US2836400A - Plating barrel - Google Patents

Description

May 27, .1958 w. H. .JAcKsoN PLATING BARREL 3 Sheets-Sheet 1 Filed June 4. 1954 May 27, 1958 w. H. JACKSON 2,836,400

PLATING BARREL Filed June 4. 1954 3 Sheets-Sheet 2 IN VEN TOR. /z .jcsaiz May 27, 1958 w. H. JAcKsoN 2,836,400

PLATIN@ BARREL Filed June 4. 1954 5 Sheets-Sheet 3 INVENToR. M//zdm /ZkfC-sarz United States raient" PLATING BARREL William H. Jackson, Birmingham, Mich., assigner to The Udylite Corporation, Detroit, Mich., a corporation of Delaware Application June 4, 1954, Serial No. 434,555

8 Claims. (Cl. 259-89) The present invention relates broadly to electroplating apparatus and more particularly to improvements in barrel plating cylinders of the type employed in electroplating barrel units.

Barrel plating cylinders are used extensively in industry for simultaneously electroplating large numbers of small articles which, because of their size, are not conveniently or economically adaptable to individual handling. In electroplating of this type, the articles are placed within a perforated cylinder and the entire unit is carried through the plating process which includes rotating and immersing the cylinder in dii'rerent types of acidic or alkaline solutions. Aside from being subjected to severe chemical punishment during immersion, the cylinders are further subjected to heavy physical punishment, due to the continuous impingement of the articles against the cylinder or against the liner or membrane when used. Because of this, it is highly essential that the cylinders and its liners or membranes possess characteristics of high strength and resistance to abrasion, buckling and deterioration. The attainment of such characteristics is relatively ditiicult because of the necessity for using electrically non-conducting materials. Y

ln the past various structural arrangements have been employed in an effort to provide the above stated characteristics. One commercial arrangement utilizes a cylinder made from an acrylic resin material designated Lucite Some difficulty has been encountered because the acrylic cylinders are limited to relatively low temperature operation. Another commercial barrel employs a liner constructed from a phenol-formaldehyde condensation product such as Bakelite The phenolformaldehyde resin liners are not completely satisfactory inasmuch as they require several laminations for strength and tend to delaminate in certain types of solutions.

in accordance with the teachings of the present invention an improved cylinder is provided for a barrel plating unit which overcomes the difticulties heretofore encountered. The cylinder is constructed with a novel rigid frame assembly having a plurality of removable corner frame members and interconnecting cylinder side wall panels, which together form a structural unit of high strength that is fully capable of withstanding the severe chemical and physical punishment to which it is subjected. The frame members are arranged to overlap the corners of the unit and to interlock with the side walll panels and hold the panels rigidly in position at all times, yet individual wall panels may be readily removed for maintenance. Moreover, the frame permits the use of unitary or segmented liners which are formed of materials having characteristics of high strength and resistance to abrasion, heat, and the corrosive effects of acids or alkalies.

Accordingly one object of the present invention is the provision of an improved cylinder for a barrel plating unit constructed in a manner to withstand severe chemical and physical punishment.

Another object of the invention is the provision of ice er L. an improved plating barrel cylinder having a frame assembly employing a plurality of removable frame members for supporting the liner.

A further object of the invention is to provide a cylinder having means for rigidly but removably supporting the liner whereby the liner may be quickly and easily replaced for maintenance.

Still another object of the present invention is the provision of a plating cylinder of high strength having separate replaceable side wall panels which are interlocked with each other.

A still further object of the present invention is the provision of an improved plating barrel cylinder employing membranes or liners having advantageously high resistance to heat, abrasion, and corrosion.

Another object of the present invention is the provision or a plating barrel cylinder which is economical to manufacture, eicient in operation and requires little maintenance.

ln the drawings:

Figure 1 is a front elevational view of a plating barrel cylinder constructed in accordance with the teachings of the present invention;

Fig. 2 is a cross-sectional view taken substantially on the line 2 2 of Fig. l;

Fig. 3 is a fragmentary, sectional, side View, showing a modification of the interlocking arrangement of Fig. 2;

Fig. 4 is a front elevational View showingV another modification of the plating barrel cylinder embodying features of the present invention.

Fig. 5 is a cross-sectional view taken substantially on the line 5-5 of Fig. 4; and

Fig. 6 is a side elevational view, in section, showing a further modification of the instant invention.

Fig. 7 is a sectional view of a panel showing the perforations.

Referring more particularly to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. l a plating barrel cylinder 10 which is adapted to receive therein a number of articles to bejelectroplated and which serves as a carrier for the articles throughout an electroplating operation. Y

The cylinder generally designated 10 preferably ,comprises a cylindrical container of polygonal cross-sectional shape having a pair of spaced, parallel end walls or heads 12 and i4 defining the end portions of the cylinder. The heads 12 and i4, which are similar in construction, are provided on their outer side with bearing bosses 16 and 1S, respectively, for receiving the lower end of a hanger (not shown) that suspends the cylinder from an overhanging rail or the like so that it may be positioned in and removed from a plating barrel tank. A pair of axially aligned bores 20 are formed in the bosses and heads to provide access for electrodes to extend into the interior of the unit. Conventionally, a driving gear (not shown) is also xedly mounted on bearing boss 1S for rotatably driving the cylinder during processing.

The end Walls 12, 14 are formed of solid corrosive resistant material and function as the foundation for the framework of the cylinder. As best shown in Fig. 2, a pair of elongated stay bolts 22 are positioned adjacent the top corners of the polygonal-shaped container and are suitably secured at their ends to the respective heads 12 and 14 for rigidly spacing the heads in position and to brace the cylinder member. Stay bolts 22 are preferably formed of high strength material such as steel or the like and are covered with a suitable protective coating 25 for protection against the corrosive eects of acidic or alkaline solutions to which it is subjected in an electroplating operation. Avwide variety of plastic coating materials now well known in the art are suitable for use as assegno' able include the vinyl resins and highly fluorinated polymerie hydrocarbons such as tetraiuoroethylene.V Vinyl resins may be applied in the formof dispersion known as pastisols, or in the form ofsheets suitably secured tothe bolts 22. If desired, Vadditional stay bolts may be provided at intermediate points aroundthe cylindentoinsure a sullicientlyY rigid and stable cylinder construction.

YAn elongated, interlocking outerframe member ,26-i,s positionedV on the outer side of the cylinder adjacent each corner thereof and preferably, is'- removably securedy at its end to the heads 12 and V14. These outer frameV members 26 are formed of a sturdy, corrosion resistant material such as a hard rubber sold commercially under the trademark Temprom and cooperate with inner Yframe members, or tumbling ribs 28, of similar material, for rigidly supporting a plurality of interlocked perforated panelsor side walls 30 therebetween, Each panel 30, which may also be formed from Tempron, is generally y rectangular in shape and is adapted to V'substantially cover cuts'such that they seat ush against each other, ywithV the outer and inner frame members 26 and 28 interlocking the panels in position. Y Y

i bers, or tumbling ribs 28 of substantially rhombic-shape Positioned on the upper portion of the cylinder 1G, vasV viewed in Fig. 2, upon the top edges of the upper ones of the panels 30 which define a supporting ledge therefor, is a door panel 31. This panel 31which serves as a door for theV cylinder,-is generally rectangular in shape and of such size as to cover one side of the polygonal-shaped cylinder. In order to lock the door panel in position, a pair of opposed retaining members 32 are provided and adapted to cooperate with a suitable latch (notV shown).

The retaining members 32, which may also be formedk of Tempron, have a lower edge portion 37 resting on the'stayY bolts 22, and yan upper edge portion 38 projecting above the edges of upper panels 30. The retaining membersy 32 are suitably secured at their ends to the heads 12 and 14, and intermediate their ends to their respective upper panels as by screws 39. The upper projecting'portion 38 is provided on its inner surface with a latch receiving groove 40. This groove serves to slidably in cross section which Vare fitted flush in the troughs formed by adjoining panels. These ribs preferably are formed of corrosive-resistant ,Tempronf The inwardly facing surfaces of these ribs 23 meet the sidewall panels 30 at obtuse angles, so that there are no internal acute angle corners which might trap Vwgorlqiieces.`

The frameV members 26 and the ribs 28 are secured together, 'for interlocking the panels together,v by a plurality of spaced, high strength bolts 43 threaded into-alignedY that the seals areV placed in compression by the bolts 43. K

ln so doing, treeing or relative twisting of the members is prevented.- Materials which are suitable for the seal include tetrauoroethylene orgvinyl sheeting or lilm available commercially Lunder-the trademark KoroseaL So that bolts 43-may be protected against corrosive solutions, the bolts are preferablyreeessed within the bores 44, and the boresabove the bolts, lilled with a protective putty 46 or other suitable material. It will he noted that with this corner support structure, the panels will be firmly retained in position to provide a rigid cylinder structure, but may be easily removed by simply removing thebolts 43. Y

EachV one of ythe panels 30.and,if desired, the door panel 31 is provided with a multitude of perforations or apertures 50to facilitate circulation of an electrolyte into and out of the cylinder 10 when it is immersed in a plating bath; Since the volume of fluid flow through theV panels has a direct effect on the eiciencyof the unit,

. it is highly'desirable that the perforatedfarea Vbe as receive a latch of any'suitable type to appropriatelyV lock i the door. VIt will be noted that the retaining members 32 serve a dual function'in `that they act with a latch as a locking means for the door panel, and as alateral y brace or support for the cylinder. Y

V'I'he panels 30 which form the body of the cylinder 10 are removably interlocked together by the inner and outer frame members 26 and 28 such that'they may be easily removed for maintenance. For this purpose and as best shown in'Y Fig. 2, the panels are provided with miter cuts such that their adjacent edges tit flush against each other to denne closed corner portions of the cylinder. Each of the panels 3i) that do not abut the door 31 is provided with a shallow longitudinal interlocking groove 40 along each of its outer edges, while the panels 3) 'immediately adjacent to the door are provided with a similarshallow groove at` their edges opposite from the door. VThe outer frame members 26 lit against the outer edges of adjoin-V ing panels and are each provided with a V-gro ove on' their inner surfaces which are formed torhave a complementary contour with the inclined panels 30. To interlock the'panels togethera pair of integral raised portions 42, constituting inwardly projecting longitudinal ribs are formed along the outer edges of each V-groove side ofV the frame members 26 to be received within therinterlocking grooves 40 of the panels. The outer'frame members 26V` areV retained in this position by inner frame meml large as possible. ln practice, however, the size of each aperture 50 is limited to a size smaller' than the size or" the articles to be electroplated, and the total perforationV area is restricted by the required strength of the material and other factors. One of the important advantageswhich inderpanels are formed of high strength materials and the panels are interlocked by grooves formed along theirk inner sides. In this embodiment, the structuralarrangement of the cylinder isressentia'lly the same as inthe first embodiment and includes aplurality of perforated, removable side wall panels 60, each 'of which is preferably constructed of Tempron and Vforms one complete side of a polygonal-shaped container. The panelsare interlocked in position by outer frame members 62 and tumbling ribs 64, Vwith the panels being linterposed between Y these members. Y.

For the purpose of interlocking the panels, as in the case of the first embodiment, each of the lower panels`60,

their upper edges are adjacent to the door panelv (not shown) and are not interlocked by corner structures. Tumbling ribs 64 which are preferably formed of Tempronf are of substantially rhombc-shape in cro-ss section and are'Y provided on their.V mating surfaces with a pair of symmetrical, raised portions 68 adapted to lit ush withinthe grooves 66, in an interlocking manner. It will be noted that the inwardly facing surfaces ofthe ribs 64V Vslope downwardly fromY an apex and meet the s' M tion,a`rticles being electr-oplated`inipingeagainst the inwardly projecting ribs and are deflected towards the interior of the cylinder, and cannot be trapped in the corners of the cylinder.

The corner supports for the cylinder comprise an outer frame member 62 having an inner support 70 of high strength material. Support 70 is formed with its inner side having an inwardly sloped V-groove 72 which defines a complementary surface with the slanting edges of kadjoining panels. The extreme ends of the supports 70 are suitably secured to oppositely disposed heads (not shown) and to the ribs 64 by steel bolts 74 spaced along the length of the support 70. These bolts 74 are received in aligned bores 76 formed in supports 70, adjoining edges of the panels 60 and ribs 64, with the head of the bolt 74 being recessed within an enlarged aperture i7 in support 7i?. Preferably, support 70 is protected against corrosive action by a coating of suitable material 7 8 such as a vinyl resin dispersion, while the bolt is protected by a protective putty inserted above the bolt in bore 77. As in the embodiment of Fig. 1, a seal 82 of Teflon or Koroseal is interposed between the panels and bolt 74 to prevent treeing It will be noted that in each of the embodiments disclosed thus far, the tumbling ribs are extended internally, throughout the length of the cylinders but preferably are not secured at their ends to the spaced heads. This con-struction allows the easy removal of the panels 30 and 60 during maintenance or the like.

Figs. 4 and 5 disclose another modification of the instant invention'uniquely adapted for plating extremely small objects wherein the pla-ting barrel cylinder is constructed with a one-piece, unitary, removable membrane or liner to form the body of the container. In this embodiment, the frame of the cylinder includes a pair of polygonal-shaped, spaced end walls or heads 102 and 104 of suitable corrosive resistant materials with each head being provided with a bearing boss 106 on its outer side for rotatably supporting the cylinder in position. Removably secured atrtheir ends to heads 102 and 104 and adjacent to the upper corners of thevpolygonal-shaped members are a pair of symmetrically spaced stay bolts 110 for rigidly tying the spaced heads together. Stay bolts 110 are suitably coated with a lm of a vinyl dispersion, plastisol, material 114 or the like and are formed from wedge-shaped metal stock having one side lying in ya horizontal plane and an adjacent side lying at an angle to the rstside in a manner such that it follows the contour of a hexagon.

Stay bolts 110, -besides serving as braces for the cylinder, further act `with a pair of door sills 116 and locking strips y120 for holdingthe ends of liner 100 in position and for supportingland locking a door panel 124 in position. inasmuch as each of the opposing door sills and locking` strips` are identical in construction and coact in identical manners with the stay bolts, only one will be described in the description below. The door sill 116 is'seated on stay bolt 110 to act as a securing member for holding the liner 100, and extends the full length of the cylinder. The inner portion of sill 116 is provided with an integral inwardly extended lip 126 having a lower arc-shaped portion 12S that follows the contour of stay bolt 110 and cooperates with stay bolt 110 for securing one end'of liner 100 therebetween as by compression. The upper portion of sill- 116 is for-med with a flat surface 4130 4which receives and seats an edge of door panel 124.

Positioned upon the outer'edge of at surface 130 is the locking strip 120. This strip which may also be formed o'r' 'l`empron, extends the full length of the cylinder and is provided with a longitudinally extending latching groove 136 that servesV to slidably receive a suitable latch (not shown) to secure panel 124 in position on sills 116. Locking strip 120, and door sill 116 are secured togetherV and to stay bolts'110 by a series'of spaced 6 bolts 132 which are threaded in aligned holes 134 formed in each of these members. Preferably, bolts 132 are recessed in strip 120 and covered with a protective coating as at 135.

It will be apparent that with this construction the ends of liner 100 are compressed between sills 116 and stay bolts 110 upon tightening of bolts 132 such that the liner is securely but removably locked in position. Moreover, the door sills and locking strips serve to support door panel 124. The door panel, as in the embodiment, of Fig. l, is of such a size as to cover one side of the polygonal-shaped member and l'its snugly between locking strips 120 and heads 102 and 104.

Spaced around the cylinder and forming the body framework therefor are a plurality of corner supports comprising elongated interlocking outer frame members 14u, each of which is securely fastened at its ends to heads 102 and 104. Each one of the outer frame members 140 comprises an elongated rod member or support 142 of high strength material having a V-groove 143 on its inner side, and longitudinally extending portions 144, and is completely encased by a suitable plastic sheath 146. Positioned internally of liner 100 and extending longitudinally therein, in juxtaposed relation to longitudinal supports 142, 144 is an inner frame member, or tumbling rib 148 of substantially rhombic-shape. The tumbling ribs 148 fabricated from Tempron or the like, are secured to the outer frame members 140 by a plurality of spaced bol-ts 150 extending through `supports 142, 144 and threaded into rib 14S. The ribs 148 and'supports 142, 144 serve to guide and support liner 100 which when passed therebetween constitutes the walls of the cylinder.

`Preferably, bolts 150 are recessed in supports 142 and covered with a protective putty-'type material to prevent t adverse corrosive action thereon.

Liner 100 which is wrapped around the cylinder framework to form the side walls of the cylinder may be satisfactorily and preferably is formed of a thin sheet of fluorinated ethylene material such as, for instance, is sold commercially under the trade names of Teon and Kel-F. These materials, while possessing excellent heat, abrasion, and corrosion resistance, are readily adapted to perforation by punching methods. By punching, the liner may be provided with much smaller perforations than have been heretofore feasible and which wouldV otherwise be exceedingly diicult and expensive to duplicate by drilling, these perforations beingV small enough to prevent the passage therethrough of extremely small articles such as needles or pins. Moreover, the linear material is exceptionally strong so that the liner may be made thinner than Y with materials previously employed. The electrical voltage drop in the electrolyte held in the perforations is decreased when the material is made thinner, thereby providing an increased efciency of the barrel plating unit.

1n the event that the cylinder need be strengthened for heavy loads, reinforcing straps 154 may be inserted at spaced locations along the length of the cylinder, positioned between individual supports 142, 144 and secured thereto. These straps may beV made from expandedV metal having a series of symmetrically arranged, diamond-shaped apertures therein as shown in Fig. 4, or other types of apertures may be provided. 1f desired, several straps spaced along their length of the cylinders may be used with the size and number being determined by the cylinder size and the load to be carried. it will be noted that the outer frame members 140 are rigidly interlocked together by a series of metal inserts 156 fitted within a rectangular groove (not shown) formed on the inner surface of head 104. The inserts 156 serve to reinforce the connections between the outer frame members 140 and the heads 102 and 104 and to enable the cylinder to stand up under relatively heavy loads.

Fig. 6 discloses a modification of the present invention which is substantially the same as thatdisclosed in Figs, l and 2 except that the inner surface of the cylinder is pro- Y unit is increased.

. Y 7 vided with an'additional unitary liner.V inasmuch as the twrorembodirnents are otherwise identical, the kreference characters designating Vcommon individual components in Figs, l and 2 have been retained in Fig. 6. Y

' Referring more particularly to Fig. 6, there is shown a plating barrel cylinder 299 including a series of interlocked, perforated side wall panels 30, interposed between tumbling ribs 2S and outer frame members 26,. The cylinder further includes a door panel 31 resting upon the upper panels Si) and adapted to be ,secured in position by locking strips 32 and a latch member (not shown), A unitary perforated liner membrane 292 Vis wrapped aroundv the cylinder and forms the inner surface of cylinder 200. This liner which isV preferably formed from a suitable material such as Teflon or Kel-F, hasV its ends interposed and secured between locking strips 32 and the upper panels 39 combination of the panels 3Q and the liner membrane 22.

is desirable in instances rwhere the load carried by the cylinder is unusually heavy anduadditional strengthV is necessary. In this modification, all the advantages above enumerated 'in connection withL the one-piece liner and replaceable panels Sti are realized. lt willbe appreciated that a barrel of the type shown invrFigs. l and 2 may be readily converted into Vone capable of handling `Vmuch smaller parts by simply adding a liner 202.

It will be apparent from the foregoing that an improved barrel plating cylinder is provided that is fully capable of withstanding heavy physical and chemical punishment to which such cylinders are subjected during an electroplating operation. Moreover, the electrical characteristics of Vthe cylinders, with respect tovpower losses suffered in the side wall panels or liners are superior to heretofore known constructions and the overall operating'eliiciency of the It will be appreciated also that the use of removable panels and liners greatly simplifies the maintenance of the cylinders.

While it will be apparent that the preferred embodiment of the invention'herein disclosed is well calculated to fuliill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change Without departing from the proper scopeor fair meaning of the subjoined claims. f j

What is claimed is: 1 Y

l. In an electroplatingV cylinder for carrying articles through an electroplating operation, a pair of spaced end walls, a pair of circumferentially spaced external spacer members extending between and secured at their ends to Ysaid end walls, a pair of elongated securing members each removablyY fastened to a diiierent one of said spacer members Vand disposed exteriorly of said cylinder, said securing members being shaped to conform to surfaces of said spacer members, a unitary perforated Vmembrane extending circumferentially from one of said spacer members to the other one thereof and having its ends secured between said spacer members and said securing members,Y `a plurality of corner supports circumferentially spaced around said cylinder between said spacer members, each one ofsaid corner supportsrincluding an outer member disposed exteriorly of said vcylinder and extending between and secured to said end walls, and an inner member disposed Within .saidV cylinder and removably secured to said outer member, said membrane extending between the inner and outer members of each one of said corner supports and being retained thereby in a predetermined position.

2. In an electroplating cylinder construction of the type having side and end walls 'defining a chamber of polygonal cross-sectional shape, and rigid frame members mounted in pairs *onand extending between `said ven'd walls, saidside walls extending and lbeing clamped-between the' two membersgof selected ones of said pairs, the improvement comprising an inner one of said frame memberseof generally rhombic cross-sectional shape disposed within saidY chamberat one of the longitudinal` i corners thereof, said inner frame member being positioned so that its inwardly facing surfaces meet the respective side walls immediately adjacent thereto at obtuse angles to prevent trapping of articles in said one longitudinal corner during operation of said cylinder.

V3. An electroplatingV cylinder construction comprising end walls and a plurality of substantially at side wall panels deiining a chamber having longitudinal corners, one side of said chamber extending between one pain of said corners being completelyV open and being closable by Y a door panel, a plurality of rigid frame members mounted on and extending in pairs `between said. end walls at the other ones of said corners, selected ones of saidpanels extending and'being clamped between the two members of Veach one of said pairs, a pair of rigid retaining members mounted onV and extending between said Yend-walls, at said one pair of corners, said retaining membersbeing disposed entirelyV exteriorly of said chamber, both of theV corners of said one pair being completely clear and unobstructed on the interior side thereof to providefor un- Y *Y obstructed'dis'charge of workpieces from vsaid chamber,

said retaining membersfbein'g adapted Yto'cooperate with a latchmember for removably securing a door panel between said one pair oftcorners to close saidchamber. Y

f 4. An electroplating cylinder construction of polygonal cross-sectional shape comprising a pair'of rigid end walls,

a pair of frame members rigidly mounted on and extend-Y ing between said endwalls at one corner of said lcon- Y.

locking engagement for positive retention of said panelsVV by said frame members'when said frame members are` urged towards each other, vand means for urging said frame members towards each other .into clamping engagement with said panels. Y

` 5. An electroplating cylinder construction comprising endywalls and a plurality'of substantially lat side wallV panels Vdefining a chamber` having longitudinal corners,

a plurality of rigid frame members mounted on and ex-` tending in pairs between said end walls at selected onesV of said corners, selected ones of said panels extendingfbetween and being clamped in position byV the two mem-V 1 bers of. each one of said pairs, ksaid panels and selected Y panels defining a chamber having longitudinal corners, yaV

plurality of rigid framel members mounted and extending in pairs between said endk walls and selected ones of1s`aid corners, selected ones of said panels extending between and being clamped inposition by the two membersA of each one of said pairs, each one of said.selected"pane 1s Y having a longitudinal grooveV in its outer surface adjacent to one edge, the outer ones of said ame members hav,- ing inwardly projecting longitudinal ribs ttinglyrposi tioned within said grooves, and means for clamping Vthe members of eachone of said pairs together with said selected panels therebetween so that saidselected panelsY are firmly secure'd'in position by interlockingengagement of said ribs in said grooves.- A Y p .Y

7. An electroplating cylinder construction comprising end walls and a plurality of rigid substantially flat side wall panels dening a chamber having longitudinalcorners, a pluralityV of rigid frame members mounted pon and extending in pairs between said end walls at selected` asssfioo ones of said corners, selected ones of said panels extending between and being clamped in position by the two members of each one of said pairs, a foraminous membrane lining said cylinder and disposed upon the inner snrfaces of said selected panels and also extending between and being clamped in position by said frame member pairs, the ends of said membrane extending exteriorly of said cylinder at two adjacent corners thereof, and means for clamping the ends of said membrane against selected ones of said panels exteriorly of said cylinder, each one of said panels being perforated to deiine apertures of a greater size than the apertures of said membrane.

8. In an electroplating cylinder for carrying articles through an electroplating process, a pair of spaced end walls, a pair of circumferentially spaced external stay members extending between and secured at their ends to said end walls, a pair of elongated securing members each removably fastened to a dierent one of said stay members and disposed eXteriorly of said cylinder, said securing members being shaped to conform to the surfaces of said stay members, a unitary perforated membrane extending CII lil

l@ circumferentially from one of said stay members to the other one thereof and having its ends secured between said stay members and said securing members, a plurality of corner supports circumferentially spaced around said cylinder between said stay members, each one of said corner supports including an outer member disposed exteriorly of said cylinder and extending between and se cured to said end walls, and an inner member disposed within said cylinder and removably secured to said outer member, said membrane extending between the inner and outer members of each one of said corner supports and being retained thereby in a predetermined position, said inner members being of generally rhombic cross section and being positioned within said cylinder so that their inwardly facing surfaces meet said membrane at obtuse King Jan. 22, 1918 Davidson Ian. 29, 1946

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