Drawing machine and drawing method

A drawing method controlling a size of an outer diameter and a size of an inner diameter of a metal tube having a hollow structure, the method comprising the steps of:

• delivering, using a first upstream capstan, the metal tube to a first drawing die;
• drawing, using a first downstream capstan, the metal tube from the first drawing die;
• applying a predetermined tension to the metal tube delivered from the first downstream capstan;
• delivering, using a second upstream capstan, the metal tube which has been delivered from the first downstream capstan and to which the predetermined tension has been applied, to a second drawing die;
• drawing, using a second downstream capstan, the metal tube from the second drawing die;
• controlling a first speed ratio between a circumferential speed of the first upstream capstan and a circumferential speed of the first downstream capstan,
• controlling a second speed ratio between a circumferential speed of the second upstream capstan and a circumferential speed of the second downstream capstan, and
• controlling the size of the inner diameter of the metal tube via the first speed ratio.

A drawing machine for controlling a size of an outer diameter and a size of an inner diameter of a metal tube having a hollow structure, the drawing machine comprising:

• a first drawing unit that includes:
• a first drawing die that reduces at least the outer diameter of the metal tube passing therethrough, thereby drawing the metal tube;
• a first upstream capstan that is provided before the first drawing die so as to deliver the metal tube to the first drawing die;
• and a first downstream capstan that is provided after the first drawing die so as to draw the metal tube from the first drawing die;
• a second drawing unit that includes:
• a second drawing die that reduces at least the outer diameter of the metal tube delivered from the first drawing unit, thereby drawing the metal tube;
• a second upstream capstan that is provided before the second drawing die so as to deliver the metal tube delivered from the first drawing unit to the second drawing die;
• and a second downstream capstan that is provided after the second drawing die so as to draw the metal tube from the second drawing die;
• a dancer that applies a predetermined tension to the metal tube;
• and
• a drawing unit controller connected to the first drawing unit, the second drawing unit and the dancer,
• wherein the drawing unit controller controls a first speed ratio between a circumferential speed of the first upstream capstan and a circumferential speed of the first downstream capstan,
• wherein the drawing unit controller controls a second speed ratio between a circumferential speed of the second upstream capstan and a circumferential speed of the second downstream capstan, and
• wherein the dancer is pivotable based on a difference between the circumferential speed of the first downstream capstan and the circumferential speed of the second upstream capstan.