Patent Grant
3991240
This invention relates to composite flame spray powder containing inexpensive cast iron as a major component, and yet which is capable, upon flame spraying, of producing a hard, wear- and scuff-resistant coating which finishes well and shows good bearing characteristics. In the flame spray art, it is well-known to flame spray various types of metal powders, blends and composites depending on the type and characteristics of the flame sprayed coating to be produced. In order to produce hard, wear- and scuff-resistant coatings which could be ground to a good finish and could be utilized in machinery as a long-wearing bearing surface, it was generally necessary to utilize relatively expensive metals as, for example, molybdenum, nickel-base self-fluxing alloys, and the like. Attempts to reduce the cost of such flame spray material as, for example, by blending the relatively expensive molybdenum with relatively inexpensive cast iron did not prove satisfactory and the coatings produced upon spraying such blends did not show all of the desired characteristics. One object of this invention is a flame spray material containing relatively inexpensive cast iron as a major component, and yet which, upon flame spraying, is capable of producing a hard, wear-resistant and scuff-resistant coating which may be ground to a smooth finish and which makes an excellent bearing surface for use between moving parts of machine elements. This and still further objects will become apparent from the following description. In accordance with the invention, it has been discovered that a hard, wear-resistant, scuff-resistant coating which may be ground to a good finish and which is excellently suited as a bearing surface between moving parts of machine components may be obtained utilizing a flame spray material containing inexpensive cast iron as a major constituent, if the flame spray material is in the form of a composite powder the individual particles of which contain, in addition to the cast iron, molybdenum and boron. The term "cast iron" as used herein and in the claims designates an alloy of iron and carbon usually containing various quantities of silicon, manganese, phosphorus and sulfur, with the carbon present in excess of the amount which can be retained in solid solution in austenite at the eutetic temperature. Alloy cast irons have improved mechanical properties, such as corrosion-, heat- and wear-resistance, and the addition of alloying elements have a marked effect of graphitization. Other common alloying elements in cast iron include molybdenum, chromium, nickel, vanadium, and copper. A composite flame spray powder, as the term is understood in the flame spray art, designates a powder, the individual particles of which contain several components which are individually present, i.e., unalloyed together, but connected as a structural unit forming the powder particles. The composite flame spray particles, in accordance with the invention, thus must contain the cast iron, a molybdenum component, and a boron component, unalloyed together, but structurally united in each individual particle. The individual components may be combined in any known or desired manner to form the composite particles, as for example, in the form of aggregates, or the like, but preferably, in accordance with the invention, the composite is in the form of a clad powder, the individual particles consisting of a cast iron core with a coating containing the molybdenum component and boron component, most preferably in the form of individual small particles of molybdenum and boron components bound to the surface of the cast iron core with a binder. The molybdenum component may consist of molybdenum per se and/or a ferromolybdenum alloy containing at least 50% Mo, and preferably from 55 to 75% Mo. The boron component may consist of boron itself and/or a ferroboron alloy containing from 10 to 30% boron, based on the alloy, and preferably 18% boron. The composite flame spray powder particles in accordance with the invention should contain at least 50% by weight cast iron, about 10 to 50% by weight, preferably 15 to 30% by weight, and most preferably about 20% by weight molybdenum, about 0.1 to 3% by weight of boron, and preferably 1% by weight of boron, all based on the combined total weight of the cast iron and molybdenum. The individual particles should have a size and a classification as is conventional in the flame spray art, as for example, a size between about -60 mesh U.S. standard screen size and +3 microns, and preferably of a size between -140 mesh and +10 microns. Most preferably, composite flame spray powder is formed by cladding or coating white cast iron powder of a size between about 170 mesh U.S. standard screen size and +15 microns with 20% by weight of molybdenum and 1% by weight of boron based on the total of the cast iron and molybdenum, both of a size of -325 mesh, and preferably between about -20 and +0.1 microns. The cast iron may be coated or clad with the finer molybdenum and boron particles in any known or conventional manner, as for example, by mixing the molybdenum and boron in a binding agent, such as a varnish or lacquer, blending the same with the cast iron and drying or setting the binder. Most preferably, as a binder there may be used a conventional phenolic varnish. Other examples of binders include conventional epoxy or alkyl varnishes, varnishes containing drying oil, such as tung oil, linseed oil, rubber and latex binders, and the like. The binder may contain a resin which does not depend on solvent evaporation in order to form a dried or set film. The binder may thus contain a catalyzed resin. The term "coating" or "cladding" as used herein is used in its conventional sense as is understood in the flame spray art and does not require a uniform or contiguous coating or cladding and simply designates the form in which the finer particles are so-to-speak adhered to the surface of the cast iron. The powders are sprayed in the conventional manner using a powder-type flame spray gun, though it is possible to combine the powder in the form of a wire or rod using a binder, such as a plastic or rubber, and spraying the same with a wire-type flame spray gun. The spraying should preferably be effected with flame spray equipment which is capable of producing sufficient heat to cause at least the heat softening of the molybdenum component of the composite. It has been found preferable to effect the spraying with a plasma-type flame spray gun. The flame sprayed coatings formed are extremely hard and wear-resistant, show excellent scuff-resistance and have superior finishing capabilities, being capable of being ground wet with a 60 grit silicon carbide wheel to a smooth finish of, for example, 5 to 20 microinches AA (arithmetic average) as determined with standard Profilometer Model QC (made by Micrometrical Manufacturing Co., Ann Arbor, Michigan) using 0.030 inch cutoff. The coatings are excellently suited as bearing and wear surfaces on machine components as, for example, for coating the circumference of piston rings, cylinder walls, piston skirts, rotary engine trochoids, seals and end plates, crankshafts, roll journals, bearing sleeves, impeller shafts, gear journals, fuel pump rotors, screw conveyors, wire or thread capstans, brake drums, shifter forks, doctor blades, thread guides, farming tools, motor shafts, lathe ways, lathe and grinder centers, cam followers, and cylinder liners. The molybdenum component, when combined with the cast iron in the composite form, and preferably as the cladding or coating, acts to substantially reduce the amount of decarburization during the spraying, and the boron appears to act as an interstitial hardner and agent for increasing the coating density and integrity. Overall the components act in conjunction with each other in the particular flame spray form to produce a superior, hard, high-scuff- and wear-resistant coating.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2219462 | Wissler | Oct 1940 | |
| 2694647 | Cole | Nov 1954 | |
| 3025182 | Schrewelius | Mar 1962 | |
| 3275426 | Rowady | Sep 1966 | |
| 3322546 | Tanzman et al. | May 1967 | |
| 3428442 | Yurasko, Jr. | Feb 1969 |
