ZA200307072B

ZA200307072B - Iron powder composition including an amide type lubricant and a method to prepare it.

Info

Publication number: ZA200307072B
Application number: ZA200307072A
Authority: ZA
Inventors: Hilmar Vidarsson; Per Knutsson
Original assignee: Hoeganaes Ab
Priority date: 2001-04-17
Filing date: 2003-09-10
Publication date: 2004-09-10
Also published as: KR20030085110A; CA2443481A1; CA2443481C; TWI247041B; EP1390171B1; CN1265920C; RU2288072C2; JP2004524449A; BR0208914B1; PL198679B1; DE60201903D1; RU2003133290A; ATE281899T1; AU2002253770B2; EP1390171A1; US20030029272A1; DE60201903T2; BR0208914A; PL366558A1; CN1503706A

Abstract

A powder composition for warm compaction comprising an iron-based powder and a lubricant powder consisting essentially of an amide described by the following formula D-Cm-B-A-B-Cm-D wherein D is -H, COR, CNHR, wherein R is a straight or branched aliphatic or aromatic group including 2-21 C atoms; C is the group -NH(CH)nCO-; B is amino or carbonyl; A is alkylene having 4-16 C atoms optionally including up to 4 O atoms m is an integer 1-10 and n is an integer 5-11.

Description

ron powder composition including an amide typ lubricant and a method to prepare it. & ) FIELD OF THE INVENTION ’ The present invention relates to metal powder compositions. Particularly the invention relates to iron- based compositions suitable for compaction at elevated temperatures.

BACKGROUND OF THE INVENTION

The powder metallurgy art generally uses different standard temperature regimes for the compaction of a metal powder to form a metal component. These include chill-pressing (pressing below ambient temperatures), cold-pressing (pressing at ambient temperatures), hot- pressing (pressing at temperatures above those at which the metal powder is capable of retaining work-hardening), and warm-pressing (pressing at temperatures between cold- pressing and hot-pressing).

Distinct advantages arise by pressing at tempera- tures above ambient temperature. The tensile strength and work hardening rate of most metals is reduced with in- creasing temperatures, and improved density and strength can be attained at lower compaction pressures. The ex- tremely elevated temperatures of hot-pressing, however, introduce processing problems and accelerate wear of the dies. Therefore, current efforts are being directed to- ‘ 25 wards the development of metal compositions suitable for % warm-pressing processes. : « The US patent 4,955,789 (Musella) describes warm compaction in general. According to this patent, lubri- cants generally used for cold compaction, e.g. zinc ste- arate, can be used for warm compaction as well. In prac-

tice, however, it has proved impossible to use zinc ste- arate or ethylene bisstearamide (commercially available - as ACRAWAX®.), which at present are the lubricants most

N frequently used for cold compaction, for warm compaction.

The problems, which arise, are due to difficulties in filling the die in a satisfactory manner.

The US patents 5,744,433 (Storstrom et al) and 5,154,881 (Rutz) disclose metal powder compositions in- cluding amide lubricants, which are especially developed for warm compaction.

The lubricant according to the US patent 5,744,433 contains an oligomer of amide type, which has a weight- average molecular weight M, of 30,000 at the most. Very high densities and green strengths may be obtained by warm compacting powder compositions when the lubricant has a molecular weight above 4000, the preferred lubri- cant molecule having a molecular weight of about 6500.

It has however been found that this lubricant has a ten- dency of sticking to the die wall, which requires fre- quent cleaning of the die. Another disadvantage is that the obtained green bodies are stained.

In the US. Patent 5,154,881 the amide lubricant con- sists of the reaction product of a monocarboxylic acid, a dicarboxylic acid and a diamine. The only lubricant tested according to this patent is ADVAWAX® 450, the com- position of which is not described in detail but the re- action product obtained includes i.a. ethylene bissteara- ’ mide according to Chemis-CIVS. Our experience of this v product is that it is difficult to obtain a constant com- “ 30 position and quality, which in turn may result in compo- nents of varying quality. This may cause problems when the lubricant is used in large scale industrial produc- tion.

OBJECTS OF THE INVENTION

An object of the present invention is to reduce or , eliminate current problems associated with large scale production.

A second object is to provide a new type of lubri- cant useful in metal compositions intended for compaction at elevated temperatures.

A third object is to provide a metal powder for pro- ducing components without stains.

A fourth object is to provide a metal composition including lubricant, which during the compaction of the metal powder does not deposit on the die wall.

SUMMARY OF THE INVENTION :

These objects are achieved by using a powder composition comprising an iron-based powder and new oli- gomer amide type lubricant. The composition may also in- clude one or more additives, such as binders, flow agents, processing aids and hard phases.

The warm compaction may be performed by mixing an iron-based powder with the oligomer amide type lubricant and optionally a binder, preheating the powder composition and compacting the metal-powder composition in a pre-heated tool.

DETAILED DESCRIPTION OF THE INVENTION

J The new amide type lubricant used according to the : present invention may be represented by the following ¢ 30 formula

D-Cna-B-A-B-Cyp-D wherein

D is -H, COR, CNHR, wherein R is a straight or branched ) aliphatic or aromatic group including 2-21 C atoms \ C is the group -NH (CH), CO-

B is amino or carbonyl

A is alkylen having 4-16 C atoms optionally including up to 4 O atoms ma is an integer 1-10 mb is an integer 1-10 n is an integer 5-11.

It is preferred that D is COR, wherein R is an ali- phatic group 16 - 20 C atoms, C is -NH (CH), CO- wherein n is 5 or 11; B is amino; A is alkylen having 6-14 C atoms optionally including up to 3 O atoms, and ma and mb which may be the same or different, is an integer 2-5.

Examples of preferred lubricants to be used in the iron based compositions according to the present inven- tion are:

CH3 (CHp) 1 gCO-[HN (CH) 11CO] -HN (CH) 1 oNH-[OC (CHy) 1 1NH]5 -

OC (CH) 16CH3

CH (CH) 14CO-[HN (CHy) 11CO]5-HN (CHy) 1 oNH-[OC (CHp) 1 1NH]3 -

OC (CHy) 1 gCH3

CHj (CHp) 1gCO-[HN (CHp) 11CO]3-HN (CH) 1 5NH-[OC (CHp) 1 1NH]3 -

OC (CHjy) 16CH3 * CH; (CHpy) 1 gCO-[HN (CH) 11COJ3 -HN (CHy) 1 oNH-[OC (CHp) 1 1NH]4 - . OC (CHy) 1 gCH3

CH; (CHp) 1 6CO-[HN (CH) 11COJ4 -HN (CHy) 1 oNH-[OC (CHp) 11 NH], -

OC(CHj)1gCH3

CH3 (CHp) 1 gCO-[HN (CHp) 11COJ4 -HN (CHy ) 1 oNH-[OC (CH5) 11 NH] - ” OC (CH) 16CH3

CH; (CHp) 16CO-[HN (CHy) 11C0]g-BN (CHy) 12NH-[OC (CHp) 11NH]g-

OC (CHy) 1 ¢CH3 5 Other examples are

CH;) CO-HN(CH,) sCO-HN (CH) ,NH-OC (CH;) sNH-OC (CH;) having the

MW 370.49;

CH; (CH,) ,0CO-HN (CH;) 1; CO-HN (CH;) 1,NH-OC (CH) 11NH-0OC (CH, ) 20,CHs having the MW 1240.10

CH; (CHz) 20CO- [HN (CHz) 1:COJ] 10-HN (CH;) 12NH- [OC (CH2) 11NH] 10-

OC (CH3) 2oCH; having the MW 8738.04

CH; (CH2) 4CO- [HN (CH) ;3CO] 3-HN (CH;) 1,NH- [OC (CH) 11NH] 3-

OC (CH; ) 4CH3 having the MW 1580.53 : 15 CH; (CH,) 4CO- [HN (CH;) sCOJ ,-HN (CH) ¢NH- [OC (CH,) sNH] ;,~0OC (CH;) 4CH; having the MW 1980.86

CH; (CHz) 20CO~ [HN (CH,) 5sCO] 7-HN (CH3) ¢NH- [OC (CH,) sNH] 7-

OC (CH, ) 20CH3 having the MW 2429.69 and

CH; (CH) 16NH- [OC (CHz) 11NH] 4 - CO (CH) 10CO- [HN (CH) 1:COJ 4 -

HN (CH,) 16CH3 having the MW 2283.73

The chemical differences between the new lubricant and the lubricant described in the US patent 5,744,433 are that the new molecule has a central diamine or diacid ‘ moiety and identical terminal groups on both ends. The chemical difference between the new lubricant and the lu- * 30 bricant described in the US patent 5,154,881 is that the new lubricant molecule includes the unit -NH{CH), CO-.

In contrast to the lubricant known from US 5 154 881 no

EBS is formed when the lubricant according to the present ’ invention is prepared. EBS has the chemical formula . CH; (CH;) 14CO-HN (CH;) ;2NH-OC (CH;) 16CH3) 1s a molecule without lactam units which is in contrast to the lubricants according to the present invention.

As regards the molecular weight of the new lubricant molecule it has been found that the preferred lubricants have a molecular weight between 1000 and 5000, most pref- erably between 1500 and 3000.

The lubricant molecule may be prepared according standard procedures for amide oligomer as described in e.g. “Principles of Polymerization” third edition by

George Odian (John Wiley & Sons, Inc.). According to the present invention the lubricant preferably consists of at least 80% of the amide having the formula described above. Thus up to 20% by weight of other types of lubri- cants may be added, as long as the advantageous proper- ties of the new lubricant is not detrimentally affected.

This lubricant, which is added to the iron-based powder is preferably in the form of a solid powder, can make up 0.1-1% by weight of the metal-powder composition, 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 an especially advantageous feature of the in- vention, since it enables high densities to be achieved. ‘ As used in the description and the appended claims, the expression "iron-based powder" encompasses powder es- & 30 sentially made up of pure iron; iron powder that has been pre-alloyed with other substances improving the strength, the hardening properties, the electromagnetic properties or other desirable properties of the end products; and particles of iron mixed with particles of such alloying elements (diffusion annealed mixture or purely mechanical * mixture). Examples of alloying elements are copper, mo- . lybdenum, chromium, manganese, phosphorus, carbon in the form of graphite, and tungsten, which are used either separately or in combination, e.g. in the form of com- pounds (Fe3;P and FeMo). Unexpectedly good results are obtained when the lubricants according to the invention are used in combination with iron-based powders having high compressibility. Generally, such powders have a low carbon content, preferably below 0.04% by weight. Such powders include e.g. Distaloy AE, Astaloy Mo and ASC 100.29, all of which are commercially available from

Hoganas AB, Sweden.

Apart from the iron-based powder and the lubricant, the new powder composition may contain one or more addi- tives such as binders, flow agents, processing aids and hard phases.

The binder may be added to the powder composition in accordance with the method described in U.S. Pat. No. } 5,368,630 (which is hereby incorporated by reference) and may be organic compounds such as cellulose ester resins, hydroxyalkyl cellulose resins having 1-4 carbon atoms in the alkyl group, or thermoplastic phenolic resins.

A type of flow agent, which can be used according to the present invention, is disclosed in the US patent 5,782,954 (which is hereby incorporated by reference). ‘ The flow agent, which is preferably a silicon dioxide, is used in an amount from about 0.005 to about 2 percent by + 30 weight, preferably from about 0.01 to about 1 percent by weight, and more preferably from about 0.025 to about 0.5 : percent by weight, based on the total weight of the met- allurgical composition. Furthermore, the flow agent should have an average particle size below about 40 nano- meters. Preferred silicon oxides are the silicon dioxide ’ materials, both hydrophilic and hydrophobic forms, com- \ mercially available as the Aerosil line of silicon diox- ides, such as the Aerosil 200 and R812 products, from

Degussa Corporation.

The processing aids used in the metal-powder compo- sition may consist of talc, forsterite, manganese sul- phide, sulphur, molybdenum disulphide, boron nitride, tellurium, selenium, barium difluoride and calcium di- fluoride, which are used either separately or in combina- tion.

The hard phases used in the metal-powder composition may consist of carbides of tungsten, vanadium, titanium, niobium, chromium, molybdenum, tantalum and zirconium, nitrides of aluminium, titanium, vanadium, molybdenum and chromium, Al, 0O;, and various ceramic materials.

The invention is further illustrated by the follow- ing examples, which are to be interpreted only as exam- ples but should not limit the scope of protection.

EXAMPLE 1

The following tables disclose a comparison of prop- erties between components prepared from powder mixtures including the lubricant according to the present inven- tion and the amide type lubricant disclosed in the US patent 5,744, 433. . ”

@ \ Table 1

Lubricant {Compaction |GD Ejec- Ejec- Spring-

Pressure (g/cm3) [tion tion back (MPa) Force Energy | (%) (N/mm2) | (J/cm?)

Orgasol 500 7.09 11.9 29.9 0.191 3501+

Table 2

Lubricant Compac- Appearance ‘ tion

N Pressure (MPa) [ewe ewn

I Cc cc

I CC I

I EN

Orgasol 500 Many stains Some deposit ee

IE Cc cu

I I CT a co

Temperature Powder/Die: 120°C/120°C * lubricant preferred according to US patent 5,744, 433

The iron-based powder was Distaloy AE available from

Hbganas AB, Sweden. This powder was mixed with 0.3% by weight of ultrafine graphite and 0.6% by weight of a lu- bricant according to the present invention. A flow en- hancing agent Aerosil® 200 was added in an amount of 0.06% by weight.

As can be seen the new oligomer amide type lubricant according to the present invention is superior not only as regards the ejection force, the ejection energy, the ' springback but also when it comes to the appearance of , 15 the compacted component. Additionally the lubricant does not deposit on the die wall.

EXAMPLE 2

The following table discloses a comparison of prop- : erties between components prepared from powder mixtures ° including the lubricant according to the present inven- tion and the amide type lubricant disclosed in the US patent 5,154,881.

As can be seen the lubricant according to the pre- sent invention is superior as regards the ejection force, the ejection energy and the springback.

Table 3

GD Ejection Ejection Springback (g/cm3) Force Energy (%) (N/mm?2) (J/cm?)

Lubricant 7.46 9.7 20.9 0.121 according to the present invention

Lubricant 7.40 15.4 21.9 0.201 according to US patent 5 154 881

Compaction pressure 700 MPa * 15 Temperature powder/Die 130°C/150°C ! The iron-based powder was Distaloy AE available from

Hoganas AB, Sweden.

This powder was mixed with 0.3% by weight of ultra- fine graphite and 0.6% by weight of a lubricant according

. to the present invention. A flow enhancing agent Aerosil was added in an amount of 0.06% by weight. a \ EXAMPLE 3

The following example discloses a comparison of den- sities of green bodies obtained with the oligomer amide lubricants which are used according to the present inven- tion and which have different molecular weights.

The iron-based powder was Distaloy AE available from

Hdéganas AB, Sweden.

This powder was mixed with 0.3% by weight of ultra- fine graphite and 0.6% by weight of a lubricant according to the present invention. A flow enhancing agent Aerosil was added in an amount of 0.06% by weight.

The powder was heated to a temperature of 130°C and the temperature of die was 150°C. The compaction pressure was 700 MPa.

Molecular Weight of

Lubricant GD (g/cm3) 2000 7,44 3000 7,41 4000 7,31

If the molecular weight of the oligomer amide lubricant is lower than (about) 2000 the properties of . the powder composition becomes worse with regards to » flow, and the lubricant will have a tendency of sticking to the die wall and the surface of the ejected compact. * 30 The sticky nature of such surfaces increases the risk of formation of rough surfaces on the final part owing to powder which may be collected onto the ejected compact.

Claims

CLAIMS A,

4 1. A powder composition for warm compaction comprising an iron-based powder and a lubricant powder, said lubricant consisting essentially of an amide represented by the following formula D-Cna-B-A-B-Cypn-D wherein D is -H, COR, CNHR, wherein R is a straight or branched aliphatic or aromatic group including 2-21 C atoms C is the group -NH (CH), CO- B is amino or carbonyl A is alkylen having 4-16 CC atoms optionally including up to 4 O atoms ma is an integer 1-10 mb is an integer 1-10 n is an integer 5-11.
2. A powder composition according to claim 1 wherein D is COR, wherein R is an aliphatic group 16 - 20 C at- oms, C is -NH (CH), CO- wherein n is 5 or 11; B is amino; A is alkylen having 6-14 C atoms optionally including up to 3 0 atoms, and ma and mb, respectively is an integer 2-5, whereby ma and mb may be the same or different.
3. A powder composition according to any one of the i, claims 1-2 wherein the lubricant consists of a compound selected from the group consisting of CH (CHp) 16CO-[HN (CHy) 11CO]2-HN (CHp) 1 ,NH-[OC (CHp) 1 1 NH], - OC (CH) 16CH3

CH3 (CHp) 14CO-[HN (CHj) 11CO]5 -HN (CH) 1 NH-[OC (CH5) 11 NH]3~ © OC (CHy) 1 gCH3 CH3 (CHj) 16CO-{HN (CHp) 11C0O]3-HN (CH3) 1oNH-[OC (CHy) 1 1NH]3~ ki OCCHj) 1 gCH3 CH3 (CH3) 1 ¢CO-[HN (CH5) 11CO}3 -HN (CHy) 1oNH-[OC (CH) 1 1NH]4 - OC (CHp) 1 CH3 CH3 (CHp) 1CO-[HN (CHy) 11CO]4 ~-HN (CH) 1 oNH-[OC (CHy) 1 {NH]4- OC (CHy) 1 CHa CH3 (CHy) 1gCO-[HN (CH5) 11COJ4 -HN (CHo) 1 oNH-[OC (CH) 11 NH]g - OC(CHjp)1gCH3 CH3 (CH3) 1gCO-[HN(CH3) 11CO]5-HN(CH5) 12NH-[OC (CHy) 1 1NH]5- OC (CHp) 1 CH3
4. A powder composition according to any one of the claims 1-3, wherein said amide has a molecular weight of 1500 to 3000 and is present in said composition in an amount of less than 1% by weight.
5. A powder composition according to any one of the claims 1-4, wherein the lubricant powder is provided in a concentration 0.2 to 0.8% by weight of the composition.
6. A powder composition according to any one of the claims 1-5, which additionally contains one or more additives selected from the group consisting of binders, processing aids, and hard phases.
7. A powder composition according to any one of the , claims 1-6, wherein said iron-based powder is p compressible, and at least 80% by weight of said lubricant powder is made up of said amide oligomer.
8. A powder composition according to any one of the claims 1-6, wherein said composition is essentially free from ethylenebisstearamide.
9. A powder composition according to any one of the claims 1-8, characterised in that said iron- . based powder has a carbon content of at most 0.04% by A weight.
10. A method for producing sintered products comprising: (a) mixing an iron-based powder with a lubricant powder as defined in the previous claims; (b) preheating the metal-powder composition, (c) compacting the metal-powder composition in a pre- heated tool, and optionally (d) sintering the compacted metal-powder composition at a temperature above 1050° C to form a sintered product.

0. : i?