US2070368A

US2070368A - Method for enameling tanks

Info

Publication number: US2070368A
Application number: US25694A
Authority: US
Inventors: Wesley G Martin
Original assignee: AO Smith Corp
Current assignee: AO Smith Corp
Priority date: 1935-06-08
Filing date: 1935-06-08
Publication date: 1937-02-09
Anticipated expiration: 1954-02-09

Description

Feb. 9, 1937. w. G. MARTINl 21,070,368

METHOD FOR ENAMELING TANKS Filed June 8,' 19:55 2 sheets-sheet 1 l i :if J: ...l

ATTORNEY.

1NVENT0R.

A v Weslgy G Martz'n I BY fw Feb- 9,' 1937- w. G. MARTIN METHOD FOR ENAMELINQ'TANKS Filed June a, 1935 2 sheets-sheet 2 I FIG. 2.

INVENTOR. Wesley @Martin KfW ATTORNEY.

Patented Feb. 9, 1937 PATENTI oFFlcE MEfrnon Fon ENAMELING TANKS Wesley G. Martin, Milwaukee, Wis., assignor to A. 0. Smith Corporation, Milwaukee, Wis., a corporation of New York Application June 8, 19.35, Serial No. 25,694

' s claims. (ci. sii- 73) This invention relates to the application of vitreous enamel linings Ito the interiorsof tanks such as are used for the storage of beer, or milk, or other liquids which would be contaminated by Contact with metal.

An object of the invention is to provide an improved method for the application of vitreous enamel coatings to the-interiors of tanks.

A further object of the invention is to provide suitable apparatus for use in connection with the method.

Other objects of the invention will be clear from the following detailed description and the accompanying drawings, in which:

Figure 1 is a side elevation of a tank within a furnace'during the fusing of the enamel;

Fig. 2 is a side elevation, partly in section, of the apparatus used in carrying out the method of this invention, and constitutes an enlarged view of the left hand portion of Figure 1;

Fig. 3 is a top plan view of the apparatus;

Fig. 4 is an enlarged sectional view taken on line tof Fig. 3,; and

Fig. 5 is a sectional view taken on line 5--5 of 25 Fig. 4.

The application of a vitreous enamel lining to the interior of a tank presents a number of serious diiiiculties. A tank some eleven feet in diameter and thirty feet long has an internal sur- 3 face in excess of one thousand square feet, and

this surface Y.should `be completely covered with y surface of the tank, and another ring'in order to produce a tank which will be satisfactory for the purpose for which it is desired.' 'Due to the large size of the tanks which may be involved, a

40 large expense is involved in an additional firing to cure any defects which may exist in apreviously applied coat of enamel. For this reason it is desirable to have methods available which l will reduce to a minimum the possibility of de- 45 i'ects in an enamel lining of a tank.

One of the objects of my invention is to provide a'method for Aenameling tanks which will enable a satisfactory lining of enamel to be applied in a single coat. `A single coat lining is .3o preferable to a multiple coat lining on the ground of greater cheapness, and for some applications has other points of superiority as well, such as4 lesser thickness and greater resistance to injury by mechanical shock. In some cases a multiple coat lining may be preferred for particular reasons. 'I'he methods of this invention are of no less value for the production oi such multiple coat linings, for it is axiomatic in the enameling industry that the ground coat should be as faultless as it can be made. While blisters and cop- 5 perheads or other defects in the ground coat may sometimes be covered up by the subsequently applied coats of enamel, this by no means invariably occurs. Furthermore, a defective ground coat may reboll when the other coats are applied 10 and in this way give rise to serious diiliculty in the production of a satisfactory enamel lining.

In my co-pending application for patent, Se rial No. 730,063, iiled June 11, 1934, and since issued as U. S. Letters Patent No. 2,004,632, I have l5 disclosed that dimculties which are frequently encountered when an enamel is burned in air may be avoided if the enamel is fused to its metal base in an atmosphere substantially devoid of free oxygen; Steels which give rise to such vdefects as copperheads or blisters, or which cause reboiling when the enamel is fused in air, can be satisfactorily enameled if the enamel is burned in a suitable atmosphere substantially devoid of free oxygen as disclosed in my co-pending application. Carbon dioxide is an example .of a suitable atmosphere which is disclosed in that application. l

The present invention is concerned specically with methods and apparatus for the convenient and rapid expulsion of free oxygen from within the tank which is being fired. In carrying out the method of this invention, it is preferred to first heat'the tank while it is filled with air in order to produce a lm of oxide on the inner sur- A face of the metal tank, and to then replace the air by a different gas before the temperature has risen suiciently to fuse the enamel.

According to this invention the air initially within the tank is driven out and replaced by 40 anotherY .gas by introducing this gas into the heated tank in solid form. This method of `filling the tank with gas possesses a number of important advantages. The solidied gas is itself of small volume but expands enormously when it is vaporized in the tank. 'Many of the tanks which are enameled on the inside are of very considerable dimensions and have a volume of several thousand cubic feet. It is desired to drive out the airl and If gas were pumped into the tank` to drive out the air it would be necessary to either supply a large pipeleading from the tank to the outside of the furnace in which it is heated,

. 0r, in case a small pipe is used, to employe. very 55 high gas velocity.' Neither of these expedients is desirable; By using gas in the solid form these difficulties .are avoided. The atmosphere desired in the tank is introduced in condensed form and expands in volume after it is within the tank.

Carbon ,dioxide is an example of a gaseous at- I mosphere which is suitable for the burning of carbon'dioxide blown into the tank tend to settle to the bottom because of their Weight. Since the tank is hot when the solid carbon dioxide is introduced, it is rapidly converted into gas. This will occur at or near the bottom of the tank. Since carbon dioxide is a much heavier gas than air it will lie beneath the air initially within the tank and' rise beneath it. ItV is, of course, not to be expected that there will be no mixing of carbon dioxide gas'with air but it will be readily appreciated that there will be much less admixture and much more effective utilizationpf the carbon dioxide if it is introduced at the Abottom of the tank. The openings provided for the exit of air should be located at the top of the tank.

In enameling a tank according to-my improved method, the tank is first made and prepared for enameling. In case the tank is fabricated from sheet steel by electric arc welding with certain kinds of electrodes, it is desirable that the welded tank be treated according tothe methods disclosed in my co-pending application, Serial No. 25,695, filed on even date herewith, in order that no. difficulty may be experienced in getting the ^enamel to adhere to the electric'arc welds. 'After the'tank has been' thus treated, the inside is sandblasted, imperfections uncoveredin the steel plates are ground out, and the ground patches are preferably sandblasted again. The sand is cleaned from the tank and a coat of enameling material is applied to its inner surface by any suitable method, as by spraying. Any suitable enameling material can be used. The coating of enaineling material is then dried. This may be conveniently done by passing a current of filtered air through the tank and heating the outside with alarge gas ame.

Suitable covers are provided for the openings in the tank. These should desirably be made as `tight as possible. One of the openings is provided with aninlet pipe of sufficient length to reach well beyond the furnace when the tank is placed within the furnace for firing. vThe opening to which the inlet pipe is connected should preferably be near the bottom of the tank. One of the openings at the top of the .tank is provided with a valve which is originally open to permit the escape y of air but which can be closed by a wire leading outside the furnace.

- Thus equipped, the tank is placed on a car and introduced into a furnaoe'for fusing the enamel.`

'I'he inlet pipe extends beyond thev furnace and is connected to suitable apparatus for introducing solid carbon dioxide chips into the, tank.

Referring to Fig. 1, the `tank I is shown supported on car 2 within the furnace 3 in which the enamel is fused. 1 'I'he furnace may be heated by any suitable means as by electricity or the combustion of'fuels. An opening 4 near the bottom of the tank is covered by a manhole cover to which the inlet pipe 6 is fastened. Another opening I near the top of the tank is provided with a valve .8 which can be closed by wire 9. A

smell tube II! is connected to the inlet pipe I5 near the tank. At its outer end the pipe is .connected to a water manometer I I for measuring the pressure differential between the gas within the tank and the outside atmosphere.

The outer end of the inlet pipe t is secured to a connector l2 which'has a branch inlet I3. The

branch inlet I3 is secured to a hose It for supplying air or other gas under pressure', and the conlto be shut oi from both.

The apparatus I6 for converting blocks of solid carbon dioxide into chips or shavings and injecting them into the tank comprises a 4rectangular box I9 supported on a suitable framework 28. A ilanged opening 2l is provided at the top of the box topermit the introduction of blocks of solid carbon dioxide. into the machine. A cover 22 is provided to close the box after it is :dlled with carbon dioxide blocks. The cover bears on gasket 23 and is held in place by clamps 24, thus assuring a tight joint.

A plunger 25'tting within the box I9 is carried on a piston rod 25. A piston 2l secured to the piston rod 26 travels in the air cylinder 28. By means of the valve 29 and ports 30 and 3l, air from a compressed air line 32 can be admitted to either end of the air cylinder 28. The piston casing 35. A toothed cylinder :3e is supported within this casing by shaft 3l running in bearings 38. The toothed cylinder is driven in the direction indicated in Flgs. 2 and 4 by an electric motor 39 supported on brackets 40. l

The lower side of the cylindrical casing 35 is connected to the fan-shaped outlet il which in turn connects with the tube I5. At the Wide end of the outlet 4I is placed a block 42 extending the full width of the outlet. This block has a longitudinal chamber 43 with which forwardly directed openings i4 communicate. The rotating cylinder 36 has teeth provided on its outer surface for shaving chips of carbon dioxide from carbon dioxide blocks d5 placed in any suitable way as by a small gas producer operated under pressure to produce an atmosphere composed essentially of carbon dioxide and nitrogen, or by a compressor forcing ue gas into the block 42; or, as indicated in the drawings,

by' a battery of liquid carbon dioxide cylinders 46. These cylinders are connected through Avalves 41 Aand pipes 48 to a header 49 which communicates with the chamber 43. An orifice or Venturi meter- (not shown in the drawings) may desirably lbe inserted in the line leading from the header 49- to the chamber 43 to indicate the rate at which carbon dioxide is being drawn from the cylinders. When carbon dioxide be connected together so that they can be used in turn.` An excessive drain from any one cylinder resultsin a lowering of its temperature and may cause its contents to freeze.

A gas burner 50 supplied with gas by tube 5| may desirably be placed below .the box I9 to keep the carbon dioxide blocks 45 from freezing to the bottom of the box.

Tie rods 52 connected to the framework of the 4 apparatus lead to an eye 53 by means of which the whole equipment may be readily lifted with a crane and placed in any desired position.

In using the method and apparatus of this invention, the tank to be lined with enameling material is provided with coverings for the openings and with an inlet pipe 6 as previously described, and is placed upon the car 2. The car is then run in to the heated furnace 3 and the tank begins to heat up. The apparatus for injecting solid carbon .dioxide into the tank is connected to the pipe 6.' As the tank heats up the air which it initially contained expandsand escapes through the opening 'I and valve 8.

' After the tank has been sufficiently heated to cause the formation of a thinfllm of oxide on the inner wall of the tank, ythe motor 39 is started and air pressure is admitted to the left hand end of the air cylinder 28 toforce blocks of carbon dioxide previouslypplaeed in the box I9 against the rotating toothed wheel 36. One or more of the valves 41 is opened to provide a current of gas from carbon dioxide cylinders 46 to blow the chips shaved from the carbon dioxide blocks by the rotating cylinder into the tank. The carbon dioxide chips are' vaporized by the heat of the tank, and the gas which is 'formed forces the air out through the valve 8. The

rate of admission of carbon dioxide to the tank is controlled by .the manipulation of valve 29 allowing air to enter the air cylinder 28 and is so regulated that the gas pressure within the the valve 8 is closed by pulling on the wire 9.

'Ihe closure of the valve will greatly diminish the rate at which gas can escape from the tank but there will ordinarily be sufficient leakage to require the continued gradual admission ofcarbon dioxide in order to maintain the pressure within the tank somewhat above the atmospheric pressure. The gradual admission of carbon dioxide rnay be effected by reducing the rate at which solid carbon dioxide chips are blown into the tank, or the valve I8 may be closed and clean flue gas under pressure admitted through the valve I1 which is so regulated as to maintain a suitable lpressure within the tank. Flue gas consists predominantly of carbon dioxide and nitrogen and when cleaned of solid particles which might deposit upon and injure the enamel, is a suitable atmosphere for the burning of enamelsi but it will not, of course, as rapidly replace the air Vwithin the tank Aas will carbonl when this stage has been reached air can be admitted through the valve Il' to maintain a n the tank while it is in a heated condition because this helps to maintain its shape.y

With the particular furnace which has been 5 used, some forty to forty-five minutes was taken for firing a tank about eleven feet in diameter and thirty feet long with walls 1,41 in thickness. About ve minutes after the tank was run into the furnace the admission of carbon dioxide was l0 begun and was continued at a sufficient rate to maintain a few inches of water pressure within the tank. The valve 8 was closed about twenty minutes after the tank entered the furnace. This reduced the rate of escape of gas from the l5 tank. Carbon dioxide was admitted slowly to make good the loss of gas by leakage and to maintain Iwithin the tank about the same pressure as before. About twenty-*five minutes after the tank entered the furnace it had reached a 20 temperature of some 1500 ,to 1600 F. The valve I1 was closed and a pressure of several inches of water was afterwards maintained by the-admission of air'. The firing was completed in about three quarters of an hour and the tank was 25 removed from the furnace to cool. Very satisfactory results have been-obtained by the use of this method of firing. Defects which frequently occur when air is the atmosphere Within the vtank are substantially eliminated. e30

' risen sumciently high to fuse the enamel and thereafter admitting air to the tank to maintain within it a pressure in excess of the atmospheric pressure. y 2. The method of fusing a vitreous enamel 5 lining to the interior 'of a tank which comprises heating the tank in a furnace with air in the tank in order to form a layer of oxide on the lnterior of the tank below the coating of enameling material introducing solid carbon dioxide within 50 the tank to force out the air which it originally contained and maintaining a carbon dioxide atmosphere within the tank until its temperature has risen suiliciently high to fuse the enamel.

3. The method of fusing a vitreous enamel 55 -lining to a tank which comprises heating the 'admitting air to the tank to maintain within it a pressure in excess of the atmospheric pressure.

4. In the fusing of a vitreous enamel lining to 55 the interior of a tank, the step which comprises replacing air within the tank with another atmosphere by introducing solid particles of the other atmosphere into the tank-and thereafter V vaporizing them'to forma gas. 70

5. In the fusing of a vitreous enamel lining to the interior of a container, the step which comprises replacing air within the container with another atmosphere while the container is being heated and before it has reached the fusing temperature of the enamel, by introducing solid. par ticles of the other atmosphere into the container and thereafter vaporizing them to form a gas.

6. In thefusing of a. vitreous enamel lining to the interior of a container, the step which. comprises replacing air within the container with carbon dioxide gas by introducing solid carbon dioxide into the container and thereafter vaporizing it to form carbon dioxide gas.

7. In the fusing of aL vitreous enamellining to the interior of a container, the steps which comprise heating the container with an omdizlng atmosphere therein to form an oxide lm on the inner'surface of the container, and thereafter replacing the atmosphere `present in the contain? er with a diierent atmosphere by introducing solid particles of said diierent atmospherein'to the container and vaporlzing them to form gas'.

8, In the fusing of a vitreous enamel lining to the interior of a container, th steps which comprise heating the container with air therein to form an oxide film on the inner surface of the containerrland thereafter replacing the air within the container with carbon dioxide gas by introducingesolid particles of carbon dioxide into the containierl and vaporizing them to form carbon dioxide" gas.

1 WESLEY G. MARTIN.