STUDIES ON THF HOT-DRAWING OF STEEL TUBES
1957 Volume 43 Issue 12 Pages 1298-1303
Details
1957 Volume 43 Issue 12 Pages 1298-1303
Among the finishing processes of seamless steel tubings, there is one in which outside diameter of tube is reduced hot through die. In this connection, tube-drawing by use of plug is unavailable from the practical point of view, resulting in the ability of free deformation of tubes in the radius direction, and therefore it is impossible for us to estimate the wall-thickness of drawn-tubes. Moreover, we must know the fact that the outside diameter of tube already-drawn becomes smaller than the inside diameter of die.
With the above in mind, the author obtained experimentally and made some observations on the variation of wall-thickness and outside diameter of tubes.
The results obtained were summarized as follows:
1) The recording of variation of drawing force ouring the hot-drawing operation with an oscillograph, showed that soon after the commencement of the operation, the drawing force shockingly increased, with the values kept almost constant after that.
2) Drawing stress increased in proportion to the reduced rate in area of tube. Any difference due to wall-thickness could not be observed. The relation between the drawing stress σl kg/mm2 and reduction rate ε % at the drawing temperature of 500°C could be shown by the following equation.
σl=1.013+0.401 ε
3) The distribution of outside diameter and wall-thickness of drawn tube in the axial direction was found small in the forward portion (pulling side), large in the backward portion. As for the distribution in the middle portion except those above-mentioned, remained almost constantl in case of thin-walled tube, with a tendency to be increased gradually towards the forward portion from the backward one.
4) As the reduction rate of outside diameter increased, the increasing rate of wall thickness became larger up to the maximum value, with a tendency to be decreased in case of thick-walled tube as compared with that of mother tube.
5) The difference between the inside diameter of die and outside diameter of finished tube became larger with the increase of outside diameter reduction rate, to a considerable degree and therefore sufficient consideration should be taken into this fact in the finishing process in question.
