US2477684A - Method and apparatus for galvanizing sheet metal vessels - Google Patents

Description

ug. 2, 1949. K. BORG ET AL v 2,477,684

METHOD AND APPARATUS FOR GALVANIZING' SHEET METAL VESSELS Filed May 17, 1945 4 Sheets-Sheet 1 Aug. 2, 1949. K.' BORG ET AL 2,477,634.'

METHOD AND APPARATUS FOR GALVANIZING SHEET METAL VESSELS Filed May 17, 1945 4 Sheets-Sheet 2 1 INVENTORS: KENNETH Boz s, .lV/feat 5, KEsLLEQe,

A fraz/wenz Aug. 2, 1949. K. BORG ET AL 2,477,684

METHOD AND APPARATUS FOR GALVANIZING SHEET METAL VESSELS 4 Sheets-Sheet 3 Filed. May' 17, 1945 1 llfilulvnln Murr-H Boes, Mc* Km L 5,2,

.4 rTo/ewns.

Aug. 2, 1949. K. BoRG ET AL 'METHOD AND APPARATUS FOR GALVANIZING 'i SHEET METAL vEssELs 4 sheets-Sheet A4 Filed May 17, 1945 www NN @NE IN VEN TORS Af/wvsrf/aee. /I//ffcx .5. KESL Eve,

wgmg 6g- ArroA/EKS Patenteci ug. 2, 1949 MELHD AND APPARATUS FOR GALVANIZ- ENG SHEET METAL VESSELS Kenneth Borg and Mack S. Kesler, Salt Lake City, Utah application May 17, 1945, Serial No. 594,274

l2 Claims. l

This .invention relates to a method of galvanizing, and more particularly to a method or galvanizing metal vessels of different kinds, but especially open top vessels having considerable depth, as for example, the metal cans used in freezing cakes of ice in the artificial ice industry.

This invention also relates to the art of smoothing out irregularities in sheet metal articles of manufacture and preventing formation of irregularities and buckling, which are inherently incident to and occur during the processes oi hot-coating or galvaniaing sheet metal vessels as ordinarily practiced, by dipping into molten metal in a so-called kettle.

The ordinary manner of galvanizing a vessel of the kind mentioned, is to suspend it over the galvanizing kettle in nearly a horizontal position; lowering one edge or corner of the open end into the bath of molten metal and then lowering the closed end so that the vessel can fill and sink below the surface of the bath similar to the way one would iill a glass with water from a pond. In removing the vessel from the bath the edge or corner of the open end is rst raised above the surface; then the closed end is raised as the vessel empties, and Finally the vessel is entirely removed from the molten bath with the open end down so that it can drain into the galvanizing kettle and cool. This way of carrying out the galvanizing operation results in buckling the side walls of the vessel, often to the extent of ruining the vessel.

In opposition to the usual procedure we suspend the vessel vertically over the galvanizing kettle with the open end pointed downward, so that the iirst contact of the vessel with the molten metal is in the form of a band or zone of substantially uniform width around the open end. Since the air inside the vessel will not allow the molten metal to enter, we vent this air space either through an aperture in the vessel bottom or through a iJ-shaped pipe extending from the interior of the vessel down through the bath of molten metal and to the air outside. As the dipped zone rises in temperature, its yield point diminishes far below the yield point of the contiguous metal Zone of cooler metal immediatellr above. As a consequence, as the metal in the dipped perimetral Zone rises in temperature, it begins to expand, but the cooler metal in the undipped adjacent zone constrains that expansion in direct proportion to the then existing moduli oi' elasticity in the cooler and the hotter zones.

Ordinarily the term galvanizing means that an article of metal such as iron or steel is coated with another metal having a much lower melting point, such as zinc. It is convenient herein, by way of illustration, to describe the invention with respect to that particular purpose, but without thereby necessarily limiting its scope.

In specifically applying the general principles previously stated, it is to be realized that in dipping a can to be galvanized into a bath of molten zinc, there is not really a complete discontinuity of temperature change between the colder and the hotter zones, and that the temperature gradient can be made suciently abrupt by regulating the speed at which the can is lowered into the molten zinc so that the yield point in the hotter zone is passed and internal stresses are distributed in the hotter zone while the more rigid metal in the contiguous cooler zone `preserves the shape of the can.

If the metal in the can is relatively thin, the dipping may proceed rather rapidly or even at discontinuous increments until the can is covered. This speed and the size and frequency of increments may be determined by observing that portion of the can immediately above the surface of the molten zinc. As long as the sides of the can bulge outward above the surface, immersion may continue. But this bulge must travel ahead of the line of immersion in order to prevent buckling or reverse curvature from occurring. Finally the can ls raised vertically out of the zinc bath as rapidly as expedient.

In practicing the invention, it has been found advantageous to employ a novel apparatus comprising a holder or so-called jig for holding a can during the galvanizing operation. The jig and its mode of use will presently be described in detail. Y

The principal objects of the invention are summarized as follows:

(a) To vertically suspend an open-ended vessel or article over a galvanizing kettle with the open end pointed downwardly, that is to say, inverting the vessel.

(b) So lowering the article that the iirst contact with the molten zinc is in the form of a band or zone around the open end, and suitably continuing the immersion.

(c) So using the energy of the heat of expansion that the internal stresses within a hot zone where the yield point of the metal is low, are uniformly distributed, while the general shape of the article is maintained by the metal in the contiguous and cooler zones in which the yield point is sensibly higher. s

(d) To provide a convenient means for lowering an open top vessel of considerable depth, in an inverted position, into a galvanizing bath of molten metal.

(e) To securely hold the vessel vertical during the galvanizing operation.

(f) 'Ilo effectively evacuate the air from the interior of a vessel having an open end and a closed end, as it is being lowered into the bath with the open end down, and to control the evacuation of air in a predetermined manner.

(g) To provide apparatus for causing the advantageous manipulation of the vessel while in a bath of molten metal, as well as to allow the advantageous removal of the vessel from the bath.

(h) rI'o cause the flux which ordinarily floats on top of a galvanizing bath, to be so influenced that the proper distribution of the galvanizing metal upon the inside surface of the vessel results. Y

(i) To eifect economies in the handling of vessels during the galvanizing process.

(i) In the phase of the` invention where the jig is used, to start .the removal of the vessel from the molten metal bath by blowing dry compressed air into V.the interior of the vessel above the plane of immersion for the purpose of expelling the molten-metalffrom the inside of the vessel and at the same time exerting a positive pres-sure against the inside surface of the side- L Figs. 1 to 5 each represent one and the same fragmentary vertical section taken through a kettle and its molten galvanizing metal content, where a thin metal ice-lfre'ezing can is being lowered into the hot galvanizing bath; the successive steps in lmmersing the can in the bath f are represented in the respective figures which serve to indicate the progress of the ensuing bulge along the walls ofthe can from where the can has ju-st entered the bath as in Fig. 2, to the point where it is fully immersed in the molten bath as in Fig. 5;

Fig. 6, a fragmentaryv section taken on the line E--B in Fig. 4;

Fig. 7, a View in perspective of a usual galvanizing kettle with portions broken away to show clearly a more perfected manner of practicing the process than that represented in Figs. 1 to 5, the molten metal immediately surrounding the can being omitted for convenience; representation includes a. jig;

Fig. 8, a diagrammatic vertical section taken along the plane indicated by the line 8-8 in Fig. 7 to show in vsuccession various positions of the jig and the can it holds for galvanizing, during the progression from the initial immersion to the point of nal. deposit of the fully galvanized can ,on the unloading platform, portions of the jig being omitted for the sakeY of clarity;

Figs. 9 to 13, onek andthe same vertical section of that portion of the jig enclosed by line 4 G A in Fig. 8, the section :being taken along a vertical plane represented by the line 9I3--9I3 in Fig. 14; and illustrating various changes taking place within the vessel during respective stages of the process;

Fig. 15, a top plan of the jig alone;

Figs. 16 and 17, a side elevation and a front elevation respectively, corresponding to Fig. 15;

Figs. 18 and 19, detailed vertical sections taken respectively on the lines Iii- I8 and lil-I9 in Fig. 15, drawn to an enlarged scale, parts being broken away for convenience;

Fig. 20, a fragmentary elevation, partly in section, showing a minor detail;

Fig. 21, an end elevation corresponding to the showing in Fig. 20, and

Fig. 22, a special Spanner wrench for sometimes rotating the axleon which the jig is supported, as shown in Fig, 'l where the Spanner wrench is drawn to a reduced scale.

Referring to the drawings, Figs. 1 to 6, the numeral 38 indicates a usual freezing can for articial ice, the canbeing made of relatively thin sheet steel, for example, No. 12, the size of the can being approximately 12 by 18 inches at the top, which is open, and 1 1 by 17 inches at the bottom, which is closed. The cans are usually about 58 inches high.

rIhe numeral 3| indicates a portion of a bath of molten metal having suiiicient depth to receive the can, and 32 a layer of flux floating on top of t'he molten metal 3l, this layer being usually several inches in thickness,

In Fig. 1 the can is suspended from, for example, a rod 33 intersecting a crossbar 34 on the inside of the can, the rod 33 hanging from a suitable support such as an ordinary hoisting block 35. The can, which has previously been punctured, for example by forming a hole 36, and inverted and placed on the suspending rod 33, is now in a position to be lowered tothe point where it is just about to contact and pass through the flux into the galvanizing bath.

In Fig. 2 the can has been vgradually lowered into the position where the rim of the canl is just being submerged in the bath. In Fig. 5, the can has been completely immersed in the bath after having passed through the successive stages inn dicated in Figs. 3 and 4. y

In Fig. 2, the eiiect of having immersed the rim of the can in the bath has been to expand the metal and create aA bulge 31, this bulge gradually crawling upward on the canv through the stages 37a., Fig. 3, and 3117, Fig. 4, until finally the can has been completely submerged as indicated in Fig. 5, During the progressof the upward travel of the bulge. 31, the effect upon the can will have been to smooth, or iron out, any wrinkles or distortion-s that may have existed in the wall 33 of the can before immersion,l so that when the can is nally drawn out of the molten bath from the position in Fig. 5, the canA will have been substantially restored to its original perfect shape. The vent opening in the can is sealed afterwards.

In order to facilitate the galvanizing action as just described, it is desirable that it be'performed by means ofi a specialy holder or jig whichl has been developedv with regard to the peculiar conditions arisingv during the'galvanizing operations.l There will now 'be described, first, the construction `of the jig., andthen. the method of using it, it being understood that this jig' is; in the present instance, designed primarily for ice freezing cans, as hereinbefore particularly mentioned. It will, therefore, be understood further that other special holding structures can be worked out in accordance with the teachings hereof, to suit any peculiar requirements and to attain any particular object.

Referring now to Figs. 15 to 21, the jig comprises a framework 40 suitably constructed of light members made of a suitable metal, in this instance iron or steel. The jig is so designed that an ice freezing vessel can gradually be inserted therein somewhat as indicated by the dotted lines 4i in Figs. 16 and 17. The exact procedure of bringing the can down into the final position in the jig will be described hereinafter with respect to Figs. 8 to 14. At this point it is sufficient to state that the framework 4 0 is composed of vertical members 42 connected to one another by means of transverse perimetral members 43 and 44, and is disposed to travel the length of a kettle.

Rigidly mounted in this structure are two pipes it and lil. Pipe 46 comprises the substantially vertical portion 46a and the inclined portion 48o, Fig. 19. At the upper terminus of the portion d8a is an air control box or cell 48, the cell being rigidly connected to the pipe at its mouth 46c, the pipe and the bottom of the cell being securely welded together at the point 49. The cell 48 is also rigidly connected to the pipe 41 at a point 55, Fig. 18. Thus the cell 48 is rigidly supported by the two pipes 45 and 41. The cell is airtight all around except at the two slots 5l and 52 which extend across one end of the cell as indicated in Figs. 18 and 19. The inclined portion 46h of the pipe 45 has its upper extremity in free com munication with the atmosphere. The pipe 41 has a U-bend 41a at its lower extremity from which the two branches 41h and 41c extend upwardly. The branch 61e has the return bend 41d, forming a loop in which is rigidly mounted a tubular casing 53 within the latter is rotatably mounted an axle 54. The tubular casing 53 is also rigidly connected to the bracket members 55 forming part of the framework. These bracket members form a brace for the framework.

At the opposite extremities of the tubular casing 53 are rigidly mounted collars 56, Figs. 17 and 20, and adjacent these collars are traction wheels 51 rigidly mounted on the axle 54; thus the wheels and axle are freely rotatable with respect to casing E3. At certain times it is desired to hold the wheels 51 stationary with respect to the jig frame, and, for this purpose, holes 51a are provided in the traction wheels, these holes being in registry with other holes 56a that extend through the collars 56. The purpose of the registering holes will be presently explained in connection with the operation of the jig.

The pipe 41, with respect to the air control cell 48, has its upper end, though closely adjacent a Wall of the cell, in free communication with the interior of the cell. Near its outer extremity, the pipe 41 is provided with an air inlet 58, Fig. 18, controlled by a check valve 59 that permits atmospheric air to flow into the pipe 41, but at the same time prevents egress of air from the pipe. Instead of atmospheric air, an alternative construction provides compressed, dry air from a suitable source (not shown). According to this alternative construction, a supply line 60, Fig. 1'7, has connected to it a flexible conduit, for example, a rubber hose 60a, the ilarlng end of which is in turn arranged for slipping onto either end of a conduit 60D, which, in this instance, is supported on uprights S2 rising from the member 53. Thus, by means of the flexible conduit, the compressed-air connection can be kept intact in all the positions of the jig in its travel along the kettle.

The particular functions of the air-control cell 48 and its appurtenances will presently be made clear while describing the operation of the .llg-

The jig, with respect to its travel along the kettle, is vsupported on the axle 54 and its wheels 51, Figs. '1 and 8, the wheels having their traction on the topof the kettle side Walls. It is frequently desirable that the wheels 51 be in the form of toothed pinions as indicated as 51e in Fig.' 21, and that these be in mesh with toothed racks 51h, so that any slippage along the line of traction is prevented. In order to provide, in this instance, for the manipulation of the jig in the kettle, a handle having the shape `of a gooseneck 41e extending from the pipe 41 is found advantageous. Hooks or lugs 39 and 45 are positioned at convenient points on the jig frame 4i) for purposes that will be explained later herein. Flow of compressed air through the system is conveniently regulated by valves 6I. The jig swings about axle 54 as indicated by the radius 83, Figs. 16 and 18.

The manner of using the jig in practicing this process is clearly indicated in Fig. 7 where 10 indicates the kettle, this being frequently built of fire brick with a lining of sheet iron or steel as indicated at 1l. Thekettle is of suitable dimensions to accommodate the class of work that may be done in a particular shop. In this instance, the kettle has considerable length and suflicient width to conveniently accommodate the jig with its load as indicated in Fig. 1, the depth of the kettle being not quite equal to the height of the jig. The kettle, however, has considerable -length for the reason that the jig and its load,

in laccomplishing the desired operation, must travel a certain longitudinal distance back and forth through the hot metal bath.

The position of the jig 40 with respect to the kettle in Fig. 1 is the one in which it is receiving the can 15, the descent of the can into the jig being attended with process features. and galvanizing results similar to those previously described in connection with Figs. 1 to 5, the exception being that the air from the inside of the can is being evacuated by means of the pipe 46. It is convenient hereinafter to refer to this pipe as the zinc pipe or conduit, while the pipe 41 is referred to as the "air pipe or conduit. The position where the can finally cornes to rest in the jig is indicated by the numeral 9 in Fig. 8.

The molten zinc bath in the kettle is designated as 12 and its upper surface as 13-With the layer of flux 14 floating thereon. In the position shown in Fig. 9, the molten zinc-will have entered the can, the level of the zinc within the can being even with the level of the bath in the kettle, the air having meanwhile been evacuated through the zinc pipe 4B so that the air control cell 48 stands approximately in the position indicated in Fig. 9 Iwhile the level of the bathstands substantially at 13, somewhat below the cell.

Duringr the operation of lowering the can 15 into the jig as just mentioned, the latter is held in an upright position by means of a rod 39a, Fig. 8, engaging the hook 39 and restingon the sidewall of the kettle. A Spannerv wrench 16, Figs. 7 .and 22, havingV the prongs 11, the stem 18, and the handle 19 is then brought into a posiemacs@ tion where the prongs. can be. pushedth'rough two diametrically opposed poles 51a of wheels 51 which, in turn, are brought into registry with two respective holes y560i of collars- 56 whereby the jig is held in approximately the position shown in Fig. 7, by a workman (not shown) holding the two ends of thehandle 19. VAs soon as the can 15 has beenlowered into the position 9 in Fig. 8, the workman, by means of the span ner wrench,y turns the jig, in this instance .in the direction of the arrow, so that the .can comes successively into-the respective positions I9, Il and I2 in the same iigure, during which time the air pipe v41 and .the zinc pipe 46 in conjunction with vthe air control cell 48 function as follows.' In moving .from the position 9 to the position I9, Fig. 8, the upper portion of the canflowers until .the air control cell Areaches the position .shown in Fig. l where the 'zinc .has flowed into the cell through the slot I .and where the cell, relatively to the surface '13 of the zinc hath, stands substantially as shown. Meanwhile the flow of zinc through the slot 5I will 'have forced a portion of the air, together 'with such iiux as may .have "been present, out through theV slot "52.

At the 'same time the ux, which previously was .on .the top of 'the zinc inthe .can as the Vlatter descended, will have been crowded 11p by 'the rising .metal into and through the space BI between the air control cell and the closed end of ythe can 15, thepath ,followed by the evacuating ux nally leading into 'the mouth of the 4zinc pipe 46, much of the flux for the moment being retained 'in the zinc pipe.

In the position of the air control ceil indicated 'in Fig. .11, the vcell has been lowered into the zinc bath' so that the relative rising of the zincv in *the cell has acted to compress the original volume ofthe air in the space 80 into the upper `part of the air control cell and 'back'in-to the' air pipe V41 and against 'the lcheck valve '59 which acts to'preven-t escape oit-he 'compressed air,the space '80 having by `this vtimev been .reduced "to `the space a. Although the volume of space 89 has been decreased on account of the 1increased pressure, that volume has also to 'increase because of the iii'gher'temperature,these two circumstances in a measure oisettifng each other.

In the 4posit-ion 4`of the can show-nin vFig. lL-'the can'wll'l'fhave"beenlowered into-'the yoathsubstan- -ft'ially to lthe yextent sho-wn, where the :can is practically submergedin the-moltenbath. 'Meam while, 'the rising zinc will havezior'ced -the ilo'ating on vthe zinc surface within the can, through the mouth r46cinto the zinccpipesll., and willhave `'followed the flux into the zinc zpipe, thereby forcing vthe iiux through mthe .zinc 4pipe and hack vinto the bath and sealing :olif any lfurther passage of air for iluxthrough'the pipe d6 with adam of molten zinc.

"In 12 vthe jigis so .located that the .open

-end-ofthef'c'anis at ahig'her :elevation thanthe closed end, thisbeing for thezpurpose o allowing v:tl-ie last small remnants .of 'the and v.the air -to :escape from 'the can at the ipoiztti '8. In'FiglZ, the airspace 8o in the air control Lcell of Fig. i0 is shown -eontracted in'ftheaspaceilb.

In movingthe j-i'gand'the can.ffrom'.'thefposi tion I2 in 1Fig. J8, a 'second tszorkman .projects an iro'n- 'bar 83 into and .through the -hooki (conveniently iomittedin this 'positionotthe die) the fiirst 4'worlnnan'fx-.empires fthe Spanner .wrench :and the :other vend of the iron par 'the vtwo workmen, walking. :on .'ppo'stte-lsidesmf the kettle and on the Iioor 85 in Fig. '7, roll the Jig in the direction of the arrow 86, Fig. 8, towards the far end of the kettle 10 Where there is no flux, the flux being normally stopped oi by a conveniently located darn 83. The jig comes to rest at a suitable point where the workmen release the handle 41e (conveniently omitted in this position of the jig) and allow the jig and vthe can to swing on the axle 54 into substantially thel'os'ition I3 where the common center of gravity is directly below the axle 54.

In` the position of the can designated I3 in Fig. 8, the 'condition in the control cell is clearly indicated in Fig. 13. Here the cell is in a position where the lip 89 has just risen slightly above the Surface 'I3 of the zinc bath thereby having released the air from the space o, allowing it to flow into the can and around the control cell and causing all the liquid zinc in the can and Ithe pipe 46 to subside to the level 13 of the bath in the kettle, vthe air in the space 64A, Fig. 13, having been supplied from the air space v361e which latter space in turn is supplied with air through `the air vpipe 41 and the check Valve Y59 or through the dry compressed air line 60.

The first workman now swings the can around the yaxle 54, hy means of the ySpanner wrench, 'to the vposition 93, where any remaining portion of the -molten zinc in the can is drained off at the open en d thereof, as indicated at 9i. After draining at the position 9i), the jig and the can are further rotated by the iirst workman suinciently to allow the ysecond workman to thrust the bar through the hook 45 and let the bar come to rest across the top of the kettle. The Afirst workman now removes the Spanner wrench from the traction wheel and grasps the -far end vof the bar, after Awhich the two workmen `to gether further rotate 'the -jig with fthe can l:by means of the bar, permitting the molten dam `in'thezinc pipe to drain out into the kettle while they walk forward and push the jig and the can into `the position 92, Fig. 8, where the can 'is .in 'the act of sliding vout ro1 the jig .onto-the vdeli-very platform 93.

The :primary purpose of the air control cell 48 is to -prev-ent either 'iiux or molten zinc from entering the air Vent pipe 41, since that pipe Y-mu'st always Vloe 'available for drawing air through 'the check vvalve 59 into the interior .of the .can :as it emerges yfrom the zinc bath. n every cycle ci operation, the v:jig must be brought into the position .where the pipe 46 is emptied of 'its residual zinc content, for exampla'posltion-desiginated lby the l`numeral 92 in Fig. 8, so as to be .ready lor-.the .next cycle.

While the primary'function of the aincell-is to f-preventfthezinc or ilux from enteringatheairvent pipe :41a Vsecondary ffunction :is to crowd the l,flux floating on ftopof fthe Vzinc within :the can, :into fthe intake fof fthe zinc pipe 46 so the'latter .will .V-actfasefiiux Siphon. Therefore, the exterior of the-'cell should be so congurated that it follows v`relatively closely the internal contour of the 'ves- :sel being fgalvanized. so that, vdue to its shape, :it -will -act to :crowd the ux as'just explained.

Moreoven 4the air cell should be -so designed that :slot v'-il passes .through ithe .flux floating onctop-ofthe `molten zinc, in 'a direction vsuch that the nluxzissheared `oif alongthe 'plane ofthe slot it -submerges through the yiiux and into :the azmasasindicated-loy the dotted 'arc I'D-in Fig. 9. 'Alsetheslot should beso located and in such razposltion thatitwll havetheadvantage of'following zpathtalrea'dy piloted; by. the lower part of the box through the flux, in order that a minimum of flux will have been allowed to enter the air cell through either of the slots l or 52. By this arrangement a portion of the air in the air cell is forced out through the slot 52 as it passes downward through the ilux toward the molten zinc, thereby preventing ingress of the flux. The dimensions of the air cell should be so chosen that the residual air space 80 left within it, as indicated in Fig. 10, is such that the effect on its volume due to increased pressure caused by immersion beneath the molten zinc surface, is principally compensated by the rise in its temperature in passing from without to within the molten zinc bath.

As clearly shown in Fig. 13, the space B4 between an outside surface of the air cell and the inside surface of the can and the interior surface of the can above the surface of the zinc, will already have been filled with hot air at the time the lip 89 at the slot 52 has risen to the elevation of the zinc surface outside the can, thus having prevented any exterior atmospheric pressure from having exerted a collapsing force on the contiguous portions of the can.

As a matter of practical construction, it is convenient to make the assembly of the air cell, the air pipe, and the zinc pipe together to lend strength to the entire mechanism.

In the common and accepted practice in hot galvanizing, it is customary to throw dry flux on the surfaces of a vessel being galvanized, as the vessel emerges from the molten bath, in order to float off all dirty flux spots. Obviously, this is an inconvenient and ineffective way to float off the dirty flux spots from the interior surfaces of a vessel that is relatively tall. As a means of circumventing this faulty practice and implementing a better and more effective practice, it is contemplated according to the invention, to blow a charge of dry flux with dry compressed air through the air pipe 41 at, or a little subsequent to, that point in the process illustrated by Fig. 13. This charge of flux partly sublimes and partly floats on the surface of the zinc inside the can, thereby washing down its interior surfaces progressively as the can emerges from its molten zinc bath.

A device for introducing the ux into the compressed air line 60 is shown at 94, Fig. 17; in this instance it is a funneled container having a removable, tight closure 95 with a regulable gate 96 to feed the flux into the air line 6l! as desired. Accordingly, the flux can be blown through the air pipe 41 in the required manner. A plug 91 (Fig. 18) prevents air from wasting through the outer end of the air pipe.

It has been observed that if one of the flat surfaces of a relatively thin sheet of metal is suddenly raised to a temperature considerably above the temperature of the other flat surface, a mechanical moment is suddenly set up which causes the sheet to bend with the hotter surface on the convex side. To prevent fiexure of this kind during the galvanizing process, it is a primary intent of the invention to introduce objects made of sheet metal, into a galvanizing bath in such a way that the corresponding points on both sides of a sheet portion thereof, are raised in ternperature at the same instant in so far as this is practicable. In line with what has just been stated it can be seen that during the successive steps of this process as set forth in Figs. 1 to 5, the principal strains are calendered from the open end toward the closed end of the can so that '10 the internal stresses created at the perimeter of contact between the molten zinc and the can have been distributed uniformly along the line of the perimeter, or in other Words, have been made to approach zero as a limit. The vresidual strain which will be left in the closed end 0f the can is relatively unimportant in that it does not interfere with the extraction of a frozen ice block from the can when in use.

It is here to be noted that the permanent buckling created in the walls of a large percentage of ice freezing cans when galvanized by faulty ordinary methods, render such cans unusable because ice blocks can not be easily removed from the cans. Such cans represent a total loss as touched upon earlier in this specicaticn.

The particular advantage of the invention is that it permits successful galvanizing of vessels made of black iron with welded seams. Competitive with this advantage is a method in common use which consists in making vessels of galvanized sheets, in which the seams are welded, and afterwards metalized where the original galvanizing was burned oif. This method entails the additional expense of metalizing. Another common but older method is to construct the can of galvanized sheets and rivet them together. Here it is necessary to put a lead gasket between formed sheets along the marginal portions to be riveted so that the mutually contiguous sheets shall be drawn tightly against the lead gaskets in order to make the seams watertight. By means of the invention it is possible to rivet the metal sheets together without any gasket, because the space between the sheet margins is thus made so small that subsequent galvanizing seals the seams.

The process of the invention is especially useful in its application to the ice-freezing cans dealt with specifically in the foregoing. This is so because the substantially plane side walls thereof readily wrinkle and otherwise deform inwardly of the can during an ordinary galvanizing procedure. Similarly, other hollow articles having plane side walls are particularly susceptible to undesirable deformation by ordinary methods of galvanization. Pursuant to the invention, deformation of the plane side walls is so controlled during the galvanizing process as to leave no undesirable nal deformation.

The various phases of the process are beneficially applied to a wide variety of sheet metal bodies which are dipped or immersed in a hot metal bath in the manner described by the provisions of the invention. Whatever the exact shape of a sheet metal body may be, the immersing procedure is conducted in such a way that a perimeter at which the initial contact with the molten metalbath takes place, lies, just before the initial contact occurs, as nearly as possible in a plane substantially parallel to the mirror surface of the molten bath.

The use of the dry compressed air to expel the molten metal from a can l5, when starting the withdrawal of the can from the bath, can be visualized by referring to Figs. 8 and 13. In Fig. 8 the position of the can just as its with drawal starts, is denoted by the numeral I3, and

the conditions within the can at that time, are represented in Fig. 13. The compressed air enters the can through the air pipe 41, its rate of entry being controlled by one of the valves 6|, Fig. 17, in accordance with the observed behavior of the can structure as it rises above the surface of the bath and moves toward the position denoted by the numeral 90.

sismos@ While specic embodiments or the; invention are herein disclosed; it is limited' only byV the terms oi the. following: claims.

Having fully' described our imfenti'on. what we clairn is:

1. A method of: galvanizi'n'g open-top metalli-c vessels of considerable depth.. comprising positioning a vessel-receiving jig in: a molten metal bath; inserting the vesselr the open end down substantially vertically in bulge-controlled stages in the jig. until' the vessel' is almost completely submergedin the molten metal bath; gradually rotating the jig in a given direction: until the lower end thereofv reaches a;` point in. proximity to the `free surface of' the bath', thereby` com.- pletelysubmerging the vessel; reversing the-rotating operation of the jig until the lowererrd thereof again reaches ai poi-nt in: proximity to the free surface of the bath; continuing. the reversed rotation of the jig until the entire vessel.l emerges from the' bath and removing the galvanized ves'- sel from the jig.

2. A method oi galvanizing open-top sheet metal vessels ot considerable depthf comprising positioning ar'eceiving j'ig substemti'al-l-y vertically in a bathV of molten metalli; suspending a vessel in an inverted position above the:` jig.; lowering the vessel into thev jigfandl into the molten bath until the vessel is largely submerged'mthe molten bath. meanwhile causing the air to bel evacuated from the interior oi the vessel during the lowering operation; tipping. the jig. until the vessel is completely submerged. inthe molten bath; reversing the tippingoperations previously enacted' and continuing the reversed tippingV operaticnsv until the jig with. its vessel emergesI from the surface of the bath, during which operationv any excess of the galvanizing metal is cleared.l from the vessel; and removing the vessel from the jig.

3. A method of. galvanizing open-top sheet metal vessels of considerable depth, comprising positioning a vessels-receiving. jig in a1 receiving position in a molten' bath of galvanlzing metal; suspending a vessel. in: an'V inverted position above the jig; lowering the vessel by bulge-observed, graduated stages into the jig; evacuating. the' air from the interior of the vessel through suitably disposed conduits; tipping the jig. with its contained vessel so that the lower end ofthe' jig rises in the bath to a point in proximity'to the surface of the bath; reversing the tipping operation until the lower part of the jig again rises to a point in proximity to the surface of theV bath but this time in the reversed position of the vessel removing any residual substances from the: vessel' and raising the vessel out of the bath'.

ll'. A method of.' galvanizing. according to claim 2, wherein the bath of molten metail has floating on its top surfacey a layer of` lurring material; wherein the vessel as it lowers intothe bath has floating within it a portonot the fluxiing material; and whereirris included the step which' comprises expelling the fluxin-g material: from the vessel after the saidI fluxing material' has contacted the inside portion of the closed end of the vessel.

5. A method of galvanizing: according to' claim l, wherein flux is floated on the surface' of the molten metal bath and wherein after' rotation of the vessel has started from the almost-submerged position thereof, the step which comprises entrapping a segregated quantity of atmospheric air to prevent flux or molten metal from subsequently interfering with the entry of breather air into the space of the entrapment.

6.V A method of galvanlzin'g according to claim 2, wherein dry, compressed air is introduced into the vessel at approximately the time the iina-l stage of emptying the molten metal from the vessel occurs.

'7. In a system of galvanizing for vessels having' an open end and a closed end, apparatus including a U-shapedy conduit for receiving a vessel to' be galvanized, said conduit having one of its branches adapted for insertion within the vessel and the other of its branches adapted to remain outside said vessel; an air-control box at the end of the rst-mentioned branch; and an aircheck at the end of thev second-mentioned branch; said apparatus with said vessel being submersible in a bath of molten metal within Which the U-conduit is operative to expel air from the vessel as it is moved into or through the molten bath.

8. A jig for use in galvanizing vessels of consderable depth and having one end thereof open, including in combination a frame adapted to receivea Vessel open-end down and to descend into a bath of molten metal having a layer of flux on the surface thereof; a conduit for air supported on said frame, said conduit having one end thereof disposed to be Within the vessel and the other end disposed to be without the vessel; an air-control cell at the first-mentioned end operative to' evacuate'entrapped air from the vessel as molten metal approaches the closed end of the vessel; and a second conduit operative to expel flux from inside the vessel, through the said second conduit being controlled by said cell.

9; A jig for use in galvanizing vessels of considerale/1e depth, said vessels having one end thereof. open, the said jig including in combination, a fra-me having a normally positioned top and bottom adapted toY receive a vessel open-end adjacent said bottom; a two-mounted conduit operatively attached to said frame and having' one mouth thereof Within said frame the other mouth being without said frame; and an air-control cell operatively positioned in communication with the rst-mentioned mouth.

10; A jig for use in galvanizing vessels comprising a frame having a topv and a bottom adapted to receive a vessel with the open-end thereof down for submerging in a bath of molten metal; a conduit for air having one end within the frame and the other end without the frame; a molten-metal conduit having one end within the frame and the other end Without the frame; and an Vair-control cell operatively connecting the air4 conduit tor the' second-mentioned conduit.

11. A galvanizing jig comprising a frame having a top and a bottom disposed to receive a vessel' open-top down; an air control cell disposed on the said frame so as to occupy a position within the frame in proximity to the top thereof; a conduit having one end thereof Within the air cell and the other end Without the frame; another conduit having one end within the frame but outside the air cell in near proximity thereto; means for suspending the jig within a galvanizing kettle; and means for swinging the suspendedv jig within the kettle.

12. A method of galvanizing sheet metal vessels having an open end and a closed end which comprises the steps enumerated as follows: moving the vessel over a bath of molten metal so that the open end thereof is near and substantially parallel to the surface of the bath; entering the end that is open into the bath and simultaneously causing the liquid metal ilowing into the vessel to expel air `from the interior thereof; moving the vessel farther into the bath in successive increments, at a rate in step with the timing of sensible bulge effects appearing in the vessel Walls in proximity to the bath surface until the vessel is submerged in the bath; introducing dry, compressed air into the vessel at approximately the time the nal stage of emptying the molten metal from the vessel occurs, the dry compressed air being accompanied by a uxing agent; and removing the vessel from the bath at a rate of speed governed by the desired cooling eiect upon the vessel.

KENNETH BORG.

MACK S. KESLER.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Harker June 13, 1905 Van Der Velden Sept. 2, 1913 Fahlman Nov. 30, 1926 Jackson l- Mar. 15, 1927 Eickmeyer Jan. 9, 1940 Marland Aug. 1, 1941 Bullock Feb. 9, 1943 FOREIGN PATENTS Country Date Denmark 1915

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