WO2006128744A1

WO2006128744A1 - Card clothing wire with a coating having a high hardness

Info

Publication number: WO2006128744A1
Application number: PCT/EP2006/060630
Authority: WO
Inventors: Peter Osselaer; Wim Pappaert; Marc Sercu
Original assignee: Nv Bekaert Sa
Priority date: 2005-05-30
Filing date: 2006-03-10
Publication date: 2006-12-07

Abstract

A card clothing wire 10 has a foot portion (12) and has teeth (14). The teeth (14) each have a front surface (16) that is covered by a coating (20) having a hardness greater than 8 GPa. The arithmetic mean roughness Ra of the front surface (16) is less than 1.0 µm.

Description

CARD CLOTHING WIRE WITH A COATING HAVING A HIGH HARDNESS

Field of the invention. The present invention relates to a card clothing wire having a foot portion and having teeth. The teeth each have a front surface and other surfaces.

Background of the invention. Carding is a process of opening and cleaning textile 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 either by needles or by saw toothed steel wires. The present invention relates to such a saw toothed steel wire or card clothing wire.

Requirements for ever increasing and higher productivities put severe demands on carding machinery and on its components. More particularly there is a need for higher production speeds, e.g. higher rotation speeds, and a longer lifetime of the various components so that standstills are reduced to a very minimum. Having regard to the highly abrasive character of the textile fibers, both the requirement of the higher speed and the requirement of the longer lifetime are considered tough.

Summary of the invention.

It is an object of the present invention to avoid the drawbacks of the prior art. It is a further object of the present invention to increase the production speed of a carding machine.

It is another object of the present invention to reduce standstills of carding machinery.

According to a first aspect of the present invention, there is provided a card clothing wire having a foot portion and having teeth. Each of the teeth has a front surface. The front surfaces of the teeth are covered by a coating having a hardness greater than 8 GPa, e.g. greater than 10 GPa, preferably greater than 15 GPa, e.g. greater than 20 GPa with values up to 25 GPa and higher. The term hardness refers to a Vickers hardness.

The front surface of the teeth is the most active surface during carding and is most subject to abrasion. So it is important that the front surface is coated with this hard coating. However, since the other surfaces of the teeth may also come into contact with the textile fibers in the carding process, all the other surfaces of the teeth are also preferably coated with this hard coating.

The hardness of the coating gives a resistance against abrasion and guarantees a long integrity of the geometry of the teeth. The hardness thus increases the lifetime of the card clothing wire.

Preferably the front surface of the teeth has such a surface morphology that the arithmetical mean roughness Ra is less than 1.0 μm, e.g. less than 0.8 μm. Having regard to the low thickness of the coating on the teeth, this flat surface morphology must be reached both under and on the coating since the coating will take over any present irregularity on the surface of the substrate. The smoothness of the front surface facilitates the sliding of the textile fibers over the front surface and allows increase of the speed of the carding process, e.g. increase of the rotation speed of the carding cylinder.

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. Preferably the other surfaces of the teeth, and possibly other parts of the card clothing wire, also have a coating of a diamond-like carbon (DLC) composition. DLC compositions (a-C: H) may be a mixture of sp2 and sp3 bonded carbon atoms with a hydrogen concentration between 0 - 80%, e.g. between 10% and 75%.

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.

In a particular embodiment of the present invention, the coating comprises at least two layers: an intermediate layer and an outer layer. The intermediate layer may function as an adhesion or tie layer between the substrate of the teeth and the outer 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. 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.

In still another embodiment of the present invention, the coating comprises an additional third layer.

As a matter of a preferable example, the coating has following three layers: a first layer, closest to the substrate of the front surface of the teeth, and comprising at least one element of group IVB, group VB or group VIB a second layer deposited on top of the first layer, comprising a diamond-like nanocomposite (DLN) composition a third layer deposited on top of said second layer comprising a diamond-like carbon (DLC) composition. -A-

This example with a three-layer coating has the advantages of providing a certain tunability of the coating properties.

Brief description of the drawings.

The invention will now be described into more detail with reference to the accompanying drawings wherein - FIGURE 1 is perspective and enlarged view of part of a card clothing wire;

FIGURE 2 is a cross-section of a first embodiment of a tooth of a card clothing wire;

FIGURE 3 is a cross-section of a second embodiment of a tooth of a card clothing wire;

FIGURE 4 is a cross-section of a third embodiment of a tooth of a card clothing wire.

Description of the preferred embodiments of the invention. A card clothing 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 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 the desired non-round profile is reached. Rolling can be carried out by means of Turks heads or by means of rolls. 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 toothed wire is subjected to some heat treatments, which aim at stress-relieving the foot of the saw-toothed wire and at hardening the teeth. Therefore, the entire saw toothed wire is heated until a temperature in the neighborhood of 600 ⁰C and the teeth get an additional heating until they reach a temperature of about 900 ⁰C. Thereafter the entire 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 ⁰C can be done by means of induction heating or by means of a gas burner. The heating of the teeth until 900 ⁰C 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.

The thus formed card clothing wire may then be subjected to a sand blasting or glass blasting operation in order to smooth the surface and to remove oxides present on the surfaces of the card clothing wires.

The result of the above-described manufacturing process is a card clothing wire 10, an example of which is shown in perspective on FIGURE 1. Following parts can be distinguished on a card clothing wire 10: - the foot 12; - the teeth 14; the front surface 16 of the teeth 14; other surfaces 18 of the teeth.

FIGURE 2 shows schematically a cross-section of a part of a tooth 14 of a card clothing wire 10. The steel front surface 16 is covered by a coating 20 having a DLC composition.

The card clothing wire 10, or at least part of the teeth 14 of the card clothing wire 10, can be covered with a DLC coating by means of a chemical vapor deposition process (CVD) or by means of a plasma assisted chemical vapor deposition process (PACVD).

A PACVD process for deposition of DLC mainly occurs as follows. The card clothing wire 10 with the oxide free surfaces is placed in a vacuum chamber.

A liquid organic precursor containing the elements C and H in suitable proportions is introduced in the vacuum chamber. A plasma is formed from the introduced precursor by an electron assisted DC- discharge using a filament with a filament current of 50-150 A, a negative filament bias DC voltage of 50-300 V and with a plasma current between 0.1 and 20 A and a composition is deposited on the card clothing wire, to which a negative DC- bias or negative RF self- bias voltage of 200 to 1200 V is applied, in order to attract ions formed in the plasma.

The base pressure in the vacuum chamber is 3xlO^"7 mbar and the typical working pressure is maintained at IxIO^"4 to IxIO^"3 mbar by diffusions pumps. The card clothing wire 10 can be cleaned by an in-situ (Ar-) plasma etching process prior to deposition. This plasma etching may last for 3 to 30 minutes. The card clothing wire 10 temperature does generally not exceed 200 °C during the deposition process. Experience with a coating 20 having a DLC composition has taught that the lifetime of a card clothing wire can be doubled in comparison with a non-coated card clothing wire.

In some alternative embodiments, the DLC coated may comprise several doping elements such as N or one or another metal (W, V,

Referring to FIGURE 3, in still some other alternative embodiments, an additional intermediate coating layer 22 is present between the steel substrate 16 and the DLC coating layer 24. Such an intermediate layer may comprise a diamond-like nanocomposite composition such as disclosed in US-A-6 228 471.

FIGURE 4 illustrates yet another third embodiment where the coating on the steel substrate 16 has three layers 26, 28 and 30: a first intermediate layer 26; a second intermediate layer 28; a top layer 30 with a DLC composition. This three-layer composition is disclosed in pending application

PCT/EP2004/013676 of applicant. The various layers 26, 28, 30 are hereinafter briefly described.

The first intermediate layer 26 The first intermediate layer 26 comprises at least one element of the group IVB, VB or VIb.

Preferably, the first intermediate layer 26 comprises titanium and/or chromium as for example a titanium layer, a chromium layer, a titanium-based layer or a chromium-based layer. A titanium-based layer 26 may for example comprise a TiC layer, a

TiN layer or a TiCN layer. A chromium-based layer 26 may for example comprise a CrN layer or a Cr₃C₂ layer.

For many applications a titanium-based layer 26 is preferred to a chromium-base layer 26 as it is easier to rework or refurbish layered structures comprising a titanium-based layer 26. For example, a reactive ion etching used to decoat will not work with a chromium-based interlayer 26.

The thickness of the first intermediate layer 26 is preferably between 0.001 and 1 μm. More preferably, the thickness of the first intermediate layer 26 is between 0.1 and 0.5 μm.

The first intermediate layer 26 may be deposited by any technique known in the art. Preferred techniques comprise physical vapor deposition techniques as sputtering or evaporating.

The second intermediate layer 28

The second intermediate layer 28 comprises a diamond-like nanocomposite (DLN) composition. A diamond-like nanocomposite composition comprises an amorphous structure of C, H, Si and O, e.g. a network of Si and O interpenetrating with a network of C and H.

Preferably, the nanocomposite composition comprises in proportion to the sum of C, Si, and O : 40 to 90 %C, 5 to 40 % Si, and 5 to 25 % O (expressed in at%).

Preferably, the diamond-like nanocomposite composition comprises two interpenetrating networks of a-C: H and a-Si :O. A diamond-like nanocomposite composition is described e.g. in EP-B- 0 988 406.

The diamond-like nanocomposite composition may further be doped with a metal, such as a transition metal of Group IV to VII. The composition can be doped to influence the conductivity of the coating. W, Zr and Ti are for example well suited as doping element.

The second intermediate layer 28 has a thickness, which is preferably between 0.01 and 5 μm. More preferably, the thickness is between 0.1 and 1 μm, for example between 0.2 and 0.5 μm. The second intermediate layer 28 may be deposited by any technique known in the art. A preferred technique comprises chemical vapor deposition (CVD), such as plasma assisted chemical vapor deposition (PACVD).

Diamond-like carbon layer 30

The diamond-like carbon layer 30 comprises amorphous hydrogenated carbon (a-C: H).

Preferably, a diamond-like carbon composition comprises a mixture of sp² and sp³ bonded carbon with a hydrogen concentration between

0 and 60 at%.

The DLC composition may be metal doped, for example to influence the electrical conductivity of the coating. Preferred doping elements are transition metals of Group IV to VII such as W, Zr and Ti.

The thickness of the DLC layer 30 ranges preferably from 0.1 to 10 μm.

The DLC layer may be deposited by any technique known in the art.

A preferred technique comprises chemical vapor deposition (CVD), such as plasma assisted chemical vapor deposition (PACVD).

It is believed that the gradation of the hardness of the layers is important to obtain the good results of a layered structure according to the present invention. These good results comprise a high degree of hardness (15-25 GPa) and high adhesion values and a smooth surface.

Claims

1. A card clothing wire having a foot portion and having teeth, said teeth each having a front surface, characterized in that at least said front surface of said teeth is covered by a coating having a hardness greater than 8 GPa.

2. A card clothing wire as claimed in claim 1, wherein said teeth further comprise other surfaces different from said front surface, said other surfaces being covered by a coating having a hardness greater than 8 GPa.

3. A card clothing wire as claimed in any one of the preceding claims, wherein at least said front surface has an arithmetical mean roughness Ra of less than 1.0.

4. A card clothing wire as claimed in any one of the preceding claims, wherein said coating comprises a diamond-like carbon composition.

5. A card clothing wire as claimed in any one of the preceding claims, wherein said other surfaces have a coating comprising a diamond-like carbon composition.

6. A card clothing wire as claimed in any one of claims 1 to 3, wherein said coating comprises at least two layers.

7. A card clothing wire as claimed in claim 6, one of said layers comprising a diamond-like carbon composition, the other comprising a diamond-like nanocomposite composition.

8. A card clothing wire as claimed in claim 6, wherein said coating further comprises an additional third layer.

9. A card clothing wire as claimed in claim 8, a first layer comprising at least one element of group IVB, group VB or group VIB, a second layer deposited on top of said first layer, comprising a diamond-like nanocomposite composition, a third layer deposited on top of said second layer comprising a diamond-like carbon composition.