US2543320A - Apparatus for spraying molten material - Google Patents

Description

M HUNTOON ETAL ,320

APPARATUS FOR SPRAYING MOLTEN MATERIAL 12, 1946 5 Sheets-Sheet l Qrwe/wtow MAURICE HUNTOON LE RQY J. JOHNSTON Feb. 27 1951 Filed Nov.

Feb. 27, 1951 M. HUNTOON ETAL 2,543,320

APPARATUS FOR SPRAYING MOLTEN MATERIAL Filed Nov. 12, 1946 s Sheets-Sheet 2 :e w a 5' I i Q i FA '5 ,4 q E5 Q I so MAURICE HUNTOON LEROY J. JOHNSTON WWW,

Feb. 27, 1951 M. HUNTOON EIAL 2,543,320

APPARATUS FOR SPRAYING MOLTEN MATERIAL Filed Nov. 12, 1946 3 Sheets-Sheet 3 gin/001M009 MAURICE Humoom LEROY J. Jouns'ron Patented Feb. 27,

UNITED STATES PATENT OFFICE AP ARATUS FOR SPRAYING MiDLTEN MATERIAL Calif a corporation Application No e er -6 Se a No- '3 9,159

8 Claims.

This invention relates to apparatus for spraying or atomizing coating materials; and it relates mo e par icular y to ap arat s of hi g a charac wh an be usefully pl y in p tectively coating fresh fruits and vegetables with a film-like covering of waxy material.

the .oomme o al p epar i n of fresh fruits an ve etables for mar t, it h l g b moo prac ice to provide them w a protective film coating of waxy mate al o de t r tard shrinka e and othe wise t m nta them i good marketa le conditio The me d h ieriound to be most effecti e and des fo his purpose invo e, as one ep in he r i procedure, melting a suitable wax or wax-like composition and finely so -vine or .ato e' the molten material, thereby su d d it n very small particles whi h, in t e f of a ve y fine spray, mist or fog, are then brought into ontact with he art les t e oe d- Said artiples are usually s bjected simultaneousl to a brushing or rubbing operation adapted to distribute the waxy mat ial un formly over their surfa es as a continuous thi In one Way of practicing such a coating procedur the molten coating material i spra into a heated chamber through which the artielse to be coated are passe t e mp ra u of the atmosphere i sa d cham r e n m ntained so high, commonly at least as high as the melting point'of the coating material employed and usually substantially higher, that the minute waxy particles discharged in o he chamber are still molten or semi-molten when they strike the a-Articles a d are thus t mo e pe fe ly sp ead over the surface thereof, by action of the revolving brushes, for example, upon which the articles travel through e heate cham er. This pre tice is illustrated by such patents as Brogden 1,641,112, Brosden and owbridee 1,940,530, Skinner 1,830,297, and Pierce 1,940,269. In another typ of procedure, disclosed in the patent to Burwiek et al. 2,364,946, the brushing chamber is unheated, and the operating conditions are such that the atomized mo t n ax par cles livered into said chamber by the atomizer or nebu ize are chi led and .neea y t e mu h oole temperature o the ch mber o ph re before they can cont c the a c es to be coated. In both ases, h wever, it wi l be s n that th initia step of melt ng and praying the l n ax i fine y div de cond t on i t to a n chamber is essential, and that provision of appa ratus capable of performing this operation most effectively and efficiently is important.

The present invention is concerned with improvements rendering more eliective, dependable and economical the operation and upkeep of spraying .Or atomizing apparatus units of the genera-l type disclosed in detail in the aforesaid patents to Skinner 1,836,297 and Pierce 19610269, more particularly. It i fpirther concerned with an improved combination of such a unit with a brushing or rubbing chamber such as is disclosed in these patents and also in Burvvick et a1. 2,364,946.

The use of apparatus units of the aforesaid type in packing houses, for spraying or atomizing molten wax in connection with the protective coating or" fresh fruits and vegetables undergoing preparation for market, has always presented certain servicing and upkeep problems which have proved extremely troublesome and, heretofore, impossible to solve satisfactorily in a practical man-her, despite repeated persistent attempts by skilled worker 'in the art continuing throughout the greater part of the "last twenty years. A serious and particularly baffling problem has been presented by the pronounced tendency of the pump pistons or plungers of the positi-ve or force feed mechanism supplying molten coating material to the spra jets, to become varnished with a tenaciously adherent gum-my material to such an extent at times that the pistons stick or freeze in their cylinders, thus a rendering it necessary to disassemble and thoroughly clean the parts of the pump mechanism more or less frequently in order to maintain it properly operative. Another difiiculty has been undue deterioration of the copper tubing through which, because of its high heat conductivity, the necessary heat units have customarily been transmitted, electrically or by steam, to melt down the solid coating material in the supply tank and maintain the molten material hi hly fluid. It ha be n the pra ti e her iore t. use such t bula atin elements in ompar t ely shor len th and to ope ate t em er hot in order o su ply t e equired am un o h t rapid y e ou h A in, muc tr b e as bee xp r e c b caus o the sp a n zle tu es be coming plugged with solid wax due to the rapidity with which they cool and freeze the wax con..- t ned in them; a th lo mo omm nl n co ntered, o ourse wh n attemptin to resume Wa in opera i ns io lowing the usu ov rnight shut-down of th packing plant.

A general object or" the present invention is to provide a spraying unit construction of the general type mentioned which can be employed for the purposes hereinabove described, substantially without encountering the difficulties and objections heretofore characterizing the use of such units for those purposes. This, as well as other objects and advantages of the invention and the manner in which they are attained, will be apparent from the disclosure hereinafter.

It was finally discovered that the gumming up and sticking of the feed pump pistons or plungers in prior spraying units was mainly due, not to resinous impurities sometimes naturally present in waxy coating material commercially available, as might naturally be supposed, but rather to the deposition on the pistons and cylinder walls of organic compounds of copper, such as copper soaps of organic acids, relatively insoluble in the molten coating material and evidently formed by reaction of certain corrosive agents present in said material upon the copper tubing of the heating elements employed in the supply tanks of those prior spraying units. Those heating elements, which were commonly short-copperjacketed electrical resistors, presented such a small heat-transfer surface that they had to be operated very hot, that is, at a relatively high skin temperature, in order to supply the required amount of heat to the coating material in the supply tank. While fatty or other organic acids may be present naturally to a small extent when a vegetable wax, such as carnauba, forms a minor part of the molten coating composition, it was found that the principal cause of coppersoap formation, and consequently of the trouble due to freezing of the pump plungers in their cylinders, was the excessively high skin temperature of the heating elements aforesaid. This caused localized overheating of such part of the waxy coating material as came into actual contact with the copper surface of the heating elements and resultant thermal decomposition or cracking to an appreciable extent. The products of such cracking of waxy material, both mineral (paraffin) and non-mineral (carnauba) include organic acids and other corrosive agents. Of course, only such coating material as actually contacted said tubes was subjected to that skin temperature. The temperature of the main body of material did not exceed that required for good fluidity, say 220 F. or thereabouts as a practical maximum.

Once the underlying cause of the troublesome sticking or freezing of the feed pump pistons in their cylinders was discovered, it became apparent that this difficulty could be overcome by suitably changing the character of the heating system employed in the wax supply tank of the spraying unit. In accordance with the principles of the invention, therefore, this is accomplished by providing for the supply tank a heating system such that the skin temperature of the heating means, that is, the temperature of the heating surfaces actually contacted by any'of the coating material, can be maintained below that at which any substantial decomposition of the coating material will occur, while at the same time the heat units required for melting the coating material and maintaining it in properly fluent condition for fine-spraying or ato-mizing can be supplied to said material at a sufficientiy rapid rate to be practical. In other words, the heating system employed in the spraying apparatus of the invention is characterized by substantially lower heat transference per unit area as compared with prior apparatus of this kind, and hence by larger area of heating surface for a given total heating capacity.

The relatively low operating skin temperature of the heating or heat-transmitting means employed in the coating material supply tank of the improved sprayingunit has thefurther advantage, where the heating tubes are copper, of greatly reducing the liability to corrosion of the tubes by fatty or other acids present naturally in the coating materials to be melted. However, partly because the use of copper tubing in such a low intensity heating system sometimes involves mechanical difficulties, and also in order further to guard against deposition of copper soaps on the feed pump pistons, a particularly desirable practical embodiment of the invention employs a heating system which presents no copper or other similarly corrodible surface which the coating material can contact. Instead, thinwalled tubing of steel is employed which is virtually immune to attack by any of the coating material components, at least at all temperatures below that sufiicient to decompose or crack the coating material. Thin-walled steel tubing possessing the required resistance to corrosion is a commercially available product.

The former difiiculty due to stoppage of the spray nozzle tubes through chilling of wax therein is overcome in the improved apparatus by locating the tubes wholly within the supply tank except for a short downwardly directed terminal portion of each projecting through and below the tank bottom, which terminal portion may itself be formed as a spray nozzle or, alternatively, may be adapted for detachable coupling to a nozzle tube extension.

The nature of the invention will be further apparent from the accompanying drawings which illustrate a desirable practical embodiment thereof. In these drawings,

Fig. 1 is a top plan view of the sprayer unit, with the cover members removed to expose the underlying parts;

Fig. 2 is a front elevation, partly broken away and in section, and with certain parts removed;

and

Fig. 3 is an end elevation, viewing the unit from the right.

Referring to the drawings, the coating material supply tank indicated generally at it], has side walls ll, bottom 12 and a removable cover l3. Mounted within the tank upon its bottom is a force feed device indicated generally at M.- While this may be of any suitable type, a particularly desirable device for the purpose is that known in the trade as the Madison-Kipp Model 0L force feed lubricator; and in the specific ap paratus here illustrated, it is this device which is employed for feeding molten coating material under pressure, in accurately adjustable small quantity, to each of the spray jets or nozzles l5, of which there are six in the present example, through the respective individual delivery tubes it, which may be of copper, for example. For the detailed construction of this force feed device, which forms no part of the present invention, reference is made to the patent to Cole-s 1,934,344. Drive shaft l! by which the device is operated extends through the sidewall of the tank and may be connected to the variable speed transmission of suitable power means (not shown) through clutch members l8, l9 and pulley or sprocket 2D; the clutch members being engaged or disengaged through operation of clutch-shifting mechanism .21. 2. .2 thrqueh. ante atal as..

5 A screen or filter member 25 aids in removing suspended solid particles from the molten material entering the intake of the force feed device.

Compressed and heated air for atomizing the molten coating material pumped to the spray nozzles is supplied to the nozzles from air supply main or reservoir 25. This latter enters the tank through one end wall, extending horizontally towards the other through the lower part of the tank and, at a point somewhat short of the other end wall, being connected to a transversely extendin air header 2?, from which individual branch air tubes or passages 28 extend downwardly to where they are joined by the respective tubes i6 carrying molten coating material fed through them by force feed device it. In the construction here illustrated, the air header 2'! and the passages 28 branching therefrom are formed in a header block or base 29 positioned on the tank bottom, with the coating material supply tubes secured to said block and leading into the respective passages as shown; thus providing a structurally compact and rigid header unit for delivery of both molten coating material and compressed air to the spray nozzles below. An air compressor (not shown) suitably connected to air main 26 supplies air thereto at a rate adequate to maintain a substantially constant pressure therein suitable for atomizing purposes; and in moving through said main and header 2?, the air is heated by the hot molten coating material in which both the main and the header are submerged.

In the present illustrative example, steam under suitable pressure provides the heat units for melting down the solid coating material placed in the supply tank and maintaining the molten wax properly fluid, as well as fOr heating the compressed air in reservoir 26. A steam heating coil or grid is therefore provided, consisting in this instance of one piece of thin-walled steel tubing 36 bent to provide a plurality of turns or convolutio-ns affording the required total length, extending continuously from inlet to outlet and supported slightly above and substantially parallel to the tank bottom. Steam is supplied to the coil through steam line 3i connected to its inlet end and provided with a control valve 32; While spent steam leaving the outlet end is carried on through pipe 33. The supply of steam to the heating coil in proper amount to maintain a body of molten coating material in the tank at a given desired temperature is automatically adjusted as necessary by means of a suitable thermo-regulator, of

which various types are well known and commercially available, adapted and arranged to govern the setting of valve 32 in the steam supply line, and thereby the rate of steam supply to the heating coil. In the present instance the thermoregulator is of the type known as the Leslie steam control, the heat-sensitive element 3d of which is immersed in the molten material in the tank and electrically connected by lead 35 to valve-actuating means 36' responsive thereto.

It will be observed that the tubes 37 which carry the mixture of air and molten coating material extend directly down through the bottom of the tank and project only a short distance below the same. These short projecting end portions 38 are threaded to enable removably attaching the downwardly directed spray nozzles 55 by means of couplings 39. Since the copper tubes which carry the molten coating material from the feed device I 5 to the detachable spray nozzles l5 lie wholly within the tank it and are submerged in the body of molten coating material contained therein, the typical normal liquid level of which is indicated by dotted line Ail, these tubes are maintained so hot throughout their entire length for a considerable period of time after any shut down that continued fluidity of coating material contained in the tubes when the shut-down occurs, for a sufficiently long time to enable adequately complete drainage therefrom, is assured. The danger of the tubes becoming stopped up through chilling and solidification of coating material remaining therein is thus obviated.

Directing the spray supply tube discharge outlets directly down through the bottom of the supply tank has another important advantage in that it enables combining the spraying unit with a heated brushing or rubbing chamber in a manner which makes for increased dependability and efficiency of operation, and lower cost of servicing. In prior art combinations of this general character, the spray unit has been mounted on the cover or roof the chamber, with the spray supply tubes extending laterally from the spray unit for some distance and then downwardly through special openings in said cover into the chamber. According to the present invention, however, an opening ll, into which the lower part of the present spray unit is adapted to fit snugly, is provided in the cover portion of the housing, indicated generally at 42, which encloses the revolving horse hair brush rolls 43 of a transverse roll polisher of well known type. the housing is heated, typically to around 200 by any suitable heating means such as steam coils 44 here shown located underneath the brush.

rolls. In this arrangement, therefore, not only is the bottom or" the supply tank ill exposed directly to heat from below, but so also are the nozzles l5. This latter consideration further en sures freedom from plugging of the spray tubes with solidified coating material during operation, which sometimes occurred in prior practice. Moreover, should the nozzle tubes by any chance fail to drain properly when a shutdown occurs and therefore become plugged with solidified coating material, the customary half-hour warming up of the brushing chamber preceding resumption of plant operation sufilces to melt such material and remedy the stoppage.

Even where the polisher chamber is unheated, as in the apparatus disclosed in Burwick et al. 2,364,946, mounting of the new spraying unit therein in the manner just described is likewise practically desirable and definitely an advance over prior constructions. Upon the rare occasions when stoppage of the short-nozzle tubes l5 may occur following shut-down, the plugged nozzles may be detached from the bottom discharge outlets 38 of the spray supply tubes and quickly replaced by spares, while the plugged nozzles can then be cleared by heating under safe conditions. This contrasts with the hazardous heating of plugged tubes directly on the job, as by means of a blow torch, which sometimes;

The atmosphere inside.

, '7 What is claimed is:

1. Apparatus for spraying normally solid heat decomposable coating material in molten condition, which comprises, in combination, a supply tank, a heating coil therein for melting solid coating material and maintaining the molten material at a temperature sufiiciently high for good fluidity, said coil being so proportioned as to present a heating surfac sufficiently large to render the coil capable, when suitabl supplied from a source of heat energy, of rapidly imparting to the coating material the heat units required for the purposes stated, at a tube skin temperature above that required for good fluidity but below the temperature at which substantial decomposition of said coating material commences, a source of heat energy for supplying said coil, a thermo-regulator device adapted and arranged to adjust the supply of energy from said source as may be necessary tomaintain the moi" ten material at a predetermined temperature above its melting point and below its decomposition point, spray means, a force feed device of the piston or plunger type mounted within said tank adjacent said heating coil, adapted and arranged to feed molten material l'rom said supply to said spray means, and means for driving said force feed device.

2. The invention defined in claim 1, wherein the heating coil is formed of a metal more resistant than copper to attack by organic acids.

3. The invention defined in claim 1, wherein the heating coil is formed of thin-walled corrosion resistant steel tubing.

4. Apparatus for spraying normall solid coat- 5- ing material in molten condition, which comprises, in combination, a supply tank, a heating coil therein for melting solid coating material and maintaining the molten material at a temperature sufficiently high for good fluidity, a force feed device mounted within and upon the bottom of said tank, delivery tubing located virtually within said tank and below the normal liquid level of the molten material, leading from the discharge of said device downwardly through said bottom, said tubing being terminally provided with spray nozzle means located beneath said bottom, means for driving said force feed device to feed molten coating material through the delivery tubing from said tank to such spray nozzle means, and means for also supplying heated air under pressure to said delivery tubing to atomize at said nozzle means the molten coating material fed thereto.

5. The invention defined in claim 4, wherein the means for supplying heated air under pressure to atomize said molten coating material includes a compressed air reservoir connected to said deliver tubing and located within said tank near enough its bottom to be wholly submerged by the normal tank content of molten coating material, and means for supplying air under pressure to said reservoir.

6. The invention defined in claim 4, wherein said force feed device has a plurality of discharge outlets to which a plurality of delivery tubes are individually connected for supplying molten coating material to a corresponding plurality of spray nozzles, a compressed air reservoir located within said tank and near enough its bottom to be wholly submerged by the normal tank content of molten coating material, means for supplying air under pressure to said reservoir, and air conduit means, located wholly within the tank and submerged by the molten coating material, connecting said reservoir with each of said delivery tubes at a location within said tank.

7. The invention defined in claim 4, wherein said force feed device has a plurality of discharge outlets to which a plurality of delivery tubes are individually connected for supplying molten coating material to a corresponding plurality of spray nozzles; a compressed air reservoir and a header conduit connected to said reservoir for receipt of compressed air therefrom, both located within said tank and near enough its bottom to be wholly submerged by the normal tank content of molten coating material, a plurality of air tubes extending downwardly from said header and connecting it with said delivery tubes individually,

8. Apparatus for spraying normally solid coating material in molten condition which con prises, in combination, a suppl tank, heating means in said tank for melting solid coating ma terial and maintaining the molten material fluid, a force feed device located within said tank and driving means therefor, spray nozzle means outside the tank, conduit means connecting said force feed device with said nozzle means for delivering molten coating material to the latter, a compressed air reservoir located within said tank near enough its bottom to be wholly submerged by the normal tank content of molten coating material, means for supplying air under pressure to said reservoir, and piping comiecting said reservoir with said conduit means.

MAURICE HUNTOON. LE ROY J. JOHNSTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,549,999 Moller Aug. 18, 1925 1,575,526 Bocher Mar. 2, 1926 1,587,736 Schenck June 8, 1926 1,741,155 Hatch Dec. 31, 1929 1,968,992 Conkling Aug. 7, 1934 1,983,140 McCathron Dec. 4, 1934 2,101,854 Haunz Dec. 14, 1937 2,123,604 Johnson July 12, 1938 2,362,926 Porch Nov. 14, 1944 2,378,184 Carlson June 12, 1945

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