Chain and belt drive design is a cinch,
right? With their unique advantages
come special requirements that must
also be considered. To find out what
these provisions are, the editors of
Motion System Design conducted a
survey among industry experts, asking
for their analysis. Here’s what they said.
What applications present the biggest challenge in terms of machine productivity?
Pete/Jason Industrial: The toughest challenges are posed by OEMs with space and cost constraints, wanting the most performance from a belt while keeping unit costs to a minimum. This involves consultations to understand drive parameters and acceptable reductions in belt life. Custom designs and testing then ensue to verify system integrity.
Tim/Belt Technologies: Precise, rapid movements in clean environments are challenging. Most drive components cannot deliver all those elements in one solution; metal belts typically can.
Steve/U.S. Tsubaki: Applications exposed to high temperatures and corrosive conditions can compromise the integrity of both the chain and the product. Frequent washdowns, outdoor operation, and even the product itself can create a corrosive environment. Two of our most challenging applications are bleach bottling and orange-juice processing, in which the products conveyed subject the chain to highly corrosive process chemicals.
Extreme heat can also reduce chain strength and hardness, which leads to early wear. Corrosion attacks chain components, causing tight joints, decreased fatigue strength, and ultimately, early chain failure. It can also flake off and contaminate the product, especially in food applications. The warning signs are obvious on carbon-steel chain — visible rust around pins and bushing or on plates. On stainless-steel chain, corrosion may be harder to see: Look for changes such as discoloration or pitting on chain surfaces.
Galen/Dodge of Rockwell Automation: Drive selection and installation are by far the two most common limiters to machine productivity. For example, if you choose a chain drive for a highspeed application, you’ll also need special lubrication systems and guards. This may not be the most ideal selection in terms of productivity because of the time required to maintain the drive. Choosing a V-belt or synchronous belt instead means no downtime for lubrication maintenance.
Improper installation can lead to decreased efficiencies, belt wear, and premature failure. This challenge is easily remedied through proper training and by following standard maintenance practices.
What are the most common pitfalls and how can they be prevented?
Steve/U.S. Tsubaki: Selecting the wrong chain for the application, at the design stage or later on, can cause major problems. This is often the result of failing to follow the selection procedure or blindly substituting one chain type for another. For example, a user selects size 80 carbon-steel chain for a system, then discovers it will operate in a corrosive environment and switches to stainless steel. But to accommodate for the smaller load capacity of stainless steel, the chain size should have also been upped — to say, 120. Now overloads and early chain failure will plague the system unless difficult, expensive retrofits are made.
Galen/Dodge of Rockwell Automation: Overdesigning a drive is another common error. Service-factor overkill can lead to shaft fatigue failure and reduced bearing life.
Pete/Jason Industrial: Worst-case performance is almost always related to a failure to follow manufacturers’ design, installation, and maintenance instructions. Designers and users need to be aware of differences in drive efficiency and maintenance requirements. Chain drives need lubrication, the lack of which often leads to failure. Similarly, V-belts require periodic inspection and retensioning.
Galen/Dodge of Rockwell Automation: One of the worst cases we’ve seen involved the improper selection of a V-belt sheave on a highspeed application. Not only will an incorrect sheave/belt combination lead to problems in the operation, but more importantly, it can be dangerous. It is essential to remain within the material speed capabilities of sheaves and sprockets. Most manufacturers stamp sheave/sprocket speed limitations directly on the face of the part.
Steve/U.S. Tsubaki: It’s important to carefully follow the selection procedure and allow for shock, speed, temperature, corrosion, and other application factors in the design phase to ensure the appropriate chain size and material are selected. Not all chains are directly interchangeable, so making the right choice in the beginning will pay off.
Tim/Belt Technologies: Often times, designs don’t leave enough room for pulleys. A correctly sized pulley will deliver the best belt performance and longest belt life. Similar problems can be avoided by asking for advice on pulley architecture early in the design stage.
What are considered “best practices” when designing with belt and chain drives?
Steve/U.S. Tsubaki: If you’re not sure what you need, ask! It’s much easier — and cheaper — to work out problems in the design phase than after a full fleet of machinery is in operation. Thoroughly review the selection procedures, and if anything is unclear, ask for help.
Overestimating the demands on your system will provide some leeway to boost production down the road. Consider using a chain that can operate at higher speeds or carry heavier loads if required in the future.
Tim/Belt Technologies: For metal belts, thinner design profiles are often better than thicker ones. They are extremely strong even when manufactured at 0.005-in. thick or less. The common theory was to increase belt thickness to improve performance, when in fact, a thinner belt has resulted in longer life and better accuracy.
Galen/Dodge of Rockwell Automation: When designing a drive, identify the mechanical drive that will provide the most benefits to an application. Start by comparing the types and styles of drives with the rotational shaft speeds required in the application. Generally speaking, the optimal speed range of chain drives is below 1,000 rpm, synchronous-belt drives is between 50 and 2,500 rpm, and V-belt drives is above 250 rpm.
In addition, belt strength and horsepower ratings have increased considerably over the last several decades. So, if you need to replace belts on a drive selected two or more decades ago, it may be overkill to use the same number of belts as previously specified. The excess capacity could lead to efficiency loss. Modifying the drive selections can increase the drive efficiency.
What can bearing MANUFACTURERS do to offset limitations?
Galen/Dodge of Rockwell Automation: Manufacturers can assist end users in selecting the proper drive for the application by comparing the performance qualities of the drives, including overhung load, belt/chain stress, product life, and cost.
Pete/Jason Industrial: Timing-belt construction is similar among all manufacturers. Sometimes teeth are covered with a nylon wear surface, which helps the belt mesh smoothly with the pulleys. The strength of the belt is derived from the helical-wound tensile cord, usually made of fiberglass. Glass is very stable and allows control over belt length; this is critical, as belt pitch must be maintained to ensure they fit their pulleys.
Steve/U.S. Tsubaki: New materials, coatings, and construction are being designed to solve specific problems for end users. Selflubricating chains require no maintenance and can extend wear life to many times that of standard chain. Corrosion-resistant chains offer trouble-free performance in wet conditions. Industrial plastic chains are available for a variety of special applications, from high friction to static electricity to antimicrobial resistance.
Pete/Jason Industrial: Some manufacturers substitute aramid fiber for fiberglass to take advantage of its higher shock resistance. Tensile cords are encapsulated by a synthetic rubber, which forms the belt body. The rubber is formulated for the best combination of flex and heat resistance, as well as for adhesion to other belt components.
Steve/U.S. Tsubaki: Performance problems are often perpetuated through a series of suppliers because no one wants to risk a sale by specifying chain higher than the original. The thinking here is that if Brand X can make do with a certain chain size, Brand Y should be able to as well. A manufacturer willing to break that cycle can significantly improve a system’s productivity.
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What can DESIGNERS do when selecting and applying belts and chains to improve productivity?
Steve/U.S. Tsubaki: Designers should think about preventative maintenance when designing chain drives. Incorporate a self-adjusting, springloaded tensioner design, for example, to avoid the overtensioning problems inherent in manual, screw-type chain designs. Allow access for periodic lubrication — sometimes chains are so buried in a system you can’t get to them.
Galen/Dodge of Rockwell Automation: Reducing overhung load is a great way to improve productivity. Larger sheaves have greater horsepower capability and less belt pull so fewer belts are needed. This reduces the overhang by narrowing the face width of the sheave or sprocket. And because belt pull has decreased, bearing life and shaft operation will improve.
Tim/Belt Technologies: Be as straightforward as possible with design criteria. Too often only fragments of a design program are given. Not knowing how the belt will interact with other parts of the overall design makes it difficult to avoid field retrofits and design changes.
Pete/Jason Industrial: One important point to remember when designing a conversion: For drives where the load is sensitive to driven speed, you can save energy by adjusting the speed ratio of the drive to end up with the same driven speed for the timing belt and V-belt.
Steve/U.S. Tsubaki: Sprocket selection is another factor. Designers often incorporate the smallest sprocket diameters possible to allow for the most compact machine footprint. But the smaller the sprocket, the sharper the turn the chain has to make around it — resulting in faster wear.
What should END USERS do (in terms of care and upkeep) to maximize belt and chain life and machine productivity?
Pete/Jason Industrial: Proper alignment and installation procedures should be followed. Too often mechanics roll belts onto a drive rather than loosen a motor base. Productivity increases are possible by using synchronous drives, which are about 5% more efficient than V-belt drives.
Galen/Dodge of Rockwell Automation: Chains should be lubricated properly, as well as cleaned and inspected on a routine basis. V-belt sheaves should be inspected for wear when operating in abrasive environments.
Pete/Jason Industrial: Cost savings can be made with synchronous belts, which require no retensioning or maintenance. They need no lubrication (unlike chains) and are generally unaffected by airborne particles or wetness. Additionally, timing belts require lower install tensions than V-belt drives. This translates into lower loads and longer life. But timing-belt drives require more precise alignment and do not provide clutching action needed for some applications.
Steve/U.S. Tsubaki: If you make the proper chain selection and then treat it horribly, it will wear away before your eyes. Maintenance checkpoints include proper centering, sprocket alignment, take-ups, and amount of chain tension and slack. Proper lubrication is essential for peak performance and maximum chain life. Follow lubrication schedules and recommendations carefully.
Tim/Belt Technologies: Adhere to the engineer’s design parameters. Items such as tensioning, belt/pulley alignment, and loads are all considered in the design. If end users operate outside those parameters, they may have difficulty achieving what the engineer set out to deliver.
Pete/Jason Industrial: As a belt seats itself into a drive, slip increases to about 4 or 5%. If properly selected and maintained, the overall efficiency of V-belts ranges from 90 to 94%. Air turbulence, flexing, creep, centrifugal losses, and slippage eat away at efficiency. Timing belts, on the other hand, are 96 to 98% efficient because of their lower bending and centrifugal losses.
How do belt and chain choices affect other areas of the machine or system?
Galen/Dodge of Rockwell Automation: Proper tensioning can lengthen bearing life and prevent shaft damage. Additionally, proper drive selection can reduce overhung load. One of the most significant tradeoffs in design consideration comes from minimum sheave or sprocket diameter. As driver diameter decreases, not only does the belt pull increase, but stresses on the belt increase due to greater bending. This decreases horsepower capability and results in needing more belts to transmit the load.
Steve/U.S. Tsubaki: Most performance tradeoffs are easily avoided by selecting the right chain. For instance, noise used to be a common drawback of chain. But new technologies have virtually eliminated that tradeoff.
Sprocket chordal action can cause some vibration issues when using chain. For example, if the chain selected is too large for a speed application, it can create excessive centrifugal force that overloads components such as shafts and bearings.
When using two strands of chain in parallel, it’s better to buy matched and tagged sets to minimize variation in elongation rates.
Overall, chain offers tremendous design flexibility. It allows reversible operation, which lets designers incorporate switchbacks to reduce conveyor footprint. It’s easy to adjust conveyor length by changing the center distance of sprockets and by adding or removing sections of chain. Chain can withstand extreme temperatures, speeds, and corrosive conditions. And an endless variety of attachments are available for a wide range of applications. Tim/Belt Technologies: As noted, all other elements of the design can impact how a belt or chain is expected to work and how the entire machine ultimately functions. Use the expertise of the belt or chain manufacturer to improve overall design.
Tradeoffs come every time a design principle is compromised for one reason or another. Understand those compromises, and the end result will be engineered for efficient manufacturing processes.