Patent RU-2315672-C2 (RU)
IPC: B21B21/00
Filed: 2005-09-09
Granted: 2008-01-27
Abstract: FIELD: rolling processes and equipment. 
     SUBSTANCE: method comprises steps of casting ingots in vacuum-electric arc furnaces; forging them to blanks; drilling central opening with diameter 100 ± 5.0 mm in blanks; heating ingots and blanks in muffle of heating furnaces till yielding temperature 1155-1180°C; piercing them to sleeves in skew rolling mills and rolling conversion tubes in pilger mills. Tube rolling in pilger mill at stable rolling process is realized at feeding sleeve to deformation zone m = 20 - 40 mm and at elongation factor μ = 2.5 - 4.0. At guiding, feed value is increased from 10 till 20 mm. When sleeve-tube temperature is less than 850°C, feed is gradually decreased till 25 mm. Pilger heads rolling around is realized at feed no more than 20 mm. At stable rolling process in pilger mill feed is increased and its value is determined according to formula m= m st  + (t init  - t crit )K; at temperature of sleeve-tube 850°C, feed is gradually decreased and its value is determined according to formula mi = m - (t crit  - t end )K1 where t st  = 20 - feed value at stable rolling process after starting and full retract way of feeding apparatus, mm; t init  = 1155 - 1180, sleeve temperature at rolling process starting, °C; t crit  = 850, critical temperature of sleeve-tube at which feed value of sleeve-tube to deformation zone is gradually decreased, °C; t end  - temperature of rolling process termination, °C; K = 0.06 -coefficient taking into account increased feed at starting of stable rolling process, at temperature decrease of sleeve-tube by 1°C, °C/mm; K1 = 0.09, coefficient taking into account lowered feed value of sleeve-tube at rolling process at lowering temperature of sleeve-tube by 1°C relative to critical temperature, mm/°C. After guiding sleeve between rolls of pilger mill and till termination of rolling in pilger mills water supply onto rolls of pilger mill is lowered by 2 - 3 times. Tubes are rolled on two mandrels heated up to 600-650°C due to rolling two-three carbonaceous sleeves for tuning. After rolling process mandrel is extracted and it is cooled in air while moving it on inclined grid for 30-45s to bath with lubricant. With use of mandrel-lifting mechanism mandrel is immersed to bath with lubricant and in 5 - 10 s it is extracted from bath, rotated in mandrel-lifting mechanism by 180 ± 20° and again it is immersed into bath with lubricant for 5 - 10s and cooled in air and transported to lock device of feeding apparatus. Then next tube is rolled. After rolling by means of hot saw pilger head is cut off and tube is carried to machine for straightening its curvature with use of heat of rolling process. After straightening process tubes with curvature exceeding 4.0 mm along length 3600 - 4000 mm are heated in chamber furnaces till temperature 750 -800°C for straightening them in heated state in press. Tubes are straightened due to bending them in opposite side by value exceeding camber by 1.5 - 2.0 times where larger values are related to tubes with larger curvature. 
     EFFECT: reduced cost of conversion process of ingot (blank) - commercial tube. 
     9 cl, 1 tbl