US3396887A - Vacuum control for moving sheets - Google Patents

Description

Aug. 13, 1968 BABE VACUUM CONTROL FOR MOVING SHEETS 2 Sheets-Sheet 1 Filed March 16. 1966 FIGJA s- '3. 1968 R. BADE 3,396,887

. VACUUM CONTROL FOR MOVING SHEETS Filed March 16. 1966 2 Sheets-Sheet 2 I VACUUM I PUMP United States Patent "ice VACUUM CONTROL FOR MOVING SHEETS Rudolf Bade, Friedrichsgabe, Post Harksheide, Bezirk Hamburg, Germany, assignor to W. R. Grace & Co.,

Duncan, S.C., a corporation of Connecticut Filed Mar. 16, 1966, Ser. No. 534,703 Claims priority, applicatio6n9Germany, Apr. 1, 1965,

4 Claims. (51. 226-1) ABSTRACT OF THE DISCLOSURE This invention relates to a device and a process for controlling moving sheets. In one aspect, the invention relates to controlling the speed and optionally the stretching or straining of moving sheets which are relatively impermeable to gases.

In processes where sheets, e.g., film, textile materials, paper or other materials, are employed, the problem is often encountered that the speed of the sheets cannot sufficiently be controlled by means of the actual driving mechanism so that additional brakes are required. Thus it is often necessary to strain the sheets by braking in order to prevent fluttering and wrinkling and to obtain satisfactory motion properties. When using stretchable sheets, it is moreover often necessary to stretch these sheets more or less and to control this stretching accurately. For this purpose, suitable brakes are required.

Heretofore, braking of moving sheets has been almost exclusively effected by passing the sheets through pairs of rolls or three cooperating rolls where the sheet movement is slowed down by corresponding pressure of the rolls against each other. Such relatively complicated roll brakes are mostly controlled by electromechanical means and thus require many moving parts which are subject to wearing. The principal disadvantage of. these brakes is, however, that it is difiicult to obtain a precise control of the braking effect. Moreover, the grip of such roll brakes with the film is very sudden and sharp so that the sheet tends to tear if it does not consist of a highly elastic material. Thus, there is a wide demand for -a process effecting a smooth, easy and accurately controllable braking of moving sheets.

It is an object of the invention to provide method and apparatus for controlling moving sheets.

Another object of the invention is to provide method and apparatus for controlling the speed of moving sheets or webs.

Yet another object is to provide method and apparatus for stretching webs.

These and other objects of the invention will be readily apparent to those skilled in the art from the following disclosure, drawing and appended claims.

These objects are broadly accomplished by passing the web, which should be relatively impermeable to gases, over and in sliding engagement with a stationary member having openings therein which are connected to a vacuum pump. The web is passed over the openings in such a way that they are effectively sealed from the ambient atmospheric pressure by the sliding film. By adjusting the amount of vacuum, the frictional engagement of the web Patented Aug. 13, 1968 or film with the stationary member is controlled so as to provide the desired resistance to movement of the web.

In one embodiment, the web is pulled over the stationary member (by any suitable driving force) and the vacuum applied through the opening in the stationary member is increased to a value sufficient to cause a stretching of the Web.

The use of vacuum or fluid pressure to move or control moving sheets is known; however, it has been the practice to employ a perforated moving surface which engages the film and transport it a finite distance. For example, a perforated roller has been used with the interior connected to a means for creating avacuum therein. A principal disadvantage of such a system is that a large number of holes are exposed to the atmosphere thus overloading the vacuum pump.

The device disclosed herein is stationary. There are no moving parts. The number of holes and position thereof is such that all holes are sealed from the ambient atmosphere by the moving film.

In a preferred embodiment, the holes are positioned in a lower portion of a channel or recess in the surface of the stationary member so that the film does not actually contact the holes but is drawn part way into the channel by the applied vacuum. This assists greatly in adjusting speed because the film surface exposed to the vacuum is much greater than would be the case where the film passes directly over the holes.

Preferably, the sheet is passed over a stationary guide surface which is plane or convex transverse to the direction of motion, especially a closed hollow cylinder, and is provided with one or several ports connected commonly via one or several regulating means with suction lines. By controlling the vacuum at the suction ports, the moving sheet can be strained or stretched, if desired. The degree of stretching is preferably controlled via the vacuum at the suction ports by an automatic mechanism measuring the speed of the sheet or the distance of marks provided on the sheet.

The brake effect of the device according to the invention is based on the fact that the moving sheet is pressed against the guide surface by the vacuum at the suction ports and slowed down by the resulting friction. The sheet is suitably guided in such a way that it covers all suction ports and thus seals them against loss of vacuum. The brake power is dependent on the degree of vacuum and in addition on the size and number of the suction ports in the guide surface as well as on the characteristics of the sheet material, i.e., especially on its gas permeability and flexibility.

For regulating the brake power and therewith controlling the straining or stretching of the sheet, automatic or hand-operated valves connected at one end with the atmosphere and consisting preferably of three-way valves are provided in the suction line.

The present invention provides a number of advantages over the roll brakes previously used. When connecting the suction ports with the suction line, the full subpressure is not reached suddenly but with a short time lag so that the brake effect on the moving sheet is not sudden and sharp. Thus, a smooth and careful speed reduction is possible, which is especially important with sensitive materials which tend to tear under strong stress. Moreover, with the device according to the invention, an extraordinarily accurate and precise control of the brake effect is possible by regulating the subpressure at the suction ports. In addition, this is possible in an especially simple manner since for this purpose only a normal regulating valve is required which can alternatively be operated by hand or automatically. Further the regulating means, i.e., generally a regulating valve, is the only moving part associated with the novel controlling device so that the device itself is notsubject to any wearing and is thus unusually re-j 1 liable. I

The invention is further illustrated with reference to the accompanying drawings.

FIGURE 1 is a perspective view, partlyin section, of an embodiment of the controlling and braking device;

FIGURE 5 is a diagrammatic view of the sheet motion according to one example wherein the. sheet is strainedand controlled according to this invention at twopoints;

small ports 7. This is preferred to usinga single longslotshaped port since the moving sheet maybe drawn into the slot. However, inorder to distribute the suction power uniformly over the entire channel 3, this channel has a step-like cross section. The sheet isonly drawn into the upper enlarged portion 8 of the channel'3so that there- 4 below, achannel-shaped hollow space 9'is formed which is connected via the suction ports 7 with the suction line I and thus'provides 'a uniform vacuum.

FIGURE 6 is a diagrammatic view of the. sheet motion according to another example wherein an? automatically. controlled stretching of the sheet is obtained by means i of a device according to the invention.

In the embodiment shown in FIGURE 1, a closed" hollow cylinder 1 is used as a guide surface. Thehollowy cylinder 1 is providcdin the area contacting asheet 4.

with a channel 3 containing. suction ports 7 annis connected via. line 5 and the regulating device 6-with a vacuum-creating device, e.g., a vacuum pump .(not shown).

As soon as a vacuum exists in the hollow cylinder 1, sheet 4 is drawn to the suction ports and pressed against the cylinder surface. In order to keep the vacuum loss at a minimum, the length of channel 3 provided .with bore holes 7 is less than the width of the sheet so that the sheet 4 seals the suction ports almost completely. In order to enlarge the contact surface between themoving sheet 4 and the hollow cylinder 1, the sheet is passed under the two rodor roller-shaped deflection elements 2, 2a positioned in the direction of movement before and behind the hollow cylinder and in parallel thereto. Thus the sheet 4 closely engages the surface of the hollow cylinder in a broad area. The cylinders 1, 2 and 2a are mounted to any suitable support means such as support frame 12. The brake effect of the device is primarily dependent on the degree of vacuum and thus also indirectly on the gas permeability of the moving sheet. The

lower the gas permeability of the sheet 4, the greater is the vacuum and thus the brake effect. Therefore, a strong brake effect can only be obtained with practically gasimpermeable materials, e.g., plastic films. For a given sheet material, the brake effect can be very precisely controlled in a wide range by a corresponding regulation of the vacuum.

FIGURE la represents a modification of the device of FIGURE 1 wherein two stationary guide members are employed in series, each having at least one channel with holes in the bottom portion thereof. Except for the addition of a to the numeral, the numerals identify elements similar to those in FIGURE 1. Preferably, the top element 2 is rotatable, but 1 and 2a are fixed. Preferably, stationary guide member l'has 2 channels with bore holes while guide members 2a has one channel 3'; all channels being in direct contact with the film so as to prevent loss of pressure; In addition, each of 1' and 2a are connected by conduits 5a and 5b to a vacuum pump.

FIGURE 2 shows a section A--A through the device of FIGURE 1. It can be seen that due to the guidance under the deflection elements 2, the sheet 4 closely engages a substantial part of the cylinder surface and thus seals the suction ports against the atmosphere. In 'a preferred embodiment (see FIGURE 3), the guide surface is provided with a recessed channel3 having one or more slot-shaped or circular suction ports 7. Preferably, the lowest point of the channel 3 isprovided with. several The device in FIGURE 4 comprises a plane guide surface 10 which is provided with several lines ofsuction ports 11 arranged diagonally to the direction of motion. Thus the sheet 4 is pressed against the. guide surface 10 by a great number of suctionports and is subject to the guide surface 10 and is subject to a particularly strong brake effect, especially if'a vacuum pump with high suction capacity is used.

I The numerous possible applications of the present in vention are illustrated by the following two examples. According to FIGURE 5, a sheet is fed from a supply roll to a processing machine. Itfrequently occurs that I the" sheet is not drawn off continuously with uniform 1 speed but discontinuously in accordance with the operating cycles of the machine. Due to its inertia, the heavy no pullf is applied to the sheet 24. Since it would lead supply roll has the tendency to continue to rotate when i to sagging or fluttering of the sheet, this must be slowed down behind the roll 20. According to the invention, this is achieved by passing the sheet over a deflection roll 22 and from there around a hollow cylinderZl having suction ports in the area of contact. The sheet 24 can run only when a pull overcoming the brake effect is applied in the direction indicated by the arrow. A second device 23 corresponding to the device 21 is provided directly before the pulling device 27 and serves for passing the sheet tautly and without fluttering and wrinkling into the driving rolls. The control of the vacuum in the hollow cylinders 21 and 23 can be effected separately or in common. This to brake the film more or less and to stretch it, if required, in order to achieve an accurate superprinting of the various colors. The control of this braking or stretching is generally effected by means of photoelectric cells responding to metering marks on the film surface.

A similar problem is encountered in packaging machines when plastic film printed with labels is used. The machine requires a certain amount of film but when printing the films with labels, the required exact distance cannot be kept constant. This is overcome by printing the film in the minus range and stretching it automatically to the required length during the packaging operation. A constant adjustable stretching force causes the film to be stretched to almost exactly the required dimension. The.

control of the exact stretching is performed by a photoelectric cell which records during passage of the film sheet whether the film now corresponds exactly to the dimension required by the machine. If this is not the case, the stretching force is continued until the exact dimension is obtained whereupon the stretching force is interrupted by the photocell. With the conventional roll brakes great difliculties are encounteredwhen the films employed have only a limited elasticity or stretchability. Since roll brakes respond very suddenly, it frequently occurs that the moving film is torn and that the automatic process is stopped thereby. This difficulty is overcome in a simple way by by heat-sealing with a printed film. The film is passed over driving rolls 31 and a dancer roll 32 connected with a microswitch (not shown) and a magnetic coupling (not shown) for driving the rolls 31 and then to a device 33 corresponding essentially to that one shown in FIGURE 1. The most important part of this device is a hollow cylinder 36 serving as a film brake, the brake effect thereof being controlled by the photocell 34. The film runs past the photocell 34 via a deflection roll 35 into the packaging machine 37. The photocell 34 responds to the metering marks on the film and prolongs the brake impulse, i.e. the period during which the hollow cylinder 36 is connected with the vacuum line, until the required stretching is obtained. The action of the film brake of this invention is so smooth that tearing of films, even those with low elasticity, can not occur. The control is effected in a simple manner in that the photocell 34 switches an electromagnetic three-way tap (not shown) by which the hollow cylinder 36 is connected either with the vacuum line or with the atmosphere.

While certain examples, structures, composition and process steps have been described for purposes of illustration, the invention is not limited to these. Variation and modification within the scope of the disclosure and the claims can readily be effected by those skilled in the art.

I claim:

1. A process for controlling a relatively gas impermeable, moving sheet which is supplied from a source having sufficient mass to be diflicult to immediately brake to a complete stop comprising the steps of:

(a) sliding said sheet over and in contact with two stationary guide surfaces as said sheet is pulled by .a driving force from said source, each of said guide surfaces having at least one opening in the area of contact;

(b) applying a subatmospheric pressure to said openings to attract said sheet toward said opening and thereby frictionally engage each of said surfaces;

(c) adjusting said pressure to control the amount of said friction and thereby regulate the speed of said sheet over said surface; and,

(d) simultaneously discontinuing said driving force and decreasing the applied atmospheric pressure to the opening in both of said surfaces so that the sheet remains taut even though said source continues to supply sheets for a small finite time.

2. Apparatus for controlling moving sheets compris- (a) at least one stationary, hollow, cylindrical, guide member having at least one channel in its surface parallel to its longitudinal axis and transverse to the direction of travel of said moving sheets, the cross section of said channel having a stepped cross section wherein the top of said channel is wider than the bottom;

(b) a plurality of openings in the bottom of said channel, said openings being distributed along the length of said channel;

(0) means for guiding said sheet over said channel and in sliding engagement with said member;

(d) means for applying a subatmospheric pressure to the interior of said :guide member so that said sheet will be attracted towards said openings by the action of said subatmospheric whereby said sheet seals the openings from the ambient atmosphere.

3. The apparatus of claim 2 wherein said cylindrical guide member has two parallel channels in its surface, each channel having a plurality of openings distributed along its lowermost portion.

4. The apparatus of claim 2 including two stationary cylindrical guide members and including means for applying a subatmospheric pressure simultaneously to the openings in the channels of each guide member.

References Cited UNITED STATES PATENTS 3,091,794 6/1963 Pillsbury 226-97 X 3,231,668 1/1966 Nishiwaki 22695 X 3,227,348 1/ 1966 Jenkins 226-196 M. HENSON WOOD, JR., Primary Examiner.

R. A. SCHACHER, Assistant Examiner.

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