US 3647646 A
Description (OCR text may contain errors)
March 7, 1972 METHOD ANDAPPARATUS FOR ELECTROPLATING CYLINDRICAL OBJECTS Filed March 4, 1968 W. M. TUCKER ETAL 2 Sheets- Sheet 1 U QZOEYGZZJQQ WILL/AM M TUCKER BARR/E M. GARDNER JOHN W HAYFORD INVENTORS ATTORNEYS' 3,647,646 METHOD'AND APPARATUS FOR ELECTROPLATING CYLINDRIGAL OBJECTS 6 Filed March 4, '1968 Milk! 9 w. M. TUCKER ErAL. I
I 2 Sheets-Sheet 2 WILLIAM M. TUCKER BARR/E M. GARDNER JOHN W. HA YFORD United States Patent Ofiice 3,647,646 Patented Mar. 7, 1972 3,647,646 METHOD AND APPARATUS FOR ELECTRO- PLATING CYLINDRICAL OBJECTS William M. Tucker, Barrie M. Gardner, and John W. Hayford, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y.
Filed Mar. 4, 1968, Ser. No. 710,035 Int. Cl. C23b 5/56, 5/68; B01k 3/00 U.S. Cl. 204-25 26 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION (1) Field of the invention The invention relates in general to the art of electroplating and in particular to a novel method and apparatus for plating a cylindrical object with a metal coating.
(2) Description of the prior art A variety of methods of effecting the electroplating of cylindrical objects have been proposed heretofore. In certain of these methods, the cylindrical object, which serves as the cathode in the plating process, has been totally immersed within the electrolyte solution and positioned in proximity to a soluble anode, composed of the metal to be used to form the plate, which is also totally immersed Within the electrolyte solution. Other plating processes have utilized a similar arrangement but employ an insoluble anode, in which case the plating metal is supplied by the electrolyte solution. In some instances, the cylindrical object has been mounted in a fixed position within the bath, while in other instances it has been subjected to rotary and/or oscillatory movement to effect agitation of the electrolyte solution in the region immediately adjacent the cathode surface. For the production of metal coatings meeting ordinary quality requirements such techniques are generally quite satisfactory. However, where it is necessary to produce a coating which meets very stringent quality standards, such as is the case in nickel plating of steel rolls used as film transport rolls in the manufacture of photographic film, serious difiiculties are encountered. In particular, it is found that numerous small pit-like defects are formed in the nickel plating, either as a result of gas bubbles which are trapped on the surface of the roll while plating and subsequently plated in, i.e. occluded in the plating structure, or as a result of fracture holes which result from the breaking away during subsequent surface grinding operations of tiny protrusions or nodules on the surface of the plating formed when conductive particles such as carbon, nickel sulfide, iron, iron oxide, and the like, fall on the roll surface during plating and become attached. These defects, even though they are very small in size, can cause stratches or gouges in the moving web of film as it passes over the roll and to avoid this problem an effort is usually made to fill in the defects in the plating with plugs of soft nickel, but, as would be apparent, this is a tedious, time-consuming and expensive procedure.
It is also known to the art to electroplate a cylinder by positioning the cylinder so that it is less than half immersed in the electrolyte solution and providing an anode of arcuate shape mounted within the electrolyte solution directly beneath the cylinder so that it is substantially equidistant from the face of the cylinder at all points. Such processes, exemplified by U.S. Pat. 1,918,627, accomplish plating only within the zone where the cylinder is immersed but utilize relatively high speed rotation of the cylinder about its axis to secure a uniform deposit over the entire face of the cylinder. They are employed where it is not necessary to plate shaft sections at the ends of the cylinder nor to plate the entire end surfaces of the cylinder and find particular utility in production of printing forms utilized in the rotary photogravure process.
It is toward the objective of providing a novel electroplating method and apparatus, capable of plating cylindrical objects at a high rate with metal coatings in which in plate defects are substantially eliminated, or at least greatly reduced in number, and adapted to permit plating of shaft sections and end surfaces as well as the face of the cylindrical object, that the present invention is directed.
SUMMARY OF THE INVENTION The present invention comprises a novel method and apparatus for electroplating a cylindrical object with a metal coating which is adapted to use in diverse applications in the electroplating arts where a high quality plating is required. While the invention is specifically described herein with reference to nickel plating of rolls used as film transport rolls in the manufacture of photographic film, it may be utilized in many other electroplating applications, as long as the workpiece is either a cylinder or of a generally cylindrical shape and the plating system is one in which a high degree of agitation of the bath is not detrimental.
In the method of this invention, the cylindrical object which is to be plated is mounted in the electroplating bath in such manner that it is only partially submerged in the electrolyte solution, i.e., so that part of it is below the level of electrolyte solution and the remaining part is exposed. More specifically, the cylinder is mounted in a generally horizontal position so that its longitudinal axis is substantially parallel to the free surface of the electrolyte solution, i.e., the surface of the electrolyte solution when the bath is in a quiescent state, and at such a level that the uppermost point on the cylindrical surface is above the free surface of the electrolyte solution. Depending on the particular requirements of the specific situation involved, the cylinder may be positioned so that its longitudinal axis is coincident with the surface of the electrolyte solution or so that it is above or below such surface, so long as a substantial portion of the cylindrical surface is immersed within the solution. The cylindrical object serves as the cathode in the plating process and an anode, which may be an insoluble anode or a soluble anode composed of the plating metal, is mounted within the bath in close proximity thereto. As the electric potential is impressed across anode and cathode to effect plating, the electrolyte solution is agitated and preferably, the cylindrical object is rotated about its longitudinal axis. The method of effecting agitation is not critical but the solution must be agitated with sufiicient force that the portion of the cylindrical object which is exposed, i.e., above the free surface of the solution, is at all times maintained completely awash with the solution, i.e. continuously and completely covered with a layer of the solution. By this means, the cylindrical object is at all times completely surrounded with electrolyte solution which acts to convey the electric current to its surface so as to effect plating at an effective rate over the entire area and yet the static head of liquid above any point on the upwardfacing surface is very low. Rotation of the cylindrical object which is being plated may be etfected in a continuous or intermittent manner, as desired, and agitation of the electrolyte solution may be accomplished by any suitable means known to the art such as (gas sparging, solution sparging, or the use of mechanical stirring apparatus.
The method of this invention provides a high plating rate and, at the same time, facilitates formation of a high quality plate which is substantially free of defects. The high plating rate achieved is primarily attributable to the fact that the high degree of agitation of the electrolyte solution efi'ectively replenishes metal ions as they are depleted from immediately adjacent the plating surface. Improvement in the quality of the deposit, i.e., freedom from in plate defects, is believed to be a result of the fact that rising bubbles in the solution attributable to the sparging, or other agitation, break as they come in contact with the surface of the cylindrical object and release the gas in such manner that it is not entrapped within the plate, as well as the fact that there is little or no opportunity for particles in the plating bath to settle out onto the rotating cylinder since above any point on the upward-facing cylindrical surface there is only a relatively small depth of solution. Moreover, as the rising bubbles reach the surface of the solution and break they violently scrub the face of the cylinder and wash away any solid particles or minute gas bubbles which have temporarily attached themselves to the cylinder and this action also contributes greatly to the elimination of in plate defects.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:
FIG. 1 is a partial top plan view of electroplating apparatus in accordance with this invention, illustrating particularly the relative positions of the anode and cathode within the plating tank.
FIG. 2 is an end view of the apparatus taken along line 2-2 of FIG. 1, illustrating particularly the position of the cathode relative to the surface of the electrolyte solution.
' FIG. 3 is a longitudinal elevation view of the apparatus taken along the line 33 of FIG. 1, illustrating particularly the construction of the anode and showing means provided for recirculation, heating, and filtering of the electrolyte solution.
FIG. 4 is a longitudinal elevation view of the apparatus taken along line 4-4 of FIG. 1, illustrating particularly the relative positions within the plating tank of the cathode and the means provided for agitating the electrolyte solution.
DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings, plating tank 10, which is rectangular in shape and made of steel plate coated on the interior side with an electrically non-conductive, chemically-resistant coating, such as rubber or polyvinyl chlo.,- ride, 'is partially filled with electrolyte solution 12. Arranged within tank in two longitudinally extending rows are a series of identical vertically disposed anodes 14, each of which is in the form of a hollow cylinder filled with chunks of electrolytic nickel and is completely immersed within electrolyte solution 12. A total of ten anodes 14are shown and these are arranged so that there are five in each row positioned so they are equally spaced from one another. Anodes 14 are made of titanium and have perforated walls adapted to retain the nickel chunks while admitting electrolyte solution 12 into the interior of the cylinder and thereby into contact with the nickel. Positioned between the rows of anodes 14 is a longie tudinally extending, horizontally disposed, cylindrical roll -16 which serves as the cathode in the electroplating process. Roll 16 is made of steel and, after being plated with nickel, is to be used as a film transport roll in the manufacture of photographic film. At each end of roll' 16, shaft sections 18 extend a short distance beyond the end of the roll.
The dimensions of anodes 14 and roll 16 can be of any reasonable magnitude, for example,.anode s 14 can be two feet high and a few inches in diameter and roll 16 can be five feet in length and a few inches in diameter. In the drawings there are five anodes 14 in each row positioned at substantially equal increments along the length of roll 16 but a lesser or greater number of anodes may be used depending on the relative sizes of the anodes and the roll being plated. Moreover, in practice a single plating tank would usually be used to electroplate at the same time a number of rolls arranged within the tank in several parallel rows, with each row being made up of two or more rolls linked together.
As illustrated in FIGS. 2, 3, and 4, anodes 14 are suspended in electrolyte solution 12 by means of anode hangers 20 carried by anode support rods 22 and roll 16 is supported in position adjacent anodes=14 by cathode hangers 24 which engage shaft sections 18 at each end of roll 16 and are carried by cathode support rod 26. Anode support rods 22 are fixedly secured to the end walls of plating tank 10 by braces 28 and cathode support rod 26 is similarly secured to the end walls of plating tank 10,
but at a slightly lower height, by braces 30. Anode hangers 20. and cathode. hangers 24 are insulated with an inert coating, such as a vinyl plastisol insulation, over their entire surface except at the points of contact with the support rods and with the anode or cathode.
It is a critical feature of this invention that roll 16 be mounted so that it is only partially submerged in electrolyte solution 12, Le. so that part of roll 16 is below the free surface of electrolyte solution 12 (the term free surface being used herein and in the appended claims to mean the upper surface of the solution when it is in a quiescent state) and the remaining part is above the free surface of electrolyte solution 12-and thus exposed to the surrounding atmosphere. Considerable variation in the exact position at which roll 16 is mounted is, however, permissible. Specifically, roll 16 should be mounted with its axis substantially parallel to the free surface of electrolyte solution 12 and preferably at such a level that about 40 to about 90 percent of the total surface area of roll 16 is immersed within electrolyte solution 12 when it is in a quiescent state. It is particularly preferred that roll 16 be mounted so that from about 50' to about 75 percent of the total surface area thereof is immersed within electrolyte solution 12.
As shown in FIG. 2, the electric current required for the process is provided by a conventional direct current source, indicated by the numeral 32, such asa low voltage high amperage generator or rectifier, connected by power supply lines 34 and 36 to anode hangers 20 and cathode hangers 24 which serve to convey the current.
As shown in FIG. 3, electrolyte solution 12 is withdrawn from tank 10 via outlet pipe 38 and pumped by means of pump 40 through filter 42 and heat exchanger.v
v series of-orifices 50, which may take the form of slots or Blower 54 can, of course, be replaced by any other suit able source of air which will maintain an adequate volumetric flow rate to effectively agitate electrolyte solution 12 and which provides air which is free of oil or other contaminants. As illustrated, sparging pipe 48 is positioned in the bath so that it is immediately below and substantially parallel to roll 16 so that the streams of bubbles S1 emerging from .orifices 50 and rising through electrolyte solution 12 will uniformly contact the surface of roll 16. To provide for rotation of roll 16 about its axis during the plating process, variable speed motor 56 is connected by way of drive shaft 58, which extends through a seal in the wallet tank 10, and coupling 60 to shaft section 18 at oneend of roll 16. An alternative method which avoids the problems encountered in providing a seal in the wallof a tank containing a corrosive liquid is to employ a submerged motor drive positioned within tank 10. Various other means of providing for rotation of roll 16 would be apparent to one skilled in the art.
In operating the apparatus of this invention, roll 16, which is to be plated with nickel, is mounted in pisition within tank and connected to the drive shaft of motor 56 which is then started so as to rotate roll 16 about its axis. Blower 54 is then put into operation with the result that a continuous stream of bubbles 51 rises from each of slots 50 in sparging .pipe 48 and breaks over roll 16 causing electrolyte solution 12Ito' be violently agitated and carried up and over, the'exposed surface of rotating roll 16'so asto keep such surface completely and continuously coveredwith alayer if electrolyte solution 12. Atfthe' same 't'ime,.pumpf4,( is'started so as to circulate electrolyte solution 12' through filter 42 and heat exchanger 44', 'whereby electrolyte'solution .12 is maintained substantiallyfree frornsolid contaminants and at the temperature lrequired for the plating" operation. As the flow of electric current from power supply source 32 is started, formation of a', nickel' plate .on the surface of roll 16 begins and opefationis vcontinued'luntil the desired thickness of nickel plate is 'achieved,vwhereupon the apparatus isf'shut down and roll16'is removed from tank 10. Before plating a e -r011, additional nickel chunks will, if necessary, be added't'o the perforated cylinders of anodes 14. T
Themethod of ,this inventionis' applicable to plating of many different types of cylindrical objects regardless of their"size, or Whetherthey'ar e solid or hollow, or composedof any I particular. material, so long as such materia is; capable of being me'talplated in an electroplating proce ssawhile the invention is described herein with particular reference to-the plating of a cylinder, and will ordinarily find fits most'l widespread application in the platingof cylinders, it ,can also be employed in plating other elongated bodies which ar"e not of circular crosss'ectiorifThus, for. example, the object to be plated may havea cross-sectional configuration which takes the form ofan o val,' an ellipse,,or a polygon. All such objects are intended toibeincluded within .the scope of the term out silver plating, zinc plating, or copper plating of cylindrical objects, as Well as nickel plating.
As pointed out hereinbefore, the cylindrical object which is to be plated is mounted so that its axis is substantially parallel to the free surface of the electrolyte solution and either coincident with or spaced therefrom so that a portion of the object is immersed in the solution and the remaining portion extends above the free surface ran objectof generally cylindrical shape as employed herein and-inthe appended claims; Moreover, if a cylinderis -provided with shaft sections at its ends, as is frequently the case, then these sections will also be plated as will the entire ends of the cylinder. If plating of these areas is notdesired'then they may, of course, be provided with'liprotective coverings to prevent plating, but, it is ordinarily desirable-:tovplate both the shaft sections and the ends of 'thecyli 'der and in such instances the method of this invention provides 'aniriaportant advantage over prior art"methods;such*as"the'niethod disclosed in U.S.'
Pat. 1,918,627, in which this is not "accomplished. -Al-' though it has been specifically illustrated herein with reference' to nickel plating the 'rnethod of this invention is applicable' tofplatihg"with other' 'metals so long as the plating system: is not' one in which vigorous agitationof the electrolyte isdetrimental, as is the case, for example, in'jch'romium plat' g'. Thus, for example, the methodand apparatus dfefscri hereinffmayfbe employed to carry of the solution. The optimum position for the cylindrical object will depend on a number of factors, particularly the diameter of the object and the degree of agitation imparted to the electrolyte solution. As indicated hereinbefore, it is preferred in practicing this invention that about 40 to about percent of the total surface area of the object be immersed when the electrolyte solution is in a quiescent state and particularly preferred that about 50 to about 75 percent be immersed. With cylindrical objects of small diameter, such as 2-inch diameter rolls, a position where the axis is coincident with the free surface, i.e. 50 percent of the total surface area immersed, is ordinarily optimum, whereas larger cylindrical objects, such as 8-inch diameter rolls, will usually require a greater degree of immersion. Generally speaking, the greater the diameter of the object the more it should be immersed so as to ensure that the agitation of the bath will be effective to maintain an adequate flow of electrolyte solution over the exposed portion of the object.
To maintain the electrolyte solution at a substantially uniform concentration and temperature at all points within the bath it is desirable to continuously recirculate a portion of the solution. Such recirculation can be accomplished by the use of any suitable pumping means known to the art. In nickel electroplating with the process of this invention, the recirculation rate should be sufficient to circulate each hour a volume of electrolyte solution which is equal to at least the total volume of solution in the tank, i.e. a tank turnover rate of at least one time per hour, and preferably equal to at least 1.5 times the total volume of solution in the tank. Moreover, since some loss of electrolyte solution will inevitably occur due to evaporation and/or leakage, make-up solution should be added during the plating process. It is also desirable to maintain the electrolyte solution at a constant level in the plating tank and for this purpose a weir (not shown in the drawing) is preferably provided at one end of the tank. The circulating system can then be arranged to remove some solution from near the bottom of the plating tank and some from the weir box. Any other suitable arrangement for maintaining a constant level of solution in the plating tank can, of course, be employed in place of a Weir.
The temperature of the electroplating bath is not ordinarily critical but it will frequently be desirable to provide means for heating the electrolyte solution so that operation at temperatures above room temperature is rendered possible. In nickel electroplating with the process of this invention, it is desirable to maintain the bath at a temperature in the range of about F. to about 175 F., and preferably in a range of about ,F.- to about F. Any conventional means of providing the necessary heat input may be employed, for example, the plating tank may be jacketed and a suitable heat transfer fluid passed through thejacket, or, in recircuIating the electrolyte solution may be passed through a heat exchanger where the temperature is raised to the necessary level before it is returned to the plating tan-k.,, In addi-i tion to heating the electrolyte solution to maintain a are sirable temperature for plating, it is also advantageous that the vcirculation system include a filter to, effect removal of any solid particles which are present in the electrolyte; solution. Any conventional type of filter may be employed, but in nickel electroplating with the method of this invention it is preferred to employ a filter capable of retaining one hundred percent of the particles greater than fi ve microns in size.
As will be apparent from the foregoing disclosure, the essential requirements of the method of this invention are (1) that the cylindrical object be properly positioned with reference to the level of electrolyte solution, as hereinbefore described, and (2) that the electrolyte solution be agitated with sufficient force that it washes over the portion of the cylindrical object extending above the free surface of the electrolyte solution, so as to scrub this portion, yet maintains this portion continuously and completely covered to an extent adequate to ensure that plating occurs thereon. It will ordinarily also be highly advantageous to rotate the cylindrical object about its axis so as to ensure uniformity of plating and the preferred embodiments of this invention include such rotation. However, the method of this invention is operable without such rotation, particularly where completely uniform plate thickness is not essential, since by maintaining the exposed surface of the object completely awash with electrolyte solution plating is taking place over the entire surface throughout the entire plating period and it is thus not necessary to rotate in order to effect plating of the entire surface. In con trast with the method of the prior art in which the cylinder is partially immersed so that plating action takes place only in the region of immersion and the purpose of rotating the cylinder is'to effect plating of the entire surface, in the method of this invention plating action is taking place at all times over the entire surface of the cylinder and the purpose of rotating is to compensate for the fact that all points on the plating surface are not equidistant from the anode so as to provide a plate of uniform thickness in spite of the lack of equidistant spacing.
Consonant with the above requirements, many variations and modifications in the method of this invention are feasible. Thus, for example, rotation of the cylindrical object may be continuous, or it may be intermittent with a short interval during which the cylinder is stationary between each period of rotation, or it may be incremental in nature with the cylinder being turned successively by a quarter turn or a half turn each time. The exact speed of rotation is not critical, but it is preferred in electroplating with nickel to employ a speed of 5 to revolutions per minute.
The required agitation of the electrolyte solution can be accomplished by any suitable means as long as the solution is agitated with sufficient force to continuously and completely cover the portion of the cylindrical object above the quiescent level of the bath with a layer of electrolyte solution of adequate thickness, for example, one quarter inch or more, to ensure that electrolytic deposition can occur at all points on the surface defined by the rotating cylinder. In other words, the agitation must be such that the solution rolls over the rotating cylinder and keeps its upper surface awash at all times. This provides the desired scrubbing action at the surface of the cylinder while at the same time ensuring that plating current is carried to all portions of the cylinder at all times. Such agitation may be accomplished by sparging with air or other inert gas such as argon or nitrogen, by solution sparging, i.e. by injecting streams of electrolye solution through a multiplicity of jets located within the bath directly below the rotating cylinder, or by mechanical stirring such as by the use of paddle wheels located near the rotating cylinder.
It is preferred to effect agitation of the electrolyte solution by means of gas sparging and particularly preferred to employ large bubble air sparging. Such preference is dictated in part by the fact that sparging is a simple, convenient and low cost method but also by the fact that it provides for a desirable heterogeneity in the conditions at the surface of the cylinder, i.e. since the rising bubbles travel along constantly fluctuating paths there is continual variation in the scrubbing action at the surface of the cylinder which is particularly effective in dislodging particles and provides excellent uniformity of plating and freedom from in plate" defects. The most effective scrubhing action is achieved by providing for the formation of large bubbles which rupture violently at the surface. Large bubble air sparging is most conveniently and inexpensively accomplished by inserting a sparging pipe into the bath immediately below the rotating cylinder and providing such pipe with a series of longitudinally spaced slots or holes so that a substantially uniform stream of air bubbles will rise along the length of the sparging pipe and cause the electrolyte solution to constantly roll over the rotating cylinder. The sparging pipe is preferably located so that it is parallel to and in line with' the longitudinal axis of the cylinder and at a distance of about 2 to about 8 inches below the bottom surface of the cylinder. The 'slots or holes should be of such size that the air bubbles will be at least /2-inch in diameter, and preferably larger, when they break at the surface, as this provides the most effec tive scrubbing action. Satisfactory results are obtained by the use of, for example, -inch diameter holes spaced 1.3 inches apart. The air supplied to the sparging pipe should be pressurized, with the optimum pressure depending on the position of the pipe within the bath. Good results are obtained by providing a pressure of about one'p.s.i.g. for each 18 inches of solution above the top surface-of the sparging pipe. The volume of air required for sparging will, of course, depend upon the specific geometry'of the plating system involved, but, in general, should be at least 2 cubic feet per minute for each square foot of surface being plated, and preferably 3 to 4 cubic feet per minute for each square foot of surface. i I The plating tank may be of any convenient geometry but will ordinarily be of a rectangular shape. The anodes may also be of any suitable shape but must be positioned in the tank in such manner that they do not interfere with the sparging pipe, or other agitating means, and should be arranged so as to provide a live anode surface extending longitudinally over at least the central three-quarters of the cylinder.
A convenient and effective procedure is to utilize anodes in which the plating metal is in the form of chunks carried in perforated baskets which are suspended in the electrolyte solution, as illustrated herein. However, other conventional types of anode construction may also be employed, for example, the anode may be a horizontally positioned perforated basket of comparable length to the cathode which is immersed in the electrolyte solution and supported in proximity to the cathode. Any conventional anode construction would be permissible in carrying out the method of this invention so long as the anode is disposed so as to be effective over the full length of the object being plated and does not interfere with the gas sparging or other means employed for agitating the electrolyte solution. Moreover, the anode need not be a soluble anode as illustrated herein but 'may be an. inert or insoluble anode, in which instance the plating metal would be supplied from the electrolyte. Thus, for exam-f ple, nickel plating can be effected using a suitable-solution of soluble nickel salts as the electrolyte and an insolu-j ble anode composed of lead, platinum, platinized titanium, or graphite. The optimum current desnity for operation of the process will depend upon the specific situation involved, including such factors as the composition and temperature of the bath, the relative positions of anode and. cathode, and so forth. It has been found that current densities of 50 to amperes per square foot ofplar ing surface, or more, are ordinarily feasible in nickel plating in the manner described herein. i
The method of this invention is particularly amenable to the production of a hard nickel plate such as is required for film transport rolls used in the manufacture of photographic film. To produce a bright, hard and tough nickel deposit, a typical plating bath will'contain nickel sulfate hexahydrate and/or nickel sulfate heptahydrate in an amount of about 24 to about 48 ounces per gallon, nickel chloride in an amount of about 4 to about 6 ounces per gallon, oric acid in an amount of about 4 to about 5 ounces per gallon, saccharin in an amount of about 0.2 to about 0.4 ounce per gallon, ammonium bifluoride in an amount of about 0.2 to about 0.4 ounce per gallon, and a low foaming surfactant in an amount sufiicient to provide a surface tension of less than about 45 dynes per square centimeter. Where it is desired to produce a soft nickel deposit, this may be readily accomplished by using a similar plating bath in which the saccharin is omitted.
The method of this invention provides a very high plating rate while at the same time providing a very high quality plate. Thus, in nickel electroplating using a free dissolving form of electrolytic nickel plating rates of from about 0.004 inch per hour to as high as about 0.006 inch per hour can be attained. These rates are achieved primarily as a result of the fact that the vigorous agitation provided results in adequate replenishment of the electrolyte surface film at the cathode to sustain a high plating rate. Furthermore, the nickel plate is substantially improved over that obtained by methods heretofore known with respect to the presence of in plate defects. Such defects are substantially eliminated, or at least greatly reduced in number, as a result of the washing action of the electrolyte solution over the surface of the cylinder. Also, since the cylinder is positioned so that it is only partially immersed, gravity head of electrolyte solution over the cylindrical surface is substantially eliminated so as to greatly minimize the settling out of solid particles onto the cylinder. Moreover, the violent agitation of the electrolyte solution causes it to constantly wash over the rotating cylinder and thereby scrub the surface so as to dislodge small bubbles and/or conductive solid particles which would otherwise be plated in. The overall result of these features of the process is that a plate which is remarkably free of defects, and thus well suited to applications requiring stringent quality standards such as plating of film transport rolls, is produced.
Apparatus constructed in accordance wlth the disclosure herein Was operated to nickel plate film transport rolls with excellent results. Both 4-inch diameter by 48- inch long steel rolls and 2-inch diameter by 48-inch long aluminum rolls were plated at a current density of 75 amperes per square foot. The plating bath was maintained at a pH of approximately 4 and a temperature of approximately 145 F. and contained 24 ounces per gallon of a mixture of nickel sulfate hexahydrateand nickel sulfate heptahydrate, 6 ounces per gallon of mckel chloride, 5 ounces per gallon of boric acid, 0.3 ounce per gallon of saccharin, 0.2 ounce per gallon of ammonium bifluoride, and suificient low foaming surfactant to maintain the surface tension below 45 dynes per square centimeter. The bath was recirculated at a rate suificient to turn the solution over about 1.5 times per hour and passed through a filter which retained all particles above 5 microns in size. The roll was suspended in the bath so that it was a little more than half immersed in the el ectrolyte solution and was adjacent to an anode cons1st1ng of 1" x 1" x /2" nickel chips contained in 2 /z-1nch diameter by 24-inch long perforated titanium baskets. Botation of the roll was at a rate of 7 /2 revolutions per minute with large bu-bble air sparging at a rate suflicient that the electrolyte solution was violently agitated and washed over the rotating roll at all times. A plating rate of about 0.006 inch per hour was achieved and the resulting plate was uniform in thickness, bright, hard, and abrasion resistant and almost completely free of in plate defects.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
We claim: 1. In a method of metal electroplating wherein the object to be plated is either a cylinder or of a generally cylindrical shape, said object serves as cathode in the plating process and is positioned adjacent to an anode which is immersed within an electrolyte solution, and an electric potential is impressed across said anode and said object to effect plating; the improvement comprising partially immersing the object in the electrolyte solution with its longitudinal axis substantially parallel to the free surface of the electrolyte solution so that a portion of the object is below said free surface and within the electrolyte solution and the remaining portion of the object extends above said free surface, and agitating the electrolyte solutron during plating of the object by sparging with a fluid introduced into the electrolyte solution directly beneath the object with suflicient force that the electrolyte solutron washes over the portion of the object extending above said free surface to maintain said portion continuously and completely covered with electrolyte solution to an extent adequate to ensure that plating occurs thereon.
2. The method as described in claim 1 further comprising the step of rotating said object about said longitudinal axis during plating.
3. The method as described in claim 2 wherein the rotation is continuous.
4. The method as described in claim 2 wherein the rotation is intermittent.
5. The method as described in claim 2 wherein said object is positioned so that from about 40 to about percent of the total surface area thereof is immersed within said electrolyte solution when said electrolyte solution 1s m a quiescent state.
6. The method as described in claim 2 wherein said object is positioned so that from about 50 to about 75 percent of the total surface area thereof is immersed within said electrolyte solution when said electrolyte solution is in a quiescent state.
7. The method as described in claim 2 wherein said object is plated with nickel.
8. The method as described in claim 2 wherein said object is plated with copper.
9. The method as described in claim 2 wherein said object is plated with zinc.
10. The method as described in claim 2 wherein said object is plated with silver.
11. The method as described in claim 2 wherein the agitation of said electrolyte solution is accomplished by sparging with an inert gas.
12. The method as described in claim 11 wherein the gas is introduced into the electrolyte solution from a sparging pipe having a series of longitudinally spaced orifices in the wall thereof which is positioned directly below and parallel to said object and at a distance of about 2 to about 8 inches therefrom.
13. The method as described in claim 12 wherein the gas is introduced into the electrolyte solution at a rate of at least about 2 cubic feet per minute for each square foot of surface plated.
14. Apparatus for electroplating with a metal coating an object which is either a cylinder or of a generally cylindrical shape, comprising:
( 1) a tank containing a body of electrolyte solution having a free upper surface,
(2) an anode immersed within said electrolyte solution,
(3) means for mounting the object adjacent said anode with the longitudinal axis of the object substantially parallel to the free surface of said electrolyte solution in such position that a portion of the object is below said free surface and within the electrolyte solution and the remaining portion of the object extends above said free surface,
(4) a sparger positioned within said electrolyte solution for introducing a sparging fluid during plating of the object into said electrolyte solution directly beneath the object with sufficient force that said electrolyte solution washes over the portion of the obiect extending above said free surface to maintain saidiportioncontinuouslyyand completely: covered --'.-;;with electrolytesolution to: an extent adequate .to
- ensure-that plating occurs thereon, and
:--1(5) means fox-impressing an electric potential across said anode-andsaid object.
1 15.-Apparatus asdescribed in claim 14 wherein said. object is rotatably mounted-and including means for rotatingsaid object about its longitudinal axis.
. 16. Apparatus as described in claim 'wherein said sparger is a gas sparging pipe. 1
v 17. Apparatus as;describedin claim 16 wherein said pipe has a-seriesof horizontally spaced orifices in the wall thereof and is positioned within said electrolyte solution directly below and parallel to said object and at a distance of about 2 to about 8 inches therefrom.
18. Apparatus as described in claim 17 wherein said orifices are of such size that bubbles which are at least about one-half inch in diameter when they reach the surface of said electrolyte solution are formed.
19. Apparatus as described in claim 15 including means for recirculating a portion of said electrolyte solution.
20. Apparatus as described in claim 15 including means for heating said electrolyte solution.
21. Apparatus as described in claim 15 including means for filtering said electrolyte solution to remove solid particles therefrom.
22. Apparatus as described in claim 15 wherein said anode is an insoluble anode.
23. Apparatus as described in claim 15 wherein said anode is a soluble anode.
24. Apparatus as described in claim 23 wherein said anode is a nickel anode.
25. Apparatus as described in claim 23 wherein said anode is a copper anode.
26. Apparatus for electroplating a cylinder with a nickel coating, comprising:
( 1) a tank containing a body of electrolyte solution having a free upper surface,
(2) an anode of free dissolving electrolytic nickel mounted so that it is immersed within said electrolyte solution,
(3) means for rotatably mounting said cylinder adjacent said anode with its longitudinal axis substantially parallel to the free surface of said electrolyte 12 solution in such position that about to/about percent of the. total surface area of said cylinder is immersed in saidelectrolytesolution-when said elec= trolyte solution is in a quiescent-statetand theremaining portion of said cylinder extendsabove said freesurface, a v (4) means for :rotating said cyliriderabout its longitudinalaxis,
, -(5) a sparging pipe positioned-within said electrolyte solution directly below said cylinder for agitating said electrolyte solution during plating of-saidcylinde'r' so that it washes ov'er the portion of said cylinder extending above said free surface to maintainsaid portion continuously. and completely covered with electrolyte solution to an extentadequate to ensure that plating occurs thereon, (6) a source of air'connected to said sparging pipe, (7) a pump for recirculating a portion of said electrolyte solution, (8) a filter through-which said electrolyte solution is passed to remove solid particles therefrom, (9) means for heating said electrolyte solution, .and 7 (10) means for impressing anelectric potential across said anode and saidcylinder;
References Cited UNITED STATES PATENTS 1,249,787 12/1917 Leuchter ..f204. 277 1,423,815 7/l922 -Park 204-277 1,473,060 11/1923 Taylor 204 -277 1,884,512 10/1932 Ballard 204-25 2,155,392 4/1939 Ballard 204 25 2,435,872 2/1948 Coulson 204 -25 FOREIGNPATENTS 873,926 3/1954 Germany "f204- 2'5 631,672 4/1963 fBelgium '204- -212 JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner US. Cl. X.R.