Method for continuous conditioning of a blanket for a compressive shrinkage apparatus

A method for continuous conditioning of a rubber blanket such as the type used on compressive shrinkage apparatus is described. The blanket includes an inner bearing surface defining a bearing face and an outer surface defining a web-contacting face. The web-contacting face is contacted under pressure with an abrasive conditioning roll while the blanket is in its regular, web treating operation. The blanket working face can thus be continuously conditioned without the need for lengthy machine stops. In this way, the conventional grinding and cleaning operations can be minimized or eliminated.

FIELD OF THE INVENTION
 The invention generally relates to a process for maintaining a consistent
 surface on and extending the lifespan of a continuous rubber blanket. More
 specifically, the invention relates to a process and apparatus for
 continuously conditioning a continuous rubber blanket such as the variety
 used in the compressive shrinkage of webs of material.
 BACKGROUND
 Many textile fabrics, and in particular those made wholly or partly from
 cellulosic fibers, have a tendency to shrink undesirably as a result of
 becoming wet or undergoing conventional laundering processes. To obviate
 undesirable shrinking, many such fabrics are customarily treated using a
 compressive or compaction shrinkage process, in order to pre-shrink the
 fabrics and increase their stability. Examples of compressive shrinkage
 processes are described in U.S. Pat. No. 2,146,694 to Wrigley, et al. and
 U.S. Pat. No. 3,469,292 to Hojyo, U.S. Pat. No. 4,156,955 to Joy, and U.S.
 Pat. No. 4,446,606 to Lawrence et al, the disclosures of which are
 incorporated herein by reference. Also, a popular compressive shrinkage
 process is known by the tradename SANFORIZE.
 In compressive shrinkage processes, a fabric web is typically laid out over
 the working face of a thick endless rubber blanket so that it is free of
 folds or wrinkles. The rubber blanket is positioned on a plurality of
 rotatable rolls which support the blanket along its 10 bearing surface,
 and the blanket is typically conveyed along an endless path by way of a
 driven cylinder which contacts the outer blanket surface. In this way, the
 fabric web placed on the outer surface of the blanket is caused to be
 carried through a number of processing stations.
 First, the fabric is typically moistened, then it is compressed along with
 the blanket between a roll and a heated cylinder or shoe. As the fabric
 and blanket pass between the nip (i.e., the point of contact between the
 two contiguous elements) and the blanket is compressed, adjacent portions
 of the outer surface of the blanket are caused to be extended. As the
 blanket and fabric leave the roll, the blanket contracts, and the fabric
 is forced to follow suit. As a result, the yarns in the warp direction are
 caused to shorten, and the filling yarns are pushed upwardly, thereby
 mechanically shrinking the fabric. The fabric is then fed to a dryer,
 where it is dried in its preshrunk condition.
 Because the rubber blanket is endless, a web of fabric can be processed in
 a continuous manner. However, the surface of the rubber blanket must be
 cooled following contact with the heated cylinder before it again contacts
 the fabric web. Such cooling is generally performed by applying water to
 the blanket as it travels between the point of web removal and the point
 of untreated fabric web lay-down. Because too much moisture on the blanket
 can interfere with proper fabric conditioning, it is generally necessary
 that the amount of water on the blanket working surface be closely
 controlled. Generally this is performed by water removal rolls, which
 squeegee the excess water from the cooled blanket. Because it is important
 that the blanket stay properly lubricated, water is often added to the
 bearing surface of the blanket at various positions throughout the
 process, e.g., before the point of fabric lay-down and following contact
 of the blanket with the heated cylinder.
 As should be apparent, the rubber blankets are exposed to great stresses
 during the compression shrinkage process as a result of the repeated
 heating and cooling, the tensions at which the blanket must be run on the
 machine, the compression forces endured by going through the nip, and the
 repeated wetting operations. Under these conditions, the working surface
 of the blanket slowly oxidizes. This results in an increase in hardness
 and a decrease in wettability. In addition, finishes present on the fabric
 surface are often transferred to the rubber surface. Over a relatively
 short time this finish tends to form a glaze on the rubber surface,
 further decreasing the wettability and friction characteristics of the
 surface. As will be readily appreciated by those of ordinary skill in the
 art, the reduction in frictional characteristics on the web-contacting
 surface of the blanket reduces its effectiveness in gripping the fabric
 web. As a result, the surface characteristics of the blanket must be
 modified to restore its frictional characteristics in order that it can
 continue to properly and uniformly process fabrics.
 For example, in commercial applications, once the blanket hardness has been
 found to deviate upwardly or downwardly about 12% from its original level,
 blanket manufacturers recommend that the blanket be ground to remove the
 dead rubber on its surface. In this way, the surface of the blanket is
 prevented from becoming too slick or from losing its ability to grab hold
 of the fabric being treated. Such grinding is usually performed by
 stopping the machine and backing the rubber blanket up against a rotatable
 roll covered with abrasive material (e.g., grinding cloth or sandpaper),
 which grinds the working face of the rubber blanket until the dead rubber
 area has been removed.
 Typically the grinding process requires the removal of about a sixteenth of
 an inch of the blanket surface with each grinding. Because, for example, a
 blanket which begins at 3 inches thick usually must remain at least two
 inches thick to work effectively, the number of grindings is thus very
 limited. As a result, the life of the rubber blanket used in these types
 of apparatus can be undesirably short.
 It can also be appreciated that intermittent grinding of the blanket
 produces a surface that is variable over time, resulting in a greater
 amount of variability in compressive efficiency, and greater variability
 in the shrinkage characteristics of the final product. As the overall
 pre-shrinkage may need to be increased to avoid producing
 out-of-specification goods, the fabric yield will be less.
 In addition, small cuts and nicks in the blanket can form and grow over
 time due to oxidation and the constant stretching and releasing of the
 blanket rubber surface. When the blanket is ground, additional blanket
 thickness must be sacrificed in order to insure that all cracks are
 removed. This contributes to a shorter blanket life.
 During grinding of the blanket, production is halted, as the blanket must
 be ground dry to avoid premature decomposition or destruction of the
 grinding cloth or sandpaper. In addition, a considerable amount of rubber
 debris is formed due to the conventional grinding process. A heavy dusting
 of talc is typically applied during the grinding process, to reduce the
 friction and heat generated and to keep the blanket from becoming too
 sticky during the grinding operation. This talc and surplus rubber
 material must be cleaned from the blanket to prevent them from collecting
 on fabrics or materials being processed after the grinding operation.
 In addition, blankets typically require frequent cleaning to remove the
 build-up of baked-on fabric finishes, oils, and the like. Again,
 production must be halted so that the blanket may be cooled, and
 detergents applied. However, if such finishes and oils are not removed on
 a timely basis, they can adversely affect the process performance as well
 as contribute to the decomposition of the rubber blanket.
 The requirements of frequent cleaning and grinding prevent the rubber
 blanket machine from operating in-line with modern webprocessing
 equipment, which generally operate continuously, and which cannot
 economically be stopped to accommodate belt cleaning and grinding. A
 typical blanket grinding operation takes about 8 hours to perform, which
 is significant lost time from a fabric producer's perspective. Therefore,
 the grinding operation is recognized as being a significant source of
 machine downtime.
 One attempt to increase the lifespan of blankets in compressive shrinkage
 apparatus is described in U.S. Pat. No. 5,791,029 to Maker, the disclosure
 of which is incorporated herein by reference. The '029 patent describes a
 rubber blanket construction having a bearing face which is beveled. The
 patentee describes that this construction reduces the tendency of the
 edges of the blanket to curve upwardly when the blanket is tensioned to
 perform a grinding operation and reduces the tendency of the edges to
 crack. While this method may reduce the tendency of the blanket to crack,
 it does not overcome the need for frequent blanket cleaning and grinding.
 SUMMARY OF THE INVENTION
 The present invention is directed to a process and apparatus for
 continuously conditioning the working face of a rubber blanket such as
 that used on compressive shrinkage apparatus. As a result, the useful life
 of the blanket can be extended to a significant extent. (For purposes of
 this invention, the term "rubber blanket" is intended to encompass all
 blankets useful in compressive shrinkage type apparatus, whether they are
 substantially all rubber, partially rubber, made from synthetic rubber, or
 the like. Similarly, although the term "continuously conditioning" is
 used, it is to be noted that this terminology encompasses substantially
 continuous conditioning methods of a like nature as well, and in
 particular, when the user has elected to discontinue the conditioning
 briefly for various reasons.)
 Because the process of the instant invention can be readily incorporated
 into the regular machine processing operations (i.e., the web processing
 operation), the need for machine downtime to allow blanket grinding can be
 eliminated. This in turn enables the apparatus to be used more
 efficiently, by not requiring the machine downtime typically required for
 conventional blanket conditioning methods. In addition, existing
 compressive shrinkage machines can be readily retrofit to form the
 apparatus of the invention, thereby minimizing associated costs.
 The invention achieves the above-noted advantages through the provision of
 an abrasive device, and in particular an abrasive roll, on the apparatus
 such that the abrasive roll is in contact with the working surface of the
 rubber blanket during regular operation of the compressive shrinkage
 apparatus during its regular web treatment process. In this way, the
 abrasive roll can provide a low level of consistent grinding for
 continuous periods of time. In a preferred form of the process, the
 abrasive roll contacts the blanket at substantially all times during
 operation of the machine and advancement of the blanket. Alternatively,
 the abrasive roll could be provided to contact the blanket less than 100%
 of the time the blanket is advancing (although constant contact is
 generally preferred.)
 The speed of the abrasive roll relative to that of the working surface of
 the blanket can be adjusted to provide the desired amount of grinding.
 Preferably, only a small differential in speeds exists, such that a
 constant low level of grinding can be achieved. Similarly, the pressure of
 the abrasive roll against the blanket can be selected to achieve an
 optimal level of grinding. Furthermore, it is particularly preferred that
 the rotation of the abrasive roll is directly associated with the travel
 of the blanket, so that the grinding operation is halted simultaneously
 upon the cessation of blanket movement. In this way the formation of
 irregularities in the blanket surface as a result of the grinding
 operation can be minimized. In other words, in the embodiments of the
 invention where the grinding is directly associated with the blanket
 movement, the risk that the blanket will cease movement while grinding
 continues can be avoided (thereby avoiding the risk that irregular regions
 of greater grinding are formed.)
 Surprisingly, a working surface having characteristics indistinguishable
 from that of the usual high speed dry grinding using talc may be achieved
 and consistently maintained, even in the hot and wet conditions typically
 associated with compressive shrinkage processes.

DETAILED DESCRIPTION
 In the following detailed description of the invention, specific preferred
 embodiments of the invention are described to enable a full and complete
 understanding of the invention. It will be recognized that it is not
 intended to limit the invention to the particular preferred embodiment
 described, and although specific terms are employed in describing the
 invention, such terms are used in a descriptive sense for the purpose of
 illustration and not for the purpose of limitation.
 With reference to the drawing, FIG. 1 illustrates one embodiment of
 apparatus according to the present invention. Although described
 specifically to correspond with the illustrated apparatus, it is noted
 that the features of the invention can be included with other similar
 types of apparatus having a continuous blanket and in particular, other
 types and configurations of compressive shrinkage apparatus. In addition,
 although described in connection with the compressive shrinkage of textile
 fabrics (such as woven, knit and nonwoven fabrics), it is noted that the
 invention would have application to other types of compressive shrinkage
 apparatus, such as those designed to process paper webs.
 The apparatus, shown generally at 10, desirably includes many of the
 elements included in a conventional compressive shrinkage apparatus. In
 particular, the apparatus 10 desirably includes a first roll 12, which
 cooperates with a heated drum 14 to form a nip 16 therebetween. The
 apparatus also desirably includes a tensioning roll 18, an idler roll 20,
 and water removal rolls 22. A rubber blanket 24 is positioned so that it
 extends around the rolls 12, 18, 20 and 22 in the manner illustrated. In
 this way, the rolls define a continuous path through which the blanket 24
 travels during the web processing operation.
 As illustrated, a web W is fed into the apparatus so that it extends in an
 overlying relationship to the web-contacting surface 24a of the blanket.
 In this way, the web of material W is compressed between the nip roll 12
 and the heated drum 14 along with the blanket 24, so that it is
 compressively shrunk in a conventional manner.
 In the illustrated embodiment of the invention, a first roll 26 is placed
 in pressure contact with the web-contacting surface of the blanket 24, and
 is allowed to be driven by the blanket at a synchronous surface speed. As
 will be appreciated by those of ordinary skill in the art, the surface
 texture and/or pressure at which the drive roll contacts the blanket
 enables the roll to be rotated upon an advancing motion by the blanket.
 Preferably, the surface of this first roll is abrasive (e.g. by way of a
 stippled or textured surface, or more preferably through the provision of
 grit particles on the surface of the roll.)
 This drive roll 26 is then differentially geared to a second abrasive roll
 28, also in pressure contact with the web-contacting surface of the
 blanket 24, so that it is driven at an asynchronous surface speed to the
 blanket. First and second backup rolls 30, 32 may also be provided in
 order to provide or increase pressure between the drive and abrasive rolls
 26, 28.
 In this way, the abrasive roll 28 serves to remove a portion of the
 web-contacting surface 24a of the blanket as the blanket circulates along
 its web-processing endless pathway. Therefore, grinding can be performed
 during the normal compressive shrinkage operation rather than as a
 separate operation.
 As will be appreciated by those of ordinary skill in the art, by increasing
 the pressure of the abrasive roll 28 against the blanket, the span of
 contact between the roll and blanket is increased, thereby also increasing
 the rate of grinding. Furthermore, the differential speed (defined as the
 magnitude of the difference in the surface speed between the first and
 second rolls 26, 28, divided by the surface speed of the faster abrasive
 roll and multiplied by 100 percent) may vary from about 2 to 95 percent,
 but should preferably lie in the range of 5 to 50 percent, and most
 preferably in the range of about 8 to 25 percent. The pressure of the
 abrasive roll against the blanket is preferably about 20 to about 2000
 pounds, and more preferably about 100 to about 1500 pounds, and most
 preferably about 200 to about 1000 pounds, such pressures being selected
 depending on, among other things, the speeds at which the machine is to be
 run and the amount of grinding desired.
 The abrasive rolls may be geared together, but are preferably coupled by
 means of a synchronous (e.g. toothed) belt. However, other means for
 achieving the speed correlation between the rolls may be utilized within
 the spirit of the invention.
 As noted above, pressure of the abrasive rolls against the blanket is
 preferably achieved by use of a back-up roll, most preferably with an
 individual back-up roll for each abrasive roll. In this way, a nip is
 created with the blanket running therebetween, with the abrasive roll
 loaded against the back-up roll, preferably by means of air cylinders. Two
 nips are preferably created. Utilizing this arrangement and two abrasive
 rolls, one can increase the pressure at one nip relative to the other, to
 thereby determine which roll serves as the drive roll, and which serves as
 the conditioning roll. This may be done intermittently, if desired, in
 order that the blanket can be abraded in both the forward and reverse
 directions.
 As a further alternative, the abrasive roll 28 could be independently
 controlled by way of supplemental drive means, to grind the blanket while
 it proceeds through its regular web processing operation. However, the use
 of an abrasive roll which is rotated in response to blanket motion is
 preferred, since this reduces machinery complexity and reduces the
 opportunity for grinding-induced blanket defects. Furthermore, additional
 rolls could be utilized as desired, to provide additional amounts of and
 locations of grinding. In addition, although illustrated as being provided
 relatively close to the web take-off location, it is noted that the
 abrasive roll(s) can be provided anywhere other than web-contacting
 portions of the apparatus, within the scope of the invention.
 The drive and abrasive rolls each desirably have abrasive surfaces. In
 particular, the abrasive rolls are preferably coated with diamond grit in
 the range of 60 to 400 grit, and more preferably in the range of 100 to
 220 grit. The grit is preferably bonded directly to the roll by means of a
 metal matrix, where the metal is resistant to corrosion. In a preferred
 form of the invention, the metal matrix is selected from the group
 consisting of nickel, chromium, other metals with similar physical
 characteristics, or combinations thereof. The grit used for the drive roll
 and the conditioning roll may be different, thus allowing abrasion with
 two different grit sizes if the functions of the drive and conditioning
 rolls are interchanged by varying the nip pressures.
 While a single roll may be used as a conditioning roll, (with a preferable
 surface speed of between 2 and 200 percent of blanket working surface
 speed) by driving the roll by means of a variable speed motor, or by belt
 or geared connection of drive elements of the compressive shrinkage
 apparatus itself, it is preferred that the conditioning roll be surface
 driven by the blanket, as this insures that the blanket is not
 accidentally damaged during a stoppage, when the roll might otherwise
 continue to rotate after the blanket has stopped. Surface driving of the
 conditioning roll also insures that the rate of conditioning is
 proportional to the blanket speed. Because the rate of blanket wear is
 also proportional to the blanket speed, the rate of conditioning and wear
 are balanced, insuring a consistent blanket surface.
 Although only a few exemplary embodiments of this invention have been
 described in detail above, those skilled in the art will readily
 appreciate that many modifications are possible in the exemplary
 embodiments without materially departing from the novel teachings and
 advantages of this invention. Accordingly, all such modifications are
 intended to be included within the scope of this invention as defined in
 the following claims. In addition, although specific terms are employed,
 they are used in a generic and descriptive sense and not for purpose of
 limitation, the scope of the invention being defined in the claims. In the
 claims, means-plus-function clauses are intended to cover the structures
 described herein as performing the recited function and not only
 structural equivalents, but also equivalent structures.