Materials feeder equipment

Details Materials feeder equipment Materials feeder equipment

1999-08-27

2001-05-22

Derrington, James (Department: 1731)

Plastic and nonmetallic article shaping or treating: processes

Outside of mold sintering or vitrifying of shaped inorganic...

Shaping or treating of multilayered, impregnated, or...

C264S645000, C264S667000, C264S678000, C264S681000

Reexamination Certificate

active

06235233

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to improved material feeder equipment. More particularly the invention concerns material feeder equipment having high precision, durable, wear resistant tetragonal zirconia polycrystal (TZP) ceramic and zirconia composite elements.
BACKGROUND OF THE INVENTION
Material feeder devices are widely used in many industries to transport particles such as powders, pellets, medicaments, metals, and the like. In compression molding operations, for instance, efficient filling of the molds with materials in the powder form has a significant bearing in determining the unit manufacturing cost (UMC). Feeder boxes are used to carry loose powder to the top of the die where it shakes dropping powder into a die cavity. The die cavity is located underneath a die retaining element or the die retaining ring which secures the die in position. The die cavity is filled by the shaking motion of the feeder box which is connected to a hydraulic actuated cylinder. The feeder box slides on a flat surface called “ware plate” in a reciprocating motion. The time interval between the two extreme locations of the feeder box, when the compacting of the powders in the die cavity is effected. The top surfaces of the ware plate, the die retaining ring and the bottom surface of the feeder box need to be in a continuous plane for smooth operation of the powder filling mechanism. When the die cavity is filled with powder, it is compressed by the action of punches making a “green part”. The proper filling of the die cavity depends, among several other factors, on the sliding motion of the bottom of the feeder box on a plate normally known as feeder box ware plate and also on the die clamp (or retaining) ring. If there is a misalignment of the feeder box with respect to the ware plate and also with respect to the die clamp (or retaining) ring or if there is a slight gap between those components, excessive powder loss results. This problem is magnified if the powder particles are very fine (submicron) or are very hard. In such cases, the jamming of the feeder box (in worst case, breakage of the feeder box or ware plate or die clamp ring) can lead to interruption of the manufacturing process and a higher UMC for the part.
Misalignment of the feeder box with respect to the ware plate and/or with respect to die retaining ring can occur due to gouging of one of the surfaces, which is a common occurrence in industrial compression molding machines where the box and the plate and also the clamp ring are usually made of metallic materials, such as steels. Our experience indicates that ceramic materials may have some unexpected advantages in such molding components, although the prior art currently does not support this conclusion. This is because most of the conventional high performance ceramics are extremely brittle. An example of a material having good hardness and strength is monolithic cubic spinel, however, this material is also highly brittle and is unusable for structural applications. Thus skilled artisans are more inclined to experiment with alternative metallic components in materials feeder. Repeated sliding of two surfaces of metal parts, as in this specific case of surfaces of feeder box and the ware plate (or die retaining ring), usually leads to excessive wear and abrasion of those surfaces leading to the loss of materials, contaminating the powder feed, and also creating a gap between the box and the plate and also between the feeder box and the die clamp ring. This gap between the feeder box and the ware plate and also between the feeder box and the die retaining ring leads to the loss of powder, and in some cases jamming of the feeder mechanism. Normally, the machine components will begin to show signs of wear at about 5000 cycles of operation. At about one million cycle, the feeder plate will have to be replaced, if not sooner. Powdered material will start leaking out from under the feeder box and falling on the rest of the movable components of the machine making maintenance a large problem. Also, the motion of the feeder box will become agitated and impede the free flowing motion of powder during die filling.
Therefore, a need persists for improved materials feeder and method of making same so that the equipment will have superior wear and abrasion resistance while being cost effective and easy to manufacture.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved, high precision materials feeder equipment that is reliable, simple to use and cost effective to manufacture.
It is another object of the invention to provide high precision materials feeder equipment in which contacting surfaces have remarkably improved wear and abrasion resistance, and therefore, a longer useful life.
It is a feature of the invention that the improved materials feeder equipment has elements having ceramic sliding surfaces comprising tetragonal zirconia ceramic materials (Y-TZP) or, alternatively, zirconia composite materials, (ZrO
2
/ZrO
2
—Al
2
O
3
or ZrO
2
—Al
2
O
3
/ZrO
2
).
Accordingly, for accomplishing these and other objects, features and advantages of the invention, there is provided, in one aspect of the invention, an improved materials feeder equipment which includes a dispenser having an inlet end and an outlet end for respectively receiving and then dispensing materials. A feeder box is provided having a first opening to receive materials dispensed from the outlet end of the dispenser and a base having a second opening for releasing the materials. Also, means are provided for controllably releasing particles from the second opening. Sidewalls surround the base for containing the materials in the feeder box. Further, a ware plate or plate-like surface is arranged in sliding contact with the base of the feeder box. Means, moreover, are provided for slidably moving the feeder box along the plate-like surface between a first position and a second position. It is important to the invention that the base has a first-sliding contact portion comprising tetragonal zirconia ceramic and that the plate-like surface has a second-sliding contact portion comprising zirconia ceramic composite, more particularly zirconia-alumina composite, (ZrO
2
/ZrO
2
—Al
2
O
3
or ZrO
2
—Al
2
O
3
/ZrO
2
).
In another aspect of the invention, a method of making a precision ceramic elements for improved materials feeder equipment includes the step of providing ceramic powder comprising either a solely of zirconia alloy or a composite comprising of first concentration of particulate zirconium oxide alloy and a second concentration of particulate aluminum oxide. The zirconium oxide alloy consists essentially of zirconium oxide and a secondary oxide selected from the group consisting of MgO, CaO, Y
2
O
3
, Sc
2
O
3
, and rare earth oxides. Moreover, wherein zirconium oxide alloy has a concentration of said secondary oxide of, in the case of Y
2
O
3
, about 0.5 to about 5 mole percent; in the case of MgO, about 0.1 to about 1.0 mole percent, in the case of CeO
2
, about 0.5 to about 15 mole percent, in the case of Sc
2
O
3
, about 0.5 to about 7.0 mole percent and in the case of CaO from about 0.5 to about 5 mole percent, relative to the total of said zirconium oxide alloy, said compacting further comprising forming a blank. A mold is provided for receiving and processing the ceramic powder. The ceramic powder is then compacted in the mold provided to form a ceramic billet. The ceramic billet is then shaped or machined so as to independently form near net-shaped ceramic elements for the improved materials feeder equipment. According to our invention, the ceramic elements include sliding surfaces for a ware plate and a feeder box. In this embodiment of the invention, after the initial shaping, the near net-shaped green ceramic elements are sintered thereby forming a sintered ceramic elements for the improved materials feeder equipment. The ceramic elements are then further machined or shaped. Alternatively, the net-shaped ceramic elements of the improved feed

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