Vibratory plating method
This application is a divisional of application Ser. No. 16,144, filed Feb. 28, 1979. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vibratory plating method which improves plating efficiency by vibrating a plating container with plating liquid therein to maintain a uniform concentration of metal ions in the vicinity of cathodes. 
     2. Description of the Prior Art 
     In a conventional plating method using a barrel, workpieces are inserted in a plating liquid in the barrel and the barrel is rotated or rocked to bring the workpieces into sliding contact with cathodes and subject the workpieces to electrodeposition. Barrel type plating methods include one using an open-top bottle type barrel which is rotated while being inclined, and another one using a rectangular or cylindrical barrel having small apertures in the entire wall thereof and being horizontally disposed in a plating liquid, and rotated or rocked to agitate the plating liquid to effect the plating of the workpieces. In the use of an inclined barrel type plating apparatus, the temperature and the concentration of the plating baths are frequently subject to changes, the insertion and withdrawal of workpieces cannot be easily carried out, and anodes having a large surface area cannot be employed. 
     In the horizontal barrel type plating method using a horizontal barrel type plating apparatus, an electric current flows through small apertures in the side wall of the barrel. Thus the plating container requires a far higher voltage than the plating container used in other plating methods in which workpieces are suspended in a plating liquid. As a result, a large amount of energy is consumed, and sparks jump across the contacts of cathode lead wires and workpieces so that the surfaces of workpieces are burnt or have holes made therein by burning. In addition, the power source and other parts will often be damaged and the plating operation cannot be conducted smoothly in many cases. 
     Plating with 3-4 microns of nickel cannot be carried out efficiently in a horizontal barrel type plating apparatus or it usually requires 60 to 90 minutes of electrodeposition even if the diameters of the apertures in the side wall of the plating barrel are increased. In addition, the amount of plating liquid removed from the plating barrel in a method using this apparatus is larger than that in a widely used plating method carried out with workpieces suspended in a plating liquid. This causes the composition of the plating bath to be changed. In other words, quality control cannot be carried out easily. The large amount of plating liquid removed from the plating barrel has caused trouble in the treatment of the waste water which is necessary for preventing the occurrence of environmental pollution, and has adversely affected the economy of the plating process. 
     These conventional plating processes have many other drawbacks in addition to those described above. They have a low productivity and the apparatus used requires a large floor space. Consequently, the quantity and dimensions of the workpieces to be plated are limited. In fact, the conventional barrel type plating processes have many problems yet to be solved including the above-mentioned problem of treatment of the waste water. Namely, in a conventional barrel type plating method, the plating of workpieces cannot be satisfactorily carried out unless they are soaked completely in a large amount of plating liquid while being rotated or rocked. Moreover, the coating plated on the workpieces does not have a uniform thickness on each part of the surfaces because of sufficient agitation of the plating liquid. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to eliminate the drawbacks described hereinbefore in connection with the conventional plating methods. 
     Another object of the present invention is to provide an ideal vibratory plating method in which only a plating liquid and workpieces are placed in a vibratory plating container and an electric current is applied to the plating liquid for carrying out the plating process. 
     Still another object of the present invention is to provide a vibratory plating method which enables the carrying out of plating processes at a high efficiency which is double that of a conventional method, because the workpieces are rolled and displaced in the bottom portion of a vibratory container containing a quantity of a plating liquid which is equal to or less than a third that used in a conventional method. 
     Still another object of the present invention is to provide an improved vibratory plating method in order to provide a uniform coating thickness on all parts of the workpiece surfaces by imparting vibratory action to the plating liquid to agitate it sufficiently. 
     To these ends, the present invention provides a vibratory plating method comprising inserting workpieces and a plating liquid in a plating container, and applying an electric current to the plating liquid while vibrating the plating container so as to cause the workpieces to be plated as the workpieces are rolled and moved independently of one another along the plating container. 
     The above and other objects as well as advantageous features of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a duplex tub type vibratory plating apparatus; 
     FIG. 2 is a cross-sectional view taken along the line 2--2 in FIG. 1; 
     FIG. 3 is a plan view of an annular vibratory plating apparatus; 
     FIG. 4 is a cross-sectional view taken along line 4--4 in FIG. 3; 
     FIG. 5 is a plan view of a core-less vibratory plating apparatus; 
     FIG. 6 is a cross-sectional view taken along the line 6--6 in FIG. 5; 
     FIG. 7 is a plan view of a spiral vibratory plating apparatus; and 
     FIG. 8 is a front elevational view of the plating apparatus shown in FIG. 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The parts, workpieces, and arrows showing the directions of the flow of the mass in a plating container, which are common to all of those drawings, are represented by the same reference numerals. 
     Referring to FIGS. 1 and 2, tubs 3a and 3b are mounted on springs 2 which are provided on a base 1. Unbalanced weights 6a and 6b are secured to the opposite ends of a shaft of a vibratory motor 5 disposed between the tubs 3a and 3b. Anode plates 9 covered with films 10 are immersed in a plating liquid 12 in the tubs 3a and 3b, the inner surfaces of which are lined with electrically insulating members 7 made of rubber, vinyl, or urethane. These anode plates 9 are secured to lids 13. Cathode plates 8 are disposed on the opposite side facing the anode plates 9 in the tubs 3a and 3b, and are secured to the lid 13 in the same manner as the anode plates 9 with the upper end portions thereof projecting out of the tubs 3a and 3b. Conductors from an external power source (not shown) are connected to the anode plates 9 and cathode plates 8 so that an electric current can be made to flow therethrough, respectively. A plating liquid is contained in the tubs 3a and 3b. Workpieces 11 in the plating tubs 3a and 3b to which an electric current is supplied may be free or fixed to the cathode plates 8. The workpieces 11 gathered in the bottom portions of the tubs 3a and 3b are rolled and circularly transferred individually and independently of one another as shown by the arrows 14 (in FIG. 2) when the vibratory motor 5 is driven. This causes the density of ions around the workpieces 11 to be uniform at all times, and the workpieces 11 can be plated uniformly at a high speed. In this case, the general movements of the contents of the vibratory plating tubs 3a and 3b are affected by the lead angle of the unbalanced weights 6a and 6b. When there is no lead angle between the unbalanced weights 6a and 6b, the contents of the tubs 3a and 3b are circulated (in one direction) in planes at right angles to the axis of the tubs 3a and 3b as shown by arrows 15 in FIG. 1. When a lead angle of approximately 15°-90°, preferably 30°, is provided in the direction of rotation of the contents of the tubs 3a and 3b to the unbalanced weight 6b to move the same to a position 6 c after a plating process has been completed, the contents of the tubs 3a and 3b are moved with a spiral motion of a large pitch in the direction of the arrow 15a, and are discharged from discharge ports 17a and 17b. Discharged workpieces 11 are fed into a receptacle 24 via a screen 18 and an outlet 19, while the discharged plating liquid is collected in a tank 20 disposed under the screen 18. The liquid collected in the tank 20 then flows into a conduit 21 connected at one end to the tank 20 and at the other end to the tubs 3a and 3b, and is filtered in a filter 22. The filtered liquid is then returned to the tubs 3a and 3b by means of a pump 23 for use with the next cycle of the plating process. 
     In the apparatus shown in FIGS. 3-8, the contents of a bowl 3 are circulated in planes including the vertical axis thereof. When a lead angle of 15°-45°, preferably 30°, is given to a lower unbalanced weight 6a in the direction of rotation of the contents of the bowl 3 with respect to an upper unbalanced weight 6b, during the plating operation workpieces are independently rolled and transferred as indicated by arrows 14a, 14b and 14c and the general contents of the bowl 3 are circulated with a spiral motion of a small pitch as indicated by arrows 15b, 15c, and 15d. In order to separate the workpieces after the plating operation has been completed, a lead angle of 60°-120°, preferably 90°, in the direction of rotation of the contents of the bowl 3 is given to the lower unbalanced weight to impel the contents of the bowl 3, and the contents are moved with a spiral motion of a large pitch as indicated by the broken-line arrow 15a. A lead angle of 15°-45°, preferably 30°, to be given to the lower unbalanced weight may then be chosen for the plating operations. On the contrary, a lead angle of 60°-120°, preferably 90°, may be chosen for withdrawing the contents of the bowl after the plating operation has been completed. These lead angles may be utilized for automatically vibrating the plating liquid. In the case where workpieces are fixed to the cathodes, a movable weight for withdrawing the workpieces is not needed and in that case a fixed unbalanced weight may be used for causing the vibration of the plating liquid. 
     According to the present invention described above, the plating efficiency and plating rate can be improved by use of the vibrating container. Namely, according to the present invention, a large quantity of workpieces can be loaded at one time in a plating container, and the current efficiency can be improved since a container having small apertures in the wall thereof which shelters the electric current can be omitted. In addition, the workpieces in the plating container are vibrated so as to be rolled and transferred independently of one another and simultaneously circulated with a spiral motion of a small pitch as shown by arrows 15. This causes the density of ions around the workpieces to be uniform so that the plating operation can be speeded up. 
     Since workpieces are rolled and transferred whether a deflector 25 such as shown in FIGS. 3 and 5 is provided in the container 3 or not, any diffusion layer formed on the surface of cathodes during the electrolysis is thin. As a result, an electric current of a high density can be used. Therefore, the plating method using plating containers according to the present invention increases the productivity to a higher level. 
     In a conventional plating method using a plating container, the plating liquid is withdrawn through the apertures in the side wall of the container after the electrolysis process has been completed, and it has therefore been very difficult to withdraw the plating liquid completely. However, according to the plating method of the present invention, workpieces alone can be sent to the following step and thus, the quantity of the plating liquid removed from the plating container is greatly reduced. This means that the loss of the plating liquid can be kept to a minimum 
     In a generally used plating method in which workpieces are suspended in a plating liquid, it is the most troublesome at present to manually suspend the workpieces and remove the same. This troublesome step and the involved labor can be eliminated by use of the plating method according to the present invention. 
     In a generally used plating method referred to above in which a plating barrel is used, only comparatively smallsize workpieces are treated because with larger workpieces indentions are formed in the workpieces due to their violent impact with each other and the machine, and because of the limited mechanical strength of the machine to resist such impact. In the plating method according to the present invention, however, comparatively large workpieces, which are at present plated while being suspended from hooks, can also be treated in a plating container. 
     Unlike a conventional plating method using a plating barrel, the plating method according to the present invention transfers only plated workpieces to the next step, and accordingly, the plating operation can be automated. 
     Unlike a conventional plating method in which abrasive chips are used, the plating apparatus according to the present invention causes no decrease in current efficiency, and the plated surface of a workpiece is not contaminated with small fragments of abrasive chips. In fact, the present invention provides an ideal plating method which carries out a plating process at a high rate. 
     Plating materials usable in the method according to the present invention are mainly copper, nickel, zinc and chromium. An example of the present invention is shown and described below. 
     EXAMPLE 
     Apparatus: Tub-type vibratory plating apparatus. 
     Capacity: 2 liters 
     Plating liquid: Solution of nickel, 1.5 liter watt bath; and 2.5 g/liter of 1,3,6-naphthalene sodium sulfonate and 0.025 g/liter of 1,4-butyne diole as brighteners. 
     Test pieces: 2000 dry cell caps of 10 mm (dia.)×2.7 mm. 
     Frequency: 800-1500 cpm 
     Amplitude: 0.5-3 mm 
     Amperage: 4 A 
     Thickness of plating: 
     Target thickness: 5.3 microns 
     Average thickness obtained: 5.29 microns 
     The results of the experiment conducted under the above-described conditions are as follows. The variance of thickness of the plating on the test pieces is small. The plating time is reduced to half the time required in a conventional plating method. Manual suspending of workpieces can be eliminated. The surface of the workpieces is uniformly plated with the same thickness at all their parts. Even light workpieces like the test pieces used in this experiment can be uniformly rolled in the bottom portion of a vibratory container without floating. The plating operation can be conducted at a very high efficiency at a high current density. 
     The present invention is not, of course, limited to the above embodiments; it may be modified within the scope of the appended claims.