Patent Publication Number: US-6905734-B2

Title: One pass polyurethane roll covering system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to now abandoned U.S. provisional application entitled, “One Pass Polyurethane Roll Covering System and Method,” having Ser. No. 60/338,218 filed Nov. 8, 2001, which is entirely incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention is generally related to roll coverings and, more particularly, is related to a system and method for covering rolls that may be used in the pulp and/or paper industry. 
     BACKGROUND OF THE INVENTION 
     Polyurethanes are often used to cover rolls used in a variety of industries, e.g., paper, lumber, printing, steel, mining and textile industries. In particular, polyurethanes are often used when special properties are desired of the covered rolls, such as abrasion resistance, tear resistance, high load bearing with high hardness, and solvent resistance. 
     In the papermaking industry in particular, a plurality of rolls are used to transport a web or the paper from the beginning of the process through the end. In the process, a slurry of approximately 95% water and approximately 5% pulp fiber is transported via a web through machinery where water is extracted from the pulp, and the resultant pulp is then pressed and dried. In the process, a continuous sheet of paper is produced and wrapped onto a large metal roll for further processing. The rolls used in the papermaking process typically range in size from approximately 12 inches in diameter and a 100 inches long to approximately 60 inches in diameter and approximately 400 inches long. Fifty (50) to 250 rolls may be used in any one paper machine including the rolls at the end that the paper is wrapped upon, i.e., the reel spool. The outer diameter of these rolls is often covered with a rubber or polyurethane to protect the roll from corrosion and to help de-water the paper. They also provide traction for the webs used to transport the fiber and water sheet that is made into paper. 
     Polyurethane-covered paper machine rolls are known to have excellent abrasion resistance and corrosion resistance, vibration dampening and load-bearing ability. Further, polyurethane covered rolls help protect the web. The beginning of the papermaking machine  10 , as depicted in  FIG. 1 , will typically carry the pulp on a web  12  (or “wire”) and will typically form a continuous loop that may encompass from approximately five to approximately thirty rolls and can be from approximately 100 inches to approximately 400 inches wide. On the wet end of the papermaking machine  10 , the wire  12  may be exposed to temperatures of approximately 120 to 180 degrees Fahrenheit (° F.). 
     The wire  12  is usually a polypropylene screen that spins in a continuous loop along the rolls. Typically, only one or two rolls are driven. The driven rolls drive the wire and the wire drives the other rollers. The wire  12  is consumable and may cost from approximately $60,000 to approximately $100,000 each and usually lasts only approximately two to nine months. In the press section of the process, depicted in  FIG. 2 , the wire  24  is usually referred to as a “felt.” The polyurethane covering on rolls contacts this expensive consumable wire or felt at a pressure of approximately 15 to 60 pounds per linear inch to give the desired traction and performance. 
     Ideally, a roll and wire  12  track like a gear. If the wire  12  cannot keep up with the driven roll, then slippage occurs and the wire  12  is abraded and becomes worn. Anything that extends the life of the wire  12  or the felt  24  is considered a significant improvement in the process. 
     On the wet end of the papermaking machine  10 , pulp is dispensed out onto the web  12  by a dispensing mechanism  14 . The web  12  then travels across a series of foils  16  that de-water the pulp. Suction can be applied via the foils  16 , or optionally, the foils  16  may have sharp edges that the pulp passes over that scrape the water off the bottom of the porous wire and creates a bit of vacuum on the trailing side of the pulp. After the pulp passes over foils  16 , or optionally during passage over foils  16 , a sheet of paper begins to form. The sheet disposed on web  12  then passes over vacuum boxes  18 , and optionally beneath a dandy roll  19 . After the sheet passes over the vacuum boxes  18 , traditionally the sheet continues on to the press section  20 , while the web  12  runs between at least one couch roll  21  and a suction pickup roll  22 , and returns via guide rolls  23  to the beginning of the papermaking machine  10 . Configurations vary by grade of product manufactured, but the process is essentially the same in all. 
     In the middle or press section  20  of the papermaking machine  10 , as depicted in  FIG. 2 , the web is pressed between large press rolls  26  that may or may not apply suction through holes in the face of one of the press rolls. The cover on the rolls  22  helps determine the width of the nip and the pressure on the web  12 . The sheet of paper, when picked up by the suction pickup roll  22 , is pulled off of web  12  and onto the felt  24 . The felt  24  comes around through the press and then is squeezed. The paper at this point is strong enough to accept a nip. In the press section  20 , the paper and felt  24  may get nipped two or three times, and be transferred from one felt section to another felt section. As shown in  FIG. 2 , for example, the sheet of paper may pass through three felt sections. 
     On the dryer section  30  of the papermaking machine, as shown in  FIG. 3 , the web  12  is usually passed over steam-heated cylinders  32  that may be of a 350° F. internal steam temperature. In the dryer section  30 , the sheet of paper is usually strong enough to be separated from the web  12  and travel on its own strength for short distances. While the paper may still be approximately 65% water, the fibers are usually bonded together enough from pressing and de-watering to form a sheet. In the dryer section  30 , the paper travels back and forth through a series of steam-heated dryers  32 . A felt may be used in the dryer section  30  to hold the paper down against the dryer cylinder  32  and to further absorb the water that is coming out of the paper. 
     At the very end of the papermaking machine  10  in section  40 , as shown in  FIG. 4 , the paper may go through a calender reel  42 , to which various coatings, sizings, etc. may be placed on the paper, e.g., for printability. The paper is then wound up on a reel spool  44 . 
     The typical process for applying polyurethane to the rolls described hereinbefore is a vertical casting process where the roller is picked up on one end and lowered into a mold that is customized for the roller. The mold is then poured, casting the bigger outer diameter on the outside of the roll. Post curing typically takes place in the mold. The roll is then removed from the casting and then tooled or ground to get the evenness and finish that is desired on the surface of the polyurethane. 
     There are some problems associated with the vertical casting process; for example, the polyurethane may disbond from the roll. Further, bubbles may be formed in the polyurethane which it is necessary to remove. An additional problem with conventional casting processes is that the custom molds are built for each roll and the polyurethane is cast with a large amount of extra stock on them because of surface defects that occur in the mold due to gas bubbles and the abuse to which the mold is subjected. This is an extremely time-consuming and expensive process and requires a lot of storage space for the molds. Further, the conventional casting process is probably not necessary for 85% of rolls in paper-making process that do not need to withstand high temperatures and/or high pressure. 
     Another process used for applying polyurethane to the roll is a rotational casting process, which is performed horizontally. In the rotational casting process, polyurethane is ribbon-flowed onto the surface of a shell as it rotates. The head of a polyurethane-dispensing mechanism traverses the roll, extruding polyurethane onto the surface of the roll at a very low pressure and flow rate. Because the polyurethane is a liquid when dispensed, the liquid must be slowly extruded so that it does not drip off of the roll during the dispensing process. Further, the polyurethane in the traditional rotational casting process is only applied in a four-inch width, and under a pressure of approximately 1,000 pounds per square inch (psi) or less. 
     Additionally, traditional rotational casting processes require that the roll be placed in an oven for curing, as well as additional post-cure cooling time before machine grinding the roll. The traditional rotational casting process can take up to approximately 16 hours from beginning until the roll is removed from the oven. Adding in post-curing time, it can take up to approximately 24 hours to completely cover one roll before machining or grinding can begin. 
     The polyurethanes that are processed in the rotational casting process are typically made from polyethers. One problem with the polyether chemicals suitable for this process is that they cannot be used in the wet end of the paper machine ( FIG. 1 ) because they absorb too much water. Therefore, they are usually used only on reel spools  44  at the very end section  40  of the machine  10  (FIG.  4 ). This is a more limited market, and is also a very expensive technology. 
     Rubber has also been used to cover and protect the rolls and is the oldest technology that has been used to cover rolls. The rubber is typically applied in an extrusion process that extrudes a ribbon on the roll starting at one end and traversing to the other, as the roll rotates. A lot of excess rubber is usually applied because the rubber has to be vulcanized on the entire roll and it shrinks in this process. An additional problem with the use of rubber is the requirement of an oven that is big enough to accommodate the entire roll core. The rubber is then cooked until it is cured on the core, resulting in a shrinkage that stresses the cover. The rubber then has to be rough tooled and ground to get the straightness and finish that is needed on the surface of the cover. Because the process of applying rubber is very inaccurate, a large amount of wasted material is usually machined off to create the desired surface. For example, in a typical process of preparing a rubber-covered roll, approximately 0.250 inch per side (0.5 inch on diameter) to approximately 0.5 inch per side (1.0 inch on diameter) is machined off. The process of applying rubber to the typical papermaking roll may take approximately three to four days, which renders this a time consuming process. 
     In the rubber extrusion process, for example, a ribbon of rubber is extruded that may be one-half inch (½ in.) wide and approximately one quarter (¼) to three-eighths (⅜) of an inch thick. That is sometimes accomplished at an angle, or vertically with the narrow end against the roll. The result is a very rough surface as the rubber is extruded because each ribbon is pressed against another ribbon, as they are stacked in multiple layers. Because the layers of rubber are being pressed, the top layer tends to bunch up more in the area of the joints. This can lead to as much as one-quarter of an inch (¼ in.) difference in the surface between the low spot and the high spot between the center of one ribbon and the joint with the next ribbon. The result is that this portion of the rubber must be machined off once it is cured. Therefore, a lot of stock must be removed in order to obtain a 100% clean rubber surface, which results in a large amount of wasted material. 
     Polyurethane has also been dispensed on to various objects, from truck beds to roll covers, through a spraying mechanism. The problem with the typical spraying process, however, is that the polyurethane is typically applied in only approximately {fraction (40/1000)} of an inch in a pass, and therefore a three-quarter inch (¾ in.) cover would require approximately 20-40 passes about the roll in order to build up the thickness of the polyurethane. 
     Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method for applying polyurethane to rolls that may be used in the papermaking industry. 
     Briefly described, one embodiment of the method, among others, can be summarized by the following steps: providing a cylindrical roll having two ends and a surface, wherein the cylindrical roll is attached to a variable speed turning fixture on said ends of the roll; providing a variable speed traversing mechanism having a nozzle to atomize the polyurethane; providing polyurethane under high pressure; and covering the surface of the roll with up to three inches of polyurethane, on the diameter, in one pass of the traversing mechanism along the length of the roll while rotating the roll via the variable speed turning fixture. One advantage of the present method is that it is a continuous operation, with all material applied in one pass down the roll, and in which there is minimal delay in waiting for the roll to cure, as curing happens without the addition of heat. Thus, post-curing time does not inhibit processing of the roll. Post-cure time at 70° F. is approximately three (3) hours for most rolls, with no supplemental heat source necessary. 
     Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a side view of the wet end of a prior art papermaking machine. 
         FIG. 2  is a side view of a press section  20  of the papermaking machine of FIG.  1 . 
         FIG. 3  is a side view of the dryer section of the papermaking machine of  FIGS. 1 and 2 . 
         FIG. 4  is a side view of the end of the papermaking machine of  FIGS. 1-3 . 
         FIG. 5  is a flow chart of one embodiment of the method of the invention. 
         FIG. 6  is a top view of a system used to accomplish the method of FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION 
     A system and method has been developed that allows efficient and easy application of polyurethane to cover rolls that may be used in the papermaking industry. Rolls used in the paper-making industry that may be covered with polyurethane using the system and method of the present invention include, but are not limited to, the following: breast rolls, wire rolls, wire return rolls, wire turning rolls, wire drive rolls, felt rolls, paper rolls, stretch rolls, guide rolls, press rolls, suction rolls, fly rolls, breaker stack rolls, size press rolls, lead-in and lead-out rolls, coater rolls, coater backing rolls, dryer felt rolls and reel spools. 
     Referring now to the drawings,  FIG. 5  depicts in brief a flowchart of the method  50  of the present invention. As shown in block  52 , a cylindrical roll, a traversing mechanism, a mixer and polyurethane components are provided. The roll may undergo surface preparation prior to being provided in block  52  of method. For example, a prior-applied cover may need to be removed. Further, the roll is typically cleaned, degreased, and then grit- or sand-blasted. The roll may then be blown with clean, dry air, and its temperature brought to at least approximately 50 degrees Fahrenheit (° F.) if necessary. Additionally, it is desired that the temperature of the roll exceed the dew point before proceeding to the next step. 
     Returning to  FIG. 5 , as depicted in block  54 , the polyurethane components are mixed in a mixer and are dispensed via the traversing mechanism onto the roll. As shown in block  56 , the roll is covered with polyurethane up to approximately one and a half inches thick per side (three inches on diameter) in one pass of the traversing mechanism while the roll rotates. It could be envisioned by one skilled in the art that any or all step(s) of the process of the present invention can be automated or performed manually. 
     Application Ser. No. 60/338,214 entitled “One Pass Polyurethane Roll Covering System and Method,” to which the present application claims priority, refers to “coating” the rolls with polyurethane. It would be understood to one skilled in the art that the term “coating” as used in that application is interchangeable with the term “covering” as used herein. 
       FIG. 6  depicts the system  60  that is used to accomplish the method  10  of the invention. The system includes a roll  62  that may be comprised of, for example but not limited to, metal, rubber, polyurethane, epoxy, and/or carbon fiber. As noted before, preferably the roll  62  is grit-blasted prior to application of polyurethane  74 , and is free of substantially all dirt, grease, debris, or other impediments that would prevent polyurethane  74  from adhering evenly to roll  62 . 
     As shown in  FIG. 6 , roll  62  is covered with polyurethane  74  and a traversing mechanism  64  is used to apply polyurethane  74  to the roll  62 . The traversing mechanism  64  is connected to a formulator proportioner  66  via the curative spray hose  68  and curative recirculation hose  69  and the resin spray hose  70  and resin recirculation hose  71 . The formulator proportioner  66  is the device that correctly proportions the ratio of curative to polyurethane resin. From the formulator proportioner  66 , the curative and resin move and recirculate through hoses  68 ,  69 ,  70  and  71  to mixer  72  of the traversing mechanism  64 . In the mixer  72 , the curative and resin are mixed, in the proportions determined by the formulator proportioner  66 . Mixer  72  may be any conventional mixer known to those skilled in the art, for example, either the static-tube mixers or spiral mixers manufactured by and commercially available from TAH Industries, Inc. of Robbinsville, N.J., USA. 
     The polyurethane  74  is comprised of the resin and curative. Prior to mixing, the resin and curative may have a viscosity of, for example but not limited to, approximately 350 centipoises. Prior to application of the two components, the two components are preferably brought to a temperature to match their viscosities, and the polyurethane mixture  74  may have a viscosity greater than, for example, approximately 100,000 centipoises. The two components are mixed in the mixer  72 , and then pumped to the dispensing mechanism  76  via an airless pumping system (not shown). Mechanical positive displacement, single-ended, linear, reciprocating pistons may be used to apply the resin and curative mixture. The pumping system may comprise chrome hardened shafts and sleeves. The dispensing mechanism  76  is any device capable of dispensing the polyurethane in a fan configuration under high pressure. Preferably, the dispensing mechanism  76  is, for example, but not limited to, a nozzle. 
     The resin may be any polyol known in the art that is used in the production of polyurethane. In one embodiment the resin may be, for example but not limited to, a polyester/polyether blended polyol. The curative may be any curative known in the art, for example but not limited to, an isocyanate, for example, polymeric diphenylmethane diisocyanate—4,4 (MDI). Suitable ratios of resin to curative range from, for example but not limited to, a ratio of approximately 1 part resin to approximately 1 part curative (1:1), to a ratio of approximately 5 parts resin to approximately 1 part curative (5:1). The polyurethane constituents are preferably kept within a specified temperature range. The resin is usually maintained at a temperature, for example but not limited to, from approximately 100° F. to approximately 150° F. The curative may be maintained at a temperature, for example but not limited to, from approximately 60° F. to approximately 130° F. 
     Returning to  FIG. 6 , from the traversing mechanism  64 , the polyurethane  74  is dispensed via dispensing mechanism  76  onto roll  62 . During application of the polyurethane  74 , the pressures and flow rates of the mixture of the two components (resin and curative) are monitored as it flows from the mixer  72  through the dispensing mechanism  76 . The polyurethane may be applied at a rate, for example but not limited to, from approximately 0.15 gallons per minute (gal/min) to approximately 2.0 gal/min. The polyurethane  74  is, in a preferred embodiment, dispensed at a pressure of approximately 1,000 pounds per square inch (psi) to approximately 5,000 psi. More preferably, the polyurethane  74  is dispensed under a pressure of approximately 1,500 psi to approximately 3,000 psi. More preferably, polyurethane  74  is dispensed under a pressure of approximately 2,000 psi to approximately 2,500 psi, but this can vary depending upon the specific characteristics of the polyurethane being applied. In particular, it is desirable to atomize polyurethane  74  being dispensed, and dispense it onto roll  62  at a pressure that does not exceed the pressure at which impact deflection off of roll  62  occurs. 
     The traversing mechanism  64  is situated upon a track  78  which allows the traversing mechanism  64  to pass along the length of the roll  62  while dispensing the polyurethane  74 . A carriage and rails that may be used in the present invention, for example, are commercially available from and manufactured by Bug-O Systems of Pittsburgh, Pa., USA. 
     Polyurethane  74  is dispensed via dispensing mechanism  76  onto roll  22 i n a fan configuration, as depicted in FIG.  6 . The exemplary fan-shaped configuration shown in  FIG. 6  can be up to approximately 30 inches wide. Alternatively, the polyurethane being dispensed covers from approximately six to thirty-six inches of the longitudinal portion of the roll. This represents a vast improvement over traditional processes that dispense polyurethane as a thick liquid, where the width in which polyurethane is dispensed is only approximately four inches wide. 
     As noted previously, polyurethane  76  is dispensed via dispensing mechanism  76  while roll  62  is rotating. In a preferred embodiment, the layer of polyurethane  74  on the cylindrical surface of the roll  62  applied on a previous rotation of roll  62  is not completely cured after one rotation of roll  62 . Thus, the polyurethane  74  presently being dispensed from the dispensing mechanism  76  becomes homogenous with the previous layer of polyurethane  74  already applied to the surface of the roll  62 . 
     In a preferred embodiment approximately 20% of the fan-shaped configuration of polyurethane  74  being dispensed contacts an uncovered longitudinal portion of the roll  62  during each revolution. Thus, approximately 80% of the fan width is contacting polyurethane already applied to the roll, while the remaining approximately 20% of the width of the fan-shaped configuration is contacting an uncovered portion of roll  62 . 
     Each end of the roll  62  is disposed upon V-block supports  80  for the bearings (not shown) of the roll  62 . The V-block supports  40  are positioned upon movable support stands  82  for the roll  62 . Optionally, the support stands  82  may be movable or stationary. At least one end of the roll  62  is attached to a variable speed turning fixture  84  via a self-aligning three jaw chuck  86  and a universal joint  88 . The turning fixture  84  is disposed upon a support stand  90 . The turning fixture  84  may turn the roll at a rate, for example but not limited to, from approximately 3 revolutions per minute (rpm) to approximately 50 rpm. 
     If the support stands  82  are movable, they may be situated upon rails  92  for moving the movable support stands  80  and the roll  62 , upon completion of the application of the polyurethane  74 . Optionally, the movable support stands  82  may have wheels attached (not shown) which allow for movement of stands  82  and which may lock upon being positioned at correct locations. The distance between the two stands  82  can be increased or decreased to accommodate rolls  62  of various sizes. An optional backdrop  94  may be provided to protect any person or object located on the opposite of the roll  62  from the traversing mechanism  64 . 
     Effectively applying polyurethane  74  to roll  62  is a balance of chemistry and mechanics of the cure rates in terms of mixing the curative and resin in the mixer  72  at the appropriate temperature, and for the appropriate amount of time prior to applying polyurethane  74  to roll  62 . The temperature at which the polyurethane  74  may be applied to roll  62  is fairly broad, for example, but not limited to a range of approximately mid-40&#39;s to approximately high 90&#39;s ° F., and preferably greater than 50° F., and above the dew point. The polyurethane  74  covering the roll has a thickness of up to approximately three inches with a viscosity of approximately 10,000 centipoises in the liquid state prior to hardening. 
     During each revolution of the roll  62 , polyurethane  74  is applied via the dispensing mechanism  76  in a layer approximately {fraction (1/2,000)} inch to approximately {fraction (1/10,000)} inch thick. Preferably, the layer of polyurethane  76  applied during each revolution is approximately {fraction (1/5,000)} inch thick. Thus, when a layer of approximately {fraction (1/2,000)} inch to approximately {fraction (1/10,000)} inch thick of polyurethane  74  is applied in a spray at a temperature of approximately 110 degrees F. to a surface of the roll  62  at approximately 70 to 73 degrees F., and at a pressure of approximately 2,500 psi, the polyurethane  74  maintains a viscosity, for example, for approximately five (5) to 30 seconds such that polyurethane  74  being applied to the surface becomes homogenous with a previous layer of polyurethane  74  already applied to the surface of roll  62 . 
     The process usually takes approximately three and a half (3.5) to six and a half (6.5) hours from the beginning of the application of polyurethane  74  to roll  62 , until the roll  62  is taken to be machine ground, at approximately 70° F. Therefore, in the time it takes to finish the application of polyurethane  74 , turn off the traversing mechanism  64 , clean the area in and around the system  62 , and move the roll  62  to the next station (not shown) to be machine ground, the appropriate amount of time has elapsed, approximately two and a half (2.5) to three and a half (3.5) hours, so that the roll  62  with the polyurethane  74  applied may be immediately machine ground. In particular, the rolls covered with polyurethane  74  via the process of the present invention reach approximately 85% of their ultimate hardness within three hours of covering, at 70° F., and are machineable at that point. Thus, post-curing time does not inhibit processing of roll  62 . 
     After application of polyurethane  74  to roll  62 , the roll may be taken to a lathe and/or roll grinder, where the surface may be finished either with a tool or belt or wheel. An additional advantage of the present invention is that a very small amount of the polyurethane material lost or wasted during the method  10  because the application process of the polyurethane  74  is very accurate. For example, wasted material will typically range from approximately 0.025 inch per side (0.050 inch on diameter) to approximately 0.075 inch per side (0.150 inch on diameter). Typically, the diameter checks come within {fraction (10/1,000)}ths of an inch of conformity with the desired diameter, dependant upon the accuracy of the roll diameter. Thus, there is much less polyurethane material wasted in order to obtain a usable surface on the covered roll than with conventional polyurethane application processes. 
     In addition to the timing of addition and mixing, and the temperature of the mixture of the resin and curative in mixer  72 , the cure rate of the polyurethane  74  is an important aspect of the method. The application rate of the polyurethane  74  to the roll  62  is preferably controlled so that the polyurethane  74  does not run or drip off of the roll  62  and onto the floor. The cure rate of the polyurethane mixture  74  can be controlled by the rotation of the roll  62 , the size of the dispensing mechanism  76 , or the rate at which the traversing mechanism  64  traverses the roll  62 . These parameters that affect the cure rate usually are a function of the size of the roll  62 . 
     The time for curing may also depend on such conditions as, for example, ambient temperature, surface temperature of the roll  62 , starting materials used (including presence of any impurities), and temperature of polyurethane  74 . The time for curing, so that the polyurethane  74  is hard to the touch, may range from approximately 10 minutes to approximately 20 minutes at a temperature of 70° F. The roll  62  may be taken to a sanding or grinding machine after application of polyurethane  74  by the present method after only approximately 180 minutes at 70° F. The roll  62  may be installed and used in a paper machine after approximately 36 hours at 70° F. temperature, when polyurethane  74  is applied via the present method  50 . 
     The polyurethane  74  may be tested prior to application of the polyurethane  74  to the roll  62  in order to determine that the thixotropic properties of the polyurethane  74  procedure are correct. The test may include inserting a wooden stick into the polyurethane mixture, immediately pulling it out, and accurately timing the number of seconds is takes for the polyurethane  74  to run off the stick. In a preferred embodiment of the test parameters of this test, the polyurethane would adhere to the wooden stick for approximately 50 seconds, but does not adhere to the wooden stick for more than approximately 60 seconds. The cure rate of polyurethane  74  may also be tested in a closed cup test with a known Shiyodou gel timer. 
     The cure rate of polyurethane  74  tested via this method is preferably from approximately 4.5 minutes to approximately 6 minutes, depending upon the ratio of the constituents. The ability to control the cure rate of the polyurethane  74  is an additional advantage of the process of the present invention. Polyurethane  74  cures at a rate at which it does not drop off of the roll onto the floor, thus avoiding a post-cure waiting period of time. 
     It should be noted that the polyurethane may be of any desired color. Depending on the pigmentation used, however, and how that pigment is saturated and mixed into polyurethane  74 , pigmentation may affect the viscosity of polyurethane  74 . Thus, cure rate may also be affected by additives to polyurethane  74 . 
     Different types of polyurethane  74  may be used in the method  10  and system  20  of the present invention. Various additives and/or fillers may optionally be added to either component, either resin or curative, prior to preparation of the polyurethane for additional advantages. The polyurethane  74  may include, for example but not limited to, any one or any combination of the following: silica; clay; isocyanates, for example, polymeric diphenylmethane diisocyanate; polyester polyol; polyether polyol; amines; polytetrafluoroethylene, or Teflon®; dyes or pigments, e.g., iron oxide, titanium oxide, and/or chromium oxide; nanoparticles; epoxies; graphite; high density polyethylene; and/or fibers. Fibers that may be added to either of the polyurethane components include, for example, but are not limited to, fibers that may include meta- or para-aramids or silica (e.g., glass fibers). 
     Silica may be added to aid in the attraction of the polyurethane  74  for the web  12  in a typical papermaking machine  10  (FIGS.  1 - 3 ). Polyurethane  74  with silica additives enables a tighter turn-up and seizes the paper better for a tighter line. 
     Polyurethane  74  may incorporate Teflon® which increases the release properties of the roll, whether it is the sheet that is being released, or the prevention of pulp build up. Further, with recycled fiber, there are often glues, pitches, tars, etc. that tend to adhere to certain surfaces and Teflon® in the polyurethane resists those particles from adhering to the roll cover. 
     Fillers or additives in polyurethane  74  can cause the polyurethane  34  to be hydrophobic. Rolls covered with hydrophobic polyurethane can run continuously on the wet end of the papermaking machine  10  ( FIG. 1 ) without absorbing water. Thus, the polyurethane covered rolls, covered by the method of the present invention, are more hydrolytically stable than rolls covered by traditional processes. Additionally, the polyurethane  74  need not incorporate any additional additives if the above-mentioned properties imparted by the additives are not desired or needed. 
     It should be emphasized that the above-described embodiments of the present invention, particularly, any “preferred” embodiments, are merely possible examples of implementations, and are merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention, and protected by the following claims.