US3768173A

US3768173A - Apparatus for drying workpieces in bulk

Info

Publication number: US3768173A
Application number: US00272646A
Authority: US
Inventors: R Jessup; A Sulfaro
Original assignee: Oxy Metal Finishing Corp
Current assignee: OMI International Corp
Priority date: 1972-07-17
Filing date: 1972-07-17
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30
Also published as: AR197908A1; JPS5529355B2; DE2329265B2; DE2329265A1; GB1400312A; JPS4944353A

Abstract

An apparatus for drying workpieces in bulk while disposed within an elongated foraminous treating barrel formed with an opening extending longitudinally of the ends thereof. The apparatus includes a framework which defines an upwardly open threedimensional chamber into which the treating barrel is adapted to be lowered and in which it is oscillated such that the opening therein is alternatively aligned with a pair of discharge ports located in opposed sides of the chamber through which heated air is discharged against the periphery of the barrel and through the opening against the workpieces therein. An exhaust port is provided in the lower region of the chamber for continuously withdrawing moisture-laden air from the chamber and from the interior of the barrel which is recirculated in admixture with make-up air by means of a blower through a heat exchanger and thereafter is discharged through the discharge ports in the chamber.

Description

United States Patent [191 .lessup et a1.

[ APPARATUS FOR DRYING WORKPIECES 1N BULK inventors: Richard J. Jessup, Bloomfield Hills; Andrew N. Sulfaro, Sterling Heights, both of Mich.

[73] Assignee: Oxy Metal Finishing Corporation,

Warren, Mich.

[22] Filed: July 17, 1972 [21] Appl. No.: 272,646

52 us. C1 214/131, 34/133, 34/13'9,

' 34/135 51 lnt.Cl. F26b25/06 531 FieldofSearch ..34/131,102,-10s,

[56] References Cited UNITED STATES PATENTS 3,718,485 2/1973 Lankford 34/109 2,503,448 4/1950 Morris 34/139 3,190,011 6/1965 Shields 34/133 2,522,448 9/1950 Husk et al.... 34/131 3,061,942 Scofield 34/133 Primary ExaminerJohn J. Camby Assistant Examiner1-1enry C. Yuen Attorney].' King Harness et al.

[57] ABSTRACT An apparatus for drying workpieces in bulk while disposed within an elongated foraminous treating barrel formed with an opening extending longitudinally of the ends thereof. The apparatus includes a framework which defines an upwardly open three-dimensional chamber into which the treating barrel is adapted to ,be lowered and in which it is oscillated such that the opening therein is alternatively aligned with a pairof 10 Claims, 6 Drawing Figures APPARATUS FOR DRYING WORKPIECES IN BULK BACKGROUND OF THE INVENTION The present invention broadly relates to apparatus for plating or chemically treating workpieces in bulk. workpieces of the type adaptable to bulk treatment are generally too small to be individually handled or placed on racks and are, therefore, most conveniently handled by placing them in foraminous treating barrels in which the workpieces are tumbled in response to a rotation or oscillation of the barrelwhile immersed in the various chemical treating solutions.

The treating barrels comprise a pair of end panels or members and a foraminous or perforate body panel extending between the end members and defining in combination an internal, substantially cylindrically shaped zone in which the workpieces are disposed. The perforate body panel may comprise a series of flat panels whereby the treating zone is of a polygonal cross'sectional configuration, such as hexagonal, for exainple, or alternatively, may be of a circular cross sectional configuration including one or a plurality of tumbling ribs therealong to impart a cascading action to the workpieces in response to a rotation or oscillation of the barre.

In the treatment of extremely small workpieces, such as washers, screws, bolts, springs, metallic stampings, electrical contacts and the like, it is necessary during the processing of workpieces, and more usually at the conclusion of a treating cycle, to effect a substantially complete drying of the workpieces to remove the residual treating solution on the surfaces thereof. The en trapment of treating solutions within the mass of workpieces and the capillary attraction of such solutions within the workpieces themselves,.as well as in the apertures of the perforate body panels of the treating barrel, has provided a continuing problem .in effecting a rapid and thorough drying of such bulk quantities of workpieces. In many instances, the workpieces at the conclusion of one processing cycle are dumped from the treating barrel into a separate drying apparatus,

whereafter they are reloaded in the treating barrel for furtherprocessing. Alternatively, theparts are retained in the original treating barrel and are subjected to arelatively time-consuming tumbling action in the presence of heated air in an attempt to effect an evaporation and substantially complete drying of the workpieces. In some instances, the excessive tumbling to which the workpieces are subjected during the drying cycle has been detrimental to the surface treatments previously applied, requiring further precautionary measures to assure satisfactory product quality.

The problems and disadvantages of prior art drying apparatuses are overcome in accordance with the bulk dryer comprising the present invention, whereby the workpieces can be conveniently retained in the orginal treating barrel and are substantially completely dried within relatively shortperiods of time while being subjected to only a minimal oscillation or tumbling during the drying cycle.

SUMMARY OF THE INVENTION can also be satisfactorily utilized in effecting a treatment of such workpieces in bulk employing a variety of gases and/or vapors as may be desired. The apparatus is eminently adapted for use in completely automatic processing systems in which work carriers, each including an elongated foraminous treating barrel, are automatically transported and successively lowered into position within an upwardly opening three-dimensional chamber defined by the framework of the dryer apparatus. The side walls of the chamber are formed with a pair of opposed discharge ports extending longitudinally thereof in addition to an outlet port formed in the lower portion of the chamber. Appropriate support means are provided on the framework for supporting the barrel in alignment relative to the chamber such that an elongated opening in the barrel can be alternatively disposed in communicative alignment with one of the discharge ports for receiving a gas discharged therefrom which impinges against the workpieces contained within the interior of the barrel. The gas discharged from the other discharge port impinges against the periphery of the barrel and serves to dislodge any entrapped treating liquids within the perforations or other openings of the body panels.

In a normal drying operation in which the gas is air, a circulation of the heated air through the interior of the barrel is facilitated by the continuous withdrawal of air from the chamber through the outlet port which is connected to an exhaust port disposed in communication with the suction side of a blower. A plenum is connected to the pressure side of the blower, which in turn is connected inseries with supply ducts connected to the discharge ports, whereby a continuous recirculation of a portion of the air is effected in admixture with an appropriate quantity of make-up air to maintain the moisture level thereof below the saturation point.

Further advantages and benefits of the present invention will become apparent upon a reading of the description of the preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic plan view of atypical processing arrangement including the treating apparatus comprising the present invention located at one work station'th'ereof;

FIG. 2 is a perspective view, with portions thereof broken away for clarity, of a typical work carrier incorporating an elongated foraminous treating barrel rotatably supported thereon;

FIG. 3 isa plan view of the dryer apparatus constructed in accordance with the preferred embodi- DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the drawings, and as may be best seen in FIG. ll, an arrangement is illustrated typical of those to which the apparatus comprising the present invention is applicable in which bulk quantities of small workpieces, such as nails, screws, bolts, washers, small metal stampings or the like, are adapted to be transported within a foraminous or porous treating barrel through a plurality of liquid treating stations to effect a cleaning and electroplating of the surfaces thereof. In accordance with the illustrated arrangement, work carriers, such as a work carrier 14 as shown in FIG. 2, are loaded and unloaded with workpieces at the input station indicated at 1, whereafter the loaded work carriers are automatically transferred through a sequentially phased process cycle typically comprising the following steps: a soak-cleaning operation at station 2; an electro-cleaning operation at station 3; a cold water rinsing step at station 4; an acid treatment at station 5; a cold water rinse at station 6; a second cold water rinse at station 7; an electroplating operation at a multiple-station treating tank indicated at 8; a cold water rinse at station 9; a second cold water rinse of shorter duration at station 10; a chromate treatment at station 11; a hot or cold water rinse at station 12; and, finally, a drying operation employing the apparatus of the present invention at station 13. Thereafter, the work carriers are again transferred to the load and unload station 1, at which the processed workpieces are removed and a fresh quantity of workpieces are loaded into the treating barrels for a repetition of the foregoing cycle. It will be understood that the dryer apparatus at station 13 can be duplicated at one or more additional stations in order to provide the requisite drying capacity and duration consistent with the timed sequence of work carrier travel in the remaining portions of the process.

Referring now to FIG. 2, the work carrier 14 comprises a generally U-shaped frame including a pair of upright side members or legs 16, connected at their upper ends to a substantially horizontal cross member 18. An elongated treating barrel comprised ofa pair of end members 22 and a foraminous or perforate body member or panel 24 extends between and is rotatably supported at the center of its end members 22 by suitable shafts affixed to the lower ends of the legs 16. The body panel 24 of the treating barrel, as best seen in FIGS. 2, 5 and 6, is formed with an elongated slot-like opening 26 extending longitudinally thereof and substantially parallel to the axis of rotation or oscillation of the barrel providing access to the interior of the barrel. The body panel and two end members define a substantially cylindrical treating zone in which bulk quantities of workpieces are adapted to be disposed during a treating operation.

As best seen in FIGS. 2, 5 and 6, the body panel 24 i is formed with an inwardly converging section disposed diametrically opposite to the opening 26 defining therewith a tumbling rib 28 which imparts a tumbling or cascading action to a mass of workpieces, indicated at 30 in FIG. 6, in response to an oscillation of the treating barrel. The tumbling rib 28 may vary in configuration so long as a satisfactory tumbling action is imparted to the workpieces which is sufficient to release any entrapped liquid therein and to expose fresh surface areas for contact with the gas or air being discharged into the interior of the barrel. In accordance with a preferred construction of the treating barrel, the slot-like opening 26 extends for the entire length of the body panel from one end member to the other end member and is of a circumferential width less than about l/6 of the circumference of the barrel and for best results, from about 1/10 to about 1/20 of the circumferential length of the barrel. The tumbling rib 28 is preferably disposed diametrically opposite to the opening and is of a generally triangular-shaped cross section as defined by two flat faces which project into the interior treatingzone at an angularity ranging from about 10 to about with respect to a tangent to the body member at the point of intersection of the tumbling rib therewith. The entire area of the body panel 24 is of a foraminous structure as provided by a plurality of perforations generally indicated at 31 in FIG. 2.

The barrel itself is comprised of a suitable high strength material which is resistant to and compatible with the acidic and alkaline treating solutions into which the barrel is adapted to be immersed during the course of its transfer through the various treating solutions. The material also is preferably of an electrically nonconductive type to enable use of the barrel in electroplating and other electrochemical treating processes and in which event a pair of dangler electrodes 32, as bestshown in FIG. 2, are employed which extend inwardly through the tubular shaft and through the centers of the end members 22 and are adapted to be disposed in electrical contact with the workpieces therein. A suitable cable (not shown) is connected to each of the dangler contacts and is adapted to be electrically connected to a bus bar at such stations at which an electroplating or electrochemical treatment is to be performed on the workpieces. Particularly satisfactory results are obtained with treating barrels comprised of plastic materials such as nylon, polymethylmethacrylate, polyethylene, polypropylene and phenol formaldehyde resins.

A controlled oscillation of the treating barrel about a central longitudinally extending axis from a first position, such as shown in solid lines in FIG. 5, to a second position as schematically illustrated in FIG. 6, is conveniently achieved by a gear train comprised of a driven gear 34 affixed to a shaft 36 rotatably supported in a guide block 38 affixed to and projecting laterally and outwardly of a leg 16 of the work carrier as best seen in FIG. 2. A driven gear 40 is affixed to the inner end of the shaft 36 and is disposed in constant meshing relationship with an idler gear 42, which in turn is disposed in constant meshing relationship with a ring gear 44 secured to or integrally formed on one of the end members 22. The driven gear 34 is adapted to be disposed in meshing relationship with a suitable drive gear when the work carrier is located at a work station in a manner and for the purposes subsequently to be described.

The drying apparatus such as located at station 13 of FIG. 1 is comprised, as best seen in FIGS. 3-5, of a pair of base beams 46 defining a platform on which the framework of the apparatus is affixed. A return duct 48 of a generally rectangular-shape cross section is affixed to the upper edges and extends longitudinally of the base beams 46. The left-hand end of the return duct 48, as best seen in FIG. 4, is connected to an angularly shaped transition section 50 which is of a progressively increasing cross sectional area on moving toward the left and is disposed with its output end connected to the lower side of a plenum chamber 52. Entry into the plenum chamber 52 from the transition section 50 is achieved through a venturi-shaped duct section 54 which is of a circular cross sectional configuration having its outlet end disposed in communication with the inlet side of a squirrel-cage type centrifugal blower 56 affixed to the end of a drive shaft 58. .The drive shaft 58, as best seen in FIGS. 3 and 4, is rotatably supported in a housing 60 and a drive pulley 62 is affixed to the projecting outer end thereof. A motor 64 is mounted on a pad 66 and is provided with a pulley 68 on the output shaft thereof, around which a drive belt 78 is trained which drivingly engages the pulley 62 for effecting a rotation of the centrifugal blower. Accordingly, the transition section 50 and the venturi-shaped duct section 54 are placed under a reduced pressure whereby air or gas flows toward the left inthe direction of the arrows as shown in FIG. 4 and into the centrifu gal blower 56, whereafter the gas or air is discharged upwardly and out of the upper section of the plenum chamber 52 into a heat exchanger 72 affixed to the dis charge side thereof.

The heat exchanger 72, as best seen in FIG. 4, comprises a plurality of heat transfer tubes 74 which are connected to a header conduit 76 at one side and a return conduit 78 (FIG. 3) on the opposite side, through which a continuous supply of a heat transfer fluid, such as steam, is circulated, effecting therewith a controlled heating of the air or gas passing therethrough. In the use of the apparatus as a dryer, the quantity and temperature of the heat transfer fluid passing through the heat transfer tubes is controlled so that the air discharged from the heat exchanger is of a preselected temperature andhumidity level to provide optimum efficiency and economy in the drying cycle. The control of the temperature of the air can readily be achieved by using, a temperature probe 80, as shown in FIG. 4, which is mounted at the discharge side of the heat exchanger and is connected through suitable circuitry to the central control panel 82 of the apparatus. The central control circuit is in turn effective through the use of a flow control valve of the types well known in the art to regulate the quantity of heat transfer fluid passing through the heat exchanger and a corresponding control of the temperature of the air discharged therefrom.

The gas or air discharged from the outlet side of the heat exchanger 72 enters a pair of longitudinally extending supply ducts 84 which. extend in spaced substantially Parallel relationship above the returnduct 48. The inlet ends of the supply ducts 84 are connected by a V-shaped baffle member 86 which effects a division of the discharged heated gas into two separate and substantially equal streams in accordance with the arrows as shown in FIG. 3. v

The return duct 48 and supplyducts 84 are disposed in communication with the dimensional upwardly opening rectangular chamber 88, into which the work carriers are adapted to be lowered for the performance of a treating operation on the workpieces carried thereby. The chamber 88 is 'comprised of a pair of side panels 90a, 98b; a pair of end panels 92a, 92b and a bottom panel 94, which are securely fastened to each other and to the base beams and return ducts 48 therebelow. Side panel 900 is formed with a longitudinally extending discharge port 96a disposed in communication with one of the supply ducts 84, as shown in FIG. 5, while side panel 90b is similarly provided with a longitudinally extending discharge port 96b disposed in communication with the other supply duct 84. The edges of the discharge ports 96a, 96b are lined with angle iron brackets 98, as best interior of a three seen in FIGS. 3 and 5, to the projecting leg portions of which resilient sealing strips 108 are affixed. The angle iron brackets 98 and sealing strips 108 along each discharge port define in combination a flexible discharge nozzle, the end of which is adapted to resiliently engage the periphery of the treating barrel 20, as shown in FIG. 5, directing the air or gas discharged therethrough in the form of a concentrated high velocity stream in impinging relationship against the periphery of the barrel and through the perforations therein, as well as through the slot-like opening 26 and in impinging relationship against the workpieces contained within theinterior of the barrel. The pressurized air discharged from the discharge ports also serves to dislodge or blow out any liquid treating solution entrapped within the perforations of the body panel of the treating barrel accelerating the draining of the treating solution and the evaporation thereof from the surfaces of the workpieces. In accordance with this arrangement, the discharge ports and the sealing strips disposed therealong are of a length corresponding substantially to the distance between the inner surfaces of the end panels of the treating barrel and the length of the elongated slot-like opening 26 therein.

A continuous withdrawal of the gas or air discharged into the interior of the treating barrel is achieved through an outlet port 102 formed in the bottom panel 94 of the treating chamber, as may be best seen in FIGS. 3 and 5, which extends centrally and longitudinally thereof and is disposed in communication with the return duct 48. The edges of the outlet port 102 are similarly lined with angle iron brackets 104, to the inward projecting leg portions of which sealing strips 106 are affixed and project such that the edges thereof are disposed in close proximity to or in resilient engaging contact against the periphery of the treating barrel.

The negative pressure present in the return duct coupled with the positive pressure present in the interior of the treating barrel provides for a pressure gradient in ducing a continuous withdrawal of gas or air from the interior of the barrel through the perforations disposed within the area .of the outlet port 102. Additional air also enters the outlet port which enters the barrel through the perforations in the body panel disposed upwardly between the vupper sealing strips as well as any leakage between the barrel periphery and the ends of the barrel and the projecting ends of the resilient sealing strips 100 and 106. Thewithdrawn air upon entering the return duct flows toward the left in the direction of the arrows, as indicated in FIG. 4, and is again drawn into the plenum by the centrifugal blower 56.

Since during a. drying operation,.a continuous build up in the moisture content of the recirculated air occurs, a suitable amount of make-up air is introduced into the recirculating duct system by means of a makeup port 188, as shown in FIG. 4, formed on the upper side of the transition section 58 over which an adjustably mounted closure member 110 is positioned. By adjusting the position of the closure member relative to the make-up port 108, a controlled amount of outside air can be drawn into the recirculatory duct system, whereby the humidity level of the recirculated air stream is maintained below the saturation point while at the same time conserving the heat in the system.

In order to assure appropriate vertical and longitudinal alignment of the treating barrel relative to the discharge ports and outlet port, suitable supporting means are provided along the upper edges of the treating chamber for removably engaging and retaining the work carrier in appropriate aligned and supported relationship. As will be noted in FIGS. 3 and 4, an angle iron reinforcing member 1 12 is affixed to the outer face of the panel 92b adjacent to the upper edge thereof, on which a U-shaped saddle 114 is securely fastened and which in turn is adapted to slidably and removably engage a lug 116 affixed to and projecting laterally of one leg 16 of a work carrier as is best seen in FIGS. 2 and 4.

In a similar manner, a saddle 118 is affixed to a support member 120 mounted on the outer surface of the other end panel 92a, which similarly is adapted to removably and slidably engage the guide block 38 projecting outwardly of the other leg 16 of the work carrier framework as shown in FIG. 2. The saddles 114 and 118 are preferably of a divergent configuration at the upper ends thereof so as to faciitate alignment of the guide block 38 and lug 116 during the descending movement of the work carrier.

As will be further noted in FIGS. 3 and 4, a suitable drive mechanism is also provided at the saddle 118 comprising a drive gear 122 connected to the output shaft of a speed reducer 124, which is drivingly connected to a reversible fluid or electrical motor 126. The drive gear 122 is adapted to be disposed in driving meshing relationship with the driven gear 34 on the work carrier in accordance with the drive train previously described in connection with FIG. 2.

The energization of the motor 126 and the corresponding oscillation of the treating barrel is controlled by the central control circuit of the apparatus contained within the control panel 82 affixed to the upper outer face of the plenum chamber 52. The control circuit incorporates a dwell timer in accordance with known practice for effecting periodic energization of the motor 126, whereby the treating barrel is oscillated from a first position, as shown in solid lines in FIG. 5, in which the elongated opening 26 is disposed in communicative alignment with the discharge port 96b to a secondposition, as shown in FIG. .6, in which the slotlike opening in the barrel is disposed in communicative alignment with the discharge port 96a. The angular movement of the treating barrel is halted when it attains the appropriate aligned position either by the incorporation of mechanical stops in the drive mechanism, by appropriate sensing devices such as limit switches for sensing the barrel position or, alternatively, by positive mechanical stops 1280, 12812, as schematically shown in FIG. 6, which are affixed to the exterior face of one of the end panels and are adapted to become mechanically engaged with an abutment 130 movably mounted on the leg 16 of a work carrier.

In operation, a work carrier having a treating barrel filled with workpieces is lowered automatically into the chamber 88 such that the guide block 38 and lug 116 on the carrier frame are disposed in supported relationship within the saddles 118 and 114, respectively. Air is continuously circulated through the duct system of the dryer apparatus by the centrifugal blower 56 while an appropriate quantity of make-up air enters the sytem through the make-up port 1108. Upon attaining the fully lowered position, the motor 126 is energized through the central control circuit, whereby the treating barrel is oscillated from a normal position in which the opening is located in an upright position to either one of the positions typified by FIGS. 5 and 6. Upon attaining that position, a suitable dwell timer is energized in the central control circuit, whereby the treating barrel is retained in that position for a preselected time period to permit a concentrated discharge of heated air through the slot-like opening in the barrel against the workpieces therein.

At the expiration of the dwell period, the motor 126 is again energized whereby the treating barrel is oscillated to the opposite position in which the opening is disposed in alignment with the other discharge port. During the oscillatory movement of the barrel from one position to the other position, a cascading of the workpieces over the tumbling rib of the barrel is effected, whereby any entrapped water or solution is dislodged and wherein when the barrel comes to rest, fresh surfaces of workpieces are exposed to the heated air discharged thereagainst. At the same time rotation of the barrel effects a traverse of the periphery thereof with the concentrated jets of air being discharged from the two discharge ducts, effecting a dislodgement of any entrapped water within the perforations of the body panel. The foregoing cycle is repeated for a preselected number of cycles, each including a dwell period of the treating barrel at the extreme aligned positions. The specific number of cycles and the dwell period at each position will vary depending upon the size, configura tion and quantity of workpieces in the treating barrel, as well as the type, quantity and volatility characteristics of the liquid treating solution and the temperature and humidity level of the drying air or gas circulated therethrough. Normally a drying period of less than about four minutes involving a dwell period at the aligned positions of about ten seconds has been found satisfactory for providing a substantially complete drying of most workpieces incorporating aqueous treating solutions thereon using saturated steam of a 6 to 12 psig as the heat exchange fluid.

While it will be apparent that the invention herein disclosed is well calculated to achieve the benefits and advantages hereinabove set forth, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.

What is claimed is:

1. An apparatus for treating workpieces in bulk while disposed in an elongated foraminous treating barrel formed with an opening extending longitudinally of the ends thereof comprising a framework defining an upwardly opening three-dimensional chamber for receiving a treating barrel adapted to be lowered therein, supporting means for removably supporting a treating barrel in aligned position within said chamber, said chamber formed with a first discharge port and a second discharge port extending longitudinally along the sides thereof and an outlet port in the lower portion thereof, drive means for oscillating a treating barrel through an angularity whereby the opening therein oscillates to and from a first position in communicative alignment with said first port and a second position in alignment with said second port, duct means including a supply duct for supplying a gas to said first and said second port for discharge against and into the barrel and the workpieces therein and an exhaust duct connected to said outlet port for withdrawing gas from said chamber, and control means for controlling the oscillatory movement of the barrel.

2. The apparatus as defined in claim 1, wherein said duct means includes a plenum connected in series with said exhaust duct and said supply duct for recirculating at least a portion of the gas discharged into said chamber through said first and said second discharge port.

3. The apparatus as defined in claim 1, wherein said duct means further includes a heat exchanger for controlling the temperature of the gas discharged into said chamber.

4. The apparatus as defined in claim 1, in which the gas comprises air and further including a plenum connected in series with said exhaust duct and said supply duct, blower means for recirculating the air withdrawn from said chamber to said supply duct, and a third port formed in said duct means at the suction side of said blower means for introducing make-up air into said duct means in admixture with the air recirculated therethrough.

5. The apparatus as defined in claim 1, further including yieldable sealing means along the edges of said first port and said second port and projecting into said chamber for engaging the periphery of a treating barrel and directing the gas thereagainst and into the opening thereof.

6. The apparatus as defined in claim 1, further including yieldable sealing means along the edges of said outlet port and projecting into said chamber for engaging the periphery of a foraminous treating barrel and enhancing the withdrawal of gas from the interior thereof.

7. The apparatus as defined in claim 1, wherein said control means includes timing means for maintaining a treating. barrel stationary for a preselected time period while disposed in said first position and in said second position.

8. The apparatus as defined in claim 4, further including closure means movably disposed relative to said third port and adjustably positionable to control the amount of make-up air entering therethrough.

9. The apparatus as defined in claim 4, further including a heat exchanger in said duct means for heating the air to an elevated temperature in order to perform a drying operation on the workpieces in the treating barrel.

10. The apparatus as defined in claim 9, further including closure means movably disposed relative to said third port and adjustably positionable to control the quantity of make-up air entering said duct means to maintain the recirculated heated air at a humidity level below the saturation point.

Claims

7. The apparatus as defined in claim 1, wherein said control means includes timing means for maintaining a treating barrel stationary for a preselected time period while disposed in said first position and in said second position.