Study of Crack formation on Mandrel Bar surface used in PQF

An investigation was carried out on the mechanism of crack initiation on mandrel bar used for the PQF operation in seamless tube manufacturing. Close observations of the mandrel bar surface suggested that crack initiation may be induced by a thermal shock. In order to check the validity of this hypothesis, a methods was proposed to improve the mandrel bar life. The paper also covers the study of temperature of various section of Mandrel Bar and its effect.

Mandrel bar plays a crucial role in producing large diameter seamless tubes in modern industries. In production line, it has to bare strong and complicate stretch, compressing touching stress and high temperature cold-hot yield stress under high speed cycling. In order to reduce these stresses lubricants are used, this stably produces a seamless steel pipe of 

high quality, while preventing seizing marks and internal flaws. Lubricants are intended to reduce the frictional resistance between the metal and the tool in order to reduce the amount of tool wear.

For proper lubrication to take place the deoxidation taking place at the piercing mill section itself should be of good quality. For this N2 + borax blowing is done just after the billet is formed into a bloom through the 

piercing mill. This bloom is then sent to the PQF line with the help of a manipulator. The bloom and the mandrel are together inserted into the PQF where the longitudinal rolling takes place resulting in the formation 

of the tube to be further sized down to the desired quantity.While the mandrel enters the bloom during rolling, it under goes a large amount of stress. To avoid this and reduce its effect lubricants are used. The 

lubricant is sprayed onto the mandrel by a lubricating tank just before the insertion. For proper coating correct amount of temperature and viscosity should be maintained .The temperature is maintained with the help of a cooling station that is divided into 4 zones each controlled and maintained according to the required quantity of water to be poured. When each parameter is maintained according to the standard values, good quality seamless tubes are produced and the life of the mandrel is increased.