at any time
- Choosing the correct material & belt size will optimize life expectancy
Our engineers are always willing to help you choose the correct belt for your application. Please feel free to contact us with any questions and assistance with selection of these belts.
Drive Type Summary: Traditional vs. Berg Alternatives
In summary, here is a table highlighting the features of each of the drive types we reviewed. As you can see, for many applications, the Berg line of molded belts can meet your needs better than other industry systems.
The engineered polymeric material was specially designed to resist many common environmental conditions, eliminate noise and eliminate the need for lubrication. Additionally, the belts were designed with flexibility in mind, giving the designer many more options when using in an application.
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Belt Drive Design Fundamentals
There are many steps to consider when designing a system for strength and longevity, and in general a logical progression to these steps, starting with the power and working our way through to belt tensioning.
Due to the variety of applications in which these belts are used, a designer must consider operating parameters that could affect the life of the belt.
Strength
The first step in designing a belt drive system is to compute the design power of the system. The required power is based on the speed and torque required to affect the desired outcome from the system. This result is then multiplied by the safety factor to determine the design power.
Next, the force in the belt is determined based on the planned sheave and sprocket size. This will be a calculation from the transmitted torque and the pitch diameter. Be sure to follow manufacturer recommendations for belt strength.
If the force from the system exceeds the strength of the belt, either larger diameter sprockets could be used (if there's room) or a different system will need to be chosen. If the target belt force is known, the sprocket size can be calculated directly using the input torque to the drive.
it's important to do these calculations prior to the design effort. It will be more difficult to fit a drive system into an existing design than to design around an appropriately selected system.
Specifications
- Identify ultimate tensile strength & recommended operating load
- Determine number of pitches in contact with a sprocket/pulley to calculate load/pin
Torque
- The power source shouldn't induce a start-up torque larger than the operating torque
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Speed & Horsepower
The second step in designing a belt system is to examine the speed of the sheaves and belt. it's important to ensure that the maximum linear speed of the belt doesn't exceed the manufacturer's recommendations. In the case of Berg molded belts, this is about 375 ft/minute.
To do this, first the velocity ratio is determined. This is calculated simply by dividing the input rotational speed by the output rotational speed.
Then, using this and the design speed for the selected belt, the sprocket size from the previous step can be checked to ensure that despite the design being strong enough for torque, the linear belt speed is not exceeded.
Once this is known, it's possible to calculate the horsepower of the system to ensure that the drive input is adequately selected.
If the input rotational speed is lower than typical motor speeds, an additional reduction could be used to achieve the desired goals.
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Reverse Bending
In many cases, a belt system is designed to drive more than one output. For example, in an automotive application, the serpentine belt can drive the power steering pump, the air conditioning compressor, the alternator, and in some cases, the water pump. While the path of this belt may seem torturous when trying to replace it, careful consideration was given to ensure that the required belt contact was made to transfer the torque needed to run the accessory at the appropriate speed.
With the Berg line of belts, it's possible to do the same thing: have the belt drive multiple components. However, special care needs to be taken to ensure long life operation of the system.
For our belts reinforced with aramid fiber (Kevlar), it's possible to connect the accessory such that reverse bending of the belt occurs. This can give a lot of design flexibility when multiple outputs are needed. Steel reinforced belts shouldn't be used in reverse bending because it will shorten the lifespan.
When designing for multiple outputs, please be sure to follow manufacturers’ recommendations for sprocket engagement with the belt. Not doing so can result in premature failure of the sprocket and or belt.
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Pulley Ratio & Alignment
Speaking of sprocket engagement, our recommendation is that the minimum engagement with the belt is five teeth at any time. This ensures that there is adequate distribution of the force over the teeth to prevent exceeding the strength capacity of the sprocket.
Now that the pulleys have been selected, it's time to start the design of the process. With the Berg system of belts, there are some additional design freedoms that you can use to increase the tolerances available to the manufacturing team, thereby helping to control costs.
If you are using a Berg molded belt that contains a single load-carrying member down the center, it's possible to have up to 7 degrees of misalignment between the sprockets. It may also be possible to rotate the output 90 degrees relative to the input shaft, provided there is enough room to properly guide the belt.
For Berg belts that contain two or more load-carrying members (for example, a ladder-style construction) these are not designed for pulley misalignment. Pulley misalignments should be held within a maximum of ½ degree misalignment from the target. Exceeding this will have a significant adverse impact on the life of the drive system.
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Direction Reversing
It's possible to use the belt system to reverse the relative directions of the input and output shafts. The advantage of doing this over using gears is that there will be virtually no backlash in the system due to the extended contact area of the belt with the sprocket. Because of this, the output rotational position can be very closely held relative to the input position in cases where this is important. Pulleys and belts won't lose their timing in the event of a direction reverse.
However, using the belts in a direction-reversing manner will require additional guides to ensure proper operation and will likely shorten the life of the belt system. Areas to monitor include the wear of both the sprocket and drive pins of the belt system. This can be avoided by making the transition as smooth as possible. Abrupt changes will cause rapid failure of the belt.
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Belt/Chain Length: Center Distance Calculations
Now it's time to determine the length of the belt that is needed for the designed application. For inline sprockets, the following calculation can be used:
| L |
Length of belt at pitch line |
| C |
Center distance |
| D |
Pitch diamter of large sprocket (for V- or O-ring belts, use pulley O.D.) |
| d |
Pitch diamter of small sprocket (for V- or O-ring belts, use pulley O.D.) |
Please note that the pitch diameter of the sprockets should be used except when using V- or o-ring belts. Then use the pulley OD for the calculation.
| N |
Number of pitches |
| L |
Length of belt (calculated prior) |
| C.P. |
Circular Pitch |
Our website has a belt length calculator that you can download to help you with this. Since most Berg belts are segmented, the number of pitches will need to be calculated to determine what to order. This is done simply by dividing the length of the belt by the circular pitch of the chosen belt. There can't be any fractions here. Please round up to the next pitch for the proper belt size.
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Tensioning
Proper tensioning of the belt system is very important to ensure transmission of torque and long life of the drive. This can be accomplished in a multitude of ways.
First, as shown below, a chain tensioner with idler can be designed into the system:
Keeping in mind the above points on reverse bending: this is typically installed inside of the belt and spring loaded, though there are cases where the idler is simply installed in a slot and manually adjusted for wear.
Another method for belt tensioning is to allow one of the sprocket shafts to float inside a slot and use a spring to apply a force to that shaft. This can be useful when space constraints prohibit other methods of tensioning. Many people have rules of thumb that they use to determine chain tension in their applications. The proper method is to measure the amount of deflection based on the center distance of the shafts for a given force.
| C |
Center distance (inches) |
| F |
Force (5% of ultimate load for belt) |
| X |
Deflection should be 1/64" per inch of center distance |
In the case of Berg belts, we recommend 1/64 of an inch of belt deflection per inch of center distance when a force equal to 5% of the ultimate belt load is applied normal to belt.
Summary
To sum up, here is how we addressed the issue of belt drive design considerations:
- When belt drives are the appropriate choice for mechanical power transmission
- Cases where belts offer the best performance characteristics & best value as a drive system
- Berg’s belt options that can help you solve challenges commonly found in belt drive systems
We also manufacture custom drive belts, and are always more than happy to help. Please feel free to contact us and find out how we can help you solve your problem.
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Please contact us with any power transmission related questions you might have as you explore Berg belts and chains.
Belt Drive Design Q&A