United States Patent Office Patented Nov
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3,537,896 United States Patent Office Patented Nov. 3, 1970 1. 2 mined that such a reducing chemical tends to damage the 3,537,896 Surface of a protective film on the surface of the work BENEFICIAL AFTER-TREATMENT OF WORKPIECES piece from the standpoint of lessening its corrosion re Walter Nohse, Lippstadt, Westphalia, and Gunter Fischer, sistance, susceptibility to finger marking, etc. It was dis Kaarst, Rhineland, Germany, assignors to Lancy covered that these chemicals and various other reducing Laboratories, Inc., Zelienople, Pa., a corporation of chemicals tend to cause damage, both to fully exposed Pennsylvania metal Surfaces as well as to a somewhat insoluble con No Drawing. Filed Sept. 23, 1968, Ser. No. 761,866 version coating, for example, in the nature of a gel type nt. C. B08b 7/04 of Surface film containing hexavalent and trivalent chro U.S. C. 134-13 8 Claims mium. It has been determined that there is a need for an 10 approach to the problem which would enable the reduc tion of the valence of soluble metal compounds, without ABSTRACT OF THE DISCLOSURE at the same time, damaging any surfaces of or protective Workpieces being moved from a surface conditioning, film on surface of the workpieces with which the solu treating Zone or bath involving chromating or dichromat 5 tion may come in contact. ing to provide a chromate conversion coating on zinc, It has thus been an object of the invention to provide a cadmium, silver, aluminum or chromium, a pickle on new and improved form of an aqueous reducing or "after' magnesium, a chromate seal on aluminum, or a chromate treating solution that may be effectively used in and be film on copper or brass, or acid pickling or etching of compatible with a continuous in-line process for work copper and cuprous alloys, or acid plating, have the 20 pieces, and, at the same time, which will accomplish its carried-over treatment liquid (drag-out) subjected to a functions in such a manner that a protective film formed valence reducing solution treatment prior to neutraliza on the metal Surfaces will remain thereon in undamaged tion or removal of its toxic content in such a manner condition to protect the workpiece during the subsequent as to avoid damage to the metal surfaces or to a gel type neutralization of its carry-over and further processing of film thereon containing both hexavalent and trivalent 25 the workpiece, whether of a mechanical or chemical chromium. In addition to finally rendering any toxic nature; carry-over innocuous, after-treatment desirably first re Another object of the invention has been to solve the duces higher valence soluble metal compounds, such as problem involved in providing a reducing solution or those of chromium or copper compounds to facilitate chemical which will be effective in lowering the valency later precipitating out and settling the metals. Hydrazine 30 of copper and chrominum ions dissolved in a waste treat hydrate is used in the reducing, after-treating solution. ment solution and without imposing undesirable limita tions on the process or damage to surfaces of the work pieces; This invention relates to an improved method of reduc A further object of the invention has been to enable an ing toxic chemical compounds that are carried over as a efficient and effective direct application of reducing treat liquid film on workpieces that have been previously sub ing solution to carry-over or drag-out liquid on a previ jected to treatment in a chromium or copper ion contain ously treated workpiece, without damage to the surface ing surface treating solution bath. of the workpiece, and to facilitate precipitating or settling A phase of the invention deals with reducing soluble out of insoluble metal compounds therefrom; carry-over compounds to lower valences in such a man 40 These and other objects of the invention will appear ner as to enable a continuous in-line treatment of work to those skilled in the art from the description and the pieces, prevent damage to the surfaces of the workpieces, claims. and better convert soluble metal compounds into insoluble Heretofore, it was thought to be necessary to provide compounds of relatively high density form to aid fast fast acting reducing compounds for converting hexavalent settling or precipitation of insoluble metals. 45 chromium into trivalent chromium or for reducing copper U.S. Pat. No. 2,725,314 discloses a continuous in-line oxides on metal surfaces in a continuous or in-line treat treatment for aqueous toxic carry-over or drag-out solu ment process. Also, a relatively high excess above a tions, wherein such carry-over liquid may be continuously stoichiometric quantity is needed to assure the comple and effectively removed from or neutralized on the sur tion of the desired reactions. While it has been desir faces of workpieces during movement through treatment, 50 able to reduce chromic acid or chromate compounds and wash and other baths. There has been a need for a better copper hydroxides in the wet film carried by the work approach to reducing the chemical compound content pieces as a drag-out solution from the previous treatment of a carried-over liquid or aqueous solution in such a bath, harm must not be imparted to the surface finish manner as to fit in with the continuous process of the whether of a chromium or copper type. Ordinarily, fast above-mentioned patent and to enable an effective valence 55 reaction types of reducing chemicals and as used in ex reducing chemical reaction on the chemical content of cess have been found to cause such damage. drag-out or carried-over liquid, without damaging the The invention deals with the provision of an aqueous previously treated surfaces of the workpiece and in an treatment solution of a reducing nature which, although effective manner such that subsequent chemical neutraliza of a rather strong reducing type, will enable continuous, tion of the carry-over may be accomplished without inter 60 in-line movement of but will not cause damage to the rupting continuous movement of the workpieces or nec surface of the workpiece as when solution comes in con essitating a disruption of an in-line movement thereof. tact therewith or is used directly on such surfaces as Experimental work has been done in connection with a applied to the toxic solution carry-over thereon. The treatment solution containing a reducing chemical such as problem is to substantially fully reduce and precipitate sodium hydrosulfite or sodium bisulfite, but it was deter chromates and chromium compounds in a drag-out solu 3,537,896 3 tion disturbing, destroying or adversely changing protec Surface. On the other hand, a similar film is completel tive compounds formed as an adherent film on surfaces ruined in one minute if immersed in a treatment solution of the workpiece. The surface film is a somewhat fragile, of equal concentration having an excess of a conven extremely thin chemical coating consisting of various tional reducing chemical, such as sodium bisulfite or chemical compounds as reaction products with the metal sodium hydrosulfite. It was further determined that hydra surface, itself. Thus, such a film is called a "conversion zine hydrate, as applied in such a solution, only acted coating' since an outer metal surface is converted from on the drag-out or carry-over and not on the surface of a metallic to a partially or completely chemical film. the metal workpiece, whether or not it has a protective A chemically formed film such as previously mentioned film or is fully exposed as pure metal. is usually very thin and may be visible or invisible de Thus, in accordance with the present process, work pending upon its content. For example, zinc, cadmium, O pieces may be moved directly from a toxic treatment Zone aluminum, and magnesium chromate films are visible or bath into and through an "after' treatment bath or while films such as formed on copper and brass may be Zone, utilizing a solution of the present invention and in invisible. Even the visible films are more often in the such a manner as to fully convert the soluble metal range of only a few Angstroms such that they provide 5 content of the carry-over or drag-out into a lower valence interference fringes rather than noticeable color. carry-over or solution. The "after treatment solution The invention deals principally with copper and its may be circulated between a bath, Zone or container in alloy films as well as chromate conversion films on various the workpiece treatment line that follows the chemical metals such as zinc, cadmium, aluminum, magnesium, treatment bath, zone or container and a treatment reser copper and cuprous alloys, silver, tin, etc. As above indi 20 voir. Additional hydrazine hydrate may be added to the cated, such chromium films are basically reaction prod solution in a hold or treatment reservoir as needed and lucts of the metal surface with the chromate chemical above a stoichiometric amount before the aqueous re and consist of a variety of hydrated metal chromates, ducing solution is returned as reconstituted to the “after' depending on the basic metal, for example, zinc chromate, treatment bath. The movement of the reducing solution cadmium chromate, etc. Such films may consist of pre 25 with its drag-out solution content is progressive to the cipitated reduced chromium salts also in hydrated form. hold reservoir as is the movement of the reconstituted It appears that the metal chromates, whether in the form reducing solution being returned from the reservoir to of a visible or invisible film, are both absorbed and ad the after treating bath or zone.