The perforation process of seamless pipe

Seamless steel pipes are divided into perforated seamless pipes and thermally expanded seamless pipes. The perforated seamless pipe is made by perforating the whole round steel, and its performance is better than other steel pipes such as welded steel tubes.

The main parameters of the pass adjustment of the perforated seamless steel pipe machine are: distance between rolls, distance between guide plates (guide plates, guide rolls), ellipticity, feed angle, rolling angle, diameter of plug, reduction rate before plug, speed of roll and guide plate Wait.

(1) Roll distance refers to the shortest distance between left and right or upper and lower roll throats. The distance between the rolls is usually determined by the billet diameter and the total reduction, and is the most important adjustment parameter.

(2) The guide disc (guide plate, guide roller) distance refers to the shortest distance at the root of the upper and lower guide discs (guide plate, guide roller). The guide plate (guide plate, guide roller) plays a role in laterally restricting and guiding the perforation deformation. The distance of the guide disc (guide plate, guide roller) directly affects the change of ellipticity.

(3) Ovality is the ratio of the distance between the guide plate (guide plate, guide roller) and the distance between the rollers. Indicates the degree of ellipse after pass adjustment. Adjusting the ellipticity keeps the section of the rolled piece in a certain elliptical shape, which can change the degree of lateral deformation of the rolled piece, control the perimeter of the section, and realize diameter expansion and equal-diameter rolling. Excessive ellipticity increases lateral deformation, which is detrimental to product quality.

(4) The rolling angle is the angle between the axis of the Φ roll and the projection of the rolling line on the horizontal plane. The rolling angle of barrel rolls is generally less than 5°. The rolling angle of the conical roll piercer of the Φ250 mm precision tube mill is 10° to 15°.

Note: The degree of "taper" of the roll is related to the size of the rolling angle. The larger the rolling angle, the greater the change in the diameter of the roll from the small end (bite end) to the large end (throwing end), and the greater the increase in the peripheral speed of the roll surface and the component speed along the rolling line. On the one hand, the incremental increase of the sub-velocity along the rolling line is beneficial to increase the deformation speed and strengthen the elongation and deformation of the metal; on the other hand, the incremental increase of the peripheral velocity of the roll surface also increases the influence on the torsion of the rolled piece. These two factors should be considered comprehensively in the design of the roll shape. At the same time, an excessively large rolling angle will also increase difficulties in equipment design.

(5) The feeding angle is the angle between the axis of the roll and the projection of the rolling line on the vertical plane. The feeding angle of the conical roll piercer of the Φ250 mm precision rolling seamless steel pipe unit is 5°～12°. The larger the feed angle, the greater the component of the roll speed in the forward direction, that is, the faster the seamless steel pipe advances, but the greater the pitch of the cross rolling extension, the greater the load of the piercer.

(6) The diameter of the plug is related to the inner diameter of the perforated capillary. Generally speaking, the larger the diameter of the plug, the larger the inner diameter of the perforated seamless steel pipe.

(7) The speed of the guide disc refers to the longitudinal linear velocity of the working surface of the guide disc. Actively rotating the guide plate, the longitudinal linear speed of the working surface should be greater than the longitudinal forward speed of the rolled piece, so there is a longitudinal dragging friction force on the rolled piece, which strengthens the longitudinal flow of the metal. The speed of the guide plate is generally controlled at 1.5 to 3.0 times of the rolling speed.

(8) Reduction rate before the top

       Refers to the diameter reduction rate of the billet at the front end (nose) of the plug, expressed in percentage.

       Reduction rate before jacking=(billet diameter-roll distance of cross section of front end of jack)/billet diameter

       The greater the reduction rate before the top, the greater the unevenness of metal deformation. As a result, the alternating shear stress and tensile stress in the central area of the seamless steel pipe billet increase during the rotation process, which easily promotes the formation of cavities and causes inward folding defects. The smaller the reduction rate before the top, the more difficult it is for the seamless steel billet to bite in (especially the secondary bite). Therefore, the principle of process adjustment is that under the condition of ensuring the biting, the smaller the reduction rate before the top, the better, and the reduction rate before the top is usually 4%~7%.

(9) Theoretical piercing speed usually refers to the longitudinal component velocity of the roll surface at the exit of the capillary tube, but the actual piercing speed is lower than the theoretically calculated roll surface longitudinal velocity due to the influence of metal slippage. However, the metal slip of the cone piercer is smaller than that of the barrel piercer, so the actual piercing speed is relatively high, so the piercing efficiency is also high.

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