US3011545A - Pressure loading means for traveling blankets - Google Patents

Description

Dec. 5, 1961 H. s. WELSH ET AL 3,011,545

PRESSURE LOADING MEANS FOR TRAVELING BLANKETS 6 Sheets-Sheet 1 Filed. March 16, 1959 INVENTORS HEWITT S. WELSH I HAROLD O. BALOUGH ATT RNEYS.

Dec. 5, 1961 H. s. WELSH ETAL 3,011,545

PRESSURE 1.0mm; MEANS FOR TRAVELING BLANKETS Filed March 16, 1959 6 Sheets-Sheet 2 b, i A

WWI I W U HEWITT S. WELSH HAROLD O. BALOUGH 6 AT FOEN EYS N I II 1% INVENTORS PRESSURE LOADING MEANS FOR TRAVELING BLANKETS Filed March 16, 1959 Dec. 5, 1961 H. s. WELSH ETAL 6 Sheets-Sheet 3 INVENIORS HEWITT s. WELSH BY HAROLD o. BALOUGH 5% 1 (91144 ORNEYS.

Dec. 5, 1961 H. s. WELSH ETAL 1 PRESSURE LOADING MEANS FOR TRAVELING BLANKETS Filed March 16, 1959 6 Shets-Sheet 4 FIG. 5.

INVENTORS HEWITT S. WELSH HAROLD O.BALQUGH BY fill)??? A ORNEYS.

PRESSURE LOADING MEANS FOR TRAVELING BLANKETS Filed March 16, 1959 Dec. .5, 1961 H. s. WELSH ETAL 6 Sheets-Sheet 6 INVENTORS HEWITT S. WELSH HHROLD O. BALOUGH ATTORN EY 3,011,545 PRESSURE LOADIN, MEANS FOR TRAVELING BLANKETS Hewitt S. Welsh and HaroldO. Balough, Short Hills,

NJ., assignors to Clupak, Inc., New York, N.Y., a

corporation of Delaware Filed Mar. 16, 1959, Ser. No. 799,808 Claims. (Cl. 162-361) The invention relates to the pressure loading of blankets in paper making, paper shrinking, fabric shrinking, and other machines, and more particularly to the maintenance of a high loading pressure which is uniformly distributed across the traveling, resilient blanket from edge to edge thereof.

This application is a continuation-in-part of our pending application S.N. 709,731, filed January 20, 1958, and now abandoned. p I

The present invention was conceived in connection with the manufacture of uncreped stretchable paper as disclosed in .Cluett Patent #2,624,245. While the utility of the invention is by no means limited to the manufacture of uncreped stretchable paper, the invention is illustratively shown and described herein as applied to that use.

The making of an uncreped longitudinally stretchable paper web according to the teaching of Cluett 2,624,245 is accomplishedby shrinking the paper web longitudinally by forces parallel to the surfaces o-fthe web while the Web is in a suitably moist condition and while it is maintained under sufficient pressure normal to its surfa e to prevent .creping or cri-nkling. An accepted method ofprovidingpar-allel forces to a web'incapable of self support for the purpose of shrinking theweb is to feed the web to a segment of travel between a rotating drum and a traveling resilient blanket. The blanket surface is accelerated in some manner prior to the point of web feed, and then th blanket surface is caused to ,decelerate after the point of web feed. The deceleration of the blanket surface While it is in contact with the .web causes the parallel forces on the web which compress or shrink the Web. I

The acceleration and subsfiqll int deceleration of the surface of the resilient blanket may be effected by feeding the resilient blanket along its travel to a nip formed by and between a pressure loaded roller and a rotating,

United States Pam-o smooth-faced drum. Asthe resilient blanket is-non-compressible, it accelerates prior to the nip in order to pass through the restriction of the nip and it decelerates after it passes through the nip. The paper Web, which is fed into the nip and into contact withfthe traveling blanket after the blanket has been accelerated, is shrunk by the parallel forces transmitted to it as the blank decelerates. The shrinkage of the web may be controlled by varying the restriction of the nip which causes the change in the surface velocity of the traveling blanket.

In accordance with conventional practice, the pressure loading roller extends across the Width of the traveling blanket and the surface of the roller travels substantially in unison with the moving blanket. The roller is mounted at its ends in bearings, which bearings are loaded by a heavy pressure in the direction to cause the roller to apply pressure to the traveling blanket to deform the blanket at the nip. i

In the manufacture of stretchable paper as disclosed in Cluett 2,624,245, it has been found necessary to apply pressure to the blanket at the shrinking nip of the-order of 150' to 200 pounds per lineal inchin order to deform the resilient blanket sufficiently to obtain various shrinkages of the paper web, andpressures ashigh as 500 pounds per lineal inch have been employed depending upon the hardness of the blanket. Additionally, asthe ice width of the moving blanket is increased, the total pressure required is'increased proportionately, Also, as the distance between the roller bearings is increased, the tendency for the pressure loaded roller to sag or bow is increased. With a conventional paper machine having a Width of about 240 inches and having a lineal speed of about 1500 feet per minute, theloading requirements.

present severe requirements on the bearings if the shrinking device is to be incorporated'in the paper machine.

If the pressure roller sags, bows, or deflects, an unequal distribution of pressure and restriction will result to compress the web unequally across its width. If different lateral zones or segments of the blanket are compressed unequally, the surface of the blanket will travel at different speeds across its width and it is impossible to feed the web to all portions of the nip at the velocity of the blanket. If a portion of the uniformly'supplied web is traveling slower than the blanket, that portion will be stretched by the higher speed of the blanket before it is condensed as the blanket decelerate's, and it will have its strength properties impaired more or less according to the magnitude of the non-uniformity of pressure. The net condensation Will also be less than it would have been if no pre-stretching had occurred. If a portion of the uniformly supplied web is traveling faster than the blanket as it enters the nip, the web will tend to pile up in advance of the nip and Will produce wrinkling and other deleterious effects. In every. such case different longitudinal Zones of the web will be treated differently, and the product will be. non-uniform in strength and extensibility and will be likely to be impaired in appearance, surface smoothness and quality.

One conventional way of combating the bowing of the pressure roller is'to increase the rigidity of the roller by increasing its diameter. But as the diameter is increased, the contact area also is increased which in turn increases the total pressure necessary to provide a given deformation for the blanket. In somecases the pressure required increases at a faster rate than the rigidity of the roller increases, so that the desired uniform pressure loading may be unattainable'by this method even with greatly increased roll diameters. The arrangement further increases the total pressure to be applied through the end bearings, and, therefore, further complicates bear ing maintenance and increases bearing failure.

7 Another conventional expedient used to reduce sagging of the pressure roller is to back up the pressure roller at frequent intervals with idler rolls through which pressure equalizing forces are applied. Such idler rolls travel with the same surface velocity as the pressure roller which complicates the problem of providing suitable bearings for the idler rolls and is apt to prove a bottleneck requiring the entire mechanism to be operated at reduced speed with resulting loss of output. The idler rolls, moreover, alter the surface finish of the pressure roller in spaced zones, and wear the pressure roller to an uneven striped contour.

It has been discovered that, even at these higher lineal pressures, the pressure roller of usual construction may be stopped with very little force, and in fact by simply holding the roller by the hands, provided the surface of theconfronting faces of the blanket and roller are sufficiently lubricated. Under these conditions the friction thus, is concerned with both the static and the dynamic Thus, the bearing problems are reduced to those existing during start-up and before the loading pressure is provided on the roller.

In a second embodiment of our invention, the pressure roller is made non-rotary. A hydrostatic lubricating film is provided between the resilient blanket and the nonrotary roller to permit initial movement of the blanket over the surface of the non-rotary roller. In this embodiment, the depth of the roller may be made greater than the width so as to prevent sagging of the roller when pressure loading is applied, or the pressure loading may be distributed along the non-rotary rod. In this embodiment, bearing problems are wholly eliminated.

Since a failure of lubricant could result in the tearing of the blanket from the drum and in other damage, it is desirable to reduce the need for lubricant to a minimum. To this end, it is a feature that the pressure cylinder or pressure beam may be either chromium plated, or polished, or coated with Teflon (Du Pont trademark for its polytetrallouroethylene resin). Through these expedicuts the need for lubricant in some of the milder applications may be completely obviated. In the manufacture 'of stretchable paper as referred to above, however, the provision of lubricant is still found to be essential to successful continued operation.

In effect, with proper lubrication no contact is made between the rubber blanket and pressure roll, but rather the contact is between rubber and the lubricating film and between the lubricating film and the pressure applicator. The lubricating film enables the blanket to travel upon and relative to the surface of the pressure applying means without detrimental effects.

An important advantage of employing a non-rotary pressure beam resides in the fact that the depth of the beam may be extended to provide great rigidity without correspondingly increasing the width or diameter extent of the pressure member, as must be done when an end loaded roller is employed. Because of this, a more concentrated pressure is applied to the blanket. This means that a given total pressure will produce a much greater local deformation of the blanket than would be realized if acylindrical roller of the required rigidity were employed, or conversely a given blanket deformation can be obtained with much less total pressure.

It is accordingly a primary object of the present invention to provide a hydrodynamic lubricating film between a traveling resilient blanket and a rotatable pressure roller to reduce the friction therebetween to a point that the pressure roller will not be driven by the traveling blanket.

Another important object of the present invention is to provide a hydrostatic film between a resilient blanket and a non-rotary pressure rod to permit the blanket to move across the surface of the pressure rod without detrimental frictional effects.

Another object of the present invention is to provide a non-rotary pressure rod having a greater depth than width for applying a uniform pressure across a traveling, resilient blanket.

A further object of the present invention is to reduce bearing and loading problems for a pressure roller.

Other objects and advantages will hereinafter appear.

In the drawing forming part of this specification:

FIG. 1 is a fragmentary view in side elevation, partly broken away, of a portion of a paper making machine in which the preferred embodiment of the present invention is-shown;

FIG. 2 is a fragmentary sectional view taken on the line 22 of FIG. 1, looking in the direction of the arrows;

FIG. 3 is a detail view in side elevation on a larger scale than FIG. 1, showing the pressure applying member of FIG. 1 in association with the blanket and the drum;

FIG. 4 is a view similar to FIG. 3 but showing another form of pressure applying member;

FIG. 5 is fragmentary view in side elevation partly broken away, showing an alternate method of applying pressure to the pressure member;

FIG. 6 is a fragmentary sectional view taken on line 6-6 of FIG. 5 looking in the direction of the arrows;

' FIG. 7 is a detailed view in side elevation on a larger scale than FIG. 1 showing the ends of the pressure applying member of FIG. 1;

FIG. 8 is a view similar to FIG. 3 but showing another embodiment of the invention in which the pressure beam is rotatably mounted, and;

FIG. 9 is a view similar to FIG. 8 but showing a further modification.

In FIGS. 1 to 3 disclosure is made of a practical and advantageous form of paper shrinking unit, which embodies features of the present invention. Although the shrinking unit is not restricted to use in on machine operations, and may be embodied in a converter for shrinking a remoistened, finished web, it is illustrated herein as embodied in a paper making machine and located after the presses and in the drying section.

The moist paper web P is shown as supplied from the preceding section of the paper machine, the web being passed, for example, from a feed couple 12 to the shrinking unit 10 over an idler guide roll 14 at a speed corresponding to the intake speed of the shrinking unit.

As in the disclosure of Cluett 2,624,245, the shrinking unit comprises a rigid nip forming member which is illustratively shown as a steam heated drum 16 of substantial diameter, say four feet. This drum is desirably chromium plated and polished, but other suitable surfaces may be used. The drum is of rigid construction and is connected to a drive shaft 17 which is rotatably driven by any suitable means. The drive shaft is desirably mounted in sturdy roller bearings at each end of the drum. Any available expedient may be resorted to for making the drum and the drum mounting rigid and unyielding.

A resilient rubber blanket 18, desirably about one inch thick is mounted on three guide rolls 20, 22 and 24 which are arranged to tension the blanket 1.8. The blanket has a run which travels on a segment of the drum 16. The blanket 18 may have a shore durometer hardness of between 50 and depending upon the application and may be provided with a non-stretchable backing of cord fabric if desired, but this is not essential. The blanket is driven by the drum 16. The rotary parts thus far described are all mounted in rigid side frame members 26 and 28, which members are disposed outside the lateral bounds of the paper web P and the blanket 18.

A rigid pressure bar 30 extends across the machine through substantially the full length of the drum 16, being supported at its ends. In one embodiment, the pressure bar 30 comprises a thick Walled but hollow metallic cylinder 34 and a rigid beam 36, FIG. 1. The cylinder 34 and the beam 36 are desirably of steel or steel alloy and are .of great strength and rigidity. The cylinder is of small diameter (say about six inches) but the total depth of the pressure bar 30, as constituted by the cylinder 34 and the beam 36, is very considerably greater than the diameter of the cylinder, 34. The cylinder 34 is disposed to engage the back of the blanket 18 and to press the face of the blanket strongly against the drum 16 in position to form a uniform nip for the paper web P. This is the shrinking nip in which the condensation of'the web takes place.

Means for applying an, evenly distributed pressure across the width, of the pressure bar 30 and for thereby causing a pressure which is 'evenly distributed acrossthe blanket 18 from edge to edge thereof. The uniform pressure is transmitted to the blanket by loading the ends of the beam 36 and by properly designing the bar 30 to uniformly transmit the loading without deflection, as shown in FIG. 1 and FIG. 2.

For the purpose of applying force to the bar 30, the bar has secured to it a plurality of linkages 32, each of which forms an element of one of a plurality of duplicate hydraulic or pneumatic devices 38. Each of the devices 38 comprises a piston 40, affixed to a piston'rod 44, which is operable by hydraulic or pneumatic pressure in a stationary housing42. The devices 38 are supported rigidly from the side frame members 26 and 28 by suitable brackets '45. Each piston is supplied with hydraulic or pneumatic fluid under pressure through a conduit 46.

As has been pointed out, it is important that evenly distributed pressure be applied to the bar '30. It is also I important, however, to be able to maintain the pressure at any predetermined level throughout a wide pressure range. Therefore, a dependable hydraulic or pneumatic pressure source is provided, capable of maintaining any desired pressure throughout a wide range. Since devices of this character are well known, no detailed showing and description are thought necessary.

Provision is also made of means for minimizing friction between the blanket 18 ar rd the pressure bar 30. One expedient consists of coating the surface of the cylinder 34, or at least the blanket contacting area thereof, with chromium, Teflon (Du Pont trademark for its polytetrafluoroethylene resin) or other suitable material.

A preferred expedient for reducing friction consists in the furnishing of a lubricant between the confronting faces of the blanket 18 and the bar 30 and in such manner asto provide ahydrostatic and a hydrodynamiclubricat- I.

ing film between the blanket 18 and the pressure bar 30. To this end the cylinder 34 is formed with passages 74 Which are adapted to deliver lubricant direetly'through 76 or other dependable source.

The liquid is drawn from the reservoir 76 through a conduit 78 by a' pump 80 and its delivered under pressure by the pump to a conduit 82. 'Iheeonduit 82 has associated with ita conventional manually adjustable'regulator valve 84, for adjustably controlling the pressure of the lubricant in the conduit 82. The valve 84 is disposed in a return-conduit 822: which runs from the conduit 82 back to the reservoir 76. The conduit 82 is connected todeliver lubricant under controlled pressure to the interior of the hollow cylinder 34. The lubricant may be supplied to the ends of the roll or to various points along the roll if the roll contains internal partitions. The regulator 84 is desirably set to maintain a lubricant pressure of the same order.

as the stress distribution in the compressed section of the rubber belt. If air is to be used as the lubricant, the reservoir 76 may be omitted and an air pump, rather than a hydraulic pump may be utilized.

The system for supplying pressure fluid to the chambers 38 may desirably be similar to the system for supplying and regulating lubricant as described.

The shrinkage of the web can be readily understood from a study of FIG. 3. If. the blanket is uniform and the thickness of the space between the bar 30 and the drum 16 is three quarters the normal, undistorted thicknes s-of the blanket, the rubber must pass through the constriction at four-thirds the normal velocity of the web engaging face of the blanket. The higher speed is the i n ake speed of the web, or the speed at which theweb is supplied by the feed rolls 12 for shrinking, and the lower speed is substantially the speed at which the Web travels after being condensed In this'suppositious case I the web wouldbe shrunk 25% and, barring unintended that area of the cylinder 34 which is covered by the blanket 18 The lubricant may consist of air or of a suitable liquid. If the blanket is formed of natural rubber the lubricant should consist of air or water or of oil which does not attack natural rubber, such as the silicone oils. If the blanket is of a synthetic rubber which isresistant to attack by oils derived from petroleum, the silicone oils are still usable but the cheaper'oils derived from petroleum may be used instead.

The, passages 74 are uniformly spaced along the face of the cylinder 34 which confronts the blanket 18. The spacing and configuration are determined by the stress distribution in the nip section of the rubber belt. The shape of the passages must be selected so that there is only minimal interference with the surface film of lubricant.

or .deliberate restretching of the moistweb, wouldbe caused to have a stretchability of 33 /3 This measure of stretchability is more than is actually required in most instances. It does not, however, represent the limit of what is practically attainable in a single pass when greater condensation and greater stretchability are desired. Because the pressure is applied so evenly. bythe pressure bar ;.30, the shrinkage of the web will be uniform across its width. Because the pressure is concentrated ina small area, a high measure ofshrinkage can be secured in a single pass, if desired. H I

When a non-rotary pressure rod is used, it is not essentialthatxthe portion of the pressure bar which actually engages the blanket be fully cylindrical in shape. In FIG. 4 disclosure is made of a pressure bar 30a for cooperating with the blanket 18a and a polished, chromium plated drum 16a. in place of the cylinder 34 a cylinder segment 34a is'provided. Except for the difference in shape between the cylinder 34 of FIG. 1 and the cylinder Slots or large holes will destroy the surface film and blanket. The relief of pressure r'nay permit rubbing of I the blanket at the edges.

This effect is not, significant on machines where the ratio of edge passages to the total number of passages is small. On machines of narrow width, where this ratio is high, the shape of the ends of cylinder 34 can be changed to maintain uniform film pressure at the edges of the blanket. Various curved shapes will accomplish this effect. A spherical end as shown in FIG. 7 is one shape that can be used to obtain a more uniform stress distribution. In FIG. 7 corresponding reference characters have. I

i been applied to corresponding parts with the subscript C added in each case. 7

Lubricating liquid may be furnishedfrom a reservoir segment 34a of FIG. 5, the structure is the same as before. Corresponding reference characters have accordingly been applied to corresponding parts with the subscript a added. in each instance, and no further detailed description will be given. No essential function of the cylinder 34 is sacrificed by the substitution of the seg- -ment 34a.

It is not essential that the blanket contacting face of the member 34a be cylindrical in form. It can be elliptical in cross section if desired, or-it can'be varied in other ways. It is essential, however,1that all blanket contacting areas be rounded, since an objectionable snubbing effect would be introduced by any requirement that the blanket turn sharp corners, and the uniform lubricating film would become more diflicult to maintain.

in FIGS 5 and 6 the general organization .is the same as in FIGS. 1 to 3 but disclosure is made ofa modified form of pressure applying means. Corresponding reference characters have accordingly been applied to corresponding parts with the subscript b added in each instance,

and the'description will be confined to theparts which are specifically different from the parts shown and described in, and in connection with, FIGS. 1 to 3.

In FIGS. and 6 the beam 36b is fixedly supported beam 36b is not made unitary with the cylinder 3412 but is made to serve as a carrier for the cylinder with means interposed for regulating the distribution of pressure along the cylinder as well as for regulating the total pressure applied.

The beam 36b pivotally supports a series of equally spaced, desirably identical, levers 90 which, through connecting plates 92' are made unitary with the cylinder 34!) in any suitable way, as by welding. The levers 90 are pivotally connected at their free, lower ends to links '94. Each link 94 extends into a housing 96 and is inflexibly connected to a pressure diaphragm 98, within the housing. Each housing 96 is rigidly and immovably supported from the beam 36b through a bracket 100. Each housing is divided by its diaphragm 98 into a pressure fluid chamber 102 and a chamber 104 which may be open to the atmosphere. Fluid under pressure is furnished to a main 46b under regulated pressure and is distributed to the several chambers 102 through separate branch conduits 104, each of which is provided with a manually adjustable regulating valve 106 for maintaining in the associated chamber 102 a desired pressure appropriate to the pressure needs of the particular segment of the cylinder 34b controlled by said chamber.

. With an arrangement of this kind a more uniform effect on the paper web from edge to edge thereof can be secured than would otherwise be available. Not only is it possible to apply uniform pressure through the cylinder from end to end thereof, but the pressure may be locally varied as required. Such variation may compensate for different tendencies toward deflection at different points along the cylinder 34b, for variations in the action of the blanket 18b at different distances from its edges, and for other variables including inequalities of manufacture;

In FIG. 8, the cylinder 34d is rotatably mounted by the beam 36d having a set of waterlubricated journaled bearings 124 positioned along its length. A lubricant spray means 120 is provided to spray the back of the resilient blanket 18a. The lubricant for the spray means 120 may be provided from the same source, or a source similar to that shown in FIG. 1. The water for the bearings 124 may be supplied from a source (not shown) in a conventional manner by a pump 125.

As the blanket 18d travels, it carries the lubricant with it in sufiicient quantities to form a substantially uniform hydrodynamic film between the confronting faces of the blanket 18d and the pressure applying cylinder 3401. Thus, during start up, the cylinder 34d may rotate, but after rotation has commenced, a hydrodynamic lubricating film will be established which will reduce the driving friction between the confronting faces sufi'iciently so that even under load conditions the cylinder 34d will not rotate. The load conditions may be imposed after the hydrodynamic film has been established. The establishment of the lubricating film sufiicientto reduce the driving friction'to a point where the cylinder 34d stops rotating is aided by keeping the wrap of the blanket 18d on the cylinder 34d to a minimum.

In FIG. 9, a further modification ,of the present invention is disclosed. In this embodiment, a babbitted journaled bearing 128 isprovided rotatably mounting the cylinder 34c. Additionally, levers 90c are provided for distributing the pressure along the cylinder 34c in the manner similar to the disclosure of FIGS. 5 and 6. In FIG. 9 corresponding reference characters have been applied to'corresponding parts with the subscript e added.

The lubricant spray means 120 also may be used in "the embodiments shown in FIGS. 3 and 4 to provide a hydrodynamic lubricating film. However, in these embodiments, internal lubricating means are preferred to provide a hydrostatic lubricating film for initial move- -ment of the blanket 18 and 18a respectively. After initial movement of the blanket is eifected and a hydrodynamic film is established, an external'lubricating meansmay maintain the lubricating film, or supplement the internal lubricating means.

While certain preferred embodiments of the invention have been illustrated and described in detail, it is to be understood that changes may be made therein'and the invention embodied in other structures. It is not, therefore, the intention to limit the patent to the specific construction illustrated, but to cover the invention broadly in whatever form its principles may be utilized.

We claim:

. 1. In a web treating machine which includes a metallic nip forming member, a blanket having a run which travels on a segment of the nip forming member, and means supplying a web to be acted upon to a nip formed by and between the blanket and the nip forming member, the improvement which comprises, in combination, a rigid non-rotary pressure applying member having a smooth, rounded surface for engaging and guiding the blanket in nip forming position and pressing the blanket strongly against the nip forming member, means forming a hydrodynamic lubricating film between the confronting faces of the rigid pressure applying member and the blanket, and means applying forces to the rigid member to assure the application through the blanket of pressure which is distributed substantially uniformly from edge to edge of the blanket.

2. A structure embodying the improvements of claim 1 in which the rigid pressure applying member is of much greater depth than width, the rounded blanket engaging surface being arcuate and of small radius as compared with the radius of the nip forming member.

3. A structure embodying the improvements of claim 1 in which the means for applying force to the rigid pressure applying member consists of a series of duplicate fluid pressure devices disposed at equal intervals, and means for supplying liquid to the devices from a common source at various predetermined pressures.

4. A structure embodying the improvements of claim 1 in which the rigid pressure applying member is formed with passages for transmitting lubricant to the confronting faces of the blanket and the pressure applying member to form said hydrodynamic lubricating film and which further includes means for pumping lubricant under pressure through said member.

5. In a machine for shrinking a web to make it stretchable while maintaining it free of creping, which machine has a rigid nip forming member, a blanket of resilient material having a run which'travels on a segment of the nip forming member, and means for supplying a shrinkable web of paper to a nip' formed by and between the nip forming member and the blanket at the intake speed of the nip, the improvement which comprises, in combination, a pressure applying member having a smooth, rounded surface for engaging and guiding the blanket in nip forming position and pressing the blanket strongly against the nip forming member, means for applying forces to the pressure applying member of such relative magnitudes and at such properly chosen frequent intervals as to assure the application to the blanket of a pressure which is distributed substantially uniformly from edge to edge of the blanket, and means for supplying lubricant to the confronting faces of the blanket and the pressure applying member to form a hydrodynamic lubricating film therebetween to eliminate frictional contact of said blanketand said pressure applying member.

' References Cited in the file of this patent UNITED STATES PATENTS 1,971,211 Cluett Aug. 21, 1934 2,021,975 Wrigley Nov. 26, 1935 2,624,245 Cluett Jan. 6, 1953 2,765,514 Walton Oct..9, 1956 2,842,092 Pomper A July 8, 1958

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