Seamless Pipe Piercing with Plug Nose Rolling Reduction Control
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Solution Overview
Problem
Existing methods for producing seamless tubes/pipes using the Mannesmann process fail to reliably prevent inner surface flaws caused by center segregation and porosity in billets, despite attempts to decrease the plug nose rolling reduction ratio.
Innovation Solution
Piercing-rolling is performed with specific conditions, including a plug nose rolling reduction ratio (TDF) that satisfies the formula TDF ≤ -0.50 × (d/Bd) + 0.06, where d is the maximum diameter of the unsound region and Bd is the billet diameter, along with continued pushing by the pusher until steady state and a roll gorge draft (GDF) between 12% and 15%, and a plug geometry where 1.8 ≤ Pl/Pd, to prevent inner surface flaws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the plug nose rolling reduction ratio is decreased to prevent inner surface flaws, then the occurrence of inner surface flaws is reduced, but the engagement of the billet into the angled rolls becomes unsteady
Solution Approach 1:
The invention changes the plug nose rolling reduction ratio parameter to a specific range (0.02 ≤ TDF < 0.06) based on the unsound region diameter, optimizing the balance between preventing inner surface flaws and maintaining stable billet engagement. This parameter optimization resolves the contradiction by finding the appropriate value range that satisfies both requirements simultaneously.
2Reliability
If the plug nose rolling reduction ratio is decreased further to reliably prevent inner surface flaws, then flaw prevention is improved, but the pusher must continue pushing until steady state is reached, increasing process complexity
Solution Approach 1:
The invention applies preliminary action by continuing the pusher operation until the piercing-rolling reaches steady state. This ensures that the billet is properly engaged and positioned before the main rolling process begins, preventing inner surface flaws while maintaining process control. The pusher's continued action in the preliminary stage resolves the contradiction by ensuring proper engagement before reducing the rolling reduction ratio.
3Manufacturing precision
If the plug nose rolling reduction ratio is optimized based on unsound region diameter, then manufacturing precision is improved, but the process requires measurement and calculation of unsound region parameters
Solution Approach 1:
The unsound region diameter is measured and the appropriate plug nose rolling reduction ratio is determined before the piercing-rolling process begins. This preliminary measurement and calculation enable precise control of the rolling reduction ratio during the actual process, resolving the contradiction by performing the measurement work in advance rather than during the high-speed rolling process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively prevents the occurrence of inner surface flaws by considering the extent of center segregation and porosity in the billet, ensuring reliable production of seamless tubes/pipes.
Implementation Method 1
the billet engaged into the angled rolls advances along the pass line while being rotated by action of the angled rolls. At this time, by the rotary forging effect, Mannesmann fracture is generated successively in the central portion of the billet until the billet reaches the plug nose, and thereby the core part of billet becomes torn off in a brittle manner.
Implementation Method 2
the billet is subjected to a wall-thickness rolling work process by the plug contacting with the central portion thereof and the angled rolls contacting with the outer circumference thereof, and thereby the hollow blank is formed.
Data Source
Figure 1~2
Figure 3(a)~4
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AI summary
By using a piercing mill that includes a pusher on the entrance side, a plug on the exit side along a pass line, and a plurality of angled rolls as being provided around the plug so as face to each other, in the case where the maximum diameter of an unsound region consisting of center segregation and porosity in a cross section of a billet is d [mm], piercing-rolling is performed under the condition that the plug nose rolling reduction ratio (TDF) expressed by Formula (1) satisfies Formula (2). TDF=Bd-D1/Bd TDF≤-0.50×d/Bd+0.06 In Formulae (1) and (2), Bd is the billet diameter [mm], and D1 is the opening [mm] between the angled rolls at the plug nose position. Thereby, when piercing-rolling is performed, the occurrence of an inner surface flaw attributable to the center segregation and porosity in the billet can be prevented reliably.