FIELD OF THE INVENTION

The present invention relates to a raising process of a woven or knitted fabric or a napping process of a woven or knitted fabric or of a composite fabric, for example a resinated cloth or similar continuous sheet material, with an improved control of the action performed by raising or napping satellite rollers of a rotating drum and a universal raising-napping machine provided with means for impressing radial vibrations of adjustable amplitude and frequency to the fabric running over the drum.

BACKGROUND OF THE INVENTION

The raising process for lifting the pile of the yarn (woof and warp) of a woven or knitted fabric is known form acient times and is performed nowadays for producing an extremely vast range of fabrics having peculiar characteristics. Blankets with enhanced thermal characteristics versus weight and so-called "pile" garments of fashionable look are few exaples of textile products that are obtained through a raising treatment of a base fabric. However, raising and/or napping treatments of woven and knitted fabrics as well as of composites formed by resin films coupled to a woven fabric to produce artificial leather substitutes, are widely used in many productions in order to confer to the fabric a characteristic felted aspect and/or a certain tactile characteristic, beside conferring for example to a certain fabric improved transpiration, absorption and/or thermal insulation characteristics. Modern universal raising machines are essentially composed of a drum formed by a plurality of satellite

or peripheral rollers that are driven in rotation at an adjustable speed in order to vary their peripheral speed by a small fraction above or below the peripheral speed of the drum and therefore of the fabric running over the satellite rollers. The outer cylindrical sur¬ face of the satellite rollers is covered with appropri¬ ate raising or napping fillets (coverings) that are chosen in function of the type of treatment to be carried out and of the characteristics of the fabric to be treated. For example, in case of a pile raising treatment of a woven cloth, the satellite rollers are covered with an appropriate raising covering, typically in the form of a tape supporting a plurality of metal needles having their points bent through a certain angle and having a population density and elastic char¬ acteristics chosen in function of the particular type of woven or knitted fabric to be treated. The orienta¬ tion of the bent points of the needles of each raising roller may be such as to determine an angle of inci- dence functionally opposed to the direction of advance¬ ment of the fabric (counterpile action) or in the same direction of advancement of the fabric (pile action) . The action of the single raising rollers may be of the same type or of an alternate type, for example of the type: ... pile/counterpile/pile/counterpile/ ... . The needles of few of the peripheral raising rollers may also have a blunt, ball or mushroom-shaped termination instead of a point termination for exerting a specific felting action of the pile raised by the other rollers of the drum and so forth.

In these machines, in an outer satellite position as referred to the rotating drum, there are at least an inlet and an outlet guiding rollers for guiding the fabric to be treated over a certain arc of circu - ference of the drum, which in the case of a single pair of inlet and outlet rollers, may be of about 270° or

even greater.

The same (universal) machine, may also be used for slightly different purposes than pile raising and spe ^¬ cifically for napping a certain fabric to produce a su- perficial finish typical of the flesh-side of a natural leather or for conferring to a woven cloth, for example a cotton cloth, a peculiar tactile characteristic.

In order to do that, it is generally sufficient to substitute the coverings of needle fillets with abra- sive coverings on the outer cylindrical surface of the satellite rollers of the drum. The abrasive coverings may be in the form of an abrasive paper tape of a given granulometry that can be readily wound over the rollers. Clearly the mode of operation of the machine is similar whether the satellite rollers are equipped with needle type, raising fillets or with abrasive napping fillets.

In the following description, reference will be made primarily to a machine equipped with pile raising needle fillets, being understood that the same conside¬ rations would be valid mu ta ti s mu tandis also in the case the needle pile raising fillets be substituted with another kind of fillets, for example with an abrasive tape of a certain granulometry for napping a cloth or a composite fabric, for example an artificial composite leather substite.

These machines are well known and widely used, in different configurations, in the textile industry. The pile raising or napping action exerted by the satellite rollers of the rotating drum of the machine may be such as to produce a certain permanent linear elongation of a fabric and a corresponding srinking of its width (or height) . Therefore, the guiding rollers of the fabric to be treated must be provided with organs for recovering the elongation eventually produced by the raising or napping process.

In case of a cloth to be raised, in order to avoid accidental tearing of junction seams of the fabric upon the passage of a seam over the pile raising drum, dedi¬ cated mechanisms detect the arrival of a junction seam and automatically revert momentarily the speed or rota ^¬ tion of the satellite raising rollers to the so-called "zero-point" speed, that is to assume a peripheral velocity identical to the peripheral velocity of the drum (and therefore of the fabric running thereon) , in order to momentarily interrupt the pulling action exerted by the needles upon the passage over the drum of the seam.

The extremely critical character of the regulation of the relative peripheral velocity of the raising rollers as referred to the so-called "zero-point" is well known, as well as the choice of the type of raising fillets (configuration density and elastic characteristics of the needles) in producing a certain result on a fabric in a most satisfactory way. An excessive "grip" (interference) of needles acting in a counterpile mode may excessively weaken or even ruin a cloth, by decisively tending to tear off the pile in an excessive manner, while a too weak "grip" may miss to produce a satisfactory result. Muta tis mutandis , similar considerations may also be made in the case all the raising rollers be exerting a pile-mode action, and also in the case when the action of the raising rollers is of an alternate type, namely: counterpile/pile/counterpile/pile and so forth. Another important aspect of this type of treatments is represented by a more or less disuniform effective¬ ness of the raising or napping rollers, due to a disuniform tension of the fabric running over the rotating drum. This may depend from a more or less marked engagement of the needles or of the abrasive particles of the raising-napping satellite rollers

along the entire arc of engagement of the fabric with the drum, as a consequence of successive elastic tensionings followed by relievings of the fabric occurring along the arc of circumference over which the fabric runs over the drum.

This tends to reduce or nullify completely the raising of napping performance of the rollers in certain zones of the arc of contact of the fabric with the drum, with an overall decline of the yield of the process, as referred to the result obtained with a single passage of the fabric over the treatment drum.

The observation of these phenomena has led to the developments of optimization techniques as the one characterized by engaging the fabric on the drum repeatedly and for shorter arcs of circumference, by employing two or more pairs of guiding (inlet and outlet) rollers and by appropriately modifying the fabric handling mechanisms of the machine. Such an improved process and relative raising machine are described in prior EP-A-0088431-B2, the description of which is herein incorporated by express reference.

In case of woven or knitted fabrics with yarn and overall strength characteristics particularly critical if referred to the peculiarity of the raising-napping process described above, the above-noted problems of regulating the action of the raising-napping rollers becomes extremely serious.

Often these problems may be overcome or lessened in a significative way only by "subregulating" the raising-napping action of the rollers of the drum and by performing a repeated number of passages of the cloth until a satisfactory raising-napping effect is obtained, without excessively weakening or ruining the base fabric. Of course certain results may be reached only with an accompanying heavy loss of productivity and therefore with a relatively high cost.

Also under substantially noncritical conditions, in terms of quality and strength of the base fabric to be treated, it is often difficult to quickly attain an op ^¬ timum regulation of the relative velocity of the 5 raising-napping rollers and therefore the definitive regulation represents almost invariably a compromise between quality of the result of the treatment and pro¬ ductivity, case-by-case privileging one or the other. These difficulties derive from the fact that for a

1° certain raising or napping fillet fitted over the rollers, the only regulation parameter left is that of fixing a certain optimal differential between the speed of the fabric, that is the peripheral velocity of the drum, and the peripheral velocity of the raising or s- -s napping rollers.

SUMMAR Y OF THE INVENTION

It has now been found and represents the object of

20 the present invention that by impressing to the fabric to be treated running over the rotating drum of a universal raising machine radial vibrations of a certain frequency and intensity a surprisingly marked improvement of the raising or napping action performed

25 by the drum's rollers is obtained.

A possible explanation of this phenomenon may be ascribed to the fact that the impression of oscilla¬ tions to the running fabric tends to modify and to make more uniform the intervals and the quality of the

30 "grip" exerted on the fabric by the points of the needles or of the abrasive granules of the raising or napping rollers during the passage of the fabric over the rotating drum of the machine along a certain arc of circum erence of the drum. The radial vibrations

35 impressed to the fabric may be seen as producing intervenient disengagements that relieve the localized

strains produced by the repeated momentary engagements of the needles or the abrasive surface of the fillets of the plurality of satellite rollers with the fabric, thus favouring an equalization of the performance of the individual rollers.

On the other hand, by referring for simplicity of description and for the generality of the problems to the case of raising the pile of the base cloth, the way of impressing said radial vibrations or oscillations to the fabric running over the machine's drum, may be so as to permit a regulation in terms of frequency as well as of intensity or amplitude of the oscillations im¬ pressed to the fabric, independently from one another and that can be made while the machine is running. This provide extremely useful means of regulation that add on the conventional regulation of the peripheral velocity differential. This permits and/or greatly facilitates a true optimization of the process while is being performed, by the ability to intervene on different process parameters.

Preferably, the radial vibration should be impressed on the fabric running over the machine's drum at regu¬ lar angular intervals generally comprised between 90° and 120°. A greater density of points of impression of radial vibrations, that is at angular distances smaller than 90°, does not appear to increase in an appreciable way, the effect of such an imposition of vibrations to the fabric, while if the points of application of vi¬ brations are angularly spaced by an angle greater than 120°, a certain decline of effectiveness is observed. Of course, the angular distance between the various points of application of vibrations to the fabric will be related to the length or arc of the machine's drum onto which the fabric is guided to run in contact therewith.

The manner in which said radial vibrations, that is

oscillations on the running fabric are impressed may be different. While in particular situations the use of pulsating compressed-air jets of intensity and frequen¬ cy independently adjustable may be satisfactory. The pulsating jet nozzles may be disposed along selected generatrix lines of the rotating drum. Such a system may be inapplicable or inefficient in terms of power consumption, as well as excessively noisy. Therefore the use of one or more baffles (laminae or blades) is generally preferred. Each blade or lamina may be slidably mounted in guides in order to be able to ef¬ fect reciprocating excursions over an essentially radi¬ al plane as referred to the machine's drum. Each re¬ ciprocating baffle or blade may fit in the separation space between two adjacent rollers of the machine's drum, so that upon its radially oriented reciprocating movement, its blunt edge (properly rounded) lifts the fabric by an adjustable radial heigth. Of course, the radially oriented reciprocating motion of the blade may be produced mechanically by a dedicated transmission that can comprise an eccetric shaft or a camshaft and one or more cranks or rods. Alternatively the recipro¬ cating motion may be impressed to the blade by electromagnetic actuators. The supporting, guiding and driving group of each radially oscillating blade may be mounted on the shaft of the revolving drum of the machine, by arranging ap¬ propriate rotating couplings and/or contacts for command fluid ducting and electrical supply and control lines, respectively, two ends of a hollow or centrally bored drum's shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The different aspects and advantages of the inven¬ tion will be more clearly illustrated through the

following description of an important embodiment of the invention and by referring to the annexed drawings, wherein:

Figure 1 is a schematic cross sectional view of the drum of a raising-napping machine, made according to the present invention;

Figure 2 is a simplified schematic, partially sec¬ tioned plan view of the machine's drum of the invention of Fig. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to the figures that show for purely illustrative purposes one of many possible forms of realization of the invention, the drum of a raising- napping machine is indicated as a whole with 1.

The drum is constituted by a hollow shaft 2 sup¬ ported horizontally on the bearings 3 and 4. Two pul¬ leys, respectively 5 and 6, support a plurality of raising-napping rollers 7. Each roller 7 is mounted on ball bearings 8 and 9 held in housings that are dis¬ tributed along a peripheral circumference of the two end pulleys 5 and 6. The drum may be rotated by a belt transmission employing a drive pulley 11, while each satellite roller 7 (raising or napping roller depending on the covering disposed on the outer cylindrical sur¬ face of the roller) is provided with its own drive pulley 10.

As may be observed in the cross section of Fig. 1, the fabric 12 to be treated is guided over the revolving drum 1 by a pair of guiding, outer satellite rollers, namely: an inlet 13 and outlet roller 14, respectively. Some machines may also permit to reverse the direction of motion of the fabric therethrough. By referring hereinbelow for simplicity of descrip¬ tion to the case of a raising treatment performed on a

cloth, the arc of circumference of the drum that is en¬ gaged by the running fabric may also be different (smaller) than the one shown in the example of Fig. 1 where it is about equal to 270°. Two rotary brushes, respectively 15 and 16, are fitted in a zone of the revolving drum that is not engaged by the fabric 12. The two rotary brushes strip the residues of pile that are inevitably teared off by the needles of the raising fillets of the rollers. The pile residues are continu- ously sucked through the mouth of a sucking vacuum conduit of the pile fragments (not shown in the figures) for dust control reasons.

As it is well known to a skilled person, by acting on the belt transmission of the rotation to the various raising rollers 7, their peripheral velocity may be varied above or below the peripheral velocity of the rotating drum, that is the speed of the fabric 12 (equality with which represents the condition commonly referred to as "zero-point") , in order to exert a raising action on the fabric.

For implementing the process of the invention, the machine is provided with organs suitable to impress to the fabric, running over the drum, radial vibrations of adjustable amplitude (or intensity) and frequency. According to the embodiment shown in the figures, the vibrations (oscillations) are impressed to the cloth 12 running over the drum 1 of the machine at points that are circumferentially spaced by 120° from one another, by radially oscillating blades or baffles 17 (three in the depicted example) . Each blade 17 fitted in the separation space between two adjacent rollers and in a manner as to exclude interference with the raising fillets that cover the outer cylindrical surface of the rollers. Each blade or baffle 17 is mounted so as to be able to effect reciprocating radial excursions substantially over a radial plane and of

independently adjustable amplitude and frequency. Opera- tively, the amplitude of the reciprocating radial mo ^¬ tion of the blades 17 is such that their edge, extends radially, from a position of maximum retraction, that may be interferring (keeping slightly lifted the running fabric) or noninterferring with the fabric 12 running over the drum, by a radial height that can be predefined (corresponding to the so-called intensity of amplitude of vibrations) which may be varied from a minimum of about 0.8 millimeters to a maximum that may reach about 8.0 millimeters. The edge of the blades 17 may be suitably rounded and preferably constituted by a cap 18 of a low-friction material capable of resisting abrasion, for example a PTFE or a nylon, eventually incorporating conducting inserts or fibers, for example carbon fibers, capable of conferring a substantially antistatic character to the material.

The oscillating frequency of the blades 17 may be regulated within a broad range, but it has been observed that the frequency should be comprised in a range, the lower and upper limits of which are tied to the peripheral velocity of the drum 1, that is to the tangential speed of the runnin fabric 12. By con¬ sidering that the peripheral speed of the drum in these machines may vary between 5 and 20 meters per minute, the frequency of oscillation of the blades may vary between about 300 and 1500 cycles per minute.

Commonly, for raising relatively long pile (for example a pile 4-8 millimeters long) it is preferred to induce oscillations of relatively large amplitude and relatively low frequency, while for raising relatively short pile or for napping a fine cloth (pile length from 0 to 0.5 millimeters) it is preferable to induce vibrations having a reduced amplitude and a relatively high frequency.

Of course, these are general criteria, while the

optimal conditions of inducing vibrations to the cloth running over the drum must be determined for each situation, because many other factors and characteris¬ tics, either of the cloth as well as of the raising fil- lets fitted over the satellite rollers of the machine's drum, concur to determine the result of the process.

According to the embodiment shown in the figures, the intensity of vibrations impressed to the cloth running over the drum is adjustable by raising or lowering the supporting and guiding group of the oscil¬ lating blade in order to vary the radial height of the edge of the blade 17 in correspondence of its lowermost radial level reached in its reciprocating motion. This modifies the intensity of the vibration impressed to the running cloth and therefore the amplitude of the oscillations of the cloth running over the drum.

Of course, the amplitude of oscillation of the blade is predefinable by modifying the parameters of the driving transmission. Other embodiments are easily recognizable, wherein it may be possible to vary the amplitude of oscillation of the blade, beside its position of "attack", during the running of the machine. This may be implemented more easily by employing an electromagnetic drive of the oscillating blades. The regulation of the amplitude may be implemented for example by modifying the relative positions of mechanical stops that define the radial distance that is covered by the reciprocating motion of the blades, which may be impressed by impulsively driven electromagnets.

In any case, the oscillating frequency of the blades may be easily and independently regulated during operation of the machine by varying the speed of a driving electric motor or the switching frequency of driving electromagnets.

The mechanism for supporting, guiding and driving

the radially vibrating blades 17 may thus be arranged in different ways. In the example shown in the figures, each oscillating blade 17 is supported by three oscillating arms 19, pivoted on a block 20 which is in turn slidingly mounted on lateral raisers or posts 21 and 22, anchored to the hollow shaft 2 of the drum by means of basements 23 and 24.

A driving electric motor 25 is mounted on each block 20 and rotates an eccetric shaft 26, on the cams 27 and 28 of which are assembled the rods 29 and 30 that transmit the reciprocating motion to the respective oscillating arms 19.

Through an actuating motor and an endless screw transmission, indicated as a whole with 31, the radial height of the block 20 may be adjusted in order to fix the position of the lowermost point of the radial excursion of the blade 17 and thus regulate the vibration effect or intensity of vibration that it impresses on the cloth 12 (in the embodiment shown, for the same amplitude of the reciprocating radial ex¬ cursions of the blade) .

Of course, by varying the length of the rods 29 and 30, it is possible to modify also the amplitude of oscillation of the blades 17 (that is the radial excursion of the edge 18 of the blades 17) . Such a pre- trimming will have an effect on the intensity of the radial vibrations that are transferred to the running cloth, which will remain adjustable during operation of the machine by varying the level of "attack" of the radially reciprocating blades.

The pneumatically operated cylinder 32 has the func¬ tion of quickly retracting the whole block 20, whenever suitable sensors detect an emergency condition, as for example the tearing of the cloth 12 (typically oc- curring accidentally in correspondence of a seam) , in order to avoid that the consequent entangling of the

cloth around the raising rollers may clog the oscil ^¬ lating blades 17 fitted in the relatively narrow separation space between adjacent rollers.

A plurality of electrical brush contacts (rotating contacts) 33 (Fig. 2) permit to supply and control the electrical motors 25 and the end-of-run positioning groups 31, while a rotating fluid coupling 34, installed at the other end of the hollow shaft 2 of the drum permits the passage of the operating fluid (co - pressed air) for the pneumatic cylinders 32.

As repeatedly mentioned above, the same machine may be differently equipped by employing abrasive papers or fillets in lieu of needle fillets for treating the sur¬ face of a cloth or of a composite fabric such as a resinated woven fabric, to nap the surface. Also in this case, the performance and productivity of the treatment process are markedly improved by impressing radial vibrations of adjustable intensity and frequency to the material running over the treatment drum of the machine. Also in this case, the possibility of indepen¬ dently intervening on different regulation parameters permits a more effective optimization of the treatment in function of the particular nature of the material to be treated, thus producing beside an improved result of the treatment also an increment of productivity.