JPH05139836A - Production of ceramics member having adjoining plural dented channels on surface - Google Patents

Abstract

PURPOSE:To obtain a ceramics material useful for journals for dynamic-pressure fluid bearing, etc., having low surface roughness, excellent thermal shock resistance and small manufacturing error. CONSTITUTION:A powdery ceramics material such as silicon carbide is press molded to give a cylindrical ceramics plastic material 1', which is rolled while being pressed against a molding face 3b of a mold 3, molded protruded parts 3a... on the molding face 3b are successively thrust into the peripheral face of the plastic material 1' to form dented channels 1a... arranged side by side at equal pitches (p) on the peripheral face of the plastic material 1'. In the operation, pitches P of the molded protruded part 3a are >=twice the pitches (p) of the dented channels and adjoining dented channels 1a are not simultaneously formed at the pitch (p). Then the plastic material 1' is burnt to give a ceramics member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ceramic member, such as a journal of a hydrodynamic bearing, which has a large number of concave grooves on the surface thereof.

[0002]

2. Description of the Related Art For example, in a fluid dynamic bearing, a ceramic journal having a large number of fluid pressure generating grooves closely arranged in parallel is used. Generally, a ceramic member is obtained by press-molding a powder material such as silicon carbide and firing it, and then forming concave grooves on the surface of this sintered body.

By the way, a sintered body obtained by firing is extremely hard and brittle, and it is difficult to form a concave groove by a normal cutting process. Therefore, conventionally, the surface of the sintered body is sandblasted. The concave groove is formed by a special surface processing method such as a method, a chemical etching method, an electric discharge machining method, a laser machining method.

[0004]

However, the conventional ceramic member obtained by forming the concave groove on the surface of the sintered body by such a surface processing method has the following problems.
In reality, there is a problem in strength, and its use is greatly limited.

That is, since the mechanical strength and chemical properties of the ceramics after sintering are completely different between the constituent crystal grains and the grain boundaries between the crystals, the sintered body is subjected to sandblasting or chemical etching. In the case of performing the surface treatment by (1), the degree of progress of crushing by sandblasting or corrosion by chemical etching differs between the crystal grains and the grain boundaries, and it is generally extremely difficult to obtain a surface roughness of 2 μRa or less. Therefore, for example, in a hydrodynamic bearing that uses a ceramic member obtained by performing such surface processing as a rotary journal, the surface roughness of the hydrodynamic groove is large, and therefore, at high speed rotation exceeding 10 ⁴ rpm. In this case, the resistance due to the viscosity of air increases, the power loss and the amount of heat generation increase, and the undesirable phenomenon that the clearance between the journal and the bearing portion fluctuates due to thermal expansion easily occurs.

Further, when the ceramic member is a sintered body which has been subjected to surface processing such as electric discharge machining or laser machining, the machining accuracy of the concave groove (particularly the machining of the corner of the dynamic pressure generating groove etc.). Precision) is low and it is difficult to use in applications that require precise groove formation as designed.

Further, in a ceramic member which has been surface-processed by a sand blasting method or a laser processing method, the work-affected layer remains on the groove forming surface, so that the resistance to thermal shock is lowered and cracks or the like are generated. May occur.

Further, all of the above surface processing methods require complicated steps, and since they are probably one-piece production methods, it is easy and economical to manufacture a ceramic member having concave grooves. Can not be done. Moreover, there is a limit to the ceramic material that can be processed and the surface shape that can be formed,
The applications of the resulting ceramic component are severely limited.

The present invention has been made in view of the above points, and it is possible to manufacture a ceramic member such as a journal for a hydrodynamic bearing which has a small surface roughness and is excellent in thermal shock resistance and has a small manufacturing error. An object of the present invention is to provide a method for manufacturing a ceramic member having a plurality of adjacent concave grooves on its surface.

[0010]

A method of manufacturing a ceramic member having a plurality of adjacent concave grooves on the surface thereof according to the present invention, which has solved this problem, is a method of pressure-molding a powdered ceramic material such as silicon carbide or tungsten carbide. On the surface of the obtained ceramic plastic body, a molding die having one or a plurality of molding convex portions is repeatedly pressed while changing the pressing position to the surface of the plastic body, so that at least adjacent concave grooves are not simultaneously formed. After forming a plurality of concave grooves adjacent to each other, the grooves are baked. In addition,
The ceramic member includes not only a ceramic member in a narrow sense but also a sintered metal member obtained by molding and firing metal powder. The ceramic material includes SiC, WC, and Ti.
Preference is given to using carbide ceramics such as C, B ₄ C. In addition to the final sintering process, the firing process also includes a binder, a plasticizer, and a binder that are added when the powder ceramic material is molded.
The heat treatment and the like performed for removing the molding aid such as the dispersant are included.

[0011]

[Function] Since the ceramic plastic body obtained by pressure-molding the powdered ceramic material has a certain degree of plasticity, the molding die is pressed against the surface of the ceramic plastic body to cause the molding convex portion to bite into the ceramic plastic body. As a result, the shape of the concave groove as the forming convex portion is accurately formed by the plastic deformation, and the concave groove having the surface roughness substantially matching the surface roughness of the forming die is formed.

The step of forming a groove by biting the molding convex portion is repeated a plurality of times while changing the pressing position of the molding convex portion against the surface of the plastic body. Is designed so that at least adjacent grooves are not formed at the same time. That is, when the forming die has only one forming convex portion, naturally, adjacent concave grooves are not simultaneously formed in each concave groove forming step, but the forming die has a plurality of forming convex portions. When a plurality of concave grooves are simultaneously formed by two or more molding convex portions in each concave groove forming step, for example, the pitch P of the molding convex portions may be a desired concave pitch. The groove pitch is set to an integral multiple of the pitch p so that adjacent concave grooves at intervals of p are not formed at one time.

By the way, when the forming convex portion is made to bite into the surface of the ceramic plastic body, a material flow occurs at the biting portion, but when P = p, adjacent concave grooves are simultaneously formed in one concave groove forming step. When p is formed, since the p is extremely small, the flow of the material due to the formation of the one concave groove and the flow of the material due to the formation of the other concave groove mutually interfere, and a smooth flow of the material is obtained. Hard to happen. Therefore, even though the ceramic plastic body is soft before firing, the biting resistance (deformation resistance of the plastic body) of the molding convex portion into the ceramic plastic body becomes large, and the biting is not sufficiently performed. The bite amount becomes shallow, there is a possibility that a desired concave groove may not be obtained, and the plastic working accuracy decreases. If the pressing force of the forming die against the ceramic plastic body is increased more than necessary in order to obtain a sufficient bite, the ceramic plastic body may be deformed or broken, and the processing accuracy may be lowered.

However, as described above, the pitch P of the molding convex portions is
When the pitch of the groove is set to be larger than the pitch p of the concave groove and the protrusion of the forming convex portion into the ceramic plastic body is simultaneously performed at a plurality of points, the distance between one biting point and the biting point adjacent thereto is sufficiently large. By so doing, the above-described interference of material flow does not occur, and even if the pressing force of the molding die against the ceramic plastic body is not so large, the formation of the molding convex portion is sufficiently performed to bite the molding convex portion. It is possible to form a highly accurate groove corresponding to the shape.

Therefore, by firing the ceramic molded body in which the recessed grooves are formed by plastic deformation as described above, the ceramics in which the recessed grooves are closely arranged at the predetermined pitch p according to the processing accuracy and surface roughness of the molding die are formed. The member can be obtained. Therefore, it is easy to manufacture a mold (for example, a mold) with high precision and extremely small surface roughness. Therefore, by using such a mold, it is possible to obtain an accurate shape as designed. It is possible to obtain a ceramic member that has unevenness with a certain and extremely dense surface roughness (for example, 0.5 μRa or less) on the surface. Moreover, when obtaining such a ceramic member, the ceramic material and the shape of the concave groove are not limited as described at the beginning.

Further, since the above-mentioned ceramic member has the concave groove formed by plastic working in the stage before sintering,
At the same time that at least adjacent concave grooves are not formed at the same time to avoid interference of material flow, internal stress generated by forming concave grooves is relaxed in the firing process, and various external forces such as cracks are generated. It is also difficult for destruction to occur.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on the embodiments shown in FIGS.

In this embodiment, the present invention is applied to the case of manufacturing the journal 1 of the hydrodynamic bearing shown in FIG. This hydrodynamic bearing forms a plurality of concave grooves, which are adjacent to the outer peripheral surface of the journal 1 and are arranged in parallel, and the dynamic pressure generating grooves 1a ...
The dynamic pressure is generated between the opposed surfaces of the radial bearing cylinder 2 and the radial bearing cylinder 2, so that the both 1 and 2 can be relatively rotated at high speed and smoothly.

First, a powder material (including an appropriate molding aid) such as silicon carbide or tungsten carbide is pressure-molded to obtain a ceramic plastic body 1'having a solid shaft shape corresponding to the shape of the journal 1.

Next, as shown in FIGS. 1 and 2, both ends of the ceramic plastic body 1'are rotatably held by appropriate rotating jigs (not shown), and these jigs are formed into a long rectangular shape. By moving along the plate-shaped molding die 3, the ceramic plastic body 1 ′ is appropriately pressed against the molding surface 3 b, which is the upper surface of the molding die 3, while rolling on the molding surface 3 b. As the molding die 3, generally, a die having high processing accuracy and capable of reducing surface roughness is used. The molding surface 3b is provided with a plurality of molding projections 3a, ... Molded convex portion 3a
The shape and the number of are set corresponding to the dynamic pressure generating groove 1a to be formed. Thus, the pitch P of the forming protrusions 3a ... Is such that, even if the plurality of forming protrusions 3a are bited at the same time, the material flow at each biting point is the material at the biting point adjacent thereto. It is set large enough so as not to interfere with the flow. Specifically, the pitch P is an integral multiple (P = mp (m> 1)) of the pitch p of the dynamic pressure generating grooves 1a. By the way, the ceramic plastic body 1 ′ has the first molding convex portion 3 a.
When the first dynamic pressure generating groove 1a is formed by
It is necessary to rotate once or more from (A)) until all the dynamic pressure generating grooves 1a are formed.
Are formed in parallel with each other at an equal pitch p and are arranged in parallel. Therefore, depending on the relationship between the number M of the dynamic pressure generating grooves 1a ... There may be a case where a new molding convex portion 3a bites into the formed dynamic pressure generating groove 1a again. When such a situation occurs, every time the ceramic plastic body 1 ′ makes one revolution, the dynamic pressure generating groove 1a newly formed immediately after that is located at a position deviated from the dynamic pressure generating groove 1a previously formed. As it is formed, the position of the molding convex portion 3a for forming this new dynamic pressure generating groove 1a is shifted by a predetermined pitch. That is, some of the adjacent molding protrusions 3a, 3a
The pitch P ′ between them is set larger than mp. For example, when M is not divisible by m, in principle, the pitches P of the molding convex portions 3a ... Are all the same (P = mp), but when M is divisible by m, the “M / m” th and “M / m + 1 ”th,“ 2 (M / m) ”th and“ 2 (M
/ M) +1 "th," 3 (M / m) "th and" 3 (M / M /
m) +1 "th ............" (m-1) (M / m) "th and" (m-1) (M / m) +1 "th adjacent pitches P of the molding protrusions 3a, 3a. Let ′ be P + p = (m + 1) p. In this embodiment, as shown in FIGS.
M = 30, P = mp = 2p, and the fifteenth molding convex portion 3
The pitch P'between a and the 16th molding convex portion 3a is 3p.

When the ceramic plastic body 1'rolls, the first molding convex portion 3a bites into the surface of the plastic body to form the V-shaped dynamic pressure generating groove 1a (Fig. 1 (A)). After that, as the ceramic plastic body 1 ′ rolls, the dynamic pressure generating groove 1 is sequentially formed on the surface thereof in the rolling direction.
a are sequentially formed at a pitch of 2p (FIG. 1 (B))
reference). Then, after the ceramic plastic body 1'has rotated once, a new dynamic pressure generating groove 1a is sequentially formed between the adjacent dynamic pressure generating grooves 1a, 1a already formed (see FIG. 1).
(See (C) and FIG. 2) All the dynamic pressure generating grooves 1a ... Are formed at a desired pitch p by two rotations.

At this time, for example, as shown in FIG.
Even if biting by the plurality of molding convex portions 3a is performed at the same time, the interval P (= 2 between the biting points).
Since p) and P '(= 3p) are larger than the pitch p of the dynamic pressure generating grooves 1a, the material flow at each bite point does not interfere with the material flow at the bite point adjacent thereto. Therefore, the ceramic plastic body 1 '
In consideration of the fact that the ceramic plastic body 1'has a certain degree of plasticity before firing even if the pressing force of the ceramics against the molding surface 3b is not unnecessarily increased, each molding convex portion 3a The biting into the plastic body 1'is carried out smoothly and sufficiently, and the dynamic pressure generating groove 1a with high accuracy is formed while avoiding the deformation of the ceramic plastic body 1 '.

After all the dynamic pressure generating grooves 1a are formed in the ceramic plastic body 1'in this manner, the ceramic plastic body 1'is fired (low temperature firing and sintering temperature for removal treatment of the molding aid, etc.). By performing the main firing (1), the journal 1 as a ceramic member having the dynamic pressure generating grooves 1a ... Which are arranged in parallel close to the outer peripheral surface as shown in FIG. 3 is obtained.

The present invention is not limited to the above-mentioned embodiments, but can be appropriately improved or modified within the range not departing from the basic principle of the present invention.

For example, as shown in FIG. 4, the dynamic pressure generating grooves 1a ... Can be formed by a molding die 3 having one molding projection 3a. Mold 3
As shown in FIG. 4 and FIG. 5, the ceramic plastic body 1 ′ has a circular arc-shaped molding surface 3 b which can be abutted on the outer peripheral surface of the ceramic plastic body 1 ′. And
The ceramic plastic body 1 ′ is intermittently moved in and out of contact with the ceramic plastic body 1 ′. Further, the ceramic plastic body 1'is a hollow shaft-shaped member, is fitted and held by the core shaft 4, and is intermittently rotated at an angle corresponding to the pitch p of the dynamic pressure generating grooves 1a. ing.

That is, in this embodiment, after the molding die 3 is pressed against the ceramic plastic body 1'and the dynamic pressure generating groove 1a is formed by the molding convex portion 3a (see FIG. 4A), the molding die is once 3 is separated from the ceramic plastic body 1 ′, the ceramic plastic body 1 ′ is rotated by an angle corresponding to the pitch p (see FIG. 2B), and the molding die 3 a is pressed against the ceramic plastic body 1 ′ again. By forming the dynamic pressure generating groove 1a adjacent to the previously formed dynamic pressure generating groove 1a ((C) in the same figure) and repeating this process, the ceramic plastic body 1'is arranged close to and in parallel with the outer peripheral surface thereof. The dynamic pressure generating grooves 1a are formed.

By thus forming one dynamic pressure generating groove 1a ... As a matter of course, the problem of material flow interference caused by simultaneous intrusion of a plurality of molding convex portions does not occur,
The dynamic pressure generating grooves 1a ... Can be formed smoothly and with high accuracy.
Of course, even when using the molding die 3 having a plurality of molding projections 3a ... As in the above embodiment, the value of m should be set appropriately in consideration of the diameter dimension of the ceramic plastic body 1 '. As a result, it is possible to always allow only one molding convex portion 3a to bite into the ceramic plastic body 1 '.

In the hydrodynamic bearing, the thrust bearing plate facing the lower end surface of the journal may be formed with a spiral hydrodynamic groove to receive the thrust load of the journal. A ceramic member, such as a thrust bearing plate or a seal ring in a dynamic pressure type mechanical seal, in which a plurality of concave grooves are formed close to each other on a non-rotating surface is also formed by a method similar to that shown in FIG. Grooves can be formed. For example, in manufacturing the thrust bearing plate 1 as shown in FIG. 7, as shown in FIG. 6, a ceramic plastic body 1 ′ formed in a disk shape corresponding to the thrust bearing plate 1 is made to correspond to the pitch p of the dynamic pressure generating grooves 1 a. The rotation is intermittently rotated at each angle, and each time the rotation is made, the dynamic pressure generating groove 1a
Thus, the molding die 3 having the one molding convex portion 3a having a shape corresponding to is pressed.

In each of the above embodiments, the case where the ceramic member having the recessed groove 1a having a relatively shallow depth is manufactured has been described, but in the present invention, the recessed groove on the surface of the ceramic member is plastically worked before firing. Because I try to
By changing the forming surface shape of the forming die or the pressing form on the ceramic plastic body, it is possible to easily obtain a ceramic member having a surface shape and surface roughness according to the application. Of course, when forming the concave groove, the surface shape of the ceramic material, groove pitch, groove depth, groove width, etc. is not particularly limited,
When the groove pitch p is extremely small and the groove depth of the concave groove is set to 1 to 200 μm (more preferably 50 μm or less), the effect of the present invention will be maximized. ..

[0030]

As is apparent from the above description, according to the present invention, there is provided a ceramic member having excellent thermal shock resistance and the like, which is exactly as designed and has a very fine groove having surface roughness. it can. Moreover, since the grooves having plasticity are formed before firing, and at least adjacent grooves are not formed at the same time, even if the pitch of the grooves is small, regardless of the material, the ceramic member Can be manufactured with high precision and easily, and the manufacturing cost can be significantly reduced by mass production. In addition, the irregular shape (groove pitch, groove depth, groove width, etc.), processing accuracy, and surface roughness of the member surface can be freely changed depending on the shape of the molding die, processing accuracy, and surface roughness. The application can be greatly expanded.

[Brief description of drawings]

FIG. 1 is a side view showing a step of forming a concave groove in an embodiment of a method according to the present invention.

FIG. 2 is a plan view of the same.

FIG. 3 is a sectional view of a hydrodynamic bearing using a ceramic member obtained by the same method.

FIG. 4 is a side view showing a step of forming a groove according to another embodiment.

FIG. 5 is a front view of a molding die used in this forming step.

FIG. 6 is a cross-sectional view showing a step of forming a groove according to still another embodiment.

FIG. 7 is a cross-sectional plan view of the ceramic member thus obtained.

[Explanation of symbols]

1 ... Ceramic member, 1a ... Dynamic pressure generating groove (concave groove), 1 '
… Ceramic plastics.

Claims (1)

[Claims] 1. A molding die having one or a plurality of molding projections is pressed onto the surface of a ceramic plastic body obtained by pressure molding a powdered ceramic material such as silicon carbide or tungsten carbide. Repeatedly pressing while changing the position, at least while adjacent grooves are not formed at the same time, while forming a plurality of adjacent grooves, characterized by performing a baking treatment,
Method for manufacturing ceramic member having a plurality of adjacent concave grooves on the surface