JPH08166332A - Life judgement method of in-furnace spray-coated roll - Google Patents

Abstract

PURPOSE: To obtain a life judgment method in which a film degradation state is judged with good accuracy and in which the generation of the exfoliation of a coating material can be estimated in advance by a method wherein it is judged that a roll has reached a life when the hardness of a spray-coated film in the central part satisfies a specific condition with reference to the initial hardness of a spray-coated film on the surface of the roll which has been measured by using an ultrasonic hardness meter. CONSTITUTION: An in-furnace roll, for a test, onto which a film has been sprayed is installed nearly in the center of a furnace 2 so as to be rotatable in synchronization with the movement of a strip 3 by a motor 4. The strip 3 is passed through inside the furnace 2, and both ends are connected to a weight 9 at the outside of the furnace via a wire 15. Then, when the hardness of a spray-coated film in the central part of the roll with reference to the initial hardness of a spray-coated film on the surface of the roll measured by using an ultrasonic hardness meter satisfied a condition by an expression of HVc<=1/2HVf, it is judged on the basis of the degradation of the sprayed film that the in-furnace spray-coated roll has reached a life. In this expression, HVC represents the mean value of the hardness of the spray-coated film in the central part of the roll (using a measured value of 10 points or higher), and HVf represents the mean value of the initial hardness of the spray-coated film on the surface of the roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal spraying roll used for a hearth roll of a heat treatment furnace or the like, and to a method for determining the life from the change in hardness due to deterioration of the thermal spray coating.

[0002]

2. Description of the Related Art In a heat treatment line, as a surface coating material for a roll in a furnace that conveys high-temperature steel plates or the like, a material that does not adversely affect the surface quality of the conveyed material, that is, a material having excellent pick-up resistance, It is desired that the material has excellent high-temperature wear resistance, and conventionally, Cr ₃ C ₂ + N has been used.
iCr system, CoCrAlYTa + Al ₂ O ₃ system, CoN
Materials based on iCrAlYTa + (Al ₂ O ₃ + Cr ₂ O ₃ ) have been used.

The above coating material gradually deteriorates in hardness due to heat cycle and oxidation due to the release of the furnace at the time of regular repair, or the influence of Mn concentrated on the surface of the carrier material, and the hardness decreases, as shown in FIG. Then, peeling 14 occurs on the thermal spraying roll 1. When such peeling of the surface coating material of the in-furnace roll occurs on the thermal spraying roll, process disturbance and quality defects of the conveying material occur, which is often a problem. In order to prevent this peeling, conventionally, the roll surface is inspected by visual inspection, a microscope, or a roughness inspection at regular intervals, and countermeasures are taken based on the inspection result.

[0004]

However, even if a slight oxidation state of the surface can be confirmed only by visual inspection such as conventional visual inspection, microscopic inspection, or roughness inspection, to what extent the film deteriorates. I don't know if
There was a problem that peeling occurred suddenly. In addition to the above-mentioned appearance check method, it was attempted to measure the deterioration state of the film with a Shore HS hardness meter without scratches on the surface and to judge by the degree of hardness change, but the film was affected by the hardness of the roll core metal. The hardness could not be measured accurately, and the criteria could not be set.

An object of the present invention is to provide a method for determining the life of a thermal spraying roll in a furnace, which can more accurately determine the deterioration state of the coating and can predict the occurrence of peeling of the roll surface coating material in advance. is there.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for determining the life of a thermal spraying roll in a furnace, wherein the thermal sprayed coating at the center of the roll is compared with the initial hardness of the thermal sprayed coating on the surface of the roll measured with an ultrasonic hardness meter. When the hardness satisfies the following conditions, it is determined that the in-furnace spraying roll has reached the end of its life due to deterioration of the sprayed coating, which is a life determining method for the in-furnace spraying roll.

HVc ≤ 1/2 HVf where HVc: average value of the hardness of the sprayed coating at the center of the roll (uses a measured value of 10 points or more) HVf: average value of the initial hardness of the sprayed coating on the surface of the roll (measurement of 10 points or more) Value used).

[0008]

As a result of various experiments, the present inventor found that when the hardness of the spray coating at the center of the roll satisfies the following conditions with respect to the initial hardness of the spray coating measured on the roll surface using an ultrasonic hardness meter: It was found that the life of the in-furnace thermal spray roll due to deterioration can be accurately determined.

HVc ≤ 1/2 HVf where HVc: average value of the hardness of the sprayed coating at the center of the roll (use a measured value of 10 points or more) HVf: average value of the initial hardness of the sprayed coating on the roll surface (measured value of 10 points or more) Use).

Further, according to the present invention, since the hardness of the sprayed coating on the roll surface is measured by using an ultrasonic hardness meter, the sprayed coating is not scratched, and the material and hardness of the roll core metal are simple. The film hardness can be measured. The ultrasonic hardness meter is commercially available and is not particularly limited. An example of an experiment conducted by the inventor will be described below.

FIG. 1 is an explanatory view showing the outline of an experimental apparatus for conducting a forced deterioration test of a sprayed coating. The furnace 2 is a model of an annealing furnace, and a test spraying roll 1 having a coating as a hearth roll is sprayed on the motor 4 in the approximate center of the furnace 2.
Therefore, it is rotatably installed in synchronization with the movement of the strip 3. The strip 3 is threaded into the furnace 2, and both ends of the strip are connected to weights 9 outside the furnace via wires 15 and the strip is reciprocable by a motor 8 via limit switches 16. ing. A load cell 10 measures the tension applied to the strip 3. The atmosphere in the furnace is adjusted by an atmosphere adjusting mixer 13 connected to the hydrogen introducing pipe 11 and the nitrogen introducing pipe 12. Furnace heating is performed by a plurality of heaters 5, and the temperature adjustment is performed via a controller based on the value detected by the thermocouple 6. In addition, 7 is a seal.

Using the above experimental apparatus, the atmosphere in the furnace was set to 4% H.
_2- N ₂ , temperature 1000 ° C, strip tension 7 kgf /
mm ² , high Mn steel is used as the material of the strip, and the strip 3 is constantly reciprocated under the conditions of the peripheral speed of the spraying roll 1 of 10 mpm and the stripping speed of 10 mpm. Steam was blown into the inside to allow natural cooling. The furnace length at this time is 1 m.

The test results are shown in Table 1. Note that FIG. 2 is a graph of a part of the results in Table 1, and the peeling occurred is shown by a filled plot. Table 1, Figure 2
When the film peeling occurs, the film hardness of each test piece after the test time of 100 to 300 hr is less than half of the initial film hardness, that is, the hardness ratio (HVc / HVf).
It can be seen that is less than 1/2.

[0014]

[Table 1]

[0015]

[Example] Used in a heating furnace of a continuous annealing line having a production capacity of 60,000 tons / month [CoNiCrAlYTa +
30 (Al ₂ O ₃ + Cr ₂ O ₃ )] system thermal spray coatings on eight furnace rolls, the thermal spray coating hardness was measured with an ultrasonic hardness meter during regular repair every six months, and the degree of coating deterioration was measured. That is, the remaining life was judged.

As a result, 3 out of 8 had already reached half or less of the initial film hardness, and when the surface was observed in detail, fine peeling had occurred, so replacement was carried out. In addition, the remaining 5 pieces have not reached less than half of the initial film hardness, and the 4 pieces have been judged to have reached the end of their service life, estimated from the period of use at the time of regular repair after half a year. Did.

After 5 months, the hardness of the remaining 5 films was measured again, and the film hardness of 4 rolls, which was judged to reach the end of life at the time of regular repair 6 months before, reached less than half of the initial film hardness, and the surface was observed. After that, fine peeling started to occur, so the replacement was carried out as planned. Although the remaining one roll has not reached less than half of the initial coating hardness, it is estimated from the usage period that it will reach the end of life before the next regular repair, and it will be put together with the four rolls. The roll was replaced.

As described above, according to the present invention, it is possible to prevent sudden peeling of the coating film and to perform planned roll replacement.

[0019]

INDUSTRIAL APPLICABILITY According to the present invention, the hardness of the sprayed coating on the roll surface is measured using an ultrasonic hardness meter, and when the hardness of the sprayed coating at the center of the roll is less than half of the initial hardness of the sprayed coating, the sprayed coating is obtained. Since it is determined that the life of the thermal spraying roll is due to deterioration, it is possible to determine the deterioration state of the coating more accurately, it is possible to predict the occurrence of peeling of the roll coating in advance, and sudden peeling of the roll coating is possible. It has become possible to prevent process troubles and quality defects due to.

Since rolls can be replaced systematically and without waste, the roll repair cost can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of an experimental apparatus for performing a forced deterioration test of a thermal spray coating.

FIG. 2 is a graph showing the results of a forced deterioration test of a thermal spray coating.

FIG. 3 is a perspective view of a thermal spray roll having a peeled portion of a thermal spray coating.

[Explanation of symbols]

 1 Spraying Roll 2 Furnace 3 Strip 4 Motor 5 Heater 6 Thermocouple 7 Seal 8 Motor 9 Weight 10 Load Cell 11 Hydrogen Introducing Pipe 12 Nitrogen Introducing Pipe 13 Atmosphere Adjusting Mixer 14 Exfoliation 15 Wire 16 Limit Switch

Claims (1)

[Claims] 1. In a method for determining the life of a thermal spraying roll in a furnace, when the thermal spraying film hardness in the central part of the roll satisfies the following condition with respect to the initial thermal spraying film hardness of the roll surface measured using an ultrasonic hardness meter: A method for determining the life of an in-furnace thermal spray roll, comprising determining that the in-furnace thermal spray roll has reached the end of its life due to deterioration of the thermal spray coating. Note HVc ≤ 1/2 HVf where HVc: average value of the hardness of the sprayed coating at the center of the roll (uses a measured value of 10 points or more) HVf: average value of the initial hardness of the sprayed coating on the surface of the roll (uses a measured value of 10 points or more) Is.