Optics: measuring and testing – Sample – specimen – or standard holder or support – Fluid containers
Patent
1991-05-10
1992-08-18
McGraw, Vincent P.
Optics: measuring and testing
Sample, specimen, or standard holder or support
Fluid containers
356440, G01N 2105
Patent
active
051393336
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a measuring cell for the spectral analysis of flowing media, in particular plastic melts, in which cell the medium to be analyzed flows between two opposing windows made of a radiation transparent material and is penetrated by radiation, where at least one window is held in a pipe, which can be moved by axial motion in the direction of the second window or away from said window in a bore of the measuring cell body with said measuring cell body being sealed, where the width of the gap between the windows and thus the layer thickness of the medium through which the radiation is to travel is variable.
The construction of such a measuring cell follows from the U.S. Pat. No. 3,177,706. In this measuring cell two windows, between whose opposing window faces the medium flows by, can be moved towards one another and away from one another. This occurs here by turning the respective receptacle for the windows, which are designed as pipes, offset stepwise, and are screwed with an external thread into the internal thread in the bore of the measuring cell body. Into one of the steps in the region between the thread and the face of the pipe is inserted a sealing ring that is made of an elastic material and that provides that no melt material that has penetrated between the inner wall of the bore of the measuring cell body and the outer surface of the pipe can escape beyond the sealing ring into the thread and to the outside.
Since the measuring cells must withstand a pressure of the flowing medium in a magnitude of several 100 bar, and in particular at temperatures of up to some 100.degree. C., extreme requirements are placed on the seal between the pipe and the measuring cell body.
Therefore, the invention is based on the problem of designing the measuring cell body and pipe in such a manner that with simple construction high pressures, in particular at high temperatures, a seal can be achieved without any problems. According to the invention, such a seal is obtained in that the cylindrical outer diameter of the pipe abuts in the region of the seal with the stepless cylindrical diameter directly against the wall of the bore and in this region exhibits oversize in the disassembled state relative to the bore, in that the wall thickness of the pipe is small with respect to the outer diameter of the pipe at least in the region of the seal and in that a layer of adhesive is inserted in a ring slot between the interior of the pipe and the shell of the window.
With this design the object is to obtain a high sealing surface compression through the direct abutting of the stepless cylindrical outer surface of the pipe against the wall of the bore without the axial mobility of the pipe in the bore of the measuring cell body being too severely hindered. This goes back to the fact that due to the relatively negligible wall thickness of the pipe, said pipe can be negligibly compressed owing to the elasticity bestowed on said pipe due to said relatively negligible wall thickness so that the sealing surface compression cannot increase excessively. The pipe enables in a simple manner the seal with respect to the window, which with its shell forms relative to the interior of the pipe a ring slot into which a layer of adhesive is inserted.
The region of the seal is designed in such a manner advantageously that said seal extends as far as the end of the bore of the measuring cell body that faces the medium. Thus it is avoided that at the face of the pipe the medium can enter between the outer surface of the pipe and the wall of the bore, so that thus the foremost point of the pipe is sealed, thus ruling out dead spaces in which the medium could collect.
To protect the window from too high radial stresses, a material that is elastic compared to the material of the window and the pipe is used. Thus, it is achieved that the elastic compression of the pipe is absorbed by the elastic material of the adhesive layer and is thus not transferred to the window. This is especially important if due to reasons relating to the
REFERENCES:
patent: 3740156 (1973-06-01), Heigl et al.
patent: 3810695 (1974-05-01), Shea
Smith et al "Infra-red Absorption Cells and Measurement of Cell Thickness", Josa, vol. 34 #3, Mar. 1944, pp. 130-134.
Stromberg et al "A Window-Configuration for High Pressure Optical Cells" Rev. of Scientific Instruments, vol. 41 #12, pp. 1880-1881.
Automatik Apparate-Maschinebau GmbH
McGraw Vincent P.
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