METHOD FOR MAKING CONVERSION TUBES OF HARD-TO-FORM KINDS OF STEELS AND ALLOYS WITH INCREASED LINEAR EXPANSION FACTOR Russian patent published in 2004 - IPC

FIELD: rolled tube production, namely manufacture of conversion tubes of hard-to-form kinds of steels and alloys with increased linear expansion factor, possibly tube rolling plants with pilger mills. SUBSTANCE: method comprises steps of rolling tubes of sleeves or of hollow billets heated until yielding temperature in pilger mills on mandrels due to periodically measured-length feed of them to deformation zone; rolling away sleeve of tube by means of rolls due to friction forces; extracting mandrel out of tube at termination period by means of feeding apparatus in such a way that leading end of jammed mandrel with tube is shifted outside line of centers of rolls by distance consisting 1.1 - 1.3 of length of rolling away of feeding apparatus; descending upper roll and performing rolling (reduction) of jammed tube on mandrel at increased feed rates and with reduction degree 0.8 - 1.2 % along diameter; extracting mandrel out of tube by means of feeding apparatus at rolling away mandrel with tube by means of rolls. Length value of extracting mandrel out of tube during one feeding and rolling away operation by action of effort of feeding apparatus consists 0.2 - 0.8 of feed value and it increases from beginning of rolling to final rolling period. Invention provides elimination of mandrel jamming at rolling, lowered coefficient of metal consumption due to lowered difference of tube walls in lengthwise direction, enhanced strength of mandrels due to lowered lengthwise thickness difference of tubes and due to elimination of mandrel curving at heating until temperature equal almost to 700 C. EFFECT: lowered loads of rolls and drive unit of pilger mill, lowered possibility of breaking rolls and spindles. 2 cl, 1 tbl