METHOD AND DEVICE FOR HARDENING PROFILE BAND FOR PISTON RINGS Russian patent published in 2000 - IPC

FIELD: heat treatment; mechanical engineering; manufacture of piston rings, springs, wire, bands. SUBSTANCE: band or wire at hot coiling are cooled in two stages: at 1st stage from temperature AC₃(TAC₃) ((TMн-(10...20)^°C) to temperature which is below temperature of beginning of martensite transformation of ((TMн-(10...20)^°C-(10 to 20) C) by 10 to 20 C at rate exceeding critical rate of cooling by 10 to 20 C/s by simultaneous cooling of band by spray blowing with air and removal of heat to water-cooled mandrel by heat conductivity; at 2nd stage from L = vτ(1+2δ/d)-(1- to 20) C to temperature of 50 to 20 C at rate of 4 to 5 C/s only due to removal of heat to water-cooled mandrel by heat conductivity. Device proposed for realization of this method includes mandrel inside which water supply/discharge unit is arranged made in form of double pipe with section of inner supply pipe and discharge hole in outer pipe which is used for communication of cavity inside mandrel with interpipe cavity; device is also provided with air sprayer made in form of spiral with slot over its inner generatrix and located coaxially relative to band hardened at clearance of 5 to 10 mm. Developed length of sprayer "L", mm is equal to τ, where V is rate of delivery of band to mandrel for coiling, mm/s; TAC₃ is duration of cooling from TMн-(10...20)^°C to τ - (10 to 20) C at rate of cooling below critical level by 10 to 20 C, s; d is outer diameter of band coiled on mandrel, mm; δ is clearance between outer diameter of band and inner diameter of sprayer coil, mm. EFFECT: improved quality and enhanced stability of quality of heat treatment; avoidance of hardening cracks. 3 cl, 2 dwg, 1 tbl