In the manufacture of boilers and pressure vessels, forming technology is one of the main manufacturing processes.
In the forming process, rolling the cylinder section is the most basic forming method. There is a lot of work involved in scrolling. Most of the forming process is carried out on a symmetrical three-roll bending machine. However, because the thickness and diameter of the cylinder section are determined according to different production process conditions, there are a considerable number of specifications and varieties.
The bending accuracy after forming depends on the “H” parameter, which is the central distance between the upper and lower rolls at the end of rolling.
This parameter is usually determined by formula (1).
It may seem that this formula is not complicated, but for manufacturers, the cumulative workload is considerable due to the diverse specifications and varieties of cylinder sections.
To simplify and facilitate the determination of the value of “H” under different conditions, this article will use the following two graphical algorithms.
Fig. 1 The end position diagram of the symmetrical three-roll bending machine
1. A graphical algorithm to calculate the parameter “H” by “nomograph calculating the square root of the sum of squares”
When a certain type of thick plate rolling mill is provided, the parameters a, r 1 and r 2 in the above formula are constant, only if R 0 are variable.
Therefore, when a certain type of plate bending machine is used to roll any thickness and radius of curvature, the corresponding main parameter “h” can be obtained by the following graphical algorithm.
First, a rectangular coordinate system is established with a as the ordinate and h as the abscissa.
Then the following drawing is performed in the coordinate system (shown in Fig. 2)
It must intersect OP = a on the longitudinal axis, take point P as the center of the circle and take (R 0 + S + r 2 ) as the radius to form a positive point a on the transverse axis of the arc intersection.
Should take point a as the center of the circle, take R 0 as the radius and reverse as a point B on the transverse axis of the arc.
Then point B is taken as the center of the circle and R 1 is taken as the radius of intersection of the arc, and a point C in the positive direction of the transverse axis of the arc is made.
Thus: OC = h.
For example,
Drum sections with S = 20 mm and d = 2000 mm are rolled on a 70 × 4000 three-roll symmetric press brake.
To calculate the value of h.
According to the data, R 1 = 350 mm, R 2 = 330 mm, 2a = 800 mm.
According to the graphical algorithm (shown in Fig. 2): h = 640mm, which is calculated by the formula:
The absolute error is only 1mm, representing 0.015% of the actual value, which is quite accurate.
If (R+S+r) is turned into a movable ruler, it is more convenient.
Fig. 2 Normogram for calculating “h”
2. A graphical algorithm for calculating “ h ” of a certain type of three-roll symmetric bending machine, which can roll the common point graphic under different thicknesses and radii of curvature;
As known above, when a certain type of press brake is provided, its parameters a, R 1 and R 2 are fixed.
So, if the relationship curve of R 0 and h under different plate thicknesses is drawn in r 0 -h coordinate system, the common point graph of R 0 and h of steel plate with different thicknesses in this type of rolling mill can be obtained .
It is very convenient to obtain the value of the main parameter “h” of the drum section in this type of plate bending machine under all different conditions.
The following is a common point diagram of a 70×4000 three-roll symmetric press brake.
Known: r 1 = 350 mm, r 2 = 330 mm, a = 400 mm
Then:
Table 1 is the calculation and drawing data table with 2mm interval.
According to practical experience, the thickness of the rolling mill is generally 6 ≤ s ≤ 40 (mm).
Generally, the section radius of the rolling drum is 400 ≤ R 0 ≤ 200 (mm).
Therefore, this range is used as the calculation drawing range.
It can be seen in table 1 that the value of “n” is basically equivalent to the plate thickness s when a certain type of plate bending machine is used to roll a certain amount of R 0 .
The error between the actual value and the actual value is less than 0.05%.
However, when the copper plate is bent, both plastic and elastic deformation occur.
Therefore, there will be a certain elastic recovery after unloading.
Therefore, in actual production, the value should be slightly lower than the actual value.
In this way, if we use the law of equivalent variation of the two, the design will be simplified and the elastic return after real bending can be compensated.
At the same time, the graph line can be reduced and the “h” value corresponding to any S can be determined under a certain R 0 .
Conclusion
The first graphical algorithm is universal, while the last one is for a certain type of plate bending machine, which type of plate bending machine corresponds to a special (kR 0 -S) copoint graph.
The results of the two graphical algorithms in teaching are very good and enlighten students a lot.
In particular, the last method has certain practicability.
It is suggested that the plate bending machine manufacturer sets up the common main diagram of (nR 0 -S) on the rolling machine or in the manual, which will bring great convenience to the manufacturer's own production.
