Apparatus for the recovery of dragged-out treatment solutions by immersion barrels

Apparatus and a method for the direct recovery of residual quantities of an aqueous solution adhering to pourable mass parts following an electrolytic and/or chemical surface treatment on the parts, in the course of which the parts are carried in a perforated immersion barrel supported on a movable carriage of a barrel treatment installation. A compressed-air chamber is provided on the carriage, into which the barrel is moved, the chamber being provided with a compressed air source to cause a current of air to flow transversely through the chamber. The compressed-air chamber essentially comprises a horizontal, upwardly cylindrically convex upper half-shell which is fixed on the carriage and which encompasses in a substantially air-tight manner the upper half of the immersion barrel when the barrel has been positioned within the chamber, and a pair of horizontal, lateral, lower, outwardly cylindrically convex quarter-shells which are capable of movement towards and away from one another. When moved together, the quarter-shells encompass the lower half of the immersion barrel in a substantially air-tight manner, except that the two quarter-shells leave open a relatively narrow longitudinal slot between their two lowermost long edges. The current of air passes into the chamber and after passing through the barrel and over its contents, leaves the chamber downwardly, entraining any dragged-out solution in the air stream. Water may be injected into the air stream, to assist removal from the parts of the dragged-out solution.

BACKGROUND TO THE INVENTION
 1) Field of the Invention
 The invention concerns a method and associated apparatus for the direct
 recovery, following an electrolytic and/or chemical surface treatment, of
 residual quantities of an aqueous solution adhering to a charge of
 pourable mass parts in a movable perforated immersion barrel. The
 immersion barrel is moved to be positioned in a compressed-air chamber,
 connected to a centrifugal fan, on a carriage of a barrel installation. A
 current of air flowing transversely through said chamber entrains the
 solution residue adhering to the charge into a tank located below the
 chamber.
 2) Description of the Prior Art
 Such an apparatus for performing the described above method is known from
 German Patent Specification DE 31 33 629 C2. The immersion barrel which is
 attached to the carriage is moved out of the treatment solution tank into
 a compressed-air chamber and when positioned therein, is subjected
 together with the contained charge of pourable mass parts to an air
 current, flowing transversely through the barrel and charge. The air
 current entrains residual solution adhering to the charge and directs it
 specifically downwards through a longitudinal slot at the base of the
 compressed-air chamber, returning it into the tank from which it was
 previously dragged out.
 The known compressed-air chamber consists essentially of two movable
 half-shells, disposed on the carriage and capable of being displaced
 towards the raised immersion barrel, so as to enclose the immersion barrel
 on all sides, apart from a narrow, open longitudinal slot on the
 underside. The compressed-air chamber is connected to a low-pressure fan
 which delivers the required quantity of air through the two hollow
 half-shells. Following completion of the blowing operation, the immersion
 barrel is moved to the next processing station by means of the carriage,
 the two movable half-shells are removed sideways from the immersion barrel
 and the latter is lowered into the tank below, containing the next
 treatment solution.
 The displaceable half-shells are hollow and are provided with openings for
 blowing the current of air therethrough and, if required, also for the
 passage of rinsing water.
 The known method provides for an unpressurized water rinsing of the charge
 and the barrel both before the blowing operation for removal of the
 dragged-out residues of treatment solution, and also simultaneously with
 the blowing operation.
 The quantity of water delivered without pressure has an extremely low
 process efficiency. Water falling in the form of droplets on the
 perforated immersion barrel rinses only the exterior of the barrel and
 runs off the latter without significant wetting of the surfaces of the
 charge of pourable mass parts contained therein.
 The described known apparatus furthermore requires a large amount of
 apparatus. Control systems must be used for the time-dependent closing and
 opening cycles of the two half-shells, timed to the raising and lowering
 operation of the immersion barrel. The half-shells are of considerable
 dimensions, as appropriate to their function, and are accordingly heavy.
 The mechanism required for carrying and for simultaneously and
 synchronously moving the two half-shells on the carriage is costly to
 produce, complex and difficult to service.
 comparable problem and solution can be found in the Published Patent
 Application DE 44 42 160 A1. Similar movable half-shells execute a
 circular arc movement, approaching from both sides of the immersion barrel
 when raised on the carriage, so as closely to enclose it. A fan provides a
 current of air required for entraining the solution residues, transversely
 through the barrel and the charge. A lower slot remains open between the
 two half-shells when moved close together, through which the drawn off
 residue passes into the tank with the treatment fluid located underneath.
 The two movable half-shells are each attached to a swivelling support arm
 connected to a special mechanism, which necessarily has to be disposed
 above the motor casing of the barrel unit which is moved into the
 compressed-air chamber.
 The aforementioned design solution obviously results in a substantially
 greater structural height which is disadvantageous for the erection of the
 barrel installation.
 The cost of the production of the proposed apparatus, however, is not
 reduced in comparison with that according to German Patent DE 31 33 629
 C2. The complicated mechanism, which is not easily accessible, is awkward
 to service; it is also exposed without protection to the corrosive air
 within the operating room.
 Although German Patent Specification DE 38 30 237 C2 proposes a simplified
 solution to the problem, which obviously reduces the production costs and
 facilitates servicing, it has disadvantages of a process nature.
 A compressed-air hood mounted on the carriage and connected to a
 compressed-air supply has essentially the spatial form of an upwardly
 convex half of a rotational cylinder. The barrel, which is moved into and
 positioned in the hood, is encompassed by the latter over the
 circumference of its upper half which is not filled with the charge of
 pourable mass parts. There is thus created a compressed-air chamber whose
 base is formed by the air-permeable slope surface of the charge, produced
 by the rotational movement of the barrel.
 The quantity of air blown into the barrel cylinder flows transversely
 through the mass of the charge and through the perforated lower half of
 the barrel casing, concomitantly drawing off, to a large degree, the
 residual quantities of the treatment solution adhering to both of the
 latter, in order to bring them directly into the tank, located underneath,
 from which they were previously dragged out.
 The current of air emerges from the lower half of the barrel cylinder as a
 free jet. In terms of fluid mechanics, the polygonal circumference of the
 lower half of the barrel forms the nozzle outlet of the air jet.
 Irrespective of its emergence speed, an air jet from a rectangular nozzle
 has a spread angle of approximately 33.degree.. The conical core of the
 jet is surrounded by a zone in which the emerging air mixes with the
 surrounding air with a high degree of vorticity. The total quantity of
 moved air becomes ever greater, the jet speed ever slower and its range
 shorter.
 It is obvious that, with a higher air speed over the surface of the charge
 parts and of the barrel cylinder, the achievable effect of drawing off the
 solution residues adhering to both of the latter and of removing them by
 means of the air current becomes correspondingly greater.
 Accordingly, in the apparatus of Patent DE 38 30 237, the cross-sectional
 area of the nozzle outlet is approximately equal to the sum of the
 surfaces of three casing sides. Such an outlet nozzle corresponds
 approximately to half the circumferential circle of the polygonal barrel
 cylinder. The air current jet spreads radially from it along the barrel,
 corresponding to a centre angle of about 180.degree..
 It has been shown that the spreading air jet containing the entrained
 solution residues goes beyond the edge of the tank into which the
 dragged-out residues of the treatment solution are to be returned.
 Particular difficulties occur in the case of bath solutions with high
 operating temperatures. Additional constructional measures are required to
 control and locally limit the resultant development of vapour which
 spreads out in the manner of a cloud.
 In summary, it may be stated that, in many cases, the known apparatus and
 associated methods according to the prior art are not capable, or are
 capable only to a limited extent, of fulfilling the stringent requirements
 of operating practice.
 OBJECTS OF THE INVENTION
 Consequently, the object of this invention is to propose apparatus and an
 operating method which to a large extent eliminate the disadvantages of
 the prior art, with the use of simple means. The terms of reference
 therefore require that the maximum return is directed to the original tank
 from which the dragged-out residual quantities came, and it is also
 simultaneously ensured that the magnitude of the current of air is reduced
 to a sufficient minimum. The apparatus is to be simplified, and reduced in
 size if at all possible.
 SUMMARY OF THE INVENTION
 The object is achieved, according to the invention, in that the
 compressed-air chamber essentially comprises a horizontal, upwardly
 cylindrically convex upper half-shell which is held against movement in a
 fixed position on the carriage and encompasses in a substantially
 air-tight manner the upper half of the immersion barrel when positioned
 within it, and a pair of horizontal, lateral, lower, outwardly
 cylindrically convex quarter-shells which are capable of movement towards
 one another and which, in turn, encompass the lower half of the immersion
 barrel in a substantially air-tight manner. The two quarter-shells leave
 open a narrow longitudinal slot between their two lowermost long edges in
 order to allow the current of air flowing through the compressed-air
 chamber, and so also transversely through the perforated immersion barrel
 and through the charge contained therein, to be discharged downwards
 through the aforementioned open longitudinal slot.
 The open longitudinal slot between the two lower ends of the movable
 quarter-shells according to the invention is located at the base of the
 compressed-air chamber and is of a width which is substantially smaller
 than that of one casing side of the polygonal barrel casing. If the barrel
 cross section is hexagonal, then the centre angle of the slot
 opening--relative to the longitudinal axis of the immersion barrel--is
 less than 60.degree..
 The narrow longitudinal slot between the two quarter-shells can be regarded
 as a rectangular nozzle outlet from the compressed-air chamber. The
 emerging air jet is directed specifically vertically downwards, i.e.,
 towards the middle of the tank container out of which the immersion barrel
 has been raised.
 The drastically reduced air volume of the narrow jet prevents the current
 of air from spreading beyond the edges of the tank and additional
 constructional measures for controlling the movement of air caused by the
 flow of air out of the compressed-air chamber--one of the principal
 disadvantages according to the prior art--are no longer necessary.
 If a numerical comparison is made with the prior art, represented by the
 subject-matter of Patent DE 38 30 237 C2, then the advantages of the
 present invention are obvious.
 A hexagonal barrel cylinder with an inside length of 850 mm and an
 inscribed circle diameter of 330 mm has rectangular, flat casing sides. If
 it is further assumed that the connected centrifugal fan delivers an air
 volume of 2200 m.sup.3 /h into the compressed-air chamber, then--according
 to the aforementioned patent--the required mean emergence speed of the air
 current from the three perforated barrel sides which are not encompassed
 by the compressed-air hood and which act as nozzle openings is 1.12 m/sec.
 The emergence angle (centre angle) of the jet, with its vertically
 downwardly directed core, is 180.degree..
 By contrast, the width of the open longitudinal slot, acting as a nozzle
 outlet, between the two opposing lower ends of the quarter-shells
 according to the invention might correspond to a centre angle of
 38.degree.. The adequately high air speed through the longitudinal slot is
 1.12 m/sec; accordingly, the output of the connected centrifugal fan
 required for this is equal to 460 m.sup.3 /h, or 21.1% of the comparative
 value (of 2200 m.sup.3 /h, according to the numerical example), or about
 one fifth of the latter. The dimensions of the fan are accordingly smaller
 and the volume of the air jet emerging from the compressed-air chamber is
 likewise reduced to about one fifth.
 The central position of the outlet nozzle at the base of the chamber
 further ensures that the flow of the relatively small volume of air
 aligned directly towards the middle of the tank remains to a large extent
 free from secondary interfering turbulences with the moved ambient air.

DESCRIPTION OF THE INVENTION
 Apparatus according to the invention has the compressed-air chamber
 connected to a compressed-air line (usually from a centrifugal fan) and,
 simultaneously, to a water supply line. The methods according to the
 invention for the application of the aforementioned apparatus which have
 as their object the recovery of the dragged-out bath solutions are
 composed of sequences of combined steps of which the fundamental elements
 consist of the current of air introduced into the compressed-air chamber
 and of defined quantities of injected water.
 The downwardly directed current of air flows transversely through the
 compressed-air chamber, and so also transversely through the immersion
 barrel positioned within it and through the charge contained within the
 barrel. This performs the function, as a motive driving force and a means
 of transportation, of intercepting, entraining and drawing off and
 returning downwards directly into tank located therebelow, the treatment
 solution in concentrated form, or a mixture of the treatment solution and
 water; in this way, the greater part of the treatment solution previously
 dragged out of the treatment tank and adhering to the surfaces of the
 charge parts and of the barrel can be returned to the tank.
 It is advantageous in performing this invention that the barrel completes
 at least one full rotation during the period during which air is blown
 through it. The current of air thus flows through all perforated casing
 sides of the polygonal immersion barrel, i.e., through all the
 perforations, including the smallest, for example of the order of
 magnitude of 2 mm or smaller.
 As the mass charge which circulates in the immersion barrel during the
 rotation of the latter slides past the open longitudinal slot between the
 two quarter-shells, the concentrated current of air flows for a period
 through the entire barrel peripheral circumference. This ensures that any
 solution residue adhering to the surfaces of the mass of parts of the
 charge, including those of a geometrically complex three-dimensional form,
 is effectively intercepted and removed.
 The casing of the barrel, which is of a rotationally symmetrical form, may
 be fitted with axially parallel, longitudinal tumbling strips on the
 inside of its perforated wall.
 In performing the invention, the immersion barrel is filled with the charge
 up to about one third of its capacity. Due to the grid-type arrangement of
 the tumbling strips, the charge mass does not slide along the wall of the
 rotating barrel, but rotates synchronously with it. The result of this
 process is that the charge is constantly circulated about its own
 longitudinal axis about three times per barrel rotation and, consequently,
 its entire periphery is guided evenly past the nozzle opening between the
 two quarter-shells. The solution residues on the mass parts are evenly,
 intensively and rapidly removed.
 A higher efficiency attainable by means of the invention is constituted by
 a substantially increased performance in the recovery of the dragged-out
 solution residues, within a greatly reduced time span.
 The simultaneously reduced air requirement renders possible the use of
 correspondingly smaller centrifugal fans.
 The compressed-air chamber according to the invention is characterised by a
 compact, space-saving mechanical structure which is easy to service and
 inexpensive to produce.
 The compressed-air chamber includes--as an integral component of the
 subject-matter of the invention--a compressed-air line connected to a
 low-pressure centrifugal fan and also includes a water line, connected to
 an appropriate supply point. The water is optionally injected directly
 into the air current or into the chamber housing itself, preferably in a
 saturated mist form, by means of nozzles.
 The centrifugal fans can be rigidly mounted in series, for example, on the
 upper half-shell of the compressed-air chamber.
 The injection nozzles, for their part, are generally also attached to the
 half-shell and disposed as an array parallel to the longitudinal axis of
 the barrel cylinder.
 According to an aspect of the invention, the time-dependent introduction of
 the current of air and of the injected water into the compressed-air
 chamber can be effected in various combinations during a holding period
 during which the immersion barrel is in the compressed-air chamber. During
 this time, both the air and the water may flow simultaneously,
 continuously or intermittently into the chamber.
 It is advantageous for the predefined volume of water to be injected under
 pressure directly into the current of air on its path to the barrel
 cylinder. In this way, the air is used as a means of transport to
 distribute and cause the injected water, uniformly dispersed, evenly and
 fully to wet all charge parts present in the immersion barrel.
 The apparatus according to the invention is employed, by means of the
 current of air and injected volume of water guided through the immersion
 barrel, for the application of some invention-specific methods which are
 characterised by combinations of different, single or multiple, steps
 proceeding in defined sequences.
 The volume of water injected directly into the current of air or into the
 compressed-air chamber and transported to the charge and the barrel is
 quantitatively approximately half of the quantity of solution dragged out
 of the treatment solution tank by the charge and the barrel.
 The aforementioned methods according to the invention are discussed
 briefly.
 The immersion barrel is moved into and positioned in the compressed-air
 chamber, the lower quarter-shells close and the current of air flows
 transversely, for a predefined period of time (during a first step),
 through the perforated barrel cylinder and through the charge within it. A
 large portion of the residual quantities of the dragged-out treatment
 solution adhering to the surfaces of the barrel body and of the charge
 parts is intercepted, entrained in the air flow and drawn off, to be
 returned into the tank, located below the chamber, from which the solution
 was previously dragged out.
 The obvious advantages of the combined action between the apparatus
 according to the invention and the associated method can be illustrated by
 means of a numerical example according to operational practice.
 Fifty percent of the dragged-out volume of the bath solution, of 25.4 l/h,
 is blown into the tank underneath during the holding period of the barrel
 cylinder in the compressed-air chamber. The prescribed dilution rate is to
 be equal to 2000.
 The rinsing water requirement according to the prior art would be 320 l/h,
 but the invention reduces this volume to 160 l/h.
 Half, i.e., 12.7 l/h, of the bath solutions otherwise carried into the
 rinsing baths is directly recovered and the rinsing water requirement is
 also halved accordingly. The consumption of salts for the neutralisation
 or decontamination installation is reduced in the same proportion; the
 level of expenditure for waste dumping is reduced accordingly (by
 reduction of the salt load from 2540 g/h to 1270 g/h).
 The immersion barrel positioned in the compressed-air chamber, together
 with the charge, is continuously traversed by the air current during its
 predefined holding period and simultaneously sprayed with a defined volume
 of injected water.
 The resultant mixture of treatment solution and water is intercepted by the
 air current and the greater part of it is brought into the tank with the
 bath solution located below the chamber.
 Metrological studies have shown surprising effects as a consequence of this
 use, according to the invention, of the apparatus and the associated
 method.
 The volume of the bath solution dragged out into the connected rinsing bath
 is further reduced to 7.6 l/h and the rinsing water requirement is reduced
 proportionately to 96 l/h. The salt load dropped to 760 g/h.
 The schematic representation appended as FIG. 4 and the summary table of
 the determined measurement values, appended as FIG. 5, show that the
 combined action, according to the invention, of the apparatus and the
 method renders possible a direct recovery of the dragged-out solution in
 the proportion of 71.08% as compared with the prior art. The consumption
 of rinsing water for the maintenance of the rinsing criterion of 2000 is
 reduced by the same percentage, of approximately 70%, in common with the
 corresponding salt load.
 The injection of the cooling water into the compressed-air chamber has a
 particular significance with respect to the apparatus. Operational
 experience has shown that, if the apparatus according to the invention is
 used, it is possible to save one stage of a multi-stage cascade rinsing.
 Experience has also shown, in the application case B, that, if a second
 step follows immediately--during which no further water is injected into
 the continuing current of air--the proportion of the treatment solution
 recovered is further increased by a substantial amount.
 During the second step, the immersion barrel expediently executes an
 additional full rotation.
 In another case of application of the invention, the greater part of the
 dragged-out bath solution on the barrel and the charge is returned in a
 first step, in a concentrated form, into the original tank by means of the
 air current in order for a defined volume of water to be injected into the
 compressed-air chamber in an immediately subsequent second step--this
 being during a full, additional, second rotation of the barrel.
 A mixture of the treatment solution and water is formed, part of which
 adheres to the surfaces of the immersion barrel and the charge and part of
 which drains off into the tank underneath. The blowing-off of the adhering
 fluid residues by the air current proceeds continuously during the second
 step.
 It has further been established, in an operational examination of a
 perforated immersion barrel of 950 mm in length and an inscribed circle
 diameter of 360 mm, that 1.2 l of bath solution was dragged out in each
 case.
 The required dilution rate of 1000 was achieved in a two-stage cascade
 rinsing with 37.9 l of water per immersion barrel.
 In the first step, 60% (or 0.72 l) of the drag-out was returned in
 concentrated form into the original tank by the air current during one
 full barrel rotation, which was a period of 10 sec.
 The subsequent second step likewise lasted for 10 sec., with 1 l of water
 being injected into the air current during this period.
 The blow-off ratio remained unchanged at 60%; a measured quantity of 1.48 l
 of the resultant mixture (with a proportion of 0.32 l of concentrate) was
 additionally returned into the tank with the bath solution.
 The sum of 0.72 l and 0.32 l gives the total quantity of 1.04 l of the
 recovered drag-out, i.e., 86.7% of the latter.
 The quantity of rinsing water required to meet the dilution rate of 1000
 was 4.7 l (by contrast with the water requirement of 37.9 l according to
 the prior art).
 Various treatment solutions, for example soak cleaning or phosphatizing
 baths, have relatively high operating temperatures which range in the
 order of magnitude of 75.degree. C. and above.
 In practical testing of the invention, it has been shown that wet steam can
 be produced when air is passed through the immersion barrel and charge,
 heated to a high temperature and wetted with the bath solution, in the
 compressed-air chamber. The saturated, warm mixture of fluid and air may
 spread out locally in the form of a cloud and be precipitated as a
 condensate on the adjacent apparatus, at room temperature.
 The consequence is corrosive damage on the metal components of the adjacent
 apparatus.
 The invention provides for a two-step method in this application case.
 The barrel cylinder positioned and rotating within the compressed-air
 chamber, together with the charge, is sprayed for the duration of a first
 step with a defined volume of water, the current of air remaining switched
 off. In the subsequent second step, a further predefined volume of rinsing
 water is injected to the continuously rotating barrel and charge, this
 time with a simultaneous air current through the compressed-air chamber.
 The purpose of the method is the reduction of the temperature both on the
 dragged-out losses adhering to the charge in the barrel, and on the barrel
 body itself.
 The process can be illustrated--in approximately commercial scale--by the
 example of an application case adapted to operational practice.
 It is to be assumed that the dragged-out quantity of solution, of 2 l,
 originates from a soak cleaning bath whose operating temperature is
 65.degree. C. The temperature of the injected water quantity, of 1 l,
 might amount to 10.degree. C.
 The mixture, of 3 l, resulting from 2 l of treatment solution and 1 l of
 water, has a mean temperature of 47.degree. C. following completion of the
 first step; following the addition of a further quantity of 1 l of water
 during a second step, this falls to only 37.5.degree. C.
 The vaporization point of such a reduced-temperature mixture is to be
 characterised as low; visual perception of vaporization of the blown-off
 drag-out residues is scarcely possible.
 Furthermore, baths with high operating temperatures have high evaporation
 losses. The quantities of water injected into the compressed-air chamber
 essentially compensate the fluid losses and the bath volumes thus remain
 virtually constant.
 Consequently, the sequence of recovery in the application case E can
 proceed under optimum conditions, without being subjected to the adverse
 effects according to the prior art.
 A further variant according to the invention renders possible a drastic and
 sudden reduction of the temperature of both the dragged-out solution
 quantities and the immersion barrel itself.
 The method according to this variant of the invention consists of a
 sequence of three connected steps.
 In the first step, the non-rotating immersion barrel is raised out of the
 treatment solution and positioned in the compressed-air chamber. The two
 lower quarter-shells close. The only remaining possibility by which the
 vapour of the hot solution can be discharged out of the chamber is through
 the narrow, open longitudinal slot between the two quarter-shells, at the
 base of the compressed-air chamber.
 The carriage then transports the immersion barrel over a tank which
 directly adjoins the tank with the hot treatment solution and contains the
 same solution, with the difference that its bath solution is at room
 temperature, i.e. a maximum of 20.degree. C.
 During a second step, the barrel cylinder, together with the charge, is
 lowered into and immersed in the lower temperature solution and assumes
 this temperature within a very short period.
 After a short period, the immersion barrel is raised out of the lower
 temperature bath solution and, in a third step, is moved into and
 positioned in the compressed-air chamber and the solution residues
 adhering to the barrel body and to the charge are brought into the tank
 with the bath solution underneath by means of the applied air current,
 perhaps with the addition of injected water.
 The method according to this variant of the invention fully precludes the
 otherwise occurring problem of scarcely controllable cloud-like
 propagations of vaporized bath solution during its recovery by means of an
 air current emerging from the compressed-air chamber. The method effects a
 sudden drop in the temperature of the solution residues adhering to the
 barrel and on the barrel itself, down to the range of the room
 temperature, i.e. about 20.degree. C.
 Operational experience with the known compressed-air chambers has shown
 that hardened layers of different bath salts come to be formed on their
 inner wall surfaces. The necessary regular cleaning of the inner walls
 presents considerable difficulties, particularly due to the rigid
 disposition of such chambers on the carriages.
 The invention offers the possibility of thoroughly rinsing the inner wall
 surface of the compressed-air chamber by a combined action of the air
 current and the injection of water into the compressed-air chamber and of
 thus washing off and removing the salts in a not yet solid, i.e., liquid,
 state.
 In the immersion process, the barrel cylinder and charge are first cleaned
 with water in a rinsing tank, to remove the still adhering solution
 residues (following a prior blowing operation to remove the concentrated
 dragged-off solution) and only then moved into and positioned in the
 compressed-air chamber of the carriage.
 For a predefined period of time, the rotating immersion barrel is exposed,
 above the rinsing bath, to the current of air flowing through it and is
 simultaneously sprayed intensively with water. The layer of liquid bath
 salts on the inner wall of the chamber is to a large extent washed out and
 the concentration of the remaining film can be characterised as negligibly
 small.
 The upper, immovable and upwardly convex half-shell of the compressed-air
 chamber attached to the carriage has at its apex an open longitudinal slot
 for the through--passage of a supporting beam of the barrel unit, so as to
 render possible its vertical upward and downward movement. Said beam
 carries, in general, a drive motor mounted on it for rotation of the
 barrel and an enveloping housing for the purpose of protecting the beam
 from dragged-off solutions draining from crossing barrel units.
 Progressive designs for the frame of barrel units (for example, according
 to the German Published Patent Application DE 44 44 103 A1) dispose said
 drive motor laterally, i.e. outside the range of the quadrangular tank
 with the bath solution, and thus enable the longitudinal slot on the apex
 of the upper half-shell to be of very small dimensions.
 The very compactly dimensioned longitudinal slot simplifies and reduces the
 size of the generally plate-like displaceable or pivotal sealing elements
 on the barrel unit or on the half-shell which are necessary in order to
 close the slot opening following positioning of the barrel in the
 compressed-air chamber.
 The closing and opening of the compressed-air chamber by means of the two
 lower hinged quarter-shells is effected by the vertical upward and
 downward movement of the barrel unit, to provide the drive force and
 control element.
 Such a closing and opening mechanism for the actuation of the
 quarter-shells can consist of a system of coupled lever arms, of which
 some of the elements are disposed on the compressed-air chamber and some
 on the barrel unit.
 A delivery volume of 1000 m.sup.3 /h of air, at a pressure of 0.3 bar, is
 stated as an example of the required output of one or more low-pressure
 centrifugal fans connected together as a group for a barrel of
 approximately 950 mm in length and an inscribed circle diameter of 360 mm.
 The pressure for the generation of a water jet sprayed into the
 compressed-air chamber by means of the injection nozzles might correspond,
 preferably, to the pressure of the water line (mains pressure) of,
 generally, 3 to 4 bar, in individual cases, however, this can be reduced
 by pressure reducing valves to approximately 0.5 bar.
 The barrel cylinder rotates continuously or intermittently during its
 holding period in the compressed-air chamber, irrespective of whether a
 blowing operation is being performed, or not.
 In order that the invention may be better understood, it will now be
 described in greater detail and certain specific embodiments described,
 referring as appropriate to the accompanying drawings.
 The particular arrangement of the embodiment of apparatus shown in the
 drawings will now be described. Referring to FIGS. 1 to 3, tank 1 contains
 the treatment solution. A cylindrical immersion barrel 2, together with a
 charge 3, assumes its operating position within the horseshoe-shaped anode
 basket 4 made from titanium with soluble metal cubes. The hexagonal
 immersion barrel 2 has a perforated casing 5 made from a synthetic,
 electrically non-conductive material.
 The carriage 6 of the automatic transport mechanism of the barrel
 installation stops above the tank 1; its compressed-air chamber, which is
 rigidly disposed thereon, is open.
 Said chamber on the carriage 6 consists essentially of an upper fixed
 upwardly convex half-shell 7 which encompasses the upper half of the
 barrel 2 when moved into it, and of two likewise outwardly convex hinged
 quarter-shells 8 which, in turn, closely encompass the lower half of the
 barrel 2 in an airtight manner.
 During the holding period of the barrel 2 positioned in the chamber, its
 circular end faces 9 form the two lateral end walls of the compressed-air
 chamber.
 The hexagonal barrel 2, together with a drive motor 11 therefor, are
 mounted on the supporting frame 10, to form a barrel unit 12. The latter
 is transported from one treatment station of the barrel installation to
 the next by means of the carriage 6, according to a predefined programme.
 The inside of the barrel casing 5 is provided with a grid of tumbling
 strips 13 for the purpose of preventing the charge 3 from sliding over the
 barrel surface, and to ensure the synchronous rotation of the barrel 2 and
 the charge 3 within it.
 Each of the two quarter-shells 8 has a respective lever arm 14 which, upon
 the upward movement of the barrel unit 12, are driven upwards by two short
 connection pieces 15 mounted on the barrel supporting arms 16 and assigned
 to each lever arm 14, thereby to force the quarter-shells to turn through
 approximately 45.degree. about their pivotal axes provided on the lower
 longitudinal edges of the half-shell. The barrel cylinder 2 is moved into
 and positioned in the compressed-air chamber, and the two quarter-shells 8
 close the latter, apart from a narrow longitudinal slot between their two
 lower ends running parallel to the longitudinal axis of the immersion
 barrel 2.
 In the reverse process, i.e., upon the downward movement of the barrel unit
 12, the two quarter-shells 8 pivot downwards unassisted, due to their own
 weight.
 In the course of its vertical movement, upwards and downwards, the
 supporting frame 10 of the barrel unit 12 has to slide through the upper
 half-shell 7. The open longitudinal slot required for this purpose is
 provided at the apex of the shell 7. When the barrel 2 assumes its
 operating position within the compressed-air chamber, the said
 longitudinal slot is sealed in an air-tight manner by a longitudinal
 plate-type segment 17 disposed horizontally and centrally above the barrel
 2. The sealing segment 17 is rigidly fixed between the two perpendicular
 supporting arms of the barrel unit.
 Thus, with the exception of the open longitudinal slot at its base, the
 compressed-air chamber encompasses, it in an all-round air-tight manner,
 the rotationally symmetrical barrel 2 positioned within it.
 A centrifugal fan 18 is connected, or a number of smaller such fans 18 are
 connected, via suitable ducts, to the compressed-air chamber, or, perhaps,
 are mounted directly on the half-shell 7.
 The current of air from the fan 18 (indicated by direction arrows in FIGS.
 2 and 3) penetrates the charge-free interior space of the immersion barrel
 2 and is distributed evenly over the slope surface of the charge 3.
 Consequently, the preferred position of the or each fan 18 is on one of
 the two sides of the half-shell 7.
 A set of injection nozzles 19 directed towards the compressed-air chamber
 is disposed so that the injected quantity of water reaches the immersion
 barrel 2, with the charge 3 within it, in the current of air coming from
 the fan 18.
 The injection nozzles 19 are mostly located on the half-shell 7 of the
 compressed-air chamber and are controlled by solenoid valves.
 The injected quantity of water should correspond to approximately half of
 the dragged-out electrolyte, and may be at room temperature. The injection
 period, in particular, for a pressure of about 3 bar, allows for the
 duration of a full barrel rotation, i.e. about 8 sec. The spray is evenly
 distributed over the full cone of the injected water jet, which consists
 of very fine drops (corresponding to a spectrum of 150 to 450 mm).
 The air flowing over and past the surface of the charge 3 of parts draws
 with it, in a first step, the greater part of the bath solution residues
 adhering to the parts.
 The arrows in FIGS. 2 and 3 which point from the barrel cylinder 2 towards
 the tank 1 indicate the path of the dragged-out solutions recovered in a
 concentrated form or as a mixture of bath solution and water.
 FIG. 3 depicts the second process step, which is characterised by the
 injection of a defined quantity of water (about 1 l) by means of the
 nozzle set 19 into the air flowing continuously through the compressed-air
 chamber following completion of the first step.
 The air, saturated with the atomized quantity of water, passes over and
 beyond the charge 3 of parts and coats them with a thin layer of water
 which immediately mixes with the residues of the concentrated bath
 solution remaining on them. The greater part of the resultant mixture is
 drawn off by the air current, removed from the barrel 2 and transported
 into the treatment solution tank 1 located therebelow.
 The air current jet emerging through the long slot at the base of the
 compressed-air chamber and containing a mixture of bath solution and water
 is directed vertically downwards and has an emergence angle of about
 33.degree..
 FIG. 4 represents schematically a method according to the invention, based
 on an application example of the associated apparatus according to FIGS.
 1, 2 and 3.
 The treatment solution might have a salt concentration of 100 g/l. The
 required dilution rate is to be 2000, rinsing being effected in a
 three-stage cascade rinsing operation. The volume of solution dragged-out
 by the barrel 2 is 25.4 l/h.
 The blow-off ratio, i.e., the percentage of the dragged-out solution
 quantity recovered by means of the air current through the compressed-air
 chamber, is approximately 50%.
 The blow-off operation proceeds in two steps; in a first step, 50% of the
 dragged-out bath solution is recovered in a concentrated form, and the
 same percentage in a second, subsequent step--with the addition of water
 atomized by means of nozzles--but this time as a mixture of treatment
 solution and water.
 The measurements taken in this actual case have shown that it was possible
 for a total of 17.8 l/h, or 71.08%, of the dragged-out bath solution to be
 directly recovered, and only 7.5 l/h, or 28.92%, of this was introduced
 into the first stage of the cascade rinsing.
 The volume of water required to meet the dilution rate of 2000 was 96 l/h.
 The concentration of the bath solution in the first stage of the cascade
 rinsing gave a measurement value of 7.94 g/l, 0.72 g/l in the second stage
 and 0.05 g/l in the third stage (or the equivalent of the dilution rate of
 2000).
 FIG. 5 supplements and summarizes in tabular form the schematic
 representation from FIG. 4, in comparison with the known prior art.
 With the use of a three-stage cascade rinsing and a bath solution drag-out
 of 25.4 l/h, a volume of 320 l/h of water would be required to meet the
 criterion of 2000. The corresponding salt load of the drag-out--according
 to the prior art--would be 2540 g/h.
 If the barrel is positioned in the compressed-air chamber according to the
 invention and if the blow-off ratio is set at 50%, then half of the
 drag-out, i.e., 12.7 l/h, is returned directly into the treatment solution
 tank The rinsing water requirement is reduced proportionately, to 160 l/h,
 the salt load falling to 1270 g/h.
 If the effect of water injection according to the invention is added to the
 recovery process, for example the injection of 12 l/h, then 17.8 l/h, or
 71.08%, of the dragged-out bath solution is directly recovered. The
 quantity of rinsing water required falls, in the same proportion, to 96
 l/h and the salt load of the remaining drag-out is reduced to 760 g/h. The
 preceding example of operational practice shows that the invention is
 capable of adequately replacing a three-stage cascade rinsing by a
 two-stage cascade rinsing.
 The process principle of a three-stage rinsing also continues to exist
 within the context of the invention; the first rinsing stage is executed
 by the injection of water into the air current within the compressed-air
 chamber containing barrel 2 with its charge 3, the two others following in
 the related two-stage cascade rinsing.
 The direct injection of the rinsing water into the air current saves a
 complete rinsing process stage. The simultaneous injection and blowing-off
 of the resultant mixture on the barrel 2 and charge 3 likewise renders
 superfluous a number of transport movements which are otherwise
 necessary--according to the prior art--for the execution of the rinsing
 operation.
 The transfer of the barrel 2 to the next rinsing compartment and lowering
 of the barrel into the latter (about 9 sec.), the rinsing in the first
 compartment of a subsequent three-stage cascade (for about 60 sec.) and
 the raising of the barrel 2 out of the latter (3 sec.) are all omitted;
 these times would add up to approximately 72 sec.
 If it is further assumed that a barrel installation--for example for acid
 galvanising--requires 7 stations for the surface treatment of the mass
 parts, then the passage time of the individual barrel units through the
 installation might be shortened, according to the invention, by about 500
 sec.
 The consistent substantial reduction of the otherwise necessary transport
 movements, the shortening of the passage times for the barrel units and
 the resultant reduction of the required cascade rinsings by one
 compartment in each case, i.e., in the case of the preceding example, a
 reduction of the barrel installation by 7 rinsing stations, constitute
 improvements by comparison with the prior art which are of exceptional
 technical and economic importance.
 The space required for the erection of such compact installations is
 accordingly smaller, fewer transport movements result in a reduction of
 the required automatic transport system and the costs of production of the
 installation are reduced accordingly.
 The economic advantages for operational practice that are attainable
 according to the invention are obvious; the consumption of chemicals for
 the different bath solutions and for the neutralization or decontamination
 of the rinsing water is drastically reduced and the rinsing water
 requirement diminishes largely proportionately to the percentage of the
 recovered quantities of electrolyte.