DESC:FIELD OF THE INVENTION
The present invention relates to spinning machines. Particularly, the invention relates to a method for plating thread guiding elements for spinning machines and more particularly to coating of travellers which are used in textile applications for improving the hardness for having a low friction, wear resistant surface and better heat dissipation.

BACKGROUND OF THE ART
The friction between ring and traveller is the main limiting factor for higher traveller speed hence the spindle speed in ring frame. ‘Friction’ may be interpreted as a process of dissipation of energy and ‘wear’ as one of the dissipation of a surface structure and or mass. As the ring travellers of ring spinning and ring twisting machines are moved at high speed on rings, both the contact face between ring traveller and ring and the contact face between ring traveller and thread are subject to high wear due to friction. As an effect of friction, micro welding/pit formation takes place in the contact area of the rings and travellers and results in lesser life. For increasing the production, higher running speeds of the ring travellers are required. By longer service lives being achieved, the costs should at the same time be lowered.

The main purpose of various surface finishes and increasing the area of contact on the travellers is to minimize the friction so as to increase the traveller speed. By the ring travellers being coated with appropriate materials, in recent years it is possible to achieve a considerable improvement in their running and operating properties. However, in the case of traveller speeds of above 40 m/sec., it has not been possible to obtain a sufficient improvement in wear resistance both at the thread passage and at the ring contact face. As the polished surfaces of the traveller wear, they become roughened, increasing the coefficient of friction between the traveller and the ring. Such increased friction results in heat build-up. It is not uncommon for the toes of travellers to burn off, which in addition to loss of production time for replacement of the traveller, can cause damage to the yarn and the ring.

DE 3545484 describes a ring traveller for a spinning machine, said ring traveller carrying a ceramic covering layer covering at least the surface region which comes into contact with the ring. The ceramic covering layer consists of one or more layers selected from a carbide layer, a nitride layer, an oxide layer, or a boride layer. The ceramic layers are applied to the core by means of the CVD or the PVD method.

US2005252191 A1 describes a ring traveller which has a covering layer over the ferrous material, at least in the region of the running faces with which it slides on a ring and said covering layer contains fine-crystalline TiCN (titanium carbonitride), CrN (chromium nitride) or VC (vanadium carbide). The main aim of this fine crystalline coating is to improve the wear resistance of the travellers.

Nickel plating often causes a transfer of material to the ring which, in turn, results in accelerated traveller wear after the nickel plating is initially penetrated. Oxidation finishes cause a softening or tempering of the hardened steel during application thereof. Ceramic finishes also soften the steel surfaces, allowing for severe wear on conventional rings. Titanium alloy composites, while offering various advantages, can exhibit problems similar to those associated with nickel plated coatings in that they tend to wear off quickly, leaving bear surfaces subject to additional wear.

To overcome the disadvantages present in the existing art, the present invention describes a process method for plating a covering layer over the surface of coated travellers to increase the hardness and corrosion resistance and to enhance the heat transfer properties thereby to improve the working performance and traveller life.

OBJECT OF THE INVENTION
It is an object of the present invention to provide a composition for coating the thread guiding elements such as ring travellers for use in textile spinning applications.

It is an object of the present invention to provide a traveller coated with a composition that results in a traveller surface having sufficient wear resistance for high speed spinning and twisting operations.

It is further another object of the present invention to provide a cover layer for travellers to produce a low friction surface thereabout.

These as well as other objects of the present invention are achieved by providing a composition for coating a cover layer over the surface of ring travellers comprising chromium or chromium alloy. The chromium plating as a covering layer over the nickel-phosphorous coating is applied especially to the travellers used in yarn spinning applications.

SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

According to the main aspect of the present invention, the ring traveller for ring spinning or twisting machine consists a core ferrous material, said core material is coated with a base layer and a covering layer, said base layer contains nickel-phosphorous and the covering layer contains fine chromium or chromium alloy particles. The combination of said Nickel and Chromium particles forms a thin “Brownish to Black” oxide layer as a covering layer over the nickel-phosphorous coating.

According to another aspect of the present invention, there is provided a method for plating ring travellers used for ring spinning or ring twisting machine, said ring traveller comprising a core ferrous material having a base layer and a covering layer, wherein said method comprising steps of: coating said core ferrous material of the ring traveller with nickel-phosphorous layer; and submerging the nickel-phosphorous coated core of the ring traveller in a bath containing a solution having a chromium oxide concentration of from about 15 g/L to about 50 g/L, a chromic chloride concentration of from about 20 g/L to about 60 g/L, a potassium dichromate concentration of from about 5 g/L to about 30 g/L, a sulphuric acid concentration of from about 10 g/L to about 50 ml/Lit, wherein said solution is maintained at a temperature from about 20° C to about 60° C for a duration of about 1 minute to 1 hour to form a thin “Brownish to Black” chromium layer as a covering layer over the nickel-phosphorous coating.
The thickness of Nickel-Phosphorous coating layer over the core ferrous material ranging from about 0.001 micron to about 25 micron. The deposition of the nickel-phosphorous over the core material comprise approximately 90 - 98% by weight of nickel, approximately 2 - 10% by weight of phosphorous. The nickel ions are produced preferably from nickel sulphate, nickel hydroxide, nickel formate or nickel carbonate. The phosphorous ions are produced from phosphorous oxide, phosphorous carbonate, phosphorous acetate or sodium hypophosphite through reduction. The deposition of chromium particles as thin covering layer over the nickel-phosphorous surface having a coating thickness of approximately 2.0 – 10.0 microns. Said chromium ions are produced from chromium trioxide and chromic chloride.

According to yet another aspect of the present invention, the preferred coating technique for the Nickel-Chromium process is preferably an electroless plating method. Alternatively, the chromium particles can be coated by any available techniques such as PVD, CVD or plasma enhanced processes.

This process method can also be used to coat the other components used in spinning machines especially in contact with yarns such as Rings, Lappet hooks, balloon control rings and thread guide plates and tubes.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

FIGS. – 1 and 1a illustrate cross-sectional view of a spinning ring and traveller in accordance with the existing art.

FIG – 2 illustrates a magnified cross-sectional view of the coating on a traveller in accordance with the existing art.

FIG – 3 illustrates a magnified cross-sectional view of the coating of covering layer on a traveller in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS
The present invention is directed to rings and travellers for use in textile applications which require the winding of yarn onto a rotating carrier such as spinning, twisting and the like. All types of travellers suitable for use on both vertical and horizontal rings including reversible and non-reversible (single-flanged) horizontal rings in guiding the yarn onto the rotating carrier are within the scope of the present invention including elliptic, "C" shaped and vertical travellers. For the convenience of describing the invention, an elliptical type traveller is taken as example for description.

FIG - 1 and 1a shows the conventional elliptical type traveller and a horizontal ring known in the existing art. The spinning frame has yarn (1) fed from drafting rolls (not shown) through guide for winding onto a bobbin (3) which is mounted about and driven by rotating spindle. A traveller (4) having an intermediate portion (5) and Toes (6) defining a gap there between is slidably mounted on a spinning ring (7). The ring includes an intermediate vertical portion (8) so called web and a flange (9) for supporting traveller (4). The ring (7) is horizontally mounted on the ring rail (10). During spinning, yarn (1) is fed through guide (2) and threaded through traveller (4) for winding onto bobbin (3). Traveller (4) serves to tension and guide the yarn as it is wound onto bobbin (3). The Ring rail (10) provides a vertically reciprocating "building motion" which further guides yarn as it is wound onto bobbin (3). The ring and traveller has a generally uniformly deposited coating about the surface thereof. In the present invention, a thin layer of chromium or chromium alloy cover layer coating is applied over the surface of the nickel-phosphorous coating on the travellers.

FIG – 2 shows the magnified cross-sectional view of the coating on a traveller according to the existing art. The preferred coating technique for this process is an electroless plating method and the chemical composition comprising Nickel and phosphorous alloy. Preferably, the traveller is coated to a thickness (12) over the surface of traveller (11) body ranging from about 0.001 micron to about 25 micron. It is to be understood, however, that FIG. 2 and 3 are not drawn to scale but presented for illustrative purposes only. Although only the electroless plating is specifically mentioned herein, other coating techniques known to be equivalent to this particular coating are included within the scope of the present invention.

BASIC COATING PROCESS
It is preferred that the metallic matrix of the basic coating is nickel-phosphorous alloy. After the pre-treatment, the travellers are submersed in a bath having a nickel ion concentration of from about 25 g/L to about 70 g/L, nickel sulphate 20 to 75 g/L, nickel hydroxide 5 to 15g/L, nickel formate 20 to 60 g/L or nickel carbonate 10 to 60 g/L, a phosphorous ion concentration of from about 5 g/L to about 15 g/L phosphorous oxide, phosphorous carbonate 10 to 40 g/L, phosphorous acetate 20 to 50 g/L or sodium hypophosphite 15 to 60 g/L, and dimethyl amine concentration of from about 10 g/L to about 50 g/L. The dimethyl amine acts as a reducing agent which reduces the nickel ions, present preferably as nickel sulphate, nickel hydroxide, nickel formate or nickel carbonate, to metallic nickel. The phosphorous oxide, phosphorous carbonate, phosphorous acetate or sodium hypophosphite can be used for getting the phosphorous ions through reduction.

The said bath also contains malic acid concentration of from about 5 g/L to about 10 g/L, and ammonium carbonate concentration of from about 15 g/L to about 45 g/L and a tri sodium citrate concentration of from about 15 g/L to about 45 g/L. The malic acid acts as an additive and ammonium carbonate acts as a buffering agent to maintain uniform coating thickness.

Preferred operation conditions are a temperature from about 70° C to about 90° C and a pH in the range of from about 4 to about 7. The duration of the process is from about 5 minutes to 4 hours. During precipitation, the bath is subjected to constant agitation by rotating the bath about 5 to 10 RPM to ensure uniform coating. Same concentration is maintained throughout the process by checking and adding the required amount of chemicals at predetermined interval. The deposition of the nickel-phosphorous surface (12) over the core material is shown in the FIG – 2. Analysis of the plated deposits indicated that the coating comprise approximately 90 - 98% by weight of nickel, approximately 2 - 10% by weight of phosphorous.

COVERING LAYER COATING PROCESS
A ring traveller according to the present invention has a core consisting of a ferrous material, which is coated with nickel-phosphorous layer and a covering layer at least in the region of the running faces with which it slides on a ring of a ring spinning or ring twisting machine or in which the thread is guided. The covering layer contains fine chromium or chromium alloy particles.

After the basic nickel-phosphorous alloy coating process, the travellers are submersed in a bath having a chromium oxide concentration of from about 15 g/L to about 50 g/L and chromic chloride concentration of from about 20 g/L to about 60 g/L. A potassium dichromate concentration of from about 5 g/L to about 30 g/L chromium trioxide 10 to 50 g/L also used in the bath which acts as a reducing agent to reduce the chromium ions, present preferably as chromium trioxide and chromic chloride. The above said composition also contains sulphuric acid concentration of from about 10 g/L to about 50 ml/Lit. The sulphuric acid acts as an additive to accelerate the process. Preferred operation conditions are a temperature from about 20° C to about 60° C and the duration of the process is from about 1 minute to 1 hour.

Surprisingly, the above said combination of chemicals composition, Ni-Cr particles and processing time formed a thin “Brownish to Black” oxide layer as a covering layer over the nickel-phosphorous coating. The deposition of chromium particles (13) as thin covering layer over the nickel-phosphorous surface (12) is shown in the FIG – 3. The deposition of coating are at the rate of approximately 0.30 – 0.35 micron/min and the thickness of coating shall be 2.0 to 10.0 micron.

The following example illustrates the preparation and application of an electroless nickel/chromium coating in accordance with the present invention.

EXAMPLE
Travellers were subjected to composite nickel plating in a nickel bath and then subjected to chrome bath.
Nickel alloy Bath Composition
Nickel Sulphate 50.0 g/L
Nickel Hydroxide 10.0 g/L
Nickel carbonate 30.0 g/L
Nickel formate 25 .0 g/L
Sodium hypophosphite 20.0 g/L
Sodium Citrate 20.0 g/L
pH 5.1
Temperature 85° C.
Time 1.5 hours

Chromium covering layer Bath Composition
Chromium Trioxide 25 g/L
Chromic chloride 30 g/L
Potassium dichromate 15 g/L
Sulphuric acid 20 g/L
Temperature 45° C.
Time 5 min

As a result, the hardness and wear resistance provided by chrome layer is greater than that of a conventional nickel-phosphorus coating. The hardness of chrome coated double layer ring traveller is 30% higher than the conventionally coated travellers. The coating provides resistance greater than that of the other coatings described above. Reduced frictions are achieved at high spinning rates when a ring and traveller, where either is coated in accordance with the present invention, or used in combination.

The result of the fine chrome covering layer on the ring travellers according to the invention have a greatly improved wear resistance at the thread passage and at the ring contact face. The wear rate, as compared with ring travellers with a conventional ceramic layer, electroplating or nickel dispersion coating, falls by approximately 80%, and the useful life of a ring traveller is prolonged up to 3 times, that is to say up to 500 operating hours. The operating costs fall significantly as a result. Owing to the covering layer, the ring traveller according to the invention has good abrasion resistance and corrosion resistance.

CLAIMS:1. Ring traveller (4) for ring spinning or ring twisting machine , said traveller comprising a core ferrous material (11), characterized in that, said core material is coated with a base layer and a covering layer, wherein said base layer contains nickel-phosphorous and the covering layer contains fine chromium or chromium alloy particles.
2. The ring traveller (4) as claimed in Claim 1, wherein the combination of Nickel-Chromium particles forms a thin “Brownish to Black” oxide layer as a covering layer over the nickel-phosphorous coating.

3. The ring traveller (4) as claimed in Claim 1, wherein said Nickel-Phosphorous coating layer over the core ferrous material (11) having thickness (12) ranging from about 0.001 micron to about 25 micron.

4. The ring traveller (4) as claimed in Claim 1, wherein the deposition of the nickel-phosphorous over the core material (11) comprise approximately 90 - 98% by weight of nickel, approximately 2 - 10% by weight of phosphorous.

5. The ring traveller (4) as claimed in Claim 1, wherein the nickel ions are produced preferably from nickel sulphate, nickel hydroxide, nickel formate or nickel carbonate.
6. The ring traveller (4) as claimed in Claim 1, wherein the phosphorous ions are produced from phosphorous oxide, phosphorous carbonate, phosphorous acetate or sodium hypophosphite through reduction.
7. A method for plating ring travellers used for ring spinning or ring twisting machine, said ring traveller comprising a core ferrous material (11) having a base layer and a covering layer, wherein said method comprising steps of :
coating said core ferrous material of the ring traveller with nickel-phosphorous layer (12); and
submerging the nickel-phosphorous coated core of the ring traveller in a bath containing a solution having
a chromium oxide concentration of from about 15 g/L to about 50 g/L,
a chromic chloride concentration of from about 20 g/L to about 60 g/L,
a potassium dichromate concentration of from about 5 g/L to about 30 g/L,
a sulphuric acid concentration of from about 10 g/L to about 50 ml/Lit, wherein said solution is maintained at a temperature from about 20° C to about 60° C for a duration of about 1 minute to 1 hour to form a thin “Brownish to Black” chromium layer as a covering layer over the nickel-phosphorous coating.

8. The method as claimed in Claim 7, wherein the chromium ions are produced from chromium trioxide and chromic chloride.

9. The method as claimed in Claim 7, wherein the chromium particles (13) are deposited as thin covering layer over the nickel-phosphorous surface (12) and the coating thickness is approximately 2.0 – 10.0 microns.

10. The method as claimed in Claim 7, wherein the coating technique for the Nickel-Chromium process is preferably an electroless plating method.