US2601863A

US2601863A - Method of cleaning hot-dip tin-plate

Info

Publication number: US2601863A
Application number: US19303A
Authority: US
Inventors: Paul N Murphy
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1948-04-06
Filing date: 1948-04-06
Publication date: 1952-07-01
Anticipated expiration: 1969-07-01

Description

July l, 1952 P. N. MURPHY METHOD OF CLEANING HOT-DIP TIN-PLATE Filed April e, 1948 avoided.

ent .manufacturing practice.

Patented July 1, 1952 UNITED N STATE METHOD oF CLEANING.Hor-DirfriN-PLATE 4Paul N; Murphy, Hobart, Ind., assignorto United States Steel Company, a corporation lof New Jersey Appucautnnpril 6, 1948, serialize. 19,30

. 1 'This 'invention relates .tothe manufacture of tin-plate and, in particular, to animproved finishingtreatment thereof, i. e., the processing subsequent to the coating with tin, whereby discoloration or the Ikformation of surface film is Prime tin-plate should exhibit a brightsilvery appearanceandbe free fromwisible surface iilms or discoloration.'but completefreedoxn from vdiscoloration is .diiioult .to achieve under "the 'pres- Two types of discoloration are frequently encountered." The first is .the development vof a straw-yellow color on the sheet "when it lis heated incident `to lithographing or otherprocesses duringfabrication. The second 'is the appearance of a similar or even deeper color on the sheets before shipment from themanufacturer'tothe customer. It has been observed that the higherthe temperature of the palm-'oil `bath through which theytinned sheets emerge from the moltenl tin in the ordinary hot-dip tinning process, vthe greaterthe tendency to discoloration. `If -the palm `oil is kept below the temperature which causes discoloration, however, theresultis the formation 'of heavy list edges and beadsof tin on thesheets.

While such defects werenot considered very se- .riousinthe past, they havenow become so be- 'ca'use vof the increasingly high standards of "ing, however, because it rhas been generally accepted that a solution "strong `enough to vdo so would etch the sheets. `As a result, the amount of oil remaining cannot be precisely controlled and is 'frequently more or less than is `considered `desirable by the user. rI'he branning operation is objectionable,furthermorabecause of the dust createdthereby `in the tin house and further because the bran ucontaminates the 'surface of the material and results in eye-holing" `or discontinuousadherence of the .lacquer film applied 'tothe ,sheets before .fabrication `fof certain arlticles, such as .packing cans. .Many `sheets are cobbled .or otherwise Qdanaged in' the branning' machine, furthermore, `andha've to be scrapped.

It is accordingly the primary object jof :my

. invention Ato. provide la method of 'n'ishing tin- `plate whereby the product is free from'discoloration as well as Yheavy list edges and beads.

A further object `is `to simplify the -nishing process and reduce the cost thereof. A `still further object is Vto eliminate the branning operation entirely. Another object -is -to Iachieve complete removal of oil from the sheets during the washing.

In a preferred practice of the invention, VI deliver sheets of hot-dip `tin-plate, astheyemerge all palm oil from the sheets.

zov

`rinsed with hot water.

from the palm oil bath -oating on the molten tin in the tin-pot, without cooling and while `the `oil adhering thereto is still fluid, `directly linto a wash tank. After immersion in a solution of soda ash contained therein, they are fconveyed to a second wash tank containing a similar but less concentrated solution and are lthen -spray- The first 1washing .solution is strong enough to remove substantially As a .nnal operation,` therefore, I apply to the sheets .just the `precise amount of oil desired by the trade. A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the Vaccompanying drawings illustrating apparatus for carrying out 'the presentrpreferred practice. the drawings:

Figures 1V and i2 together constitute a -central vertical section through a :line of apparatus for subjecting tinned sheets `to the` finishing i is of Yknown construction andthe showingithereof 'is' largely diagrammatic since no detailed description is -necessary. It has aplurality 'of fexit rolls I'6 therein. Deflecting yrolls |612 above the 4tin-pot progressively bend .the sheets emerging successively therefrom for .delivery laterally of the pot. A guide chute I1 extends downwardly from 1a point adjacent the delector rolls and directs each sheet between a pair of entry or yfeed-'in rolls I8 journaled `on the near rsid'e of vthe wash tank I I.

Additional .pairs of traction lrolls I9 and 2B convey the sheet through Ithe "washing'solutioncontained in the tank Ill. The

4sheet is then passed between two Apa-irs of iwiping rol-ls 2'I which remove excess `washing .fso-

L lution by squeegee action, and discharged fonto InY y I1. vcomplete/removal' of the oil from the sheet in any suitable means.

which it enters the second wash tank I2.

accises tional traction rolls 24 and 25. The last of these delivers the sheet to two pairs of wiping rolls 26 which remove excess solution therefrom and deliver the sheet to a roller table 27. As the sheet passes over the table, it is subjected to a hotwater rinse by spray jets from pipes I3. A tank 28 is provided below the table for collecting the rinse Water flowing from the sheet.

The oiler I4 through which the sheet then passes comprises a pair of pinch rolls 29 which feed the sheet forward onto a roller table 3|).vv

Oil is supplied to the rolls 29 by a stack of rolls 3|, the upper one of which engages the bottom pinch roll. The bottom roll 3| rides on a wick 32 immersed in palm oil contained in a reservoir 33. The rolls 3| are provided with wiper blades 34 for controlling the amountof oil transferredY thereby.

After passing through the oiler and being delivered by the pinch rolls thereof onto the table 30, the sheet is engaged by pinch rolls I and `delivered thereby to a piler (not shown).

-The apparatus preferred for carrying out my g improved method having been descrbed'in detail, it remains to explain further the successive operations performed thereby upon the Vtinned sheet. The operation of the tin-pot is similar to prior practice except that I maintain the temperature of the palm-oil bath floating on the molten tin at a temperature between 460 and 480 F. The upper limit is controlled so that the -tin coating will be solidified by the time the sheet reaches the last set of exit rolls I6. This facilitateshandling of the material during subsequent processing. Moreover,

With the oil at the temperature stated, it remains highly fluid as the sheet bends over and falls down onto the guide This is advantageous from the standpoint of the two-stage cleaning afforded by the tanks II and I2. To insure entry of the sheets into the first wash tank before substantial cooling of the sheet and stiifening of the oil thereon, the rst wash tank is placed as close as possible to the tin-pot and the cooling conveyor, usually incorporatedin a tinning line, is omitted or made as short as possible.

The first wash tank II contains an aqueous solution of from 0.5% to`l.5% of soda ash or anhydrous sodium carbonate.

The solution is heated toa temperature of from 180 to 200 by The conveying rolls in the wash tank are driven and preferably the two rolls of each` pairare driven at slightly different speeds, thereby producing a rubbing action on the sheet. l The speed of the rolls is such as to cause the sheet to be immersed in the solution for -from Y5 to l0 seconds.

` The solution in the first wash tank, by`reason of its concentration and temperature, is effective to remove most of the I oil adhering to the sheet as a result of its passage f through the palm-oil bath floating on the molten f tin, on emerging from the tin-pot. rolls 2| remove washing solution adhering to the The wiping sheet and deliver it tothe roller table 22 from This tank contains an aqueous solution of from 0.10% to 0.25% of soda ash or anhydrous sodium carbonate and is maintained at approximately the same temperature as the solution in the rst wash tank. The rolls in the tank I2 are driven in the same manner as those of tank I Ii. As the it obviously eliminates v heavy list edges and beads of tin which would adhere to the sheet if the oil were maintained at a lower temperature.

, frequently occurs.

oil on both sides thereof.

`transferred from the wick to the pinch rolls 29 sheet passes through the solution in tank I I, the last trace of adherent palm oil is removed. Excess washing solution is removed from the sheet as it traverses the rolls 36 and it is then thoroughly rinsed by the spray jets of hot water (-200 F.) from pipes I3 as it passes along the table 21.

The nal operation of my improved method is the application to the sheet ofv a'predetermined amount of palm oil as it passes through the rolls 29 of oiler I4. It will be evident that, in the interval between the passage of successive sheets, the rolls 3| will transfer a film of oil from the wick to the rolls 29. This lm is applied to the sheet as it passes between the last-mentioned rolls. As a result, the sheets emerging onto the roller table 30 have a predetermined coating of The amount of oil and applied thereby to the sheet is controlled by adjusting the Wiper blades 34 engaging the transfer roll 3| and varying the speed of the latter. The finished sheets, coated with palm oil, are delivered by the lpinch rolls I5 to a piler and, after piling, are ready to be stored or shipped.

It will be apparent from the foregoing that the method of my invention is characterized by numerous advantages. In the first place, the sheets produced thereby are characterized by unusual freedom from discoloration despite the fact that the palm-oil bath in the tin-pot is maintained at a higher temperature than has heretofore been thought feasible. As a matter of fact, the material produced by my method is entirely free from discoloration when shipped'and does not develop this defect when lithographed under normal conditions. The tendency of tin-plate to discolor is graded on a numerical scale from zero to ten, the latter indicating very bad discoloration. vMy method makes possible the production of tin-plate possessing stain resistance of grades 1 and 2. This compares with the production of grades 3 and 4 by the conventional method of finishing tin-plate.

A further advantage is that the luster and reflectivity of tin-plate processed by my method are greater than that of the product resulting from the prior practice while no spangling is produced. My method, furthermore, eliminates the branning treatment altogether and thus does away with difficulties resulting from eye-holding as well as the objectionable contamination of the air in the vicinity of the processing apparatus by bran dust. Finally, the percentage of prime sheets produced is substantially increased as a result of the elimination of the branner in which cobbling'or other damager to the sheets As a result, the invention makes possible a reduction in maintenance and production costs.

Although I have illustrated and described but a preferred practice of the invention, it will be understood that changes in the procedure disclosed may be made without departing from the spirit of the invention or the scope ofthe appended claims. Y

I claim: Y Y

1. In a method of finishing hot-dip tin-plate, the steps including delivering sheets as they emerge from the palm oil oating on the molten tin in a tin-pot, before substantial cooling of the sheets, directly intoa hot soda-ash solution having a concentration between .5% and 1.5%, then passing the sheets through a second hot soda-ash solution having. a concentration between .10%

6. REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Ferm Dec. 27, 1938 Rath Sept. 12, 1944 Croft Sept. 26, 1944

Claims

1. IN A METHOD OF FINISHING HOT-DIP TIN-PLATE, THE STEPS INCLUDING DELIVERING SHEETS AS THEY EMERGE FROM THE PALM OIL FLOATING ON THE MOLTEN TIN IN A TIN-POT, BEFORE SUBSTANTIAL COOLING OF THE SHEETS, DIRECTLY INTO A HOT SODA-ASH SOLUTION HAVING A CONCENTRATION BETWEEN .5% AND 1.5% THEN PASSING THE SHEETS THROUGH A SECOND HOT SODA-ASH SOLUTION HAVING A CONCENTRATION BETWEEN .10% AND .25%, THEREBY REMOVING SUBSTANTIALLY ALL THE OIL ADHERING TO THE SHEETS ON LEAVING THE TIN-POT.