Process for producing hollow structures such as ducts, silos, or shelters, and structures obtained by this process

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Listed from its EPO record in Patent Yard's archive of European patents past their term. Its claims, description and drawings are in the EPO PDF and on Google Patents, and the Claude kit works from them.

Why it's free to use

• Filed October 29, 1982 and granted December 18, 1991. A European patent lasts at most 20 years from filing, so its term ended October 29, 2002.
• A supplementary protection certificate, which can extend a medicine or crop-protection patent, adds at most five and a half years, so even that would have ended by April 29, 2008.
• We check European rights only. A US or other national patent in its family could still be in force: check its family on Espacenet or Google Patents.