Roll Covering

Abstract

A roll capable of operating at high speeds and high nip pressures having an outer shell of a composite material formed by bonding a needled nonwoven mat of either acrylic fibers, polyester fibers or mixtures of these fibers with an epoxy resin so that ten to forty percent by weight of the composite is fiber. The covering above described may be manufactured by winding a continuous strip of the mat, said mat having been saturated with the resin onto a roll at a uniform speed and with a lead sufficient to build a plurality of layers in one pass while simultaneously unwinding the strip from a strip holding means under brake tension to permit winding so as to decrease the width of the strip by at least three percent.

Description

BACKGROUND OF THE INVENTION

The quest for the ideal roll covering material began at the very first time that rolls per se were employed in commercial processes. Rolls have been manufactured from various metals, such as cast iron, bronze, aluminum, stainless steel, and the like, for various applications with varying degrees of success. Likewise, rolls have been covered with rubber, natural and synthetic, fiber glass, plastic compositions and other synthetic materials. Again these materials have not been found to be satisfactory in a number of instances.

The very nature of a roll requires that it be capable of rotation, oftentimes in a load bearing arrangement. As industrial processes become more sophisticated, and greater production is sought, oftentimes the roll must operate under conditions where the peripheral speed of the surface exceeds 6,000 ft. per minute or nearly 70 miles an hour. Also, the force against which the roll is bearing may exceed 1,000 pounds per linear inch of roll face width. The environment in which these operations take place may be corrosive, changing in temperature, or otherwise adverse. Moreover, the surface of the roll may be required to contact products which may be damaged by the roll if the surface is not sufficiently free from abrasiveness or other damaging characteristics. It is imperative from an economic standpoint that a roll be developed that has a substantially increased cover life.

An improved roll covering which would be capable of operating at high speed under high load without being adversely effected by environmental conditions during operation would supply a long felt need in a wide variety of industries. This is particularly true in the paper industry.

DESCRIPTION OF THE PRIOR ART

A number of coverings for rolls have been proposed for use under the conditions described above. Many of these materials are presently being used, oftentimes only because no better material has been available. In most cases, the selection of the roll covering material is a compromise, blending the various limitations due to cost both of construction and attendant wear on the device on which it operates, resistance to corrosive attack, ability to withstand continued use without repeated replacement, and the like.

OBJECTS OF THE INVENTION

It is therefore a primary object of the present invention to provide a new and superior roll covering material which is capable of operating at high speeds and high loading conditions without adverse effects on the covering from the environmental conditions or on the object with which it is in contact.

Another object of this invention is to provide a roll covering which is suitable for use in the paper making process.

Another object of this invention is to provide a roll covering derived from a composite material or from a needled nonwoven mat selected from a group consisting of acrylic fibers, polyester fibers and mixtures thereof and bonded with an epoxy resin.

Yet another object of this invention is to provide a method for manufacturing a roll according to the present invention.

Still another object of this invention is to provide a method for manufacturing a roll capable of operating at high speeds and under high loading for sustained periods of time.

Other objects will become apparent upon a reading of the instant disclosure.

DESCRIPTION OF THE INVENTION

It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. It has been discovered that a roll may be made which is capable of operating at speeds in excess of 6,000 ft. per minute and at nip pressures in excess of 1,000 lbs. per linear inch for a substantially extended period of time. This roll has an outer cover or shell comprising a composite material formed from a needled nonwoven mat selected from the group consisting of acrylic fibers, polyester fibers and mixtures thereof. This mat has been bonded with a thermosetting resin of the epoxy type. The composite has from 10 to 40 percent by weight of fibers and from 90 to 60 percent by weight of resin. A preferred range of said fibers is from 15 to 30 percent, with 85 percent to 70 percent by weight of said resin. Most preferred is a composite material containing from 20 percent to 25 percent of said fibers and from 80 percent to 75 percent by weight of said resin. The phrase "needled nonwoven mat" as used herein refers to a mat of nonwoven fibers the tensile strength of which is greatly improved by a standard needling process well known to those versed in the art.

The rolls made in accordance with the present invention preferably have a ratio of the modulus of elasticity of the fibers prior to their being used to the modulus of elasticity of the cured resin ranging from 10:1 to 1:10. Most preferred is the instance where the above ratio of modulus of elasticity of fibers to resin ranges from 3:2 to 2:3.

In construction of the roll according to the present invention, it is preferred to use a nonwoven needled mat of either acrylic fibers, polyester fibers, or mixtures thereof, having a weight of at least 4 ounces per square yard. Most preferred is a mat having a weight of at least 10 ounces per square yard. In choices of resin, it is preferred to use an epoxy type resin having an epoxide equivalent weight of at least 100. Most preferred is an epoxide equivalent weight of from 175 to 200.

It has further been discovered that rolls made of the composite material, according to the present invention, may be manufactured to include a plurality of land areas adjacent one another so as to define a plurality of grooves in a generally circumferential direction on the roll surface. It is preferred to construct rolls with grooves such that there are at least four grooves per inch of axial length.

It has further been discovered that the rolls having a composite material cover derived from a needled nonwoven mat of either acrylic fibers, polyester fibers, or mixtures, and bonded with an epoxy type resin may be manufactured according to the following method. Basically, the method comprises the steps of winding a continuous strip of the mat after the mat has been saturated with said resin, onto a roll shell at a uniform speed and with a lead sufficient to build up a plurality of layers of said mat in one pass. Simultaneously with the winding step, the strip is unwound from a strip holding means under sufficient brake tension or back tension to cause tension in the strip as it contacts the roll shell. This back tension or brake tension should be sufficient to permit winding the strip on the roll so as to decrease the width of the strip by at least 3 percent. The lead nip may be adjusted or controlled to achieve the desired thickness of the finished cover in one pass. Due to the construction of a needled nonwoven mat, tension has the effect of stretching the mat in the direction of the tension, with an accompanying decrease in the width of the strip. To eliminate entrained air, the strip is saturated with the resin prior to the winding. Once the saturated strip has been wound on the roll, the resin is allowed to cure to form the composite material. Simple machining then prepares the surface for use.

One advantage of the composite material of the present invention, when used as a roll covering surface, is that simple machining may prepare the roll for any use desired. For example, it is relatively simple to crown the roll as is conventional. A smooth surface can readily be placed on the roll shell. Moreover, grooves may be made in the roll in a generally circumferential direction to permit the use of the roll in the many instances where circumferential grooving is desired to assist in fluid removal, for example.

It has further been discovered that in the method of manufacturing rolls according to the present invention, it is preferred to stretch the trailing edge of the strip at least 3 percent more than the leading edge of the strip is stretched, so that at the point of contact of the strip on the roll, the tension not only decreases the width of the strip by at least 3 percent, but increases the trailing edge by 3 percent more than the leading edge. Due to a build up of the layers as the lead advances, the effective diameter which the trailing edge sees is greater than the diameter seen by the leading edge.

The preferred method for creating brake tension in the strip, against which the winding tension operates, is to restrain the strip holding means from which the strip is unwound.

In a preferred embodiment, the brake tension is controlled by passing the strip over a dancer roll means to position a dancer roll in response to the amount of brake tension in the strip. The dancer roll means includes a device for adjusting the brake tension and thereby adjusts the position of the dancer roll. This means for adjusting the brake tension can be set to continuously adjust the position of the dancer roll to a desired position such that the brake tension is sufficient to decrease the width of said strip by at least 3 percent during winding. Moreover, due to the continuous movement of the dancer roll in response to the amount of brake tension, along with the continuous adjustment of the brake tension in response to the position of the dancer roll, a constant amount of brake tension can be provided so that the amount that the width of the strip is decreased, whether 3 percent or 6 percent or whatever, remains constant within the limits of the apparatus. Varying weights in varying positions on the dancer roll will permit adjustment of the tension in the strip at this point, since the strip supports the weight of the dancer roll.

It has still further been discovered that in the manufacture of a roll according to the present invention, the brake tension which is necessary to the manufacture of the roll may be stabilized by passing the strip oover a plurality of sliding tension surfaces. These sliding tension surfaces are balanced against a spring balancing tension, such that the degree of sliding tension varies with the amount of spring balancing tension to eliminate substantial changes in the brake tension.

For a more complete understanding of the present invention, as well as a description of additional features and advantages thereof, reference is hereby made to the accompanying drawings, in which:

FIG. 1 is a simple perspective view of a roll having a covering according to the present invention;

FIG. 2 is a partially cutaway view showing the covering of the present invention which has been provided with land areas and grooves;

FIG. 3 represents a schematic drawing showing a method of manufacturing a roll according to the present invention;

FIG. 4 is a schematic drawing showing the effect of sliding tension on the present invention; and

FIGS. 5A, 5B, and 5C are schematic figures showing the effect of nip pressures and speeds on various covering materials.

As shown in FIG. 1, a roll covering 14 according to the present invention has been placed on a core 12 of a roll having journals 10. The roll covering 14 may be provided with a plurality of land areas 16, as shown in FIG. 2, so as to define a plurality of grooves 18 in a generally circumferential direction on the roll surface. As has been stated above, it is preferred that there be at least four grooves per inch of axial length.

As stated above, the composite material from which the outer shell or covering of the roll of the present invention is made, is derived from a needled nonwoven mat bonded with an epoxy type resin. It is preferred that the amount of resin in the finally cured roll range from 60 to 90 percent by weight. More preferred is a composite in which from 70 percent to 85 percent by weight of the material is resin. Ideally, 75 percent to 80 percent by weight of the composite material should be cured resin. The resin itself may be any of the epoxy type resins which are commercially available. Many manufacturers have for sale an epoxy type resin, most of which are prepared from an epoxide which contains epoxy groups that are cured with either diamines or dibasic anhydrides. Epoxides are prepared in a number of ways, such as by the reaction of phenol and acetone to produce Bisphenol-A, which in turn is reacted with epichlorohydrin to yield the epoxy intermediate. Polyamines or other conventional curing agents are then reacted with the epoxy intermediate to produce the final resin. It is preferred that the epoxy type resin contain an epoxide equivalent of at least 100 and it is most preferred that the epoxide equivalent weight range from 175 to 200.

The mat which forms the balance of the composite material of the present invention ranges from 10 percent to 40 percent by weight of the total composite. It is preferred that from 15 percent to 30 percent by weight of the composite be fibers and ideally, from 20 to 25 percent of the composite material will be fibers. As has been stated above, the fibers from which the needled nonwoven mat are made of either acrylic fibers, polyester fibers or mixtures thereof. Acrylic and polyester fibers are widely available on a commercial scale.

The method of manufacturing the acrylic or polyester fibers into a needled nonwoven mat is also well known in the art and many needled nonwoven mats are commercially available. Basically, needled nonwoven mats are prepared in the following manner. A felt or web of the fibers is first prepared. These fibers may be unsupported or they may be supported by a thin woven support which forms a small percentage of the total material. This web of fibers is then passed through a needling board in a conventional manner in which a plurality of barbed needles are passed into and out of the web, mechanically entangling and felting the fibers. High speed commercial operations are presently employed which operate at up to and exceeding 900 needleboard lifts per minute, which is to say that a plurality of needles contained on a board are inserted into the web and removed at least 900 times per minute as the web passes by the needling position of the manufacturing process.

FIG. 3 schematically shows the method of the present invention for preparing rolls containing the composite material described above. A strip of the needled nonwoven mat 20 is contained on a spool 21 mounted on a lazy Susan type strip holding means 22 in the form of a continuous strip. The roll 60 which is to be covered is rotated by a drive means (not shown) in the direction of arrow 49. This rotation of roll 60 provides a winding tension which causes the strip 20 which is saturated by a resin to be continuously wound onto the roll 60, with a slight lead such that the strip partially overlaps itself to form a plurality of layers of said mat 20 on the roll 60 in one pass. The strip 20 is further subjected to brake tension in the reverse direction of the tension caused by rotation of the roll 60 in the direction of arrow 49 so as to decrease the width of said strip by at least 3 percent. Preferably, the tension under which the strip 20 is applied to the roll 60 is sufficient to stretch the trailing edge of the strip 20 by at least 3 percent more than the leading edge is stretched, at the point of contact of said strip on said roll. By stretching the trailing edge more than the leading edge, the strip itself accommodates the greater thickness at the trailing edge of the strip, where a plurality of layers have been built up.

To create the brake tension necessary for the above practice, the strip 20 passes through a dancer roll means which includes idler rolls 25 and 26 and dancer roll 27, as shown in FIG. 3. Dancer roll 27 is supported by pivot arm 28 about pivot point 29. A weight 30 is added to provide the ideal brake tension necessary to accomplish the proper winding under tension. Responsive to the position of the dancer roll 27 and attached to the pivot arm 28 is a sensing device 31 which may be a conventional air supply valve which is adjustable by movement of the pivot arm 28. Air is then passed through line 32 to air brake 33 which, depending upon the position of the dancer roll 27, acts to retard the rotation of the lazy Susan 22 to a varying degree. Thus, if the brake tension acting against the winding tension should increase, the winding tension would cause the dancer roll 27 to move upwards. Movement of the dancer roll 27 upwards would cause a movement of the pivot arm 28 signalling the device 31 to decrease the amount of air being passed through line 32 to air brake 33. When less air is provided to the air brake 33, rotation of the lazy Susan 22 is less restrained, and the brake tension decreases. Decreasing the brake tension in the lazy Susan 22 permits a lowering of the dancer roll 27. Thus it can be seen that movement of the dancer roll 27 will determine the amount of brake tension on the lazy Susan 22 means for holding the strip as it is being unwound.

To further stabilize variations in the brake tension, the strip 20 is then passed over a plurality of slide tension surfaces which are as shown in FIG. 3 consist of a plurality of nonrotating bars 36, 37, 38, 39 and 40. Depending upon the amount of wrap of the bars 36 through 40, varying amounts of brake tension or drag will be forced upon the strip 20. As shown by the equation in FIG. 4, the amount of tension T1 is equal to the force pulling the material over the surface T2 times e (approximately 2.72 -- the number upon which the natural logarithm system is based) raised to the power formed by the product of the coefficient of friction f and the angle of wrap a in radians. Thus with a greater angle of wrap, the tension T2 needed for passage over the member M will be increased.

As shown in FIG. 3, the sliding tension surfaces 36, 37, 38, 39 and 40 provide a sliding tension which is balanced against a spring tension. The sliding members 37 and 39 are mounted on members 41 and 42. Spring means 43 is connected to the opposite ends of members 41 and 42 so as to attempt to draw members 37 and 39 towards each other.

As the web 20 slides over the stationary nonrotating surfaces 36, 37, 38, 39 and 40, a degree of brake tension or drag is incurred. As a result of this drag, the members 37 and 39 are pulled further apart. In addition, the amount of wrap of the strip 20 about all of the slide members 36 through 40 is decreased, therefore decreasing the brake tension acting upon the strip 20. However, as the members 37 and 39 move further apart, members 41 and 42 mover further apart as well, creating an increase in the tension of spring 43. The spring 43, as it is stretched, causes an increase in the tension balancing against the sliding tension surfaces, tending to cause the members 41 and 42 to come closer together. It is readily apparent that, upon a selection of suitable surfaces for the sliding members 36, 37, 38, 39 and 40, so as to determine a suitable coefficient of friction with respect to the strip 20, and by appropriate selection of a spring 43, an equilibrium situation will be achieved whereby a controlled amount of sliding tension caused by the passage of the strip 20 over part of each of the sliding members 36, 37, 38, 39 and 40 will be balanced by the balancing spring tension in spring 43. Thus substantial changes in brake tension will be eliminated.

The net result of all of the balancing of tensions is to create a constant winding tension which is capable of decreasing the width of the web 20 as it is applied to the roll 60 under winding tension. By proper selection of values, depending upon the particular fibers and the density of the needled nonwoven mat (braking strength) suitable brake tension can be achieved to decrease the width of the web by at least 3 percent. A number of rolls have been prepared using this process wherein a 6-inch wide strip has been wrapped on a roll such that the width of the strip at the point of contact with the roll was slightly greater than 5 1/2 inches.

All that remains to complete the manufacturing process is the addition of the resin to the mat. This, as shown in FIG. 3, is accomplished by saturating the mat 20 with a resin supplied from tank 52 in the direction shown by arrow 53. The resin is applied to one side of the strip only, to permit escape of entrained air. The downward run of the mat around roll 44 permits formation of a flooded nip 45 formed by rolls 44 and 46. Tension on the roll 46 causes the excess resin from the nip 45 to be forced through the strip 20 to expell any remaining entrained air and further saturate the strip 20. After this saturation, the strip then passes through the bath in tank 48 and is drawn up on roll 60. In many instances, an excess of resin is applied, perhaps as much as two or three times as much as needed, which excess is later drained from the roll prior to curing of the resin and collected in tank 50. In fact, the tension under which the roll is being wound acts to squeeze excess resin from the saturated mat, so as to leave a mat containing from 10 to 40 percent by weight of fibers and 90 to 60 percent by weight resin. Preferred composite materials contain from 15 percent to 30 percent by weight fibers and from 85 percent to 70 percent by weight of said resin. Ideally, it has been found that composite materials containing from 20 percent to 25 percent by weight of fibers have been from 80 percent to 75 percent by weight of resin are preferred.

Once the resin has cured, machining, grooving, grinding and other modifications of the roll may be preformed to ready the roll for use in a wide variety of applications. The roll may be used in the textile industry, metal working, printing, and other industries which require the use of rolls. Many uses in the paper industry have been found for rolls having the composite material covering of the present invention.

It has been found that rolls made according to the present invention, which have been grooved with generally circumferentially oriented grooves are particularly suitable in press sections in the paper making industry. A number of trials have demonstrated that the covers of the present invention have the following advantages. There is no groove closing during operation, and a permanent crown may be placed on the roll due to the zero creep of the material. Moreover, operation under varying temperature conditions is possible without the adverse effects found when land areas crack when using other cover materials. Oftentimes, the interior of a surface will be at a substantially higher temperature than the surface which is receiving cooling, either intentionally from showers or by the water present in the paper. Composites of the present invention have been found to withstand these variations in temperature without cracking the lands whereas rubber and other materials do not. Moreover, no effect has been observed when these rolls have been contacted with chemicals and solvents used as felt cleaners in press sections.

The fiber pickup in the grooves is kept to an absolute minimum, since the composite itself may be readily machined and polished to a smooth finish.

Experimental tests employing covers of the present invention have shown that rolls with or without grooves may operate at speeds up to 6,000 feet per minute and 1,000 lbs. per linear inch for substantial periods of time without any failure. Rolls installed in press sections of paper making facilities on a trial basis have operated for periods in excess of 3 months, without failure, whereas conventional covering materials such as rubber were unable to last as long as a week. Moreover, superior paper is possible to be manufactured due to the thermal shock resistance of the present invention. Water showers using 55.degree. F. water were employed in a press section with no adverse effect. This is contrasted with rubber covered rolls which were unable to operate with showers below 110.degree. F.

Smooth ungrooved rolls have also permitted the use of gloss calender operations and have materially improved the economics of such a paper making process. In prior attempts, the use of a stainless steel roll or other metal roll in contact with a second metal roll was found to be substantially damaging to paper. Accordingly, a stainless steel roll was operated against a softer roll covering material to obtain the desired effect on the paper. However, these softer materials were unable to withstand the operating conditions for any commercially feasible length of time, thereby significantly raising the costs of such a process. As shown in FIG. 5A, a rubber covered roll, operating in a nip with a stainless steel roll, with the stainless steel roll being the driving roll, is subjected to substantial pressures which destroy the rubber covering. Specifically, the speed of the stainless steel roll SS at it surface S is governed by the driving speed of the roll SS. Since the stainless steel roll SS is the driving roll, the speed of the rubber covered roll R at the nip SN is equal to the speed S of the stainless steel roll. However, since rubber is incompressible and elastic, the surface of the roll at the nip is stretched, thus the speed of the rubber covered roll R at its surface at a point away from the nip SR is less than the speed of the stainless steel drive roll SS. With each revolution of the rubber covered roll, the surface speed will change. This constant change of surface speed soon destroys the rubber covering.

Shown in FIG. 5B is an instance where a stainless steel roll SS is mated with a filled roll F under similar circumstances. Again the speed S of the stainless steel roll SS, the driving roll, is constant around the entire circumference. This speed S is equal to the speed SN at the nip of the filled roll F. However, since the filled roll is compressible, the surface is compressed at the nip, and the surface speed SF of the filled roll F at a point away from the nip is greater than the speed S of the stainless steel roll SS. Again this constant rapid change in the speed of the surface of the filled roll soon destroys the roll.

Shown in FIG. 5C is a similar arrangement using a stainless steel roll SS as a driving roll and a roll C formed according to the present invention. In this instance, the speed S of the stainless steel roll SS again remains constant. This speed S, since the stainless steel roll SS is the driving roll, is equal to the speed SN of the roll C at the nip. Since the roll according to the present invention is capable of being stretched, as is rubber, an effect similar to that of FIG. 5A is found. However, since the composite of the present invention is also capable of being compressed, the effect on the surface as shown in FIG. 5B is also found. Thus, with both stretch and compression, the speed SC of the roll C according to the present invention does not change with respect to the speed S of the stainless steel roll or the speed SN of the nip. Although there is some stress and compression of the material, the surface itself does not change speed. The substantial increase in the life of the surface of a roll having the composite of the present invention is not only theoretically predictable but has been observed experimentally. This substantial improvement in the life of the roll covering has made feasible the economics of such a paper making apparatus.

It has been discovered that the rolls made as described herein have particularly advantageous properties which were not expected. The composite has a high modulus elasticity (both fiber and resin) which is not obtainable in compounded elastomers of hardness necessary for use in commercial practice. The roll covers have an unusual ability to withstand high nip loads and speeds and yet are capable of sustaining very severe shock loads without damage. It has extremely low hysteresis. The composite as described herein has practically no creep under dynamic conditions, resulting in a "non-marking" cover. The essentially zero flow of the material permits maintenance of the crown shape, eliminates corrugation and prevents groove closing. As mentioned above, there is no variation in the surface speed entering and leaving the nip region.

As has been stated above, the rolls of the present invention may be employed in a wide variety of industries for a substantial number of uses. In those instances where the roll must operate at high speed and/or under high loading conditions, use of the rolls of the present invention will offer substantial increases in the life of a roll covering and will materially improve the practice of the particular process. In the paper industry, rolls according to the present invention may be used as press rolls, calender pressure rolls, suction rolls (with holes drilled in a conventional manner), grooved suction rolls, rolls where the amount of crown is variable, suction pressure rolls, wet end rolls (such as breast rolls, couch rolls, wire turning rolls, and table rolls), breaker stack rolls, machine calender rolls, and the like. The range of roll surface hardness may be provided by a suitable choice of fiber density, and resin.

Claims

What is claimed is:

1. A roll adapted to operate at high speed and high nip pressures having an outer shell comprising:

a composite material formed from plural layers of a needled nonwoven mat selected from the group consisting of acrylic fibers, polyester fibers and mixtures thereof,

said layers being bonded with a thermosetting resin of the epoxy type.

2. A roll adapted to operate at high speed and high nip pressures having an outer shell comprising:

a composite material formed from plural layers of a needled nonwoven mat selected from the group consisting of acrylic fibers, polyester fibers and mixtures thereof,

said layers being bonded with a thermosetting resin of the epoxy type,

said composite having from 10 percent to 40 percent by weight of said fibers and from 90 percent to 60 percent by weight of said resin.

3. The roll of claim 2 wherein said composite contains from 15 percent to 30 percent by weight of said fibers and from 85 percent to 70 percent by weight of said resin.

4. The roll of claim 2 wherein said composite contains from 20 percent to 25 percent by weight of said fibers and from 80 percent to 75 percent by weight of said resin.