MXPA00002178A - Lubricant for metallurgical powder composition - Google Patents

Abstract

This invention relates to a lubricant for metallurgical powder compositions. According to the invention the lubricant contains a polyolefine-based polymer, which has a weight-average molecular weight Mw of 500-10000. The invention further concerns a metal-powder composition containing the lubricant, method for making sintered products by using the lubricant, and use of the same in cold and warm compaction.

Description

LUBRICANT FOR METALLURGICAL POWDER COMPOSITION DESCRIPTIVE MEMORY This invention relates to a lubricant for powder metallurgical compositions, as well as to a metal powder composition containing the lubricant. In addition, the invention relates to a method for making products specified through the use of the lubricant, as well as the use of the lubricant in a metallic powder composition in compaction. More specifically, the invention relates to lubricants which upon pressing result in products having high resistance to transverse rupture. The lubricant according to the invention also has the advantage that it can be used for hot and cold compaction. In the industry, the use of metal products made by compaction and concretion of metallic powder compositions is increasing its extension. Various different products are being produced that vary in shape and thickness, and the quality requirements placed on these products are that the fabricated metal products have high density as well as high strength. In the compaction of metal, different standard temperature scales are used. Therefore, cold pressure is predominantly used to compact metal powder (the powder has room temperature). Cold pressure and hot pressure require the use of a lubricant. Compaction at temperatures above room temperature has obvious advantages, which results in a product of higher density and higher strength than compaction at lower temperatures. Most of the lubricants used in cold compaction can not be used in high temperature compaction, since they appear to be effective only within a limited temperature range. A less effective lubricant increases the wear of the compaction tool. The wear of the tool is influenced by various factors, such as the hardness of the tool material, the applied pressure and the friction between the compacted metal powder and the tool wall when the powder is compacted and ejected. The last factor is closely related to the lubricant used. The force of expulsion is the force necessary to expel the compacted metallic powder from the tool. Since a high ejection force not only increases the wear of the compaction tool, but also can damage the compacted metal powder, this force of preference must be reduced.

However, the use of a lubricant can cause problems in the compaction, and therefore it is important that the lubricant is well suited to the type of compaction carried out. In order to achieve satisfactory performance, the lubricant must be forcefully expelled from the porous structure of the powder composition in the compaction operation, and must be introduced into the interspace between the compacted metal powder and the tool, thereby lubricating the walls of the compaction tool. By means of said lubrication of the walls of the compaction tool, the ejection force is reduced. Another reason why the lubricant has to emerge from the compacted metallic powder is that otherwise it would create pores in said compacted powder after concreting. It is well known that large pores have an adverse effect on the dynamic resistance properties of the product. An object of the new lubricant according to the present invention is to make possible the production of compaction products having a high transverse rupture strength, high raw material density, as well as concreted products having a high concretion density and strength. lower expulsion from the lubricant in combination with metal powders. Since the compacted metallic powder is subject to considerable stresses when ejected from the compaction tool and since the product must be kept together during handling between compaction and concretion without breaking or, in some other way, to be damaged, it is important with the high resistance to the transverse rupture. This is important especially in the case of thin parts. The lubricant according to the invention contains a polyol-olefin-based polymer, having an average molecular weight MW of 500-10 000. Polyolefins are a group of thermoplastic polymers with different degrees of crystallinity. The polyolefins are subdivided into simple polyolefins, poly (α-olefins) and copolymers based on olefins and / or α-olefins. The copolymers can also include other types of comonomers, such as vinylacetates, acrylates, styrenes, etc. Poly (α-olefins) include polymers, such as polypropylene and poly (1-butene). However, simple polyolefins include polymers such as branched chain low density polyethylene and linear chain high density polyethylene. Linear chain polyethylenes of relatively low molecular weight are referred to as polyethylene waxes. The polymer according to the invention is preferably a polyethylene wax. The lubricant according to the invention can be used in hot and cold compaction, but in hot contacting, the weight average molecular weight (weight) of the lubricant is preferably 1000-10 000. Preferably, the lubricant of The invention has a polydispersity multiplied PM of less than 2.5, preferably less than 1.5.

In addition, the invention relates to a metal powder composition containing a metal powder and the aforementioned lubricant, as well as to the methods for making particular products, cold and hot compaction. The method for cold compaction according to the invention includes the steps of: a) mixing a metal powder and a lubricant with a metal powder composition. b) compacting the metal powder composition with a compacted body, and c) concreting the compacted body, making use of a lubricant according to the invention, which has a weight-average molecular weight (MWO) of 500-10,000. for the hot compaction according to the invention includes the steps of: a) mixing a metal powder and a lubricant with a metal powder composition, b) preheating the metal powder composition to a certain temperature, c) compacting the composition of metallic powder that was heated in a hot tool, and d) concreting the compacted metallic powder composition by using a lubricant according to the invention, having a weight-average molecular weight (MWO) of 1000-10,000.

The present invention also relates to the use of the lubricant according to the invention in a powder metallurgical composition in cold and hot compaction. The lubricant may constitute 0.1-2.0% by weight of the metal powder composition according to the invention, preferably 0.2-0.8% by weight, based on the total amount of the metal powder composition. The possibility of using the lubricant according to the present invention in low amounts is a particularly convenient characteristic of the invention, since it allows the compacted metallic powder and the concreted products having high densities to be obtained economically. As used in the description and appended claims, the term "metallic powder" encompasses iron-based powders essentially composed of iron powders containing not more than about 1.0% by weight, preferably not more than 0.5% by weight. approximately, of normal impurities. Examples of such highly compressible metallurgical grade iron powders are the ANCORSTEEL 1000 series of pure iron powders, eg, 1000, 10000B and 1000C, available from Hoeganaes Corporation, Riverton, New Jersey and similar powders available from Hóganás AB, Sweden. . For example, the ANCORSTEEL 1000 iron powder has a typical sieve profile of approximately 22% by weight of the particles below a No. 325 sieve (USA series) and about 10% by weight of the particles greater than a sieve. 100 with the remainder between these two sizes (trace quantities greater than No. 60 sieve). ACORSTEEL 1000 powder has an apparent density of 2.85-3.00 g / cm3, approximately, almost always 2.94 g / cm3. Other iron powders that may also be employed in the invention are typical iron sponge powders, such as an ANCOR MH-100 powder from Hoeganaes. The iron-based powders can also include iron, preferably substantially pure iron, which has been prealloyed, bound by diffusion or mixed with one or more other alloying elements. Examples of alloying elements that can be combined with iron particles include, but are not limited to, molybdenum, manganese, magnesium, chromium, silicon, copper, nickel, gold, vanadium, columbium (niobium), graphite, phosphorus, aluminum; binary alloys of copper and tin or phosphorus; ferroalloys of manganese, chromium, boron, phosphorus or silicon; ternary and quaternary eutectics with a low melting point of carbon and two or three of iron, vanadium, manganese, chromium and molybdenum; tungsten or silicon carbides; silicon nitride; aluminum oxide; and manganese or molybdenum sulfides, and combinations thereof. Almost always, the alloying elements are generally combined with the iron powder, preferably the substantially pure iron powder in an amount of up to about 7% by weight, more preferably from about 0.25% to about 5% by weight, more preferably from about 0.25% to about 4% by weight, although in certain specialized uses the alloying elements may be present in an amount of about 7% to about 15% by weight, of the iron powder and the alloying element. Therefore, the iron-based powders may include iron particles that are in admixture with the alloying elements that are in the form of alloying powders. The term "alloy powder" according to the present invention refers to any element or compound in particles, as already mentioned, physically mixed with the iron particles, whether that element or compound finally forms an alloy with the iron powder . In general, the particles of the alloying element have a weight average particle size of less than about 100 microns, preferably below about 75 microns, more preferably below about 30 microns. The binding agents are preferably included in the mixtures of iron particles and alloying powders to avoid the formation of fine dust and the segregation of the alloying powder from the iron powder. Examples of binding agents that are commonly employed include those described in the U.S. Patents. Nos. 4,483,905 and 4,676,631, for Engstrom, and the US patent. No. 4 834 800 for Semel, which are incorporated herein by reference in their entirety. In addition, the iron-based powder may be in the form of iron that has been previously allied with one or more of the alloying elements. The prealloyed powders can be prepared by making a molten iron material and the desired alloying elements, and then by atomizing the molten material, whereby the atomized droplets form the powder upon solidification. The amount of the incorporated alloying element or elements depends on the desired properties in the final metal part. The prealloyed iron powders incorporating said alloying elements are available from Hoeganaes Corp., as part of its ANCORSTEEL powder line. Another example of iron-based powders is the diffusion-bonded iron-based powder, which contains substantially pure iron particles having the aforementioned alloying elements agglutinated by diffusion to their outer surfaces. Such commercially available powders include the DISTALOY 4600A diffusion bound pellet available from Hoeganaes Corporation, which contains about 1.8% nickel, about 0.55% molybdenum and about 1.6% copper, and the DISTALOY 4800A diffusion bound pellet available from Hoeganaes Corporation, which contains approximately 4.05% nickel, around 0.55% molybdenum and about 1.6% copper. Powders of similar grade are also available from Hóganás AS, Sweden. A preferred iron-based powder is made of prealloyed iron with molybdenum (Mo). The powder is produced by atomising a pure iron melt material substantially containing from about 0.5% to about 2.5% by weight of Mo. An example of that powder is the ANCOSTELE 85HP steel powder from Hoeganaes, which contains about It is 0.85% by weight of Mo, less than about 0.4% by weight, in total, of other materials, such as manganese, chromium, silicon, copper, nickel, molybdenum or aluminum, and less than 0.02% by weight of carbon, approximately. Another example of such powder is the ANCORSTEEL 4600V steel powder from Hoeganaes, which contains about 0.5-0.6% by weight of molybdenum, about 1.5-2.0% by weight of nickel and 0.1-0.25% by weight of manganese approximately, and less than about 0.02% by weight of carbon. Another prealloyed iron-based powder that can be employed in the invention is described in the US patent. No. 5 108 93 for Causton, entitled "Steel Powder Admixture Having Distinct Pre-alloyed Powder of Iron Alloys," which is hereby incorporated by reference in its entirety. This composition of steel powder is a mixture of two different prealloyed iron-based powders, one of them is a pre-alloy of iron with 0.5-2.5% by weight of molybdenum, and the other is a pre-alloy of iron with carbon and with around of at least 25% by weight 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 mixture is in proportions that provide at least about 0.05% by weight of the transition element component to the steel powder composition. An example of such a powder is commercially available as ANCORSTEEL 41 AB steel powder from Hoeganaes, which contains about 0.85% by weight of molybdenum, to about 1% by weight of nickel, about 0.9% by weight of manganese, about 0.75% by weight of chromium, and about 0.5% by weight of carbon. Other iron-based powders that are useful in the practice of the invention are ferromagnetic powders. An example is a substantially pure iron powder composition in admixture with iron powder that has been prealloyed with small amounts of phosphorus. Even other iron-based powders that are useful in the practice of the invention are iron particles coated with a thermoplastic material to provide a substantially uniform coating of the thermoplastic material, as described in US Pat. No. 5,198,137 to Rutz et.al, which is incorporated herein by reference in its entirety. Preferably, each particle has a substantially uniform circumferential coating around the iron core particle. Sufficient thermoplastic material issued to provide a coating of approximately 0.001-15% by weight of the iron particles when coated. In general, the thermoplastic material is present in an amount of at least 0.2% by weight, preferably around 0.4-2% by weight, and more preferably around 0.6-0.9% by weight of the coated particles. Preferred thermoplastics are, for example, polyethersulfones, polyetherimides, polycarbonates or polyphenylene ethers, which have a weight average molecular weight ranging from about 10,000 to 50,000. Other polymer-coated iron-based powders include those containing a coating interior of iron phosphate as mentioned in the US patent No. 5,063,011 to Rutz et.al, which is incorporated herein in its entirety. The particles of pure iron, prealloyed iron, diffusion bonded iron or thermoplastic coated iron can have a weight average particle size of only 1 μm or less, or up to about 850-1000 μm, but in general the particles will have a size of average particle in weight ranging from 10-500 μm approximately. Those having an average particle size of maximum number up to 350 μm are preferred. approximately, preferably 50-150 μm. In addition to the metal powder and the lubricant according to the invention, the metal powder composition may contain one or more additives selected from the group consisting of binders., processing aids and hard phases. The binder can be added to the powder composition in accordance with the method described in US-P-4 834 800 (which is incorporated herein by reference), and can be mixed in metal powder compositions in amounts of about 0.005-3% by weight , preferably about 0.05-1.5% by weight, and more preferably about 0.1-1% by weight, based on the weight of the iron and alloy powders. The processing aids employed in the metal powder composition may consist of talc, forsterite, manganese sulfide, sulfur, molybdenum disulfide, boron nitride, tellurium, selenium, barium difluoride and calcium difluoride, which are used separately or in combination.

The hard phases employed in the metal powder composition may consist of tungsten, vanadium, titanium, niobium, chromium, molybdenum, tantalum, and zirconium carbides, aluminum nitrides, titanium, vanadium, molybdenum and chromium, Al203, B4C, and various Ceramic materials. With the aid of conventional techniques, the metal powder and the lubricant particles are mixed to obtain a substantially homogeneous powder composition. Preferably, the lubricant according to the invention is added to the metallic powder composition in the form of solid particles. The average particle size of the lubricant may vary, but is preferably in the 3-150 μm range. If the particle size is very large, it becomes difficult for the lubricant to leave the porous structure of the metallic powder composition during compaction, and the lubricant can then give rise to large pores after concretion, resulting in a powder compacted metallic that presents deteriorated resistance properties. In cold compaction according to the invention, the steps are the following: a) mixing a metal powder and a lubricant according to the invention, containing a polyolefin-based polymer, having a weight-average molecular weight ( PMpeSo) of 500-10,000 to obtain a metallic powder composition, b) compact the metallic powder composition to obtain a compacted body, and c) concretize the compacted body. In cold compaction according to the invention, it is preferable to heat the compacted body before step c) to a temperature above the melting point peak of the lubricant for a sufficient period to obtain the same temperature in essence throughout the body compacted With this treatment, the compacted body, still unscrambled, has a high resistance to transverse rupture, which facilitates the handling and processing of the compacted body between compaction and concretion without breaking or otherwise damaging. As will be apparent from the following tests, these improved transverse rupture resistances are not achieved with the use of examples of lubricants available in the market for cold compaction, which makes the lubricant in accordance with the invention special. In hot compaction according to the invention, the metal powder composition is preheated conveniently before being supplied to the preheated compaction tool. In such preheating of the metal powder composition, it is important that the lubricant does not begin to soften or melt, which would make the powder composition difficult to handle when filling the compaction tool, which in turn results in a compacted body that it does not have a uniform density and that it has a poor reproduction capacity of weights a ^ .li? - ^ f. ^. ^. ñ tfH_ B ^ áblUS **. ^ "of the part. In addition, it is important that partial lubrication does not occur, that is, the lubricant must be a uniform product. Therefore, it is important that the polydispersity PMpeSo / PMnumber is less than 2.5, and preferably less than 1.5. The steps of the hot compaction process are the following: a) mixing a metal powder and a lubricant according to the invention, which contains a polymer based on polyolefin with a weight-average molecular weight (PMpeSo) of 1000-10 000; b) preheating the mixture to a predetermined temperature, preferably at a temperature below the peak melting point of the lubricant; c) transferring the hot powder composition to a die, which is heated to a temperature, preferably a melting point peak temperature of the lubricant or below; and compact the composition; and d) concreting the compacted metal powder composition. In step b) of the method, the metal powder composition is preferably preheated to a temperature of 5-50 ° C below the melting point of the polymer. Next, some tests will be explained to illustrate that the invention is effective and gives rise to products of high raw material density, as well as high resistance to transverse breaking. sat ^ ü PROOF 1 The following table 1 mentions several lubricants, indicating the peak melting point, the weight average molecular weight (MWO). the polydispersity (PMPeso PMnúmero). the density of measured raw material (DMC) and the ejection force (F. Ex.) in the cold compaction of ASC 100.29 (marketed by Hóganás AB) mixed with 0.5% by weight of graphite, 2% by weight of Cu- 200 and 0.6% by weight of lubricant. The compaction pressure was 600 Mpa.

TABLE 1 Lubricants in cold compaction outside the scope of the invention PEW 3700 is a polyethylene wax within the scope of the invention. PEW 2000 is a polyethylene wax within the scope of the invention. Wax-EBS is an ethylene-bis-stearamide wax.

The raw material density was measured in accordance with ISO 3927 1985, and the ejection force was measured in accordance with the Honogan Method 404. The melting point peaks for the lubricants are indicated as the peak values of the point curve of fusion, which was measured with the help of the Differential Scanning Calorimetry (DSC) technique in a DSC Model 912S instrument available from TA Instrumets, New Castle, DE 197 201 E.U.A. As shown in Table 1, similar raw material densities can be obtained, and the same low ejection force remains with the lubricant having lower MW / PM number (PEW2000) according to the invention, as with EBS-wax.

PROOF 2 The following table 2 mentions a comparison of lubricant PEW 2000 and wax-EBS, which is related to the heating of the compacted body before concretion, so that the compacted body is heated to a temperature higher than the peak melting point of the lubricant for a sufficient period to obtain in essence the same temperature throughout the compacted body. The metal powder compositions contained the following ingredients.

Composition 1 (invention) ASC 100.29, marketed by Hóganás AB 2.0% by weight of Cu-200 0.5% by weight of graphite 0.6% of PEW 2000 Composition 2 (wax-EBS) ASC 100.29, marketed by Hóganás AB 2.0% by weight of Cu-2000 0.5% by weight of graphite 0.8% of wax-EBS TABLE 2 Compacted bodies treated with heat before concretion * 1) Treated with heat at a temperature of 150 ° C for 60 minutes. * 1) Treated with heat at a temperature of 150 ° C for 60 minutes.

As it appears in table 2, the resistance to the transverse rupture (RRT) is considerably improved by the treatment by heating the compacted body of raw material of composition 1, while the resistance to transverse rupture of the compacted body of material Crude in composition 2 is not significantly improved by the heating treatment. The improved transverse rupture resistance provides a compacted body of raw material, which can be handled and processed before concretion. This possibility is the most desirable in many areas.

PROOF 3 The following table 3 shows several lubricants, indicating the peak melting point, the weight average molecular weight (MW weight). polydispersity PMpeso / PMnumber. the pressure of compaction (Pres. of Comp.), the density of measured raw material (DMC) and the ejection energy (in. Ex.) in cold compaction of ASC 100.29 (marketed by Hóganás AB) mixed with 0.45% in lubricant weight and 0.15% methacrylate binder.

TABLE 3 Lubricants in bonded metal composition in cold compaction * outside the scope of the invention.

PEW 655, PEW 1000, PEW 2000 and PEW 3000 are lubricants according to the invention and are polyethylene waxes. As shown in Table 3, the ejection energies are lower for the lubricants according to the invention than for the lubricant which is outside the scope of the invention.

PROOF 4 Table 4 below mentions several lubricants, indicating the melting point peak, the powder temperature, the tool temperature and the raw material density (DMC), and the ejection force (F. Ex.). The metallic powder compositions contained the following ingredients: Distaloy® AE, marketed by Hóganás AB 10 0.3% by weight of graphite 0.6% by weight of lubricant according to Table 4. The compaction pressure was 600 MPa.

TABLE 4 15 Lubricants in hot compaction i-ifttt-.fcd-iM- 7 £ £ j * í ^^ J ¡ÉK ^^^ g2 * Lubricant X1 is a lubricant in accordance with PCT / E95 / 00636, which essentially consists of an amide-type oligomer with a weight average molecular weight (PMpeSo). of 18,000. As shown in Table 4, the density of raw material (DMC) is slightly higher with the lubricant according to the invention. The ejection force is greater with the lubricant according to the invention, but it is still low enough to be acceptable. In comparison with the material containing wax-EBS or lubricant X1, the materials mixed with lubricants according to the invention give a comparable raw material density (DMC) and ejection forces (F. Ex). When a cold compacted body where the material was mixed with lubricants according to the invention is treated by heating before concretion, it obtains an improved raw material strength compared to a material mixed with EBS-wax. The improved raw material strength makes it possible to process and handle the compacted body prior to concretion without breaking or otherwise damaging.

Claims (18)

NOVELTY OF THE INVENTION CLAIMS

1. - A lubricant for the compaction of powder metallurgical compositions, further characterized in that it contains a polyolefin-based polymer, having a weight average molecular weight PMpeSo of 500-10,000.

2. A lubricant according to claim 1, further characterized in that the polymer is a polyethylene wax.

3. A lubricant according to claim 1 or 2, further characterized in that it has a weight-average molecular weight (MW weight) of 1000-10,000.

4. A lubricant according to any of claims 1-3, characterized also because it has a polydispersity PMweight / PM number less than 2.5, preferably less than 1.5.

5. A metal powder composition for compaction containing metal powder and a lubricant, further characterized in that the lubricant contains a polyolefin-based polymer having a weight-average molecular weight (MWO) of 500-10,000, preferably 1000 -10 000.

6. - A metallic powder composition according to claim 5, further characterized in that the polymer is a polyethylene wax.

7. A metallic powder composition according to any of claims 5 to 6, further characterized in that it has a polydispersity PMweight PM less than 2.5, preferably lower 1.5.

8. A metallic powder composition according to any of claims 5 to 7, further characterized in that it contains one or more additives selected from the group consisting of binders, processing aids, alloying elements and hard phases.

9. A metallic powder composition according to any of claims 5 to 7, further characterized in that it contains a binder and one or more additives selected from the group consisting of processing aids, alloying elements and hard phases.

10. A metallic powder composition according to any of claims 5 to 9, further characterized in that it comprises a greater amount of a metal powder consisting of iron-based powder, which has a weight average particle size that goes about 25-350 μm, and a minor amount of a solid lubricant comprising a polyolefin-based polymer, having a weight-average molecular weight (MWO) of 500-10,000. .. ",, _. __ ". ,, .., _ ^« ^. Ste ^ si »» * ^^ ...

11. - A metallic powder composition according to claim 10, further characterized in that the lubricant constitutes 0.1-2.0% by weight of the total composition, preferably 0.2-0.8% by weight.

12. A method to produce specific products, which includes the steps of: a) mixing a metal powder and a lubricant to obtain a metallic powder composition, b) compacting the metallic powder composition to obtain a compacted body, and c) concreting the compacted body; further characterized in that the lubricant contains a polyolefin-based polymer, having a weight-average molecular weight (PMPeso) of 500-10,000.

13. A method according to claim 12, further characterized in that the body is compacted before passage. c) is heated to a temperature above the melting point peak of the lubricant for a period sufficient to obtain essentially the same temperature throughout the compacted body.

14. A method for making specific products, including the steps of: a) mixing a metal powder and a lubricant to obtain a metallic powder composition, b) preheating the metal powder composition to a predetermined temperature, c) compacting the hot metal powder composition in a hot tool, and d) concreting the compacted metal powder composition; further characterized in that the lubricant contains a polyolefin-based polymer, having a weight-average molecular weight (MWO) of 1000-10,000.

15. - A method according to claim 14, further characterized in that the metal powder composition in step b) is preheated to a temperature below the melting point peak of the polyolefin, preferably at a temperature of 5-50 °. C below the melting point peak of the lubricant.

16. A method according to claim 14 or 15, further characterized in that the tool before step c) is heated to a temperature of the melting point peak of the polyolefin or below, preferably at a temperature of 50 ° C below the melting point peak of the lubricant.

17. The use of a lubricant, which contains a polyolefin-based polymer, having a weight-average molecular weight (MW weight) of 500-10,000, in a powder metallurgical composition in cold compaction.

18. The use of a lubricant, containing a polyolefin-based polymer, having a weight-average molecular weight (MW weight) of 1000-10 000, in a powder metallurgical composition in hot compaction. "- - - ao ^ - ^ - J ^« aa-a ^ a = aAJ. ~ ».. t ^. - ^ ,, -._ ,. - ....