Coating processes – Measuring – testing – or indicating – Thickness or uniformity of thickness determined
Patent
1985-12-31
1987-11-03
Beck, Shrive P.
Coating processes
Measuring, testing, or indicating
Thickness or uniformity of thickness determined
118712, 427 10, 73150R, B05D 104
Patent
active
047042974
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the assessment of the coating of a surface with a powder and more particularly, but not exclusively, the efficiency with which an electrostatic technique applies an insulating polymeric powder coating for subsequent fusing on a surface.
The technique of depositing a coating of powder on a surface by means of electrostatic force is well-known and widely used to deposit coatings of various materials such as epoxy, polyester, polycarbonate, polypropylene, nylon, and combinations of these materials, for subsequent fusion by heating. However the coating process is not easy to control except by trial and error methods which themselves are not always consistent in their results when applied in apparently identical circumstances.
It is an object of the invention to assess the coating of a surface with a powder to provide information about the coating action to assist in its control and mitigate the problems of the uncertain nature of the process at present.
According to the invention there is provided an apparatus for destructive assessment of a particulate coating including means to apply radiation to a deposited particulate coating and means to measure the radiaton passed through the coating, means to disturb a small region of the particulate coating in a reproducible manner, means to measure the radiation passed through the disturbed coating, and means to determine the change in the radiation transmissibility of the deposited particulate coating as a result of the disturbance whereby an indication of the effect on the coating of the reproducible disturbance is provided as an indication of the adherence of the coating and the efficiency or otherwise and the deposition of the coating.
The apparatus may include means to repeat the disturbance at the already disturbed coating to permit a further such determination.
Specifically the apparatus may include a conductive surface connectable to ground and to which a coating of powder may be applied by electrostatic means, fluid pressure means to disturb a small region of the coating, means to send infra-red radiation through the coating and the surface, and any support therefor, to measure the change in the transmissivity of the coating resulting from the disturbance.
The conductive surface may be a metallic coating on a glass support to form a test piece.
The means to disturb the coating may be a fluid pressure duct, such as a hypodermic needle, surrounded by a housing sealable to a coating and provided with a controllable source of fluid pressure, such as compressed air suppliable in bursts of set time and pressure. The means to detect radiation may be a solid-state detector of infra-red radiation associated with the fluid pressure duct. The means to apply radiation may be an opposed source of said radiation. The radiator and detector may be interchanged.
The apparatus may be arranged to pass the radiation normally or at another angle through the coating and any supporting surface and substrate, which are radiation-transmissive. The radiation may be reflected, to pass twice through the coating for measurement, for an opaque substrate or supporting surface.
The radiation may be other than infra-red, for example in the form of microwaves or from radio-active decay, such techniques being well-known in the art for measuring material thickness.
According to the invention there is provided a method of assessing a particulate coating including applying a coating to a surface, permitting or causing radiation to pass through the coating and measuring the radiation passed through the coating, disturbing a small region of the coating in a reproducible manner, again permitting or causing radiation to pass through the coating including the disturbed region and measuring the radiation passed through the disturbed coating, determining the change in the radiation passed through the coating as a result of the disturbance and indicating the change as the effect on the adherence of the coating to the surface of the reproducible disturbance and thence of the effi
REFERENCES:
patent: 2773412 (1956-12-01), Huck
patent: 4276767 (1981-07-01), Cartwright
patent: 4301764 (1981-11-01), Campion
patent: 4393699 (1983-07-01), Seiler
patent: 4417478 (1983-11-01), Jon et al.
Technisches Messen, vol. 49, nr. 11, 1982 (Munchen, DE), C. Linhart et al.: "Beruhrungslose Bestimmung der Dicke von Oberflachenbeschichtungen durch thermische Messverfahren", pp. 391-398, see p. 397, part 4.
Binns Ian D.
Makin Brian
Beck Shrive P.
National Research Development Corporation
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