JPH0247809A - Threaded permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a threaded permanent magnet also favorable in dimension accuracy without recourse to cutting or cutting processing, accordingly without requiring heat treatment either, and without lowering corrosion resistance by making a remaining stress layer substantially not exist at the surface of a threaded permanent magnet. CONSTITUTION:This is manufactured by uniting it with a jig such as stainless copper, etc., that the shape of corresponding male thread is cut in case of forming female thread and with a jig that the shape of female thread is cut in case of forming male thread so as to sinter them. Coating treatment by flame coating of ceramic such as zirconia, etc., and others are applied to the surface of the jig to prevent the seizure. Also, a Nd-Fe-B magnet which is a sintered magnet and is mechanically sticky containing much Fe is optimum for forming screw thread as it follows the shape of the jig and does not crack. In a word, the permanent magnet consisting of 2-28% B, 8-30% R and Fe for the residual by atom percentage becomes optimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a permanent magnet that is threaded without cutting or grinding that leaves a residual stress layer.

[Prior Art] Permanent magnets are essential to modern life as important electrical and electronic components, and requirements for their shapes are also diversifying. For example, there is a need for threaded permanent magnets. Conventionally, magnets have been widely used as magnetic flux generating elements, but as various types of assemblies have appeared, it is possible to automate assembly if the magnet body has threads.
Customers began to request that it could be simplified and downsized.

In addition, threaded permanent magnets are easy to adjust the gap, and like permanent magnet NMR-CT (nuclear magnetic resonance tomography), which has been attracting attention in recent years, fine adjustments can be made on-site after assembly at the factory. Suitable for those who have no choice but to use it.

In such cases, conventionally, extremely difficult cutting and grinding processes had to be used to cut threads on the magnet.

[Problems to be Solved by the Invention] However, when cutting or grinding is used, there are problems such as deterioration of corrosion resistance and deterioration of magnetic properties due to a processed damaged layer.

There has been an invention in the past that attempts to remove the process-affected layer by aging treatment at 500 to 900°C (Japanese Patent Application Laid-Open No. 140-1989).
Publication No. 108). The publication states that this treatment improves the squareness of the demagnetization curve.

However, JP-A-61-140108 does not describe the composition of the magnet at all, and although there are examples of the effect of improving magnetic properties, there is no mention of corrosion resistance. Therefore, although the structure of the invention is unclear, according to research by the present inventors as described later, when such a structure is adopted, an R-rich layer is formed on the surface, resulting in an extremely low corrosion resistance. This is easily predicted, and as in the invention described in JP-A-61-264157, it is necessary to form an anti-oxidation coating on the surface. This is because R is selectively oxidized to oxygen, and corrosion progresses deep into the magnet body starting from there.

Accordingly, one object of the present invention is to provide a threaded permanent magnet that does not require cutting or grinding, does not require heat treatment, does not reduce corrosion resistance, and has good dimensional accuracy.

[Means for Solving the Problems] In order to solve these problems, the present invention provides a threaded permanent magnet characterized by substantially no residual stress layer on its surface.

To form a female thread, use a jig made of stainless steel or other material cut in the shape of a corresponding male thread, and conversely, to form a male thread, use a jig in the shape of a female thread. It can be manufactured by sintering.

In order to prevent seizure, the surface of the jig is preferably coated with ceramic such as zirconia by thermal spraying. The material of the jig should be chosen to have a large coefficient of linear expansion, depending on the material of the permanent magnet to be manufactured.

If the permanent magnet in the present invention is a sintered magnet, it may be Alnico, Mn-Al-C magnet, SmCo, or Sm.

Co□, Nd-Fe-B magnets can be selected, but the optimal one is Nd, which contains a large amount of Fe and is mechanically sticky.
-Fe-B magnets are optimal because they can form screw threads according to the shape of the jig without cracking. Next, Sm--Go based magnets, which have excellent magnetic properties, are suitable.

In other words, B is 2 to 28% in atomic percentage, R is 8 to 30% (where R is at least one rare earth element including Y), and the balance is Fe (a portion can be replaced by an additional element M including Co). A permanent magnet consisting essentially of is most suitable for the present invention.

The reason for limiting the above-mentioned components is the conventionally known reasons (for example, Japanese Patent Application Laid-open No. 5
9=132104, 59-89401).

That is, if B is less than 2%, the coercive force will be less than 1 kOe, which is undesirable, and if it exceeds 28%, the Br will be less than about 4 kG, making it impossible to compete with hard ferrite magnets.

In addition, R must be 8% in order to make the coercive force 1 k Oe or more.
The above is necessary, and from the viewpoint of flammability, difficulty in industrial handling, and cost increase, it is set to 30% or less. Here, R can be one or more kinds including Y, but Nd is particularly preferred because of its magnetic properties.

Mainly composed of Pr, it may be partially replaced with Ce or Mitsushi metal for the purpose of cost reduction, and heavy R such as Dy and Tb may be partially replaced for applications requiring heat resistance. If R is less than 8% in atomic percentage, the coercive force will be less than 1 kOe, which is undesirable, and if it exceeds 20%, the corrosion resistance will drop significantly, which is not preferred.

Furthermore, it can contain up to 50% Co (Japanese Unexamined Patent Publication No. 59-6
4733), the addition of Go has the effect of increasing Tc and improving heat resistance, but if it exceeds 50%, the coercive force i
This is because Hc becomes less than 1 kOe.

Furthermore, a conventionally known additive element M can be contained.

The predetermined additive elements include A1, Ti, ■, Cr, Mn,
Zr, Hf, Nb, Ta, Mo.

Addition of known additive elements such as Ge, Sb, Sn, .Bi, Ni, W, etc. does not have any adverse effect on the effects of the present invention.

The above-mentioned "sintering" is not necessarily limited to sintering in the narrow sense of powder metallurgy, but may be anything that involves a reaction similar to a sintering reaction at high temperatures. This includes those that are pressed, and also those that are subjected to warm plastic processing. Or rather than ultra-quick cooling,
This is because even if the cast alloy is warm-processed, it is sufficient to insert a thread-shaped jig at that time, and there is no reason to limit it to the powder metallurgy method.

The present invention will be explained below with reference to Examples.

[Example] (Example 1) Nd 14%, 88%, Nb1. ．． An alloy having a composition of 2% Fe and the balance Fe was produced by arc melting. The obtained ingot was coarsely pulverized using a stamp mill and a disc mill, adjusted to 32 meshes or less, and then finely pulverized using a jet mill. The grinding medium is nitrogen gas, and the grinding particle size is 3.5 μm (F.

S, S, S). Here F, S, S, S are Fisc
herSub-8ieve 5izer,
The measurements are shown using a Fischer particle size analyzer using the air permeation method.

The obtained finely pulverized powder was subjected to transverse magnetic field molding (
(pressure direction and magnetic field direction are perpendicular).

ISO screw M12. A jig sprayed with zirconia was inserted into the surface of 5US304'll', which had a male screw having a length of 10 mm cut on the outer periphery, to form a female screw. Molding pressure is 2 tons/c
m”.The obtained molded body was heated to 11 m in an argon atmosphere.
Sintering was carried out at 00°C for 1 hour, and after sintering, it was rapidly cooled in an argon stream.

(Comparative Example) The same procedure as in this example was performed except that a jig was inserted and molded, and after sintering, an M12 thread of Is○ was cut on the inner periphery using an inner periphery grinder. In this case, the yield of grinding was extremely poor and it was necessary to prepare as many as eight samples to obtain one sound sample, and the processing had to take a long time.

Compare the magnetic properties of the threaded magnets obtained in Table 10
According to the present invention, there is no deterioration in magnetic properties, but in the case of the comparative example, the deterioration is significant.
PCT test (Pressure) in water vapor at atmospheric pressure
The results are shown below for evaluating the corrosion resistance of Cooker Te5t).

In this table, "durability time" indicates the time until rust occurs as a result of the PCT test. It can be seen that the comparative example is extremely bad. This is thought to be due to residual stress in the surface layer due to thread cutting.

Table 1 [Effects of the Invention] According to the present invention, a threaded permanent magnet can be obtained by a simple method without deterioration of magnetic properties.

This can be expected to lead to the development of new uses for permanent magnets, such as magnets that can be easily finely adjusted in NMR-CT devices.

-3:

Claims (3)

[Claims] (1) A threaded permanent magnet characterized by substantially no residual stress layer on its surface. (2) 2-28% B and 8-30% R in atomic percentage
(However, R is at least one kind of rare earth element including Y),
The threaded permanent magnet according to claim 1, wherein the threaded permanent magnet consists essentially of Fe (part of which can be replaced with a metal element containing Co). (3) Claim 1 which is a rare earth element-cobalt based permanent magnet.
Threaded permanent magnets as described in .