Conveyors: fluid current – Intake to fluid current conveyor – Load receptacle type
Reexamination Certificate
1999-03-11
2001-04-24
Ellis, Christopher P. (Department: 3651)
Conveyors: fluid current
Intake to fluid current conveyor
Load receptacle type
C406S088000, C406S085000, C406S124000, C406S137000, C406S144000, C406S146000, C239S008000, C239S693000, C239S310000
Reexamination Certificate
active
06220791
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a system for aerosolizing powders for use in powder spray painting and other powder spray applications. In particular, the present invention is directed to a system for generating an air stream of aerosolized fine powder by forming a turbulent powder cloud from which powder is extracted, which results in a powder spray to a workpiece having a constant powder mass deposition rate.
A steady flow rate of unagglomerated powder particles from the powder spray device is essential to the formation of a smooth, uniform-thickness powder layer on the substrate to be painted in powder spray paint applications. Conventionally, fluidized beds or vibrating troughs have been used to feed powder into the powder spray system. For example, U.S. Pat. No. 5,745,954 to Shutic discloses a powder painting system including a fluidized powder bed. In the disclosed device, powder is fed into a powder feed hopper and falls to the fluidized bed at the bottom of the hopper. The fluidized bed is maintained through the use of pressurized air inlets in the floor of the hopper and rotating baffles. Suction tubes at the top of the hopper extract powder from the fluidized bed.
U.S. Pat. No. 5,654,042 to Watanabe et al. also discloses a powder coating system utilizing a fluidized bed. To improve performance of the device, Watanabe et al. also discloses the use of low-pressure gas pulses directed counter to the normal flow direction of the powder out of the hopper. These low-pressure gas pulses create microvibrations within the powder intake to alleviate adherence and cohesion among powder particles at the pump inlet.
Other prior art devices have attempted to solve the problem of uniform powder flow without fluidized beds. U.S. Pat. No. 5,752,788 to Crum discloses a powder spray device using a vaned impeller to distribute powder before it is delivered to a powder spray gun. The device includes a control system to adjust the rate at which powder is metered to the powder spray gun so that the mass of powder exiting to the powder spray gun remains relatively constant.
In addition, U.S. Pat. No. 4,116,367 to Kataoka et al. discloses an apparatus for supplying powder to a continuous metal casting mold. In this device, powder is fed down into a hopper with compressed air openings along its sides. The powder falls from the hopper through a hole in the bottom, and enters an intake section where the powder is pushed upward by air nozzles. The powder is then sent by a screw to a horizontal air nozzle, which pushes the powder toward the spray nozzle device.
None of these devices is completely satisfactory in operation for steady delivery of powders, and this problem remains as one of the primary difficulties in powder spray painting. In particular, these devices are unable to create a flow of powder in which powder is for the most part separated into individual particles prior to delivery of the powder to the powder sprayer.
SUMMARY OF THE INVENTION
The present invention overcomes the limitations of the prior art by creating a uniform cloud of powder from which powder is extracted and delivered to a spray gun or other aerosolized powder application. The powder is originally fed into a powder reservoir of the disclosed device. Compressed air is forced into the powder, thereby agitating the powder and creating a cloud of aerosolized powder that rises upwards on the air stream.
The powder passes through a hole in the top of the powder reservoir and enters a chamber connected to the powder reservoir. The chamber is shaped roughly as a funnel, with the diameter of the chamber generally increasing with height. As the aerosolized powder rises in the chamber, the air flow speed, and hence the upward air drag force on the powder particles, decreases due to the increasing diameter of the chamber. At some point, the air drag force on a powder particle becomes equal to the particle weight, and a cloud of powder collects in the chamber in the vicinity of this equilibrium height. It is believed that the formation of a powder cloud in the chamber is enhanced by the Bernoulli effect because the air pressure in the chamber increases with height as the air flow speed decreases. The resulting powder cloud is approximately stationary, internally turbulent, and has an approximately uniform space and time averaged mass density.
Aerosolized powder is extracted from the powder cloud by a Bernoulli tube which passes horizontally through the chamber at the equilibrium height of the cloud. Tests have shown that aerosolized powder consisting of single powder particles can be extracted from the device at a uniform rate. The rate of powder extraction can be varied simply by varying the air flow rate through the Bernoulli tube.
It is therefore an object of the present invention to provide a system for the aerosolization of powders using a turbulent powder cloud.
It is a further object of the present invention to provide a system for the aerosolization of powders that produces a uniform distribution of powder when the powder is distributed onto a substrate.
It is a still further object of the present invention to provide a system for the aerosolization of powders wherein single powder particles can be extracted from the system at a uniform rate.
Further objects and advantages of the present invention will be apparent from a consideration of the following detailed description of the preferred embodiments in conjunction with the appended drawing as briefly described following.
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Board of Trustees of the University of Arkansas
Dougherty J. Charles
Ellis Christopher P.
Ridley Richard
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