Plastic article or earthenware shaping or treating: apparatus – Forming surface and means feeding fluent stock thereto – Trap measuring compartment
Reexamination Certificate
1999-10-15
2002-06-11
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Forming surface and means feeding fluent stock thereto
Trap measuring compartment
C406S050000, C406S091000, C406S127000, C141S067000
Reexamination Certificate
active
06402500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to techniques and apparatus for delivering particulate material and filling cavities in a uniform and consistent manner during successive filling operations. The invention relates in particular to powder delivery systems for delivering particulate material and filling closed cavities, such as die cavities of die-casting machines, and for filling open cavities, such as containers on food packaging production lines.
2. Description of the Related Art
Powder delivery systems are used for delivering particulate material and filling die cavities of, e.g., die-casting machines prior to powder compaction in processes for fabricating consolidated parts for automotive, aerospace, micro-electronics, pharmaceuticals vitamins, etc. Powder typically is gravity-fed from a main hopper to the, die cavity by transfer through a flexible tube to a feedshoe or fillshoe, which deposits powder into the die cavity. The process of depositing powder in the die cavity is called “die filling.”
The process of powder delivery and filling by gravity is the most common way of delivering powder and filling a die cavity. The feedshoe is pushed forward between the surface of the die cavity and a top punch, and positioned on top of the die cavity. Depending on powder flow characteristics, cavity shape and size, type of die-casting machine, and filling method, the feedshoe is typically mechanically vibrated while on top of the die cavity to loosen the powder, break any clumps and ensure that the die cavity is full before the feedshoe is retracted.
There are several problems associated with prior art processes for powder delivery and filling of a die cavity.
One such problem is variation in filling conditions during successive filling operations, i.e. from part to part. Variations in filling conditions from part to part result in variations in weight from part to part, and a non-uniform fill of the die cavities. A non-uniform fill results in variations in density between the front and back of the part and in distortion of the part during sintering. Typically, part specifications include limits on acceptable variations in part weight and on acceptable variations in density within the part. Parts that do not meet the specifications are rejected.
The variations in filling conditions from part to part are due, in part, to variations in head pressure, clumping, surge, and dead zones of material within the feedshoe. The head pressure is due to the powder in the feedshoe, the flexible tube and the main hopper. As a result of the powder delivery system design, wherein the flexible tube is typically connected to the backside of the feedshoe, the powder in the back of the die cavity is subjected to a higher head pressure than the front of the die cavity.
During operation, the feedshoe is pushed forward and centered above the die cavity and then retracted before compacting. The movement of the feedshoe across the die cavity results in the back of the die cavity being subjected to the higher head pressure for a longer period of time than the front of the die cavity. These effects combine to produce variations in part density between the back and the front of the part, which result in distortion during sintering.
Clumping and surge of the powder within the feedshoe and flexible tube contributes to non-uniform filling of die cavities. Mechanical shaking of the feedshoe above the die cavity can break clumping in the powder and improve fill uniformity but is not consistent during successive filling operations.
A further problem results from fine powders/particulate materials, which do not have good flow characteristics, thus posing a serious problem for the die filling operation. Lubricants are added to reduce interparticle friction and improve flowability, thereby requiring an energy intensive delubing cycle after compacting to remove all added lubricants.
A further problem is that mechanical shaking of the feedshoe causes segregation of fine powders/particulate materials from coarse powders/particulate materials resulting in a loss of uniformity in particle size distribution and chemical composition. This powder segregation results in powders with different apparent densities and chemical composition being filled in the die cavity during successive powder filling operations.
A solution to these and other problems is needed. Such solution is provided by the novel invention recited herein.
BRIEF SUMMARY OF THE INVENTION
The invention contemplates supplying a technique land apparatus for delivering particulate material and filling cavities in a uniform and consistent manner during successive filling operations. In preferred embodiments, the invention provides a powder delivery system for delivering particulate material and filling closed cavities, such as the closed die cavities of die-casting machines; or for filling open cavities, such as open containers on food packaging production lines.
Die Casting and Sintering
The three basic steps for producing parts by the press and sinter process are mixing, compacting and sintering. In step one, mixing, elemental or prealloyed powders are mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients. The lubricant reduces interparticle friction and improves the flow characteristics of the powder mixture. In step two, compacting, mixed powder is fed into a precision die on a die-casting machine and is compacted. Compacting the loose powder produces a “green compact” which has the size and shape of the finished part when ejected from the die. In step three, sintering, the green compacts are placed on a wide-mesh belt and slowly moved through a controlled atmosphere furnace. The parts are heated to below the melting point of the base material, held at the sintering temperature, and then cooled.
Tabletting and Dry Compaction
The production of pharmaceutical preparations, e.g. vitamins, or tablets containing an active medicament in a carrier or other suitable excipient, requires precise and homogeneous mixation techniques. Similarly, candies usually must have an acceptable hardness, mouthfeel, and duration within the mouth. These characteristics can depend in part upon the homogeneity of the composition in the tablet form.
Dry powder, or a semidry paste, is placed within a tablet mold and subjected to pressure. The amount of pressure usually determines the hardness of the tablet, and consequently its lifetime within the mouth (subject, of course, to chewing). It is important for dosage amount and appearance that the powder feed correctly into the tabletting machine.
The Closed Cavity Device
In one embodiment, the invention provides a method and apparatus for powder delivery and filling of a closed cavity, such as a die cavity of a die-casting machine. The apparatus includes a mini-hopper, a transport device, a delivery chute and a gas control unit.
The mini-hopper has a porous distributor plate for partitioning the mini-hopper into a first partition in which the bed of particulate material is stored and a second partition separate from the first partition and in communication with the first partition via the porous distributor plate. An inlet port is provided for receiving a compressed gas in the second partition at a low pressure, whereby only the bottom surface of the bed of particulate material becomes fluidized by migration of the compressed gas through the porous distributor plate and into the first partition.
The transport is connected to the side of the mini-hopper and delivers powder/particulate material from the mini-hopper to the delivery chute. The transport has a porous distributor plate for partitioning the transport into a first partition in which the particulate material flows and a second partition separate from the first partition and in communication with the first partition via the porous distributor plate.
The delivery chute can function as the powder discharge unit directly above the die cavity. Fluidizers are embedded in the delivery chute to ensure t
Parrish Phillip A.
Raman Rajkumar
Rowland Roderick
Zahrah Tony F.
Matsys
Millen White Zelano & Branigan P.C.
Nguyen Thu Khanh T.
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