US2796223A - Web tensioner - Google Patents

Description

June 18, 1957 Filed July 22, 1954 I A. L. DETWEILER WEB TENSIONER 4 sheets sheet I.

A. 1.. DETWEILER 2,796,223-

Jl me 18, 1957 WEB TENSIONER 4 sheo'tssheet 2 Fiied July 22, 1954 June 18, 1 A. L. DETWEILER 2,795,223

WEB TENSIONER Filed July 22, 1954 4 Sheets-Sheet s June 18, 1957 v DETWEILER 7 WEB TENSIQNER 7 Filed July 22, 1954 4 Sheets-Sheet 4 .of moving webs, as fabric,

WEB TENSIONER Abraham L. Detweiler, 'Barriugton, 111.

Application July 22, 1954, Serial No. 445,114

14 Claims. (Cl; 242-75.3)

This invention relates .to means for handling a moving web and more particularly to improved means for tensioning a moving web.

In apparatus for handlingv a moving web, particularly at high speeds, it is usually necessary to provide means for insuring that the web is constantly maintained under the proper tension in order to prevent jamming or tearing. The tensioning means must'operate rapidly to compensate for rapid variations which may occur in .the travel of the web.

An example of a situation where such rapidly variable tensioning is necessary is found in high speed rotary printing presses to which paper is delivered from a roll that is out of round. It is readily apparent that in acase of this nature the speed and tension of-the paper will vary considerably during each revolution of the roll and that the tensioning means must have a very rapid response .with the handling of a paper Web as in aprinting press,

it is to be understood that it may be used with-other types sheet plastic, sheet rubberand the like. 7

As a corollary to the provision of a tensioning apparatus having a short response time in --order to permit it .to follow rapid variations in the speedandtension of the web, the apparatus shouldhave a low inertia. A tensioning apparatus with low-inertia will be better able .to compensate for rapid variations in the speed and :ten-

sion of the web and will have less tendency to break theweb.

One type of tensioning-apparatus which has been in common use for many years includes aresiliently-mounted roller over which the web passes, the resilient mounting of the roller providing no-tension in the web. The

roller and mounting are necessairly heavy; and if the mounting allows movement of the roller sufficient to take up any appreciable slack, the inertia forces are such that response is too slow to cope with rapid fluctuations in rate of web-travel, regardless of how sensitive a detector element is incorporated in the system.

it is amajer feature of this invention-to provid-e tension- 1 ing means for a moving web, having-ahegl-igible inertia with the resulting extremely fastresponse and minimization of the danger of tearing A particular feature is the provision, in an apparatus for handling a moving Web, of means for tensioningthe web comprising means for supporting a portion of the web and means for creating a differential pressure Ion opposite sides of such portion of the web. Anotherfea- '2 ture is the provision of means for supporting a portion of the web at two spaced points along the length thereof and means for creating a differential pressure 'on opposite sides of the web intermediate the points of support to cause the web to form a bulge therebetween, constantly maintaining tension .in the web.

A further feature is the provision of means for automatically reducing the pressure dilferential when the bulge exceeds a predetermined size.

Another feature is the provision of means for applying a variable braking force to the web in accordance with the size of the bulge therein.

Still a further feature is the provision of surface means adapted to be engaged by a variable portion of the bulge, the radius of .the bulge decreasing as the length thereof increases.

Yet another feature is the provision of means operable as the function of the size of the .bulge to affect .or control the speed of the web.

"Still another feature is the provision of means for supporting a portion of the web at spaced points along the length ithereof, means defining an enclosure adjacent at least a portion of the web and means connected to the enclosure for'creating :a differential pressure on opposite sides of at least that part, of the portion of the web adjacent the enclosure.

These featuresare combined in a simple system with a high degree of inherent stabilit thus eliminating any necessity for extremely sensitive controls and accurate adjustments. The invention may be used with a method of control'such as is indicated herein or it can be used with controls existing on presses.

Further features and advantages will readily be apparent from the followingspecification and from the drawings, in which:

Figure l is a fragmentary side. elevational view of a web tensioning apparatus according to this invention, with a portion broken away;

'Figure 2 is anpenlarged elevation-a1 view taken the line 22-92 of Figure l Figures 3, 4, 5, 6, 7, 8, 9, l0 and 11 are side elevational views similar to Figure 1 showing modifications of the invention; and

Figure 12 is a side elevational view similar to Figure l-showing an automatic control arrangement.

Referring now to Figure 1 of the drawings, reference along numera1 20 indicates a web of sheet material, such as paper, being fed from a-roll 21 carried on shaft 22 to some desired utilizing apparatus, such as a rotary printing press (not shown). After the paper web 20 leaves roll 21, it passes over a pair of support members spaced along the length thereof, as roller members 23 and 24. A pair of side plates 25 and 26 are positioned on either side of web 20 between rollers 23 and 24 and, together with plate member 28, define an enclosure surrounding the portion of the web between'the rollers and extending outwardly therefrom in a direction generally perpendicular to'the plane of'the web.

Side plates 25 and 26 may be spaced apart a sufiicient distance to provide a small clearance, as up to an inch or so between each of the plates and the respective adjacent edge of web 26 (Figure 2). A blower 29 has its outlet 2% connected to an opening 28a in plate member 28; the blower may be driven by'any suitable means such as electric motor 3%}.

When the blower 29 is in operation the air delivered therefrom enters the enclosure defined by side plates 25 and 26 and plate member 28 raising the pressure therein above that of the atmosphere outside. The pressure differential'then existing on the opposite surfaces of web 20. causesthe web to form a bulge 20a extending into the "space between the side plates 25 and- 26 intermediate support members 23 and 24. The size of this bulge will vary according to the tension in web 20 as determined at least in part by the difference between the rate at which the web is delivered from roll 21 and the rate at which it passes on to further apparatus, as the aforementioned printing press. The web 20 itself is the only element of this system whidh moves in maintaining the desired tension. From this it is apparent that the system will respond quite rapidly to variations in the speed of the web, constantly maintaining the desired tension by varying the size of the bulge 20a. there are no heavy moving parts pulling against the web, there is little or no chance of it tearing or breaking during rapid fluctuations.

A pair of plates 31 and 32 are pivotally mounted between side plates 25 and 26 on the outside of the bulge 20a in the web as by pivot rods 31a and 32a respectively. (The term outside of the web will be used herein with reference to the enclosure defined by side plates 25 and 26 and plate member 28.) The plates 31 and 32 are positioned so as to be contacted by the bulge 20a in the web as it increases in size; in Figure 1, the bulge is shown in contact with a portion of plate 31. Plates 31 and 32 act as brake members and when the bulge 20a increases to such an extent that it contacts these plates, the friction therebetween reduces the pull of the web on roll 21 automatically reducing the rate of delivery of paper. This braking action compensates to a certain extent for the variations in the tension in the web and reduces the amplitude of the variations in bulge size necessary to maintain tension in the web. Plates 31 and 32 are pivotally mounted so that the angle thereof with respect to the bulge portion 20a of the web may be varied to provide different control characteristics, as may be desired.

In order to obtain the maximum utilization of the pressurized air delivered by blower 29, plate member 28 may be sealed to the web as by means of a [felt strip 33 at either end thereof and bearing against web 20 where it passes over the roller members.

It is preferable that the air from blower 29 be delivered tangentially against web 20, and for this reason the. outlet 29a of the blower is positioned adjacent roller member 23. The air delivered by the blower rotates within the enclosure providing a greater force on the web than would be obtained if a stream of air were directed straight toward it; plate member 28 is preferably curved as shown in the drawing to enhance this rotating action of the air within the enclosure.

The difference in the air pressure within the enclosure and the pressure outside, which may be termed the differential pressure applied to the web, determines the hoop tension in the web. The hoop tension (T) in pounds per inch width of web is equal to the differential pressure (AP) in pounds per square inch times the radius (R) of the bulge in inches (T=APR).

A study of the relationship between the differential pressure and the hoop tension shows that if the tension within the bulge of the web decreases as the depth of the bulge increases the operation will be stable. (The depth of the bulge is defined as that distance shown as dimension D, Figure 10.) If, however, the tension is permitted to increase as the size of the bulge increases, opera tion will become unstable.

One means for preventing the occurrence of such unstable operation is illustrated in Figure 3. Here, web 49 passes over rollers 41 and 42 and through an enclosure including side plates 43 and 44 (side plate 43 being broken away). Blower 45 directs a stream of air tangentially at web 40. The position of the bulge 40a of the web shown in broken lines illustrates the situation when there is a small amount of slack in the web. In this position, the hoop tension in the web is relatively high as the radius of curvature of the web is large. As the slack in the web increases, the size of thebulgewill Furthermore, as

increase and the radius of the bulge will decrease reducing the hoop tension therein, until the bulge reaches a semicircular shape shown in solid lines at 40a. If the depth of the bulge were allowed to increase beyond this point the bulge would expand, the radius increasing with the resultant increase in the hoop tension. Such an increase in the hoop tension would cause a further increase in the size of the bulge with a resultant increase in the hoop tension, creating an unstable operating condition. Accordingly, in the embodiment of Figure 3, side plates 43 and 44 are terminated short of the point at which the bulge assumes the shape of a semicircle in order that the pressure differential on opposite sides of the web will automatically be relieved before the bulge exceeds a semicircular shape. This prevents the system from entering an unstable condition.

If for some reason, the space available for the tensioning apparatus will not permit the positioning of the supporting rollers a suflicient distance apart to provide the desired flexibility in the system without the bulge exceeding a semicircular shape, the modifications shown in Figure 4 may be utilized. Here "again, the web 50 passes over spaced rollers 51 and 52 and between side plates 53 and 54. Blower 55 sends a stream of air against the web which will respond to variations in tension by forming a bulge of varying size. So long as the amount of slack to be taken up is not very large, the bulge will form as discussed above taking positions shown in broken lines at 500: and 5011'. A third roller 56 is mounted intermediate rollers 51 and S2. and offset therefrom so as to be contacted by the web if the bulge increases appreciably beyond the size shown at 50a. When the web contacts the third support, roller 56, two bulges 50b and 500 are formed, each acting in a manner similar to that heretofore described. This arrangement provides for taking up a large amount of slack in the web without making the individual bulges of excessive size. Again, side plates 53 and 54 are terminated short of the point at which bulges 50b and 500 would exceed semicircles.

Figure 5 shows another structure by which the total size of the bulge may be allowed to increase without exceeding a semicircle. As before, web 60 passes over rollers 61 and 62 and between side plates 63 and 64. A plate member 65 is provided along the outer surface of the bulge 60a in web 60 and in addition to providing a braking effect has a configuration which reduces the radius of the bulge as it increases in depth, preventing it from exceeding a semicircular shape. For example, the radius of bulge at 60a is smaller that that of the bulge shown at 60a.

Figures 6, 7 and 8 each show a web passing over rollers 71 and 72 and through an enclosure including side plates 73 and 74. In Figure 6, a flat braking surface 75 is shown. With such a flat braking surface the braking effort in pounds per inch width of web is equal to the length in inches of the portion of the web contacting the braking surface times the air pressure in pounds per square inch times the coefficient of friction between the web and the braking surface.

In Figure 7, a concave braking surface 76 is shown; with this arrangement the braking eflort will be less than that achieved with a flat plate, as the hoop tension in the web tends to pull the web away from the braking surface. Figure 8 illustrates a similar system in which the braking surface 77 is convex; here sincethe web tends to follow surface 77, the braking effort will be increased over that found with a flat braking surface.

Under most circumstances a concave braking surface will be most desirable. This is particularly true in situations where the system is designed to have the capacity to take up a considerable amount of slack in the web inasmuch as the use of a concave surface will avoid excessive braking effort as the effective bulge size increases.

It should be noted that the hoop tension produced in the web by the differential pressure applied thereto should always be sufficient to overcome the friction between the web and the braking surface preceding the bulge, otherwise the web would not slip properly over the braking surface and would have a tendency to form slack at the leading edge of the braking surface.

Figure 9 shows a system in which the bulge 80a inv web 80 is constrained by two braking surfaces 81 and 82. The first or leading surface contacted by the web, surface 81, is concave while the trailing surface 82 is convex. In addition the open ends of the braking surfaces approach each other to prevent the bulge 80a from exceeding a semicircle as it increases in depth. As stated previously, the tension in the bulge should decrease as the depth of the bulge increases. The second brake surface 82 prevents this decreased tension in the bulge from reaching the press by increasing the braking between bulge and press.

Figure illustrates a further modification in which the roller support members shown in the previous figures are replaced by curved surfaces 90 and 91 over which web 92 slides. Again, braking surfaces 93 and 94 limit the size of bulge 92a. In this arrangement it is preferable that the depth, D, of bulge 92a be less than the space, L, between the points of support 90 and 91. It is also preferable to operate this system at a relatively low air pressure and a relatively high tension in the web being delivered to the press or other web utilizing apparatus. Otherwise, the braking effort would be excessive.

In Figure 11, a source of vacuum 100 is substituted for the blower shown in the other figures for supplying the required pressure differential. Here, the rollers 101 and 102 and side plates 103 and 104 are similar to those shown in the other drawings. Plate member 105, which completes the enclosure, is placed on the outer side of the bulge 106a formed in web 106 and exhauster 100 connected thereto lowers the pressure within the enclosure establishing the desired pressure dilferential on opposite sides of the web.

Figure 12 illustrates an arrangement by which the size. or depth of the bulge 110a in web 110 is utilized to control the delivery of the web from the supply roll to the tensioning apparatus. The tensioning apparatus itself is similar to that shown in Figure 7 with the web 110 passing over rollers 111 and 112 and between side plates 113 and 114. An annular vane 115 is positioned within the enclosure adjacent discharge opening 116a of blower 116 to provide a more desirable utilization of the flow of air therefrom. A concave braking surface 117 is provided adjacent roller 111 and forms one wall of an evacuated chamber 118. Braking surface 117 is provided with openings 117a arranged across substantially the entire surface thereof. The interior of chamber 118 is connected through a regulating valve 119 to a source of vacuum (not shown) and directly to a valve control diaphragm chamber 120 which is in turn connected to a hydraulic control valve 121. Hydarulic control valve 121 is connected to a cylinder arrangement 122 which controls the tension applied to the brake bands 122a of the web supply roll (not shown).

As the depth of the bulge 110a increases, more and more of the small openings 117a in braking surface 117 are covered causing an increase in the level of vacuum within chamber 118 and within chamber section 120a of diaphragm valve control 120. The valve core 12111 is drawn to the right by valve control 120, connecting cylinder 122 to hydraulic supply 123 in the proper manner to tighten the brake bands 12211 on the supply roll. This results in a reduction in the speed of the web 110 with a resulting decrease in the size or depth of bulge 110a. On the other hand, if the depth of the bulge 110a is reduced, more and more of the small openings 117a are uncovered, reducing the vacuum level within chamber 118 and in diaphragm valve control 120. Valve core 121a is moved to the left connecting cylinder 122 to the return line of the hydraulic supply 123 and reducing the tension applied to brake bands 122a of the supply roll allowing the speed of the web to increase.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the lengththereof; means for creating a differential pressure on opposite sides of said web intermediate said spaced points, said web forming a bulge between said points of support in response to said pressure differential; and means for automatically reducing said pressure differential before said bulge exceeds a predetermined size.

2. An apparatus. of the character described in claim 1, wherein said pressure differential is reduced before said bulge extends beyond asemicircular shape.

3. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the length thereof; means for creating a differential pressure on opposite sides of said web intermediate said spaced points, said web forming a bulge between said points of support in response to said pressure differential for maintaining tension in said web; and means for applying a variable braking force to said web in accordance with the' size of said bulge.

4. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the length thereof; means for creating a differential pressure on opposite sides of said web intermediate said spaced points, said web forming a bulge between said points of support in response to said pressure differential for maintaining tension in said web; and means providing at least one braking surface adapted to be engaged by a variable portion of said bulge.

5. Apparatus of the character described in claim 4, wherein said braking surface is concave.

6. Apparatus of the character described in claim 4, wherein said braking surface is convex.

7. Apparatus of the character described in claim 4, wherein said braking surface is flat.

8. Apparatus of the character described in claim 4, wherein there are a plurality of braking surfaces.

9. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the length thereof; means for creating a differential pressure on opposite sides of said web intermediate said spaced points, said web forming a bulge between said points of support in response to said pressure differential for maintaining tension in said web; and surface means adapted to be engaged by a variable portion of said bulge, the radius of said bulge decreasing as the depth thereof increases.

10. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: a pair of supports spaced along the length of said web for supporting a portion thereof; a third support intermediate said pair of supports and oflset therefrom; means for creating a pressure differential on opposite sides of said Web intermediate said pair of supports, said web forming a bulge between said pair of supports in response to said pressure differential and, when extended, contacting said third support to form two bulges.

11. In an apparatus for handling a moving web, combined means of the character described for tensioning the web; comprising: means for supporting a portion of said web at spaced points along the length thereof; means for creating a differential pressure on opposite sides of said web intermediate said spaced points, said web forming a bulge between said points of support in response to said pressure differential; and means operable as a function of the size of said bulge to affect the tension of the web before it is delivered to the supporting means.

12. In an apparatus for handling a moving web, combined means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the length thereof; means for creating a differential pressure on opposite sides of said web intermediate said spaced points, said Web forming a bulge between said points of support in response to said pressure differential; and means operable as a function of the size of said bulge to control the tension of said web at a point spaced from the supporting means.

13. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the length thereof; means defining an enclosure adjacent at least part of said portion of the web; and means connected to said enclosure for creating a ditferential pressure on opposite sides of at least the part of said portion of the web adjacent said enclosure.

14. In an apparatus for handling a moving web, means of the character described for tensioning the web, comprising: means for supporting a portion of said web at spaced points along the length thereof; means, including References Cited in the file of this patent UNITED STATES PATENTS Pfarrwaller Nov. 12, 1940 Phelps May 11, 1954

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