Coating processes – Measuring – testing – or indicating
Reexamination Certificate
1999-09-24
2001-09-25
Parker, Fred J. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S459000, C427S475000, C427S485000
Reexamination Certificate
active
06294216
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for charging powder by utilizing frictional electrification. Also, the present invention relates to a powder coating apparatus, and a method of using such a powder charging apparatus in such a powder coating apparatus.
2. Description of the Related Art
An electrostatic power coating method is one for coating charged powder onto the surface of an article to be coated by electrostatic forces. In general, a corona electrification or a frictional electrification is utilized in a method for charging the powder. The corona electrification is excellent in controllability of an electrification rate and an electrification charge amount. Accordingly, a large charge amount can be given to the powder for a short period of time. However, it requires a high voltage and suffers from a problem that the apparatus therefor becomes large and expensive. On the other hand, since the frictional electrification is based upon a contact electrification, it does not require an electric power source. Accordingly, the powder may be charged in a less expensive manner and in a safe manner with a simple apparatus.
However, the frictional electrification suffers from a problem that the charging rate is low and it takes a long time to obtain a predetermined charge amount.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a powder charging apparatus and a method therefor which may charge powder at a high charging rate while utilizing a frictional electrification.
Also, an object of the present invention is to provide a powder coating apparatus, and a method of using such a powder charging apparatus in such a powder coating apparatus.
According to the present invention, there is provided a powder charging apparatus comprising: a delivery tube for delivering powder; an electrification member disposed in the delivery tube; and a vibrating means for imparting at least one of a vibration to the powder and the electrification member to be delivered within the delivery tube to accelerate a contact between the powder and the electrification member.
A vibrator disposed in the delivery tube may be used as the vibrating means. An inner wall surface of the delivery tube and the surface of the vibrator may be used as electrification members. A TEFLON, i.e., polytetrafluoroethylene, coating layer may be formed on the inner wall surface of the delivery tube and the surface of the vibrator.
It is possible to take a structure in which a metal mesh having a mesh size through which the powder may pass is provided across an interior of the delivery tube, and a number of carriers which have a size by which the electrification member cannot pass through the size of the metal mesh and which may be trapped within the delivery tube by the metal mesh are used as the electrification members. The vibrator may be mounted on the metal mesh as the vibrating means.
Furthermore, the electrification member may be disposed within the delivery tube for feeding a predetermined amount of the powder and the electrification member is a screw to be driven by a driving means. The vibrating means may vibrate the screw.
A charge amount detecting means for detecting a charge amount of the powder and a controller for controlling an amplitude and/or a frequency of the vibration by the vibrating means so that the charge amount to be detected by the charge amount detecting means is kept at a predetermined value may be provided. In this case, a feed unit for feeding the powder through the delivery tube may be provided, and the controller controls the vibrating means so that the charge amount per unit weight of the powder is kept at a predetermined value on the basis of the feed amount of the feed unit and the charge amount detected by the charge amount detecting means.
A powder charging method in accordance with the present invention is a method of vibrating the powder delivered within a delivery tube, and/or the electrification member disposed within the delivery tube, to thereby accelerate the contact between the powder and the electrification member. Furthermore, it is possible to detect a charge amount of the powder and to control an amplitude and/or a frequency of the vibration so that the detected charge amount is kept at a predetermined value. Also, it is possible to control the amplitude, and/or the frequency, of the vibration on the basis of a feed amount and the charge amount of the powder so that the charge amount per unit weight of the powder is kept at a predetermined value.
A powder coating apparatus according to the present invention is provided with a spray unit for spraying an article to be coated with the powder charged by the above-described powder charging apparatus according to the invention.
Alternatively, the powder coating apparatus is provided with a booth where an article to be coated is held, a fluidizing layer of the coating powder formed on a bottom portion of the booth with a top side of the fluidizing layer being opened, and a spraying apparatus for extracting the coating powder from the fluidizing layer and spraying the coating powder into the booth from a top portion of the booth after charging the coating powder by the above-described powder charging apparatus according to the invention. In this case, it is possible to provide an electric field forming means for forming an electric field for sticking the coating power sprayed into the booth to the article to be coated or a feeding air forming means for feeding a pressurized air for depressing the coating powder sprayed into the booth toward the article to be coated.
A powder coating method according to the invention is a method wherein the powder charged in accordance with the powder charging method of the invention is sprayed to the article to be coated.
Alternatively, it is possible to fluidize coating powder on a bottom portion of a booth, extract the fluidized coating powder and spray the coating powder into the booth from a top portion of the booth after charging the coating powder in accordance with the powder charging method of the invention and introduce an article to be coated in the booth. In this case, it is possible to form an electric field for introducing the coating powder to, and around, the article to be coated, or to feed pressurized air for depressing the coating powder toward the article to be coated.
REFERENCES:
patent: 4597534 (1986-07-01), Roud
patent: 5753302 (1998-05-01), Sun et al.
“Powder Coatings”, Ed by Nicholas P. Liberto, pp. 82-85, 1994.
Ikezaki Kazuo
Yamamoto Masahiro
Nihon Parkerizing Co. Ltd.
Parker Fred J.
Wenderoth , Lind & Ponack, L.L.P.
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