US2683208A - Apparatus for perforating - Google Patents

Description

July 6, 1954 ANDREWS 2,683,208

APPARATUS FOR PERFORATING Filed Oct. 21, 1952 2 Sheets-Sheet ,l

2s as A o 44 45 I I 22 1s A no (:2 26

INVENTOR.

1 j; 5 ALVADORE M. ANDREWS BY ATTORNEY y 6,- 1954 A. M. ANDREWS 2,683,208

APPARATUS FOR PERFORATING Filed Oct. 21, 1952 2 Sheets-Sheet 2 /////l)//I//IIIIIIIIIIIIIII//////A I N V EN TOR. I ALVADORE M'. ANDREWS MM 1. @W J ATTORNEY Patented July 6, 1954 UNITED STATES PATENT OFFICE APPARATUS FOR PERFORATING Alvadore M. Andrews, Portland, Oreg.

Application October 21, 1952, Serial No. 316,037

7 Claims. 1

The present invention relates to a method and means for perforating sheets of material and more particularly to a new and improved method and means for perforating sheets of heat fusible plastic material having relatively high dielectric strength.

In some instances, such as in the manufacture of lawn irrigator or sprinkler hose from thin plastic sheeting, it is necessary to provide a multiplicity of small diameter perforations through the plastic material without so weakening the material about the perforations that the water pressure within the hose can cause failure of the hose at such points. A cylindrical sharp edged punch is not feasible for forming fine perforations having a diameter such as from 7 to thousandths of an inch. It is also impractical to pierce or puncture the sheet with a pointed instrument. Either the piercing or punching method is actually a tearing or shearing operation which creates fine, radially extending rips through the material adjacent the aperture or opening. If sheets perforated by such methods are placed under stress, the rips about the perforations creep through the sheet and rapidly lengthen to such an extent that the product formed of the perforated material is rendered useless.

Another method used heretofore to perforate sheets of various materials is to place the sheet to be perforated between a pair of pointed electrodes across which a high voltage is applied. The high voltage will cause the portion of the sheet between the electrodes to break down whereby an opening will be formed in the sheet. This method is not practical, however, for perforating relatively narrow strips of plastic and other material having a high dielectric strength since the potential necessary to break down the strip to perforate the same is so high that the electrodes frequently discharge about the side edges of the strip rather than through the strip and, of course, no opening will be formed. Also the life of the electrodes is extremely short because of the high temperature of the are.

It is a general object of the present invention, therefore, to provide a new and improved method and apparatus for perforating sheets of material.

More particularly it is an object of the invention to provide a new and improved method and apparatus for perforating sheets of material of high dielectric strength.

A more specific object of the invention is to provide a method and means for perforating a sheet of material whereby the edges of the perforations will be smooth and continuous and the adjacent portions of the sheet free from rips and tears.

Another object of the invention is to provide apparatus for electr c-perforating openings of predetermined diameter in sheet material of high dielectric strength.

Other objects and advantages of the present invention will become more apparent hereinafter.

In accordance with the illustrated embodiment of the invention, plastic strips are fed through a machine having means to break down the dielectric strength of the strip at selected points as, for example, by rupturing the strip by piercing or puncturing it at the selected points. The strip is thereafter passed between a pair of substantially planar faced. electrodes between which is impressed a voltage suflicient to cause arcing through the strip at the ruptured points. The high temperature of the arc will cause the surrounding portions of the strip to melt and fuse and the arc is maintained for a predetermined length of time to form an opening in the strip of the desired diameter.

For a more detailed description of the invention reference is made to the accompanying drawings wherein:

Fig. 1 is a top plan view of a machine constructed in accordance with the present invention for perforating a strip of plastic;

Fig. 2 is a cross-sectional view taken substantially along line 2--'2 of Fig. 1;

Fig. 3 is an enlarged cross-sectional view taken along line 3--3 of Fig. 2;

Fig. 4 is an enlarged fragmentary view taken substantially along the line 4-4 of Fig. 1 and showing the arrangement of the electrodes;

Fig. 5 is an enlarged top plan view of a section of the plastic strip; 7

Fig. 6 is a large cross-sectional View of the plastic strip taken along the line 6-6 of Fig. 5; and

Fig. '7 is a view of a sprinkler hose made from material perforated in accordance with the present invention.

Referring now to the drawings, the machine of the present invention comprises a table ill over the surface of which is drawn an elongated sheet or strip ll of material to be perforated, such as, for example, a strip of vinyl chlorideacetate plastic which is characterized by its high dielectric strength. Rotatably mounted at one end of the table II] is a pair of vertically disposed rollers l2 and I3 adapted to frictionally engage the strip ll therebetween to draw the same through the machine, or from right to left as viewed in Figs. 1 and 2. Any suitable means may be provided to drive the rollers l2, it which means are indicated in the drawings by a shaft l4 connected to any suitable prime mover (not shown) and driving the upper roller 12 by suitable pulleys and belts indicated at [5 or any other suitable means. A spool I! is provided to wind the perforated strip as it leaves the machine, which spool is suitably journaled on supports indicated at I8 and driven by suitable means as from the upper roller l2 by the pulley and belt arrangement indicated generally at 19. To retain the strip H in a predeterminedpath suitable guide means are provided on table 10 including the guides 20, 2| mounted-on the table It" just forwardly of the drive rollers -:;I2, 13 ,on-each of the opposite sides of the path of the strip H and the guides 22, 23 mounted similarly at the foremost end of the table [0.

Means are provided ion the machine for reducing the dielectric strength of the strip ill at 7 selected points therealong as it passes through the machine. 'Mountedion the forward end of the machine are meansfor .piercingor puncturing openings throughvthe strip at predetermined points therealong comprising anupper puncturing roll Y25 and a cooperative platen roll 26, which rolls are mounted with their adjacent peripheral portions tangential to the. surface .of the table L0, and between which rolls the strip ll passes in its course athrough the machine. The puncturing roll -25 is mounted on a shaft 27 which shaft is suitably journaled on a pair of oppositely disposedsupporting brackets 28 up standing from the-table 10. The platen roll 26 is mounted on a shaft 29 the-opposite ends of which shaft are suitably journaled in oppositely disposed supporting brackets Bil-depending from the table i=6. Though the puncturing roll .25 and the platen roll 26may be positively driven, the frictional engagement-of the moving strip therebetween will cause the rolls to rotate and to perform their functions. As shown in the drawings, the rolls 25, Mare-mounted on the table Iii-so as torotate freel-y about their respective axes.

Thepuncturing roll 25 includes an inner cylindrical portion 33 having a plurality of circumferentially spaced apart puncturing needles 3 3 'mounted'thereon. The needles 34 are cooperatively received in radially extending circular openings 35 formedinthe cylindrical portion 33 and are releasably secured in place by lock screws SBwhich are threaded through the side of the cylindrical portion 33 as-shown in Fig. 3. The needles 34 each extend radially outwardly from the periphery of the cylindrical portion 33 a substantially equal distance and are adapted to just contact .the periphery of the platen roll 26 as. the rolls 25, 26 rotate- Preferably, the platen roll 26 is rubber covered so that at :least the .outer peripheralportion thereof has a slight degree of resiliency whereby the needles 34 may more easily pierce the strip II and-will not be as rapidly blunted as would be the case if the platen roll were provided with-a hard surface.

Means are provided to remove .the strip l i from the needles 34 after the piercing step which means comprises an annular ring 38 of a .compressible, resilient material such as sponge rubber disposed about the cylindrical portion 33. The normal thickness of the ring 38 is such that it is greater than the distance that the needles project from the periphery of the cylinder 33,,

the material of the ring being compressible'inwardly as it comes in contact with the portion of the strip I 1 adjacent the platen roll 26 where by the needles 34 will project outwardly of the compressed ring to puncture the strip l l as each needle rotates into contact with the platen roll. As the compressed portion of the ring 33 rolls free of engagement with the platen roll 26, such portion will expand to the normal thickness of the ring 38 disengaging the needles .34 and the strip H.

The needles are preferably very fine and sharp such as, for example, a No. 10 phonograph nee- ,dle whichneedle will pierce or rupture the sheet as indicated at ,35 in Figs. 5 and 6. Such a rupture 39'rea'lly has no finite cross-sectional area but, as shown, merely comprises small tears through the material. If the perforated strips are to be used in the formation of sprinkler units as shown in Fig. 7 the perforations are preferably formed in a plurality of spaced apart rows as indicated in Fig. 5 and which may be accomplished by staggering the needles 34 in roller :33

in different axially spaced apart radial planes.

Mounted on the table I 0 between the puncturing rolls 25, 26 and the drive rollers l2, :I3 is -a pair of planar faced electrodes '43, 44 positioned to receive the strip I therebetween with the faces of the electrodes substantially parallel with the surfaces of the strip 1 l. Preferably, the'low er electrode 43 is embedded in the table lll with the surface of the electrodes 43 substantially flush with the surface of the table H3. The upper electrode 45 is mounted on an arm 45 supported on the table i by a bracket includingan elongate base portion 46 upstanding from and extending longitudinally of the table [0." The arm 55 is releasably clamped between the base portion 46 and a clamping bar t! extending longitudinally of the base portion 48 and secured at its opposite ends to the base portion 46 by bolts 48. This arrangement permits longitudinal adjustment of the position of the electrode 44 in respect to the electrode 53, the reason-for which adjustment will become apparent hereinafter. The arm 45 is preferably formed'of an electrically insulating, resilient material and is arranged to bias the electrode at downwardly into contact with the upper surface of the strip H.

The electrodes 3, as are each elongated int-he width of the strip II and'is disposed centrally of the strip so that the oppositeedges of-the strip 5 l extend downwardly from each of the opposite side edges of the electrode lid This arrangement is preferred to minimize the possi-- bility of arcing occurring between the upp r nd lower electrodes across the side .of the stri grcli rather than through it.- The electrode 44 has .a.

width at least as great as the distance between the two outermost rows of perforations, as shownvv in Fig. 5.

Circuit means are connected to the electrodes for impressing a potential between, them,whi ch is greater than the dielectric strength of the air gap between the electrodes and sufiicient to create an arc discharge through the ruptures 39 in the strip H. The potential applied to the electrodes 43, 44 is of course less than the. normal dielectric strength of the material being perforated to preclude the possibility of breaking down the material at unselected points. Suitable circuits will be readily apparent to those skilled in the art and the circuit means therefore has only been schematically illustrated in Fig. 2 and is indicated generally by the numeral 49. In perforating vinyl chloride-acetate sheets having a thickness of from about 0.006 inch to 0.010 inch, I have found it expedient to employ an ordinary 11,000 volt neon sign trans former with the opposite secondary terminals connected to the electrodes 43 and 44.

In the operation of the machine the driving rollers 12 and I3 are set in motion to draw the strip I i through the machine at a desired rate of speed. The strip is first punctured as it passes between the puncturing roll 25 and the cooperating platen roll 26 as above described and then proceeds between the electrodes 43 and 44. Though the strip H may be of a high dielectric strength as, for example, if it is a sheet of a vinyl chloride-acetate plastic, the ruptured areas through the strip provide a weakened path through which are discharge between the electrodes will occur in preference to other portions of the strip. As the electrodes begin to discharge through the ruptures 39 in the strip II, the heat of the arc will, of course, melt the adjacent material, the surface tension of the molten material causing it to form meniscus like bulges 52 on each of the opposite surfaces of the sheet which molten material will solidify to define an opening 53 of finite diameter as most clearly shown in Fig. 6. The edge of the opening 53 resulting from such fusing or melting will be comparatively smooth and continuous and the strip will be free from any radially extending rips or tears so that upon application of stress to the strip the opening will merely expand and the strip will not tear or rip. Moreover, the bulges 52 will reinforce the opening to further deter the ripping or tearing of the strip. The size of the openings may be regulated by controlling the period of time an arc is maintained through an opening, which control may be effected by varying the effective length of the electrodes such as, for example, by changing the length of either electrode or by changing the position of the upper electrode 44 so that only a fractional portion thereof overlaps the lower electrode 43. The speed at which the strip ll moves through the machine may be varied to lengthen or shorten the period of time within which any opening is between the electrodes and correspondingly lengthen or shorten the period of arcing through each puncture. The temperature of the arc may also be increased or decreased by increasing or decreasing the current value of the discharge, the higher current values resulting, of course, in larger openings through the sheet if conditions are otherwise the same.

While material perforated in the manner described will have many uses, a particularly useful application of thin, perforated strips of plastic is in the formation of sprinkler hoses such as the hose illustrated in Fig. '7 and more fully described and claimed in my co-pending application Serial No. 318,065, filed October 31, 1952. The hose shown in Fig. '7 comprises a pair of elongate parallel tubes or conduits 55, 56 which may be individually formed from the perforated strip 1 l by the method described and claimed in my Patent No. 2,500,053, issued March '7, 1950. According to that method, the opposite side portions of the strip Il may be overlapped with a thread impregnated with a bond effecting liquid disposed between them. The overlapped portions are then pressed together, which pressing will express the liquid from the thread and effect a bond between the overlapped portions. A pair of tubes thus formed are then united together in any suitable manner so that the openings 53 in each tube will be in the relative positions shown in Fig. 7, that is with openings 53 in each tube arranged slightly to the side of the uppermost portion of a tube and away from the other tube so that water will spray laterally from the hose on each of the opposite sides thereof.

Having illustrated and described a preferred embodiment of the invention, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. I claim as my invention all such modifications as come within the true spirit and scope of the appended claims.

I claim:

1. A machine for perforating at preselected points an elongate strip of heat fusible material comprising means for drawing said strip through said machine at a predetermined rate, means for puncturing said strip at preselected points therealong as it passes through said machine, and a high voltage discharge means including a pair of electrodes positioned to receive the punctured strip therebetween; said electrodes being elongate in the direction of travel of said strip and of predetermined length whereby an are discharge will occur through each of said punctures for a predetermined length of time.

2. In a machine for perforating at preselected points an elongate strip of heat fusible material of high dielectric strength, the combination comprising a pair of oppositely disposed rotatable rollers adapted to engage said strip therebetween and to draw said strip longitudinally through said machine, means for driving said rollers, a puncturing means positioned forwardly of said rollers to puncture said strip at preselected points therealong as it passes through said machine, a pair of electrodes positioned to receive the punctured strip therebetween, said electrodes having opposed parallel, planar faces substantially parallel with the surfaces of said strip as it passes through said machine, said electrodes being of substantial surface area, at least one of said electrodes being of lesser width than the width of said strip, high voltage supply means operatively connected to said electrodes for impressing a potential therebetween and guide means for guiding said strip through the machine with the opposite side edges of said strip positioned outwardly from the corresponding side edges of said one electrode.

3. In a machine for perforating at preselected points an elongate strip of heat fusible material of high dielectric strength, the combination comprising a pair of oppositely disposed rotatable rollers adapted to engage said strip therebetween and to draw said strip longitudinally through said machine at a predetermined rate, means for driving said rollers, a puncturing means positioned forwardly of said rollers to puncture said strip at preselected points therealong as it passes through said machine, a pair of juxtaposed electrodes positioned between said rollers and said accepts puncturing meanssand adapted 'to :receiveasaid strip: therebetween, said electrodes havingvzope posed parallel, planar faces zpositioned to: .;be aligned substantially parallel *with 131118 surfaces of said strip, said electrodeszbeing :of substantial surface'area :and elongated in the direction of travel of-tsaid' strip, :at least .0118 :of said electrodes beingzof lesser width than said strip and arranged to receive said strip with thezr opposite edges lof-the strip extending :outwardly of each of .the opposite :side edges of said-one electrode, and circuit :means connected to said electrodes for impressing a potential between said electrodes greater than .the dielectric strength; of the air gap therebetween whereby :arc idischarge will occur between said electrodes through; the punctures in said strip ,as it passes 'betweenusaid electrodes.

:1. In 'a machine for perforating an elongate strip of 'a heat vfusible material having .high :dielectric strength, the combination comprising means :for drawing said sheet lengthwise through said machine, means fortpuncturing .aiplurality of openings staggered in a pluralityof parallel rows through said sheet, a pair of electrodes adapted to receive the punctured sheet'therebetween, each of said electrodes having a width greater than the spacing between the outside rows of said punctured openings, and circuit meansconnected to said electrodes for'impressinga high voltage therebetween whereby-a high voltage are discharge will occur through said openings to heat and fuse the annular edges of said punctured openings.

5. .In a machine for perforating'at preselected points an elongate strip of heat fusible material of high dielectric strength, the combinationcomprising means to draw said strip longitudinally through said machine,. a puncturing vmeans to puncture openings in said strip in av plurality of laterally spaced apart rows, a pair of juxtaposed electrodes positioned to receive the punctured strip therebetween, said electrodes having opposed parallel, planar faces positionedto-be substantially parallel with the surfaces of said strip, said electrodes being of substantial surface .area

andr-elongatedf'imthe direction of travel-of :said strip, :each' of said electrodes having a greater widthzthan the :spacing between the outsidezrows of punctured'iopenings, said electrodes :being positlonedto receive said 'rows or punctured openings therebetweemat leastone of said electrodes being of lesser width'than said strip and arranged to receive said strip with the opposite edges of the stripextending outwardly of each of the 'oppoe site -sides=edges of said one electrode; and circuit means connected to said'electrodes for impressing a potential between .said electrodes'greater than the dielectric strength of thezair gap therebetween whereby arc discharge will 'occurbetween said electrodes :through the punctures in said strip as it passes =between said electrodes.

*6; In a perforating machine of the classsdescribed, the combination comprising means for drawing a sheet to .be perforated through said machine, high voltage discharge means including a pair of electrode means having opposed parallel; planar faces-andadapted to receive said sheet .therebetween with said faces parallel torthe surfaces of said sheet and resilient ,meansfor urging-said electrodes-into contact with said sheet.

7. In a machine for perforating at preselected points an 'elongatestripof heat fusible material, means fordrawing said strip throughsaidmachine, means for puncturing said strip at .preselected points therealong as it passes through said machine, high voltage discharge means including a pair of electrode ,positioned to receive the punctured strip therebetween,.-said electrodes being elongate in the direction of travel of said strip, and means vadjustably supporting .one of said electrodes for adjustment relative to the other in said direction of travel.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2204, 573 Medwicket a1 June '25, I940 2;224,941 Weimer Dec, I7, 1940 2,338,069 Meaker et al. -Oct. '30, 1945 2,550,366 Meaker et a1 Apr. 24, 1951

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