The rolling line of the used welded pipe machine is all rolls on the welded pipe unit, including leveling rolls, forming flat rolls, guide rolls, squeeze rolls, deburring idlers, calendering rolls, sizing rolls, straightening rolls and other rolls. It is also the reference line for the installation and adjustment of related auxiliary equipment such as uncoilers, spiral loopers, flying saws, conveyor rollers, etc. It is the general term for the rolling bottom line and rolling center line, just like the human body. The spine plays a pivotal role in all process parameters of welded pipe production.

The role of the rolling line

In fact, there is no such a physical line on the used welded pipe machine. The rolling line is only represented by thin steel wires when the unit is installed or when the roll is changed. This invisible line usually exists in the following aspects:

(1) Viewed from the side of the welded pipe unit, it is called "rolling bottom line", which is the installation reference for the throat diameter of all lower flat rolls and the outermost point of the complete arc of all vertical rolls. The line connecting the point and the outermost point of the complete pass of all vertical rolls must coincide with the rolling bottom line.

The rolling bottom line has the characteristics of uniqueness and diversity.

Uniqueness is the only calibration benchmark for each specific roll change and its production cycle;

Diversity means that the rolling bottom line has different shapes such as "horizontal", "uphill", "downhill", "straight line" and "curve".

The difference in the rolling bottom line will have an important influence on the amount and nature of the longitudinal extension of the edge of the formed tube blank.

(2) From the top of the used welded pipe machine, it is called "rolling center line", which is the symmetrical line of all the roller passes and front and rear supporting equipment. important.

When the horizontal rolling bottom line is used, the projection of the rolling center line coincides with it.

It can be seen that the relationship between the rolling bottom line and the rolling center line is: the rolling bottom line can be used as the rolling center line, which is also the reason why only the rolling bottom line is pulled instead of the rolling center line in the daily roll changing operation.

(3) Many faults and defects in welded pipe production, such as deviation, torsion, crushing of the formed pipe blank, and even severe partial wear of the roll, are directly or indirectly related to the improper adjustment of the rolling line.

(4) The rolling line is also the installation benchmark for auxiliary equipment such as uncoiler, spiral looper, shearing butt welding machine, leveler, flying saw, conveying roller table, etc. supporting the welded pipe unit. For example, there is a reasonable drop between the installation elevation of the flat head machine and the straightening machine and the horizontal rolling bottom line elevation of the welded pipe unit, so that the round pipe can be rolled naturally between these production processes and unnecessary tumbling between the processes can be reduced.

(5) It is also an important basis for the design of the bottom diameter of the flat roll and the thickness of the vertical roll ring for the welded pipe unit whose bottom line elevation cannot be adjusted.

Principles for choosing a rolling bottom line

Which rolling bottom line to choose depends on the specifications of the welded pipe, the condition of the unit, the material of the pipe blank and the normal production speed of the welded pipe unit. Generally, the following four basic principles can be followed:

(1) The principle of pipe diameter and wall thickness ratio (D/T ratio). Its essence is to emphasize the stiffness of the formed tube blank. Take the formed tube blank of the same strength as φ25*0.5 and φ50*1.0 as an example. Although the D/T ratio of the two is 2%, their slenderness ratios are quite different. Large, that is, the ratio of the length of the forming rack interval to the radius of gyration of the deformed tube blank section. The smaller the slenderness ratio, the greater the stiffness of the formed tube blank in the forming interval, and the greater the ability of the formed tube blank to resist instability; on the contrary, the smaller the stiffness, the easier the formed tube blank is to be unstable. Obviously, the radius of gyration of the φ50 pipe section is much larger than that of φ25. That is to say, if the same rolling bottom line is selected, φ25 is more prone to instability, while φ50 is relatively stable.

(2) The principle of the unit. The elevation of the lower shaft of some welded pipe units is not adjustable, so the bottom line can only be rolled horizontally.

(3) The principle of tube blank material. It is required to select the rolling bottom line according to the strength, softness and hardness of the tube blank. When producing high-strength welded pipes, the sizing section advocates the use of "convex" or "horizontal + convex" rolling bottom lines, so that straightening will reduce detours and be smoother.

(4) The principle of speed. During normal production, for the unit with faster welding speed, the sizing rolling bottom line is larger than that of the unit with slower speed, and vice versa. Because of the slow unit, the cooling time of the welded pipe and the time it is subjected to the straightening force in the sizing machine are longer than those of the fast unit, the stress balance is more sufficient, and the straightness of the welded pipe will be better.

Therefore, whether the rolling bottom line is properly selected or not will have a huge impact on the transverse deformation, section deformation and longitudinal deformation of the welded pipe blank in the used welded pipe machine.