CN1250684C - Iron powder composition including an amide type lubricant anjd a method to prepare it - Google Patents

Abstract

The invention concerns a method of preparing an iron-based powder comprising the steps of mixing and heating an iron-based powder, at least one oligomer amide type lubricant, at least one fatty acid and optionally one or more additives to a temperature above the melting point of the lubricant and subsequently cooling the obtained mixture. The invention also comprises the mixture of the iron-based powder, the oligomer amide type lubricant and the fatty acid.

Description

Iron powder composition containing amide type lubricant and its preparation method

field of invention

The present invention relates to a metal powder composition and a method for preparing the composition. In particular, the present invention relates to iron-based compositions which have consistent apparent density and fluidity at different temperatures.

Background of the invention

In the field of powder metallurgy, different standard temperature specifications are commonly used for the compaction of metal powders to form metal components. These include cold pressing (pressing below ambient temperature), ambient pressing (pressing at ambient temperature), hot pressing (pressing at a temperature above ambient temperature where the metal powder remains work hardened) and Moderate temperature pressing (pressing at a temperature between normal temperature pressing and hot pressing).

Compression at a temperature above ambient temperature has clear advantages. The tensile strength and work hardening rate of most metals decrease with increasing temperature, and improved density and strength can be achieved at lower compaction pressures. However, the extremely high temperature of hot pressing introduces processing problems and accelerates wear of the die. Therefore, current efforts are aimed at developing metal compositions suitable for medium temperature pressing.

US Patent 4,955,789 (Musella) generally discloses intermediate temperature compaction. According to the patent, lubricants commonly used for cold compaction, such as zinc stearate, can also be used for moderate temperature compaction. In practice, however, it proved impossible to use zinc stearate or ethylene bisstearamide (commercially available as ACRAWAX®) in moderate temperature compaction, which are currently the most commonly used for cold and moderate temperature compaction. of lubricants. The problem that arises is that it is difficult to fill the mold in a satisfactory manner.

US Patents 5,744,433 (Storstrom et al.) and 5,154,881 (Rutz) disclose metal powder compositions including amide lubricants, which have been developed specifically for moderate temperature compaction. US Patent 5,744,433 discloses lubricants for metallurgical powder compositions containing amide type oligomers with a weight average molecular weight Mw of up to 30,000. In US Pat. No. 5,154,881, amide lubricants consist of reaction products of monocarboxylic acids, dicarboxylic acids and diamines. Particularly preferred for use as a lubricant is ADVAWAX.(R) 450, an ethylene bisstearamide product.

Although the lubricants disclosed in these two patents were developed specifically for moderate temperature compaction and work well in many cases, it has been found that when these lubricants are used in , ran into a different problem.

Contents of the invention

It is an object of the present invention to reduce or eliminate problems currently associated with large-scale production.

Another object is to provide a new class of lubricants which can be used in metal compositions intended to be compacted at high temperatures.

A further object is to provide an iron-based powder composition having excellent flow rate and apparent density.

A further object is to provide a powder composition which generates minimal dust and whose preparation does not require the use of organic solvents.

Yet another object is to provide a method for moderate temperature compaction of such metal powder compositions.

By a powder composition comprising an iron-based powder, at least one oligomeric amide type lubricant, at least one fatty acid and optionally one or more additives such as flow agents, processing aids and hard phases, These objectives can be achieved. Wherein the oligomeric amide type lubricant is represented by the following formula: DC _ma -BABC _mb -D, wherein D is -H, COR, CNHR, wherein R is a linear or branched chain containing 2-21 carbon atoms aliphatic group; C is the group -NH(CH) _nCO- ; B is amino or carbonyl; A is an alkylene group optionally including up to 4 oxygen atoms and having 4-16 carbon atoms; ma is an integer of 1-10; mb is an integer of 1-10; and n is an integer of 5-11.

Method of the present invention comprises the following steps:

- mixing and heating the iron-based powder, lubricant, fatty acid and additives (if any) to a temperature above the melting point of the lubricant; and

- cooling the resulting mixture. wherein said lubricant is an oligomer amide type lubricant as defined above.

Detailed description of the invention

The expression "iron-based powder" as used in this specification and the appended claims includes powders consisting essentially of pure iron; pre-alloyed with other substances which improve the strength, hardness properties, electromagnetic properties or other desired properties of the final product iron powder; and iron particles mixed with particles of this alloying element (diffusion-annealed mixture or purely mechanical mixture). Examples of alloying elements are nickel, copper, molybdenum, chromium, manganese, phosphorus, carbon and tungsten in the form of graphite, which can be used independently or in combination, for example in the form of compounds ( _Fe3P and FeMo). Unexpectedly good results were obtained when the lubricants of the present invention were used in combination with iron-based powders having high compressibility. Generally, such powders have a low carbon content, preferably below 0.04 wt%. Such powders include, for example, Distaloy AE, Astaloy Mo and ASC100.29, all of which are commercially available from Hoganas AB, Sweden.

The lubricant used in the present invention is a new lubricant, which can be represented by the following formula:

DC _ma -BABC _mb -D

Wherein D is -H, COR, CNHR, wherein R is a linear or branched aliphatic or aromatic group containing 2-21 carbon atoms;

C is a group -NH(CH) _n CO-;

B is amino or carbonyl;

A is an alkylene group optionally including up to 4 oxygen atoms and having 4-16 carbon atoms;

ma is an integer of 1-10;

mb is an integer of 1-10;

n is an integer of 5-11.

Preferred lubricants have the following chemical structure, wherein D is COR, wherein R is an aliphatic group having 16-20 carbon atoms; C is -NH(CH) _nCO- , wherein n is 5 or 11; B is amino; A is an alkylene group optionally including up to 3 oxygen atoms and having 6-14 carbon atoms; ma and mb are the same or different integers of 2-5.

Examples of such lubricants may be selected from:

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₂ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₂ -OC(CH ₂ ) ₁₆ CH ₃ ;

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₂ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₃ -OC(CH ₂ ) ₁₆ CH ₃ ;

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₃ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₃ -OC(CH ₂ ) ₁₆ CH ₃ ;

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₃ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₄ -OC(CH ₂ ) ₁₆ CH ₃ ;

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₄ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₄ -OC(CH ₂ ) ₁₆ CH ₃ ;

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₄ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₅ -OC(CH ₂ ) ₁₆ CH ₃ ;

CH ₃ (CH ₂ ) ₁₆ CO—[HN(CH ₂ ) ₁₁ CO] ₅ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₅ -OC(CH ₂ ) ₁₆ CH ₃ .

Other examples are:

_CH3CO -HN( _CH2 ) _5CO -HN(CH2) _2NH -OC( _CH2 ) _5NH -OC( _CH3 ) with a MW _of 370.49;

MW of 1240.10

CH ₃ (CH ₂ ) ₂₀ CO-HN(CH ₂ ) ₁₁ CO-HN(CH ₂ ) ₁₂ NH-OC(CH ₂ ) ₁₁ NH-OC(CH ₂ ) ₂₀ CH ₃ ;

MW of 8738.04

CH ₃ (CH ₂ ) ₂₀ CO—[HN(CH ₂ ) ₁₁ CO] ₁₀ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₁₀ -OC(CH ₂ ) ₂₀ CH ₃ ;

MW of 1580.53

CH ₃ (CH ₂ ) ₄ CO—[HN(CH ₂ ) ₁₁ CO] ₃ -HN(CH ₂ ) ₁₂ NH—[OC(CH ₂ ) ₁₁ NH] ₃ -OC(CH ₂ ) ₄ CH ₃ ;

MW of 1980.86

CH ₃ (CH ₂ ) ₄ CO—[HN(CH ₂ ) ₅ CO] ₇ -HN(CH ₂ ) ₆ NH—[OC(CH ₂ ) ₅ NH] ₇ -OC(CH ₂ ) ₄ CH ₃ ;

MW of 2429.69

_CH3 ( _CH2 ) _20CO- [HN( _CH2 ) _5CO ] _{7- HN} ( _CH2 ) _6NH- [OC( _CH2 ) _5NH ] _7- OC( _{CH2)20CH3 ;} and

MW of 2283.73

CH ₃ (CH ₂ ) ₁₆ NH—[OC(CH ₂ ) ₁₁ NH] ₄ —CO(CH ₂ ) ₁₀ CO—[HN(CH ₂ ) ₁₁ CO] ₄ —HN(CH ₂ ) ₁₆ CH ₃ .

The oligomer amide type lubricant added to the iron-based powder is preferably in the form of solid powder, which may account for 0.1-1 wt%, preferably 0.2-0.8 wt%, of the total metal powder composition. The possibility of using the lubricant of the invention at low levels is a particularly advantageous feature of the invention, since it enables high densities to be achieved.

The fatty acid used in the present invention is preferably a fatty acid having 10-22 carbon atoms. Examples of such acids are oleic acid, stearic acid and palmitic acid. Although the amount of fatty acid used is small, the effect on flow rate and apparent density is significant. The amount of fatty acid used is generally 0.005-0.15%, preferably 0.010-0.08%, and most preferably 0.015-0.07%, calculated on the total weight of the powder composition. A fatty acid content below 0.005 makes it difficult to achieve a uniform distribution of fatty acids. If the content is higher than 0.15%, there is a considerable risk of fluidity deterioration.

The melting point of the fatty acid should be lower than that of the amide oligomer lubricant.

In addition to the iron-based powder and the lubricant, the new powder composition may contain one or more additives selected from processing aids and hard phases.

Processing aids used in the metal powder composition may consist of talc, forsterite, manganese sulfide, sulfur, molybdenum disulfide, boron nitride, tellurium, selenium, barium difluoride, and calcium difluoride. The processing aids may be used alone or in combination.

The hard phase used in the metal powder composition can be composed of carbides of tungsten, vanadium, titanium, niobium, chromium, molybdenum, tantalum and zirconium; nitrides of aluminum, titanium, vanadium, molybdenum and chromium; Al ₂ O ₃ and various Composed of ceramic materials.

In U.S. Patent No. 5,782,954, a class of flow agents that can be used in the present invention are disclosed (herein incorporated by reference), it is preferably silicon dioxide, and its consumption is about 0.005 to about 2 wt%, preferably about 0.01 to about 1 wt%, more preferably From about 0.025 to about 0.5 wt%, based on the total weight of the metallurgical composition. Additionally, the average particle size of the flow agent should be below about 40 nanometers. Preferred silicon oxides are silica materials in both hydrophilic and hydrophobic forms, commercially available from Degussa in the Aerosil series of silicas such as Aerosil 200 and R812 products.

According to an embodiment of the present invention, the iron-based powder, at least one oligomeric amide type lubricant, at least one fatty acid and optionally one or more additives such as processing aids and hard phases are heated to a specific lubricant The melting point of the resulting mixture is then cooled to a temperature lower than the melting point of the lubricant and higher than the melting point of the fatty acid, and a powdery flow agent is added to the resulting mixture, and then the mixture is mixed and cooled.

Brief description of the drawings

Figure 1 shows the effect on the apparent density of the combination of an oligomeric amide type lubricant as defined above and a fatty acid (stearic acid).

Figure 2 shows the effect on the flow rate of the combination of lubricant and fatty acid (stearic acid) as defined above.

The powder mixtures tested were prepared by dry blending Distaloy AE (iron-based powder from Höganös AB, Sweden) with 0.6% by weight of organic material lubricated by the oligomeric amide type as defined above agent and 0.03wt% or 0.05wt% stearic acid. 0.3 wt% graphite was also added and the resulting mixture was heated to 165°C. The mixture was cooled to 110[deg.] C. and 0.06% by weight of Aerosil(R) was added at this temperature. Essentially the same results were obtained when Aerosil was added at ambient temperature.

The results disclosed in Figures 1 and 2, respectively, demonstrate the significant and unexpected benefits obtained with the powder compositions of the present invention with respect to both apparent density and flow.

Dust reduction was also tested for the above mixture comprising 0.03 wt% stearic acid compared to a mixture prepared according to US Patent 5,368,630. This known mixture also comprises 0.6% by weight of organic material, but in this case the organic material consists of 0.55% by weight of lubricant and 0.15% by weight of organic binder (cellulose butyrate). In both blends, the iron-based powder is Distaloy AE. It is known that the preparation of a mixture comprises a dry blend of iron-based powder, a lubricant according to this US patent and 0.3% by weight of graphite. The organic binder was dissolved in acetone and added to the dry mixture, followed by thorough mixing. Acetone was removed and 0.06 wt% Aerosil(R) was added to the dry mixture.

The test results are summarized in the table below: sample Dusting (mg/m ³ .min.g[mix]) Mixtures of the invention 41 Mixture according to US Patent 5,368,630 70

Claims (11)

1. A powder composition comprising iron-based powder, at least one oligomer amide type lubricant, fatty acid and optionally one or more additives, Wherein said oligomer amide type lubricant is represented by following formula: DC _ma -BABC _mb -D Wherein D is -H, COR, CNHR, wherein R is a linear or branched aliphatic group containing 2-21 carbon atoms; C is a group -NH(CH) _n CO-; B is amino or carbonyl; A is an alkylene group optionally including up to 4 oxygen atoms and having 4-16 carbon atoms; ma is an integer of 1-10; mb is an integer of 1-10; n is an integer of 5-11. 2. Composition according to claim 1, characterized in that the melting point of the fatty acid is lower than that of the amide lubricant. 3. Composition according to claim 1, characterized in that the fatty acid has 10-22 carbon atoms. 4. Composition according to claim 3, characterized in that the fatty acid is selected from oleic acid, stearic acid, palmitic acid or combinations thereof. 5. The composition of claim 1, characterized in that the lubricant has the following chemical structure, wherein D is COR, wherein R is an aliphatic group having 16-20 carbon atoms; C is -NH(CH) _nCO -, wherein n is 5 or 11; B is an amino group; A is an alkylene group optionally including up to 3 oxygen atoms and having 6-14 carbon atoms; ma and mb are the same or different integers of 2-5 . 6. The composition according to claim 3, characterized in that the fatty acid is used in an amount of 0.015-0.15% by total weight, based on the powder composition. 7. Composition according to any one of claims 1-6, characterized in that the composition comprises one or more additives selected from the group consisting of binders, flow agents, processing aids and hard phases. 8. Composition according to claim 7, characterized in that the flow agent is used in an amount of 0.005-2 wt%, based on the total weight of the metallurgical composition, and that the flow agent has an average particle size below 40 nm. 9. Composition according to claim 8, characterized in that the flow agent is silicon dioxide. 10. A method of preparing an iron-based powder composition, comprising the steps of: a) mixing and heating the iron-based powder, at least one oligomeric amide type lubricant, at least one fatty acid and optionally one or more additives to a temperature higher than the melting point of the lubricant, and b) cooling the resulting mixture, Wherein said oligomer amide type lubricant is represented by following formula: DC _ma -BABC _mb -D Wherein D is -H, COR, CNHR, wherein R is a linear or branched aliphatic group containing 2-21 carbon atoms; C is a group -NH(CH) _n CO-; B is amino or carbonyl; A is an alkylene group optionally including up to 4 oxygen atoms and having 4-16 carbon atoms; ma is an integer of 1-10; mb is an integer of 1-10; n is an integer of 5-11. 11. Process according to claim 10, characterized in that the mixture obtained in step a) is cooled to a temperature below the melting point of the lubricant and above the melting point of the fatty acid, and a pulverulent flow agent is added to the mixture.

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