Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating predominantly single metal or alloy substrate of...
Reexamination Certificate
1999-12-01
2001-03-13
Bell, Bruce F. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating predominantly single metal or alloy substrate of...
C205S243000, C205S283000, C205S284000, C204S198000, C204S203000, C204S206000, C204S207000, C204S210000, C204S225000, C204S232000, C204S237000, C204S239000, C204S269000
Reexamination Certificate
active
06200452
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to hard chromium-plating of elongated metal members such as bars, tubular elements and the like, which are generally referred to below as “bars”, and more generally relates to a method and to an apparatus for the continuous electrolytic chromium-plating of bars with high-speed circulation of the electrolytic fluid, while the bars are fed through one or more chromium-plating anodes.
STATE OF THE ART
The currently known chromium-plating plants generally comprise a long chromium-plating anode, of varying shape, which is totally immersed into an electrolytic bath within a large chromium-plating tank capable of containing 1000-3000 or more liters of electrolytic solution, through which the bars to be plated are continuously advanced at a constant working speed; sealing sleeves or special gaskets prevent the liquid escaping from the chromium-plating bath in the region of through-openings for the bars specially provided at the opposite end walls of the tank.
The electrolytic solution is continuously or periodically renewed, by causing it to recirculate between the chromium-plating tank in which the anode is immersed and an additional tank separately arranged or containing the same chromium-plating tank.
In general the chromium-plating anode is totally immersed in the electrolytic solution, while maintaining substantially static conditions of the bath, both in the tank and inside the chromium-plating anode, with respect to the advancing bar to be plated.
Examples of chromium-plating apparatus of the kind mentioned above may be found, for example, in U.S. Pat. Nos. 3,751,344, 3,852,170, 4,419,194 and 4,466,618.
As already mentioned, in the apparatus known from the abovementioned patents large quantities of electrolytic solution are required in the chromium-plating bath, resulting in a high energy consumption in order to keep the electrolytic solution at the required temperature for chromium-plating each specific type of bar.
Moreover, in these apparatus of the known type, both owing to the substantially static condition of the chromium-plating bath, and to the dimensions of the anode and the chromium-plating tank, it is not possible to achieve precise control of the chromium deposition onto the bar as it advances, resulting therefore in a unhomogeneous depositing of chromium, and formation of deep cracks.
Finally, in chromium-plating apparatus of the known type, owing to the static condition of the chromium-plating bath, as well as the immersed disposition of the anode, it is possible to supply the latter only with low current densities, equal to or less than 30-50 A/dm
2
; all this limits the speed of advancing the bars through the chromium-plating anode, thereby conditioning the productivity of the plant.
Consequently, a conventional chromium-plating plant, in addition to being bulky and difficult to manage, is characterized by an extremely low productivity as a result of its constructional and functional characteristics.
In order to partly overcome these and other drawbacks, EP-A-0,259,922 suggests recirculating the electrolytic solution between a tank containing the chromium-plating bath, and the anode while maintaining inside the chromium-plating anode a flow direction which is substantially parallel to the longitudinal axis of the same anode and the bar to be plated.
According to certain embodiments illustrated in this document, the electrolytic solution is supplied from one end of the anode and discharged into a tank from the opposite end of the anode, so as to obtain the desired axial flow.
According to another embodiment, it is envisaged using a long anode supplied with electrolytic fluid at both its ends and provided, at the top with a central opening through which the electrolytic solution over flows, being collected in an underlying container.
According to a third embodiment, the electrolytic solution is supplied centrally to the anode and discharged into the tank at the two opposite ends of the said anode.
In all cases, therefore, there inside the chromium-plating anode, one or more axial flows of electrolytic solution will exist which move in the same direction or in the opposite direction of and parallely to the advancing bar.
Such a solution has proved to be unsuitable for the hard chromium-plating of bars since it does not provide homogeneous and constant temperature conditions of the bath over the entire length of the anode; in particular the flow of electrolytic solution which flows axially through the chromium-plating anode, tends gradually to heat up, being in contact with the bar over the entire length of the anode, thus involving non-uniform chromium-plating and chromium-deposition conditions over the whole length of the bars to be plated. Finally, owing to the impossibility of maintaining constant temperature conditions of the chromium-plating solution inside the anode, due to the considerable length of the latter, of about two or three meters, with these apparatus of the known type also, it is difficult or impossible to operate with high densities of the chromium-plating current and consequently increase the speed of the bars and the productivity of the plant.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a method and an apparatus for the continuous chromium-plating of bars, tubular elements or elongated members and the like, by means of which it is possible to adequately control the temperature of the bar in the chromium-deposition zone, or inside the anode, using the same electrolytic solution flowing through the anode to keep the bar temperature at a substantially constant and uniform suitable value over the whole length of the anode, which may be substantially reduced in respect to the anodes of known plants. In this way it possible to operate with current densities of about 150-400 A/dm
2
which are much higher than those of conventional apparatus, namely increase considerably the operating speed of the same plant.
A further object of the present invention is to provide a method and an apparatus for the continuous chromium-plating of bars by means of which it is possible to obtain uniform and controllable chromium-deposition conditions, over the whole length of the anode or chromium-plating zone.
A further object is to provide a method and an apparatus of the type defined above, by means of which it is possible to deposit several superimposed layers of chromium by a single pass of the bar through several anodes, while maintaining suitably controlled chromium-plating conditions.
Yet another object of the invention is to provide a chromium-plating method and an apparatus comprising several chromium-plating anodes in which the chromium-plating conditions of the bar in each anode may be varied and/or individually controlled, independently of the chromium-plating conditions in the other anodes of the same apparatus.
Another object of the invention is to provide a improved chromium-plating method and an apparatus both from the point of view of the quality of the chromium-plating obtained and from the costs and the time required to complete a chromium-plating operation of a bar having the required thickness of chromium layer or layers plated on the bar.
BRIEF DESCRIPTION OF THE INVENTION
The general principle which forms the basis of the present invention and which is substantially distinguishing from the chromium-plating methods and apparatus previously known resides in the use of a particular chromium-plating anode structure performing both the function of a container for a required quantity of the electrolytic solution which is necessary for chromium-plating and which may be continuously renewed by causing it to circulate at high speed as the bar is advanced longitudinally inside the anode itself, and the distributor function of the electrolytic flow solution inside the anode, as well as an effective control means for maintaining controlled and uniform temperature conditions of the bar during the entire chromium-plating process.
Therefore, according to a first aspect o
Bell Bruce F.
Young & Thompson
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