March 7, 2019

New BHS mixer for the Grand Paris Express

“The Grand Paris Express project includes four new subway lines in the greater Paris area. This will double the subway system available in Paris.”

Unibéton, a French subsidiary of the HeidelbergCement Group, is producing special ready-mix concrete formulations for the ‘Grand Paris Express’ project. To improve the production process, the company replaced a planetary mixer with a twin-shaft batch mixer from BHS-Sonthofen. This means that a mixer equipped with frequency converters for more efficient processing is used for the first time in France.

The Grand Paris Express is Europe’s largest urban transport and infrastructure project to date. Four new subway lines will be constructed and three existing lines will be expanded. In Issy-les-Moulineaux, in the catchment area of Paris, Unibéton is using concrete formulations that require longer mixing times than usual. To make sure that Unibéton will be able to reliably deliver homogenous mixtures batch after batch, the company’s management decided to replace one of their planetary mixers with a more powerful machine. The unit of choice was a DKXS 4.50 twin-shaft batch mixer from BHS-Sonthofen.

“The construction firms that are part of the Grand Paris Express project work with concrete formulations that contain numerous binders and additives as well as concrete plasticizers. Our mixing technology enables very dynamic movement processes during the mixing cycles and thus offers a perfect and sustainable solution for these new concrete formulations,” explains Alexandre Bernabé, Sales Manager for the French market at BHS-Sonthofen. The company invented the twin-shaft batch mixer more than 130 years ago and has continuously refined it ever since. Unlike existing mixing systems that use circular movements, the twin-shaft batch mixer implements a three-dimensional mixing principle that allows the various materials to mix intensively. This process is primarily used in the turbulent overlap zone of the two mixing circuits.

The twin-shaft batch mixer thus delivers a consistently high level of homogeneity in a short amount of time. The cement and additives for ready-mixed concrete are optimally processed. Additives in particular mix quickly and uniformly. Both the duration of the mixing cycles and the energy consumption can be reduced with the three-dimensional mixing principle.

The new mixer has decisive advantages for ensuring the uniformity of the special concrete recipes. “We produce about 750 cubic meters of concrete per day with our line of mixers. And per month, that number is 15,000 cubic meters,” reports Stéphane Haffreingue, Operations and Production Manager at Unibéton in the Paris area and in Issy-les-Moulineaux. “The twin-shaft batch mixer allowed us to significantly increase our quality.” The system is driven by two motors with an output of 80 kW each, which are connected to frequency converters. The mixers also feature automatic central lubrication, a high-pressure cleaning system and a moisture measuring probe. The discharge gates are safely opened by a hydraulic cylinder.

Frequency converters control the mixing speed

BHS-Sonthofen installed its first twin-shaft batch mixer of type DKX with two frequency converters in France for Unibéton. The converters play an important role in the processing of special formulations. “Additives and concrete plasticizers cause air bubbles during the mixing process. We use the frequency converters to prevent that,” Bernabé explains. The frequency converters from Danfoss were designed to regulate and throttle the rotational speed at the end of each mixing cycle. This means the concrete does not retain air to the same extent. Instead, the air rises to the surface.

BHS-Sonthofen delivered the mixer on time in August 2017. To ensure quick commissioning, BHS worked together with Taillefer. The French expert for industrial boiler construction handled all replacement work – from dismantling the old system and assembling the new mixer through to installing the new steel structure and the platforms. Taillefer also supplied the discharge funnel that was designed according to BHS specification. “With two parallel production lines, the replacement was quite challenging. But due to the close collaboration with Unibéton and suppliers such as Taillefer, we were able to deliver on time,” Alexandre Bernabé points out.

Taillefer worked with BHS-Sonthofen to ensure the quick commissioning of the mixer.

The new twin-shaft batch mixer from BHS-Sonthofen contributed to the quality of the concrete mixtures for the Grand Paris Express in Issy-les-Moulineaux.

The three-dimensional mixing concept facilitated the thorough mixing of materials, shorter mixing times and lower energy consumption.

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