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Method for treating brass

a brass and brass technology, applied in the field of brass treatment, can solve the problems of limited lead leaching from brass plumbing components, affecting the strength, workability and machinability of the final alloy of brass, and affecting the strength of brass added to the final alloy,

Inactive Publication Date: 2003-05-29
THE FORD METER BOX COMPANY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0004] Lead exhibits a relatively low solubility in solid solution in brass alloys due to the atomic size of lead atoms which is larger than copper or zinc. The low solubility of lead in brass alloys causes the lead to precipitate in lead-rich regions dispersed throughout brass alloys. The tendency toward precipitation is particularly notable near the surface of brass articles. In addition to improving the machinability of brass adjacent to the surface, the precipitation of lead near the surface increases the tendency of lead present on the surface to leach into water.
[0008] The present disclosure provides a simple, relatively efficient process for treating brass which removes leachable lead therefrom.
[0014] According to theory, chelating agents possess acid-base characteristics and chelation is an equilibrium reaction. Accordingly, during the course of the present invention, the inventors found that using high pH solutions in conjunction with chelating agents improved the removal of lead from brass articles.
[0024] A post-treatment bath containing either thiourea or sodium persulfate was determined to reduce the metal oxide present on the brass parts that were darkened by the primary treatment bath. A thiourea or sodium persulfate post-treatment bath containing thiourea and ammonium chloride or sodium persulfate, respectively, having a near neutral pH of about 6 or 3, respectively, was found to be particularly useful.
[0025] In an alternative embodiment, an application of hydrogen peroxide can be used either as a pre- or post-treatment to the caustic / EDTA treatment. In this embodiment, the use of hydrogen peroxide, as a treatment bath, for example, can assist to produce an evenly colored part appearance. It is appreciated that in one embodiment the hydrogen peroxide may be used in lieu of the persulfate.

Problems solved by technology

The amount of lead added to brass affects its strength, workability and machinability of the final alloy.
For such uses, the amount of lead that is required to affect the desired strength machinability of the brass causes concerns with the leachability of the lead into the environment where such faucets, valves, fittings and related products are used.
Recent standards have significantly limited the acceptable amount of lead that can be leached from brass faucets, valves, fittings and related products.
While the amount of lead that can be leached from brass plumbing components is generally low, it is nonetheless possible that the amount of lead that can be leached from such components may exceed current or planned standards.
Brass articles that are treated with a caustic such as sodium hydroxide have an appearance that may not be acceptable in the brass fixture industry.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 2

[0034] Brass articles that are treated with sodium hydroxide have an appearance that is not acceptable in the brass fixture industry. The uneven brownish-black appearance produced during treatment in the primary treatment bath is believed to be a copper oxide layer. In this example formulations for a post-treatment bath that would restore the brass appearance without compromising the leachable lead content that was reduced by the primary treatment bath were evaluated.

[0035] Initially a thiourea post-treatment bath that contained acid components (sulfamic acid and hydrogen chloride) was tested. This bath composition was found to create excessive effervescing of the brass articles due to hydrogen gas that evolved as the acid dissolved the brass, exposing a fresh layer of lead. Such newly exposed lead was determined to be susceptible of further leaching. Accordingly, it was decided to remove the acid components from the post-treatment bath.

[0036] As a result of experimental testing, a ...

example 3

[0038] Having established that smaller brass parts could be effectively pretreated with an aqueous solution containing citric acid and sodium persulfate, followed by treatment in a caustic solution containing EDTA while subjected to 40 kHz ultrasonics, further testing was conducted to determine whether this treatment scheme could be used to treat an array of brass articles, including larger brass parts.

[0039] In this example, eight different articles having a total combined weight of about 30.5 pounds were treated to mimic conditions for a full scale treatment operation. Information on each article is provided in Table 1 as follows:

1 TABLE 1 Internal Volume Part Letter Part Name Weight (lbs.) (liters) A 3 / 4" Key Meter 1.7 0.023 Valve B 3 / 4" Ball Meter 2.0 0.024 Valve C 3 / 4" Check Valve 1.3 0.051 D 1" Ball Meter Valve 3.1 0.032 E 3 / 4" Ball Valve 1.9 0.022 Curb Stop F 1" Pack Joint Nut 2.7 0.088 G 2" Angle Meter 9.4 0.22 Valve H 2" Ball Valve Curb 8.4 0.25 Stop

[0040] In this example, ...

example 4

[0048] In this example nine 2 inch check valves weighing 9.1 lbs. each were consecutively pretreated for 30 seconds in a single 5 liter aqueous bath containing 10% citric acid 10% sodium persulfate. Following pretreatment, each check valve was rinsed in a separate 3 liter bath of deionized water.

[0049] Each check valve was then consecutively treated in a 16.2 liter caustic / EDTA bath (5% NaOH, 1% EDTA) for the following time increments 20, 40, 60, 60, 40, 20 40, 60, and 20 minutes while undergoing sonication at 40 kHz. Following treatment, each check valve was rinsed in a separate 3 liter deionized water bath for 5 minutes.

[0050] Total metal removed was calculated from samples of the treatment bath and subsequent rinse bath. These values which are given as mg. metal / lb. brass are listed in Table 4.

4 TABLE 4 Treatment Duration (min) Lead Copper Zinc 20 64.5 10.7 2.2 40 92.7 12.6 2.9 60 77.9 12.1 2.7

[0051] The average mass of metal removed per pound of brass (mg. / lb.) treated was compa...

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Abstract

Brass articles having leachable lead are contacted with an aqueous caustic solution that contains a chelating agent. A brass article can optionally be post-treated by contacting it with an aqueous solution containing hydrogen peroxide.

Description

[0001] The present application is related to and claims priority as a Continuation-in-Part to U.S. patent application Ser. No. 09 / 652,799, filed on Aug. 31, 2000, entitled METHOD FOR TREATING BRASS. The present application is also related to and claims priority as a Continuation-in-Part to U.S. patent application Ser. No. 10 / 217,190, filed Aug. 12, 2002, entitled METHOD OF TREATING BRASS, which is a Continuation-in-Part to U.S. patent application Ser. No. 09 / 795,551, filed Feb. 28, 2001, now U.S. Pat. No. 6,432,210, entitled METHOD OF TREATING BRASS, which is a Continuation-in-Part to U.S. patent application Ser. No. 09 / 652,799, filed on Aug. 31, 2000, entitled METHOD FOR TREATING BRASS. To the extent not included below, the subject matter disclosed in those applications is hereby expressly incorporated into the present application.[0002] The present invention relates to a process for treating brass. More particularly, the present invention is directed to a process of removing lead ...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B08B3/12C23F1/00
CPCC23F1/00B08B3/12
Inventor COTE, EDWARD L.WENZEL, ANDREW D.AGNESS, LANCE E.
Owner THE FORD METER BOX COMPANY