Plastic article or earthenware shaping or treating: apparatus – Stock pressurizing means operably associated with downstream... – Plural orifices
Reexamination Certificate
1999-02-26
2001-02-27
Pyon, Harold (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Stock pressurizing means operably associated with downstream...
Plural orifices
C425S38200R, C425S464000
Reexamination Certificate
active
06193498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a die plate for use in extruding a viscous material. More particularly, a die plate is shown that permits rapid extrusion of material and that has an extended service life.
2. Background of the Invention
Existing die plates used in the extrusion of viscous materials are formed from flat metal plates with a multiplicity of holes drilled through the plates. The holes through the plates are of substantially equal diameter and of substantially uniform diameter throughout their lengths. The holes through existing extrusion die plates are also spaced parallel to each other and substantially equal distance from each other.
A common problem with existing extrusion die plates is that the area around the perimeter of a group of holes through the plate tends to rip or tear away from the solid portion of the plate under the pressure of the extruder. The extruder generally forces a viscous or pasty material through the holes in the extruder die plate to form a plurality of cylinders of the viscous material that may be broken up into small particles for the preparation of solid granules.
The thickness of the extruding die plate controls the length of the holes through the die plate, which constitutes one of the factors affecting the power consumed by the extruder. The thickness of the die plate also affects the strength of the die plate, and hence resistance to failure by tearing along the boundary between the perforated section of the die plate and the solid support portion of the die plate. A change in the thickness of the die plate, and therefore in the length of the holes through the die plate, presents problems because it affects not only the pressure required to extrude the viscous materials through the die plate but also the rheology or flow characteristics of the material extruding through the die plate. The feed rate at which the viscous material is extruded through the die plate can also be changed in order to affect the pressure exerted on the die plate. A problem with reducing the feed rate in order to lower the back pressure on the die is a resultant lower production rate and reduced economy. The characteristics of the material being extruded, such as viscosity, can also be changed in an attempt to reduce the stress on the die plate during extrusion. Changes to the material characteristics of the extrusion materials is generally either impossible or undesirable as a result of the required characteristics of the end product.
SUMMARY OF THE INVENTION
In view of the foregoing problems with conventional die plates, the die plate according to one aspect of the present invention was developed to permit rapid extrusion of a solid viscous material under pressure while maintaining an extended service life of the die plate as compared with conventional die plates.
A die plate according to an aspect of the present invention includes a solid support area and a perforated area that borders on the solid area. The perforated area includes a main portion having holes through the die plate that are spaced from each other by first distances, and a transitional area separating the main portion from the solid support area and having holes through the die plate that are spaced from each other by second distances greater than the first distances.
The solid supporting section of the die plate separates the perforated portion of the die plate into a plurality of smaller perforated extruding sections. Each of the smaller perforated extruding sections has a major portion of holes through the die plate that are spaced from each other by first distances and a transition portion of holes through the die plate that are spaced from each other by second distances greater than the first distances. The transition portions surround the major portions in each smaller perforated extruding section and separate the major portions from the solid supporting section.
The solid supporting section of the die plate is shaped in accordance with the structure of the extruder used to force viscous material through the die plate. A typical extruder screw used for forcing the viscous material through the die plate is a screw-type extruder such as the six inch extruder sold under the trademark “EXTRUD-O-MIX” made by Hosokawa Bepex Corporation of Minneapolis, Minn. The extruder includes a beveled blade that wipes viscous material over the face of the die plate and pushes the material through the holes in the die plate.
The solid support section on the die plate borders perforated areas of the die plate through which the viscous material is extruded. The spacing, and therefore the amount of die plate material between the holes through the die plate in the transitional areas adjacent the solid support section is greater than the amount of material between the holes in a major portion of each perforated area. The increase in the amount of material between holes through the die plate closer to the solid support sections improves the strength of the die plate at the perimeters the perforated areas, thus increasing the service life of the die plate.
REFERENCES:
patent: 756259 (1904-04-01), Malone et al.
patent: 2408713 (1946-10-01), Webb
patent: 2798252 (1957-07-01), Cummings, Jr.
patent: 3153392 (1964-10-01), Verona
patent: 3361860 (1968-01-01), Fassbener
patent: 4088433 (1978-05-01), Simpson
patent: 4111632 (1978-09-01), Leaver
patent: 4465452 (1984-08-01), Masuzawa
patent: 5567493 (1996-10-01), Imai et al.
Castle Amy E.
Kirk Shane K.
Thrasher Mark A.
Blake Esq. Michael J.
Del Sole Joseph S
Eastman Chemical Company
Gwinnell Harry J.
Pyon Harold
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