@misc{GrafGrossSponagel1987,
  author    = {Graf, G{\"u}nter and Groß, Heinz and Sponagel, Stefan},
  title     = {Verfahren zur Herstellung eines Dichtringes mit einer Dichtlippe : Patentschrift DE3621241C1 ; Ver{\"o}ffentlichungstag der Patenterteilung : 25.06.1987},
  publisher = {Deutsches Patent- und Markenamt},
  address   = {M{\"u}nchen},
  pages     = {5 S. : Ill.},
  year      = {1987},
  language  = {de}
}
@misc{SponagelGrafGross1987,
  author    = {Sponagel, Stefan and Graf, G{\"u}nter and Groß, Heinz},
  title     = {Verfahren zur Herstellung eines Dichtringes : Patentschrift DE3621242C1 ; Ver{\"o}ffentlichungstag der Patenterteilung : 25.06.1987 / Anmelder: Fa. Carl Freudenberg. Erfinder: G{\"u}nter Graf ; Heinz Groß ; Stefan Sponagel},
  publisher = {Deutsches Patent- und Markenamt},
  address   = {M{\"u}nchen},
  pages     = {5 S. : Ill.},
  year      = {1987},
  language  = {de}
}
@misc{SponagelGrafGross1989,
  author    = {Sponagel, Stefan and Graf, G{\"u}nter and Groß, Heinz},
  title     = {Method for manufacturing a sealing ring : United States Patent 4,861,536 ; date of patent: Aug. 12, 1989 / assignee: Firma Carl Freudenberg. Inventors: Gunter Graf ; Heinz Gross ; Stefan Sponagel},
  publisher = {[United States Patent and Trademark Office]},
  address   = {[Alexandria, VA]},
  pages     = {5 S. : Ill.},
  year      = {1989},
  language  = {en}
}
@misc{SponagelGrafGross1989,
  author    = {Sponagel, Stefan and Graf, G{\"u}nter and Groß, Heinz},
  title     = {Method for the manufacture of a sealing ring with a sealing lip having hydrodynamically acting return elements : United States Patent 4,850,097 ; date of patent: Jul. 25, 1989 / assignee: Firma Carl Freudenberg. Inventors: Gunter Graf ; Heinz Gross ; Stefan Sponagel},
  publisher = {[United States Patent and Trademark Office]},
  address   = {[Alexandria, VA]},
  pages     = {4 S. : Ill.},
  year      = {1989},
  language  = {en}
}
@book{GrafGrossSponagel1988,
  author    = {Graf, G{\"u}nter and Groß, Heinz and Sponagel, Stefan},
  title     = {Verfahren zur Herstellung eines Dichtringes : Europ{\"a}ische Patentschrift EP0250642B1 ; Ver{\"o}ffentlichungstag der Patentschrift: 11.02.1988},
  publisher = {Europ{\"a}isches Patentamt},
  address   = {[M{\"u}nchen u.a.]},
  pages     = {5 S. : Ill.},
  year      = {1988},
  language  = {de}
}