6.8　Withdrawal Unit or Drive of Segment

6.8.1　The withdrawal and straightening machine of square or round billet caster preferably adopts hydraulic screw-down.

6.8.2　The withdrawal and straightening machine of small square or round billet caster preferably adopts the integral five-roll stand.The withdrawal and straightening machine of big square or round billet caster preferably adopts the interchangeable single stand.

6.8.3　The withdrawal and straightening roll and bearing of withdrawal and straightening machine shall adopt the water cooling，and the bearing of roll shall adopt the bearing with big clearance.

6.8.4　The withdrawal and straightening machine of square billet，round billet or beam blank caster preferably adopt the upper roll drive or simultaneous drive of both upper and bottom roll.The quantity of drive roll shall be determined according to the withdrawal and straightening force and the numbers of withdrawal and straightening machine.If the drive speed of upper and bottom roll of withdrawal and straightening machine arranged in the bow are not same，the electric control should ensure the synchronous running of inner and outer bow of strand.

6.8.5　The maximum opening of withdrawal and straightening machine shall be determined as per the conditions that the strand after being cut into several sections can be withdrawn in case the strand is solidified and cannot be straightened.In case the square billet caster adopts the rigid dummy bar，in addition to satisfaction of strand withdrawal requirement，the screw-drown cylinder of withdrawal and straightening machine shall still meet the requirement of dummy bar disconnection and emergency treatment of strand.

6.8.6　The withdrawal and straightening machine shall adopt the heat prevention and cooling measures.If the structure of withdrawal and straightening machine for square or round billet is allowed，the strand preferably runs in the cooling channel，and stand of withdrawal and straightening machine shall adopt the water cooling structure.

6.8.7　The screw-down roll of withdrawal and straightening machine of round billet caster shall strictly control its screw-down force.When the withdrawal and straightening machine has multiple stands，the screw-down force shall gradually increase along the strand withdrawal direction.The screw-down limit unit can be provided in case of necessary.The roll surface of withdrawal and straightening machine shall have arc-shaped groove，and its diameter shall be bigger than the maximum diameter of strand.

6.8.8　The drive unit of slab caster segment shall be designed as fast disconnection when changing segment and shall be arranged outside the secondary cooling chamber.

6.8.9　The drive unit of slab caster shall be arranged in front as much as possible and shall ensure that the dummy bar is clamped by at least two pairs of drive rolls when dummy bar is in the cast waiting position.

6.8.10　The drive unit of withdrawal and straightening machine or segment shall adopt VVVF drive.When the gear reducer of drive mechanism which is used for clamping of dummy bar in case of stop has no self-locking，the brake shall be provided.When encoder is used for length measurement and tracking of dummy bar，the encoder can be installed on the motor shaft，and the protection shall be provided.

6.8.11　The withdrawal and straightening capacity of drive unit of withdrawal and straightening machine or segment shall meet the requirement of withdrawal and straightening of strand when its temperature is slightly decreased in case of emergency.

6.8.12　Arrangement of drive unit and electric motor of withdrawal and straightening machine shall avoid the direct radiation of hot strand.