Patent ID: 9186715
Filing Date: 2015-11-17
Classification: B21D,B23P

Abstract:
1. A mandrel for bending a rectangular duct body, comprising: a rectangular pole having a round part formed at a front end of said rectangular pole; and first, second and third rollers sequentially aligned adjacent to said round part, wherein said round part and said first, second and third rollers are formed between first and second connection pieces, wherein a first shaft pin is installed to sequentially run through said first connection piece, said round part and said second connection piece, wherein a second shaft pin is installed to sequentially run through said first connection piece, said first, second and third rollers and said second connection piece, wherein said first, second and third rollers are individually rotatable, wherein when said first, second and third rollers are exposed to a friction resulting from a bending action within said rectangular duct body, circular oil grooves formed in sides of each of said first, second and third rollers and filled with lubricating oil serve to reduce said friction between said rectangular duct body and said first, second and third rollers, between said first, second and third rollers and said connection pieces, between said shaft pins and said first, second and third rollers, and between said first, second and third rollers themselves, and wherein a protruded part and a depressed part are formed along an outer periphery of said first, second and third rollers so that depression parts are formed inside said rectangular duct body when said bending action of said rectangular duct body is performed.