The uneven wall thickness of steel pipes is mainly represented as uneven spirally wall thickness, uneven straight wall thickness and the ends are too thick or too thin, even the grinding technique is one of the important factors. The following are the reasons to cause the uneven wall thickness and corresponding measures.
1. The helical uneven thickness
Reasons:
(1) The centerline and angle have some errors caused by grinding machine, and the low pressure also contribute to it. Generally, these deficits are spirally distributed alongside the steel pipe.
(2) Centering rollers. During the grinding process, if the centering rollers are open prematurely or improper adjustment will also result in the uneven wall thickness.
Measures:
(1) Adjust the centerline of grinding machine and make the angles at the same degree, and adjust the machine according to the given parameter table.
(2) In terms of the second situation, according to the processing speed to open the centering rollers to avoid the wobbling of the top jack. The open degree of centering rollers should be adjusted based on diameters of steel pipes, and take the jumpiness of steel pipes into consideration.
2. Linear uneven thickness
Reason:
(1) The improper adjustment of mandrel saddle position, when the mandrel contact with one side of the steel pipe, it will cause fast cooling and uneven wall thickness.
(2) The gap between strip rolling is too small or too large.
(3) Deviation of centerline of pipe rolling mill.
(4) Uneven pressure of single and double rack, and cause the both sides of steel pipes too thick or too thin which forms the linear symmetric deviation.
(5) Fracture of security mortar and large difference in inner and outer rolling gap, cause non- linear asymmetric deviation.
(6) Improper adjustment of rolling machine, drawing and piling of steel all can result in the uneven thickness.
Measures:
(1) Adjust the mandrel saddle in correct height and guarantee aligning of mandrel and steel pipes.
(2) When replacing the rolling components, keep the gap based on specifications and keep consistency with the rolling table.
(3) Using the optical device to adjust the rolling centerline and correct the centerline in the machine during yearly maintenance.
(4) Replace the fractured mortar timely and examine the related components regularly in order to change broken parts in time.
(5) Avoid drawing and piling of steel during rolling process.
3. Uneven thickness in head and tail parts
Reasons:
(1) The cutting slope and bent is too large and the incorrect pass-centering holes are major reasons to cause uneven thickness in the head of steel pipes.
(2) During the processing, the extending coefficient is too large and the high rolling speed causes the unstable rolling.
(3) Unstable shot is also one of the reasons to the uneven thickness in the tail of steel pipes.
Measures:
(1) Check the quality of steel tube and prevent the enlarging slope and pressure, correct the pass-centering holes when replace and check for components.
(2) Take a relatively slow penetration rate in order to ensure the stability and uniformity of wall thickness. When the speed of rolling is changing, the corresponding direction disc should also be adjusted accordingly.
(3) Focus the situation of direction disc and check the plate bolt, reduce the vibration of rolling and keep the stability during the processing.
