US20140271329A1

US20140271329A1 - Methods for solventless bonding of metallurgical compositions

Info

Publication number: US20140271329A1
Application number: US14/203,930
Authority: US
Inventors: Kalathur S. Narasimhan; Christopher T. Schade
Original assignee: Hoeganaes Corp
Current assignee: Hoeganaes Corp
Priority date: 2013-03-14
Filing date: 2014-03-11
Publication date: 2014-09-18
Also published as: BR112015023225A2; JP2016517475A; WO2014159318A1; CA2906347A1; EP2969316A1; KR20150127214A; CN105228774A

Abstract

The present invention is directed to methods of preparing a bonded metallurgical powder composition comprising melting a binding agent and blending the melted binding agent with a metallurgical powder mixture, in the substantial absence of solvent, for a time sufficient to form the bonded metallurgical powder composition. Bonded metallurgical powder compositions prepared using these methods are also described, as well as compacted powder metallurgical parts prepared using them.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/781,331, filed Mar. 14, 2013, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention is directed to solventless methods for bonding metallurgical powder compositions.

BACKGROUND

Coating or bonding of metal powders is important for improving performance of the powders, as well as for reducing dusting during handling of powder mixtures. Methods for coating or bonding powder mixtures have been previously described. See, e.g., U.S. Pat. Nos. 2,648,609; 3,117,027; 4,731,195; 6,280,683; and 6,602,315.
Some of these bonding methods use a combination of high shear and high applied pressure to coat powder particles with polymers or waxes. These methods can cause agglomeration of the powder, producing a web like structure. In other methods, the powder is fluidized and then coated with binding materials that are dissolved in a solvent. Typically, the binding materials are in a solution comprising 75%-95%, by weight, of solvent. After the particles of the powder are coated, the solvent must be removed—a process which can be time consuming, costly, and dangerous since many of the solvents used are flammable liquids.
The coating processes described in U.S. Pat. Nos. 6,602,315 and 6,280,683 use solventless “dry bonding.” These processes mix the metal powder and additives with polymer binders having a small particle size range, at a temperature below the melting point of the polymer. While advantageous, the scope of these methods is limited because of the small particle size requirement for the binders.
New methods for preparing bonded metallurgical powder compositions are still needed.

SUMMARY

The present invention is directed to methods of preparing a bonded metallurgical powder composition comprising heating a binding agent, in the substantial absence of solvent, to a temperature above the melting point of the binding agent for a time sufficient to melt the binding agent; and blending the melted binding agent with the metallurgical powder mixture, in the substantial absence of solvent, for a time sufficient to form the bonded metallurgical powder composition. The present invention also includes bonded metallurgical powder compositions prepared using these methods, as well as compacted powder metallurgical parts prepared using them.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention provides improved methods for bonding, that is, particle-coating, to produce non-agglomerated, coated particles. These methods use substantially no solvent to produce bonded metallurgical powder compositions.
According to the invention, bonded metallurgical powder compositions can be prepared by heating a binding agent, in the substantial absence of solvent, to a temperature at or above the melting point of the binding agent for a time sufficient to melt the binding agent.
As used herein, “solvent” refers to any organic solvent, for example, acetone, methylene chloride, toluene, benzene, ethanol, hexanes, and the like.
As used herein “substantial absence of solvent” refers to 0% to less than 5%, by weight of the binder, of solvent. Preferred embodiments will include less than 5%, by weight of the binder, of solvent. Even more preferred embodiments will include less than 2%, by weight of the binder, of solvent. Yet more preferred embodiments will include less than 1%, by weight of the binder, of solvent. In exemplary embodiments, the binder comprises no added solvent. The amount of solvent present can be determined using any conventional methods known in the art.
In the methods of the invention, the coating material, also referred to as the “binder,” can be any solid polymer or wax with a defined melting point. Examples of binding agents falling under this description include but not limited to: stearamides, behenic acid, oleamides, polyethylenes, paraffin wax, ethelyne bissstearamides and cotton seed waxes. In some embodiments of the invention, the binding agent melts when heated to a temperature of between about 50° C. and about 150° C. In other embodiments of the invention, the binding agent melts when heated to a temperature of between about 50° C. and about 110° C. In preferred embodiments of the invention, the binder is polyethylene.
Other binding agents for use in the invention include, for example, polyglycols such as polyethylene glycol or polypropylene glycol; glycerine; polyvinyl alcohol; homopolymers or copolymers of vinyl acetate; cellulosic ester or ether resins; methacrylate polymers or copolymers; alkyl resins; polyurethane resins; polyester resins; or combinations thereof. Other examples of binding agents that are useful are the relatively high molecular weight polyalkylene oxide-based compositions described in U.S. Pat. No. 5,298,055. Useful binding agents also include the dibasic organic acid, such as azelaic acid, and one or more polar components such as polyethers (liquid or solid) and acrylic resins as disclosed in U.S. Pat. No. 5,290,336, which is incorporated herein by reference in its entirety. The binding agents in U.S. Pat. No. 5,290,336 can also act advantageously as a combination of binder and lubricant. Additional useful binding agents include the cellulose ester resins, hydroxy alkylcellulose resins, and thermoplastic phenolic resins described in U.S. Pat. No. 5,368,630.
The binding agent can further be solid polymers or waxes, such as polyesters, polyethylenes, epoxies, urethanes, paraffins, ethylene bisstearamides, and cotton seed waxes, and also polyolefins with weight average molecular weights below 3,000.
In exemplary embodiments of the invention, the weight of the binding agent is about 10% by weight, based on the weight of the bonded metallurgical powder composition. In other embodiments, the bonded metallurgical powder compositions of the invention will comprise about 0.1% to about 5.0%, by weight of the bonded metallurgical powder composition, of binding agent. In other embodiments, the bonded metallurgical powder compositions of the invention will comprise about 0.1% to about 3.0%, by weight of the bonded metallurgical powder composition, of binding agent. In other embodiments, the bonded metallurgical powder compositions of the invention will comprise about 0.1% to about 2.0%, by weight of the bonded metallurgical powder composition, of binding agent. In other embodiments, the bonded metallurgical powder compositions of the invention will comprise about 0.1% to about 1.0%, by weight of the bonded metallurgical powder composition, of binding agent.
According to the invention, the melted binding agent, in the substantial absence of solvent, is applied to a metallurgical powder mixture.
As used herein, “metallurgical powder mixture,” refers to metallurgical powders comprising an metal-based powder. The metallurgical powder compositions of the invention preferably include at least 80 wt. % of an metal-based metallurgical powder. Preferably, the metallurgical powder compositions of the invention preferably include at least 90 wt. % of an metal-based metallurgical powder.
Preferred metal-based metallurgical powders of the invention are iron-based powders.
Substantially pure iron powders are powders of iron containing not more than about 1.0% by weight, preferably no more than about 0.5% by weight, of normal impurities. Examples of such highly compressible, metallurgical-grade iron powders are the ANCORSTEEL 1000 series of pure iron powders, e.g. 1000, 1000B, and 1000C, available from Hoeganaes Corporation, Riverton, N.J. For example, ANCORSTEEL 1000 iron powder, has a typical screen profile of about 22% by weight of the particles below a No. 325 sieve (U.S. series) and about 10% by weight of the particles larger than a No. 100 sieve with the remainder between these two sizes (trace amounts larger than No. 60 sieve). The ANCORSTEEL 1000 powder has an apparent density of from about 2.85-3.00 g/cm³, typically 2.94 g/cm³. Other substantially pure iron powders that can be used in the invention are typical sponge iron powders, such as Hoeganaes' ANCOR MH-100 powder.
Metallurgical powder mixtures of the invention can be prealloyed iron-based powders are stainless steel powders. These stainless steel powders that are commercially available in various grades in the Hoeganaes ANCOR® series, such as the ANCOR® 303L, 304L, 316L, 410L, 430L, 434L, and 409Cb powders. Also, iron-based powders include tool steels made by powder metallurgy methods.
Metallurgical powder mixtures of the invention can also be substantially pure iron powders prealloyed with alloying elements, such as for example molybdenum (Mo). Iron powders prealloyed with molybdenum are produced by atomizing a melt of substantially pure iron containing from about 0.5 to about 2.5 weight percent Mo. An example of such a powder is Hoeganaes' ANCORSTEEL 85HP steel powder, which contains about 0.85 weight percent Mo, 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. Other examples of molybdenum containing iron based powders are Hoeganaes' ANCORSTEEL 737 powder (containing about 1.4 wt. % Ni—about 1.25 wt. % Mo—about 0.4 wt. % Mn; balance Fe), ANCORSTEEL 2000 powder (containing about 0.46 wt. % Ni—about 0.61 wt. % Mo—about 0.25 wt. % Mn; balance Fe), ANCORSTEEL 4300 powder (about 1.0 wt. % Cr—about 1.0 wt. % Ni—about 0.8 wt. % Mo—about 0.6 wt. % Si—about 0.1 wt. % Mn; balance Fe), and ANCORSTEEL 4600V powder (about 1.83 wt. % Ni—about 0.56 wt. % Mo—about 0.15 wt. % Mn; balance Fe). Other exemplary iron-based powders are disclosed in U.S. Pat. No. 7,153,339, which is incorporated herein by reference in its entirety.
An additional pre-alloyed iron-based powder is disclosed in U.S. Pat. No. 5,108,493, which is incorporated herein by reference in its entirety. These steel powder compositions are an admixture of two different pre-alloyed iron-based powders, one being a pre-alloy of iron with 0.5-2.5 weight percent molybdenum, the other being a pre-alloy of iron with carbon and with at least about 25 weight percent of a transition element component, wherein this component comprises at least one element selected from the group consisting of chromium, manganese, vanadium, and columbium. The admixture 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 Hoeganaes' ANCORSTEEL 41 AB steel powder, which contains about 0.85 weight percent molybdenum, about 1 weight percent nickel, about 0.9 weight percent manganese, about 0.75 weight percent chromium, and about 0.5 weight percent carbon.
Metallurgical powder mixtures of the invention can also be diffusion-bonded iron-based powders which are particles of substantially pure iron that have a layer or coating of one or more other alloying elements or metals, such as steel-producing elements, diffused into their outer surfaces. A typical process for making such powders is to atomize a melt of iron and then combine this atomized an annealed powder with the alloying powders and re-anneal this powder mixture in a furnace. Such commercially available powders include DISTALOY 4600A diffusion bonded powder from Hoeganaes Corporation, which contains about 1.8% nickel, about 0.55% molybdenum, and about 1.6% copper, and DISTALOY 4800A diffusion bonded powder from Hoeganaes Corporation, which contains about 4.05% nickel, about 0.55% molybdenum, and about 1.6% copper.
The particles of iron-based powders used herein, such as the substantially pure iron, diffusion bonded iron, and pre-alloyed iron, have a distribution of particle sizes. Typically, these powders are such that at least about 90% by weight of the powder sample can pass through a No. 45 sieve (U.S. series), and more preferably at least about 90% by weight of the powder sample can pass through a No. 60 sieve. These powders typically have at least about 50% by weight of the powder passing through a No. 70 sieve and retained above or larger than a No. 400 sieve, more preferably at least about 50% by weight of the powder passing through a No. 70 sieve and retained above or larger than a No. 325 sieve. Also, these powders typically have at least about 5 weight percent, more commonly at least about 10 weight percent, and generally at least about 15 weight percent of the particles passing through a No. 325 sieve. Reference is made to MPIF Standard 05 for sieve analysis.
As such, metallurgical powder mixtures can have a weight average particle size as small as one micron or below, or up to about 850-1,000 microns, but generally the particles will have a weight average particle size in the range of about 10-500 microns. Preferred are iron or pre-alloyed iron particles having a maximum weight average particle size up to about 350 microns; more preferably the particles will have a weight average particle size in the range of about 25-150. In a preferred embodiment, metallurgical powder compositions have a typical particle size of less than 150 microns (−100 mesh), including, for example, powders having 38% to 48% of particles with a particle size of less than 45 microns (−325 mesh).
The described iron-based powders are preferably water-atomized powders. These iron-based powders have apparent densities of at least 2.75, preferably between 2.75 and 4.6, more preferably between 2.8 and 4.0, and in some cases more preferably between 2.8 and 3.5 g/cm³.
Corrosion resistant metallurgical powder mixtures incorporate one or more alloying additives that enhance the mechanical or other properties of final compacted parts. Alloying additives are combined with the iron powder by conventional powder metallurgy techniques known to those skilled in the art, such as for example, blending techniques, prealloying techniques, or diffusion bonding techniques. Preferably, alloy additives are combined with an iron-based powder by prealloying techniques, i.e., preparing a melt of iron and the desired alloying elements, and then atomizing the melt, whereby the atomized droplets form the powder upon solidification.
Alloying additives are those known in the powder metallurgical industry to enhance the corrosion resistance, strength, hardenability, or other desirable properties of compacted articles. Steel-producing elements are among the best known of these materials. Examples of alloying elements include, but are not limited to, chromium, silicon, graphite, copper, molybdenum, nickel, and the like, or combinations thereof. The amount of the alloying element or elements incorporated depends upon the properties desired in the final metal part. Pre-alloyed iron powders that incorporate such alloying elements are available from Hoeganaes Corp. as part of its ANCORSTEEL line of powders. When used, the metallurgical powder mixtures comprise from 0.10% to about 10%, based on the weight of metallurgical powder mixture, of alloying powders. Preferably, the metallurgical powder mixtures comprise from 0.20% to about 5%, based on the weight of metallurgical powder mixture, of alloying powders.
The melted binding agent can be applied to the metallurgical powder mixture using any of the methods known in the art. One exemplary method is spray application.
In some embodiments of the invention, the metallurgical powder mixture can be heated prior to and/or during the application of the melted binding agent. For example, the metallurgical powder mixture can be heated at a temperature of about 60° C. to about 85° C., prior to and/or during the application of the melted binding agent.
Once the melted binding agent is applied to the metallurgical powder mixture, the melted binding agent and the metallurgical powder mixture are blended, in the substantial absence of solvent, for a time sufficient to form the bonded metallurgical powder compositions of the invention. For example, the blending may take between 1 and 5 minutes, depending on the amount of binder. Any blending methods known in the art can be used. Preferably, the blending methods allow for heating and blending to occur at the same time. The blending can occur in a mixer at low shear, that is, about 20 to about 30 rpm, or at high shear, that is, greater than 30 rpm. Blending devices that can be used with the methods of the invention include drum mixers, for example, and Elrich Mixer, paddle mixers, for example, an S. Howes mixer, a Nauta blender, and a Littleford Blender. Other methods of blending, such as a Wurster coater, can also be used.
One advantage of the present invention is that, in contrast to the dry-bonding methods described in U.S. Pat. Nos. 6,602,315 and 6,280,683, the binder does not need to be of any particular size because it will be melted prior to adding it to the metallurgical powder. As such, the binder can start as coarse chucks or prills that are several inches in size.
In the methods of the present invention, the polymer is preferably melted in a vessel that is separate from the mixing blender that contains the metallurgical powder. As a result, the metal powder in the blender does not need to be heated to the softening or melting point of the polymer being sprayed. This results in a large energy savings, as compared to other dry-bonding methods known in the art. The methods of the invention have lower energy consumption as compared to solvent-bonding processes because solvent evaporation, recovery, and disposal is not necessary. The methods of the invention are, therefore, more energy efficient and more environmentally friendly.
Any method of melting can be used, but direct heating of the vessel containing the polymeric material is acceptable.
The metallurgical powder compositions of the invention may be formed into a variety of product shapes known to those skilled in the art, such as for example, the formation of billets, bars, rods, wire, strips, plates, or sheet using conventional practices.
The bonded compositions are then compacted by conventional techniques known to those skilled in the art. Generally, the bonded metallurgical powder compositions are compacted at more than about 5 tons per square inch (tsi). Preferably, the metallurgical powder compositions are compacted at from about 5 to about 200 tsi, and more preferably, from about 30 to about 60 tsi. The resulting green compact can be sintered. Preferably, a sintering temperature of at least 2000° F., preferably at least about 2200° F. (1200° C.), more preferably at least about 2250° F. (1230° C.), and even more preferably at least about 2300° F. (1260° C.), is used. The sintering operation can also be conducted at lower temperatures, such as at least 2100° F.
Sintered parts typically have a density of at least about 6.6 g/cm³, preferably at least about 6.68 g/cm³, more preferably at least about 7.0 g/cm³, more preferably from about 7.15 g/cm3 to about 7.38 g/cm³. Still more preferably, sintered parts have a density of at least about 7.4 g/cm³. Densities of 7.50 g/cm³are also achieved using the metallurgical powder compositions of the invention.
Those skilled in the art will appreciate that numerous changes and modifications may be made to the preferred embodiments of the invention and that such changes and modifications may be made without departing from the spirit of the invention. The following examples further describe the metallurgical powder compositions.

Examples

Example 1

The blending of polyethylene (Polywax 655) binder with iron-based and alloy powders was conducted using two methods. Method A was a method described in U.S. Pat. No. 6,602,315. Method B was a method according to the present invention. The test composition contained 0.80% graphite as the alloying powder, 98.45% ANCORSTEEL A1000 iron-based powder, and 0.75% polyethylene.
For Method 1A, the polyethylene was ground to a mean particle size of 20 microns and added to a blender comprising the test composition. The contents of the bender were heated to about 180° F. (82° C.).
For Method 1B, the polyethylene was heated to a temperature above its melting point and sprayed into a blender comprising the test composition. The contents of the bender were heated to about 180° F. (82° C.).
Table 1 shows the dust resistance or bonding efficiency for graphite in the utilizing the two bonding techniques. The composition prepared according to Method 1B had improved bonding efficiency.

	TABLE 1

	Bonding Method	Bonded Graphite (%)

	Method 1A	84
	Method 1B	95

Example 2

The test composition included 2.9% ferrophosphorus (Fe₃P) (average particle size=10 microns) as the alloying powder, 98.45% ANCORSTEEL A1000B iton-based powder, 0.20% polyethylene, 0.50% ethylene bisstearamide (average particle size—20 microns).
The test composition for Method 2A included 2.9% ferrophosphorus (Fe₃P) (average particle size=10 microns) as the alloying powder, 98.45% ANCORSTEEL A1000B iron-based powder, and 0.20% polyethylene. For Method 2A, the polyethylene was dissolved in acetone and combined with the other components according to the solvent-based bonding methods known in the art. One of the disadvantages of dissolving the binder in a solvent is that the solubility of the binder is limited. In addition, the limited amount of dissolved binder is not enough to provide proper lubrication for compaction, so additional lubricant must be added to the solvent bonded mix so compaction can take place. For Method 2A, the additional lubricant is 0.50% ethylene bisstearamide (“EBS”) (average particle size—20 microns).
For Method 2B, the polyethylene was melted and spray-applied to the other components using a method of the invention. No EBS was needed for the test composition used in Method 2B, as the amount of binder was not solubility limited.
Table 2 shows bonding efficiency for Fe₃P in the utilizing the two bonding techniques. The composition prepared according to Method 2B had improved bonding efficiency.

	TABLE 2

	Bonding Method	Bonded Graphite (%)

	Method 2A	80
	Method 2B	97

Example 3

In the solvent-bonding methods of the prior art, the additional lubricant is added in powder form, which can be prone to dusting. If the additional lubricant is added during the bonding process, some of the binder acts to bind the additional lubricant and is not available to bond the alloying powders, for example, Fe₃P. This is in contrast with the methods of the present invention, since the polymer acts both as binder and lubricant.
For the premix, the test composition comprised 0.8% graphite as the alloying powder (average particle size=6 microns), 98.45% ANCORSTEEL A1000 iron-based powder, and 0.75% EBS (average particle size=20 microns). The test composition was mixed using conventional mixing techniques
For Method 3B, the test composition comprised 0.8% graphite as the alloying powder (average particle size=6 microns), 98.45% ANCORSTEEL A1000 iron-based powder, and 0.75% polyethylene. The polyethylene was melted and spray-applied to the other components using a method of the invention
An advantage of the bonding methods of the invention is that the binder forms a thin coating around the outside of the iron powder, which then acts to “glue” any additive particles; in this example, graphite. Since the binder acts as a lubricant, the amount of lubricant added in powder form can be eliminated or reduced greatly. Since there is limited surface area on the iron-based powder for the particles to be bonded, the smaller the number of particles to be attached to the base powder, the better the bonding efficiency. This can be seen in Table 3, where the bonding efficiency (as measured by the total carbon) using Method 3B is 95% versus Method 3A, where the bonding efficiency is only 55%.

	TABLE 3

	Bonded Graphite (%)

	premix	55
	Method 3B	95

Example 4

A binder or lubricant's effect on apparent density and flow is important. Apparent density is a measure of how much powder can fill a fixed volume, with a higher value associated with better filling of a die to produce a part. The flow of a powder is the time necessary to fill the die cavity (a fixed volume). Since the production of PM parts involves repeatedly filling the die, the better the flow (lower time) the more parts that can be produced within a fixed time, therefore increasing the productivity of the part production process. The shape of a powder particle or bonded particle can have an influence on the flow and apparent density of a powder mixture. A more rounded shape improves both the apparent density, by improving the particle packing, and the flow, by reducing the particle friction.
In a bonded mixture of powder, the shape of the powder can be considered as a combination of the base powder, the alloying powders, the lubricant, and the binder. In the methods of the present invention, since the binder can be applied uniformly around the base powder, the bonded particle tends to be more spherical, as compared to bonded powders produced using “dry bonding” methods of the prior art.
The compositions of the mixes used in this Example are:
Premix: 2.0% 8081 copper powder (average particle size=20 microns), 0.80% graphite as the alloying powder (average particle size=8 microns), 96.45% ANCORSTEEL A1000B iron-based powder, 0.75% of EBS (ethylene bisstearamide) (average particle size=20 microns).
Mix for Method 4A: 2.0% 8081 copper powder (average particle size=20 microns), 0.80% graphite as the alloying powder (average particle size=8 microns), 96.45% ANCORSTEEL A1000B iron-based powder, 0.75% polyethylene, which was melted and sprayed according to the present invention.
Mix for Method 4B: 0.20% EBS, 2.0% 8081 copper powder (average particle size=20 microns), 0.80% graphite as the alloying powder (average particle size=8 microns), 96.45% ANCORSTEEL A1000B iron-based powder, 0.55% polyethylene, which was melted and sprayed according to the present invention, plus an additional 0.20% of EBS (average particle size=20 microns).
Mix for Method 4C: 2.0% 8081 copper powder (average particle size=20 microns), 0.80% graphite as the alloying powder (average particle size=8 microns), 96.45% ANCORSTEEL A1000B iron-based powder, 0.20% polyethylene, dissolved in acetone. In addition there was 0.50% of EBS with an average particle size of 20 microns. Polyethylene was applied using solvent-based methods of the prior art.
Table 4 shows the flow and apparent density of the powders bonded according to the invention (Methods 4A and 4B) versus a standard premix and the solvent-bonded mix (Method 4C).

TABLE 4

Sample	Apparent Density	Flow

Premix	2.99	40.0
Method 4A	3.68	28.7
Method 4B	3.57	30.8
Method 4C	3.29	31.4

Method 4A, with 0.75% sprayed polyethylene, shows an improvement in the apparent density (higher) and flow (lower) than a premix of similar composition. Both Methods 4A and 4b performed better than either the premix or the standard solvent bonded mix (Method 4C).
In general, it is difficult to obtain an apparent density greater than 3.40 g/cc in either a premix or solvent-bonded mix. With the premix, the electrostatic forces of the unbound polymer and the frictional effects of the additives tend to have a negative influence on apparent density and flow. With solvent-bonded mixes, since solubility limits the amount of binder, the bonded particle tends to have a more irregular shape than the bonded particles prepared according to the invention. The improved apparent density and flow observed using the methods of the invention can lead to improved dimensional control and weight consistency on the compacted part.

Example 5

Binder should also be able to function as a lubricant. Lubricants are needed to assist the compaction and ejection of parts from a die and to reduce friction at the start and during ejection. If the binder can act as a lubricant, the forces necessary to compact the part can be reduced and higher densities can be achieved.
The material bonded according to the invention shows similar improvement in the apparent density and flow similar to the results seen in Table 4.
Strip and slide, which are measurements of the ejection characteristics of powder mixes, are shown in Table 5. The strip pressure is the pressure necessary to start the compacted part moving from the die during the ejection cycle. The lower the strip pressure, the easier the part is to remove from the die and the less force required by the compacting press. The slide pressure is the force necessary to keep the part moving out of the die until it is free of the constraints of the die. In most cases the lower the slide pressure, the easier it is to remove from the die and the better the surface finish.
Table 5 shows ejection forces (strip and slide) for three different compaction pressures (30, 40, and 50 tsi). The material bonded according to the invention shows a lower strip and slide versus the conventional premix and the solvent-bonded mix. The green density of the material prepared according to the invention is comparable to the premix and is improved over the solvent-bonded mix.
Table 5 shows the results of compaction properties of the various mixes. The mixes used in this experiment are A1000+0.80% graphite+0.75% organic materials. “Premix” refers to unbonded material. MB#1 and MB#2 are bonded material prepared according to the invention, that is, the binder was melted in the substantial absence of solvent and blended with the other materials. The binder used in MB#1 and MB#2 was behenic acid and ethylene bi-stearamide. MB#1 has 0.40% of the total lubricant from the binder. MB#2 has the binder being used also as the lubricant. AB 1 (Ancorbond 1) was bonded using solvent-bonding, and is used as a comparison. AB1 includes an organic binder comprising polyethylene, polyglycol, and ethylene bi-stearamide. In the tested mixtures, the combination of binder and ethylene bi-stearamide is 0.75%, by weight of the mixture.

TABLE 5

Apparent			Green	Green
Density	Flow	Pressure	Density	Strength	Strip	Slide

Material	(g/cm³)	(secs)	(tsi)	(MPa)	(g/cm³)	(psi)	(MPa)	(psi)	(MPa)	(psi)	(MPa)

PREMIX	3.11	NF	30	416	6.72	1608	22	3719	52	1912	27
			40	555	7.00	2037	28	4110	57	2179	30
			50	694	7.14	2211	31	4158	58	2419	34
MB #1	3.51	31	30	416	6.74	1171	16	3004	42	1633	23
			40	555	6.99	1526	21	3319	46	1615	22
			50	694	7.11	1679	23	3567	50	1633	23
MB #2	3.43	31.4	30	416	6.74	1245	17	3043	42	1616	22
			40	555	6.99	1727	24	3311	46	1658	23
			50	694	7.12	1869	26	3438	48	1603	22
AB1	3.21	27.6	30	416	6.69	2057	29	3025	42	1713	24
			40	555	6.94	2608	36	3621	50	1828	25
			50	694	7.08	2893	40	4167	58	2186	30

Example 6

An exemplary method of the invention includes heating a mixture of metal powder and alloying powders to a preselected temperature in a blending device. The binder is melted is a separate vessel and is they sprayed into the blending device, while the mixture is blended. The resulting bonded powder is the cooled to ambient temperature. Additional additives can be added at this time.

Claims

What is claimed:

1. A method of preparing a bonded metallurgical powder composition comprising:

melting a binding agent, in the substantial absence of solvent;

and

blending the melted binding agent with a metallurgical powder mixture, in the substantial absence of solvent, for a time sufficient to form the bonded metallurgical powder composition.

2. The method of claim 1, wherein the binding agent comprises less than 5% by weight of solvent, based on the weight of the binder.

3. The method of claim 1, wherein the binding agent comprises less than 2% by weight of solvent, based on the weight of the binder.

4. The method of claim 1, wherein the binding agent comprises no added solvent.

5. The method of claim 1, wherein the binding agent is a stearamide, behenic acid, an oleamide, a polyethylene, paraffin wax, an ethylene bisstearamide, a cotton seed wax, or a combination thereof.

6. The method of claim 1 wherein the melting step includes heating the binding agent to a temperature above the melting point of the binding agent for a time sufficient to melt the binding agent.

7. The method of claim 6, wherein the binding agent is heated to a temperature of between about 50° C. to about 110° C.

8. The method of claim 1, wherein the binder is polyethylene.

9. The method of claim 1, wherein the metallurgical powder mixture comprises

at least about 80% by weight, based on the weight of the mixture, of a metal-based powder; and

at least one alloying powder.

10. The method of claim 9, wherein the metallurgical powder mixture comprises at least about 90% by weight of the metal-based powder.

11. The method of claim 9, wherein the metal-based powder is an iron-based powder.

12. The method of claim 9, wherein the metallurgical powder mixture further comprises 0.20% to about 5.0%, by weight of the composition, of alloying powers.

13. The method of claim 1, wherein the bonded metallurgical powder composition comprises about 0.15% to about 2.0%, by weight of the composition, of the binding agent.

14. The method of claim 6, wherein the metallurgical powder mixture is heated to between about 60° C. to about 85° C.

15. The method of claim 1 in which, prior to the blending step, the melted binding agent is applied to the metallurgical powder, in the substantial absence of solvent, by spraying the powder with the melted binding agent.

16. The method of claim 6, in which, prior to the blending step, the melted binding agent is applied to the metallurgical powder, in the substantial absence of solvent, by spraying the powder with the melted binding agent.

17. The method of claim 16 in which the binding agent contains less than 2% by weight, based on the weight of the binder, of solvent.

18. A bonded metallurgical powder composition prepared according to the method of claim 1.

19. A compacted powder metallurgical part prepared using the bonded metallurgical powder composition of claim 6.