US3010260A

US3010260A - Apparatus for forming openings in blanks or paper web from which envelopes are formed

Info

Publication number: US3010260A
Application number: US711041A
Authority: US
Inventors: Subklew Hermann
Original assignee: Berkley Machine Co
Current assignee: Berkley Machine Co
Priority date: 1957-01-26
Filing date: 1958-01-24
Publication date: 1961-11-28
Anticipated expiration: 1978-11-28

Description

H. suBKLl-:w 3,010,260 APPARATUS FOR FORMING OPENINGS 1N BLANKs 0R PAPER Nov. 28, 1961 WEB FROM WHICH ENVELOPES ARE FORMED Filed Jan. 24, 1958 2 Sheets-Sheet 2 WR I...

w S ihm ATTRNEY United States Patent O 3,010,260 APPARATUS FOR FORMlNG OPENINGSJN BLANKS R` RAPER WEB FROM WHICH EN- VELOPES ARE FORMED Hermann Subklew, Neuwied, Rhineland, Germany, as-

signor to Berkley Machine Company, Kansas City, Mo., a corporation of Missouri Filed Jan. 24, 1958, Ser. No. 711,041 Claims priority, application Germany Jan. 26, 1957 8 Claims. (Cl. 51-78) This invention relates to an apparatus for forming openings in the blanks or paper web from which envelopes are formed, and particularly on high speed rotary envelope making machines, the openings being to provide windows which may or may not be subsequently covered with a .transparent patch and through which the address portion of a letter placed inside a finished envelope may be seen to supply the mailing address.

Such machines operate at high speed and the blanks or webs from which the envelopes are formed are kept in constant continuous movement, consequently it has been ditcult to form the window openings'with the blanks or web in motion. I

It has been the practice to die cut the envelopeblanks and openings therein .by pressing a die through a stack of sheets and then ,feeding the blanks with the openings therein from a stack. This requires separate equipment to provide the blanks and the necessity of transporting the blanks and inserting them in la stack in the envelope making machine. Considerable power is alsoj required to operate the die press.

Another method is die cutting of the windows directly in the envelope making machine, but this requires momentarily stopping the blanks or web while cuts are being made through the materialthereof and restricts the production of an otherwise continuous rotary envelope making machine. For this reason, rotary cutting cylinders have been devised for cutting through theblanks or paper web with the blanks or web in motion. This has usually been accomplished by providing the cutting cylinders with one or several knives, acting against a hardened steel roller which serves as a matrice.L The knife, cylinder and matrice roller are arranged in a slantwise direction or spiral blades are used to produce as nearly as possible a shear cut progressive with movement of the blank or web. The latter method also has numerous disadvantages. When the knife cylinder acts on the matrice roller of hardened steel, there is a considerable springiness in the knife blades, which results in a more squashing action rather than a clean cut through the material. There is also considerable wear on the knife edges because of their impact on the hard steel matrice roller. Consequently, these disadvantages result in reduced eliiciency of the machine. Also, at higher working speeds greater pressure is required between the knife cylinder and the counter-roller which increases the wear on the parts and otherwise interferes with satisfactory cuts being produced.

It is, therefore, the principal object of the present invention to provide a novel apparatus for providing the window openings directly in a continuous rotary type envelope making machine, which overcomes the difficulties of the present methods and permits operation of the envelope making machine at the higher speeds.

Other objects of the invention are to provide an apparatus involving the grinding ont of portions of the material of the blanks or web to form -the openings neatly and rapidly; to provide 'a grinding operation wherein both the envelope material and grinding element rotate in contact only where the marginal edge of the window is to be formed; and to provide a method and apparatus wherein the envelope material is presented to the grinding element lCe in' a manner to permit passing of the material at substantially high speeds.

In accomplishing these and other objects of the invention, we have provided an improved apparatus illustrated in the accompanying drawings, wherein:

FIG. l is a longitudinal section through an apparatus constructed in accordance with .the present invention, the section being taken on the line 1 1 of FIG. 3.

FIG. 2 is a fragmentary perspective sectional view of the segment which provides the support for backing the blanks or web for effecting grinding contact of the grinding element with the blanks or web, as the case may be.

FIG. 3 is a plan View of the apparatus, of slightly smaller scale than FIG. 1 and with upper feed roller and pressure wheels removed to better illustrate the construction of the revoluable cylinder and the passes for the paper web or blanks, parts being shown in section for better illustration,

Referring more in detail lto the drawings:

1 designates an apparatus for forming openings such as windows in envelope blanl and in web material from which the envelopes are formed in a rotary type envelope making machine. The apparatus 1 is interposed between upper and lower feed or guide rollers B and D of the rotary envelope making machine, and which rollers feed the envelope blanks or the web material from a previous operating station to a subsequent station. For simplicity of illustration and understanding of the present invention, these steps of the envelope making machine are not shown, ras they speciiically form no part of the present invention, it being sufficient that the rollers B and D of the machine guide the envelope blanks or paper web material into and from the window forming apparatus 1.

The window forming apparatus 1 broadly includes a revolvable cylinder A, around which the web material or blank is extended as it passes from the guide roller B to `the guide roller D, a grinding cylinder or wheel C that cooperates with the cylinder A to grind through the material of the blanks or web, pressure rollers' F and G for pressing the material of the blanks or web to the cylinder A, -a mechanism E for moving the grinding wheel to and from the cylinder A, and a scrap collector H for receiving the material ground out of the blanks or web.

The cylinder A and guide rollers B and D are supported on

horizontal shafts

2, 3 and 4 to carry the web or blanks 5 between the peripheral faces 6, 7 and 8 thereof, whereby the blank or web 5 is guided to and from wrapping relation with the cylinder A. The

shafts

2, 3 and 4 are driven in timed relation by gearing, as

indicated at 9, FIG. 3, and which in turn is operated in timed relation with the operating parts vof the previous and subsequent stages of the envelope making machine, not shown. The blank or web 5 thus extends a substantial distance around the cylinder A to accommodate the pressure rollers F and (3, the grinding roller C, and the scrap collector I-I, so that the entire windowforming operations are carried out while the blank or web is carried around the cylinder A. The cylinder A comprises a core 10 having end disks or flanges 11 and 12. The core is adjustable longitudinally of the shaft 2 by

collars

13 and 14 to position the window opening in the blank or web. The cylinder A also has a bar 15 extending parallel withthe shaft 3Av and has its ends fixed thereto bycollars 16 and 17, the flanges 11 and 12.

being provided with notches 18 to pass the bar 15 therethereof is a plate or pad 19 having an arcuate outer face 20 inset below the peripheral faces 21 of the flanges. or disks 1 1 and 12 to accommodate an arcuate'platen 22 thereon, so that the outer face 23 of the Vplaten 22 fregisters laterally' with the peripheral faces 21 of the disks Y inthe form of an elongated rectangle, having the long side faces 24 and V25 thereof extending in the longitudinal direction'of the cylinder A and the end faces 26 and 27 extending in the circumferential direction of the cylinder Af It is to be understoodothat the platen 22 may be other shapes and sizes, dependent upon the shape of the opening to be formed. Surrounding the platen 22 and held in face to face contact with the side and end faces 24-25 :and 26-27'thereof is a thin, at, hardened band 28, which, for example, may be 0.1 mm. in thickness. However, it is to be understood that the material of the bandv 28 may be thicker, as may be required in accordance with the thickness of the envelope material or the speed with which-the machine is operated. The band 28 provides a frame on the cylinder A and is preferably mounted with its inner edge 29 bearing upon the face 20 of the pad 19 and its outer edge 30 projects slightly beyond the face ofthe platen22 and the periph'- eral faces 21 of the disks 11land 12 toV constitute supports for the envelope material.Y vThe supports .thus prio-v vided locate the site ofthe perimeter lof the window opening to be formed. The band y28 Vis clamped-t0 the side and end-races 24-25 and 26-27 of napraten 22 by clamping strips 31 that aresecured tothe -pad 19 by fastening devices such as screws 32. o The-width of the band vand the depth of the side and end faces ofthe platen 22 are such that the edges 30 of the band project from the surface 23 of the platen, asindicated by the distance "a designated in FIGS. 2 and 3.

' Y The bar 15 has an arcuate .face 33y registering with the peripheral faces 21-of the disks or flanges A11 and 12 of the core and whichvis carried under the roller B to enga'gejthe blank or web to carry it around the cylinder AL In order to grip the blank or web, the arcuate face Y33 Vhas ka plurality of portsr34 through which avacuum drawn by way of channels 35 extending longitudinally of the bar and which connects at `one end vwith a radial port 36in the collar 17 and which in turn connects j with a channel 27 extending longitudinally of the shaft 3, the outer end being closedV byV a plug 38. The vacuum is drawn through the ports and channels through a radialV port 39 in the Yshaft and which connects with a channel 40 in a valve disk 41 that rotates in contact with a-platc 42 lhaving a channel 43 that connects with a source of vacuum, not shown. The valve disk 41 and plate 42 have yports 44 and 45 that are adapted to registerrnear the point where the face 33 of the bar 15 makes contact with the blank `or web to carry the blank or web around the cylinderfA tothe roller B, where they ports 44 and 45' move out of contact to breakV the vacuum and release lthe blank to the roller D. A blank or web is thus held to the cylinder A and extended over vthe face of the platen 22 and the projecting outer edges 30 of the band 28 with the Vblank or web bearingdirectly upon the edges 30 ofthe band. K 'Y Y v The grinding wheel C includes a cylindrical body 46 that is supported concentrically on arshaft 47 and between clamping disks 48`and 48'. The ends of the shaft 47 are suitably journaled in bearing brackets 49 and 50 that are carried upon a table 51 of the mechanism E. The table 51 is carried on an under table 52 that isrmounted Von a bed frame 53. The under face of the table 52 has a transverse dovetail groove 54 engaging a transversedovetail-VSS on the, bed frame, whereby the table 52 is Vadapted to be moved transversely to Vcenter the grinding wheel C in proper registry with the lateral adjustment In the illustratedinstance, the platen 22 isV The grinding face A60 ofthe grindingwheelC is cylindrical to "make tangential contact'with those portions of the material of the blank or web backed by the outer edges 30 of the band 2,8, wherebyV only the portion ofthe material extending across the edges ofV `the 'band is removed .by grinding, to thereby cut outa port1on 61 of waste material corresponding in shape to the platen 22, and which, when subsequently removed, together with the material removed by grinding, leaves an opening in the blank or web to form a-window opening. Y

VThe grinding wheel C is` moved to. and from the cylinder A vby shifting the table`51 on the 'table 52.

The plate 52 carries

spacedapart guide shafts

62 and 63 of the platen 22.V The table 52f'isV actuated transversely` by a threaded shaft 56 which is operated by` aehand wheel. i

57,?the shaft 5,6 being rotatably carriedjby the bed frameV andfhaving threaded connection with a depending lug 58 Y on the under side of the table. The grinding wheel C5 is driven at high speed by means ofva pulley 59 (FIG. 3) that 'is actuatedv through a belt connection with a Vmotor or a rotary part ofV the envelope making machine.

that are carried between ears 64 on the tableV 52,-and which pass through depending ears 65 on the table 51 (FIG. l). The supporting table 51 is shifted'by means of a shaft 66 having Va threaded end 67V rotatable in a nut 68 that ldependsfrom thertable 51, as shown in FIG. l. The Yends of the shaft .'66are suitably journaled in lugsk 69 ,and 70 on the table 52, also best shown in FIG. l; fO'ne end of the shaft 66v carries a wormV gear 71 which meshes witha worm 72 on a shaft 73 which is adapted to be turnedmanuallyby a hand wheel 74 on thelouteru end of the shaft 473. lThe'shaft 73 is locked in adjusted position by a'jamb nut 75, as shown in v3. The womrshaft 73 is rotatably mounted on the table 52 in suitable bearings 726, Y

.'lhepairs ofrollers F and G consist of rubber or otheryielfdble vmateiialand are journaled in arms 77 and 78 Vpivotay mounted on'the bear-ing brackets 49 and 50 of'thetable 51, lso that the resilient peripheries 79 thereof press thef blank or web andserve toy securethe material to the surface 21 :of the" disks 1 1f.and 12 as it passes between'th'e'cylinder A and thefgrinding wheel 0, and tohold it undertensionwhile the window is being ground'to'the size Ydetermined bythe `edges v30v of theband 28. i l A' Y Y Y The waste pieces ygroundout ofV the materialy of the blanks( or web are discharged by blasts of air into the waste collector Hf This `accomplished by admitting compressed air 'through a port 80in a valve plate 81 that contacts an adjusting Ydisk `82 which engages lthe opposite side of the valve disk 41. 'The Vair is/dicharged through a port 83 in the yvalve vplate .81 at the .time the platen Vis moved across the'open top Vof the' scrap collector l-l.

VThe port 83 of the valve plate connects with a channel V8,4 that extends longitudinally of the shaft 2 and discharges through a radial port 85 into an internal annular recess 86 of the core 10. The air then passes through radial ports `87 that extend through the pad 19 and platen`22 to discharge against the'faceV of the waste material and blow it from the face of theplaten into-the scrap collector `VH. VThe ports inthe valve plate and disk are so, located that the air pressure will be shut off as the bar 15 of the' cylinder passies the holder and to allow the face of the bar to cooperate with the feed'cylinder D for continuing the movement ofthe blank or web after the opening has been lformed therein.

Assuming that the V'window-forming apparatus ,is-'con-Y structedrand installed in a rotary type envelope making machine, with the grinding wheel C imposed in cooperation with the feed` rollers B and D, and assum` ing that the proper shaped band '28' and platen 22 have ibeen'applied to the arcuate surface 20 of `the pad 19, the operation is as follows:

When the'envelope making machine is 'ofthe web type,

the webV 5 from which :envelopes are Yformed is passed and overthe roller D,` sothat4 the envelope material is convexly curved around `the cylinder A. Threading of the web isv most veasily accomplished when the-grinding wheel is in retracted position. This is eiected by loosening thejjambnut andk rotatingthe hand wheelY in the proper direction to turn the wormgear 71 and the screw shaft 66, soV thatthe; nut 68.islmoved.retractivelyonthe threaded end 67 of the shaft. After the web is in position and the core of the cylinder A has been adjusted on the shaft 2 to properly locate the band 2S in relation to the site of the window opening to be formed, the hand wheel 57 is operated to adjust the grinding wheel relatively to the lengthwise direction of the platen. This is eifected by turning the hand wheel 57 in the proper direction to shift the table S1. The hand wheel 74 is then operated to turn the shaft 66 and shift'the table 51 so that the grinding wheel is in a position to grind through only those portions of the material of the paper Web that overlie and are supported directly upon the outer edges 3i) of the band, and to bring the pairs of resiliently faced rollers F and G into position for engaging the sides of the web overlying the peripheral faces 21 of the flanges or disks 11 and 12 to smooth the material of the web which spans the space between the supported portions thereof.

When the machine is in operation, the rollers B and D and cylinder A all rotate in timed relation with the various stage operations (not shown) of the envelope making machine, so that the window openings are formed in the proper spaced apart location in the lengthwise direction of the web 5. During rotation of the cylinder A, the bar 15 passes under the feed roller B and the vacuum is established through the ports 34 to draw the web into contact with the arcuate face 33 of the band and to grip the web so that as the cylinder A revolves, the web is drawn tightly over the outer edges 30 of the band 28. As the band is carried toward the grinding Wheel, the periphery of the grinding wheel rst contacts the material of the web extending over the advanced longitudinal edge of the band 28, grinding through the material to form a linear slitlike opening along the length thereof, and as the cylinder A continues its rotation, the grinding action is concentrated along the portions of the material engaging the arcuate edge faces of the endmost portions of the band to effect similar slitlike openings at right angles to the ends of the first formed slitlike opening, and as the portion of the material overlying the outer edge of the rearmost portion of the band comes into position, a corresponding linear slit is ground thereinto by the grinding action fof the wheel C. The material surrounded by the slitlike openings thus formed is not affected by the grinding wheel, but provides an intact panel that is carried with the web over the collector H. By this time the valve disk 81 has moved into position so that blasts of compressed air are discharged through the ports 87 to displace the waste material that is encompassed by theslits or narrow slots thus formed into the collector I-I. When the air supply port is moved out of registry, the air blast is shut ofi and the web continues its travel around the roller D If the apparatus has been installed .in a machine adapted for feeding blanks from a stack, the blanks are fed from the stack and passed through the machine in successive order, so that they pass through the Windowforming apparatus substantially in the same manner as the webjust described. v

It is obvious that the invention provides an apparatus for accurately and neatly forming windows by supporting the sheet material, of which the envelopes are constructed, within and along the perimeter of the opening to be formed, and that only the supported material is ground Vthrough in lthe grinding step to provide a very narrow slit or slot coextensive with the perimeter of the opening to leave a substantially solid panel of waste material within the enclosing limit of the slit, and that the opening is completed by displacing the panel of waste material which is encompassed by the slit. It is also obvious that all of the steps are Vadapted to be carried out while maintaining the envelope material convexly curved and in motion through lia curved path to facilitate the lgrindin g step.

From the foregoing, it is obvious Ithat the grinding wheel, in cooperation with the projecting edges of the band on the revolving cylinder A, provides for formation of the window openings at high speed and While the blanks or web are also traveling -at high speed through the machine. It is also obvious that the'thinness of the band :and 'high speed of the grinding Wheel result in a smoothly continuous edge about the perimeter of the window opening and that all of the window openings are of the same size and shape, since the size and shape is controlled by the size and shape of the band.

. What I claim and desire to secure by Letters Patent 1s:

1. An apparatus for producing openings in sheet material of which envelopes are formed, including -a rotatable member, means supporting said member for rotation on a fixed axis, a frame on said rotatable member and having a relatively t-hin edge defining the site of the perimeter of the opening to be produced, means on said rotatable member for gripping the sheet materiall to carry the sheet material over said frame and across the relatively thin edge thereof, a grinding wheel having a cylindrical grinding surface, means for supporting the grinding wheel with its axis in parallel relation with the axis of the rotatable member and with the cylindrical grinding surface thereof adapted to progressively contact the portions of said sheet material backed by said thin edge, and means for operating the grinding wheel to grind through said portions of Ythe sheet material to provide a rectangular slit in said sheet material for forming the perimeter of said opening.

2. An apparatus for producing openings in sheet material of which envelopes are formed, including a rotatable member, means supporting vsaid member for rotation on a iixed axis, a generallyrectangular frame on said rotatable member and having 'arrelatively thin edge defining the site of the perimeter of the openingto be produced, means on said rotatable member for Kgripping the sheet material to carry the sheet material over said frame and across the relatively thin edge thereof, a grinding wheel having a cylindrical grinding surface, means for supporting the Igrinding wheel with its axis in parallel relation with the axis of the rotatable member and with the cylindrical grinding surface thereof adapted to contact the portions of said sheet material backed by said ed-ge of the rectangular frame, means for operating the grinding yWheel to grind through said portions of the sheet material to provide a rectangular slit in said sheet material for forming the perimeter of said opening` and to leave a substantially solid panel of wast-e material, and means for discharging air under pressure through an area of the rotatable member bounded by said frame and -against the panel of waste material encompassed by said rectangular slit.

3. An apparatus for producing arwindow opening inV sheet material of which envelopes are formed, including a rotatable member, means supporting said member for rotation on a fixed axis, `a platen conforming in shape to the opening to be formed and having a curved surface concentric Withthe axis orf rotation of said member, means for securing the platen to the rotatable member, a relatively thin band surrounding the platen and having an edge projecting outwardly from the curved surface of the platen, means for clamping the band to the platen, means on said rotatable member for gripping the sheet material to carry the sheet material over said platen and across said projecting edge of the band for locating the perimeter of said window opening, a grinding wheel having a cylindrical grinding surface, means for supporting -the grinding wheel with its axis in parallel relation with the axis of the rotatable member and -with the cylindrical grinding surface thereof adapted to progressively contact the portions of said sheet material on said projecting edge of the band lto provide awsli-t yabout the perimeter of said window opening, and means for operat- Y ing the 'grinding `wheel to grind through said portions of the vsheet material.

4. An apparatus for producing a window opening in sheet material of whichenvelopes are formed, including a rotatable member, means supporting said member for rotation on a fixed axis, .a platen conforming in shape tothe opening to be formed land having acurved surface concentric with the axis of rotation of said member, means for securing the platen to the rotatable member, a relatively thin band surrounding the platen and having an edge projecting outwardly Vfrom the curved surf-ace of the platen, means for clamping the band to the platen, means on said rotatable member for gripping the sheet material to carry the sheet material "over said platen and across said projecting 'edge of the band for'locating the perimeter of `said window opening, a grinding wheel havingra` cylindrical grinding surface, means for suppor-ting the grinding wheel with its axis in parallel relation with the axis of t-herotatableV member and with the cylindrical grinding surface thereof `adapted to contact the portions of said sheet material on said projecting edge, means for operating the grinding Wheel to grind through said portions of the sheet lmaterial for forming a slit aboutthe perimeter of vsaid window opening and leavera substantially solid panel of -waste material encompassed by said slit and conforming to the shape of the platen, said platen having extending through the platen, 'and means associated with the rotatable memi ber for discharging `air through s-aid ports for displacing the panel of Waste material encompassed by said band.

'5. An apparatus for producing openings in sheet material of which envelopes are formed, including -a rotatable memberymeans supportingl said member for rotation on allixed anis, a platen conforming in shape to the opening to be formed and having Va curvedk surface concentric` Withthe axis of rotation of said member, means for securing the platen to the lrotatable member, a rela tively thin band surrounding the platen Iand having an edge projecting from the curved lsurface ofthe platen, means on said rotatable member for gripping the sheet material to-carry the sheet material Vover said platen and across said projecting edge of the band, a grinding wheel'having a cylindrical grinding surface, means for supporting-the grinding wheelrwith its -axis in parallel relation with the axis of the rotatable member and with the cylindrical grinding surface thereof adapted to contact the portions of said Vsheet material on said projecting edges, pressure wheels carried by the grinding wheel supporting means for contacting the sheet material 'on opposite sides of the platen, means'for shifting the grinding wheel Vsup-porting means to adjust contact of the grinding wheel, means for operating the grinding wheel to grind through'said portions of the sheet material, and V kmeans associated with the rotatable member for displacing the material'overlying said platen.

6. In-an apparatus foi-.producing windows in envelopes, alrotatable shaft, a core member adjustable longi-V tudinally-on the shaft and Ihaving end tlan'gesproviding peripheral 'faces for supporting the Sheet material Vof which'the envelopes are formed, a transverse bar extending-along said shaft andY through said flanges and having an arcuate face registering with the peripheral faces of thek flanges, a pad carried by thencore intermediately of ,theanges, Aa platen supported on 4the pad, a band surrounding the platen with one edge abutting the pad and the other edge projecting Yradially from the face of the platen, said barv having vacuum ports extending -through the larcaute face thereof vfor drawing a vacuum to effect gripping of the sheet lmaterial of which the envelopes are formed and to effect wrapping of the sheet material over the platen and across theprojecting edges of the band, a grinding device having a grinding surface, and means forV supporting the `grinding device with the grinding surface thereof in grinding contact with t-he portions of the sheet material that are carried across said projecting edges of the band.

7.1111 an apparatus for producing windows in envelopes, Va rotatable shaft, a core member Vadjustable longitudinally on the shaft and having end flanges providing peripheral faces for supporting the sheet material of which the envelopes are formed, -a transverse bar extendingl along said shaft and through notches in said ilanges and having an arcuate face registering with the peripheral faces of the flanges, a pad carried by the core intermediately of the flanges, a platen supported on the pad, a band surrounding the platen with one edge :abutting Vthe pad and the'ot'her edge projecting Yradially breyond the face of the platen, said bar having vacuum por-ts extending through the arcuate face thereof for drawing a vacuum to effect gripping of the sheet material of which the `envelopes are formed and to effect wrapping of the sheet material over Itheplaten and across the projectingedges ofthe band, a grinding device having a grinding surface, and means for supporting the grinding devicerwith the grinding surface thereof in grinding kcontact with the portions of the sheet material thatare carriedacross said projecting edges of the band, said platen having air discharge ports for blowing out material removed by said grinding. i

8. An apparatus for producing windows in envelopes including a supporting device provided with va generally rectangular frame having a relatively narrow edge projecting from the supporting device for backing the sheet material and defining the site of the Iperimeter of the window in said sheet material, means for movably mounting theisupporting device, .la grinding device having a grinding surface movable Vacross said relatively narrow edge of the frame, means for feeding the sheet material of which such envelopes are formed bet-Ween said frame portion of the suppotring device -andsaid grinding surface of the grinding device, means on the supporting device for gripping the `sheet material for movement therewith, means on lopposite sides of the grinding device for pressingthe sheet material' against the supportin-g device on opposite sides of the frame for smoothing the YIsheet material-across saidrframe, and means for actuating the grinding device for grinding through the portions of the material extend-ing across the relatively narrow edge of said frame to provide a continuous slitforming the perimeter ofthe window.

References Cited in the file of this patent g UNTTED STATES PATENTS Hellbe'rg 1 Oct. 13, 1959