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Big Kalrez® 7075 Sold By Ehlers

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Chemical Industry Applications


Hermann Linden Maschinenfabrik GmbH & Co. KG, of Marienheide, Germany, has chosen giant 1.7 metre O-rings of Kalrez® Spectrum™ 7075 perfluoroelastomer from DuPont™ Performance Elastomers to seal its double-arm (Z) kneaders, used to process aggressive chemicals at temperatures from 100°C to 300°C in the chemical, pharmaceutical, paints, plastics and other industries. The company reports extended service life, reduced maintenance costs, and improved productivity, resulting from a six-fold increase in mean time between repairs (MTBR) compared with the aramid-based sheet gaskets previously fitted.

Hermann Linden supplies mixers and kneaders to industrial customers for high-viscosity product mixing. Originally, both sides of the mixing trough were sealed with asbestos-free sheet gaskets of aramid fibres, fillers and high-temperature-resistant asbestos substitutes. But these seals were prone to occasional leaks that could be difficult to repair. Even flat seals with metal inserts failed to achieve more than a slight increase in service life.

The challenge for Linden was to find a long-term method of sealing the trough and side walls. Although one side could be welded directly to the trough, eliminating the seal, the second side still had to be removable - demanding a different solution to the sealing problem.

Linden decided to work with customers to seek alternatives that would extend service life, reduce maintenance costs and improve productivity. One suggestion was to caulk the groove with soft metal. However, this was rejected as being costly to replace and not very maintenance-friendly. Instead, an O-ring seal was proposed since it would be easy to fit and replace, and require far lower contact pressure to seal reliably, compared with the flat seal.

"We looked for a sealing material that could withstand kneader operating conditions over several years," explained Alexander Schneider, general manager of Linden. "In these applications, the seal must resist temperature cycles from 100°C to 300°C, and exposure to the chemicals used."

Linden asked customers to test a silicone seal, a graphitized aramid-fibre cord and a perfluoroelastomer seal under typical operating conditions. Although the silicone seal stood up to high temperatures, it was severely attacked by the process chemicals. The graphitized aramid fibres resisted the chemicals but charred at high temperatures. Only the perfluoroelastomer seal withstood both aggressive chemicals and high temperatures.

"The mixing trough in one application had a working capacity of 2750 litres requiring an O-ring with a diameter greater than 1.5 m," said Johannes Lächer, former general manager of Linden and now a consultant to the company. "We searched for a manufacturer that could produce perfluoroelastomer O-rings in this size without problem. We finally chose O-rings of DuPont™ Performance Elastomers Kalrez® Spectrum™ 7075 perfluoroelastomer because of its good price/performance ratio, and availability in the required dimensions at short notice." The result is a Kalrez® O-ring with a cord thickness of 9.66 mm and a diameter of 1705 mm, optimized for the specified groove dimensions.

"We are enthusiastic about the performance of the Kalrez® perfluoroelastomer O-rings and calculate at least a six-fold increase in maintenance intervals compared with the flat seals currently used. We plan to use Kalrez® parts for our other kneaders and mixers, operating in similarly challenging conditions." said Schneider.

Kalrez® Spectrum™ 7075 sets new standards for seals used in challenging chemical processes. The DuPont™ Performance perfluoroelastomer offers even lower compression set (15 per cent after 70 hours at 204°C), higher thermal stability (continuous service at up to 326°C) and better chemical resistance than Kalrez® 4079, the previously accepted industry standard. In addition, it provides an exceptionally smooth surface. For applications requiring even broader chemical resistance, DuPont™ Performance Elastomers recommends Kalrez® Spectrum™ 6375 for continuous service temperatures up to 275°C. The company produces and supplies Kalrez® perfluoroelastomer O-rings to customer specifications.

About DuPont™ Performance Elastomers

DuPont™ Performance Elastomers, a global supplier of specialty elastomers with headquarters in Wilmington, Del., is a subsidiary of the DuPont™ Company, with more than $1 billion in sales. The company is the industry leader in chloroelastomers, ethylene elastomers and fluorinated elastomers, serving the automotive, chemical, construction, general rubber, plastics and wire and cable industries.

About Hermann Linden

Hermann Linden Maschinenfabrik GmbH & Co. KG was founded in 1940 as a family business producing mixers and kneaders for laboratory use. Today, with some 42 employees, Linden manufactures mixers, kneaders and agitators in laboratory, pilot-scale and production scale sizes and capacities from 1 to 6000 litres, for worldwide use. Typical industry applications include chemicals, pharmaceuticals, plastics, cosmetics, paints and coatings, confectionery, cements and sealants. All machines are individually produced to exact customer requirements, and are delivered fully assembled on special transporters.


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