Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-06-27
2001-09-04
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S019000, C134S022190, C134S026000, C134S028000, C134S034000, C134S035000, C134S036000, C134S041000, C134S042000
Reexamination Certificate
active
06284053
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a selective deleading process and bath for plumbing components made of a lead-containing copper alloy. Particularly, the present invention relates to a process and a bath which enable a thorough elimination of the copper located on the surface of said components, without in the meantime altering the ratios existing among the other metals forming the alloys.
BACKGROUND OF THE INVENTION
Lead is known to be added in small quantities to copper alloys, such as brass and bronze, in order to favour machining and moulding operations of the pieces made of said alloys. As a consequence of the thermal and mechanical stresses due to the working operations, lead tends to segregate in small globules which emerge to the surface of the pieces. In the case of plumbing components for drinkable water distribution systems, such as taps and valves, this phenomenon is particularly undesirable, because by coming into contact with lead on the surface of said components, water is contaminated in a considerable measure often exceeding the limit of 10 &mgr;g/l recommended by the World Health Organization and laid down by the law in force in some countries, such as the NSF61 in force in USA.
The problem of lead contamination of drinking water has been already tackled and a few methods and processes for the treatment of the surfaces of taps and valves aiming to reduce the superficial lead thereof have been proposed.
EP 0 683 245 describes a process wherein the above mentioned components are treated with a water solution of an acid that forms with lead a substantially water-insoluble compound. The preferred acid for such a treatment is an oxy-acid of phosphorus, for example orthophosphoric acid.
In EP 0 695 833 is described a process based on the use of a two-component solution: the first component promotes the superficial lead dissolution and is formed of chloride ions, whereas the second one complexes the ions in solution, subtracting them to the equilibrium of the dissolution reaction and allowing thus more lead to dissolve. The latter function is performed by pyrophosphate ions.
Patent application WO97/06313 describes a process in two steps. In the first step the brass components are treated with a water solution of a non-oxidizing acid, chosen among sulfamic acid, fluoboric acid, methanesulfonic acid, fluosilicic acid, acetic acid and mixtures thereof, or alternatively are treated with a mixture of an oxidizing acid and a peroxide in water, preferably a mixture of citric acid and hydrogen peroxide. In the second step, which has the purpose of passivating the brass component surfaces, a basic solution of sodium hydroxide, sodium silicate or mixtures thereof having a pH within 10 and 13 is used.
Application EP 0 892 084 describes a single-step process, wherein the brass components are treated with the solution of a detergent and an acid, preferably acetic acid or nitric acid or a mixture thereof.
Patent application WO98/30733 describes another process in two steps. The first step consists in the treatment of brass components with a hot solution of sodium or potassium hydroxide, having a pH higher than 10 and suitable for removing dirt and residues from the casting of such components and for removing most of the superficial lead. The second step consists in dipping said components in a water solution of a carboxylic acid containing 1 to 8 carbon atoms and 1 to 4 carboxylic groups, preferably an acetic acid water solution, in order to complete removal of superficial lead.
Among said known processes, some solve the problem of lead contamination of drinking water by pushing the elimination of said polluting metal under the requested limit, but a consequent technical problem is generated, i.e. the alteration of the chemical composition of the alloy resulting in the deterioration of the treated piece. From the tests carried out, it is clear that the treatments made according to the teachings of said prior art patents provide for lead elimination, but at the same time also the other constituents of brass or bronze are attacked. Therefore, owing to these treatments, the alloy chemical composition is modified, resulting in a deterioration of the component aesthetic appearance. In some cases, even a change of the color of said components from yellow to red was noticed, indicating the increased copper percentage. However, none of the above listed patents considers the problem of selectivity in lead elimination.
SUMMARY OF THE INVENTION
Object of the present invention is providing a process for the thorough elimination of the superficial lead of plumbing components made with copper alloys which is free from said drawbacks. Said object is achieved according to the present invention by means of a traditional pickling process which is made selective by dipping the treated and washed pieces in a deleading bath before the usual finishing step. The main features of the deleading process according to the present invention are specified in the first claim and further features are specified in the following claims. Further, the present invention comprises a selective deleading bath whose features are specified in claim
7
and following claims.
An advantage of the deleading process according to the present invention consists in that it enables lead which is located on the surface of said components to be eliminated in a very thorough way, thus reducing lead release in water under the limit of 10 &mgr;g/l laid down by the strictest laws and in the meantime is substantially inactive towards the other metals forming the alloy.
Another advantage of the deleading process according to the present invention consists in that it can be successfully used not only in the treatment of brass, but also in that of bronze and of other metal alloys whose main constituent is copper.
An advantage of the deleading bath according to the present invention is the economicity thereof. In facts, it allows treating a large number of pieces by maintaining unchanged its effectiveness; as a result the use thereof involves a considerable economic gain with respect to the prior art.
Another advantage of the deleading bath according to the present invention consist in that it does not require the use of solutions containing fluorides or other highly dangerous substances.
Further advantages and features of the selective deleading process and bath according to the present invention will appear to those which are skilled in the art from the following detailed description of some embodiments thereof with reference to
FIG. 1
that graphically shows the variation of the lead and zinc quantities dissolved in the deleading bath as a function of the quantity of treated brass.
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patent: WO 98/30510 (1998-07-01), None
patent: WO 98/30733 (1998-07-01), None
Bonomi Angelo
Carrera Stefano
Franzosi Giuliano
Carrillo Sharidan
Michael & Best & Friedrich LLP
Ruvaris S.r.l.
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