Abrading – Machine – Rotary tool
Reexamination Certificate
2003-06-19
2004-10-19
Nguyen, Dung Van (Department: 3723)
Abrading
Machine
Rotary tool
C451S541000
Reexamination Certificate
active
06805620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a grindstone, such as a gear-tooth honing stone, having a resinoid abrasive structure including abrasive agglomerates each of which is provided by a vitrified abrasive structure.
2. Discussion of the Related Art
A gear-tooth honing operation is known as a hardened-gear finishing operation that is intended to reduce the noise of spur or helical gears (e.g., which are to be used in a vehicle transmission unit) after their heat treatment. That is, such a gear-tooth honing operation is effected for removing a distortion of the gear caused during the heat treatment, and for improving accuracy of each tooth of the gear. As a gear-tooth honing stone used in the gear-tooth honing operation, there is known a resinoid grindstone in the form of an internally-toothed honing wheel having an annular main body provided by an abrasive structure in which standard abrasive grains such as alumina oxide grains and silicon carbide grains are held together by a binder including a resin bond that is made of a thermosetting resin such as phenol and epoxy. The annular main body has, in its inner circumferential surface, a teeth profile portion which is to be meshed with external teeth of a gear as a workpiece. Such an internally-toothed honing wheel is subjected to a dressing operation with a dressing gear having a surface on which diamond abrasive grains are fixed in an electrodeposition method. In a honing operation executed after the dressing operation, the work gear is brought into engagement at its external teeth with the teeth profile portion of the internally-toothed honing wheel, and is rotated about its axis while being reciprocated in the axial direction, whereby the surface of each tooth of the work gear is ground or honed.
The resinoid grindstone is elastically deformed in a larger amount when a grinding load is applied thereto, than a vitrified grindstone. Further, the resinoid grindstone has a smaller degree of strength for holding or bonding the abrasive grains together, and a lower degree of wear resistance than the vitrified grindstone. Due to such characteristics thereof, the resinoid grindstone is not capable of satisfying a recent demand for grinding or removing a larger volume of stock from a workpiece with a higher efficiency, even where the abrasive structure of the resinoid grindstone is modified to have a higher density and a higher grade (that corresponds to the degree of strength with which the binder or bond holds the abrasive grains in the bond setting).
Where the resinoid grindstone takes the form of a honing stone (like the above-described internally-toothed honing wheel) having a teeth profile which is formed in its outer or inner circumferential surface and which conforms to teeth of a gear to be honed or ground as a workpiece, the honing stone has to be periodically or cyclically dressed so as to maintain its teeth profile so that the shape of the gear teeth finished by the honing stone is maintained. That is, when the teeth profile is changed to a certain extent due to wear of the honing stone, or when the amount of wear of the honing stone exceeds a predetermined amount, the honing stone has to be subjected to a dressing operation for rectifying or reshaping the teeth profile. The dressing cycle or interval is closely related with a service life of the honing stone. The wear resistance of the honing stone could be improved by using a resinoid grindstone of a high grade. However, such a resinoid grindstone having the high grade does not have a high degree of sharpness and is not accordingly capable of removing a large volume of stock from a workpiece with a high efficiency.
SUMMARY OF THE INVENTION
The present invention was made in the light of the background art discussed above. It is therefore an object of the present invention to provide a resinoid grindstone or a gear-tooth honing stone which has a high degree of wear resistance and is capable of removing a large amount of stock with a high efficiency. This object of the invention may be achieved according to any one of the first through fourteenth aspects of the invention which are described below.
The first aspect of this invention provides a resinoid grindstone comprising a main body having an abrasive structure in which abrasive agglomerates are held together by a binder including a resin bond, wherein each of the abrasive agglomerates includes abrasive grains which are held together by an inorganic bond, and wherein the binder further includes a filler such that a ratio of a strength of the abrasive agglomerates to a strength of the binder is not higher than 1.5.
In the resinoid grindstone according to this first aspect of the invention, each of the abrasive agglomerates included in the resinoid abrasive structure is provided by the plurality of abrasive grains held together by the inorganic bond, so that each abrasive agglomerate has a size larger than that of each of the abrasive grains included in each abrasive agglomerate. Each of the abrasive agglomerates, which are held by the resin binder, has a high rigidity owing to its vitrified abrasive structure. That is, the high rigidity of each abrasive agglomerate enables the present resinoid grindstone to have a large depth of cut with respect to a workpiece, while the resinoid grindstone as a whole has a certain degree of elasticity owing to the resinoid abrasive structure. Although each abrasive agglomerate is held together by the rein binder, each abrasive agglomerate having the relatively large size is supported at its relatively large area by the binder so that each abrasive agglomerate is not displaced by a large distance away from the workpiece during a grinding operation. Owing to this relatively large size of each abrasive agglomerate and presence of pores in the vitrified abrasive structure of each abrasive agglomerate, the resinoid grindstone is capable of removing a large amount of stock from the workpiece with a high efficiency. Further, owing to the relatively large size and also concavities and convexities in the surface of each abrasive agglomerate, each abrasive agglomerate is held together by the binder with a high bonding strength, thereby reducing removal of the abrasive agglomerates from the resinoid abrasive structure and accordingly improving the wear resistance.
Further, in the resinoid grindstone of this first aspect of the invention, the strength of the binder is increased by the incorporation of the filler in the binder such that the ratio of the strength of the abrasive agglomerates to the strength of the binder is not higher than 1.5. This arrangement makes it possible to improve a surface smoothness of the ground workpiece with a reduced risk of damaging or scratching the surface of the ground workpiece. Moreover, this arrangement serves to prolong the service life of a dressing tool which is used to dress the grindstone. It is noted that a content of the resin bond (included in the binder), a content of the abrasive agglomerates and a content of the filler (included in the binder) are preferably 15-30 wt %, 10-40 wt % and 40-75 wt %. This preferable proportions of the components are effective to further improve the grinding efficiency and the durability of the resinoid grindstone.
According to the second aspect of the invention, in the resinoid grindstone defined in the first aspect of the invention, the strength of the abrasive agglomerates is smaller than the strength of the binder. Namely, the ratio of the strength of the abrasive agglomerates to the strength of the binder is lower than 1.0., so that the surface smoothness of the ground workpiece is further improved with a further reduced risk of damaging or scratching the surface of the workpiece. Further, the service life of the dressing tool is further prolonged.
According to the third aspect of the invention, in the resinoid grindstone defined in the first or second aspect of the invention, the filler is provided by second abrasive grains each having a size which is not sma
Iwai Kouji
Kusakabe Tsuguo
Sato Yasushi
Nguyen Dung Van
Noritake Co., Limited
Oliff & Berridg,e PLC
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