US2554803A - Apparatus for the application of finishing materials by dipping - Google Patents

Description

May 29, 1951 Filed Sept. 12, 1949 APPARATUS FOR THE APPLICATION OF F. WYSOCKI FINISHING MATERIALS BY DIPRING 4 Sheets-Sheet 1 IN VEN TOR.

May 29, 1951 R. F. WYSOCKI 2,554,803

APPARATUS FOR THE APPLICATION OF FINISHING MATERIALS BY DIPPING Filed Sept. 12, 1949 4 SheetsSheet 2 f/(i Q INVENTOR.

' ROBfRT/TWKYOfK/ EMA/ May 29, 1951 R. F. WYSOCKI 2,554,803

APPARATUS FOR THE APPLICATION OF FINISHING MATERIALS BY DIPPING Filed Sept. 12, 1949 4 Sheets-Sheet 3 IN VEN TOR.

mew/1' WKYOCK/ May 29; 1951 R. F. WYSOCKI APPARATUS FOR THE APPLICATION OF FINISHING MATERIALS BY DIPPING .4 Sheets-Sheet 4 Filed Sept. 12, 1949 'I'IIIHEM I l INVENTOR. BY KOSE/U/TWUWK/ lGS Patented May 29, 1951 APPARATUS FOR THE APPLICATION FINISHING MATERIALS BY DIPPING Robert F. Wysocki, Lakewood, Ohio, assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Application September 12, 1949, Serial No. 115,226

3 Claims.

This invention relates to a method of and apparatus for the application of finishing materials by dipping, and more particularly to the construction and operation ofdip tanks for the application of industrial finishes such as paints, varnishes, lacquers, enamels and the like.

It is highly desirable to apply finishing materials to articles by dipping because the operation can be carried out rapidly and economically by conveyors which automatically dip the work into and withdraw it from dip tanks containing the finishing material; the operation may be made entirely automatic and there is almost no waste of material. In spite of the economy of dip application, the method is limited in use for various reasons. For instance, while many small objects can be dipped successfully, large areas and involved shapes create problems in obtaining uniform appearance of the finished surface, free from irregularities such as streaking, ribbing, silking, flooding and floating. In some cases such defects of finish appearance are inconsequential, as in the case of industrial shelving, for example; on the other hand, where a high quality of surface is required, as in the case of oflice equipment such as filing cabinets, desk drawers, legs and the like, dipping has not heretofore been considered feasible.

A general object of the present invention, therefore, is the provision of a method and apparatus for the application of finishing materials by dipping whereby a much better quality of surface finish is obtainable than has been heretofore possible by dipping, and by means of which the approach to optical perfection obtainable may exceed that of application by spraying. Other objects include the provision of methods of applying finishes and obtaining this improved quality of surface which can be carried out simply and economically, and the provision of various forms of relatively simple and inexpensive apparatus for carrying out the method.

In dipping finishes, it is desirable to have the contents of the dip tank homogeneous, particularly the top layer. It is also necessary to have the top layer as free as possible from turbulence and movement with respect to the work. Lack of uniformity of the material in the top layer may result in streaking and in uneven deposits. Turbulence in the top layer may result in frothing of the coating material and the production of layers of uneven thickness with bubbles, sags and the like. One solution of the problem of maintaining the required homogeneity is to agitate the material in the tank, whereas a solution of the problem of avoiding turbulence in the top layer of the material is to eliminate agitation. Ac cordingly, most commercial methods involve a compromise, as much agitation as necessary being used to insure a reasonably homogeneous mixture, but the agitation being kept below an amount that will unduly affect the quality of the coating. In many instances, the compromise is unsatisfactory. Frequently, a so-called float of oily or unpigmented vehicle, or of different colors will appear in the top layer of the material in the dip tank. The presence of a float frequently causes streaking of the finish and off color spots that impair the uniform appearance of the finish. Various methods of agitation have been employed in an effort to insure homogeneity of the material; circulating pumps, submerged propeller-like agitators and ripple boards for producing small waves on the surface of material in the tank have been used but have. not solved the problem or have only partially done so. With these and other prior devices, it has often been impossible to eliminate floating without agitating the tank to such an extent that foaming occurs and bubbles and sags are produced on the work.

The problem in dip finishing is particularly acute when certain recently developed enamels and the like, formulated to produce finishes of exceptionally high quality from a visual standpoint, are employed. These enamels contain additives which improve their sheeting-out qualities and produce surfaces free from streaking and corduroy effects when the dipping operation is carried out in a tank in which the material is not greatly agitated and at the same time is substantially homogeneous and free from floating. The difficulty arises from the fact that in some instances, at least, the additives seem to increase the tendency to create floating to such an extent as to render impractical automatic dipping with the usual type of equipment.

According to the present invention, the desired uniformity and homogeneity of the coating material in the dip tank and particularly in the top layer of the dip tank is maintained without requiring excessive agitation by continuously skimming the surface layer of the material in the tank, thus creating a gentle current or flow of the coating material in the upper layers of the finishing material. skimming removes incipient fioats and/or non-homogeneous components in the surface layers of the material in the tank before the floating becomes sufficiently extensive or the non-homogeneity becomes sufficiently great to have an adverse effect on the finish. The surface flow appears to have the effect of continuously supplying to the surface layers of the tank finishing material having the desired homogeneity and quality. This method eliminates the difliculties ordinarily encountered in dip tanks because lack of homogeneity in the coating material ordinarily first appears on the surface of the tank and by constantly replenishing the material in the surface layers by the skimming operation, the separation of the components of the coating material to an extent sufficient to damage the finish is prevented without excessive. gr undesirable agitation of the contents of the ank.

Preferably, the skimming operation is carried out in such manner as to create a mild current in the upper layers of the material of the; tank in the same direction as the movement of the work through the tank. With this arrangement, while a sufiicient current maybe maintained in the upper layers of the tank to insure proper quality of the coating material'in these layers, the effect of the current is to reduce the relative motion between the work and the finishing material in the important surface layers of the finishing material thus making it possible to approach the ideal condition of withdrawing the work through a calm and relatively stationary surface layer of finishing material.

Preferably, the above skimming operation is carried out by providing a submerged weir in the dip tank and withdrawing the finishing material from a trough behind the weir at such a rate that the finishing material fiows' smoothly over the weir without frothing or excessive turbulence. The material withdrawn from the trough is preferably returned to the dip tank by a circulating pump and may be filtered before being returned to the tank. The material so withdrawn is returned to the tank through submerged nozzles, outlets, or jets so disposed that the proper movement' of the contents of the tank is facilitated in the desired direction. If any supplemental circulation of the contents of the tank is required, to prevent settling for instance, the returned material should pass through the same or similarly disposed nozzles, outlets, or jets. Preferably, the weir is disposed near the exit end of the tank, that is, the end from which the dipped work is withdrawn, in order to create the desired flow in the upper layers in the direction of movement of the work through the tank. Various arrangements of apparatus may be employed to accomplish this result; several such arrangements are shown in the accompanying drawings.

Referring now to the drawings, which are somewhat diagrammatic, Figure 1 is a longitudinal cross section through a preferred form of the dip tank embodying my invention and shows a conveying mechanism for carrying work into and out of the tank; Figure 2 is an enlarged sectional detail showing the nature of the flow of finishing material over the weir; Figure 3 is a plan view of a dip tank similar to the tank of Figures 1 and 2 but embodying a modified form of circulating apparatus; Figure 4 is a longitudinal cross-section of the dip tank shown in Figure 3, the section being indicated by line 4-4 of Figure 3; Figure 5is a view of a portion of a dip tank embodying a modified form of weir; Figure 6 is a plan view showing a dip tank embodying a weir curved in the horizontal plane; Figure '7 is an end elevational view with parts in section illustrating a weir curved in a vertical plane; Figure 8 is a fragmentary longitudinal section of the end of a dip tank embodying a pivoted adjustable weir; Figure 9 is a similar section of a dip tank embodying a slideable adjustable weir; Figure 10 is a fragmentary perspective view showing the end of a dip tank in which the vertical and horizontal positions of the weir in the tank are both adjustable; Figure '11 is a plan view of 'a tank in which the weir is disposed along the side of the tank; Figure .12

is a transverse sectional view of the .tanksh own 4 in Figure 11, the section being taken along the line |;2--l2' of Figure 11; Figure 13 is a plan view of a round dip tank having an annular weir; and

Figure 14 is a transverse sectional view through the round dip tank, the section being indicated by line l4'l'4 of Figure 13.

Referring now to Figure 1 of the drawings, reference character In indicates a dip tank of generally conventional construction modified to embody the present invention. The tank Ill is rectangular in plan, has straight vertical side Walls one ofv which is indicated at I I and sloping end walls l2 and IS. A conveyor indicated in general at I5 is disposed above the tank. The conveyor may be of any conventional construction and embodies a plurality of work-supporting units It which are moved along the track I! by any convenient means such as a chain. Each of the units it is provided with a hook it from which the work W to be coated is suspended, for example, by wires 29. The work may be any article susceptible to coating by dipping, such as the filing cabinet drawers illustrated in the drawing. As is customary, the work is suspended at one corner in order to provide for proper drainage of excess coating material. The track H has a sloping entry portion 2!, a connecting horizontal portion 22, and a sloping exit portion 23, the sloping portions of the track being approximately parallel to the sloping end walls of the tank. By means of the sloping tracks, the work is dipped gradually into the tank and then removed from the coating material within the tank, the rate or" removal being governed by the slope of the exit portion 23 and the rate of travel of the conveyor. These factors are controlled in manners known to those skilled in the art depending on the qualities of the material in the tank in order to give the desired thickness of coating. After leaving the dip tank, the articles may or may not be conveyed through a drying oven, depending upon the nature of the finishing material employed.

The apparatus just described is typical of dip tanks heretofore employed and with which it has been impossible constantly to secure high quality work, the difliculties being due, as noted above, to the presence of floats and the like and other evidence of non-homogeneity in the upper layers of the finishing material in the tank or to efiects resulting from excessive agitation of the material in the tank.

In order to eliminate these difliculties, as explained above, the present invention contemplates the provision of a submerged weir 25 which (ax-- tends from side wall to side wall of the tank and beneath the surface level 26 of the finishing material in the tank. The weir comprises a plate having a horizontal upper edge 21 and lies generally parallel to the sloping end I2 of the tank, the bottom edge of the plate being connected to the end wall of the tank by a narrow plate 28. The weir 25 and plate 28 thus define a trough 30 which receives the finishing material that flows over the weir.

In order to create the desired flow of finishing material in the tank, a circulating pump 3| is provided. The intake of the pump 3| is connected to trough 30 by conduit 32 and to the bottom of the tank by conduit 33, valves 34 and 35 being provided to control the flow through these conduits.

The discharge of the pump leads through filters 36 to discharge conduits 31, 38 and 39 all leading to the tank [0. The return of finishing material to the tank through these conduits is controlled by valves 40, 4| and 42. A by-pass conduit 44 controlled by valve 45 is connected across the filters 36 so that the tank can be kept in operation while the filters are being cleaned or removed by opening the normally closed valve 45 and closing the valves 46 and 41 in the filter connections.

In operation, the pump is driven at a speed comparable with the speed of pumping in a conventional dip tank of the same size in order continuously to filter the material. The valve 34 is opened sufficiently to withdraw finishing material from the trough 30 at a rate such that the finishing material will flow smoothly over the weir without any frothing or excessive turbulence which might result in the'entrapping of air in the finishing material. The appearance of the material as it flows over the weir is indicated in Figure 2. It will be noted that there is no waterfall effect and that the fiow is smooth in character. The level of the finishing material above the horizontal edge of the weir and the rate of withdrawal of material from the trough together determine the character of flow. Ordinarily, it is satisfactory to maintain the level of the finishing material from one-half inch to one inch above the weir. This creates a flow in the upper layers of the tank sufficient to maintain the desired flow characteristics in these layers.

If it is desired to withdraw and recirculate more finishing material from the tank than is withdrawn through the conduit 32, the valve 35 is opened to withdraw additional finishing mate rial through the conduit 33. All of the finishing material withdrawn from the tank is recirculated, the return pipes 31, 38 and 39 being arranged as indicated in the drawing to direct the flow of returning finishing materials in such manner as to cause a slow but rather general circulation of material in the tank as indicated by the arrows in Figure 1.

With this arrangement, a surface flow in the direction of movement of the work through the tank is maintained without any excessive turbulence being created in the tank. This circulation maintains the required homogeneity of the material and provides a surface layer which moves in the same direction as the movement of the work as it is being withdrawn from the tank,

practice and makes possible the consistent production of finishes of higher quality from the standpoint of appearance than have heretofore been obtainable by dipping processes. The apparatus and method are particularly successful when used in connection with organic finishes containing additives that alter the interfacial relationships of the finishes in order to improve sheeting-out qualities of the finishes. These additives seem to have the effect of increasing difficulties with fioats in conventional dipping tanks but the difficulties are entirely eliminated with tanks embodying the present invention.

With this and other forms of the invention, material withdrawn from the tank by the dipping operation and losses due to evaporation and the like may be made up by periodically adding material to the tank by any convenient means to maintain the level in the tank substantially constant. I

In Figures 3 and 4 a tank generally similar to the tank of Figures 1 and 2 is illustrated, but here the tank is provided with a weir 5! which extends parallel to the end wall 52 to a point spaced a slight distance above the bottom 53 of the tank from which point it extends in a horizontal plane as indicated at 54. The horizontal portion 54 of weir 5| is connected to the bottom 53 of the tank by curved plates 55 which provide a restricted passageway 56 in communication with the chamber 5! formed by the weir.

In order to create circulation within the tank, a propeller type agitator or impeller 58 is disposed within the passageway 55. This is driven by motor 59 and shaft 60, the shaft extending through a stuffing box 6| in the end wall 52. Operation of the propeller 58 creates a circulation in the tank as indicated by the arrows in Figure 4 by withdrawing finishing material from the chamber 51 and discharging it into the tank. This type of apparatus is effective when filtering of the finishing material is not desired; the operation, insofar as the dipping is concerned, is generally similar to that described in connection with Figures 1 and 2.

The arrangement shown in Figure 5 is also similar to that shown in Figures 1 and 2 and may be used with a circulating and filtering system such as shown'in Figures 1 and 2. In this form of the invention, however, the tank is provided with an end wall 66, the upper part 61 of which constitutes the enclosed weir. The upper edge of the portion 61 is disposed at the desired level beneath the upper edge of the side walls 68. The side walls extend beyond the end wall 6'! as shown, and the trough 69 which receives the finishing material flowing over the weir is constituted by a sloping end member in and a horizontal member H which extends between member 18 and end wall 55. The finishing material is withdrawn from the trough 69 through the conduit "I2 which leads to a pump or other circulating apparatus.

For some purposes it may be desirable to create flows in the surface layers of the tank in lateral 'as well as longitudinal directions. When this is desired, an arrangement such as is shown in Figure 6 may be employed. The tank is rectangular and the weir 86 is curved so that the surface fiow of the finishing material will be longitudinal in the central portion of the tank and partially lateral in the vicinity of the sides of the tank and the side portions 81 of the weir. The trough or chamber 38 which receives the materials flowing over the weir is closed on the bottom by a connecting plate interposed between the weir 85 and the bottom 89 and end of the tank in the manner of the plate 28 shown in Figure 1. A circulating system such as shown in Figure 1 may also be employed, the finishing material being withdrawn from the trough 88 through orifice 9|, and, if necessary, from the bottom of the tank through orifice 92. The recirculated and filtered finishing material may be returned to the tank through discharge orifices 53, 34 and 95, these orifices .being connected with the circulating pump and filter through conduits such as shown in Figure 1.

' For some purposes, it may be important to create a greater flow in one portion of the tank than in another. For example, it may be desirable to remove more finishing material from the mid-portion of the tank than from the edges.

'The arrangement to accomplish this result is shown in Figure '7 wherein the tank I00, which is ener l similar tan '9 n F gure 1,, s v d dwith a w H hav n r u per ge- QZ s that. t depth o h ma r a and h ce the volume thereof, that flows overthe weir is greater at the center than at the edges of the weir. In this form of the invention, the trough for receiving finishing material is enQlOSfid 91 the bottom by a plate I03 similar to the plate 28 in Figure l. The circulating system involves a motor driven pump I94 which is preferably: of a positive displacement type, filter I35 and suitable conduits and valves arranged in the manner described in connection with Figures 1 and 2.

While the depth of finishing material flowing: over the weir may be controlled by regulating; the volume of material in the tank, it is also possible to control this depth by adjusting the position of the weir. In Figure 8, the tank III) is pro.- vided with a weir III which is hinged as at H2 to the connecting plate I I3. An arm I I4 secured to the weir I I I near the side of the tank projects above the edges of the tank and is provided with a clamping screw I I5 by which itmay be clamped to the arcuate segment IIE supported by the end II! and side H8 of the tank. By this arrange-. ment the height of the weir may be rapidly and accurately adjusted.

A similar arrangement for accomplishing substantially the same result is shown in Figure 9. Here the tank I is provided with a weir I2 I which is slidingly fitted between the transversely extending vertical plates I22 and I23. The weir I2I with the plates I22 and I23 and the horizontal plate I24 define the trough I25 which receives finishing material that flows over the weir. The weir I2I is adjustably supported from the sides of the tank by threaded rods I25 secured to the ends of the weir and provided with wing nuts I21 which engage brackets I28 secured to the side walls I29 of the tank. Although one end only of the weir is shown in the drawing, an identical arrangement is employed at the other end of the weir.

In both Figures 8 and 9 the same general type of circulating apparatus as described in connection with Figures 1 and 2 may be employed. Figure 9 shows a tank with a vertical end wall I30 but it is to be understood that the slideable weir may be used with sloping end walls and the pivoted weir of Figure 8 may be used with verti- Gal end walls. Also, a circulating system such as shown in Figures 3 and 4 may be utilized with devices of these types.

The arrangement shown in Figure 10 embodies a tank I in which the weir is adjustable horizont lly as well as vertically. The weir I36 forms one side of a box constituting the trough I31, the remaining portions of the box being formed by a rear plate I38, end plates I39 and a bottom plate I40. The box is supported by threaded rods MI and wing nuts [52 which engage brackets I43 that are slideable along the upper edges of the sides Hit of the tank. Connection from the trough I3! formed by the box I38 to the circulating system is made by pipes I45 and flexible conduit I48 which leads to the end I41 of the tank. Pipe I48 connects the flexible conduit I46 to the circulating system which may be similar to that shown in Figures 1 and 2.

While it is preferred for most purposes that the flow be longitudinally of the tank, for some purpose it may be important to create a transverse flow. For such purposes the arrangement s wn in F res 1 and 2 s p id d h rei the ank- 150 has a weir 15' extend n :lon itu clinally of the ank, nd s aced appr priate distance irom the side wall I52. The weir I5] s. in e fo of bent P at the q i ontslpwtion I 53 thereof terminating in a downwardlylex: tending flange I 5.4 which is secured to the side wall I52 to provide the trough torreceiving the finishing m te al w n o e he wei n is modification the finishing material is withdrawn iirom the trough I 55 through a manifold I56 which is connected to circulating pump I51. A filter I58 is provided with appropriate valves and the recirculated material is returned to the tank through orifices I 59 I60 and IBI preferably ar-.- ranged to create circulation within the tank in the direction oi the arrows in Figure 12. Thus, in this modification as in the others, the circue lation adjafifint he bottom oi the tank is opposite to that in the upper surfacelayers.

For small tanks and particularly for hand p i g a ran em n s t apparatus as how Figures 13 and 14 is desirable. Here the edge I65 of the cylindrical tank I66 constitutes a cir-s cular weir, and an-ann-ular trough I61 is provided; outside of the weir- I-65 by the annular member I68 which projects above the weir I65 and which has an inwardly extending bottom portion I69,

secured to the cylindrical tank wall. The finishing material may be withdrawn at the desired rate from the trough through a plurality of spaced orifices I10 which are connected to the conduit I'II leading to the pump I12 through a manifold I13. The recirculated material is returned to the tank through a centrally disposed orifice -I 14, thus providing an upward now of material in the cent te of e t nk an r al y ou ward fl w from the center over the weir in the upper layers lot the material.

From the foregoing description of various forms of my invention, it will be evident that I "have provided a simple and effective method and ap paratus whereby the desired characteristies can be maintained particularly in the upper layers of finishing material in dipping tanks. This result can be obtained without agitation of material other than that obtained by circulation of the ter a in e t y so m intai in the desired characteristics in the upper layers of the material, better finishes can be produced by dip ping methods than have heretofore been possible. Thu h p a i n of fin she y d pp n which he, least expensive mod of ap a ion o finishing material, can be extended to articles requ ri e c h g al of surface p ar nce h i ing has n e re be eas e- 'I 'he apparatus is simple and relatively inexpemsive, n slight c n es being required to o norte t ven n i x s in d pin anks and. inasmuch as conventional dipping practice ordinarily requires the circulation of the finishing material in the tank through filters by means of pumps, no additional expensive equipment is required; the only changes necessary to adapt existing dip tanks to the practice of the inventtion being the inclusion of the weir and changes in the piping of the circulating system.

'While several arran ements embodying the invention have been shown herein, those skilled in the art will appreciate that numerous other arrangements can be devised to suitv different operating' conditions and different designs of tanks all wi in h t achin s of the invent on- Therefore it is to be understood that the foregoing desc i tion is not iven by way of limitation of the n e tion but rather by way of example and that the invention is not limited thereby, the scope of the invention being defined in the appended claims.

I claim:

1. An apparatus for applying finishing materials that are subject to the formation of fioats, such as paint, enamel, varnish, lacquer and the like to articles, said apparatus comprising an elongated dip tank containing the finishing material, means for creating a gentle current longitudinally of the dip tank in the upper layers of the material and continuously skimming the surface of the tank to prevent the formation of fioats thereon, said means comprising a weir submerged beneath the surface of the finishing material in the tank adjacent one end only thereof, said weir defining a chamber separated from the main body of the material in said tank by said weir, pump means including a conduit communicating with said chamber for withdrawing finishing material from said chamber to reduce the level of the material therein as compared to the level of the main body of material in said tank, thereby causing the finishing material to fiow across said weir and into said chamber and creating a current in the surface layers of said main body of material longitudinally of said tank toward 'said weir, conveyor means for dipping articles into the tank near the end thereof remote from said weir, conveying them toward said weir and withdrawing them from said tank near said weir, a conduit communicating with said pump means for returning withdrawn finishing material to said tank, said conduit discharging into said tank through an orifice disposed at a level slightly below the level of the upper edge of the weir and adjacent the end of the tank remote from the weir and opening toward the weir, whereby the discharge of material from said opening contributes to the creation of said current toward said weir, and an other conduit communicating with said pump means for returning withdrawn finishing material to said tank, said other conduit discharging into the main body of material in said tank through an orifice near said weir at a lower level than said weir, said orifice being disposed to create a flow of the material along the bottom of the tank in a direction opposite to said current in the upper layers of the material.

2. An apparatus for applying finishing materials that are subject to the formation of floats, such as paint, enamel, varnish, lacquer and the like to articles, said apparatus comprising an elongated dip tank containing the finishing material, said tank having an outwardly sloping end wall, means for creating a gentle current longitudinally of the dip tank in the upper layers of the material and continuously skimming the surface of the tank to prevent the formation of floats thereon, said means comprising a weir submerged beneath the surface of the finishing material in the tank adjacent said sloping end wall, said weir and said sloping end wall defining a chamber separated from the main body of the material in said tank by said weir, pump means including a conduit communicating with said chamber for withdrawing finishing ma terial from said chamber to reduce the level of the material therein as compared to the level of the main body of material in said tank, thereby causing the finishing material to flow across said weir and into said chamber and creating a current in the surface .layersof said main body of material longitudinally of said tank toward said weir, conveyor means for dipping articles into the tank near the end thereof remote from said weir, conveying them toward said weir and withdrawing them from said tank near said weir, a conduit communicating with said pump means for returning withdrawn finishing material 'to said tank, said conduit discharging through an orifice disposed at a level slightly below the level of the upper edge of the weir and adjacent the end of the tank remote from the weir and opening toward the weir, whereby the discharge of material from said opening contributes to the creation of said current, and another conduit communicating with said pump means for returning finishing material to said tank, said other conduit discharging through a second orifice disposed adjacent said sloping end wall below the level of said chamber, said orifice being directed downwardly along said sloping end wall, whereby discharge of material from said opening oreates a fiow of the material downwardly along said sloping end wall and along the bottom of said tank in a direction opposite to said current in the upper layers.

3. An apparatus for applying finishing materials that are subject to the formation of floats, such as paint, enamel, varnish, lacquer and the like to articles, said apparatus comprising an elongated dip tank containing the finishing material, said tank having an outwardly sloping end wall, means for creating a gentle current longitudinally of the dip tank in the upper layers of the material and continuously skimming the surface of the tank to prevent the formation of floats thereon, said means comprising a weir submerged beneath the surface of the finishing material in the tank adjacent said sloping end wall, said weir and said sloping end wall defining a chamber separated from the main body of the material in said tank by said weir, pump means including a conduit communicating with said chamber for withdrawing finishing material from said chamber to reduce the level of the material therein as compared to the level of the main body of material in said tank, thereby causing the finishing material to flow across said weir and into said chamber and creating a current in the surface layers of said main body of material longitudinally of said tank toward said weir, conveyor means for dipping articles into the tank near the end thereof remote from said weir, conveying them toward said weir and withdrawing them from said tank near said weir, and a conduit communicating with said pump means for returning withdrawn finishing material to said tank, said conduit discharging through an orifice disposed adjacent said sloping end wall below the level of said chamber, said orifice being directed downwardly along said sloping end wall, whereby discharge of material from said opening creates a fiow of the material downwardly along said sloping end wall and along the bottom of said tank in a direction opposite to said current in the upper layers.

ROBERT F. WYSOCKI.

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

UNITED STATES PATENTS Number Name Date 1,191,216 Nivling July 18, 1916 ,531,839 Booraem Mar. 31, 1925 2,112,245 Luckhaupt Mar. 29, 1938 2,165,364 Ferngren July 11, 1939 2,195,670 Ferngren Apr. 2, 1940

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