JPS6118131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method of testing for and preventing the possibility of the occurrence of defects such as cracks, crazing, etc. on the surface of an object exposed to mechanical forces, and In particular, but not exclusively, it relates to methods of testing for and preventing the possibility of such defects in rolling mill rolls.

Particular examples of objects having surfaces that are subjected to strong mechanical forces during use include rolls, such as those used in rolling mills. Such rolls are of course very expensive to manufacture and it is therefore desirable to have as long a service life as possible.
A new rolling roll has a maximum diameter that can be used in the rolling mill housing and when this diameter is reduced to a certain minimum value the roll must be discarded. Such a reduction in diameter is unavoidable.
This is because cylindrical rolls are subject to wear and damage due to the strong forces they are subjected to, requiring periodic re-dressing and reshaping of the rolls.

It is well known that when stress is applied to the surface of a crystalline material, especially a metal object, the materials surrounding it, including the surface of the object, become work-hardened and brittle. Therefore, if stress is applied to the rolls of the rolling mill during operation, the surface of the rolls may become work hardened, leading to fatigue and cracking of the metal. Here, "cracks" and "cracks" are names given to surface defects in the steel industry, and refer to the phenomenon in which metal pieces separate from the roll surface and form shallow recesses for convection. In addition, a "flap-shaped crack" is another type of defect in which two adjacent portions of a roll are relatively displaced and a crack is formed between the radially protruding portions. It refers to the cracks that occur. Such defects can only be removed by removing the portion of the roll periphery containing the defect, for example by turning or grinding, but the amount of material removed is usually is typically many times greater than the amount required for redressing, and can even reach the point where further use of the roll is impossible, thereby reducing the useful life of the roll considerably, e.g.
It can be shortened by as much as %. Furthermore,
The necessity of very frequent replacement of the rolls and the imprints on the rolled product in the event of cracks or cracks in the rolls have a negative effect on the working efficiency of the rolling mill.

The hardening that occurs in mill rolls usually occurs in the form of a circular band around the circumference of the roll, and usually, but not always, immediately adjacent the portion of the roll surface that contacts the edge of the strip material being rolled. Maximum near the edges. Eddy current conductivity testing is a well-known non-destructive testing method to obtain an indication of the hardness of a material. In this case, the phenomenon that the electrical conductivity of a metal usually decreases as its hardness increases is utilized. However, it must be noted that this method is prone to large errors. This is because certain variables may affect conductivity without affecting hardness, and vice versa. Therefore, the results obtained with such non-destructive testing methods are qualitative but not quantitative in nature.

SUMMARY OF THE INVENTION Accordingly, a principal object of the present invention is to provide a method for testing the possibility of the occurrence of cracks, fractures, and similar defects on the surface of an object.

A more specific object of the invention is to provide a method for testing the surface of rolling mill rolls for the possibility of cracking, splitting, and similar defects.

Another object of the invention is to propose a method for testing the surface of objects, in particular of rolling rolls, for the possibility of cracks, splits and similar defects, and subsequently reducing at least such a possibility. It is in.

For the above purpose, according to the present invention, there is provided a method for testing the possibility of occurrence of defects such as cracks and fractures on the surface of an object, and the method includes: Determine the rate of change in hardness and detect locations along the reference direction that have a rate of change greater than a predetermined known maximum value, thereby determining the possibility of the occurrence of defects on the surface of the object and the conditions it will undergo during operation. A test method is proposed that involves predicting the

Hardness is preferably tested using non-destructive testing methods.

A test object for which a rate of change larger than the above maximum value is detected is prohibited from use from the beginning, or if it has already been used, is prohibited from further use.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Referring in the drawings, and in particular to FIGS. 1 and 2, the roll 10 is shown along its axis 12 by an upright standard support 14, as can be seen from the schematic representations.
It is installed so that it can rotate around the center. On the other hand, the upright support 14 is a solid base (not shown).
installed on top. Considering the weight of the roll,
Some mechanical means may be required to rotate the roll about its axis on a standard support, such as a suitably sized grinder or lathe type drive.

A pair of additional standard upright supports 16 mount a carriage or carriage 18 for movement parallel to axis 12. This carriage slides on a rod 20 extending between standard supports and is driven in a sliding manner by a threaded rod 22 which is rotated by an electric motor 24 via a reduction gearing 26. Carriage 1
8 has an arm 28 secured to it, at one end of which is a slidably mounted rod 30, and at one end of which rod 30 carries a bearing pad 32. The rod 30 and therefore also the bearing pad 32 are
A spring 34 pushes the pad 32 in the direction in which it is pressed against the roll circumferential surface. At the end of the rod 30, an eddy current detection device 3 is fitted by means of a suitable adjustment device 38.
6 is attached, and the position of the detection device is adjusted so that the pad 32 maintains sufficient contact with the roll circumferential surface as it scans the roll circumferential surface. Those skilled in the art will readily be able to conceive of other types of lateral motion mounting devices for the same purpose, such as mounting the rolls on the crossfeed of a grinding machine or lathe.

The detection device 36 is connected by a cable 40 to a combined eddy current test device and chart recorder, and the motor 24 is controlled in a known manner by the recorder portion of the device as follows. That is, the diagram or graph drawn by the device 36 is controlled in such a way that it corresponds to one scan across the entire width of the roll 10. In this way the device
Directly generate diagrams or graphs such as those shown in FIGS.

Using the method of this invention, the surface of the object is more likely to develop defects, such as cracks and fractures in the case of metal rolls, when subjected to mechanical forces encountered during normal operation. It was found that predictions can be made with high accuracy.

In a preferred test method, information directly corresponding to or representative of certain physical parameters of the material of the object measured at or immediately adjacent to the surface along a suitable reference direction is obtained. , non-destructive testing methods are used. Surface areas along the reference line that have a rate of change of the above physical parameters greater than a predetermined maximum amount for the particular material and the particular test conditions to which the material is subjected are susceptible to defects such as cracks and fractures. It was found to have a high probability as a potential part of the occurrence. If such a potential part is identified,
Appropriate processing may be performed to reduce the rate of change below the predetermined maximum level.

Currently, the rate of change in hardness is the main physical parameter to be considered, but other parameters could also be used, such as distortion of the crystal lattice, dislocations, and differences in the effectiveness of heat treatments. .

The method of the invention was first applied to testing hot rolling mill packing rolls to predict the likelihood that such rolls would fail in service due to the development of cracks or splits. It has been found that, using the method of the invention, steps can be taken to substantially reduce, if not completely eliminate, the possibility of such defects occurring in future use of the roll. Ivy. Furthermore, the method of the invention can be successfully used to obtain specifications for new rolls that have been pre-tested before being used, and that during the testing phase the rate of change in hardness exceeds the maximum amount mentioned above. If it is found that the substance is present, appropriate preventive measures can be taken. Also, the exam is
Although it can be carried out at any time during mill operation, it is convenient to carry out the test as a routine operation when the roll is removed for reshaping.

Such rolls are a particular example of objects with surfaces that are subjected to high mechanical forces in normal use and are typically 1.676 m (66 in) wide, and 1.334 m (52.5 in) wide when new. ) has a diameter of These specialized rolls are discarded when, in normal operation, their diameter is reduced by wear and repeated reshaping to 1.232 m (48.5 inches). Small cracks are
Usually removed by grinding, large cracks and fractures may require recutting the roll on a lathe, and if the cracks are quite deep, the roll may be completely removed without further use. will be discarded. The invention also provides that when a certain depth of grinding or cutting is required to reduce the likelihood of defects in rolls that are predicted to fail,
It can be used to accurately determine its depth. Also, in the case of defective rolls, it is possible to use the invention to completely eliminate the defects and prevent their recurrence as much as possible.

The inventors believe that in the case of steel objects, such as rolling mill rolls, measuring the magnetic permeability or electrical conductivity of the metal with an eddy current measurement device is based on the above-mentioned physical parameters.
It has been discovered that this is a non-destructive testing method that is particularly suitable for obtaining measurement results that can be correlated with the hardness of the material that makes up the roll surface. In the drawing, 3rd
Please refer to the diagram. This figure shows that it is possible to obtain a close correlation between eddy current conductivity and hardness, in this example Shore hardness.
That is, since the chemical composition and heat treatment of such rolls are usually substantially uniform, variations in eddy currents can be directly related to hardness, as shown in FIG. However, as mentioned above, errors can always occur because eddy current readings are also influenced by other parameters such as crystal orientation, which do not necessarily predict the likelihood of defect occurrence. Tests to date have yielded a correlation of approximately 95%. Furthermore, the specific relationship between the eddy current reading and the absolute value of hardness is different from roll to roll and must be determined for each roll. It is of course also possible to use other known methods, such as measuring magnetic permeability. However, eddy current devices are particularly preferred due to their simplicity, accuracy and robustness.

Other forms of nondestructive testing that provide readings that correlate to hardness may also be used in the method of the present invention, such testing methods include ultrasonic machines, heated roll infrared testing, and holographic testing. It is being Devices are also known that provide hardness readings directly to meters or recording devices, but these devices are not suitable for use with mill rolls because they inherently leave marks on the surface being tested. Since the surface of this type of roll is highly polished, markings are undesirable.

The test scan shown in FIG. 3, performed using the apparatus shown in FIGS. 1 and 2, was carried out along a line parallel to the roll axis. In the figure, the width of the roll is plotted in inches on the vertical axis, and the shore hardness and eddy current conductivity in arbitrary units are plotted on the horizontal axis. In FIG. 3, the eddy current scan pattern obtained by apparatus 40 is shown as a solid line, while the corresponding shore hardness measured by the direct test method is shown as a dotted line. It is very clear that there is a close correspondence between these two measurements. The corresponding rate of change in eddy current reading or hardness per linear inch of roll width is represented by the slope of each pattern curve. As will be understood by those skilled in the art, device 42 can be configured to obtain a graph representing the rate of change directly by providing suitable differentiating circuitry.

The reference line for the measurement can alternatively be a helix around the roll surface coaxial with the roll axis, but as already mentioned, in the case of steel mill rolls, the main points to consider are Since the parameter is hardness, and regions of different hardness usually exist in the form of circular bands, it has been found that a linear graph of the form shown can best give the required information. . If desired, the scans can be repeated along the axis at spaced intervals around the circumference of the roll.

As an example, for a typical new steel hot rolling mill backing roll of the type described, a test equipment Automation Industries Model
UM1500), it has been found that if the rate of change of eddy current per linear inch is less than about 10 to 11, the likelihood of cracking or splitting is sufficiently low that the roll is acceptable. However, values of 8 or less are more reliable and preferred. The hardness and/or eddy current pattern of a roll is not static, but varies considerably over its lifetime, primarily due to work hardening during rolling. Measurements of the roll during use should therefore be made at regular intervals, and especially when the roll is removed and the surface is reshaped to the desired rolling shape.

The method of the invention can only indicate the level of probability that a particular roll will fail in normal use, and therefore any particular roll that gave a low rate of change reading is It will be understood that there is no guarantee that it will not become defective.
per linear inch using the test equipment described above.
It was found that rolls giving an eddy current rate of change reading of 15 or more had a high probability of defect occurrence, while rolls giving a reading of 10 or less had a low probability. More specifically, these readings can be categorized as follows.

a 5 or less per linear inch: A standard value that should preferably be obtained with a new roll, and an outstanding value that indicates that the roll will be satisfactory throughout its service life.

b Between 5 and 8: Good standard for new rolls and excellent standard for used rolls.

c Between 8 and 11: Insufficient value in the new role, acceptable value in the used role.

d between 11 and 14: Values that are not completely acceptable with new rolls, or not well tolerated with used rolls, to justify lathing or grinding until better tolerances are achieved.

e 14 or more: A value indicating that the probability of cracking is high and that it is essential to perform correction processing before using the roll later.

One special factor that has come to the inventor's attention that may alter the above-mentioned values (it must be emphasized again that the above-mentioned values were obtained with a specific test setup) is , a high but prima facie acceptable rate of change is immediately followed by another high rate of change in the opposite direction. Although each individual rate of change may be individually acceptable, the close succession of these rates represents an undesirable situation in which remedial work should be performed.

When considering the rate of change in shore hardness, approximately
A percentage change of 2.5 or less is a desirable value for new rolls, 2.5 to 3.6 can be considered acceptable for used rolls, and readings of 3.6 or higher indicate the need for rework. can. However, these values cannot be directly applied to the surfaces of other objects. This is because acceptable values can vary considerably in average hardness. For example, a rate of change that is acceptable for an object with an average shore hardness of 65 may be completely unacceptable if the shore hardness is only about 50.

FIG. 4 clearly shows the effect of work hardening in the peripheral area of the steel roll and the changes obtained by removing the surface layer of the roll.
Test scan curve #1 was obtained at a diameter of 1.33 m (52.335 inches) and shows the presence of the most rapidly changing portion of eddy currents between points A and B. However, the actual rate of change is only 5
, which is well within the required values for new rolls, as well as for used, work-hardened rolls. Test curves #2, #3 and #4 are 0.0889 cm (0.035 inch) and 0.191 inch respectively
cm (0.075 inch) and 0.343 cm (0.135 inch)
The case where the skin is removed one by one is shown, and it can be seen that the properties of the roll material gradually change as the work-hardened portion of the roll material is removed, and the roll surface almost certainly returns to its original properties. Test curve #5, with 0.485 cm (0.191 inch) of skin removed, is sufficiently similar to test curve #4 to indicate that there is no more material to remove.

Currently, the preferred mechanical processing applied to an object to reduce the rate of change in hardness below a desired maximum value involves cutting or grinding away the outer portion of the object to expose areas with less variation in hardness. That's true. In the case of bucking rolls for hot rolling mills, which exhibit characteristics that indicate the possibility of defects, it is not sufficient to pre-remove up to 0.101 cm (0.040 inch) by grinding during the reshaping process; 1.78cm
(0.70 inch) ± 0.51 cm (0.20 inch) should be removed. This large amount of material removal is comparable to the 2 inches (5.1 cm) or more of material removal required to remove an actual crack or crack. Other treatments that may be used include, for example, appropriate heat treatments and surface annealing.

Referring now to Figures 5 and 6, which show two graphs obtained for cracked rolls, the location of the crack along the axis is indicated relative to the portion of the graph with a high rate of change. ing.

In the graph of FIG. 5, the eddy current readings are completely depicted, but the shore hardness is only partially graphically represented. The cracking is approximately per inch.
Located in the vicinity of an eddy current change of 25 units, the corresponding change in shore hardness is approximately 3.5/inch in this example. As mentioned earlier in connection with rolling mill rolls, it is the areas adjacent to the roll ends that are most exposed to the greatest stresses;
Most cracks and cracks appear in this area. All the required information can therefore be obtained with a hardness and/or eddy current graph limited to such an end section.

In the graph of FIG. 6, only eddy current curves are shown. As can be seen from the figure, two cracks have occurred in the axial direction, and one
A rate of change of about 32 units per inch is obtained.

The methods of this invention are also applicable to other surfaces formed from other materials, and a series of relatively simple tests determine whether they are desirable, acceptable or suitable for a particular device or application. Maximum values for the rate of change of physical parameters, in particular hardness and/or eddy current conductivity, can be quickly set for consideration of unacceptable or unacceptable conditions.

Although hardness values are expressed in this specification as Shore values, those skilled in the art will readily understand that other measurement systems may also be used to express corresponding values, such as Vickers hardness and Brinell hardness. Also, a number of different tables can be prepared for rapid conversion from one system to another.

Another example of application of this invention is the finishing of the roll surface of a cold rolling mill. By testing the roll surface prior to shot blasting or polishing, areas of significantly different hardness can be detected which, if not removed, will result in imperfections in the finished surface. If such an area is detected, processing is performed to remove such area before shot blasting, polishing, etc. are performed. It will be appreciated that this method is preferred over the traditional method of visually inspecting the surface. This is because conventional methods cannot sufficiently detect such problem areas.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing a steel roll for a rolling mill and an apparatus for measuring and graphically displaying the surface hardness of the roll, and FIG. 2 is an enlarged view showing the apparatus of FIG. 1 in detail. Perspective view, Figure 3 is a graph showing shore hardness readings and eddy current (permeability) readings across the width of the roll for a typical rolling mill roll, and Figure 4 is a graph showing the shore hardness readings and eddy current (magnetic permeability) readings for a typical rolling mill roll. Figure 5 is a graph similar to Figure 3 showing eddy current readings across the width of the roll before and during machining consisting of sequential removal, but along the length of each roll. The eddy current readings, the shore hardness readings adjacent to the end of the roll, and the location of cracks in this roll are shown; Figure 6 shows the eddy current readings in yet another roll and the cracks in this roll. It is a graph showing the position of. In the figure, 10...roll, 14, 16...stand,
18... Carriage table, 20... Rod, 22... Threaded rod, 24...
Electric motor, 26... Reduction gearing, 32... Bearing pad, 34... Spring, 38... Adjustment device, 40... Cable, 42... Eddy current test recording device.

Claims (1)

[Scope of Claims] 1. In a method of testing the possibility of defects such as cracks and fractures on the surface of an object, a hardness change rate along a reference direction is determined for at least a portion of the object including the surface, and a predetermined 2. A test method comprising detecting locations along said reference direction having a rate of change greater than a known maximum value determined, thereby predicting the probability of occurrence of defects on the surface of the object and the conditions to which it will be subjected during operation. 2. The test method according to claim 1, wherein the surface of the object is the outer cylindrical surface of a cylindrical steel rolling roll. 3. The test method according to claim 1 or 2, wherein the surface is made of a ferromagnetic material and the hardness is measured using an eddy current measuring device. 4. The test method according to any one of claims 1 to 3, wherein the surface is an external cylindrical surface of a cylindrical roll, and the reference direction is a line parallel to the roll axis. 5. Claim 2, characterized in that the predetermined maximum value of the hardness change rate in the steel rolling roll is approximately 2.5 shore hardness per linear inch.
The test method described in either Section or Section 3. 6. characterized in that the initial predetermined rate of change in hardness in the steel rolling roll is about 2.5 Shore hardness per linear inch and the other predetermined maximum value is about 3.6 Shore hardness per linear inch. A test method according to claim 2 or 3.