The present invention relates to a carding flat having a card clothing.

Background of the invention.

Carding flats are used in the process of carding. Carding is a process of opening and cleaning fibers. The carding process separates fibers from each other, lays them parallel and condenses them into singular untwisted bunches or strands. 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, which may be either steel wire needles or saw tooth steel wires.

Summary of the invention.

It is an object of the present invention to increase the life time of a carding flat.

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 carding flat with card clothing. The card clothing is at least partially covered with a coating that has a hardness greater than 8 GPa, e.g. greater than 10 GPa, e.g. greater than 15 GPa, as measured by means of a nano- indenter. This hard coating may comprise a diamond-like carbon

(DLC) composition, a diamond-like nanocomposite (DLN) composition, or a metal-carbon composition, such as a tungsten carbide (WC) composition or a WCC composition. In a preferable embodiment of the invention, the coating comprises a diamond-like carbon (DLC) composition, e.g. a DLC having an amorphous network of carbon and hydrogen. DLC compositions (a-C: H) may be a mixture of sp2 and sp3 bonded carbon atoms and may have a hydrogen concentration between 0% - 65%, e.g. between 10% and 65% (percentages are atomic percentages).

The thickness of this DLC coating ranges from 0.5 μm to 10 μm, e.g. from 1 μm to 5 μm. This DLC coating combines the advantages of

having a high degree of surface hardness with hardness values above 10 GPa (nano indentation) and a smooth surface. The high hardness increases the resistance against abrasion. The smoothness of the surface may increase the speed of the carding process without harming its quality.

Instead of DLC the coating may be of a diamond-like nanocomposite (DLN) composition. 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.

The card clothing may be formed by means of either wire needles or by saw tooth wires.

If the card clothing is formed by wire needles, at least the top of the wire needles is covered with the hard coating. The wire needles are usually inserted in a carrier element. This carrier element must preferably be able to withstand temperatures above 100 ⁰ C in order to survive the DLC coating process in an undamaged way.

If the card clothing is formed by saw tooth wires, at least the front surface of the saw tooth wires is covered with the hard coating.

The carding flat further has a support element. The saw tooth wires are fixed to this support element either mechanically or by means of welding or by a combination of a mechanical fixing or a welding.

Having regard to the DLC coating process which occurs in a vacuum environment all adhesive bonding is to be avoided since adhesives may contain solvents that become free during the DLC coating process and that disturb the coating process.

For the same reason the carding flat and the card clothing - irrespective of the form: either wire needles or saw tooth wire - are

preferably free from lubricants or fats, since lubricants or fats may harm the adhesion between the coating and the card clothing.

Possibly, a tie layer may be present between the substrate of the steel wire needle or saw tooth steel wire and the hard coating. This tie layer may be a doped DLC composition, a DLC composition with other H-content than the top-layer, a DLN composition, a doped DLN composition, chromium, or titanium or a titanium alloy or TiN composition, , Ti (C, N) coatings, i-C coatings, metal-carbon (Me-C) coatings such as WC or WCC, CrN coatings, SiN coatings, or a combination thereof.

The hard coating on the card clothing may be formed by a stack of multiple layers, e.g. DLN-DLC-DLN-DLC such as disclosed in US-A- 6 228 471.

Brief description of the drawings.

The invention will now be described into more detail with reference to the accompanying drawings wherein

FIGURE 1 illustrates wire needles in a carrier for a carding flat;

FIGURE 2 and FIGURE 3 illustrate saw tooth wires in a carding flat.

Description of the preferred embodiments of the invention.

A needle 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 1.60 %;

-A-

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 and / or wet drawn until a desired final diameter is reached.

FIGURE 1 illustrates wire needles 10 in a carrier 12 for a carding flat. The wire needles 10 are usually in the form of a U where the two legs of the U penetrate through carrier 12. The connecting leg 14 of each U can be seen at the bottom of carrier 12. The wire needles 10 may be arranged in various patterns in the carrier 12.

Usually the wire needles 10 are obliquely arranged or may present a bending or both. The tops 16 of the wire needles 10 have been hardened, e.g. by having passed them through a flame.

The carrier 12 with the wire needles 10 may be subjected to a

PACVD process for deposition of DLC.

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 carrier 12 with the needles 10, the needles 10 and parts of the carrier 12 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. nr^.s ^"1 (10 seem), rf (radio-frequency) power 90 W, cathode tension 500 V and time 5 min. After the plasma etching process, a DLC coating is allowed to grow on the needles 10 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.nr^.s ^"1 .

The plasma etching may last for 3 to 30 minutes. The wire needle

10 temperature does generally not exceed 200 °C during the deposition process. The temperature of the carrier 12 may be kept lower than 200 ⁰ C during the PACVD process. However, it is preferable that the carrier 12 may withstand temperatures above 100 ⁰ C, e.g. above 120 ⁰ C.

At least the tops 16 of the wire needles 10 are to be covered with DLC. However, the rest of the surface of the wire needles 10 and some parts of the carrier 12 may also be covered with DLC.

In some alternative embodiments, the DLC coating 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.

Reference is now made to FIGURE 2 and to FIGURE 3 which both illustrate carding flats 20, 40 with resp. saw tooth wires 22, 42 as card clothing.

A saw tooth wire 22, 42 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 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 28, 48 and the top leg of the L will house the eventual teeth 24, 44.

After this profiling, the teeth 24, 44 are formed in the profile wire by means of a laser operation, a cutting operation or a punching operation. The teeth 24, 44 may take various forms and have varying pitches, depending upon the application. The forming of the teeth 24, 44 may be followed by a deburring operation. Thereafter the formed saw toot wire 22, 42 is subjected to some heat treatments which aim at stress-relieving the foot 28, 48 of the saw tooth wire 22, 42 and at hardening the teeth 24, 44. Therefore, the entire saw tooth wire 22, 42 is heated until a temperature in the neighborhood of 600 ⁰ C and the teeth 24, 44 get an additional heating until they reach a temperature of about 900 ⁰ C. Thereafter the entire saw tooth wire 22, 42 is quenched so that the foot 28, 48 is stress relieved and the teeth 24, 44 are hardened since the teeth 24, 44 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 24, 44 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.

A carding flat 20, 40 is formed by putting fixed and predetermined lengths of a saw tooth wire 22, 42 in parallel next to one another on a support 30, 50. The whole carding flat 20, 40 goes into a vacuum chamber where at least the front surface 26, 46 of the teeth 24, 44 are coated with DLC. Preferably, however, the whole surface of the teeth 24, 44 is coated with DLC.

In a first embodiment, illustrated in FIGURE 2, the saw tooth wires

22 are only mechanically anchored to the support 30 by means of ledges 32, 34. Adhesive bonding, such as disclosed in US-A- 4 221 023, is avoided for the reasons mentioned above. Similarly, any lubricant or fat is removed before putting carding flat 20 into the vacuum chamber.

In a second embodiment, illustrated in FIGURE 3, the saw tooth wires 42 are anchored to the support 50 by one or more welds 52 and by mechanical means, namely ledges 54 and 56. Here again, adhesive bonding, lubricants, grease and fats are all preferably avoided.

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 coating 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. 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 diamond-like nanocomposite (DLN) coatings, doped diamond-like (DLC) coatings, TiN coatings, Ti (C,N) coatings, i-C coatings, wolfram carbide coatings, 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.