US3827296A

US3827296A - Surface flaw detecting device for coated wire

Info

Publication number: US3827296A
Application number: US00280873A
Authority: US
Inventors: Y Hidaka
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-17
Filing date: 1972-08-15
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: JPS4828294A; JPS559655B2

Abstract

A device advantageously usable at the output end of a wire coating line to detect surface flaws in the coated wire and place thereon visual flaw-indicating marks. It includes a feeler and a marking roller both arranged along the path of wire travel and the latter is operable under control of an electric signal from the feeler action with an appropriate time lag.

Description

Minted States Eatent 1191 1111 3,827,296 Hidalta Aug. 6, 1974 SURFACE FLAW DETECTING DEVICE FOR 2,932,382 4/1960 James 340/259 x COATED WIRE 3,069,570 12/1962 Abodie ZOO/61.13 X 3,154,943 11/1964 Garrett et a1. 73/160 Inventor: Yoshihisa Hidaka, 26-14 Matsubara 3,263,499 8/1966 Gith a a1 73/160 3-chome, Setagaya-ken, Tokyo, Japan Primary Exammer--R1chard C. Quelsser Filed! g- 1972 Assistant ExaminerDanicl M. Yasich 21 Appl' NO: 2 0 73 Aim/Hey, Agent, or Firm-Oldham & Oldham CO.

[30] Foreign Application Priority Data [57 ABSTRACT Aug. 17, 1971 Japan 4662023 A device advantageously usable .at the output end of a [52] 11.8. C1. 73/160, 340/259 Wife Coating line to detect Surface flaws in the coated [51] Int. Cl. G011 5/00, B6511 25/00 wire and place thereon visual flaw-indicating marks- It [58] Field of Search 73/160; ZOO/61.13; 28/64; n l a feeler and a marking roller both arranged 340/259 along the path of wire travel and the latter is operable under control of an electric signal from the feeler ac [56] Referen e Cit d tion with an appropriate time lag.

UNITED STATES PATENTS 2,671,199 3/1954 Truit 73/160 X M Clams 9 Drawing Flgures ELECTRICAL SECTION PAIENTED M18 3, 8217, 296

sum

1 or 3 vm- 12 1 3 E 25' 5 J0 ELECTRICAL SECTION 15 SURFACE FLAW DETECTING DEVICE FOR COATED WIRE BACKGROUND OF THE INVENTION According to the usual practice followed in coating fine copper or other wires with synthetic resin material such as vinyl resin or Nylon, the wire to be coated, of a very large length, is caused continuously to proceed through a bath of melted synthetic resin and through a coating die, which is mounted on the bath tank at the rear end thereof to form a continuous and uniform coat of synthetic resin on the wire surface. The coated wire, leaving the die, is next led through a cooling tank and is finally wound on an appropriate reel as a finished product. Such product, however, must often be rejected upon inspection on account of different forms of surface flaw, such as protuberances due to inclusion of some foreign matter in the resin layer, local lack or separation of the film coating, and fine wavy surface irregularities depending upon the process conditions including the composition of synthetic resin material used, the temperature of the resin bath and the physical state of the die hole. Moreover, since the coating operation is ordinarily performed with a high travelling speed of wire of a few 10 or 100 meters per minute, it has been impossible to find out surface flaws such as mentioned above during the travel of the wire coated. In fact, it has been usual practice to inspect the whole length of coated wire with the naked eye after completion of the coating operation to visually identify surface flaws. This practice, however, is very troublesome and ineffi- ,cient, requiring much labor and high skill in operation.

SUMMARY OF THE INVENTION The present invention is intended to overcome such difficulties previously involved in inspection of coated wires and provides a highly efficient surface flaw detecting device which includes feeler elements arranged to scan the entire peripheral surface of a travelling coated wire lengthwise thereof and bendable with passage of any surface flaw to produce an electric signal and also includes a marking mechanism operable upon reception of the signal from the feeler elements to make a definite ink, paint or other identification mark on the wire surface at the very location of the flaw detected. The signal output of the feeler elements is properly amplified and formed into a waveform appropriate to operate a relay provided for marker operation. The identification marks thus made on the wire surface can obviously serve to facilitate visual identification and removal of the "flawed wire portions when the product wire is subsequently inspected for surface flaws.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawings, illustrating one preferred embodiment of the invention and its modification;

FIG. 1 is a schematic diagram of the process of manufacturing coated wire including a surface flaw detecting device of the present invention;

FIG. 2 is a side elevational view, partly in section, of the flaw detecting section of the device shown in FIG.

FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a perspective view showing one form of feeler element provided with electromagnetic induction type signal means;

FIG. 5 is a view similar to FIG. 4 showing another form of feeler element provided with capacitance type signal means;

FIG. 6 is a fragmentary front view of the feeler show ing the tip arrangement around the line of wire travel;

FIG. 7 is a side elevation of the marking section of the device provided to place marks on the travelling coated wire at each flaw location;

FIG. 8 is a block diagram showing the electrical connection of the device including an induction type flaw detecting section; and

FIG. 9 is a fragmentary diagram showing the electrical connection of the device including a capacitance type flaw detecting section.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will next be described in detail with reference to the accompanying drawings, which illustrate one preferred embodiment of the invention arranged at the output end of a conventional wire coating line.

Referring first to FIG. 1, the wire 1 to be coated is drawn into melting tank 2 holding a bath of synthetic resin with which the wire 1 is to be coated and leaves the bath tank 2 through a die 3 provided in the end wall thereof as a coated wire W carrying a coat of resin reduced to a definite thickness. The wire thus coated is subsequently cooled by passing through a cooling tank 4, arranged forwardly next to the bath tank 2, and further proceeds horizontally to a free rotating guide pulley 6 and, turning around the latter, proceeds upwardly to a tension control device. As shown, this device includes a bearing frame 7 to which is fixed a horizontal shaft 8 carrying two pulleys 9 and 9 freely rotatably mounted thereon and a floating pulley l0 suspended immediately under the bearing frame 7. The coated wire leaving the guide pulley 6 proceeds to and around one of the two fixed pulleys, e.g., pulley 9, and successively passing over the floating pulley 10 and the other fixed pulley 9', proceeds to a take-up reel 12 to form a coiled product thereon. Reference numeral 11 indicates an electric motor provided to drive the reel 12 and reference numeral 13 indicates a weight suspended from the shaft of floating pulley 10 to serve the purpose of applying a definite tension to the wire 1 or W throughout its travel. The arrangement and process described hereinbefore is conventional.

According to the present invention, however, there is arranged a surface flaw detecting device in the line of process and particularly along the horizontal path of coated wire W between the cooling tank 4 and guide pulley 6. The device is comprised of three sections including a flaw detecting section A, an electrical section B and a marking section C. The detecting and marking sections A and C are arranged in properly spaced relation to each other with their respective axes of reference placed in aligned relation with the line of wire travel and are both electrically connected with the electrical section B.

As shown in FIGS. 2 and 3, the detecting section A is mounted on a vertical base wall 5 arranged parallel to the line of wire travel on the back side thereof as viewed in FIGS. 1 and 2. The detecting section includes two sets of pulleys arranged in spaced relation to each other and each including three pulleys rotatably mounted on respective horizontal shafts fixed to the base wall 5. As shown, the three pulleys in each set are arranged in a triangular formation in a common vertical plane including the line of wire travel. Two of the three pulleys (15, 16) or (150, 160) defining the base of the triangle are each disposed just beneath the line of wire travel with its periphery kept in contact with the coated wire W. The

remaining pulley

17 or 170, forming the top apex of the triangle, is arranged so as to press the coated wire slightly downward thereby to lightly clamp the wire in cooperation with the lower pulleys (15, 16) or (150, 160). As will readily be understood, this arrangement serves to keep the coated wire W travelling between the two sets of pulleys free from any oscillation depite of the high travelling speed of the wire.

Fixed to the front face of the base wall between the two sets of pulleys is a feeler support wall 18 which extends at right angles to the line of wire travel and has a through opening, through the center of which the line of wire travel extends. A plurality, three in the shown example, of feeler elements D are fixed by a set screw 14 to the forward side of the support wall 18, i.e., the

wall side on which the travelling wire leaves the wall,

radially around the line of wire travel in a circle centered thereon and at equal angular intervals as shown in FIGS. 3 and 6, the feeler elements D are each comprised of a resilient metal or other strip 19 angularly bent at an obtuse angle of approximately 120 and an arm strip 20 fixed at one end to the angular intermediate portion of the resilient strip 19 as by riveting or welding. Fixed to the tip end of the resilient strip 19 are a pair of feeler projections 21 as shown in FIGS. 4 or 6, for example, in the form of small jewel stones or steel balls having smooth curved surfaces. As shown in FIG. 4, the rocker arm strip 20 has a permanent magnet 22 fixed to its free end. The feeler elements D are each fixed to the support wall 18 at the other end of the bent resilient strip 19 as indicated in FIG. 2 in a manner such that the base leg portion of the bent strip 19 extends substantially parallel to the line of wire travel with the tip leg portion thereof extending forwardly at an acute angle to the travelling coated wire. In this manner, the projections 21 of the feeler elements D are arranged around the periphery of the coated wire W, as clearly shown in FIG. 6, and kept in contact with the wire at light and uniform pressure. As shown in FIG. 2, the arm strips 20 of the feeler elements D are arranged radially in a plane substantially normal to the line of wire travel and the permanent magnets 22 fixed to the tips of these strips are disposed in a circle centered on the line of wire travel at equal angular intervals. With such arrangement, the feeler projections 21 can precisely scan the surface of the fast running coated wire W lengthwise thereof, causing the respective associated resilient strips 19 to bend at the fixed end thereof according to the irregularities on the wire surface. This causes similar rocking movement of the permanent magnets 22 fixed to the end of rocker arm strips 20. It is to be noted that any flawed wire portion having a substantial diameter can pass the feeler projections 21 smoothly at high speed owing to the acute angle at which the tip leg of each of the resilient strips 19 carrying feeler projection 21 extends to the coated wire W.

Referring again to FIG. 2, a plurality, three in the illustrated example, of bracket arms 24 are fixed to the support wall 18 radially at equal angular intervals in an arrangement corresponding to that of rocker arm strips 20 of feeler elements D. Fixed to each of the bracket arms 24 is a detecting coil 25 which together with the permanent magnet 22 carried on the adjacent rocker arm strip 20 forms an electromagnetic induction type detector unit.

The marking section C is arranged on a vertical base wall 27 disposed on the back side of the line of wire travel in spaced parallel relation thereto, as shown in FIG. 7, and includes a backing or support roller 28 rotatably mounted on the base wall 27 and along the periphery of which the coated wire W proceeds. Also, a bell crank lever 31 is pivotally mounted on the base wall 27 by way of a pivot shaft 26 fixed thereto and carries at the end of one arm a marking roller 29 formed of rubber or other material impregnable with ink, paint or other marking medium and at the end of the other arm a soft iron or other magnetically susceptible piece 30. As shown, the marking roller 29 is disposed opposite to the backing roller 28 with respect to the line of wire travel. A coiled tension spring 32 secured at one end to the base wall 27 is connected at the other end to the lever arm carrying the marking roller 29 to serve the purpose of normally keeping the roller 29 in a position spaced apart from the backing roller 30 with the aid of a stop screw 33 adjustably mounted on the base wall 27 for abutting engagement with the lever arm'carrying the iron piece 30. The iron piece 30 is thus normally held slightly spaced apart from a solenoid 34 secured to the base wall 27 and, upon energization of the solenoid, is attracted thereby to cause the bell crank lever 31 to rock in a direction such that the marking roller 29 is lowered to press the travelling coated wire W against the backing roller 28 and thus turning on its own axis makes an identification mark on the surface of the coated wire W with ink, paint or other material impregnated.

Description will next be made of the mode of electrical operation of the device of the invention with reference to FIG. 8.

The electrical section of the device indicated at B in FIG. 1 is comprised of an electrical amplifier unit 35, an electrical signal forming unit 36 and a relay unit, solenoid 37 and contact 39, as shown in FIG. 8. The electrical amplifier unit 35 serves to amplify the voltage change caused in the detecting section A upon operation thereof. Incidentally, in the flaw detecting section A, the permanent magnets 22 on the three respective feeler elements D are fixed to the respective arm strips 20 so that they have a polarity all in the same direction and accordingly the three detecting coils 25 associated with the respective permanent magnets 22 are arranged to have an electromagnetic polarity oriented in the same direction and connected in series with each other. With this arrangement, the voltage changes as induced in the detecting coils 25 by the feeler elements arranged to rock at the same time and in the same inward or outward direction are of one and the same plus or minus sign and added up. Also, the electromagnetic detector units are each designed so that the voltage change induced therein by rocking movement of the associated feeler element D is enough to form a voltage signal effective to operate the relay unit of solenoid 37 and contact 39.

In this connection, the electrical signal forming unit 36 is designed to shape and form the output signal from the amplifier unit 35 into a signal form appropriate to effectively operate the relay unit by eliminating signal noises ordinarily present in the amplifier output on account of the fine oscillation of the travelling coated wire W, induction occurring in the related circuits or other noise sources involved.

The signal forming unit 36 also includes a time limit adjusting circuit designed to adjust the time interval between the instant of flaw detection in the flaw detecting section A and the instant at which in the marker section C the marking roller 29 is operated in response to the flaw detection and another time limit adjusting circuit adapted to adjust the energization time of relay unit, which determines the length of the mark to be made on the coated wire W. The former adjusting circuit is set in accordance with the linear distance between the flaw detecting section A and marking section C and with the travelling speed of coated wire W so that the coated wire W leaving the flaw detecting section A may be properly marked for the flaw detected at the very instant when the flawed wire portion comes substantially immediately beneath the marking roller 29. The length of marks made on the wire surface in this manner can be adjusted as desired by adjustment of the time of relay energization so that wire leaving the flaw detecting section A may b precisely marked for visual identification of the flaw detected at the very instant when the flawed wire portion comes substantially beneath the marking roller 29.

The length of the marks made on the surface can be adjusted as desired by properly setting the time of relay energization, as stated above. The relay units including contact 39 and so is fed with the formed signal output from the electric signal forming unit 36 and is held energized to keep its contact 39 closed as long as such signal output continues. Thus, the relay unit 37 is operable to make and break the electric circuit including an electric power source 38 and solenoid 34 in the marker section C through the intermediary of the relay contact 39 to keep the solenoid 34 energized as long as the signal contines.

To summarize, each time when some surface flaw in the travelling coated wire passes through the flaw detecting section A, the feeler elements D are caused instantaneously to make slight rocking movement to produce an electrical signal in the form of a voltage change induced in the detector units and such voltage change is amplified by the amplifier unit 35 and them formed by the signal forming unit 36 into an appropriate signal form to energize the relay unit 37 and hence the electromagnetic solenoid 34 in the marking section C. The energization of the solenoid 34 can be made to occur a predetermined limited length of time after the instant of flaw detection and continue for a predetermined limited length of time by properly presetting the two time limit adjusting circuits included in the signal forming unit 36.

As shown in FIG. 1, the flaw detecting section A of the device of the present invention can advantageously be arranged at the output end of a conventional wire coating line forward of its cooling stage in a manner so that the coated wire W may proceed through the opening in the support wall 18 and through the two spaced sets of pulleys, keeping contact with the respective pairs of lower pulleys (l5, l6) and (150, 160) under the pressure of respective top pulleys (l7) and The marking section C is arranged next to the detecting section A at an appropriate distance therefrom in the direction of wire travel in a manner so that the coated wire W leaving the flaw detecting section A may proceed over the backing roller 28 in contacting relation therewith. Subsequently, these sections are connected electrically with the electric section B as required and, in the conventional manner, the coated wire W is led over the guide pulley 6 and the pulleys of the tension control device to the take-up reel 12 to be wound thereon.

In operation, the coated wire W proceedsunder a predetermined tension without effecting any lateral oscillation between the two sets of pulleys in the flaw de tecting section A, thus passing at all times through a point at which the tips of the resilient feeler strips 19 get together. In this manner, the feeling projections 21 forming the tips of the respective resilient strips 19 are held in feeling contact with the periphery of the coated wire W radially in three different directions to effectively scan the entire peripheral surface of the wire during its travel. Accordingly, any surface flaw in the coated wire W, such as local protuberance, separation or unevenness of the wire coating, causes at least one of the feeler elements D to jump or rock instantaneously about its fixed end 14 at the instant when the flawed wire portion passes through the gathered set of feeling projections 21 at high speed. In this manner, the permanent magnet 22 on such feeler element D acts to produce an electric signal in cooperation with the adjacent detector coil 25 for each flaw detected such signal is led through the amplifier unit 35, signal fonning unit 36 and relay unit of solenoid 37 and contact 39 to cause the solenoid 34 in the marker section C to attract the magnetically susceptible piece 30 for a predetermined limited length of time so that the marking roller 29 is actuated to place an identification mark of a predetermined length on the adjacent side of the coated wire W. It goes without saying that the flaw detecting section A, amplifier unit 35, signal forming unit 36 and relay solenoid 37 are electrically properly connected with each other in advance of the operation and the electrical circuit of the marking section C is held at all times in a state prepared for signal reception.

FIG. 5 illustrates a modified form of detector unit which includes a pair of electrode plates 22a and 25a instead of the magnet 22 and detecting coil 25 used in the previous example and, when actuated, produces an electric signal according to the change in capacitance between the two electrode plates. One of the electrode plates 22a is secured to the arm strip 20 as a movable electrode and cooperates with the other electrode plate 25a, which is a fixed electrode.

As will be readily understood, a plurality, for example three, of such capacitance units are used in association with the respective feeler elements D and are connected with a signal amplifier unit 35 in parallel with each other, as shown in FIG. 9. In this instance, the amplifier unit 35 and succeeding electrical components including the relay unit required to actuate the marking roller 29 in section C are similar in arrangement as well as in function to the corresponding parts shown in FIG. 8.

Incidentally, the length of time elapsing from the instant when any surface flaw in the coated wire W has been detected in the detecting section A until the marker section C is operated to bring the marking roller 29 into contact with the surface of the coated wire W may vary, though only to a limited extent, with different factors including the characteristics of the electric circuits, performance of the relay unit, solenoid 37 and contact 39, structure of the marker section C and I the travelling speed of coated wire W. To meet this situation, appropriate time-limit adjusting means are provided in the signal forming unit 36 according to the present invention, as described hereinbefore, and on the other hand the flaw detecting and marking sections A and C are formed as independent assemblies electrically connected to each other by cord means so that the two sections may be arranged at any selected distance from each other. Thus, the device of this invention can readily be arranged in any line of wire coating process in a manner so that flaw identification marks be made on the travelling coated wire at locations substantially coinciding with the surface flaws by properly setting the time limit adjusting circuit means and selecting the distance between the flaw detecting and marking sections A and C of the device in consideration of the lapse of time between the flaw detection and the marking operation.

While one preferred embodiment of the invention and its modification have been shown and described, it is apparent that various changes and modifications may be made without departing from our invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the scope of the invention.

What is claimed is:

l. A surface flaw detecting device for coated wire, comprising a feeler member composed of resilient sensing strips (19) to be held in contact with a travelling coatedwire and movable upon passage of flaws in the coated layer on the wire, rocker arm strips (20) connected with said respective feeler strips (19) and movable therewith so that upon detection of a flaw in said coated wire by the resilient sensing strip, an electric signal is generated in transmitters (22, 22a, 25a) operable with rocking movement of one or more of said respective rocker arm strips to change the relationship of parts of the transmitters, and the generated electric signal is transmitted to an electric unit whereby a marking roller is operable by means under control of the signal output from said electric signal transmitters to mark the coated wire with ink or the like meidum at locations of the flaws detected.

2. A surface flaw detecting device as claimed in claim 1, in which said sensing strips each take the form of an angular bent plate fixed at one end to a stationary support wall (18) formed with an opening through which the coated wire (w) travels in a manner so that the other end portion of the bent plate extends forwardly in the direction of wire travel to make contact with the coated wire (W) at an angle thereto, said rocker arm strips (20) being integrally secured to the intermediate angular portion of said respective bent plates.

3. A surface flaw detecting device as claimed in claim 1, in which said electrical signal transmitters are each comprised of a magnet (22) secured to the tip of the associated rocker arm strip (20) and a detecting coil (25) energized by the magnet.

4. A surface flaw detecting device as claimed in claim 1 in which said electrical signal transmitters are each in the form of a variable capacitor comprised of a movable electrode plate (22a) secured to the tip of the associated rocker arm strip (20) and a fixed electrode plate (25a).

5. A surface flaw detecting device as claimed in claim 1, in which a plurality of said resilient strips are positioned in substantially equally circumferentially spaced relation to the wire.

6. A surface flaw detecting device as claimed in claim 1, in which said marking roller (29) is rotatably mounted on a pivotal lever, and a solenoid (34) controlled by means of the signal output from said electrical signal transmitters operablyconnects to and controls the position of said lever to bring it into contact with the surface of the travelling coated wire when receiving a predetermined signal output.

7. A surface flaw detecting device for coated wire, comprising a feeler means composed of a plurality of resilient sensing strips (19) operably held in contact with circumferentially spaced portions of a travelling coated wire and movable upon passage of flaws in the coated layer on the wire, individual rocket arm strips (20) secured to and movable with each of said respective sensing strips (19) so that upon detection of a flaw in said coated wire by the resilient sensing strip, an electric signal is generated in one of several two part electro-magnetic electric signal generators (22, 25; 22a, 25a) one part of which is secured to and movable with a respective one of said rocker arm strips, a fixed member adjacent said one part, the second part of said generator having an air gap separation from said first part at all times but being electromagnetically coupled therewith and being secured to said fixed member so as to generate a signal upon rocking movement of one or more of said respective rocker arm strips producing relative movement between said two parts, and the generated electric signal is transmitted to an electric unit whereby a marking roller is operable by means under control of the signal output from said electric signal generators to mark the coated wire with ink or the like medium at locations of the flaws detected.

8. A surface flaw detecting device as claimed in claim 7, in which said marking roller (29) is rotatably mounted on a pivotal lever, a solenoid (34) energized by the signal output from said electrical signal generators operably controls the position of said lever to bring it into contact with the surface of the travelling coated wire, and signal amplification and control means connect to said signal generators and to said solenoid to provide an actuating signal therefor.

9. A surface flaw detecting device as in claim 7 and where a solenoid controls said marking roller, signal amplification and control means connect to said signal generators to provide an actuating signal to said solenoid, and a plurality of said signal generators are provided and the sum of such signals is transmitted to said signal amplification and control means.

10. A surface flaw detecting device as claimed in claim 7, in which said one parts of said electrical signal generators are each comprised of a permanent magnet (22) secured to the tip of the associated rocker arm strip (20) and said second parts comprise respective detecting coils (25) energized by said magnets to have the energization varied by movement of said strips.

11. A surface flaw detecting device as claimed in claim 7, in which the plurality of said strips are positioned in substantially equally circumferentially spaced relation to the wire, and contact means are secured to end portions of said strips and protrude therefrom to contact peripheral portions of the wire.

' C UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 7, Dated August 6, 1974 Inventor s It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 28, "b" should be be Column 5, line 35, after "39 and", delete "so" and insert solenoid 37-- Column 7, Claim 1, line 48, meidum" should be medium Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents po'mso (wsg) l USCOMM-DC wan-pee A U.S GOVERNMENT PRINTING OFFICE 1 0-356-33,

Claims

1. A surface flaw detecting device for coated wire, comprising a feeler member composed of resilient sensing strips (19) to be held in contact with a travelling coated wire and movable upon passage of flaws in the coated layer on the wire, rocker arm strips (20) connected with said respective feeler strips (19) and movable therewith so that upon detection of a flaw in said coated wire by the resilient sensing strip, an electric signal is generated in transmitters (22, 25; 22a, 25a) operable with rocking movement of one or more of said respective rocker arm strips to change the relationship of parts of the transmitters, and the generated electric signal is transmitted to an electric unit whereby a marking roller is operable by meAns under control of the signal output from said electric signal transmitters to mark the coated wire with ink or the like meidum at locations of the flaws detected.

6. A surface flaw detecting device as claimed in claim 1, in which said marking roller (29) is rotatably mounted on a pivotal lever, and a solenoid (34) controlled by means of the signal output from said electrical signal transmitters operably connects to and controls the position of said lever to bring it into contact with the surface of the travelling coated wire when receiving a predetermined signal output.