Patent ID: 6631542
Filing Date: 2003-10-14
Classification: B21B,B23P,C21D,C23C,F16G,Y10T

Abstract:
A method of manufacturing a laminated ring for use as a belt in transmitting power in a continuously variable transmission, comprising the steps of:severing a cylindrical drum, which comprises a sheet of maraging steel with welded opposite ends, into a plurality of rings of predetermined width, the maraging steel being a low-carbon steel containing from 17-19% of Ni, and Co, Mo, and Ti; correcting circumferential lengths of the rings; aging the rings by placing the rings into an aging chamber, heating the aging chamber to a predetermined aging temperature, and keeping the rings at said predetermined aging temperature for a predetermined period of time; thereafter, nitriding said rings by transferring the rings from said aging chamber into a nitriding chamber which is disposed independently of said aging chamber and has been heated to a predetermined nitriding temperature, while maintaining said rings at said aging temperature, keeping said rings at said nitriding temperature in an atmosphere containing at least an ammonia gas for a predetermined period for time, and cooling said rings; and stacking the rings into a laminated ring, wherein said rings are aged in a temperature range of from 480-500Â° C. for less than 60 minutes so that hardness of the rings is less than a maximum value, and nitrided in a temperature range of from 480-500Â° C. at the nitriding temperature which is the same as or higher than said aging temperature for a period of time ranging from 45-60 minutes so that the aged hardness of the rings reaches the maximum value.