JP2003120681A - Method for manufacturing resin ball retainer for bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a ball retainer capable of easily manufacturing the retainer at low costs, a resin ball retainer excellent in retaining property of lubricant, and capable of obtaining sufficient dimensional precision of an inner peripheral surfaces of pockets. SOLUTION: This method for manufacturing the resin ball retainer for the bearing is intended to manufacture by injection molding a resin ball retainer 10 arranged along a peripheral direction on an annular body 11 with the pockets 12 opening to one side axially of the annular body 11, and retaining rotationally the balls. A finely recessed and protruding processed portions 25 are previously formed by electric discharge machining on an outer periphery surface of a pocket forming die element 20 for forming the pockets 12 in the injection moulding die. During injection moulding, finely recessed and protruding portions 15 for retaining oil are formed by transferring the finely recessed and protruding processed portions 25 on the inner peripheral surfaces of the pockets 12 during the injection moulding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a crown-shaped resin ball retainer which is incorporated in a state in which balls are rotatably held between an inner ring and an outer ring of a rolling ball bearing.

[0002]

2. Description of the Related Art As shown in FIG. 4, rolling ball bearings (5)
Is a plurality of balls (8) between the inner ring (6) and the outer ring (7)
Is rotatably held, and a ball retainer (1) is used to hold the plurality of balls (8) at equal intervals in the circumferential direction.

In recent years, as such a ball cage (1),
In order to reduce the weight and the cost, as shown in FIGS. 5 to 7, there is an increasing tendency to adopt a crown-shaped resin ball retainer (1).

This ball retainer (1) is provided with an annular body (2), and a plurality of pockets (3) opening toward one side in the axial direction of the annular body (2) are formed around the one side in the axial direction. It is formed at predetermined intervals in the direction. The ball retainer (1) is mounted between the inner ring (6) and the outer ring (7) in a state where the ball (8) is rotatably held in the pocket (3) to form a bearing (5). It is what is done.

In such a ball bearing (5), by injecting a lubricant such as grease into the inner peripheral surface of the pocket (3) of the ball cage (1), the balls (8) and
The frictional resistance between the cage (1), the inner ring (6), the outer ring (7), and the like is reduced, so that a stable rotation state can be obtained.

[0006]

By the way, the present inventor analyzed the above-described resin ball cage (1) for the purpose of improving its performance. ) The inner peripheral surface of the pocket is finished to be smooth.
Therefore, the retaining force of the lubricant on the inner peripheral surface of the pocket becomes low, the amount of the lubricant injected into the inner peripheral surface of the pocket progresses early, the lubrication becomes insufficient, and the frictional resistance increases to increase the bearing performance. Was found to decrease. In detail,
The conventional resin ball retainer (1) is usually manufactured by injection molding, but when the resin molded product as the retainer is taken out during mold opening after molding in this injection molding, the mold release is performed. The mold surface is formed as smooth as possible in order to improve the property. For this reason, the surface of the ball cage (1) to be molded is made smooth, and as a matter of course,
It has been found that the inner peripheral surface of the pocket is also formed smoothly, so that the retaining force of the lubricant is reduced and the above-mentioned problem of the lubricant reduction occurs.

For reference, the surface roughness (Rmax) of the inner peripheral surface of the pocket in the conventional ball cage (1) was measured and found to be 1 to 3 μm.

[0008]

On the basis of the above analysis results, the present inventor has been investigating various means for improving the retention performance of the lubricant, and as a result, has examined the inner circumference of the pocket of the ball cage (1). We have found a structure that finishes the surface to a rough surface.

In order to embody the structure, first, a technique for forming a minute uneven portion on the pocket inner peripheral surface by barreling the pocket inner peripheral surface of the cage (1) after injection molding is described. I tried. However, in this trial technique,
After injection molding, barrel processing needs to be performed separately,
It was concluded that not only would it be difficult to manufacture the cage due to the increased number of work steps, but also the production cost would increase.

As another trial technique, a fine concavo-convex processed portion is previously formed by shot blasting on the outer peripheral surface of a mold element for forming a pocket in an injection molding die, and the above-mentioned fine portion is formed at the time of injection molding. An attempt was made on a technique for forming a fine uneven portion for retaining oil on the inner peripheral surface of the pocket by transferring the uneven processed portion.

In this trial technique, since the finely processed portion is transferred onto the inner peripheral surface of the pocket at the same time as the injection molding, the number of working steps does not increase, and the easiness of manufacturing and cost reduction can be expected. .

However, since the fine concavo-convex processed portion obtained by the shot blasting process has a large variation in the concavo-convex degree, the fine concavo-convex portion obtained by transferring the processed portion also has a large irregularity degree. Therefore, it has been difficult to finish the inner peripheral surface of the pocket with high dimensional accuracy, and it has been concluded that it is difficult to maintain the ball (8) in a stable state with high positional accuracy.

In particular, in a small diameter ball bearing used in precision equipment such as a hard disk drive for a personal computer,
Since the cage (1) has a small pocket size,
When the positional accuracy is lowered, the contact pressure between the ball (8) and the contact portion around the ball (8) becomes uneven, and abnormal noise is generated.
There is concern about problems such as early deterioration due to uneven wear.

The present invention has been made in view of the above circumstances, and has a simple and low-priced resin ball retainer that is excellent in the ability to retain a lubricant and can sufficiently obtain the dimensional accuracy of the inner peripheral surface of the pocket. An object of the present invention is to provide a method for manufacturing a resin ball cage for bearings that can be manufactured at low cost.

[0015]

The inventor of the present invention found a peculiar structure capable of achieving the above-mentioned object as a result of thorough experiments and researches on resin ball cages, and made the present invention. I arrived.

That is, the present invention ejects a resin ball retainer in which a plurality of pockets, which are open to one side in the axial direction of the annular body and hold balls so that they can roll, are provided in the annular body along the circumferential direction. A method of manufacturing by molding, wherein a fine concavo-convex processed portion is previously formed by electrical discharge machining on the outer peripheral surface of a pocket forming die element for forming the pocket in an injection molding die, and injection molding is performed. At the time, the gist is to form the oil-holding fine concave-convex portion on the inner peripheral surface of the pocket by transferring the fine concave-convex processed portion.

In the method of manufacturing the resin ball cage for bearings of the present invention, since the fine irregularities are formed on the inner peripheral surface of the pocket, the performance of retaining the lubricant on the inner peripheral surface of the pocket can be improved. .

Further, a fine concavo-convex portion is formed in advance on the outer peripheral surface of the pocket forming die element by electric discharge machining, and during injection molding, the fine concavo-convex portion is transferred to retain oil on the inner peripheral surface of the pocket. Since the fine concavo-convex portion is formed, the fine concavo-convex portion on the inner peripheral surface of the pocket can be formed at the same time as the injection molding. It can be prevented from increasing.

Further, since the fine unevenness processed portion is formed on the die element by using the electric discharge machining capable of highly accurate processing, the unevenness of the unevenness in the processed portion is reduced,
A mold element with high dimensional accuracy can be formed. Therefore, the inner peripheral surface of the pocket molded by the mold element can be finished with high dimensional accuracy, and the ball can be reliably held in a stable state with high positional accuracy.

On the other hand, in the present invention, the surface roughness (Rmax at the finely textured portion of the pocket forming mold element is Rmax.
It is preferable to adopt a configuration in which) is set to 10 to 20 μm.

That is, when this structure is adopted, high dimensional accuracy can be obtained while sufficiently retaining the lubricant on the inner peripheral surface of the pocket.

In the present invention, in the electric discharge machining, a voltage is applied between a metal workpiece such as a die element and an electrode as a machining tool through an electric discharge machining liquid as an insulating medium. Then, spark discharge is performed, and the high temperature at that time finely melts and removes the surface layer of the workpiece.

Since this electric discharge machining is a thermal machining,
Unlike mechanical processing such as shot blasting and barrel processing, even high hardness metal materials that are difficult to cut can be processed with high precision, precision processing, curved surface processing,
Sphere processing and the like can be performed with high precision.

In the electric discharge machining, the roughness of the electric discharge machined surface can be freely adjusted by appropriately changing the gap (discharge gap) between the workpiece and the electrode, and the unevenness degree can be varied. It is possible to obtain a satin-finished processed surface with a small amount.

[0025]

1 is a perspective view showing a resin ball retainer (10) manufactured by a manufacturing method according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a pocket periphery of the retainer (10). FIG. As shown in both figures, this ball cage (10) is a synthetic resin crown type obtained by injection molding, and is provided with an annular body (11), and the annular body (11) has a shaft. Open towards one side of the direction,
In addition, a plurality of pockets (12) for rollingly accommodating and holding balls are formed at equal intervals in the circumferential direction.
Furthermore, on the inner peripheral surface of the pocket (12), a fine satin-like oil-holding uneven portion (15), which will be described in detail later, is formed.

As the injection molding die for manufacturing the ball cage (10) of the present embodiment, those generally used in manufacturing the crown-shaped resin cage can be used, and for example, they are arranged vertically. An axial draw type mold in which the mold is opened in the axial direction can be preferably used.

In this metal mold, for example, a cavity corresponding to the shape of a cage is provided on the facing surface of a fixed lower mold and a movable upper mold, and a holding mold is provided on the facing surface of the movable mold. A pocket forming mold element (20) specific to the present embodiment is incorporated for forming a container pocket.

As shown in FIG. 3, the mold element (20) has a partial sphere (21) corresponding to the inner peripheral shape of the pocket (12) of the retainer (10) and one end of the sphere (21). And a rod (22) connected to each other.

Here, in this embodiment, a fine textured processed portion (25) having a satin finish is formed on the outer peripheral surface of the partial sphere (21) by electric discharge machining. That is, the mold element (2
The partial sphere (21) of 0) and the electrode made of copper or the like are arranged so as to be connected to each other, and the mold element (20) side is connected to the ground.
The electrode side is connected to a power source and a voltage is applied between the two. As a result, arc discharge is generated between the partial sphere (21) and the electrode, and due to the high temperature at that time, the partial sphere (2
Partially spherical body (21) by finely melting and removing the outer surface part of 1)
A finely textured processed portion (25) is formed on the outer peripheral surface of, and the surface is finished to have a satin rough surface.

As the electrode used for electric discharge machining, for example, an electrode having an inner spherical surface (concave spherical surface) shape having a predetermined curvature corresponding to the outer peripheral surface of the partial spherical body (21) can be used to perform electric discharge machining once. Thus, the fine concavo-convex processed portion (25) can be formed in the entire required region of the partial sphere (21).

In the present embodiment, the outer surface of the partial sphere (21) is cut and removed by electric discharge machining. Therefore, the removed portion and the removed amount are taken into consideration in advance.
The dimensions of the partial sphere (21) before electric discharge machining are set.
That is, the final dimension finishing on the outer peripheral surface of the partial sphere (21) is also simultaneously performed by electric discharge machining.

Further, in this embodiment, the surface roughness of the fine concavo-convex processed portion (25) can be adjusted by appropriately changing the discharge gap between the electrode and the die element (20) in the electric discharge machining. Is. For example, when the discharge gap is increased, the surface roughness increases.

Here, in the present embodiment, the surface roughness (R) in the fine concavo-convex processed portion (25) of the die element (20).
max) is set to 10 to 20 μm, preferably 15 μm or more. That is, if the surface roughness is too small, it is not possible to sufficiently secure the retaining force of the lubricant on the inner peripheral surface of the pocket in the ball cage (10) to be manufactured, and the lubricant is reduced early. As a result, the frictional resistance increases and the bearing performance may deteriorate, which is not preferable. On the contrary, when the surface roughness is too large, the ball cage (10) manufactured
The unevenness of the inner peripheral surface of the pocket in the case is varied, the sliding resistance with the ball is increased, the rotating torque is increased, and the bearing performance may be deteriorated, which is not preferable.

In the present embodiment, the mold element (20) having the above structure is incorporated in the above axial draw type injection molding mold.

Then, a molding material made of a thermoplastic resin such as polyamide resin (66 nylon) or polyacetal resin is injected into the cavity through the sprue, runner and gate of the injection molding die to solidify,
The movable mold is moved in the axial direction to open the mold. After that, a ball retainer (1
0) is taken out by kicking out the ejector pin mounted in the mold.

Ball cage (10) as this resin molded product
At the same time as the above-mentioned injection molding, the inner peripheral surface of the pocket (12) of
By transferring 5) as it is, the processing part (25)
The oil-retaining fine concavo-convex portion (15) having the same surface roughness (Rmax = 10 to 20 µm) as the above is formed.

The ball cage (10) manufactured in this way is
Similar to the conventional example, the rolling ball bearing is formed by assembling the balls in the respective pockets (12) so as to be rollably held between the inner ring and the outer ring.

In this ball bearing, since the fine irregularities (15) are formed on the inner peripheral surface of the pocket of the retainer (10), the retaining force of the lubricant on the inner peripheral surface is increased, and the periphery of the ball is surrounded. The lubricant is supplied without interruption. Therefore, increase in frictional resistance due to oil shortage and early deterioration can be prevented, and a stable rotating state can be maintained for a long period of time.
High quality and performance can be obtained.

Further, in the ball cage (10) of the present embodiment, a fine concavo-convex processed portion (25) is previously formed on the die element (20) by electric discharge machining, and the processed portion (2
By transferring 5) during injection molding, the fine concavo-convex portion (15) is formed on the inner peripheral surface of the pocket, so that it is not necessary to separately perform barrel processing or the like for forming the fine concavo-convex portion (15). Therefore, it is possible to prevent an increase in the number of working steps. Therefore, the manufacturing can be easily performed, the production efficiency can be improved, and the cost can be reduced.

Further, in the present embodiment, since the fine concavo-convex processed portion (25) is formed on the die element (20) by using the electric discharge machining capable of high-precision machining, there is little variation in the concavo-convex degree. A mold element (20) having high dimensional accuracy can be formed. Therefore, this mold element (20)
The inner peripheral surface of the pocket of the ball cage (10) molded by the method can be finished with high dimensional accuracy, and the ball can be reliably held in a stable state with high positional accuracy. The ball cage (10), and eventually the bearing. The quality as a product can be further improved.

In the above embodiment, the fine concavo-convex portion (25) is formed on almost the entire outer circumference of the partial sphere (21) in the mold element (20), and the inner circumference of the pocket in the ball cage (10) is formed. Fine irregularities (15) on almost the entire surface
However, the present invention is not limited to this, and the fine concavo-convex portion may be partially formed only in a required region of the inner peripheral surface of the pocket. For example, a partial sphere (2
It is also possible to partially perform electric discharge machining in 1) to partially form fine irregularities in a region having the highest rotational peripheral velocity of the ball, that is, a region corresponding to the periphery of the so-called equator.

[0042]

As described above, according to the method of manufacturing the resin ball cage for bearings of the present invention, the fine irregularity processed portion is previously formed on the outer peripheral surface of the pocket forming die element by electric discharge machining. Every time, during injection molding, since the fine irregularities are formed on the inner peripheral surface of the pocket by transferring the irregularity processed portion, the fine irregularities improve the lubricant retaining performance on the inner peripheral surface of the pocket. In the assembled state,
Lubricant can be supplied around the ball without interruption. Therefore, it is possible to prevent an increase in frictional resistance and early deterioration due to oil shortage, to maintain a stable rotating state for a long time, and to obtain high quality. Further, since the fine irregularities on the inner peripheral surface of the pocket are formed at the same time as the injection molding, there is no need to separately process for the formation of the fine irregularities, the increase in the number of working steps can be prevented, and the manufacturing is easy. , Can reduce the cost. Further, since the fine concavo-convex processed portion is formed on the die element by using the electric discharge machining capable of highly precise machining, it is possible to form a die element with high dimensional accuracy with little variation in the degree of concavity and convexity. Therefore, the inner peripheral surface of the pocket molded by this mold element can be finished with high dimensional accuracy, the ball can be reliably held in a stable state with high positional accuracy, and the quality as a ball cage is further improved. The effect is that it can be done.

In the present invention, when the surface roughness of the finely textured portion of the die element is set within a specific range, there is an advantage that the above effects can be obtained more reliably.

[Brief description of drawings]

FIG. 1 is a perspective view showing a resin ball retainer for a bearing manufactured by a manufacturing method according to an embodiment of the present invention.

FIG. 2 is an enlarged perspective view showing the vicinity of a pocket in the ball cage according to the embodiment.

FIG. 3 is a perspective view showing a pocket-forming mold element used in the manufacturing method of the embodiment.

FIG. 4 is an upper sectional view showing a bearing to which a conventional resin crown-shaped ball cage is applied.

FIG. 5 is a plan view showing a conventional crown-shaped ball cage.

FIG. 6 is a side sectional view showing a conventional crown-shaped ball cage.

FIG. 7 is an enlarged perspective view showing the periphery of a pocket in a conventional crown-shaped ball cage.

[Explanation of symbols]

10 ... Ball cage 11 ... Ring body 12 ... Pocket 15 ... Fine irregularities for oil retention 20 ... Mold element for pocket formation 25 ... Fine irregularity processing part

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Claims (2)

[Claims] 1. A resin ball cage manufactured by injection molding, wherein a plurality of pockets, which are open to one side in the axial direction of the annular body, and which rotatably hold balls are provided along the circumferential direction. A method of forming a fine concavo-convex portion on an outer peripheral surface of a pocket-forming mold element for forming the pocket in an injection-molding die by electric discharge machining in advance. A method for manufacturing a resin ball retainer for bearings, characterized in that fine oil-holding fine irregularities are formed on the inner peripheral surface of the pocket by transferring the fine irregularities processed portion. 2. The method for producing a resin ball cage for bearing according to claim 1, wherein the surface roughness (Rmax) in the finely textured portion of the pocket forming die element is set to 10 to 20 μm.