US2141382A - Apparatus for treating plated strip metal - Google Patents

Description

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H H MMW I H H'I WIMEW H I I M I I IHH HH HI IWHIHHHF T IH Dec. 27, 1938. J. F. FERM APPARATUS FOR TREATING PLATED STRIP METAL Filed Aug. 10, 1938 Dec. 27, 1938. J. F. FERM APPARATUS FOR TREATING PLATED STRIP METAL F iled Aug. 10, 1958 2 Sheets-Sheet 2 INVENTOE /OH/vfi ERM.

Patented Dec. 27, 1938 UNITED STATES PATENT OFFICE John F. Ferm, Midland, 2a., assignor to Pittsburgh Crucible Steel Company, Pittsburgh, Pa., a corporation of Pennsylvania Application August 10, 1938, Serial No. 224,101

6 Claims. (c1. ace-3) This invention relates to apparatus for treating metal coated material, such as tin-coated or plated sheet or strip steel, for imparting to the coating, a smooth surface of high lustre approxi- 5 mating mirror brightness.

Strip steel may be coated with tin by a process of electrodeposition from a tin plating bath. The process may be made continuous by feeding the strip from a roll through the plating bath and 10 out again. The tin coating thus applied to the strip has, however, a dull appearance, requiring further treatment for imparting the mirror finish required by the trade. This may be imparted by passing the plated strip through a hot oil bath 7 15 of appropriate temperature and other characteristics, uch asa bath of palm oil maintained at about 475 to 500 F., whereby the tin coating softens and fuses to form the requisite bright surface. However, upon so brightening the coat- 20 mg, the tin must be cooled and hardened rapidly in a non-oxidizing atmosphere to retain its bri1-" liance and prevent surface crystallization or spangling. Air cooling is, therefore, unsatisfactory for this reason and for the additional reason 25 that the molten surface of the tin is marred by air jets incident thereon. Hardening may be accomplished by passing the strip rapidly from the hot oil bath into a cool oil bath maintained at a sufliciently low temperature to harden the 3 tin quickly, for example, about 135 to 150 F.

A problem is presented, however, in passing the strip through the hot oil bath and thence into the cool oil bath in such manner that'the tin coating will not be exposed to atmospheric or oxidizing 35 conditions or to mechanical marring, while the tin is in a'molten or plastic state caused by immersionin the hot oil bath. If, for example, the known expedient were employed of passing the strip by means of a series of feed or guide rolls, 40 firstdown into the hot oil bath, thence up out of this bath and over and down into the cool oil bath, the strip must of necessity pass over a number of such rolls while the tin is molten or plastic, whereby the rolls would leave imprints in the brightened surface and thus destroy the smooth, mirror finish. Likewise, unless an appropriate reducing atmosphere were maintained above the baths, the tin coating would be subject to oxidation causing a'dulling of the surface during pas- 50 sage of the strip between the baths. The provision for and maintenance of such a reducing atmosphere adds both to the complexity of the apparatus and to the expense of its operation. a In accordance with one aspect of the present 55 invention, I overcome defects of the character aforesaid by arranging the hot and cool oil baths in tanks situated adjacent one another and by interconnecting the two with a duct such that the strip may be fed in a straight line from a point outside the hot oil bath, through the hot 5 bath and thence through the duct into the cool oil bath. The strip passes over a feed roll just prior to immersion in the hot oil bath, but does not enco er any additional feed roll or other mechanic azllelement until it has reached such a 10 point in t cool oil bath that the coating has been well hardened, at which point the strip passes over a second feed roll and out of the bath.

The fact that the hot and cool baths are in .direct liquid contact with each other through the duct interconnecting the two, introduces an additional problem of preventing the establishment of rapid thermal exchanges between them such as would bring them quickly to a common equilibrium temperature. If, for example, the baths are merely separated by a partition having an orifice therein or by a duct extending horizontally between the tanks, pressure differences between the hot and cold baths are bound to establish themselves at various elevations within the orifice or duct due to the different density of the hot oil in comparison with the cool oil, in consequence ofwhich convection currents will be established between the baths bringing them rapidly to a common temperature and thus rendering the brightening process inoperative.

In accordance with a further aspect of the invention I have overcome this difliculty by arranging the interconnecting duct in inclined rela- 5 tion, preferably such that it slopes downwardly from the hot oil to the cool oil tank, and to such a degree that its entry into the cool oil bath is situated entirely below its entry into the hot oil bath. With this arrangement the surface level 40 of the hot oil bath will so adjust itself in relation to the surface level of the cool oil bath by appropriate transierences of liquid between the two through the duct, that the hot and cool oil baths will be in approximate pressure equilibrium with- 5 in the duct at a level intermediate between the levels at which the duct enters the hot and cool oil baths respectively. By virtue of this arrangement, the hot andcool oil baths will contact each other in a horizontal surface, the opposing pressures at all points of which are the same, so that there is no tendency for establishing convectionf'currents in the manner aforesaid thereby to destroy the difference in temperature of the baths. Also, owing to the downward slope of the duct from the hot to the cool oil bath, the hot and hence less densaoil will be situated within he duct above the cooler and hence denser and more viscous oil thereby further stabilizing the tendency of the two baths to remain in equilibrium at the surface of equal pressure above described. Furthermore, owing to the relatively small cross-sectional area of the duct, thermal exchanges occurring by conduction, diffusion or otherwise between the two baths will be slight.

The arrangement above described has proved quite effective in practice where the speed of the strip through the duct is not too great. If, how- 'ever, the rate of feed of the strip is high, it tends to carry a portion of the hot oil along with it through the duct into the cool oil bath. This tendency may be effectively ofiset in accordance with a further feature of the invention by directing one or more jets of cool oil under pressure into the duct at its entrance into the coil oil bath with or without the introduction of additional jets at points further along the duct, and by correspondingly abstracting oil from the duct at some point further along the same toward its entrance into the hot oil bath. As an additional refinement oil may be withdrawn from the duct at a point adjacent the hot oil bath and passed through a. heater to be returned thence to the hot bath. With these refinements the strip may be fed as rapidly as desired from the hot to the cool oil bath without disturbing the temperatures thereof. Moreover, the hot bath may be maintained at the desired temperature with but little heating. so that the system operates efficiently as well as efi'ectively.

Referring now to the drawings:

Fig. 1 is a diagrammatic sketch illustrating the thermal exchanges occurring by convection between the hot and cool oil baths when interconnected by an orifice or horizontal duct;

Fig. 2 is an analogous sketch illustrating the manner in which such thermal exchanges are preventedby the use of an inclined duct in accordance with the invention;

Fig. 3 illustrates schematically one modification of apparatus in accordance with the invention for imparting a bright surface to coated strip material, such as tin coated strip steel;

Fig. 4 is a fragmentary view of the Fig. 3 apparatus as modified to incorporate various of the refinements above described; while Fig. 5 is a view similar to Fig. 4 of a further modification.

Referring to Fig. 1, hot and cool oil baths l and 2 are separated by a simple partition 3 having an aperture 4 therein whereby the hot and cool oil baths 5 and 6 are interconnected. Representing the densities of the hot and cool oil by d and d1, respectively, and the surface elevations of the hot and cool baths by h2 and hi, the pressure heads of the two baths are in equilibrium at but one elevation x, where:

The surface elevations will so adjust themselves by interchange of liquid between the tanks that the elevation a: will lie about midway of the orifice as shown. Below this elevation the hydrostatic tirely below its entry 9 into the hot oil bath, as

is indicated by the diiference in elevations I0 and i I representing respectively the highest point of entry 8 and the lowest point of entry 9 into the hot and cold baths. The upper surfaces of the two baths will so adjust themselves as explained that the two baths will now be in hydrostatic pressure equilibrium at some level 1: within the duct, which is intermediate between levels I0 and I, i. e., intermediate between any level at which the duct enters the baths, respectively. Therefore, the baths will be exposed to each other only over a horizontal surface at :1: upon.

which the pressures exerted by the baths will be equal and opposed, so that no pressure differences productive of convection currents and thus accompanying thermal exchanges can exist. Such differences of pressure as do exist between these baths above and below surface at :0, being counteracted by the retaining action of the inclined walls of the duct, which thereby isolates the two baths except through the horizontal surface of constant pressure aforesaid. This, together with the relatively small area of surface contact between the baths in the duct minimizing transference of heat by difiusion, and the sluggishness to such imparted by the high viscosity of the cool oil, provides an effective thermal seal between the baths which has proved entire'y satisfactory in servicewhere the speed of the strip is not too great.

Referring now to Fig. 3 disclosing one form of apparatus for brightening tin-coated steel strip and the like in accordance with the invention, the strip 20, having previously been coated by passage through an electroplating bath and otherwise been appropriately cleaned and prepared for the brightening bath, is fed over a roll 2|, and thence in a straight line, through a hot oil bath 22 contained in tank 23, and through duct 24 interconnecting the hot oil bath with a cool oil bath 25 contained in tank 26, whereupon the strip passes over a second feed roll 21 immersed in the cool oil bath and having its periphery in alignment with the exit from the duct as shown. Thereafter the strip passes out of the cool oil bath and between a pair of squeegee rolls 28, made of soft rubber or the like, for removing the greater portion of the oil adhering to the strip. The duct 24 extends downwardly from the hot oil to the cool oil tank as explained and to such a degree that its entrance into the cool oil bath is situated wholly below its entrance to the hot oil bath.

In order to assure that the coating on strip 20 will be fully hardened before the strip contacts roll 21, an extension 29 to duct 24 may be pro-.

ly preventing hot oil from being carried along by the strip into the cool oil tank, such as tends to occur at high speeds of operation. Cool oil is directed into the entrance of the duct into the cool oiltank by the jets 29 thereat, and may also be additionally introduced into the duct from one or more pressure lines 32, 33, controlled by valves 34, 35 and appropriately positioned along the duct. The cool oil thus introduced may be drawn off by an intake or suction line 36 positioned further along the duct toward the hot oil tank. In this way a cool oil seal is maintained in the duct between the intake line 36 and the entrance of the duct into the cool oil tank, with a relatively sharp dividing line between hot and cool oil being maintained adjacent the intake pipe 36. As a result the strip passes so rapidly from the hot to the cool oil and the coating thereof chilled and hardened so quickly as to prevent all tendency to crystallization or spangling of the coating. As an additional aid to maintaining a sharp dividing line in the duct between the hot and cool oil and also to maintain the hot oil bath at the proper temperature, 011 may be drawn off from the duct adjacent the hot oil tank by an intake line 31, passed through a heater 38 heated by steam pipes 39, and returned thence to the hot oil bath through a pipe supplemented by interposition of a pump if required. With this arrangement the cool oil circulates in the duct as indicated by the arrow 4|, while the hot oil circulates as indicated by arrow 42, whereby relatively sharp line of division between hot and cool oil is maintained in the duct in the region between the intake lines 36 and 31.

The arrangement and operation of the Fig. 5 modification is generally similar to that of Fig. 4. The cool oil intake line 36 extends from duct 24' to an oil cooler 43 wherein the oil is cooled and returned to the nozzles 29 over pressure line 44. In order to maintain the cool oil bath 25 at its proper temperature, an intake line 45 may be provided which draws off from the top of tank 26 the warmer layer of cool oil collecting at the surface of the bath and passes the same intothe cooler, whence it is returned to the bath through nozzles 29.

As in the Fig. 4 modification, hot oil is withdrawn from duct 24 adjacent its entrance to the hot oil bath by intake line 31 and after circulation through heater 39, returned to bath 22. In this instance a gravity circulation is employed by extending a duct 45 between the heater and hot oil tanks at the surface level of the oil. Also the oil is drawn off both above and below the coated strip as shown.

It will be understood of course that the invention may be employed in its elementary form shown in Fig. 2 or in conjunction with any one or more of the additional features shown and described in connection with Figs. 3, 4 and 5.

What I claim is:

1. Apparatus for treating plated strip metal comprising: a first tank containing a hot bath for softening saidplating, a second tank containing a cool bathfor hardening said plating, a

40, the circulating being duct joining said tanks and having an entry into the second tank situated below its entry into the first tank, and means for conveying said strip through said hot bath and duct into said cool bath, said conveying means having no contact with said strip metal while said plating is in said softened condition.

2. Apparatus for treating plated strip metal having a surface deposit of a relatively low melting point metal, comprising: a taining a hot bath adapted to soften and brighten said surface deposit, a second tank containing a cool bath for hardening said brightened deposit, a duct joining said tanks and having an entry into the second tank situated below its entry into the first tank, and means for conveying said strip metal through said hot bath and duct into said cool bath, said conveying means having no contact with said strip while said deposit is in said softened condition.

3. Apparatus for treating plated strip metal comprising: a first tank containing a hot bath, a second tank containing a cool bath, a duct joining said baths and having an entry into the second tank situated below its entry into the first tank, and means external to said hot bath and duct for conveying said strip metal therethrough and into said cool bath.

4. Apparatus for treating plated strip metal comprising: a first tank containing a hot bath, a second tank containing a cool bath, a duct joining said tanks and having an entry into the second tank situated below its entry into the first tank, said hot and cold baths being in substantial pressure equilibrium within said passage, and means external to said hot bath and duct for conveying said strip metal therethrough into said cool bath.

5. Apparatus for treating plated strip metal comprising: a first tank containing a hot bath, a second tank containing a cool bath, a duct joining said tanks and having an entry into the second tank situated below its entry into the first tank, means for conveying said strip metal exclusively in contact with the liquid of said baths, from said hot bath and through said duct into the said cool bath, means for injecting c001 liquid of said baths into said duct, and means for withdrawing liquid from said duct, the means for injecting said liquid being disposed closer to said second tank than the means for withdrawing said liquid.

6. Apparatus for treating plated strip metal comprising: a first tank containing a hot bath, a second tank containing a cool bath, a duct joining said tanks and having an entry into the second tank situated below its entry into the first tank, means for conveying said strip metal, exclusively in contact with the liquid of said baths, from said hot bath said cool bath, means for injecting cool liquid of said baths into the entry of said duct into said second tank, and means for withdrawing liquid from said duct at a point spaced from said entry.

JOHN F. FERM.

first tank conand through said duct into 0

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