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How to solve the difficulties in forming thick-walled pipes of second-hand large welded pipe units?

How to solve the difficulties in forming thick-walled pipes of second-hand large welded pipe units?

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  • Release time:2021-09-01 14:30
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【概要描述】The solutions to the forming difficulties of thick-walled pipes of the second-hand large welded pipe unit include special forming unit solutions, rough forming pass solutions, fine forming pass solutions and comprehensive solutions, etc.

How to solve the difficulties in forming thick-walled pipes of second-hand large welded pipe units?

【概要描述】The solutions to the forming difficulties of thick-walled pipes of the second-hand large welded pipe unit include special forming unit solutions, rough forming pass solutions, fine forming pass solutions and comprehensive solutions, etc.

  • Sort:Q&A
  • Auth:
  • Source:
  • Release time:2021-09-01 14:30
  • Pvs:
Detail

The solutions to the forming difficulties of thick-walled pipes of the second-hand large welded pipe unit include special forming unit solutions, rough forming pass solutions, fine forming pass solutions and comprehensive solutions, etc.

 

second-hand large welded pipe unit

 

Special forming unit solution

Most of the large and medium-sized welded pipe units or special thick-walled pipe units are equipped with an edge planer or a milling machine. Before the straight tube blank enters the first forming flat roll, the raw material edge is planed and milled in advance to complete the welding parallel butt. The application of this plan in the welding industry is relatively complete. The disadvantage is that the investment is large, especially for small welded pipe units, the relative investment is higher.

 

Rough forming pass solution

The basic idea of ​​using the edge double-half-via W pass to deal with the forming problem of thick-walled pipe is to pay attention to the deformation characteristics of thick-walled pipe's wide deformation blind zone, large rebound and large difference between inner and outer circumferences, and logarithmic billets within the range of the deformation blind zone. Implement excessive deformation. In other words, if there is no deformation blind zone and springback, the formed tube will show a ∧-shaped butt state; when there is a deformation blind zone and springback at the edge of the deformed tube blank, it just reaches the parallel butt state. In this way, although the deformation blind zone cannot be eliminated, the edge V-shaped butt joint can be eliminated, and the process goal of the parallel butt joint of the weld seam can be achieved. The double-radius W hole pattern at the edge can eliminate the influence of the V-shaped opening of the thick-walled pipe deformation dead zone and its springback on the welding while the deformation dead zone still exists, realize the parallel butt joint of the welds, and ensure the forming of the thick-walled pipe from the deformation process. quality.

 

Precision forming pass solution

Under the condition of round precision forming closed hole, it is difficult not only to increase the deformation of the edge of the tube blank, but also to reduce the diameter excessively. However, this process goal can be achieved by adopting a flat oval precision forming closed hole type. The forming idea of ​​the flat ellipse closed pass is: "flat ellipse + springback = circle", so that the thick-walled tube can be fully deformed in the flat oval closed pass. At the same time, it is beneficial for the tube blank to smoothly enter the hole pattern and reduce the difficulty of operation.

 

second-hand large welded pipe unit

 

(1) The connotation of the flat-ellipse closed-mouth pass of the second-hand large-scale welded pipe unit. The flat ellipse closed pass of the second-hand large welded pipe unit means that the pass curve of the closed pass roll is an ellipse with the long axis in the horizontal direction, the short axis in the vertical direction and the difference between the long and short axes is not too large. Its connotation has two points:

 

A: Micro-ellipse and macro-circle. Since the ellipse of the ellipse is not large, the ellipse can be roughly regarded as a circle with a diameter of φ, as shown by the red line in the figure, and this red line is the hole profile of the circular closed-hole roller. Unified in the following formula.

 

second-hand large-scale welded pipe unit

 

In the formula, △ is the difference between the long and short semi-axes of the elliptical hole, △=2~4mm, the larger the wall-to-diameter ratio, the larger the value; bf is the correction value of the guide ring wall thickness and arc length; B is the width of the tube blank. The formula not only shows the internal connection between the flat ellipse hole type and the round closed hole pattern, but also stipulates the key dimensions of the flat ellipse closed hole pattern, which is an important basis for the design of the flat ellipse closed hole pattern.

 

B: The arc lengths of the holes are equal. Starting from the actual production of welded pipes, the arc length of the flat elliptical closed hole roller must be equal to the arc length of the round closed hole. This is also a basic principle that should be followed in the design of flat elliptical closed hole rollers.

 

(2) The function of the flat-ellipse closed-mouth pass of the second-hand large welded pipe unit. In addition to having all the functions of the closed hole type, the flat ellipse closed hole type has its outstanding function in that it can force the edge of the high-strength thick-walled pipe to deform.

 

A: The edges of the billet are forced to be fully deformed. Comparing the black and red hole patterns in the figure, it is easy to see that when a thick-walled tube runs into a flat oval hole pattern, the first deformation is the edge and bottom of the tube blank. In the case of a circular closed hole, the distance is short S, and the horizontal is long S:

second-hand large-scale welded pipe unit

The combined solution of the two formulas can be S=△>0.

 

The result proves two points: first, the edge of the tube blank is the first to be deformed by the force in the flat oval pass, and the deformation force on the edge is the most direct, and the effect is the most significant; second, because the width of the flat oval pass is in the horizontal direction The upper part is larger than the round hole type, and there is a "△mm gap" between them, so there is no need to worry about the tube blank being massively reduced in diameter.

 

B: The deformed tube will rebound after it leaves the roll pass constraint, and the rebound of the thick-walled tube is greater. Springback makes the deformation degree of the tube blank not up to people's expectations. Therefore, controlling and "eliminating" the springback has always been the goal pursued by our tube-making technicians. Analyzing the first formula, it can be seen that the size of the flat elliptical tube in the vertical direction is smaller than the diameter of the circular closed hole, so the difference between the two can be used to offset the springback of the tube after leaving the flat elliptical hole. In this way, compared with the round hole type tube blank after springback, the springback of the flat oval tube blank can be regarded as zero.

 

C: Improve roll sharing. By reducing the gap between the rollers in the figure, not only can the flat elliptical hole be further flattened; at the same time, the flat elliptical hole can be changed to an approximate round hole by increasing the roller gap, that is, the contour of the closed hole can be on a long axis. Change between an ellipse with a minor axis of (2a-roll gap) and a circle with a "diameter" of 2a. Then, the width range of the tube blank that can be formed by the flat elliptical closed-hole roll is: (2b-roll gap gap) π-bf ≤ B ≤2aπ-bf

It can be seen that this flat oval pass with multiple changes with the gap between the rolls realizes the sharing of rolls within a certain range.

 

(3) The design principle of the flat ellipse closed pass of the second-hand large welded pipe unit:

 

A Principle of equal perimeter. The error between the two is required to not exceed 1mm.

B. The principle of not much difference between the long and short axis. This is to ensure that the tube blank can become a basic cylindrical shape after leaving the flat elliptical closed hole shape and rebound. The first formula is a concrete manifestation of this principle.

C. The principle that the sum of the long and short semi-axes is equal to the diameter of the corresponding circular closed hole.

 

Comprehensive solution

The double-radius W hole on the edge of the rough forming section and the flat elliptical closed hole pattern of the fine forming section are comprehensively applied to a set of thick-walled pipe hole patterns, giving full play to their respective advantages in each forming stage, and jointly solving the thick-walled pipe forming blind zone and The difficulty of forming the rebound, the effect will be better. At the same time, the hazards of the large diameter difference between the inside and outside of the thick-walled pipe are also alleviated.

 

 

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