US2008879A - Method of coating articles - Google Patents

Description

A. C. SIMMONS METHOD OF COATING ARTICLES l I p l l lJuly 23, 1935.

r A/f/l/.e-A/af? A. QSVMMoA/s BY hlwww Ano/wir 45 invention, one embodiment of anvv appara' means of which the method may be practiced, as

Patented y\July 23, 1935 UNITED sTATEs PATENT OFFICE comme.l (ci. en -mz) This .invention relates to a method of coating articles. and more particularlyto a method of hot galvanizing articles.

Itis common practice in galvanizing articles to provide a molten bath of zinc covered with a suitable fluxing material to prevent the zinc from oxidizing. The articles to be galvanized, particularly in the case of small articles, are placed in a perforated basket and dipped in the zinc bath ur' and before removing the basket from the bath the layer of flux, which may be several inches thick,

must be skimmed to one side to prevent it from coming into contact with and thereby contaminating the galvanized articles as they are resuch a heavy coating of zinc on the articles that usually, particularly in the case of screw threaded articles and other articles requiring close tolerance limits, other methods must be resorted to' after the articles have been dipped to remove the excess zinc therefrom in order to provide a smooth uniform coating and bring the articles within the desired tolerance limits. 1

It has been attempted to overcome the above mentioned diiculties'by adding various metals to the zinc bath to increase the uidity thereof, some of the metals added being aluminum, tin, antimony, bismuth, or a combination of these metals. When certain of these metals are added, 30 particularly aluminum, it becomes very diicult to maintain the proper immersion iiux on the surface oi' the bath. and the alloy becomes unstable when the surface is exposed to the reducing action. of the flux. 'Ihe addition of aluminum '35 also retards .the galvanizing operation because the zinc aluminum alloy does not adhere to ferrous metals as readily as unalloyed zinc, thereby prolongingthe time required to applya given thick-v ness of coating. l v 4 An object of this invention is to provide an improved method of coating articles in an expeditious and economical manner to provide a smooth, uniform coating.

In accordance with the general features f the by applied'to the galvanizing of small articles, comprises a molten zinc bath covered with a uxing material and a molten zinc aluminum alloy bath adjacent thereto, the alloy bath being maintained sufficiently full so that the fluid level thereof will be located above the level of the-zinc bath and arranged to overow into the zinc bath when the alloy is displaced upon the dipping of articles therein. In practicing the method l'a' basket of moved from the bath. This method also leaves.

method of this invention, and

articles to be galvanized is dipped into the zinc bath, where they acquire a heavy coating, and then withdrawn without skimming the flux from the surface of the bath and immediately dipped into the zinc aluminum bath adjacent the point 5 of overflow which serves to wash the articles of any excess zinc. carried thereon from the zinc bath, due to the-greater fluidity of the alloy bath, and gives the articles a smooth, uniform coating.

During the dipping of the zinc coated articles l0 I into the zinc aluminum bath the flux carried from the zinc bath floats to the surface of the alloy bath and the level of the latter bath is sufficiently raised so that the flux carried thereinto Iis washed back into the zinc bath. Before remov- 15 ing'the basket of articles from the alloy bath it is moved horizontally while immersed therein to another position farther away from the point of overflow to insure that none f the flux will come into contactwith the alloy washed articles as 20 they are withdrawn. f

Other objects and advantages of this invention will more fully appear from the following detailed description taken in connection with the accompanying' drawing which illustrates one embodi- 25 ment of an apparatus by means of which the method may be practiced, in which Fig. 1 is a diagrammatic side view, partly in section, ofan apparatus used in practicing the Fig..2 is a vertical section taken 2 2 thereof.

Referring tothe drawing, the numeral I0 inf dicates a galvanizing receptacle or tank containing a bath II of molten zinc, the level of 30 on the line -which is indicated at I2. 'I'he bath of zinc II is kept molten and at a desired temperature by any suitable heat applying means (not shown). AnyA suitable galvanizing flux, such as sal-ammoniac, indicated at I3, and which is several 40 inches thick, can be used on the surface of the zinc bath. Inserted in and adjacent one end of the tank I0 is a receptacle or tank I4 having upper side anges v I5 supported upon similar flanges I6 of the tank I 0 with its side, end, and 45 bottom walls spaced from the walls of the tank |u. The left end wan of the tank I4 is cut down so that its upper edge I 'I is below the upper edge .of the right end wall of the tank Il. 'I'he level I2 of the zinc bath II is kept suitably 50 below the upperedge I1 of the left end wall of the tank I4 so that the molten zinc will not flow into the tank I4.

A bath I8 comprising alsumcient volume of molten zinc aluminum alloy is maintainedrin the '55 l hereinbefore and the articles to be galvanized tank I4 so that when the alloy is displaced by the immersion therein of the articles tobe treated to be presently described, its iluid level, indicated at I9, will rise 'and overiio'w in the plane of the-upper edge I1 of the left endwall and wash theflux carried thereinto with the articles into the zinc bath II. the alloy bath I8 is not at -all critical but in practice from .2% to .1% faluminum is added, which makes the bath more fluid for a purpose made apparent hereinafter. While -in the -embodiment of the apparatus illustrated the alloy bath I8 is kept molten by the heat transmitted from the molten zinc bath II which surrounds the tank I4 individual heating means could be used for each bath and thus eliminate the1 attack'of zinc on the outside surface of the tank I4, which is of iron.

In practicing the invention, the baths II and I8 are first prepared in the manner described are placed in a perforated basket 'which is thensubmerged or dipped into the zinc bath II by suitable handling means, fragmentarily indicated at 2l, as shown at the left end of the tank Ill (Fig. l) The basket 20 is left submerged in Y the bath I I for a suitable period of time and then withdrawn without skimming the flux. I3 from the surface of the bath, with the result that a quantity of ilux will be left deposited on the up- -the plane of the upper edge I1 of the left wall v of the tank I 4, the'flux I3 carried along by the basket 20 from the zinc bath I I floats to the surface of the bath I8. -The immersion of the coat- `ed articles in the alloy bath -IIiraises the level I9 thereof suiiiciently to cause the ilux I3 thereon to -be Washed back into the zinc bath I1. Although the surface of the bath I8 is not at all times clear of the ux I3, since al1 of it may not be washed overthe edge I1, at each dipping of 4a basket 20 of coated articles, it will at least iloat over towards the edge I1 or the overow point, as indicated at 23.- After being submerged for a suitable period of time in the alloy bath .I8 at the position 22, the basket 20 of treated; articles is moved horizontally, while still Aimmersed in the bath, to a position indicated at24 farther away from the point of Overilow Where the surface of the alloy bath is free of the ilux I3, or other foreign matter, thereby insuring that none of the'ilux, or foreign matter, which may still remain-on the surface -of .the bath adjacent the edge I1 ofthe tank I4 will come-into contact with and contaminate the articles which havebeen treated and washed in the alloy bath when they are vWithdrawn therefrom. The bas ke't 20 of galvanized 'articles is'then withdrawn from the alloy bath I8 at the position 2l, which step completes the method of this invention.

I t is understood that although the excess zinc washed from thearticles in the. alloy bath I8 helps to maintain the latter bath full to overflowing when the articles are immersed therein so that it will b e effective to wash the ux into the zine bath II inthemanner above described.

The range ofaluminum init may be necessary at times to make suitable additions of zinc and aluminum to the 'alloy bath I8, particularly of aluminum, since some of the aluminum is` removed bythe ilux Washed into the .bath I I. The aluminum in the alloy bath I8 is a strong deoxidizing agent and tends to make the zinc quite uid so that there will be only a small excess of zinc, if any, on the objects when -they are withdrawn from the bath I8. Thus a very smooth and more uniform coating is imparted to articles .which have 'immediately preceding been given a galvanizing coating, and thereby permitting', particularly in the case of screw threaded articles and other articles, -the bringing of them within the desired tolerance limits. It will be understood that due to the deoxidizing .effect of the aluminum in the alloy bath, it is lnot necessary to have this bath covered by a flux. It will be obvious that in the method of galvanizing objects hereinbefore described wherein a' combination of a zinc bath and a zinc aluminum alloy `bath is employed articles may be expeditiously and economically treated as com'- pared'to the use of a single-zinc aluminum al1-oy bath, since the latter type of bath requires a abv tively small articles carried ina basket or other type of carrier, it should be understood that the :same is applicableto large articles With or with- 'the invention is also applicable to any case wherev it is desirable to immerse articles rst in a bath having a covering of flux and then into a bath requiring no ilux, assuming, of course, that the two baths are of such materials that a small portion of each maybe safely allowed to mix with the other bath.

What is claimed is: 1. A method of coating an article which comprises first passing the article through flux floating upon a bath of -molten metal and immersing -it in said bath, withdrawing the coated article therefrom andv moving it through the ux, vimmersing it in a second bath of molten metal which is'sufiiciently fulll to cause,iiux carried thereinto with the article and washed from the article to .be washed from the second bath in an oveilow thereof. when the article is immersed therein, and

then withdrawing the article from the secondv washed from the second vbath in an overflow thereof when the article is immersed therein, and then withdrawing the article from the second bath.

3. A method of coating an article which'com-v prises first passing the article through a lay'er of flux iioating upon a bath of molten metal and immersing it in said bath of molten metal, withdrawing the coated article therefrom and through the layerof flux, immersing it in a'second bath of molten metal which is sufficiently full t'o cause flux carried thereinto with the article and washed from the article to be washed from the second bath in an overflow thereof when the article is immersed therein, moving, the article while still immersed to a position removed from its'initial position of immersion, and then withdrawing the article from the second bath. l

4. A method of galvanizing an article which comprises first immersing thearticle in a bath of molten zinc having flux floating upon its surface, withdrawing the zinc coated article therefrom and through the flux, immersing it in a bath of molten zinc aluminum alloy which is sufficiently full to cause flux carried thercinto with the article and Washed from the article to be washed from the alloy bath in an overflow thereof when the article is immersed therein, and then withdrawing the alloy treated zinc coated article from the alloy bath.

5. A method of galvanizing an article which comprises first immersing the article in a bath of molten zinc having a layer of flux floating upon its surface, withdrawing the zinc coated article therefrom and through the flux, immersing it in a bath of molten zinc aluminum alloy which is sufficiently full to 'cause flux carried thereinto with the article and washed from the article to be Washed from the alloy bath into the'zinc'bath in an overflow of the alloy bath when the article is immersed therein, moving the article while still immersed to a position removed from its initial position of immersion, andthen wthdrawingthe alloy treated zinc coated article from the alloy bath.

6. A method of galvanizing articles in a bath of molten zinc having a flux thereon and a bath of molten zinc aluminum alloy which comprises immersing the articles in the zinc bath, withdrawiing the articles from the zinc bath and through bath to cause overflowing thereof to wash the flux removed from the articles from the second bath, and then withdrawingl the articles fromthe second bath.

'7. A method of galvanizing articles in a bath of molten zinc having a flux thereon and a bath' the flux, immersing the articles in the second'v overflowing of the second bath to wash the flux removed from the articles over the end of the second bath, andthen withdrawing the articles from the second bath. p

8. A method of galvanizing articles in a bath `of molten zinc having a flux thereon and a bath of moltenizinc aluminum alloy which comprises immersing the articles in the zinc bath, with-l drawing the articles from the zincfbath and through the ux, immersing the articles in the second bath adjacent anend thereof to cause overflowing ofthe second bath to wash the flux removed from the articles over the end of the second' bath and into the zinc bath, lmoving the articles while still immersed in the secondbath to a position removed from their initial position of immersion, and then withdrawing the articles from the second bath.

9. A method of galvanizing articles in a bath `of molten -zinc having a flux thereon anda bath of molten zinc aluminum alloy which comprises Y through the ux, immersing the articles in the second bath to cause overflowing thereof to wash the flux removed from the articles from the second b'ath, moving the articles while still irnmersed in the second -bath to a position removed from their initial position of immersion, and then withdrawing vthe articles from the second bath.

ANDREW c. sIMMoNs.v

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