US3666370A - Strip flatness inspection method - Google Patents

Strip flatness inspection method Download PDF

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US3666370A
US3666370A US3666370DA US3666370A US 3666370 A US3666370 A US 3666370A US 3666370D A US3666370D A US 3666370DA US 3666370 A US3666370 A US 3666370A
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strip
light
source
angle
line
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Elwood F Seasholtz
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Bethlehem Steel Corp
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Bethlehem Steel Corp
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/84Systems specially adapted for particular applications
    • G01N21/88Investigating the presence of flaws or contamination
    • G01N21/8803Visual inspection

Abstract

A METHOD OF VISUALLY INSPECTING PORTIONS OF MOVING STEEL SHEET OR STRIP IN A CONTINUOUS PROCESSING LINE, WHEREIN THE STRIP IS SUPPORTED IN A SUBSTANTIALLY HORIZONTAL POSITION, THE ANGLE OF ELEVATION AT WHICH THE STRIP IS SUPPORTED IS ADJUSTED WITHIN A RANGE FROM ABOUT HORIZONTAL TO 25* BELOW HORIZONTAL, A DIFFUSED LIGHT SOURCE OF SPECIFIED WIDTH IS POSITIONED ON THE SIDE OF THE STRIP OPPOSITE AN OBSERVER, AND THE LIGHT FROM SAID SOURCE IS DIRECTED DIAGONALLY ACROSS THE STRIP AND IS CAUSED TO IMPINGE DIRECTLY THEREON AT A LOW ANGLE. THE STRIP IS THEN VIEWED ALONG ITS ROLLING DIRECTION AT A SPECIFIED LOW ANGLE ABOVE THE PLANE OF THE STRIP. A SECOND DIFFUSED LIGHT SOURCE PERMITS A VERTICAL STRAND OF STRIP ADJACENT A FREE LOOP OF THE STRIP TO BE VIEWED ACROSS THE STRIP AT RIGHT ANGLES TO THE ROLLING DIRECTION FOR A FURTHER INSPECTION OF THE STRIP.

Description

E. F. SEASHOLTZ Filed July l5I 1970 www m mmw STRIP FLATNESS INSPECTION METHOD Il ON May 30, 1972 INVENTOR f/u/ooal E Jeas/m/z United States Patent O U.S. Cl. 356-200 3 Claims ABSTRACT OF THE DISCLOSURE A method of visually inspecting portions of moving steel sheet or strip in a continuous processing line, wherein the strip is supported in a substantially horizontal position, the angle of elevation at which the strip is supported is adjusted within a range from about horizontal to 25 below horizontal, a diffused light source of specified Width is positioned on the side of the strip opposite an observer, and the light from said source is directed diagonally across the strip and is caused to impinge directly thereon at a low angle. The strip is then viewed along its rolling direction at a specified low angle above the plane of the strip. A second diffused light source permits a vertical strand of strip adjacent a free loop of the strip to be viewed across the strip at right angles to the rolling direction for a further inspection of the strip.

BACKGROUND OF THE INVENTION The iield of art to which my invention relates is that of a method and arrangement for visually observing moving steel sheet and strip whereby an inspector can determine quickly and surely the existence and location of any undesirable deficiencies in shape or atness.

Steel sheet or strip serving as the base metal for continuous galvanizing or tinning is made by cold reduction between highly polished rolls, and theoretically the finished product when supported on a liat table should reflect bright light exactly like a perfectly dat mirror to the point of observation. The act of observation may, of course, be performed either by a human eye or the viewing lens of some optical device such as an ordinary camera or a television camera. The commonest source of light has comprised very intense illumination, as by an incandescent filament in a plain bulb directly above the strip.

The reiiected light from a prime surface will thus be concentrated quite closely, but when localized defects are present, they tend to spread or diffuse the light more or less Widely. Also, as noted in Burns 3,176,306, col. 2, lines 5-32, if the eye or viewing lens is located in the direct path of specular (mirror-like) observation, the defects will show as dark areas, but if the observer is located ot the path of specular observation, defects will appear as bright areas against a dark background.

Many such defects are the results of conditions which occurred during rolling. Shape defects are caused by length differences in the rolling direction at various areas across the Width. Thus, what are termed buckles occur in an area which has been elongated (or reduced) more than adjacent areas. Quarter buckles occur at locations about midway between the center and the edge of the strip. Edge buckles and center buckles occur ice near the edges or the center, while ruflies or wavy edges occur on the actual edges.

Shape defects which involve the bowing of the strip are termed in-line bow or cross-bow, according to the direction of bow.

I have found that low angles of lighting and observation longitudinally of the strip in the direction of rolling give the observer the best dened perception of buckles and ruflies, while in-low bow or cross-bow are bettter perceived by cross-viewing toward a light source across the strip.

SUMMARY OF THE INVENTION The growing importance of proper panel atness on continuously galvanized sheet or strip (or broadly similar tin mill products) has greatly increased the utilization of known types of shape correction machines, but it is obviously both unnecessary and expensive to subject the large proportion of satisfactory material to additional treatment on such machines.

Nevertheless, all dependable methods of inspection for shape determination of strip still depend essentially on visual observation, either by the unaided human eye or through standard optical instruments.

It is the object of my invention to establish a method which prescribes, as a result of extensive experimentation, exactly what sighting conditions, steps and devices are necessary for obtaining perfectly consistent and trustworthy visual shape observations.

DESCRIPTION OF THE DRAWINGS In the annexed sheet of drawings:

FIG. l is a side elevational view of the type of apparatus which is preferred to be utilized for the purpose of practicing the method of strip inspection which constitutes my invention; and

FIG. 2 is a top plan view of said apparatus.

DESCRIPTION OF THE INVENTION Referring now in more detail to the drawings, what is shown is essentially only the surface inspection portion of an otherwise largely conventional continuous strip galvanizing line. This inspection portion will be understood as being located generally in the line of the longitudinally moving galvanized strip between a roller leveller and final chemical cleaning and drying equipment for the strip, which items are Well known in the art and therefore are not shown.

In such a continuous strip galvanizing line, and following a roller leveller (not shown), the mill floor 1 is provided with a iirst depression or recess 2, a moderately deep looping pit 3, an upright support 4, and a second recess 5.

Mounted at the first lioor recess 2 is a first upright rectangular structural steel frame 6 upon which is mounted a first bridle roll unit 7 and a curved depending strip guide 8 having spaced idle rollers 9 thereon.

Upon the support 4 is mounted conventional raising and lowering means 10, such as a fluid pressure actuated jack located substantially longitudinally centrally beneath a at inspection table 11 fabricated of structural steel members 12 and having idle rollers 13 in a curved entry guide portion. 14 and an idle exit roller 15.

The forward end of said inspection table is supported on a bracket 16 which is pivotallymountedas at 17 on a' second upright rectangul-ar steel frame 18 at the second floor recess 5. On said frame 18 are also mounted side guide means (not 4shown) and a second bridle roll unit 20.

From the roller leveller mentioned above, the galvanized strip 21 travels through the first bridle roll unit 7 and over the guide S, from whence the slack portion of the strip descends in a Vertical strand 22 and then rises to form a long loop or catenary portion 23 of the strip. The further portion 24 of the strip then traverses the guide 14 and over the table 11 and roller 15 past the side guide means (not shown) and the second bridle roll unit 20 which advances the strip in synchronism with the first bridle roll unit 7.

It would theoretically be possible for the eye of an observer and a suitable light source to be aligned along the longitudinal center of the strip in the rolling direction, but this condition is not attainable with a continuous processing line. Therefore, the observer 25 and the control console 26 for the roller leveller (not shown) are located on one side of the strip, adjacent the vertical strand 22, and two differing light sources 2,7 and 28 are positioned basically on the other side of the strip.

The first light source 27 is a wide horizontal panel type light in a rectangular open box 29 about l0 feet wide and 1 foot high mounted above thev second bridle roll unit 20 and enclosed one or more electrically activated conventional fluorescent tubes (not shown); Said box 29 is provided with a plurality of removable shutters (also not shown) for adjusting the height and/or thickness of a light slit, which by means of a white translucent cover 30 is transmitted in the form of a diffused light impinging on the strip 24 on the table 11 and reflected to the observer 25.

The eye of said observer 25 may be taken as being about feet above the general oor line 1, and so at about the same level on the opposite side of the vertical strand 2v2 of the strip is centered the second light source 28, which can be a vertically disposed but generally similar type of diffused light about 2 feet wide and 4 feet high which may optionally be provided with a plurality of diagonal block stripes 35 thereacross.

The inspection table 11 needs only to be wide enough to support flat and with some marginal room a straight section of strip of the predetermined width, typically about 36 to 54 inches, and also of adequate length to support a sufficient number of cycles of the waviness pattern to provide a good shape observation of the strip. If the inspection table were to be used alone to support a cut section of strip which was stationary, a table length sufiicient to support a section embracing four or tive cycles (4 to 6 feet) of the pattern would be adequate, provided that both the light source and the observer were in line with the center of the strip along the rolling direction. In a continuous production line, however, as noted above, it is not feasible to locate the light source 27 and observer 25 over the center of the strip, and therefore a slight diagonal line of sight 31 as shown in dotted line in FIG.

2 of the drawings must be used. For such diagonal sightthe angle of inclination of the table 11 and the section of l strip thereon may be adjustable from about 0 to 25 with the horizontal.

Assuming the observers eye to be 5 feet `above the floor, as noted above, his first line of sight 31 should be 'and directed toward thev Ycenter of said' table'at an Vangle of 10 to 160 from the strip rolling direction. The preferred angle of inclination of the table is the lower or 25 tilt shown in FIG. 1 in solid lines, although the table may be raised to horizontal if the relative positions of the observer and of the light sources to the strip remain essentially unchanged.

For optimum observation of buckles and rufes in the strip, however, I have found it to be necessary for uniform lighting that the Width of the first light source 27 should be at least twice the width of the strip. The diffused light from said light source 27 must also impinge upon the strip at'a very small first lightv angle as at 32, i.e. about 2 to 6 with the plane of the strip, and the first observation angle 33 should be about 6 to 13 above the strip. Said light angle 32. should be less than about one-half the observation angle 33 in order to avoid the confusing effects either of specular reflection or excessive diffusion of the light.

The tension on the moving strip also should not exceed a maximum of `500 psi., as otherwise the flatness will appear deceptively better than it actually is. l' The arrangement shown in FIG. 1 has the further advantage that the observerrZS without changing his location at the control console 26 Vis able to scan on the second sight line 34 across the vertical strand 22 to the light source 28, which enables some undesired bow shape conditions such as Vcross-bow to be most clearly seen. This step pro-I vides additional assurance against strip defects.

In order to observe conditions of cross-bow in this manner, however, I have discovered that the vertical strand 22 in the free loop of strip shown in FIG. 1 must have a length which is at least two or three times the strip width. If sufficient vertical length is not available, the crossbow condition will not be evident because of the constraints imposed by the guide rollers 9 and the catenary portion 23 of the loop.

While the diagonal black stripes 35 across the surface of the light source 28 as shown in FIG. 1 are helpful in observing the cross-bow condition, they are not absolutely necessary, and may therefore be omitted if such omission is desired.

I claim: Y

1. Amethod of visually inspecting moving metal strip or the like for detecting buckles and the like atness defects, comprising the following steps: v

(a) supporting a section of said strip in a substantially horizontal position;

(b) adjusting the angle of inclination at which saidstrip is supported Within a range from about horizontal to 25 below horizontal;

(c) positioning an elongated source of unreected diffused light of a width at least twice the strip Width on the side of the strip opposite an observer;

l(d) directing the diffused light from said light source diagnoally across the strip and causing said diffused light to impinge on the strip at a low angle above the plane of the strip; and

(e) viewing said impinged light by Vreiiection'froni the strip along its rolling direction at anangle of about 6 to 13 degrees above the plane of the strip; the angle of light impingement on the strip being less than one half of said angle of viewing. i

2. A method as claimed in claim 1V for further inspecting asection of metal strip, comprising the following additional steps:

(a) providing a free loop of the strip;

(b) disposing a slack section of the strip of a length at least twice the strip width in a vertical strand adjacent to the free loop of the strip;

(c) stationing a second unreected diffused light source on the'opposite side of said verticalstrand of said @strip and directed toward said observer; andV 6 (d) viewing said second diffused light source across 2,548,551 4/ 1951 Morrison 356-200 said Vertical strand of strip at right angles to the roll- 2,099,012 11/ 1937 Goodrich et al 356--237 ing direction and thereby detecting bow-shaped de- 3,184,798 5/ 1965 Burnet et a1. 250-219 S UX fects in the strip. 3. A method as claimed in claim 2, in which the view- 5 FOREIGN PATENTS ing surface of the light source in subparagraphs (c) and 792,245 3/1958 Great Britain 356 209 ,(d) of that claim is provided with a plurality of spaced diagonal black stripes thereacross. RONALD L WIBERT, Primary Examiner References Cited 10 F. L. EVANS, Assistant Examiner UNITED STATES PATENTS Us. CL XR. 2,502,414 4/1950 Bradley 356-237 S56-210, 237

3,176,306 3/1965 Burns 356--200 TEE STATES PATENT OEETCE Pfl-1050 569 EETTTTEATE e EeEETTN Patent No. 3,666,370 Dated May 3o, 1972 Inventor(s) E. F, SeaShOlbZ It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column Uf, line 3, "160" should read -16 Column LL, claim l, subparagrapll` (d) line 2, "diagnoally" is misspelled. It should read diagonally.

Signed and sealed this 17th day of October 1972.

(SEAL) Attest:

EDWARD M.FI.ETCHIR,JR. ROBERT GOTTSCHALK Commssonel^ of`Patents s Attestng Officer

US3666370A 1970-07-15 1970-07-15 Strip flatness inspection method Expired - Lifetime US3666370A (en)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3992111A (en) * 1974-02-01 1976-11-16 Ciba-Geigy Ag Apparatus for detecting defect locations at the surface of a moving reflecting material
US4099884A (en) * 1975-07-25 1978-07-11 Paul Nash Optical inspection systems
WO1985003776A1 (en) * 1984-02-14 1985-08-29 Diffracto Ltd. Panel surface flaw inspection
US4920385A (en) * 1984-02-14 1990-04-24 Diffracto Ltd. Panel surface flaw inspection
US5168322A (en) * 1991-08-19 1992-12-01 Diffracto Ltd. Surface inspection using retro-reflective light field
US5206700A (en) * 1985-03-14 1993-04-27 Diffracto, Ltd. Methods and apparatus for retroreflective surface inspection and distortion measurement
US5225890A (en) * 1991-10-28 1993-07-06 Gencorp Inc. Surface inspection apparatus and method

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3992111A (en) * 1974-02-01 1976-11-16 Ciba-Geigy Ag Apparatus for detecting defect locations at the surface of a moving reflecting material
US4099884A (en) * 1975-07-25 1978-07-11 Paul Nash Optical inspection systems
WO1985003776A1 (en) * 1984-02-14 1985-08-29 Diffracto Ltd. Panel surface flaw inspection
US4629319A (en) * 1984-02-14 1986-12-16 Diffracto Ltd. Panel surface flaw inspection
US4920385A (en) * 1984-02-14 1990-04-24 Diffracto Ltd. Panel surface flaw inspection
US5206700A (en) * 1985-03-14 1993-04-27 Diffracto, Ltd. Methods and apparatus for retroreflective surface inspection and distortion measurement
US5168322A (en) * 1991-08-19 1992-12-01 Diffracto Ltd. Surface inspection using retro-reflective light field
US5225890A (en) * 1991-10-28 1993-07-06 Gencorp Inc. Surface inspection apparatus and method

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