US3543452A - Finishing process for metallic surfaces - Google Patents

Description

3,543,452 FINISHING PROCESS FOR METALLIC SURFACES Charles J. Guenther, Mankato, Minn., assignor to International Business Machines Corporation, Armonk, N.Y-, a corporation of New York No Drawing. Filed Mar. 1, 1968, Ser. No. 709,790 Int. Cl. B24b 1/00 US. Cl. 51313 9 Claims ABSTRACT OF THE DISCLOSURE A method for improving surface smoothness of a surface having particles of a hard, wear resistant substance embedded in a metal matrix involving a minimum of matrix particle removal. Parts to be finished are tumbled or vibrated in an aggressive media in the presence of a liquid containing a wetting agent.

BACKGROUND OF THE INVENTION This invention pertains to surface finishing and more particularly, to enhancing the surface smoothness of parts having a surface layer of hard abrasion resistant particles embedded in a metal matrix.

When a machine part in use is subject to contact with another article such as a business machine subjected to contact with a moving record medium, it is required that a Wear resistant surface be provided at locations of contact. It is necessary that the surface presented is abrasion resistant and further presents a smooth enough surface to avoid damage to the medium being handled. One means of providing a wear resistant surface is to plate a metal part with a metal matrix material which carries particles of hard wear resistant material. A common matrix using this procedure is a nickel matrix bearing silicon carbide particles which is electroplated on the part. While this processing of the part provides a wear resistant surface that protects the machine of which the parts are a portion, the contact surface so provided may be sufficiently irregular to damage the record medium with which it must come in contact.

To overcome this disability it is necessary that the smoothness of the finish be improved. This must however be accomplished without compromising the surfacing material when the latter has been applied to the part as by electroplating and comprises only a thin layer. Grinding polishing or other surface treatment that improves the surface finish by removal of material must be accomplished with great care to assure that the surfacing layer is not wholly removed or compromised in its effectiveness by removing the abrasion resisting particles from the surface of the matrix. There is further a tendency for a grinding or polishing device to push particles along the matrix surface to gall and deface the surface rather than shear the particle to a uniform height to improve the sur face regularity.

Parts which are to have the surface improved might be tumbled with metal shot, but in such a process damage is likely to occur to parts as a result of the Weight of the media even if liquid is utilized to overcome a portion of the weight disability through floatation. In additon, it will be necessary to have a media which was sufficiently hard to be effective in treating the surface presenting principally silicon carbide particle surfaces. Heavy shot would tend to chip the metal coating or dent the coating, impairing the bond between the surface material and substrate and rendering the surface material susceptible to chipping.

nited States Patent Patented Dec. 1, 1970 In the process of this invention the parts are loaded into a tumbling barrel or vibratory container in intimate contact with an aggressive media of preformed ceramic bodies. Also included is a liquid including a wetting agent and where it is desirable to accelerate the action, a light grinding compound is utilized. When tumbled or vibrated in the presence of such media, a surface finish improvement based on the arithmetical average standard (AA) can be achieved in the realm of a reduction from the approximate AA of the part surface as plated to an 8AA, far surpassing the required 32AA specified in many environments. Of equal importance is the fact that this improved surface condition is attained without significant removal of wear resistant material. In many instances it is hardly possible to identify any removal of the particles of wear resistant material. Although an aggressive particle is utilized in the preformed media, the observed result of the process is a peening action wherein the wear resistant particles such as silicon carbide are kneaded into a metal matrix, such as nickel with negligible particle removal. As a consequence, the density of such particles at the surface is at least as great subsequent to processing as it was prior to processing. It will accordingly be appreciated that the method of this invention has particular utility when used on parts having a relatively thin electroplated coating of a metal matrix containing Wear resistant particles.

It is an object of this invention to provide an improved process for enhancing the surface smoothness of part surfaces formed of discrete additive particles of wear resistant material in a metal matrix.

It is a further object of the method of this invention to improve the surface smoothness of a surface formed of particles of wear resistant material in a metal matrix without reducing the density of wear resistant material particles at the matrix surface.

It is also an object of this invention to provide a method for enhancement of the surface smoothness of an electroplated metal matrix containing wear resistant ma terial particles which does not impair the bond between the electroplated surface material and the substrate material.

The foregoing and other objects, features and advantages of the'invention will be apparent from the following more particular description.

DETAILED DESCRIPTION When a tumbling operation is utilized, the barrel is loaded to the operating level with preformed ceramic media. Normally a single size media body is utilized with the size and shape determined by the part configuration. The media body must be of a size and shape to reach corner or short redius portions of part surfaces to be treated, but must not be of a size which might lodge in an apertured or notched portion of the part or parts being processed. To simplify this determination and also separation at the end of the process it is normal practice to process parts of a single design in a given operation. Water is thereafter added to substantially the level of the media and a wetting agent or a combined wetting agent and compound added in an amount of three ounces per cubic foot of media. Following tumbling of the media sufficiently to assure a satisfactory mixture of the component portions thereof, the parts are added to the media mass in a volumetric ratio of one volume of parts to four volumes of media. The time of the tumbling operation varies depending upon the initial surface condition, the final surface condition required and whether a grinding compound is used, but normally a three to five hour cycle time is required.

When it is desirable or necessary to restore the color and remove oxides or remove a residue build-up on processed parts, a secondary tumbling process may be utilized using preformed media and water as above and one ounce of detergent for each cubic foot of media. A norm one hour cycle time is utilized when this secondary operation is used.

In the tumbling process the entire mass of media and parts is continuously revolved causing media elements to fall back against the part surfaces during one portion of the cycle. Where parts of a more delicate nature are being processed, a vibratory process often proves more satisfactory.

In the vibratory process, the vibratory tub is loaded to the operating level with preformed ceramic, abrasive media selected in accordance with part requirements as in the tumbling process and a quantity of water added sufficient only to maintain media and part surfaces moist. A low foaming wetting agent or a low foaming grinding compound including a finely ground abrasive and low foaming detergent is added in an amount of about three ounces per cubic foot of media. Following thorough admixture of the media within the vibratory tub, parts to be processed are added in the ratio of one volume of parts to four volumes of media. The cycle time varies in accordance with the initial and terminal surface conditions and whether a compound is used varying from one to five hours.

Following the primary cycle the parts are rinsed and a secondary process may be used to remove residue and restore the color by removal of oxides by vibrating media and parts using one ounce of low foaming detergent The part to be processed is aluminum coated with a nickel matrix carrying silicon carbide particles. The part is not delicate, having a minimum thickness of one-fourth inch, with no surfaces requiring close alignment and therefore may be tumbled. A preformed triangular media inch on each side and 7 inch thick of aluminum oxide is selected since the part includes a 0.219 inch diameter aperture in which smaller size media particles might lodge.

A tumbling barrel is loaded with the above media to the operating level. Water is added to the operating level, and a compound containing finely ground silicon carbide and detergent is added in the amount of three ounces per cubic foot of media. The media is tumbled sufficiently to effect mixing and the parts added. The cycle time is four hours following which the processed parts are separated from the media by screening.

The part surface as plated has a surface character in a nominal range of 90110AA with a mean value of IOOAA while a final surface condition is specified as not in excess of 32 AA. After the tumbling process as specified the surface of the coating of silicon carbide and nickel has attained a finish in the range of 2530AA.

EXAMPLE II The part to be processes is formed of aluminum with an electroplated coating of nickel carrying particles of silicon carbide. The part has a half inch diameter aperture, a 0.63 inch slot and a series of 0.188 inch diameter apertures. The part being elongated with a relatively thin cross section vibratory processing is selected.

The media used is preformed triangular bodies of aluminum oxide inch on each side and "E1 inch thick. This media body is sufliciently small to pass through the half 4 inch aperture and the slot while being excluded from the 0.188 inch apertures. The vibratory tub is loaded with media to the operating level and water added in sufiicient quantity to maintain the media and part surfaces moist. Thereafter a grinding compound formed of finely ground aluminum oxide and low foaming detergent is added. Following mixing of the media the parts are added, subjected to a five hour vibratory cycle and rinsed after processing.

The part as received following electroplating of the silicon carbide and nickel coating has a surface finish with a mean value of 100AA, falling within the range of 110AA, while the required final finish is 32AA. Following the vibratory process as defined above, a surface finish in the range of 16-25AA is attained.

While the invention has been particularly described with reference to preferred embodiments thereof, it will be understood that the foregoing and other changes in the form and details may be made therein without depart ing from the spirit and scope of the invention.

What is claimed is:

1. A method of treating the surface of an article having particles of hard, abrasion resistant material embedded in a matrix of metal to remove irregularities and establish a smooth surface finish without causing significant removal of material comprising:

establishing relatively sliding contact between said article and an aggressive preformed ceramic media in the presence of a liquid containing a wetting agent.

2. The method of claim 1 wherein said sliding contact is induced by tumbling said article in the presence of said ceramic media and said liquid is water present in a quantity to bring the level of said water to the level of said media.

3. The method of claim 2 wherein said media comprises preformed bodies of aluminum oxide.

4. The method of claim 2 wherein said water has therein a light grinding compound comprising a finely ground hard, wear resistant material and a detergent comprising said wetting agent.

5. The method of claim 3 wherein the article surface to be treated is an electroplated nickel matrix having discrete particles of silicon carbide homogeneously dispersed therein and the performed media bodies are of a size and configuration to prevent lodging thereof in article apertures or recesses.

6. The method of claim 1 wherein said article and ceramic media are held within a container and said sliding contact is induced by imparting a vibratory motion to said container holding said article and said ceramic media.

7. The method of claim 6 wherein said liquid is water present in sufficient quantity to maintain a liquid film on article and media surfaces throughout the vibratory operation.

8. The method of claim 7 wherein said liquid has therein a low foaming grinding compound comprising a low foaming detergent that functions as said wetting agent and finely ground hard, wear resistant material.

9. The method of claim 7 wherein the article surface to be treated is an electroplated nickel matrix having discrete particles of silicon carbide homogeneously dispersed therein and the preformed media bodies are of a size and configuration to prevent lodging thereof in article apertures or recesses.

References Cited UNITED STATES PATENTS 6/1913 Uebersax 51-313 3/1966 Bishop 51313 US. Cl. X.R. 51-317