METHOD FOR MANUFACTURE AND OPERATION OF PILGER MILL MANDRELS FROM STEEL FOR PRODUCING OF HOT ROLLED PIPES OF LARGE AND AVERAGE DIAMETER Russian patent published in 2004 - IPC

FIELD: pipe rolling industry.

SUBSTANCE: method involves forging, thermal processing of mandrel bars; providing mechanical processing of mandrels for finished size; grinding surface and operating to failure state by thermal crack lattice; after forging operation, providing rough mechanical processing of mandrel bars followed by thermal processing of mandrel bars to produce on their surface of sorbite layer of 40-50 mm depth. During operation, before initiation of intensive formation of thermal crack lattice, mandrels are reground for smaller diameter until appearance in sorbite microstructure of individual portions of perlite, with value of perlite being determined from expression: D_r=D_i-2Δ, where D_r is minimal diameter of mandrel after regrinding, mm; D_i is initial diameter of mandrel after finishing of manufacture process, mm; Δ is thickness of mandrel surface layer having structure of sorbite, mm. First regrinding of mandrels for smaller diameter is performed through 0.75-0.80, second regrinding - through 0.5-0.55 and third regrinding - through 0.3-0.35 of their average initial strength. After third regrinding procedure, mandrels are operated to failure. Extent of removal of metal from diametric portions is increased by 1.2-1.3 times per each subsequent regrinding procedure. Method allows pipes of 273-550 mm diameter to be produced.

EFFECT: reduced consumption of mandrel owing to multiple regrinding thereof for smaller diameter until initiation of intensive formation of thermal crack lattice and appearance of individual perlite portions in microstructure of sorbite and, accordingly, reduced cost of reconstructing hot rolled pipes for pipe rolling equipment with pilger mills.

4 cl, 1 tbl