JP3008105B2 - Ultrasonic inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an ultrasonic device for nondestructively testing materials, and more particularly to an ultrasonic device for nondestructively testing large cast cylinders.

[0002]

BACKGROUND OF THE INVENTION In the manufacture of tissue paper and paper towels, a web of paper fibers is formed and pressed into a Yankee dryer. Once dry, the web is scraped off the surface of the Yankee dryer to give the web a crepe texture that gives the paper its soft absorbency. Yankee dryers are usually large, usually 12 to 25 feet in diameter, since only a single dryer is used. In addition, the Yankee dryer is heated by steam at pressures up to 160 psig. Yankee dryers are 400 inches long and can weigh over 100 tons. Due to its large size and high operating pressure, Yankee dryers typically have a cylindrical wall thickness greater than 2 inches. Yankee dryers are generally formed from cast iron, a material with good separation properties if the surface is polished correctly. Therefore, the surface of the Yankee dryer must be re-polished periodically to maintain the correct surface finish.

[0003] A Yankee dryer is a pressure vessel and must take the safety precautions normally employed in all pressure vessels or boilers. U.S. Pat. No. 4,398,421 discloses an apparatus for measuring the thickness of a workpiece, which is useful for measuring the wall thickness of a steam boiler. While it is useful to determine the wall thickness of a Yankee dryer, it is also desirable to detect small voids in the wall thickness of the dryer.

[0004] Existing ultrasonic inspection systems have a limited ability to detect or find small voids near the surface of a cast iron part. Ultrasonic signals in cast iron are scattered and reflected from grain boundaries present in cast iron. This property of cast iron
It makes it very difficult to detect small discontinuities. Even measuring thickness in cast iron can be difficult. One national study has been to measure the thickness of cast iron using certain conventional techniques.
They have found errors in excess of 40%. Ultrasonic transducers typically have a maximum interface area of 1/2 inch, where surface discontinuities cannot be detected.

[0005] The X-ray method is used to inspect the rolls of a Yankee dryer. However, X-ray methods require the use of cumbersome and dangerous radioactive sources. In practice, X-ray images are produced only from a limited part of the Yankee dryer. Furthermore, X-ray images are not effective in detecting cracks as thin as hair. This is because such cracks hardly reduce the density of the material. However, cracks as thin as hair are usually detectable by ultrasound.

[0006] August 1, 1996, described here for reference.
U.S. application Ser. No. 08 / 690,763, filed on Jan. 15, discloses an ultrasonic inspection method capable of detecting a Yankee dryer flaw with a high signal to noise ratio.

The application states that if an ultrasonic signal is directed at a specific angle to the surface to be examined, about 10 percent of the signal will appear as a Harris wave propagating in a test plate at 90 degrees to the surface. Is shown. The vertically propagated signal is
Polarization results in the signal detecting flaws with a greatly improved signal-to-noise ratio. The particular angle is between the angle at which the ultrasonic signal is refracted to propagate parallel to the surface of the metal plate and the angle at which the ultrasonic signal is reflected by the test plate. Using shear waves, for water incident media and cast iron refractive media, that particular angle is about 33 degrees from normal. For steel, the specific angle is about 31 degrees. For brass, the angle is about 50 degrees.

While detecting a flaw, this particular angle produces a signal with no apparent time of flight, which means that the depth of the flaw cannot be determined in the disclosed manner.
How to find the depth of the wound using ultrasonic energy
Calibration can be difficult. Normal calibration methods require drilling a flat-bottom hole from the surface opposite the surface from which the ultrasound is to be performed. Flat bottom holes are difficult to drill and difficult to precisely align parallel to the inspection surface.

[0009]

What is needed is a method for performing a thorough inspection of a Yankee dryer that can determine the depth of a flaw detected for a material defect.

[0010]

SUMMARY OF THE INVENTION The ultrasonic inspection method and apparatus of the present invention are based on a calibration method and empirically observed inspection angles. The large dryer shell is made from cast iron due to its cost and good web separation properties. The cylindrical shell is typically cast with the axis of the dryer oriented vertically. Located on the bottom of the casting, a part of a cylindrical surface called a "dirt ring" is formed with a cylindrical shell, which part is used to make the casting shell into a dryer. Separated from

The cast cylinder, along with the attached "dirt ring", is made into a finished cylinder by attaching the cylinder to an internal support and placing it on a lathe so that the surface of the roll can be machined. The surface of the casting is finished to a smooth cylindrical surface with adjacent "dirt rings".

A calibration hole is drilled into the "dart ring" from the end of the cylindrical shell. Drill a calibration hole parallel to the surface of the cylindrical shell. A number of holes are drilled to form an array of holes spaced around the circumference at various depths from the cylindrical surface. Machining arrays of holes of various diameters. Calibration holes are relatively inexpensive and relatively easy to machine because the bottom of the hole does not need to be flat.

[0013] The cutting tool traversing the casting surface is replaced by an ultrasonic transducer mounted on a fixture that provides a coupling medium between the transducer and the casting surface. The mounting offers the possibility of adjusting the spacing between the transducer and the surface. A fixture is also provided to change the angle of the transducer with respect to the surface.
By rotating the casting through the fixture and the transducer mounted on it, the ultrasonic transducer is traversed over a "dirt ring" with a calibration hole. The transducer generates high frequency acoustic pulses traveling from the outwardly facing cylindrical surface into the casting. The transducer receives signals reflecting from the thickness of the cylinder or discontinuities in the acoustic path within the cylinder as the ultrasonic energy penetrates the casting. A computer or other signal processing device calculates the time required for the signal to travel from the transducer and return to the transducer. From this calculation,
Determine the depth to which the signal returns. Alternatively, the return signals are categorized into different depth ranges depending on whether the return signals fall within a particular time gate.

A clear signal corresponding to a calibration hole having a depth that varies from directly in contact with the surface to over an inch can be found by adjusting the angle at which ultrasonic energy is transmitted to the cylindrical surface. I know from experience. This angle tends to be slightly smaller than the angle best disclosed in US application Ser. No. 08 / 690,763 filed Aug. 1, 1996. This angle can be easily determined by trial and error and appears to be about 23 degrees from normal to the casting surface for cast iron.

By traversing a "dirt ring" having holes of known size and depth, the sensor is adjusted to maximum sensitivity and the data received from the sensor is correlated with known discontinuities in the casting. By doing so, the sensor can be calibrated. The transducer then traverses over the entire surface of the casting and stores the data for analysis and for future use in the maintenance and repair of dryer rolls formed from the casting.

After the inspection is completed, the "dirt ring"
Is removed from the rest of the casting and a final machining operation is applied to the surface of the casting.

It is a feature of the present invention to provide a method for inspecting the outer shell of a cast dryer that can reliably detect discontinuities and locations therein.

Yet another feature of the present invention is to provide an ultrasonic transducer fixture in which the transducer can be adjustably mounted to the surface of the dryer.

Another feature of the present invention is to provide a data record that can be fed to a Yankee dryer to aid in maintenance and repair of the dryer.

Further objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0021]

DETAILED DESCRIPTION OF THE INVENTION Referring more particularly to FIGS. 1-3, where like numbers refer to like parts, a Yankee dryer casting 20 is shown attached to a machining station 22. FIG. ing. Yankee dryers are used to dry tissue paper webs. The wet tissue web is pressed against the surface of a steam dryer roll, typically 12 to 25 feet in diameter. Hot air is blown onto the surface of the web as the web is brought into close contact with the dryer surface and the web is carried by the Yankee dryer. As the web dries, the doctor scrapes the tissue web off the surface of the Yankee dryer, removing the web and simultaneously applying crepe to the web. This improves its absorbency and gives the web a soft surface texture.

Surface separation characteristics are critical to the proper functioning of a Yankee dryer. Cast iron, preferably class 60 cast iron, is used to achieve the required surface properties. Yankee dryers are typically internally heated by steam. Therefore, when the dryer is in use, usually about 16
A pressure vessel pressurized to 0 psig. The size of the castings and the required high uniformity make the equipment very expensive.

During the life of the Yankee dryer, at regular intervals throughout the surface, the surface must be polished as it wears. Polishing the surface can expose hidden defects on the dryer surface, which must be repaired. Since the Yankee dryer is a pressure vessel, the presence of flaws on the outer shell of the dryer is always a concern.

Inspection of the material making up the cylindrical wall of the Yankee dryer is to preserve the overall integrity of the pressure vessel and to determine when the surface of the dryer rolls will wear as the surface of the dryer roll is worn with use. It is highly desirable for both to provide the ability to predict

Conventional ultrasonic techniques are not very effective with cast iron due to the large number of grain boundaries inside the material. Normal,
The dryer is inspected by bouncing the ultrasonic energy from the inner surface of the dryer shell and monitoring the ultrasonic signal for attenuation twice as it passes through the shell thickness. This gives only limited information about the presence of material defects. ASTM standards have been developed for this type of measurement.

The method of the present invention uses the ultrasonic transducer shown in FIG.
24 is adopted, and this is attached to the fixture 26. The fixture 26 is adjustable to position the U-shaped hole 28 against the surface 30 of the casting 20. The fixture 26 is mounted on a lead screw 32 and is movable in a direction parallel to the surface 30 of the Yankee dryer shell 36 and in a direction parallel to the axis 34 of the cylindrical casting 20 of the dryer.

The casting 20 comprises a cylindrical outer shell 36 forming the outer shell of the Yankee dryer, and a portion 38 of the casting 20 called "dirt ring". "Dirt ring"
38 has a surface 40 formed of a Yankee cylindrical shell 36 and coextensive with a surface 42 of the Yankee cylindrical shell 36. The "dirt ring" also has a thickness comparable to the thickness of the Yankee shell 36. `` Dart ring '' 38
Is processed from the Yankee shell 36 to form a finished dryer.

The "dirt ring" 38 does not form part of the finished dryer and can be used to calibrate the test procedure. Previously, a calibration hole was drilled from the back side 44 of the dirt ring. These holes required a flat bottom that was tangent to the surface from which the ultrasonic test was to be performed. Machining flat-bottom holes is a difficult and expensive procedure. Holes that exhibit a curvature when viewed from the outer cylindrical surface are considered impractical methods because they cause extensive scattering of the ultrasound beam.

The improved inspection process of the present invention is drilled from the edge 48 of the "dirt ring" 38 parallel to the axis 34 of the dryer and located a known distance below the surface 40 of the "dirt ring". The hole 46 is used. The hole 46 has a curved surface expected to scatter the ultrasonic signal. However, it has been found that correctly positioning the transducer with respect to surface 40 produces a clearly identifiable signal that can be correlated with hole 46. The holes 46 are machined as a group of holes with uniform spacing between the holes. A typical hole size corresponding to the smallest wound size is one millimeter in diameter. Other holes having diameters of 3, 5, and 10 millimeters are also machined into "dirt rings" 38.

The transducer 24 is located in a tank 52 having a U-shaped hole 28 engaged with a "dirt ring" surface 40. The fitting is U-shaped on the tank 52 equipped with the converter 24.
A mounting bracket 50 is provided for positioning the aperture 28 relative to the "dirt ring" surface 40. A compressible gasket 54 surrounds the U-shaped hole 28 and seals the hole against the surface of the casting 20. Tank 52 is filled with water or oil, preferably an organic oil such as castor oil. The entire casting 20, including the "dirt ring" 38, is rotated with respect to the machine frame 23. When rotated, hole 46 passes through the front of U-shaped hole 28. The transducer 24 is energized and sends periodic pulses of ultrasonic energy toward the surface 40 of the "dirt ring" 38.

By trial and error, transducer 24 is adjusted until a strong signal is detected from hole 46 as hole 46 passes under transducer 24. The fixture 26 connects the converter 24 to the shaft 34 of the casting 20.
It is designed to rotate around an axis 56 parallel to.
Rotation about axis 56 adjusts the angle of incidence between the ultrasonic beam and a line perpendicular to surface 30 of casting 20. Transducer 24 is slidably mounted on a block 58 that moves transducer 24 back and forth with respect to surface 30 of casting 20. The transducer 24 is thus adjustably mounted above the surface 40 of the "dirt ring" 38.

In connection with the tank 52 filled with water,
At a 23-28 degree angle, with the transducer approximately 2 inches to 21/4 inches away from the surface 40, a clear signal returning from the test hole having a time of flight related to the depth of the test hole. Have been found. By monitoring the signal received as the calibration hole 46 moves under the transducer 24,
The optimal spacing and angle for detecting the holes 46 are easily determined. Calibration hole under surface 40 of "dirt ring" 38
Since the position of 46 is known, the depth of hole 46 can be correlated with the time of flight of the ultrasonic signal.

The correlation between the depth of the flaw and the time of flight of the signal can be made by controlling the return signal with a time gate. Time gating of the signal divides the return signal into various parts having a time of flight between two predetermined times. Typically, a single time gate can be used to simplify the returned data. Dart ring 38 and calibration hole 46
Is scanned below the surface 40 with a single time gate corresponding to the first 1/10 inch of the thickness of the casting 20. Other useful time gates can be correlated with the band of material making up a layer of casting 2/10 to 5/10 inches thick, but it is even possible to use up to the full thickness of the casting. Dryer rolls, especially those of Yankee dryers, can be as thick as 4 inches, and this technique can be used to correct the thickness of the dryer by properly using a time gate that is correlated with the calibration holes. Can be used to detect

Computer 60 or other signal processing device calculates the time it takes for the signal to travel from transducer 24 and back to transducer 24. The return signal may also be correlated with its flight time on a point-by-point basis within the speed and data rate capabilities of computer 60 and data storage system 62. In this way, the data records are uniquely correlated with the position of the cylindrical surface, each individual record examines the cast cylindrical shell from the surface with ultrasonic energy, and each position of the cylindrical surface. A number of individual records can be assembled, including at least one value corresponding to the recorded value obtained by recording the time-of-flight related value of the signal reflected at the surface.

Once the ultrasonic transducer 24 has been calibrated, the fixture 26 with the transducer 24 is scanned over the surface 42 of the casting 20. High scan speeds, such as between 6 inches and 24 inches per second, have been found to be practical. The collected data can be stored in data storage system 62 and then viewed on monitor 64. The monitor 64 can display a map of the casting 20 in a separate layer corresponding to the depth at which the flaw was detected. The monitor display 66 shown in FIG. 1 shows a number of calibration holes at various depths below the surface 40 of the "dirt ring" 38.

For a casting having a spiral pattern 68 with a diameter of 25 feet separated by a 1/8 inch subsequent scan, the scanning process takes about one to four hours per foot of casting length.

As shown in FIG. 1, the mounting fixture 26 includes a feed screw
Installed on 32. The fixture 26 can be attached by a combined tool stand (not shown). Tank 52 is tank 52
Bracket 50 by pivot mount 70 installed underneath
Mounted on This allows the gasket 54 to be tilted forward toward the casting surface 30. Swivel extension mechanism 72
Connects the back side 74 of the tank 52 to the upright flange 76.
The screw rod 78 passes through the flange 76, and the nut 80 on the opposite side
78 is locked in place, thus locking the tilt angle of the tank 52.

The converter 24 has a block 58 inside the tank 52.
Is slidably mounted. Block 58 is the axis
Tightly mounted on a threaded rod 82 that rotates around 56.
A scale plate 84 having an indicator 86 is attached to the rod 82.
The surface 30 of the casting is rotated by the rotation of the scale 84 and the connected rod.
The position of the converter 24 with respect to the vertical line is controlled. tank
A scale 88 mounted on side 90 of 52 allows the angle of transducer 24 to be determined. A lock nut (not shown) on the threaded portion (not shown) of the shaft opposite scale plate 84 can be used to lock the shaft in place.

The transducer 24 includes at least a straight movement in a direction away from the casting surface and a rotation including changing the angle of the direction in which the ultrasonic transducer 24 faces relative to a normal to the casting surface. It should be understood that any suitable mechanism having two degrees of freedom can be mounted. The rotation of the transducer is preferably about an axis parallel to axis 34 of casting 20.

A dual ultrasonic transducer can be used, and one of the ultrasonic signals is used to record the backside reflectance required by the ASTM test standard to provide attenuation data for the entire thickness. It should be understood that they can be collected. Therefore, the data of flaw detection and depth is
Together with the data needed to meet the requirements of

A wide range of ultrasonic energies has been used for ultrasonic testing on solid materials, and in particular, ultrasonic frequencies of 1 to 10 MHz have been found to be effective.

It should be understood that the data collected in data storage system 62 can typically be 20 megabytes or more and can accommodate a finished dryer composed of casting 20. The data can be provided on a high-density storage medium such as a DVD (Digital Versatile Disk) or made available to purchasers over the Internet or a similar data network. This data can also be supplied as part of a service contract in conjunction with data made available with other services to maintain and repair the dryer over its useful life.

After the casting 20 is inspected, the dryer is completed by removing another 1/20 inch of material from the surface, removing the dirt ring, and providing the ends and heads with the necessary internal tubing.

It is to be understood that this invention is not limited to the particular arrangements and arrangements of components illustrated and described herein, but such modifications thereof are intended to fall within the scope of the appended claims. Is done.

[Brief description of the drawings]

FIG. 1 is an isometric view of a dryer roll casting being inspected using ultrasonic energy.

FIG. 2 is an isometric view of a portion of the dryer roll casting of FIG. 1, showing a calibration hole machined parallel to the surface of the dryer.

FIG. 3 is a partially cutaway isometric view of a fixture for adjustably installing and coupling an ultrasonic transducer to the surface of the dryer roll of FIG. 1;

[Explanation of symbols]

 20 Yankee dryer casting 22 Machining station 24 Ultrasonic transducer 26 Fixture 28 U-shaped hole 30 Cast surface 32 Feed screw 34 Shaft 36 Yankee dryer shell 38 Dart ring 42 Shell surface 46 Calibration hole 50 Mounting bracket 52 Tank 54 Gasket 56 Axis 58 Block 60 Computer 62 Data storage system 64 Monitor 66 Monitor display 82 Screw bar 84 Scale plate 86 Pointer 88 Scale

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Dennis A. White United States, Illinois 61080, South Beloit, South Eighths Street, 114 5681996 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (6)

(57) [Claims] 1. Defects and discontinuities in the outer shell of a dryer roll
A method of ultrasonically inspecting a cast outer shell of a dryer roll to detect and determine its depth ; mounting the cast outer shell of a dryer having a surface for rotation about an axis of symmetry. step: a step of punching parallel to at least one hole for calibration on the surface of the dryer roll shell, at least one of which
Holes are provided at the end of the dryer roll shell.
In the dirt ring, the dirt ring is dry
Drying while extending as a continuation of the outer shell of the mill
Has the same thickness as the mill roll shell; after the calibration is completed, remove the additional dart ring
Steps above the hole for the calibration, adjacent to the surface of the roll shell mounting an ultrasound transducer, providing an ultrasonic coupling medium between the transducer and the roll shell surface; step of Generating a high-frequency sound pulse from the ultrasonic transducer ;
A step for directing a pulse at a certain angle to the roll shell
Flop; perpendicular to the plane in contact with the surface of the roll shell; rotated to step the roll shell about the axis so that the surface is above the hole for the calibration passes under the transducer the ultrasound transducer across the surface of the roll shell; the distance of the transducer from the transducer angle and the roll shell surface about a line, the step of adjusting the reflection signal is detected from the hole for the calibration wherein is installed as determined in the calibration step of vessels step scanning with an ultrasonic transducer; and the thickness of the roll shell also
Is reflected from discontinuities and defects in the path of sound waves
Receiving a signal into the ultrasonic transducer.
And, thereby, defects or discontinuities in said roll outer inner shell
Dryer characterized by knowing the depth and range of depth
Method of ultrasonic inspection of the shell of the shell . 2. A method size and depth different plurality of holes parallel to opened to the surface of the roll shell, can be simulated wounds of various sizes and depths to detect a defect the The method according to claim 1, wherein the ultrasonic transducer can be calibrated. Wherein the step of receiving said signal, the B
Performed by a transducer with a sensor mounted in a tank of coupling fluid sealed against the surface of the shell
Is the transducer is moved within the tank with the sensor
The method according to claim 1, characterized in that adjustable angle and distance between the transducer and the dryer shell surface is. Wherein said sensor is around the roll outer freedom directions of translational movement away from the direction and the surface towards the surface of the shell, and parallel to the axis of symmetry of the cast dryer roll shell axis 4. The method of claim 3 , wherein the method is mounted to provide at least two degrees of freedom, including rotational degrees of freedom. 5. The signal received from the transducer is such that the return signal is of a specific depth or sound below the surface of the dryer roll .
The method of claim 1, wherein the method is time gated to fall within a time frame corresponding to the passage area. 6. An apparatus for use in drying a paper web, having a cylindrical surface on which to dry the paper, and having a thickness of at least 1 inch radially inward from the cylindrical surface. Dryer rolls comprising a cast cylindrical shell having: and each uniquely correlating a position on said cylindrical surface; and
Each examined with ultrasonic energy to the cast cylindrical shell from the surface, recorded values obtained by recording the values related to the time of flight of the reflected signal to the surface at each position on the cylindrical surface at least one data comprising a plurality of records containing the value record corresponding to; have, each recording, ultra sound which is reflected at each position on the cylindrical surface
At least two recorded values corresponding to the wave energy records
Have at least two recorded values at different times
Is a record of the reflected ultrasonic energy recorded from the
Thus giving a value relating to the time of flight; the data records are each recorded at a location on the cylindrical surface.
In addition to a plurality of records that uniquely correlate with the home position, the cylinder
Obtained from a second cylindrical surface cast integrally with the cylindrical surface
A second record containing the calibration data, wherein the calibration data
Inspecting the second cylindrical surface portion with ultrasonic energy;
The hole for calibration is
Various depths from the second surface, parallel to the second cylindrical surface
The device is provided at a distance from one another .