Manufacture of seamless tubes made of steel or the like

Claim 1

A PROCESS FOR COLD ROLLING OF A SMALL DIAMETER STEEL TUBE COMPRISING THE STEPS OF PASSING A STEEL TUBE HAVING AN INNER DIAMETER OF BETWEEN 10 AND 20 MM. IN COLD CONDITION WITH AN ELONGATED CYLINDRICAL MANDREL BAR OF UNIFORM CROSS SECTION AND A DIAMETER SUBSTANTIALLY SMALLER THAN THE INNER DIAMETER OF THE TUBE LOCATED IN THE INTERIOR OF SAID TUBE ALONG A PLURALITY OF SUCCESSIVE ROLLING STATIONS, AND ROLLING SAID TUBE AT EACH OF SAID ROLLING STATIONS ALONG A PLURALITY OF SPACED ARCUATE PORTIONS DISTRIBUTED ABOUT THE AXIS OF THE TUBE AND FORMING PART OF A CIRCLE CONCENTRIC TO SAID AXIS AND HAVING A TOTAL PERIPHERAL LENGTH ABOUT SAID AXIS GREATER THAN ONE HALF OF THE PERIPHERY OF THE TUBE SO AS TO COMPRESS SAID SPACED ARCUATE PORTIONS AGAINST SAID MANDREL WHILE SIMULTANEOUSLY LEAVING BETWEEN SAID THUS COMPRESSED ROLLED ARCUATE PORTIONS A PLURALITY OF IN-BETWEEN TUBE PORTIONS WHICH ARE NOT SUBJECTED TO ROLLING AND THUS ARE UNCOMPRESSED AND WHICH ARE STRESSED IN LONGITUDINAL DIRECTION OF THE TUBE BY THE ELONGATION OF THE TUBE DUE TO SAID ARCUATE STATIONS THEREOF BEING ROLLED, SAID SPACED ARCUATE PORTIONS BEING ROLLED AT ANY ONE OF SAID ROLLING STATIONS BEING ANGULARLY DISPLACED WITH RESPECT TO THE SPACED ARCUATE PORTIONS BEING ROLLED AT THE PRECEDING AND AT THE FOLLOWING ROLLING STATION, SAID ROLLING AT ANY PAIR OF CONSECUTIVE ROLLING STATIONS BEING CARRIED OUT AT A SPEED DIFFERENCE GREATER THAN THAT REQUIRED TO COMPENSATE FOR ELONGATION OF THE TUBE BETWEEN THE RESPECTIVE PAIR OF CONSECUTIVE ROLLING STATIONS SO AS TO PROVIDE A POSITIVE STRETCH AT LEAST AT THOSE PORTIONS OF THE TUBE WHICH ARE LOCATED ADJACENT SAID ARCUATE PORTIONS THEREOF BEING ROLLED AND SO AS TO MAINTAIN ALL PORTIONS OF THE STEEL TUBE DURING COLD ROLLING IN COLD FLOW CONDITION.