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Artificial Weathering using an Enclosed Carbon Arc Source
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Scope and Field of Application
This is a method of determining the resistance of paint films and allied materials to artificial weathering. It aims to replicate the degradation caused by sunlight and rainfall. If you are more concerned with colour fading of surfaces exposed to sunlight indoors, please refer to our light fastness testing page
Like all laboratory tests, the method described here has its advantages and limitations and these are summarised, in general terms, on our Testing Paints for Resistance to Weathering page.
The main disadvantages of the BS 3900-F3 method are:-
- the standard is obsolete.
- there is no control of temperature/humidity in the chamber.
- the enclosed carbon arc is not a good approximation to natural sunlight.
In spite of this the method is still widely used, the advantages being:-
- it is the only method available that can accommodate large/heavy samples.
- it has been in use for many years and users have built up substantial correlation data with natural weathering.
In addition to this method you may also wish to consider the advantages and limitations of the fluorescent lamp and the xenon arc tests.
There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.
The actual standard is a copyright-protected document and we are not able to provide you with copies. If required however, you can easily obtain a copy from the British Standards Institution.
Summary of Method
The test samples are mounted around the inside of a drum which rotates slowly around an arc lamp enclosed by a borosilicate glass cylinder. The chamber also contains water atomisers which are used to spray the samples with distilled water and a fan which is used for ventilation. Apart for a daily maintenance period, the arc runs continuously while the fan and the water atomisers are switched on and off in a prescribed manner.
The standard states that paint systems that give results that correlate most successfully with natural weathering include oil-modified alkyds and oleoresinous paints. It also states that 12 weeks continuous exposure is equivalent to three to four years exposure to natural weathering in the UK.
Sample Requirements
In addition to the normal 150 x 100 mm or 150 x 75 mm test panels, we can accommodate samples up to 300 x 300 x 180 mm. Individual samples can weigh up to 5 Kg and the total chamber load is limited to 50 Kg.
The standard does not specify the number of replicates but we would normally recommend running samples in triplicate especially in cases where a variable substrate like wood is used.
If you wish, we can prepare the test panels. The quantity of liquid paint we needs depends on the method of application. We will be pleased to advise you regarding our requirements.
Accreditation
Although PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS), we are not accredited to carry out this particular test.
Please contact Peter Collins for further details.
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