US2914893A - Method and apparatus for packaging in a pre-stretched wrap of subsequently shrinkable material - Google Patents

Description

Decal, 1959 Filed March 11. 1952 RST 2,914,893

. C. J. BE METHOD AND APPARATUS FOR PACKAGING IN A PRE-STRETCHED.

WRAP OF SUBSEIQUENTLY SHRINKABLE MATERIAL 4 Sheets-Sheet 1 Snnentor f/e4. J. 554957 attorneys Dec. 1. 1959 c. J. BERST 3 METHOD AND APPARATUS FOR PACKAGING IN A-PRE-STRETCHED WRAP OF SUBSEQUENTLY SHRINKABLE MATERIAL Filed March 11, 1952 4 Sheets-Sheet 2 l I z 3nnentor c. J. BERST 2,914,393

FOR PACKAGING IN A PRE-STRET Dec. 1 1959 METHOD AND APPARATUS CHED WRAP OF SUBSEQUENTLY SHRINKABLE MATERIAL Filed March 11, 1952 4 Sheets-Sheet 3 attorneys C. J. BERST Dec. 1, 1959 2,914,893 PACKAGING IN A PRE-STRET LY SHRINKABLE MATERIAL CHED METHOD AND APPARATUS FOR WRAP OF SUBSEQUENT 1952 4 Sheets-Sheet 4 Filed March 11.

Snnentor 62924. J. BEEsT- Gttomegg METHOD AND APPARATUS FOR PACKAGING IN A PRE-STRETCHED WRAP F SUBSEQUENTLY SHRINKABLE MATERIAL Carl J. Berst, Madison, Wis.

Application March 11, 1952, Serial No. 276,014 Claims. (Cl. 53-30) This invention relates to a method and apparatus for packaging in a pre-stretched wrap of subsequently shrinkable material.

The wrap used is any one of the plastics with a memory which are elastic but, unlike natural rubber, require an appreciable time interval for stretching and contraction, usually with adefinite dwell in expanded form. Typical materials are the nitrile rubbers. See U.S. Patents 2,234,994 and2,502,240.

The method here involved is one in which the stretching' operation precedes packaging and the packaging is eifected without any necessity for tension on the wrap during the interval between the stretching and contraction of the wrapping material.

Assuming that the margins of the wrapping material are securely anchored about the article to be wrapped while the wrappingmaterial is in distended form, the

subsequent shrinkage of the wrapping material will draw the wrap firmly about the article. The resulting package is one in which the article is under permanent compression and the wrapper is under permanent tension such as to eliminate air from the package and to leave the wrapper substantially wrinkle-free about the article. The machine I have devised for wrapping packages in this manner includes an attachment to an otherwise conventional wrapping machine. In addition to the conven tional drag brake which holds the supply roll of wrapping material to lightly tension the web withdrawn therefrom, I supply an intermittently acting brake which substantially wholly arrests the rotation of the supply roll at all times except when web is being fed into the machine for wrapping purposes. This brake is applied before the web advance has been completed, so that the "final web advance into the wrapper is subject to a high degree of tension. A bight in the web is formed about a yieldable pulley and, with the supply roll fully stopped, the continued advance of the web is made possible only bythe yielding of this pulley. During the dwell of the feed rolls, the Web is held at one end by the feed rolls and at the other end by the supply roll which is maintained stationary by the operation of the special brake: With the ends of the web section thus fixed, the web is stretched by the gradual return of the yieldable pulley to its original position. Thus when the brake is released preliminary to the next advance of the feed rolls, a stretched length of web is fed into the wrapper.

The material used is well adapted for heat sealing and United States Patent O the heat used for sealing, supplemented, if desired by machine which are concerned with the present invention. Fig. 3 is a view taken in section on the line 3--3 of Fig.2.

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Fig. 4 is an end elevation of the mechanism shown in Fig. 2.

Fig. 5 is a side elevation of the mechanism shown in Fig. 2, portions of the machine frame being broken away.

Fig. 6 is an enlarged detail view in perspective of the supply roll, mandrel and brake.

Fig. 7 is a detail view in side elevation of the control parts used.

Fig. 8 is a diagrammatic view of the manner in which the control shown in Fig. 7 effects the intermittent operation of the brake shown in Fig. 6.

Fig. 9 is a detail view on the scale of Fig. 6 showing the mounting of the supply roll mandrel and the manner in which the brake is applied thereto.

Fig. 10 is a detail view taken in section on the line 10-10 of Fig. 9.

Fig. 11 is an enlarged detail view in section of the mounting for one end of the yieldable tensioning roll.

Fig. 12 is a view taken in section on the line 12-12 of Fig. 11.

Fig. 13 is a diagrammatic view showing successive packaging steps in the method of this invention.

The invention is not specifically concerned with the type of packaging machine employed, with the exception of those portions of the machine which pre-stretch the wrapper and thereafter heat seal it to facilitate wrapper shrinkage. These parts of the machine may be added to various types of commercial wrapping equipment. The machine shown, byway of example, includes a'wrapping table at 1 with a central aperture at 2 directly above the ram 3 which elevates the article 4 and the expanded sheet 5 of wrapping material through the table aperture to fold the sheet margins 6 and 7 downwardly, as shown in Fig. 13. After these margins have been folded into lapping positions beneath the article, and the ends have been folded as indicated at 8 in Fig. 13, a heat sealing bar 9 is used to heat seal the margin 10, and other heat sealing plates are used at 11 and 12 to heat seal the lapping ends of the wrapper. This heat, and any other heat to which the wrapper is subject, tends to expedite the contraction on to the article after the package has been completed as shown at 15. The original dimension of the sheet, prior to stretching, is indicated in dotted lines at 16 in Fig. 13. The full lines show the actual dimension of the sheet as stretched at the time of the wrapping operations above described. The lengthening effected by stretching amounts, in actual practice, to about one inch in each foot of both the longitudinal and lateral dimension of the sheet.

The stretching, as well as the ensuing packaging, may be done by hand. In the machine operation, I employ a tension of 40 to 50 pounds on the web and maintain this tension for an appreciable period of several seconds. The maintenance of tension need not be as long as the interval required for wrapping, as most of the synthetic webs having the memory characteristic will tend to maintain a dwell, prior to contraction, for as long a period as the duration of the tension. One nitrile web, for example, begins elongation under a pull of 25 pounds and will extend about 10% in eight seconds under this tension. By using a higher tension, the time required for the stretching of the web may be reduced. In any event, the web will hold its stretch for a period approximating the period for which it was subjected to tension. While the web retains its stretch, a sheet may be cut from it and the sheet may be used to wrap an article so that, as the wrapping material thereafter shrinks, the article will be subjected to compression and the material will remain under tension about the article. It is desirable that the lapping margins of the wrapping material be mutually adherent to maintain the tension. Where this adhesion-is effected by heat sealing, the shrinkage of the wrapper will be accelerated and I have found it expedient to subject the whole wrapped package to radiant heat, immediately following the heat sealing operation, so that all portions of the wrapper will uniformly commence to shrink at an accelerated rate. Bulbs for radiating heat are shown at 17 and 18 in Fig. 13.

In the conventional machine illustrated, the web 20 is fed into the wrapper by feed rolls 21, 22 (Fig. 2 and Fig. 3) and by belt conveyors 24. The advancing web passes a stationary shear blade 25 with respect to which the shear blade 26 is reciprocable to sever the sheet 5 from the advanced end of the web.

In order to stretch the web prior to its advance into the wrapper, as above described, the conventional wrapping machine has been modified in the following particulars, which are supplied by way of exemplification:

The supply roll 28 is mounted on an expanding mandrel 29. The jaws 30', which form a part of the present invention, are expanded into the core 31 of the roll by manipulation of a nut 32 at the free end of the mandrel.

At its other end, the mandrel is shouldered at 33 and its reduced end portion 34 is rotatable into bearing 35 at the lower end of an arm 36 pendant from a supporting bracket 37. The mandrel has, conventionally, brake shoes at 38 at the outer ends of radial fins 39, the tapered end portions 40 of which project into a bore 41 in the end of the mandrel. Here they are engaged by the tapered end 42 of an expanding screw 43 which is externally accessible for adjustment of the frictional drag to which the mandrel is subject. The brake shoes operate in a counterbore 44 of bearing 35 as best shown in Fig. 9. The purpose of the frictional drag thus applied is to maintain sufficient tension on the web to prevent overrun following sucessive advances of the web from the supply roll.

For the purposes of the present invention, an intermittently operable and more positive brake is added to the continuously effective drag brake above described. The arm 45 connected with the mandrel suspending link 36, as best shown in Fig. 4, carries a mounting plate 46 to which is connected at 47 one end of the split ring 48 which comprises the brake band. Any desired lining may be used at 49. The free end portion 50 of the brake band has a lug 51 connected with bell crank 52. Fastened to the other arm of the bell crank is the connecting rod 53 of pneumatically operable piston 54, which reciprocates in cylinder 55 mounted on the plate 46 as shown in Figs. 6 and 8. In the lowered position in which the connecting rod 53 is shown in Fig. 6, the tension on the brake band is relaxed and the mandrel is free to rotate. In the raised position in which the piston 54 is shown in Fig. 8, the bell crank is caused to oscillate counterclockwise as viewed in Fig. 6, thereby tightening the band 48 upon mandrel 29 to arrest mandrel rotation.

The piston position is determined by a rotary valve 57 which is oscillated approximately 90 by the armature rod 58 of a solenoid 59. The rod is normally advanced by the bias of spring 60 to the position shown in Fig. 8, in which position the valve 57 places the air supply line 61 in communication with pipe 62 leading to the lower end of cylinder 55. In this position of the valve, the pipe 63, from the upper end of cylinder 55, is placed in communication with the air exhaust line 64. Thus the brake 48 is normally applied to the mandrel 29 to preclude rotation thereof. When the solenoid 59 is energized and the rod 58 is drawn downwardly against the bias of spring 60, the valve 57 is oscillated for about 90 to place pipe 63 in communication with the air line 61 and pipe 62 in communication with the exhaust line 64. This abruptly forces piston 54 to the bottom of cylinder 55, thus releasing the brake. The release of the brake is so timed to the operation of the web feed as hereinafter descirbed that the brake is released momentarily prior to web advance and is re-applied before the web advance is completed. Thus no friction other than that of the drag brake shoes 38 resists the initial rotation of the supply roll 28, but the final rotation of such roll occurs before the complete length of web has been fed into the wrapper so that the completion of the web feeding operation is possible only in consequence of the yielding of the roll or pulley 65 about which the web is trained as best shown in Fig. 3.

The yieldable roll or pulley 65 may be mounted in the manner shown in Fig. 11. Its reduced end portion 66 fits into a bushing 67 in the arm 68' of a slide 68 which is guided on a rod 69. It is also apertured to receive the adjusting screw 70 into bracket 71 by which rod 69 is supported. The screw 70 is threaded in a nut 72, also guided on rod 69, and socketed at 73 to provide a seat for a compression spring 74 which supports the slide 68, thereby also supporting the yieldable tensioning roll 65.

After the bight 75 of web 20 passes over the yieldable tensioning roll 65, the web is carried downwardly to pass between feed rolls 76 and 77 and other feed rolls at 78 and 79. These pairs of feed rolls, together with the feed rolls 21 and 22 of the wrapper, are intermittently actuated for web advance by means hereinafter to be described, and their actuation continues after the motion of the mandrel 26 and supply roll 28 has been arrested by brake 48. The continued withdrawal of the web 20 after the supply roll 28 is at rest is accommodated by the yielding of the tensioning roll 65 against the compression of its supporting frame 74, it being understood that the structure shown in Figs. 11 and 12 is duplicated at the other end of such roll.

By adding the feed roll pairs 76, 77 and 78, 79, which are spaced from the main feed rolls 21 and 22, Imake it possible to stretch the web laterally as well as longitudinally through the operation of the obliquely disposed roll pairs 80 and 81 at one side of the web and 82, 83 at the other side thereof. The oblique disposition of these rolls as best shown in Figs. 2 and 3, is such that as the web advances to the left, these rolls pull its side margins outwardly, thus giving lateral stretch. This stretch is maintained during the period of dwell between successive intervals of operation of the various feed rolls.

The various feed rolls are desirably synchronously driven. Any desired means may be used for this purpose but, by way of exemplification, I will describe the means actually employed.

The wrapping machine is supplied with a cam shaft 84 carrying at 85 a cam for the arm 86 which is connected by link 87 with one of its folding blades. At the end of shaft 84-, the fly wheel 88 is provided with a crank pin 89 for a crank 90 connected with a rack 92 operating in a guideway 93 and meshing with a pinion 94. As the fly wheel rotates (in synchronism with the wrapping operations of the wrapping machine), the rack 92 is reciprocated upwardly once in each wrapping cycle and is then retracted downwardly as viewed in Figs. 2 and 7.

The pinion 94 is concentric with a driven shaft 96 to which it is connected in one direction of operation by an overrunning clutch 97. Bevel gears 98, 99 connect shaft 96 with the shaft 100 of the lower feed rolls 22. The opposite end of shaft 100 is connected by chain 102 with the shaft 103 of feed roll 79. This shaft has a gear at 104 meshing with an idler 105 which communicates power to another idler gear 106 which in turn meshes with gears 107 and 108 on shafts 109 and 110, respectively, of feed rolls 78 and 76 as best shown in Fig. 5. Shaft 103 and shaft 111 (feed roll 77) also carry sprockets 112 and 113, respectively, over which passes a chain 114 communicating motion to a sprocket 115. From this sprocket, as best shown in Fig. 5, motion is communicated by belt 116 to the shaft 117 on which the oblique feed roll 83 is mounted. Sprocket 118 on convenient to control the supply. roll brake 48 from arm diagrammatically in Fig. .8, the. closing of the switch will momentarily release brake 48 to permit the supply roll mandrel 29 to rotate. As soon as arm 86 commences its forward movement, the switch 125 is re-opened to deenergi ze the solenoid 59, whereby spring 60 moves valve57 to a position such that the brake is re-applied.

Thus the-machine performs mechanically the method operations which might otherwise be performed by hand and which includes first, the relatively free advance of the web from the supply roll to deliver previously stretched portions thereof into the wrapper, where such previously stretched portions are cut off and used for wrapping before they can contract.

Meantime, as the web advances, the supply roll is rotating relatively freely at first, subject only to the conventional friction drag, but before the feeding operation has been completed, the supply roll is abruptly arrested and the continued feeding movement of the web can occur only in consequence of the yielding of the tension roll at 65 about which the bight 70 of the web is trained. During the ensuing dwell, after the feeding operation has stopped and the package is being wrapped, the tension roll 65 is maintaining the web under tension and as the web stretches, this roll will rise to maintain the tension.

In addition to the longitudinal tension achieved in ,this manner, the web is also subjected in the course of each advance to lateral tension by the pairs of oblique rolls as above described. The lateral tension is also maintained during the dwell so that when each successive length of web isvfed into the wrapper, it is tensioned both longitudinally and laterally.

I claim.

1. The method of packaging an object in a synthetic plastic film of the type which is elastically expansible under tension and slowly contracts after an appreciable dwell following release of such tension, which method comprises the prolonged tensioning of a length of web of such material for a sufficient interval to effect the stretching thereof to a materially increased area, releasing said tension and severing from such web a sheet including a portion of said stretched web length, wrapping said object in the severed sheet while said sheet retains its increased area, and anchoring the margins of said sheet about the object before the material of said sheet is fully contracted whereby the contraction of the material of the sheet about the object after the wrapping operation has been performed and said margins anchored maintains the sheet under tension and the object under compression.

2. In a machine for wrapping objects in films which may be distended under tension and which are of a slowly contractible type capable of holding its distended form for an appreciable interval after such tension is released, the combination with a supply roll mandrel provided with a brake adapted, when applied, substantially to arrest mandrel rotation, of a feeder for withdrawing web from the supply roll on said mandrel, means for the intermittent operation and alternate dwell of the feeder, synchronized means for the control of said brake, said last means being adapted to apply the brake while the feeder continues in operation and to release the brake immediately in advance of each operation of the feeder, leaving the brake applied during the feeder dwell, and a tensioning roll movable across the path of web advance and about which a bight of said web is trained between the mandrel and the feeder, said tensioning roll having a yieldable mounting for supplying web out of said bight to the feeder during the continued operation of the feeder after said brake arrests mandrel rotation, and

means biasing said mouting in a direction to increase the bight of 'saidweb by stretching the Web during the dwell of said feeder and the continued application of said brake. r

a 3. The device of claim 2 in further combination with a second feeder spaced from the feeder first mentioned and means between said feedersfor drawing in opposite lateral directions the respective side marginal portions of said web, whereby the web may be subjected to lateral as well as longitudinal tension during the feeder dwell. I

4. The device of claim 3 in which said laterally operable tension means comprises obliquely disposed pairs of rolls acting divergently outwardly upon web marginal portions passing between the rolls of the respective pairs.

5. A feeder for a wrapping machine comprising in combination a pair of feed rolls having means for their intermittent rotation and alternate dwell, whereby to intermittently advance the length of web engaged between said rolls, a mandrel for a supply roll for said web, a tensioning roll offset from a direct line between the supply roll and the feed rolls aforesaid and about which a bight of said Web is trained, yieldable mountings for the ends of the tensioning roll, said mountings being yieldable in a direction to decrease such bight and being subject to a bias in an outward direction tending to increase such bight, means for exerting such outward bias upon the tensioning roll mounting, a drag brake acting on said mandrel to prevent overrun thereof following the operation of the feed rolls in a web withdrawing direction, a second brake movable to and from mandrel arresting position, and means for applying said second brake during continued operation of said feed rolls, maintaining said second brake applied during the dwell of said feed rolls and releasing said second brake upon the initiation of feeding operation of said feed rolls, whereby said tensiong rolls is retracted against said bias upon the application of said second brake to supply from said bight web material during the continued operation of said feed rolls, said tensioning roll, by-reason of its said bias, exerting stretching tension on said web to increase its said bight during the dwell of said feed rolls.

6. The device of claim 5 in further combination with a second set of feed rolls spaced from the first mentioned feed rolls in the direction of web advance and lateral tensioning means disposed between the first and second sets of feed rolls in engagement with opposite marginal portions of the intervening web.

7. The device of claim 6 in which said lateral tensioning means comprises pairs of rolls limited in axial extent to engage the web only adjacent its lateral margins, the rolls of the respective pairs being obliquely disposed in outwardly divergent planes so that as they rotate in engagement with the web margins they will tend to draw such margins oppositely.

8. The device of claim 7 in further combination with driving connections for the said pairs of lateral tensioning rolls mechanically connected with the first and second feed rolls aforesaid for synchronous operation.

9. An attachment for a Wrapping machine having feed rolls and a reciprocable folding blade and an actuating arm therefor, said attachment comprising a mandrel support, a supply roll mandrel mounted on the support and from which a web of wrapping material may be drawn by said feed rolls, a tensioning bar materially offset from the direct path between a mandrel and the feed rolls, supports for the ends of said bar,-ways extending transversely to said path and in which said supports are guided 7 for reciprocation to and from said path, means biasing said supports outwardly away from said path, a mandrel arresting brake, and means for the intermittent advance and dwell of said feed rolls, and means comprising a timing switch on said arm, and actuating connections controlled by said switch for applying said brake during the continued advance of the feed rolls and releasing said brake upon the initiation of feed roll advance. 7

10. A machine for wrapping objects in a film comprising means for stretching in tension a resiliently stretchable wrapping film of a slowly contractible type capable of holding its distended form for an appreciable interval after such tension is released, means 'for releasing said tension and means for severing the film into a sheet, means for applying said film sheet during said interval about an object to be wrapped, and means for anchoring the free margins of said film sheet before said film sheet contracts, whereby the subsequent contraction of said film sheet will draw the film sheet tightly about the wrapped object, said stretching meanscomprising means 2,072,330 Grady et a1. Mar. 2, 1937 2,178,922 Smith .NOV. 7, 1939 2,260,064 Stokes Oct. 21, 1941 2,490,781 Cloud Dec. 3.1, 1949 2,549,122 Osterhof Apr. 17, 1951 2,597,041 Stokes May 20, 1952 OTHER REFERENCES Mechanical Behavior of Higher Polymers, by- Turner Alfrey Jr., 1948 (received in Patent Ofiice April 21, 1948), published by Inte'rscience Publishers, Inc., New

20 York; cited part: pages 446 to 450, inclusive.

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