Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Forming articles by uniting randomly associated particles
Patent
1995-08-11
1997-09-30
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Forming articles by uniting randomly associated particles
264 71, 264123, 425174, 425352, 425456, B29C 4302
Patent
active
056723130
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of manufacturing a powder molding using a mold for compression molding, and a powder feeder for use in the manufacture of such a power molding.
2. State of the Prior Art
FIG. 6 illustrates a conventional method of manufacturing a powder molding. In this method, a powder molding is manufactured by moving a powder feed shoe box 2 containing powder to a position over a cavity 21 formed in a mold 20 to drop the powder in the box 22 into the cavity 21, backing the shoe box 22, and compressing the powder in the cavity 21 by lowering an upper punch 23.
A powder molding is usually sintered subsequently. If the density of the powder molding is uneven, the dimension of the powder molding tends to be uneven when sintered, so that the sintered product tends to be uneven in dimension, too.
In this conventional method, powder is dropped by gravity into the cavity 21, so that the powder tends to form a bridge in the cavity. This leads to uneven density of the powder.
The powder in the shoe box 22 spontaneously drops into the cavity 21 while moving the shoe box 22 to over the cavity. Then, by backing the shoe box 22, any portion of the powder protruding from the surface of the mold 20 is scraped off by the edge of the shoe box 22, so that the top of the powder in the cavity is leveled out. This causes unevenness in the density of the powder.
In order to make the density of the powder packed in the cavity of the mold uniform, trials were made to vibrate the mold after filling powder in the cavity. But by vibrating the mold, the mold tends to displace or may be worn. If the mold moves, it may be broken by interfering with the upper punch.
Unexamined Japanese Patent Publication 5-69195 discloses a method of feeding powder in which a high-frequency AC current is supplied through a coil surrounding the mold to microscopically oscillate a material powder containing magnetic substances by producing an eddy current in the powder.
But in this method, it is impossible to use a powder other than magnetic powders. Also, an extra space has to be provided around the mold to mount the coil. This leads to reduced rigidity of the die set. Moreover, a magnetic field produced by the coil tends to unnecessarily magnetize the mold and the powder molding. In order to oscillate the powder with a sufficient strength, a high voltage is required. This pushes up the production cost.
SUMMARY OF THE INVENTION
An object of this invention is to provide a method of manufacturing a powder molding which makes it possible to pack a material powder in a cavity of a mold with high and uniform density, and a powder feeder for use in this method.
According to this invention, there is provided a method of manufacturing a powder molding comprising the steps of feeding a material powder into a cavity formed in a mold for compression molding through a bottom opening formed in a shoe box while oscillating the material powder while it is in the shoe box until the density of the powder in the cavity increases to at least 1.1 times the apparent density, and compressing the powder in the cavity.
The powder in the shoe box should preferably be oscillated at an oscillating frequency of 10-200 Hz and an oscillating pressure of 1-50 kg.
The powder feeder for use in the manufacture of a powder molding comprises a shoe box mounted to move toward and away from a cavity formed in a mold for compression molding, and an oscillator mounted on the shoe box for oscillating the shoe box.
In order to effectively oscillate the powder in the shoe box, a plurality of top- and bottom-open cells are preferably provided in the shoe box at its lower portion.
By feeding powder from the shoe box into the cavity of the mold, while vibrating the shoe box, the vibration of the shoe box is transmitted through the powder in the shoe box to the powder in the cavity, so that the density of the powder in the cavity increases.
If the density of the powder in the cavity is at a valve at least 1.1 times the appa
Shiga Ryuji
Takano Yoshishige
Takeda Yoshinobu
Sumitomo Electric Industries Ltd.
Theisen Mary Lynn
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