Accelerated weathering apparatus

Details Accelerated weathering apparatus Accelerated weathering apparatus

2002-03-15

2004-04-13

Gagliardi, Albert (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Methods

C250S252100, C250S492100, C073S865600

Reexamination Certificate

active

06720562

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to an apparatus for accelerating the weathering effects on test specimens, and more particularly, to an accelerated weathering apparatus having discharge lamps as a concentrated light source for accelerating the deterioration of color, composition, and/or structure of test specimens which includes improved control and calibration structure and methods of operation. The preferred embodiment of the present invention for testing specimens uses fluorescent ultraviolet lamps as the light sources that approximate natural sunlight in the ultraviolet portion of the spectrum and the deterioration caused thereby and will be described with particular reference thereto. However, it will be recognized that other discharge lamps may be used as sources, the primary example being xenon lamps or any other source.
BACKGROUND OF THE INVENTION
A conventional testing apparatus using discharge lamps as shown in
FIG. 1
has eight ultraviolet lamps
10
provided in a test chamber
12
and arranged into symmetric downwardly divergent rows when viewed in cross-section. Specimens
14
to be tested are attached to two opposite specimen supporting walls of the housing of the test apparatus so as to face inwardly toward the lamps and receive the irradiance therefrom. In the machine shown, there are two specimens, an upper specimen and lower specimen; however, there may be only a single specimen or more than two. The rear surface of the specimens
14
is exposed to the atmospheric air outside the machine. Outside air is heated and blown into the interior of the chamber
12
to regulate the temperature in the chamber
12
. Water in the moisture supply tank
16
is heated by conventional means and evaporated to supply moisture into the chamber
12
.
In the above-described testing machine, one example of the machine's operation includes applying irradiance rays to the specimens
14
at a temperature of 60° C. for sixteen hours and then the lamps
10
are turned off and the interior of the chamber
12
is kept at 50° C. to create humidity for eight hours. These two steps, which constitute one cycle of a deterioration testing operation, are repeated continuously. While the lamps are off, the humidity in the chamber
12
is high, and the rear surface of the specimens is exposed to the outside air at a low temperature. Accordingly, the surfaces of the specimens are wetted due to condensation. Thus, the wetting of the specimens, the applying of ultraviolet irradiance, and the drying are repeated, which speeds the deterioration of the specimens. It is to be appreciated that the above description is just one type of cycle for which machines of this nature can be used.
Problems, however, exist with the apparatus shown in FIG.
1
. Initially, there is no provision for sensing the output of the fluorescent lamps
10
, in order to track their rate of degradation or control the irradiance output. A normal procedure for attempting to provide a uniform output from the lamps, in such a device, is to rotate the positions of the lamps at predetermined time intervals in a predetermined sequence. Testing of the lamps to detect actual output is not provided; rather, assumptions are made as to the likely output, and the rotation sequence is made in consideration of the assumptions.
Another drawback of this type of device is that there is no provision for conditioning the lamps during start-up and operation. Accordingly, the life of the lamps is compromised and the accuracy of any test is skewed. There is also no ability to calibrate the irradiance emitted from the lamps.
Various attempts have been made to improve on the above-noted drawbacks of the conventional testing apparatus shown in FIG.
1
. Among these is an apparatus from Atlas Electric Devices Company, called Atlas Ci35 FADE-OMETER®; an apparatus from Heraeus called XENOTEST® 1200 CPS; U.S. Patent to Suga, U.S. Pat. No. 4,544,995 issued Oct. 1, 1985; U.S. Patent to Kockott, et al., U.S. Pat. No. 4,544,995 issued Apr. 27, 1971; and U.S. Patent to Fedor et al., U.S. Pat. No. 5,206,518 issued Apr. 27, 1993.
The Atlas device is arranged for use with a xenon arc lamp and includes a closed loop irradiance monitor as its primary light control system. The monitor, using a light pipe, interference filter and photosensitive diode feeding into solid-state electronics, maintains predetermined irradiance levels and totalizes the energy received by the samples through an integrator. This device is also equipped with manual irradiance controls for use when periodically calibrating the system.
The apparatus from Heraeus is also directed for use with xenon arc lamps. This device employs three light detectors to detect the output of three individual xenon arc lamps.
A conventional apparatus including elements of these two above-discussed devices includes discharge lamps, which can be of a xenon type, that are vertically disposed. A filter surrounding the discharge lamps is provided to allow only desired wavelengths of light to pass. Sensors are provided to sense the output of the vertically positioned discharge lamps, and a rotating specimen holding rack is positioned to encircle the discharge lamps. Each of the detectors is provided to detect the irradiance produced from a respective discharge lamp over time. The rotating specimen holding rack rotates the specimens located in the specimen holding rack. The sensors are provided to track the output of the discharge lamps, and the rotating specimen holding rack attempts to provide each of the specimens with an average overall equal amount of irradiance. Inner walls are used to direct reflective light of the discharge lamps outward to the specimens.
Another device, employing ultraviolet lamps in an arrangement similar to
FIG. 1
, is known to include a single sensor. However, in such an arrangement it is necessary to match the characteristics of the lamps prior to placing them in such a device. This is required since the sensor will sense only the lamps closest to its location. Thus, the sensor will assume the lamps placed distant from it are operating the same as the lamps it actually senses.
The Suga patent attempted to improve on the prior art device shown in
FIG. 1
by adjusting the alignment of the row of discharge lamps
10
of
FIG. 1
into a nonsymmetric arrangement. The discharge lamps
10
are not disposed immediately below each other. Rather, they are in a specifically positioned arrangement. This was done in Suga in an attempt to provide irradiance to the samples
14
with a more uniform distribution.
The Kockott, et al. patent is directed to a device using an elongated source of irradiation inside a cylindrical carrier surface. Kockott, et al. discloses three approaches to provide a uniform distribution of irradiance to the samples. First, mirrors are arranged to reflect usable light; second, a light source is designed to increase light intensity at its ends; and, third, collimating discs are used to inhibit divergence of the radiation emitted from the source.
The Fedor et al. patent is directed to an apparatus similar in structure to the apparatus shown and described in
FIG. 1
which has an improved light output controller and light beam distribution in the test chamber. Fedor et al. discloses an apparatus including a housing with a test chamber and a specimen supporting wall located inside of the chamber. A light source is provided in the test chamber. A ballast arrangement is connected to the light source for controlling the amount of power the light source receives from a power source. A controller is connected to the ballast arrangement, to produce a ballast control signal for controlling operation of the ballast arrangement according to a desired set-point value. A light source detector is disposed within the specimen supporting wall in order to detect irradiance existing in the test chamber so the light source detector can generate an irradiance signal, which is then input to the controller. The controller uses the irradiance signal to adjust the ballast control signa

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