Physical - Metallurgical Faculty
Speciality: Metal Forming
The growth of consumer demands rolled to his quality and increased competition require producers to search for new technologies and transform them into production. One of the most promising technologies in this field is asymmetric rolling.
Asymmetrical rolling process is called a process in which there is no complete symmetry about the horizontal plane, ie different diameters of work rolls, different state of their surface, or one of the rolls is non drive are also possible options that rolls have different speeds, and others.
This method allows the direct form of rolling lag reduced by rolling to obtain better mechanical properties.
The major advantage of this type of improvement rolling production is possibility of its implementation on modern units without complete Reconstruction of.
In this work will examine various options for the asymmetric bars, Explore their influence on the lateral strain of thick bands, and also provides a method of rolling strip resornoy using high-speed asymmetry.
The purpose of this study is to search for and study of alternative rolling thick bands that improve quality. To achieve the objectives set out in the master's work and the following tasks:
The object of study - the process of broadening of the metal in the deformation in asymmetric rolling.
Methods of research include the physical modeling on the laboratory mill and mathematical processing of experimental results.
The opportunity to demonstrate how the developed method of rolling resornoy bands on modern continuous and linear high-grade mills.
The main part sheets and strips, including more than 4mm thick, is used by consumers with rectangular edges. However, straight edge is not always beneficial. Upon receipt of such springs as: trapezoid-speed, T-shaped, trapezoidal need different width top and bottom.
Symmetrical rolling process is the so-called "simple case of" rolling - a process in which the diameters of upper and lower rolls are equal, as a neutral corner, and as equal to their circumferential speeds. In the deformation zone at the same time identify two zones of the zone and the zone of the backlog of advance. But in practice, we can confidently say that this "simple case of" rolling does not exist, ie difficult to observe all the conditions for a symmetrical process. Thus, the process is symmetric rolling is a special case of an asymmetric process.
Possible causes of the asymmetry of the longitudinal rolling can be divided into six main groups:
Asymmetric rolling process has the following advantages:
When the process of asymmetric direction of forces in the deformation and the values are changed, and this leads to a change in deformation conditions on the driving and driven rollers, and compression of the leading roller is higher than from the slave. Omni directional frictional forces can prirovnyat to step forward and back stress arising directly in the deformation.
After analyzing all types of asymmetry, we can say that the influence of the broadening of the master and slave rollers can get high-speed roller asymmetry or asymmetry.
If you roll the broadening of the asymmetry depends on roll diameter, ie the greater the difference between the diameters, the greater the mismatch and the dependence of the broadening. In practice, implementation of such a process is time consuming, because smaller diameter roller with feed him large forces will be subject to frequent replacements, resulting in unnecessary costs in material terms. It was therefore chosen speed asymmetry, because rolls will be the same diameter and they will act the same power, and replacement of engines would be more cost effective than replacement of the rolls.
Investigation of the mechanism of broadening of the metal under asymmetric rolling was carried out on samples of lead. Rheological properties of lead picked up the rheological properties of steel at a temperature of hot rolling.
Studies conducted on laboratory mill 100 (the length of the rolls 170 mm).
Objective: to study the influence of the absolute reduction and bandwidth to the broadening of the master and slave rollers in asymmetric rolling.
Asymmetry created during rolling due to the difference of rotation speed of rolls: the lower roll - leading, the top - driven. Thickness and width of the sample was measured at three points along the length: head, middle and tail of the sample. Sample thickness was measured using a micrometer, and the width - caliper. Rolling was carried out on specimens with a cross section 29x29 mm (H / L = 1.0) and 16x32 mm (H / L = 0,5) in several passes to get the strip thickness of 6-10 mm. But at the 100 laboratory mill drive rolls through gear crate, so the drive was on the roller mill 100 and driven from the mill 250. The results of the rolling samples are given in Table
| Pass number | Thickness, H, mm | The width of the leading roll, B1, mm | The width of the driven roll, B2, mm |
|---|---|---|---|
| 0 | 21.8 | 42.4 | 42.5 |
| 5 | 19.2 | 46.7 | 44.6 |
| 10 | 10.1 | 51.4 | 44.7 |
Photo platen transverse profile of the band after asymmetric rolling is shown in the picture:
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| Picture - Photo platen cross-section sample mm 28x42 |
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As a result of this experiment it was found that the broadening of the leading roll more than the part of the slave.
Such a redistribution of broadening conditioned by large compression adjustment layers from the leading rolls and inhibition of extracts from the less deformed strata adjacent to the driven rolls. As a result, more high-rise direction compresses the layers are forced to further deform in the transverse direction.
In addition, the rate of metal from the roll at a higher rate (the lead) is higher than that of the roll at a slower rate (slave). Consequently, the metal in contact with high-speed roller having compressive stress and the contact area of metal with a low-speed roll - the tensile stress, which leads to a redistribution of near-contact broadening.
On the drive roller peripheral speed increases, thus broadening his party should also increase. Nevertheless, the broadening depends on the thickness of the strip. Therefore, in the high-band reduced zone of advance and the friction force in it, reduces the effect of sustaining the stress, which makes it easier for the metal in the longitudinal direction. This decreases the proportion of the displaced volume, which accounts for the broadening. With decreasing thickness of the lag when they start to deform middle layers of the metal band broadening begins to lead decreases rapidly-increasing, outstripping the value of broadening in symmetric rolling process. And the thinner becomes bar, the proportion of the displaced volume per broadening not-increasing.
In such a way, in asymmetric rolling process of compression and redistribution of rates leads to a redistribution of broadening.
On the basis of these studies was developed by way of rolling spring strip, which has a cross-sectional shape in the form of a trapezoid. Which includes the heating of billets and its subsequent rolling in the rectangular caliber crimp the group stands, subsequent rolling into cylindrical rolls on a smooth barrel and rolls with the caliber of bevel edge in roughing and finishing stands of a group fasonnom caliber, characterized in that the rolling of the cylindrical rollers for smooth barrel commit to the mismatch of speeds, which depends on the difference between the width of the finished strip from the rolls, with more and less speed, respectively, composes not less than 1.020.
The application of this utility model allows for the expense of high-speed asymmetric rolling to form the tackle with the cross-sectional shape which is similar to the form of fire, increase the intensity of shear deformation, which leads to a refinement of grain in the metal, and as a consequence, increases the level of mechanical properties.
Thus the tests: