This paper briefly introduces the sheet leveling method, the principle of roller sheet leveling, the common types of roller leveling and the method of determining the main parameters.
Leveling as a process method is widely used in metallurgy, shipbuilding, petrochemical, boiler, metal forming and other industries. Defects such as bends, arcs, and waves of metal sheets need to be leveled. Some metal sheets also need to be leveled after cutting or stamping. Generally, there are two methods of leveling metal sheets: mechanical leveling and thermal correction. According to the principle of leveling, mechanical leveling can be divided into leveling using one transverse bending method; leveling using the stretching method; and leveling using multiple alternating transverse bending methods supplemented by a certain positioning force. flat (Figure 1). Commonly used leveling equipment includes the following types:
Three common leveling methods
- Leveling on the press is carried out by using a reverse bending method between the movable press head and two fixed fulcrums. It is mainly used for leveling medium-thick plates and panels. This method has low productivity and The operation is complicated and the accuracy is not easy to guarantee.
- Leveling on a tensile leveling machine or tension leveling machine is to apply tension that exceeds the yield point of the material at both ends of the sheet to cause elastic-plastic deformation, thereby leveling the sheet. It is mainly used for non-ferrous metals. For the leveling of thin plates, the productivity of the stretch leveling machine is low and the part clamped by the clamps needs to be cut off, resulting in sheet material loss. There is no such disadvantage during tension leveling.
- The leveling on the roller sheet/plate leveling machine is when the sheet passes between the staggered rollers, the sheet is leveled by multiple transverse alternating bends supplemented by a certain tensile force. It can be used for Cold leveling of various metal sheets is an ideal method for leveling sheets and panels. Because roller levelers are highly productive and easy to mechanize, and can be used stand-alone or online, they have a wide range of applications.
Usually, the yield point of the leveling plate, the ratio of the yield point to the strength limit, the size of the plate, the original condition of the plate, the leveling accuracy requirements, the production ring, the process flow or the online requirements, etc. are designed and selected by the designer and the user. Basic basis for roller sheet/plate leveling machine types and parameters.
Basic principles of roller leveling process
The bending deformation process of roller sheet leveling is consistent with elastic theory.
Roller leveling process is performed between the upper and lower rows of work rolls arranged in a staggered manner. One row of work rolls is located in the middle of the gap between the other rows of work rolls to form a staggered arrangement. The distance between the upper and lower rows of work rolls can be adjusted. During leveling, the gap between the upper and lower work rollers should be adjusted slightly smaller than the thickness of the plate to be calibrated, the inlet side should be fully plastically deformed and the outlet side should be fully elastically deformed. When the sheet is engaged during leveling, the work roller uses the “Bauschinger effect” of the material to perform multiple alternating bends in the forward and reverse directions of the sheet, gradually changing the multiple original curvatures into a single curvature and finally becoming smooth. Smooth, the residual stress of the plate is reduced and evenly distributed.
Types and characteristics of roller plate leveling machines
According to the arrangement of the work rolls, the roller sheet leveling machine can be divided into three types: upper roller single type, roller row parallel type, and roller row non-parallel type (Figure 2).
- According to the number of layers of work rolls and back-up rollers, roller levelers with back-up rollers can be divided into four-layer structure types and six-layer structure types.
- According to the adjustment method of the gap between the upper and lower rows of work rolls, the roller leveler can be divided into two types: upward adjustment type and downward adjustment type.
- According to the structure of the main machine part, roller leveling machines can be divided into four-column types, frame types, and box type.
- According to the driving mode, plate roller leveling machines are divided into hydraulic type and mechanical type. According to the transmission form, it can be divided into roller leveling machines with universal shaft transmission, main drive of separate rollers and separate drives of upper and lower rows of work rollers.
Characteristics of 2 types commonly used roller sheet leveling machines
Usually roller sheet leveling machines are divided according to the arrangement of the work rolls: that is, they are divided into single upper roller type, parallel roller row type and non-parallel roller row type. The characteristics of these structural forms are discussed below.
Upper roller single-type plate leveling machine
Each upper row of work rolls of Upper roller single-type plate leveling machine(Figure 2a) can be adjusted up and down independently. Since there are generally no support rollers, the diameter and distance of the work rolls are large.
This type of roller leveler is mainly used for leveling medium and thick plates. The gap between the upper and lower rows of work rollers can be easily adjusted according to work needs. Due to the large working roll diameter and roll distance, its leveling accuracy is poor and is generally used as a rough calibration machine or online.
Parallel roller row type and non-parallel roller row roller type sheet leveling machine
(Figure 2b) The upper and lower rows of parallel roller leveling machines are arranged in two parallel rows. The upper row of work rollers (including guide rollers on both sides) can move up and down. At the same time, the guide rollers on both sides can also move up and down monotonically. It is mainly used in middle Thick slab leveling. The upper and lower rows of work rollers of the non-parallel roller leveling machine are at a certain angle. The upper row of work rollers can move up and down. At the same time, the angle can be tilted relative to the lower row of work rollers. It is mainly used for leveling thin medium plates. But in recent years, there has been a trend of using it for leveling medium and thick plates. Both leveling machines are equipped with support rollers and have high leveling accuracy. They are currently the most widely used roller leveling machines.
Performance comparison of two types of roller sheet leveling machines
|Performance||Non-parallel roller rows||Roller row parallel type|
|Leveling principle||The upper and lower roller rows are at a certain angle. The opening gradually increases from the entrance side to the exit side, and the bending curvature of the sheet gradually decreases. The sheet on the entrance side is plastically deformed, and the degree of plastic deformation gradually decreases when moving toward the exit side. It is completely elastically deformed to the outlet side. The deformation characteristics of this leveling process: it can better level the irregular bends of the plate. At the same time, since each subsequent work roller always gives a horizontal tension to the plate to be calibrated, it is particularly beneficial to eliminate the internal stress of the plate. Its leveling process is most consistent with the leveling principle||The gap between the guide rollers on the exit side must cause the sheet to undergo complete elastic deformation, and before that, the sheet to the entrance side undergoes elastic-plastic bending with the same degree of deformation.|
|Movement status||There is a certain speed difference between the import and export sheets, and there may be relative sliding friction between the sheets and the rollers.||The speed difference between import and export sheet materials is very small|
|Feeding status||Not conducive to sheet metal biting||The guide rollers can be adjusted up and down individually to facilitate feeding.|
|The force of the whole machine||The force on the whole machine is smaller (0.9 times that of parallel roller type)||The whole machine is stressed|
|Main motor power||smaller||Larger|
|Machine structure||More complex||simpler|
|Usage performance||It is generally one-way feeding, mainly used for thin and medium plates, and has a tendency to be used for medium and thick plates.||It can be fed in two directions and leveled repeatedly. It is mainly used for thick plates.|
|Leveling accuracy||Higher than roller row parallel type||Lower than the roller row non-parallel type|
As can be seen from the above table, due to different structures, the performance and characteristics of roller sheet leveling machines with parallel roller rows and non-parallel roller rows are also different.
In recent years, with the development of leveling machine technology, improved roller leveling machines with non-parallel roller rows and variable roller pitch roller leveling machines have appeared. Hydraulic leveling machines that can automatically adjust the leveling force and automatically compensate for the elastic deformation of the work roll have also appeared.
non-parallel roller row leveler
The improved roller leveler with non-parallel roller rows (Figure 2d) absorbs the advantages of the non-parallel roller row leveler. At the same time, because the first work roll in the upper row on the entrance side can move up and down independently by a smaller distance, thus greatly improving the biting conditions of the plate.
The variable roller spacing type roller sheet leveling machine adopts a combined arrangement of large and small rollers. According to the different thicknesses of the sheet being leveled, different work rollers are involved in leveling by adjusting the pressing and lifting of the work rollers. This kind of machine can level the sheet material in a thickness range up to 10 times with high leveling accuracy.
The hydraulic leveling machine that can automatically adjust the leveling force and automatically compensate for the elastic deformation of the work roll is used for leveling sheets or panels (such as quenched saw blades) that are particularly difficult to level and require high leveling accuracy. The leveling accuracy can reach 0.1mm/m.
Top 4 important parameters of roller plate leveling machine
The parameters of the roller sheet leveling machine include the working roller distance t, the working roller diameter d, the number of rollers n, the length of the roller body L and the leveling speed v, etc. Correct selection and determination of these parameters are crucial to ensuring the leveling quality and machine structural size. The rationality and power consumption have an important impact.
Roller distance t
The roller distance is the most important parameter of the roller sheet leveling machine. It determines the thickness range of the leveling sheet, the structural size of the machine, and also affects the transmission power.
When selecting or determining the roller distance, it must not only meet the quality requirements when leveling the minimum plate thickness, but also meet the strength requirements when leveling the maximum plate thickness.
The maximum allowable roller distance tmax is:
Where: hmin——sheet elastic modulus, mm;
E——sheet elastic modulus, MPa;
σs——sheet yield point, MPa.
Assuming that D=0.95t and the contact stress is not greater than 2σs, the minimum roller distance tmin derived from the contact strength is:
In the formula: hmax——maximum plate thickness for leveling, mm.
The minimum roll distance tmin derived according to the torsional strength of the work roll is:
In the formula: b——maximum board width for leveling, mm;
σ0——Allowable torsional strength of work roll, MPa.
tmin is calculated according to equation (2) and equation (3) respectively and then takes the larger value.
Finally, determine the roller distance tmin<t<tmax (try to take the smallest value), and it should be rounded according to JB 1465.
Roller diameter D
The roller parallel machine can take (0.85~0.9)t, and in large machines it can also take 0.7t. D of the machine with non-parallel roller rows can be taken as (0.9~0.95) t.
Number of rollers n
Increasing the number of rollers means increasing the number of alternating bends of the sheet, thereby improving the leveling accuracy, but it will also increase the work hardening and machine power and complicate the structure. Therefore, on the premise of ensuring the leveling quality, the number of work rollers should be reduced as much as possible. number.
Thin plates are more difficult to level than thick plates. Therefore, the thinner the plate, the greater the ratio of plate width to plate thickness, and the more serious defects such as scooping and arcing. The roller distance should be reduced to increase the elastic-plastic bending deformation of the plate. However, due to the limitation of tmin, the roller distance cannot be selected too small. Therefore, the number of rollers is often increased to improve the leveling quality. Therefore, the thinner the plate, the greater the ratio of plate width to plate thickness, the higher the yield point of the plate, and the greater the number of work rolls.
The number of working rollers of the roller sheet leveling machine is ≥ 5 rollers, generally 5 to 29 rollers.
Roller body length L
L depends on the maximum plate width bmax, and is generally selected according to L=bmax+(100~300) mm.
Leveling speed v
For a separately set roller sheet leveling machine, the leveling speed v depends on the productivity requirements of the leveling machine and should take into account the specifications and temperature of the sheet. Generally, the speed is higher during hot calibration and lower during cold calibration; the speed for calibrating thin plates is higher and the speed for calibrating thick plates is lower. The recommended leveling speed is 4~20m/min.
For leveling machines set up on production lines, their leveling speed matches the production line speed and is often adjustable.
The above briefly introduces the leveling principle, type, characteristics and method of determining the main parameters of the roller plate leveling machine. Selecting a reasonable roller sheet leveling machine type and parameters can not only ensure that user requirements are met to the maximum extent, but also the designer’s need to ensure that the designed product has an advanced structure, reasonable functions, low cost, and easy use and maintenance.