KR101943608B1 - Electro-polishing method of Fe-based green compact for powder metallurgy product - Google Patents

Abstract

The present invention relates to an electro-polishing method of Fe-based green compact using an electro-polishing device having an electrolytic bath in which an anode, a cathode, and an electrolyte are accommodated, which comprises the following steps of: a) enabling Fe-based green compact of the anode to be in contact with the electrolyte; and b) applying voltage or a current to the anode and the cathode to remove burr of the Fe-based green compact. The electrolyte comprises 4-11 wt% of an inorganic acid, 5-15 wt% of water, and the remainder consisting of an alcohol-based solution.

Description

[0001] The present invention relates to an electropolishing method for an iron-based powder compact for powder metallurgy products,

The present invention relates to an electrolytic polishing method of an iron-based powder molded article, and more particularly, to an electrolytic polishing method of an iron-based molded product which removes burrs generated during molding by electrolytic polishing.

Generally, an iron-based sintered product is manufactured by molding a raw material powder and sintering it.

However, a burr (bur) remains on the outer surface of the iron-based sintered product after such a molding or sintering process.

To remove these burrs, a mechanical processing process such as a brush is performed. However, the sintered product processed by the mechanical processing process is not smooth in its surface, and burrs may still exist on the outer surface thereof.

Electro polishing is performed by using a metal product dissolved in an electrolytic solution as an anode and using a metal insoluble in an electrolyte as a cathode and applying a voltage between the anode and the cathode to form a metal Thereby causing electrolysis at the surface of the product and polishing the surface of the metal product. In order to polish a metal product by electrolytic polishing, an electrolytic solution (electrolytic solution) is filled in an electrolytic bath, a metal product to be polished is set as an anode, a negative electrode not dissolving in the electrolytic solution is provided, DC power is applied. In electrolytic polishing, when a current is applied even under the condition that the metal product is not easily dissolved in the electrolytic solution, the metal product is forcibly dissolved little by little.

When electrolytic polishing proceeds, a high viscosity liquid layer (viscous layer) containing a large amount of dissolved metal ions from the positive electrode surrounds the positive electrode. In the viscous layer saturated with metal ions, the metal is no longer dissolved and forms a high positive potential, so that it is actively bonded with oxygen to form an oxide film. At this time, the dissolved metal ions are mainly accumulated in the concave portion of the metal surface, and the metal is not dissolved because the migration and spreading of the metal ions are small in the concave portion and the electricity is not good. On the other hand, in the convex portion of the metal surface, since the metal ion layer is formed thin, the current is concentrated, and the metal surface is easily dissolved, and the surface of the product as a whole is smoothed.

Regarding such electrolytic polishing, Korean Patent No. 0739298 discloses an electrolytic polishing apparatus and an electrolytic polishing method using the electrolytic polishing apparatus. However, when general steel is used for electrolytic polishing, soot is generated and the appearance of the product is not good. In addition, when electrolytic polishing is carried out using a powder metallurgy molded article, there is a problem that the outer surface of the powder metallurgy molded article is rapidly melted in a specific electrolytic solution and the quality of the final sintered molded article is lowered.

Disclosure of the Invention The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a powder metallurgical product which requires high dimensional precision, and which removes burrs, which are inevitably generated in a mold separating part, And a method of electrolytic polishing of an iron-based molded product.

The present invention also provides a method of producing an iron-based sintered alloy using an electrolytic polishing method of an iron-based molded article.

However, the technical problem to be solved by the present invention is not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, an electrolytic polishing method of an iron-based molded article according to an embodiment of the present invention is an electrolytic polishing method of an iron-based molded product using an electrolytic polishing apparatus including an anode, a cathode, and an electrolytic bath containing an electrolyte, ) Bringing the iron-based molded article of the anode into contact with the electrolyte; And b) applying a voltage or an electric current to the anode and the cathode to remove burrs of the iron-based molded article.

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the electrolytic solution may be composed of 4 to 11% by weight of inorganic acid, 5 to 16% by weight of water, and a residual alcohol-based solution.

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the iron-based shaped article may contain 0.1 to 0.9% by weight of carbon and the balance iron.

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the iron-based shaped article is a metal alloy containing 0.6 wt% or less phosphorus (more than 0 wt%), 3.0 wt% or less copper (more than 0 wt%), 5.0 wt% (More than 0 wt%), molybdenum 3.0 wt% or less (more than 0 wt%), and chromium 4.0 wt% or less (more than 0 wt%).

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the density of the iron-based shaped article may be 6.5 to 7.5 g / cm ³ .

In the electrolytic polishing method of an iron-based molded article according to an embodiment of the present invention, the alcohol-based solution may include at least one or more selected from the group consisting of C1 to C5 alkyl alcohols and C1 to C5 alkoxy alcohols.

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the alcohol-based solution may be composed of 65 to 85% by weight of C1 to C5 alkyl alcohol and 5 to 15% by weight of C1 to C5 alkoxy alcohol .

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the inorganic acid may be selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid, perchloric acid, chromic acid, and nitrous acid.

In the electrolytic polishing method of an iron-based molded article according to an embodiment of the present invention, the voltage may be applied at 20 to 60 V in step b).

In the electrolytic polishing method of the iron-based shaped article according to an embodiment of the present invention, the time for applying the voltage may be 10 to 90 seconds.

The present invention also includes a method for producing an iron-based sintered alloy using the electrolytic polishing method of the iron-based shaped article.

The method for producing an iron-based sintered alloy according to an embodiment of the present invention includes a step of sintering the iron-based shaped article described above in a reducing atmosphere.

In the method of manufacturing an iron-based sintered alloy according to an embodiment of the present invention, the sintering may be performed at 1000 to 1300 ° C.

The present invention also includes an iron-based sintered product produced by the above-described method for producing an iron-based sintered alloy.

In the electrolytic polishing method of an iron-based molded article according to the present invention, the burr is removed by using the above-described iron-based molded product and an electrolytic solution, whereby the dimensional accuracy and surface appearance are improved.

Further, the present invention can remove burrs of metal products for internal combustion engines having a complicated structure. In the case of powder metallurgy products, soot is not generated by the reduction reaction of the sintering atmosphere gas such as nitrogen or hydrogen in the sintering process after molding, There is an advantage that an additional surface treatment process is not necessary.

1 is a schematic diagram showing that one end of an iron-based molded article according to an embodiment of the present invention is performed by electrolytic polishing,
2 is a process diagram showing an electrolytic polishing method of an iron-based molded product according to an embodiment of the present invention,
3 is a SEM photograph of an iron-based sintered alloy manufactured according to an embodiment of the present invention.

FIG. 1 is a schematic view showing that one end of an iron-based molded article according to an embodiment of the present invention is performed by electrolytic polishing, FIG. 2 is a process diagram showing a method of electrolytic polishing of an iron- And FIG. 3 is a SEM photograph of an iron-based sintered alloy manufactured according to an embodiment of the present invention.

In describing the present invention, " burr " means formed on the outer surface of a molded article or a sintered article. For example, as shown in FIG. 1, the burr may be formed at one end of the iron-based shaped article, or may be formed in the form of a layer on the outer surface of the iron-based shaped article.

As a result of studies on an electrolytic polishing method of an iron-based molded article, it has been found that the iron-based alloy produced by electrolytically polishing such an iron-based molded article contains an excessive amount of nickel, chromium, molybdenum, It was confirmed that problems such as erosion occurred on the surface of the alloy.

In order to solve this problem, by controlling the composition of the iron-based molded product and the electrolyte composition generated in the molding process, it is possible to prevent erosion by electrolytic polishing while sufficiently removing burrs and to prevent the erosion by electrolytic polishing, Electrolytic polishing method of iron-based molded product was developed.

 The present invention provides an electrolytic polishing method for an iron-based molded article (10) using an electrolytic polishing apparatus (1000) including an anode (100), a cathode (200) and an electrolytic bath containing an electrolyte, And an electrolyte; And b) applying a voltage or an electric current to the anode and the cathode to remove burrs of the iron-based molded article.

At this time, it is preferable that the electrolytic solution is composed of 4 to 11% by weight of inorganic acid, 5 to 16% by weight of water, and a residual alcohol-based solution.

2, the electrolytic polishing method of an iron-based molded article according to an embodiment of the present invention includes the steps of producing an iron-based molded article (S10), supplying an electrolytic solution (S20), and electrolytic polishing step S30 ).

The step (S10) of producing an iron-based molded article is a step of charging the iron-based powder into a metal mold and pressurizing the iron-based molded article with a press to prepare an iron-based molded article. The iron- / cm < ² > to produce the iron-based molded article.

In the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the iron-based shaped article may contain 0.1 to 0.9% by weight of carbon and the balance iron. The carbon content is preferable for improving the reaction rate during electrolytic polishing of the iron-based molded product and an electrolytic solution to be described later. Further, the content of carbon can be improved in the wear resistance by solidifying the Fe-base matrix in the production of the iron-based sintered alloy to be described later to strengthen the matrix structure and forming carbides with chromium (Cr) or the like.

The iron-based molded article may contain, in addition to the carbon, 0.6 wt% or less of phosphorus (more than 0 wt%), 3.0 wt% or less of copper (more than 0 wt%), 5.0 wt% or less of nickel , More than 0% by weight of molybdenum (Mo), and not more than 4.0% by weight of chromium (exceeding 0% by weight).

If the content of molybdenum (Mo) in the composition of the iron-based molded article exceeds 3.0% by weight, burrs of the iron-based molded product may not be removed sufficiently during electrolytic polishing.

 In addition, iron-based molded articles containing the above-described elements (carbon, phosphorus, copper, nickel, molybdenum, chromium, and iron) can be solid-dissolved in an Fe-based matrix during production of an iron-based sintered alloy to be described later to improve strength and heat resistance.

Meanwhile, in the electrolytic polishing method of an iron-based shaped article according to an embodiment of the present invention, the iron-based shaped article may have a density of 6.5 to 7.5 g / cm ³ .

When the density of the iron-based molded product is less than 6.5 g / cm ^3, the density of the iron-based molded product is too low to maintain the shape when the electrolyte is supplied, and the iron-based powder may be separated during the electrolytic polishing to contaminate the electrolyte. In addition, the reaction rate of electrolytic polishing may be lowered due to contaminated electrolytic solution.

On the other hand, when the density of the iron-based molded product is more than 7.5 g / cm ³ , pores are formed in the iron-based molded product, and cracks, lamination and the like may occur.

Next, a step S20 of supplying the electrolytic solution stored in the electrolytic bath 200 to the iron-based molded product is performed.

As described above, the present invention performs electrolytic polishing in order to remove burrs of iron-based molded articles generated in a processing step such as a molding step. The burr is mainly formed on the outer surface or one end of the iron-based molded article, and the burr is removed by applying a voltage or an electric current after bringing the electrolyte into contact with the burr.

In one embodiment of the present invention, the electrolytic solution may include an inorganic acid, an alcohol-based solution, and water.

The inorganic acid serves to improve the removal rate (or polishing rate) of the burr of the iron-based molded article. That is, the inorganic acid increases the concentration of hydrogen ions in the electrolytic solution, thereby lowering the pH of the electrolytic solution, thereby increasing the conductivity and eventually removing burrs of the iron-based molded product. At this time, it is preferable that the inorganic acid contains 4 to 11% by weight based on the total weight of the electrolytic solution.

In one embodiment of the present invention, the inorganic acid may be selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid, perchloric acid, chromic acid, and nitrous acid, It is better to achieve the purpose of.

The alcohol-based solution increases the resistance of the viscous layer on the surface of the iron-based molded article and acts as an insulating film during electrolytic polishing. That is, it is possible to prevent the formation of the metal oxide rapidly due to binding with oxygen after reduction of the Fe metal ion having a strong oxidizing power upon electrolytic polishing. At this time, the alcohol-based solution may include at least one or more selected from the group consisting of C1 to C5 alkyl alcohols and C1 to C5 alkoxy alcohols.

Specifically, the C1 to C5 alkyl alcohols may include methanol, ethanol, propanol, butanol, 2-ethylhexanol, and the like.

The C1 to C5 alkoxy alcohols include 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, methoxybutyl alcohol, ethoxybutyl alcohol, propoxybutyl alcohol, butoxybutyl alcohol and the like .

Meanwhile, in one embodiment of the present invention, the electrolytic solution may be used in an amount of 65 to 85% by weight of C1 to C5 alkyl alcohol, 5 to 15% by weight of C1 to C5 alkoxy alcohol, and 5 to 15% by weight of water . The electrolytic solution satisfying the above content level can further improve the deburring performance described above in the electrolysis application step (S30) described later.

Finally, an electrolytic polishing step (S30) is performed in which the anode is connected to the iron-based molded product, the cathode is connected to the electrolytic solution, and a voltage is applied to remove the burr.

In one embodiment of the present invention, in the electrolytic polishing step (S30), the DC voltage may be applied at a voltage of 20 to 60 V, preferably at a voltage of 30 to 50 V.

At this time, the voltage application time may be 10 to 90 seconds.

Meanwhile, the electrolytic polishing reaction formula in which the burrs of the iron-based molded product are removed in the voltage polishing step (S30) according to the present invention will be described.

That is, in the step of applying the voltage (S30), the burr and the electrolytic solution of the iron-based molded article satisfy at least one of the following reaction formulas 1 to 4:

[Reaction Scheme 1]

Fe -> Fe ^{3 +} + 3e ^-

[Reaction Scheme 2]

H ₂ O → 2H ⁺ + O ^2-

[Reaction Scheme 3]

_{2Fe + 3H 2 O → Fe 2} O 3 + 6H + + 6e -

[Reaction Scheme 4]

Fe ₂ O ₃ + 3H ^{+ -} > 2Fe ^{3 +} + 3H ₂ O

The present invention also provides a method of producing an iron-based sintered alloy using the electrolytic polishing method of the iron-based shaped article.

That is, the method for producing an iron-based sintered alloy according to the present invention includes a step of sintering the iron-based shaped article described above in a reducing atmosphere.

Here, the reducing atmosphere may mean an atmosphere in which a mixed gas containing hydrogen exists.

Further, in the method of manufacturing an iron-based sintered alloy according to an embodiment of the present invention, the sintering may be performed at 1000 to 1300 ° C, preferably 1100 to 1200 ° C. When the above sintering temperature range is satisfied, the iron-based sintered alloy according to the present invention can be improved in wear resistance, heat resistance, strength and the like.

The present invention also includes an iron-based sintered product using the above-described iron-based sintered alloy.

That is, the iron-based sintered alloy according to the present invention can be used for a metal product for an internal combustion engine having a complicated structure. Examples of the sintered product include a sensor ring, a rotor, and a hub, which are sintered parts for an internal combustion engine.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the examples.

Example 1

A metal powder having the composition shown in Table 1 and a lubricant were mixed. At this time, the lubricant was 0.8 parts by weight based on 100 parts by weight of the metal powder. Thereafter, the mixed powder was charged into a mold and molded by a press to a molding density of 6.6 g / cm ³ or more to prepare an iron-based molded article.

Next, 1000 mL of an electrolytic solution obtained by mixing 9 wt% of distilled water, 73 wt% of ethanol, 10 wt% of 2-butoxyethanol, and 8 wt% of perchloric acid was poured into an electrolytic cell provided with a cathode made of Pt.

Thereafter, the iron-based molded article was connected to a power source with an anode, and a burr-generated portion of the iron-based molded article was immersed in the electrolyte, and a voltage of 30 V was applied for 30 seconds.

Example 2

A voltage of 50 V was applied for 30 seconds in the same manner as in Example 1.

Example 3

The composition of the metal powder listed in Table 1 was used in the same manner as in Example 1.

Example 4

The composition of the metal powder listed in Table 1 was used in the same manner as in Example 1.

Example 5

The composition of the metal powder listed in Table 1 was used in the same manner as in Example 1.

Example 6

The composition of the metal powder listed in Table 1 was used in the same manner as in Example 1.

Example 7

The composition of the metal powder listed in Table 1 was used in the same manner as in Example 1.

Comparative Example 1

The composition of the metal powder listed in Table 1 was used in the same manner as in Example 1.

C
(weight%) Mo
(weight%) P
(weight%) Cu
(weight%) Ni
(weight%) Cr
(weight%) Fe Example 1 0.15 0.85 0.45 Honey. Example 3 0.15 2.8 0.45 Honey. Example 4 0.15 0.85 0.45 2.0 1.0 0.8 Honey. Example 5 0.15 0.85 0.45 2.0 3.6 2.7 Honey. Example 6 0.15 0.85 0.45 2.0 5.0 2.7 Honey. Example 7 0.15 0.85 0.45 2.0 3.6 4.0 Honey. Comparative Example 1 0.15 3.5 0.45 Honey.

Example 8

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Example 9

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Example 10

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Example 11

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Example 12

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Example 13

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Comparative Example 2

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Comparative Example 3

The composition of the electrolytic solution listed in Table 2 was used in the same manner as in Example 1.

Distilled water
(weight%) ethanol
(weight%) 2-butoxyethanol
(weight%) Perchloric acid
(weight%) Example 1 9 73 10 8 Example 8 9 73 10 4.5 Example 9 9 73 10 11 Example 10 6 80 6 8 Example 11 12 67 13 8 Example 12 One 90 One 8 Example 13 16 60 16 8 Comparative Example 2 10 75 12 3 Comparative Example 3 14 70 14 12

The iron-based molded articles prepared in the above Examples and Comparative Examples were charged into a mesh belt furnace and sintered at a temperature of 1115 to 1155 ° C at 120 ± 5 mm / min and in a nitrogen atmosphere or a nitrogen atmosphere containing 20% Respectively. An SEM photograph of the final sintered product according to Example 1 is shown in FIG.

The average size of burrs was measured using a three-dimensional roughness meter (Mahr, MarSurf XCR20) by using the above-described examples and comparative examples. The average size of the burrs is listed in Table 3 below. As shown in Table 3, the iron-based sintered alloy product produced according to the present invention was found to have an average bur size of about 19 μm.

Average size of burr
(μm) Example 1 11 Example 2 5 Example 3 26 Example 4 14 Example 5 31 Example 6 37 Example 7 38 Example 8 19 Example 9 8 Example 10 13 Example 11 9 Example 12 25 Example 13 7 Comparative Example 1 56 Comparative Example 2 52 Comparative Example 3 16, crack occurrence, surface unevenness

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (14)

a) contacting an electrolytic solution with an iron-based molded product of the anode; And b) removing a burr of the iron-based molded product by applying a voltage or an electric current to the positive electrode and the negative electrode,
The electrolytic solution includes inorganic acid, water and alcohol-based solution,
Wherein the alcoholic solution comprises 65 to 85% by weight of C1 to C5 alkyl alcohol and 5 to 15% by weight of C1 to C5 alkoxy alcohol.
A method of electrolytic polishing an iron-based shaped article using an electrolytic polishing apparatus comprising an anode, a cathode, and an electrolytic bath containing an electrolytic solution.
The method according to claim 1,
Wherein the electrolytic solution comprises 4 to 11% by weight of inorganic acid, 5 to 16% by weight of water, and an alcoholic solution.
The method according to claim 1,
Wherein the iron-based shaped article comprises from 0.1 to 0.9% by weight of carbon and the balance iron.
The method of claim 3,
The iron-based shaped article may contain at least 0.6 wt% phosphorous (greater than 0 wt%), 3.0 wt% or less copper (greater than 0 wt%), nickel 5.0 wt% or less (greater than 0 wt%), molybdenum 3.0 wt% ), And 4.0 wt% or less (more than 0 wt%) of chromium.
The method according to claim 1,
Wherein the iron-based shaped article has a density of 6.5 to 7.5 g / cm < ³ >.
delete delete 3. The method of claim 2,
Wherein the inorganic acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid, perchloric acid, chromic acid, and nitrous acid.
The method according to claim 1,
Wherein the voltage is applied at 20 to 60 V in step b).
The method according to claim 1,
Wherein the time for applying the voltage in the step b) is 10 to 90 seconds.
A method of producing an iron-based sintered alloy using the electrolytic polishing method of the iron-based molded article of claim 1.
12. The method of claim 11,
Wherein the manufacturing method comprises a step of sintering the iron-based shaped article in a reducing atmosphere.
13. The method of claim 12,
Characterized in that the sintering is carried out at 1000 to 1300 占 폚.
An iron-based sintered product produced by the manufacturing method of claim 11.

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