Sharing China-Made with Global Customers
Sharing China-Made with Global Customers
The expansion of longitudinally welded pipes is a pressure forming process that uses hydraulic or mechanical methods to apply force from the inner wall of the steel pipe, causing it to expand radially. The mechanical method is simpler and more efficient than the hydraulic method, and is employed in the most advanced large-diameter longitudinally welded pipe production lines worldwide. The process involves the following stages:
The segmented fan-shaped blocks at the end of the expansion machine expand radially.
The steel pipe is divided into sections along its length, achieving plastic deformation in steps.
The fan-shaped blocks open until they touch the inner wall of the steel pipe. Within the step length range, the radii at all points on the inner circumference of the pipe are nearly uniform, providing initial rounding of the steel pipe.
The fan-shaped blocks begin to reduce their movement speed from the front section until they reach the required position, which corresponds to the inner circumference of the finished pipe as per quality standards.
From the position reached in the previous stage, the fan-shaped blocks further reduce their speed until they reach the position required by the process design, which is the pre-springback inner circumference of the steel pipe.
The fan-shaped blocks hold their position at the pre-springback inner circumference for a period of time to stabilize the pressure, as required by the equipment and expansion process.
The fan-shaped blocks quickly retract from the pre-springback inner circumference position to the initial expansion position, achieving the minimum contraction diameter as required by the expansion process.
This method ensures that the longitudinally welded pipes achieves the desired dimensional and quality standards through a controlled and efficient mechanical expansion process.
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