US2068904A - Galvanizing process - Google Patents

Description

Jam. 26, 1937. A. F. BRADLEY GALVANIZING PROCESS Filed May '7, 1934 I .2 5 Q/ero I, Bra dye e1.

Patented Jan. 26, 1937 UNITED STATES GALVANIZIN PROCESS Albert F. Bradley, Sterling, 111., assignor to Northwestern Barb Wire Company, Sterling,

11]., a corporation of Illinois Application May 7, 1934, Serial No. 724,305

3 Claims.

This invention relates to a process for galvanizing iron or steel wire.

Coatings of zinc, iron or steel produced by exposing the surface of the iron or steel to the action of molten zinc adhere firmly to the iron or steel by reason of a thin layer of zinc iron alloy or mutual solution of the two metals occurring at the surface of contact. This alloy, however, has the disadvantage of being very brittle so that where a wire or other flexible metal is galvanized there is a tendency for the alloy to break when the wire is bent, thus causing the entire coating of zinc to loosen or peel off.

In the present invention, this difiiculty is overcome by the application of the zinc to the iron or steel under conditions which favor the formation of a very thin and therefore flexible coating of zinc iron alloy under a coating of zinc. It is therefore an object of this invention to provide a galvanized wire or sheet which may be flexed or bent without causing the zinc layer to loosen or peel off.

It is a further object of this invention to provide a suitable process for producing such a galvanized wire or sheet.

Other and further objects will be evident from the following specification and the accompanying drawing.

As shown on the drawing:

Figure 1 represents a vertical section taken lengthwise of my apparatus with parts shown in elevation.

Figure 2 is a sectional view of a modified form of a portion of the apparatus shown in Figure 1.

Figure 3 is a sectional view'of a further modification of the apparatus shown in Figure 1 with parts shown in elevation.

The coating of iron-zinc alloy forms during the passage of the wire throughthe molten zinc and its thickness is dependent to some extent on the time during which the wire is in the zinc. The greater the time of passage of the wire through the zinc the greater the opportunity for the iron to dissolve in the zinc and the thicker 45 will be the coat of alloy formed. When a short passage time is used, however, a comparatively i thin; weakcoating will be formed.

In order to overcome this difilculty, therefore, I have devised a process in which the wire is first subjected to the action of the molten zinc for a short period suflicient to produce but a thin coating ofiron-zinclalloy and is thereafter cooled under .non oxidizing conditions to freeze the zinc or zinc alloy coating without the formation of a zinc oxide. Such an oxide always forms if hot zinc is exposed to air and interferes with the proper adherence of the second coating of zinc. It is then again passed through either the same or a separate zinc bath. The'second coating of zinc adheres to the surface of the first coating and consequently contains practically no iron while the first coating contained a relatively large quantity.

The product resulting from this process differs from that of previously known galvanizing processes in that there is a relatively thin coat of the brittle alloy of zinc and iron, the major proportion of the coating being the outside coat of practically pure zinc. This results in a product which may be bent or twisted without the galvanizing coming loose from the iron or cracking and-permitting moisture to get in the pores of the steel causing rusting.

As shown in the drawing, the reference numeral 5 represents a tank containing molten zinc in which both the first and second passes of my process may be made. This zinc may be advantageously kept at a temperature of about 875 F. Wire-or sheet material 6 to be galvanized passes over a driven roller 1 into the tank 5 and under idler rollers 8 and I0 and then passes into a chamber II. The length of the pass through the molten zinc may be 14 or 15 feet. The chamber ll contains an inert or reducing gas which may enter from any suitable source attached to a pipe l2. A driven roller l3 in the chamber ll supplies power to draw the wire or sheet through the tank during this first pass. The wire or sheet is preferably cooled in this chamber sufficiently to solidify the first coating of zinc.

From the chamber l l, the wire or sheet 6 passes under idler rollers i5 and I 6 thereby being exposed a second time to the action of the molten zinc bath. This second pass may be of the same length and duration as the first one. On leaving the bath, the material passes through a wiper H which removes any surplus zinc and the sheet or wire is then cooled by passage around an idler roller" and a driven roller 2| where it is cooled by water or other liquid in a tank 22.

A modification of my process in which the material. 8 is water cooled between passes is 11- lustrated in Figure 2. In this modification the material 6 after leaving the' roller Ill passes over an idler roller 25 and under a larger driven roller 26 being cooled by water in a tank 21. From there it passes over roller-28 and into the tank 5 for the second passage through the zinc bath.

Li U

A preferred modification of the invention, however, incorporates both the cooling between passes and the non-oxidizing features of the invention and is illustrated in Figure 3. There the material '6 passes from roller Ill over a roller 3| into a tank of water 32 and around a driven roller 33. It then passes over a roller 36 and back into the tank to make the second passage heavy layer of practically pure zinc on its surface and a very thin layer of a zinc-iron alloy underneath. Ordinary galvanized wire has a coating of zinc in which the alloy extends almost a to the surface of the zinc coating causing it to peel off or crack when the wire is bent. In this respect, the ordinary galvanized wire varies materially from my improved product.

The speed of the wire may vary over a wide range. In general, the larger sizes of wire require more time and consequently a slower speed since more time is needed to bring them to the temperature of the bath. For example, when it is desired to galvanize wires having diameters between .0348 and .192 inches the most effective speed will vary from 210 to 46 feet per minute.

It will be understood that the speeds and tank sizes mentioned are not critical but onlyillustrate operative and efficient conditions for operating this process. If the tank be lengthened, the speed of the wire may be increased or the tank may be shortened and the speed of' the passes decreased. Also, the temperature of the zinc bath is not critical and may be varied somewhat if desired.

- It will be understood that while I have described this invention as applied to the production of galvanized wire, sheet material may also be run through the apparatus and treated in the same manner. While rigid articles may also be treated by this process, it is advantageous principally in the treatment of flexible articles, since the principal difference between this and othermethods of galvanizing is that in this process the ent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

. 1. The process of producing a non-brittle ga vanized ferrous metal article which comprises exposing a ferrous metal base to the action of a molten zinc bath until a thin coating of ferro zinc alloy is formed on the base, cooling the coated base in a non-oxidizing atmosphere to freeze the coating thereon, exposing the cooled coated base to the action of a molten zinc bath to form a relatively thick coating of pure zinc over the thin ferro zinc alloy coating, removing excess zinc from the article and cooling the article to freeze the zinc thereon.

2. The process of producing zinc coated ferrous wires which comprises dipping the ferrous base wire in a molten zinc bath to form a thin coating of ferro zinc alloy thereon, cooling the coated wire in a non-oxidizing atmosphere to freeze the coating thereon, again dipping the ferrous base wire in a molten zinc bath to form a relatively thick coating of zinc over the ferro zinc alloy coating, removing excess zinc from the wire and cooling the coated wire to freeze the zinc thereon.

3. The process of producing flexible galvanized ferrous metal wires which comprises drawing a wire through a molten zinc bath to form a ferrous zinc alloy coating thereon, removing the coated wire from the zinc bath directly into a chamber having a non-oxidizing atmosphere, reversing the direction of travel of said wire in said chamber and again immersing the wire into the same molten zinc bath without exposing the wireto the outside atmosphere to form a relatively thick coating of substantially pure zinc covering the ferrous zinc alloy coating, removing the wire from the zinc bath, wiping off excess molten zinc from the wire and cooling the coated wire to freeze the zinc thereon,

ALBERT F. BRADLEY.

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