PU timing belt AT3 639 - Conti® Synchroflex

Conti Synchroflex AT3 639 – endless timing belt for precise industrial drives

With 213 teeth spread over a pitch length of 639 mm, the Conti Synchroflex AT3 639 is designed for precise transmission of rotation, timing and position. The belt is cast endlessly in PU and has integrated steel cord tension elements that stabilize the length during normal operation. The nominal tooth pitch is 3 mm and the tooth profile must match the profile of the pulleys exactly. It is not sufficient for another belt to have approximately the same length or width. This is the standard version in the specified profile. It must not be confused with a possible GEN III version or a double-sided DL belt with the same pitch length.

Fixed specifications

• Pitch length: 639 mm
• Number of teeth: 213
• Tooth profile: AT3
• Tooth pitch: 3 mm
• Material: cast polyurethane with steel cord
• Brand: Conti Synchroflex

These specifications can be used as a check against the marking on the old belt or against the machine's spare parts list. The pitch length is not necessarily the same as a measurement across the outside of the belt, and the number of teeth is therefore often the safest additional check. If in doubt, both the belt and timing belt pulleys should be examined before ordering a replacement.

How tooth geometry works

The metric AT geometry has trapezoidal teeth with a larger tooth volume than the standard T profile. The purpose is to distribute the load advantageously in the tooth mesh and achieve higher tooth strength without making the drive unnecessarily large. The profile requires suitable AT timing belt pulleys with the same pitch; a visual similarity to other profiles is not evidence of compatibility.

Belt construction

The belt body consists of wear-resistant polyurethane, which encloses high-strength steel cord. The materials each have their own function: PU forms the teeth and protects the belt against mechanical wear, while the cord tensioning elements provide high longitudinal stiffness and limit post-elongation. Continental describes the design as maintenance-friendly and lubrication-free. This does not mean that the drive can be ignored; pulleys, alignment and pretension should still be checked.

The construction behind this variant

This item is a single-sided standard design. The teeth are located on the inside of the belt, while the back is smooth. It should not be confused with a double-sided DL version or the red GEN III series. If the machine is originally dimensioned for a specific variant, a change should only be made after a technical assessment of load, pulleys and preload.

Checking when replacing

The product's 213 teeth provide a convenient length check. Multiplying the number of teeth by 3 mm gives a pitch length of 639 mm. If an existing belt has a different number of teeth, it is not the same size, even though it may look almost the same length. Also check that the teeth on the pulleys match the AT3; the same pitch number alone is not always sufficient.

Which drives is the product compatible with?

The application examples in the catalogue include small power drives, handling equipment, compact positioning axes and light synchronous feeds. This shows that the profile can be used in both power transmission and motion control. However, the specific belt must only be finally selected when the machine's torque, speed, center distance and pulley geometry are known. When simply replacing a spare part, the safest method is usually to copy the documented profile, length, design and width.

Width selection and price calculation

The belt width is not written in the product name because the same pitch length is collected on one product page. The starting pu is 6 mm. Integer widths from 6 to 50 mm can be selected on this product page. The original supplier widths for this length are 6, 8, 10, 12, 16, 20, 25, 32 and 50 mm. Other intermediate sizes are offered as cut-to-size versions of the same type of timing belt sleeve when they are within the selection shown. The number of teeth, pitch length and profile do not change when the width is changed.

Disc geometry and tooth engagement

The tooth profile of the timing belt pulleys must correspond to the AT3 of the belt, and their pitch must be 3 mm. The transmission ratio is determined by the ratio of the number of teeth of the pulleys, not by the width of the belt. A larger pulley usually reduces the bending load, while a very small pulley gives more bending per revolution. The angle of engagement and the number of teeth in mesh must be sufficient for the current load.

Correct splice in the timing belt tensioner

The timing belt pulleys must be parallel and in the same plane. Even minor misalignments can cause the belt to move towards a flange and cause edge or cord damage. The belt should be installed without being twisted, sharply bent or pressed over a flange with a tool. The center distance is adjusted to achieve the calculated preload. Too high a tension increases the bearing and cord load, while too low a tension can cause tooth jumps at load peaks.

Temperature, media and service

The standard material is specified for ambient temperatures from -30 °C to +80 °C. Applications close to the limits, especially below -10 °C or above +50 °C, may require special sizing. The service life is not only affected by the material, but also by load peaks, bending, pulley size, alignment and environment. Keep the drive clean and do not remove deposits with sharp tools that could damage the teeth. If the belt operates in chemically exposed areas, food environments, clean rooms or at extreme temperatures, a suitable special design should be considered.

Checking teeth, back and edges

A properly running timing belt should move smoothly without continuous contact against one flange. Regularly check the teeth for deformation, the back for ctiming bars and the edges for frayed areas. Abnormal noise or heat can be an early sign of incorrect tension or pulley failure. A systematic check of pulleys and belt is more effective than trying to hide symptoms with lubricant.

Technical questions about the product

Conti Synchroflex AT3 639: what does the steel cord mean for the function of the belt?

The steel cord tension members absorb the longitudinal tensile load and provide high longitudinal stiffness. This helps maintain pitch and position during operation. The cord must not be kinked, exposed or damaged during installation, as local damage can weaken the belt.

Conti Synchroflex AT3 639: what temperature can the belt work at?

The standard version is specified for ambient temperatures from -30 °C to +80 °C. At temperatures below -10 °C or above +50 °C, adapted sizing may be required.

Conti Synchroflex AT3 639: what is the difference between AT3 and a GEN III belt?

This product is the standard version. GEN III is a separate reinforced series with red high-performance PU and denser, two-filament steel cord. The same profile and length therefore do not mean that the products are identical.

Conti Synchroflex AT3 639: how does preload affect operation?

Correct pretension keeps the teeth in stable engagement and reduces the risk of tooth jump. Too low a tension can cause impact and jump under load, while too high a tension increases the load on the cord, pulleys and bearings. The correct value must be determined based on the drive's dimensioning.

Conti Synchroflex AT3 639: how to check if the length is correct?

Count the teeth and check the pitch. 213 teeth times 3 mm gives 639 mm pitch length. Then compare the profile and design with the marking or the machine parts list. A measurement around the outside of the belt alone is not accurate enough.

Conti Synchroflex AT3 639: can the belt be installed by pressing it over the pulley flange?

This should be avoided. The belt should be installed by adjusting the center distance or following the correct installation procedure for the machine. Forcing it over a flange can damage the cord pullers, teeth or belt edge. After installation, the pulleys must be parallel and the pretension must be correct.

Conti Synchroflex AT3 639: does the number of teeth change when the belt width is changed?

No. All width choices on this product page have the same pitch length of 639 mm and the same number of teeth of 213. Only the width of the belt, and thus the price and possible load capacity, changes. The width must still match the pulleys and the technical dimensioning.

How many teeth does the Conti Synchroflex AT3 639 have?

The belt has 213 teeth. The number of teeth is calculated by dividing the pitch length of 639 mm by the tooth pitch of 3 mm. The result is 213, and this number can be used as an additional check when identifying an existing belt. A different number of teeth means a different pitch length.

The most important thing about this size

In summary, this is a Conti Synchroflex PU timing belt with a fixed geometry of 3 mm pitch, 213 teeth and 639 mm pitch length. The width is selected separately, but does not change the length or number of teeth. A safe replacement requires that the entire designation and the specific version match the machine documentation.