BRPI0620868A2 - metallurgical powder composition - Google Patents

Abstract

COMPOSITION OF METALLURGICAL DUST. The present invention relates to a metallurgical composition for producing compacted parts, comprising: (a) at least about 80 percent of an iron or iron-based powder; (b) up to about 20 weight percent of at least one binding powder; (c) from about 0.05 to about 2 weight percent of a binding agent comprising a C ~ 14 ~ C ~ 30 ~ fatty alcohol; and (d) from about 0.001 to about 0.2 weight percent of a flow agent.

Description

Patent Descriptive Report for "METALURGIC POWDER COMPOSITION".

Field of the Invention

The present invention relates to a novel metal powder composition for the metallurgical powder industry. Particularly the invention relates to an iron-based powder composition comprising a binder for binding additives, such as binding elements, to the iron-based particles.

Background of the Invention

In industry the use of metal products made by compacting and sintering the iron-based powder composition is becoming increasingly widespread. The quality requirements of these metal products are continuously increased and as a consequence new powder compositions having improved properties are developed. Some of the most important properties of the final sintered product are the density and dimensional tolerances, which must be consistent. Problems with size variations in the final product often stem from the lack of homogeneity in the powder mix to be compacted. These problems are especially pronounced with powder mixtures that include dusty components, which differ in size, density and shape, one reason why segregation occurs during transport, storage and handling of the powder composition. This segregation implies that the composition is not uniformly composed, which in turn means that parts made of the powder composition are composed differently and consequently have different properties. Another problem is that fine particles, particularly those of lower density such as graphite, cause dust to be produced during handling of the powder mixture.

The small particle size of the additives also creates problems with the powder flow properties, that is, the ability of the powder to behave as free flowing powder. A weakened flow manifests itself in the increased time to fill a mold cavity with dust, which means lower productivity and a higher risk of variations in compacted component density, which can lead to unacceptable deformations after the sintering. In addition, to eject the compact mold component, minimize wear on the mold surface and to obtain parts that have good scratch-free surface finish, it is essential that the force required to eject the mold component is low.

Attempts have been made to solve the problems described above by adding different binding agents and lubricants to the dust composition. The purpose of the binder is to firmly and effectively bond the small size particles of additives, such as bonding components, to the surface of the base metal particles and, consequently, to reduce the problems of segregation and dust formation. The purpose of the lubricant is to reduce internal and external friction during compaction of the powder composition and above all to reduce the force required to eject the final compacted product from the mold.

Various organic binding agents have been developed, see, for example, U.S. Patent 4,483,905 (Engstrom) 1 4,676,831 (Engstrom), 4,834,800 (Semel), 5,298,055 (Semel), 5,290,336 ( Luk), 5,368,630 (Luk). U.S. Patent No. 5,480,469 (Storstrom) provides a brief review of the use of binding agents in the powder metallurgy industry.

Recently published patent WO 2005/061157 discloses a binder / lubricant combination of polyethylene wax and bistestearamide ethylene. In the composition of the powder used for compaction, polyethylene wax is present as a coating layer on iron or iron-based particles and binds the binder particles and the bis-stearamide ethylene particles to the iron particles or Iron base. It is preferred that the composition also includes a fatty acid and a flow agent. A good combination of Apparent Density, Flow, Agglutination and Lubrication properties for the metallurgical powder composition, containing a binder / lubricant combination including polyethylene wax and ethylene bisstearamide is achieved when the average molecular weight of polyethylene is between 500 and 750. It has now been found that iron-based compositions having noticeably improved apparent density and also improved flow can be obtained if fatty alcohols are used instead of polyethylene wax. It has generally been found that fatty alcohols in combination with flow agents give interesting results with respect to bulk density and flow. Bulk density is essential for tool design. A powder with low bulk density needs a higher filling height, which unnecessarily results in high pressure tools, which in turn will result in longer compaction and ejection strokes. As previously mentioned, flow is important for productivity. It has also been unexpectedly found that when the new metal powder compositions, which include fatty alcohols as a binder and a flow agent, are compacted, the obtained green compacts have excellent weight stability, i.e. a low weight dispersion within a set. of green compact. This property is of course of prime importance for the production of a high performance product.

Fatty alcohols have been mentioned in the patent literature along with lubrication in U.S. Patent No. 3,539,472. Specifically, this patent teaches that small amounts of fatty alcohols may be included in lubricants consisting mainly of amides or diamides. The patent is not concerned with bound mixtures.

Also in Japanese patent application 04-294 782, publication number 06-145701 mentions that fatty alcohols may be used as lubricants. Specifically mentioned are C30 alcohols, C50 alcohols and C60 alcohols. The application text also mentions higher fatty alcohols as binders.

Summary of the Invention

The present invention then relates to a novel metallurgical powder composition comprising an iron or iron-based powder, at least a binding agent, and a fatty alcohol as a binder. To perform satisfactorily, the fatty alcohol must be a straight or branched saturated or unsaturated, preferably saturated and straight chain, C14-C30 fatty alcohol. The new powder composition should also include a flow agent. The present invention also relates to a method of producing the above composition.

Detailed Description of the Invention

Metallurgical powder compositions contain an iron or iron-based powder in an amount of at least 80% by weight of the metallurgical powder composition. Iron-based powder can be any type of iron-based powder such as water-atomized iron powder, reduced iron powder, pre-alloyed iron powder or diffusive iron-based powder. - are. Such powders are, for example, ASC100.29 iron powder, Distaloy AB diffusion-linked iron-based powder containing Cu, Ni and Mo, Astaloy CrM and Astaloy CrL iron-based powder pre-bonded with Cr and Mo, all available from Hõganás AB, Sweden.

Iron powder or iron-based particles usually have an average particle size of up to 500 microns; more preferably the particles will have an average particle size in the range of about 25-150 microns, and more preferably 40-100 microns.

Examples of bonding elements that are bonded to the iron or iron-based particles may be selected from the group consisting of graphite, Cu, Ni, Cr, Mn, Si1 V, Mo, P1 W, S and Nb. These additives are generally powders having a particle size smaller than iron-based powder, and most bonding elements have a particle size smaller than about 20 μm. The amount of binder in the powder metallurgical compositions depends on the specific binder and the desired final properties for the sintered component. It can usually be up to 20% by weight. Other powder additives that may be present are hard phase materials, liquid phase forming materials and machining enhancing agents.

Fatty alcohols used to bond the optional binding elements and / or additives are preferably saturated, straight chain and contain from 14 to 30 carbon atoms since they have an advantageous melting point for the melt bonding technique used. to connect the connecting elements and / or other optional additives. Fatty alcohols are preferably selected from the group consisting of cetyl alcohol, stearyl alcohol, arachidyl alcohol, behenyl alcohol and lignoceryl alcohol, and more preferably selected from the group consisting of stearyl alcohol, arachidyl alcohol and beenyl alcohol. The amount of fatty alcohol used may be between 0.05 and 2, preferably between 0.1 and 1 and more preferably between 0.1 and 0.8% by weight of the metallurgical composition. Also fatty alcohol compositions may be used as binders.

To impart satisfactory flow to the new powder compositions, flow agents are added. Such agents are previously known, for example, from U.S. Patent No. 3,357,818 and U.S. Patent 5,782,954 which describe which metal, metal oxides or silicon oxide may be used as a flow agent.

Especially good results were obtained when carbon black was used as a flow agent. The use of carbon black as described in co-pending Swedish application 0401778-6 which is incorporated herein by reference. It has been found that the amount of carbon black should be between 0.001 and 0.2% by weight, preferably between 0.01 and 0.1%. Furthermore, it has been found that the primary particle size of the carbon black should preferably be below 200 nm, more preferably below 100 nm, and most preferably below 50 nm.

According to a preferred embodiment, the specific surface area should be between 150 and 1000 m2 / g as measured by the BET method.

To increase the compressibility of the powder, and to facilitate the ejection of the green component, an organic lubricant or a combination of different lubricants may be added to the metallurgical powder composition. The lubricant may be present as a free particulate powder or agglomerated to the surface of the iron-based powder.

Although fatty alcohol that is used as a binder has lubricating properties, it may be convenient to use an additional lubricant. The type of solid organic lubricant of the invention is not critical, but due to the disadvantages of metallic organic lubricants (which generate metal oxide residues during sintering), the organic lubricant preferably does not include metal. Zinc stearate is a commonly used lubricant giving good flow properties and high apparent density. However, despite generating zinc oxide residues during sintering, another disadvantage is that the material can generate stains on the surfaces of sintered components. Thus, the organic lubricant can be selected from a wide variety of organic substances that have lubricating properties. Examples of such substances are fatty acids, waxes, polymers, or derivatives and mixtures thereof. Preferred lubricants are primary amides such as stearic amide, arachidic amide and behenic amide, secondary amides such as stearyl stearic amide, and bisamides such as ethylene bisestearamide.

Regarding the amounts, it has been found that the amount of fatty alcohol should be from 10 to 90% by weight of the weights of the combined binder, flow agent and lubricant. The total amount of binder, flow agent and optionally lubricant may range from 0.1 to 2% by weight of the metallurgical powder composition.

Brief Description of Drawing

Figure 1 is a diagram showing the difference in weight dispersion at different production rates when using a metallurgical powder composition according to the invention compared to conventional metallurgical powder compositions.

The invention is further illustrated by the following non-limiting examples.

Example 1

Different metallurgical mixtures of iron-based powders were prepared according to table 1. As iron-based powder, water-atomized iron powder ASC100.29 available from Hóganàs AB, Sweden was used. Except for binders, lubricants and flow agents as per Table 1, 2% by weight of the total iron-based copper powder blend, mesh 100, available from Makin Metal Powder Ltd., and -0, 8% by weight of the total graphite iron blend, UF 4 (available from Graphit Kropfmühl AG, Germany).

Ethylene bisestearamide (EBS) was made available as Licowax® by Clariant (Germany) and silicon dioxide was made available as Aerosil by Degussa AG (Germany). Behenyl alcohol, stearyl alcohol and cetyl alcohol were available from Sasol Germany GmbH and carbon black were available from Degussa AG.

In the AC & HI blends, 0.6% by weight of the total iron-based powder blend of a lubricant (called "C18-22 primary amide" below) consisting essentially of straight-chain saturated primary amides of technical grade was used. having chain lengths of 18, 20 and 22 carbon atoms, thus containing stearic amide (about 40%), arachidic amide (about 40%), and behenic amide (about 20%). As a lubricant in the D-F mixture, 0.6% ethylene bisestearamide (EBS) and 0.8% ethylene bisestearamide (EBS) were used. In mixtures AE & H-J, 0.2 wt% of the total fatty alcohol iron-based powder mixture was used (in H a mixture of two fatty alcohols was used), and in the mixture F, 0.2% by weight of the total iron powder mixture of a polyethylene wax having a molecular weight of 655 (a binder according to WO 2005/061157) was used.

The components in mixtures A-F & H-J were vigorously mixed, and during mixing the temperature was increased to above the melting point of the binder, for mixtures A-E & H-J to 75 ° C and for mixture F to 105 ° C. During subsequent cooling, the finer particles of the mixture were bonded to the surface of the larger iron-based powder particles by the solidifying binder. In case a fluxing agent was added, it was added after solidification of the binder during the cooling of the mixture. The mixture components G were mixed without any heating as this mixture was not agglutinated. Table 1. Prepared mixtures of ferrous metallurgical powder.

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Hall flow rate was measured according to ISO 4490 and bulk density was measured according to ISO 3923. Table 2. Flow rate and bulk density of iron-based metallurgical powder mixtures

<table> table see original document page 10 </column> </row> <table>

Table 2 shows that despite good flow rates, a substantial increase in bulk density is obtained when using iron-based powder compositions according to the invention.

For mixtures C, D, G, Η, I and J the lubricating properties were also measured by recording the total energy per developed area required to eject a compacted sample from the mold as well as the peak ejection force per involved area. . The components were ring shaped with an outside diameter of 55mm, an inside diameter of 45mm and a height of 15mm, and the applied compaction pressures were 400, 500, 600 and 800 MPa. Table 3. Peak ejection force and ejection energy

<table> table see original document page 11 </column> </row> <table>

Table 3 shows that when using a composition containing cetyl alcohol (16 C) or beenyl alcohol (22 C), or a mixture of stearyl alcohol (18 C) and beenyl alcohol, and the amide mixture (primary fatty amides) As a lubricant / binder combination for producing a compacted component, the total energy required to eject the component is substantially reduced.

Example 2

Weight stability, that is, weight diffusion between components during a production run, was also recorded when producing components for mixtures C, F and G. Ring-shaped components having an outer diameter of 25 mm, an inside diameter of 19 mm, and a height of 15 mm were compacted in a continuous production run at 600 MPa compaction pressure, and at three different compaction rates (10, 15, and 20 strokes per minute). 250 components were produced from each mix and at each production rate. (For mix G rates greater than 10 strokes / minute were not achievable due to incomplete tool filling).

Figure 1 shows the weight stability obtained at each compaction rate for mixtures C, F and G expressed as standard deviation for component weights. As can be seen from Figure 1, a substantial improvement in weight stability is achieved when producing components from the mixture according to the invention (mixture C) compared to components produced from a mixture according to WO 2005/061157 ( mixture F) and compared to the components produced from a non-agglutinated premix containing the commonly used ethylene bisestearamide lubricant (mixture G). This is especially pronounced at higher compression ratios.

Claims (12)

1. A metallurgical powder composition for the production of compacted parts, comprising: (a) at least about 80 weight percent of an iron or iron-based powder; (b) up to about 20 weight percent of at least one binding powder; (c) from about 0.05 to about 2 weight percent of a binder comprising a C14-C30 straight or branched saturated or unsaturated fatty alcohol; and (d) from about 0.001 to about 0.2 weight percent of a fluxing agent. A powder composition according to claim 1, wherein the fatty alcohol is saturated and straight chain. A powder composition according to claim 1, wherein the fatty alcohol is selected from the group consisting of cetyl alcohol, stearyl alcohol, arachidyl alcohol, beenyl alcohol and lignoceryl alcohol. A powder composition according to claim 1, wherein the fatty alcohol is selected from the group consisting of stearyl alcohol, arachidyl alcohol and beenyl alcohol. A powder composition according to claim 1, wherein the flow agent is selected from the group consisting of carbon black and silicon dioxide. A powder composition according to claim 1, wherein the fluxing agent is carbon black. A powder composition according to claim 6, wherein the particle size of the carbon black is preferably below -200 nm, more preferably below 100 nm, and most preferably below 50 nm. A powder composition according to claim 1, further comprising an organic, powder-free, metal-free lubricant. A powder composition according to claim 8 in which 10. that the powder-free, metal-free organic lubricant is selected from the group consisting of stearic amide, arachidic amide, benthic amide, stearyl stearic amide and ethylene bisestearamide. A powder composition according to claim 8, wherein the organic, powder-free and metal-free lubricant is beenamide. 12. A method of producing a metallurgical powder composition for producing compacted parts, comprising: providing the following components: at least 80% by weight of an iron or iron-based powder, up to 20% by weight from at least one binder powder, from 0.05 to 2% by weight of a bonding agent comprising a C1-4 C10 fatty alcohol and from 0.001 to 0.2% by weight of a flow agent; mixing the above components at a temperature above the melting point of the binder; and cooling the mixture.