US2172933A - Galvanizing process - Google Patents

Description

J. R. DAESEN ET AL GALVANIZING PROCESS sept. 12, 1939.

Patented Sept. 12, 1939 GALVANIZIN G PROCESS John R. Dacsen, Oak Park, and Albert F. Bradley, Sterling, Ill., assignors to Northwestern Steel and Wire Company,

Application June 2l,

6 Claims.

This invention relates to process and apparatus .for galvanizing ferrous metal articles such as steel wire, strip metal and the like to provide a ferro-zinc alloy coating on the wire covered with a substantially pure zinc coating. More specifically the invention relates to the treatment of ferrous metal articles between zinc dips to increase the thickness of the ferro-zinc alloy coating on the wire.

When a ferrous metal article such as wire or the like is dipped in molten zinc baths at galvanizing temperatures between 850 to 900 F., the zinc will alloy with the ferrous metal to form a ferro-zinc alloy coating on the article. This alloy coating contains'iron and zinc in varying proportions such as FeZn; FeZna; and FeZn'z. The iron content in the alloy decreases with the increase in distance from the wire. 'I'hus the inner zone of the coating adjacent the article may be FeZn; the middle zone may be FeZns and the outer zone FeZn'z to pure Zn.

It is only possible to build up a ferro-zinc alloy coating of limited thickness on the wire in a single zinc dip because alloy in excess of this limited thickness is ,dissolved o by the solvent action of zinc on the alloy.

It has heretofore been proposed to put a heavy coating of zinc and ferro-zinc alloy on wire by treating the coated wire after the first zinc dip in a molten lead bath for the purpose of increasing the iron content in the alloy coating thereon. The thus treated coated wire is then dipped in a second zinc bath to receive a coating of substantially pure zinc thereon. The first coating is not appreciably dissolved off of the wire by the second zinc bath because the increased iron content of the alloy raises the melting point of the coating. A

We have found, however, that molten lead has a solvent iniluence on the coating obtained in the first dip and tends to dissolve olf appreciable amounts of the coating.

Further, the lead will alloy with the ferro-zinc alloy formed on the wire to produce a modified coating which might be unsatisfactory for some purposes.

According to this invention, ferrous metal articles are passed between molten zinc dips `through a heatxcontrolled medium which does 50 not dissolve appreciable amounts of zinc or zinc alloy from the coated article and which assists the formation of ferro-zinc alloy on the article. The preferred medium to eilect the formation of a desired ferro-zinc alloy coating on the ferrous 55 metal article is a molten salt bath maintained at a corporation of Illinois 1937, Serial No. 149,410

(Cl. ill-70.2)

temperatures not lower than the temperatures of the zinc bath.

Examples of suitable salt baths are as follows:

Example 1 Percent s Zinc chloride 50 Sodium chloride 50 (The above salt bath has a melting point of ('I'he above` salt bath hasa melting point around 600 F.)

Since the usual galvanizingtemperatures for hot dip galvanizing processes are between 850 F. 20 to 900 F. (specifically 860 F.) the salt baths are maintained at the temperatures of the zinc bath or above. Suitable temperatures for the salt bath are from 850 to 1200 F.

It is then an object of this invention to in- 25 crease the ferro-zinc alloy layer on galvanized metal articles.

It is a further object of this invention to treat ferrous metal articles between zinc dips in a galvanizing process ina heat controlled medium for 30 assisting the formation of ferro-zinc alloy on the coated wire without dissolving off substantial amount of zinc from the wire.

A further object of this invention is to utilize a molten salt bath between zinc dips in a galvanizing process for raising the iron content of ferrozinc alloy coatings on the article.

Another object of this invention is to permit successive coatings on a metallic base without intervening oxidation of the coatings. 40

A further object of this invention is to provide apparatus for carrying out the process of the invention.

Another object of the invention is to provide a bridge between zinc pans in a galvanizing apparatus for housing a salt bath through which ferrous metal articles such as wires can pass between zinc dips.

Other and further objects of this invention will become apparent to those skilled in the art from the following detailed description of the annexed sheet of drawings which discloses a preferred embodiment of apparatus according to this invention utilized in carrying out the process of the invention.

On the drawing:

Figure 1 is a vertical cross-sectional view with parts illustrated somewhat diagrammatically, taken longitudinally through the apparatus of this invention.

Figure 2 is a top plan .view of the apparatus shown in Figure 1.

As shown on the drawing:

In Figures 1 and 2, the reference numeral I0 designates walls of ceramic material, brick, refractory material or the like dening a rectangular open topped heating chamber Ia.

A pan II having flanges I2 around the peripheral edges thereof is mounted in the heating chamber Illa with the edges I2 of the pan resting on top of the walls I0.

Vertical walls I3 and I4 are mounted in the heating chamber Illa in spaced parallel relation for supporting the bottom of the pan- I I. walls I3 andY I4 also provide baiiles for a purpose to be hereinafter described.

Additional walls I5 of brick, ceramic material, or refractory material dene an open topped rectangular heating chamber I5a in spaced 1ongitudinal relation from the heating chamber IIIa. A second pan I6 having flanges, I1 around the periphery thereof is mounted in the heating chamber I5a with the flanges I1 resting on top of the walls I6.

Additional vertical walls, of brick, refractory material, or other ceramic material such as .the walls I6 and I9, are disposed within the heating chamber I6a and support the bottom of the pan I6. The walls I6 and I3 also provide baffles for a purpose to be hereinafter described.

Between-the heating chambers IIIa and I6a additional vertical walls 26 and 2I are provided for defining with the end walls Il and I5 supports for arches 22, 23 and 24 to provide an oven chamber 24a. The sides of the oven chamber are closed by brick or ceramic material walls 25 and 25a.

As best shown in Figure 2, the wall 20 is in spaced relation from the back side wall 26a while the wall 2i is in spaced relation from the front side wall 26 of the oven construction. 'I'he oven chamber 24a thus provided is between the heating chambers I6a and I5a.

As shown in Figure 1, the pan II receives zinc or zinc spelter 26 therein to supply the zinc for the first coating on the ferrous metal article being galvanized. The second pan I6 likewise contains zinc or zinc spelter 21 therein. 'I'he zinc 21 is usually substantially pure zinc.

A bridge member 23 operatively connects the two pans II and I6. 'Ihe bridge member 28 has a rectangular outer wall 29 and a bottom portion 36 connected to the side portions of the walls 23 but spaced from the end portions of' the wall. The bottom 36 rests on the walls 2l) and 2l of the oven construction 26 and also on the flanges I2 and I1 of the pans II and I6.

'I'he ends of the bottom 30 are turned down as at 3i to extend respectively into the zinc baths 26 and 21 in the pans II and I6. Likewise, the end portions of the outer walls 29 of the bridge member extend into these zinc baths.

A salt or a mixture of salts 32 is disposed in the bridge member 23 and floats on top of the zinc baths 26 and 21 as best shown in Figure 1.

The heating chamber Illa is heated by means of a fluid fuel injected through nozzles 33 and 34. The nozzle 33 communicates with the chamber Ita between a side wall of the chamber and the baille wall I3. 'I'he nozzle 34 communicates with The` the chamber between a side wall of the chamber and the baule I4. As shown in Figure 2 the baffles I3 and I4 do not extend to the end of the cham ber Illa so that the burning fuel circulates around the ends of the bafiles I3 and I4 into the space between the bailles where it is completely burned. The burned products of combustion are drawn ofl' through a duct 36 into a stack 36 from which they are discharged to .the atmosphere.

The heating chamber Ila is similarly heated by fluid fuel injected through nozzles 31 and 33 and the burning gases pass around the ends of the baiiles I3 and I3 to have a tortuous path in the heating chamber. The burned products of combustion are discharged through a duct 33 into the stack 36.

The pans II and I6 are thus heated to maintain the zinc baths 26 and 21 within galvanizing temperatures between 850 and 900 F.

The salt 32 in the bridge member 23 is heated by radiation from the oven 24a. The oven 24a is heated by fuel injected into the oven through a nozzle 43 or a plurality of nozzles and the burning gases pass around the walls 23 and 2I as best shown in Figure 2 for heating the arches 22 to 24 which arches in turn heat the bottom oi the bridge member 26 for maintaining the salt J2 in a molten condition. 'I'he salt bath 32 is preferably maintained at temperatures not lower than the temperatures of the zinc bath. Temperatures from 900 to 1200 F. are preferred for the salt bath.

'Ihe burned products of combustion from the oven 24a are discharged through a duct 4I into the stack 36.

When the apparatus of this invention is utilized for galvanizing steel wires, a wire W, or a plurality of such wires in spaced parallel relation, is fed over a roll 42 and under rolls 43 and 44 submerged in the zinc bath 26 so that the wire passes through the zinc bath to receive a coating of 'zinc' thereon. l

'I'he wire W' is then directed around a roll 46 inl the salt bath 32 and the wire passes directly from the zinc bath into the salt bath in the bridge member 23 without contacting the atmosphere since the s alt floats on top of the molten zinc.

During the,l passage of the wire through the molten salt bath 32 the zinc coating on the wire is maintained at a temperature near or above its melting point which causes it to unite rapidly with the iron of the wire and raises the iron content of the ferro-zinc alloy layer.

After passing through the salt bath 32, the wire W passes directly to the second zinc bath over a roller 46 at the end of the bridge member 23 and under submerged rollers 41 and 43 in the second zinc bath 21 for `passage through this bath to receive a second coating of zinc thereon around the ferro-zinc alloy coating thereon. The wire does not contact the atmosphere between zinc dips and is introduced into the second zinc bath in a heated condition at an optimum temperature desired for receiving the second coating thereon. 'Ihe wire W is guided out of the zinc bath 21 around a roller 49.

The process of this invention thereby provides for the coating of a ferrous metal article such as a wire with zinc; the heat-treatment of the zinc coating on the wire in a molten salt bath to convert the coating into a ferro-zinc alloy of enhanced character! tics without dissolving off appreciable amounts of zinc from the wire. The

zinc coated wire is passed directly into the salt bath from the rst zinc bath without contacting the atmosphere. The heat treated Wire is then immersed in a second zinc bath for covering the ferro-zinc alloy coating on the wire with a substantially pure zinc coating.

In some instances it may be desirable to cool the Wire before passing the same into the second zinc bath. For this purpose the wire W can be directed around guide rolls 50 and 5| disposed above the salt bath 32 so that the wire is removed from the salt bath into the atmosphere before it is submerged in the second zinc bath. No deleterious effects of the coating on the Wire result since the salt will solidify on the coating to protect the same against contacting the atmosphere. The wire may be removed from the salt bath for any desired length of travel to obtain a desired cooling effect and the cooled wire is then re-immersed in the salt bath for melting olf of the crystallized salt thereon before immersing the wire in the second zinc bath and for heating the wire to an optimum temperature.

If it is desired to keep the wire submerged in the salt bath without contacting the air, it is possible to vary the temperature in various parts of the salt bath so that the heat is high at the entrance and considerably below the melting point of zinc in the latter part of the bath.

From the above description it should be understood that the molten salt bath or flux in- -creases the iron content in ferro-zinc alloy coatings obtained in a hot dip galvanizing process to provide coatings that are malleable. Prior to this invention it `was impossible to build up a nonbrittle ferro-zinc alloy coating of appreciable thickness on a ferrous metal article which could be subsequently coated with another layer of coating, such as of pure zinc, because the heating media heretofore used dissolved off appreciable amounts of the coating or resulted in an oxidation of the coating. The salt flux used in this invention has much less amnity for zinc than iron or steel has, and so it favors the formation of the ferro-zinc alloy and still at the same time protects the alloy against oxidation. The salt bath or flux is maintained at temperatures not lower than the galvanizing temperatures used for the zinc bath but temperatures as high as 1200 F. may be used for the salt bath.

We are aware that many changes may be made and numerous details of the process and apparatus may be varied through a wide range without departing from the principles of this invention, and we, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

.We claim as our invention:

1. The process of hot galvanizing a ferrous metal article which comprises passing the article through a molten zinc bath maintained at temperatures between 850 to 900 F. to form a zinc coating on the article and heat treating the coated article in a molten salt bath heated to temperatures not lower than the temperature of the zinc bath to increase the ferro-zinc alloy content of the coating.

2. The process of increasing the thickness of ferro-zinc alloy coatings on zinc coated ferrous metal articles which comprises heating the coated article to temperatures not lower than the coating temperature and between 850 to 1200 F. in a non-oxidizing molten salt bath having substantially no solvent action on the zinc alloy.

3. In a multi-dip hot galvanizing process, the step which comprises passing a ferrous metal article between zinc dips through a directly heated molten salt bath which does not dissolve substantial amounts of zinc from the article to heat the article for assisting the formation of ferrozinc alloy on the article and to adjust the temperature of the article as it enters the next zinc bath.

4. The process of hot galvanizing ferrous metal wires which comprises passing a wire through a zinc bath maintained at temperatures between 850 to 900 F. to form a zinc coating on the wire, passing the coated wire directly from the zinc -bath into a salt bath without contacting the wire with the atmosphere, heating the sait bath to temperatures between 850 to 1200 F. for converting the zinc coating on the wire into a ferro-zinc alloy of increased iron'content and passing the Wire from the salt bath through a second zinc bath toreceive a coating of substantially pure zinc thereon.

5. In a double dip hot galvanizing process, the step which comprises passing a ferrous metal article between zinc dips through a salt bath comprising mol en zinc chloride and sodium chloride at temper tures between 850 to 1200 F. to assist the formation of ferrozinc alloy on the article.

6. The process of hot galvanizing a ferrous metal article which comprises passing the article through a molten zinc bath maintained at temperatures between 850? to 900 F. to form a zinc coatingon the article, and treating the coated article in a non-metallic, non-oxidizing sait bath having little or no solvent action on the zinc coating and maintained at temperatures not lower than the temperature of the zinc bath and between 850 to 1200 F. to convert the coating into a non-brittle ferro-zinc alloy of increased iron content.

JOHN R. DAESEN.

ALBERT F. BRADLEY.

Images