Method for calibration of assel rollers

A method of calibrating a generally conical forming roller of an Assel-type mill for rolling tubes about a mandrel rotatable about a mandrel axis, the mill having at least three said forming rollers circumferentially spaced about the mandrel, each said forming roller including a conical entrance, a working shoulder, a smoothing part and a rounding part, and being operatively rotatable about a forming roller axis oriented relative to the mandrel axis by a first angle .alpha., each said forming roller being further oriented relative to the mandrel axis by a second angle .gamma. defined between the mandrel axis and said forming roller axis, comprising the steps of:

• (a) adjusting the second angle .gamma. of each forming roller to be approximately in the range 7.degree. to 17.degree., said adjustment depending on the rolling tube diameter and the length of the smoothing part of each roller, said second angle .gamma. decreasing with increasing tube diameters;
• (b) adjusting the first angle .alpha. of each forming roller to be approximately in the range 7.degree. to 30.degree.;
• and
• (c) providing an orientational relationship between the rounding part and the smoothing part of each forming roller defined by a third angle .beta. in the range of approximately 4.degree. to 15.degree. and defined between the mantle extension of the rounding part of the forming roller and a mantle extension defined along a circumferential periphery of the forming roller smoothing part.