How did the Velcro get its name

02.09.2009 12:00

The steel Velcro fastener - inspiration from nature

Dr. Ulrich March Central press & communication
Technical University of Munich

Velcro fasteners have established themselves across the board in industry and households. But they have a catch: they are too weak for many applications. Velcro fasteners made of spring steel have now been developed at the Chair of Forming Technology and Foundry Engineering at the Technical University of Munich. They are resistant to chemicals and can withstand a pull of up to 35 tons per square meter even at 800 ° C.

When the Swiss inventor George de Mestral had to laboriously pluck the many burdock out of his dog's fur after a hunting trip over 60 years ago, he had an ingenious idea: Based on nature's example, he constructed a fastener from many small loops and hooks, the Velcro fastener. "The unbeatable advantage of a Velcro connection is that it is easy to close and open again," explains Josef Mair, employee at the Department of Forming Technology and Foundry (utg) at the Technical University of Munich. The hook-and-eye principle is therefore used in a variety of ways: as an alternative to shoelaces, for attaching medical bandages and prostheses or as cable protection sleeves in the electronics of automobiles and aircraft.

Unfortunately, common Velcro connections made of plastic are not particularly resistant to heat and aggressive chemicals. "But in the automotive sector, for example, it can get very hot. Even a vehicle parked in the blazing sun can reach temperatures of 80 ° C. Temperatures of several hundred ° C occur near the exhaust manifold. Aggressive disinfectants are used for cleaning in hospitals and when building facades conventional Velcro straps are too weak, "Mair explains the problem. Under the direction of Professor Dr.-Ing. Hartmut Hoffmann developed the utg as part of a joint project started in 2005 by the Federal Ministry of Education and Research (BMBF) in close cooperation with partners from industry, a solution: "Metaklett", the steel Velcro connection.

Temperatures above 800 ° C or aggressive solvents are no problem for "Metaklett" - and that with a holding force of up to 35 tons per square meter when pulled parallel to the Velcro surface. Vertical to the Velcro surface, it still withstands a tensile force of seven tons per square meter. Nevertheless, it can be loosened and reclosed quickly and without any tools, like a Velcro fastener on a child's shoe.

As a material, the researchers chose a spring steel that combines high elastic deformability with high strength. On the computer they designed various three-dimensional models for the optimal interlocking of the elements. Promising candidates built them as prototypes and subjected them to extensive tests. About 40 variations of the geometry called "Flamingo" alone were tested on the computer. They studied their bond strength and their behavior at extreme temperatures in order to explore the limits of their resilience.

Two of the tested models finally made the race: a snap lock, namely the flamingo, and a hook-and-eye system called the duck's head. Both consist of a 0.2 mm thick hook tape and an equally thick eyelet or perforated tape. The duck head model is based on the established plastic Velcro tape. Numerous filigree steel hooks can grip into the eyelets of a punched loop tape at any angle.

The second variant, the flamingo, is even more stable. It consists of wider hook elements that snap into the openings of a perforated strip. They are curved so that they deform elastically when applied lightly and slide into the holes, similar to the plastic buckles on backpack straps. They immediately return to their original shape and withstand a counter-pull like an expanding rivet thanks to the resiliently spreading arms.

In order for the hooks to snap into place, however, they must first be positioned at the correct angle, namely parallel or perpendicular to the perforated strip. Depending on the direction of the applied force, this connection can withstand a load of 7 to 35 Newtons per square centimeter. After an initial loss of about 20 percent during the first ten attempts, the bond strength remained constant over countless repetitions.

"The animal names were created to differentiate the various models. The hook shapes are vaguely reminiscent of a duck's head and a flamingo on one leg." explains Mr. Mair the creative nomenclature. As a third alternative, the scientists conceived the "Hybrid" model, which combines a hook tape made of steel with a loop tape made of plastic and can thus fasten textiles in a stable, reversible way.

Possible fields of application for Metaklett are in principle all areas that are dependent on easily detachable but stable connections, for example the building technology industry, in particular air conditioning and ventilation as well as vehicle construction. "Metaklett is suitable for a wide range of applications in which the combination of simple production and high load-bearing capacity of the connection is crucial," the jury of the steel innovation award justified the award of the project. In this award, which is only given every three years, the metallic Velcro fastener was able to prevail against over 100 competitors in the category "Steel in Research and Development" and was awarded third place on June 30th.

The research project was funded by the Federal Ministry of Education and Research (BMBF) within the framework concept "Research for tomorrow's production".

Dipl.-Ing. (FH) Josef Mair
Technical University of Munich
Chair for Forming Technology and Foundry Industry (utg)
Walther-Meißner-Strasse, D 85747 Garching
Tel .: +49 89 289 14540
Fax .: +49 89 289 14547
Email: [email protected]

Additional Information: MetaKlett website website steel innovation award

Features of this press release:
Mechanical engineering, traffic / transport, materials science, economics
Research results, research projects