Seamless steel pipes, precision rolled steel pipes, and cold-drawn steel pipes occasionally encounter eccentricity issues during the manufacturing process, primarily due to perforation. Various factors can affect the geometric accuracy of the forming zone formed by the roll, head, and guide plate, ultimately exacerbating the uneven wall thickness within the capillary.
Roller
1. Roll Centerline Deflection: Incorrect installation of pressure screws on either side of the punching machine, thread or bearing wear, or horizontal deflection of the axial direction between the two rollers can cause distortion within the deformation zone. This will result in uneven wall thickness. 2. Feed Angle: A significant misalignment of the feed angle can prevent parallel alignment between the rolling cone of the head and the roll, contributing to uneven wall thickness. 3. Roll Speed: Inappropriate roll speed can affect the precision of wall thickness.
Guide Plate
1. Guide Plate Distance: The guide plate is used to maintain the center line during perforation. If the guide plate spacing is too large, it will cause significant vertical fluctuations, making the top unstable and resulting in uneven capillary wall thickness. 2. Uneven Guide Plate Wear: Any uneven wear between the upper and lower guide plates can exacerbate uneven wall thickness.
Head
1. Plug Shape Design: The design of the plug taper is critical. Ideally, it should be parallel to the exit cone of the roll. Traditional plug designs based on the Matveyev formula can lead to misalignment, causing deformation in the gradually widening gap. This results in inadequate rolling of the tube wall and consequently uneven capillary wall thickness. This problem is exacerbated as the feed angle increases. 2. Ejector Rod Stiffness: Insufficient stiffness of the ejector rod can cause it to bend during the piercing process, causing it to lose its centered position. This will result in uneven wall thickness in the capillary tube passing through. 3. Plug Wear: Uneven wear or damage to the plug can also contribute to the problem.
Centering and Heating of Tube Blanks
Eccentricity in the center hole and uneven heating of the tube blanks (especially on the opposite sides) can cause uneven wall thickness.
Punch Stiffness, Structure, and Adjustment
Problems with the stiffness of the punching machine body, unreliability of the locking mechanism, inaccurate adjustment of the ejector rod centering device, and downward offset of the roll center line from the rolling mill center line can all affect the uneven wall thickness in capillary tubes. Adjustments to improve the stability of the rolled product must be made carefully to avoid asymmetric changes in the tool relationships within the deformation zone.
In conclusion, the complete elimination of eccentricity in seamless steel tubes is challenging. However, it can be managed by applying rigorous control measures at each step of the manufacturing process to ultimately minimize the problem.
