MXPA98001623A - Powder and agglutants system for use in pol molding - Google Patents

Abstract

A system of binder powders for manufacturing agglomerated parts from particulate material and a method of injection molding part for agglomerate is provided. The particulate material includes ceramics, metallic and intermetallic powders. Preferably, the selected powder particles are covered with one or more additives depending on their shapes and surface chemistry to create a powder system. The additives may include antioxidants, coupling agents, surfactants, elastifying agents, dispersants, plasticizers / compactizers and lubricants. The active surface additives are designed to improve the interface between the powder and the binder. The powder system can be mixed or combined with a binder system in an inert atmosphere to form a system of powders and binders, or raw material, for molding powders. The binder system may contain one or more components that are removed before conglomerating the powder. The powder and binder system can also be molded around an expandable core before conglomerating

Description

SYSTEM OF POWDERS AND AGGLUTANTS FOR USE IN POWDER MOLDING TECHNICAL FIELD The present invention relates to systems of powders and binders for manufacturing conglomerate components from particulate material, and a method of molding parts for conglomerate by injection of powder.

BACKGROUND OF THE INVENTION [0002] Powder injection molding is a well known technique for manufacturing articles from particulate material and examples of such systems are shown in: U.S. Patent No. 5,415,830, Zhang et al., U.S. Patent Number 5,397,531, Peiris et al., U.S. Patent No. 5,332,537, Hens at al., U.S. Patent No. 5,155,158, Kim et al., U.S. Patent No. 5,059,388, Kihara et al., U.S. Pat. U.S. No. 4,765,950, Johnson, U.S. Patent 4,661,315, Wiech, U.S. Patent No. 4,415,528, Wiech, U.S. Patent No. 4,225,345, Adee et al., And U.S. Patent No. 4,197,118, Wiech. In these prior art systems, powders and binders are mixed to form raw material that is molded by injection of powders. The production of the raw material is the most important step in the technology of injection molding of powders. If the components are manufactured from inferior raw material, it will be difficult, if not impossible, to produce consistent components of high tolerances without secondary processes such as coining and machining.

The homogeneity of the raw material and the accuracy of the composition are a major challenge for manufacturers who use powder injection molding. Problems with the components such as cracking and non-uniform shrinkage during the de-agglomeration and conglomerate can be followed up to the production of the raw material.

The conventional practice in powder injection molding is that powders having the elemental composition of the desired final product are mixed with an additive and a binder mixture to form the raw material. The binder mixture may contain two primary components in a heterogeneous mixture. The first component of the binder, also called the main component, is typically a polymer component such as a wax or a water soluble component. The foregoing is used, in part, to provide a means to transport the powder into the mold. The main component is typically designed for good moldability and easy removal during the deagluing phase. The second component of the binder, also called the pillar component, is used to retain the shape of the compact while the first component is removed. The pillar component is removed, generally, just before the dust particles begin to conglomerate.

These known raw materials have solid charges of about 50 to 60 percent by volume. Such systems have inherent problems in that a relatively large proportion of the raw material is agglutinate which is used to make the raw material fluid, which causes a significant shrinkage of the molding components during the de-agglomeration and the conglomerate. Moreover, during the thermal elimination of binder, the components are heated through the molding temperature of the raw material, which causes the loss of shape. Shape loss also occurs in these prior art systems because the binding components with a lower molecular weight decompose or volatilize during the mixing of the raw material and during injection molding. As a result of this shrinkage and deformation, the parts manufactured by these known methods may require expensive support equipment to retain the shape of the molded component before the conglomerate.

In addition, the parties may require machining after the conglomerate if the tolerances are not met. The parts are also limited to relatively small component sizes.

SUMMARY OF THE INVENTION The present invention provides a new and improved powder and binder system and a new and improved method for injection molding of powders. The powder and binder system of the present invention can be used as raw material in any internal injection molding process in which the ceramic, metal or intermetallic particles are injection molded.

The present invention provides an injection moldable powder and binder system comprising powder particles coated with at least one additive, and a binder combined with the powder particles. In accordance with another feature of this invention, an injection moldable powder system is provided and comprises a mixture of a prealloyed powder and an elemental / semi-elemental powder. In accordance with another feature of this invention, an injection moldable powder system is provides and comprises a mixture of a prealloyed powder and an elemental powder / master alloy. In accordance with another feature of this invention, there is provided an injection moldable powder system comprising a mixture of prealloyed powder, an elemental / semi-elemental powder and an elemental / master alloy powder.

According to still another feature of this invention, an injection moldable powder and binder system is provided in which the powder and the binder are combined in an inert atmosphere. According to still another feature of this invention, an injection moldable powder and binder system is provided which comprises a powder for injection molding and a binder system in which the binder components are combined in an inert atmosphere.

According to yet another feature of this invention, there is provided an injection moldable powder and binder system comprising a powder for injection molding and a binder system containing a binder component and a softener / compatibilizer component, wherein the system Binder is combined with the powder.

The present invention further provides a method for injection-molding powders parts for conglomerate comprising the steps of shaping a core, molding a powder and binder mixture around the core and removing the core of the powder and binder mixture and removing the binder to conglomerate the powder.

These and other features, as well as the scope, nature and use of the present invention will be apparent to those skilled in the art from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an enlarged and highly schematized example of a spherical particle size distribution that maximizes the charge of solids from the powder and binder system; Y Figure 2 is a schematic illustration enlarged to a large extent of the shapes of the powder particles.

DESCRIPTION OF THE PREDILLE EXAMPLES The powder and binder system of the present invention is applicable to any powder injection molding technique in which a powder or binder mixture, also called a raw material, is used for injection molding of powders. The powder particles in particular can be ceramic, metallic and / or intermetallic, depending on the desired characteristics of the final product. The powder and binder system of the present invention allows the injection molding of powders with increased solids loading resulting in less shrinkage and deformation during de-agglomeration and conglomeration.

The powder and binder system provides greater interparticular friction and a greater number of contact points between particle and particle after deagglutination. During the critical phase when all the binder is thermally removed but the conglomerate has not started, shape retention is largely achieved by interparticular friction and particle-particle contacts. By having a greater amount of powder in the molded component, the retention of the shape is this phase is significantly improved. As a result, the component is more robust and easier to handle during the clustering and conglomerate stages. This reduces the production cost of the injection molded components since the expensive support components are not needed and the components are no longer as sensitive to handling, ie sensitive to vibration. In addition, the components manufactured with this new and improved system and dust and binder method can be produced with greater tolerances than previously possible.

According to one example of the present invention, the powder and binder system can be optimized for the powder injection process by sorting, covering, agglutinating, mixing and / or modifying powders to achieve the particle size and distribution of the powder. Shapes and surface chemistry that are optimal for injection molding. The powders required for the composition of the final product are chosen according to their size and shape distribution and surface chemistry. Powders of a particular size, shape or surface chemistry chosen that can not be compatible with a binder are covered with one or more additives. Different powders are then mixed to ensure a size distribution that produces a maximum charge of solids and is mixed or combined with a binder system of one or more constituents. This allows the additive and the binder to perform their functions more effectively and ensures that the maximum load of solids is obtained.

If metal powders are to be injection molded, powders are typically chosen from four types: pre-alloyed powders, elemental powders, semi-elemental powders and master alloy powders. A prealloyed powder has the desired composition of the final product, that is, each of the grains or particles contains all the elements of the final product. To produce this powder, a steel having the desired composition can be melted and subsequently pulverized. For the molding of powders by injection, prealloyed powders atomized with gas and water can be used.

An elemental powder is typically composed of only one element. For example, if a steel consisting of 92% iron and 8% nickel is going to be made by injection molding powders using elemental powders, 92 / elemental powder of carbonyl steel can be mixed with 8% elemental powder. Nickel to achieve the desired alloy.

Semi-elemental powders are added to an elemental powder to achieve the desired composition of the elements. For example, instead of adding 15% elemental chromium powder to an iron-based powder to form 17-4PH stainless steel, 30% of a semi-elemental chrome-iron powder consisting of 50% iron and 50% chromium mix with the iron-based powder. A mixture of elemental and semi-elemental powders that can meet the correct composition of the desired final product is known as a semielemental elemental powder.

Similarly, a master alloy powder consists of the correct proportions of all the elements for the desired end product, except the base powder which is present only in small portions. For example, if the desired final alloy consists of 78% iron, 15% chromium, 4% chromium and 3% copper, a master alloy can be prepared and contains only 20% iron, while chromium, Nickel and copper are in a ratio of 15: 4: 3. To create the desired final powder, the master alloy must be mixed with elemental iron powder. The mixture of the elemental and the master alloy is known as an elemental powder / master alloy.

It has been found that a combination of 40 to 70 percent prealloyed powder with to 60 percent elemental / semi-elemental powder and / or 30 to 60 percent elemental master alloy powder results in improved moldability and improved conglomerate performance. The combination of different types of metal powders reduces the conglomerate temperature necessary for a given material to achieve a diffusion of the different phases. The higher temperatures of conglomerate can raise the problems as it is the evaporation of the elements of lower temperatures in the alloy, that is to say, copper in stainless steel.

The powder systems for the powder injection molding (PIM) raw material according to the present invention are chosen by combining or mixing powders to optimize the size and distribution of the form as well as the surface chemistry of the particles . This selection can influence and control viscous and plastic flow, evaporation-condensation, lattice, diffusion of the grain-limiting surface and conglomerate mechanisms. According to one example of the present invention, the size and the shape distribution and surface chemistry of the powder or powders used significantly affects the properties of the PMI product.

The size distribution of the particles in a powder can influence, for example, the loading of solids, the moldability and the diffusion during the conglomerate. The shape of the particles is important for the flow behavior and shape retention during the thermal process. Surface chemistry can influence the way in which a powder and binder system is prepared and what additives should be applied to the powder.

The powder size of a powder batch is classified using D90 measurements and IT GAVE. Measurements D90 indicates that 90% of the batch of powder in question is smaller than this size. The DIO measure indicates that 10% of the powder batch in question is smaller than this size. The different powders are chosen and / or mixed to maximize the D90 / D10 ratio, while maintaining the fraction of the particles above the average particle size between 50 and 80% by volume.

Powders of different particle sizes are mixed to optimize the packing characteristics of the powder and to optimize the amount of solids loading in the powder system. Figure 1 shows an enlarged and largely schematic example of a particle size distribution that maximizes the charge of solids from the powder and binder system by distributing particle sizes of multiple modalities. The correct amount of small particles must be available to fill gaps between larger dust particles. As an example, the combination of 40 to 70% of a powder of larger particles, for example, a portion classified or an atomized powder, with 30 to 60% of a minor particle powder, for example, a classified portion or an elemental / semi-elemental powder, produces a much higher solids loading level in PIM than the individual powders. Using these size distributions, stainless steels have been injection molded with solids loading greater than 72% by volume, resulting in reduced shrinkage and better shape retention during de-agglomeration and conglomeration.

It has been found that smaller particle sizes should be chosen for powders used at lower percentages in the desired product. The above results in higher achievable solids loads, better moldability and better diffusion during the conglomerate. For example, assuming that a desired alloy contains 80% of element A, 15% of element B, 3% of element C and 2% of element D. The required conglomerate temperature will be lower and the physical properties of the injection-molded component will be higher, if element A is 15 microns, B is 8 microns, and C and D are 2.5 microns. The larger particle sizes for the base element leads to a more homogeneous mixture and better diffusion during the conglomerate.

Figure 2 shows a schematic illustration greatly enlarged of the shapes of the powder particles. The shapes of the particles can be defined in three general categories: spherical, irregular and angular. The spherical powders 10 can be produced by gas atomization, by the carbonyl iron process or by other processes that produce a shape of each powder particle that is almost or perfectly spherical. Irregular powders 13 are produced by water atomization or other processes that produce a powder particle shape that may be irregular or a little league The angular powders 16 are crushing or grinding processes from the beta or other processes that result in powders that are angular in their shape.

According to the exemplary of the present invention, the powders of different forms are mixed to optimize the packing and flow behavior, and to maximize the retention of shape of the component during the thermal processing. While spherical powders generally flow better than irregular powders, the shape retention characteristics of irregular powders is superior. Similarly, irregular powders generally flow better than angular powders, shape retention characteristics are superior for angular powders. Mixtures of 55 to 95% spherical powders combined with 5 to 45% of this is irregular or angular powders or a combination of the same, can result in better flow behavior and better shape retention in the final stages of deglutination and the initial stages of conglomerate.

According to this invention, powders with different surface chemistry are mixed or combined in some other way to take advantage of different characteristics that each of the different types of powders exhibit. The surface chemistry of the powders is dictated by the powder preparation method. As an example, it has been shown that to produce a stainless steel or a tool steel, the use of 40 to 60% powder atomized with gas with 5 to 30% powder atomized with water and 10 to 35% carbonyl powder, and 5 to 30% of mechanically prepared semielemental powder produces a powder system with very high solids content, superior moldability, better debonding characteristics and better behavior in the conglomerate.

According to this invention, a powder can be covered with an additive before combining the powder with other powders having different surface chemistry. Figure 2 shows an example of a powder system containing powder particles covered with an additive. These additives 19, 21 and 23 may include coupling agents, antioxidants, surfactants, lubricants, dispersants, elastifying agents, plasticizers / compactizers and others. The additives are used, in part, to ensure that the binder effectively covers or couples the dust particles. Some surface chemistries may react or be incompatible with the binder and, therefore, need to be covered with an additive prior to the introduction of the binder. Different surface chemistries with different additives can be treated to allow the appropriate additives to perform their function more effectively.

These additives are applied by known methods which include solvent-milking techniques, dry / wet lamination, fluidization techniques, spray drying, dry dispersion or other techniques. The additives designed to interact directly with the powder surface, such as antioxidants, surfactants, dispersants or coupling agents, are used for the initial coverage of the powder. The application sequence of the active surfactants is dependent on the chemistry of the powder and varies according to the known chemical properties.

The powder and binder systems according to the present invention are structured to allow rapid processing or separation of the reactive or incompatible components. For example, a metallic powder that can react or be incompatible with the abutment component of the binder, it is pretreated with an organometallic coupling agent or an active taut agent, typically at levels of 0.3 to 15 percent of the weight of the binder. This pretreated powder can then be covered with the pillar phase at levels 4 to 45 percent of the weight of the binder and can be mixed or combined with the rest of the binder components. As a result of this structuring, there are coherent binder phases that allow lower pillar phase levels and faster processing. The coherent phases also allow the isolation of incompatible or reactive elements. In this way the materials that could not be mixed in a random manner are consolidated into usable raw material.

Os antioxidants, such as thermal stabilizers or metal shunts can also be used individually or in combination with another to stabilize polymers containing reactive metals. More reactive materials can cause catalytic decomposition of the polymers. The large surface areas of the powder exaggerate this problem. Typical levels of these additives vary between 0.1 and 2.5% by weight of the binder. For example, 1% Tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate) methane is used in conjunction with 1% 1,2-bis- (3,5-di-tert-butyl- 4-hydroxyhydrocinnamoyl) hydrazine to stabilize a water-soluble binder system with acetal base used with carbamoyl iron.

The organometallic coupling agents are used to improve the interface between the polymer and the surface of the powder. The rheological properties and the loading ability of the binder systems are greatly improved by coupling the organic and inorganic phases of a powder binder system. The metallic functionality is chosen in view of the powder used and the acceptable decomposition products. The organic part of the coupling agent is chosen based on the polymer used for the pillar.

For carbide-cobalt tungsten, an organometallic coupling agent with titanium base (titanate) can be used with WC-Co. powder. The functionality of titanium coupling agent has an affinity for the powder surface and the chemistry of the alloy tolerates inorganic decomposition products (titanium ceramics). Typical levels vary between 0.5 and 15% by weight of the binder. For example, 10% by weight of titanium binder IV 2,2 (bis 2-propenolatomethyl) butanolate, tri (dioctyl) phosphate-0 is used with an acetal-based water-soluble binder system. Other titanates such as the aliphatic amino titanate and the aliphatic carboxyl titanate can also be used.

For alumina, an aluminum-based coupling agent (aluminate) can be used with alumina powder. The functionality of the coupling agent aluminum has an affinity for the surface of the alumina. Typical levels vary between 0.5 and 15% by weight of the binder. The thermal decomposition of the coupling agent in the air produces alumina, leaving no contamination due to the coupling agent. As an example, 10 weight percent of the diisopropyl (oleyl) acetyl acetyl aluminate binder can be used as a coupling agent in an acetal-based water soluble v system. Other aluminates can also be used.

For carbonyl iron, a silicone-based coupling agent (silane) with carbonyl iron coated with silica can be used. The functionality of silicone exhibits an affinity for the silica surface of iron carbonyl and the decomposition product of silica is tolerable in most ferrous alloys. Typical levels vary between 0. 3 and 8% by weight of the binder. For example, 1.2% by weight of the binder N - (- aminomethyl) - - aminopropyltrimethoxysilane is used in an acetal - based water - soluble binder system.

A titanate is another example of a coupling agent that can also be used with carbonyl iron without coverage. The decomposition products of the titanate are acceptable titanium ceramics. Typical levels vary between 0.5 and 8% by weight of the binder. For example, 4% by weight of titanium binder IV 2,2 (bis 2 -propenolatommethyl) butanolate, tri (dioctyl) phosphate - = can be used in a water-soluble binder system based on cellulose acetate butyrate. Other titanates such as aliphatic amino titanate and aliphatic carboxyl titanate can be used in the same way.

The additives can be covered over the powder in a sequential or simultaneous manner. The powders can be treated with the additive (s) necessary before combining the powder with other powders that require a different additive. Powders should be covered to prepare a layered or onion-type particle / additive interface. Figure 1 shows spherical particles 5 covered with a single layer of an additive 8. In a preferred specimen, a monolayer on the molecular level of these additives is applied in a sequential manner.

The ceramic, metallic or intermetallic powder system is then prepared with one or more binder components to form a powder and binder system. This preparation can occur by covering the powder with one or more binder components or by mixing or combining the powder and the binder component. For example, a The binder binder layer can be applied to the powder particles by a known method of coverage, or the pillar can be combined first with the main binder component and then mixed or blended with the powder.

A plasticiser / compatibilizer can be added to the abutment to lower the viscosity of the powder and binder system. A plasticizer / compatibilizer such as monoglycerol monostearate can also serve to ensure a more heterogeneous mixture of the binder components. The pillar and the main component, together with other additives such as the plasticizer / compatibilizer and internal mold lubricants can be combined sequentially or simultaneously with the powder.

According to the present invention, the main binder and abutment components are various different molecular weights are used to achieve good fluidity, good green strength of the molded component and a wide range of temperatures in which the binder system decomposes during the de-agglutination. Binding components with a high molecular weight have a higher melting point and exhibit higher strength and greater memory effects. The binding components with low molecular weight are liquid at really low temperatures but are a bit weak and have little memory effect. As a result, the low molecular weight binder components flow well at low temperatures and maintain their molded shape. These binder components can decompose at low temperatures to remove them after molding.

The high molecular weight binder components give a molded part a lot of strength, but they have a high viscosity and a bad memory effect, that is, if It exerts pressure on a binder during molding. The residual pressures will remain in the molded part, which may involve the part during the de-agglutination. The higher molecular weight polymers also decompose at a much higher temperature. It is desirable to decompose some of the binders at a temperature close to the particle conglomerate point. This minimizes the weak phase during which all the binder has been removed and the molded parts are held together by the interparticular friction and the contact between particle and particle.

It is preferred to use several binder components of the same chemical composition, in different molecular weights. For example, a polypropylene can be used with a molecular weight as low as 40,000, along with other polypropylenes in the range of 80,000, 100,000 and 150,000 molecular weight. These are combined together within the binder system. The resulting moldability is very good due to the low molecular weight component and the green strength is good due to the high molecular weight component. In addition, the polymer decomposes over a broader range of temperatures.

Any polymer used as the main component of the binder in the injection molding technique, including waxes and other water soluble components, can be used as a main component in the present invention. Polyethylene glycol is an example of a major binder component that is soluble in water that can be used with many powders of low reactivity such as stainless steel or alumina. A major component with modified functionality, such as methoxypolyethylene glycol, is used with materials that exhibit more reactive surfaces such as iron, copper, or carbide-cobalt tungsten. The substitution of a functional unit of Methoxyl by a hydroxy functionally allows the use of more reactive metals, higher solids loads and lower ash content, that is, the impurities left after thermal decomposition. A methoxypolyethylene glycol can also be used with materials such as stainless steel and alumina to provide greater purity due to the lower content of residual ash. Typical levels of the main component are from 40 to 90% by weight of the binder.

Any polymer that is used as the abutment component of the binder in the injection molding technique can be used as a pillar component in the present invention. For example, binder systems for less reactive powders, i.e. stainless steel or alumina, can utilize a pillar component of acetal-based polymer, such as poly-oxymethylene. Typical amounts of acetal polymer are 10 to 45% by weight of the binder. The acetal is strongly plasticized by certain polymers used as main components of the binder, such as polyethylene glycol and glycol methoxy polyethylene. Additional plasticizers / compatibilizers may also be used.

More reactive materials such as iron may require a mixture of acetal and acrylic polymer as the pillar component. Typical acrylic colors vary from 2 to 35% by weight of the binder. If a water-soluble main component is used, a plasticizer / compatibilizer can be added to compatibilize the acrylic and the water-soluble component. Although the main component can plastify the acetal heavily, it may be desirable to further plasticize the acetal by adding a plasticizer / compatibilizer at levels of from 1 to 15% by weight of the binder. As an example, a mixture of 30% by weight of the binder acetal and 10% by weight of the binder polymethylmethacrylate is used with iron powders to provide a better molded surface finish and flexibility of the molded parts. In addition, 5% by weight of the binder of a compatibilizer / plasticizer such as monoglycerol monostearate is used to compatabilize and plasticize the binder phases, which provides lower melt viscosities and high solids loads. The acrylic component can also help give the injection molding component more elasticity and flexibility during injection.

The main components such as glycol polyethylene or hydroxypolyethylene glycol have a very slight or no plasticizing effect in certain polymers, for example, polyolefins and acrylics. Consequently, the water-soluble phase is extracted more rapidly. If the pillar component is not heavily plasticized by the main component, the addition of a polymer serves to modify the crystalline behavior of the main components. The acetal can be used to effect this behavior with water-soluble main components. Typical acetal levels vary from 2 to 20% by weight of the binder. The acetal is plasticized by the water-soluble component and serves to suppress the crystalline behavior of the water-soluble component.

Other polymers can also be used to suppress this behavior. Due to this lack of interaction between the pillar and water-soluble phases, the water-soluble component can be extracted more quickly. A mixture of 25% by weight of the polypropylene binder and 7% by weight of the acetal binder is used with stainless steel or iron to provide a faster de-agglutination system. They can also use appropriate plasticizers / compatibilizers. As an example, 5% by weight of the Paraffin binder and 5% by weight monoglycerol monostearate binder is used.

Another pillar approach would be to use a polymer that has a specific functionality according to the surfaces of the powder. Polymers that have an affinity with the surface of the powder allow the polymer to behave as an active tensing agent and at the same time a pillar component. Because the foregoing provides structure to the binding phases, smaller amounts of abutment are used if a faster deagglutination is desired. The above is also used to isolate incompatible or reactive materials. For example, a cellular ester, cellulose acetate butyrate is used with carbonyl iron in 10% by weight of the binder and provides a rapid deglutination of the compacts with a coherent phase structure. Appropriate plasticizers / compactizers can also be used.

Individual binder components, or powder and binder systems can be combined by mixing or combining them in an inert atmosphere to ensure that the lower molecular weight components do not decompose at this stage. By mixing or combining the binder components, or the powder and binder system, some binder components can begin to decompose at temperatures before other components reach the liquid state. The mixture or combination in an inert atmosphere allows the use of binder components with very high and very low melting temperatures together. The mixing or combination unit, in addition to the collection unit, must be purged with an inert gas.

The mixture of the individual binder components or the powder and binder system can be made using a prior art mixer.

The combination of the powder and binder systems is carried out using a twin or interconnected screw type mixer with co-rotating or counter rotating screw or arrows. The combination equipment can use very high gear types to combine the raw material to break up the powder agglomerates during the mixing process. The above results in a much more homogeneous dust and binder system.

EXAMPLE ONE An exemplary composition of a powder and binder system for iron carbonyl powder is: 1.2% N - (- aminomethyl) - - aminopropyltrimethoxysilane 1.0% Tetrakis [methylene (3,5 - di - tert - butyl - 4 - hydroxyhydrocinnamate) ] methane 1.0% 1,2-bis - (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl) hydrazine 4.0% monoglycerol monostearate 10.0% Polymethyl methacrylate 30.0% Poly oxymethylene 52.8% methoxy polyethylene glycol EXAMPLE TWO An exemplary composition of a powder and binder system for carbide-cobalt tungsten powder is: 10.0% Titanium IV 2,2 (bis 2-propenolatomethyl) butanolate, tris (diocryl) phosphate-0 1. 0% Tetraquis [methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane 1. 0% 1,2-bis - (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl) hydrazine 5.0% monoglycerol monostearate 30.0% Poly oxymethylene 53% methoxypolyethylene glycol The powder and binder system of the present invention is injection molded according to the techniques practiced in the art. These prior art techniques are used to inject the powder and binder system into a mold to form a component; to de-agglutinate the component by removing one or more of the binder components; and to conglomerate the powder system in the component. Non-limiting examples of powder injection techniques in which the powder and binder system of the present invention can be applied are given in: U.S. Patent No. 5,415,830, Zhang et al., U.S. Patent Number 5,397,531, Peiris et ai, U.S. Patent No. 5,332,537, Hens at al., U.S. Patent No. 5,155,158, Kim et al., U.S. Patent No. 5,059,388, Kihara et al., U.S. Patent. No. 4,765,950, Johnson, U.S. Patent 4,661,315, Wiech, U.S. Patent No. 4,415,528, Wiech, U.S. Patent No. 4,225,345, Adee et al., and U.S. Patent No. 4,197,118, Wiech.

These known powder injection techniques allow the injection molding of raw material at solids loads between 50 and 60% by volume, which results in shrinkages in the range of 14 to 20%. According to the present invention, the system of powder and binder can be injection molded with solids loads of more than 72% by volume, which results in a shrinkage in the range of 9 to 14%.

According to another aspect of the present invention, the expandable cores are used for the injection molding of powders. The expandable cores can be used where, for example, a complex internal cavities formation is required, which would be impossible or very expensive to form using conventional molding technology. Either a prior art PBVI raw material, or a powder and binder system as presented herein, is molded by an injection molding technique known in the art, around or by covering a shape or core element. The core is then removed during post-molding processing. This core can be removed by a known extraction technique, including chemical extraction, thermal extraction or any other appropriate method whereby the shape of the core is not retained during extraction. A cavity in the shape of the nucleus remains where the nucleus was. Expansible cores are particularly beneficial for very complex cavities or internal cavities with limited access from the outside of the part.

The expandable core may require a single phase or multiple extraction phases depending on its composition. The number of phases required for core extraction depends on the number of core components.

Generally, the number of extraction phases is the same as the number of components. One or more core components can also be a binder component.

Core processing can begin before incorporating the core into the compact. A core of two or more components may have one or more components removed before injection molding the raw material around the raw material of at least one last remaining component. The remaining component or components can be interconnected. It has been found that this preliminary extraction decreases the time required for the extraction of the expandable core after molding.

After extraction of the expandable core, any remaining binder component is removed by techniques known in the art. The injection molded part is then conglomerated by known techniques.

Although the present invention has been described in terms of currently preferred specimens, it should be understood that such a discovery should not be construed as limiting. Several alterations and modifications will undoubtedly be apparent to those with experience in the technique after having read the previous discovery. In accordance with the foregoing, it is intended that the appended claims be construed as covering all alterations and modifications within the real spirit and scope of the invention.

Claims (14)

1. CLAIMS: 1. An injection mouldable powder and binder system comprising. (a) powder particles, each particle has a respective surface; (b) an additive selected from the group consisting of coupling agents, antioxidants, surfactants, lubricants, dispersants, elastifying agents, plasticizers / compactizers, which cover a portion of said respective particular surface; and (c) a binder combined with said powder particles.
2. 2. The powder and binder system according to claim 1, wherein said coupling agent is an organometallic coupling agent.
3. 3. An injection mouldable powder and binder system comprising: (a) a powder for injection molding; (b) a binder system, comprising a removable polar component and a plasticizer / compatibilizer wherein said plasticiser / compatibilizer compatibilizes said polar component.
4. 4. The powder and binder system according to Claim 1 wherein said binder is composed of a first and second binder component.
5. 5. The powder and binder system according to Claim 1 wherein said antioxidant is selected from the group consisting of phenolic, a thioester synergist, a tocopherol, a tocotrienol and a hydroquinone ether.
6. 6. The powder and binder system according to Claim 3 wherein said plasticiser / compatibilizer is a glycerol ester.
7. 7. The powder and binder system according to claim 1 wherein said additive is a thermal stabilizer or a metal deactivator.
8. 8. The powder and binder system according to Claim 1 wherein said powder particles are selected from the group consisting of a metal powder, a ceramic powder and an intermetallic powder.
9. 9. The powder and binder system according to claim 1 wherein said elastifying agent is selected from the group consisting of an elastomer, an acrylic polymer and an inorganic polymer.
10. 10. The powder and binder system according to claim 1 or claim 3 further comprising a powder system comprising: a prealloyed powder; and an elemental / semielemental powder or a master alloy powder or both.
11. 11. The powder and binder system according to claim 1 or claim 3 wherein said powder and said binder are combined in a substantially inert atmosphere.
12. 12. A process for molding by powder injection components from the powder and binder system according to Claim 1 or Claim 2, comprising the steps of: (a) molding said powder and binder system to form a component; (b) de-agglutinate said component by at least partially removing said binder; and (c) conglomerating said powder.
13. 13. A method for molding by powder injection comprising the steps of: (a) forming an element within a predetermined shape; (b) combining a powder and a binder to form a homogeneous mixture of binder and powder; (c) injection molding said mixture around said element to form an apparatus; (d) removing a substantial portion of said element from said apparatus by means whereby the shape of the element is not retained during extraction; (e) removing a substantial portion of said binder; and (f) conglomerate said apparatus.
14. 14. A method for injection molding metal powder comprising the steps of: (a) combining at least two metal powders chosen from the group consisting of prealloyed powders, elemental powders, semi-elemental powders and master alloy powders to form a powder system; (b) covering said powder system at least in part with an additive; (c) combining said powder system and a binder to form a powder and binder system; (d) molding said powder and binder system to form an apparatus; (e) de-agglutinate said apparatus by at least partially removing said binder; and (f) conglomerating said apparatus. EXTRACT OF THE INVENTION A system of powders and binders for manufacturing agglomerated parts from particulate material and a method of injection molding parts for agglomerate is provided. The particulate material includes ceramics, metallic powders and intermetallic powders. Preferably, the selected powder particles are covered with one or more additives depending on their shapes and surface chemistry to create a powder system. The additives may include antioxidants, coupling agents, surfactants, elastifying agents, dispersants, plasticizers / compactizers and lubricants. The active surface additives are designed to improve the interface between the powder and the binder. The powder system can be mixed or combined with a binder system in an inert atmosphere to form a system of powders and binders, or raw material, for molding powders. The binder system may contain one or more components that are removed before conglomerating the powder. The powder and binder system can also be molded around an expandable core before conglomerating.