US2827723A - Apparatus for removing metal from the surface of a metal object - Google Patents

Description

March 25, 1958 F. E. CLARK ,7

APPARATUS FOR REMOVING METAL FROM THE SURFACE OF A METAL OBJECT Filed Nbv. 26. 1954 2 Sheets-Shee t 1 ll/1mm INVENTOR BY ATTORNEY March 25, 1958 F. E. CLARK 2,827,723

' APPARATUS FOR REMOVING METAL FROM THE 7 SURFACE OF A METAL OBJECT Filed Nov. 26. 1954 2 Sheets-Sheet 2 INVENTOR ATTORNEY United States Patent 6 F ice APPARATUS FOR REMCWKNG METAL FROM THE SURFACE OF A METAL ()BJECT Fraii'cisE. Clark, San Gabriel, Caiif., assignor to Turco Products, Inc; LosAngeles, Calif a corporation of California Application November 26, 1954, Serial No. 471,266

19Claims. (Cl. 41'-9) invention'relates to the etching or the removaljof metaljfrom 'the surface ofa metal'object, e. g., one composed'of iron, nickel, titanium, magnesium, Zinc, aluminum or their alloys. More particularly, the invention is concerned with novel apparatus and procedure for this purpose, especially for the treatment of aluminum and its alloys.

It is known to etch acid soluble metals such as magne'sium, zinc and'their alloys with an acid solution such as aqueous nitric acid. It is also known to etch alkali soluble metals such as aluminum and its alloys with a solution having a solvent action on the aluminum or alloy surface, such as a hot aqueous alkali solution, e. g., one containing'sodium or potassium hydroxide. One method 'of carrying out'the etching process employing acids is to immerse the'rn'etal part to be etched in the etching bath, while another'is to splash the solution contained in a bath againstth'e work, the surface of which is to be etched or dissolved away, The prior art method for etching alkali 'sol'uble metals'such as aluminum or its alloys is by immersion.

However, the use of the conventional methods, for example, immersion, for etching metal parts'often produces non-uniform etching and is diflicult to control. V

Mc'ireover, where aluminum and its alloys are to be etched, conventional procedures have proved unsatisfactory because of the formation of a precipitate of alumirium hydroxide and/ or hydrated aluminum oxides in the solvent or etching bath, particularly when the concentration of alkali in the solution is reduced due to the reaction of the alkali with the metal. The formation of 'such precipitates not only interferes with the action of the etching solution on the work but tends to form a scal'eon the etching tank or equipment which becomes most difiic'ult to remove. The precipitates tend to fill the tank and must be removed periodically. Also, the strength of the solution gradually decreases and the etchingsolu'tio'n' must be revitalized by addition of fresh or" its alloys.

Another'object is to design novel apparatus particularly adapted for the unifornncontrolled etching or removal :ofn etai from the surface of a work piece composed of aluminum or its alloys.

A still further object of the invention is the provision ofn ovel apparatus for the eiiicient controlled removal of metal from the surface of an aluminum or aluminum .alloy part using a solvent or etching bath, including means for maintaining the bath substantially free of solids or fpr'ecipitate's which become suspendedin the"solvent bath.

V 2,827,723 Patented Mar. 25, 1958 placed overthejsurjfa'ce of the metal work piece to produce the 'desiredetch pattern. V V

Yetcanotherfobject is to provide novel apparatus for theefiicientj etchingiorfremoval of metal fromthe surface of an aluminumalloy work piece, by movemen'tfof ah alkali solution over thje work piece under-conditions to prevent substantial and uneven undercutting of the metal ofth'e work piece below and adjacent to'the'edgs of amaskplacedtherebn, and includingmeans forthe rapid renijoval'o'f the solids formedjinthe etching reaction from 7 said solution, and for maintaining the strength of"saidsolution I V V ,V

A st ill fur'theh objectis'the provision of procedure for the efii'cient removal ofmetal from the'surface of a metal work piecesufch as aluminum or an aluminum alloy using a suitable solvent solution, which maintains any undercutting'of th nifetal of the work piece beneaththe edges of the mask 'uniform and'at a minimum.

A still further objectis to provide apparatus and procedu're for removing precipitate formed in an etching reaction, for example," when etching'aluminum or'its alloys with caustic alkali, from the etching zone. A Other objects and advantages will become apparent from the following descriptionofthe invention: According to the invention, metal solvent or etching solution contained in a bath is caused to flow laterally over the surface of a work piece properly mounted for thispurpose. The metal part to be etched maybe 'c ed on selected portions of thesurface with a protectivemasking coating to inhibit or prevent attack by the etching agent while adjacent portions are available for such attack. Preferablyfthe work pieces are supported in a receptacle, the bottom of'which is disposed on an incline so that the solution is conveniently conveyed by gravity into contact with the 'Work pieces. In' preferred practice, the work pieces are mounted so that the surfac es to' be etched are in a plane parallel to the lateral dir'ection of flow of'thejetching solution. During flowi of theetching solutionabout and -over the surface of the work pieces, the latter are preferably rotated to cancel out the directional etching eif ects of the liquid flow. I c

In this manner, while a certain amount of etching may take place under the edges of a mask on the surfaces of the Work piece, rotation thereof while the solution is flowing thereover' renders such undercutting uniform, and prevents the highly undesirable deep undercuttingjbeneath an edge of the mask facing opposite'to thedirectionof fluid flow, and substantially less undercutting beneath those edge portions of the mask facing in the direction of flow of the solvent liquid. V I V Continuous movement of the etching liquid overjthe surface of the metal work piece also facilitates attack thereof by the solution in the selected, forexample, unmasked, areas of the work piece, and has a fi'ushingeffect on such surface. So-called smut and other precipitates loosened by the reaction, are carried away by this flushing action. This is noted particularly where the work piece being processed is aluminum or an alloy thereof, in which case such flushing action also aids in preventing formation of adherent scale on thecontaining vessel. Sifnut appears on surfaces of aluminum alloys, particularly when aluminum is alloyed with" elements, such a's'for example, copper, iron and silicon, etc. Such aluminum alloys, when etched with caustic soda, produce a'liilm which is black'a'n'd highly adherent to the surface'. These smuts are insoluble in water and most acids. TIie'yJare soluble in HNOg, mixturescrnNogan-d "HgSOf'ndih v the, aforementioned solids, and foam.. Solids. formedin the etching reaction become suspended in. the laterally flowing stream of etching solutlonwhich flows at a, rate such as to maintain the solidssuspended' at leastuntil the stream has pa'ssed'beyond the-etching zone so that essentially no solids drop to the. bottom'of the receptacle,

,for example, trough, inthe etching zone. The resulting liquid mixture containing solids. or. precipitate 'such as I aluminum hydroxide and/or alumina formed in the e tching reaction and suspended in the bath, is removed to a second zone maintained ate-lower temperature, wherein the solids are settled out of the mixture and removed, and

the remainingclear liquor. is withdrawn. Such liquor ,can be added to the solution, if desired, to replenish or may be recirculateddirectlyto the :bath, but is'first preferably conducted .to a third zone in which make-up or recesses 16 (see Fig. 4) are formed at intervals along the bottom of the trough, and a turntable 18 for supporting a work piece 29 is positioned in each of wells 16. Three wells and turntables are shown in the instant embodiment, for convenience, but it is of course understood that more or less than three such wellsand turntables can be disposed along the bottom of the trough. Turntables 13 are each supported for rotation above the bottom of the wells by means of a central shaft 22 passing through the bottom 1210f the trough normal thereto, 21 packing gland being provided between each of the shafts 22 and the bottom of the trough to form a liquid seal. A motor (not shown) of low R. P. M. drives the turntables Why a system of belts 28 and pulleys 30 mounted on the lower ends of the shafts 22, the pulleys being held against longitudinal movement on such shafts by collars 32 fixed to the shafts by set screws 34. A work piece 20, for example, having a mask 21 thereon, which may be any suitable type of resist, is fastened to each of the turntables 18 by any suitable means such as the rotatable clamps represented by numeral 36.

revitalize the main etching or solvent bath. The resulting solution cauthen be heated to the proper temperature and recirculated to the etching bath in the first zone. The process of removal of solids and recirculation of liquor to the bath-may be carried out either intermittently or continuously, preferably the latter.

The lower end of; the trough is pivotally supported on the upper shoulder of a vessel 39 by means of pivot pin 41, and the upper end of the trough is supported on a bracket 38 connected by a bolt 40 to a vertical support '42, said support having a number of apertures 44 there- 7 in to receive bolt 40 for adjustment of the height of 'Apparatus foundparticularly advantageous forcarry- 1 ing out the above procedure includes a trough, preferably inclined, in which are positioned in spaced apart relation a series of preferably rotatable supports or turntables on which the work pieces are designed to be supported Such supports vcan be rotated by a suitable drive, and means are provided for feeding solvent or etching solution to the top of the trough to permit such fluid to flow by gravity over, under and around the rotating work pieces. Means are also included to adjust the amount offeed and the. rate of efllux, and hence the depth of .the liquid flowing in the trough.

The lower end of the trough is connected to a settling vessel having means therein to facilitate rapid settlingof any suspended solids in the liquid mixture conveyed from bracket 38 so as to impart to trough 10 any desired degree of slope for adjusting the rate of flow of liquid along the trough. The slope of the'trough shown in the drawing is relatively large and favors a high rate of flow laterally over the surface of the work pieces. An-enclosure .6 is provided at the upper end of trough 10, and is formed by a rear wall 48, side Walls 50 (see Fig. 2), and a forward wall 52 of substantially less height than rear wall '48.

An adjustable plate or weir member54 is positioned on the forward wall 52 of the enclosure 46. Plate 54 is provided near both ends thereof with transverse slots 56 for the main tank, and means to permit withdrawal of the resultingclearliquor. Such liquor is then conductedto a make-up tankhaving agitating means, and'wher'ein make-upiliquid can be added to the clear liquor'from the settling vessel. The resulting solution is then pumped culation to the work pieces supportedin the trough.

' through a heater back to the top of the trough for recir- In the foregoing manner, .and particularly when aluminumparts are being etchedusing an alkali solution,

precipitated material is rapidly and efficiently removed 7 in liquid'suspension from the. etching or treating zone to prevent interference of such material with the etching The invention will be more clearly understoodby referment taken in connection with the accompanying drawings wherein:

operation, and the' resulting clear solution substantially free of solids is recirculated to the etching zone.

. ence to the following description of .a preferred embodi- Fig. 1 is an essentially schematic assembly'view of the apparatus of the invention, shown mostly in section;

Fig. 2 is a section taken on line 2-2 of Fig. 1; Fig. 2a is a section taken on line 2a2a of Fig. 2;

i Fig. 3 is a plan view of the trough shown in Fig. 1

taken on line 3.3 thereof; a r a Fig. 4 is a section taken on line 4-4 of Fig. 3;

Fig. 5 is an enlarged section across a workpiece,"

taken on line 55 of Fig. 3; and V 7 Fig.6 is a cross section of 'a 'trough and showing a modified structure for rotatably supporting the 'work pieces in the trough. r r

Fig. 7 is a View taken on line 77 of Fig. 1'." Numeral 10 represents an inclined trough having a bottom 12 and A series of spacedwells receiving bolts 58 for securing plate 54 to wall 52 by means of nuts 60. It is seen that the height of the top edge 62 of plate 54 canbe varied by moving such plate and the slots 56 therein vertically with respect to bolts '58, and tightening the nuts 60 at the desired vertical posi- "tion .of plate 54. Hence, it is seen that the amount and depth of liquid flowing in trough 10 can be varied by adjustment of plate or Weir 54.

Etching or solvent liquid is discharged through multiple pipes, or outlets 64 from a manifold 66, into the tank or enclosure 46, from which the liquid flows over the top edge 62 ofplate 54 and into'the trough 10. The liquid circulates downward therein .by gravity, flowing around and over the turntables 18 and the work pieces 20 positioned thereon. As the work pieces rotate on the turntables, a small amount of substantially equal undercutting indicated at 68 and 69 in Fig. 5, takes place beneath the inner opposite. edges 79 and 7 1,of the mask21. The :amount of such undercutting is purposely exaggerated in Fig. 5 for illustration.

It is not essential in carrying out the invention that the work pieces be rotated, especially when the surfaces to be etched are unmasked. However, such rotation is particularly advantageous where the parts being etched 'have masked or irregular surfaces where undercutting by the laterally flowing etching solution will take place. Thus, if the masked workpieces 20. were not rotated according to theinvention, uneven and generally substantial undercutting wouldvtake place at 68 and 69. Thus, vsludge would tend to accumulate in the undercut beenath the .mask' edge '74 facing in the direction opposite to fluid the direction of fluid flow, hence producing uneven under- .cuts. 7 a

gate 72 is positionedacross the trough near, the

2,8 lower end thereof. The gate is mounted for vertical adjustment on a pair of guide numbers 73 by means of nut and bolt assemblies 74, the bolts passing through slots 75 in the gate. By manipulating the bolts 74 and moving the gate 72 up or down, the size of the opening 75 below the gate can be varied providing an additional means for controlling the depth of liquid flow in the trough. I The employment of a laterally flowing body of etching fluid according to the invention, permits the use of trough with the work pieces in an inclined or horizontal position instead of the usual'etching tank with the parts in a vertical position. In addition to the other advantages previously noted, this feature of the invention permits the rapid disengagement of hydrogen gas formed during etching from the surface of the etched part, whereas in the ordinary etching tank containing a body of relatively quiescent liquid, and in which the etched body is suspended vertically, the hydrogen gas tends to stream along the face of the work pieces.

The body of flowing liquid, for example, alkali solution, which reaches the lower end of trough 10 following reaction of the alkali with the work pieces, for example, aluminum or an alloy thereof, has suspended solids therein which are formed in such reaction in the manner previously noted. This liquid mixture is continuously dischargedinto the settling vessel 39 on which the lower end of the trough 10 is supported. Vessel 39 has a scraper 76 positioned adjacent the bottom 78 of the vessel, the scraper being rotatably supported on a central shaft 80 which is rotated by a pulley 82 driven by a belt 84 from a motor (not shown). The liquid mixture drops from the lower end of the trough 10 through a cylindrical baflie 86 suitably mounted axially within vessel 39 and passes downwardly to the lower portion of the vessel. The fluid then rises in vessel 39 in the annular space 83 between the baflie 86 and the side wall 90 of the vessel, and flows through an aperture 92 in the upper end of wall 90, into an adjacent tank 94. The path of fluid flow is indicatedby the arrows in Fig. 1. In this manner the suspended solids are deposited at the bottom of vessel 39 and substantially clear liquor flows into the makeup tank 94.

Rotation of scraper 76 maintains the solids in a thick suspension atthe bottom of vessel 39, and the solids are continuously discharged through a bottom outlet 96 of the vessel into a conveyor 98 having a screw feed 100 which is driven by a motor 102, the solids being withdrawn at the opposite end of the conveyor.

The clear solution discharged into make-up tank 94 is agitated therein by an agitator 104 driven by a motor 106 mounted at the bottom of the tank. Additional alkali solution may be introduced into tank 94 from pipe 112 by means of pump 114 and valve 116, to replenish the alkali lost in passage of the liquid through the system and by the etching reaction in trough 10, while makeup water may be added through pipe 108, valve 110 and pipe 112.

The solution in tank 94 is discharged through pipe 118 into the intake of pump 120, which pumps the liquid through valve 122 into a heater 124 to bring the solution up to the desired temperature, and then circulates the heated liquid through pipe 126 connected to the manifold 66, and back into the tank 46 and trough10.

The process of the invention can thus be carried out by continuous operation.

While turntables 18 have been shown as being supported for rotation on the bottom of the trough 10, turntables or supports rotatably suspended and driven from overhead can be utilized. Referring to Fig. 6 showing a modification of this type, numeral 130 represents a trough, preferably inclined as in the case of trough 10. The trough 130 has vertical sides 132 connected to its bottom 134, each of the sides 132 having a flange 136 extending laterally along the upper edge thereof. A plurality of U-shaped straps 138, one of which is shown in 6 Fig; 6, having flanges 140 at the extremities of their legs 142, are connected at spaced intervals along the' sides 132 of trough by bolting the flanges 136 and of the trough and straps together withbolts 144.

Suspended from a thrust bearing positioned in a fixture 147 above the tank, and passing through a hearing 146 in the cross member148 of each of the straps 133 is a vertically adjustable shaft 150 having connected at its lower end clamps 152 and l53 for grasping and holding a work piece 154 suspended in trough'130 above the bottom thereof. Clamp 153 is laterally adjustable along a plate 155 connected to shaft I'50, bymeans of the bolt and nut assembly 157 received in slot 159 at the upper end of clamp153'; A pulley 156 is keyed to the upper end of the shaft 150, and a belt- 158 driven bya motor (not shown) engages the pulley for rotationthereof and shaft 150. The fluid flowing in trough 1'30 below and above the work piece 154- will etch either or both the upper and lower surfaces 160 and 162 of the work piece 154 according to the invention, preferably while the work piece is being rotated. According to the instant modification, it is seen thatby suspending'the work pieces from the supports or clamps 152 and 153 above the trough, the work pieces can be introduced into or removed from the laterally flowing stream of etchant without stopping the dew thereof and without requiring the operator to place his hands in the etching liquid, by lifting shaft 150 in its-bearings 1'45 and 146 sufiiciently to raise the clamps 152 and work piece clear of the solution. Further, in the modification'of-Fig. 6, the trough 13.0'is free of structure at the bottom thereof, and this reduces any tendency to'trap precipitate along the bottom of the trough.

Although the invention has-been described above chiefly in connection with the etching of square'orrectangular metal plates, it is to be understood that metal parts or surfacesof other shapes, for example, circular or irregular, can beetched by means of the lateral flow etching liquid concept of the invention, preferably but not necessarily in conjunction with rotation of the metal part.

In order to prevent or reduce the formation of hard, adherent scale, there may beadded to'the alkaline etching solution agents which keep the precipitate floccul'ent.

According to the preferred embodiment of the invention for etching or removing metal from an aluminum or aluminum alloy material, which is alkali soluble, a hot aqueous solution is generally employed 'containingan'alkali such as sodium or potassium hydroxide, trisodium phosphate, soda ash or the like, or mixtures thereof. Preferably, a sodium hydroxide solution is used. Temperature of the solution is generally maintained in a range say from 100 F. to about boiling, during treatment, although lower temperatures may be used. Generally, thealkali concentrations employed in such solutions range from 0.1 to 10 normal, and if sludge modifiers "are used, they may be employed in amounts sufficient to produce. a non-adherent sludge or precipitate, as for exa'inpie; 0.5% to 10% by weight of the alkali.

While the invention has been described particularly in' connection with the etching of aluminum or an alloy thereof by means of alkali solution, it is of course un-' derstood that acid soluble metals such as magnesium, iron, nickel, titanium and zinc can also be effectively etched by the apparatus and procedure disclosed herein, employing acid etchants such as aqueous nitric acid, hydrofluoric acid or mixtures thereof, depending on the particular metal, and if no sludge or precipitate is formed in. the etching reaction, vessel 39 may be omitted. Also, it is noted that aluminum and its alloys may also beetched by means of an acid etching solution, such as hydrochloric acid or ferric chloride solution.

Instead of employing an inclined trough and gravity flow of-etching liquid down said trough, it will be recognized by those skilled in the artthat I may use other means'to cause flow of etching liquid laterally with respect to the rotating work pieces, .Thus,' foi' eiiample, turntables 18 can be mounted for rotation in a horizontal for rotation within the trough with the plane of such turntables horizontal and thus disposed at an acute angle to the trough 10 and the direction of liquid flow therein.

While I have described a particular embodiment of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appendedclaims.

I claim: a 1. A device for the removal of metal from a metal work piece which comprises an inclined trough, a rotatable support for said work piece mounted in said inclined trough, means for rotating said support and means for feeding a liquid to said inclined trough.

2. A' device for the removal of metal from a metal work piece which comprises an inclined trough, a rotatable supportfor said work piece mounted in said in- ,clined trough, means for rotating said support, means for feeding a metalsolvent liquid to said inclined'trough, and means for adjusting the depth of liquid flowing in said trough. V t l 7 3. A device for the removal of metal'froma metal work piece which comprises an inclined trough, a rotatable support for said work piece mounted in said inclined trough, means for rotating said support, means for feeding a metal solvent liquid to said inclined trough,

and means for recirculating liquid from the bottom of pieces which comprises. an inclined trough, 'a plurality of rotatable supports for said. workpieces mounted-along said trough, the plane of said supports being substantially parallel to said trough, means for rotating said supports, means for feeding a, metal solvent liquid to said trough at a point above the uppermost rotatable support in said trough, means for adjusting the depthof liquid in said trough, and means'for recirculating liquid from the bottom of said. trough to saidiliquid'feeding means.

' 6QA devicefor the removal of metal frorna metal work piece which comprises a container, a, support for said work piece mounted in said container, means-for feeding liquid through a side of said container for lateral flowof said liquid over said support, means for removing said liquid from a second'side of said container, a tank connected-to the secondside 'of'said container, means insaidtank to permit settling of" solid material from a fluid :miXture discharged froms'aid container, means for drawing ofi substantially-clear liquid from said tank, and means' for recirculatingsaid clear liquid to said liquid feeding means; i I e 2 V 7."A device for the removaltofnretal'fromthesun face of a metal work piece comprises a conduit, a rota-table support for said workpiece mounted in said conduit, means for roitating'saidsupport, means for feeding a liquid to said conduit for lateral flow of said liquid with respect to said support, a tai 1k connected to the discharge end of'said Conduit, means in said tank to permit settling of solidmaterialifrom atfiuid mixture discharged from said conduit, means'for. drawing off substantially vessel connected to said outlet and means for recirculating liquid from said vessel to said liquid feeding means.

"clear liquid from said tank, and means for recirculating said clear liquid to saidliquid feeding means. 7

8. A device for the removalv of metalsfrom the surface of a metal work piece whichcomprises' an inclined trough, a rotatable support for said workpiece mounted in said trough, means for rotating said support, means for feeding a metal solvent liquid to said trough, means for adjusting the depth of liquid in said trough, a tank connected to the lower end of said trough,, means in said tank to permit settling of solid material from-a fluid mixture discharged from said trough, meansfordrawing ofi substantially clear liquid from said tank, and means for recirculating said clear liquid to said liquid feeding means.

9. A device for the removal of metal from the surface of a metal work piece which comprises an inclined trough, a rotatable support for said work piece mounted in said trough, means for rotating said'support, means for feeding a metal solvent liquid to said trough, means for adjusting the depth of liquid in said trough, a tank connected to the lower end of said trough, means in said tank to permit settling of solid material from a fluid mixture discharged from said' trough, means for drawing off substantially clear liquid from an Outlet in said tank, a liquid make-up it). A device for the removal of metal from metal work pieces which comprises an inclined trough, ,a plurality of rotatable supports for said work pieces mounted along said trough, substantially parallel thereto, means for rotating said supports, means for feeding a liquid to said trough at a point above the uppermost rotatable support in said trough, a tank connected to the lower end' of said trough, means. in said tank to permit settling of solid material from a fluid mixture discharged from said trough, means for'drawing off substantially clear liquid from said tank and means for recirculating said'clear liquid to said liquid feeding means.

11. A device for the removal of metal from metal work pieces which comprises an inclined trough, a plurality of rotatable supports for said workpieces, said supports being suspended over said trough and spaced from each other therealong, means for rotating said supports, means for feeding a liquid to said trough at a point above the uppermost rotatable support in said'trough, means for adjusting the depth of liquid in said trough, a tank connected to the lower end of said trough, .meansin .said tank to permit settling of solid materialfrom a fluid mixture discharged from said trough, means for drawing face of metal work piecestwhich comprises'an inclined ,trough, a plurality of turntables mounted alongsaid trough for supporting said work pieces, means for driving said turntables, means for feeding a metal solvent liquid to said trough at a'point above theuppermost turntable in said trough, means for adjusting the depth of liquid in said trough and means for recirculating liquid 1 from the bottom of said troughto'said-liquid feeding means. a V

13. A device 'for'the'removal ofjmetal from the surface of metal work pieces which comprises an inclined trough,

a plurality of turntables mounted along said trough for supporting said work pieces, the plane of said turntables being substantially parallel to said trough, means for driving said turntables, means for feeding a metal solvent liquid to said trough at' a point above the uppermost turna table in said trough, means for adjusting the depth of liquid in said trough, ja'tank connectedto the lower end of said trough, a rotatable scraper positioned adjacent the bottom of said tank, means for rotating said scraper, a

:bafie adjacent the inlet to said tank for directingincorning.

fluid downward in said tank, means for drawing ofi liquid from an outlet in said tank in the upper portion thereof, a screw conveyor connected to the bottom of said tank for withdrawing solid material therefrom, a liquid makeup vessel connected to said outlet of said tank, an agitator in said vessel and means for recirculating liquid from said vessel to said liquid feeding means.

14. A device for the removal of metal from the surface of metal work pieces which comprises an inclined trough, a plurality of turntables mounted along said trough for supporting said work pieces, means for driving said turntables, means for feeding a metal solvent liquid to said trough at a point above the uppermost turntable in said trough, an adjustable weir positioned above said uppermost turntable for controlling the depth of liquid in said trough and means for recirculating liquid from the bottom of said trough to said liquid feeding means.

15. A device for the removal of metal from the surface of metal work pieces which comprises an inclined trough, a plurality of turntables mounted along said trough for supporting said work pieces, means for driving said turntables, means for feeding a metal solvent liquid to said trough at a point above the uppermost turntable in said trough, an adjustable weir positioned above said uppermost turntable adjacent the upper end of said trough, an adjustable gate positioned adjacent the lower end of said trough, said weir and gate permitting control of the depth of liquid in said trough, and means for recirculating liquid from the bottom of said trough to said liquid feeding means.

16. An apparatus for the removal of metal from a metal work piece comprising, a tank forming a reservoir for liquid etching solution, said reservoir having an inlet at one end thereof and an outlet at substantially the opposite end thereof for said solution, means for supporting said work piece in said reservoir, means for rotating said supporting means, and means for continuously flowing a stream of said solution through said reservoir from said inlet to said outlet, whereby said work piece is etched by said solution by contact with said solution flowing through said reservoir.

17. An apparatus as defined in claim 16, and further including means for regulating the depth of said solution flowing through said reservoir.

18. An apparatus as defined in claim 16, and further including means for separating solids from said etching solution, and means for conducting said solution from said reservoir to said separating means.

19. An apparatus as defined in claim 18, and further including means for recirculating the solution from said separating means to said inlet in said reservoir.

References Cited in the file of this patent UNITED STATES PATENTS 1,166,378 Levy Dec. 28, 1915 2,141,162 Brandt Dec. 27, 1938 2,194,607 McDevitt Mar. 26, 1940 2,568,803 Guenst Sept. 25, 1951 2,592,729 Pennell Apr. 15, 1952 FOREIGN PATENTS 388,411 France May 30, 1908

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