US2852410A - Use of titanium article support for hot dip galvanizing apparatus - Google Patents

Description

Sept. 16, 1958 R. H. BREWER USE OF TITANIUM ARTICLE SUPPORT FOR HOT DIP QALVANIZING APPARATUS Filed March 16, 1954 T '2 c l I v E m H HT W M; M k 0 1' W W 0 0A A m w I l AQ W J M v L k F1 J K 1/ WW w M n r. am Hm i 1 F. 6 oz 5% 4 WW d M M I I I I I I .|.l| I I I 7 7 Q 8 United States Patent USE OF ARTICLE SUPPORT FOR HOT DIP GALVANIZING APPARATUS Richard H. Brewer, Warren, Ohio, assignor to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Application March 16, 1954, Serial No. 416,665

1 Claim. (Cl. 117-51) The present invention relates to hot dip galvanizing apparatus, and particularly to structure for supporting articles being galvanized as they are immersed in a bath of molten zinc and in other baths, such as those commonly used in typical galvanizing processes.

In a conventional hot dip galvanizing process, the articles to be galvanized are placed on supporting structures, commonly hooks, attached to a suitable conveyor mechanism. The conveyor mechanism carries the articles sequentially over a series of tanks containing preliminary bath treatment mixtures and then over a tank filled with molten zinc. As the conveyor passes over each tank, the articles are lowered into the tank, both the articles and the supporting structure attached to the conveyor being then immersed in the liquid in the tank. A typical series of preliminary tanks includes: a pickle tank containing a solution of dilute sulfuric acid; a hot water rinse tank; and a flux tank containing a hot solution of zinc ammonium chloride. The hot zinc bath follows this series, and a final water rinse tank completes the apparatus.

Considerable time and eifort have been expended in the past in an efiort to find a material which may be used to construct the hooks or other supporting members mounted on the conveyor and which support the articles being galvanized. These hooks are subjected to repeated cycles of immersion in highly corrosive chemical solutions at high temperatures, followed by exposure to air and subsequent immersion in molten zinc. All these immersions and exposures tend to corrode and wear away the material of the hook or other supporting structure at a rapid rate. Certain materials have been found, e. g., Monel metal, which resist corrosion satisfactorily, but which are rapidly coated by the molten zinc. This zinc coating dissolves in the next passage through the acid 'bath, resulting in rapid contamination of the acid and consequent high acid consumption. Prior to the present invention, no material was known which would resist I corrosion and which would not pick up zinc.

which must be immersed in these solutions and in the molten zinc. The rate of corrosion of the solutions on these parts is definitely known, and the parts are designed with a suflicient thickness to give a certain duration of usable life. At the end of that time, the parts are discarded and replaced with new ones.

The metal titanium has been known for some time as having high corrosion resistance at low temperatures, but it has also been known as being very active chemically at high temperatures, and for that reason has been considered unsuitable for any application where it might be subjected to temperatures such as that encountered in exposure to molten zinc at 860 F. Furthermore, tests of titanium continuously exposed to molten zinc have shown that after several (-to 20) hours exposure, the titanium is attacked by the zinc, initially by the formation of a zinc coating. After a few more hours, an active corrosive attack takes place. Such tests tend to confirm the sus- 2,852,410 Patented Sept: I6; 1958 picion that titanium would be unsuitable for use in hot dip galvanizing apparatus:

However, a number oftestshave now-beenmadewith titanium supporting structures inconnectiom with timetioning-"hot dip galvanizing apparatus: It has been" found that, contrary'to all expectations; titaniumjhooks prepared for such purposes do not 'pick up-zinc andare' not corroded, even after repeated passage through the galvanizing cycle. The reason forthis unexpected resistance to coating by' the zincand to corrosion has notyet been definitely determined, but it isbelievedthat some sort of passivation actiontakesplace; either-as a resultjofdip= ping the titanium into the pickling and flux solutions, or as a result of the exposure of the titanium to the air between dips in the molten zinc.

In any event, regardless of theory, experience has shown that titanium parts when used in intermittent exposure to the acid and zinc baths of the galvanizing line, will withstand a far greater total time of zinc immersion than in a situation of continuous immersion, as mentioned above.

In the accompanying drawings:

Fig. 1 is a somewhat diagrammatic plan view of a hot dip galvanizing line to which the present invention may be applied;

Fig. 2 is an elevational view of a simple hook formed of titanium and usable in the hot dip galvanizing process in accordance with the present invention, and

Fig. 3 is a perspective view of a basket which may be formed of titanium for use in the galvanizing cycle to support parts being galvanized.

Referring to the drawings, Fig. '1 shows a pickle tank 1, a rinse tank 2, a flux tank 3, a galvanizing pot or tank 4, and a cooling tank 5.

A conveyor (not shown) runs along a path connected by the dotted line 6 and extends over each of the tanks 1 to 5. The conveyor includes equipment of a type well known in the art for lowering articles depending from the conveyor into the respective tanks as the article supporting structures pass over the tanks. The article supporting structure may take the form of a hook 7 as shown in Fig. 2, having a thread 7a on its upper end for attachment to the conveyor. The hook 7 is formed of titanium, for example titanium metal in forms which are commercially available and which may include minor alloying ingredients conventional in such metal.

'In a typical process, the book 7 and the articles to be galvanized depending from it are subjected to the following cycle:

(1) Immersion for 12 minutes in the pickle tank 1 containing a sulfuric acid solution having a strength of 12% by volume and maintained at 190 F;

'(2) A quick dip in a hot water rinse 2 also maintained at 190 F.;

(3) A quick dip in a flux tank 3, containing solution of zinc ammonium chloride, also maintained at 190 F. (This solution contains 300 pounds zinc ammonium chloride to gallons of water); i

(4) Three minutes drying in the air;

(5) Immersion in the molten zinc pot for thirty seconds. The zinc is maintained at a temperature of 860 F. and the top of the tank is covered with a 1" blanket of "ammonium chloride;

'( 6) A clip in cooling water at 99 F.

It has been found that the titanium hook used in the cycle described above shows no corrosion and no deposition of zinc on it even after repeated operation through the cycle.

Fig. 3 shows a basket 8 which may be formed of titanium and used to support parts being carried through a galvanizing cycle. The invention is equally applicable to other working parts which are subjected intermittently t0 the conditions in the several tanks of the galvanizing apparatus. Such parts to which the invention is applicable include, for example, cradles, chains or tools.

-I claim:

In a method of hot dip galvanizing, which includes the steps of moving a support repeatedly through a cycle including the steps of placing an article to be galvanized on the support, immersing at least a part of said support and the article supported thereon successively in a pickle tank containing dilute sulfuric acid, a flux tank 10 containing a solution of zinc ammonium chloride, and a tank containing molten zinc, thereby galvanizing the artiale, and removing the galvanized article from said support; the improvement which comprises using supports formed of titanium so that said supports may be moved repeatedly through said cycle without being attacked sub- References Cited in the file of this patent UNITED STATES PATENTS Watrous July 13, 1920 Pheem et al Aug. 29, 1950 OTHER REFERENCES 15 March 15, 1949, pp. 9, 13, 14, 19, 20 and 21.

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