KR20050095258A - A thin-plate method for nd-temporary magnet - Google Patents

Abstract

According to the present invention, the chemical polishing process is reduced according to the length ratio by the acid treatment after cutting to have an extended length as much as the thickness to be reduced for each dimension of the product. It solves the problem of having the thickness, and also relates to the thinning method of Nd-based sintered magnets that can freely thin the thickness of the sintered magnet while preserving the product quality, that is, the magnetic properties or uniform surface roughness. .

Description

A thin-plate method for Nd-temporary magnets

The present invention relates to a method for thinning Nd-based sintered magnets, and more particularly, to a method for thinning Nd-based sintered magnets used in motors, actuators, magnetic sensors, and magnetic circuits of various electronic products.

Currently, permanent magnets are used in various motors, actuators, magnetic sensors, and magnetic circuits such as home appliances, office automation products, acoustic devices, medical devices, mobile communication terminals, and the like. It has been widely used because it can be manufactured inexpensively.

However, since Alnico magnets and ferrite magnets have a theoretical limit in obtaining high residual magnetic flux densities of 0.5T or more, a study on new types of permanent magnets has been conducted to apply them to devices requiring high functionalization. Since the 1960s, rare earth permanent magnets have been invented utilizing the strong crystal magnetic anisotropy of hard magnetic materials.

Among these rare earth permanent magnets, Sm-Co magnets are known as typical permanent magnets having a high residual magnetic flux density of 0.5T or more. However, since both Sm and Co are expensive materials, their manufacturing costs are inevitably expensive.

Nd-based (Nd-Fe-B) magnets, another rare earth-based permanent magnets, exhibit excellent magnetic properties of 40-50 MGOe class, which is about 10 times more energy-efficient than Alnico and ferrite magnets, and are relatively inexpensive for the entire weight of Fe (Fe). ), Which is 60 to 70% by weight, is inexpensive compared to Sm-Co magnets, and resource constraints on material components are also rapidly being widely used in recent years.

Such Nd-based permanent magnets are largely divided into sintered magnets formed by the powder metallurgy process and quenched magnets manufactured by the liquid quenching method. Among these, the manufacturing process for the sintered magnets is as follows.

Nd-based sintered magnet as described above is the melting and casting process of inducing melting and casting the raw material to form an alloy ingot (Ingot) of the Nd-Fe-B phase; A powder manufacturing step of hydrotreating to improve the grinding ability of the prepared ingot, and then grinding the powder into several micrometers in a low oxygen atmosphere; It is generally produced through a bulking process of manufacturing the powder into a magnet by magnetic field molding and sinter densification at a temperature of 1000 to 1100 ° C.

Nd-based sintered magnets manufactured as described above can be produced at a relatively low cost by melting, cooling, and heat-treating processes compared with quenched magnets, while quenched magnets are isotropic, whereas sintered magnets are higher due to magnetic properties that are anisotropic. Sintered magnets are frequently used because they have a residual magnetic flux density.

On the other hand, according to the trend of small size, light weight, and light weight, various electronic products including video, audio equipment, mobile phones, permanent magnets mounted on magnetic sensors and magnetic circuits also require high performance, miniaturization, and light weight.

However, until now, the shape processing of Nd-based sintered magnets is limited to mechanical methods, so the reproducibility does not come out at the product thickness of 0.5mm, so the process state is very unstable, and the sintered body breaks when cutting. In general, cutting by a 0.3 mm thick diamond wheel has been shown to limit the sintered magnet having a thickness of 0.6 mm, which is twice the thickness of the wheel.

Therefore, the present invention is configured to solve the above problems, the thickness of the Nd-based sintered magnets used in motors, actuators, magnetic sensors and magnetic circuits of various electronic products by chemical acid treatment rather than mechanical processing method The present invention relates to a thinning method of an Nd-based sintered magnet that can be made thin.

The present invention to achieve the above object,

A loading step of mounting an ingot (Ngot-Fe-B) sintered magnet in a cutting machine;

Cutting the loaded sintered magnet to a desired standard using a diamond wheel;

A degreasing step of removing the cutting oil and the adhesive by collecting the cut sintered magnet;

In the thinning method of Nd-based sintered magnet comprising; step of barrel polishing the degreasing sintered magnet in a high-speed centrifugal polishing machine,

Cut to have an extended length equal to the length of the thickness to be reduced with respect to the dimensions of the product to be obtained in the cutting step,

It is achieved by providing a method for thinning Nd-based sintered magnets, characterized in that a chemical polishing step of dipping the sintered magnets subjected to barrel polishing to an acid solution and reducing them to the desired dimensions while stirring.

Hereinafter, the present invention will be described in more detail.

First, the Nd-Fe-B-based sintered magnet manufactured by the conventional melting, cooling, and heat treatment process is made into an ingot block, bonded to a jig in the block state, and then cut. It goes through a loading step of mounting on the machine.

The sintered magnet mounted on the cutting machine as described above is subjected to a cutting step that is cut according to the specifications set by the user by a diamond wheel, in which case the thickness of the thickness to be reduced for each dimension to be obtained as the final product It is desirable to cut to have an extended length by the length.

For example, in order to obtain a coin-shaped sintered magnet by cutting a cylindrical ingot, the diameter of the sintered magnet formed after cutting is the thickness of the thickness to be reduced later on to the original diameter of the small magnet to be obtained as the final product. Is to have an extended length equal to the length.

In addition, when obtaining a sintered magnet by cutting a cube or cuboid ingot, the horizontal and vertical lengths of the sintered magnets formed after the cutting are respectively equal to the horizontal and vertical lengths of the sintered magnets to be obtained as final products. It is to have an extended length as long as the thickness to be reduced.

In addition, when cutting a polyhedron-type ingot such as a pentagonal or a hexahedron, the length of the thickness to be reduced later is applied to each dimension in the same manner as described above to cut to have an extended length.

 As such, the sintered metal cut to have an extended length for each dimension is subjected to a degreasing step of removing the foreign matter, ie cutting oil and binder components, deposited on the surface of the alkali degreasing solution, ie, cutting oil.

The degreasing solution used in the degreasing step is an aqueous solution containing sodium hydroxide (NaOH) and 5% by weight of a degreasing agent, respectively, by immersing and cleaning the sintered metal in the degreasing solution at a temperature of 50 to 60 ° C. for 10 minutes. Is done.

The desintered sintered metal is subjected to a polishing step for removing burr and scale and surface treatment in a high-speed centrifugal polishing machine. The polishing step as described above will be omitted since the conventional barrel polishing method for the metal is applied as it is.

As described above, after removing the abrasive by ultrasonic cleaning of the sintered metal subjected to barrel polishing, it is subjected to a chemical polishing step of dipping in an acidic solution and reducing it until it reaches a desired size while stirring. Such chemical polishing step is preferably performed in a stirrer equipped with an ultrasonic wave or a vibrator, more preferably, a cylindrical barrel is installed in the stirrer to enable the inflow and rotation of the acid solution, and the sintered magnet is put into the barrel. It is better to carry out by barrel method of treatment.

It is preferable to maintain the temperature 20 to 30 ℃ during the acid treatment, which is a problem that the manufacturing process is prolonged due to too slow to shrink when the acid treatment is performed at less than 20 ℃, on the contrary 30 ℃ If the acid treatment is carried out in excess of, the shrinkage is too fast to control the process.

Such acid solution is preferably such that the pH concentration is within the range of 0.2 ~ 1.0, it is impossible to control the operation due to overreaction when the pH concentration is lower than the above, the toxic gas of nitrate-based This is because there is a problem that the working environment is not good, because when it is maintained higher than the above pH concentration, the process of shrinking is too slow and the manufacturing process is prolonged.

The acid solution used as described above may be selected from nitric acid (Conc-HNO ₃ ), sulfuric acid (Conc-H ₂ SO ₄ ) or hydrochloric acid (Conc-HCl) solution, more preferably nitric acid solution is used. . When acid treatment is carried out in sulfuric acid or hydrochloric acid solution, salts generated during corrosion are attached to the surface of sintered magnet, resulting in a product with uneven roughness, whereas nitric acid by-product nitrogen oxide is evaporated to give an aqueous solution. Because it dissolves in the phase, it is possible to obtain a product with good working environment and smooth surface and uniform illumination.

In addition, during the above acid treatment, the angled parts, such as the corners of the product, have a larger degree of shrinkage than other parts, so that the sharp part disappears and the corners are smoothly formed, so that the product is immediately processed without any additional polishing process. It is possible to use.

The sintered magnet chemically polished to the desired size through this acid treatment is washed with clean water and then dried to complete the sintered magnet having a thin thickness. In addition, nickel (Ni) or zinc (Zn) plating, ceramic coating, Teflon coating, and peering coating on the surface of the sintered magnet manufactured to improve the corrosion resistance and physical properties of the product. Coating of the same organic material may optionally be carried out.

Nd-based sintered magnets, which have undergone such a thinning process, are cut to have an extended length equal to the thickness to be reduced for each dimension of the product, and then a reduction process according to the length ratio is added through acid treatment. Solve the problem of having a thickness of less than 0.5mm only, it is also possible to freely thin the thickness of the sintered magnet while maintaining the quality of the product, that is, the magnetic properties or uniform surface roughness as it is.

Nd-based sintered magnets thinned by the above-described method have recently been used for various home appliances, office automation products, acoustic devices, medical devices, mobile communication terminals, etc., which require high performance, miniaturization and light weight, and various motors, actuators, and magnetic sensors. And magnetic circuits.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are merely illustrative of the present invention, and the present invention is not limited by the following Examples.

<Example 1>

The ingot Nd-Fe-B-based sintered magnet block is bonded to a jig and transferred to a cutting tool for mounting, and then 0.6 mm thick, 2.35 mm wide, using a 0.3 mm thick diamond wheel. Cut to 15.35 mm rectangular parallelepiped, and the cut sintered magnet was immersed and washed for 10 minutes at a temperature of 50 ° C. in a 1 L degreasing solution to which 50 g of sodium hydroxide (NaOH) and a degreasing agent were added, respectively, and then degreased. The metal was put into a high-speed centrifugal grinding machine, barrel-polished, the ultrasonically washed the polished sintered metal was removed to remove the abrasive, and the polished sintered metal was stirred at a temperature of 20 ° C. in a stirrer containing a nitric acid solution having a pH of 0.2, 0.5, or 1.0, respectively. Chemical polishing was carried out at to obtain a thin plated sintered magnet having a thickness of 0.25 mm, a width of 2 mm, and a length of 15 mm, respectively. The thin plated sintered magnet was washed with water and dried, and then nickel (Ni) plating was performed on the surface thereof so that the coating thickness was 20 μm.

The time taken for chemical polishing and the error rate for each value, and the surface Gauss through a Gaussian meter for the thinned sintered magnet as described above are shown in Table 1 below.

PH Time Measurement result % Error Surface Gauss (G) 1.0 14 minutes Within 3% 883 0.5 8 minutes Within 3% 869 0.2 4 minutes Within 3% 846

<Example 2>

The ingot Nd-Fe-B-based sintered magnet block is bonded to a jig and transferred to a cutting tool for mounting, and then 0.3 mm thick diamond wheel has a thickness of 0.6 mm, width 2.3 mm, Cut into 15.3 mm long rectangular parallelepiped, and the cut sintered magnet was immersed and washed for 10 minutes at a temperature of 50 ° C. in a 1 L degreasing solution to which sodium hydroxide (NaOH) and 50 g of a degreasing agent were added, respectively, and then degreased. The metal was put into a high-speed centrifugal polishing machine, barrel-polished, and the abrasive was removed by ultrasonic cleaning of the polished sintered metal, and the polished sintered metal was 25 ° C. in a stirrer containing a nitric acid solution having a pH of 0.2, 0.5, and 1.0, respectively. The chemical polishing was carried out at to obtain a thin plated sintered magnet having a thickness of 0.3 mm, a width of 2 mm and a length of 15 mm, respectively. The thin plated sintered magnet was washed with water and dried, and then zinc (Zn) plating was performed on the surface thereof so that the coating thickness was 7 μm.

The time taken for chemical polishing and the error rate for each value, and the surface Gauss through a Gaussian meter for the thinned sintered magnet as described above are shown in Table 2 below.

PH Time Measurement result % Error Surface Gauss (G) 1.0 10 minutes Within 3% 1083 0.5 7 minutes Within 3% 1124 0.2 3 minutes 30 seconds Within 3% 1068

<Example 3>

The ingot Nd-Fe-B type sintered magnet block is bonded to a jig, transferred to a cutting tool, and mounted.Then 0.3 mm thick diamond wheel, 0.6 mm thick, 2.2 mm wide, Cut into 15.2 mm cuboid shape, and the cut sintered magnet was immersed and washed at a temperature of 50 ° C. for 10 minutes in a 1 L degreasing solution to which sodium hydroxide (NaOH) and 50 g of a degreasing agent were added, respectively, and then degreased. The metal was put into a high-speed centrifugal polishing machine, barrel-polished, ultrasonically washed to remove the abrasive, and then the polished sintered metal was stirred in a stirrer containing a nitric acid solution having a pH of 0.2, 0.5, or 1.0, respectively. The chemical polishing was carried out at to obtain a thin plated sintered magnet having a thickness of 0.3 mm, a width of 2 mm and a length of 15 mm, respectively. The thin plated sintered magnet was washed with water and dried, and then the surface was subjected to a Teflon coating treatment having a coating thickness of 10 μm.

The time taken for chemical polishing and the error rate for each numerical value and the surface Gauss through a Gaussian meter for the thinned sintered magnet as described above are shown in Table 3 below.

PH Time Measurement result % Error Surface Gauss (G) 1.0 8 minutes Within 3% 1472 0.5 5 minutes 30 seconds Within 3% 1382 0.2 3 minutes Within 3% 1469

As a result of looking through Examples 1 to 3, the sintered magnet having a thickness of up to 6 mm through mechanical cutting could be thinned to have a thickness of 2.5 to 4 mm through chemical polishing. It was confirmed that the thickness of the sintered magnet can be freely thinned while maintaining the quality, ie, residual magnetic flux density and uniform surface roughness.

As described above, in the thinning method of the Nd-based sintered magnet of the present invention, the chemical polishing process is reduced according to the length ratio by acid treatment after cutting to have an extended length by the thickness to be reduced for each dimension of the product. According to the present invention, the problem of having a thickness of less than 0.5 mm by the conventional mechanical method has been solved, and the thickness of the sintered magnet can be freely thinned while preserving the product quality, that is, the magnetic property or uniform surface roughness. Can be.

In addition, the present invention provides a variety of motors, such as various household appliances, office automation products, sound equipment, medical equipment, mobile communication terminals, etc., which require high performance, miniaturization and light weight of Nd-based sintered magnets, It can be usefully used in actuators, magnetic sensors and magnetic circuits.

Claims (6)

A loading step of mounting an ingot (Ngot-Fe-B) sintered magnet in a cutting machine; Cutting the loaded sintered magnet to a desired standard using a diamond wheel; A degreasing step of removing the cutting oil and the adhesive by collecting the cut sintered magnet; In the thinning method of Nd-based sintered magnet comprising; step of barrel polishing the degreasing sintered magnet in a high-speed centrifugal polishing machine, Cut to have an extended length equal to the length of the thickness to be reduced with respect to the dimensions of the product to be obtained in the cutting step, The method of thinning Nd-based sintered magnets is characterized in that the chemical polishing step of dipping the sintered magnet after the barrel polishing in an acidic solution and shrinking until the desired size is obtained while stirring. The method of claim 1, wherein the chemical polishing step is a thinning method of Nd-based sintered magnet, characterized in that the acid solution is maintained at a temperature of 20 ~ 30 ℃. The method according to claim 1 or 2, wherein the acidic solution has a pH of 0.2 ~ 1.0 thinning method of Nd-based sintered magnet, characterized in that. The method of claim 3, wherein the acid solution is selected from nitric acid (Conc-HNO ₃ ), sulfuric acid (Conc-H ₂ SO ₄ ) or hydrochloric acid (Conc-HCl) solution, more preferably nitric acid solution is used Thinning method of Nd type sintered magnet made into. The method of claim 4, further comprising coating the organic material such as nickel (Ni) or zinc (Zn) plating, ceramic coating, Teflon coating, or peering coating on the surface of the sintered magnet after the barrel polishing step. Thinning method of Nd-based sintered magnet, characterized in that it comprises. Nd-based sintered magnet characterized in that the thinning by the thinning method of claim 1.