Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Post sintering operation
Reexamination Certificate
2002-05-08
2004-05-18
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Post sintering operation
C002S022000, C002S022000, C002S002120
Reexamination Certificate
active
06737016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for manufacturing a sintered bearing, and specifically relates to a process for manufacturing a sintered slide bearing in which the bearing surface of the slide bearing or the grooved surface of hydrodynamic bearing is sealed.
2. Related Art
Sintered bearings includes some different types of bearings such as: an oil-impregnated bearing whose sliding surface is self-lubricated; an oil-impregnated bearing with a hydrodynamic groove formed on the inner peripheral surface or a terminal surface thereof; and a fluid type slide bearing (Japanese Laid-Open Patent Publication (JPA) No. S64-83920, etc) in which a slide bearing or a hydrodynamic grooved slide bearing is enclosed in a cup-shaped housing and a lubricating oil is filled in the housing to supply it to the periphery of the bearing.
The fluid type slide bearing is used for the polygon miller drive of a laser beam printer, a spindle motor of a disc drive and the like. The lubricating oil is possibly composed of an oil with low viscosity or a magnetic fluid, and, in the case of using the magnetic fluid, a permanent magnet is provided adjacent to the bearing. In order to enhance the action of dynamic pressure more highly, it is important that, among the pores of the bearing, those on the surface, especially on the bearing surface, be blocked or decreased (i.e. pores be closed). As the closing measures, there are a method that a sintered bearing is formed in high density, a method that a finish processing such as various blast finishings or tumble polishings is carried out to the bearing, and a method that a resin to be impregnated and cured in the pores is used for sealing the pores (Japanese Laid-Open Patent Publication (JPA) No. H11-62948, etc). The sealing of pores with a resin is carried out specifically by procedures of the impregnation of a resin, the removal of an extra resin, and the curing of the resin (Japanese Laid-Open Patent Publication (JPA) No. H7-216411).
The above-mentioned sealing of pores with a resin does not have a problem of weight increase such that arises in the case of making the bearing in high density, and it has relatively better efficiency in production in comparison with other measures for closing pores. However, it has the following problems. Namely, since the resin impregnated is shrunk when being cured and the impregnation amount and shrinking ratio become uneven, it is difficult to certainly regulate the opening ratio of the surface or the degree of sealing pores and pores cannot be perfectly blocked by the resin impregnated and cured at one time. Moreover, the smoothness of a bearing surface is also damaged at the cured condition of the resin. It may be also considered that viscosity of the resin to be used is made low and a vacuum impregnation is also applied, in order to certainly and sufficiently impregnate the resin. However, it takes much time and is inefficient. In the fluid type slide bearing as described above, there are some occasions, as described in Japanese Laid-Open Patent Publication (JPA) No. H10-112955, where the pores of a bearing is impregnated with a thermoplastic having a coefficient of thermal expansion which is larger than that of the material of the bearing, so that, after the curing, fine gaps are produced in the pores at a low temperature condition and those fine gaps are blocked by the expansion of the resin when the temperature is raised. However, it is difficult to control the amount of the resin to be impregnated and cured.
BRIEF SUMMARY OF THE INVENTION
In order to solve the above-mentioned problems, it is an object of the present invention to provide a process for manufacturing a sintered slide bearing in which the treatment for sealing pores of the sintered bearing body using a resin is carried out, and which enables to manufacture a sintered slide bearing having pores in which gaps are made small or blocked, by an decreased number of steps while keeping quality.
In order to achieve the above-mentioned object, a process for manufacturing a sintered slide bearing according to the present invention comprises: preparing a sintered porous bearing body from a powdered metal material; penetrating into the sintered porous bearing body a resin material in a fluidable state; hardening the resin material in the sintered porous bearing body; and repressing the sintered porous bearing body after the hardening of the resin material, to reduce a gap produced between the sintered porous bearing body and the hardened resin material by volume reduction caused on the resin material at the hardening.
The features and advantages of the manufacturing process according to the present invention over the proposed methods will be more clearly understood from the following description of the embodiments of the present invention
DETAILED DESCRIPTION OF THE EMBODIMENTS OF INVENTION
Embodiments of the process for manufacturing a sintered slide bearing according to the present invention will be described.
In the present invention, the impregnation and curing of a resin are carried out to a sintered porous body that includes a sintered body obtained direct by sintering a green compact which is formed by pressing a powdered metal into a predetermined shape, and a pre-sized article obtained from the sintered body by pre-sizing the sintered body. If the sintered body is completely repressed by coining or sizing, which are carried out in general as the secondary processing, the pores of the sintered body are deformed and shrunk by compression, causing a reduced impregnation property with a resin. This generates fluctuation of impregnation amount and the shortage of impregnation when the impregnation is performed at a normal pressure, and the falling off is caused by them. Therefore, in order to prevent the above problems, the resin is impregnated into the pores of the sintered body and cured before it is placed in a die to repress the sintered porous body for plastical processing. In accordance with the above procedure, it is preferably impregnated and the resin in pores becomes in conditions of close packing or perfect sealing. In other words, gaps in the pores can be surely and ideally closed by the subsequent plastic processing or repressing.
Here, the sintered porous body after the plastic processing, may be further treated with coining or sizing as the secondary processing, depending on the modes of the slide bearing. Specifically, (1) a mode in which gaps in the pores are reduced or blocked by a plastic processing which is carried out after impregnation and curing of the resin, and grooves or the like are mainly formed by coining or sizing as the subsequent secondary processing, and (2) a mode in which gaps in the pores are reduced to a predetermined value by the plastic processing which is carried out after impregnation and curing of the resin, and grooves or the like are formed by coining or sizing as subsequent secondary processing while the reduced gaps in the pores are further reduced or blocked, are included. Alternatively, the plastic processing itself can also include the coining or sizing for determining the shape or dimensions which are generally carried out as a secondary processing for the porous sintered body. This mode can be carried out without using an additional die for a plastic processing. If the slide bearing to be produced is in a small size and the precision of dimensions of the sliding surface and the like is highly required, it is preferred, in order to enhance dimensional precision of the final product, that a porous sintered body to which a preliminary sizing is carried out so as not to substantially crush the pores of the sintered body is used to impregnate with a resin to be cured, before the plastic processing and/or another processing including it or coining or sizing as a secondary processing in the similar manner to the above. The resin to be used is preferably a resin which has wettability to the sintered body for exhibiting impregnation property and has low visco
Shikata Hideo
Tokushima Hidekazu
Yano Tadayoshi
Hitachi Powdered Metals Co, Ltd.
Kilpatrick & Stockton LLP
Mai Ngoclan
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