Method for applying lubricant onto mandrel bar, method for controlling thickness of lubricant film on mandrel bar, and method for manufacturing seamless steel pipe
View Patent ↗In applying a non-graphite-based lubricant composed of, by mass %, 10 to 70% of an oxide-based lamellar compound and 30 to 90% of boric acid onto a mandrel bar, the lubricant film thickness is set from a predetermined master curve for the lubricant film thickness corresponding to an amount of mica. This stably produces a seamless steel pipe of high quality, while preventing seizing marks and internal flaws.
1. A method for applying a non-graphite-based lubricant composed of, by mass %, 10 to 70% of an oxide-based lamellar compound and 30 to 90% of boric acid onto a mandrel bar, characterized by setting the lubricant film thickness from a predetermined master curve which is set in a range satisfying the following formulas (1) and (2):
t ≦−54 ln ( q )+324 (1)
t ≧−28 ln ( q )+124 (2)
where t denotes the lubricant film thickness (mm) and q denotes the amount (%) of mica of the lubricant.
2. The method for applying a lubricant onto a mandrel bar according to claim 1 , wherein the lubricant film thickness is adjusted by a discharge condition of the lubricant and a bar-sending speed.
3. A method for controlling a lubricant film thickness on a mandrel bar, characterized by comprising steps of
determining the amount of mica of the lubricant,
applying the lubricant by adjusting the discharge condition of the lubricant and/or a bar-sending speed so as to make the lubricant film thickness correspond to the amount of mica by the method according to claim 1 ,
measuring an actual lubricant film thickness, and then
adjusting the discharge condition of the lubricant and/or the bar-sending speed in accordance with the measurement.
4. A method for manufacturing a seamless steel pipe by using a mandrel bar with a lubricant applied thereon by the method according to claim 1 or 2 .
5. The method for manufacturing a seamless steel pipe according to claim 4 , wherein the seamless steel pipe is a seamless steel pipe made of stainless steel.