KR20070027758A - Powder metallurgical composition comprising carbon black as flow enhancing agent - Google Patents

Abstract

The invention concerns a powder metallurgical composition comprising iron or iron-based powder and a minor amount, I.e. o.001-0.2 wt-%, of carbon black. The carbon black acts as flow enhancing agent. ® KIPO & WIPO 2007

Description

Powder metallurgical composition comprising carbon black as flow enhancer {POWDER METALLURGICAL COMPOSITION COMPRISING CARBON BLACK AS FLOW ENHANCING AGENT}

The present invention relates to an iron-based powder metallurgical composition. More particularly, the present invention relates to compositions comprising a flow agent that improves fluidity but also improves apparent density.

Powder metallurgy compositions are known for preparing powder metallurgy powders. The production of powder metallurgical powders involves the filling of powders in compacting tools, compacting powders and subsequent sintering of the compacted bodies. The requirement for the filling of the powder is that the powder is free flowing and has sufficient flow. High flow rates of the powder are essential for achieving high production rates that provide lower production costs and better economics for each powder produced.

Another factor essential for manufacturing efficiency and economics is apparent density. Apparent density is essential for tool design. Powders with low apparent density require an undesirably high compaction tool, which in turn requires a higher fill height that will result in longer compression strokes and lower compaction performance.

Fluidity improvers are already known. U.S. Patent No. 3 357 818 describes that silicic acid can be used for this purpose. US Pat. No. 5,782,954 describes that metals, metal oxides or silicon oxides can be used as flow agents.

It is an object of the present invention to provide a powder metallurgical composition with improved powder properties such as flowability and apparent density.

It was unexpectedly found that by adding a small amount of carbon black to the iron-based powder composition, the properties of the powder composition can be improved. In addition, the addition of a controlled amount of carbon black does not deteriorate the properties of the green and sintered powders prepared from the new iron-based composition and these properties can be improved.

Generally, powder metallurgical compositions include iron or iron based powders and lubricants. The composition may comprise a binder, graphite and other alloying elements. Hard phase materials, liquid forming materials and machinability enhancers may also be included.

The iron-based powder may be any form of iron-based powder, such as water-atomised iron powder, reduced iron powder, pre-alloyed iron powder or diffused iron-based powder. Such powders include, for example, diffusion alloyed iron based powder Distalloy AB, including iron powder ASC100.29, Cu, Ni, and Mo, iron based powder atalloy CrM, and prealloyed atalloy CrL with these, All are available from Hoganas Ave, Sweden.

The amount of carbon black in the iron-based powder composition according to the invention is between 0.001 and 0.2% by weight, preferably between 0.01 and 0.1% by weight. The main particle size of the carbon black is preferably 200 nm or less, more preferably 100 nm or less, most preferably 50 nm or less. The specific surface area is, in a preferred embodiment, between 150 and 1000 m 2 / g measured by the BET method. However, other forms of carbon black with other surface areas and major particle sizes may be available.

Carbon black is generally used as filler and color pigment in rubber materials. It is also used for electrical conductivity and may be used to reduce static electricity in the product. Carbon black in compositions with iron or iron based powders is described in US Pat. No. 6,602,315. The patent describes a composition in which the alloying powder is bonded to the iron-based powder, to which carbon black can be added by means of a binder. No. 6 602 315 does not describe any content, particle size or effect of carbon black, only the bonding material. Patent application JP 7-157838 also describes a powder composition comprising carbon black. The purpose of carbon black here is to remove oxygen from the base material.

The composition according to the invention may comprise an alloying element selected from the group consisting of graphite, Cu, Ni, Cr, Mn, Si, V, Mo, P, W, S and Nb.

In order to enhance the compressibility of the powder and to facilitate the discharge of the green component, a lubricant or combination of other lubricants may be added to the powder metallurgical composition. The lubricant may be present as a specific powder or may be bonded to the surface of the iron-based powder. By adding a binder that dissolves in the solvent accompanying the evaporation of the solvent, the lubricant can be bound to the surface of the iron-based powder. The binder may be added in a natural liquid state with the ability to form a film around the iron-based powder. Another alternative is to use the lubricant as a binder by heating the composition above the melting point of one or more of the lubricant compositions or above the melting point of the lubricant by cooling the composition to a temperature below its melting point.

Lubricants are from groups consisting of fatty acids, amide waxes such as ethylene bissteramide (EBS), or other derivatives of fatty acids such as metal steramides, polyalkylenes such as polyethylene, polyglycol, amide polymers, or amide oligomers Can be selected. Preferably the lubricant is selected from the group consisting of polyalkylenes, amide waxes, amide polymers or amide oligomers.

The binder is selected from the group consisting of cellulose ester resins, high molecular weight thermoplastic phenolic resins, hydroxyalkylcellulose resins, and mixtures thereof. Preferably the binder is selected from the group of cellulose ester resins and hydroxyalkylcellulose resins.

Other possible additives are machinability improvers, hard phase materials and liquid formers.

According to a preferred embodiment carbon black is used as a flow agent in the mixture to be bonded, ie the mixture, for example fine powdered alloying element particles are bonded to the surface of the iron or iron-based powder particles by a binder, which mixture is Often it has poor flow characteristics. If carbon black is used in the combined mixture, it is preferably added after the bonding action is achieved. The bonding action can be achieved by heating to a temperature above the melting point of the binder during mixing and cooling the mixture until the binder solidifies. The binder may be added and dissolved in the solvent. The binding action is in this case achieved by evaporating the solvent by heating or vacuum. The composition is compressed and sintered to achieve fine powder metal powder.

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

Example 1

Three forms of carbon black are selected with various specific surface areas and particle sizes according to Table 1. Specific surface area is determined by the BET method. Particle size is measured by electron microscopy and represents the major particle size of carbon black.

* Available from Degussa AG, Germany.

Iron-based powder ASC100.29, available from Swedish Gaganas Abbe, contains 0.77% by weight graphite, 0.8% bonding / lubrication system (0.2% polyethylene (polywax 650) and 0.6% ethylene bis-steramide (EBS) Consisting of). The mixture is heated and subsequently cooled while mixing at a temperature above the melting point of the polywax. At temperatures below the melting point of polywax, 0.03% carbon black is added. Three different forms of carbon black are tested according to Table 1. Both mixtures are prepared as reference mixtures. Reference mixture C was prepared along the experimental mixture except for 0.8% graphite and no flow agent was added. A reference mixture R 0.8% graphite and 0.06% ^® Aerosil ^® A-200, available from Degussa AG, is added.

Powder properties are measured. Flow characteristics are measured using standard methods, and Hall-Flow cup and apparent density, AD according to ISO-4490, are measured using standard method ISO 3923.

The results of the powder properties are shown in Table 2.

The experiment shows that the addition of carbon black to the powder metallurgical mixture improves the flow rate and AD compared to the mixture without any flow agent. The addition of CB1 shows a nearly equal flow improvement in the process of improving flow and AD compared to the addition of known flow agents but with a higher AD compared to the addition of flow agent A-200.

Example 2

Carbon black form CB1 is chosen to determine the optimal amount to be added to the iron-based powder mixture. The mixture is prepared according to the description of Example 1. The amounts added of alloying elements, binders / lubricants, flow agents and graphite are shown in Table 3.

A reference mixture, R1 without flow agent, and R2 with commercially available flow agent, are trademarked Aerosil A-200 available from Degussa AG.

The experimental powder according to ISO 2740 is compressed at a pressure of 600 MPa and sintered at 1120 ° C. in 90/10 N ₂ / H ₂ atmosphere. In Table 4 the mechanical properties are prepared for the powder composition according to Table 3.

As shown in Table 4, carbon black in an amount added 0.06% affects tensile strength, TS, yield strength, YS, and elongation, A. If 0.04% by weight and less carbon black is added, there is little influence on the mechanical properties.

Example 3

Example 3 shows that new flow agents can be used in compositions for high temperature compression. 3000 g of one experimental mixture, B5, and one reference mixture, R3, are each prepared as follows.

ASC 100.29 is a mixture of 13.5 g hot lubricant trademark Promold ^® , 24 g graphite, 60 g copper powder, residual iron powder, available from Morton International, Cincinnati, Ohio. Mix thoroughly during 45 ° C. heating. In addition, 4.5 g of cellulose ester resin dissolved in acetone are added and the mixture is mixed for 5 minutes. During the second mixing of 10 to 30 minute cycles, the solvent is evaporated while maintaining a material temperature of 45 ° C. Eventually, 1.8 g of the trademark Aerosil A-200 flow agent is added and mixed thoroughly.

As an experimental mixture of 60 g of copper powder, 23.1 g of graphite, 13.5 g of a hot lubricant trademark promold available from Morton International, Cincinnati, Ohio, and residual iron powder, ASC 100.29 was completely heated at 45 ° C. during heating. Are mixed. In addition, 4.5 g of cellulose ester resin dissolved in acetone are added and the mixture is mixed for 5 minutes. During the second mixing cycle of 10 to 30 minutes, the solvent is evaporated while maintaining a material temperature of 45 ° C. Eventually, 0.9 g of carbon black CB1 flow agent is added and mixed thoroughly.

The flow and AD of the two mixtures are measured according to ASTM B 213 at a temperature of 120 ° C. In Table 5, a substantial increase in AD is achieved for powder mixtures according to the present invention, and it can be shown that substantially the same flow rates are achieved for compositions containing fresh flow agents as compared to compositions containing known flow agents. .

Example 4

Example 4 shows that flow agents can be used in combination with various iron-based powders. The mixture is prepared according to the method of Example 1, in which the same binder / lubricant system is used. The amounts of iron-based powders and additives used are shown in Table 6. Identification RA, RB, RC, RE and RF indicate that the mixture is a reference mixture containing 0.06% flow agent Aerosil A-200 available from Degussa AG. Identification C, E, and F indicate that the mixture is a reference mixture without any flow agent. Carbon black CB1 is used for all mixtures. The iron or iron-based powders used are: atomized plain iron powder from Hoganas Abbe, ASC 100.29,

Diffusion-alloyed iron-based powder comprising Cu, Ni, and Mo from Disganloy AB, Distaloy AB,

Prealloyed iron-based powders containing Cr and Mo from Asganese Abe, Astalloy CrM,

It is a prealloyed iron-based powder atalloy CrL containing Cr and Mo from Hoganagas Abe.

The powder properties of the powder mixture are measured. The experimental powder according to ISO 2740 is compressed at a pressure of 600 MPa and sintered at 1120 ° C. in 90/10 N ₂ / H ₂ atmosphere. Mechanical properties such as green strength, GS, dimensional change, DC as well as sintered density, SD are determined and the results are shown in Table 7.

Table 7 shows that carbon black has improved flow, AD and green strength in mixtures with various base powders compared to mixtures containing known flow agents.

Example 5

Example 5 shows that the new flow agent improves the flow of the plain mixture (unbound mixture) without any binder. Three mixtures were prepared comprising iron powder ASC100.29, 2% copper powder, 0.5% graphite, 0.8% ethylene bissteramide as lubricant and different amounts of carbon black CB1 according to Table 8. Mixtures without any carbon black are used as reference mixtures. Flow rates are measured in various mixtures.

As shown in Table 8, carbon black addition of the unbound mixture improves the flow rate.

Claims (7)

A powder metallurgical composition comprising iron or iron based metal powders, lubricants and / or binders and carbon black, The amount of carbon black is 0.001 to 0.2% by weight, preferably 0.01 to 0.1% by weight, Powder metallurgical composition. The method of claim 1, The particle size of the carbon black is 200 nm or less, preferably 100 nm, more preferably 50 nm or less, Powder metallurgical composition. The method according to claim 1 or 2, The specific surface area is at least 100 m 2 / g, preferably at least 150 m 2 / g and more preferably at least 200 m 2 / g, Powder metallurgical composition. The method according to any one of claims 1 to 3, Comprising an additive selected from the group consisting of alloying elements, machinability improvers, hard phase materials and liquid phase formers, Powder metallurgical composition. The method of claim 4, wherein The alloying element is selected from the group consisting of graphite, Cu, Ni, Cr, Mn, Si, V, Mo, P, W, S and Nb, Powder metallurgical composition. The method of claim 5, One or more particles of the alloying element selected from the group consisting of graphite, Cu are bonded to iron or iron-based powder particles, Powder metallurgical composition. Use of carbon black as flow enhancer in iron based powder compositions.