em guc go phát được mấy cái bàng sáng chế liên quan đến ciment concerte và machine tools

https://docs.google.com/viewer?url=p.../US3800636.pdf
https://docs.google.com/viewer?url=p.../US3618432.pdf
https://docs.google.com/viewer?url=p.../US2010557.pdf
https://docs.google.com/viewer?url=p.../US4622194.pdf
https://docs.google.com/viewer?url=p.../US3800636.pdf
https://docs.google.com/viewer?url=p.../US4907478.pdf