| 主权项 |
1. A pilger die of a pilgering apparatus for producing a dashpot tube for a nuclear fuel assembly through two pilgering processes including a first-step pilgering process and a second-step pilgering process within an allowable error range of 3% or less, the pilger die being configured to conduct the second-step pilgering process and comprising:
a pilger groove; a working section formed along a circumferential outer surface of the pilger die by grinding such that a radius Rx(x) of the pilger groove is reduced from, at a pilgering start point, a half of an initial outer diameter of a first-pilgered zirconium alloy tube formed by the first-step pilgering process of a material tube to, at a pilgering end point, a half of a final outer diameter of a second-pilgered zirconium alloy tube formed by the second-step pilgering process; a sizing section extending a predetermined length from a tail end of the working section, the sizing section being formed by grinding so that the radius Rx(x) of the pilger groove has a constant value in the half of the final outer diameter of the second-pilgered zirconium alloy tube; a roll off section extending a predetermined length from a tail end of the sizing section, the roll off section being formed by grinding such that the radius Rx(x) of the pilger groove is increased from the half of the final outer diameter of the second-pilgered zirconium alloy tube; and a pocket section connecting the roll off section to the working section, wherein the working section is formed by grinding such that the radius Rx(x) of the pilger groove is a radius (Dx(x)/2) of a circle having a center at a position spaced apart from the circumferential outer surface of the pilger die by a die gap (Ws) in the radial direction, a pilger die equation for defining the outer diameter of the second-pilgered zirconium alloy tube is Dx(x)=ODf+X(x)Cx·(ODs−ODf−MTd(x)·WL−MC(x))+X(x)·MTd(x)·WL, and a pilger mandrel equation for defining an outer diameter of a pilger mandrel is Mx(x)=IDf+X(x)Cx·(IDs−IDf−MTm(x)·WL−MC(x))+X(x)·MTm(x)·WL, where: WL=a length of the working section; x=relative position coordinates (1.0, 0.9, . . . , 0.0, −0.1, −0.2 . . . ), wherein the length WL of the working section is sectioned into equal parts, and a relative position coordinate of the tail end of the working section is designated as 0.0, and relative position coordinates of the sectioned parts are increased in an increment of 0.1 from the position of 0.0 towards a left side to a leading end of the working section having a relative position coordinate of 1.0, and the relative position coordinates are reduced in decrements of −0.1 from the position x=0.0 towards a right side; X(x)=a distance rate (x·WL/40) from 0.0 of the working section to a position coordinate x; Mx(0.0)=an outer diameter of the pilger mandrel when x is 0.0, Mx(0.0) being set to a value greater than a final inner diameter of the second-pilgered zirconium alloy tube by 1.5% to 3.5%; Mx(1.0)=an outer diameter of the pilger mandrel when x is 1.0, Mx(1.0) being set to a value greater than the initial outer diameter of the first-pilgered zirconium alloy tube by 0.2% to 0.5%; ODs=the initial outer diameter of the first-pilgered zirconium alloy tube; ODf=the final outer diameter of the second-pilgered zirconium alloy tube; Cx=a curve value (1.9-2.3) of the groove; Mx(x)=an outer diameter of the pilger mandrel at a position coordinate x; MTd(x)=MTm(x)=a decrement of the outer diameter of the pilger mandrel from the position coordinate 0.0 towards the right side to a position coordinate x=(the outer diameter of the pilger mandrel when x is 0.0−Mx(f))·(−x)/the number of sectioned parts, (x= . . . 0.1, 0.0, −0.1, . . . ,); Mx(f)=an outer diameter of a tail end of the pilger mandrel, Mx(f) being set to a value less than the final inner diameter of the second-pilgered zirconium alloy tube by 5% to 8%; Mx(1.0), which is an outer diameter of the pilger mandrel when x is 1.0, is set to a value less than an initial inner diameter of the first-pilgered zirconium alloy tube by 0.7 mm to 3.56 mm; Mx(0.0), which is an outer diameter of the pilger mandrel when x is 0.0, is set to a value greater than a thickness of W(0.0) by 1.5% to 3.5%; MC(x)=a mandrel clearance=0.381 mm·|x|; IDs=the initial inner diameter of the first-pilgered zirconium alloy tube; and IDf=the final inner diameter of the second-pilgered zirconium alloy tube.
|
