Designing Timing Belts with Cleats: Materials, Forces and Fastening Methods Explained
Cleats are key elements in automation systems. Discover the versatility of cleats and find the ideal cleat geometry for your application.
1. Introduction: Why cleated timing belts are indispensable
Wherever processes run automatically, not only the drive power but also the position, the cycle and the timing must be transmitted precisely. Whenever conveyed goods are to be moved, separated, aligned or provided in a defined position, timing belts with cleats, also called cleated timing belts, are used.
The combination of a timing belt and the cleats mounted on it enables precise positional conveying. In contrast to smooth conveyor belts or pure drive belts, cleated belts assume a defined mechanical function: They ensure that the conveyed goods are transported synchronously, reliably and with high repeat accuracy.
Possible applications include Pick-& Place systems, packaging machines, palletizers, sorting lines, CNC handling units as well as in the pharmaceutical and food processing industries.
For cleats on timing belts to function perfectly, several factors must be coordinated: forces, geometries, materials, manufacturing processes and fastening.
In this article, you will learn everything you need to know about cleats. Among other things, the following questions are addressed:
- Which functions can cleated timing belts perform?
- Which forces occur in a cleated timing belt?
- From which materials can cleats be manufactured?
- How can cleats be fastened to timing belts?
- Which cleat geometries are possible?
- What should be considered in the design and arrangement of cleats on timing belts?
- Which additional options do innovative manufacturing processes offer?
2. Timing belts with cleats as carriers of mechanical functions
A conventional timing belt is a drive component for positive transmission of torques. By additionally using cleats, this pure drive element becomes a conveying medium that can transport a wide variety of goods.
A cleated timing belt consists of two main components:
- the belt itself, usually made of polyurethane with an integrated tension member of steel or Kevlar, and
- one or more cleats that are attached to the back of the belt and perform the desired carrier function.
The decisive advantage of this combination lies in the precise controllability of motion sequences. In addition, the combination of cleats with timing belts makes it possible to implement both synchronous conveying processes and complex, indexed conveying movements. For example, when components have to be inserted into a processing or packaging station in a defined position.
3. Forces and loads on cleated timing belts
When cleated timing belts are used, several types of forces occur simultaneously:
- Tensile forces in the belt (along the span),
- Shear and compressive forces on the cleats (transverse or perpendicular to the direction of travel),
- Acceleration and deceleration forces resulting from the mass moment of inertia of the conveyed goods.
High alternating loads occur especially during starting and stopping. Each cleat must not only accelerate or decelerate the dead weight of the conveyed goods, but also the dynamic additional forces resulting from the motion sequence. Particularly with short cycle times, high speeds or vertical conveying (e.g. on sorting lines), the loads increase exponentially.
The greatest load peaks typically occur
- during abrupt accelerations (“hard start-up movements”),
- during changes of direction in intermittent processes,
- in the event of collisions with stops or mechanical end positions.
For this reason, the type and magnitude of the loads should be analyzed precisely when dimensioning timing belts and cleats. Questions such as the following help, among others:
- How large is the mass to be moved?
- Within what time should the conveyed goods be accelerated or decelerated?
- How large will this make the shear load on the connection between cleats and timing belt?
The position and width of the cleat also play a role: the further outwards or more asymmetrically a cleat is positioned, the greater the lever forces that can occur.
Last but not least, the tensile forces in the belt must also be considered. The task of the tension members is to absorb the longitudinal forces, if possible without the timing belt being deformed or elongated, as this would have a direct negative effect on positioning accuracy.
For a good conveying solution, it is therefore essential to precisely match the conveyed goods, the motion parameters, the cleat shape, the belt width, the tension member material and the fastening technique to one another.
4. Geometry and shape of cleats
The geometry of the cleats is the key to their function. Only when shape, position and size are precisely matched to the application can the desired carrier performance be reliably achieved.
In practice, various basic shapes have proven effective:
- Rectangular cleats: universally applicable, easy to manufacture
- Trapezoidal cleats: favorable force distribution, reduced stress peaks
- Rounded or inclined cleats: ideal for smooth transitions and sensitive conveyed goods
- Radial cleats: for rotating or circularly synchronized movements
- Multiple cleats: for complex motion profiles or wider conveyed goods
In addition to these classic variants, special shapes are also becoming increasingly important, tailored specifically to special requirements:
- Spring cleats: These cleats have a flexible zone or an integrated spring mechanism that yields when in contact with the product and then returns to its original shape. Spring cleats have proved particularly effective for very sensitive parts or products with uneven thickness, such as tea bags, bubble wrap packaging, biscuit packs or textiles. The spring structure gently compensates for height differences and thus ensures safe transport of the product.
- Fan cleats: Fan cleats are very long and flat and are made of glass-fiber-reinforced material. They can be arranged at a very tight pitch. They are particularly suitable for the individual transport of flat and lightweight products such as baby diapers, hygiene products or envelopes.
- Cleats with brushes: For gentle handling of particularly sensitive goods such as fruit or textile fabrics, brush cleats are suitable. The height and material of the bristles as well as the spacing of the brushes from one another can be freely selected.
- 3D-printed cleats: 3D printing opens up completely new possibilities in cleat design. Complex geometries, integrated functions (e.g. channels, recesses, flexible zones) or ultra-lightweight structures can be realized without the need for mold making. Especially in special-purpose machine construction or for small series, printed cleats are economical and quickly available. They can be individually produced from all thermoplastic plastics.
What is important for all cleat shapes is this: The geometry must match the motion and the conveyed goods precisely. Another aspect is the dead weight of the cleats. At high cycle rates and high speeds, the mass moment of inertia has a considerable effect on system dynamics. Here, targeted lightweight construction, for example through material recesses, cavities or 3D printing, can contribute to energy savings and low-wear operation.
The design of the cleat geometry should therefore always take the following aspects into account:
- Force progression during engagement
- Mass inertia and system dynamics
- Contact surfaces and positive locking
- Material properties with regard to wear, temperature and chemical resistance
For individual requirements, it is advisable to seek advice from an experienced belt and cleat manufacturer. Alphabelt also offers you a cleat configurator and an extensive cleat library for your project.
5. Arrangement of cleats on the timing belt
Not only the shape, but also the arrangement of the cleats on the timing belt influences the function of the system. Here, precision and repeatability are particularly important. The following tips should therefore be taken into account during planning:
- The preferred cleat pitch is an integer multiple of the tooth pitch. So-called pitch conflicts could otherwise lead to misalignment, uneven running or increased belt load. Nevertheless, deviating arrangements in any number and sequence are also possible if they make sense from a design and functional point of view.
- Cleats should ideally be positioned opposite a tooth. The reason: at the teeth, a timing belt is bent less during deflection due to its greater material thickness than at the tooth gaps. The bending load is therefore lower at the teeth, which results in lower loading of the weld zone between belt and cleats and better force transmission.
- Mounting tolerances should be in the tenth-of-a-millimeter range, especially when several belts are operated in parallel.
- The belt guidance must also be matched to the cleats: A frame that is too tight or incorrectly positioned guide rails can cause cleats to jam, wear or even shear off.
Depending on the application, cleats are arranged
- centrally over the entire belt width (e.g. for narrow workpieces),
- off-center (e.g. for asymmetrical conveyed goods),
- offset or distributed over several tracks (e.g. for larger goods),
- or also in combination, for example with one guiding cleat and one supporting profile.
In any case, a precise design of the cleat arrangement is a prerequisite for a long service life, smooth running and exact repeat accuracy in the process.
6. Support of cleats
In practice, cleats and cleat fastenings are subjected to considerable forces. These arise from:
- inertial forces during acceleration and deceleration (e.g. in cyclic operation),
- frictional forces on slide rails,
- gravity in inclined or vertical conveying systems,
- centrifugal forces in the rotation of the timing pulleys,
- as well as the cleat’s own inertia during the transition between linear and circular motion.
In order to safely absorb these loads, additional supports are required, especially in the case of high accelerations, heavy conveyed goods or large cleat dimensions. A support should be designed in such a way that the acting forces act as far as possible in the lower cleat area. There, the weld can absorb shear stresses significantly better than bending stresses.
Cleats can be supported on one or both sides:
- Cleats supported on one side: to reduce bending forces on one side
- Cleats supported on both sides: for symmetrical force absorption and high loading capacity, especially in alternating movements.
The supports are designed as reinforcements of the cleat. The following must be taken into account: Especially with long cleats in the longitudinal direction, the bending capability of the timing belt is reduced, which can be critical with small pulley diameters. Particularly with long supports, the bending radius could become so large that the belt could no longer be guided around the timing pulleys without problems. This would lead to impermissible stresses and promote tearing of the weld joint. However, cleats and their supports do not have to be welded over their entire base area. It is sufficient if the support can bear against the timing belt under compressive load. The weld areas should be designed only as large as necessary, but as small as possible to ensure reliable function.
Furthermore, in many cases support via slide rails is also possible. Here, a support rail (sliding strip) is used, which runs under the belt and thus provides additional stability – both for the belt and for the cleats attached to it.
Smart positioning and support of the cleats make a decisive contribution to specifically reducing bending stresses and optimizing force application surfaces.
7. Fastening techniques in comparison
The secure connection of the cleats to the timing belt is one of the most important aspects when designing a cleated timing belt. It has a decisive influence on service life, load capacity and process reliability. Several fastening methods have proven themselves depending on the area of application and requirements:
- thermal welding
- mechanical fastening using screw systems
- bonding
- fastening using magnet systems
Thermal welding is the standard method for polyurethane belts. In most cases, the cleat is also made of polyurethane (PUR), i.e. the same material as the timing belt. This material identity allows a full-surface thermal connection that reliably withstands high continuous loads and dynamic stresses. The following processes are used:
- Mirror welding: The cleat and the back of the belt are heated evenly at the contact surfaces and then joined together under pressure.
- Friction welding: Controlled relative movement under pressure generates frictional heat, which melts the materials at the contact surface.
Both methods produce a form-fit and force-locking connection that is hygienically safe and particularly durable. However, it is not reversible: subsequent modifications or retrofitting are not possible.
Screw connections, on the other hand, are flexible and even modular in the ATN system. For applications that require subsequent adjustment or flexibly combinable cleat geometries, the ATN system is ideal. On the tooth side, it has pockets for accommodating threaded nuts. Cleats are screwed on mechanically here, which offers the following advantages:
- Interchangeability of individual cleats
- Variable positioning for format changes
- Variety of usable cleat geometries, including complex special shapes
The ATN system is used in particular in packaging technology, on sorting lines or in applications with frequent product changes. It combines high mechanical stability with maximum design freedom. However, the overall height is often greater than with welded cleats. In addition, screwed cleats offer more surfaces where dirt can accumulate at the contact areas with the belt, which is why they are more critical in terms of hygiene.
Adhesive bonds are rarely used and only in exceptional cases. They are occasionally used where thermal welding is not possible or mechanical fastening would be too complex. Bonding is generally less load-bearing and must be carried out very carefully. It is not recommended for permanently stressed series applications.
Magnet systems are used when a quick exchange of cleats is required for different conveyed goods or when individual cleats need to be replaced quickly and easily due to damage or wear. Compared to screw systems, magnet systems offer the most flexible and fastest way to change or reposition cleats. Modern neodymium magnets are currently the strongest permanent magnets available on the market and offer excellent holding force even with very small dimensions in the millimeter range. The magnets are embedded directly in the cleats and in the belt body made of PU. The cleats equipped with magnets in this way can simply be placed on the magnetic areas of the timing belt and removed just as easily. However, this high flexibility comes at a slight cost to positioning accuracy.
8. Materials: cleats and belt as a unit
Timing belts and cleats should be both mechanically and thermally compatible with each other in order to ensure long service life and functionality. Ideally, belts and cleats are made of the same material.
Polyurethane is considered the standard material. It combines high abrasion resistance, good flexibility and thermal shape stability. PU is particularly suitable for conveying and positioning applications subject to dynamic loads. Most timing belts for cleat applications are made of cast or extruded PUR and are reinforced with tension members made of steel or aramid.
The cleats are made of the same PU material as the back of the belt. This ensures:
- a permanently stable, wear-resistant connection,
- a homogeneous weld seam without material transition,
- minimal risk of detachment even under alternating loads.
Depending on the application, PU cleats can have different Shore hardnesses in order to achieve, for example, shock-absorbing or particularly stable properties. This makes it possible to reliably implement both sensitive and robust conveying tasks.
The material behavior of PU remains stable over a wide temperature range. In addition, it is resistant to many chemicals and has high resistance to oils and greases, a key advantage in industrial environments.
In the ATN timing belt system, other materials can also be used, since the cleats are not welded but mechanically fastened with screws. Therefore, timing belts and cleats do not necessarily have to be made of the same material. However, cleats made of polyurethane are also preferably used here, as they can be easily manufactured using standard production processes (casting, waterjet cutting, milling and even 3D printing). If necessary, coatings such as non-stick coatings made of Teflon can also be easily applied to PU cleats.
In individual cases, cleats made of other materials can also be fastened via the screw system, such as aluminum, stainless steel, glass-fiber-reinforced plastics or engineering thermoplastics (e.g. POM, PA). Their use can be useful under certain circumstances, but is not very widespread.
9. Conclusion: Precision through planning – fully exploiting the potential of cleated timing belts
Cleated timing belts open up a wide range of possibilities for automated product handling. They ensure precise indexing, among other things, and offer highly flexible conveying solutions. The correct technical design is crucial here:
- Mechanical: define forces due to acceleration, cleat geometry, positioning accuracy
- Dynamic: take changes in speed and mass inertia into account
- From a manufacturing perspective: weigh up welding accuracy, tolerances, manufacturing processes
Thanks to modular mounting systems such as the ATN system, cleats can also be mounted or replaced subsequently if required, which is ideal for format adjustments or prototype construction.
The combination of precise manufacturing, correct material selection and careful design ensures that the cleated timing belt reliably fulfills its function, whether in packaging systems, assembly lines or for the transport of sensitive products.
At Alphabelt, we have well over 1000 different cleats in our range. On request, we manufacture customer-specific cleat geometries for you, starting from just a single piece! We will be happy to advise you on which manufacturing process is best suited to your application. Discover the variety of our cleat and timing belt solutions in our shop today.
Get informed, choose and request directly now!