Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-12-21
2001-02-27
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S237000, C204S240000, C204S271000, C204S275100, C204S276000, C204S277000, C204S278000, C118S303000, C118S407000, C118S417000
Reexamination Certificate
active
06193858
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the use of spouted beds of particles, pieces, parts and other small objects for the treatment thereof in a liquid or gaseous fluid. The invention has particular application for the electroplating of small parts which are difficult to plate by conventional means. The invention also has application in the fields of wastewater treatment, electrowinning, electrochemical synthesis, anodic electrochemical smoothing, anodizing, electrophoretic polymer coating, and physical coating, as well as in the general field of spouted bed applications.
BACKGROUND OF THE INVENTION
Barrel plating in which objects are tumbled in a perforated horizontal rotating drum is a common method of electroplating small parts. Representative technology is disclosed in U.S. Pat. No. 4,822,468 by Kanehiro and U.S. Pat. No. 4,769,117 by Shino, et al. Many very small parts cannot be plated effectively in a barrel due to poor contact with the current feeder or fouling on the interior of the drum. These problems often necessitate the addition of plating media (typically some type of smooth metal shot) to the barrel to improve cathodic contacting and part motion.
The use of media significantly increases the required plating time and current because the media is also plated and therefore, the plating cost per part is increased. Additionally, many small parts are fragile or can interlock and may be damaged by tumbling with heavy media. Consequently, these parts cannot be plated successfully in barrels.
U.S. Pat. No. 5,487,824 by Greigo discloses an integrated electroplating system designed specifically to electroplate very small parts which employs a horizontal accelerating rotating drum to maintain a packed bed of parts in motion during electroplating.
U.S. Pat. No. 3,654,098 by Backhurst et al. and U.S. Pat. No. 3,703,446 by Haycock et al. disclose fluidized bed cathodes. Although fluidized beds have excellent liquid-solid contacting, fluidized bed cathodes suffer from poor electrical contact between the fluidized particles, non-homogeneous electrical potentials and particle segregation effects. Additionally, it is difficult to maintain the entire bed fluidized when the particles are changing in size, and possibly density, due to metal deposition. It is unlikely that the potential benefits of the fluidized bed approach will be realized in a practical electrodeposition system.
Typical spouted beds consist of a cylindrical vessel with a conical bottom section. The vessel contains a bed of particles which form the spouted bed. Fluid is introduced into the spouted bed vessel at the bottom of the conical section as a jet. This fluid jet penetrates the bed of particles contained in the spouted bed vessel, entraining particles and forming a “spout” of upward moving particles and fluid. The particles disengage from the fluid flow in a region above the particle bed and then fall on top of the downward-moving annular bed. The “pumping action” provided by the spout circulates the particles through the vessel in a torroidal fashion; upwards in the spout and downwards in the annular moving bed. A “draft pipe” may be incorporated into the vessel to assist in the fluid transport of the particles. The draft pipe consists of a tube which is fixed coincident with the location of the spout, directly above and aligned with the liquid jet. The draft pipe delays the dispersion of the liquid jet and allows particle transport over a broader range of fluid velocities while also stabilizing the liquid flow.
U.S. Pat. No. 4,272,333 by Scott discloses the use of a moving bed electrode (MBE), in which conductive particles move downward vertically in a packed bed between two electrodes, the anode being shielded with a membrane. The necessity of using a membrane to shield the anode makes this configuration less attractive for practical applications, since the mechanical abrasion of the moving bed of particles can damage the membrane in a short time. Additionally, metal deposition on the membrane may be a complication.
An article by Hadzismajlovic et al. published in
Hydrometallurgy
, Vol. 22, pages 393-401 (1989), and U.S. Pat. No. 1,789,443 by Levin disclose the use of spouted bed cathodes with anodes suspended above the spouted bed surface. Although this configuration may eliminate the complication of shielding electrodes using membranes, several operational problems may be encountered with this configuration. Many electrolytes have poor electrical conductivity; therefore, it is advantageous to have the cathode and anode in close proximity in order to reduce the voltage drop over the cell. This cannot be accomplished in these prior art systems, since the spout would collide with the anode. Additionally, the projected spouted bed geometric surface area is very limited, impairing electrode performance.
Conventional spouted beds also suffer from a particle recirculation problem commonly referred to as “dead spots”, where a portion of the particle bed is stagnant. Dead spots usually exist at the outer edge of the spouted bed surface and are attributable to a failure of the spout to deposit particles at the circumference of the spouted bed. In an attempt to remedy this problem, spouted beds with very steep bottom cone angles have been adopted. In all cases, the radius of the spouted bed has been strictly limited to the distance to which particles in the spout can be transported radially outward by the fluid flow.
SUMMARY OF THE INVENTION
In the present invention, a distribution shield consists of a solid conical section extending from the vicinity of the upper edge of a draft pipe downward and radially outward towards the vessel sidewall above or beyond the outer edge of a downwardly moving packed bed surface, and is used to convey parts, pieces, particles or other small objects to the outer edge of the spouted bed by preventing the objects from falling near the center of the spouted bed surface. Instead, the objects disengage from the spout and are deposited on the upper surface of the distribution shield. The objects then move along the top surface of the distribution shield until they are deposited at or beyond the outside edge of the moving bed surface.
Use of the distribution shield totally eliminates stagnant areas at the circumference of the spouted bed. Moreover, the distribution shield allows very large diameter spouted beds to be constructed at modest fluid flow rates, since it is no longer necessary to transport objects to the spouted bed circumference dynamically via the fluid flow. Additionally, when a distribution shield is used, large diameter shallow spouted beds with shallow bottom cone angles may be employed. In this type of bed, the motion of the objects is more radially inward rather than downward. This type of spouted bed is particularly advantageous for circulating fragile objects where the weight of a deep bed may crush or break the objects and is particularly useful for spouted beds of conductive or partially conductive parts used as high performance electrodes where large projected areas and shallow bed depths are desirable.
A portable electroplating apparatus, which incorporates a pump and a vessel which defines a spouted bed electrolytic reaction chamber, is also provided by the present invention. The portable electroplating vessel can be conveyed from process tank to process tank by hand, automated plating system, or hoist. The spouted bed vessel is mounted on a platform with the pump to provide the necessary electrolyte flow for the spouted bed chamber. It is advantageous to incorporate a liquid by-pass circuit and adjustment valve so that the liquid flow to the spouted bed chamber can be adjusted. It is also desirable for the spouted bed vessel to be easily detachable from the portable apparatus and also for the internal components to be easily detachable from the vessel to facilitate parts unloading.
In a further modification of the invention, each process tank may be equipped with a corresponding pump and control valve having a coupling or docking station to which the
Hradil Edward
Hradil George
Pollock Vande Sande & Amernick
Valentine Donald R.
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