GB2175607A - Apparatus and a process for removing residual liquid from a processing barrel - Google Patents

Abstract

In an electro-plating or similar processing installation, where bulk items 3 are processed in a perforate treatment barrel 2, liquid is removed from the barrel 2 and the contained bulk items 3 by placing the barrel 2 in a prismatic chamber 1 the dimensions of which conform closely to the shape of the barrel, the chamber having an air blowing duct 12 and an air suction duct 11 both opening into a lower part of the chamber 1. Air is then circulated through the chamber, by drawing air out of the chamber through the air suction duct 11 and blowing air into the chamber through the air blowing duct 12. The air stream 4 will thus flow through the barrel 2 in the chamber 1 and over the surfaces of items contained in the barrel. Liquid may be recovered at the original concentration from the air stream 4 for re-use in a treatment bath. Rinsing may simultaneously be performed by spraying water into the chamber, or the process may be operated to perform drying of the bulk items. <IMAGE>

Description

SPECIFICATION Apparatus and a process for removing residual liquid from a processing barrel This invention relates to an apparatus and a process for removing residual liquid remaining on and within an electro-plating barrel and on its charge of bulk items, following removal of the barrel from a treatment bath - which term includes a bath of fresh water for rinsing purposes.

Atreatment barrel, loadedforexamplewith metallic screws to be electrolytically plated, normally is sequentially treated in various solutions. There are bath solutionsforchemical degreasing, etching, electrolytically plating, and in some cases passivating. Between its immersion in individual solutions, the barrel is rinsed with water. After leaving the last treatment station, the plated bulk items are again rinsed with waterandthen dried.

Atypical hexagonal barrel suitable for electroplating may have a length of 900 mm and a width across the flats of350 mm. The usual diameter of the perforations in the peripheral wall (casing) of the barrel is 3 mm.The total surface area of all the bulk items forming the charge may be 4 m2. When the barrel is lifted out ofthe electrolyte after plating has been completed, the residual solution extracted from the bath (the 'drag-out') may be allowed to drip for 15 seconds. The quantity of electrolyte introduced into the subsequent rinsing water bath is, from experience, around 1 .5to 2.5 litres.

The extraction by the barrel and its charge of so much treatment solution can often bring into question the economics of a plating plant. Only part of the bath salts are useforthe deposition of a metal coating orthe treatment of the surfaces; with copper, nickel or zinc electrolytes the losses of salts so carried off lies between 10% and 20% ofthetotal salt usage. These salt losses not only represent a considerable financial loss, theyalso cause a very high consumption of rinsing water, with the consequent canalization costs, continuous extra costs for chemicals, for the correspondingly larger instal lation, for the decontamination and neutralisation of the waste water, and for transport ofthe salts, and sludge disposal.

The magnitudes of the extracted treatment solutions determine the required quantities of water in the subsequent rinsing baths, in order to arrive at a satisfactory rinsing criterion. A considerable importance therefore is given to the rinsing process, because it strongly influences the quality of the coatings and the cost ofthewhole process. Whilethere is a requirementfora good rinsing effectforan electroplating orchemical process, on the other hand the water consumption should be kept low.

Usually, either dip rinsing (in which bulk items in the barrel are dipped in a water-filled container) orspray rinsing (in which the barrel and its contents are sprayed with waterjets) are employed.With dip rinsing, itis usual to arrange several rinsing stages one afterthe other, connected in a cascade, with the waterflow opposite to the direction of treatment. In this way, the water consumption is greatly reduced, but the cost ofthe installation isveryhigh.

By contrast, spray rinsing demands a high equipment cost, an optimum arrangement of the spray device, and the application of refined spray techniques. The limits of such rinsing are defined bythe largequantitiesof solutions removed, and accordingly demand considerable minimum quantities of rinsing water.

It is known to recover some of the treatment solution extracted from a treatment bath by means of a suction device. One such device has brushes arranged to wipe against the barrel and a suction strip associated with the brushes for the whole barrel length. The device is arranged to follow the barrel movement (by operation of weights) asthe barrel is lifted from a treatment bath, lying againstthe underside ofthe barrel. Airissucked in through the suction opening of the strip, and piped to a liquid separator. With such a device, it is possibleto remove treatment solution carried by the barrel, particularly in the perforations, for re-use. Also, liquid will be drawn out from between the individual items of the barrel charge, but only to a small extent.

The concentrated solution extracted from the treatment bath is in this way recovered in a concentrated state, ratherthan being lost in a rinsing bath. It is also possible to use this device on a rinsing bath, such that with many water rinsing processes, rinsing fluids ofvarious concentrations can be recovered.

The described known device actually removes the liquid only from the perforations of the barrel; liquid removal from the surfaces of the bulk items is practically non-existent. This results in a very long process time, reducing the utilisation of the installation.

It has also become known,forthe recovery of residual liquid carried by the bulkitems,to make use of an air stream which passes through the barrel. Itis also known to dry the barrel charge with such an airstream, following rinsing.

It is further known to force a stream of airthrough the perforations ofthe barrel casing. For this purpose,the barrel is placed in a prismatic chamber, located at a drying station. In a lower corner ofthe chamber there is an opening to a duct, the housing around the opening fitting in an airtight manneragainstthe polygonal barrel casing, and air being blown through the opening on to the perforated casing. The barrel has to be appropriately positioned with respect two the opening, and approximately one quarter of the surface ofthe barrel casing communicates with the duct.

Two flaps made of a flexible material are fastened to the upper and lower edges ofthe duct opening, to bear on the barrel casing during the rotation thereof. Air blown into the duct thugs is forced to enter the barrel, through the perforations. It is importantto ensu re that the ai r strea m from the duct is directed diagonally upwardly within the barrel, and thus againstthe direction in which any residual treatment solution or rinsing watercarried bythe bulk items will naturally drip and fall.

If now barrel rotation in this known device takes place such that the charge moves away from the air delivery duct, the air force into the barrel will generally flow overthe surface ofthe mass of items. The airflowwill thus be over only a small outer region of the total surfaces to be dried, and the efficiency of the drying process must therefore be very low. If howeverthe barrel is rotated in the opposite direction, the charge will remain in the region ofthe barrel casing which lies immediately overthe airdelivery duct, sothatthe airflowwill be through the charge of bulk items.Nevertheless, such rotation causing the mass of items to overlie the ductwill havethe effectthatdropsfalling downwardly will be flung back into the charge bythe airstream: therewillthus bean effect which is the direct opposite of what is required.

It will of course be appreciated thatthe charge of bulk items forms a pourable conglomerate mass. If their stream does not penetrate that charge, butflows overthe exposed surface only, then ineffective drying inevitåblywiil result Another known device has the object of overcoming this problem. The barrel again is placed in a prismatic chamber, the upper part of which is open. A duct is arranged at the bottom ofthe chamber, to be connected in an air-tight manner two the polygonal barrel casing. Unlike the previously-described case, air is drawn out through the ductatthe bottom ofthechamber; the resulting airstreamflowsthroughthecharge inthe direction in which drops of any residual treatment solution or rinsing water will fall. The barrel is rotated as air is drawn through the charge to mixthe bulk items.

The barrel, which is polygonal in cross section, isgenerallyonlyone-thirdfilledwith bulk items, in orderto allow a thorough mixing ofthe items. The cross section of the mass of items in the rotating drum approximates to a semi-circle,thediameterofwhich is inclined at an angle of about450to the horizontal. The airstream through the charge takes the path of least resistance; in the case ofthe described known device it will pass mostly through the regions atthe two ends ofthe diameter. The total surface of items in the charge istherefore quite unevenly subjected to the airflow and any residual bath solution will unevenly be removed. A correspondingly largertime isthus required sufficientlyto removethe residual liquid.This however hasthe disadvantage that some surfaces will be exposed to the drying air stream for an unnecessarily long time, which may leave drying marks on the surfaces.

If the treatment ofthe bulk items is fortechnical purposes, the just-described device can be used with caution, principally because of the formation of spots; but if the treatment is for decorative purposes,thenthe use ofthis device is excluded.

In addition to the foregoing, use of the device may result in a reduction of the quality of the surfaces, especially with metal-plated coatings which tend to oxidize. This is also noticed in a barrel installation for cyanide silvering, where the rejection of spotted parts was so great that the drying had to be carried out in a conventional centrifuge.

If the barrel has to undergo a multi-stage rinsing using the described drying device between stages,then there is a great increase in the required processing time: the individual rinsing stages with fluids of reducing concentration demand so much timethatthe transport ofthe bulk items through the whole plating or chemical plant is considerably restricted.

The described known arrangements do not technically solve the problem of having a directional and sufficiently strong airstream through the conglomeration of bulk items in the barrel. The process using these devices have only a small and accordingly inadequate solution recovery and inefficient drying.

A principal object ofthis invention is a substantial improvement in the efficiency of solution recovery and drying processes ofthe described sort, without additional constructional expenditure and lengthened operation times.

Afurther object is the provision of apparatus which may be used to permitthe recovery oftreatment solutions remaining in a barrel and on its charge after removal of the barrel from a treatment solution bath,the solution recovery being at the original concentration ofthe solution.

According to one aspect ofthis invention, therefore, there is provided apparatus for removing residual liquid remaining within and on a perforated electro-chemical plating barrel and on its charge of bulk items following removal ofthe barrel from a liquid bath, which apparatus comprises an open-topped chamber of rectangular shape in plan and into which the barrel may closely but rotatably be placed with its axis generally horizontal, an air blowing duct opening into the chamber at a lower partthereoffor substantiallythe whole length ofthe chamber, an airsuction ductalso opening intothe chamberforsubstantiaIlythewhole iength thereof ata position generally belowthe barrel when placed in the chamber, and means to cause the generation ofa stream of air entering the chamberthroughthe air blowing ductand leaving the chamberthroughtheair suction duct, wherebythe air stream will pass from the air blowing duct th rough the perforations of a barrel placed in the chamber, through a charge of bulk items in the barrel and then outthe barrel through the perforations thereof to leave the chamber through the air suction duct.

The air stream should impinge on the wet surfaces ofthe bulk items with the highest possible velocity, in orderto fulfil three basic requirements: 1. Residual bath solution or rinsing water on the surfaces should be driven off quickly and intensively as possible, as with a centrifuge. Ifthis mechanical effect occurs quickly, then hardly any residual fluid evaporates to form spots.

2. The unavoidably evaporated proportion ofthe treatment solution or rinsing water should be reduced to a minimum, to minimise the spotformation.

3. The time period during which the items are exposed to the air stream should be short, to minimisethetime of the overall treatment.

The airstream passing through the barrel will pass oversubstantiallyall of the surfaces ofthe bulk items and can be separated into two effective components: a blown stream, and a suction stream.

In this invention, the blown air stream is aimed directly through the perforated barrel casing either immediately into the charge itselfortowards the free upper side ofthe charge. The suction air stream, on the other hand, necessarily is drawn through the charge from the inner space of the barrel, leaving the barrel through the perforated casing against which the charge lies. The path, volume, velocity and concentration of the air stream through the charge are determined by the direction of these components, controlled bythe combined action of the over- and under-pressure ducts.

The air stream may have a generally laminarflowthrough the drum casing and charge, and is largely directed downwardly, that is to say, in the direction offal of any liquid drops. If the effective direction ofthethe drawn air stream and the dripping liquid agree, there is achieved an accelerated removal of residual liquid; the short path through the charge enables a high airvelocity, free from local turbulences, so that residual liquid may literally be torn away from the wetted surfaces.

As an example, the drying time in a barrel of usual dimensions (900 mm in length and 350 mm across the flats) is around 6 to 16 minutes with a known device; apparatus according to this invention drastically reduces this time by around 50%. The assumed temperature ofthe pre-warmed air used is approximately 60"C.

The air blowing duct and the air suction duct may extend at the mostoverthe lower half of the perforated barrel casing. The suction duct preferably covers that part of the barrel casing which is directly covered bythe charge of bulk items, and advantageously lies to both sides of a perpendicular line passing through the barrel axis. The drying process is thus concentrated in the lowerhalfofthedrum.

According to a second aspect of this invention, there is provided a process for removing residual liquid remaining within and on an electro-plating barrel and on its charge following removal ofthe barrel from a liquid bath, wherein the barrel is placed in apparatus of this invention as defined above such thatthe preforated casing ofthe barrel lies adjacent the openings ofthe air blowing and suction ducts, an air stream is caused to flow from the air blowing duct through the perforated casing of the barrel into the interiorthereof, through the charge of bulk items and outofthe barrel through the perforated casing into the air suction duct thereby to entrain residual liquid in the air stream, and the barrel is at least intermittently rotated to mixthe items ofthe charge.

This process may be modified, to give a combination process in which firstly residual treatment solution is removed by means of the directional air stream, and then rinsing ofthe bulk items is carried out. Instead of rinsing the drum and its charge bya usual dipping process, so diluting the residual treatment solution, the undiluted solution is firstly to a large degree removed, whereafter rinsing takes place.

The removed treatment solution can be recovered, for delivery back to the treatment bath from which itwas extracted. In this way, 50% or more ofthe original solution is directly recovered for pumping back to the original bath.

This recovery process does not involve great expense, and moreover reduces considerably the salts content of the waste water. The consumption of rinsing water as well as the cost for decontamination and neutralizing are proportionately reduced.

In orderthatthe invention may better be understood two specific embodiments of liquid removal apparatus will now be described in detail, referring to the drawings, and two Examples of processes using the apparatus will be described, all byway of illustration only. In the drawings: Figure 1 shows a cross section through an octagonal electro-plating barrel positioned above a chamber configured in accordance with this invention for the recovery of extracted treatment solutions orforthe drying ofthe charge of bulk items loaded in the barrel; Figure2 shows the barrel in the lowered position in the chamber, and the arrangement of the air ducts thereof; Figure3shows a single or multi-stage rinsing process being performed in the chamber; and Figure4shows a chambermodifiedto enhance the airflowthrough a barrel placed in the chamber.

In the drawings, there is shown a chamber 1 for the removal of residual treatment solution or rinsing water carried by a treatment barrel 2 and its charge of bulk items 3, orforthe drying ofthe charge in the barrel.The chamber 1 constitutes one station of an electro-plating installation, which is preferably equipped with an automatictransport mechanism (not shown). Alifting device 21 is connected to the barrel byan arm 22.

The barrel has a perforated casing 23, a removable lid 24 and two end walls 25, one of which is provided with a toothed wheel to permit rotation to be imparted to the barrel by a motor (not shown) in the direction ofthe arrow n. Radially projecting ribs 26 are connected to the end walls and extend parallel to the barrel axis.

At the bottom ofthe chamber 1 are provided an airsuction duct 11 and an air blowing duct 12. The suction opening BC ofthe air suction duct lilies to both sides of a perpendicular plane extending through the barrel axis and the duct 11 is so arranged that on rotation of the barrel 2 the charge 3 lies directly opposite the opening BC. The air blowing duct 12 is arranged so that air leaving its opening AB either impinges directly on the charge 3 or else streams through the bulk items. In either case, the air stream is over the items of the charge, as shown by arrow 4. The openings and BC are preferably segments of an arc arranged side-by-side, each extending forthefull axial length ofthe barrel, with the opening AB smallerthan opening BC. A radial blower (not shown) draws airthrough the suction duct 11,creating the airstream 4through the barrel 2.

The barrel 2 is lowered into the chamber 1 afterthe barrel and its charge 3 have previously been dipped into a containerfilled with a chemical orelectro-chemicaltreatmentsolution. The air stream 4 entrains residual treatment solution (as indicated by the dot-density in the airsuction duct 11 as compared with that in the air blowing duct 12). The air stream 4 moves away from the barrel 2 downwardly in a nearly vertical direction to arrive, in certain cases, at a drop or liquid separator. There, the smallest, still separable, liquid particles (called boundary drops) will be held back on the stream grating ofthe separator, for re-use in the treatment bath.

This described arrangement enables a high airflowvelocityto be obtained even with a high liquid content; it therefore makes possible a particularly intensive and fast liquid removal or drying ofthe bulk items 3 by rapidly carrying away any liquid or dampness on their surfaces.

In the case of a closed drying aircircuit,the air is ledfromthe drop separatorto a heating unit (notshown).

The drying airtemperature should not in general exceed 70"C, so as notto damage the plated items, and may be blown into the air duct 12 by a radial blower.

Before the circulating drying air enters the barrel 2, a small volume can in some cases be vented tothe surroundings. This should immediately be cpmpensated by an equivalent volume of fresh air at a lower relative humidity, which may be drawn from the same region. For example, the relative humidity ofthevented air might be 90% whereas the air drawn from the same region might have a relative humidity of around 40to 45%. In this case of a non-closed circuit circulating air arrangement, it may not be necessary to employ a drop separator, drying being achieved just by the heating unit.

Figures 1,2 and 3 show an octagonal barrel 2, the periphery of which is defined bythe ribs 26 and planar perforate plates 23; the bottom ofthe chamber 1 is shaped closely to fit against the barrel. Blowers, as described above, may serve adequatelyto give the required closed orvented air circulation. Any small gaps between the ribs 26 and the chamber parts will not give rise to problems. if however a very high efficiency of fluid removal or drying is required, flexible flaps 27 (Figure 4) can be provided to seal againstthe barrel.

If drying process in the chamber 1 isto be accelerated, the barrel and its charge can be rinsed in hotwater (up to 90"C) before being lowered in the chamber 1. This assists the rate of evaporation of any fluids on the bulk items.

Partial removal ofthe treatment solution may be achieved, followed by single or multiple rinsing operations which use water sparingly. Instead of, as is usual, rinsing the barrel by dipping in a large volume ofwater,thus diluting the solution, first only a part ofthe concentrated treatment solution may be removed, which may be recovered, as described above. The rinsing process then can take place, either by spraying, or dipping, or bya combined spray and dip rinsing. In Figure 1,the barrel 2 is shown lifted up, above the chamber 1. In Figure 2, the barrel is shown inside the chamber 1 where the air stream 4 may remove quantitavely 50% or more ofthe treatment solution carried by the barrel 2 and the charge 3.Practically loss-free recoveryofthattreatment solution at its original concentration can be obtained from the air stream, for return to the treatment bath. In Figure 3, spray rinsing is shown, preferably with water. A rinsing device 5 is shown schematically in the drawings, and comprises a spray bar 51 extending the length ofthe barrel 23. The bar 51 has a series of holes on the underside and can be moved horizontallyto permitthe barrel 2 to be moved into and out of the chamber 1. A pump 52 is arranged to feed rinsing watertothespraybar51.

In a preferred process of the invention, the pump 52 and a blowerforthe air stream 4 can be switched on at the same time. Then, rinsing can be effected intensively and quickly by means ofthe air stream and rinsing water mixture. The concentration of any residual treatment solution still remaining on the charge 3 and the barrel 2 is greatly reduced in an exceptionally short time, using a surprisingly small amount of water. Example 1 below gives numerical data for this process.

Another possibility is for the barrel 2 and charge 3 firstto be washed with a given quantity of water. The blower is then switched on until the air stream 4 reduces the quantity of carried diluted liquid to the required level. This alternate rinsing and drying may be repeated until the desired degree of dilution is achieved.

Example 2 below gives numerical data forthis process.

When the required dilution degree oftreatmentsolution has been reached, the charge in the barrel can be dried with the pre-heated air stream 4. During this, the barrel 2may be turned intermittently and segmentally.

The drying process is in most cases finished within 4to 5 minutes. The airtemperature clearly has to be limited, in order to avoid spoiling heat sensitive coatings on the bulk items.

Though the air suction duct 11 should always be arranged belowthe barrel 23, two air-blowing ducts 12 could be provided. The airfrom one such duct 12 may be directed directly into the charge 3, and the airfrom the other duct 12 could pass overthefree surface of the mass of items constituting the charge 3. The rinsing device 5 could be arranged at any desired position with respect to the chamber 1, or could even be insidethe barrel 2.

Particularly as compared with the necessary time and labour costfor drying by other processes, such as transferring the charge 3 out of the barrel into a centrifuge or for other operations, the energy costfor drying by the described apparatus is small.

Two specific Examples of processes of this invention will now be described, both based on average values of operational practice.

A barrel 900 mm long and 350 mm across the flats was used. The barrel casing perforations were of3 mm, and the total surface area ofthe bulk items in the barrel was 4 m2. With a dripping time of 15 secondsfollowing removal from a bath, the amount of extracted treatment solution remaining amounted to 1.5 litres.

Example 1 In a first stage of this invention, about 50% ofthetreatmentsolution extracted by the barrel and its charge was removed by the air stream forcibly lead through the barrel and charge. 0.75 litres of treatment solution in its original concentration was directly recovered, which could advantageously be returned through a pump for immediate re-use in the treatment bath.

In a second stage, rinsing waterwas sprayed on the barrel and its charge, during which the air stream simultaneously continued to flow through the charge in the barrel. The water was sprayed on to the upper half of the barrel at a rate of 1 litre of rinsing water every 7.5 seconds. Both the barrel and its charge weretherefore constantly and properly washed with a rinsing water/air mixture; the concentration of the 0.75 litre solution remaining afterthefirststagewas continually reduced, extraordinarily quickly.

The following table sets out the technical measurements of the described sequence. The concentration of the extracted residual solution during the constant rinsing with completely de-salted water and the equally constantly operating air stream were measured. The air stream was advantageously adjusted so that a little residual but greatly diluted fluid remained on the items, before a subsequent treatment step. The small and reducing concentration ofthe treatment solution rinsing-water mixture still present during the rinsing phase appears in the form of droplets and/orfilms; thefilm thickness averaged 2um.

TABLE X 7.5 15.0 22.5 30.0 30.0 37.5 45.0 52.5 Y 42.9 18.3 7.8 3.4 1.4 0.6 0.3 0.1 X = the time in seconds after commencement of rinsing, at a rate of 1 litre every 7.5 seconds.

Y = the concentration ofthe residual solution on the items, %.

0.1% concentration ofthe residual solution corresponds to an advantageous rinsing criterion of cO = 1000.

The above table clearly shows the surprisingly high efficiency of the process according to the invention; a quantity of only 8 litres of rinsing water was sufficient to reach a rinsing criterion of c0 = 1000 in only 60 seconds.

The quantity of 8 litres of treatment solution rinsing water mixture has a concentration of 9.3% and can therefore be regarded as a concentrate. A particular advantage ofthe process accordingly is that the recovered aqueous solution is sufficiently concentrated, to permit its immediate re-use. Particularly if the treatment has evaporation losses as a result of elevated process temperatures, the recovered concentrate can be fed back directly to the bath itself.

The continuously inflowing rinsing watercanfall on the barrel from a pipe provided with a row of holes and extending along the barrel casing, or can be sprayed under pressure by means of a row of jets on to the upper surface ofthe barrel casing. The downwardly directed air stream through the barrel casing and the charge thus picks up the inflowing rinsing water and washes outthe barrel perforations rapidly and extremely intensively, as well as rinsing the charge. Any residual solution is mixed with the clean constantly inflowing rinsing water, and through this is constantly diluted.

To perfect the described process, the barrel and its charge may finally be dipped in a rinsing bath, fed with fully de-salted water. Then, if there were still present isolated areas of residual solution in any part of the barrel or its charge which had not completely satisfied the rinsing criterion, then these now will reach the necessary dilution degree with absolute certainty. The minimum requirement of rinsing water and almost complete elimination of waste water treatment, maintains exceptionally low costs.

Example 2 This Example is a combination process of this invention: firstly recovery of the bath solution at the original concentration, and then multi-step rinsing.

As in Example 1, the barrel loaded with a charge of bulk items was brought into a prismatic chamber, andthe air stream was directed through the barrel and charge. Exposure to the air-stream reduced the extracted residual treatment solution by about 50%, to about 0.75 litre. This first part ofthe process according to the invention can be called Stage 1. In this way for example, up to 50% ofthe extracted electrolyte can be recovered at the original concentration, to be fed back directly to the treatment bath for re-use.

In Stage 2 (pre-rinsing), the barrel and its charge were rinsed with 4.7 litres of water obtained from Stage 3 (after-rinsing). In Stage 2 a concentrate (a mixture of the remaining 50% oftreatment solution and ofthe rinsing water) of 42.2% was obtained, and in the Stage 3 (after-rinsing) 4.7 litres of rinsing water were used, after which the concentration thereof was 5.8%.

In Stage4 (clear-rinsing), the desired degree of dilution ofthe original residual solution was obtained. 9 litres of fully de-salted rinsing water were supplied, and the concentration of the finally remaining solution on the items fell to 0.44%: a rinsing criterion Of cO = 228.

At, ortowards, the end of each Stage 1,2 and 3, the quantity of solution carried by the barrel and its charge was reduced to about 50%, by means of the airstream.

In the particular cases of Examples 1 and 2, the residual liquid carried was reduced to about 50%. The process can however be operated to remove a far greater quantity of liquid, to give greater recovery of extracted treatment solution at its original concentration.

By adding together the effects of direct recovery ofthe extracted treatment solution at its original concentration and the recovery of concentrate by single or multiple-step rinsing using an air/water mixture, then in all more than 90% of the extracted solution can be recovered for re-use.

Afterthe residual solution has been dilutedtothe required degree, the air stream alone maybe usedtodry the bulk items and barrel to the required extent.

In the case of drying, it is useful when the barrel is brought into the chamberto allow it initially to be stationary, forthis may favourably influence the removal of residual liquid. While the barrel is stationary, the pre-warmed air stream flows through the charge at full intensity, and the natural direction offall ofthe drops under gravity as well as the direction of the airstream cause an accelerated removal of the residual solution.

Then, the barrel can be rotated and the drying process continued. In certain cases it may be advantageous intermittently to rotate the barrel as drying progresses, for this may shorten the drying time.

If rinsing is the prime purpose ofthe process, then a closed air circuit using a single blower may be sufficient.

If, however, drying ofthe charge in the barrel is to be achieved by means of the circulating air stream,then higher efficiency can be obtained with an open circuit, where a fraction (about a fifth) ofthe circulating air quantity is given up to the environment, on the pressurised side ofthe circulating air path. This vented air may have a relative humidity of up to about 95%, and is immediately replaced bya similarvolume of airdrawnfrom the ambient into the sub-atmospheric pressure side ofthe air circulation path. The replacement airtypically will have a far lower relative humidity (about40%), so increasing the effectiveness ofthe drying process.

In an electroplating installation, there is normally a rinsing bath arranged before a treatment bath. The level in the treatment bath must be maintained, and the recovery of treatment solution assists in this, as the recovered liquid can be returned directly into the bath, atthe original concentration. However, in orderto ensure a constant level in the treatment bath (particularly where the evaporation losses are small), the quantity of residual rinsing water carried by the barrel and charge from the immediately preceding rinsing bath hasto be reduced proportionately to the quantity of directly recovered treatment solution. The removal of such excess rinsing water can likewise be performed in the same manner as the solution recovery. Where evaporation is high (above 50"C), the removal of rinsing water may not be desirable.

In view ofthe rapid removal of residual treatment solutions, their fast dilution by means of the rinsing water/airmixture and short drying times, it is possible to use the process of this invention advantageously in an installation with an automatic transport mechanism, where individual barrels are moved automatically according to a predetermined program. The surprisingly short cycle times of the process of this invention permit its use in various chemical and electro-chemical treatment baths of an installation, without limiting the transport capacity thereof.

Claims (17)

1. Apparatus for removing residual liquid remaining within and on a perforated electro-chemical plating barrel and on its charge of bulk items following removal of the barrel from a liquid bath, which apparatus comprises an open-topped chamber of rectangular shape in plan and into which the barrel may closeiy but rotatably be placed with its axis generally horizontal, an air blowing duct opening into the chamber at a lower part thereof for substantially the whole length ofthe chamber, an air suction duct also opening into the chamberforsubstantiallythe whole length thereof at a position generally below the barrel when placed in the chamber, and means to causethe generation of a stream of air entering the chamberthrough the air blowing duct and leaving the chamberthrough the air suction duct, whereby the air stream will pass from the air blowing duct th rough the perforations of a barrel placed in the chamber, through a charge of bulk items in the barrel and then out ofthe barrel through the perforations thereof to leave the chamberthrough the airsuction duct.

2. Apparatus according to claim 1,whereintheair-blowing duct and the air suction duct lie immediately adjacent one another and the openings thereof extend predominantly around the lower half ofthe peripheral surface of a barrel placed in the chamber.

3. Apparatus according to claim 1 or claim 2, wherein the opening ofthe air-suction duct lies predominantly adjacentthat region of the perforated surface of a barrel placed in the chamberwhich will be covered bythe charge of bulk items contained within the barrel, as the barrel rotates.

4. Apparatus according to any of claims 1 to 3, wherein the opening ofthe air-suction duct is adjacentthe lower part ofthe barrel, to both sides of a perpendicular line through the axis of rotation of the barrel.

5. Apparatus according to any of claims 1 to 4, wherein means are provided to spray rinsing water into a barrel placed in the chamber, preferably overthefull length ofthe barrel.

6. Apparatus according to any of claims 1 to 5, wherein a dip-rinsing bath is provided, preferably arranged to be fed with running water, which bath is disposed to receive a barrel after leaving the air chamber.

7. Apparatus according to any of claims 1 to 6, wherein there is a blower arranged to cause the air stream to flowthrough the chamber, and a heat unitfor circulating air, and optionally a drop separatorforthe airflow.

8. Apparatus according to any of claims 1 to 7, wherein flexible flaps are secured to the long edges ofthe openings ofthe air blowing duct and air suction duct, which flaps may effect an air seal againstthe casing of a barrel placed in the chamber. a barrel placed in the chamber.

9. Apparatus according to any of claims 1 to 8 and substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 orin Figure 4 ofthe accompanying drawings.

10. A process for removing residual liquid remaining within and on an electro-plating barrel and on its charge following removal ofthe barrel from a liquid bath, wherein the barrel is placed in apparatus according to any ofthe preceding claims such that the perforated casing of the barrel lies adjacent the openings of the air blowing and suction ducts, an airstream is caused to flowfrom the air blowing ductthroughtheperforated casing ofthe barrel into the interiorthereof,through the charge of bulk items and outofthe barrel through the perforated casing into the air suction duct thereby to entrain residual liquid in the air stream, and the barrel is at least intermittently rotated to mixthe items of the charge.

11. A process according to claim 10, in which rinsing water is at least intermittently introduced into the barrel during performance of the residual liquid removal process, thereby to dilute the concentration ofthat residual liquid.

12. A process according to claim 10, in which the concentration ofthe residual liquid is reduced down to a given concentration level with the barrel in the chamber whereafter the barrel is removed from the chamber and is dipped in a dip-rinsing bath.

13. A process according to claim 11 or claim 12, in which residual liquid removal is performed alternately with rinsing either by spraying or by dipping, the liquid removal and rinsing being alternately performed until the degree of dilution ofthe original residual liquid reaches a predetermined value.

14. A process according to claim 13, in which the barrel and its charge are rinsed by dipping in baths, each subsequent rinse being performed in a bath having a lower concentration of residual liquid than the preceding rinsing bath.

15. A process according to any of claims 11 to 14, wherein residual rinsing water carried by the barrel and its charge following the final rinsing thereof are removed using the apparatus accordingto any of claims 1 to9, prior to the barrel being dipped in a subsequent treatment bath.

16. A process according to any of claims lotto 15, in which the air stream is caused to flow until substantially all ofthe surfaces ofthe bulk items of the change are substantiallywhollydry.

17. A process according to any of claims lotto 16 and substantially as hereinbefore described with reference to the accompanying drawings.