US3008849A - Method of galvanizing pipe - Google Patents

Description

tional practice.

3,008,849 METHOD OF GALVANIZING PIPE Andrew F. Kritscher, Lafayette, Calif., assignor to United States Steel Corporation, a corporation of New Jersey No Drawing. Continuation of application Ser. No.

683,411, Sept. 11, 1957, which is a division of application Ser. No. 570,235, Mar. 8, 1956, now Patent No. 2,844,122, dated July 22, 1958. This application Aug. 22, 1960, Ser. No. 50,921

1 Claim. (Cl. 117-97) This invention relates to the coating of pipe with zinc by immersion in molten spelter and, in particular to a method capable of making a product of good quality at high speed and low cost.

This is a continuation of my application Serial No. 683,411, filed September 11, 1957, now abandoned, which is, in turn, a division of my application Serial No. 570,- 235, filed March 8, 1956, now Patent No. 2,844,122, dated July 22, 1958.

It has been the practice heretofore, in the continuous galvanizing of pipe, to introduce successive lengths of pipe endwise into the spelter bath, with the leading end lower than the trailing end, then to lowerthe trailing end below the surface of the bath and raise the leading end,

after which the pipe lengths are removed by endwise movement in the same direction as that in which they were introduced (The Making, Shaping and Treating of Steel, 6th Ed., p. 1193). Apparently, as the leading end enters the bath, the spelter flowing up into the pipe is chilled by contact therewith and freezes, forming a zinc plug a short distance inwardly from the leading end which, for the moment, prevents the further rise of spelter up through the interior of the pipe. In the meantime, contaminants such as dross and ash floating on the bath enter the trailing end as it is lowered into the bath. Eventually, as the pipe is heated by the bath, the plug adjacent the leading end is melted. By this time, a substantial hydrostatic head may exist, tending to force spelter up through the pipe toward the trailing end thereof, but there is no assurance that dross and ash accumulated in the pipe will be flushed out as .the pipe length is purged by spelter rising through it. In fact, ash which has already come in contact with the pipe will adhere tightly despite the purging effected by the rising spelter. As a result, the interior of the pipe may not be completely coated with zinc and may have dross adhering thereto which is objectionable.

I have invented a novel method for coating pipe which res Patent fully shown in my Patent 2,844,122. In general terms, it includes a feed-in table, means for delivering pipe lengths singly therefrom and lowering them onto an entry conveyor sloping downwardly toward the preheating bath. Conveyors extending down into the bath along an inclined plane, cause progressive immersion of the lengths. A pusher affords positive driving force endwise of the lengths. Spaced stop plates arrest the entering lengths successively while the conveyors are effective to shift the lengths laterally and then withdraw them from the bath through the moltenspelter. An exit or discharge conveyor provided with an air-blast pipe receives the emerging lengths and a transfer mechanism places them on a magnetic holding table where they are subject to a blast of steam for removing excess zinc from the interior. The pipe lengths are then ready for shipment, after overcomes the aforementioned objection to the conven- In accordance with the invention, I introduce a length of pipe in the normal way into a preheating bath which may be molten lead or zinc, but I do not immerse the trailing end until the pipe has become heated sufliciently to melt the plug formed therein adjacent the entry end by chilling, thus permitting the pipe to fill with clean molten metal. This precludes the initial entry of dross and ash into the trailing end. I then completely immerse the pipe length, introduce the trailing end into a coating bath from below and withdraw it through the coating oath. Preferably, the preheating bath is lead and the coating bath of zinc spelter floats thereon, being confined by a dam to a limited portion of the surface of the lead bath. This permits the end of the pipe length which trails as the length enters the lead bath, to be moved laterally under the spelter and brought out through the latter. This practically prevents any dross from being deposited on the interior of the pipe and insures such finishing treatment or operations as may be desired.

A complete understanding of the invention may be obtained from the following flow diagram illustrating the preferred practice:

Feed pipe length longitudinally on a downward slant into a preheating bath of molten lead.

Temporarily stop the length with its trailing end slightly above the surface of the bath.

Move length laterally while maintaining its trailing end above the surface of the bath.

When pipe length is sufficiently heated to melt any lead initially frozen therein, resume feeding of length down into bath until the trailing end is immersed.

Move trailing end under a bath of molten spelter floating on said lead bath.

Withdraw length through said spelter bath on an upward slant. in a direction opposite that in which length was initially fed into lead bath.

The invention provides a method capable of galvanizing pipe rapidly and efliciently. It has, for example, handled regularly a throughput per minute of fromt 25 to 30 twenty-one foot lengths of 4" to 1 /2" pipe, yielding 96% prime product. This is at the rate of 200 tons per turn, nearly three times the production obtainable with conventional equipment. Since the lengths of pipe are thoroughly preheated by the lead bath, any plug of metal formed in the interior thereof on initial entry into the bath, is fully melted before entry of the length into the zinc bath. Since the trailing ends of the pipe lengths remain above the surface of the lead bath until after such melting of the plug, the deposit of ash or surface contaminants from the surface of bath on the interior of the lengths is avoided. The pick-up of dross on the pipe is prevented by introducing the pipe lengths into the zinc bath from below, while full of clean molten lead.

I The preheating of the lengths in the lead bath also recomplete coating and freedom from bare patches caused by the presence of ash.

I have provided a novel form of apparatus for carrying out the method outlined above. This apparatus is duces the thickness of the layer of zinc-iron alloy between the surfaces of the pipe and the exterior coating layer of zinc. This provides better adherence of the coating and increased corrosion resistance. The invention also makes it possible to obtain a very high zinc efiiciency, i.e., the ratio of zinc actually deposited to the total zinc consump- 3 tion. This ratio, on a percentage basis, was about 96% or higher.

Although I have disclosed herein the preferred practice of my invention, I intend to cover as Well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

A method of coating pipe comprising the steps of moving a pipe length longitudinally on a forward and downward slant into a preheating bath of molten metal, temporarily arresting the length while its trailing end re mains slightly above the surface of the bath, moving the length laterally while maintaining the elevation of its trailing end, then when the length is sufiiciently heated to melt any plug of metal initially frozen therein, advancing the length farther down into the bath to immerse the trailing end, moving the trailing end under a bath of molten coating metal floating on said preheating bath and Withdrawing the length through said coating bath in a direction substantially opposite that in which the length was initially introduced in the preheating bath.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ser. No. 206,083, Ulbricht (A.P.C.), published May 4, 1943.