MXPA00003906A - Improved metallurgical compositions containing binding agent/lubricantand process for preparing same - Google Patents

Abstract

Improved methods for coating particulate materials at low shear conditions and preferably below the melting point of the coating material are provided. In one aspect, metallurgical compositions are provided that contain a metal-based powder bound to an alloying powder or powders by way of a low melting polymer or wax binding agent, which is preferably polyethylene. The binding agent is blended with the metal-based and alloying powders at elevated temperatures preferably below the melting point of the binding agent. The bonded metallurgical composition can be used in compaction processes to manufacture compacted parts that can be sintered to impact strength.

Description

IMPROVED METALLURGICAL COMPOSITIONS THAT CONTAIN AGLUTIENT AGENT / LUBRICANT AND PROCESS TO PREPARE THE SAME FIELD OF THE INVENTION This process refers to a coating process and compositions prepared by this process. The invention relates specifically to iron-based metallurgical compositions, and more particularly to metallurgical compositions containing a binder that also provides lubrication during the compaction process used to form a part.

BACKGROUND OF THE INVENTION The coating of particles is an important process for modifying particles and the surface properties of the particles. Methods for coating particles include the Wurster process as described in U.S. Patent 2,648,609; 3,127,027; and 3,253,944 and more recently in U.S. Patents 4,731, 195 and 5,085,930 in which the particles are fluidized in some way and the fluidized particles are then spray coated with coating materials dissolved in various solvents or the coating materials are sprayed on the particle cores as a low viscosity melt; Spray coating is also done in which the particles and the coating material is passed through a suitable atomizer. An example of this method is shown in U.S. Patent 4,675,140 in which the coating material is a molten polymer. An interesting method is presented in U.S. Patent 5,262,240 in which the coating is effected by mixing the particles with a latex and drying the resulting mixture. In this process a coated aggregate is produced. Well-known methods for coating particles with thin organic layers can use a surface active agent such as organosilanes or fluorocarbons to modify the surface properties. In this method the particles are soaked in a solution and the surface active agent reacts with the particle. U.S. Patent 4,994,326 is an example of such a process and the materials resulting from the treatment. Finally, a preferred method for coating particles is mixed by hot mixer or high cut dry. A number of patents describe this process. U.S. Patent 4,233,387 describes a process wherein electrophotographic carriers are treated with thermoplastic resins at approximately 163 ° C. The resulting mixture is then cooled, milled, to an appropriate size and used to load toners in a photocopier. U.S. Patent 4,774,139 describes a process for coating paraffin on hot melt thermoplastic resin. U.S. Patent 4,885,175 describes a method for coating a sweetener with a molten wax, cooling the mixture, and grinding the cooled mass to the desired size. Finally, as an example in this hot melt mixing process, U.S. Patent 4, 1356, 566 describes the coating of iron powders with a polymer and additives by mixing the ingredients in a high cut blender at temperatures above the melting point of the polymeric coating material. In all the above cases the processes lack a number of important aspects. In processes like Wurster's, all methods involve having a particle that is fluidizable. Typically, this is a particle with at least an average size of 50 microns. In addition, in processes such as Wurster, if solutions are used, such as the coating vehicle, the solvent, water or organic solvent, it must be removed by drying. This is tedious for water solutions and dangerous for flammable liquids. In direct atomization methods there is the difficulty of separation of the coated and uncoated particles. Although the United States Patent 4, 675, 140 describes a method for particle separation, this technique is not universally applicable to all materials. There are two problems that hinder the application of hot mixing methods, in which the processing temperature is above the melting point. First, agglomeration is an undesired side effect of this process. For many applications the subsequent grinding and sorting processing can be difficult or very expensive. Second, the operation of the process above the melting point results in higher energy costs, which is always undesirable. U.S. Patent 5, 147,722 teaches a method in which the coating of the particles can be done below the melting point of the polymeric binder. Under the conditions of this process with mixed high cut and high applied pressure, the particles are coated, but a matrix is formed as a network. However, agglomeration is not desired for various compositions and the use of high-cut, high-pressure mixers adds capital and extra operating costs. U.S. Patent 5,236,649 also teaches that the coating of particles can be done at a temperature lower than the melting point of the coating material. However, as in U.S. Patent 5, 147,722, the process requires high cut mixing to obtain a good coating. The use of coated particles has application in decorative masonry, defenders for oil wells, to cover flavors in the food and pharmaceutical industries and in the metallurgical powder industry. The metallurgical powder industry has developed metal-based powder compositions, usually iron-based powders, which can be processed into integral parts of metal having various shapes and sizes for use in various industries, including the automotive and electronics industries. A processing technique for producing the parts from base powders is to load the powder into a die cavity and compact the low powder at high pressures. The resulting green compact is removed after the die cavity and sintered to form the final part. The industrial use of metal parts made by compaction and sintering of metal powder compositions is rapidly expanding to a multitude of areas. The manufacture of these parts with powdered metal compositions provides substantial benefits compared to having to use a molten alloy in the manufacturing process. For example, powdered metal compositions allow the manufacturing process to proceed with only one high pressure compaction die machine and one sintering furnace. The different parts are made by simply replacing the compaction matrix. In addition, there is no need to handle molten alloys. In the manufacture of such parts, powders of iron or steel particles are often mixed with at least one other alloying element which is also in the form of particles. These alloying elements allow obtaining greater strength and other metallic properties in the final sintered part. The alloying elements typically differ from the iron or base steel powders in size, shape and particle density. For example, the average particle size of iron-based powders is typically about 70-100 microns, or more, while the average particle size of most alloying ingredients is less than about 20 microns, more frequently less than about 15 microns, and in some cases less than about 5 microns. The alloying powders are deliberately used in such a finely divided state to promote rapid homogenization of the alloying ingredients by solid state diffusion during the sintering operation.

The presence of materials of different particle size leads to problems such as segregation and dust formation in transportation, storage and use. The iron powders and alloying elements are initially mixed in a homogeneous powder. The dynamic handling of the powder mix during storage and transfer causes the smaller alloy powder particles to migrate through the interstices of the iron-based powder matrix, resulting in a loss of homogeneity of the mixture, or segregation . On the other hand, air currents that can develop within the dust matrix as a result of handling can cause the smaller alloy powders, particularly if they are less dense than the iron powders, to migrate upwards. If these floating forces are sufficiently high, some of the alloying particles can, in the phenomenon known as raising dust, escape entirely from the mixture, resulting in a decrease in the concentration of the alloy element. Several organic binders have been used to bind or "stick" the finer alloy powder to the thicker, iron-based particles to avoid segregation and dust pick up for the powders to be compacted at ambient temperatures. For example, U.S. Patent 4,483,905 to Engstrom teaches the use of a binder which is broadly described as being "sticky or greasy" in an amount of up to about 1% by weight of the powder composition. U.S. Patent 4,676,831 to Engstrom describes the use of certain byproducts of the production of wood pulp as binders. Also, the Patent of E. U. No. 4,834,800 to Semel discloses the use of certain polymeric film-forming resins that are insoluble or substantially insoluble in water as binding agents. Several other types of binding agents are disclosed in the patent literature. Polyalkylene oxides having molecular weights of at least about 7,000 are described as binders in the U.S. Patent. 5,298,055. Combinations of organic and basic acid and one or more additional components such as polyethers, liquid polyethers, and acrylic resins as binders are described in U.S. Patent 5,290,336. Binders that can be used with lubricants for high temperature compaction are described in U.S. Patent 5,368,630. The Patent of E. U. , 5,480,469 ("Patent 469") provides a brief review of the use of binding agents in the powder metallurgical industry. Patent 469 notes that it is important to have not only a powder composition having the alloying powder adhered to the iron-based powder by means of the binder, but also to have a lubricant present to achieve adequate compressibility of the powder composition within of the matrix and decrease the forces required to remove the part of the matrix. Patent 469 discusses several references disclosing the use of a binding agent in conjunction with a lubricating powder, such as a metal soap, to be mixed with the iron-based and alloying powders. This mixture is then heated and mixed to melt the binder and lubricant and to bind the alloy powder to the iron-based powder. This mixture is then cooled to form the final composition. Patent 469 describes an improvement for this type of technology using a diamide wax as the binding agent whereby a metal soap lubricant is not required. The presence of a binding agent should not adversely affect the compressibility of the powder metallurgical composition. The "compressibility" of a powder mixture is a measure of its behavior under various conditions of compaction. In the technique of powder metallurgy, a powder composition is generally compacted under high pressure in a matrix, and the compacted "green" part is removed after the matrix and sintered. It is recognized in this technique that the density, and usually the strength, of this green part varies directly with the compaction pressure. In terms of "compressibility", it is said that a powder composition is more compressible than another if, at a given pressure of compaction, it can be compressed to a higher green density, or alternatively, if it requires less compaction pressure to obtain a density in specific green. If the binder has good "internal" lubrication characteristics, the compressibility of the powder composition will increase and result in a green density greater than a given compaction pressure.

Therefore, there is a need for a coating process that can provide a simple and inexpensive method for coating a variety of particles. In the powder metallurgical industry there is a specific need for a metallurgical composition containing the powder (s) of alloy (s) bonded to the metal-based powder where that composition can be prepared in a process without solvent. The binding agent used in the metallurgical composition must function to decrease the amount of dust and / or segregation of the alloying powder (s) and also not adversely affect the compressibility of the composition.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an improved method for particle coating that uses a low cut, low temperature method to produce coated, non-agglomerated particles. In one embodiment, of the present invention provides improved powder metallurgical compositions containing a greater amount of a metal-based powder bound to a minor amount of at least one alloying powder. The particulate powders that can be coated according to the present invention include metal powders such as iron, copper, nickel, cobalt, chromium, aluminum, zinc, silicon, manganese, silver, gold, platinum, palladium, titanium, their alloys and mixtures thereof; inorganic oxides such as alumina, silica, and titania; inorganic compounds such as common table salt, peroxide bleaches, bath salts, calcium chloride, and inorganic fertilizers such as potash; and solid organic compounds such as polymers, acids and bases. The core of the particles can be in any form such as beads, flakes, fibers and needle-like particles wherein at least one dimension, in an average number, is in the range of 10 microns to 1 cm, preferably in the range of 20 microns at 0.75 cm and most preferably in the range of 25 -10,000 microns. The coating material, also referred to herein as a binding agent or material, particularly with respect to powder metallurgical compositions, may be a solid, low melting point polymer or wax, v. g. , a polymer or wax having a softening temperature below 200 ° C, preferably below 150 ° C, and more preferably between about 65-95 ° C. Examples of solid polymeric binder include polyesters, polyethylenes, epoxies and urethanes. Examples of waxes include paraffins, bis-stearamides, and cottonseed waxes. The solid binder may also be polyolefins with weight average molecular weights below 3000, and hydrogenated vegetable oils which are triglycerides with C? 4.2 alquilo alkyl moiety and derivatives thereof, including hydrogenated derivatives, v. g. , cottonseed oil, soybean oil, jojoba oil and mixtures thereof. The solid coating material is preferably reduced to an average particle size in at least one dimension of less than 200 or 100 microns, and preferably in the range of 0.01 to 50 microns, more preferably between 0.01 and 20 microns. The coating process of the present invention can be a "dry" bonding process that does not require a solvent for the binder. The process used involves the mixing of a suitable binder in the preferred range of particle size, with the core particles, and any alloying particles or any additives at ambient or elevated temperatures. The mixture is then mixed gently using a conventional mixer under low-volume conditions. The mixture is preferably heated to at least 40 ° C and preferably to a temperature below the melting point of the binder, mixed, and then cooled to provide the final product. The powder metallurgical compositions of the present invention are they prepare by mixing the metal-based powder with the alloy powder (s) at ambient or elevated temperatures and mixing the binder with those powders at either ambient or elevated temperatures. During the mixing process the binder is contacted with the metal-based and alloying powders at temperatures of at least about 49 ° C. This mixed composition can then be cooled to ambient conditions. The temperature of the mixing process is preferably conducted at a bulk powder temperature which is below the melting point of the binder. The preferred binder for powder metallurgical applications is polyethylene wax. The polyethylene wax is preferably introduced into the mixture of metal-based and alloy powders in its solid state. If it is introduced in its solid state, it can be used in various forms such as spheres, fibers or flakes. Particularly advantageous results are obtained by using a polyethylene wax in the form of spheres having an average particle size of less than about 50, and preferably less than about 30, microns.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved process for the formation of coated particles, improved powder metallurgical compositions, methods for the preparation of these compositions, and methods for using those compositions to make compacted parts. The powder metallurgical compositions comprise a metal-based powder, preferably an iron-based metal powder, in admixture with at least one alloy powder, and a binding agent for adhering the alloy powder to the metal-based powder. The preferred binder for powder metallurgical applications is a polyethylene wax having an average molecular weight weight of less than about 4000, more preferably less than about 2000. It has been found that the use of polyethylene wax as a binder for the powder metallurgical composition provides superior resistance to dust removal / segregation and also provides improved strength and ejection behavior of the green compact.

The particles that can be coated according to the present invention include metal powders such as iron, copper, nickel, cobalt, chromium, aluminum, zinc, silicon, manganese, silver, gold, platinum, palladium, titanium, their alloys and mixtures thereof; inorganic oxides such as alumina, silica, and titania; inorganic compounds such as common table salt, peroxide bleaches, bath salts, calcium chloride, and inorganic fertilizers such as potash; and solid organic compounds such as polymers, acids and bases. The core of the particles can be in any form such as beads, scales, fibers and needle-like groups in which at least one dimension, in an average number, is in the range of 10 microns to 1 cm, preferably in the range of 20 microns at 0.75 cm and most preferably in the range of 25 -10,000 microns. The powder metallurgical compositions of the present invention comprise metal powders of the type generally used in the powder metallurgical industry, such as iron-based powders and nickel-based powders. Metal powders constitute a major portion of the powder metallurgical composition, and generally constitute at least about 80 weight percent, preferably at least about 90 weight percent, and more preferably at least about 95 weight percent. by weight of the composition.

Examples of "iron-based" powders, as the term is used herein, are substantially pure iron powders, iron powders pre-alloyed with other elements (e.g., iron-producing elements) to increase strength, property of hardness, electromagnetic properties, or other desirable properties of the final product, and iron powders to which such other elements have been bound by diffusion. Substantially pure iron powders that can be used in the invention are iron powders containing not more than about 1.0% by weight, preferably not more than about 0.5% by weight, of normal impurities. Examples of such highly compressible metallurgical grade powders are the ANCORSTEEL 1000 series of pure iron powders, v. g. , 1000, 1000B, and 1000C, available from Hoeganaes Corporation, Riverton, New Jersey. For example, the ANCORSTEEL 1000 iron powder has a typical screen profile of approximately 22% by weight of the particles below a No. 325 mesh (EU Series) and approximately 10% by weight of the particles greater than one. No. 100 mesh with the remainder between these two sizes (trace quantities larger than No. 60 mesh). ANCORSTEEL 1000 powder has a bulk density from about 2.85-3.00 g / cm3, typically 2.94 g / cm3. Other iron powders that may be used in the invention are typical sponge iron powders, such as ANCOR MH-100 powder from Hoeganaes. The iron-based powder can incorporate one or more alloying elements that increase the mechanical or other properties of the final metal part. Such iron-based powders can be iron powders, preferably substantially pure iron, which has been pre-alloyed with one or more such elements. The pre-alloyed powders can be prepared by making an iron melt and the desired alloying elements, and then atomizing the melt, whereby the atomized droplets form the powder by solidification. Examples of alloying elements that may be pre-alloyed with the iron powder include, but are not limited to, molybdenum, manganese, magnesium, chromium, silicon, copper, nickel, gold, vanadium, niobium, graphite, phosphorus, aluminum and combinations thereof. The amount of the incorporated alloying element or elements depends on the desired properties in the final metal part. Pre-alloyed iron powders incorporating such alloying elements are available from Hoeganaes Corp. as part of their ANCORSTEEL line of powders. A further example of iron-based powders are diffusion-bound iron-based powders which are pure iron particles substantially having a layer or coating of one or more other metals, such as steel-producing elements, diffused in their external surfaces. Such commercially available powders include the DISTALOY 4600A diffusion bound powder from Hoeganaes Corporation, which contains about 1.8% nickel, about 0.55% molybdenum, and about 1.6% copper, and DISTALOY 4800A diffusion bound powder. Hoeganaes Corporation, which contains approximately 4.05% nickel, approximately 0.55% molybdenum and approximately 1.6% copper. A preferred iron-based powder is that of pre-alloyed iron with molybdenum (Mo). The powder is produced by atomising a pure iron melt substantially containing from about 0.5 to about 2.5 weight percent Mo. One example of such powder is the steel powder ANCORSTEEL 85H P from Hoeganaes, which contains about 0.85 percent by weight. Mo weight, less than about 0.4 weight percent, in total, of such other materials as manganese, chromium, silicon, copper, nickel, molybdenum or aluminum, and less than about 0.02 weight percent carbon. Another example of such a powder is the ANCORSTEEL 4600V steel powder from Hoeganaes, which contains about 0.5-0.6 weight percent molybdenum, about 1.5-2.0 weight percent nickel, and about 0.1-0.25 weight percent. manganese weight, and less than about 0.02 weight percent carbon. Another pre-alloyed iron based powder that can be used in the invention is described in US Patent No. 5,108,493, entitled "Steel Powder Mixture Having Pre-alloyed Powder Distinct from Iron Alloys", which is incorporated into the present in its entirety. This steel powder composition is a mixture of two different pre-alloyed iron-based powders, one that is a pre-alloy iron with 0.5-2.5 weight percent molybdenum, the other being a pre-alloy iron with carbon and with at least about 25 weight percent of a component of a transition element, wherein this component comprises at least one element selected from the group consisting of chromium, manganese, vanadium and niobium. The mixture is in proportions that provide at least about 0.05 weight percent of the transition element component to the steel powder composition. An example of such a powder is commercially available as ANCORSTEEL 41AB steel powder from Hoeganaes, which contains about 0.85 weight percent molybdenum, about 1 weight percent nickel, about 0.9 weight percent manganese, about 0.75 weight percent. 100 percent by weight of chromium, and approximately 0.5 percent by weight of carbon. Other iron-based powders that are useful in the practice of the invention are ferromagnetic powders. An example is a pre iron powder. alloyed with small amounts of phosphorus. Iron-based powders that are useful in the practice of the invention also include stainless steel powders. These stainless steel powders are commercially available in various grades in the ANCOR® series from Hoeganaes, such as the powders of ANCOR® 303L, 304L, 316L, 410L, 430L, 434L, and 409Cb. The iron or pre-alloyed iron particles may have a weight average particle size as small as one micron or less, or up to approximately 850-1000 microns, but generally the particles will have a particle size with average weight in the range of approximately 10-500 microns. Preferred are pre-alloyed iron or iron particles having a particle size with average maximum weight of up to about 350 microns; more preferably the particles will have a particle size with average weight in the range of about 25-150 microns, and most preferably 80-150 microns. The metal powder used in the present invention may also include nickel-based powders. Examples of "nickel-based" powders, as that term is used herein, are substantially pure nickel powders, and nickel powders pre-alloyed with other elements that increase strength, hardening ability, magnetic properties, or other desirable properties of the final product. The nickel-based powders can be mixed with any of the above-mentioned alloy powders with respect to the iron-based powders. Examples of nickel-based powders include those commercially available as the Hoeganaes ANCORSPRAY® powders such as N-70/30 Cu, N-80/20, and N-20 powders. The metal-based powder may also include any combination of the metal-based powders described. The powder metallurgical compositions of the present invention also include a minor amount of at least one alloy powder. As used herein, "alloy powders" refers to materials that are capable of alloying with the metal-based powder by sintering. Alloy powders that can be mixed with metal-based powders of the type described above are those known in the metallurgical art to increase the strength, hardening ability, magnetic properties, or other desirable properties of the final sintered product. The elements that produce steel are among the best known of these materials. Specific examples of alloying materials include, but are not limited to, molybdenum, manganese, chromium, silicon, copper, nickel, tin, vanadium, niobium elementals, metallurgical carbon (graphite), phosphorus, aluminum, sulfur and combinations thereof. Other suitable alloying materials are binary copper alloys with tin or phosphorus; Ferro-alloys of manganese, chromium, boron, phosphorus or silicon; tertiary and quaternary eutectic carbon of low melting point and two or three of iron, vanadium, manganese, chromium and molybdenum; tungsten or silicon carbides; silicon nitride; and manganese or molybdenum sulphides. The alloying powders are in the form of particles that are generally finer in size than the metal powder particles with which they are mixed. The alloy particles generally have a particle size with a weight average below about 100 microns, preferably below about 75 microns, more preferably below about 30 microns, and most preferably in the range of about 5 microns. 20 microns. The amount of alloy powder present in the composition will depend on the desired properties of the final sintered part. Generally the amount will be less, up to about 5% by weight of the total weight of the powder composition, although as much as 10-15% by weight may be present for certain specialized powders. A preferred range suitable for most applications is about 0.25-4.0% by weight of the total powder composition. The binder of the present invention can include solid, low melting point polymers or waxes having a softening temperature below about 200 ° C, preferably below about 150 ° C, more preferably between about 50 ° C - 1 10 ° C, and even more preferably between 65 ° -95 ° C. Examples of polymeric binding agents include polyesters, polyethylenes, epoxies and urethanes. Examples of waxes include paraffins, ethylene bis-stearamide (ACRAWAX), and cottonseed wax. The binder may also include solid polyolefins with molecular weights with a weight average below 3000, and solid hydrogenated vegetable oils that can be generally described as triglycerides having C14-24 side chains., and derivatives thereof, including halogenated derivatives, such as cottonseed oil, soybean oil and jojoba oils and mixtures thereof. The binder is preferably reduced to an average particle size in at least one dimension of less than 200 microns, and preferably less than 100 microns, with a preferred range of between 0.01 and 50 microns and most preferably in the range between 0.01 and 20 microns. Therefore, particles in the form of spheres, needle beads, flakes, or fibers are preferred. Methods for preparing the binder material to obtain a small particle size include grinding, crushing, spray drying, melt atomization, extrusion, trimming and direct reaction. The melt atomization is most preferably used to prepare the binder material in the size ranges listed above. Additional additives may be added to the binder material as needed such as pigments, other metals, inorganic compounds such as salts, graphite, or carbon black, inorganic oxides such as aluminate, silica, and titanium. A preferred binder of the present invention particularly for powder metallurgical applications is a solid polyethylene wax having a weight average molecular weight below about 4000, preferably about 2000 or less, and generally from about 100 to about 4000 , and even more preferable from about 500 to about 2000. Suitable polyethylene waxes are commercially available from the Petrolite Specialty Polymer Group as the Polywax series, such as Polywax 500 and Polywax 2000. The polyethylene wax preferably has a melt viscosity at the range of 1 to about 500 cps, more preferably between about 3 and 50 cps. The melting point of the polyethylene wax is preferably between 50 ° C and 200 ° C, and more preferably between 75 ° C and 130 ° C. A preferred average particle size for the binder, such as polyethylene wax, for powder metallurgical applications, it is between about 1 and about 50, and even more preferably between about 1 to about 25, microns to aid in contact between the binder with the iron and alloying powders during the mixing process. Spherical particles having sizes above these ranges can be used, but it has been found that the temperature of the mixing process must be increased in such cases to ensure adequate ligation. If the particulate binder is not spherical, at least one dimension of the particles is within the ranges established for the spherical particles. The particle size of the binding agents can be determined by such methods as laser diffraction techniques. The particle size of the binding agents can be reduced to these ranges by spray-mist techniques commonly known in the industry. The powder metallurgical composition can be prepared by various mixing techniques. It is common to all techniques that the mixing of the polymer or binder waxing agent with the metal-based and alloying powders is conducted at a powder mixing temperature of at least about 27 ° C, preferably at least about 50 ° C. ° C, generally in the range between about 50 ° -190 ° C, more preferably between about 65 ° -90 ° C. In certain situations, and particularly when the binder is used in the form of solid flakes or spheres of size smaller particle, it is preferred to mix the binder with the metal-based and alloying powders at a temperature below the melting point of the binder to improve the properties of the green compact and limit the ejection forces required to remove the compact from the binder. cavity of the matrix. A) Yes, in certain situations, it is preferred to mix the solid binder with the metal-based and alloying powders at a temperature between about 3-35 degrees Celcius, preferably between about 5-30 degrees Celsius, and more preferably between about 8-25 Celsius. Celcius degrees, below the melting point of the binder. For example, it has been found that beneficial properties are obtained when using polyethylene having a melting point of about 88 ° C an Mw of about 500, and a particle size with average weight of about 20 μm to mix the material of polyethylene with the metal-based and alloying powders at a temperature of approximately 65 ° C. The metal-based powder can be mixed initially with the alloy powder (s) to form a homogeneous mixture under ambient or temperature conditions elevated mixing. The binder, preheated either partially or completely, can then be mixed with the metal or alloy-based powders in an appropriate container in which the temperature of the powder mixture can be maintained at a desired level for a sufficient time to make contact with a substantial, if not complete, portion of the metal-based and alloy powders. The mixing of the binder is preferably continued until a homogeneous mixture is obtained. Alternatively, the binder can be mixed with the metal-based and alloy-based powders at the beginning, and this mixture can then be heated to the appropriate chosen mixing temperature and the mixing is conducted at that temperature or range of temperatures until a homogeneous mixture. In any process, the mixed composition is then cooled to room temperature with intermittent or optional continuous mixing. The concentration of the binding agent in the metallurgical composition (containing the metal-based and alloying powders together with other lubricants, etc.) is in the range from about 0.05 to about 2, preferably from about 0.25 to about 1.5. and more preferably from about 0.5 to about 1, percent by weight. Concentrations of the binding agent below these levels do not result in effective ligation between the alloy powder and the metal-based powder, and concentrations above these levels generally result in poorer green density and strength properties. Following the mixing of the binder in the metallurgical composition, and preferably after the composition has been cooled to a point, typically at least below the melting point of the binder, and preferably below about 65 ° C , more preferably below about 50 ° C and more preferably below about 40 ° C, and commonly when the composition is at room temperature, a conventional lubricant may be optionally added and mixed until a homogeneous composition is obtained. The amount of lubricant added can range from about 0.01 to about 2, preferably from about 0.05 to about 1 weight percent of the final metallurgical composition. Typical lubricants include stearate compounds, such as lithium, zinc, manganese and calcium stearates commercially available from Witco Corp.; waxes such as ethylene bis-esteamides and polyolefins commercially available from Shamrock Technologies, Inc.; Commercially available zinc and lithium stearate mixtures of Alean Powders & Pigments such as Ferrolube M, and mixtures of ethylene bis-stearamides with metal stearates such as Witco ZB-90 metal stearates and synthetic waxes such as "ACRAWAX" or "PM 100" available from Glyco Chemical Company. The powder metallurgical compositions as described above can then be compacted in a matrix to form a metal part in accordance with conventional practices. The resulting green compact can then be sintered according to conventional practices.

EXAMPLES The following examples, which are not intended to be limiting, have certain embodiments and advantages of the present invention. Unless stated otherwise, any percentages are on a weight basis. In each of the examples (except the CONTROL composition in Example 1), the metallurgical compositions were prepared by first mixing the iron-based powder (ANCORSTEEL 1000B from Hoeganaes Corporation) with the alloying powders, and subsequently heating this mixture to a temperature about 93 ° C. This heated mixture was then charged to a mixing vessel heated to the test temperature and mixing was conducted until the composition reached the test temperature. The binder was then added to the mixing vessel and continuous mixing was conducted until a homogenous mixture was obtained. The mixed composition was then cooled to room temperature with intermittent mixing to improve the cooling operation. The alloy powders used were graphite powder (Asbury grade 3203) from 2 to 6 μm and nickel powder (International Nickel Inc., grade I NCO 123). The compositions were then compacted into green bars in a matrix at a pressure of 7.75 tons per square centimeter (tcc) and in a matrix and powder temperature of approximately 63 ° C. The physical properties of the metallurgical compositions and of the green bars and sintered were generally determined according to the following test methods and formulas: Property Test Method Apparent Density (g / cc) ASTM B212-76 Flow (sec / 50 g) ASTM B213-77 Green Density (g / cc) ASTM B331 -76 Green Resistance (kg / cm2) ASTM B312-76 Green Expansion GE (%) = 100r (length of green bar) - (length of array)] Matrix length The tape pressure measures the static friction that must be overcome to initiate the ejection of a compacted part from a matrix. It was calculated as the quotient of the load necessary to initiate the ejection on the cross-sectional area of the part that is in contact with the surface of the matrix, and was reported in units of kg / cm2. The sliding pressure is a measure of the kinetic friction that must be overcome to continue the ejection of the part from the cavity of the matrix; it is calculated as the quotient of the average load observed as the part that crosses the distance from the point of compaction to the mouth of the matrix, divided by the surface area of the part, and is reported in units of kg / cm2. The dust-raising resistance of the metallurgical test compositions was determined using the method set forth in U.S. Patent No. 5,368,630, which is incorporated herein by reference in its entirety. The mixtures were tested for strength to lift dust by separating the finest powder from the thickest powder by washing and casting with a controlled flow of nitrogen. The test apparatus consisted of a vertically mounted cylindrical glass tube in a two liter Erlenmeyer flask equipped with a side hole to receive the flow of nitrogen. The glass tube (17.5 cm long, 2.5 cm internal diameter) was equipped with a 400 mesh screen plate placed approximately 2.5 cm above the mouth of the flask. A sample of the mixture to be tested (20-25 grams) was placed on the screen plate and nitrogen was passed through the tube at a rate of two liters per minute for 15 minutes. At the end of the test, the mixture was analyzed to determine the relative amount of remaining alloy powder in the mixture (expressed as a percentage of the concentration before the alloy powder test), which is a measure of the strength of the the composition to the loss of the alloy powder through loss of dust and / or segregation.

EXAMPLE 1 The following example illustrates that the temperature at which the polyethylene binder is applied to the metal-based and alloying powders is important for the effectiveness of the binding between the metal-based powder and the alloying powders. In this example, the metallurgical composition consisted of 96. 25% ANCORSTEEL 1000B as the metal-based powder, together with 2% nickel powder and 1% graphite powder as alloy powders, plus 0.75% Polywax 500, which is a polyethylene binder that has an Mn of approximately 500 and a melting point of 88 ° C. The Polywax 500 used for the test had a particle size with average weight of approximately 20 μm. This particle size distribution was obtained by taking the Polywax 500 product having an average particle size of 2 mm and atomizing the polymer. The "bound" composition was prepared according to the general procedures of the example set forth above where the mixing temperature was 65 ° C and the "Control" composition was prepared by mixing the constituents of the composition at room temperature. The apparent density of the Control sample was 3.03 g / cc and 2.83 g / cc for the ligated sample; no sample exhibited flow. Table 1 shows the dust resistance or binding efficiency of the polyethylene binder, the green properties of the compacts, and the values of the matrix ejection forces for the two compositions. Mixing the composition with the polyethylene binder at a temperature of about 65 ° C resulted in a significant increase in the powder resistance of the composition and an increase in the green strength of the compact. The green density was also increased indicating that the polyethylene binder applied at the higher mixing temperature provided some internal lubrication for the composition during compaction.

TASLA 1 Example 2 Various levels of the polyethylene binder used in the Example 1 were used to effect the powder resistance in various metallurgical compositions prepared by dry blending the binder with the metal-based and alloying powders according to the procedures of the general example discussed above. The test compositions contained 2% nickel and 1% graphite as alloying powders. The compositions contained 0.5%, 0.75% and 1% polyethylene (Polywax 500) with the remainder of the composition being a powder based on iron, ANCORSTEEL 1000B of Hoeganaes. The test temperature for the mixing step of the polyethylene with the rest of the powder metallurgical composition was 68 ° C. The apparent density of the samples was 2.92, 2.38 and 2.89, respectively for the test samples of 0.5%, 0.75. % and 1%; the samples did not exhibit flow. Table 2 shows the dust resistance or bonding efficiency of the various levels of the polyethylene binder, the green properties of the compacts, and the values of the ejection forces of the matrix for the three compositions. The increase in polyethylene concentration resulted in higher dust resistance and lower ejection forces, however, it was found that green density and strength disappear. TABLE 2 Example 3 The mixing of the polyethylene binder with the iron-based and alloying powders was conducted at various temperatures using the binder described in Example 1. The test compositions contained 2% nickel and 1% graphite as the alloy powders in conjunction with 96.25% ANCORSTEEL 1000B iron-based powder together with 0.75% polyethylene. The mixing temperatures tested for the bulk temperature of the mixed powder compositions were 38 ° C, 65 ° C, 77 ° C and 104 ° C. The test compositions mixed at 65 ° C and 77 ° C were prepared in accordance with the general procedures outlined above. The test composition mixed at 38 ° C was prepared by initially mixing the iron-based and alloying powders and mixing in a vessel maintained at 38 ° C with the subsequent addition of the polyethylene at a mixing temperature of 38 ° C. Test mixed at 104 ° C was prepared by initially heating the powders with iron and alloy base at 93 ° C and mixing in a vessel maintained at 93 ° C with the subsequent addition of polyethylene at a mixing temperature of 104 ° C. apparent of the samples was 2.88, 2.83, 2.90 and 2.92, respectively for the test samples of 38 ° C, 65 ° C, 77 ° C and 104 ° C; the samples did not exhibit flow. Table 3 shows the dust resistance or bonding efficiency of the various mixing temperatures for the polyethylene, the green properties of the compacts, and the values of the ejection forces of the matrix for the four compositions. It was found that the polyethylene does not affect the bonding until a mixing temperature of about 65 ° C was reached. At higher mixing temperatures the internal and external lubricity of the polyethylene decreased resulting in decreased green densities and increased ejection pressures, respectively.

TABLE 3 Example 4 Polywax 500 obtained from Petrolite is melted at 93 ° C and atomized in a normal melt atomization system at 2.1 1 kg / cm2, 7.03 kg / cm2 of air pressure, and at a rate of 22.7 kg. per hour. The resulting 50 micron average particle size material is used as it is without screening or further processing. 10 grams of Polywax 500 binder was added to 100 g of Tsumura bath salt (approximately 0.5 cm in diameter) with 2.5 g of Clariant copper phthalocyanine pigment and mixed in a 1 liter PK mixer at 65 ° C for 30 minutes. minutes After cooling, with a mixer, the coated and colored product was removed from the mixer. The salt was uniformly coated with good adhesion of the binder and pigment to the core salt particle. In another experiment, a small bath salt, Tsumura Sea Pouri Salt Base, approximately 1000 microns in diameter, was coated with 1 1 g of Polywax 500 and 2.75 g of Clariant copper phthalocyanine with the same conditions as those listed above with results of similar coating and adhesion.

Example 5 Using the Polywax 500 as prepared in Example 4, glass beads were coated with various pigments. The glass beads, Glass Spheres-Series A, were obtained from Potters Industries, Carlstadt NJ and are approximately 1000 microns in diameter. The procedure for coating for three pigments, Dianisidine Orange 2915 by Engelhard Cleveland, Ohio, Titania MT-100-HD by Daicolor-Pope Clifton, New Jersey, or copper phthalocyanine by Clariant and was to add 681 g of glass beads, 6.8 g of binder, and 6.9 g of pigment to a Vee Blender of 2 liters of Patterson-Kelly and heated at 71 ° C for 30 minutes with a mixer and then cooled with a mixer for 30 minutes. The resulting product was uniformly coated with good adhesion. In a second series of experiments with these materials the coating was made with 36 g of pigment. Although the final product was more intense in color, the resulting uniformity of coating and adhesion were the same.

Example 6 Sand obtained from the Ottawa plant of Unimin degrees Minispheres 4900 and Granusil 4030 were coated with Polywax 500 in a Patterson-Kelly Vee Blender of 38.37 cubic decimeters at 65 ° C with a mixer for 2 hours and cooled with a mixer for 1 hour. The resulting material was uniformly coated and tested for hydrophobicity by placing it in water. No wetting was observed and the coating appeared to be stable after a week of immersion. The samples were used in a water filtration system with good bacteria removal.

Claims (27)

1. REVIVAL DICTION EN 1. An improved metallurgical composition resistant to segregation-resistant dust containing alloy powder to be bound to the metal-based powder by a binder, comprising: (a) at least 80 weight percent powder with metal base; (b) between about 0.25-4.0 weight percent alloy powder; and (c) between about 0.05 and about 2 weight percent of binder for the metal-based powder and the alloy powder where the binder is a low melting solid polymer or wax having a softening temperature by below 65 ° C and has an average particle size in at least one direction. The metallurgical composition of claim 1 wherein the binder comprises polyester, epoxy, urethane, paraffin wax, ethylene bis-stearamide, or cottonseed wax. The metallurgical composition of claim 1 wherein the binder comprises polyethylene having a weight average molecular weight below about 4000. 4. The metallurgical composition of claim 3 wherein the composition comprises at least 80% by weight. 100 percent by weight of a metal-based powder. The metallurgical composition of claim 4 wherein the polyethylene binder has a weight average molecular weight of about 2000 or less. The metallurgical composition of claim 4 wherein the metallurgical composition comprises between about 0.25 to about 2 weight percent polyethylene binder. The metallurgical composition of claim 6 wherein the polyethylene binder has a weight average molecular weight between about 500 and about 2000. The metallurgical composition of claim 1 wherein the binder is a solid polyolefin, of low melting point with a weight average molecular weight below 3000 or a solid vegetable oil or hydrogenated derivative thereof. 9. A method for preparing a segregation-resistant powder-resistant metallurgical powder composition, comprising: (a) providing a powder mixture with a metal base and at least one alloy powder; (b) mixing with said metal-based powder and said at least one binder-binding alloy powder to form an initial mixture, wherein the binder is a solid, low-melting polymer or wax having a softening temperature by below 150 ° C, and wherein the binder has an average particle size in at least one direction of less than 100 microns; (c) raising the temperature of the initial mixture to at least 50 ° C, but below the melting point of the binder to effect agglutination between the metal-based powder and the at least one alloying powder by the binder; and (d) lowering the temperature of the mixture to room temperature to thereby form the powdery metallurgical composition, wherein the metal-based powder is present in an amount of at least 80 weight percent, the alloy powder is present in an amount of between about 0.25 and about 4 weight percent, and the binder is present in an amount between about 0.25 and about 2 weight percent, based on the total weight of the powder metallurgical composition. The method of claim 9 wherein the binder comprises polyester, epoxy, urethane, paraffin wax, ethylene bis-stearamide, or cottonseed wax. The method of claim 9 wherein the binder comprises polyethylene having a weight average molecular weight below about 4000. 12. The method of claim 11 wherein the composition comprises at least 80 percent by weight. weight of a powder based on iron. The method of claim 12 wherein the polyethylene binder has a weight average molecular weight of about 2000 or less. 14. The method of claim 1 wherein the metallurgical composition comprises between about 0.25 to about 2 weight percent polyethylene binder. The method of claim 14 wherein the polyethylene binder has an average number of molecular weight between about 500 and about 2000. 16. The method of claim 12 further comprising introducing the binder to the binder mixture. metal-based powder and at least one alloy powder where the binder is substantially in the form of spherical particles having an average particle size in volume below about 50 microns. 17. The method of claim 1 wherein the mixing step is conducted at a temperature from about 3 to about 30 degrees Celcius below the melting point of the binder. The method of claim 9 wherein the binder is polyethylene having a molecular weight between about 500 and about 2000 and wherein the volume average particle size of the polyethylene before the mixing step is between about 1 and about 25 microns. 9. The method of claim 9 wherein the binder is a solid, low melting polyolefin with a weight average molecular weight below 3000 or a solid vegetable oil or hydrogenated derivative thereof. 20. A method for manufacturing a compacted metal part, comprising: (a) providing a metallurgical composition comprising: (1) at least 80 weight percent metal-based powder; (2) between about 0.25-4.0 weight percent alloy powder; and (3) between about 0.05 and about 2 weight percent of the metal-based powder binder and alloying powder where the binder is a low melting point polymer or wax having a softening temperature below 150 ° C and has an average particle size in at least one direction of less than 1000 microns a greater amount of a metal-based powder; (b) compressing said metallurgical composition in a matrix at high pressures to form a compacted part; and (c) sintering said compacted part. twenty-one . The method of claim 20, wherein the binder comprises polyethylene having an average weight-average molecular weight below about 4000, polyester, epoxy, urethane, paraffin wax, ethylene bisestemiramide, or seed wax. cotton. 22. The method of claim 21, wherein the metallurgical composition comprises at least 80 weight percent of an iron-based powder. 23. The method of claim 22 wherein the binder is polyethylene having a weight average molecular weight of between about 500 and about 2000. 24. A method for preparing a coated particle comprising: (a) providing base particles that have an average dimension in a direction between 10 microns and 1 cm; (b) mixing with the base particle a coating material, solid comprising a low melting point polymer or wax having a softening temperature below 200 ° C, a low melting point polyolefin with a molecular weight in average weight below 3000, or a solid vegetable oil or hydrogenated derivative thereof; and (c) coating the coating material on the base particles under low shear conditions at a temperature of at least 49 ° C and below the melting temperature of the coating material. 25. The method of claim 24 wherein the coating material is a polyester, a polyethylene, an epoxy, or a urethane. 26. The method of claim 24 wherein the coating material is a paraffin, an ethylene bis-stearamide, or cottonseed wax. 27. The method of claim 24 wherein the coating material has an average particle size in at least one dimension of less than 1000 microns.