GB2056884A - Coatings on textile machinery - Google Patents

Abstract

An article for use in textile machinery in frictional contact with testiel fiber having a coating of hard ceramic platelets in a matrix. Preferably the particles are alumina and the matrix is nickel. The coating is preferably formed by electroless plating techniques where the ceramic platelets are suspended in the plating solution during deposition of the matrix metal.

Description

SPECIFICATION A coated article and a method for its production The invention relates to a coating for elements in frictional contact with textile fibers in high speed textile machinery.

Presently the most productive method of texturizing yarns or threads is the crimping of such yarns by setting a false-twist in the yarns. The false-twist texturizing method is generally well-known and is discussed by Arthur Weller, "The Principles of Friction Twisting," J. Tex. Inst., 1960, No. 2, P. 66.

The high speed machinery that performs this false-twist operation include numerous elements such as "discs" and "bushing" which twist and propel the yarn as it is texturized. The throughput of yarn texturized by conventional high speed machinery is approaching 1 ,000 meters a minute, and the discs and bushings rotate at speeds as high as 15,000 to 18,000 rpms. In the future rotation speeds may exceed 20,000 rpm.

The operation of such machines at such speeds reduces the investment and energy cost of operation by significantly increasing the productivity of the machine. As a result, there is a continuai striving to further increase the speed of such machines.

Typical false-twisting machinery is disclosed in U.S. Patents 3,955,350 to Schuster and 3,932,985 to Naylor.

In such false-twist machines, friction drive elements, such as "discs" and "bushings," are used to texture the yarn by placing a falsetwist on the yarn. Conventionally, discs have been used to produce large denier yarns such as polyester, and bushings have been used to produce finer denier yarns such as nylon.

All false-twist elements, whether discs, bushings, or other elements, must be wear resistant and have a surface that will not damage the yarn. The elements which twist the yarn must also have a high coefficient of friction and yet not have a surface that will damage or abrade the yarn. A false-twist element with a rough surface tends to break the filaments of the yarn being texturized, thereby damaging the tenacity and appearance of the yarn. Furthermore, abrasion of the yarn results in the formation of particulate flakes of yarn material known as "snow". The formation of this "snow" hinders operation of the machinery and presents a potential health hazard.

The surfaces of the elements contacting the yarn should: have a high coefficient of friction, be smooth, be wear resistant, have a high hardness, be uniform and be indifferent to atmospheric conditions and chemical agents. Other optimum characteristics would be lightweight and low cost and low abrasive characteristics.

Surfaces which have been used on friction elements in the past can be divided into two major classes. The first group are soft materials, such as polyurethane. Such materials have good all around characteristics, but exhibit a relatively short useful life, often measuring only weeks or months.

The second group are hard materials, of which ceramic-coated metal, diamond coating and solid ceramics is typical. These coatings rely on the mechanical keying or roughness of the surface to grip the filaments of the yarn.

Diamond coatings have not been able to meet the requirement of uniformity cause filament breakage and snow formation and are expensive. Plasma coated ceramics have had similar problems with uniformity and abrasion of the yarn. Additionally, the surface of plasma coated ceramics is subject to glazing which diminishes the coating's coefficient of friction.

Currently, solid ceramic rimmed metal discs are utilized as friction elements in many high speed false-twist machines. The principal problem with these ceramic discs is their weight, and consequently the speed at which they can be operated. Solid ceramic elements operated at high speeds of rotation have been known to explode or shatter. This inherent shortcoming of solid ceramic elements presents extreme danger to operators of falsetwist machines and also limits the operating speed and efficiency of false-twist machines.

Furthermore, the properties of the ceramics do not seem to be uniform.

The present invention overcomes the problems and disadvantages of the prior art by providing a coating for the friction elements of textile machines which is smooth, strong, wear resistant, uniform and has a high coefficient of friction. This coating has been found to be particularly successful when applied to the surface of discs and bushings.

It is therefore an object of the invention to provide a coating for friction elements used in textile machinery that will contact the textile material without detrimentally affecting the textile material.

It is a further object of the invention to provide a durable coating for a friction element for false-twist machinery disposed to contact the yarn passing therethrough that will impart a false-twist to such yarn while reducing damage to the yarn such as the production of "snow" or breakage of filaments.

Still a further object of the invention is to provide an inexpensive durable coating with a particularly useful coefficient of friction for a friction element for false-twist machinery that is disposed to contact the yarn passing therethrough.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the instrumentalities and combinations, particularly pointed out in the appended claims.

SUMMARY OF THE INVENTION To achieve the objects in accordance with the purpose of the invention, as embodied and broadly described, the invention comprises: a surface coating for a friction element disposed to contact textile fibers with the coating comprising hard ceramic platelets in a matrix.

Preferably the ceramic platelets are alumina in a matrix of nickel.

The invention also comprises a method of forming a surface coating on the surface of a friction element that is disposed to contact textile fibers. A friction element having a polished metal surface is immersed in an electroless metal plating solution which includes hard ceramic platelets that are kept in suspension in the solution. The friction element is maintained in the solution until the coating is of the desired thickness. The coated elements is thereafter heat treated.

Preferably, the ceramic platelets are alumina and the electroless plating solution is a nickel plating solution.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and expiana- tory only and are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

OF THE DRAWINGS: Figure 1 is a perspective view of a friction disc coated with the coating of the present invention; Figure 2 is a cross-section of Fig. 1 along lines 2-2 showing the coating in cross-section; Figure 3 is a perspective view of a bushing having the coating of the present invention; Figure 4 is a cross-section of Fig. 3 taken along lines 4-4 and showing the coating of the present invention; Figure 5 is a photomicrograph at 2000x showing a surface of a disc coated with the present invention; Figure 6 is a photomicrograph at 2000x showing a surface of a prior art friction disc formed of a solid ceramic.

Figure 7 is a photomicrograph at 4000x showing a surface of a disc coated with the present invention.

DESCRIPTION OF THE PREFERRED EMBODI MENTS Reference will now be made in detail to the preferred embodiment of the invention, examples and illustrations of which are depicted in the accompanying figures and photomicrographs.

As embodied herein, the present invention is a surface coating for a friction element disposed to contact textile fibers.

As depicted in Figs. 1-4, the coating 20 and 25 may be applied to friction elements 10 and 1 5 disposed to texturize a thread or yarn by imparting a false-twist thereto. Two major types of such friction elements are utilized in most false-twist machinery. The first, depicted in Figs. 1 and 2 is the "external" friction element in which the yarn twist is obtained by yarn contact with the outer edge of the rotating element termed "discs". The second, depicted in Figs. 3 and 4 is an "internal" friction element known as a "bushing". In the internal friction element, the yarn twist is obtained through the contact with the internal arcuate surface of the rotating friction element.

While the present invention has shown particular utility as a coating on such "bushings" or "discs", it should be noted that the coating disclosed herein may also be used on other components of textile machinery having need of its unique properties. Examples of such uses would be rotors and beaters in the openend spinning machinery used in the cotton industry. Furthermore, it is believed that the coating of the present invention would increase the life and efficiency of cutting blades used in the textile fiber production and the tobacco industry.

The coating of the present invention comprises hard ceramic platelets in a matrix. Such a coating has a cornbination of properties making it particularly useful for the applications generally described above.

As depicted in Figs. 1-4, the coating of the present invention is disposed on the surface of a solid member. In the embodiments shown, the member is a friction element for a falsetwist texturizing machine. The properties of the solid member on which the inventive coatings are placed are determined by the function of the element which is coated. As previously described, the false-twist friction elements are rotated at extremely high speed and must therefore be light, strong and dimensionally stable.

Preferably the solid member coated to form the coated false-twist friction element is comprised of metal, most preferably an alloy of aluminum. Solid aluminum elements have been used with success with the present invention, but other materials or composite structures could be used with the coating of the present invention as long as the surface receiving the coating can be rendered smooth and the coating of the present invention ap plied thereto. For example, it is believed that solid steel friction elements could be successfully used.

Particular success has been experienced using an aluminum alloy for the solid member and placing the surface of the coating of the present invention thereon. In such an embodiment, the surface of the coating of the present invention showed the condition of the surface receiving the coating. As an example, a surface receiving the coating was polished to a surface finish of 2 microinches R.M.S. and was then coated. The coated member showed excellent properties as a friction element in a false-twist apparatus.

The invention also contemplates coating a false-twist element having a lightweight, inexpensive body made from materials such as aluminum or plastic and including an outer tire (disc) or inner ring (bushing) of steel or another metal onto which the coating could be applied. Such a false twist element would be lightweight and inexpensive and yet would have a durable working surface which would not dent as easily as a solid aluminum disc or bushing.

The use of hard ceramic platelets in a matrix is the crux of the present invention.

Such platelets form a surface that has a particularly high coefficient of friction while actually reducing abrasion and breakage of textile fibers in frictional contact with such surfaces.

As most clearly depicted in Fig. 7, the ceramic platelets (alumina in this embodiment), apparently due to their thickness to diameter radio, appear to lie substantially flat to the surface of the element being coated.

The alumina platelets used in the preferred embodiment shown have a thickness to diameter ratio of about 1 to 5. It is believed that the orientation of such platelets is at least partially responsible for the unique properties of the coating of the present invention. Irrespective of the actual mechanism of achieving such properties, the use of hard ceramic platelets, as opposed to hard ceramic granular particles, exhibit totally unexpected superiority.

During experimentation and comparison, the inventor has measured the coefficients of friction for several materials used as friction elements. The coefficients of friction were: solid ceramic (alumina.346 chrome oxide plasmas coating-. 385 4 micron diameter alumina platelets in metal matrix-.462 This data demonstrates the superiority of the friction elements having coatings of the present invention. The achievement of this higher coefficient of friction without sacrificing the smoothness of the coating permits friction elements with the present coating to develop a high number of twists in the yarn being texturized, without unduly abrading the yarn.

The hard ceramic platelets of the present invention are preferably alumina. This material is extremely hard, chemically unreactive and available in a pure form as platelets of various diameters. Although alumina is the preferred species of ceramic, platelets other than ceramic platelets may also be operable.

Particular success has been experienced in the embodiments depicted herein using purified, calcined aluminum oxide in platelet form that is ordinarily used in a fluid vehicle as an abrasive.

As previously disclosed, such platelets normally have a thickness to diameter ratio of 1 to 5. The present invention appears to be operable with platelets having diameters up to about 50 microns. The practical range for the platelet size, however, lies in the range of from .5 to 20 microns.

There is some indication that the optimum size of the platelets for use in false-twistng of yarns is dependent upon the size of the yarn being treated. For the embodiment depicted herein, particular success has been experienced using alumina platelets having a diameter in the range of from 1 to 6 microns. It appears that large platelets have a tendency to permit slippage and therefore are not useful in a false-twist application.

The inventor has found that an electroless solution containing platelets within a specified narrow range produces the best results. In particular, the inventor has successfully used a solution containing platelets in the range of 1-3 microns, a solution containing platelets in the size range of 3-5 microns and a solution containing platelets in the size range of 5-7 microns.

For yarns in the range of 70 to 1 50 denier, a platelet size of about 2 to 4 microns has proved to be desirable. There is also some evidence that once the size of the platelets exceeds the optimum size, surging of the yarn being false-twisted may occur.

The matrix used to form the hard ceramic platelets into a coating is preferably a metal.

Particular success has been achieved in forming a coating using a nickel matrix. As will be disclosed hereinafter, a process of electroless plating has been used to form a coating of alumina platelets in a nickel matrix by suspending the alumina platelets in the plating solution. The member receiving the coating was an aluminium bodied friction element for a false-twist apparatus of the type depicted in Figs. 1 and 2. The surface of the element disposed to contact the thread or yarn to impart the false-twist thereto was the portion of the member having the coating thereon.

The means by which the coating was applied and the characteristics of the coating produced will be disclosed in greater detail in the following discussion of the preferred method of coating.

PREFERRED METHOD OF PRODUCING THE COATING An electroless plating technique is the preferred method of forming the coating of the present invention. Such a process for the production of coatings including particulate material is described in U.S. Patent Re.29,285 and the references cited therein.

The cited reissue patent discloses methods of electroless plating various metals with diamond particles imbedded therein.

In such techniques, the surface finish of the solid article receiving the coating affects the surface finish of the coating placed thereon.

Therefore, the surface finish of the article to be coated should be smooth and free of imperfections and scratches. Where the article to be coated is intended to contact textile fiber as, for example, a friction element imparting a false-twist to yarn or thread, the surface of the article to be coated should have a polished surface. The inventor has found that a finish of four microinches R.M.S. has worked, although both rougher or smother surfaces may achieve the best results for a particular application. For example, a surface finish of two microinches or better for a metal surface on such an article has been found to provide an excellent surface for a coating of alumina in a matrix of nickel.

The article to be coated is immersed in an electroless metal plating solution that contains hard ceramic platelets in suspension. The platelets can be kept in suspension by means mechanically stirring the solution. A mechanical stirring rod, a pump or impeller may be used.

In the embodiment of the invention, wherein the article being coated is a friction element for a false-twist apparatus, care must be taken with respect to size and shape of the container for the solution to insure that the suspension of platelets is uniform. The temperature of the bath is controlled and uniform, and the chemical constituents of the plating solution can be maintained to a degree that the process will produce a uniform coating on the article immersed therein. The element to be coated can be left stationay, can be constantly rotated or can be moved at intervals.

The inventor has found that continued rotation of friction elements produces a uniform coating.

For coating a friction element, it has been found useful to use a relatively small container and use a new batch of plating solution for each batch of articles produced.

The use of relatively small batches and fresh plating solution with each batch produces a uniform coating that does not require polishing to achieve an excellent surface finish. Such a practice may be overly conservative if means of accurately monitoring and controlling the plating solution can be utilized.

The plating solution used is determined by the type of metal to be used as the matrix for the ceramic platelets. Particular success has been experienced using nickel as the metal in combination with ceramic platelets of alumina.

Electroless plating solutions for various metals are available commercially as for example, Enplate 41 8 a product of Enthone Inc., which is an electroless nickel plating solution.

In accordance with the invention, the object to be coated is immersed in an electroless metal plating solution which includes about 2 to 10 grams/liter of hard ceramic platelets that are kept in suspension in the plating solution. The composition of the optimum solution depends upon the size of the platelets and the intended application of the coating.

As an example, an optimum solution for coating a disc with alumina platelets in the size range of 1 to 3 microns appears to be one containing about 8 grams of platelets per liter of nickel solution. The apparent optimum solution for coating a disc with alumina platelets in the size range of 3 to 5 microns appears to be a solution having 2 grams of platelets per liter of solution.

Preferably the ceramic platelets are alumina and the electroless metal plating solution, and hence the metal for the matrix, contains nickel. The electroless coating process can be done over a wide range of temperatures, the speed of the coating process increasing with temperature. The use of such plating solutions is preferably done at a temperature in the range of from 1 75OF. to 1 85'F. At such temperatures, the coating of alumina platelets in a nickel matrix is applied at the rate of about .5 mils (13 microns) per hour. Coating thickness of about .5 to 0.8 mils have proved to be useful in embodiments used in falsetwist apparatus, and, in conformance with the above deposition rate, such coatings were produced by electroless plating in about 1 hour.

The hardness of the coating produced by such an electroless plating process can be improved by a heat treatment. An aluminaplatelet coating can be heat treated to its maximum hardness by subjecting an article to heat treatment in a non-oxidizing atmosphere at a temperature of 750"F for one hour. Also, for an aluminum bodied friction element having a coating of alumina in a nickel matrix, heating at 500to. in an oxidizing atmosphere for about 1 2 hours has proved to materially harden the coating.

A alumina-plaatelet coating produced on an alumina disc in accordance with the present invention is shown in the photomicrographs of Figs. 5 and 7. Prior art ceramic surfaces are shown at comparable magnifications in the photomicrograph of Fig. 6.

As is evident in Figs. 5 and 7, the coating of the present invention provides a surface texture totally unlike that of the ordinary ceramic surface. Because of the flat, plate-like shape of the particulate ceramic (platelets) used in the present invention, the platelets have a tendency to align in the coating with the larger dimension of the platelets roughly parallel to the surface being coated. With the platelets aligned in such a manner in the coating, a fiber in contact with the coating is gripped by the edges of such platelets.The manner in which the platelets grips the fibers is apparently different than granular ceramic particles or diamonds which cause local abasion and filament damage of the fiber material and produce "snow". The coatings of the present invention effectively engage such fibers without producing the amount of fiber damage or "snow" exhibited by conventional materials.

EXAMPLE A 2.4 liter container was maintained at a temperature of about 178 F. About 0.4 liters of an electroless nickel plating solution of Enplate 418 containing 25 grams of alumina platelets along with 2.0 liters of deionized water comprised the coating solution. The alumina in the 1-3 micron size range was kept in suspension with a magnetic stir rod. A mandrel was used to support 10 disc-like false-twist friction elements, and two of such mandrels were placed in the coating solutions and rotated for approximately 1 hour.

Upon removal from the coating solution, the articles had a smooth coating of alumina platelets in a matrix of nickel. The deposited coating was approximately 0.7 mil (18 microns) thick.

The hardness of the deposited coating was determined to be 48 on the Rockwell C scale.

The coated elements were then subjected to a heat treatment of 500 F. in an air atmosphere and the hardness of the coating was increased to 70 on the Rockwell C scale. The surface of the coated element did not require any further polishing or treatment.

The coefficient of friction of the element surface was determined to be .462. The elements so produced have shown exceptional utility in false-twist apparatus significantly reducing the production of "snow" and exhibiting excellent resistance to wear.

The present invention has been disclosed in terms of its preferred embodiments. The scope of the invention is not limited to such embodiments and is determined by the scope of the appended claims.

Claims (33)

1. A surface coating for a friction element disposed to contact textile fibers, said coating comprising hard platelets in a matrix.

2. The surface coating of claim 1 wherein said platelets are ceramic platelets.

3. The surface coating of claim 1 wherein said matrix is metal and said platelets are alumina.

4. The surface coating of claim 3 wherein said coating has a coefficient of friction greater than .4.

5. The surface coating of claim 3 wherein said matrix is nickel.

6. The surface coating of claim 5 wherein said coating has a Rockwell C hardness of about 70.

7. The surface coating of claim 3 wherein said platelets have a diameter in the range of from about .5 to 20 microns.

8. The surface coating of claim 3 wherein said platelets have a diameter in the range of from 1 to 6 microns.

9. The surface coating of claim 3 wherein said platelets have a diameter in the range of 1 to 3 microns.

10. A friction element for false-twisting thread comprised of a central member having a thread-contacting surface about an axis of rotation, said surface having a coating thereon, said coating comprising alumina platelets in a metal matrix.

11. The friction element of claim 10 wherein said alumina platelets are applied to form said coating by electroless plating of said metal to said surface of said central member, said alumina platelets being suspended in the plating solution from which said metal matrix is formed.

1 2. The friction element of claim 11 wherein said central member is metal and said thread-contacting surface of said central element on which said coating is placed has a surface finish of at least 2 microinches R.M.S.

1 3. The friction element of claim 11 wherein said central member is aluminum and said metal matrix is nickel.

14. The friction element of claim 10 wherein said metal matrix is nickel and said alumina particles have a diameter in the range of from 1 to 6 microns.

1 5. The friction element of claim 14 wherein said coating has a coefficient of friction greater than .4.

1 6. The friction element of claim 1 4 wherein said coating has a Rockwell C hardness of about 70.

1 7. The friction element of claim 10 wherein said alurnina platelets are oriented with the large dimension of the platelets roughly parallel to the surface of the friction element.

1 8. The friction element of claim 10 wherein said central member is aluminum and said thread-contacting surface is steel.

1 9. The friction element of claim 10 wherein said coating is approximately 1 3 microns thick.

20. A method of forming a surface coating on the surface of a friction element disposed to contact textile fibers comprising the steps of: (a) providing said friction element with a polished metal surface to be coated; (b) immersing said friction element in an electroless metal plating solution which normally includes about 1 to 10 grams but as much as 100 grams per liter of hard ceramic platelets that are kept in suspension in said solution; and (c) maintaining said friction element within said solution until said coating is of the desired thickness.

21. The method of claim 20 wherein said hard ceramic platelets are alumina, and the metal in said metal plating solution is nickel.

22. The method of claim 21 wherein said metal plating solution is kept at about 180 F.

23. The method of claim 20 further comprising heat treating the coated friction element.

24. The method of claim 23 wherein said hard ceramic platelets are alumina, and the metal in said metal plating solution is nickel.

25. The method of claim 24 wherein said heat treatment step comprises exposing the coated friction element to an oxidizing atmosphere at about 500 F. for about 12 hours.

26. The method fo claim 24 wherein said heat treatment steps comprises exposing the coated friction element to a non-oxidizing atmosphere at about 750"F. for about 1 hour.

27. The method of claim 24 wherein said alumina platelets have a diameter in the range of from 1 to 6 microns.

28. The method of claim 24 wherein said alumina platelets have a diameter in the range of 1 to 3 microns.

29. The method of claim 27 wherein said surface coating has a coefficient of friction greater than about 4.

30. The method of claim 24 further comprising the step of constantly rotating the friction element while it is immersed in said electroless metal plating solution.

31. The method of claim 24 further comprising the step of periodically rotating the friction element while it is immersed in said electroless metal plating solution.

32. A friction element substantially as hereinbefore described with reference to Figs.

1, 2, 5 and 7 or Figs. 3-5 and 7 of the accompanying drawings.

33. A method of forming a surface coating substantially as hereinbefore described.