The Belt Doctor’s Prescription for Longevity in Motion Control

In industrial automation and motion control, the humble belt is often overlooked. Yet it plays a major role, enabling conveyors and machines to move with precision and reliability under demanding conditions. Getting these belts right is a complex blend of materials science, engineering design and real-world know-how.

Jim Hammond, known in the industry as the “Belt Doctor,” brings a physicist’s rigor and a maker’s passion to this challenge. After rescuing a twice-bankrupt belt manufacturing company in the early 1990s, Hammond engineered a unique robotic production process and introduced thermoplastic elastic belts designed primarily for motor-driven roller (MDR) conveyors.

These belts differ fundamentally from standard timing belts used inside robots: They’re elastic, absorbing vibrations and shocks to protect equipment and extend service life, but they require sophisticated coordination with sensors and brakes to achieve precise container positioning.

Hammond, a physicist with an engineering mindset sharpened at places like the Jet Propulsion Lab and PerkinElmer, saw a way forward for the failing company. Applying his love of machines and hands-on skills that he gained through machine shop courses and years of tinkering with lathes and milling machines, he designed and built a unique robotic manufacturing system.

Programmed by his son Scott, a former IBM top programmer, he told Machine Design this proprietary “super robot” doesn’t just automate production; it actively corrects errors mid-run, ensuring belts are made stronger than anyone expected, he said.

MD: Which factors most significantly influence belt slip under varying load and speed conditions, and what design or operational adjustments can minimize slip in critical manufacturing processes? 

JH: The factors are: belt and roller/pulley material (its coefficient of friction), the system’s moment of inertia, the motor ramp up/down speed, container bottom types, environment (especially temperature, dustiness and moisture), container rubbing contact with conveyor frame (if any), conveyor levelness or incline/decline. 

To minimize slip for critical positioning, timing belts or timing chains are required. Elastic belts, by themselves, cannot be used for positional accuracy and precision control. However, such requirements can be achieved by coordinated use of conveyor sensors and brakes (especially popup brakes) that can stop containers at certain positions.

MD: What materials and reinforcement options are available for industrial belts, and how do different material choices affect durability and performance in harsh environments like high temperature, chemical exposure or heavy contamination? 

JH: Industrial belts can be made from plastics (primarily polyurethane, PVC, polyester), rubber (various types, especially EPDM), modular plastic, Activated Roller Belt (ARB) technology, chains, thin sheets of flat stainless steel. Plastic and rubber belts can be reinforced with polyester, non-stretch Kevlar (aramid), Nylon (polyamide), steel cord and almost any other kind of plastic cord or fabric. 

Each belt material is rated for high and low temperatures and chemical exposures. Our website, www.durabelt.com, has data sheets, frequently asked questions and web pages specifying the ranges of environments, including wash down chemicals, where each belt type can and cannot operate. For example, our main product, TPU round belts, should not be washed down with bleach as that will reduce belt lifespan.

Belts reinforced with non-stretch materials, timing belts and timing chains rarely work with even light contamination, so they must have a clean environment. Round, vee and poly-V belts can work in high contamination if the contamination falls out or is squeezed out as it goes around pulleys.

Round and vee polyurethane belts can work well in wet environments where they squeeze out the water when going around pulleys. Flat belts can work well with heavy contamination, provided they use wipers that wipe away contamination and/or have corrugated sidewalls and cleats that prevent contamination from getting under flat belt surfaces.

MD: How do you determine the optimal pulley diameter for power transmission efficiency and the best groove profile to maximize belt life in continuous production environments? What trade-offs must be considered?

JH: Every time a belt bends, the outer edge of the bend stretches and the inner edge gets compressed. This stresses the belt molecules and creates internal heat. The hotter the belts get, the more the long chain molecules tend to break up. The greater the bending angle and the faster it bends, the more stress and heat build up, so the shorter the belt’s lifespan will be. Therefore, the optimum pulley diameter is the largest diameter that is practical for a given application.

Minimum Pulley Diameter (MPD) is probably determined with the Zwick Flexometer that measures Tensile Fatigue Endurance (flex life) along with observation of how the belt comes off the pulley. Belts should not flare but rather be parallel to the line connecting pulley centers.

MD: What are the common failure modes seen in belt-driven systems operating under heavy industrial loads? How do you detect early warning signs and which predictive maintenance techniques are most effective to prevent downtime? 

JH: The most common premature failure mode occurs when the belt is abused. This often happens when there is a container jam (like when containers get caught on a frame edge or at a divert) or unexpected accumulation. When the jammed container stops, the rollers underneath stop and the belt stops, but the motor keeps running. That causes the belt to slip on the motor, so the resultant friction overheats the belt, forcing it to abrade and/or melt.

Even if the belt survives, overheating can cause it to lose some of its elastic memory. To prevent this, PLCs should sense the stoppage and shut down the motor within 4 sec. If they are set at 30 sec. to “power though the jam,” then the belt will probably need to be replaced.

Another abuse happens when a pop-up brake stops a box, but the motor keeps running, thereby causing the belt to slip. Again, the PLC should shut down the motor within 4 sec. If you need to square boxes so a pallet-loading robot can grab them, do not power the last idler rollers with belts, but accelerate the container and/or tilt the last zone so gravity will accelerate the container to force it to square itself against the brake.

Belts can also slip if the motor ramps up or down too quickly. You can often get an early warning that a belt is slipping if you hear a squeak when heavy rollers or heavily loaded rollers start or stop. Moreover, the bright color of new polyurethane belts usually gets muted by dust after running for a month. That dust is often scraped off when belts slip so it is easy to see slipping belts at a distance. Therefore, when some belts are more brightly colored than others, it means that they are being stressed, so PLC's ramp up/down speed should be reduced. 

Of course, another common failure mode occurs when environmental chemicals attack belts. Polyurethane is resistant to most oils and greases, but it does not like acids or alkalis. Most beverages—even beer and fruit juice—are acidic, so care must be taken to prevent spills from exposing belts to beverage acids.

Acids and alkali often affect rubber belts so the same applies to them. Only our Hytrel polyester round belts usually work well in acid and alkali environments. Hytrel belts are also used in extremely cold environments (down to -40°F) like in ice cream plants and sushi warehouses.

MD: Can you explain how belt drives contribute to vibration damping in precision machine tools? How does their performance compare to gear drives in terms of frequency response and energy dissipation? 

JH: Highly elastic belts absorb the energy caused by vibrations and shocks better than inelastic belts. Such energy absorption produces waste heat that gets dissipated into the environment. Metal gears are hard and inelastic, so they do not absorb vibrations and shocks, but rather transmit them.

Therefore, if a motor vibrates excessively, gears and inelastic belts can transmit its vibrations and shocks to precision machine tools, causing them to vibrate, be less precise and fail prematurely. Conversely, standard conveyor rollers wobble as they rotate. Inelastic belts transmit wobbling vibration to MDRs, causing bearing wear and amperage spikes that can reduce MDR lifespan.

MD: How does cost affect belt choice?

JH: Our thermoplastic polyurethane belts are the least expensive belts and can be produced quickly in large quantities at any length and in many colors. 

Since polyurethane belts are the most elastic belts, they are the best at absorbing vibrations, so they probably run the quietest. Their high elasticity also helps protect and extend the life of motors and bearings from vibrations and shocks better than virtually all other belts. They also use less energy than most other belts, when running on low cost, standard "wobbly" rollers. Polyurethane belts’ inexpensive color coding facilitates fast, fool-proof installations where several slightly different lengths are used. 

Our round “O-ring” belts are extruded, so they have the same amount of urethane on the outer diameter and the inner diameter, as opposed to injection-molded O-ring belts that have less material on the inner diameter. This means that unlike molded O-rings, our O-ring belts spiral like candy canes whenever they are misaligned or used on curves, so they likely last longer because they don't tend abrade and lift out of grooves or excessively wear like most other belts (except ConveyDyn D-shaped belts that slip fairly easily to stay in grooves). 

Furthermore, our extruded polyurethane belts significantly reduce costs because they do not require finger guards like all other belts where employees can accidentally put their fingertip underneath them. Since our belts stretch more, they are safer because they can stretch to accommodate the fingertip and let it quickly roll out from under them without causing severe damage.

MD: Are Dura-Belt's belts environmentally friendly, biodegradable, green and recyclable, with a relatively low carbon footprint?

JH: Unlike virtually all rubber belts, all our TPUs belts can be recycled—melted down and reused in other products. Moreover, 96% of our round, flat and vee belts are made from thermoplastic ester-based polyurethane that if left in sunshine (UV), water or underground bacteria for a decade or two will ultimately biodegrade. Our webpage provides these details: