KR102260776B1 - Powder mixture for powder metallurgy and method for preparing the same - Google Patents

Abstract

Provided is a powder mixture for powder metallurgy that has very good fluidity, can be ejected from a green compaction mold with little force, and has suppressed mold galling during molding. A powder mixture for powder metallurgy comprising a raw material powder, a binder, and graphite powder, wherein the raw material powder contains iron-based powder of 90% by mass or more of the raw material powder, and the average particle diameter of the graphite powder is less than 5 µm; _{The ratio of the mass (m b} ) of the binder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m b} /(m _r + m _g )×100] is 0.10 to 0.80 mass%, and the ratio of the graphite minutes by weight (m _g) of the total of the mass (m _r) and the black smoke minute mass (m _g) of the raw material powder _{[m g / (m r +} m g) × 100] is 0.6 to 1.0 mass%, the surface of the raw material powder is coated with at least a part of the binder, and the surface of the binder coated on the surface of the raw material powder is coated with at least a part of the graphite powder , powder mixtures for powder metallurgy.

Description

Powder mixture for powder metallurgy and method for preparing the same

The present invention relates to a powder mixture for powder metallurgy, and more particularly, to a powder mixture for powder metallurgy in which die galling is suppressed and can be ejected from a mold with little force during molding. The present invention also relates to a method for producing the powder mixture for powder metallurgy.

In powder metallurgy, raw material powder containing iron-based powder as a main component is molded using a mold to obtain a molded article (green compact), and sintered parts are manufactured by sintering the molded article. And for the purpose of improving the moldability at the time of the said shaping|molding, it is generally performed to add a lubricant to the said raw material powder, and to make the lubricant adhere to the surface of the metal mold|die used for the said shaping|molding. If the lubricant is not used, since the iron-based powder contained in the raw material powder and the mold are in direct contact, the frictional force increases. As a result, there arise problems that compression cannot be achieved to the desired green density during molding, or that a large force is required to take out the molded product from the mold after molding.

For this reason, various lubricants are used at the time of compaction. As the lubricant, for example, a metal soap such as lithium stearate or zinc stearate, or an amide lubricant such as ethylenebisstearoamide is used.

Moreover, in patent document 1, using graphite powder for lubricity improvement is proposed. By coating the surface of the iron-based powder with graphite, the lubricity of the surface of the iron-based powder is improved. In addition, since direct contact between the iron-based powder and the mold is avoided by the interposition of graphite, mold galling is prevented.

Japanese Laid-Open Patent Publication No. 2005-330547

As proposed in Patent Document 1, by using the iron-based powder coated with graphite powder, friction during molding can be reduced and the ejection force from the mold can be reduced. However, it turned out that the powder mixture of patent document 1 has the following problems.

In Patent Document 1, a dispersion liquid in which graphite and a binder are dispersed in water or an organic solvent is used to coat the surface of the iron-based powder with graphite powder, so a manufacturing facility capable of handling liquid raw materials is required. In particular, there is a need to provide an apparatus for recovering and treating the used solvent.

In addition, in Patent Document 1, a binder is used to make the graphite powder adhere to the iron-based powder. As a result of examining the powder mixture obtained by the above method, it was found that the binder was also present on the surface of the graphite powder adhered to the iron-based powder. As a result of the presence of the binder on the surface of the powder, the fluidity of the powder mixture cannot be sufficiently improved.

The present invention has been made in view of the above reality, and an object of the present invention is to provide a powder mixture for powder metallurgy that has excellent fluidity, can be ejected from a green compaction mold with little force, and suppressed mold galling during molding. . Another object of the present invention is to provide a method for producing the powder mixture for powder metallurgy without using a solvent.

MEANS TO SOLVE THE PROBLEM The present inventors acquired the following recognition as a result of earnestly researching in order to solve the said subject.

(1) When the raw material powder, graphite powder, and binder are mixed simultaneously, the binder is also coated on the surface of the graphite powder, and the outermost surface of the raw material powder cannot be uniformly coated with graphite.

(2) After coating the binder on the surface of the raw material powder, it is possible to prevent the surface of the graphite powder from being coated with the binder by coating the fine graphite powder. And as a result, it is possible to obtain a powder mixture for powder metallurgy that is very excellent in fluidity, can be ejected from the mold with little force during molding, and in which mold galling is suppressed.

This invention is based on the said recognition, The summary structure is as follows.

1. A powder mixture for powder metallurgy comprising a raw material powder, a binder, and graphite powder, the powder mixture comprising:

The said raw material powder contains 90 mass % or more of iron-base powders of the said raw material powder,

The average particle diameter of the graphite powder is less than 5㎛,

_{The ratio of the mass (m b} ) of the binder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m b} /(m _r + m _g )×100] is 0.10 to 0.80 mass %,

_{The ratio of the mass (m g} ) of the graphite powder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m g} /(m _r + m _g )×100] is 0.6 -1.0 mass %,

The surface of the raw material powder is coated with at least a part of the binder,

A powder mixture for powder metallurgy, wherein a surface of the binder coated on the surface of the raw powder is coated with at least a part of the graphite powder.

2. The powder mixture for powder metallurgy according to 1, wherein the binder is 1 or 2 or more selected from the group consisting of fatty acid amide, copolyamide, polyurethane, and polyethylene.

3. The powder mixture for powder metallurgy according to 1 or 2, wherein the raw material powder contains one or two or more auxiliary materials selected from the group consisting of alloy powder and machinability improvement powder.

4. A first mixing step of mixing the raw material powder and the binder at a temperature equal to or higher than the melting point of the binder to obtain a binder-coated powder;

a second mixing step of mixing the binder-coated powder and graphite powder having an average particle diameter of less than 5 μm at a temperature equal to or higher than the melting point of the binder to obtain a powder mixture for powder metallurgy;

The said raw material powder contains 90 mass % or more of iron-base powders of the said raw material powder,

_{The ratio of the mass (m b} ) of the binder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m b} /(m _r + m _g )×100] is 0.10 to 0.80 mass %,

_{The ratio of the mass (m g} ) of the graphite powder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m g} /(m _r + m _g )×100] is 0.6 -1.0 mass %,

A method for preparing a powder mixture for powder metallurgy.

5. The method for producing a powder mixture for powder metallurgy according to the above 4, wherein the binder is 1 or 2 or more selected from the group consisting of fatty acid amide, copolyamide, polyurethane, and polyethylene.

6. The method for producing a powder mixture for powder metallurgy according to 4 or 5 above, wherein the raw material powder contains one or two or more auxiliary raw materials selected from the group consisting of alloy powder and machinability improving material powder.

The powder mixture for powder metallurgy of the present invention has very excellent fluidity. Therefore, while being able to extract|extract from a metal mold|die with little force at the time of shaping|molding, continuous shaping|molding can be performed without raise|generating a die|mold galling. Therefore, the yield of a molded article improves and high productivity can be implement|achieved. Moreover, according to the manufacturing method of this invention, the said powder mixture for powder metallurgy can be manufactured without using a solvent.

(Form for implementing the invention)

Hereinafter, the present invention will be specifically described.

The powder mixture for powder metallurgy of the present invention contains raw material powder, a binder, and graphite powder as essential components. Hereinafter, each said component is demonstrated.

[Raw Powder]

As the raw material powder, a powder containing iron-based powder is used. The proportion of the iron-based powder in the raw material powder may be 90% by mass or more, but more preferably 95% by mass or more. In addition, the upper limit of the ratio of the iron-base powder in raw material powder is not specifically limited, It may be 100 mass %. That is, the raw material powder may consist only of iron-based powder. However, from the viewpoint of imparting various characteristics to the finally obtained sintered body, it is preferable to use a mixed powder comprising an iron-based powder and an auxiliary material to be described later as the raw material powder.

[iron powder]

The iron-based powder is not particularly limited, and any iron-based powder can be used. Examples of the iron-based powder include iron powder (so-called pure iron powder) and alloy steel powder. As the alloy steel powder, a prealloy steel powder (completely alloyed steel powder) in which an alloying element is pre-alloyed at the time of melting, a partially diffusion alloyed steel powder in which an alloying element is partially diffused into iron powder, and an alloying element in addition to the prealloyed steel powder are partially diffused It is preferable to use 1 or 2 or more selected from the group consisting of hybrid steel powder. Here, "iron-based powder" refers to a metal powder having an Fe content of 50% by mass or more, and "iron powder" refers to a powder composed of Fe and unavoidable impurities.

The method for producing the iron-based powder is not limited, and an iron-based powder produced by any method may be used. Examples of the iron-based powder that can be suitably used include an atomized iron-based powder produced by an atomization method, or a reduced iron-based powder produced by a reduction method. and the like.

Although the average particle size of the iron-based powder is not particularly limited, it is preferably set to 70 to 100 µm. In addition, unless otherwise stated, the particle diameter of iron-base powder shall be the measured value by dry sieving based on JISZ 2510:2004.

[Supplementary Ingredients]

The auxiliary material is not particularly limited, and arbitrary materials such as those commonly used as auxiliary materials in powder metallurgy can be used. As said auxiliary material, it is preferable to use 1 or 2 or more selected from the group which consists of alloy powder and machinability improving material powder. As said powder for alloys, in general, a metal powder can be used. As said metal powder, it is preferable to use 1 or 2 or more selected from the group which consists of Cu powder, Ni powder, and Mo powder, for example. Moreover, as said machinability improving material, MnS etc. are mentioned, for example. The ratio of the said auxiliary material in raw material powder shall be 10 mass % or less.

[bookbinder]

The surface of the raw material powder is coated with at least a part of the binder. As the binder, any binder can be used as long as it can make graphite powder adhere to the surface of the raw material powder. For example, one or two or more selected from the group consisting of fatty acid amides such as fatty acid monoamide and fatty acid bisamide, and organic resins can be used. Especially, it is preferable to use an organic resin, and it is more preferable to use 1 or 2 or more resin chosen from the group which consists of copolyamide, polyurethane, and polyethylene.

Addition amount of binder: 0.10-0.80 mass %

If the addition amount of the said binder is less than 0.10 mass %, the surface of raw material powder cannot fully be coat|covered with a binder. Therefore, the addition amount of a binder shall be 0.10 mass % or more. On the other hand, when the addition amount of a binder exceeds 0.80 mass %, a binder will also coat|cover the surface of graphite powder, and fluidity|liquidity will fall. Therefore, the addition amount of a binder shall be 0.80 mass % or less. Here, the amount of the binder added is the ratio _{of the mass (m b} ) of the binder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m b} /(m _r + m _g ) ×100]. In other words, the mass of the binder when the total mass of the raw material powder and the graphite powder is 100 parts by mass is 0.10 to 0.80 parts by mass.

It is preferable that the said binder is powdery. When the average particle diameter of the binder is less than 5 µm, the cost for pulverizing to the particle diameter increases, and the raw material cost becomes high. Therefore, from a viewpoint of reducing cost, it is preferable that the average particle diameter of a binder shall be 5 micrometers or more. On the other hand, when the average particle diameter of the binder exceeds 100 µm, the time required for uniform mixing with the raw powder increases, and productivity decreases. Therefore, from a viewpoint of further improving productivity, it is preferable to make the average particle diameter of a binder into 100 micrometers or less.

When the melting point of the binder is 60° C. or higher, it is possible to prevent the fluidity of the powder mixture from being lowered even in summer when the temperature is high. Therefore, it is preferable that melting|fusing point of a binder is 60 degreeC or more. On the other hand, when the melting point of the binder exceeds 160° C., the required time and energy increase in order to heat above the melting point of the binder, and productivity decreases. Therefore, it is preferable that melting|fusing point of a binder is 160 degrees C or less from a viewpoint of improving productivity further.

[Graphite Flour]

The surface of the binder coated on the surface of the raw material powder is coated with at least a part of graphite powder. In other words, the surface of the raw material powder is coated with graphite powder through a binder. By coating the surface of the iron-based powder with graphite powder through the binder, the lubricity of the surface of the iron-based powder is improved. In addition, since the graphite powder is interposed, direct contact between the iron-based powder and the mold is avoided, so that the iron-based powder does not adhere to and accumulate on the surface of the mold, and as a result, mold galling is less likely to occur.

Average particle size of graphite powder: less than 5㎛

In general, the particle size of graphite powder used in powder metallurgy is about 5 to 20 μm. On the other hand, iron-based powders generally have an average particle diameter of about 70 to 80 µm, and a maximum of about 250 µm. When the particle sizes of the graphite powder and the iron-based powder have such a relationship, it is difficult to uniformly coat the graphite powder on the surface of the iron-based powder. In this invention, in order to coat|cover the graphite powder uniformly on the surface of the raw material powder containing iron-base powder, the average particle diameter of graphite powder is made into less than 5 micrometers. On the other hand, although the lower limit of the average particle diameter of graphite powder is not specifically limited, When a particle diameter is made small too much, the energy required for grinding|pulverization increases, and it becomes economically disadvantageous. Therefore, it is preferable that the average particle diameter of graphite powder shall be 100 nm or more.

Addition amount of graphite powder: 0.6-1.0 mass %

When the amount of graphite added is less than 0.6% by mass, the outermost surface of the iron-based powder cannot be sufficiently coated with the graphite powder, and the surface of the iron-based powder is exposed. Therefore, in order to fully acquire the effect of the coating|cover by graphite powder, it is necessary to make the addition amount of graphite powder 0.6 mass % or more. On the other hand, graphite powder is finally consumed for carburizing at the time of sintering, and although characteristics, such as intensity|strength of a sintered compact, are improved, when the addition amount of graphite powder exceeds 1.0 mass %, the characteristic of a sintered compact falls on the contrary. Therefore, the addition amount of graphite powder shall be 1.0 mass % or less. In addition, the amount of graphite powder added here is the ratio _{of the mass (m g} ) of the graphite powder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m g} /(m _r + m) _g )×100].

[Manufacturing method]

Next, the manufacturing method of the said powder mixture for powder metallurgy is demonstrated. A manufacturing method in one embodiment of the present invention includes a first mixing step of mixing a raw material powder and a binder at a temperature equal to or higher than the melting point of the binder to obtain a binder-coated powder, and the binder-coated powder and an average particle diameter of less than 5 µm has a second mixing step of mixing the graphite powder at a temperature equal to or higher than the melting point of the binder to obtain a powder mixture for powder metallurgy.

If the binder and graphite powder are mixed in advance, the viscosity of the binder increases, and as a result, it becomes difficult to uniformly coat the binder on the surface of the raw material powder. Therefore, prior to the step of coating the graphite powder, a step of coating the surface of the iron-based powder with a binder is performed. Accordingly, only the binder can be uniformly coated on the surface of the raw material powder. From the said viewpoint, it is preferable to add and mix only a binder with respect to the raw material powder in a 1st mixing process. Moreover, in the 2nd mixing process, it is preferable to add-mix only graphite without adding a binder with respect to the raw material powder (binder-coated powder) coated with the binder.

In addition, when the binder and graphite powder are simultaneously coated on the surface of the raw material powder, the binder is also coated on the surface of the graphite powder, so that the effect of coating with the graphite powder cannot be sufficiently obtained. Then, by coat|covering graphite powder after coat|covering a binder, it can prevent that the surface of graphite powder will be coat|covered with a binder. In other words, in the powder mixture for powder metallurgy obtained by the method of the present invention, the surface of the raw material powder is uniformly coated with the graphite powder adhered through the binder. In addition, since the binder is hardly exposed on the surface of the raw material powder particles and the graphite powder is on the outside, it is excellent in fluidity and ejectability during mold molding.

There is no restriction|limiting in particular as a mixing means used in a 1st mixing process and a 2nd mixing process, Arbitrary things, such as various well-known mixers, can be used. From the viewpoint of easy heating, it is preferable to use a high-speed bottom stirring mixer, an inclined rotating fan-type mixer, a rotating hoe-type mixer, or a conical planetary screw-type mixer.

The mixing temperature at the time of implementing the said 1st mixing process and a 2nd mixing process is made into melting|fusing point (T _m ) or more of the binder to be used. In addition, the use that are used in combination the plurality of binders having a melting point different from, the highest of the melting points of a plurality of binder to use as the T _{m. It is preferable to set it as T m} +20 degreeC or more, and, as for the said mixing temperature, it is more preferable to set it as _{T m +50 degreeC or more.} On the other hand, the upper limit of the mixing temperature is not particularly limited, but if the mixing temperature is excessively high, the production efficiency decreases and adverse effects such as oxidation of the iron-based powder occur. Therefore, T _m +100° C. or less is preferable.

The powder mixture obtained as mentioned above can be used for manufacture of the sintered compact by powder metallurgy. The method for producing the sintered body is not particularly limited and can be produced by any method, but usually, the powder mixture for powder metallurgy is filled in a mold, compression-molded, sizing as necessary, and then sintering. good to do The compression molding is generally performed in a temperature range from room temperature to 180° C., but in particular, when it is necessary to increase the density of the green compact, warm molding in which both the powder and the mold are preheated and molded may be employed. The obtained sintered compact is further optionally subjected to carburizing-quenching, and heat treatment such as bright-quenching and high-frequency quenching can be performed to obtain products (such as mechanical parts).

In addition, to the powder mixture for powder metallurgy of the present invention, after the second mixing step, one or both of an additional auxiliary material and a lubricant may be optionally added. As the additional auxiliary material, the same as the auxiliary material contained in the above-mentioned raw material powder can be used. In addition, as the lubricant, it is preferable to use a lubricant other than an organic resin, and it is more preferable to use one or two or more lubricants selected from the group consisting of fatty acids, fatty acid amides, fatty acid bisamides, and metal soaps.

Example

Hereinafter, the configuration and effect of the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following example.

A powder mixture for powder metallurgy was prepared in the following procedure. First, the raw material powder and the binder were heated to a predetermined mixing temperature while mixing with a high-speed bottom stirring mixer (first mixing step). As said raw material powder, the raw material powder which consists of an iron powder (Atomized iron powder JIP301A by JFE Steel Co., Ltd.) as an iron-base powder, and Cu powder as an auxiliary material was used. Table 1 shows the type of binder used, the addition amount of each component, and the mixing temperature.

Next, in the said high-speed bottom stirring type mixer, graphite powder was further added, and it mixed in the state heated to the said mixing temperature (2nd mixing process). After the mixing was completed, the obtained powder mixture for powder metallurgy was discharged from the mixer. As the graphite powder, commercially available graphite powder having an average particle size shown in Table 1 was used.

In addition, for comparison, in some comparative examples, instead of adding graphite powder in the said 2nd mixing process, graphite powder was added in the said 1st mixing process. In addition, in some comparative examples (No.17), it mixed at room temperature, without heating in the said 1st mixing process and 2nd mixing process. In No. 17, since mixing was performed without heating, the surface of the raw material powder did not become the state coat|covered with the binder and graphite powder.

Next, for each of the obtained mixed powders for powder metallurgy, the flowability was measured and the molded body was press-molded in the order described below.

(Fluidity)

50 g of the obtained powder mixture for powder metallurgy was filled in a container having an orifice diameter of 2.5 mm, and the time from filling to discharge was measured to determine the fluidity (unit: s/50 g). In addition, other measurement conditions were based on JISZ2502:2012. The fluidity is an index indicating the fluidity of the mixed powder at the time of filling the mold, and the smaller the value of the fluidity, the better the fluidity of the mixed powder is. In addition, in some comparative examples, the powder mixture for powder metallurgy did not flow and was not discharged from the orifice.

(Pressure molding)

In the pressure molding, the powder mixture for powder metallurgy was pressure-molded using a mold to obtain a molded article having a diameter of 11.3 mm and a height of 11 mm. The molding pressure in the press molding was 686 MPa. The force (ejection force) required for ejecting the molded article from the mold and the green density of the obtained compact (average of the molded article) were measured. In addition, in some comparative examples, mold galling occurred and molding could not be performed.

The measurement results were as shown in Table 1. As can be seen from this result, the powder mixture for powder metallurgy that satisfies the conditions of the present invention has very good fluidity, can be ejected from the green compaction mold with little force, and mold galling during molding is suppressed. there was.

Claims (6)

A powder mixture for powder metallurgy comprising a raw material powder, a binder, and graphite powder, the powder mixture comprising:
The said raw material powder contains 90 mass % or more of iron-base powders of the said raw material powder,
The melting point of the binder included in the powder mixture for powder metallurgy is 81° C. or more,
The average particle diameter of the graphite powder is less than 5㎛,
_{The ratio of the mass (m b} ) of the binder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m b} /(m _r + m _g )×100] is 0.10 to 0.80 mass %,
_{The ratio of the mass (m g} ) of the graphite powder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m g} /(m _r + m _g )×100] is 0.6 -1.0 mass %,
The surface of the raw material powder is coated with at least a part of the binder,
A powder mixture for powder metallurgy, wherein a surface of the binder coated on the surface of the raw powder is coated with at least a part of the graphite powder. According to claim 1,
The powder mixture for powder metallurgy, wherein the binder is one or two or more selected from the group consisting of fatty acid amide, copolyamide, polyurethane, and polyethylene. 3. The method of claim 1 or 2,
The powder mixture for powder metallurgy, wherein the raw material powder contains one or two or more auxiliary materials selected from the group consisting of alloy powder and machinability improving material powder. A method for preparing a powder mixture for powder metallurgy, comprising:
A first mixing step of mixing the raw material powder and the binder at a temperature equal to or higher than the melting point of the binder to obtain a binder-coated powder;
a second mixing step of mixing the binder-coated powder and graphite powder having an average particle diameter of less than 5 μm at a temperature equal to or higher than the melting point of the binder to obtain a powder mixture for powder metallurgy;
The said raw material powder contains 90 mass % or more of iron-base powders of the said raw material powder,
_{The ratio of the mass (m b} ) of the binder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m b} /(m _r + m _g )×100] is 0.10 to 0.80 mass %,
_{The ratio of the mass (m g} ) of the graphite powder to the sum of _{the mass (m r} ) of the raw material powder and the mass (m _{g ) of the graphite powder [m g} /(m _r + m _g )×100] is 0.6 -1.0 mass %,
A method for producing a powder mixture for powder metallurgy, wherein a melting point of the binder included in the powder mixture for powder metallurgy is 81° C. or higher. 5. The method of claim 4,
The method for producing a powder mixture for powder metallurgy, wherein the binder is one or two or more selected from the group consisting of fatty acid amide, copolyamide, polyurethane, and polyethylene. 6. The method according to claim 4 or 5,
A method for producing a powder mixture for powder metallurgy, wherein the raw material powder contains one or two or more auxiliary materials selected from the group consisting of alloy powder and machinability improving material powder.