JP2006078271A - Ultrasonic flaw detection method of steel bar - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method of a steel bar hardly influenced by foreign substances and air bubbles attached to a surface of the steel bar, and accurately and inexpensively implementing ultrasonic flaw detection of defects that exist in the inside of the steel bar. <P>SOLUTION: When the ultrasonic flaw detection of the steel bar 1 is implemented by a probe 5 as the steel bar 1 is rotated axially on an axis within an ultrasonic transmitting medium 3, the ultrasonic flaw detection is implemented while the steel bar 1 is made to contact an elastic body 4, such as brush and urethane. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flaw detection method for steel bars used as rolling element materials for rolling bearings such as roller bearings.

Since steel bars used as rolling element materials for roller bearings are generally produced by rolling a steel material, defects such as ground are often present inside the steel bar. For this reason, when steel makers use steel bars as rolling element materials for roller bearings, they are immersed in an ultrasonic transfer medium such as water, and in this state, ultrasonic testing is performed while rotating the steel bars around the axis. By doing so, it is inspected whether or not there is a defect inside the steel bar. In this case, if foreign matter or bubbles are attached to the surface of the steel bar, it is difficult to accurately detect the defects existing inside the steel bar. For this reason, conventionally, ultrasonic inspection of a steel bar is performed while jetting a jet stream to the steel bar (see Patent Document 1), or the steel bar is supersonic while being removed with a degassing device so that bubbles do not adhere to the surface of the steel bar. Sonic flaw detection is performed.
JP 2002-296247 A

However, there is a problem that the foreign matter adhering to the surface of the steel bar cannot be completely removed by the method in which the jet water flow is sprayed on the steel bar to remove the foreign matter and bubbles, and the method using the degassing device has a problem that the degassing device is not used. Since it is expensive, there has been a problem of increasing the flaw detection cost.
The present invention has been made paying attention to such problems, and it is possible to accurately detect defects existing inside the steel bar at a low cost without being greatly affected by foreign matter and bubbles adhering to the surface of the steel bar. It is an object of the present invention to provide an ultrasonic flaw detection method for steel bars that can be subjected to ultrasonic flaw detection.

In order to achieve the above object, an ultrasonic flaw detection method for a steel bar according to the invention of claim 1 is characterized in that, when the steel bar is ultrasonically flawed while rotating the steel bar around an axis in an ultrasonic transmission medium, Ultrasonic flaw detection is carried out while bringing an elastic body into contact with the steel bar.
An ultrasonic flaw detection method for a steel bar according to a second aspect of the invention is the method for ultrasonic flaw detection of a steel bar according to claim 1, wherein the average surface roughness of the steel bar is within a range of 0.3 to 2.0 μmRa. Features.

  In the ultrasonic flaw detection method for a steel bar according to the present invention, by performing ultrasonic flaw detection while bringing an elastic body into contact with the steel bar, foreign substances and bubbles attached to the surface of the steel bar can be removed by the elastic body. Therefore, it is not necessary to inject a jet water stream into the steel bar or use an expensive degassing device when ultrasonically testing the steel bar while rotating the steel bar around the axis in the ultrasonic transmission medium. In addition, it is possible to perform ultrasonic flaw detection with high accuracy and low cost for defects existing inside the steel bar without being greatly affected by foreign matter or bubbles adhering to the surface of the steel bar.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an ultrasonic flaw detection method for a steel bar according to the first embodiment of the present invention. In the figure, reference numeral 1 denotes a steel bar as an inspection object. When this steel bar 1 is subjected to ultrasonic flaw detection, the steel bar 1 is placed in an ultrasonic heat transfer medium 3 such as water stored in a storage tank 2. Immerse. Next, an elastic body 4 such as a brush or urethane is brought into contact with the surface of the steel bar 1, and the steel bar 1 is rotated around the axis in this state. The steel bar 1 is ultrasonically flawed by the ultrasonic flaw detection probe 5 while moving the elastic body 4 and the ultrasonic flaw detection probe 5 in the axial direction of the bar steel 1.

  In this way, when ultrasonic flaw detection is performed while the elastic body 4 such as a brush or urethane is brought into contact with the steel bar 1, the foreign material 6 and the bubbles 7 attached to the surface of the steel bar 1 are removed by the elastic body 4. Therefore, when ultrasonic inspection is performed on the steel bar 1 while rotating the steel bar 1 around the axis in the ultrasonic conductive medium 3, a jet water flow is sprayed on the steel bar 1 or an expensive deaerator is used. Since it is not necessary, it is possible to ultrasonically detect defects existing inside the steel bar 1 accurately and at low cost without being greatly affected by the foreign matter 6 and the bubbles 7 adhering to the surface of the steel bar 1.

  In order to confirm the above-mentioned effect, the inventor has a diameter of 0.5 mm on an end face of a test piece 8 as shown in FIG. 2, that is, a steel bar (material: SUJ2, spheroidized annealing material) having an outer diameter of 60 mm and a length of 1000 mm. A test piece 8 in which a drill hole 9 having a depth of 10 mm was artificially provided at an inner diameter position of 10 mm from the outer diameter surface of the steel bar was produced. The echo intensity of the drill hole 9 of the test piece 8 is 80 by the ultrasonic flaw detection method of the steel bar according to the present invention and the conventional method (jet water flow method) using a focus type probe having a frequency of 15 MHz and a vibrator diameter of 12 mm. Ultrasonic flaw detection was performed at an amplifier strength of%. The flaw detection result is shown in FIG. In addition, the flaw detection range was 5 to 15 mm below the surface, diameter 60 mm, and length 1000 mm.

  From the results of the flaw detection test shown in FIG. 3, in the conventional method in which ultrasonic flaw detection is performed while jetting a jet stream on the steel bar, the number of detected errors with S / N ≧ 2 is 8, whereas In the ultrasonic flaw detection method, it can be seen that the number of detected errors when S / N ≧ 2 is zero. This is because the foreign body and bubbles adhering to the surface of the steel bar are removed by the elastic body when the elastic body 4 such as a brush or urethane is brought into contact with the steel bar.

  Therefore, in the ultrasonic inspection method for a steel bar according to the present invention, when the steel bar is ultrasonically flawed while rotating the steel bar around the axis in the ultrasonic conductive medium, a jet water stream is injected into the steel bar or degassed. Since there is no need to use an apparatus, it is possible to ultrasonically detect defects existing inside the steel bar with high accuracy and low cost without being greatly affected by foreign matter or bubbles adhering to the surface of the steel bar.

  Next, the present inventors produced test pieces 8 having surface roughness of 0.3 μmRa, 0.5 μmRa, 0.7 μmRa, 1.5 μmRa, 2 μmRa, 8 μmRa, and 10 μmRa. Then, using a focus type probe having a frequency of 15 MHz and a transducer diameter of 12 mm, ultrasonic testing is performed with an amplifier strength at which the echo intensity of the drill hole 9 of the test piece 8 is 80% by the steel bar ultrasonic testing method according to the present invention. did. The flaw detection results are shown in FIG. In addition, the flaw detection range was 5 to 15 mm below the surface, diameter 60 mm, and length 1000 mm.

  From the flaw detection test results shown in FIG. 4, it can be seen that when the surface roughness of the test piece 8 is greater than 2 μmRa, the number of detected errors with S / N ≧ 2 increases rapidly. When the surface roughness of the test piece 8 exceeds 2 μmRa, as shown in FIG. 5, the foreign matter 6 and the bubbles 7 attached to the surface of the test piece 8 enter the valley of the roughness, and the foreign matter 6 and the bubbles 7 are removed. This is because the elastic body 4 cannot be removed from the surface of the test piece 8.

  Therefore, when the steel bar 1 is subjected to ultrasonic flaw detection in the steel bar ultrasonic testing method according to the present invention, the average surface roughness of the steel bar 1 is preferably 2 μmRa or less, but the average surface roughness of the steel bar 1 is 0. In order to finish to less than 3 μmRa, it takes a long time of grinding, which causes a significant increase in grinding cost. Therefore, it is desirable that the average surface roughness of the steel bar 1 is in the range of 0.3 to 2 μmRa. .

It is a figure for demonstrating the ultrasonic flaw detection method of the steel bar which concerns on the 1st Embodiment of this invention. It is a perspective view which shows the test piece produced by this inventor. It is a figure which shows a flaw detection result when the test piece shown in FIG. 2 is ultrasonically flawed by the ultrasonic flaw detection method of the steel bar which concerns on this invention, and the conventional method. It is a figure which shows the relationship between the surface roughness of a test piece when the test piece is subjected to ultrasonic flaw detection by the ultrasonic flaw detection method for steel bars according to the present invention, and the number of detected errors of S / N ≧ 2. It is a figure for demonstrating the reason which the surface roughness of a steel bar shall be 2 micrometers Ra or less by the ultrasonic flaw detection method of the steel bar concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel bar 2 Storage tank 3 Ultrasonic transmission medium 4 Elastic body 5 Probe for ultrasonic flaw detection 6 Foreign object 7 Bubble 8 Test piece 9 Drill hole

Claims (2)

  An ultrasonic flaw detection method for a bar steel, comprising performing ultrasonic flaw detection while bringing an elastic body into contact with the steel bar when the steel bar is subjected to ultrasonic flaw detection while rotating the steel bar around an axis in an ultrasonic conductive medium.   2. The method for ultrasonic testing of steel bars according to claim 1, wherein the average surface roughness of the steel bars is in the range of 0.3 to 2.0 [mu] mRa.

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