Reasons and methods for centering seamless steel pipes

When hot-rolling seamless steel pipes, the centering of the tube blank is to make the plug correspond accurately to the axis of the tube blank during perforation, and the center position of the tube blank section is along the axis of the tube blank.A circular hole of a certain size is machined like a funnel.

The reasons why seamless steel pipes need billet centering:

(1) The problem of uneven wall thickness of the capillary head can be improved. When the perforation is bitten once, because the front end of the broken pipe has a centering hole, the front end of the pipe blank is deformed and the depression increases. Uneven wall thickness and end loss after tube rolling.

(2) Increase the reduction amount before the plug to improve the secondary bite condition of the tube blank. During perforation, the secondary bite is greatly affected by the centering and non-centering of the tube blank.Due to the centering of the tube blank, the length of the horizontal projection of the contact arc in the perforated cone increases, the centering actually increases the amount of compression before the plug, increasing the contact area,Therefore, the dragging friction force of the roll to the tube blank is increased, which is beneficial to realize the secondary bite.When the alloy steel is perforated, since the compression amount before the top is not given much, it is more important to improve the secondary bite condition and reduce the uneven wall thickness of the front end of the capillary through centering.

(3) Reduce the wear of the nose of the plug and prolong the life of the tool. Centering can reduce the instantaneous impact of the contact between the tube blank and the nose of the plug during the perforation process, and increase the instantaneous contact area to make the contact smooth.In this way, the wear of the nose of the plug is reduced and the life of the plug is improved. For small diameter (<80 mm) tube blanks and when rolling thin-walled tubes (S<5 mm), the centering method can be used to simplify the process. At this time, automatic centering can be realized by forming a funnel-shaped cavity on the front end face of the tube due to surface deformation during two-roll cross-rolling.

The method of centering the tube blank
There are two ways to center the tube: cold centering and hot centering.

(1) Cold centering: Before the tube blank is heated, drill holes on a special tube centering lathe. Or burn holes with oxygen-b fast flame or arc method. Cold centering is only used for stainless steel and high alloy steel, etc. The machining method is adopted to make the position of the centering hole more accurate. The disadvantage is that the shape of the drill hole is improper during cold centering, and it is easy to produce the defect of centering inward folding.

(2) Hot centering: After the tube blank is heated, it is sent to the hot centering machine for punching, and then goes to the punching machine for perforation. The hot centering equipment is arranged on the process flow line, and the front end of the broken pipe is centered in a hot state with a pneumatic or hydraulic punch. This method has high production efficiency and can realize automatic operation. The metal is centered in the hot state, the energy consumption is small, and there is no metal consumption. In addition, since the shape of the hot-centering punch is easily adapted to the nose of the plug, a good shape of the centering hole can be obtained, which is beneficial to avoid centering inward fold defects.

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