US 3803014 A
Description (OCR text may contain errors)
United States Patent 1111 3,803,014
Atkinson v Apr. 9, 1974  ELECTROLYTICALLY DEBURRING 2,341,158 2/1944 Nachterran 204/206 2,971,810 2/ l 961 Ressler MOVING STRIP I 3,527,678 9/1970 Suzuki 204/15  Inventor: Edward S. Atkinson, M1ch1gan City, 3, 9, 972 r r et Ind. 3,467,593 9/1969 Dickson et al. 204/224 M  Assignee: National Steel Corporation,
Primary E.\'uminerF. C. Edmunds e Filed; 1972 Attorney, Agent, or Firm-Shanley & ONeil 211 Appl. No.: 299,736
52 u.s.c1. 204/206, 204/129.1 51 1111.01 B23p 1/02  ABSTRACT  Field of Search 204/1295, 129.55, 129.6, Y
204/129.65, 224 M, 206-21 1, DIG, 7 Trimmed edges of moving metallic strip are electrolytically deburred. Resulting strip is suitable for hot-dip  References Cit d coating or electroplating.
UNITED STATES PATENTS 893,814 7/1908 Schmitz 204/206 10 Claims, 4 Drawing Figures ELECTROLYTICALLY DEBURRING MOVING STRIP BACKGROUND OF THE INVENTION This invention relates to treatment of metallic strip previous to hot-dip coating or electroplating.
In typical manufacture of steel strip suitable for coating (zinc, teme and aluminum are common hot-dip metals) or plating (tin, chromium or zinc are common platings), slabs are rolled at elevated temperatures to produce hot rolled strip which in turn is pickled, cold rolled, and annealed. The hot rolled strip is sometimes slit to produce narrower widths. The cold rolled strip is often continuously side-trimmed to establish accurate and uniform width and to produce parallel edges. Such slitting and trimming leaves a longitudinal edge with a downwardly extending thin, sharp fin or ridge. Slitting leaves one or two such edges and trimming leaves two such edges. The term trimming is used hereinafter to include both slitting and trimming and the ridge resulting from either is denoted side-trim burr. Such burr is undesirable because it causes a heavy edge coating in any subsequent hot-dip or plating process. Also the burr can damage strip processing apparatus.
It is known to mechanically treat side-trim burr thereby obviating these problems. Mechanical deburring is accomplished by ploughs which are circular knives arranged at an angle to the edge of the strip such that the knife edges shear off the burr. They are usually used in conjunction with masher rolls. These are coneshaped rolls which mash the remainder of the burr flat. Mechanical deburring is difficult and involves considerable maintenance problems relating to the knives.
The main object of this invention is the provision of a deburring system in which the difficulties and maintenance problems associated with mechanical deburring are overcome.
Other objects of the invention will appear from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates a deburring system embodying principles of the present invention.
FIG. 2 is a cross-sectional view on line 2-2 of FIG. 1.
FIG. 3 is a view of a portion of the view of FIG. 2. FIG. 4 is a cross-sectional view illustrating alternative apparatus within the scope of the invention in conjunction with a portion of a strip to be deburred.
DETAILED DESCRIPTION With references to FIGS. l-3, a tank defines a container having a bottom wall 12, a top wall 13, a back side wall 14, a front side wall (not shown), an end wall 16 and an end wall 18. The end of tank 10 near end wall 16 is denoted the strip entrance end. The end of tank 10 near end wall 18 is denoted the strip exit end. An enclosure 20 communicates with the interior of tank 10 through top wall 13 at the strip entrance end and enclosure 22 communicates with the interior of tank 10 through top wall 13 at the strip exit end. Enclosure 20 has an inlet 24 outside tank 10 and an outlet 26 in the interior of tank 10. Enclosure 22 has an inlet 28 in the interior of tank 10 and an outlet outside tank 10 (not shown). A conduit 30 having a valve 82 communicates with the interior of tank 10 through end wall 18. The tank 10 is adapted to contain a bath 34 of electrolyte.
A travel path 36 for movement of metallic strip through tank 10 comprises a conductor roll 38 outside tank 10 and within enclosure 20, a sink roll 40 within tank 10 at its strip entrance end, a tensioning roll 41 within tank 10 toward its strip exit end positioned lower than roll 40, a sink roll 42 within tank 10 at its strip exit end positioned lower than roll 40 but higher than roll 41, and an exit roll 44 outside tank 10 and in enclosure 22. Thus, conductor roll 38 is upstream of the strip entrance end of tank 10 and exit roll 44 is downstream of the strip exit end of tank 10.
Positioned within tank 10 on each side of travel path 36 is an electrode 46 (see FIG. 2). Each electrode 46 is positioned to establish a working gap 48 (see FIG. 3) between the electrode and the burr on an adjacent edge of strip moving along the travel path 36.
Conductor roll 38 is electrically connected to the positive side of a generator 50 (or other suitable source of electric power) and electrodes 46 are electrically connected to the negative side of generator 50.
A lower guide roll 52 which is outside of tank 10 and of enclosure 20 near the strip entrance end and an upper guide roll 54 within enclosure 20 upstream of conductor roll 38 provides means for guiding strip to travel path 36.
In operation, metallic strip 56 having opposite trimmed longitudinal edges which are to be deburred continuously passes under guide roll 52, enters enclosure 20 through inlet 24, and passes over guide roll 54, over conductor roll 38, and through outlet 26 into tank 10 and into electrolyte bath 34. The strip then passes under sink roll 40, past electrodes 46, over tensioning roll 41, under sink roll 42, out of the bath of electrolyte, into inlet 28 of enclosure 22, out of tank 10, over exit roll 44 and then out of enclosure 22. Thus, strip 56 followstravel path 36 through tank 10 and through the bath of electrolyte in the tank.
Since the electrodes 46 are positioned on each side of the travel path within bath 34, an electrode 46 is po sitioned within the bath adjacent each longitudinal edge of the strip 56 to establish a working gap 48 (FIG. 3) between the electrode and the burr on an adjacent edge of the strip.
Conductor roll 38 imparts a positive potential to strip 56 passing over it so that the strip 56 functions as an anode. The electrical connection from the negative side of generator 50 imparts a negative potential to each of the electrodes 46. As a result, an electric circuit is formed between the strip 56 and each electrode 46 so that current can flow through the electrolyte of bath 34 which is present in each working gap 48.
The potential difference, that is the voltage, and the working gap are such as to obtain electrochemical machining action at each longitudinal edge of the strip to remove side trim burr 57. After washing, the strip is suitable for hot-dip coating or electroplating. The removed metal'either reacts chemically to form a sludge or reacts chemically to go into solution depending on the electrolyte as discussed in detail later. Hydrogen released at the electrodes and oxygen released at the strip edge are vented from the apparatus through ductwork (not shown) communicating with the interior of tank 10 through top wall 13.
Usually the strip 56 is passed through tank at a speed consistent with the speed of the strip through other processing steps, for example, cleaning or coating. If a speed can be utilized independent of the speed of the strip through other processing steps, a speed is selected so that with the length 58 (FIG. 1) of the electrodes46 and the voltage and working gap which are desired to be utilized, a desired amount of deburring will occur. Increased strip speed can be compensated for by increased electrode length, increased voltage or reduced working gap while decreased strip speed can be compensated for by decreased electrode length, decreased voltage or increased working gap. In general,
strip speeds which are usually utilized range from about 100 feet per minute to about 2,500 feet per minute.
The electrolyte is one suitable for the electrochemical machining of the metal being processed. Such electrolytes are described at pages 234 and 235 of Volume 3 of the Metals Handbook (eighth Edition). Preferably, a sludging electrolyte is utilized. With these electrolytes, the anodically removed metal reacts to produce an insoluble product denoted sludge. An example of a very suitable sludging electrolyte is an aqueous sodium chloride solution. If a sludging electrolyte is used, rolls 40, 41 and 42 should be positioned sufficiently above the bottom wall 12 of tank 10 so thatthe sludge formed during processing will build up to a level where it interferes with the strip or electrodes only after a relatively long period of time so that sludge removal will only have to be carried out infrequently. Non-sludging electrolytes can also be used. These retain the removed metal in solution and do not produce a sludge under electrochemical machining conditions; but, a larger content of dissolved metal gives a greater tendency for metal to plate out of solution on the electrodes.
Besides being dependent on time of exposure of an edge of the strip to an electrode which is dependent upon electrode length and strip speed, deburring action, that is, metal removal, is dependent upon current density. The current density is a viariable of potential difference (voltage) and working gap. With the present process and apparatus, the. current density tends to concentrate in the side trim burr; as a result, there will be a greater tendency for the removal of the side trim burr than for the removal of other portions of the strip.
A preferred current density is readily established by trial and error by varying the voltage or working gap and noting the deburring results to define the particular voltage and working gap most suitable for a particular typeof strip. If the current density is too low, all the burr will not be removed though the sharpest edges of the burr will be dulled to achieve some advantage. If the current density is too high, not only will the entire burr be removed, but metal will be removed from the. edge of the strip resulting in inefficiency though this will not be fatal to the operativeness of the system. Current density can be increased by increasing the voltage or decreasing the working gap. Current density can be decreased by decreasing the voltage or increasing the working gap. I
Usually, a voltage in the range of 4 to 30 volts dc will be suitable.
The working gap is defined for convenience herein in terms of the spacing of the extreme end of the burr and the nearest point on the exposed conductive portion of the electrode to which it is adjacent. A suitable working gap for use in the present invention has such a spacing ranging from one-thirtysecond of an inch to about 1 inch. Preferably, such spacing ranges from onesixteenth of an inch to one-half inch.
Turning now to a description of the electrodes, it is preferred that these have a configuration and construction which gives the greatest current density at the burr of the adjacent strip edge. Such occurs when the electrodes have an exposed conductive portion conforming to a strip edge to be deburred.
FIG. 2 shows such an electrode. It has a C-shaped exposed conductive surface which defines an elongated slot 62 for receiving a strip edge. Deburring will occur regardless of the upward or downward orientation of the burr. In trimming as described hereinbefore the burr is all oriented downwardly because of the nature of the trimming process; however, if the strip is recoiled prior to deburring, the burr can face either upwardly or downwardly as the strip passes through the electrolyte bath adjacent the electrode depending upon how the strip was recoiled. Thus, the C-shaped electrodes depicted in FIG. 2 are highly desirable since they obviate coiling in a particular way to achieve deburring results.
FIG. 4 shows an electrode with an inverted L-shaped active conductive surface. With this electrode, the strip must be oriented with the burr facing upwardly. An upright L-shaped electrode can be utilized where the burr faces downwardly.
It is highly preferred that the portion of the electrode to be submerged, except for the surface adjacent the portion of the strip to be deburred, that is except for the slot receiving the strip in the case of the C-shaped electrode, is enclosed by rubber, polyvinyl chloride, or other electric insulating substance. This reduces or avoids removal of metal other than the burr from the strip so that the strip does not depart from permitted tolerances and uniform results are achieved. Such insulation is denoted by reference numeral 63a.
So far as the conductive portion 63b of the electrode is concerned, any good conductor of electricity which is compatible with the electrolyte bath under conditions of deburring is satisfactory. Preferred materials are copper or stainless steel.
With reference to FIG. 1, the electrodes are mounted on carriers 64. With references to FIGS. 1-4, a passageway 66 extends through the interior of each carrier 64 and through the interior of each electrode 46 having an outlet 68 opposite the strip edge to be deburred. Each passageway 66 communicates at its inlet with a conduit 70. During operation electrolyte is introduced continuously through conduits 70and passageways 66 exiting outlets 68 so that it impinges against the adjacent strip edge. Such impingement prevents the sticking of precipitate to the strip and causes circulation of the electrolyte thereby controlling undesired heat buildup. Such circulation also has the advantage of moving gas bubbles from the area of the strip edge so that such bubble removal is regular resulting in more uniform processing.
The continuous addition of the electrolyte makes up for drag-out of electrolyte on the strip leaving tank 10. Conduit 30 and valve 82 (FIG. 1) are provided to remove electrolyte from the tank should such removal be necessary or desired. Such electrolyte may be recirculated after removal of entrained particles.
It is highly preferred that strip flutter be minimized. This reduces the possibility of the electrode and strip touching resulting in arcing and burning of the strip. To this end, the strip 56 is deflected over roll 41 so as to produce tension on the strip and the rolls 40, 41 and 42 have relatively large diameters (e.g. 1 foot) and are relatively positioned so that the span between the rolls 40 and 41 is minimized and ranges for example from 2 to 5 feet as measured along the travel path.
It is also highly preferred that the lateral alignment of the strip with respect to the electrode be maintained. This also reduces the possibility of the electrode and the strip touching resulting in arcing and burning of the strip.
FIG. 1 shows apparatus for maintaining such alignment. Within enclosure 20 and outside of tank means to detect lateral misalignment of the strip is shown in the form of a photoelectric device 71 comprising a light source 72 at each edge of the strip that directs light toward a detector unit 74, each associated light source and detector unit being positioned so that the edge of the strip intercepts a light beam on that side if the strip becomes misaligned in that direction. If desired, the strip can normally intercept the light beams with misalignment being indicated by a light beam getting through to a detector unit. In either case a signal is generated or terminated to indicate misalignment. The detector units 74 are electrically connected to a strip steering unit 76 which in response to detection of lateral misalignment corrects the misalignment by steering the strip.
Units for steering strip in response to detection of strip edge misalignment are well known and commercially obtainable. Some of these instead of responding by detecting by photoelectric means respond to detecting by pneumatic or other means. For examples of strip steering units disclosed in patents of the assignee of the present application, see US. Pat. Nos. 3,175,813 and 3,188,063. Patents of an assignee from whom strip guide control systems are commercially available are US. Pat. Nos. 3,039,483; 3,533,542; 3,586,904 and 3,570,735. For an example of a strip guide control unit for an electroplating apparatus see Nachtman U.S. Pat. No. 2,341,158.
instead of a detector 74 sending a signal to a steering unit, the detector 74 can send a signal via an electrical connection to a motor 78 which moves the electrodes 46 in respnse to a signal from 74 to maintain the electrodes spaced from the strip.
A combination of strip steering and electrode moving can also be utilized.
A specific operating example follows: the apparatus shown in FIGS. 1-3 is utilized. The tank 10 has depth of 3 feet and a width of 90 inches. The rolls 40, 41 and 42 each have diameters of 1 foot and the distance between rolls 40 and 41 as measured along the travel path is about 4.5 feet. The tank 10 contains an aqueous sodium chloride electrolyte containing 2 pounds of sodium chloride per gallon of water. Side trimmed 48 inch wide steel strip is passed through the reservoir at a strip speed of 180 feet per minute. A working gap is utilized having a spacing as hereinbefore defined of one-eighth inch. The lateral alignment of the strip is maintained utilizing a strip steering unit responsive to a photoelectric strip edge detector which is outside the tank. Each electrode has a length of 3 feet. A dc potential difference of 18 volts is applied. Substantially complete deburring is achieved with substantially no removal of other metal from the edge of the strip. After washing, the strip is readily coated or plated without the heavy edge buildup normally associated with the coating of strip which has not been deburred.
While the above embodiment is described in terms of the use of two electrodes deburring opposite longitudinal edges, the invention is intended to encompass apparatus with a single electrode or multiple electrodes deburring a single edge.
Thus, the above is to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
What is claimed is:
1. Apparatus for deburring a trimmed edge of moving metallic strip comprising a. means defining a container for a bath of electrolyte,
b. means defining a travel path for the metallic strip through the container,
c. electrode means positioned within the container on at least one side of the travel path to establish a warking gap between said electrode means and an adjacent edge of the strip moving along the travel path, said electrode means having an exposed conductive portion configured and positioned so as to be opposite both said strip edge and also a marginal portion of at least one strip surface adjacent said edge, and means for imparting a positive potential to the strip and means to impart a negative potential to said electrode means to form an electric circuit between the strip and the electrode means so that current can flow through electrolyte which is present in each working gap to remove side trim burr by electrochemical machining action.
2. Apparatus of claim 1 which additionally comprises means for minimizing strip flutter.
3. Apparatus of claim 2 wherein the means for minimizing strip flutter comprises tensioning means.
4. Apparatus of claim 1 which additionally comprises means outside the container for maintaining the lateral alignment of the strip within the container.
5. Apparatus of claim 4 wherein the alignment maintaining means comprises means to detect lateral misalignment of the strip and means responsive to the detection to correctthe misalignment.
6.-Apparatus of claim 1 wherein the electrode means has a configuration and construction which gives the greatest current density at the burr of the adjacent strip edge.
7. Apparatus of claim 6 wherein the electrode means has a C-shaped exposed conductive portion which defines an elongated slot for receiving the adjacent strip edge.
8. Apparatus of claim 7 wherein the portion of the electrode to be submerged is enclosed by insulation except for the slot receiving the strip.
9. Apparatus of claim 1 wherein the electrode means contains a passageway for the introduction of electrolyte into the container with means forming an opening designed to impinge the electrolyte against the adjacent strip edge.
10. Apparatus of claim 6 wherein the electrode means has an L-shaped exposed conductive portion.