Abrading – Abrading process – Tumbling
Reexamination Certificate
2001-06-22
2003-05-06
Nguyen, George (Department: 3723)
Abrading
Abrading process
Tumbling
C451S035000
Reexamination Certificate
active
06558230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for polishing and chamfering a rare earth alloy, and a method and machine for sorting out polishing media. More particularly, the present invention relates to a polishing and chamfering method using polishing media, like a barrel polishing method, a method for sorting out polishing media used for polishing from objects to be polished, and a machine used for the sorting of the polishing media.
2. Description of Related Art
Rare earth alloys have been used as materials for strong magnets. Rare earth magnets produced by magnetizing rare earth alloys have been suitably used as a material for a voice coil motor (VCM) for positioning a magnetic head of a magnetic recording apparatus, for example.
Barrel polishing has been conventionally employed due to its superiority in mass-productivity for polishing and chamfering work pieces of a rare earth alloy. As used herein, chamfering refers to polishing a work piece to round the edges of the work piece. Two types of barrel polishing, rotary barrel polishing and vibration barrel polishing, are available. Rotary barrel polishing is widely used because a machine for this polishing is inexpensively available.
Rare earth alloys are brittle materials and are therefore easily chipped. To avoid chipping, it is generally suitable to adopt vibration barrel polishing rather than rotary barrel polishing. The reason is presumed to be that in vibration barrel polishing, a spiral flowing state is established, and this reduces collision between polishing media (hereinafter referred to as “media”) and objects to be polished and also between objects to be polished. Media and objects to be polished are rubbed against each other while flowing spirally in the same direction. In this way, polishing proceeds moderately.
Japanese Laid-Open Patent Publication No. 5-208360 discloses a vibration barrel polishing method in which a spiral flow is generated in a liquid in which all of the media and objects to be polished are immersed when a barrel bath is in the horizontal position, and describes that chipping can be further suppressed by this method.
The present inventors examined in various ways the methods for chamfering a rare earth alloy and found that, although the above conventional vibration barrel polishing method can suppress chipping to some extent, it may fail to provide uniform chamfering. In particular, this failure in uniform chamfering occurs when a plurality of flat work pieces are to be polished at one time, for example. In such a case, the work pieces firmly adhere to each other in the barrel bath, and thus part of edges of the work pieces are kept away from contact with the media.
In addition, chipping may occur even using the vibration barrel polishing method when the object to be polished is a work piece of a rare earth alloy including a rigid major phase mainly causing a brittle fracture and a grain boundary phase causing a ductile fracture, such as a rare earth alloy produced by sintering (hereinafter, referred to as a “rare earth sintered alloy”).
Chipping may also occur in a process of sorting out the media from the work pieces (objects to be polished) after the barrel polishing process, in which work pieces tend to collide against each other. As the sorting method, generally used is a method (called a “sifting method”) in which a mixture of media and work pieces is put in a sieve and the media are selectively dropped through the sieve under vibration. In this sifting method, the work pieces left on the sieve inevitably collide against each other, and thus chipping occurs.
In addition, the work pieces made to firmly adhere to each other in the barrel polishing process as described above are kept in the adhesion state in the sorting process. This means that a liquid medium (typically, water) with which the work pieces firmly adhere to each other is kept in touch with the work pieces for a comparatively long time. The rare earth alloy described above, which is highly susceptible to corrosion (easily rusts), should preferably be swiftly cleaned and surface-treated after chamfering. However, swift execution of these processes is difficult for such work pieces that firmly adhere to each other, and thus corrosion tends to occur.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method, in which polishing media is used to polish work pieces like a barrel polishing method, for chamfering a rare earth alloy that can suppress chipping of work pieces and also suppress adhesion of work pieces to each other during polishing to enable uniform chamfering.
Another object of the present invention is to provide a method for sorting out ball media while suppressing collisions between objects to be polished, and a machine for sorting out ball media permitting such sorting.
The method for chamfering a rare earth alloy of the present invention includes the following steps: preparing rare earth alloy work pieces, feeding the rare earth alloy work pieces, media, a liquid medium, and spacer particles (0.1% to 10% by volume of the liquid medium) into a container, and subjecting the rare earth work to polishing by vibrating the container.
The liquid medium is preferably fed into the container so that at least three-fourths of the bulk volume of the rare earth alloy work and the media are immersed in the liquid medium.
The average particle size of the spacer particles is preferably in a range of 0.05 mm to 1 mm, more preferably in a range of 0.1 mm to 0.5 mm.
The specific gravity of the media and the specific gravity of the spacer particles are preferably 4 or less.
The media preferably include alumina grains and a binder, and the weight percentage of the alumina grains is in a range of 45% to 48%. The porosity of the media is preferably 3% or less.
In the step of subjecting the rare earth work pieces to polishing, the container is preferably vibrated so that the amplitude in the horizontal direction is 0.4 mm or more and the amplitude in the vertical direction is 0.15 mm or more. Also, the container is preferably vibrated at an acceleration of 800 mm/sec
2
or more in the horizontal direction.
Ball media is preferably used as the media.
The method for sorting out ball media of the present invention includes supplying a mixture including ball media and an object to be polished to a slope, and allowing the ball media to roll along the slope to be removed from the slope, and the object to be polished to stay on the slope.
The step of supplying a mixture preferably includes the step of moving the slope. More preferably, the slope includes a ring belt having an opening in the center, and the slope is moved by rotating the ring belt.
The method may further include the step of collecting the ball media dropping from the opening formed in the center of the ring belt.
The machine for sorting out ball media of the present invention includes a slope including a ring belt having an opening in the center, for receiving a mixture including ball media and an object to be polished, and a driver for rotating the slope.
The slope preferably includes a rubber layer on the surface.
Hereinafter, the function of the present invention will be described.
The method for chamfering a rare earth alloy of the present invention, which adopts a polishing method utilizing vibration of a mixture of polishing media and work pieces, like a vibration barrel polishing method, can suppress chipping of work pieces of a highly brittle rare earth alloy. In particular, by using balls as the media, chipping can be further effectively suppressed. Especially, ball media are preferably used for work pieces including a rigid major phase mainly causing brittle fracture and a grain boundary phase causing a ductile fracture, such as work pieces of a rare earth alloy produced by sintering (rare earth sintered alloy), which are especially easily chipped. Moreover, using ball media makes it possible to employ a method for sorting out ball media described later. By employing this method, chipping in
Hiyoke Toshifumi
Kondo Sadahiko
Sasaki Toshiaki
Costellia Jeffrey L.
Nguyen Dung Van
Nguyen George
Nixon & Peabody LLP
Sumitomo Special Metals Co. Ltd.
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