US2348698A

US2348698A - Method of roller coating

Info

Publication number: US2348698A
Application number: US351900A
Authority: US
Inventors: John S Thompson
Original assignee: Parker Rust Proof Co
Current assignee: Parker Rust Proof Co
Priority date: 1940-08-03
Filing date: 1940-08-03
Publication date: 1944-05-09
Anticipated expiration: 1961-05-09

Description

2 Sheets-Sheet 1 May 9, 1944. J. s. THOMPSON METHOD OF ROLLER COATING Filed Aug. 5, 1940 May 9,1944. J. s. THoMPsoN METHOD oF ROLLER coATING Filed Aug. 3, 1940 2 Sheets-SheKet 2 Patented May 9, `1 944 2,848,698 METHOD oF ROLLER coA'rING John S. Thompson, Detroit, Mich., assignor to Parker Rust Proof Company, Detroit, Mich.

Application August 3, 1940, serial No. 351,900

7 Claims.

This invention relates to the coating of metal and particularly to prepare the surface of metal to receive paint, dye, lacquer or the like, and is a continuation in part of my application, Method of roller coating, Serial No. 199,129, filed March 31, 1938. It has been known for some time that the surface of metal may be changed or converted from one of metal to one of non-metal by the use of various solutions. The art first taught the submerging of the article to be coated or converted into the solution and allowing the article to remain therein until the coating operation had been completed. Later it was discovered that coating could be obtained by spraying the solution upon the article to be coated either while the article remained stationary or while it was being passed through a chamber upon a conveyor, the spray bombarding the article with solution and bringing about the conversion necessary to completely coat the article. It has now been discovered that fine corrosion retarding coatings may be obtained upon metal surfaces by passing the metal through a plurality of rollers which have Ibecome wet with a solution which will convert the surface from one of metal to one of nonmetal.

In the preparing of metal surfaces to resist corrosion a great many solutions are known which in turn form many types of coatings, according .to the solution used. Of the better known coatings the phosphates, chromates, oxalates, and oxides lead the field today.

The method herein disclosed is particularly useful at the mill or point of metal manufacture because it enables the manufacturer to coat the sheets as they come from the nal manufacturing step preparatory to shipping. The problem has presented itself of preventing corrosion of sheets between the time they leave the mill and the time they reach the point where they are to be used. At times the sheets are not used for weeks and even months and in this interval ,corrosion sets in and necessitates an additional operation to remove this rust, before painting. With the present method the sheets are treated immediately following the last manufacturing step so that the method lits into the modern mill or modern manufacturing plant as another `step or operation and saves the user forwarding his stock to a jobber or separate plant to have his sheets prepared for painting. l n

The principal object of the present invention is to provide a new and improved method for converting the surface of metal from one of metal to one of non-metal.

Another object of the present invention is to provide a new and improved method of coating metal which aids in the precleaning of the sheets, the rollers per-forming a scrubbing and pressure action thereon which lessens the effect of extraneous and deleterious lmatter that usually adheres to the sheets in their travel through the various manufacturing steps.

A still further object is to provide a new and improved method for coating metal whereby thc surface of the metal is not only transformed from one of metal to one of non-metal, but the sheets are dried, Water rinsed and acid rinsed to prepare them for the immediate application of paint, lacquer, dye or the like.

The above and other objects will appear more fully from the lfollowing more detailed description, and from the drawings, wherein Fig. 1 is a top plan view of the apparatus used to carry out this method of coating metal; and

Fig. 2 is a section of the apparatus taken substantially on the line 2-2 of Fig. 1.

Referring now to the drawings, the numeral I9 designates supporting means for supporting the superimposed apparatus for carrying out the method herein disclosed. Conveniently located at one end of the apparatus is a solution reservoir Il above which is suitably located an additional solution reservoir I2 for a purpose later to be described. Conveniently located at the other end of the apparatus is a pair of rinsing tanks I3, I4, and midway between the solution tanks and rinsing tanks there is provided a heating and drying chamber comprising a heat producing means, which in the drawings is shown as a gas pipe I5 having a plurality of holes I6 therein for the gas flame which in turn impinges a base plate having a plurality of flns I1 formed integral with the base of the heating chamber merely as an illustrative example.

and running transversely thereof to provide a greater heating area to said chamber. Any well known heating means, such as coal or electricity may be used, gas being used in this illustration Immediately above and formed integral with the heating means Just described is a heat circulating chamber into which air is brought from atmosphere through duct I9, said duct being provided with damper means 28 to close the duct when required. A circulating fan 2| is conveniently provided within the heat circulating chamber I8, the same being rotated by means of motor 22. superimposed upon and built integral with the heat circulating chamber I8 is a drying chamber 23. A warm air duct 24 connects heat circulating chamber |8 and drying chamber 23 and a plurality of directional bales 25 act to direct the warm air in the circuitous path desired. An additional duct 26 is provided to connect the drying chamber 23 with the heat circulating chamber I 8 and to return part of the air back into the heat circulating chamber and deposit the same directly back to the circulating fan 2| so that it may -be again passed over the heated fins I1 and returned to the drying chamber 23. A damper 21 is conveniently located within duct 26 so that this duct may be closed when desired. -A hood 28 is located directly above and built integral with the drying chamber 23 and provides means for taking oil' the fumes by means oi' a stack 29 having a damper 38 located therein to close the stack when desired. Suspended within the drying chamber 23 is a pair oi' endless conveyor` chains 3| with a plurality of spaced transverse ribs 32 supported thereon (shown -best in Fig. 1 of the drawings) said ribs having secured thereto a plurality of pointed pins 33 which act as supports for the metal sheets as they are carried by the conveyor. The pins are tapered or pointed to reduce the area covered on the sheet by the pin so that practically the entire sheet will receive warmed air during the drying operation. The conveyor chains 3| are trained about a pair of sprocket wheels 34, and to prevent the conveyor chains from sagging there are provided supports 35 comprising a pair of angle irons which in turn support each chain as they make their run. The numeral 36 designates a transverse opening or slot provided to allow the sheets to pass into the drying chamber 23 and numeral 31 designates an opening or transverse slot to allow the sheets to pass from the drying chamber 23 to the rinsing operation.

Suitably located within the solution reservoirs is the mechanism for applying the corrosion retarding solutions which comprises a solution feeding roller 38 which is at all times partially submerged in the solution, contained in reservoir I2. Roller 38 is at all times in mesh with a driving roller 39 which in turn is in mesh with a driven solution feeding and spreading roller 48. Driven roller 4| is at all times partially submerged in solution reservoir II and is at all times in mesh with driven solution spreading and feeding roller 42. To compensate for the various thicknesses of sheets which are passed between rollers 48 and 42 there is provided vertical adjusting means located adjacent lower reservoir I I, the adjusting means comprising a slidable bearing 43 for adjusting roller 42 and a slidable bearing 44 for adjusting roller 4| by means of adjusting screws 45, 46. Roller 48 is mounted on shaft 48, the shaft being mounted in arm 49, which is integral with -arm 58 which is rotatably mounted on shaft '"41. The numeral 5I designates a portion of the machine frame in which shaft 41 is mounted. Portion 52 of the machine has a slot 53 formed therein to allow for movement of bolt 54 so that the same may be either raised or lowered in said slot, said adjustment permitting roller 48 to be moved toward or away from roller 42. These rollers are operated through a train of gears 55, 56, 51 which are suitably mounted on the end of shafts 41, 48, 58. 'I'he lower feeding rolls 42 and 4| also are operated through gears 59 and 88,

v gear 59 being directly beneath gear 51 and in mesh with same. 'The machine frame projection 52 has mounted thereon a scraper 6| which is provided with an adjusting means 62. Lower coating roller 42 is also provided with an adjustable scraper 63 provided with adjusting means 64. The main driving means comprises pulley 65 having a belt 66 trained thereon, said pulley being secured to shaft 41 so that when the shaft is rotated gear 56 is rotated and in turn rotates gears 55, 51, 59 and 68. A pair of guide rollers 61, 68 are provided to guide the sheets so that they will pass between the coating rollers 48, 42. Steam pipes 69 and 18 are provided in the upper and lower solution reservoirs to keep the solution at the temperature desired for processing. A drain pipe 1| is provided in reservoir to clean out the same when necessary.

After the sheets have passed through the drying chamber 23 a plurality of apposed guide rollers 12, 13, 14, 15 carry'the sheets between rinsing means comprising a pair of transverse pipes 19, 11 containing a plurality of apertures therein to allow the rinsing medium to escape onto the sheets. 'I'hese pipes are fed by stand pipe 18 and directional bales 18, 80, direct the spray so that it impinges directly upon the sheets and thoroughly sprays the entire area. beneath the pipes. Another pair of rollers 8|, 82 drive the sheets between an additional rinsing means comprislng a, pair of transverse pipes 83, 84, containing a plurality of apertures therein to allow the rinsing medium to escape onto the sheets. These pipes are fed by stand pipe and directional bailies 86, 81, direct the spray so that it impinges directly upon the sheets and thoroughly sprays the entire area. beneath the pipes. An additional pair of driving rollers 88, 89, carry the sheets from beneath spray pipes 83, 84, and out of the apparatus. Driving rollers 12, 15, 8| and 88 are driven by belts 98, 9|, 92, 93 trained about pulleys 84, 95, 96, 91 (see Fig. 1 of drawings). 'I'he rollers as shown are of rubber and bonded to shafts as follows: roller 12 to shaft 98, roller 13 to shaft 99, roller 15 to shaft I 88, roller 14 to shaft |8I roller al to shaft luz, roller sz to shaft los, roue; 88 to shaft |84, and roller 89 to shaft |85. Although rubber is shown, any adsorbent material may be used, or metal rollers smooth or suitably corrugated may be substituted. Steam coil |86 is conveniently located in reservoir I3 to keep the rinsing solution at the desired temperature and steam coil |81 is located in reservoir I4 to keep the rinsing solution in this reservoir at the desired temperature. A drain pipe |88 is located in the bottom of reservoir I3 so that the same may be dumped when necessary.

Although the process may be operated with many different corrosion resistant solutions to coat many types of metals, such as iron, steel, zinc, cadmium, copper and lead, there are given below a few specific examples of corrosion retarding solutions. These examples are given by way of illustration and not limitation, it being understood that wide deviations are possible in ingredients, proportions. temperatures, etc., without departing from the spirit of the invention:

To coat zinc use- Parts by volume 1. '75% phosphoric acid 8 60% nitric acid 6 Water To coat zinc, iron and cadmium use- 2. Zinc dihydrogen phosphate lbs-- 8.2

50% zinc nitrate solution lbs-- 36.5 '70% nitric acid av.ozs 14 Copper carbonate grams-- 57 Wetting agent (Novonacco NN) ..cc 'Z5 Water lbs-- 74 To coat iron and steel use- Per cent 3. Zinc dihydrogen phosphate 2.8 75% phosphoric acid 2.5 Chromic acid 1.0 Wetting'agent (Novonacco NN) .4 Balance Wate To coat iron and stee1 use- 4. Zinc dihydrogen phosphate grams 140 Copper nitrate do 28 Water liters.k 4

To coat iron and steel use- Per cent 5. 100% phosphoric acid 8.5 Chromic acid 9.0 Wetting agent (Duponol) 1.0 Balance Water To coat zinc use- 6. Oxalic acid grams-- 360 Sodium nitrate do 120 Ferrous sulfate -do 60 Fullers earth 1bs 4 Water gallon 1 To coat iron, zinc, cadmium, copper and lead use- 7. Oxalic acid lbs-- A rinse with a solution containing chromic acid or other hexavalent chromium compounds, preferably in an acid medium may be used following the use of any of the above coating solutions to enhance the corrosion-resistance and paint-bonding properties of the coatings.

In some instances it is diilicult to obtain uniform wetting of the metal by the coating solution especially where relatively high concentrations of chromic acids or other hexavalent chromium containing solutions are employed. In such instances it may be necessary to rst pre-treat the metal by means of solutions which will produce a surface which is more reactive with the hexavalent chromium containing solution than the untreated metal.

The first treatment, as indicated above, may result in a coating essentially oxide, a coating of a metallic deposit, a coating of a salt of iron and additional salts, if desired, or in mixtures of any two or all three of the types mentioned, and may include sulphides or other ingredients which perform like functions.

For example, the first step may be treatment with any one of the many known phosphate coating solutions, or with solutions of organic coating acids, such as described in Patent No. 1,911,537, to Robert R. Tanner, for example. But, if a solution of this type is employed. whether with or without oxidizing agents, accelerating metal compounds, or other obvious modifications, the treatment should be limited so as to produce a much thinner coat than has been hitherto generally desired as a product of such solutions, so that the major part of the nal coating is produced by the second treatment, and preferably so that the second solution may treat the metal surface as well as the product of the iirst treatment.

The following examples will serve to illustrate means by which oxide coats may be produced upon metal.

Upon steel, rst coatings have been produced by treating the surface of the metal with a solution for two minutes where the solution contained as its active chemical 2.5% of the nitrates of manganese, chromium, magnesium, cobalt, iron. lead, cadmium, zinc, aluminum, mercury, or copper, or 5% nitrate of strontium, barium, or calcium.

Widely different concentrations of solutions may be employed and likewise the temperature and time of treatment may be varied, such variations in the strength of the solution, and the time and temperature of treatment being adjusted to obtain the desired thickness of coating in accordance with the principles stated in con-` nection with the detailed disclosure of the second treatment.

As a specific example a solution of the following analysis may be applied to steel sheets by rollers and be allowed to stand in contact with the metal for a period o! thirty seconds.

The metal which during this time receives a coating which is predominantly oxide, after receiving a water rinse, is roller coated with a solution having the analysis of Per cent Phosphoric acid 6 Chromic acid 3 Trivalent chromium .5

The coated sheet is then heated at a temperature of 550 F. for 10 minutes in order to render the applied film insoluble.

The general procedure involving the application of solutions adapted to coat the metals by means of rolls is carried out as follows:

The solution to be used to convert the surface of the metal to be treated from one of metal to one of non-metal is rst placed in the solution reservoirs Il and I2 and the solution` for rinsing is placed in the rinsing solution containing tanks I3 and I4. If desired, steam is then injected into the various steam coils in the reservoirs sothat the corrosion retarding and rinsing solutions will become heated to the desired temperature. The means for heating the heating chamber beneath the fins I1 is then ignited and fan 2| is turned on. The damper 20 in duct I9 remains at its dotted line open position, as shown best in Fig. 2 of the drawings, so that air is brought in from atmosphere and heated. Inasmuch as it is necessary to have the proper pressure on the Work |09 as it passes between rollers 40 and 42, and also to compensate for the various thicknesses of material being run through said rollers, the gear train controlling these rollers must be adjusted so that the proper opening remains constant all during the run. To adjust solution spreading roller 48, bolt 54 located in slot 53 in frame portion 52 is moved upwardly, and, inasmuch as rollers 48, 39 and 3B are journaled in movable arm 58, which in turn is rotatably mounted on shaft 41, gears 55, `56 and 51 located on the ends of shafts 41, 48 and 58 respectively, remain in mesh and the peripheral rubber surface of rollers 48, 39 and 38 also remain in frictional engagement ready for use. To compensate for this upward movement of rollers 48, 39 and 38, rollers 42 and 4| must be moved upwardly so that the gearing on their shafts is also in mesh and the gear 59 remains in mesh with gear 51. Adjusting screw 45 allows for movement upwardly or downwardly of roller 42 and adjusting screw 46 allows for movement upwardly or downw :ily of roller 4|, so that their gears 59 and 68 are always in mesh and the face of these two rollers are always in frictional contact. The scraper 6| mounted on machine frame projection 52 is then adjusted by means of adjusting screw 62 so that the proper pressure is brought to bear on roller 39, said scraper preventing any sludge from contacting solution spreading roller 48, and also to provide a means to control even distribution of the corrosion retarding solution when transferred to roller 48. 'I'he lower coating roller scraper 63 is also similarly adjusted by means of adjusting screw 64 for a like purpose. The solution spreading gear train is now set in motion beit 66 turning on pulley 65 in a counter-clockwise direction which in turn drives driving roller 39 in a counter-clockwise direction as shown by the arrow in Fig. 2 of the drawings. As rollers 40 and 38 are in mesh with driving roller 39 roller 38 will turn in a clockwise direction and roller 48 in a clockwise direction, as shown by the arrow in Fig. 2 of the drawings. Roller 38 being partially submerged in coating solution in reservoir I2 picks up solution, and inasmuch as rollers 39 and 48 are in frictiona-l contact at all times this solution is transferred to solution spreading roller 48 which in turn transfers the solution to the work |89. Likewise roller 4| is also partially submerged in coating solution in reservoir and inasmuch as roller 4| is in mesh with solution spreading roller 42 at all times, solution is transferred to roller 42 and thence to the work |89, the rollers turning in the direction of the arrows shown in Fig. 2 of the drawings. The work |89 passes first through guide rollers 61, 68 and when the work is passed between solution spreading rollers the pressure exerted upon the work by the rollers tends to squeeze the solution between the rollers and the surfaces of the Work, thereby causing wetting of said surfaces, and consequently the surface of the work is quickly transformed from one of metal to one of non-metal. Upon the completion of the conversion step, i. e., converting the surface from one of metal to one of nonmetal, by means of the spreading rollers 48, 42, impregnated with corrosion retarding solution, the work passes through opening 36 into drying chamber 23, where it is picked up by conveyor 3| and transported through this heating chamber at a predetermined speed to allow for a thorough drying of the work. In some cases, depending upon the type of solution being used, and the character of the work being'processed, heat may be required to produce the coating, the rollers merely serving as a means of application. Also,

in some cases, after applying the solution, by means of the rollers, time is required to complete the conversion of the surface of the metal from one of metal to one of non-metal, heat not being necessary.

'I'he conveyor chains 3| which in turn support the transverse cross members 32 having the supporting pins 33 thereon is driven by a source of power not shown, at a convenient speed to thoroughly dry the work before it reaches the rinsing operation. There is an opening between each cross member to allow heated air to pass therebetween, and inasmuch as the work is supported by the pointed pins 33 the heated air is allowed to contact the under surface o1.' the work and dry the same. Warm air also passes around the ends of the conveyor and between the sheets, as shown best by the arrows in Fig. 2 of the drawings and thus the air above the top of the work becomes warmed and infturn tends to dry the top of the sheets as they pass along on the conveyor. If it is desired to increase the temperature of the air within the hood 28, the damper 38 in stack 29 is closed and the warm air will follow a circuitous path back down through duct 26 and will again be blown by fan 2| over the heating means in the base of warm air chamber |8 and up through duct 24 and directional baffles 5 to again be used as a drying agent for the ork. Damper 28 in duct I9 may also be closed so that no fresh air will enter the warm air chamber 8 and this in turn will raise the temperature of the air already in drying chamber 23, and convert drying chamber 23 into a baking oven of any desired temperature.

When the work |89 has been dried it passes from the conveyor through opening 31 and between driving and guide rollers 12, 13, 14, 15, rollers 12 and 15 being driven by means of belts 98, 9| trained about pulleys 94, 95 (see Fig. 1 of the drawings). Rollers 13, 14 are rotated by friction contact with the work. As the work leaves rollers 15, 14, it is passed between rinsing pipes 16, 11, which run transversely of the work so that the sprays from the apertures therein thoroughly rinse the entire surface of the work passing beneath the pipes, the directional bailies 19, 88 guide the rinsing solution directly on the work. The rinsing solution, usually water at this step of the process, is heated in reservoir I3 by means of steam coil |86 and is pumped to riser pipe 18 by a pumping means, not shown, from whereI it enters pipes 16, 11. 'After rinsing, the solution runs off the work and falls into reservoir |3 to be repumped to riser 18 and used over and over again. 'Ihe work then passes between drivrg roller 8| and driven roller 82, driving roller 96, driven roller 82 being rotated by frictional contact with the work as it moves between the rollers. The work is then passed between a pair of additional rinsing pipes located directly above reservoir I4, the pipes being located above and below the work and run entirely across the work. A number of apertures allows the solution to be sprayed onto the work and directional bafes 86, 81 guide the ow of solution directly against the work. The rinsing solution is heated in reservoir |4 by means of steam coil |81, and is pumped, by means not shown, to riser pipe 85 from where it is carried to pipes 83, 84 and onto the work, the excess solution returning to reservoir I4. This final rinsing solution usually contains a dilute solution of chromic acid, phosphoric acid, oxalic acid or a salt of iron, chromium or being driven by belt 92 trained about puuev aluminum, such as aluminum nitrate or sulphate, ferrous sulphate, ferric nitrate and chromic sulphate or nitrate. It has been found that by the use of a final rinse, such as that described above. paint blistering is reduced to a minimum. The solution may be used from 150 to 180 F. From i to 21 ounces of the acid or salt per 100 gallons of water is the preferred strength from the standpoint of economy, although stronger solutions are just as effective. A treatment of one minute in these solutions is sufcient. Following the above described rinse, the work passes between driving roller 88 and driven roller 89, driving roller 88 being driven by means of belt 93 trained about pulley 91, roller 89 being driven by frictional contact with the work. Having passed through the last two mentioned rollers the work is ready to be force dried or air blown, following which paint may be applied.

As an example of a solution for coating zinc, iron and cadmium to be fllowed with a chromic acid rinse, the following is given:

To 'I4 pounds of water add- Zinc dihydrogen phosphate lbs 8.2 50% zinc nitrate solution lbs 36.5 '70% nitric acid av. ozs-- 14 Copper carbonate grams-- 57 .Wetting agent (Novonacco NN) cc 75 (Novonacco is a trade-marked product, obtained by the interaction of a hydrocarbon with sulphuric acid, the product is manufactured by The National Aniline and Chemical Company, Inc., of New York, N. Y.) A coating produced with the above solution may be followed by a rinse comprising 14 ozs. of chromic acid per 100 gals. of water used.

It will be seen from the above description that there is here set forth a new and unique method of coating metal preparatory to-painting. This method may be installed at the mill and become another step in the manufacture of sheets or it may be installed in the jobbing plant where the sheets may be treated before painting and formed into the finished article. Also one side only of the sheet need be coated, the reservoir holding the coating solution supplying either the upper or lower coating roller may be emptied so that only one roller receives solution. Where common immersion or spray methods of applying chemically reactive corrosion retarding solutions are employed and the solution is applied over and over again, it must be replenished with proper chemicals to keep it in balance so that it will coat successfully. The roller method herein disclosed requires replenishing ofthe solution reservoirs insofar as the solution being used is concerned,

but where the applying rollers transfer the solution from the solution reservoirs to the work and the solution stays on the work and is not returned to the solution reservoirs, the problem of keeping the solution in balance is overcome.

What I claim is:

1. In the chemical treatment of a metallic surface to form a corrosion-resistant paint-holding base thereon, the steps of moving a metallic surface in non-immersed condition past a roll having a yielding surface thereon, pressing the roll against the metallic surface during said moving, feeding an aqueous solution containing paintbase-fonning chemicals between said roll surface and saidmetallic surface, adjusting the pressure of the roller against the metallic surface so that said solution is pressed into chemically reactive contact with said metallic surface and the desired amount of solution remains on said metallic surface and forming a paint-holding coating on the metallic surface from the chemicals so applied and their reaction products.

2. A method in accordance with claim 1 and comprising rst applying a nlm of the solution to a roller and then transferring the solution from the roller to said surface.

3. A method in .accordance with claim 1 wherein the treated metallic surface is of the class consisting of iron, zinc and their alloys.

4. A method in accordance with claim 1 wherein the treating solution is an aqueous solution of compounds of P04 and of compounds of hexavalent chromium. Y

5. A method in accordance with claim 1 wherein the treated metallic surface is of the class consisting of iron, zinc and their alloys and the treating solution is an aqueous solution containing compounds of P04.

6. A method in accordance with claim l wherein the treated metallic surface is of the class consisting of iron, zinc and their alloys and the treating solution is an aqueous solution containing compounds of P04, and comprising the added step of applying a solution containing hexavalent chromium to coating produced by said chemicals.

'1. In themethod of providing a metallic surface with a corrosion retarding and paint-bonding coating, the steps of moving said surface in a non-immersed condition past a roll, feeding to said surface in a position to be spread on the surface by said roll a solution adapted to prodtclng a more chemically reactive surface than is the metallic surface with a solution containing hexavalent'chromium, and thereafter applying in the same manner a solution containing hexavalent chromium.

JOHN S. THOMPSON.