The invention relates to a fiber processing roll having a card clothing in the form of a saw tooth wire.

Background of the invention.

Fiber processing rolls are frequently used in the treatment of fibers in the textile industry. More particularly, fiber processing rolls may be used in the pre-carding stages, the carding stage and the post- carding stage, and relate to, amongst others, carding as such and combing.

The carding process separates fibers from each other, lays them parallel and condenses them into singular untwisted bunches or strands prior to spinning. The carding process can be done by hand or by machines. If done by means of machines, the working components are formed by the card clothing. The card clothing may take the form of saw tooth steel wires. The saw tooth steel wires may be present on cylindrical rolls.

The carding process is a very abrasive process. This abrasive character is accentuated by the speed of current carding processes.

As a result there is an urgent need to increase the life time of the various components used in the carding process.

Summary of the invention.

It is an object of the invention to increase the life time of a fiber processing roll.

It is a further object of the present invention to increase the time between two successive standstills of a carding machine.

According to the invention, there is provided a fiber processing roll having a card clothing in the form of a saw tooth wire. At least part of the saw tooth wire is covered with a coating that is selected from the group consisting of a diamond-like carbon, diamond-like nanocomposite, a doped diamond-like carbon and a doped diamond- like nanocomposite, or a combination thereof. These coatings may have a high degree of hardness, e.g. a hardness above 8 GPa, e.g.

above 10 GPa, as measured by means of a nano-indenter. The coatings may also have a low coefficient of friction against steel, as measured by means of a ball-on-disc test. The high degree of hardness extends the life time of the fiber processing rolls. The saw tooth wire is helically wound on the roll in several revolutions. The saw tooth wire has a leading end, which is the end when starting the winding on the roll, and a trailing end, which is the end when finishing the winding on the roll. Both the leading end and the trailing end are fixed to the roll, preferably only in a mechanical way or only by means of welding or by a combination of both.

Most preferably, adhesives are avoided in fixing the saw tooth wire to the roll. As will be explained hereafter, the reason lies in the PACVD process for applying the coating to the saw tooth wire.

Diamond-like carbon (DLC) coatings is an amorphous carbon based coating. DLC coating may be a mixture of sp2 and sp3 bonded carbon atoms with a hydrogen concentration ranging from 0% to 65% (atomic percentage).

Diamond-like nano-composite (DLN) coatings (a-C: H/a-Si:O) are commercialized under the trademark DYLYN ^® and comprise C, H, Si and O, e.g. a network of Si and O interpenetrating with a network of C and H : a-Si:O enhances high temperature stability, leads to lower friction & lowers films stress a-C: H provides diamond-like properties.

Turning to the roll, there are several ways of fixing the saw tooth wire in a mechanical way to the roll.

In one embodiment, the roll has a helical groove for receiving the saw tooth wire.

In another embodiment only the leading end and the trailing end of the saw tooth wire are fixed to the roll and the foot of the saw tooth

wire of one revolution abuts against the foot of the saw tooth wire of an adjacent revolution.

In yet another embodiment the foot of the saw tooth wire of one revolution interlocks with the foot of the saw tooth wire of an adjacent revolution.

A fiber processing roll according to the invention can be used at various places in a process of treating textile fibers.

The fiber processing roll can be used as: a licker-in to feed fibers into the carding cylinder; a doffer to remove fibers from the carding cylinder; a carding roll located in the periphery around a carding cylinder; a comber roll to treat fibers after the carding process as such but before the spinning process.

Brief description of the drawings.

The invention will now be described into more detail with reference to the accompanying drawings wherein FIGURE 1 gives an outer view of a fiber processing roll;

FIGURE 2 gives a cross-section of a first embodiment of a fiber processing roll;

FIGURE 3 gives a cross-section of a second embodiment of a fiber processing roll; FIGURE 4 illustrates part of a cross-section of a third embodiment of a fiber processing roll.

Description of the preferred embodiments of the invention. A saw tooth wire can be made as follows.

Starting product is a wire rod (usual diameters 5.5 mm or 6.5 mm) with a steel composition along the following lines: a carbon content ranging from 0.30 % to 2.0 %, e.g. from 0.5 to 1.2 %; e.g. from 0.6 to 1.1 %; a silicon content ranging from 0.10 % to 2.5 %, e.g. from 0.15 to

-A-

1.60 %; a manganese content ranging from 0.10 % to 2.0 %, e.g. from 0.50 to 0.90 %; a chromium content ranging from 0.0 % to 2.0 %, e.g. from 0.10 % to 1.50 %; e.g. from 0.10 % to 0.90 %; a vanadium content ranging from 0.0 % to 2.0 %, e.g. from 0.05 % to 0.60 %, e.g. from 0.10 % to 0.50 %; a tungsten content ranging from 0.0 % to 1.5 %, e.g. from 0.1 % to 0.70 %. In some compositions either chromium or vanadium is present. In some other compositions both chromium and vanadium are present. The amounts of sulfur and phosphorous are preferably kept as low as possible, e.g. both below 0.05 %, e.g. below 0.025 %.

The wire rod is cold and dry drawn until an intermediate diameter is reached. The desired non-round profile may be obtained by further rolling or by profile drawing. Rolling can be carried out by means of Turks heads or by means of rolls. Profile drawing can be done by means of profile drawing dies. The profile depends upon the application can be square, rectangular, or take an L-form. The basis leg of the L forms the foot and the top leg of the L will house the eventual teeth.

After this profiling, the teeth are formed in the profile wire by means of a laser operation, a cutting operation or a punching operation. The teeth may take various forms and have varying pitches, depending upon the application. The forming of the teeth may be followed by a deburring operation.

Thereafter the formed saw toot wire is subjected to some heat treatments which aim at stress-relieving the foot of the saw tooth wire and at hardening the teeth. Therefore, the entire saw tooth wire is heated until a temperature in the neighborhood of 600 ⁰ C and the teeth get an additional heating until they reach a temperature of about 900 ⁰ C. Thereafter the entire saw tooth wire is quenched so that the foot is stress relieved and the teeth are hardened since the teeth are subjected to a much greater jump in

temperature.

The global heating until 600 ⁰ C can be done by means of induction heating or by means of a gas burner. The heating of the teeth until 900 ⁰ C can be done by means of an additional gas burner, or by passing the teeth through a plasma arc or torch. The quenching operation can be done in an oil bath or in a bath of polymers.

Preferably teeth and possibly also other parts of the card clothing wire are oxide free. Various alternatives exit to obtain this oxide free status.

As a first alternative, the surfaces are made oxide free in a mechanical way. This can be done e.g. by post-treatments such as sand blasting, glass blasting, or brushing.

As a second alternative, the surfaces are made oxide free in a chemical way. This can be done by etching the card clothing wire in

HCI or in H ₂ SO ₄ and carefully rinsing and drying the card clothing wire afterwards.

A third alternative is just to avoid the creation and presence of oxides. This can be achieved, e.g. by carrying out the most critical steps of the processing in an oxide free environment, e.g. under a protective gas atmosphere.

Reference is now made to FIGURE 1 which shows an outer view of a fiber processing roll 10. A predetermined length of a saw tooth wire 20 is helically wound on the roll 10 and is fixed thereto.

Various alternatives exist to fix the saw tooth wire to the roll 10.

In a first embodiment illustrated in FIGURE 2, the leading end of saw tooth wire 20 is fixed by means of weld 12 to the cylindrical surface

14 of roll 10. The length of saw tooth wire is then helically wound on the cylindrical surface 14 under a tension and the trailing end of saw tooth wire 20 is fixed again by means of a weld (not shown) to the cylindrical surface 14 of roll 10. A foot 22 of one revolution of a saw tooth wire 20 abuts against the foot 22 of an adjacent

revolution of a saw tooth wire 20.

In a second embodiment illustrated in FIGURE 3, both the leading end and the trailing end of saw tooth wire 20 may be fixed to the roll by means of welds (not shown) just as in the embodiment of FIGURE

2. The difference with the embodiment of FIGURE 2 is that the anchorage of the saw tooth wire 20 to the roll 10 is more secured due to the fact that the feet 26 of the saw tooth wire 20 have a particular profile so that a foot 26 of one revolution of a saw tooth wire 20 interlocks with a foot 26 of an adjacent revolution of a saw tooth wire 20.

FIGURE 4 shows a third embodiment. The cylindrical surface of roll 10 has a helical groove 16. The feet 28 of sawing wire 20 have such a profile that a force fit into the groove 16 is possible.

After fixing a predetermined length of the saw tooth wire 20 to the roll 10, the roll 10 with the saw tooth wire 20 is cleaned to avoid all fat, grease or lubricants present. The whole is then placed in a vacuum chamber where a PACVD process takes place to obtain a hard diamond-like carbon (DLC) coating on at least the working surface of the teeth 24 of the saw tooth wire 20. A vacuum is created in the reactor until a typical background pressure of 10 ^"5 mbar is obtained. Before depositing the DLC coating on the saw tooth wire substrate, the saw tooth wire and parts of the cylinder are made extra clean by means of a plasma/etching process whereby an Ar/H ₂ plasma (for example with a 1/1 ratio) is ignited in the reactor. The operating pressure may be 1.5 Pa, the gas flow 0.017 Pa. m ³ . s ^"1 (10 seem), rf (radio-frequency) power 90 W, cathode tension 500 V and time 5 min. Following the plasma etching process, a DLC coating is allowed to grow on the saw-tooth wire on the basis of the plasma which is ignited in methane to which H ₂ was added as a diluent. Operating rf power is 100 W, operating pressure is 10 Pa and gas flow is 0.085 Pa.rr^.s ^"1 . The saw tooth wire temperature does generally not exceed 200 °C

during the deposition process.

The thickness of the finally deposited DLC coating ranges from 0.5 μm to 10 μm, e.g. from 1 μm to 5 μm.

The combination of low pressure and high temperature during the

PACVD process is the reason that adhesives, particularly with solvents, are to be avoided in fixing the saw tooth wire to the roll. The presence of adhesives may seriously harm the adhesion of the DLC coating to the saw tooth wire. In the same way, the presence of lubricants and grease must be avoided as well on the rolls.

Preferably the working surface of the teeth 24 of the saw tooth wire 20 is covered with a diamond-like carbon coating. However, in order to avoid having to block out the other parts of the saw tooth wire 20 and the roll 10 and having regard to the very thin layer of DLC deposited by means of the PACVD process, it is preferable to have coated the whole saw tooth wire 20 and, possibly, also parts of the cylinder roll 10.

In some alternative embodiments, the DLC coated may comprise several doping elements such as N or one or another metal (W, V, ...)■ In still some other alternative embodiments, an additional intermediate coating between the steel substrate and the DLC coating may be provided. Such an intermediate coating may be a diamond-like nanocomposite coating such as disclosed in US-A-6

228 471.

In still another embodiment, there may be an intermediate layer under the top hard coating layer. This intermediate layer may function as an adhesion or tie layer between the substrate of the steel saw tooth wire and the top hard coating layer. The intermediate tie layer may be selected from a group consisting of DLC coatings with another H-content than the top layer, diamond- like nanocomposite (DLN) coatings, doped diamond-like (DLC) coatings, TiN coatings, Ti (C,N) coatings, i-C coatings, Me-C, i.e.

metal-carbon composition coatings such as WC or WCC, SiN coatings, CrN coatings or a combination hereof. The thickness of this intermediate layer is preferably between 0.001 and 1 μm. More preferably, the thickness of the intermediate layer is between 0.1 and 0.5 μm.