Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
1997-11-19
2001-08-07
Ip, Sikyin (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S901000, C134S003000, C216S105000, C216S106000, C216S107000
Reexamination Certificate
active
06270590
ABSTRACT:
TECHNICAL FIELD
The present invention relates to low lead release plumbing components made of copper-based alloys containing lead, e.g lead brass components for potable water distribution circuits. The invention further relates to a method for obtaining the same by a selective surface etching thereof in order to either reduce or completely eliminate the labile surface Pb layer (almost exclusively consisting of Pb and/or Pb salts) responsible for the Pb release and representing the so-called Pb surface “smearing”.
BACKGROUND ART
Well known is the phenomenon leading to the creation of surface layers of metallic Pb (or of its salts), by segregation of Pb from the base alloy as a consequence of the thermal-mechanical stresses caused by reachining and or molding of brass alloy elements containing lead. Such a phenomenon is a particularly undesirable one, in that the creation of the said lead surface layer may easily cause, at work, the release into the environment of Pb ions, a heavy metal known to be highly polluting and toxic to human health.
On the other hand, plumbing components such as mechanic parts for cocks and valves designed to operate in potable water distribution circuits and systems, cannot but undergo, during the manufacturing process, a number of machine work operations (lathing, drilling, threading, etc.). Moreover, a Cu—Zn base alloy containing also limited amounts of Pb (generally up to 3-5% by weight) facilitates machine working and leads to more effective and accurate surface finish. Furthermore, besides facilitating machine working (it furthers chip-breaking), the presence of Pb is also instrumental to the elements forming process, whether the latter is carried out directly by smeking or by molding/die-casting.
The mechanism of Pb release has long been investigated and is based on the creation, on a zinc oxide surface layer, segregated from the base alloy, of Pb salts (hydroxycarbonates), due to surface stresses of the alloy as a consequence of both machining and shear stress during the molding process, and due further to Pb reactivity with water vapor and atmosphere carbon dioxide. It is however only very recently (March 1995) that a Certified testing procedure for evaluating the Pb release of plumbing components designed to potable water distribution has been approved and issued in print by the major United States Normalization Agency, i.e. N.S.F. The test procedure is known as U.S. NSF
STD61. It has been shown that the phenomenon of Pb release is largely present in the commercial components for potable water distribution of any type, even in those components wherein surface coating, for example chromium or nickel plating, is extensively carried out, for haestetical reasons, on all the surfaces in view: in fact, the phenomenon depends on those limited surfaces designed to remain in contact with water when the taps, cocks etc. are closed, which are internal surfaces not in view and, therefore, normally not coated and, anyway, very difficult to be coated properly.
SUMMARY OF INVENTION
The aim of the present invention is therefore to furnish low lead release components made of copper-based alloys, in particular brass plumbing components for potable water distribution circuits, which, at the same time, can be subjected to usual working operations, by machining and/or molding, without any drawback with respect to the known alloys containing lead.
The present invention accordingly relates to mechanical components made of a copper-based alloy and adapted to be subjected, during their production stage, to working operations carried out either by machining, molding or die-casting, in particular plumbing components made of brass alloys and designed for potable water distribution systems, characterized in that said copper-based alloy contains a predetermined amount of lead as an alloying element; and in that, in combination, respective surfaces of the components designed to be exposed, in use, to any fluid released in the environment, are substantilly free from lead and lead salts.
In particular, said components are designed to collect potable water therein and are able to release in synthetic drinking water, after 15 days of test according to U.S. NSF STD61, an amount of Pb of no more than 0.025 &mgr;g for each ml of the internal volume of the components delimited by metallic surfaces exposed to contact with potable water during testing.
It is also included in the invention, according to a further aspect thereof, a mechanical component made of a copper-based alloy containing lead, and subjected, during its production stage, to working operations carried out either by machining, molding or die-casting, in particular a plumbing component made of brass and designed for potable water distribution systems, characterized in that respective surfaces of said component, which surfaces are designed to be contacted in use by potable water, present, under XPS surface analysis, an atomic surface composition such that the surface content in Pb is lower than or equal to the content in Pb according to the nominal composition of the alloy.
The invention further relates to a method for obtaining low Pb-release metal components made of copper-based alloys containing lead and designed to be employed in water distribution systems, in particular lead brass plumbing components for potable water circuits, said method comprising the following steps:
a selective etching of surfaces of said components designed to be exposed, at work, to the water, for removing almost entirely the Pb and Pb salts present thereon as a consequence of a mechanical working and/or of molding/die-casting operations carried out onto said components; and
a passivation of said surfaces.
In particular, the selective etching step is carried out by exposing said surfaces to the action of a non-oxidizing acidic aqueous solution, of an acid capable of forming soluble Pb salts.
In particular, said acid is selected from the group consisting of: sulfamic acid, fluoboric acid, methanesulfonic acid, fluosilicic acid, acetic acid and mixtures thereof.
According to another embodiment of the invention, the selective etching step is carried out by exposing said surfaces to the action of an oxidizing acidic aqueous solution of an organic acid mixed with a peroxide. Preferably, the organic acid employed is citric acid and the peroxide is hydrogen peroxide.
Said passivation step follows said selective etching step and is carried out by exposure of said surfaces to the action of a basic aqueous solution, preferably a strong base aqueous solution.
Between said two steps, there is also provided for an intermediate rising stage.
Preferably, the basic aqueous solution contains a strong base selected from the group consisting of: NaOH, sodium silicate, and mixtures thereof; and the passivation step is carried out keeping the solution to a pH comprised between 10 and 13.
Said exposure operations are carried out, according to the invention, by simply dipping said components into said treating solutions; while said rising operations are carried out by immersion in tap water at ambient temperature. Moreover, during said exposure to the action of said solutions, said solutions are subjected to ultrasonic agitation, in order to hit said surfaces of the components with ultrasonic waves.
In so doing, the ensuing selective etching of the surface lead, segregated from the alloy, affects, however, neither alloy composition nor surface finish resulting from machining (or from any other kind of working) to which said components have been subjected. Said etching operation, therefore, causes the surface lead, segregated from the alloy, to be removed so that lead is no longer released, during operation, by the elements so treated. Moreover, the removed lead can be easily recovered from the etchant, for example, by electrolysis, particularly in the presence of acid aqueous solutions. The aforementioned process, therefore, guarantees high environmental safety.
The following passivating step, moreover, contributes to creation on the exposed surfaces of said comp
Europa Metalli S.p.A.
Ip Sikyin
Ladas & Parry
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