JP2023029010A - Encoder manufacturing method - Google Patents

Abstract

To provide an encoder manufacturing method with which it is possible to suppress the occurrence of cracks during manufacturing and thereby manufacture with high yield an encoder that excels in magnetic characteristics.SOLUTION: Provided is a method for manufacturing a toric encoder which is magnetized to multiple poles in the circumferential direction, the method including a step for injection molding in an annular shape, via a film-like gate 46, a magnet material toward metal molds 41, 42 having a cavity 43 formed in the shape of an encoder and curing it to obtain a compact. The magnet material contains magnetic powder which is 65 vol% or greater with respect to the total volume of the magnet material and a thermoplastic resin that fixes magnetic powder to each other. The thickness t1 of the film-like gate 46 in the axial direction of the encoder is made to be 50% or greater of the thickness t2 of the cavity.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method of manufacturing an encoder used to detect the number of revolutions of a rotating body.

In automobiles, anti-skid is used to prevent skidding (a phenomenon in which the wheels slide when they are almost stationary), and traction control is used to effectively transmit driving force to the road surface (control of unnecessary spinning of the drive wheels, which tends to occur when starting or accelerating). The number of revolutions of the wheels is detected in performing the above operations.

FIG. 1 is a cross-sectional view showing part of a typical rolling bearing having a rotation speed detection device. As shown in FIG. 1, the rotation speed detection device 10 is a rolling bearing having an outer ring 21, an inner ring 22, and a plurality of rolling elements (not shown) arranged between the outer ring 21 and the inner ring 22. It detects the number of revolutions of the inner ring 22 thus constructed.

Specifically, the rotation speed detection device 10 is composed of an encoder 11 attached to a slinger 23 fixed to an inner ring 22 and a magnetic sensor 12 axially opposed to the encoder 11 . The slinger 23 cooperates with a seal member 30 fixed to the outer ring 21 to constitute a sealing device for the bearing. Leakage is prevented. Further, the encoder 11 is press-molded and joined to the outer surface of the slinger 23 coated with an adhesive.

The annular encoder 11 is magnetized alternately in the circumferential direction with N poles and S poles (that is, in multiple poles). is detected by the magnetic sensor 12, the rotation speed of the inner ring 22 is detected.

Various methods have been proposed for detecting the number of revolutions of the wheels with higher accuracy in the encoder configured in this way. For example, Patent Document 1 describes a step of annularly injection-molding a magnet material containing 60 to 80% by volume of magnetic powder and a thermoplastic resin as a binder for the magnetic powder from a ring gate; A method of manufacturing an encoder is disclosed, comprising the steps of: magnetizing multi-poles in the circumferential direction using .

According to the manufacturing method described in Patent Document 1, since a method of injecting a specific magnet material from a ring gate is used, an encoder having excellent magnetic properties and mechanical strength can be manufactured.

Japanese Unexamined Patent Application Publication No. 2007-3503

However, when the content of the magnetic powder is increased, the magnetic properties of the obtained encoder are improved, but there arises a problem that the hardness of the encoder is increased and the toughness is decreased. For example, when injection molding is performed using the magnetic material described in Patent Document 1, cracks are likely to occur in the ring gate region in the mold release step of removing the molded product from the mold.

Cracks in the ring gate area do not affect the molded product because the ring gate area is usually cut after removing the molded product from the mold to form a product part in the shape of the encoder. However, depending on the content of the magnetic powder in the magnet material and the release conditions, cracks may start in the ring gate region and propagate to the encoder portion. Therefore, there is an increasing demand for a method of manufacturing an encoder that can further suppress the occurrence of cracks, improve the yield, and have excellent magnetic properties as compared with the conventional method of manufacturing an encoder.

The present invention has been made in view of such problems, and provides an encoder capable of suppressing the occurrence of cracks during manufacturing, thereby enabling the manufacture of encoders with excellent magnetic characteristics at a high yield. The object is to provide a manufacturing method.

For the purpose of improving the magnetic properties of the encoder, the present inventors have devoted themselves to a method of manufacturing an encoder that can suppress the occurrence of cracks even when the content of magnetic powder in the magnet material is increased. I did a lot of research. As a result, after injection molding the magnetic material, the ring gate region, which is the thinnest, cannot withstand the strain received when the molded body is separated from the mold. rice field.
Accordingly, the present inventors came up with the idea that cracks can be suppressed by optimizing the thickness of the gate connected to the encoder-shaped die. The present invention has been made based on these findings.

That is, the above object of the present invention is achieved by the following configuration [1] relating to the method for manufacturing an encoder.

[1] A method for manufacturing an annular encoder magnetized in multiple poles in the circumferential direction, comprising:
a step of circularly injection molding the magnet material through a film-shaped gate toward a mold having a gap portion in the shape of the encoder, and curing the magnet material to obtain a molded body;
The magnetic material contains magnetic powder that accounts for 65% by volume or more of the total volume of the magnetic material, and a thermoplastic resin that bonds the magnetic powder together,
A method of manufacturing an encoder, wherein the thickness of the film gate in the axial direction of the encoder is 50% or more of the thickness of the gap.

Further, preferred embodiments of the present invention related to the encoder manufacturing method relate to the following [2] to [5].
[2] Manufacture of the encoder according to [1], characterized in that the thickness of the film gate in the axial direction of the encoder is 50% or more and 80% or less of the thickness of the gap. Method.

[3] The method of manufacturing an encoder according to [1] or [2], wherein the magnetic powder is anisotropic ferrite.

[4] Before the step of injection molding, a step of housing a metal part to be adhered to the encoder in the mold;
After the step of injection molding, at least a part of the metal part is extruded by an extrusion member attached to the mold, and the molded body and the metal part adhered to the molded body are removed from the mold. and
In the step of injection molding, the position of the extrusion member is set so that the distance between the tip of the extrusion member and the metal part is 0.3 mm or less, [1] to A method for manufacturing an encoder according to any one of [3].

[5] The thermoplastic resin is a polyamide resin,
The magnet material further contains, with respect to 100 parts by weight of the polyamide resin,
4,4′-bis(α,α-dimethylbenzyl)diphenylamine which is 0.5 parts by weight or more and 2 parts by weight or less;
0.25 parts by weight or more and 2 parts by weight or less of 2-mercaptobenzimidazole,
The content of the 4,4′-bis(α,α-dimethylbenzyl)diphenylamine is 0.5 or more and 2.0 or less in weight ratio with respect to the content of the 2-mercaptobenzimidazole. The method for manufacturing an encoder according to any one of [1] to [4].

According to the present invention, in the step of annularly injection-molding a magnetic material toward a mold having an encoder-shaped gap, the magnetic powder accounts for 65% by volume or more of the total volume of the magnetic material, and the magnetic powder Due to the use of a magnetic material containing a thermoplastic resin that bonds them together, an encoder with excellent magnetic properties can be produced.
In addition, since the thickness of the film-shaped gate in the axial direction of the encoder is 50% or more of the thickness of the gap portion during the injection molding, the film-shaped gate can be It is possible to suppress the occurrence of cracks in the portion, and to suppress the occurrence of cracks in the encoder.

FIG. 1 is a cross-sectional view showing part of a typical rolling bearing having a rotation speed detection device. 2 is a perspective view showing an encoder in the rotational speed detection device of FIG. 1. FIG. FIG. 3 is a cross-sectional view showing the method of manufacturing the encoder according to the first embodiment of the present invention. FIG. 4 is a plan view showing part of an injection mold used in the encoder manufacturing method according to the first embodiment of the present invention. 5 is a cross-sectional view showing an enlarged portion A of FIG. 3. FIG. FIG. 6 is a cross-sectional view showing a method of manufacturing an encoder according to the second embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of a method for manufacturing an encoder according to the present invention will be described in detail below with reference to the drawings.
Since the encoder manufactured by the manufacturing method according to the present embodiment can be applied to the general rolling bearing shown in FIG. , are described below. 2 is a perspective view showing an encoder in the rotational speed detection device of FIG. 1. FIG.

<1. Rolling bearing>
As shown in FIG. 1 , the rolling bearing 20 includes a fixed outer ring 21 and an inner ring 22 rotatably configured with a plurality of rolling elements (not shown) interposed between the outer ring 21 and the outer ring 21 . The rotation speed detection device 10 includes an encoder 11 provided on a slinger (metal part) 23 fixed to an inner ring 22 so as to be concentric with the inner ring 22, and a magnetic sensor 12 disposed opposite the encoder 11 in the axial direction. It is configured.

The slinger 23 is an annular metal member having an L-shaped cross section, and has a cylindrical portion 24 and a flange portion 25 extending radially outward from one axial end of the cylindrical portion 24 . . The slinger 23 is fixed to the inner ring 22 by fitting the cylindrical portion 24 onto the axial end of the inner ring 22 .

A seal member 30 fixed to the outer ring 21 is in sliding contact with an inner surface 25a of the flange portion 25 of the slinger 23 facing the inner space of the bearing. The slinger 23 and the seal member 30 constitute a bearing sealing device. This prevents foreign matter such as dust from entering the inner space of the bearing and leakage of the lubricant to the outside of the bearing.

Note that the rotation speed detection device 10 described above is not limited to rolling bearings, and can be applied to hub units that support wheels in vehicles such as automobiles.
Further, for example, if a cap or the like is provided to cover the opening between the outer ring 21 and the inner ring 22, the sealing device including the slinger 23 does not necessarily have to be provided. In that case, the encoder 11 is fixed to the inner ring 22 using an attachment member (metal part) instead of the slinger 23 .

<2. Encoder>
As shown in FIG. 2, the encoder 11 is an annular magnet that is magnetized to have multiple poles on one side, with S and N poles alternately spaced in the circumferential direction. It is adhered to the outer surface 25b. The encoder 11 rotates together with the inner ring 22, and periodically changes the magnetic flux density at points near the encoder 11 while the inner ring 22 rotates once. The rotation speed detection device 10 detects the rotation speed of the inner ring 22 by detecting this change in magnetic flux density with the magnetic sensor 12 .

<3. Encoder manufacturing method>
Next, referring to FIGS. 3 to 5, a method of manufacturing an encoder according to the present embodiment will be described using the encoder 11 described above as an example.
FIG. 3 is a cross-sectional view showing the method of manufacturing the encoder according to the first embodiment of the present invention. FIG. 4 is a plan view showing part of an injection mold used in the encoder manufacturing method according to the first embodiment of the present invention. Furthermore, FIG. 5 is a cross-sectional view showing an enlarged portion A of FIG.

(Mold)
The shape of the mold will be described with reference to FIGS. 3 and 4. FIG. As shown in FIG. 3 , the mold 40 has a fixed mold 42 and a movable mold 41 arranged to face the fixed mold 42 . The fixed side mold 42 and the movable side mold 41 are each divided into a plurality of mold pieces, but they are omitted in this specification.
The stationary mold 42 is formed with a sprue 47 that serves as a passage for injecting the magnet material into the mold. A main runner 45a, an annular sub-runner 45b, and an annular film gate 46 are formed between the movable mold 41 and the fixed mold 42, respectively. Furthermore, an annular cavity 43 for molding the encoder 11 is formed inside the film-like gate 46 .

Further, an annular space 44 that accommodates the cylindrical portion 24 of the slinger 23 is formed continuously with the cavity 43 on the inner side of the annular cavity 43 in the movable mold 41 .
Further, the movable mold 41 is formed with a slit 48 and a plurality of holes 49 and 50 into which an extrusion member for pushing out the molded body is inserted. Specifically, the slit 48 is formed in an annular shape so as to communicate from the annular space 44 to the outside of the movable mold 41 , and an annular extrusion ring (extrusion member) 26 for pushing the slinger 23 into the slit 48 . is inserted. The holes 49 are formed at a plurality of locations along the annular sub-runner 45b so as to communicate from the sub-runner 45b to the outside of the movable mold 41, and the plurality of ejector pins 27 are inserted through the plurality of holes 49. be.

Further, the hole 50 is formed so as to communicate from the sprue 47 to the outside of the movable mold 41 , and the sprue lock pin 28 is inserted through the hole 50 . The sprue lock pin 28 is provided with a notch 47a at its tip, so that the compact and the sprue lock pin 28 are temporarily locked when the magnetic material is injected into the mold in a later step and cooled. configured to be

As shown in FIG. 4, the sub-runner 45b is an annular space provided concentrically outside the cavity 43, and the film-like gate 46 communicates the inner circumference of the sub-runner 45b and the outer circumference of the cavity 43 over the entire circumference. It is connected to both so that Also, the main runner 45a is connected to the outer peripheral edge of the sub-runner 45b at one point in the circumferential direction.

(Details of how the encoder is manufactured)
The details of the encoder manufacturing method using the mold configured as described above will be described below.
In the slinger 23, the cylindrical portion 24 is inserted into the movable side mold 41 in advance so that the cylindrical portion 24 is accommodated in the annular space 44, and the inner surface 25a of the flange portion 25 is in the area of the cavity 43 in the movable side mold 41. It is attached to the movable side mold 41 so as to be in close contact.

First, the annular ejector ring 26 is inserted into the slit 48 , the ejector pin 27 is inserted into the hole 49 , and the sprue lock pin 28 is inserted into the hole 50 .
In this embodiment, the position of the ejector ring 26 is set so that the distance between the tip 26a of the ejector ring 26 and the end surface of the cylindrical portion 24 of the slinger (metal part) 23 is 0.3 mm or less.

In this embodiment, since the shape of the extrusion ring 26 and the slinger 23 are both annular, the distance between the tip 26a of the extrusion ring 26 and the end surface of the cylindrical portion 24 of the slinger 23 is set to 0.3 mm or less. This means that it should be 0.3 mm or less at any location on the ring. In other words, the maximum distance between the tip 26a of the push ring 26 and the end surface of the cylindrical portion 24 of the slinger 23 is 0.3 mm.

Next, the molten magnet material is injected into the mold 40 through an injection pipe (not shown) connected to the sprue 47 . At this time, the molten magnet material is injected from the main runner 45a into the sub-runner 45b via the sprue 47, passes through the sub-runner 45b, passes through the film-shaped gate 46, and flows under high pressure into the cavity 43 having an encoder-shaped gap. is injected into

In this embodiment, the magnetic material used is one containing magnetic powder in an amount of 65% by volume or more with respect to the total volume of the magnetic material and a thermoplastic resin that bonds the magnetic powder together. , using anisotropic ferrite. Anisotropic ferrite is a single crystal with a hexagonal columnar or hexagonal plate shape, and can be aligned by applying a magnetic field to increase the magnetization strength. Therefore, when injecting the magnet material into the cavity 43 , a predetermined current is applied to coils (not shown) arranged at both ends of the movable mold 41 and the fixed mold 42 so that the polarity is the same in the axial direction of the cavity 43 . A (unidirectional) magnetic field is applied to magnetize the magnetic material.
A specific magnetic material that can be used in the method for manufacturing an encoder according to this embodiment will be described later.

As shown in FIG. 5, in this embodiment, the thickness t1 of the film gate 46 is designed to be 50% or more of the thickness t2 of the encoder-shaped gap in the cavity 43. . In this specification, the thicknesses t1 and t2 represent the axial thicknesses of the manufactured encoder, and the thickness t2 of the encoder-shaped space in the cavity 43 refers to the thickness of the manufactured encoder 11. It is the thickness of itself and does not include the thickness of the slinger 23 .

If the thickness of the manufactured encoder 11 itself varies depending on the measurement position, the thickness t2 of the gap is the thickness of the main area of the encoder 11 . In addition, the "main area" refers to the area having the largest area when the areas of the areas having different thicknesses are compared in the encoder 11 having different thicknesses depending on the measurement position.

Thereafter, by cooling the sprue 47, main runner 45a, sub-runner 45b, film gate 46 and the magnet material filled in the cavity 43, an integrally molded body 51 is obtained.
At this time, a plurality of pulse currents, which start at a current higher than the current at the time of injection molding and whose polarities are alternately reversed and whose amplitudes are attenuated, are passed through the coil (not shown), and the polarities alternate in the axial direction of the cavity 43. The magnet material is demagnetized by applying a magnetic field whose strength is attenuated while reversing to . The magnetic material magnetically formed in this way has a high degree of orientation of the magnetic powder contained therein, and is in a state very close to axial anisotropy, and has excellent magnetic properties.

An adhesive layer (not shown) is provided on the outer surface 25b of the flange portion 25 of the slinger 23. This adhesive layer is semi-cured to such an extent that it does not flow out due to the magnet material injected at high pressure. there is Therefore, after cooling, the outer surface 25b of the flange portion 25 of the slinger 23 is adhered to the magnet material.

After that, the movable mold 41 is separated from the fixed mold 42 . At this time, since part of the molded body 51 is locked by the sprue lock pin 28 , the molded body 51 is separated from the fixed side mold 42 while being in close contact with the movable side mold 41 .
After that, the extrusion ring 26 , the ejection pin 27 and the sprue lock pin 28 are slid toward the molding 51 to separate the molding 51 and the slinger 23 from the movable mold 41 .
Further, by separating the portion molded by the cavity 43 and the portion cured in the film-like gate 46, an encoder portion to be the encoder 11 is formed.

After that, the encoder section is superimposed on the magnetizing yoke and magnetized to have multiple poles in the circumferential direction. The number of poles of the encoder 11 is preferably about 70 to 130 poles, more preferably about 90 to 120 poles. As a result, the encoder 11 having the slinger 23 adhered to one surface in the axial direction can be manufactured.

Next, the effect of manufacturing an encoder by the manufacturing method described above will be described below.
In the conventional general manufacturing method, the thickness of the gate is designed to be, for example, 30 to 40% of the thickness of the encoder portion. When removing from the mold, a crack may occur at the gate portion, and the crack may start from this crack and propagate to the encoder portion.

In particular, when the magnet material of this embodiment, which will be described later, is used, the thickness t1 of the film gate 46 is set to the thickness t2 of the encoder (the thickness of the gap of the mold formed in the shape of the encoder). If it is less than 50%, cracks are likely to occur in the molded portion of the film gate 46 .
Therefore, in the encoder manufacturing method according to the present embodiment, the thickness t1 of the film gate 46 is designed to be 50% or more of the thickness t2 of the encoder. As a result, cracks in the film-like gate 46 can be suppressed when the molded body 51 and the slinger 23 are separated from the movable mold 41 .

On the other hand, although the upper limit of the thickness t1 of the gate is not particularly specified, if it is 80% or less of the thickness t2 of the encoder, the portion formed by the cavity 43 and the portion hardened in the film-like gate 46 Difficulty in separation can be suppressed.
Therefore, in this embodiment, the thickness t1 of the film gate is preferably 80% or less, more preferably 60% or more and 70% or less, of the thickness t2 of the encoder.

Further, generally, as the content of magnetic powder in the magnet material increases, cracks are more likely to occur during manufacture of the encoder. This is because as the amount of magnetic powder increases, the content of the thermoplastic resin decreases and the toughness of the entire molded body decreases. This is considered to be due to the inability to withstand the strain received when the mold is released from the mold.
In this embodiment, the content of the magnetic powder is as high as 65% by volume or more with respect to the total volume of the magnet material. Therefore, the occurrence of cracks can be suppressed, and an encoder with excellent magnetic properties can be manufactured.

If the content of the magnetic powder in the magnet material is less than 65% by volume with respect to the total volume of the magnet material, it becomes difficult to obtain magnetic properties for detecting the number of rotations with high accuracy, and the pitch is narrow. It becomes difficult to magnetize the magnet into multiple poles in the circumferential direction. On the other hand, the upper limit of the content of the magnetic powder is not particularly limited, but as the content of the magnetic powder increases, the content of the thermoplastic resin as a binder decreases. The magnetic powder content is preferably 74% by volume or less.
More preferably, the content of the magnetic powder with respect to the total volume of the magnet material is 68% by volume or more and 72% by volume or less.

Furthermore, in this embodiment, the position of the push ring 26 is set so that the distance between the tip 26a of the push ring 26 and the tip surface of the cylindrical portion 24 of the slinger 23 is 0.3 mm or less.
Thus, if the relative positions of the extrusion ring 26 and the slinger 23 are properly controlled, the extrusion ring 26 can push the slinger 23 out with a uniform force in order to remove the compact from the mold. Accuracy can be improved. Therefore, it is possible to prevent the compact from being distorted due to the gap between the extrusion ring 26 and the slinger 23, and furthermore to suppress the occurrence of cracks during the manufacture of the encoder.

In this embodiment, the ejector pins 27 and the sprue lock pins 28 are also inserted through the plurality of holes 49 and 50 provided in the movable mold 41 for removing the molded body from the mold. However, when the molten magnetic material is injected into the mold 40, the magnetic material comes into contact with the tips of the ejector pin 27 and the sprue lock pin 28. Therefore, the position of these pins depends on the distortion of the compact. It has no effect. Therefore, it is only required that the relative position of the push ring 26 for pushing out a part of the slinger 23 is controlled as described above.

However, in this embodiment, it is not always necessary to adhere the slinger 23, which is a sealing device, to the encoder. You may In this way, when a metal part such as the slinger 23 or the mounting member is integrally manufactured with the encoder, if the distance between the tip of the extruded member and the metal part is set to 0.3 mm or less, cracks may occur during the manufacture of the encoder. can be suppressed.

Moreover, the material of the slinger 23 as a sealing device and the mounting member for mounting the encoder 11 to the rotating body is preferably a magnetic material in that the magnetic properties of the encoder 11 are not degraded. As the magnetic material, ferritic stainless steel (such as SUS430) or martensitic stainless steel (such as SUS410), which has a certain level of corrosion resistance or higher, should be preferably used in consideration of the usage environment when the mounting member or the like is exposed. can be done. If the mounting member or the like is not exposed, corrosion resistance is not required so much, so cold-rolled steel (SPCC) or the like may be used in consideration of cost.

In the present embodiment, an adhesive layer is provided on a part of the slinger 23 or the mounting member for the purpose of adhesion to the encoder 11. The adhesive constituting the adhesive layer is heat from the molten magnet material, Alternatively, an adhesive that is completely cured by secondary heating after injection molding can be preferably used. In consideration of heat resistance, chemical resistance and handling properties, it is possible to use phenolic resin adhesives and epoxy resin adhesives that can be diluted with a solvent and whose curing reaction progresses in two stages. preferable. Furthermore, in order to improve the adhesive strength between the slinger 23 or the mounting member and the adhesive layer, the surface on which the adhesive layer is to be provided may be roughened by, for example, shot blasting.

(magnet material)
Next, magnet materials used in the method for manufacturing an encoder according to this embodiment will be described below.
In this embodiment, the magnetic material used is one containing magnetic powder in an amount of 65% by volume or more with respect to the total volume of the magnetic material, and a thermoplastic resin that bonds the magnetic powder together. The effect of using the magnetic powder in an amount of 65% by volume or more with respect to the total volume of the magnet material is as described above.

The magnetic powder is preferably anisotropic ferrite. Anisotropic ferrite is a single crystal and has a hexagonal columnar or hexagonal plate shape, and can be aligned by applying a magnetic field to increase the magnetization strength. Examples of anisotropic ferrite include ferrite magnetic powders such as strontium ferrite and barium ferrite, as well as rare earth magnetic powders with excellent magnetic properties such as samarium-iron-nitrogen, samarium-cobalt, and neodymium-iron-boron. It can be used preferably. In order to improve the magnetic properties of the ferrite magnetic powder, it is also possible to use a powder mixed with a rare earth element such as lanthanum. These magnetic powders may be used singly or in combination of two or more.
Since rare earth magnetic powder has lower oxidation resistance than ferrite magnetic powder, when using rare earth magnetic powder, nickel electroplating, A surface treatment layer such as electroless nickel plating, epoxy resin coating, silicon resin coating, or fluorine resin coating may be provided on the surface of the encoder.

The thermoplastic resin that bonds the magnetic powder together is preferably a polyamide resin.
A polyamide resin is a resin that is excellent in fatigue resistance and heat resistance, and has the effect of improving the thermal shock resistance of the magnet portion, so it can be suitably used as a resin composition of a thermoplastic resin.

Examples of polyamide resins include polyamide 6 (PA6), polyamide 12 (PA12), polyamide 612 (PA612), polyamide 610 (PA610), polyamide 11 (PA11), modified polyamide 6T (PA6T), and polyamide 9T (PA9T). ), polyamide MXD6 (PAMDX6), modified polyamide 12, and the like can be used.

Depending on the usage environment of the encoder, there are many opportunities to contact with water, so it is more preferable to use a low water-absorbing polyamide resin. is more preferred.
Furthermore, since the binder preferably has heat resistance, it is particularly preferable to select PA6T, PA9T and PAMXD6 among the above polyamide resins.

Also, in this embodiment, the magnet material preferably further contains 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and 2-mercaptobenzimidazole. 4,4′-bis(α,α-dimethylbenzyl)diphenylamine is an amine-based antioxidant, and is contained in the magnet material together with 2-mercaptobenzimidazole to prevent oxidative deterioration of the polyamide resin. can be done.

If the amount of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is 0.5 parts by weight or more with respect to 100 parts by weight of the polyamide resin, the antioxidant effect of the polyamide resin can be sufficiently obtained. On the other hand, even if the amount of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is more than 2 parts by weight, the antioxidant effect cannot be further enhanced. Further, when the content is 2 parts by weight or less, elution of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine from the compact can be prevented when the magnet material is cured.

Further, when the amount of 2-mercaptobenzimidazole is 0.25 parts by weight or more with respect to 100 parts by weight of the polyamide resin, the antioxidant effect of the polyamide resin can be sufficiently obtained. On the other hand, even if the amount of 2-mercaptobenzimidazole is more than 2 parts by weight, the antioxidant effect cannot be further enhanced. Further, when the content is 2 parts by weight or less, it is possible to prevent elution of 2-mercaptobenzimidazole from the compact when the magnet material is cured.

Therefore, the magnet material is 0.5 parts by weight or more and 2 parts by weight or less of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and 0.25 parts by weight or more with respect to 100 parts by weight of the polyamide resin. and 2-mercaptobenzimidazole, which is 2 parts by weight or less.

Furthermore, if the content of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is 0.5 or more in weight ratio with respect to the content of 2-mercaptobenzimidazole, the antioxidant of the polyamide resin You can get the full effect.
On the other hand, even if the content of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is set to 2 or more in weight ratio with respect to the content of 2-mercaptobenzimidazole, the antioxidant effect of the polyamide resin is improved. Can't improve more. Further, when the content of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is 2 or less in weight ratio with respect to the content of 2-mercaptobenzimidazole, addition of 2-mercaptobenzimidazole You can get the full effect.

Therefore, the content of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is preferably 0.5 or more and 2.0 or less by weight with respect to the content of 2-mercaptobenzimidazole. .

The magnet material used in the production method of the present embodiment may contain a phosphorus compound as a heat stabilizer during melt molding. In addition, magnetic materials include amine antioxidants, imidazole antioxidants, impact resistance improvers, inorganic fillers, plasticizers, flame retardants, antistatic agents, matting agents, nucleating agents, weather stabilizers, It may contain an ultraviolet absorber, a coloring agent, a release agent, and the like.

<4. Modified Example of Encoder Manufacturing Method>
Next, with reference to FIG. 6, a modification of the method for manufacturing the encoder described above will be described.
FIG. 6 is a cross-sectional view showing a method of manufacturing an encoder according to the second embodiment of the invention. In FIG. 6, the same or equivalent parts as those of the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted or simplified.

A mold 80 used in the encoder manufacturing method according to the second embodiment has a movable mold 81 and a fixed mold 82 .
As in the first embodiment, a main runner 85a, a sub-runner 85b, a film gate 86 and an annular cavity 83 are formed between the movable mold 81 and the fixed mold 82. As shown in FIG. However, the main runner 85a, the sub-runner 85b, and the film gate 86 are formed inside an annular cavity 83, and a sprue 87 is formed at the center of the annular cavity 83 in the stationary mold 82. there is
The main runner 85a extends radially from the sprue 87, for example, in four directions, and is connected to the inner peripheral edge of the sub-runner 85b at four points in the circumferential direction.

The method of manufacturing the encoder using the mold 80 configured in this way is the same as in the first embodiment.
That is, in the second embodiment as well, the thickness of the film gate 86 is designed to be 50% or more of the thickness of the encoder. It is possible to suppress the occurrence of cracks in the film-like gate 86 during removal.

In addition, since the magnet material has a magnetic powder content of 65% by volume or more with respect to the total volume of the magnet material, it is possible to manufacture an encoder with excellent magnetic properties.
Furthermore, since the relative positions of the extrusion ring 26 and the slinger 23 are appropriately controlled, the compact can be prevented from being distorted when the slinger 23 is pushed out by the extrusion ring 26, and the occurrence of cracks can be suppressed. be able to.

Although the method of manufacturing the encoder has been described according to the first and second embodiments, the present invention is not limited to the above configurations. For example, the slinger or mounting member may be adhered to the compact after molding without being pre-assembled into the mold.
Also, in the first and second embodiments, the annular film-like gate is connected to the entire circumference of the cavity, but the film-like gate does not necessarily have to be annular, and is partially connected between the sub-runner and the cavity. There may be parts that are not physically connected.

The encoder manufacturing method according to the present embodiment is suitable for manufacturing bearing encoders for automobiles, etc., which require high magnetic force.

A mold 40 shown in FIG. 3 was prepared, and the slinger 23 was inserted into the movable mold 41 so that the cylindrical portion 24 of the slinger 23 was accommodated in the annular space 44 . Also, the annular ejector ring 26 was inserted into the slit 48 , the ejector pin 27 was inserted into the hole 49 , and the sprue lock pin 28 was inserted into the hole 50 .
Next, a magnet material containing magnetic powder with the content shown in Table 1 below was produced, and this molten magnet material was injected into the mold 40 via the sprue 47 . At this time, the magnet material was magnetized by applying a magnetic field from both ends of the movable mold 41 and the fixed mold 42 .

After that, the sprue 47, the main runner 45a, the sub-runner 45b, the film gate 46 and the magnet material filled in the cavity 43 were cooled and demagnetized.
After that, after the movable mold 41 is separated from the fixed mold 42, the ejector ring 26, the ejector pin 27 and the sprue lock pin 28 are slid toward the molded body 51, and the molded body 51 and the slinger 23 are moved to the movable side. It was separated from the mold 41 and the generation of cracks was observed.
After that, the part formed by the cavity 43 and the part hardened in the film-like gate 46 were separated to form an encoder section, and the encoder section was magnetized to manufacture an encoder.

In addition, each magnetic material containing magnetic powder in the content shown in Table 1 below was used to prepare a test piece, and according to the plastic-Izod impact strength test method in accordance with JIS K 7110: 1999, Izod impact values were measured. Note that the test piece was not notched.
Further, a test piece was prepared in the same manner as above, and the magnetic flux density was measured according to JIS C 2501:1998 to calculate the residual magnetic flux density.

The components other than the magnetic powder of the magnet material used are shown below, and the thickness of the film-shaped gate with respect to the thickness of the encoder, the distance between the tip of the extrusion ring and the slinger, and the measurement results are shown in Table 1 below. .

(magnet material)
[Magnetic powder]: Strontium ferrite 63% to 75% by volume of the total volume of the magnet material
[Thermoplastic resin]: A mixture of polyamide 12 and polyamide 12 elastomer 25% to 37% by volume relative to the total volume of the magnet material
[Heat stabilizer]: N,N'-diphenyl-p-phenylenediamine 1 part by weight per 100 parts by weight of thermoplastic resin (used only in Comparative Example 1)
[Antioxidant]: 1 part by weight per 100 parts by weight of 4,4'-bis (α, α-dimethylbenzyl) diphenylamine thermoplastic resin
2-Mercaptobenzimidazole 1 part by weight per 100 parts by weight of thermoplastic resin

In the above examples and comparative examples, the shapes of the extrusion ring and the slinger are both annular. It represents that it is 0.3 mm or less. In other words, the maximum distance between the tip of the pusher ring and the slinger is 0.3 mm.

As shown in Table 1 above, as the magnetic powder content increases, the residual magnetic flux density increases, but the Izod impact value decreases. This is because as the magnetic powder content increased, the thermoplastic resin content decreased and the toughness decreased.
However, when comparing Example 1 and Comparative Example 2, the contents of the magnetic powder are the same and the magnetic properties are the same. A crack occurred. This is because, in Examples 1 and 2, the thickness of the film-shaped gate with respect to the thickness of the encoder is within the range of the present invention (67%), while Comparative Examples 1 and 2 are within the range of the present invention. This is because it is outside the range of (44%).

In Example 2, the magnetic powder content was increased more than in Comparative Example 2, and excellent magnetic properties were obtained. Moreover, in Example 2, since the thickness of the film-shaped gate with respect to the thickness of the encoder is within the range of the present invention (67%), cracks did not occur.
Comparative Example 1 had the lowest magnetic powder content, a high Izod impact value, and no cracks. The magnetic flux density was remarkably lowered and the magnetic properties were degraded.

As described above, according to the method for manufacturing an encoder according to the present invention, even if the content of magnetic powder is increased, the occurrence of cracks can be suppressed. can be manufactured.

10 Rotation Speed Detector 11 Encoder 12 Magnetic Sensor 20 Rolling Bearing 21 Outer Ring 22 Inner Ring 23 Slinger 26 Ejection Ring 27 Ejection Pin 28 Sprue Lock Pin 40, 80 Dies 41, 81 Movable Side Dies 42, 82 Fixed Side Dies 43, 83 cavity 45a, 85a main runner 45b, 85b sub-runner 46, 86 film gate 51 molding t1 thickness of film gate 46 t2 thickness of space having encoder shape

Claims (5)

A method for manufacturing an annular encoder magnetized in multiple poles in the circumferential direction, comprising:
a step of circularly injection molding the magnet material through a film-shaped gate toward a mold having a gap portion in the shape of the encoder, and curing the magnet material to obtain a molded body;
The magnetic material contains magnetic powder that accounts for 65% by volume or more of the total volume of the magnetic material, and a thermoplastic resin that bonds the magnetic powder together,
A method of manufacturing an encoder, wherein the thickness of the film gate in the axial direction of the encoder is 50% or more of the thickness of the gap. 2. The method of manufacturing an encoder according to claim 1, wherein the thickness of said film gate in the axial direction of said encoder is 50% or more and 80% or less of the thickness of said gap. 3. The method of manufacturing an encoder according to claim 1, wherein said magnetic powder is anisotropic ferrite. Before the step of injection molding, having a step of housing a metal part to be bonded to the encoder in the mold,
After the step of injection molding, at least a part of the metal part is extruded by an extrusion member attached to the mold, and the molded body and the metal part adhered to the molded body are removed from the mold. and
The position of the extrusion member is set so that the distance between the tip of the extrusion member and the metal part is 0.3 mm or less in the step of injection molding. 4. The method for manufacturing the encoder according to any one of 3. The thermoplastic resin is a polyamide resin,
The magnet material further contains, with respect to 100 parts by weight of the polyamide resin,
4,4′-bis(α,α-dimethylbenzyl)diphenylamine which is 0.5 parts by weight or more and 2 parts by weight or less;
0.25 parts by weight or more and 2 parts by weight or less of 2-mercaptobenzimidazole,
The content of the 4,4′-bis(α,α-dimethylbenzyl)diphenylamine is 0.5 or more and 2.0 or less in weight ratio with respect to the content of the 2-mercaptobenzimidazole. The method for manufacturing the encoder according to any one of claims 1 to 4, wherein:

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