US2390007A

US2390007A - Apparatus for continuously hot dip coating of tin on coiled strip

Info

Publication number: US2390007A
Application number: US516551A
Authority: US
Inventors: Sherman Clifton William
Original assignee: Dominion Foundries and Steel Ltd
Current assignee: Dominion Foundries and Steel Ltd
Priority date: 1943-12-31
Filing date: 1943-12-31
Publication date: 1945-11-27
Anticipated expiration: 1962-11-27

Description

Nov. 27, 1945. c. w. SHERMAN 2,390,007

APPARATUS FOR CONTINUOUSLY HOT DIP COATING OF TIN ON COILED STRIP Filed Dec. 51, 1943 2 Sheets-Sheet 1 Nov. 27, 1945. c. w. SHERMAN 2,390,007

APPARATUS FOR CONTINUOUSLY HOT DIP COATING OF TIN ON COILED STRIP 2 Sheets-Sheet 2 Filed Dec. 31, 1945 Elma/whoa Patented Nov. 27, 1945 APPARATUS FOR CONTINUOUSLY HOT DIP COATING OF TIN N COILED STRIP Clifton William Sherman, Ancaster, Ontario, Canada, assignor of one-third to Dominion Foundries & Steel Limited, Hamilton, Ontario, Canada, and one-third to C. W. Sherman, trustee for Dominion Foundries & Steel Employees Savings and Profit Sharing Fund Application December 31, 1943, Serial No. 516,551

6 Claims. (Cl. 91-124).

This invention relates to an apparatus for continuously hot dip coating of tin on coiled strip.

In the ordinary method of producing tin plate stock a mild or low carbon steel strip is used as a base on which the plating is effected. In this ordinary method of coating a strip of desired thickness is drawn off from an ingot, passed through a brittle scale remover which removes the magnetic brittle iron oxide from the surfaces of the stock. The uncoated stock is then passed through a looping bath to remove all possibe remaining iron oxide and red oxide dust. From the bath the stock passes and is sprayed by water for forcible further cleaning. Upon the stock being thus cleaned it is passed through several sulphuric acid baths for pickling or removing all of the oxide that is so held by the strip that it could not be removed by the previously described steps. Then the stock is subjected first to a hot water spray for removing the sulphuric acid and then to a further cold water spray after which the stock is given a hot water rinse to raise its temperature to such point as will effect prompt drying upon exposure to the atmosphere. This last hot water rinse further acts to remove any traces of sulphuric acid or oxides. In order to hasten the drying process the stock is exposed to the action of a blower, after which it is oiled with mineral oil to prevent any oxidization and is then coiled and weighed.

The stock, in this condition, may be stored indefinitely but when it is desired to plate this stock it is passed through a series of rolls known as a leveler which flattens the stock and removes thecurvature due to the coiling. When flattened, the stock is cold rolled, being provided with a suitable coating of soluble oil to assist the rolling and acts as a coolant. After the rolling process the stock is treated to an alkaline spray wash to remove the oil used in cold rolling and is then hot water sprayed 'and roller brushed to remove all free alkaline solution after which it is submitted to an electrolytic alkaline bath for removing the last traces of oil. After this alkaline bath the stock passes through a further bank of scrubbing brushes and cold water rinse to leave the stock as clean as possible and it is again heated and dried by a hot water and a hot air drier, after which the stock is again coiled. This completes the process of preparing the stock inordinary machines prior to annealing and finishing.

In" tinning under the conventional process the stock, treated as above, is annealed by'dry heat to soften the metal hardened in cold rolling, the annealing taking place in an atmosphere of neutral gas. The stock is then tempered to give the required polish and hardness, is roll sheared (trimmed) and separated into sheets. It is to be noted that at this point the process accomplished by the new apparatus will be seen diverged from the commonly used apparatus since the new process provides for a continuous process which does not require the separation of stock into sheets while being tinned.

In the conventional process these sheets are then pickled and washed in crates, and stored, and then passed through a flux, a bath of molten tin, and up through an oil bath. In the oil bath rollers press against the now tinned sheet on each side thereof, these rollers being supposed to control the thickness of the tin coating on the stock. It is to be noted that the rollers above mentioned are necessarily located in the oil bath to more or less control the coating, and the oil temperature has a controlling effect on the thickness of the tin deposited. Due to the often inaccurate control of the thickness of the tin coating on the stock the conservation of tin has not hitherto been effectively accomplished.

One important object of the present invention is to provide an apparatus whereby the thickness of the tin plating on stock may be accurately controlled, and uniformity of that thickness attained, so that only such quantities of tin as are actually needed will be used, thus effecting the conservation of tin since none will be wasted by excess or unnecessary thickness of coat.

A second important object of the invention is to provide means to improve the quality of coating of equivalent weights of tin on the stock whether the same be deposited by the heretofore known electrolytic or hot dip process.

A third important object of the invention is to reduce the labor of tin plating by providing.

an apparatus which will reduce handling by combining steps in a continuous manner thereby to eifect a lower cost of production and a greatly enhanced out-put.

The presentconventional type of white pickling introduces some undesirable conditions in the actual tin plating of the base plate in the conventional hot-dip machine. Hot water is a better rinsing agent than cold water. It can be employed in this new hot-dip apparatus but not in the conventional hot-dip apparatus. If warm or hot water is employed as a rinsing agent in connection with the conventional method of pickling, the plate becomes green or oxidized while being rinsed and transferred from the crates to the boshes. It can and often does occur even when cold water is used.

In the conventional system of tinning, white pickling and rinsing is an extraneous step in the process. The new apparatus provides for pickling and rinsing as a continuous feature.

No storage of plate after rinsing is required. Pickling and rinsing take place almost simultaneously with timing; the pickling of the plate being thus greatly simplified. The new apparatus provides for a system of pickling similar to that used in the black pickling of hot rolled strip.

The number of moving parts in the new apparatus is greatly reduced over that of the conventional hot-dip machine. In actual tinning in the pot the new apparatus conserves tin by eliminating the drip edge. This cannot be eliminated in the conventional hot-dip machine. This drip edge has been estimated to comprise from 7% to of the weight of tin coating per base box of plate. A further saving in tin lies in the ability of the new apparatus to apply a lower coating than that obtainable by the conventional hotdip process. The range is greater than that accomplished by conventional apparatus. Coatings can be applied by the new apparatus from .20

8 lbs. per base box.

The physical and chemical characteristics of the plate processed by the new apparatus are improved. A sample of plate processed by the new apparatus possessing the same coating weight as a sample taken from a sheet processed by the conventlonal hot-dip method has a better protective surface. Its coating is moreevenly applied. In fact, it is uniformly applied. The conventional method coats the plate in a "hill and va e" manner. A better bond results from the new apparatus than in electrolytic tinning previous to "reiiowing. Reflowing is unnecessary with the new apparatus.

The alloy layer is considerably less than that possessed by tin plate processed in the conventional hot-dip machine. Because of this more tin is released for actual protection of thebase plate.

The improved equipment for the remainder -of the tin plating process removes the oil and polishes the plate much similar to that in the conventional hot-dip method. The washing and polishing of the plate is accomplished by a washer and polisher built to accommodate the fast moving strip.

It is further to be noted that the new apparatus removes all necessity for storing stock until tinned in a bath of weak muriatic acid as is done in the conventional process to prevent posbefore entering the flux and by heating this strip there is prevented particles of flux being carried through and trapped between the tin and oil layers of the bath, such undesirable condition causing a matte finish and sweaty plate instead of the high polish desirable.

Finally the gas and oil spray used just before recoiling the tin plate strip gives an additional means for controlling the thickness of the coating, and effecting uniformity of the coating.

With the above and other objects in view the invention consists in certain novel features embodied in the apparatus hereinafter fully described, the apparatus being diagrammatically vention.

Figure 1B is'a similar illustration of the right 7 hand end of the machine.

Figure 2 is a perspective view of a broken portion of a section of a run of the strip in intimate association with a certain spraying device.

It is to be understood that Figure 13 illustrates the portion of the machine wherein raw stock enters the machine, this end being preferably termed the rear end, while Figure 1A shows what is preferably known as the front end.

Mounted on suitable standards it is a reel or drum l'i holding a strip of stock such as mild or low carbon steel, the strip being coiled on the drum. This strip is indicated at l2 and passes over an idler roll I 8 located above the rear end of a pickling bath I4 containing the usual pickling acid. The strip l2 dips down into this bath and passes around a rear idler roll I! and a front idler roll it and then upwardly from the bath to run over a roll I! and under a roll l8, the rolls l1 and I8 acting to express much of the pickling solution, these rolls being rubber or rubber coated so that they act as squeeze rolls. After passing over the roll I! the strip l2 passes down into a bath N of clear water and is held beneath the surface of this water by the idler rolls 2' and 2|. This bath is the equivalent of a water rinse bath and from it the strip passes upwardly between rubber squeeze rolls 22 to enter a flue 22 and passes up that fine to a roll 24.

At 25 is a furnace for melting tin in a tin pct 28 and from this furnace a flue 21 communicates with the flue 22 adiacent the'lower end thereof so that the strip i2 is dry heated as it passes and downwardly through a heating device 28 readily than a 'hot surface. These particles offend by causing a smoky or rough surface to the coated or tinned stock. Heated or hot stock does not attract these particles, and acquires less but suflicient flux. The device 28 preferably consists of a pair of heating elements closely embracing the strip I 2 but not touching the same so that the latter may pass freely between the heating elements.

In the upper part of the tin pct 28 is a well 30 located directly below the lower end of the heater 28 and this well is arranged to hold the necessary flux 3|. Thetin 82 is melted in the lower part of the pct 26 and is covered by a heavy layer of oil 38. The strip l2 after passing through the flux enters the molten tin, passes down under an idler roll 84 and up past a spring tensloned idler roll 88 serving to keep the strip taut. This strip then extends through the oil bath 88 on top of the tin.

At 36 is a furnace and air from a suitable source of compressed air enters this furnace through a pipe 31, is heated in the furnace and passes out through a pipe 38 which communicates with a sprayer 39 arranged to force this hot air against the opposite sides of the ascending run of the strip I2. 7

This so-called sprayer may consist of any suitable structure designed to deliver a uniform spray and a typical form is well illustrated in Figure 2. In that embodiment the sprayer conveniently consists of a pair of hollow opposed arms or bifurcations 39a preferably having narrow slits 39b through which the gas or fluid is equally and forcibly driven against the strip l2, in passing, and these arms are commonly united at one end in the form of a distributing box 390, and as can be seen, intimately embrace the upward run of thestrip l2. This spray treatment forms one of the most importantfeatures of our invention. A valve 40 controls the air or fluid flow through the pipe 38.

An oil tank orreservoir 4| is provided and from this reservoir a pipe 42 leads to a pump 43 driven by a suitable motor 44. From the pump 43 a pipe 45 leads to the oil in the tin pot 26, the flow of oil being controlled by a valve 46. In order to maintain a uniform level of the upper surface of the oil in the tin pot there is provided a pipe 41 which leads from the desired level of oil in the tin pot back to the tank 4|, the oil being delivered to the tank through a filter. This pipe may be well termed the over-flow pipe.

From the pipe 45 extends a branch 48 which leads to the sprayer 39 and is controlled by a valve 49. By this means any desired proportion of oil or hot air may be used'in the sprayer 39. It is obvious that when necessity requires the valves 40 and 49 may be so'regulated that the sprayer may be used only with the hot air, only with the oil, or with a mixture of both. At times it is desirable to alternately spray air and oil and obviously the control of the valves permits this or any other condition of spraying which is found to produce'the best results. Furthermore while the pipe 39 has been referred to as a hot air pipe it is to be noted that this pipe may be used to convey super-heated steam or any other gas to the spray 39.

The sprayer 39 is used to regulate, by its action,

the thickness of the coating deposited on the base metal, by washing back excess plating metal from the base metal strip and depositing the same through the oil bath back into the plating bath. At this point the thickness of the deposited coating on the base metal may be accurately controlled and uniformity of that thickness effected. After passing upwardly through the sprayer 39 the now tinned strip passes through a second sprayer 50 of similar character to the sprayer 39 but preferably provided through a pipe with air which may be either hot or cold and this second sprayer assists in driving back to the oil bath any oil which may remain on the tinned strip after passing through the sprayer 39. This sprayer 50 is located at the top of a hood 50a and by this means the newly tinned strip is held from contact with the outer atmosphere so that oxidizing is avoided and no waste of oil can occur. The strip then passes up and over an idler roll 52 and down to a coiling drum 53 driven by any suitable means such as is indicated by a motor 54.

It will now be seen that this improved apparatus is fitted to accomplish a continuous process under which very long strips of stock may be continuously tin coated from a coiled stock and. without any severance, the tinned strip re-coiled or otherwise prepared for storage. I

There has thus been provided a simple and eflicient device of the kind described and for the purpose specified.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, therefore, desired to confine-the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

Having thus described the invention, what Ls claimed is:

1. In an apparatus for producing plated metal, means to hold a long length of base metal, means to pass the metal through cleaning means -in preparation for plating, means to dry the base metal passing from the cleaning means, .a heater, means to pass the base metal through the heater for heating the same, a flux bath, means to pass the heated metal through the flux bath, a coating bath, means to pass the metal from the flux bath directly through the coating bath, an oil bath resting on top of the coating bath, means to pass the metal from the coating bath through the oil bath, uniform pressure spray means, means to pass the metal through the spray means to uniformly remove excess coating and the oil, and means to dry the coated metal in prepara tion for storage.

2. In an apparatus for producing plated metal, means to hold a long length of base metal, means to pass the metal through cleaning means in preparat on for plating, means to dry the base metal passing from the cleaning means, a heater, means to pass the base metal through the heater for heating the same, a flux bath, means to pass the heated metal through the flux bath, a coating bath, means to pass the metal from the flux bath directly through the coating bath, an oil bath resting on top of the coating bath. means to pass the metal from the coating bath through I the oil bath, uniform pressure fluid spray means,

means to pass the metal through the spray means to uniformly remove excess coating, pressure dryspray means, and means to pass the metal through the second spray means to remove the fluid and to dry the metal in prepara tion for storage.

3. In an apparatus for producing plated metal, means to hold a long length of base metal, means to pass the metal through cleaning means in preparation for plating, a flux bath, means to pass the metal through the flux bath, a coatin bath, means to pass the metal from the flux bath directly through the coating bath. an oil bath resting on top of the coating bath, means to pass the metal from the coating bath through the oil bath, uniform pressure spray means. means to pass the metal through the spray means to uniformly remove excess coating and the oil, and means to dry the coated metal in preparation for storage.

4. In an apparatus for producing plated metal, means to hold a long length of base metal, means to pass the metal through cleaning means in preparation for plating, a flux bath, means to pass the metal through the flux bath, a coating bath, means to pass the metal from the flux bath directly through the coating bath, an oil bath resting on top of the coating bath. means to pass the metal from the coating bath through the oil bath, uniform pressure fluid spray means, means to pass the metal through the spray means to uniformly remove excess coating, pressure dry spray means, and means to pass the metal through the second spray means to remove the fluid and to dry the metal in preparation for storage.

5. In an apparatus for producing plated metal, means to hold a long length of base metal. a pickling bath, means to pass the metal through the pickling bath, means to express excess material from the pickling bath, a washing bath, means to pass the base metal from the pickling bath through the washing bath, means to express excess washing material, means to dry the base metal passing from the washing bath, a flux bath, means to pass the metal through the flux bath, a coating bath, means to pass the metal from the flux bath directly through the coating bath, an oil bathresting on top of the coating bath, means to pass the coated strip from the oil bath to a spraying mechanism for uniformly removing excess coating material and also the oil, further means in the path of the coated material to remove the remainder of oil therefrom, said further means including a housing to prevent contact of atmospheric air to the plated material. and means to reassemble the plated material. 1

8. In an apparatus for producing plated metal, means to hold a long length of base metal, means to pass the metal through cleaning means in preparation for plating, a flux bath, means to pass the metal through the flux bath, a coating bath, means to pass the metal from the flux bath directly through the coating bath, an oil bath resting on top of the coating bath, means to pass the metal from the coating bath through the oil bath, pressure spray means. means to pass the metal through the spray means to remove excess coating and the oil, and means to dry the coated metal in preparation, for storage, said spray means including a pair of parallel hollow arms'arranged one on each side of the path of the freshly coated metal and extending at least the width of the metal, said arms having spraying openings directed to the path of the metal and arranged to efi'ect a spray of equal force and of equal distribution against each face of the travelling metal throughout its width.

CLIFTON WILLIAM SHERMAN.