METHOD FOR ROLLING SEAMLESS HOT ROLLED CASING TUBES WITH BUTTRESS THREAD Russian patent published in 2007 - IPC B21B21/00 

FIELD: processes for rolling seamless hot rolled casing tubes of given size having buttress thread.

SUBSTANCE: seamless hot rolled casing tubes with dimensions 426 x (10 - 12)mm having buttress thread are rolled in tube rolling plant 8 - 16" with pilger mills. Method comprises steps of casting ingots with hot top or without it; repairing ingots; heating ingots up to yielding temperature; piercing ingots to sleeves at mean diameter raising 10.2% and along length of ingot - 6.0 - 14.8%; rolling in pilger mill tubes with diameter 244,5, 273.1, 298.5, 323.9, 339.7, 406.4, and 473.1 at tilting sleeves-tubes by 90 ± 10° and saw cutting of them by measured lengths; heating sleeves-tubes in gas roller furnace; calibrating them in sizing mill at total reduction by diameter up to 1.0%; straightening them in skew-roll straightening machine and subjecting to electromagnetic control; marking; inspecting; trimming ends; realizing preliminary reception; subjecting tubes to ultrasound flaw detection; repairing their surface; subjecting repaired tubes to ultrasound flaw detection; cutting thread; screwing on couplings; hydraulically testing tubes; inspecting them; marking; weighing and painting. Steel ingots of given strength group without hot top are subjected to rolling for making tubes with size 585/540 x 1700 mm; ingots with hot top are subjected to rolling for making tubes with size 585/570 x 1900 mm. Cone shaped ingots having or having no hot tops are heated in heating furnaces till 1260 - 1280°C for 7.5 - 9/0 h at tilting in 20 - 25 min by angle 135°< α < 225° and they are soaked at such temperature for 25 - 30 min. Then ingots having no hot tops are rolled in skew rolling mill with diameter raising 5 - 10%; ingots with hot tops are rolled with diameter raising 2.5 - 5.5%. Tubes are rolled in pilger mill at feeding sleeve to deformation zone 15 - 20 mm while providing polishing coefficient 2.5 - 3.0 and tilting sleeve-tubes by angle 70 ± 5°. Then tubes are calibrated in sizing mill at total reduction along diameter 2.4 - 2.8 %, straightened in skew-roll straightening machine.

EFFECT: lowered metal consumption due to decreased quantity of flaws of metallurgical and rolling-process origin, reduced quantity of waste material caused by wall thickness difference and out-off-roundness due to more strict allowances for rolling, lowered number of thread-rejected tubes, less (by two times) loss of yield, reduced cost of commercial tubes of given assortment.

5 cl, 1 tbl