optibelt ZRS for Cylindrical Bores

A key characteristic of every Timing Belt Pulley is the pitch (t). It describes the distance between the centers of two adjacent tooth gaps and determines the pitch of the Timing Belt Pulley.

The pitch is measured on what is known as the effective diameter. This is a theoretical dimension that lies outside the Timing Belt Pulleys. The effective diameter is therefore larger than the pulley’s outer diameter and corresponds to the effective line of the Timing Belt.

As shown in the figure above, the teeth of the Timing Belts and the Timing Belt Pulleys are precisely matched. In the area where the Timing Belts wrap around the pulleys, the Timing Belts’ teeth engage positively with the tooth slots of the Timing Belt Pulleys, ensuring slip-free operation.

Our standard Timing Belt Pulleys are available as solid pulleys, plate pulleys, or spoked pulleys. When selecting the appropriate design, keep in mind that solid and plate pulleys are generally rated for higher permissible circumferential speeds than spoked pulleys.

Optibelt ZRS Timing Belt Pulleys in small and medium diameters are equipped with flanges on both sides as standard. These prevent the Timing Belt from jumping off the pulley or slipping sideways.

Larger pulley diameters, which are often used in combination with smaller Timing Belt Pulleys to achieve high gear ratios (i ≠ 1), are, in contrast, designed without flanges. However, it is generally recommended to equip the driving Timing Belt Pulley with flanges on both sides.

In this context, please refer to our design drawings, which provide information on the specific design of each pulley.

Our standard Timing Belt Pulleys are manufactured in accordance with the ISO 254 quality standard and are available with Taper-Bushing system or for cylindrical bore. Timing Belt Pulleys with cylindrical bores are supplied pre-drilled as standard, with the exception of very small diameters. Upon request, they can also be supplied with possible finishing operations, such as: finished bore including keyway in accordance with DIN, as well as mounting threads for adjusting screws.

Optibelt ZRS gray cast iron Timing Belt Pulleys are statically balanced as standard, regardless of size and design. Balancing is performed in one plane to balance class G16, allowing for use at peripheral speeds of up to 30 m/s.

Gray cast iron Timing Belt Pulleys should not be used for applications with speeds of 30 m/s or higher. Timing Belt Pulleys machined on all sides generally meet or exceed balance class G16 in accordance with ISO 21940 and are therefore not typically subjected to separate balancing.

For high speeds and in drives with particularly high requirements for smooth operation, dynamic balancing in two planes to balance class G6.3 or finer is recommended. This applies in particular to:

• Timing Belt Pulleys with circumferential speeds of 30 m/s or higher
• Applications up to the maximum permissible belt speed
• Drives with increased requirements for smooth operation, even at lower speeds

If there is clearly visible wear on the Timing Belts or Timing Belt Pulleys, the affected components should be replaced. To ensure reliable operation, it is recommended to perform regular visual inspections of the Timing Belt Pulleys.

Checking the outer diameter provides additional assurance. Deviations from the specified dimensions may indicate wear and may require a more detailed inspection.

Detailed instructions on the installation and alignment of shafts and Timing Belt Pulleys, as well as on the design and calculation of drives using Optibelt Timing Belts, can be found in the corresponding technical manuals.

Depending on the profile and number of teeth, our standard Timing Belt Pulleys are available in steel, aluminum, or gray cast iron. The choice of material should be based on the requirements of the specific application.

Due to their lower hardness and wear resistance, aluminum Timing Belt Pulleys are preferably used in lighter-duty drives with low belt tensions and moderate speeds. In applications with a higher number of teeth in mesh, the softer material can also offer advantages.

Steel or gray cast iron Timing Belt Pulleys, on the other hand, are significantly more wear-resistant. However, their greater weight increases the moment of inertia during continuous acceleration. For the Taper Bushing system, we supply standard Timing Belt Pulleys exclusively in steel or gray cast iron.

Corrosion Protection

The surfaces of our standard Timing Belt Pulleys are finished according to the material:

• Cast iron: phosphated surface
• Steel: Black oxided surface
• Aluminum: bare surface

In addition to the standard versions made of cast iron, aluminum, and steel, we offer numerous other materials as well as custom surface treatments upon request. Our application engineers will be happy to advise you on selecting the optimal solution for your application.

The T-profile with metric pitch according to ISO 17396 / DIN 7721 Part 2 is one of the most commonly used Timing Belt profiles. Compared to traditional inch-based trapezoidal profiles, it has taller teeth, thereby enabling greater power transmission.

T-profile Timing Belts may only be used with T-profile Timing Belt Pulleys. Due to its characteristics, this profile is primarily used in new designs for applications with lower loads.

Thanks to the thinner tensile member diameter and narrower teeth compared to AT and HTD profiles, T-profile Timing Belts are more flexible and can be used on smaller Timing Belt Pulleys with smaller diameters.

Both the T-profile and the AT-profile are characterized by very low clearance between the Timing Belts and the Timing Belt Pulleys. With the AT-profile, this clearance is even smaller than with the T-profile. The high fit accuracy makes both profiles particularly suitable for positioning tasks.

The AT profile, conforming to ISO 17396, represents a further development of the proven T-profile and is often preferred in new designs, particularly for high-performance drives. It is also a trapezoidal profile; however, the teeth are taller and wider.

Among all trapezoidal profiles, the AT Timing Belt has the widest tooth width, thereby achieving the highest tooth shear strength and the highest allowable specific tooth force. For applications with high positioning accuracy requirements, the AT profile is particularly recommended because it offers even less play between the Timing Belt and the Timing Belt Pulleys than the T profile. For optimal performance, AT Timing Belts must be used exclusively with AT Timing Belt Pulleys.

The HTD (High Torque Drive) M-profile, conforming to ISO 13050, is an evolution of the classic inch-based Timing Belt profile. It features a circular-arc tooth profile with metric pitch and was developed specifically for power and linear drives.

Thanks to its wider and taller teeth, the HTD profile can reliably transmit high torques. The combination of high tooth height and semicircular tooth geometry ensures even force distribution across the teeth and provides exceptionally high protection against tooth skipping. In addition, the HTD profile is characterized by exceptionally smooth operation.

Compared to the AT profile, the HTD profile has larger tooth flanks. However, the tooth clearance between the Timing Belts and the Timing Belt Pulleys is also greater, resulting in lower positioning accuracy than with an AT profile. For applications with high positioning accuracy requirements, the further-developed trapezoidal AT profile should therefore be preferred.

HTD Timing Belts, as well as Timing Belts with the Optibelt/Omega profile, can be used in standard HTD Timing Belt Pulleys. Timing Belts with the RPP profile are also compatible with HTD Timing Belt Pulleys.

The optibelt DELTA CHAIN high-performance Timing Belt, when used in combination with the appropriate optibelt ZRS DC Timing Belt Pulleys, enables slip-free and synchronous power transmission of up to several hundred kilowatts. This system is particularly well-suited for applications involving high torques and heavy dynamic loads.

The overall width can generally be significantly reduced for power drives with small and medium center distances. The optibelt DELTA CHAIN opens up numerous application possibilities. Among other things, it is suitable for applications that were previously reserved for roller chains. Compared to chain drives, the Timing Belt Drive offers advantages such as lower weight and a more compact design.

The optibelt DELTA CHAIN Timing Belt and the corresponding optibelt ZRS DC Timing Belt Pulleys are standardized according to ISO 13050.

The involute tooth profile of the optibelt DELTA CHAIN Timing Belt ensures optimized tooth engagement and a precise fit in the exactly matching teeth of the corresponding optibelt ZRS DC Timing Belt Pulleys.

The so-called G-profile was developed exclusively for high-performance Timing Belts and is not compatible with other profile systems. Therefore, it cannot be combined with Optibelt/Omega, HTD, RPP, or STD profiles.

Optibelt ZRS 8MDC Timing Belt Pulleys are available in 12 mm, 21 mm, 36 mm and 62 mm widths. Optibelt ZRS 14MDC Timing Belt Pulleys are available in 20 mm, 37 mm, 68 mm, 90 mm and 125 mm widths. This ensures that there is a suitable solution available for a wide variety of performance requirements and installation situations.

The first Timing Belts were developed with a trapezoidal profile and inch-based pitch. They were originally designed for synchronous power transmission.

Thanks to the large contact area of the teeth, the trapezoidal tooth profile is suitable not only for power transmission but also for numerous material-handling applications. However, because the teeth are relatively low, power transmission is limited to the low- to medium-range.

Due to their American origins, the dimensions of this profile series are specified in inches (“in”). The width and length codes commonly used today were derived from the inch-based specifications for length and width.

The trapezoidal profile is standardized according to ISO 19347 and ensures reliable compatibility between Timing Belts and Timing Belt Pulleys. The classic optibelt ZR Timing Belt is used with optibelt ZRS Timing Belt Pulleys of the same profile and width designation. The following rule applies: Inch-based Timing Belts can only be combined with inch-based Timing Belt Pulleys.

The inch-based trapezoidal profile is primarily used today in the aftermarket. In new designs, particularly in Europe, however, it plays only a minor role.

For new drive designs, modern profiles such as the Optibelt Omega profile are increasingly preferred due to their higher performance. Therefore, it is recommended to use this profile generation for new developments.