PU timing belt AT3 399 - Conti® Synchroflex

Conti Synchroflex AT3 399 – endless timing belt for precise industrial drives

With 133 teeth distributed over a pitch length of 399 mm, the Conti Synchroflex AT3 399 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.

Key technical data

• Pitch length: 399 mm
• Number of teeth: 133
• Tooth profile: AT3
• Tooth pitch: 3 mm
• Material: cast polyurethane with steel cord
• Brand: Conti Synchroflex

The technical data below describes the part of the product that does not change when a different belt width is selected. Pitch length, tooth pitch and number of teeth remain identical for all width choices. However, the width affects the available belt cross-section width and the price calculated on the product page. Correct sizing must always take into account torque, speed, number of teeth in mesh, pulley diameters, service factor and any counter-bending.

What characterizes the AT3 profile?

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.

Standard, GEN III or DL ​​– this version

The standard version is selected when the supplier's article data does not specify GEN III or DL. This is an important product distinction, because different versions can share both profile and length. Therefore, on this product page, it is the standard version that is described. The belt width can be selected, but the basic construction and tooth geometry are not changed.

Compare with the existing belt

The product's 133 teeth provide a convenient length check. Multiplying the number of teeth by 3 mm gives a pitch length of 399 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.

Typical applications and sizing

Continental cites small power drives, handling equipment, compact positioning axes and light synchronous drives as examples for this profile family. The examples describe the general application area of ​​the profile, but are not an approval for any specific installation. The final belt width and pretension must be selected based on the transmitted torque, starting and shock loads, operating time, pulley sizes, speed and the number of teeth in simultaneous engagement. For safety-critical or heavily loaded drives, an actual calculation should be made.

How the width variants work

This product line has been created with 6 mm as the base width because this is the width of the selected item and thus the SKU used for inventory control. Integer widths from 6 to 50 mm can be selected on this product page. The widths that appear as standard widths in the supplier data are marked separately in the options. The price surcharge is calculated as a percentage of the base width: doubling the width results in a surcharge of 100%. The technically necessary width should be selected according to the load and not only according to the price.

Timing belt pulleys and transmission ratios

The pulleys and belt should be considered as a single tooth engagement. Correct AT3 geometry ensures that the load is distributed over the tooth flanks rather than concentrated on tooth tips or edges. The drive ratio is selected by the number of teeth on the pulleys, while the belt's 133 teeth and 399 mm pitch length determine the required combination of pulleys and center distance. When changing the drive, the geometry should be calculated.

Practical advice for installation

Proper installation begins with clean, undamaged pulleys with the correct profile. Teeth and grooves should be checked for deposits, bars and wear before the new belt is fitted. The pretension should be based on the drive's calculation and should not be selected based on a random hand feel. After the initial run-in, it is a good idea to check grooveing, noise, temperature and whether the belt runs centrally.

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 molded PU belt is maintenance-friendly and does not require lubricant. Regular visual inspection is still relevant: look for ctiming bars, frayed edges, shiny tooth flanks, foreign body impressions and abnormal side contact. Sudden changes in noise or grooveing may indicate misalignment, too low tension or worn pulleys.

Signs of improper operation

Uniform light polishing of the tooth flanks may be normal, but localised spalling, ctiming baring or severe wear should be investigated. Wear on one edge often indicates misalignment or persistent flange contact. Damage to tooth tips may be due to incorrect profile, foreign bodies or inadequate engagement. If cord becomes visible or the belt has a sharp break, it should not continue in service without assessment.

Technical questions about the product

Conti Synchroflex AT3 399: can the belt run with counter-bending?

The possibility depends on the profile, cord design, the diameter of the rollers and the specific belt routing. Counter-bending increases the bending load and must be included in the dimensioning. A roller on the belt back must have sufficient diameter and be positioned so that tooth engagement and grooveing are not impaired.

Conti Synchroflex AT3 399: can this belt be used at high rpm?

The Conti Synchroflex series is designed for precise and fast synchronous drives, but the permissible speed depends on the profile, pulley diameter, belt width, load and peripheral speed. A high speed must therefore not be approved based on the product name alone; the drive must be calculated.

Conti Synchroflex AT3 399: can the belt be shortened or assembled to a different length?

No. This is a cast endless timing belt with a fixed pitch length. It can be cut to width within the available options, but the circumference and number of teeth cannot be changed. If the length needs to be changed, a different cast belt size is required.

Conti Synchroflex AT3 399: what happens if the discs are not aligned?

Misalignment can cause the belt to wander towards a flange, causing edge pressure, heat and wear damage. It can also affect tooth engagement and reduce service life. Check both the parallelism of the shafts and the alignment of the pulleys.

Conti Synchroflex AT3 399: can AT3 be used on a different tooth profile with the same pitch?

No, not without documented compatibility. The 3 mm tooth pitch describes the distance between the teeth, but the shape and clearance of the tooth flanks may differ. The belt must be used with pulleys manufactured for the AT3 profile. Visual similarity is not sufficient documentation.

Conti Synchroflex AT3 399: when should the timing belt pulleys be replaced?

Pulleys should be evaluated if the tooth grooves are worn, sharp, crooked or damaged. A new belt on worn pulleys may have poor load distribution and short life. Also check flanges for bars and side contact and the grooves for foreign objects.

Conti Synchroflex AT3 399: can the belt be turned upside down on the pulleys?

The standard version is single-sided with teeth on the inside and a smooth back. It must run with the teeth in the corresponding tooth grooves; the back is not an alternative tooth side.

Conti Synchroflex AT3 399: is the polyurethane oil and chemical resistant?

The standard PU is described as resistant to simple oils, grease and petrol as well as certain acids and bases. This does not mean universal chemical resistance. In the case of continuous contact, high concentrations or cleaning agents, the specific liquid, temperature and exposure time should be assessed.

Summary

The product brings together the specified AT3 profile and length on one side, so that the appropriate width can be selected without creating a separate item for each cut. The main technical data is 399 mm pitch length and 133 teeth. If in doubt about load or pulley compatibility, the drive should be calculated before ordering the belt.