|Title of Invention||
METAL POWDER COMPOSITION COMPRISING A DRYING OIL BINDER
|Abstract||The present invention concerns a powder metallurgical composition for making compacted parts. The composition comprises an iron based powder, graphite and a binder comprising a drying oil and a drying agent.|
Technical Field of the Invention.
The present invention relates to a powder metallurgical composition for Taking compacted parts. Specifically the invention concerns a bonded iron powder composition comprising an improved binder.
'in industry the use of metal products manufactured by compacting and sintering iron-based powder compositions is becoming increasingly widespread. The quality requirements of these metal products are continuously raised, and as a consequence new powder compositions having improved properties are developed. Some of the most important properties of the final, sintered products are the density and dimensional tolerances, which above all have to be consistent. Problems with size variations in the final product often originate from inhomogenities in the powder mixture to be compacted. These problems are especially pronounced with powder mixtures including pulverulent components which differ in size, density and shape, a reason why segregation occurs during the transport, storage and handling of the powder composition. This segregation implies that the composition will be
made of the powder composition are differently composed and consequently have different properties. A further problem is that fine particles, particularly those of lower density, such as graphite, cause dusting in the handling of the powder mixture.
scale production and these problerr.s can lead to unacceptable product inhomogenities and too broad weight scatter range of the compacted parts. After extensive studies it has now been found that these problems arise when the drying times of the oil vary and cannot be adequately controlled . The present invention concerns a solution of this problem.
Summary of the Invention
An object of the present invention is thus to provide a new powder metallurgical composition for making compacted parts with low weight scatter ranges. This new composition is well suited for large scale production of the compacted parts and it is distinguished by a minimum of segregation during transport, storage and handling, by a low level of dusting and by adequate flow characteristics .
This object is achieved by using a drying oil in combination with a drying agent as a binder. Thus the present invention concerns powder metallurgical comoosi-tions for making compacted parts, which compositions com-
ally other alloying elements, lubricants or additives, and a binder comprising a drying oil and a drying agent.
Detailed Description of the Invention
The drying agents of the present invention are compounds facilitating the controlled drying of a drying
Co, Mn, Pb, Zr, or Ca salts of octanoic or naphthenic acids, whereof -cobalt naphthenate is most preferred.
Depending on the type of drying agent used, the optimal rate of addition to the drying oil can easily be established through experiments.
In this context a drying oil may chemically be described as ,an ester of a polyunsaturated fatty acid and a polyol, which polymerises (cures) through a reaction with Oxygen, form,ing solid films capable of binding finer particles to the iron based powder particles. In a preferred drying oil the polyunsaturated fatty acids derive from rail oil fatty acids or linseed oil fatty acids and the polyol is preferably chosen from the group of glycerol, propan-1,3-did, penta-, dipenta- or tripentaerythritol.
The binder is added to the iron based powder composition in amounts of 0.01-1 wt%, preferably 0.01-0.5 wt%. The amount of the drying agent in the binder is 0.01 - 5 wt% depending on the type of drying oil and drying agent used and the preferred drying time. According to a presently preferred embodiment of the invention the drying
preferably between 0.1 and 1 w% of the binder.
The purpose of the binder is, as stated above, to firmly and effectively bind the small size particles of graphite, other alloying elements and other additives to the surface of the base metal particles and, consequently, reduce the problems of segregation and dusting.
The drying time of the -binder is preferably controlled to a value of less than 4 hours by the addition of at least one drying agent to the drying oil. Furthermore, in order to facilitate the production of homogenous bonded powder mixtures on an industrial scale before the binder has dried completely, it is preferred that the drying time should not be shorter than about 30 minutes. However, other preferred intervals of the drying time may be of interest depending on the amount, type and size of the material to be bound, and/or on other parameters. The preferred interval of the drying time can easily be established by experiment. The above drying time values refer to measurements at ambient temperature and humidity with the aid of a Rhopoint Thin Film Analyser (TFA).
The characteristics of the other components of the metallurgical powder composition of the present invention are now briefly discussed.
The iron or iron-based powder may be an essentially pure iron powder or a mixture of different iron-powders
which is admixed with the pulverulent additives. The
partially alloyed powder. The particle size of the iron or iron-based particles preferably have a maximum weight average particle size up to about 500 μm.
Examples of alloying elements are copper, molybdenum, chromium, nickel, manganese, phosphorus, carbon in the form up graphite and tungsten, which are either used separately or in combination. The commonly used elements
Furthermore, the compositions according to the present invention may include common additives such as sintering aids, hard phase materials, machinability improving agents.
Examples of lubricants are metal stearates e.g. zinc stearate, and amide waxes e.g. ethylene bisstearamide. The lubricant may be included in the metallurgical composition in amounts up to 1.5 wt%.
The invention is further illustrated by the following non-limiting examples concerning a preferred embodiment of the present invention. Example 1
This example concerns the relationship between the drying times and the added amounts of drying agent.
As binder a drying oil comprising tall oil esters, obtained through the esterification of tali oil fatty acids and dipentaerythritol, and a drying agent were used. As drying agent a 10 wt% solution of cobalt naphtenate was used.
In order to control the drying time of the drying
with the drying oil. The relationship between the added amount of drying agent, as percent by weight of the drying oil, and the drying time, measured at ambient temperature and humidity with the aid of a Rhopoint Thin Film Analyser (TFA), is shown in Table 1 below.
As can be seen the amounts of the drying agent cobolt naphtenate in tall oil ester should vary between 0.3 and 0.6 w-% in order to obtain suitable drying times.
This example demonstrates the effect of the amount of drying agent in the binder on weight scatter of the produced compacted parts.
The same drying oil and drying agent as in example 1 were used.
Two iron powder mixtures A and B, respectively, were prepared. Both mixtures contained the atomised iron powder AHC 100.29 available from Hoganas AB, 2 wt% of a copper powder, 0.8 wt% of graphite UF-4, and 0.8 wt% of zinc stearate as lubricant. To the first mixture, 0.05 wt% of .the binder comprising 0.25 wt% drying agent and balance drying oil was added, and to the second mixture, 0.05 wt%
drying oil was added.
From each of the mixtures, 200 pieces of a component, having a target weight of 250 g, were produced in an industrial environment. Every piece was weighed, and pieces having a weight deviation of more than ±1.25 g were rejected. Table 2 shows the number of rejected
As can be seen from Table 2 the addition of a drying agent in an amount sufficient to control the drying time to between 30 minutes and 4 hours clearly reduces the number of rejcted pieces when producing a component in an industrial environment.
the claim 1, wherein the drying oil comprises an ester of a polyunsaturated fatty acid and a polyol.
3. A powder metallurgical composition according to any
of the claims 1-2, wherein the polyunsaturated fatty acid
is derived from, tall oil or from linseed oil.
4. A powder metallurgical composition according to
claim 2, wherein the polyol is selected from the group of
glycerol, propan-1,3-diol and dipenta- or tripentae-
5. A powder metallurgical composition according to
any of the claims 1 - 4, wherein at least one component
of the drying agent is selected from the group of oil
soluble Zn, Co, Mn, Pb, Zr, or Ca salts of octanoic or
6. A powder metallurgical composition according to
claim 5, wherein the drying agent is cobalt naphthenate.
7. A powder metallurgical composition according to
any of the claims 1-5, wherein the amount of drying
agent in the binder is 0.01-5 wt%-
8. A powder metallurgical composition according to
between 0.01-1 wt%, preferably between 0.01-0.5 wt%.
9. A powder metallurgical composition according to
any of the claims 1-8, wherein the binder has a drying
time of 0.5-4 hours.
10. A powder metallurgical composition according to
any one of the claims 1-9, further comprising graphite.
12. A powder metallurgical composition according to any on eof the claims 1-11 further
comprising at least one
additive selected from the group comprising of alloying elements, sintering aids, mach inability improving agents and hard phase materials.
|Indian Patent Application Number||3972/CHENP/2007|
|PG Journal Number||07/2013|
|Date of Filing||11-Sep-2007|
|Name of Patentee||HOGANAS AB|
|Applicant Address||SE, 263 83 HOGANAS,|
|PCT International Classification Number||C09F 9/00|
|PCT International Application Number||PCT/SE06/00123|
|PCT International Filing date||2006-01-27|