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CONTI® SYNCHROFLEX – A German Benchmark

CONTI® SYNCHROFLEX – A German Benchmark

SYNCHROFLEX is the benchmark for the German DIN standard and the industry for more than 50 years

A rare view behind the scenes of CONTI® SYNCHROFLEX production in Dannenberg

Only a few products from a company become an industry standard for other manufacturers and even find their way into the German DIN standard. The CONTI® SYNCHROFLEX polyurethane timing belt from ContiTech is one of these rare examples. It has been produced for the Mulco Group in Dannenberg near the river Elbe since 1961. What is the secret of the success of this timing belt, how has it been further developed, and how will it be updated for future machine generations?

Manufacturing process of the CONTI® SYNCHROFLEX. Fig.: ContiTech

The Synchroflex T series was the first standardised tooth profile and pitch system on the market and was defined in 1962 in DIN 7721. This standard is still valid worldwide. “The higher performance AT series has been included in the standard since 2014,” says Thomas Winkler, who specialises in industrial application engineering at ContiTech. “We use casting technology for producing the Synchroflex. This allows an extremely high variety of belts and customised solutions at relatively economical prices. By using more than 1600 different moulds, different cord materials and polyurethane mixtures, we can offer several thousand different variants of the Synchroflex timing belt,” says Winkler. Rolf Marwede, Manager of the polyurethane belts sector adds: “A timing belt type as original equipment in the automotive sector has a life of about ten years; then it is followed by the next generation. In industry we have much longer product and life cycles. Our timing belts are therefore designed for a much longer lifetime. The Liftinstitut in Amsterdam certified a lifetime of at least 15 years for the ContiTech polyurethane in the latest certificate – that doesn’t include the permissible storage time of five years. So we are talking about products that are made to last for at least 20 years without any loss of quality.”

Casting method of the CONTI® SYNCHROFLEX

The use of mould inner cores onto which the tension member (cord) is wound was established in the mid-fifties and is still commonly used today. The core with the wound-on cords is immersed in a cylindrical mould filled with the special castable polyurethane, which flows into the smallest interstices through capillary action. Each core tooth has a minute ridge – the winding nose – that keeps the cord at a defined distance from the core to ensure that the cord is completely covered by the polyurethane.

When the polyurethane has cured in a continuous furnace, the sleeve is taken out of the mould and cut to the desired width on a cutting machine. “The casting method offers the enormous advantage of allowing noses, ridges or second toothing to be cast at the same time. These application-specific timing belts can be used for carrying out a wide range of transport tasks, and offer a very high added value in addition to the drive function itself,” Detlef Harbecke, Area Manager for the industrial sector, explains.

In-house polyurethane development and production

According to Sector Manager Rolf Marwede, even the competitors admit that the ContiTech belt offers the highest performance comparatively speaking. He attributes this in particular to the raw materials and the way they are processed. Contitech uses PU with the polymer base polyester. With the suitable expertise, this offers superior properties for timing belts. “We manufacture our own polyurethane, both for the cast polymers for the Syncronflex and Synchrochain belts, as well as for the thermoplastic polyurethanes for the product family Synchrodrive and Polyflat. In comparison to our competitors, we can optimise the PU specifically for use in belts. That is unique in the industry,” says Rolf Marwede.

“Our polyurethane is not available on the market in this form. We develop, mix and improve it with additives specifically for use in timing belts,” Dr. Stephan Brocke, Material Research F&E PUR (R&D), confirms. The three main components for the polyurethane are no secret: Polyol, isocyanate and cross-linking agents. “Many years of know-how are necessary to ensure optimum storage, processing and use of additives to get the most out of the plastic. We also further enhance the performance of the polyurethane by tempering the sleeves. Only very few suppliers do that,” says Dr. Brocke, not without pride.

Quality tests are carried out on the company’s own test rigs during series production runs. Improvements in the polyurethane, the tensile cords and the finished timing belts are also tested. Standard tests include tensile elongation behaviour, abrasion, tensile strength, the bond between the cord and the polyurethane, and the swelling behaviour. Which diameters and bending arrangements are suitable for which cords? Answers for the sales partners such as TransDev in the UK and solutions for customers can be directly determined by the manufacturer in Dannenberg.

CONTI® SYNCHROFLEX polyurethane timing belt. Fig.: Mulco

Tooth shear strength increased by 20 percent

The optimisations with regard to the polyurethane and its processing lead to considerably higher permissible surface pressure, which is reflected in an approximately 20 percent higher tooth shear strength in the new catalogue specifications. In addition, the design of the CONTI® SYNCHROFLEX timing belts of the types AT GEN III and ATP can be based on at least 16 instead of the former 12 load bearing teeth.

A complete system: belt plus timing belt pulleys

The performance of the CONTI® SYNCHROFLEX can be fully utilised only if the pulleys are precisely tailored to the belt – this includes the pitch accuracy of the belt and pulley meshing, and the roughness profile. Optimised geometrical alignment of the timing belt and pulley achieves tooth meshing with an even smaller friction path, improved load distribution and thus smaller peak load at the tooth. A finer surface quality reduces the friction coefficient and contact temperature.

Optimum balance

The performance and service life of the timing belt drive are almost entirely dependent on the quality of the components. ContiTech has achieved a very high standard with the Synchroflex timing belt. The cords, the tension member density, the in-house developed polyurethane and the tooth shear strength are perfectly balanced. The belt pulleys, produced according to the mulco manufacturing standard, ensure the performance of the timing belt and pulleys as an overall system. Or as Tomas Paul, Production Manager, sums up: “The whole is greater than the sum of its parts.”

Superfine individual wires made of high-quality steel cord increase the flexibility of the tension members and also allow miniature-scale applications. Fig.: Mulco
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